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Amidophosphine complexes of ruthenium (II) Petrella, Michael John 2003

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AMIDOPHOSPHINE COMPLEXES OF RUTHENIUM (II) by MICHAEL JOHN PETRELLA B. Sc. (Hon.), McMaster University, 1997  A thesis submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY  We accept this thesis as conforming to the required standard  T H E U N I VERS FT Y OF B R I T I S H C O L U M B I A  April 2003 © Michael John Petrel la, 2003  In presenting this thesis i n partial fulfilment of the requirements f o r an a d v a n c e d degree at the U n i v e r s i t y of B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree that p e r m i s s i o n f o r extensive c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . It is understood t h a t copying or p u b l i c a t i o n of t h i s thesis for financial g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n .  Department o f  CHEMISTRY  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r , Canada  Date  Columbia  J u n e 27, 2003  ABSTRACT  The preparation and reactivity o f ruthenium(II) complexes that incorporate the chelating amidophosphine ligands [NPN] (where [NPN] = PhP(CH SiMe NPh) ) or [P N ] (where [P N ] = 2  2  2  2  2  2  2  PhP(CH SiMe NSiMe CH ) PPh) are presented. The reaction of the dilithium salt [P N ]Li (S) 2  2  2  2  2  2  2  2  (S = 1,4-dioxane) with the ruthenium starting material [RuCl (cod)] (cod = 1,5-cyclooctadiene, 2  x  r] :ri -C8Hi ) generates the diamido complex (P N ]Ru(r| :r| -C8Hi ) and the reaction with 2  2  2  2  2  RuCl (PPh ) 2  3  gives  3  the  ort/zo-metalated  2  2  species  2  [P NNH]Ru(C H PPh ). 2  6  4  The  2  cyclooctadiene complex reacts with hydrogen gas (one atmosphere) to give the dihydrogen-hydride species [P NNH]Ru(T] -H )(H).  2  2  fluxional  The minimum longitudinal relaxation time  2  2  [P N ]  2  (7i(min)) for the hydride ligands in this complex is 62 ms (at 240 K ) and the JHD coupling 1  constant in the H D isotopomer is 15 Hz. These data both lead to an estimated H-H distance of 1.2 A corresponding to an elongated H moiety.  The or^o-metalated species reacts with H  2  forming the monohydride complex [P NNH]RuH(PPh3). 2  2  Exposure of this hydride species to an  atmosphere o f deuterium gas results in the incorporation o f deuterium into both the N-H and Ru-H sites.  Whereas the dihydrogen complex catalyzes the hydrogenation of olefins under mild  conditions the monohydride complex is inactive.  Reaction o f pSTPN]Li (S) 2  2  (S = tetrahydrofuran) with [RuCl (cod)] 2  3  x  generates the  2  ruthenium cyclooctadienyl complex [NPNH]Ru(r| :r\ -CgHn) that forms via deprotonation of the cyclooctadiene ligand by one o f the amido donors o f the tridentate ligand. This product exists in equilibrium as a mixture o f two diastereomers; inter-conversion of the two isomers occurs via intramolecular proton transfer between the amido side-arms of the [NPNH] ligand. The solid-state molecular structure o f one o f the isomers was determined by X-ray crystallography and it shows that the complex adopts a distorted trigonal bipyramidal (a Y-shape in the trigonal plane) coordination geometry. This structure allows for maximal 7t-overlap o f the amido lone pair with the metal L U M O . hydride  Exposure of [NPNH]Ru(r| :r| -C8Hii) to H gas yields the three ruthenium  complexes  C6Hs)]Ru(H) . 2  3  2  2  [NPNH(r| -C H5)]RuH,  [NPNH ]Ru(H) (C D )  6  6  2  2  7  8  and  [NPNH (r| 6  2  Each o f these complexes contains an r| -bound arene group; in two o f the 6  complexes this moiety is the amino phenyl group o f the chelating ligand set and in the other it is a coordinated solvent molecule. Each o f these three hydride products is inactive toward olefin and imine hydrogenation reactions, however, the cyclooctadienyl complex [NPNH]Ru(r| :r| -C8Hii) 3  ii  2  does reduce these substrates. The catalytic hydrogenation studies that have been performed with all of these complexes are also discussed.  The attempted preparation of [NPN] and [P2N2] ruthenium alkylidene and vinylidene complexes is reported. The terminal alkynyl complex [NPNH](P Pr3)Ru(CCPh) forms from the l  reaction of the dilithium salt of the [NPN] ligand with Cl (P Pr3) Ru(=CCHPh) via deprotonation i  2  2  of the vinylidene ligand. The addition of hydrogen gas to this complex produces the thermally unstable bis-dihydrogen dihydride complex pSTPNH2]Ru(ri -H2)2(H)2. The Ti(min) value for the 2  metal-bound hydrogen atoms within this complex is 51 ms observed near 220 K. The dilithium salt of the [P N ] ligand reacts with Cl2(P'Pr3)2Ru{=CC(SiMe )(Ph)} to give the five-coordinate 2  2  3  vinylidene complex [P2N2]Ru{=CC(SiMe3)(Ph)}.  Olefin metathesis reactions including the ring  opening metathesis polymerization of norbornene and cross metathesis with styrene are unsuccessful with this complex, however, it does react with H2 (4 arm) to generate the previously described dihydrogen-hydride complex [P NTSrF£]Ru(ri -H2)(H). 2  2  TABLE OF CONTENTS ABSTRACT  ii  TABLE OF CONTENTS  iv  LIST OF TABLES  ix  LIST OF FIGURES  xiii  GLOSSARY OF TERMS  xx  ACKNOWLEDGEMENTS  xxiv  DEDICATION  xxv  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry 1.1  1  An introduction to amide and phosphine ligands  1  (i)  Phosphine ligands in transition metal chemistry  2  (ii)  Amido ligands in transition metal chemistry  5  (iii)  Metal-Amide (M-N) bonding considerations  6  (iv)  Preparation of late transition metal amide complexes  9  (v)  Reactivity of the late transition metal-amide bond  11  1.2  The mixed-donor amidophosphine ligands [PNP], [P2N2] and [NPN]  1.3  [PNP] ruthenium(lI) chemistry  20  1.4  Scope of this thesis  23  1.5  References  23  17  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P N ] Ligand Sets 2  2  30 30  2.1  Introduction  2.2  Synthesis and characterization of [P N ]Ru(r| : r i - C H ) (1)  30  (i)  Synthesis and structure of [P N ]Ru(ri : T I - C H ) (1)  30  (ii)  Variable-temperature NMR spectroscopy of  2  2  2  2  8  2  2  2  12  8  2  1 2  [P N ]Ru(ri : r | - C H ) (1) 2.3  36  2  2  2  2  8  12  Synthesis and characterization of [P NNH]Ru(C H PPh ) (2) 2  (i)  6  4  2  40  Synthesis and NMR spectroscopic characterization of 40  [P NNH]Ru(C H PPh ) (2) 2  6  4  2  (ii)  X-ray diffraction study of [P NNH]Ru(C H PPh ) (2)  41  (iii)  Mechanism for the formation of complex 2  45  2  iv  6  4  2  2.4  Synthesis, characterization and solution dynamics of exo- and  endo-3)  e n d o - f N P N H l R u C I - S ^ - S . e ^ - C s H n ) (exo-3 and  46  (i)  Reaction of [ N P N ] L i 2 ( C H 0 )  (ii)  Solid-state molecular structure of diastereomer endo-Z  (iii)  Considerations into the identity of the s e c o n d species and  4  8  with [RuCI (cod)]  2  46  2  50  possible fluxional processes  2.5  56  (iv)  Variable-temperature N M R studies of endo-Z and exo-3  59  (v)  Postulated mechanism for the inter-conversion of endo-Z and exo-3  67  Synthesis, characterization and reactivity of the ruthenate complexes {[NPN]Ru(1-3:n. -5,6: T I - C H H ) } { M T H F } (4) (M=Li) and (5) (M=Na) 3  2  B  (i)  Synthesis of the ruthenate complexes {[NPN]RU(1-3:TI -5,6:TI -C8HII)KMTHF} (4) (M=Li) and (5) (M=Na)  70  (ii)  X-ray diffraction study of compounds 4 and 5  71  (iii)  Solution structure of compounds 4 and 5  74  (iv)  Regeneration of the equilibrium mixture of endo-Z and exo-3 by  3  2  addition of acid to 4 or 5 (v)  75  Reaction of compounds 4 and 5 with M e S i C I : formation of the two 3  independent diastereomers  endo-  and exo-[NPN(SiMe )]Ru3  (1-3:n. -5,6: n - C H ) (endo-6 and exo-6) 3  1 1  Attempted synthesis of [ N P N ] R u ( P P h ) 3  (i)  76  2  8  2.6  70  78  2  Reaction of [NPN]l_i2(C H 0)2 with R u C I ( P P h ) 4  8  2  3  3  78  2.7  S u m m a r y and conclusions  79  2.8  Future work  80  (i) 2.9  2.10  Reaction of 3 with carbon monoxide  Experimental  80 89  (i)  General procedures  89  (ii)  Materials  90  (iii)  Synthesis and reactivity of complexes  90  References  98  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation 3.1  3.2  Introduction  105 105  (i)  Catalytic homogeneous hydrogenation by transition metal complexes ...105  (ii)  T h e activation of dihydrogen (H ) by transition metal complexes 2  Hydrogenation of [P N ]Ru(n. : n . - C H ) (1) 2  2  2  2  8  v  12  106 109  (i)  Reaction of [P N ]Ru(r| : r | - C H ) (1) with hydrogen g a s 12  109  (ii)  Spectroscopic identification of the intermediate hydride complex 9  110  (iii)  Characterization of complex 10 as a fluxional dihydrogen-hydride  2  2  2  2  8  complex by variable-temperature N M R spectroscopy and D  2  labelling studies (iv)  112  T h e dynamic behaviour of complex 10 in solution: isotopic perturbation of equilibria and proton-hydride exchange processes via proton-hydride exchange processes via protonic-hydridic  (v) 3.3  bonding interactions  118  Proposed mechanism for the formation of complex 10  124  Hydrogenation of [ P N N H ] R u ( C H P P h ) (2) to give the monohydride 2  6  4  2  complex [ P N N H ] R u H ( P P h ) (11) 2  128  3  (i)  Synthesis and characterization of [ P N N H ] R u H ( P P h ) (11)  (ii)  Reaction of 11 with deuterium gas and evidence for proton-  2  128  3  hydride exchange 3.4  131  Catalytic hydrogenation studies with [ P N N H ] R u ( H ) H (10) and 2  2  [ P N N H ] R u H ( P P h ) (11) 2  3.5  133  3  Hydrogenation of exo- and enofo-[NPNH]Ru(1-3:ri -5,6:ri -C8H ) 3  2  11  (exo-3 and endo-Z)  (i)  135  Reaction of an equilibrium mixture of exo-3 and  endo-Z with H  2  (ii)  Isolation and characterization of [ N P N ( H ) ( r | - C H ) R u H  (iii)  Isolation and characterization of [NPNH2]Ru(H) (ri -C H ) (13)  (iv)  Evidence for proton-hydride bonding in the solution structure of  (12)  6  6  5  6  2  7  8  136 139  complex 13 from measurement of the minimum Ti values  142  (v)  Isolation and characterization of [NPNH (n -C H )Ru(H)2 (14)  144  (vi)  Proposed mechanism for the formation of the three ruthenium  6  2  hydride complexes 12,13  6  5  and 14  145  (vii)  L o s s of H from complex 14 to give complex 12  150  (viii)  Solution epimerization of complex 16 resulting in the formation  2  of a mixture of diastereomers (ix)  155  Catalytic hydrogenation studies with complexes 3,12,13 and 14 and speculations into mechanistic details  3.6  135  158  Synthesis of a new [NPN] ligand with variation at the amide positions and its application to ruthenium(ll)  163  (i)  T h e need for ligand variation  163  (ii)  Synthesis and characterization of [ P h P ( C H S i M e N M e ) L i 2  vi  2  2  2  C H 0 ( [NPN]l_i C H 0 ) (17) and its reaction with [RuCI (cod)] Me  4  8  2  2  4  8  2  2  x  164  3.7  Summary and Conclusions  166  3.8  Future Work  168  (i)  Catalytic ionic hydrogenation utilizing [NPN(H)(r| -C H5)RuH (12) 6  6  as a precursor (ii)  168  Another strategy toward the synthesis of amino-deuterated complexes of 14  (iii) 3.9  3.10  170  Reaction of [ N P N ] L i C H 0 (17) with early transition metals Me  2  4  8  2  Experimental  171 174  (i)  General procedures  174  (ii)  Materials  174  (iii)  Synthesis and reactivity of complexes  174  References  184  Chapter 4: Reaction of the Amidophosphine Ligands [NPN] and [P N ] with 2  2  Ruthenium(ll) Alkylidene and Vinylidene Complexes  196  4.1  Introduction  196  4.2  Reaction of [NPN]Li (C H 0) and [ P N ] L i ( C H 0 ) with 2  4  8  2  2  2  2  4  8  2  (PCy ) CI Ru(CHPh) 3  4.3  2  198  2  Synthesis and characterization of [NPNH](P Pr )Ru(CCPh) (20)  200  (i)  Reaction of [NPN]Li (C H 0) with (PPrakCfeRufCCHPh)  200  (ii)  Solid-state and solution characterization of  i  3  2  4  8  2  [NPNH](P Pr )Ru(CCPh) (20)  201  i  3  (iii)  Speculations into the identity of the second species that forms in THF  206  4.4  Reaction of [NPNHKPPr^RufCCPh) (20) with H  4.5  Reaction of [P N2]Li (C H 0 ) with (PPr^ClzRufCCHPh)  4.6  Reaction of [NPN]Li (C H 0) and [P N ]Li (C H 0 ) with  2  2  4  2  8  4  207  2  212  2  8  2  2  2  2  4  8  2  (PPr )2CI Ru{CC(SiMe )Ph} 3  4.7  4.8  2  214  3  (i)  Synthesis and characterization of [P N ]Ru{CC(SiMe )Ph} (24)  214  (ii)  Attempted synthesis of [NPN](P Pr )Ru{CC(SiMe )Ph}  222  2  2  3  i  3  3  Reactivity studies of [P N ]Ru{CC(SiMe )Ph} (24)  223  (i)  Reaction of 24 with olefin substrates  223  (ii)  Reaction of 24 with H  225  2  2  3  2  Summary and Conclusions  226  vii  4.9  Future Work (i)  4.10  228  Synthesis of [NPN](MgBr) (C H 0) (26) 2  4  8  Experimental  4.11  228 232  (i)  General procedures  232  (ii)  Materials  232  (iii)  Synthesis and reactivity of complexes  233  References  237  Appendix 1: X-ray Crystal Structure Data  244  Appendix 2: H NMR Longitudinal Relaxation (T ) Measurements  251  Appendix 3: Estimated Rate Constants for Kinetic Analyses  258  1  A  viii  LIST OF TABLES  Table 2.1  35  Selected bond lengths, angles and dihedral angles in [P N ]RU(TI :TI -C8H ) 2  2  Table 2.2  Page  Title  Table  2  2  12  (1).  Calculated rate constants (k) for the fluxionality of the [P N ] ligand in the 2  2  39  complex [P N2]Ru(r| :r| -C H ) (1). 2  2  8  2  Table 2.1  12  35  Selected bond lengths, angles and dihedral angles in [P N2]Ru(ri :ri -C8H ) (1). 2  2  2  Table 2.2  12  Calculated rate constants (k) for the fluxionality of the [ P N ] ligand in 2  the complex [P N2]RU(TI :TI -C8H ) 2  2  2  Table 2.3  12  2  39  (1).  43  Selected bond lengths, bond angles and dihedral angles in the complex [ P N N H ] R u ( C H P P h ) (2). 2  Table 2.4  6  4  2  Selected bond lengths, angles and dihedral angles in [NPNH]Ru(1-3-ri -5,6-ri -C Hii) 3  2  8  Table 2.5  endo-  51  (endo-Z).  ' H resonances of the cyclooctadienyl ligand for complexes 1  3-6  62  including J H coupling constants for complex exo-3 (determined from H  simulation data).  Table 2.6  1 3  C resonances of the cyclooctadienyl ligand for complexes  3-6. J 2  PC  62  values (Hz) are given in parenthesis.  Table 2.7  Calculated equilibrium constants (K) for the equilibrium between diastereomers  Table 2.8  endo-Z  65  and exo-3 in toluene-d 8  Calculated rate constants for the reversible intramolecular proton transfer responsible for the inter-conversion of diastereomers  and exo-3.  ix  endo-Z  69  Table 2.9  {[NPN]Ru(1-3-ri -5,6-Ti -C H )KMTHF}, 3  2  8  Table 2.10  72  Selected bond lengths and angles in the complexes 11  Selected bond lengths and angles (CO)  M = Li (4) and M = Na  (5).  [NPNH]Ru(1-3-Ti -5,6-r| -C8Hii)3  82  2  (7).  Table 2.11  Selected bond lengths and angles in complex  8.  Table 3.1  C o m p a r i s o n of H-H distances (OHH) in s o m e related ruthenium(ll)  88  118  dihydrogen-hydride complexes and the method in which they were determined.  Table 3.2  Selected bond lengths and angles in the complex [ P N N H ] R u H ( P P h )  Table 3.3  Catalytic hydrogenation studies utilizing complexes  2  10  3  and  11  (11).  129  135  as  precursors.  Table 3.4  [NPN(H)(TI -C H )]RUH  (12).  6  6  Table 3.5  5  2  2  7  8  (13).  143  Ti(min) values measured for the hydride and pendant amino proton nuclei in complexes  Table 3.7  140  A collection of selected bond lengths and bond angles in the complex [ N P N H ] R u ( H ) ( C H )  Table 3.6  138  Selected bond lengths and bond angles in the complex  12,13,14 and 15  in toluene-d and 500 M H z . 8  A summary of the catalytic studies performed for the hydrogenation of  159  imine and alkene substrates using complexes 3,12,13 and 14 a s precursors.  Table 4.1  Selected bond lengths and bond angles in [ N P N H ] ( P P r ) R u ( C C P h )  Table 4.2  A comparison of hydride chemical shift (8 ), multiplicity (m),  i  3  H  J  2  PH  (20).  and  Ti(min) values for the hydride ligands as well a s phosphine chemical shifts (8P) in complex 21 and related bis dihydrogen complexes.  x  204  211  Table 4.3  Selected bond lengths and bond angles in [P N2]Ru{CC(SiMe )Ph} (24).  Table 4.4  Selected bond lengths and bond angles in [ N P N ] ( M g B r ) ( C H 0 )  Table A1  Crystallographic Data and Structure Refinement Data for  3  2  2  4  complexes [ P N ] R U ( T I : T | - C 8 H I ) (1), [P NNH]Ru(C H4PPh2) 2  2  2  2  2  2  6  8  (26).  217  231  A4 (2),  e/ido-[NPNH]Ru(1-3-ri :5,6-Ti -C8H i) (endo-3) a n d 3  2  1  {[NPN]Ru(1-3-ri :5,6-ri -C8H i)KLi»THF} 3  (4).  2  1  Table A2  Crystallographic Data and Structure Refinement Data for complexes {[NPN]Ru(1-3-r| :5,6-Ti -C H )KNa.THF} 3  8  [NPNH]Ru(1-3-r| :5,6-  (5),  2  11  A5  3  T l - C H n ) ( C O ) (7), {[PhN(H)Si-Me2CH ][(C H )C(0)N(Ph)SiMe CH2]2  8  2  [Ph]}PRu(CO)  Table A3  4  8  (8) and [ P N N H ] R u H ( P P h ) 2  3  11  2  (11).  Crystallographic Data and Structure Refinement Data for complexes  A6  [ N P N ( H ) ( T I - C H ) ] R U H (12), [NPNH2]Ru(H) (ri -C H ) (13), 6  6  6  5  2  7  8  [NPNH](P'Pr )Ru(CCPh) (20) and [P N2]Ru{CC(SiMe )Ph} (24). 3  Table A4  3  2  Crystallographic Data and Structure Refinement Data for  A7  complex [ N P N ] ( M g B r ) » ( C H 0 ) (26). 2  Table A5  2  A9  (10).  2  Temperature and Ti values for the ruthenium hydride in [P NNH]RuH(PPh ) 2  Table A7  8  Temperature and Ti values for the ruthenium hydrides in [P NNH]Ru(H )H  Table A6  4  3  A10  (11).  Temperature and Ti values for the ruthenium hydride in  A11  [NPN(H)(TI -C H )]RUH(12). 6  6  Table A8  5  Temperature and Ti values for the ruthenium hydride and amino  A12  proton in the complex [NPNH2]Ru(H) (r| -C7D ) (13). 6  2  Table A9  Temperature and  T\ values for the  8  ruthenium hydrides and amino  proton in the complex [ N P N H ( T | - C H ) ] R U H 6  2  6  XI  5  2  (14).  A13  Table A10  Temperature and 7i values for the amino protons in the complex  [NPNH2] (15).  xii  A14  LIST OF FIGURES  Figure 1.1  Page  Caption  Figure •  Orbital representation of the a andrc-bondinginteractions between  2  a phosphine ligand and a metal center.  Figure 1.2  Measurement of the cone angle (<\>) for a phosphine donor (PR3) with  4  ball-and-stick representations of the P P h (<|) = 145°) and P C y ligands 3  3  (<j)=170°). Figure 1.3  Various bonding modes of an amido ligand to a transition metal.  6  Figure 1.4  A qualitative molecular orbital diagram illustrating the interaction  8  between a 7t-symmetry amide lone pair of electrons (p ) and the n  (a) empty and (b) filled c^-orbitals of a transition metal.  Figure 2.1  Ruthenium(ll) complexes that act as precursors for the catalytic  31  reduction of ketone and imine substrates. Both chiral and achiral complexes are shown.  Figure 2.2  O R T E P representation (thermal ellipsoids shown at 50 % probability)  35  of the solid-state molecular structure of [P N ]Ru(ri :ri -C8H 2) (1). The 2  2  2  2  1  silyl methyl groups of the [P N ] ligand have been omitted for clarity. 2  Figure 2.3  2  Depiction of the fluxional behaviour of complex 1 in solution via  37  twisting of the [P N ] framework about the amido nitrogen atoms. 2  Figure 2.4  2  38  The effect of temperature on the methylene resonance of the cyclooctadiene ligand in the 500 MHz H NMR spectrum of 1  [P N2]Ru(r, :r| -C H ) (1). 2  2  Figure 2.5  2  8  12  Arrhenius plot for the fluxionality of the [P N ] ligand framework 2  2  in the complex [P N ]Ru(r| :r| -C H ) (1) (R = 0.9920 and E = 2  2  2  2  2  8  12  18.6 ± 1 . 6 kcal mol" ). 1  xiii  a  39  Figure 2.6  T h e solid-state molecular structure ( O R T E P representation, 50 %  42  thermal ellipsoid probability) of [P NNH]Ru(C H4PPh2) (2) a s 2  6  determined by X-ray crystallography. T h e silyl methyl groups of the [P NNH] ligand have been omitted for clarity. 2  Figure 2.7  Proposed mechanism for the formation of the observed species 2.  46  Figure 2.8  T h e 500 M H z H N M R spectrum of complex 3 in toluene-ofe at 298 K  48  1  (upper spectrum) and 245 K (lower spectrum).  Figure 2.9  51  T h e solid-state molecular structure ( O R T E P depiction shown at 50 % thermal ellipsoid probability) of endo-[NPNH]Ru-  (l-S-r^-S.e-r^-CsHu) (endo-3) a s determined by X-ray diffraction. T h e amino proton (H43) w a s refined isotropically.  Figure 2.10  54  A qualitative representation of the two possible Jahn-Teller distortions in a diamagnetic trigonal bipyramidal structure of an d  6  M L complex. T h e ligand and metal antibonding combinations 5  are shown.  Figure 2.11  55  A schematic representation of the amide lone pair orbital (p ) and y  empty ruthenium orbital (d ) overlap in complex xy  endo-3.  Figure 2.12  T h e four possible diastereomers of [NPNH]Ru(1-3-r| -5,6-rv -C Hi )  Figure 2.13  T h e labelling convention used for H and  3  2  8  1  1 3  1  (3).  C N M R assignments  58  60  of the cyclooctadienyl ligand in complexes containing this ligand.  Figure 2.14  T h e J-modulated C{ H} N M R spectrum for endo-3 and exo-3 obtained 13  1  61  at 245 K in toluene-d highlighting the cyclooctadienyl carbon resonances. 8  T h e C H resonances point up and the C H resonances point down. 2  Figure 2.15  A region of the 500 M H z H{ P} N M R spectrum of isomers 1  31  endo-3 and  exo-3 highlighting the downfield shifted cyclooctadienyl proton resonances at 245 K in toluene-af . 8  xiv  64  Figure 2.16  endo-3 and  Van't Hoff plot for the equilibrium between diastereomers  65  exo-3 ( R = 0.9954). 2  Figure 2.17  T h e N - H region of the 2-D E X S Y spectrum for the mixture of  endo-3  66  and exo-3. Obtained at 298 K in toluene-ds, 500 M H z and a mixing time of 0.4 s .  Figure 2.18  Eyring plot for the inter-conversion of diastereomers  endo-3 and exo-3  69  ( R = 0.9922). A/-/* = 1 6 + 1 kcal mol" and A S * = 4 ± 4 eu. 2  Figure 2.19  1  O R T E P representation (50 % thermal ellipsoid probability) of the  72  solid-state molecular structure of {[NPN]Ru(1-3-ri -5,6-ri -C8H )}3  2  11  {Li THF} (4) as determined by X-ray diffraction. T h e [NPN] ligand silyl methyl groups have been omitted for clarity and only the ipso carbon atoms of the amido phenyl rings are shown.  Figure 2.20  O R T E P representation (thermal ellipsoids shown at 50 % probability)  82  of the solid-state molecular structure of the complex [NPNH]Ru(1-3-r) -5,6-ri -C8H )(CO) (7) as determined from X-ray diffraction. 3  2  11  T h e silyl methyl groups of the [NPNH] ligand have been omitted for clarity. T h e amino hydrogen atom H(34) was located and refined isotropically.  Figure 2.21  A depiction of how the metal L U M O (d^ orbital) in the complex  84  lr(PR ) (H)(CI)(r| -C6H5) extends away from the hydride ligand. 1  3  Figure 2.22  2  A schematic representation of the bonding combination between the  85  silyl moiety and the metal d^ orbital in exo-3.  Figure 2.23  O R T E P depiction of the solid-state molecular structure of complex 8 as  87  determined by X-ray diffraction. Thermal ellipsoids are shown at the 50 % probability level.  Figure 3.1  T h e bonding s c h e m e for a transition metal r j - H complex involving 2  2  o-donation from H and n back-bonding from the metal centre. 2  xv  107  Figure 3.2  Depiction of the intramolecular heterolytic cleavage of H by an amido 2  109  ligand via a-bond metathesis. Figure 3.3  Proposed structure of the intermediate complex 9.  112  Figure 3.4  Dihydrogen-hydride complexes of ruthenium(ll) that are related to  113  complex 10. Figure 3.5  High-field region of the H{ P} NMR spectrum of the isotopomers 1  31  117  10 (H ), 10-di (H D) and 10-d (HD ) (C D , 500 MHz, 300 K). The upper 3  2  2  2  7  8  spectrum was recorded 1 hour after the addition of D gas and the lower 2  spectrum was recorded after 16 hours. Figure 3.6  Plot of chemical shift of the hydride resonance in 10 (orange diamonds)  119  and 10-d (green circles) as a function of observation temperature 2  (from 215 to 300 K).119 Figure 3.7  Equilibria for partially deuterated complexes of an M(H )(H) species.  120  Figure 3.8  Exchange of the ruthenium-bound hydrogen atoms in complex 10  122  2  occurring via a transient trihydrogen complex. Figure 3.9  ORTEP representation (thermal ellipsoids shown at 50 % probability)  129  of the solid-state molecular structure of [P NNH]RuH(PPh ) (11) as 2  3  determined by X-ray crystallography. The ruthenium hydride H(50) was located and refined isotropically, the amino proton was not located.  Figure 3.10  Hydride region of the 500 MHz H NMR spectrum of 1  131  [P NNH]RuH(PPh ) (11) recorded in benzene-cfe at 500 MHz and 298 K. 2  Figure 3.11  3  An ORTEP representation of the solid-state molecular structure of [NPN(H)(ri -C H )]RuH (12) as determined by X-ray crystallography with 6  6  5  thermal ellipsoids shown at the 50 % probability level. The ruthenium hydride, H(1), and amino proton, H(28), were located and refined isotropically.  xvi  138  Figure 3.12  T h e solid-state molecular structure ( O R T E P representation,  140  50 % thermal ellipsoids) of [NPNH2]Ru(H)2(C H ) (13) a s determined 7  8  by X-ray crystallography. T h e ruthenium hydrides (H(42) a n d H(43)) as well a s the amino hydrogen atoms (H(1) and H(18)) were all refined isotropically.  Figure 3.13  High-field region of the 500 M H z H N M R spectrum highlighting the 1  145  hydride resonances of the complex [NPNH (ri -C6H5)]Ru(H)2 (14) in 6  2  benzene-06-  Figure 3.14  T h e two possible enantiomers of complex  12 that  may form from the  148  hydrogenation of complex 3. T h e configurational designations refer to the metal centre and the phosphorus atom, respectively.  Figure 3.15  Possible role of the amine ligand in facilitating r| -bonding of the imine 2  162  substrate.  Figure 3.16  E x a m p l e s of [NPN]Zr and [NPN]Ta dinitrogen complexes.  172  Figure 4.1  T h e mechanism for olefin metathesis utilizing the Grubbs' catalyst (A).  197  A cross metathesis reaction is shown.  Figure 4.2  O R T E P representation (50% thermal ellipsoids) of the solid-state  204  molecular structure of [ N P N H ] ( P P r ) R u ( C C P h ) (20) a s determined by i  3  X-ray diffraction. T h e silyl methyl groups of the [NPNH] ligand a n d the isopropyl methyl groups of the P'Pr ligand have been omitted for clarity. 3  T h e amino proton H(58) w a s located.  Figure 4.3  T w o possible diastereomers of complex 20. Isomer A is distorted  207  trigonal bipyramidal (Y-shape) and isomer B is square pyramidal.  Figure 4.4  T h e P{ H} N M R spectrum for the reaction of 20 with H . T h e 31  1  2  208  magnitude of coupling for the two doublets is 225 H z .  Figure 4.5  S o m e examples of octahedral ruthenium(ll) bis dihydrogen complexes.  xvii  209  Figure 4.6  O R T E P representation (50% thermal ellipsoids) of the solid-state molecular structure of [P N2]Ru{CC(SiMe )Ph} (24)  as determined by-  3  2  217  X-ray diffraction. T h e silyl methyl groups of the [P N ] ligand have been 2  2  omitted for clarity.  Figure 4.7  A n illustration of the two stabilizing bonding interactions in five-  219  coordinate vinylidene complexes of the type L (H)(CI)Ru(CCHR), 2  which adapt distorted trigonal bipyramidal (or Y-shaped) structures. In A n-donation from the Cl lone pair (p ) to the empty metal xy orbital y  occurs. In B back-donation from the filled metal x^-y  2  vacant p-orbital on C  orbital to the  of the vinylidene occurs. This c a n only take  a  place if the C p H group lies in the xy plane. 2  Figure 4.8  A qualitative representation of the bonding s c h e m e for the vinylidene  222  ligand in complex 24.  Figure 4.9  T h e ring-opening metathesis polymerization of norbornene  224  (highlighted) and vinylidene complexes that are used a s catalyst precursors.  Figure 4.10  O R T E P representation (50% thermal ellipsoids) of the solid-state molecular structure of [NPN](MgBr) ( C H 0 ) (26) 2  4  8  231  as determined by  X-ray diffraction.  Figure A1  O R T E P representation (50 % thermal ellipsoids) of the solid-  A3  state molecular structure of {[NPN]Ru(1-3-ri :5,6-r| -C8H )}3  2  11  { N a « T H F } (5) as determined by X-ray diffraction. T h e [NPN] silyl methyl groups have been omitted for clarity and only the  ipso  carbon  atoms of the amido and phosphine phenyl rings are shown.  Figure A2  Plot of temperature versus Ti for the ruthenium hydrides in [P NNH]Ru(H )H 2  Figure A3  (10).  2  Plot of temperature versus Ti for the ruthenium hydride in [P NNH]RuH(PPh ) 2  A9  3  (11).  xviii  A10  Figure A4  Plot of temperature versus 7"i for the ruthenium hydride in the complex [NPN(H)(r| -C H )]RuH 6  6  Figure A5  5  A11  (12).  Plot of temperature versus 7~i for (a) the ruthenium hydrides and (b) the amino protons in the complex [NPNH ]Ru(H) (r| -C7D8) 6  2  Figure A6  2  (13).  Plot of temperature versus T i for (a) the ruthenium hydrides and (b) the amino proton in the complex [ N P N H ( r | - C H ) ] R u H 6  2  Figure A7  A12  6  5  2  (14).  Plot of temperature versus 7~i for the amino protons in the complex [NPNHa]  (15).  xix  A13  A14  GLOSSARY OF TERMS  The following abbreviations, most of which are commonly found in the literature, are used in this thesis.  A  Angstrom  Anal  analysis  atm  atmosphere  Ar  aryl (or argon)  binap  2,2'-bis(diphenylphosphino)-l,l'binaphthyl  br  broad  Bu  n-butyl group, - C H 2 C H 2 C H 2 C H 3  *Bu  tertiary butyl group, -C(CPi3)3  Bz  benzyl  n  1 3  carbon-13  C  Ca  carbon atom in the a position  Cp  carbon atom in the P position  cal  calories  Calcd  calculated  CCD  charge coupled device  cod  1,5-cyclooctadiene, CsH^  COSY  correlated spectroscopy (NMR experiment)  cm  centimetres  cm"  1  wave number  Cp  cyclopentadienyl, C5H5  c *  pentamethylcyclopentadienyl group, CsMes  cryst  crystal  Cy  cyclohexyl  d  doublet  dd  doublet o f doublets  deg(or°)  degrees  dppe  1,2-bisdiphenylphosphino)ethane  dppm  bis(diphenylphosphino)methane  P  XX  D or H  deuterium  1- D  one dimensional  2- D  two dimensional  d"  numbers of af-electrons  d  n-deuterated  2  n  E  energy of activation  a  eu  entropy units (cal mol" K" )  Et  ethyl group, -CH CH  'H  proton  { H}  proton decoupled  A//*  enthalpy of activation  A//°  standard enthalpy  HOMO  highest occupied molecular orbital  Hz  Hertz, seconds"  /  nuclear spin  IPR  isotopic perturbation of resonance  IR  infrared  VAB  n-bond scalar coupling constant between nuclei A and B  K  Kelvin  k  Boltzmann constant  kcal  kilocalories  1  2  !  1  3  1  6  Li  lithium-6  7  Li  lithium-7  L  neutral two-electron donor  LUMO  lowest unoccupied molecular orbital  M  central metal atom (or molar, when referring to concentration)  M  +  parent ion  m  meta  m  multiplet (NMR spectroscopy)  mm  millimetres  Me  methyl group, -CH  MHz  megahertz  mL  milliliter  3  xxi  mmol  millimole  MO  molecular orbital  mol  mole  NBD  2,5-norbornadiene  NMR  nuclear magnetic resonance  [NPN]  diamidophosphine ligand PhP(CH SiMe NPh)  o  ortho  OTf  triflate anion, "OS0 CF  ORTEP  Oakridge Thermal Ellipsoid Plotting Program  p  para  31  2  2  P  2  2  3  phosphorus-31  Ph  phenyl group,  PHIP  para hydrogen induced polarization  [PNP]  amidodiphosphine ligand, N(SiMe CH PPh )  [P N ]  diamidodiphosphine ligand, PhP(CH SiMe NSiMe CH ) PPh  ppb  parts per billion  ppm  parts per million  'Pr  isopropyl group, -CH(CH3)  q  quartet  R  hydrocarbyl substituent  R  coefficient of determination for a linear regression  ROMP  ring opening metathesis polymerization  reflns  reflections (X-ray crystallography)  AS  entropy of activation  AS°  standard entropy  s  singlet  2  2  i  SiMe  3  -C6H5  2  2  2  2  2  2  2  2  trimethylsilyl group, Si(CH.3)3  t  triplet  T  temperature in Kelvin or °C  THF  tetrahydrofuran ( C H 0 )  tmen  tetramethylethylenediamine, M e N C H C H N M e  TON  turnover number (mol products per mol catalyst)  V  unit cell volume  4  8  2  xxii  2  2  2  2  2  VSEPR  valence-shell electron pair repulsion  VT  variable temperature  win  width at half height  w  weak  X  halide substituent  rf  n-hapto bridging or absorption coefficient (X-ray crystallography)  P  density  Pcalc  calculated density  X  excited state lifetime (NMR)  V  spectrometer frequency  Vxx  vibrational band for bond xx  X  wavelength  6  chemical shift in ppm  u-X  bridging X-ligand  °C  degrees Celsius  xxiii  ACKNOWLEDGEMENTS Over the last five years I have been granted the opportunity to study, learn and experience many of the joys and frustrations that chemical research has to offer. For this I am grateful to my research supervisor Professor Mike Fryzuk who did his best to insure that the joys outweighed the frustrations. His insights into the art of setting up a Schlenk line have remained with me since day one. For the excitement and many good times that have unfolded each and every day in the lab I would like to thank my lab mates both past and present. To Bruce MacKay, Michael Shaver, James Corkin, Lara Morello, Chris Carmichael, Erin Baker and Drs. Chris Kozak, Sam Johnson, Fran Kerton, Laleh Jafarpour, Volker Schmitz, Peihua Yu and Wolfram Seidel, your many helpful suggestions over the years are greatly appreciated. I am especially grateful to Dr. Sam Johnson who taught me to face a challenge from all directions and to answer questions, not with answers, but with more questions.  The UBC support staff are also thanked for their expertise and assistance:  Dr. Nick  Burlinson, Marietta Austria and Liane Darge (NMR), Mr. P. Borda and Mr. M. Lakha (elemental analysis), Steve Rak and Brian Ditchburn (glassblowing), as well as the personnel of the Mechanical Engineering and Electronics shop. I am especially indebted to Dr. Brian Patrick for solving every crystal structure presented in this thesis. Without his help, much of this work would have been merely speculative.  To my good friends Barry and Rosaleen, Dave and Kelly, Udo, Tanja, Lynsey, Chris and Rob, you have all made my experience in Vancouver one of the most memorable in my life. I would also like to thank the Bricklayers, the greatest basketball team that the chemistry department has produced, and with whom I have shared great times both on and off of the court. I would not be known as "clutch" i f not for you guys.  Finally, and most importantly, I am grateful to my family whose support and faith have truly been my pillar of strength.  Michael John Petrella  xxiv  To my Parents with love and respect  xxv  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Me  2  Me  Chemistry  2  Chapter 1  Amido and Phosphine Ligands in Transition Metal Chemistry  1.1  An introduction to amide and phosphine ligands The structure, stabilization and reactivity patterns o f a transition metal complex are  governed in large part by the ligands that surround the metal center. A suitable choice o f 1  ligands can allow for the production o f well-defined reaction centers within a transition metal complex, and the chemistry exhibited by these species can often be "fine-tuned" by simple modification o f the ligand sphere; to this end, much effort has been devoted to the development o f new ancillary ligands. In the Fryzuk research group, this goal has entailed the design and synthesis o f chelating (or macrocyclic) ligand sets comprised o f neutral phosphine donors and mono-anionic amide donors.  Before discussing the various mixed-  donor ligands that have been developed in our lab, a brief discussion concerning these two individual donor types w i l l be given.  1  References  begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  (i)  Phosphine ligands in transition metal chemistry  Phosphine ligands are one o f the most important classes o f ligands in transition metal chemistry. ' Phosphines are neutral, t w o electron donors and have the general formula P R 3 2 3  (where R = H, alkyl, aryl or halide). A phosphine ligand binds to a metal center through 0 donation o f its lone pair to an empty metal orbital.  They also possess 7t-accepting  capabilities allowing for back-donation from a filled metal orbital to an empty orbital on the phosphine ligand.  This orbital has been described as being either a c/-orbital  3  or an  antibonding sigma orbital ( o * ) ; current consensus favours the latter given the relatively high 4  energy o f a phosphorus J-orbital.  A representation o f this synergistic bonding scheme is  given i n Figure 1.1. The 7t-accepting ability o f phosphine ligands renders them as useful donors for electron-rich late transition metals (i.e. metals in low oxidation states).  a-bond  71-bond  R  R  w  R empty metal orbital  P  l  n  n  p  n  a p  i  w  filled metal orbital  r  R  P y a* orbital e m  t  Figure 1.1. Orbital representation o f the o and 7t-bonding interactions between a phosphine ligand and a metal center.  Phosphine ligands can exhibit a range o f o-donor and 7t-accepting capabilities depending on the nature o f the R-groups bound to the phosphorus atom.  5  As electron-  donating groups are placed on the phosphorus atom, for instance, the G-donating ability w i l l  2  References begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  increase whereas the 7i-accepting ability w i l l decrease. The electron-rich phosphine P Bu3 is l  a stronger o-donor than PPI13, which in turn is a stronger a-donor than PF3 (which contains electron withdrawing fluorine atoms). On the other hand, the metal-phosphorus ^-interaction for these same ligands would be strongest for PF and weakest for P'Bu . 3  3  The electronic  properties o f a metal center can therefore be fine tuned by substitution o f electronically different phosphine ligands.  Modification o f the phosphine substituents w i l l also have an effect on the steric attributes o f the ligand. A n evaluation o f the steric demands o f a ligand can be deduced by measurement o f its cone angle. This entails measuring the "cone" swept out by the ligand at 2  the metal center; in its simplest form, the cone angle is defined as the angle ((])) o f a cylindrical cone centered 2.28 A from the phosphorus and touches the outermost atoms o f the substituent R groups (Figure 1.2). The triphenylphosphine ligand (PPh3) has a cone angle o f 145 . 0  3  Replacement o f the phenyl groups with cyclohexyl substituents yields the bulkier  PCy ligand, which has a cone angle o f 170°.  The reactivity o f a metal complex can also be  3  3  tuned by modifying the bulk o f the ligands in its coordination sphere. For example, whereas the complex RhCl(PPh )3 (Wilkinson's catalyst) 3  processes, the species RhCl(PMe3) conditions.  7  3  6  is effective in olefin hydrogenation  does not hydrogenate olefins even under extreme  A n important step in the catalytic cycle for Wilkinson's catalyst is dissociation  o f a phosphine ligand in order to access the active species and the use o f the bulkier PPh  3  ligands facilitates this important step (as opposed to PMe3).  3  References begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  Figure 1.2. Measurement o f the cone angle ((])) for a phosphine donor (PR3) with ball-andstick representations o f the PPh (()) = 145°) and PCy ligands ((j) = 170°). 3  3  In addition to the numerous monodentate phosphine ligands that exist there are many examples o f polydentate phosphines including bidentate ligands such as R2PCH2CH2PR2 or 2  R2PCH2PR2,  and  tridentate  chelates  such  as  HC(CH PR ) 2  2  3  or  N(CH CH PPh ) . 2  2  2  3  Furthermore, a variety o f chiral phosphine ligands (mono- and polydentate) have been synthesized allowing for the preparation o f chiral metal complexes; these species are useful in facilitating enantioselective transformations and are employed in asymmetric synthesis and catalytic processes. 8  9  A n additional advantage o f using phosphine donors in metal complexes is that the phosphorus-31 ( P ) nucleus has a nuclear spin of Vi and is 100 % abundant making it readily 3I  observable by nuclear magnetic resonance ( N M R ) techniques.  10  It is a relatively sensitive  nucleus (relative sensitivity = 0.07 with respect to ' H ) so that P N M R acquisition times and 3 1  sample concentrations are usually low. The chemical shift window for  4  3 1  P N M R is rather  References  begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  large and therefore allows for phosphine ligands in different chemical environments to be easily distinguished. Coupling o f the phosphorus-31 nucleus to other spin-active nuclei (e.g. 'H,  1 3  C , L i ) can provide significant details into the solution structure o f a complex and the 7  number o f peaks present in a P N M R spectrum can allow for the symmetry o f a complex to 3 I  be deduced.  Monitoring the progress o f a reaction by  3 1  P N M R spectroscopy is also a  valuable tool.  (ii)  Amido ligands in transition metal chemistry  A n amide ligand (or amido ligand) is a negatively charged donor, ~ N R R ' (where R, R' = hydrogen, alkyl, aryl or silyl groups) that results from the deprotonation o f an amine HNRR'. In valence bond terms, an amido ligand has two lone pairs o f electrons and thus is capable o f three types o f bonding modes as shown in Figure 1.3.  11  In structure A the amide  is bound to the metal via a a-bond leaving one electron pair localized on the nitrogen atom; this requires that the nitrogen centre is sp  3  hybridized and has a pyramidal geometry.  An  amide ligand can also act as a 7t-base in which donation o f the remaining lone pair o f electrons to a suitable vacant orbital on the metal occurs.  This results in a planar  sp  2  hybridized nitrogen atom (structure B ) . The ability to partake in ft-bonding interactions with amide substituents (e.g. aryl or silyl groups) can also yield a planar nitrogen a t o m .  12  In C,  both lone pairs are involved in o-bonding to two separate metal centers such that the amide acts as a bridging ligand; in this coordination mode, the amido ligand is sp hybridized. This 3  bonding mode is often favoured for smaller amide ligands such as the parent amido moiety NH . 2  5  References  begin on page 23  Chapter 1: Amido and Phosphine  6>  M  Ligands in Transition Metal  Chemistry  <R'  N  M  R  N-. \"""R' R C  B  A  /  M  Figure 1.3. Various bonding modes o f an amido ligand to a transition metal.  (iii)  Metal-amide (M-N) bonding considerations  Amide ligands have been used as anionic donors for both the early transition m e t a l s ' ' 11  12  14  as well as for the lanthanides.  13  13  and late  The reactivity patterns o f the amide  linkage when coordinated to a late transition metal, however, are distinctively different from those o f early metal complexes. Whereas early transition metal amide bonds are generally thermodynamically and kinetically stable,  13  late transition metal amide complexes have been  shown to be much more r e a c t i v e . - "  16  This difference has commonly been explained i n  terms o f the hard-soft acid-base theory.  17  According to this premise an amido ligand (a hard  11  14  donor) is better suited with the early transition metals (hard acceptors) due to the compatible donor-acceptor properties, whereas M - N linkages are characteristically weak with late metals due to a mismatch o f these hard, basic ligands with soft late metals.  Another rationalization that has been given for the observed difference in reactivity o f the M - N bond between early and late transition metals involves the interaction o f the amido lone pair o f electrons with the metal J-orbitals.  18  As illustrated in Figure 1.4 (a), complexes  that have low valence electron counts (e.g. < d ) can be stabilized via 7t-bonding between the 4  nitrogen lone pair and an empty metal d-orbital o f correct symmetry. Early transition metals in high oxidation states commonly have d° electron counts, and are therefore well suited for amido ligands since they can allow for derealization o f 71-electron density from the donor onto the metal. I n contrast, the presence o f d electrons on a metal centre in close proximity K  to a ligand heteroatom lone pair results in 7t-electron conflict that increases the reactivity o f  6  References  begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  the heteroatom moiety. As shown in Figure 1.4 (b), this interaction keeps the m i l population o f two electrons on the amide nitrogen atom (and thus keeps the Br^nsted basicity and nucleophilicity high). It also raises the energy o f the metal ^-electrons, thus enhancing the oxidizability o f the metal center. For late transition metal complexes in low oxidation states the c/-orbitals w i l l most likely be occupied (e.g. ruthenium(II) has a </ valence electron count) thereby destabilizing the metal-amide bond.  According to this qualitative bonding  scheme amido donors should be well suited for the preparation o f high-valent late transition metal complexes. The oxidation o f ruthenium(II) amine complexes, for example, results in the formation o f stable ruthenium ( I V ) amido complexes [Ru(bpy){H2NCMe2CMe2NH} ]  2+  2  (where bpy = 2,2'-bipyridine) and [ R u ( L ) { H N C M e C M e N H } 2 ] 2  2,3-dimethylbutane).  2  2  2+  (where L = 2,3-diamino-  19  7  References  begin on page 23  Chapter 1: Amido and Phosphine  R  Ligands in Transition Metal  Chemistry  R'  M  N  M  Figure 1.4. A qualitative molecular orbital diagram illustrating the interaction between a Ksymmetry amide lone pair o f electrons (p ) and the (a) empty and (b) filled a^-orbitals o f a n  transition metal.  The electrostatic-covalent (E-Q  theory o f b o n d i n g ' 20  21  has also been used to describe  the interaction between a transition metal and an anionic donor such as an amide l i g a n d . 22  23  This theory states that every bond has both an electrostatic and a covalent component; in the case o f a metal amide bond ( M - N ) it was shown that the electrostatic component has a greater contribution to the bond strength than does the covalent component. In other words, a transition metal has a greater inclination to bind electrostatically than covalently to an amide ligand. Since the electronegativity of the transition series increases from the early to  8  References  begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  the late metals, the electrostatic interaction between an amido ligand and a transition metal decreases from left to right across this series.  Accordingly, electropositive early transition  metals w i l l have a stronger electrostatic metal-amide interaction and consequently a stronger M - N bond.  (iv)  Preparation of late transition metal amide complexes  A variety o f synthetic strategies are available for the incorporation o f an amide unit onto a late transition m e t a l . ' 11  14  One o f the most convenient procedures involves the  metathesis o f a transition metal halide or triflate complex with an alkali metal amide. Care must be taken i n this transmetalation process since reduction i n lieu o f metathesis is a common side reaction and in many cases the choice o f cation and solvent system is crucial to the  success  o f these  reactions.  11  The ruthenium(II)  diphenyl  amido  complex  Cp*(PMe3)2Ru(NPh2) has been prepared via salt metathesis as depicted in Scheme 1 . 1  2 4  Me P 3  Scheme 1.1  9  References begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  The protonation o f basic ligands such as alkoxides or alkyls by amine ligands ( o ligand metathesis) is another route that has been employed for the preparation o f late transition metal amido complexes. The addition o f diphenyl amine (PI12NH) to the hydroxy complex C p \ P M e ) R u ( O H ) , for example, affords Cp\PMe3) Ru(NPli2); the amido and 3  2  2  hydroxy complexes exists as an equilibrium mixture (Scheme l . l ) .  This methodology is  2 4  also applicable in the rhenium-amide system shown in equation 1.1.  I n this system the  equilibrium can be driven towards the rhenium anilido complex by the use of 4 A molecular sieves, which sequester the methanol that is generated.  15  CO  CO PhNH,  OC  • Re-C  OC  MeOH  OC^*  [1.1]  ^Re<  OMe  NHPh  Other methods that have been employed for the preparation o f late transition metal amide complexes include the deprotonation o f a coordinated amine ligand (equation 1.2) and nucleophilic attack o f a coordinated imine ligand (equation 1.3). ' 25  L M-*—N n  L Mn  /  \  R  11  26  R R'  L M  + B'  n  [1.2]  R'  H  V  + BH  N.  /  /  -N  -H  R  [1.3]  + Nu" S  R'  C:  R'  10  References  H  Nu  begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  (v)  Reactivity of the late transition metal-amide bond  (a)  Protonation reactions of late metal amides  The majority o f late transition metal amide complexes display reactivity at the M - N bond that is more closely related to the chemistry that might be expected o f an alkali metal amide rather than the reactivity o f a charge-neutral organic amine.  Late metal amides have  15  been shown to act as Br^nsted bases and undergo protonation reactions with a variety o f acids.  16  In the example shown in equation 1.4 protonation o f the aryl amide ligand by water  generates a dinuclear nickel species containing two hydroxy bridges along with an equivalent o f aryl amine.  27  The substituents at the amido nitrogen position have been shown to play a key role in the observed basicity o f the amido ligand in late metal systems. The parent amido complex TpRu(CO)(PPh )(NH ) (Tp = tris{pyrazolylborate}), for instance, can deprotonate weak 3  2  acids including phenylacetylene (pK ~ 23) at room temperature. a  28  The related complex  TpRu(CO)(PPh )(NHPh) bearing a phenyl-substituted amido ligand on the other hand was 3  11  References begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  unreactive towards weak acids even at elevated temperatures for prolonged periods (72 h at 70 ° C ) .  28  It was suggested that the presence o f the amido phenyl ring mitigated the amido  basicity via derealization o f the nitrogen lone electron pair.  (b)  Late metal amides as nucleophiles and migratory insertion reactions  Related to the protonation reactions discussed above are the reactions o f late metal amides with electrophiles and Lewis acids. Nucleophilic chemistry has been reported for the platinum (II) complex (dppe)(Me)Pt{N(Me)(Ph)} (dppe = Ph PCH CH2PPh2) with acetyl 2  chloride and CD3I as shown i n Scheme 1.2.  2  29  NMePh  (dppe)(Me)Pt{N(Me)(Ph)}  PhN(CH )(CD ) 3  3  Scheme 1.2  Heterocumulenes (e.g. C 0 , CS , RNCO) have commonly been used to probe the 2  nucleophilicity  o f metal  2  alkoxide  and amide  complexes.  The amido  complex  Cp*(PPh3)(H)Ir(NHPh) undergoes nucleophilic insertion chemistry with carbon disulfide to form the metalloxanthate complex Cp*(PPh3)(H)Ir(SC(S)NHPh) as shown in equation 1.5.  15  The product o f this reaction is a result o f net nucleophilic attack by the amido nitrogen atom at the electrophilic carbon o f the CS molecule. 2  12  References  begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  s The reaction o f CO2 with ruthenium(II) anilido complexes o f the type  (r| 6  arene)(PMe3)(R)Ru(NR'Ph) is related to the iridium system discussed above, and also provides evidence for nucleophilic behaviour o f the amido nitrogen a t o m .  30  This chemistry  is summarized in equation 1.6. The addition o f carbon dioxide to the ruthenium complexes results in the net insertion o f CO2 into the Ru-N bond to give a metal carbamate complex. Given the electronic saturation at the metal centre a likely reaction pathway involves direct attack o f the nitrogen lone pair on CO2 followed by Ru-O bond formation.  While the  reaction with complex A proceeded to only 70 % conversion, the quantitative formation o f the carbamate complexes was observed with B and C. It was postulated that the increased electron richness o f the /?ara-toluamide ligand in C and the better electron donating ability o f the methyl ligand in B (versus the phenyl group in A) makes the amido nitrogen atom more nucleophilic; this difference in reactivity supports a nucleophilic insertion process.  A: R = Ph, R' = Ph B: R = Me, R' = Ph C: R = Ph, R' = p-tol  The migratory insertion o f unsaturated molecules into the M - N bond o f late transition metal amido complexes has also been r e p o r t e d . ' ' 11  13  14  31-35  Whereas the insertion o f CO into  References  begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  metal-carbon bonds is a widely observed phenomenon in organometallic relatively fewer examples with metal amides are k n o w n . ' 15  36  chemistry  3  I n one report the facile  37  insertion o f carbon monoxide in an iridium anilido complex was shown to take place (equation 1.7).  The platinum amide complex (dppe)(CH )Pt(NHCH Ph) preferentially  34  3  2  inserts carbon monoxide into the Pt-N bond to generate (dppe)(CH )Pt{CONH(CH Ph)}. 3  33  2  However, in many cases the addition o f carbon monoxide to a late transition metal amide complex does not result in its insertion into the M - N bond. For example, the complex ( r f C Me5)(PMe ) Ru(NPh ) reacts with CO by displacement o f PMe 5  3  2  2  complex ( T i - C M e ) ( P M e ) ( C O ) R u ( N P h ) , 5  5  5  3  PPh  2  2  2  2  with the  CO Ph P3  -NHAr  Ir-  Ph P' 3  [1.7]  \  NHAr  CO  PPh,  (c)  2  33  2 CO  co-  fra«s-(PEt ) (H)Pt(NHPh)  3  -Ir  to give the carbonyl  and the platinum (0) species (PEt ) (CO) Pt is  24  2  generated upon addition o f CO to the complex concomitant formation o f aniline.  3  P-hydride elimination  A viable decomposition route for late transition metal amide complexes is P-hydride elimination (Scheme 1.3); given that the amide ligand ~ N R is isoelectronic with an alkyl 2  moiety ~CR it is not surprising that P-hydride elimination occurs since this is also a common 3  decomposition pathway for metal a l k y l s . > 11  38  40  14  References  begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  R H-  /  M-  -X  M-  X = CR , NR or 0 2  R  H M-  M-  R  Ii X  -H R R  Scheme 1.3  This process can be a useful preparative reaction for the synthesis o f late transition metal hydride complexes as shown in Scheme 1.4 for the reaction o f lithium dimethyl amide ( L i N M e ) with R u C l ( P P h ) . 2  2  3  41  4  The use o f L i N ( C D ) M e in the reaction w i t h RhCl(PPh ) 3  3  3  generated both RhH(PPh ) and RhD(PPh ) isotopomers in a ratio o f 6:1 (thus giving a 3  3  3  3  deuterium isotope effect, k#lkv o f 6), indicating that cleavage o f the C-H bond is the ratedetermining step.  41  One way to circumvent this decomposition pathway is to utilize amido  substituents that do not contain [3-hydrogen atoms such as the trimethylsilyl moiety or the phenyl group; the complexes RuH{N(SiMe3)2}(PPh ) and Pt(PEt )(NPh ), for example, 3  have successfully been prepared.  2  2  2  11  15  References begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  LiNMe, (- LiCI) RuCI (PPh ) 2  3  Chemistry  Ru(H)CI(PPh ) + PPh 3 3  3  4  2 LiNMe,  Ru(H) (PPh ) 2  (-2 LiCI)  3  4  Scheme 1.4  (d)  Hydrogenolysis of metal amides  O f particular importance to this thesis is the ability o f a late transition metal-amide bond to effect the heterolytic cleavage o f dihydrogen.  Recent experimental studies have  11  shown the metal-amide linkage in late transition metal complexes to be highly polarized and possess significant ionic character. ' 15  23  This feature is well suited for the deprotonation o f a  coordinated H2 ligand as depicted in equation 1.8. I n this heterolytic cleavage process a metal hydride and an amine ligand are formed.  5"  8  H-  -H  +  H  H  ,.n»R'  L M-  L M-H  n  n  8~  /  [1.8]  •N-.., , 1(R  R The first example o f the activation o f dihydrogen by a late metal amide complex was reported in the Fryzuk research group and involved an iridium (I) [PNP] system (equation 1.9).  42  Since the amine ligand is anchored within the chelating ligand set it does not  dissociate from the metal centre. [PNP] complexes o f r h o d i u m ( I ) ' 43  44  and ruthenium(II)  45  were also shown to be capable o f splitting H2 in a heterolytic fashion. The cleavage o f H2 by ruthenium amido moieties has been proposed as a key step in catalytic hydrogenation o f ketones  and imines  mechanism  by ruthenium(II)  complexes  that  operate  by the bifunctional  4 6 - 4 9  16  References  begin on page 23  Chapter 1: Amido and Phosphine  1.2  Ligands in Transition Metal  Chemistry  The mixed-donor amidophosphine ligands [PNP], [P N ] and [NPN] 2  2  In the Fryzuk research group, hybrid ligands that contain phosphine and amide donors in a chelating array have been developed. It was envisioned that by combining these " h a r d " and "soft" donor types within a single ligand scaffold, these ligands would be suitable for coordination to a variety o f metals in various oxidation states. The first such ligand utilizing this  combination  of  donor  types  was  the  tridentate  amidodiphosphine  N ( S i M e C H P R ) 2 , abbreviated [ P N P ] (where R = Me, 'Pr, B u or P h ) . R  2  2  (  2  50  ligand  This mono-anionic  ligand contains an amido donor flanked by two phosphines; it is an extremely versatile ligand that has been successfully applied to both early and late transition metals.  51  The pendant  phosphine donors are well suited for coordination to low oxidation state late transition metals whereas the central amide binds strongly to high oxidation state early transition metals. 12  13  The chelating nature o f the [ P N P ] ligand assists stabilization o f the apparent mismatch in R  donor types, and thus aids in securing the ligand to a variety o f metals.  Although an  overview o f the chemistry o f the [ P N P ] ligand w i l l not be given in this thesis, a summary o f R  R  [ P N P ] complexes o f ruthenium(II) w i l l be given in a later section. The preparation o f the  lithiated ligand precursor [ P N P ] L i is shown in equation 1.10. For alkyl phosphines, a single R  step procedure is possible, which involves the addition o f the commercially available disilazane H N ( S i M e C H C l ) with three equivalents o f L i P R ; two equivalents functionalize 2  2  2  2  the chloromethyl side-arms and the third equivalent deprotonates the amine generating a lithium amide. Metal complexes o f [ P N P ] are easily prepared by reaction o f the lithiated R  ligand precursor with metal halide via salt metathesis.  17  References  begin on page 23  Chapter  Me .Si.  Cl  Me Si  2  H  1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  Me .Si. 2  3 LiPR THF  <  2  -2 LiCI -HPR  Cl  Me Si  2  Li  [1.10] R  R  2  2  R = Me, 'Pr, Bu r  Ri[PNP]Li  The [P2N2] macrocycle is another mixed-donor ligand that has been developed in the Fryzuk research group.  52  I t is a four-coordinate, dianionic ligand that can be considered an  extension o f the tridentate [ P N P ] set i n which the two phosphine donors have been linked R  with  an additional  disilazane  moiety.  The preparation  o f the dilithium  [P2N ]Li2-(C4H 0 ) (where, [ P N ] = PhP(CH SiMe NSiMe2CH2)2PPh and C H 0 2  8  2  2  2  2  4  2  8  2  salt  is 1,4-  dioxane) is outlined in Scheme 1.5. The dilithium salt o f the macrocycle is a useful precursor to [P2N2] metal complexes and both early and late transition metal species have been prepared via salt metathesis reactions with metal halide starting m a t e r i a l s .  53-60  The relative  ease at which this ligand is prepared is quite remarkable. Macrocyclic ligand synthesis is often achieved by employing very high dilution techniques or by utilizing metal templates to enforce ring-closure. ' 61  62  It is possible that the L12N2 core within this ligand facilitates ring-  closure via phosphine coordination. Since the phosphine atoms within the [P2N2] ligand are able to exhibit different stereochemistries '  63 64  that can result in two isomeric forms o f this  ligand, it also impressive that the syn-\?2^2\ isomer (shown i n Scheme 1.5 with the phosphine phenyl groups oriented in the same direction) can be exclusively prepared by the appropriate choice o f solvent and temperature. Only the syn isomer is utilized in the work discussed throughout this thesis, and as such this prefix w i l l be omitted. A n advantage o f the [P2N2] macrocycle is that the steric and electronic properties o f this ligand can be modified by varying the substituent o f the phosphine donor.  18  References  begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  2PhPH  Chemistry  2  2 Bu"Li  Me  Me  2  2  L=1,4-dioxane, C H 0 4  Me  Me  2  8  2  2  [P N ]Li (C H 0 ) 2  2  2  4  8  2  Scheme 1.5  A drawback o f some metal complexes that contain the [P2N2] macrocycle is that they are often coordinatively and electronically saturated, and this can result i n the formation o f very stable species with unreactive metal centers. One way to alleviate this problem is to allow for more coordinative unsaturation at the metal centre; this has been achieved by the development o f the diamidophosphine ligand PhP(CH SiMe2NPh)2 (abbreviated as [NPN]). 2  The synthesis o f the dilithium salt o f the [NPN] ligand is given i n Scheme 1.6.  65  Similar to  the [ P N ] ligand the [NPN] donor set is dianionic, however, it is a tridentate chelating 2  ligand.  2  It can be considered as a variant o f the [P N2] ligand with one o f the phosphine 2  ligands removed. Also, whereas i n the [ P N ] macrocycle only the phosphine groups could 2  2  19  References  begin on page 23  Chapter  1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  be changed, the [NPN] chelate allows for modification o f both the phosphorus and nitrogen donors.  Me 2  Me -Si.  Et 0 THF  2  2  r  + 2 LiHNPh  Cl  -2 LiCI  Cl  2  .Ph  N' H  Cl PhPH 4 Buli 2  Ph  p—-Li.  Me  S = THF, C H 0  L l  4  8  2  Ph 2  [NPN]Li (C H 0) 2  4  8  2  Scheme 1.6  1.3  [PNP] ruthenium(ll) chemistry A summary o f the chemistry o f ruthenium(II) complexes that incorporate the  tridentate [PNP] ligand set is shown in Scheme 1.7. [PNP]Li with RuCl (PPh ) 2  3  3  45  The reaction o f the lithium salt  generates the amide complex [PNP]RuCl(PPh ) (A). 3  The  presence o f the soft phosphine donors and the chelating nature o f the [PNP] array help to stabilize the hard amido donor towards the soft ruthenium(II) centre. In addition, the lack o f  20  References  begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  P-hydrogen atoms on the amido donor eliminates the possibility o f P-hydride elimination as a decomposition pathway.  Treatment o f complex A with one atmosphere o f hydrogen gas  generates the hydrido-amide complex [PNHP]RuHCl(PPh ) (B); the coordinated amide 3  ligand i n A acts as a base and cleaves the H2 molecule heterolytically. This reaction is the first reported example o f the heterolytic activation o f H2 by a ruthenium-amide species. The hydrogenation product actually exists as a pair o f isomers (B and B') and both contain an intramolecular hydrogen bond between the amino proton and the chloride ligand.  I n an  attempt to prepare ruthenium alkyl complexes the reaction o f complex A with lithium alkyl and Grignard reagents was performed. I n all o f these cases the product that formed was the ortho-metalated complex [PNP]Ru(C6H4PPh ) (C). 2  Upon exposure o f complex C to an  atmosphere o f hydrogen gas it is converted to the monohydride amide [PNP]RuH(PPIi3) (D). Interestingly,  no further  reaction  is observed with  excess  H . 2  The addition o f  triethylphosphine to complex A also results i n orf/zo-metalation o f the triphenylphosphine ligand and generates the complex [PNHP]RuCl(C6H4PPh ) ( E ) . It was proposed that 2  coordination o f PEt to the open site o f the square pyramidal geometry o f A forced the PPh 3  3  ligand i n closer proximity to the amide nitrogen, thus assisting removal o f the phenyl ortho hydrogen atom. Complex E reacts with dihydrogen to give the previously identified hydrido amine complex B'.  21  References begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal  22  Chemistry  References  begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  1.4  Scope of this thesis In this thesis an investigation into the chemistry o f ruthenium(II) complexes that  incorporate the mixed-donor [NPN] and [ P N ] ligands is undertaken. Two different roles 2  2  for these ligand sets were envisioned. I n one capacity the reactive nature o f the rutheniumamido moiety was exploited to effect the heterolytic cleavage o f molecular hydrogen in an attempt to prepare ruthenium complexes with cw-coordinated hydride and amine ligands. Coordinatively saturated ruthenium(II) complexes that contain cw-located hydride and amine ligands have been reported to be among the most active species for catalytic ketone and imine hydrogenation r e a c t i o n s . ' ' 46  49  66  Chapter 2 presents the synthesis and characterization  of various ruthenium(II) amido complexes o f the [ P N ] and [NPN] ligands. Whereas X-ray 2  2  diffraction proved to be o f fundamental importance in the characterization o f these new species, the utility o f N M R spectroscopy including variable-temperature and isotopic labeling studies to elucidate structure and solution behaviour is also described. The reactivity o f these complexes with hydrogen gas is discussed i n Chapter 3 along with catalytic hydrogenation studies o f olefin and imine substrates. The second role that was anticipated for the [ P N ] and [NPN] ligands was for these ligand sets to act as stabilizing ancillary 2  2  donors and to examine their influence i n known catalytic processes involving ruthenium(II) systems. I n particular, modification o f ruthenium alkylidene and vinylidene complexes that have been used i n olefin metathesis processes has been investigated.  I n Chapter 4 the  reaction o f the [ P N ] and [NPN] ligand sets with alkylidene and vinylidene precursors is 2  2  described together with structural characterization o f the new complexes and their reactivity towards H and olefin substrates. 2  1.5  References  (1)  McAuliffe, C. A . Comprehensive Coordination Chemistry; Wilkinson, G., Gillard, R.  D. and McCleverty, J. A., Eds; Pergamon Press: London, 1987; V o l . 2.  23  References begin on page 23  Chapter 1: Amido and Phosphine  (2)  Ligands in Transition Metal  Chemistry  Cotton, F. A.; Wilkinson, G.; Murillo, C. A . ; Bochmann, M . Advanced Inorganic  Chemistry: A Comprehensive Text; 6th ed.; John Wiley and Sons, Inc.: Toronto, 1999.  (3)  Collman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition Metal  Chemistry; University Science Books: M i l l Valley, 1980.  (4)  Marynick, D. S. J. Am. Chem. Soc. 1984,106, 4064.  (5)  Greenwood, N . N . ; Earnshaw, A . Chemistry of the Elements; 2nd ed.; Butterworth-  Heinemann: Oxford, 1997.  (6)  Osborn, J. A . ; Jardine, F. H.; Young, J. F.; Wilkinson, G. J. Chem. Soc. A. 1966,  1711.  (7)  Jones, R. A.; Real, F. M.; Wilkinson, G.; Galas, A . M . R.; Hursthouse, M . B.; Malik,  K. M . A. J. Chem. Soc, Chem. Commun. 1979, 489.  (8)  Comarov, I. V.; Borner, A . Angew. Chem. Int. Ed. 2001, 40, 1197.  (9)  Knowles, W . S. Acc. Chem. Res. 1983,16, 206.  (10)  Pregosin, P. S.; Kunz, R. W . NMR Basic Principles and Progress; Springer-Verlag:  Heidelberg, 1979; V o l . 16.  (11)  Fryzuk, M . D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1.  (12)  Lappert, M . F.; Power, P. P.; Sanger, A . R.; Srivastava, R. C. Metal and Metalloid  Amides; John Wiley and Sons Canada Limited: Toronto, 1980.  (13)  Kempe, R. Angew. Chem. Int. Ed. 2000, 39, 468.  24  References  begin on page 23  Chapter  1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  (14)  Bryndza, H. E.; Tam, W . Chem. Rev. 1988, 88, 1163.  (15)  Fulton, J. R.; Holland, A . W . ; Fox, D. J.; Bergman, R. H. Acc. Chem. Res. 2002, 35,  44.  (16)  Fulton, J. R.; Bouwkamp, M . W . ; Bergman, R. G. J. Am. Chem. Soc. 2000, 122,  8799.  (17)  Pearson, R. G. J. Chem. Educ. 1968, 45, 581.  (18)  Caulton, K. G. New. J. Chem. 1994,18, 25.  (19)  Chiu, W . H.; Peng, S. M . ; Che, C. M . Inorg. Chem. 1996, 35, 3369.  (20)  Drago, R. S.; Wong, N . M . ; Ferris, D. C. J. Am. Chem. Soc. 1992,114, 9 1 .  (21)  Drago, R. S. Applications of Electrostatic-Covalent Models in Chemistry; Surfside:  Gainesville, FL, 1994.  (22)  Holland, P. L.; Andersen, R. A.; Bergman, R. G. Comments Inorg. Chem. 1999, 21,  115.  (23)  Holland, P. L.; Andersen, R. A . ; Bergman, R. G.; Huang, J.; Nolan, S. P. J. Am.  Chem. Soc. 1997,119, 12800.  (24)  Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W . ; Bercaw, J. E. J. Am. Chem.  Soc. 1987,109, 1444.  (25)  Martin, G. C ; Boncella, J. M . Organometallics 1989, 8, 2968.  (26)  Martin, G. C ; Boncella, J. M.; Wucherer, E. J. Organometallics 1991,10, 2804.  25  References  begin on page 23  Chapter 1: Amido and Phosphine Ligands in Transition Metal Chemistry  (27)  VanderLende, D. D.; Abboud, K. A . ; Boncella, J. M . Inorg. Chem. 1995, 34, 5319.  (28)  Jayaprakash, K. N.; Gunnoe, T. B.; Boyle, P. D. Inorg. Chem. 2001, 40, 6481.  (29)  Bryndza, H. E.; Fultz, W . C ; Tarn, W . Organometallics 1985, 4, 939.  (30)  Boncella, J. M . ; Eve, T. M ; Rickman, B.; Abboud, K. A . Polyhedron 1998,17, 725.  (31)  Cabeza, J. A . ; del Rio, I.; Grepioni, F.; Moreno, M . ; Riera, V . ; Suarez, M .  Organometallics 2001, 20, 4190.  (32)  Cabeza, J. A.; del Rio, I.; Moreno, M . ; Riera, V . Organometallics 1998,17, 3027.  (33)  Cowan, R. L.; Trogler, W . C. Organometallics 1987, 6, 2451.  (34)  Rahim, M . ; Ahmed, K. J. Organometallics 1994,13, 1751.  (35)  Rahim, M . ; Bushweller, H.; Ahmed, K. J. Organometallics 1994, 13, 4952.  (36)  Hauger, B. E.; Huffman, J. C ; Caulton, K. G. Organometallics 1996,15, 1856.  (37)  L i , J. J.; L i , W.; James, A . J.; Holbert, T.; Sharp, T. P.; Sharp, P. R. Inorg. Chem.  1999, 38, 1563.  (38)  Driver, M . S.; Hartwig, J. F. / . Am. Chem. Soc. 1995,117, 4708.  (39)  Cetinkaya, B.; Lappert, M . F.; Torroni, S. Chem. Commun. 1979, 599.  (40)  Hartwig, J. F. J. Am. Chem. Soc. 1996, 118, 7010.  (41)  Diamond, S. E.; Mares, F. J. Organomet. Chem. 1977,142, C55-C57.  26  References begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  (42;  Fryzuk, M . D.; MacNeil, P. A . Organometallics 1983, 2, 682.  (43  Fryzuk, M . D.; MacNeil, P. A.; Rettig, S. J. Organometallics 1985, 4, 1145.  (44  Fryzuk, M . D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc. 1987,109, 2803.  (45  Fryzuk, M . D.; Montgomery, C. D.; Rettig, S. J. Organometallics 1991, 10, 467.  (46  Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001, 66, 7931.  (47  Noyori, R.; Ohkuma, T. Angew. Chem. Int. Ed. 2001, 40, 40.  (48  Abdur-Rashid, K.; Faatz, M . ; Lough, A . J.; Morris, R. H. J. Am. Chem. Soc. 2001,  123 7473.  (49  Abdur-Rashid, K.; Lough, A . J.; Morris, R. H. Organometallics 2001, 20, 1047.  (50  Fryzuk, M . D.; MacNeil, P. A.; Rettig, S. J.; Secco, A . S.; Trotter, J. Organometallics  1982,7,918.  (51  Fryzuk, M . D. Can. J. Chem. 1992, 70, 2839.  (52;  Fryzuk, M . D.; Love, J. B.; Rettig, S. J. Chem. Commun. 1996, 2783.  (53  Fryzuk, M . D.; Love, J. B.; Rettig, S. J. Organometallics 1998,17, 846.  (54  Fryzuk, M . D.; Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 2001,123, 1602.  (55  Fryzuk, M . D.; Kozak, C. K.; Patrick, B. O. Inorg. Chim. Acta 2002, 345, 53.  27  References  begin on page 23  Chapter  (56)  1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  Fryzuk, M . D.; Kozak, C. K.; Bowdridge, M . R.; Patrick, B. O.; Rettig, S. J. J. Am.  Chem. Soc. 2002,124, 8389.  (57)  Fryzuk, M . D.; Kozak, C. K.; Mehrkhodavandi, P.; Morello, L.; Patrick, B. O.; Rettig,  S. J. J. Am. Chem. Soc. 2002,124, 516.  (58)  Johnson, S. A . Ligand Design and The Synthesis of Reactive Organometallic  Complexes of Tantalum for Dinitrogen Activation; University o f British Columbia: Vancouver, 2000.  (59)  Kozak, C. M . Activation of Small Molecules by Low Valent Niobium Complexes  Stabilized  by a Bis(Amidophosphine)  Macrocycle;  University o f British Columbia:  Vancouver, 2002.  (60)  Leznoff, D. B. Paramagnetic Organometallic Complexes; University o f British  Columbia: Vancouver, 1997.  (61)  Lindoy, L. F. The Chemistry of Macrocyclic Ligand  Complexes; Cambridge  University Press: 1989.  (62)  Kyba, E. P.; Davis, R. E.; Hudson, C. W.; John, A . M . ; Brown, S. B.; McPhaul, M . J.;  L i u , L. K.; Glover, A . C. J. Am. Chem. Soc. 1981,103, 3868.  (63)  Ansell, C. W . G.; Cooper, M . K.; Dancey, K. P.; Duckworth, P. A . ; Henrick, K.;  McPartlin, M ; Tasker, P. A . J. Chem. Soc, Chem. Commun. 1985, 439.  (64)  Caminade, A . M . ; Majoral, J. P. Chem. Rev. 1994, 94, 1183.  (65)  Fryzuk, M . D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S. A.; Koetzle, T.  K. J. Am. Chem. Soc. 2001,123, 3960.  28  References  begin on page 23  Chapter 1: Amido and Phosphine  Ligands in Transition Metal  Chemistry  Abdur-Rashid, K.; Lough, A . J.; Morris, R. H. Organometallics 2000,19, 2655.  29  References  begin on page 23  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand  Chapter 2  Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  2.1  Introduction  In recent years 18-electron ruthenium(II) complexes bearing cis-coordinated primary or secondary amine and hydride ligands have been employed as precursors for the catalytic asymmetric reduction of prochiral ketone and imine substrates.  1-10  Complexes of this type are  among the most active species for the hydrogenation of polar substrates, and in addition, these compounds display remarkable chemoselectivity in that preferential reduction of polar C=0 or C=N functionalities over non-polar C=C groups is observed.  11  This important process supplies  chiral alcohol and amine products in high yields and excellent enantiomeric purities. The desire for such compounds is significant in the pharmaceutical and agricultural chemical industries as well as in the field of synthetic organic chemistry.  12-28  Some examples of ruthenium(II)  complexes that catalyze the hydrogenation of imines and ketones are shown in Figure 2.1. For his many accomplishments in the area of asymmetric hydrogenation, including the development of chiral ruthenium(II) systems capable of effecting the rapid asymmetric reduction of prochiral  30  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand  imine and ketone substrates, Professor Ryoji Noyori of Nagoya University in Japan was awarded the Nobel Prize in Chemistry for the year 2 0 0 1 .  29  He shared this award with Dr. William S.  Knowles and Professor K. Barry Sharp less who were also recognized for their contributions in 30  31  asymmetric synthesis.  H  2  PPh  3  Figure 2.1. Ruthenium(II) complexes that act as precursors for the catalytic reduction of ketone and imine substrates. Both chiral and achiral complexes are shown.  An intriguing proposal to rationalize the observed chemoselectivity and the very high turnover rates has been developed. ' ' " 1 2 32  35  This process, illustrated in Scheme 2.1, has been  coined the "metal-ligand bifunctional mechanism" since it involves a cooperative effort between the transition metal hydride and the coordinated amine ligand. This is an intriguing hydrogenation mechanism since the substrate never binds to the metal centre at any point during the catalytic cycle.  Rather, acting in an outersphere process, both the Ru-H hydride and N-H proton are  simultaneously delivered to the ketone or imine functionality.  A key companion step in this  scheme includes the formation of an intermediate ruthenium amide complex that heterolytically cleaves a molecule of H2 regenerating the catalytically active species, and thereby completing the cycle.  31  References begin on page 98  Chapter  2: Synthesis,  Solution  Dynamics  and Reactivity  of Ruthenium(ll)  Complexes  Incorporating  the [NPN]  and [P2NJ Ligand  Sets  (X = O or NR")  Scheme 2.1  The ability of the ruthenium amide (Ru-N) unit to heterolytically activate molecular hydrogen was first reported in the Fryzuk group utilizing the mixed-donor [PNP] (where [PNP] = N(SiMe CH PPh)2) ligand set. 2  2  36  The details of this process are discussed in Chapter 1. Since the  coordinated amine moiety and hydride ligand in the product of this reaction are not c/s-disposed (a feature necessary for catalysis) its catalytic potential has not been investigated.  In an attempt to generate complexes containing cw-coordinated hydride and amine ligands we examined the incorporation o f the amidophosphine ligands, [NPN]Li2'(C4HgO)  2  ([NPN] =  PhP(CH SiMe NPh) ), and l^^jLfe'CCUHgCfe) ([P N ] = PhP(CH2SiMe NSiMe CH2)2PPh) onto 2  ruthenium(II).  2  2  2  2  2  2  A general outline summarizing the intended goal of this project is shown in  Scheme 2.2. Rather than preparing new catalysts for the hydrogenation of ketones and imines, our focus was aimed at examining the individual steps involved in the metal-ligand bifunctional mechanism. We sought a stable and isolable ruthenium amido species (A) that could react with H2 to generate a stable and isolable ruthenium complex with czs-coordinated amine and hydride ligands (B). The stoichiometric addition of an imine (or ketone) substrate could then possibly regenerate an unsaturated ruthenium amide species (C).  In this fashion, a step-by-step  examination of the catalytic hydrogenation of ketones or imines would be possible.  32  References  begin on page  98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [PsNJ Ligand S  [NPN]l_i (C H 0) 2  4  8  2  +  B  [CI RuL ] 2  n  H, 2LiCI H, [NPN]RuL  S  [NPNH ]RuH  [NPNH]RuH  n  2  2  - UnH2 n  C — X I I H H  C=X  (X = O or NR)  Scheme 2.2  In order to study the reactivity o f ruthenium(II) complexes bearing the tridentate [NPN] and macrocyclic  [P2N2]  ligands, a means o f introducing these ligands to the metal centre was  required. One procedure that has been successfully employed for the preparation o f late transition metal amide complexes is the metathetical reaction of alkali metal amides with metal halide precursors. This method was used for coordination of the [PNP] ligand set to iridium (I), rhodium (I) and ruthenium(II). '  Due to the convenient synthesis and ease o f isolation o f the [ N P N ]  36 37  and  [P2N2]  3 9  38  ligands as the dilithium salts, metathesis seemed a viable route for the preparation of  their ruthenium(II) complexes.  The compounds [RuCl2(cod)] (where cod = 1,5-cyclooctadiene, r| :r| -C8Hi2) 2  x  2  and  RuCl2(PPh3)3 were utilized as the ruthenium(II) precursors. Both compounds are readily prepared, and because they contain two chloride ligands it was anticipated that metathesis with the lithium salts of the [NPN] and [ P N 2 ] ligands would provide the corresponding diamido-ruthenium(II) 2  complexes, [NPN]RuL and [P N ]RuL (where L 2 = T ( : r i - C g H i 2 or L = PPh3). Moreover, it was 2  2  2  2  2  2  suspected that reaction of the resulting complexes with hydrogen gas would result in the elimination o f either cyclooctane (CsHi6) or triphenylphosphine (PPI13) allowing for the facile preparation of hydrido-amine ruthenium(II) complexes. The remaining sections o f this chapter  33  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and /P Ay Ligand 2  describe the synthesis, characterization and reactivity of various ruthenium(II) complexes that incorporate the [NPN] and [P2N2] ligand sets.  Chapter 3 will focus on the hydrogenation  reactivity of these compounds including catalytic studies.  2.2  Synthesis and Characterization of [P N ]Ru(r| :r| -C H 2) (1)  (i)  Synthesis and Structure of  2  2  2  8  [P2N ]RU(T| :TI -C8H 2) 2  2  2  2  1  1  (1)  The reaction o f the colourless ligand salt ^ ^ J I ^ G t H g C ^ with the brown starting material [RuCi2(cod)] generates a dark yellow-brown solution from which [P N2]Ru(r| :r| 2  x  2  2  C8H12), (1), can be isolated in 73 % yield (equation 2.1). Compound 1 is the first ruthenium complex of the [P2N2] ligand that has been prepared; [P2N2] complexes of other transition metals have previously been investigated.  40-45  Because the yellow diamido species 1 is only moderately  soluble in hexanes, it can be separated from the more soluble dark coloured impurities by rinsing the crude product mixture with hexanes. The slow evaporation of the hexanes rinsings gives yellow crystals of 1.  [2.1]  1 The solid-state molecular structure of 1 as determined by a single crystal X-ray diffraction study is shown in Figure 2.2, with selected bond lengths and angles highlighted in Table 2.1. The complex adopts a distorted octahedral geometry in which the amido donors of the [P2N2] ligand set and the olefin donors of the cyclooctadiene ligand lie in the equatorial plane. The phosphine ligands occupy the axial positions with a P(l)-Ru(l)-P(l)* angle of 152.18(4)°. The compound  34  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand S  exhibits C2 symmetry in the solid-state; a C2 axis of rotation runs through the cyclooctadiene ligand and bisects the N-Ru-N angle. A comparison of the P-M-N-Si dihedral angles in [P2N2] metal complexes has previously been used to measure the degree o f twist present in the ligand backbone.  44  A substantial difference between dihedral angles indicates a high degree o f twist in  the [P2N2] ligand and this feature reduces the symmetry of the complex. In complex 1, the P ( l ) R u ( l ) - N ( l ) - S i ( l ) and the P ( l ) * - R u ( l > N ( l ) * - S i ( l ) * dihedral angles are identical (145.33(14)°) further demonstrating the symmetrical nature of the complex.  Figure 2.2. ORTEP representation (thermal ellipsoids shown at 50 % probability) of the solidstate molecular structure o f [P2N ]Ru(r| :r| -C8Hi2) (1). 2  2  2  The silyl methyl groups o f the [P2N ] 2  ligand have been omitted for clarity.  Table 2.1. Selected bond lengths, angles and dihedral angles in [P N ]Ru(r| :ri -C8Hi2) (1). 2  2  Atom Ru(l) Ru(l) Ru(l) Ru(l) C(13)  Atom N(l)/N(l)* P(l)/P(l)* C(13)/C(13)* C(14)/C(14)* C(14)  35  2  2  Distance (A) 2.223(2) 2.3908(7) 2.200(3) 2.202(3) 1.386(4)  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligan 2  Atom P(l) N(l) P(l) P(l) N(l) N(l) N(l)  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom P(l)* N(l)* N(l) N(l)* C(13) C(13)* C(14)  Atom P(l) P(l) P(l)* P(l)*  Atom Ru(l) Ru(l) Ru(l) Rufl)  Atom N(l) N(l)* N(l) N(l)*  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom  Angle (°) 152.18(4) 92.91(12) 75.88(6) 84.99(6) 158.62(10) 92.40(10) 163.67(9)  N(l) P(l) P(l) P(l) P(l) C(13) C(14)  Atom C(14)* C(13) C(13)* C(14) C(14)* C(13)* C(14)*  Angle (°) 90.59(10) 83.98(8) 116.39(8) 120.34(8) 80.40(8) 90.15(16) 90.51(17)  Dihedral Angle (°) -145.33(14) -158.50(13) -158.50(13) -145.33(14)  Atom Si(l) Si(2)* Si(2) Si(l)*  The smaller N-Ru-N bite angle of 92.91(12)° compared to the larger P-Ru-P bite angle of 152.18(4)° is consistent with the previously observed binding of the [P N ] ligand in which the 2  2  amide donors are typically cis while the phosphines are located approximately trans to one another. Similar to [P N ] complexes o f the early transition metals, the ruthenium centre in 1 is 2  2  perched on, rather than nested in, the macrocycle.  (ii)  Variable-Temperature  NMR  Spectroscopy of  [P2N2]RU(T) :T) -C HI2) 2  2  8  (1)  The room temperature ' H N M R spectrum of complex 1 in toluene-^ is indicative of a C v 2  symmetric solution structure. For instance, the [P N ] ligand in 1 gives rise to two resonances for 2  2  the silyl methyl protons at 8 0.4 and 8 0.5. These correspond to the silyl methyl groups directed to the "top" and "bottom" o f the ligand (where top refers to the side o f the ligand to which the metal is bound). I f the C symmetry evident in the solid-state molecular structure of 1 was maintained in 2  solution, four silyl methyl proton resonances would be expected. In addition, there is a single peak present for the four methylene protons of the cyclooctadiene ligand and a broad signal for the eight methyl protons. The  13  C { H } N M R spectrum at this same temperature is also consistent 1  with complex 1 exhibiting C v symmetry in solution. Two resonances for the silyl methyl carbon 2  nuclei are observed and only one peak for the [P N ] methylene carbon nuclei is present; no 2  36  2  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligan  coupling to the P nucleus could be resolved. The cyclooctadiene ligand has a single methylene 3 l  carbon resonance at 8 70.0 and a single methyl carbon resonance at 8 25.0.  The higher symmetry o f complex 1 in solution as evidenced by the ' H and C { ' H ) N M R 13  data is due to the conformationally flexible nature of the [P2N2] ligand. It has previously been suggested that a locked conformation o f the [P2N2] ligand may arise from electronic effects due to a n-interaction o f the amide lone pairs with metal-based orbitals.  44  In the case o f complex 1, the  metal orbitals o f correct symmetry available for such a Jt-bonding interaction (d , d^ or d ) are Ky  filled.  yz  Consequently, ligand to metal 7t-donation is eliminated allowing for greater flexibility  within the [P2N2] ligand framework.  A geometry of C2V symmetry can be rationalized via a  twisting motion of the [P2N2] ligand about the amido nitrogen atoms o f the macrocycle, as shown in Figure 2.3.  At room temperature this fluxional process occurs rapidly such that two apparent  mirror planes o f symmetry exist in complex 1. One o f these is contained within the N-Ru-N plane while the other is contained within the P-Ru-P plane,  fn the solid-state the [P2N2] ligand is  conformationally rigid allowing only for a C2 axis of rotation.  Figure 2.3. Depiction of the fluxional behaviour of complex 1 in solution via twisting of the [P2N2] framework about the amido nitrogen atoms.  A variable-temperature  N M R study o f complex 1 was undertaken and the effect of  temperature on the olefinic proton resonances of the cyclooctadiene ligand in 1 is shown in Figure 2.4. As the temperature is lowered, the singlet that is observed at room temperature begins to broaden until decoalescence occurs at 234 K. At the low-temperature limit (198 K ) two signals are present at 8 2.6 and 8 3.0, each integrating to two methylene protons. Also at 198 K four  37  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and {P Nz] Ligand 2  signals are present for the silyl methyl groups of the [P N ] ligand between 8 0.3 and 8 0.8. The 2  2  broad peak for the cyclooctadiene methyl protons collapses to four singlets and the [P N ] 2  methylene protons remain as two peaks.  2  Although the resolution at this temperature was not  adequate to distinguish the anticipated couplings, the features present in the low-temperature limiting spectrum are consistent with C symmetry, as observed in the solid state. 2  1111  3.1  1 1 1 1 1 1 1 1 1 1 1 1 1  3.0  11111111111  2.9  2.8 ( p p m )  11111111  2.5  2.6  2.T  Figure 2.4. The effect of temperature on the methylene resonance of the cyclooctadiene ligand in the 500 MHz *H N M R spectrum of [P N ]Ru(r) :n -C Hi ) (1). 2  2  2  2  8  2  A line-shape analysis of the methylene protons of the cyclooctadiene ligand from 212 K to 243 K combined with an Arrhenius plot of the resulting rate constants provided an activation barrier of 18.6 ± 1.6 kcal mol" for the twisting motion of the [P N ] framework within complex 1. 1  2  2  The Arrhenius plot is shown in Figure 2.5 and the rate constants are given in Table 2.2.  38  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligan  Table 2.2. Calculated rate constants (k) for the fluxionality o f the [P2N2] ligand in the complex [P N ]RU(TI :TI -C8H 2) (1). 2  2  2  1  2  Temperature, T (K)  - Rate Constant, k (s" ) 1  5 304 ± 265  243 ± 1  865 ± 43  234 ± 1  560 ± 28  230 ± 1  433 ± 2 2  227 ± 1  66 ± 3  219 ± 1  18± 1  212 ± 1  10 • 9-  87-  ln(k) _ 6  o" 43210 H 0.004  1  1  1  1  1  1  1  1  0.0041 0.0042 0.0043 0.0044 0.0045 0.0046 0.0047 0.0048 1/T (K ) 1  Figure 2.5.  Arrhenius plot for the fluxionality of the [P2N2] ligand framework in the complex  [P N ]Ru(r| :ri -C8H 2) (1) ( R = 0 . 9 9 2 0 and E = 18.6 ± 1.6 kcal mol" ). 2  2  2  2  2  1  1  A  39  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligan 2  2.3  Synthesis and Characterization of [P NNH]Ru(C H4PPh2) (2)  (i)  Synthesis and NMR Spectroscopic Characterization of  2  6  [P NNH]Ru(C H PPh2) (2) 2  6  4  The reaction of RuCl (PPh )3 with the [P2N2] ligand did not afford the expected 2  3  diamidodiphosphine ruthenium(II) complex [P2N2]RuPPh3. Rather, the compound isolated was the product of or/7zo-metalation o f the triphenylphosphine ligand, [P NNH]Ru(C6H4PPli2) (2), as 2  shown in equation 2.2. The propensity for the PPI13 ligand to ortho-metalate is well known not only for complexes o f ruthenium(U) ' but for other metals as w e l l . ' 36 46  47  Previous studies in the  48  Fryzuk laboratory have shown that the related species [PNP]RuCl(PPli3) suffers a similar fate upon addition o f triethylphosphine, resulting in the formation of [PNHP]RuCl(C6Pi4PPh ).  36  2  Me Si: Me Si^  Ph  2  [P N ]Li dioxane 2  2  2  RuCI (PPh ) 2  3  2  2  f t Me s(NH  toluene  y  2  - 2LiCI -2PPh  [2.2]  Me SQ 2  3  3  v  Ph  Stirring a solution containing an equimolar mixture of [P2N ]Li 'C4H802 and RuCl2(PPh )3 2  2  3  in toluene results in the formation o f an orange-brown coloured solution within three hours. Removal o f LiCI  is accomplished by  filtration, however,  separation of  2 from  free  triphenylphosphine proved more difficult due to the similar solubilities o f these two compounds in hydrocarbon solvents.  Isolation of 2 was successfully accomplished by the addition of two  equivalents o f anhydrous CuCl; this generates an insoluble "CuCl'PPh3" oligomeric complex  49  that is more easily removed by filtration.  Diagnostic o f complex 2 is the P{'H} N M R spectrum, which shows a doublet (at 8 25.8) 31  and a triplet (at 8 -11.8) for the ancillary phosphine donors of the [P2NNH] ligand set and the P(C6H Ph ) ligand, respectively ( Jpp = 31 Hz). 2  4  2  40  These signals integrate in the ratio 2:1. An  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand S  upfield shift for the P nucleus o f the P(C6H4PIi2) ligand has been observed in other complexes 31  that incorporate an or^o-metalated triphenylphosphine ligand.  50  The equivalency o f the  phosphorus centres in the [P NNH] ligand is consistent with the proposed structure, which has C 2  s  symmetry.  The room-temperature 500 MHz ' H N M R data is also consistent with the proposed structure of complex 2 shown in equation 2.2. Four resonances for the silyl methyl groups of the [P2NNH] ligand set are observed between 8 0.40 and 8 0.60 in accordance with a mirror plane of symmetry contained within the equatorial plane o f the octahedral coordination geometry o f 2. The ligand methylene protons give rise to two sets o f overlapping resonances consisting of a secondorder A A ' B X pattern. A singlet at 8 2.8 has been ascribed to the amino proton (N-H). The aromatic protons o f the triphenylphosphine and [P2N2] phosphorus phenyl substituents occur as overlapping resonances between 8 6.5 and 8 8.2.  (ii)  X-ray diffraction study of [P NNH]Ru(C H PPh2) (2) 2  6  4  Single crystals of [P NNH]RuP(C H PPh2) (2) suitable for an X-ray diffraction study were 2  6  4  grown by the slow evaporation o f a saturated pentane solution. The solid-state molecular structure of 2 as determined by X-ray crystallography is shown in Figure 2.6 with selected bond lengths and bond angles detailed in Table 2.3. Complex 2 crystallizes with two crystallographically distinct but structurally related molecules in the asymmetric unit, in addition to one molecule of /7-pentane. The following structural discussion will be concerned with only one o f the molecules for the sake of brevity.  41  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand Sets  Figure 2.6. The solid-state molecular structure (ORTEP representation, 50 % thermal ellipsoid probability) of [P NNH]Ru(C E(4PPh2) (2) as determined by X-ray crystallography. 2  6  The silyl  methyl groups of the [P2NNH] ligand have been omitted for clarity.  42  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligan  Table 2.3.  Selected bond lengths, bond angles and dihedral angles in the complex  [P NNH]Ru(C H4PPh ) (2). 2  6  2  Atom Ru(l) Ru(l) Ru(l) Ru(D  Atom C(26) C(26) N(2) C(26) N(2) P(3) C(26) N(2)  Atom C(26) N(2) P(3) P(2)  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom N(2) P(3) P(3) P(2) P(2) P(2) P(l) P(l) Atom P(l) P(2) Ru(l) P(3)  Distance (A) 2.034(5) 2.260(4) 2.2989(13) 2.3248(13)  Atom Ru(l) Ru(l) N(l) N(2)  Atom P(l) N(l) •H(101) H(101)  Angle 0 99.66(18) 68.39(14) 167.65(12) 93.96(14) 86.15(11) 97.51(5) 93.80(14) 84.41(11)  Atom P(3) P(2) C(26) N(2) P(3) P(2) P(l) N(l)  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) H(101)  Atom Ru(l) Ru(l) N(l) Ru(l)  Atom C(26) C(26) H(101) N(l)  Atom C(25) C(25) N(2) H(101)  Distance (A) 2.3565(13) 2.414(4) 0.73(6) 2.404  Atom P(l) P(l) N(l) N(l) N(l) N(l) N(l) N(2)  Angle (°) 93.02(5) 168.67(5) 178.48(18) 79.33(17) 112.55(13) 87.12(11) 84.99(11) 137.72  Angle (°) 86.4(3) -101.9(3) -15.1 -172.7  The geometry of complex 2 was found to be distorted octahedral with the two phosphine donors of the [P NNH] ligand occupying the axial positions; these are pinched back from an ideal 2  trans disposition giving  a P(l)-Ru(l)-P(2)  angle o f  168.67(5)°.  The  ort/zo-metalated  triphenylphosphine ligand as well as the amide and amine ligands all lie in the plane of the octahedron with a combined equatorial angle of 359.93°. The orientation of the o-bound phenyl group lies nearly orthogonal to the P-Ru-P axis as indicated by the P(l)-Ru(l)-C(26)-C(25) torsion angle of 86.4(3)°.  As a consequence, a mirror plane of symmetry exists within the  equatorial plane of the complex rendering the phosphine donors of the macrocycle magnetically  43  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Liga  equivalent.  This is in accordance with the solution structure of 2, which shows only one  resonance for these phosphine ligands in the P { ' H } N M R spectrum. The N(l)-Ru(l)-N(2) bond 3 I  angle o f 79.33(17)° is quite low in comparison to complex 1, which has a N-Ru-N bond angle of approximately 92°.  We speculate that the smaller bond angle is a consequence of an  intramolecular hydrogen bonding interaction between the amino proton and the amido nitrogen atom (to be discussed in greater detail later).  The Ru-P bond distances (2.3248(13) and 2.3565(13) A ) for the [P NNH] ligand of 2  complex 2 are slightly elongated compared to P(3) o f the coordinated triphenylphosphine (2.2989(13) A ) . Presumably this structural feature is due to the high trans influence o f phosphines relative to that of amides. This difference, however, is not as significant as that which is observed in the isoelectronic species [PNHP]RuCl(C6H4PPh2).  In this complex, the phosphine donors of  51  the tridentate ligand are displaced 2.3945 A on average from the metal centre, whereas the Ru-P distance for the triphenylphosphine ligand is 2.2545 A . These distances are comparable to those found in RuCl2(PPh ) , > 52  3  3  53  in which the two mutually trans triphenylphosphine ligands exhibit  Ru-P distances of 2.374(6) and 2.388(7) A , while the remaining phosphine (trans to an open site) is located 2.230(8) A from the metal. The shorter Ru-P distances for the phosphine donors of the [P2NNH] ligand in 2 may be the result of a "macrocyclic effect" in which an H-dentate macrocyclic ligand gives more stable complexes than the most similar «-dentate open chain ligand or H-unidentate ligands of similar type.  5 4  The longer Ru(l)-P(3) distance in complex 2, on the  other hand, may be a consequence o f minimizing steric interactions with the [P2NNH] ligand set.  Structural features of the four-membered ring of the metalacycle are typical of other such rings found in the literature. For instance, the C-Ru-P angle o f 68.39(14)° measured in 2 is similar to that found in the ruthenate complex K[RiiH (C H4PPh )(PPh )2] 2  related species [PNHP]RuCl(C H PPh ) (68.24(8)°). 6  4  2  2  6  5 1  3  5 5  (67.6(3)°), as well as the  fn the ruthenate complex, the Ru-C  distance is 2.098(11) A whereas in the tridentate [PNHP] complex it is observed to be 2.054(3) A . In 2, a slightly shorter Ru-C distance o f 2.034(5) A was found. This trend in bond distances is in accordance with the trans-influence differences between PPh , Cl and amine donors 3  respective complexes.  56  in the  The ruthenium-amine bond length in complex 2 is likewise lengthened  (2.414(4) A ) by the high trans influence o f the ortAo-metalated aryl group.  44  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligan  An interesting feature evident in the solid-state molecular structure of complex 2 is the presence of a hydrogen bond between the amino proton (H(101)) and the amido nitrogen (N(2)). A similar bonding interaction was also evident between the amine and chloride ligands in the complex [PNHP]RuCl(C6H4PPh2), as well as in other complexes of rhodium and iridium that also incorporate this tridentate ligand system.  57  The N H " N distance of 2.404 A in complex 2 is  shorter than the expected van der Waals contact distance of 2.7 A between these two nuclei.  58  Also indicative o f the presence o f a bonding interaction between the hydrogen and amido nitrogen atom is the fact that the amine hydrogen lies nearly in the plane of N ( l ) , N(2) and Ru(l) illustrated by the Ru(l)-N(l)-H(101)-N(2) torsion angle of-15.1°, thus, minimizing the N H N separation.  (iii)  Mechanism for the formation of complex 2 The structure of complex 2 in solution is consistent with the solid-state structure in which  the ortho-metalated triphenylphosphine ligand as well as the amide and amine donors occupy the equatorial positions o f an octahedron. The axial phosphine ligands are related by a mirror plane of symmetry that is contained in the equatorial plane. The position of the donor ligands within the equatorial plane, however, cannot be ascertained in solution by the ' H and P { ' H } N M R data. 31  Since removal of the ortho hydrogen atom occurs by an amido donor it may be expected that the resulting amine and o-aryl ligands would be arranged cis to one another in the product. In fact, the solid-state data shows that the amine ligand is located trans to the or/Ao-metalated carbon atom. One rationalization for this may be that the reaction of the [P2N2] ligand with RuCl2(PPh3)3 is not kinetically controlled and that the formation of complex 2 proceeds under thermodynamic control. The position of the donors in the equatorial plane may be governed by electronics and arranged according to the relative trans influences of phosphine, amine, aryl and amide ligands. The known trans influence decreases in the order PPh3 > C6H5 > amine  56  suggesting that the  amido ligand in 2 may exhibit the weakest trans influence. This rearrangement deserves a further comment. Figure 2.7 depicts a plausible reaction pathway for the formation of the isolated species 2.  For simplicity, only the donor atoms contained in the equatorial plane are shown.  It is  speculated that the amine donor in the kinetic product dissociates, undergoes inversion, and recoordinates allowing for an intramolecular hydrogen bonding interaction with the coordinated amido ligand. A similar transformation was found to occur upon ort/zometalation in the complex  45  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand S  [PNHP]RuCl(C6H PPh ). 4  2  Consequent transfer o f the amino proton to the amide nitrogen atom  generates the observed complex 2.  N»...„.  Ru:  Ru: N*  p thermodynamic product  kinetic product  formation of a hydrogen bond followed by proton transfer  amine dissociation, inversion and recoordination  P H: ligand backbone omitted for clarity  N'  Figure 2.7. Proposed mechanism for the formation of the observed species 2.  2.4  Synthesis,  Characterization and Solution Dynamics of exo-  and  e n c / o - I N P N H l R u t l - S ^ ^ S ^ i r i ^ C s H u ) (exo-3 and endo-Z)  (i)  Reaction of [NPN]Li ( C H 0 ) with [RuCI (cod)] 2  4  8  2  2  x  As discussed earlier, the reaction o f the macrocyclic [P2N2] ligand with [RuCl2(cod)]  x  generates the species [P2N2]Ru(ri :r| -C8Hi2) (1) via metathetical exchange o f the two chloride 2  ligands with the amide ligands.  2  In a similar fashion, we anticipated that the outcome o f the  reaction between the tridentate [NPN] ligand with [RuCl2(cod)] would be the formation o f the x  diamidophosphine complex [NPN]Ru(ri :ri -C8Hi2). That this was not the isolated product from 2  2  this reaction was immediately apparent upon inspection o f the room-temperature ' H N M R spectrum. The number of peaks present implied the existence o f two species (of low symmetry) in 46  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligan 2  solution, and furthermore, the broadened resonances were indicative of a fluxional process occurring in solution.  The ' H N M R spectra at 298 K and 245 K are shown in Figure 2.8.  Combustion analysis of the red crystalline solid that was isolated from this reaction was consistent with the formulation of the expected product, [NPN]Ru(n :r| -C8Hi2), suggesting that the isolated 2  2  products were structurally related isomers of this species.  As portrayed in Scheme 2.3, the products that are formed in the reaction between the [NPN] ligand and [RuCl2(cod)] are a pair o f diastereomers. Transfer o f an allylic C-H atom o f x  the cyclooctadiene ligand to one o f the amido donors of the [NPN] ligand occurs generating a mixture o f the two species exo- and e«<io-[NPNH]Ru(l-3-ri :5,6-ri -C8Hii) (exo-3 and endo-3, 3  2  3  2  respectively). Deprotonation of the cyclooctadiene ligand generates a 1-3-n -allyl, 5,6-T] -olefin coordinated cyclooctadienyl ligand and a [NPNH] ligand array. The activation of an allylic C-H bond o f a coordinated cyclooctadiene moiety resulting in the formation o f a cyclooctadienyl ruthenium(II) complex has previously been reported.  59-61  The terms "exo" and "endo" are used to  distinguish the two diastereomers, and they refer to the orientation of the amino side-arm of the [NPNH] ligand set with respect to the methylene unit bridging the olefin and allyl donor groups of the cyclooctadienyl ligand. In the endo diastereomer the pendant amino ligand and the bridging methylene unit are oriented towards the same "side" of the metal, whereas in the exo isomer, the amino ligand is positioned to the opposite face o f the metal and points away from the bridging methylene unit.  47  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligand 2  'Y.5 ' '  Vo' ' ' 'e'.5  ' ' 's'.o ' ' s'.s  ' ' V.o' ' '  't'.s ' ' 't'.O ' ' 'i'.S ' '  3!o' ' ' '2!5' ' ' 2'.0' ' ' lis' ' ' 'i!o' ' ' 'o!5' ' ' o'.6  I  (ppm)  245 K  7.5  7.0  6.5  6.0  5.5  5.0  4.5  4.0  3.5  3.0  2.5  2.0  1.5  1.0  0.5  0.0  (ppm)  Figure 2.8. The 500 MHz U N M R spectrum o f complex 3 in toluene-ofg at 298 K (upper l  spectrum) and 245 K (lower spectrum).  48  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand  The identification and characterization of the diastereomers exo-3 and endo-3, as well as an understanding of the dynamic behaviour of these two species in solution proved to be a formidable task. Techniques including X-ray crystallography, variable-temperature one- and twodimensional N M R spectroscopy ('H,  13  C { ' H } and P { ' H } ) in addition to performing labelling 31  and reactivity studies all provided valuable insights into this system. The following sections outline, in chronological order, the steps that were taken in order to gain a complete understanding of the process shown in Scheme 2.3.  Ph  /  PhHN  exo-3  Scheme 2.3  49  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and /P /\y Ligand 2  (ii)  Solid-state molecular structure of diastereomer endo-3  The solid-state structural identification o f the diastereomer endo-3 provided the first insight into the details of the reaction o f the [NPN] ligand with [RuCi2(cod)] . Single crystals o f x  the isomer endo-3 suitable for an X-ray diffraction study were isolated by the slow evaporation of a concentrated hexanes solution.  The solid-state molecular structure is shown in Figure 2.9;  pertinent bond lengths and angles can be found in Table 2.4. Transfer o f an allylic C-H atom of the cyclooctadiene ligand to an amido nitrogen atom is clearly evident from the solid-state molecular structure, which shows the r) -allyl, n -olefin coordination mode adopted by the 3  2  cyclooctadienyl ligand. The protonated side arm of the [NPNH] ligand is also apparent and it does not coordinate to the metal centre.  The amino proton (H43) was located and refined  isotropically. The complex exhibits a five-coordinate, distorted trigonal bipyramidal geometry at ruthenium (with the allyl donor occupying two coordination sites and the olefin donor one coordination site). The amide and the allyl moieties are contained within the trigonal plane, while the phosphine and olefin ligands occupy the axial positions.  The P(l)-Ru(l)-C(25) and P(l)-  Ru(l)-C(26) bond angles are 163.35(7)° and 162.61(7)° respectively, indicating a nearly trans disposition between the phosphine and olefin donor groups.  The allyl moiety o f the  cyclooctadienyl ligand is symmetrically bound to ruthenium with an average Ru-C n i bond a  distance o f 2.184 A.  The complex [Ru(l-3-r] :5,6-ri -C8Hi )(ri -C6H5BF3)] 3  2  6  1  5 9  y  also exhibits a  symmetrically coordinated allyl function.  50  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and /P Ay Ligand Se 2  Figure 2.9.  The solid-state molecular structure (ORTEP depiction shown at 50 % thermal  ellipsoid probability) of e«(/o-[NPNH]Ru(l-3-ri :5,6-ri -CgHii) (endo-3) as determined by X-ray 3  2  diffraction. The amino proton (H43) was refined isotropically.  Table 2.4. Selected bond lengths, angles and dihedral angles in e«t/o-[NPNH]Ru(l-3-ri :5,6-r| 3  2  C H n ) (endo-3). 8  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) C(25)  Atom N(l) P(l) C(25) C(26) C(29) C(30) C(31) C(26)  Atom C(29) C(30) N(l) N(2) N(l) N(2) N(l)  Distance (A) 2.019(2) 2.3024(6) 2.300(3) 2.332(2) 2.187(2) 2.169(2) 2.195(2) 1.354(4)  51  Atom C(30) C(31) C(7) C(19) Si(l) Si(2) H(43)  Distance (A) 1.408(4) 1.411(4) 1.430(3) 1.392(3) 1.734(2) 1.727(2) 3.419  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Liga  Atom P(l) P(l) P(l) P(l) P(l) P(l) N(l) N(l)  Atom  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  N(l) C(25) C(26) C(29) C(30) C(31) C(25) C(26)  Atom C(25) C(26) N(l) P(l) P(l) P(D  Angle 0 87.32(6) 163.35(7) 162.61(7) 95.22(7) 83.98(7) 103.09(7) 97.09(9) 90.06(9)  Atom C(26) C(25) Ru(l) Ru(l) Ru(l) Ru(l)  Atom C(29) C(31) C(29) C(25) N(l) N(l)  Atom N(l) N(l) N(l) Ru(l) Ru(l) Si(l) C(29)  Atom C(30) C(30) C(31) C(26) C(7) Si(l)  Atom Ru(l) Ru(l) Ru(l) N(l) N(l) N(l) Ru(l)  Atom C(29) C(30) C(31) Si(l) C(7) C(7) C(31)  Angle (°) 147.35(9) 170.65(9) 142.72(9) 124.3(1) 123.6(2) 112.2(2) 68.2(1)  Dihedral Angle (°) 10.7 1.7 164.8 176.2 172.2(2) -5.8(1)  Although 3 may be considered an unsaturated, 16-electron species, the presence o f the %donating amido ligand can also result in a formal 18-electron configuration at the metal centre. An indication of a 7t-bonding interaction can be portrayed structurally by a short metal-nitrogen bond distance as well as a trigonal planar coordination geometry at the amido nitrogen a t o m . ' 62  63  In the case of endo-3 the ruthenium amide (Ru(l)-N(l)) bond length is 2.019(2) A. In contrast, the coordinatively saturated species [P N2]Ru(r) :r| -C8Hi2) (1) has a Ru-N bond length o f 2  2  2  2.223(2)  A.  The  six-coordinate  C6Me )(PMe3)(Ph)(NHPh) 6  65  complexes  cw-Ru(H)(PMe ) (NHPh) 3  and  64  4  Ru(n 6  bearing the anilido ligand have ruthenium to nitrogen distances o f  2.160(6) A and 2.121(3) A, respectively. The shorter Ru-N bond length in the five-coordinate endo-3 can be attributed to derealization o f the amido nitrogen lone pair to a vacant metal dorbital. Also consistent with the existence of a rc-bonding interaction is the planar, 5p -hydridized 2  geometry displayed by the amido nitrogen atom (sum o f angles = 360°); planarity of the amido unit necessarily occurs to maximize 7t-bonding with the metal centre. This planarity, however, could also arise from similar ^-interactions existing between the amide nitrogen atom and the neighbouring silicon atom or phenyl ring. The N ( l ) - S i ( l ) bond length (1.734(2) A) exists in a range commonly found for planar silyl amine and silyl amide compounds  62  implying K-  delocalization between these two nuclei. The bond distance (1.430(3) A) from the amido nitrogen (N(l)) to the phenyl ipso carbon (C(7)) o f the amido moiety is longer than that of aniline (1.398  52  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligan  A) suggesting minimal 7i-delocalization into the amido aromatic ring in complex endo-3. In an earlier report, an inverse correlation between Ru-N and N - C i phenyl amido systems had been noted.  pso  bond distances in ruthenium(II)  66  Theoretical calculations have shown that a diamagnetic d ML5 complex distorts away 6  from the Jahn-Teller active trigonal bipyramidal structure. '  Two more stable structures are  67 68  possible: a square pyramid and a distorted trigonal bipyramid. Figure 2.10 gives a qualitative representation of these two types o f distortions. Only the x -y and xy set of J-orbitals are shown 2  2  since the geometrical preference is governed by these two orbitals. Increasing the angle 9 to 180° (giving a square pyramid) stabilizes the xy orbital while the x -^ orbital is raised in energy. 2  2  Conversely, decreasing the angle 6 below 120° (giving a distorted trigonal bipyramid, namely a Yshape in the trigonal plane o f the five-coordinate structure) increases the energy o f the xy orbital and stabilizes x -y . 2  2  53  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and /PjAy Ligand Sets  Square Pyramidal  Trigonal Bipyramidal (TBP)  Distorted T B P (Y-shape)  xy  >4 x -/ 2  120°<6< 180°  Figure 2.10.  e< 120°  A qualitative representation of the two possible Jahn-Teller distortions in a  diamagnetic trigonal bipyramidal structure o f an d  6  ML  5  complex.  The ligand and metal  antibonding combinations are shown.  These two extreme geometries were found to be very close in energy and the preference for one over the other comes from a subtle balance of the o and 7t properties o f the ligands. The presence o f 7t-acceptors, for instance, favours the square pyramidal structure. When one o f the ligands is a 7i-donor, a distorted trigonal bipyramidal geometry is observed with this ligand located opposite to the acute angle in the equatorial plane of the molecule. This finding has also been observed experimentally. 69  72  This geometry permits the formation o f a partial double bond  between the empty metal of-orbital (xy) and the lone pair o f the Jt-donor.  This manifests as a  shortening in the M-X bond and in the case of a single-face Ji-donor, a preferred orientation to  54  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P N2] Ligand Set 2  maximize orbital overlap. No such ^-interaction is present in the square pyramidal structure since all o f the symmetry adapted of-orbitals are filled.  The observed geometry of endo-3 in the solid-state coincides well with the theoretical predictions, and on the basis of orbital symmetry allows for amide-to-ruthenium multiple bonding to take place. The P(l)-Ru(l)-N(l)-Si(l) dihedral angle o f -5.8(1)° indicates that the plane o f the amide donor is perpendicular to the equatorial plane of the molecule, and this allows for maximal overlap of the filled amido lone pair orbital (p ) with the empty d y  xy  metal orbital. A qualitative  depiction o f this overlap is shown in Figure 2.11. Complex 3 can therefore be regarded as a "71stabilized" unsaturated complex.  z  P(1)  3  Figure 2.11. A schematic representation o f the amide lone pair orbital (p ) and empty ruthenium y  orbital (d ) overlap in complex endo-3. xy  Reactivity studies with complex 3 are also suggestive o f "7t-stabilized unsaturation" at the metal centre. For example, no reactivity was observed (as monitored by ' H and P { H } N M R 3 1  !  spectroscopy) upon addition o f neutral donor ligands including pyridine, THF and various phosphines  (PPI13,  P'Pr3 and PCy3). Steric considerations should not be neglected, however, as  they may also play a role in the observed lack o f reactivity.  The reaction o f complex 3 with  carbon monoxide will be discussed in the Future Work section o f this chapter. Derealization o f the amido lone pair onto ruthenium may also account for the fact that the amino side-arm of the [NPNH] ligand does not coordinate to the metal centre. A decrease in the electrophilicity o f late 55  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand  transition metal complexes containing 7i-donating ligands such as amide and alkoxide ligands has been reviewed.  (iii)  73  Considerations into the identity of the second species and possible fluxional processes  It was stated earlier that the room-temperature ' H N M R spectrum of 3 indicated the presence of two species in solution, and furthermore, the number o f resonances observed suggested that these complexes were o f low symmetry. The characterization of endo-3 in the solid state showed that it is chiral, exhibiting C\ symmetry. The structure of this complex allowed for considerations to be made regarding the identity of the second species as well as related fluxional processes in solution.  In a previous report, it was demonstrated that upon substitution of the cyclooctatriene ligand by phosphorus donor ligands in the complex [Ru(l-3-r| -5,6-r| -C8Hii)(r| -C8Hio)][PFei], 3  2  6  the cyclooctadienyl fragment undergoes isomerization to yield the r| -bound cyclooctadienyl 5  ligand.  60  The driving force for this isomerization process was postulated to arise from steric  effects. In the presence of bulky phosphine ligands, the l-5-ri -coordination mode is favoured 5  since it occupies a smaller portion of the metal's coordination sphere, thus minimizing steric interactions.  The ability o f the cyclooctadienyl ligand to isomerize, as demonstrated in the above example, led us to speculate that the second product isolated from the reaction o f the [NPN] ligand with [RuCl2(cod)] could be a related species in which the cyclooctadienyl ligand had undergone a x  rearrangement. Scheme 2.4 portrays two possibilities. As depicted in A the rf-allyl, r| -olefin 2  bound cyclooctadienyl ligand may isomerize to the r] -allyl coordination mode. Alternatively, as 5  shown in B, the t| , r| -coordination mode may remain intact although effectively rotated by 180° 3  2  such that the phosphine and olefin donors are now cis to one another.  The highlighted section of Scheme 2.4 illustrates possible mechanistic pathways for the conversion o f endo-3 into the two speculative isomers A or B. For simplicity, the complexes are shown as viewed through the cyclooctadienyl ligand and bisecting the P-Ru-N angle. Only the 56  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligan  phosphorus and amido nitrogen atoms of the [NPNH] ligand set have been shown for clarity. Abstraction o f one o f the bridging allyl protons (Hh or Hh) o f the complex endo-3 generates a ruthenium-hydrido species; isomerization to either A or B evolves through this common intermediate.  Migration of the hydride occurs at the same position, then complex endo-3 is  regenerated. Migration of the hydride into the carbon bearing H , however, would result in the e  formation of complex A , whereas migration into the carbon with H generates complex B. g  If  either of these pathways were reversible an equilibrium would be established and this could account for the broadened resonances that were observed in the room temperature ' H N M R spectrum. As will be shown this process is unlikely based on ' H and C { ' H } N M R spectroscopy l 3  as well as reactivity studies.  Scheme 2.4  57  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] andp NJ Ligan 2  Additional fluxionality may arise from epimerization equilibria in 3. Examination of the solid-state structure of endo-3 shows that the ruthenium and the phosphorus nuclei are both chiral centres. Complex 3 is an example o f a chiral-at-metal complex that also contains an additional stereocentre; complexes o f this type are known to undergo configurational processes.  74  Epimerization in complex 3 can result in the formation o f four diastereomers; these are shown in Figure 2.12. The complexes endo-3 and exo-3 differ in the chirality displayed at the phosphorus centre (similarly for endo-3' and exo-3'). Inter-conversion of these complexes involves transfer of the amino proton from one arm of the [NPNH] ligand to the other. The isomers endo-3 and exo-3' (or exo-3 and endo-3'), on the other hand, have inverted chirality at the metal centre.  The  complexes exo-3 (in Figure 2.12) and complex B (in Scheme 2.4) are the same species. Inversion at ruthenium involves fluxional behaviour associated with the cyclooctadienyl ligand.  Ph  Ph  exo-3'  endo-3  inversion at P  inversion at P  Ph  Ph inversion at Ru  SiMe  ^SiMe  2  2  PhHN  endo-3'  exo-3  Figure 2.12. The four possible diastereomers of [NPNH]Ru(l-3-n :5,6-ri -C8Hii) (3). 3  58  2  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [PiNrf Ligan  It is apparent that complex 3 is capable o f displaying a variety o f fluxional processes related to both the cyclooctadienyl as well as the [NPNH] ligands. In order to determine the nature o f the two species in solution variable-temperature N M R studies were required.  (iv)  Variable-Temperature NMR Studies of endo- and exo-[NPNH]Ru(1-3-ri - 5,63  rf-CsHn) (endo-3 and exo-3) The room-temperature ' H N M R spectrum of a bulk sample of 3 consists of many broadened resonances, which hampered peak assignments (see Figure 2.8). The P { H } N M R 3I  1  spectrum at the same temperature contains one peak at 8 33.0. Cooling the sample, however, results in two singlets in the P { ' H } N M R spectrum in the ratio 2:1 establishing the presence of 3 I  two species (one major and one minor) in solution. We have not been able to determine which diastereomer is the major or minor species, therefore, in the following discussion concerning the variable temperature N M R studies we assume that endo-3 is the major isomer in solution.  Interestingly, identical spectra ('H and P { ' H } ) are obtained whether a single crystal of 3 31  is employed for the N M R investigations or a bulk powdered sample. This suggests that a dynamic equilibrium exists between the two species in solution. At 245 K the fluxional process responsible for the inter-conversion of the two species is slow enough to allow for the identification o f endo-3 and exo-3 as the two complexes in solution. Full characterization of these two isomers was based on low-temperature ' H , P { H } and C { ' H } N M R data. In addition, two-dimensional homo- and 31  !  I 3  heteronuclear correlation experiments allowed for the complete assignment of the resonances attributed to both of the diastereomers.  A collection of the ' H and  13  C assignments for the  cyclooctadienyl ligand of isomers endo-3 and exo-3 is given in Table 2.5 and Table 2.6 respectively, together with data for other complexes containing this ligand.  The labelling  convention used for assignment o f N M R peaks corresponding to the cyclooctadienyl ligand that will be used in the following discussion is shown below in Figure 2.13.  59  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligan  H,'9 7 3 6^H  Figure 2.13.  f  The labelling convention used for *H and  13  C N M R assignments o f the  cyclooctadienyl ligand in complexes containing this ligand.  The ./-modulated  13  C{'H} N M R spectrum obtained at 245 K (shown in Figure 2.14)  identifies the presence of ten C H and six CH2 resonances for the cyclooctadienyl ligand, consistent with an r] -allyl, T| -olefin coordination mode for each isomer. 3  2  contains two doublets at 8 108.1 (V  PC  = 10.5 Hz) and 8 61.4 (V  PC  Complex endo-3  = 6.5 Hz) in the C{'H} N M R 13  spectrum that have been ascribed as the olefinic bound carbon atoms C2 and Ci respectively; these show a two bond coupling with the trans located phosphine donor. The allyl carbon resonances occur at 8 71.6 (Ce), 8 61.6 (C5) and 8 35.6 (C7). For these latter peaks no scalar coupling to the 31  P nucleus could be resolved; a much smaller coupling would be expected due to the cis  orientation between these two donor groups. These data agree with the solid-state structure, which shows that the olefin and phosphine donors are *ra«s-disposed to one another.  60  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligan  c  Ci  c c  2  3  8  f  >  \  /  c  4  c  c  7  Ce  5  c  C (endo)  6  5  (endo) C (endo)  C (exo)  2  C (exo)  6  2  (endo)  /  /  Ci (endo)  7  c  8  (exo) (exo)  tup  / \ ^5 C-,  (exo)  C3  C (exo)  C (exo) 4  (exo;  ' c (endo; C ' ( °) (endo) 3  e n d  4  denotes an impurity  Figure 2.14. The ./-modulated C { H } N M R spectrum for endo-3 and exo-3 obtained at 245 K in 1 3  ]  toluene-^ highlighting the cyclooctadienyl carbon resonances. The CH resonances point up and the CH2 resonances point down.  The 500 MHz ' H N M R spectrum of endo-3 shows four silyl methyl and four methylene proton resonances o f the [NPNH] ligand indicating that the asymmetry o f the complex is maintained in solution. In addition, there are 11 inequivalent cyclooctadienyl proton resonances. The olefinic protons are shifted furthest downfield at 8 4.25 (Hb) and 8 4.23 (H ) respectively. a  The terminal allyl proton resonances are found at 8 4.20 (H ) and 8 2.85 (H ), whereas the central e  allyl proton (Hf) is significantly upfield shifted at 8 1.64.  g  The protons o f the methylene unit  bridging the olefin and allyl groups (Hh and Hh-) are observed as multiplets at 8 2.70 and 8 2.00. The remaining methylene proton environments o f the cyclooctadienyl ligand are located at 8 2.63 (H ), 8 1.58 (H .), 6 2.18 (H ) and 8 1.50 ( H ) . The two-dimensional ' H - H COSY and ' H - C ]  c  c  d  13  d  HMQC data aided in the assignment o f the cyclooctadienyl proton environments.  The amino  proton o f the dissociated side-arm o f the [NPNH] ligand occurs as a singlet at 8 6.63.  61  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand  Table 2.5. *H resonances of the cyclooctadienyl ligand for complexes 3-6 including J H coupling H  constants for complex exo-3 (determined from simulation data).  H H H HeH H . H H Hg H H . a  b  c  d  d  e f  h  h  exo-3: J  exo-3 4.68 3.92 1.83 1.30 2.20 1.75 3.50 1.50 3.37 3.09 2.15  endo-3 4.23 4.25 2.36 1.58 2.18 1.50 4.20 1.64 2.85 2.70 2.00  5 2.17 2.29 1.18 1.07 1.76 1.33 3.10 3.45 4.35 3.45 2.50  4 2.20 2.45 1.60 1.10 1.70 1.40 3.40 3.42 4.30 3.40 2.50  = 7.80 Hz, J h = 7.70 Hz, V*- = 7.30 Hz, V  3  3  a b  a  14.60 Hz, 7 3  cd  = 7.60 Hz,  bc  V - = 6.00 cd  Hz, J 3  5.60 Hz, J 'e = 5.80 Hz, J f = 8.00 Hz, V 3  3  d  e  c d  = 6.20 Hz, J ' = 6.10 Hz,  2  b c  c d  Hz,  V> = dd  CC  V =  17.0 Hz,  de  = 9.90 Hz, J& = 7.90 Hz, J&> = 4.20 Hz, J > = 3  fg  J < =  3  V- - = 8.60  = 7.20 Hz,  exo-6 4.50 3.87 2.08 1.45 2.12 1.75 3.60 1.43 3.27 2.95 2.20  endo-6 4.25 4.00 2.10 1.47 2.25 1.85 4.16 1.52 2.90 2.77 2.05  3  2  hh  19.30 Hz. (Determined using the simulation software in the N M R program Mestrix)  Table 2.6.  13  C resonances of the cyclooctadienyl ligand for complexes 3-6. Jpc values (Hz) are 2  given in parenthesis.  c, c c c c c c c 2  3  4  5  6  7  8  endo-3  exo-3  61.4(6.5) 108.1 (10.5) 30.3 32.8 61.6 71.6 35.6 25.2  65.3 (5.8) 110.0 (11.3) 27.0 36.3 64.9 70.8 36.5 26.6  4 32.6 (6.5) 67.8 (5.5) 29.8 30.4 46.2 (2.2) 100.5 44.3 (18.9) 22.3  5 33.2 (6.4) 68.2 (5.8) 27.9 27.7 46.0(2.1) 100.5 45.0(19.2) 22.7  endo-6  exo-6  61.6 (6.3) 107.6(10.6) 28.5 35.0 61.8 70.1 35.6 25.5  62.9 (5.9) 108.1 (11.6) 26.9 36.9 63.7 69.9 36.2 26.5  Inspection of the C resonances (Table 2.6) for the cyclooctadienyl carbon nuclei of the 13  minor isomer show that they are only slightly shifted with respect to endo-3 suggesting a very similar coordination mode adopted by this ligand. Furthermore, two doublets at 8 110.0  ( JPC 2  -  11.3 Hz) and 8 65.3 ( JPC = 5.8 Hz) indicate that the phosphine donor is located trans to the olefin 2  62  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Liga  moiety, a feature that was also evident in the  13  C { ' H } N M R spectrum o f endo-3. These data  implicate exo-3 as the second species in solution (and not endo-3' nor exo-3' as shown in Figure 2.12).  The H N M R data also supports the formulation of the second species in solution as the ]  diastereomer exo-3.  Figure 2.15 shows a region o f the 500 MHz ' H { P } N M R spectrum 31  highlighting the downfield shifted cyclooctadienyl resonances. In addition to exhibiting a similar trend in the chemical shift of the proton environments (refer to Table 2.5 as well), it can also be seen that they display similar coupling patterns. Once again this suggests that the coordination mode adopted by the cyclooctadienyl ligand is the same in both species. The olefinic protons exist furthest downfield at 8 4.68 (H ) and 5 3.92 (Hb) with the two terminal allyl protons at 8 3.50 a  (H ) and 8 3.37 (H ). Although the central allyl proton (Hf) is obscured by neighbouring peaks its e  g  presence at 8 1.50 was confirmed by ' H - ' H and ' H - C correlation experiments. The significant I3  up field shift of this proton also occurs for isomer endo-3. The remaining cyclooctadienyl proton resonances are tabulated in Table 2.5. To further assist in the characterization o f isomer exo-3 a calculation of the spin system o f the cyclooctadienyl proton environments was performed. The calculated coupling constants, found in Table 2.5, are similar to those obtained for other complexes known to contain a T | , n -cyclooctadienyl ligand bound to ruthenium(II). 3  2  60  An  asymmetric solution structure is also apparent from the four silyl methyl and four methylene proton environments o f the [NPNH] ligand set. The amino proton occurs at 8 6.35, shifted 0.28 ppm upfield from the amino proton o f endo-3.  63  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand  endo-Z  — 1 — 1  4.8  1  4.6  1 — 1 — 1 1 4.4 4.2  1—1 4.0  1  1 — 1 1 3.8 3.6  1  1  3.4  1  —  3.2  11  1  1  3.0  1  2.8  '  1  2.6  (ppm)  Figure 2.15. A region of the 500 MHz ' H { P } N M R spectrum of isomers endo-3 and exo-3 31  highlighting the downfield shifted cyclooctadienyl proton resonances at 245 K in toluene-^.  The presence of a complex containing a r| -ligated cyclooctadienyl ligand can be dismissed 5  from the ' H N M R data. Previous reports on complexes that contain a t| -cyclooctadienyl moiety 5  indicate that the central allyl proton occurs downfield between 8 6.0 and 8 7.2 as a (expected) triplet.  60  In this system, no such resonance is observed in the temperature range employed for the  ' H N M R studies.  In addition, there was no hydride resonance apparent throughout this  temperature range suggesting that the cyclooctadienyl ligand does not exhibit any fluxional behaviour; reactivity studies (section 2.5 (v)) confirmed this speculation.  Analysis of the variable-temperature *H N M R data confirmed the existence o f an equilibrium mixture o f the species endo-3 and exo-3 in solution. Integration of the amino proton resonance for each of the diastereomers at various temperatures gave relative concentrations o f the two isomers and allowed for the evaluation o f the equilibrium constants according to the expression in equation 2.3. A van't H o f f plot (shown in Figure 2.16) permitted the determination  64  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligan  of the following thermodynamic parameters for the equilibrium process: AH - 0.93 ±0.10 kcal 0  mol" and A5° = 1.62 ± 0.20 eu. 1  Ph  Ph  /Ph  Me Sr-\- \  J§  N  Me Sf  2  2  .Ph Me |iy"~  K  N :  [2.3]  <  2  Ph  PhHN  exo-3  endo-3 K=[exo-3]/[encto-3]  Table 2.7. Calculated equilibrium constants (K) for the equilibrium between diastereomers endo3 and exo-3 in toluene-^.  Temperature, T (K) 293 ± 1 285 ± 1 265 ± 1 . 245 ± 1 225 ± 1  Equilibrium Constant, K 0.46 ± 0.04 0.43 ± 0.04 0.39 ± 0.04 0.34 ± 0.04 0.28 ± 0.03  -0.60  j  -0.70 -0.80 -0.90 f- -1.00 -1.10 -1.20 -1.30 -1.40  -  0.0032  0.0034  0.0036  0.0038  0.0040  0.0042  0.0044  0.0046  1/T(K ) 1  Figure 2.16. Van't Hoff plot for the equilibrium between diastereomers endo-3 and exo-3 (R = 2  0.9954).  65  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and P2N2} Ligan  Figure 2.17 highlights the N - / / region o f the two-dimensional E X S Y ' 75  76  spectrum  obtained at room temperature (500 MHz, t ; = 400 ms) for the mixture o f endo-3 and exo-3 in m  x  toluene-t/8. A positively phased cross-peak between sites in a 2D-EXSY spectrum indicates that these nuclei are in chemical exchange (just as a cross-peak in a COSY spectrum indicates scalar coupling between the sites). The cross-peak between the two amino protons illustrates that these two nuclei are in chemical exchange, providing further evidence for the dynamic equilibrium that exists in solution.  No cross peaks were observed between the amino protons and any of the  cyclooctadienyl proton resonances indicating that the ~H-H proton does not get incorporated into the cyclooctadienyl ligand.  Cross peaks were also observed for the cyclooctadienyl ligand,  however, due to the broadened and overlapping resonances at 298 K, they could not be assigned to specific proton environments.  The [NPNH] silyl methyl and methylene resonances between  isomers also gave rise to positively phased cross-peaks as would be expected.  endo-3 (N-H)  Figure 2.17. The N-/f region of the 2-D EXSY spectrum for the mixture o f endo-3 and exo-3. Obtained at 298 K in toluene-Jg, 500 MHz and a mixing time o f 0.4 s.  66  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and foNrf Ligand  (v)  Postulated mechanism for the inter-conversion of endo-Z and exo-3  The inter-conversion of the two diastereomers endo-3 and exo-3 requires inversion of chirality at the phosphorus atom. We propose that the mechanism for this process involves the direct transfer of the N-//proton from one arm of the [NPNH] ligand to the other via the transition state that is illustrated in Scheme 2.5. Shifting o f the phosphine ligand to the "bottom" o f the metal and the close approach of the amine side-arm to the ruthenium centre allows for the N - / / proton to reside in a bridging position between both nitrogen atoms. Transfer o f this proton from one arm to the other followed by dissociation of the resulting amine ligand and finally coordination of the phosphine back to the site trans o f the olefin donor acts to invert the chirality of the phosphorus atom. The proposed six-coordinate transition state resembles the structure of the stable and isolable ruthenate complexes 4 and 5. The solid-state molecular structure of 4 is shown in Figure 2.19. In the case of complex 4, a lithium cation (rather than a proton) bridges the two nitrogen atoms. A related transition state has been postulated for aryloxide/phenol proton exchange in a pentamethylcyclopentadienyl nickel (II) system.  67  77  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and /PJA/J/ Ligand  Ph  exo-3  Scheme 2.5  The solid-state molecular structure of complex endo-3 shows that the amino hydrogen atom is positioned towards the amido nitrogen atom. Although the distance between these two nuclei (3.419 A ) is too long to be considered a hydrogen bond, the observed orientation may be the result of an electrostatic attraction between these two nuclei. A hydrogen bonding interaction was evident in the solid-state structure of the complex [P2NNH]Ru(PC6H4Ph2), (2), with a N H  N  distance of 2.404 A . This species forms as the sole product by the irreversible intramolecular protonation of one o f the amido ligands o f the [P2NNH] ligand set, as shown in Figure 2.7. The equilibrium process depicted in Scheme 2.5 is similar, although it involves a reversible intramolecular protonation o f a ruthenium amido ligand that is fast on the N M R timescale at room temperature.  The variable temperature ' H N M R data also permitted a kinetic investigation into the mechanistic details for the process that inter converts isomers endo-3 and exo-3. Line-shape  68  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [PzNz] Liga  analysis of the N-H resonances allowed for the rate constants to be determined at several temperatures and used in an Eyring plot to calculate the activation parameters o f AH  i  - 16 ± 1  kcal mol" and AS* = 4 ± 4 eu for this process. The calculated rate constants are tabulated in Table 1  2.8 and the Eyring plot is shown in Figure 2.18.  Table 2.8. Calculated rate constants for the reversible intramolecular proton transfer responsible for the inter-conversion of diastereomers endo-3 and exo-3.  Temperature, T (K)  Rate Constant, k ( s ) 1  320 308 293 285  648 ± 32 308 ±15 61 ± 3 30 ± 2  0.003  0.0031  0.0032  0.0033  ±1 ±1 ±1 ±1  0.0034  0.0035  0.0036  1/T (K- ) 1  Figure 2.18. Eyring plot for the inter-conversion of diastereomers endo-3 and exo-3  (R 2  0.9922). AH* = 16 ± 1 kcal mol" and AS = 4 ± 4 eu. 1  1  69  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand S  2.5 Synthesis, characterization and reactivity of the ruthenate complexes {[NPNJRutl-S-Ti^e-Ti^CsHnJHMTHF} (4) (M = Li) and (5) (M = Na) (i)  Synthesis of the ruthenate complexes { [ N P N ] R U ( 1 - 3 - T I - 5 , 6 - T I - C 8 H I I ) } { M T H F } 3  2  (4) (M = Li) and (5) (M = Na) The addition of one equivalent o f LiN(SiMe3)2 to an equilibrium mixture of endo-3 and exo-3 in toluene generates the ruthenate complex {[NPN]Ru(l-3-T| :5,6-r| -C8Hii)} { L i T H F } 3  2  (4),  as portrayed in Scheme 2.6. The insolubility o f the initially formed orange solid in hydrocarbon solvents (hexanes, benzene and toluene) suggests that it has an oligomeric structure, {[NPN]Ru(l3-T) :5,6-T| -C8Hii)Li} . 3  2  n  62  Addition o f THF to the reaction mixture dissolves the solid giving the  monomelic species 4 as an orange crystalline material in 92 % yield. The synthesis o f complex 5 is analogous to that of 4 but employs NaN(SiMe3)2 as the base.  The addition o f an external base to an equilibrium mixture of endo-3 and exo-3 generates a single, non-fluxional ruthenate complex. We propose that the stable ruthenate species (4 or 5) may be regarded as structurally related analogue of the proposed transition state for the interconversion of the two diastereomers o f complex 3 as shown in Scheme 2.5.  70  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand  Ph  /Ph  Me Sr-\-N.  X  2  <  SiMe  /  2  PhHN exo-3  endo-3 MN(SiMe ) 3  2  - HN(SiMe ) 3  2  {[NPNJRUCTI^TI^CSHUJM},,  NEt HCI 3  - NEt -MCI  3  THF  4 (M = Li)  5 (M = Na)  Scheme 2.6  (ii)  X-ray diffraction study of compounds 4 and 5 Figure 2.19 shows the solid-state molecular structure of complex 4 as determined by a  single crystal X-ray diffraction study. The solid-state structure of complex 5 can be found in the Appendix section of this thesis. Selected bond lengths and angles for both compounds are given in Table 2.9.  71  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P NJ Ligand Se 2  Figure 2.19.  ORTEP representation (50 % thermal ellipsoid probability) o f the solid-state  molecular structure o f  {[NPN]Ru(l-3-n :5,6-Ti -C Hn)} { L i THF} (4) as determined by X-ray 3  2  8  diffraction. The [NPN] ligand silyl methyl groups have been omitted for clarity and only the ipso carbon atoms of the amido phenyl rings are shown.  Table 2.9.  Selected bond lengths and angles in the complexes {[NPN]Ru(l-3-r) :5,6-r| 3  2  CgHi,)} { M T H F } , M = Li (4) and M = Na (5).  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) N(l)  Atom N(l) N(2) P(l) C(29) C(30) C(31) C(33) C(34) M(l)  Distance ( A ) 4 5 2.275(2) 2.251(2) 2.364(2) 2.347(2) 2.2944(6) 2.2799(6) 2.179(2) 2.162(2) 2.176(2) 2.182(2) 2.364(2) 2.380(2) 2.180(2) 2.187(2) 2.224(2) 2.225(2) 2.004(5) 2.429(2)  Atom N(2) 0(1) N(l) N(2) N(l) N(2) C(29) C(30) C(33)  72  Atom M(l) M(l) C(7) C(19) Si(l) Si(2) C(30) C(31) C(34)  Distance ( A ) 4 5 2.010(5) 2.425(2) 1.956(5) 2.246(2) 1.410(3) 1.404(3) 1.414(3) 1.405(3) 1.745(2) 1.724(2) 1.729(2) 1.723(2) 1.424(4) 1.420(4) 1.396(4) 1.394(4) 1.384(4) 1.385(4)  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand S  N(l)-Ru(l)-N(2) N(l)-Ru(l)-P(l) N(2)-Ru(l)-P(l) N(l)-Ru(l)-C(29) N(l)-Ru(l)-C(31) N(l)-Ru(l)-C(33) N(l)-Ru(l)-C(34) N(2)-Ru(l)-C(29) N(2)-Ru(l)-C(31) N(2)-Ru(l)-C(33) N(2)-Ru(l)-C(34) P(l)-Ru(l)-C(29)  Atom-Atom-Atom  Angle (°)  Atom-Atom-Atom  86.49(7) 87.12(5) 84.28(5) 97.13(9) 100.97(8) 156.22(8) 167.14(9) 175.46(9) 110.04(8) 83.52(8) 98.12(9) 98.60(7)  89.11(7) 86.66(5) 85.15(5) 93.60(8) 101.50(8) 158.64(8) 164.62(8) 175.56(8) 109.21(8) 83.62(8) 98.81(8) 98.52(7)  P(l)-Ru(l)-C(31) P(l)-Ru(l)-C(33) P(l)-Ru(l)-C(34) C(31)-Ru(l)-C(29) C(31)-Ru(l)-C(33) C(31)-Ru(l)-C(34) C(29)-Ru(l)-C(33) C(29)-Ru(l)-C(34) N(l)-M(l)-N(2) M(l)-N(l)-Ru(l) M(l)-N(2)-Ru(l)  Angle (°) 4 5 163.77(7) 163.38(6) 113.17(7) 112.56(7) 81.44(8) 80.94(7) 66.6(1) 66.80(9) 62.87(9) 62.58(9) 88.8(1) 88.40(9) 92.1(1) 92.63(9) 78.9(1) 79.39(9) 104.8(2) 83.33(7) 84.5(2) 94.33(7) 82.0(2) 92.05(7)  Inspection o f the solid-state molecular structure of complex 4 shows that the T| -allyl, n 3  2  olefin coordination mode of the cyclooctadienyl ligand has been maintained, and that the [NPN] ligand is bound to the ruthenium in a facial manner. The amido donors bridge the lithium and ruthenium centres forming a "L1N2RU" core.  Complex 4 is six-coordinate at ruthenium and  exhibits G symmetry in the solid state. The 7i-allyl function occupies two sites and the olefin the third site of one face of a distorted octahedron; the amido and phosphine donors of the tridentate [NPN] ligand fill the remaining coordination sites.  Deviations from an ideal octahedral  coordination geometry arise due to constraints imposed by the chelating [NPN] ligand as well as the cyclooctadienyl ligand.  For example, the P(l)-Ru(l)-C(31) and N(2)-Ru(l)-C(31) bond  angles (163.77(7)° and 110.04(8)° respectively) show that the terminal allyl carbon atom, C(31), is bent away from its ideal apical position.  In addition, atom C(31) is approximately 0.18 A  further displaced from the metal centre than are C(29) and C(30) o f the allyl donor.  An  unsymmetrical coordination mode for the cyclooctadienyl ligand in related ruthenium(II) systems has previously been reported.  60  One rationalization for this structural feature may be the  minimization o f steric interactions between the methylene unit of the cyclooctadienyl ligand with the aromatic rings of the amido donors. Alternatively, the longer Ru(l)-C(31) bond length may be a consequence of the high trans influence of the phosphine ligand.  The 6/5-amide bridged  "L1N2RU" core is asymmetric containing one shorter (2.275(2) A ) and one longer (2.364(2) A ) ruthenium to nitrogen distance; the amido to lithium distances are equivalent within experimental error.  The Ru-N bond lengths in 4 are longer than that found in endo-3 (2.019(2) A ) .  Coordinative saturation at the ruthenium center does not allow for Ti-donation from the amido lone 73  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Liga  pair o f electrons and consequently both the amide donors exhibit a pseudo-tetrahedral coordination geometry.  The lithium atom in complex 4 adopts a planar, three-coordinate  geometry with a molecule o f THF completing its coordination sphere.  The molecular structure of complex 5 was found to be similar to 4 in the solid-state. An asymmetrically bound cyclooctadienyl ligand is also evident in the solid-state structure of 5 displaying similar bond lengths and angles to those observed in 4 (see Table 2.9).  Significant  variations arise in the "NaN Ru" core of the complex and these are a consequence of the larger 2  ionic radius of sodium as compared to lithium; this results in an elongated distortion of the bimetallic core. For instance, the average M-N distance of 2.008 A in 4 increases to 2.427 A in complex 5 and the N ( l ) - M ( l ) - N ( 2 ) bond angle of 104.8(2)° in 4 decreases to 83.33(7)° in 5.  (iii)  Solution structure of compounds 4 and 5  Complexes 4 and 5 were fully characterized in solution at room temperature by ' H , 31  P { ' H } and C { ' H } N M R spectroscopy; the labelling convention for the cyclooctadienyl ligand I 3  portrayed in Figure 2.13 will be used in the following discussion. Analysis o f the crude product indicates the formation of only one species in the reaction of endo-3 and exo-3 with external base. The asymmetry of 4 and 5 evident in the solid-state is maintained in solution denoting a rigid solution structure. To support this, the  13  C { ' H ) N M R spectra (for both 4 and 5) contain four  resonances for the silyl methyl carbon atoms and eight resonances for the inequivalent cyclooctadienyl carbon nuclei. Once again, the J-modulated C { ' H } spectra confirmed the T| :ri 13  3  2  coordination mode of the cyclooctadienyl ligand, as in complex 3. Differences in the coordination of the cyclooctadienyl ligand arising in the six-coordinate "ate" complexes, however, are apparent by inspection o f the C resonances for these complexes (see Table 2.6). The greatest variation in 13  peak positions occur for the ruthenium bound carbon nuclei. The central allyl carbon (C^) for instance, is shifted downfield from ca. 8 71.0 in endo-3 and exo-3 to ca. 8 100.0 in complexes 4 and 5. The olefin carbon atom, C2, experiences an upfield shift of similar magnitude from ca. 8 110.0 (in endo-3 and exo-3) to ca. 8 68.0 (in 4 and 5). Differences are also manifested in the scalar coupling of the cyclooctadienyl carbon nuclei to the P nucleus. Whereas coupling to the 31  31  P nucleus could only be distinguished for the trans disposed olefin nuclei (Ci and C2) in endo-3  and exo-3, it is also present for the terminal 7t-allyl carbon atoms C5 and C7 in complexes 4 and 5.  74  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and fP Nz] Ligand 2  No coupling to the central allyl carbon nucleus could be measured in either 4 or 5. As anticipated from the solid state structures, C7 of the cyclooctadienyl ligand experiences the greatest coupling ( -/PC 2  = 1 9 Hz) due to its near trans disposition with the phosphine donor.  The H N M R spectra of complexes 4 and 5 are each comprised of four silyl methyl L  resonances, four ligand methylene resonances, 11 inequivalent cyclooctadienyl proton resonances, and three sets of ortho, meta and para phenyl proton resonances for the [NPN] phenyl groups. This number of peaks is consistent with a C\ symmetric structure in solution. The changes in chemical shift locations of the cyclooctadienyl protons (as compared to endo-3 and exo-3) mirror those of the carbon nuclei to which they are attached (see Table 2.5). The complete assignment of the proton environments in complexes 4 and 5 was accomplished with the aid of two-dimensional correlation ('H-'H and 'H- C) experiments. 13  The  31  P { ' H } N M R spectrum of 4 consists o f a  singlet at 8 44.3, which indicates that in solution the phosphine ligand remains bound to ruthenium and does not coordinate to the lithium centre; in such a case, one would expect a 1:1:1:1 quartet due to coupling to L i ( / = 3/2, 92.6% abundance). Likewise, the L i { ' H } N M R spectrum of 4 7  7  contains a singlet at 8 -2.50. For complex 5, a singlet at 8 46.8 is observed in the P { ' H } N M R 31  spectrum.  (iv)  Regeneration of the equilibrium mixture of endo-3 and exo-3 by addition of acid to 4 or 5  As shown in Scheme 2.6, the equilibrium mixture of endo-3 and exo-3 can be regenerated by the stoichiometric addition of NEt3 HCl to the ruthenate complex 4 (or 5). -  Utilizing the  deuterium-labelled acid in the above reaction allows for selective deuteration at the amine nitrogen atom. The assignment of the N-H resonance in the *H N M R spectrum of the diastereomers of complex 3 were verified by synthesis of the amino-deuterio derivatives endo-3-d\ and exo-3-d\. Allowing an equilibrium mixture of the deuterium labelled derivatives to sit for extended periods did not result in the incorporation of deuterium into the cyclooctadienyl ring as monitored by 'H N M R spectroscopy. This result is consistent with the two-dimensional EXSY data, which do not show a cross peak between the amino protons and cyclooctadienyl hydrogen atom sites. Unfortunately, the broadness in the variable-temperature H spectrum and the absence of a low2  75  References begin on page 98  Chapter  2: Synthesis,  Solution  Dynamics  and Reactivity  of Ruthenium(ll)  Complexes  Incorporating  the [NPN] and [P2N2] Ligand  Sets  temperature limiting P { ' H } spectrum did not permit an evaluation o f the isotope influence on the 31  kinetics of the equilibrium process.  (v)  Reaction of compounds 4 and 5 with Me SiCI: 3  formation of the two  independent diastereomers endo- and exo-[NPN(SiMe3)]Ru(1-3-t| - 5,6-n 3  2  CsHu) (endo-6 and exo-6) The above example illustrates the basic behaviour o f the ruthenate complexes towards acidic compounds such as NEtyHCl regenerating the equilibrium mixture o f endo-3 and exo-3. This reactivity prompted us to investigate the ability o f compounds 4 and 5 to act as nucleophilic reagents. Nitrogen-silicon bonds can be made conveniently by the addition o f alkali metal amides with silyl chloride precursors.  62  Formation o f the N-Si linkage is facilitated by the formation o f  MCI ( M = alkali metal), which provides a thermodynamic driving force. In fact, formation o f the N-Si linkages in the backbone o f the [NPN] and [P2N2] ligands proceeds via this route. In an earlier report, the tungstenate complex, [Cp*WMe3(NLi)] , was shown to react with Me3SiCl x  resulting in the formation of Cp*WMe3NSiMe3.  78  I f the equilibrium that is established between  the two diastereomers endo-3 and exo-3 occurs by the reversible intramolecular protonation o f a ruthenium amide ligand, as postulated, then it can be assumed that replacement o f the N-H proton by the bulkier trimethylsilyl group (giving N-SiMe3) may slow down or hinder this exchange process all together.  Addition o f an excess o f chlorotrimethylsilane (Me3SiCl) to a solution o f 4 or 5 in toluene results in a change in colour from orange to red over a period o f 24 hours. Removal o f the volatile components under vacuum followed by rinsing o f the resulting red solid with pentane allows for the isolation o f the two independent diastereomers endo- and exo-[NPN(SiMe3)]Ru(l-3-r| -5,6-r| CgHji) (endo-6 and exo-6, respectively), as shown in equation 2.4. The two isomers are formed in approximately 50% yield each.  Attempts to separate the two complexes via crystallization have  failed thus far.  76  References  begin on page  98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [PzNJ Ligand Sets  Ph  [2.4]  exo-6 (46%)  Unlike the room-temperature H N M R spectrum for endo-3 and exo-3, which is comprised !  o f broadened peaks, the "H N M R spectrum (at 298 K ) for complexes endo-6 and exo-6 contains well resolved resonances for all proton environments implying that the two species do not exhibit any fluxionality.  In fact, examination o f the ' H and P { ' H } N M R spectra as a function of 31  temperature (from 200 to 360 K ) show that the two species are not in equilibrium since no change in product ratios could be discerned. These results provide further evidence for the mechanism depicted in Scheme 2.5 for the inter-conversion of the diastereomers o f species 3.  As was  expected, the bulky trimethylsilyl group is not exchanged between the two isomers, and consequently, they remain independent o f one another. In addition, these results show that the cyclooctadienyl ligand in these two complexes (and by extension in endo-3 and exo-3) remains conformationally rigid; it does not isomerize, for instance, to an T| -coordinated cyclooctadienyl 5  ligand.  The characterization of endo-6 and exo-6 was based on solution N M R studies. 13  The  C { ' H } and ' H N M R data were diagnostic for these two isomers. A trans disposition between  the phosphine and olefin donors in these complexes is indicated by the coupling of the P nucleus 31  77  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligand Sets 2  to the olefinic carbon atoms. In endo-6, for example, C\ occurs as a doublet at 8 61.6 (Vpc = 6.3 Hz) and likewise C2 appears as a doublet at 8 107.6 (Vpc = 10.6 Hz). Complex endo-3 shows very similar resonances for these two nuclei, as is detailed in Table 2.6, with nearly identical coupling constants (6.5 Hz and 10.5 Hz respectively). A similar trend is observed for exo-6 and exo-3. The 13  C chemical shifts o f the remaining cyclooctadienyl carbon nuclei are only slightly shifted,  suggesting that a very similar coordination mode is adopted by this ligand for the related endo and exo isomers of complexes 3 and 6.  The room-temperature *H N M R spectrum for a mixture o f endo-6 and exo-6 resembles the low-temperature spectrum (245 K ) for an equilibrium mixture o f endo-3 and exo-3. A survey o f Table 2.5 shows that the respective isomers o f complexes 6 and 3 display similar chemical shifts for the cyclooctadienyl proton environments.  The central allyl proton (Hf) in all four species  experiences the greatest amount o f shielding and is shifted furthest upfield between 8 1.40 to 8 1.65. The olefinic protons ( H and Hb), on the other hand, are downfield shifted between 8 3.85 a  and 8 4.70 in all o f the complexes. Both the endo and exo isomers o f complex 6 have four ligand silyl methyl proton resonances; the ligand methylene resonances for both isomers overlap with the cyclooctadienyl resonances and occur between ca. 8 1.0 and 8 1.5. The terminal amino silyl methyl (N-SiM^) signal for endo-6 occurs as a singlet at 8 0.15 and integrates'for nine protons. The presence o f a singlet for this group implies that there is free rotation of the trimethylsilyl group about the N-Si bond. For the isomer exo-6 this resonance appears as a singlet at 8 0.12. The remaining phosphine, amine and amido phenyl resonances occur at expected positions between 8 6.8 and 8 7.7. The P { ' H } N M R spectrum contains two singlets at 8 32.9 and 8 32.3 31  for complexes endo-6 and exo-6, respectively.  2.6 Attempted Synthesis of [NPN]Ru(PPh )  3 2  (i)  Reaction of [NPN]Li  2  (C H 0) with RuCI (PPh ) 4  8  2  2  3  3  Reactions o f RuCl2(PPh3)3 with the tetrahydrofuran adduct o f the lithiated ligand precursor, [NPNJI^tC+HgCTh, were performed under a variety o f conditions but in all cases a mixture o f products was formed as indicated by ' H and P { H } N M R spectroscopy. Solvents 3 1  78  !  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligand Sets 2  such as toluene, benzene and diethyl ether were all utilized giving similar results in each case. The  31  P { ' H } N M R spectrum of the crude product mixture shows free triphenylphosphine  indicating that the [NPN] ligand does coordinate to the metal centre; formation of the anticipated five-coordinate species [NPN]Ru(PPh3)2, however, can be dismissed. A five-coordinate complex could adopt either a square pyramidal or a distorted trigonal bipyramidal coordination geometry. A square pyramidal complex would be expected to give rise to a triplet and a doublet for the P j l  nucleus o f the [NPN] and triphenylphosphine ligands, respectively.  A trigonal bipyramidal  complex on the other hand would be expected to exhibit a doublet of doublet coupling pattern for each o f the inequivalent P nuclei. Neither o f these diagnostic coupling patterns was observed. 31  There are many resonances that exist as simple doublets suggesting that there is one equivalent of the chelating [NPN] ligand and one equivalent of coordinated triphenylphosphine per metal centre, giving species of the general formula "[NPN]RuPPh3".  Inspection of the ' H N M R spectrum  allows for speculations to be made regarding the identity of some o f the products that formed in this reaction. A broad singlet at 8 2.9 appears in a location very close to the amino proton of complex 2 (N-H at 8 2.8) in which ort/zo-metalation of the triphenylphosphine ligand occurs. This suggests that the species [NPNH]Ru(C6H4PPh ) containing an ort/zo-metalated PPI13 ligand may 2  have formed. Also evident in the *H N M R spectrum are multiplets in the region 8 4.0 to 8 5.2, reminiscent o f a coordinated arene moiety. Similar features are present in hydride complexes of ruthenium containing the [NPNH] ligand set.  In these systems, the phenyl substituent o f the  amine donor as well as aromatic solvent molecules (toluene or benzene) were shown to coordinate to the metal centre in an r| fashion (Chapter 3). It is possible that similar products are being 6  formed in this case.  2.7  Summary and Conclusions The synthesis o f ruthenium(II) complexes that incorporate the mixed-donor macrocyclic  [P2N2] and tridentate [NPN] ligand sets is described, with the purpose o f utilizing these compounds as precursors for the catalytic hydrogenation o f imine substrates.  The reaction of  [P2N2]Li 'C4H80 with [RuCl2(cod)] generates the diamidodiphosphine complex [P2N ]Ru(r| :r| 2  2  2  x  CsH ) (1) as a yellow crystalline solid in excellent yield. 12  solution and in the solid-state.  2  2  Complex 1 was characterized in  At room temperature 1 displays C2 symmetry in solution, V  79  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  however, cooling the solution results in a C 2 symmetric complex consistent with the solid-state molecular structure.  The reaction between the dilithium salt of the  ligand with  [P2N2]  RuCl (PPh )3 yields the species [ P N N H ] R u ( C H P P h 2 ) (2) in which ort&o-metalation of the 2  2  3  6  4  triphenylphosphine ligand occurs. The solid-state molecular structure of 2 shows that there is an intramolecular hydrogen bonding interaction involving the amine proton and amide nitrogen atom of the [P NNH] ligand. 2  The ligand [ N P N ] L i ( C H 0 ) 2 reacts with [RuCl (cod)] to give an 2  4  8  2  x  equilibrium mixture of endo-3 and exo-3. The diastereomers of 3 are formed via deprotonation of the cyclooctadiene moiety by the [NPN] ligand; transfer of the resulting amino proton between the [NPNH] side-arms establishes the observed equilibrium.  Deprotonation of co-ligands is a  common occurrence in related ruthenium(II) systems containing the [NPN] and  [P2N2]  ligand sets.  Formation of the ruthenate complexes {[NPN]Ru(l-3-r| :5,6-n -C Hn)} { M T H F } (4, M = L i or 5 3  2  8  M = Na) is accomplished by the addition of MN(SiMe3)2 ( M = L i or Na) to a mixture of endo-3 and exo-3. These ruthenate species are non-fluxional in solution as evidenced by the N M R data. Complexes 4 and 5 react with acidic compounds to regenerate an equilibrium mixture of endo-3 and exo-3, or with chlorotrimethylsilane to give the two independent diastereomers endo- and exo[NPN(SiMe3)]Ru(l-3-r| -5,6-ri -C8Hii) (endo-6 and exo-6, respectively). 3  2  Although reaction of  the [P N ] and [NPN] ligands with the ruthenium(II) precursors did not yield the expected 2  2  products in all cases, the complexes that were obtained contain a ruthenium amide unit necessary for the heterolytic activation o f molecular hydrogen.  This reactivity will be discussed in the  following chapter.  2.8  Future Work  (i)  Reaction of 3 with carbon monoxide We envisioned that the stoichiometric addition of a neutral donor ligand to an equilibrium  mixture of the diastereomers exo-3 and endo-3 would eliminate the inter-conversion process and possibly allow for the separation of two coordinatively saturated analogues of these two species. As was previously described, complex 3 was found to be unreactive towards neutral donors such as pyridine, THF and various phosphines. The addition of one equivalent of CO gas to a red solution o f 3, however, resulted in an immediate change in colour to orange. The reaction was  80  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand Sets  performed in an N M R tube and the 'Pi and P{'PI} N M R spectra both indicated the formation of 31  only one product, [NPNH]Ru(l-3-ri :5,6-ri -C8Hii)(CO) (7), as shown in equation 2.5. 3  Ph Me Si'; /  Ph ^Ph Me Sr\-N.  H  2  2  2  Jfc  Ph  Me Sr-\— N 2  <^SiMe;  Ph'  PhHN Me Sr 2  endo-3  [2.5]  exo-3  1  eq. CO PhHN  The slow evaporation o f the N M R solution (toluene-^) allowed for the isolation of single crystals o f complex 7 suitable for an X-ray diffraction study. The solid-state molecular structure of 7 is shown in Figure 2.20 and selected bond lengths and angles are given in Table 2.10. The geometry of 7 is best described as distorted octahedral with the olefin and phosphine ligands occupying the axial positions, and the amide, CO and allyl donors contained within the equatorial plane. We have previously described 3 as a 7t-stabilized unsaturated complex involving a bonding interaction between the amido lone pair o f electrons with the metal L U M O (d  xy  orbital). The  addition o f CO to 3 generating the coordinatively saturated complex 7 would render the amido ligand a o-donor with minimal 7i-bonding interactions. The longer R u ( l ) - N ( l ) bond distance o f 2.212(2) A in 7 compared to 2.019(2) A in 3 supports this notion. The bond angles about the amide nitrogen atom (N(l)) indicate a planar geometry; this is most likely due to ^-interactions with the neighbouring silicon atom or phenyl ring. Interestingly, the plane o f the amide donor is tilted away from the equatorial plane o f the molecule (P(l)-Ru(l)-N(l)-C(7) = 138.8(2)°). This may be due to a stabilizing effect on the nitrogen lone pair by decreasing the orbital overlap of these electrons with the filled d orbitals of the metal. K  81  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and  [P2NJ Ligand  Sets  Figure 2.20. ORTEP representation (thermal ellipsoids shown at 50 % probability) o f the solidstate molecular structure o f the complex [NPNH]Ru(l-3-r| :5,6-r| -C8Hn)(CO) (7) as determined 3  from X-ray diffraction.  2  The silyl methyl groups of the [NPNH] ligand have been omitted for  clarity. The amino hydrogen atom H(34) was located and refined isotropically.  Table 2.10. Selected bond lengths and angles [NPNH]Ru(l-3-r] :5,6-ri -C8H,i)(CO) (7). 3  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom N(l) P(l) C(26) C(27) C(28) C(31) C(32)  Distance (A) 2.212(2) 2.2853(6) 2.356(2) 2.202(2) 2.200(2) 2.407(2) 2.334(2)  Atom C(26) C(27) C(31) N(l) N(2) N(l)  82  Atom C(27) C(28) C(32) Si(l) Si(2) H(34)  2  Distance (A) 1.385(4) 1.424(3) 1.355(4) 1.720(2) 1.729(2) 0.75(3)  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand Sets  Atom P(l) P(l) P(l) P(l) P(l) P(l) N(l) N(l) N(l)  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom  Atom  Angle 0 78.78(5) 88.11(7) 104.18(6) 101.85(6) 168.31(6) 157.73(7) 104.70(8) 94.80(8) 160.53(8)  N(l) C(25) C(26) C(28) C(31) C(32) C(25) C(26) C(28)  N(l) N(l) C(25) C(25) C(25) C(25) Ru(l) Ru(l) Si(l)  The room temperature *H, ^ P J / H }  and  13  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) N(l) N(l) N(l)  C{'H}  Atom C(31) C(32) C(26) C(28) C(31) C(32) Si(l) C(7)  Angle (°) 105.24(8) 84.71(8) 158.74(9) 94.77(9) 80.26(9) 110.65(9) 116.04(9) 123.2(1) 120.7(1)  CO)  N M R spectra all show features  characteristic of complex 7. The P { H } N M R spectrum consists o f a singlet at 8 46.0 and the 31  13  1  C{'PI} N M R spectrum shows eight resonances for the inequivalent cyclooctadienyl carbon  centres. Two of these resonances at 8 69.9  (Jpc 2  = 6.72 Hz) and 8 105.1  (Vpc = 7.63  Hz) are  observed as doublets due to coupling with the trans phosphine ligand, a finding consistent with the solid state structure. The ' H N M R spectrum is diagnostic o f an asymmetric complex; four silyl methyl proton, four methylene proton and 11 cyclooctadienyl proton resonances are all observed. The amino proton in 7 is located as a singlet at 8 2.40.  The fact that only one product is formed in this reaction suggests that the addition o f CO may occur preferentially with one isomer o f 3. In the molecular structure o f 7 it can be seen that the dissociated amine arm o f the [NPNH] ligand set is oriented to the opposite face o f the metal as the methylene unit that bridges the olefin and allyl donors o f the cyclooctadienyl ligand. The amine arm and the CO ligand are positioned to the same face o f the metal. This implies that a molecule o f CO reacts with the diastereomer exo-3 by displacing the pendant amine arm away from the metal centre.  A decrease in the concentration o f exo-3 would cause a shift in the  equilibrium between these two isomers producing more exo-3. I f the equilibrium shift occurs faster than the reaction o f CO with endo-3 then only complex 7 would be generated.  We speculate that the metal centre may be more accessible in exo-3 thereby increasing its reactivity with CO. In the solid-state molecular structure o f 7 it can be seen that the dissociated amino side-arm bends away from the ruthenium centre in order to minimize steric interactions with the bound CO ligand. In a similar fashion, the ethylene unit o f the cyclooctadienyl ligand (bridging C(28) and C(31)) is oriented away from the metal centre. This is reflected in the longer 83  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  ruthenium bond distance for C(31) of the olefin donor as compared to atom C(32) (2.407(2) A vs. 2.334(2) A). The longer Ru-C distances observed for C(26) and C(27) of the allyl donor are most likely a consequence o f their approximately trans disposition with the CO ligand, which has a strong trans influence. It appears as though the amine side-arm and the ethylene unit "spreadout", thereby opening an otherwise hindered coordination site at the metal centre. I f the analogous complex with endo-3 is envisioned, the amine side-arm and the methylene fragment of the cyclooctadienyl ligand would be required to be displaced away from the metal centre,  ft is  possible that the methylene bridge cannot effectively bend away from the metal centre and this causes enough shielding of the metal, not allowing for coordination o f a molecule of CO.  Given the distorted trigonal bipyramidal structure o f exo-3 one would also expect that its reaction with CO would generate two products since there are two possible sites for attack, namely in the two wide angles o f the trigonal plane. Yet, only one species is formed. The stereospecific addition o f CO to distorted trigonal bipyramidal d metal complexes, when there are different 6  ligands occupying the equatorial positions, is a common observation.  67  One rationalization that  has been given for this behaviour is that the metal L U M O is not equally developed in both wide angles due to the lack o f symmetry in the complex.  67  An example of this is illustrated in Figure  2.21 for the complex h(PR3)2(H)(Cl)(r| -C6H5), in which the addition o f CO occurs trans to the 1  hydride ligand.  By hybridizing away from the weaker donor the L U M O is stabilized by higher  empty orbitals.  A  Figure 2 . 2 1 .  depiction o f how  the metal L U M O  Ir(PR ) (H)(Cl)(ri -C6H5) extends away from the hydride ligand. 1  3  (d  xy  orbital)  in the  complex  67  2  84  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  In exo-3 the allyl moiety occupies the positions subtending the acute angle in the equatorial plane. According to the above explanation the observed stereospecific addition o f CO to exo-3 suggests that the two "ends" of the allyl function could have different donor properties so that the metal L U M O is extended preferentially in one direction. The allyl ligand, for instance, may more appropriately be envisioned as an r ) - ^ 2  symmetrical r| centre in 3.  1  donor with localized electron density rather than a  function with delocalized electron density when coordinated to the ruthenium  3  Figure 2.22 shows the bonding combination for the allyl ligand with the metal d  xy  orbital (the metal orbital with which it has the greatest overlap), which indicates that a nodal plane is present at the central carbon atom, not permitting electron derealization over all three positions of the allyl ligand.  The asymmetry of the allyl ligand could account for the observed  stereospecific addition of CO to exo-3. Theoretical calculations should be performed in order to gain more insights into the electronic structure of 3 in order to verify or discount this hypothesis.  z  3  Figure 2.22.  A schematic representation of the bonding combination between the allyl moiety  and the metal d  xy  orbital in exo-3.  It would be interesting to scale-up the reaction between complex 3 with one equivalent of CO to examine if similar reactivity occurs on a larger scale. Due to the small surface area of the  85  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  solution in an N M R tube the observed reactivity may be governed by the rate at which CO can dissolve into the solution.  As shown in Scheme 2.7, the reaction of complex 3 with an excess of CO results in the formation of a ruthenium (0) tetracarbonyl species (8) over a period of several hours. Monitoring the reaction by ' H and P { ' H } N M R spectroscopy reveals the initial formation of 7, which reacts 31  slowly with CO to yield 8. After 30 minutes a solution of the reaction mixture contains complex 7 in ca. 90 % yield and complex 8 in ca. 10 % yield, as assayed by integration of their P N M R 31  signals.  After 12 hours complex 8 is the only species remaining in solution.  Minor peaks  (comprising less than 1 % of the reaction mixture) present during this conversion are most likely due to short-lived intermediates suggesting that initial migratory insertion is the rate limiting step in this process.  Scheme 2.7 - The solid-state molecular structure of 8 as determined by X-ray diffraction is shown in Figure 2.23. Selected bond lengths and angles are highlighted in Table 2.11. The five-coordinate  86  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  species contains three CO ligands in the plane of a trigonal bipyramidal structure with a fourth CO ligand and the bulky phosphine donor located at the axial coordination sites. Complexes of this type are known, although their preparation usually entails the addition of a phosphine ligand to [Ru(CO) ]. 5  79  The X-ray structural analysis of the related species [Ru(CO) {P(OMe) }] 4  80  3  indicates that the ruthenium centre adopts a trigonal bipyramidal geometry with an axial phosphine ligand, similar to that observed in 8. The bond distances and angles in complex 8 coincide well with those determined in [Ru(CO)4{P(OMe)3}].  The most significant difference  between the two complexes is the longer ruthenium-to-phosphorus distance in 8 of 2.3856(7) A compared to 2.309(2) A, which can be attributed to the steric bulk of the phosphine ligand in 8.  Figure 2.23. ORTEP depiction of the solid-state molecular structure of complex 8 as determined by X-ray diffraction. Thermal ellipsoids are shown at the 50 % probability level.  87  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  Table 2.11. Selected bond lengths and angles in complex 8.  Atom Ru(l) Ru(l) Ru(l) Atom P(l) P(l) P(l) P(l) C(34)  Atom P(l) C(34) C(35)  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Distance (A) 2.3856(7) 1.934(3) 1.917(4)  Atom C(34) C(35) C(36) C(37) C(35)  Angle (°) 88.67(9) 177.78(11) 87.49(10) 90.45(9) 92.12(14)  Atom Ru(l) Ru(l)  Atom C(36) C(37)  Distance (A) 1.929(4) 1.928(3)  Atom C(34) C(34) C(35) C(35) C(36)  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(D  Atom C(36) C(37) C(36) C(37) C(37)  Angle (°) 123.35(4) 115.47(13) 90.34(14) 91.09(15) 121.07(14)  The room temperature N M R data for complex 8 are indicative of dynamic behaviour for this species in solution. The P { ' H } N M R spectrum, for example, contains a broad resonance at 31  8 20.7. The ' H N M R spectrum also consists of broadened resonances. No structural information can be gleaned from this data, although resonances for the silyl methyl, cyclooctadiene, and aromatic environments are all observed. Peaks located between 8 5.2 and 8 5.8 are consistent with a dissociated cyclooctadiene fragment. Five-coordinate, d transition metal complexes are known 8  to exhibit fluxional behaviour.  81  Inter-conversion between square pyramidal and trigonal  bipyramidal coordination geometries is possible. As well, the rearrangement of ligands between axial and equatorial positions within a trigonal bipyramidal ground state structure can occur; this can proceed via the Berry mechanism or the "turnstile rotation" mechanism. Further studies are required to unequivocally characterize complex 8.  Low temperature H , P { ' H } and l  3 l  13  C{'H}  N M R spectroscopy, as well as solution and solid-state infra-red spectroscopy will provide new details into this system.  The use of  13  C-labelled carbon monoxide will assist in these  investigations.  A possible mechanism for the formation of complex 8 could involve initial insertion of CO into the ruthenium-carbon bond of the allyl moiety in complex 7 resulting in a ruthenium-acyl species. In regards to the molecular structure of 7 (Figure 2.20) this insertion step would occur at C(28) (rather than C(26)) due to its nearly cw-disposition with the CO ligand. The addition of four equivalents o f CO could then displace the olefin donors of the cyclooctadienyl ligand and  88  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  induce the reductive elimination of the acyl group to the amide nitrogen. This mechanism would yield a 1,4-cyclooctadiene moiety.  The cyclooctadiene fragment in the crystal structure was  disordered but was successfully modelled as containing both 1,4- and 1,5-cyclooctadiene groups. This suggests that an alternative route for the formation of 8 is also possible. The amido donor in 7 is located cis to the CO ligand and so it is likely that initial insertion of CO into the Ru-N bond also takes place. Reductive elimination from C(26) of the allyl function would generate a 1,5cyclooctadiene fragment. Obviously, more studies are necessary to provide further evidence for either of these postulated pathways. The addition of an equivalent of CO to complex 7 could be a very informative reaction. The use o f C-enriched carbon monoxide in these studies and homo13  and heteronuclear N M R investigations could also be potentially very informative. reactivity was observed in nickel (II) complexes containing the [PNP] ligand set. > 82  2.9  Experimental  (i)  General Procedures  Similar  83  Unless otherwise stated, all manipulations were performed under a dry, oxygen-free atmosphere of dinitrogen or argon by means of standard Schlenk or glove box techniques (Vacuum Atmospheres HE-553-2 glove box equipped with a MO-40-2H purification system and a -40°C freezer). Toluene and hexanes were purchased in anhydrous form from Aldrich and deoxygenated by passage through a tower containing Q-5 catalyst and further dried by passage through a tower containing alumina under a positive pressure of dinitrogen. Anhydrous THF was pre-dried by refluxing over CaFL: and then distilled under argon from sodium benzophenone ketyl. Anhydrous diethyl ether was stored over sieves and distilled from sodium benzophenone ketyl under argon.  Deuterated benzene, tetrahydrofuran and toluene were dried by refluxing over  sodium and potassium alloy in a sealed vessel under partial pressure, then trap-to-trap distilled and degassed by three freeze-pump-thaw cycles prior to use. Nitrogen and argon were dried and deoxygenated by passage through a column containing activated molecular sieves and MnO. Unless otherwise stated, H , ' H { P } , H , P { ' H } , !  31  2  31  i 3  C { ' H } , L i { ' H } and variable-temperature 7  N M R spectra were recorded on a Bruker AMX-500 instrument operating at 500.1 MHz for *H spectra, a Bruker AV-300 instrument (300.1 MHz), or a Bruker AC-200 instrument (200.1 MHz).  89  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligand Sets 2  ' H N M R spectra were referenced to internal C D H (7.15 ppm) or C7D7H (2.09 ppm), 6  31  5  P{'H}  N M R spectra to external P(OMe) (141.0 ppm with respect to 85% H3PO4 at 0.0 ppm), and 3  13  C { ' H } N M R spectra to CCsD (128.4 ppm). A l l 8 values are given in ppm units. Infra-red 13  6  spectra were recorded on an A T I Matton Genesis Series FTIR Spectrometer as KBr pellets. Elemental analyses were performed in the Department o f Chemistry at the University o f British Columbia by Mr. P. Borda or Mr. M . Lakha. Complexes for which elemental data is not reported were not yet submitted for analysis at the time this thesis was completed.  (ii)  Materials  The  compounds  [NPN]Li -(C H 0) , 2  4  8  38  2  [P N ]Li -C H 0 , 2  2  2  4  8  39  2  [RuCl (cod)] 2  84 x  and  RuCl (PPh3)3 were prepared according to reported literature procedures. NEt 'DCl was prepared 85  3  2  by the dropwise addition o f aqueous deuterium chloride to a solution o f triethylamine in diethyl ether.  The solid was collected by filtration and dried under vacuum.  triisopropylphosphine  and  tricyclohexylphosphine  (Strem  Triphenylphosphine,  Chemicals),  LiN(SiMe3) , 2  NaN(SiMe ) , N E t H C l , pyridine, CuCl and chlorotrimethylsilane (Aldrich) were used without 3  2  3  further purification.  RuCl "3H 0 was obtained on loan from Johnson-Matthey, as well as 3  2  purchased from Precious Metals Online.  (iii)  Synthesis and Reactivity of Complexes  [ P N ] R U ( T I : T I - C 8 H I 2 ) (1) 2  2  2  2  A solution o f [ P N ] L i C H 0 (0.734 g, 1.16 mmol) in 10 m L o f THF was added to a 2  2  2  4  8  2  slurry o f [RuCl (cod)] (0.324 g, 1.16 mmol) in 10 m L of THF. The mixture was stirred at room 2  x  temperature for three hours yielding a yellow-brown solution. The mixture was evaporated to dryness in vacuo and the resulting solid was extracted into 20 mL of toluene and filtered through Celite. The solvent was removed until a thick oily residue remained. Addition o f hexanes (10 mL) caused a yellow solid to precipitate from the solution. The solid was collected on a frit and washed with hexanes until the dark impurities were removed. The remaining solid was dried under vacuum to yield [P N ]Ru(r) :r| -C8Hi ) (1) (0.628 g, 73 % ) . X-ray quality crystals were 2  2  2  2  2  obtained by the slow evaporation o f the hexanes rinsings and contained one equivalent o f co-  90  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  crystallized hexane. H N M R ( C D , 298 K, 500 MHz): 8 0.40 and 0.50 (s, SiCtf , 24H total), !  6  6  3  5 0.95 and 1.42 (m (br), P-CH , 8H total), 8 1.82 (m, cyclooctadiene -CH , 8H), 8 2.91 (s (br), 2  2  cyclooctadiene -CH, 4H), 8 7.12 (m, overlapping, PPh-para, I H ) , 8 7.20 (m, PPh-meta, 4H), 8 (m, PPh-ortho, 4H). ^ P l ' H } N M R ( C D , 298 K, 202.5 MHz): 8 44.5 6  (s).  6  I 3  C{'H} NMR  (C D , 298 K, 125.8 MHz): 8 7.0 and 9.0 (s, SiCH ), 8 25.0 (s (br), cyclooctadiene - C H ) , 8 28.0 6  6  3  2  (s (br), P-CH ), 8 70.0 (s, cyclooctadiene - C H ) , 8 127.5 (s, overlapping, PPh-para), 8 128.5 (s, 2  PPh-weto), 8 131.0 (s, VYh-ortho), 8 143.0 (s (br), VPh-ipso). H N M R ( C D , 198 K, 500 MHz): !  6  6  8 0.30 to 0.60 (s, overlapping, S1CH3, 24H total), 8 0.90 (s (br), P-CH , 2H), 8 1.30 (s (br), 2  overlapping, P-Ci/2 2H), 8 1.30 (s (br), overlapping, cyclooctadiene -CH2, 2H), 8 1.90 (s, cyclooctadiene -CH2, 2H), 8 2.09 (s, cyclooctadiene -CH ,  2H), 8 2.20 (s, cyclooctadiene  2  -CH , 2  2H), 8 2.60 (s (br), cyclooctadiene -CH, 2H), 8 3.00 (s (br), cyclooctadiene - C H , 2H), 8 6.80 to 7.15 (m, overlapping, PPh-mgta and para, 6H total), 8 7.80 (s (br), PVh-ortho, 4H).  [PNNH]Ru(CHPPh2) (2) 2  6  4  Toluene (30 mL) was added to a mixture of [ T ^ ^ ' C ^ C b (0.170 g, 0.268 mmol) and RuCl (PPh ) (0.256 g, 0.267 mmol). 2  3  3  The initial slurry was stirred for three hours at room  temperature resulting in the formation of an orange-brown coloured solution, which was filtered to remove insoluble LiCI. Anhydrous CuCl (0.054 g, 0.536 mmol) was subsequently added to the solution and the contents stirred for 12 h. The mixture was filtered and the filtrate was evaporated until approximately 2 mL of toluene remained.  Addition of pentane (10 mL) caused the  deposition of [P NNH]Ru(PC6H4Ph ) (2) as an orange solid. The solid was collected by filtration, 2  2  rinsed with a minimum amount of pentane and dried in vacuo to yield 0.207 g of 2 (86 % ) . Single crystals suitable for an X-ray diffraction study were grown by the slow evaporation o f the pentane soluble rinsings.  There were two independent molecules in the asymmetric unit as well as a  molecule of co-crystallized pentane. N M R ( C D , 298 K, 500 MHz): 8 0.39, 0.41, 0.58 and 0.60 6  6  (s, SiCH , 24H total), 8 1.40 (m, overlapping, F-CH , 4H), 8 1.53 (m, overlapping, ?-CH , 4H), 8 3  2.80 (s, N-#),  2  8 6.52 - 8.12 (m, Y-Ph, [P NNH] and PC H Ph , 24 H total). 2  ( C D , 298 K, 202.5 MHz): 8 25.8 (d, / 2  6  6  2  6  4  31  2  P{'H} NMR  = 31 Hz, [P NNH], 2P), 8 -11.8 (t, J 2  P P  2  91  P P  = 31 Hz,  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P NJ Ligand Sets 2  PC H Ph , IP). Anal. Calcd. for 6  5  C42H57N2P3S14RU:  2  C, 56.28; H, 6.41; N 3.13. Found: C, 56.11;  H, 6.58; N, 3.29.  For complexes 3 through 6 the following labelling convention is employed for assignment of 'Hand C nuclei of the cyclooctadienyl moiety: 13  endo- and exo-[NPNH]Ru(1-3-r| -5,6-ri -C8Hii) (endo-3 and exo-3) 3  2  Toluene (30 mL) was added to a mixture of [NPN]Li2(GjHgO^ (1.06 g, 1.78 mmol) and [RuCl2(cod)] (0.50 g, 1.78 mmol) and the mixture was stirred for two days at room temperature. x  During this time the initial brown slurry turned red and a colourless solid formed. The mixture was then filtered through Celite and the solvent removed under reduced pressure leaving an oily solid. A small amount of hexanes (ca. 5 mL) was added to dissolve the solid and the mixture was allowed to stand in a closed vessel for 48 hours during which time complex 3 crystallizes from solution. The supernatant was decanted and the red crystals were washed with hexanes. Yield: 0.90 g, 78 %. A further crop of crystals was obtained by the slow evaporation of the supernatant. Isomer endo-3: H N M R ( C D , 245 K, 500 MHz): 5 0.08 (s, br, SiC// , 6H), 8 0.34 (s, SiC// , ]  7  8  3  3  3H), 8 0.43 (s, SiC# , 3H), 8 0.76 (m, A A ' B X , PC//H, 1H), 8 1.0 (m, A A ' B X , 3  (m, A A ' B X , PC/7H, 1H), 8 1.50 (m, CHdftr, 1H), 8 1.58 (m, CHcH ; (m,  CHH ; h  2.85 (m, CHg,  1H),  8 2.18  (m,  1H),  CHMd',  1H), 8 4.20 (m, CH , e  8 2.36  (m,  CH U -, C  1H), 8 4.23 (m, CH ,  C  1H),  8 2.70  1H), 8 4.25 (m, CH ,  a  2  1H), 8 1.64 (m, CH/,  e  2.00  2H), 81.17  PCH ,  b  (m,  CH H , h  w  1H), 8 1H),  8  1H), 8 6.63 (s, NT/,  1H), 8 6.82 - 7.42 (m, overlapping, NP/i, NFLP/? and P/Vz,). " P ^ H } N M R ( C D , 245 K, 202.5 7  MHz): 8 33.4 (s).  13  C { ' H } N M R ( C D , 245 K, 125.8 MHz) selected peaks: 8 25.2 (s, C ,), 8 7  8  8  30.3 (s, C ), 8 32.8 (s, C ), 8 35.6 (s, C ), 8 61.4 (d, G , J 2  3  8  4  7  PC  = 6.5 Hz), 8 61.6 (s, C ), 8 71.6 (s, 5  Q ) , 8 108.1 (d, C , Jvc = 10.5 Hz). Isomer exo-3: *H N M R ( C D , 245 K, 500 MHz): 8 0.09 (s, 2  2  7  92  8  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  overlapping, SiC// , 3H), 5 0.28 (s, SiC# , 3H), 8 0.32 (s, overlapping, SiC// , 6H), 5 0.85 (m, 3  3  3  overlapping, A A ' B X , PCH , 2H), 8 1.0 (ra, overlapping, A A ' B X , PCH , 2H), 8 1.30 (m, CH H ; 2  2  IH), 8 1.50 (ra, overlapping, CH , IH), 8 1.75 (m, CH H ; f  (m, overlapping, CU H ; h  d  C  C  I H ) , 8 1.83 (m, Gr7 H ., I H ) , 8 2.15 c  d  c  I H ) , 8 2.20 (m, CHM*, I H ) , 8 3.09 (m, CH H >, I H ) , 8 3.37 (m, CH , A  h  h  S  IH), 8 3.50 (m, CH , I H ) , 8 3.92 (m, CH , I H ) , 8 4.68 (m, CH , I H ) , 8 6.35 (s, N # , I H ) , 8 6.82 e  b  a  7.42 (m, overlapping, NP/z, NHPA and PPh). V  a b  6.20 Hz, J - = 6.10 Hz,  = 7.60 Hz, l / . = 6.00 Hz, J  3  2  bc  8.60  Hz,  Hz, V 13  g h  2  J  d d  - = 17.0 Hz,  J . = 14.60 Hz, V CC  3  J  d e  = 5.60  = 7.80 Hz, Vah = 7.70 Hz, V 3  c d  cd  Hz, V - = 5.80  - = 4.20 Hz, V h h ' = 19.30 Hz.  d  31  Hz,  e  3  J  e f  = 8.00  Hz,  3  J  f g  c d  a h  . = 7.30 Hz, V  = 7.20 Hz, V  = 9.90  Hz, V  g  h  c d  =  b c  =  -=  7.90  P { ' H } N M R (C D , 245 K, 202.5 MHz): 8 32.9 (s). 7  8  C { ' H } N M R ( C D , 245 K, 125.8 MHz) selected peaks: 8 26.6 (s, C ,), 8 27.0 (s, C ), 8 36.3 (s, 7  8  8  C ), 8 36.5 (s, C ), 8 64.9 (s, C ), 8 65.3 (d, Ci, V 4  7  5  3  = 5.8 Hz), 8 70.8 (s, C ), 8 110.0 (d, C , J?c = 2  P  C  6  2  11.3 Hz). Infra-red (KBr): v(NH) at 2945 cm' and 2906 cm" . Anal. Calcd. for C^H^NzPRuSiz: 1  1  C, 59.69; H, 6.73; N, 4.35. Found: C, 59.68; H, 7.09; N, 4.35.  Addition of neutral donor ligands to a mixture of endo-Z and exo-3 In an N M R tube complex 3 (0.040 g, 0.062 mmol) was dissolved in benzene-ofe (~ 1 mL). To the resulting red solution a ten-fold excess o f triphenylphosphine (0.163 g, 0.621 mmol) was added. Monitoring the reaction mixture by *H and P { H } N M R spectroscopy over a time period 31  1  of 24 hours revealed the presence o f unreacted 3 and free PPh . 3  A similar procedure was  employed for the following donor ligands: THF (0.045 g, 0.621 mmol), pyridine (0.049 g, 0.621 mmol), tricyclohexylphosphine (0.174 g, 0.621 mmol) and triisopropylphosphine (0.107 g, 0.621 mmol). In all cases the N M R data indicated that no reaction had taken place.  {[NPN]Ru(1-3-r| -5,6-Ti -C Hii)}{LiTHF} (4) 3  2  8  A solution o f LiN(SiMe )2 (0.064 g, 0.384 mmol) in toluene (10 mL) was added dropwise 3  to a toluene solution o f 3 (0.247 g, 0.384 mmol) (20 mL) and the mixture was stirred at room temperature for three hours during which time an orange solid precipitated from the solution. The solvent was removed under reduced pressure until half volume and hexanes (20 mL) was added to 93  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  ensure complete precipitation. The orange solid is insoluble in aromatic solvents. THF was added to a mixture o f the orange solid in toluene until it completely dissolved. Removal o f the volatiles in vacuo and addition d f hexanes caused the deposition o f 3 as an orange micro-crystalline solid. The solid was filtered, washed with hexanes and dried under vacuum. Yield: 0.255 g, 92 %. X ray quality crystals were grown by the slow evaporation o f a saturated toluene solution. ' H N M R  (C D , 298 K, 500 MHz): 8 0.10, 0.20, 0.35 and 0.50 (s, S1C//3, 12 total), 8 1.00 (m, A A ' B X , 6  6  PC//H, 1H), 1.07 (m, CH H , C  1H), 8 1.14 (m, overlapping, OCH C77 , 2H), 8 1.18 (m, 2  C  2  overlapping, CH R ; 1H), 8 1.33 (m, C H ^ . , 1H), 8 1.44 (m, A A ' B X , PCH//, 1H), 8 1.65 (m, C  C  A A ' B X , PC//H, 1H), 8 1.73 (m, overlapping, A A ' B X , PCH//, 1H), 8 1.76 (m, CH K >, 1H), 8 d  d  2.17 (m, CH , 1H), 8 2.29 (m, CH , 1H), 8 2.50 (m, CH//,,-, 1H), 8 3.06 (m, overlapping, a  b  O C / / C H , 2H), 8 3.10 (m, overlapping, CH , 1H), 8 3.45 (m, overlapping, CH H ; 2  2  e  h  h  1H), 8 3.45  (m, overlapping, CH , 1H), 8 4.35 (m, CH , 1H), 8 6.58 (t, NPh-para, 1H), 8 6.78 (t, N'Ph-para, f  g  1H), 8 7.70 (m, NPh-weto, 2H), 8 7.20 (m, overlapping, NPh-ortho, 2H), 8 7.20 (m, overlapping, PPh-para, 1H), 8 7.39 (m, N'Ph-meta, 2H), 8 8.05 (m, A X , FPh-ortho, 2H), 8 8.30 (d, N'Phortho, 2H).  31  P { ' H } N M R ( C D , 298 K, 202.5 MHz): 8 46.8 (s). 6  6  13  C { ' H } N M R ( C D , 298 K, 7  8  125.8 MHz) selected data: 8 22.7 (s, C ), 8 27.7 (s, C ), 8 27.9 (s, C ), 8 33.2 (d, C , J  = 6.4  2  8  4  Hz), 8 45.0 (d, C?, V P C = 19.2 Hz), 8 46.0 (d, C , J  PC  = 2.1 Hz), 8 68.2 (d, C , J 2  2  5  3  P C  2  ?C  = 5.8 Hz), 8  100.5 (s, C ). 6  {[NPN]Ru(1-3-ri -5,6-Ti -C Hii)}{NaTHF} (5) 3  2  8  Complex 5 is prepared in a similar fashion as 4. (0.054 g, 0.294 mmol) o f NaN(SiMe ) 3  2  and (0.189 g, 0.294 mmol) of 3 were employed. Yield: 0.193 g, 89 %. X-ray quality crystals were grown from a saturated toluene solution at - 4 0 °C. H N M R ( C D , 298 K, 500 MHz): 8 !  6  6  0.10, 0.20, 0.35 and 0.50 (s, S1C//5, 12 total), 8 1.00 (m, A A ' B X , PC//H, 1H), 1.07 (m, CHc//c-, 1H), 8 1.14 (m, overlapping, O C H C / / , 2H), 8 1.18 (m, overlapping, C// H ., 1H), 8 1.33 (m, 2  CH H ; d  d  2  C  C  1H), 8 1.44 (m, A A ' B X , PCH//, 1H), 8 1.65 (m, A A ' B X , PC//H, 1H), 8 1.73 (m,  overlapping, A A ' B X , PCH//, 1H), 8 1.76 (m, CHjH*, 1H), 8 2.17 (m, CH , 1H), 8 2.29 (m, CH,„ a  1H), 8 2.50 (m, CRH , 1H), 8 3.06 (m, overlapping, OC// CH , 2H), 8 3.10 (m, overlapping, CH , 2  h  2  e  1H), 8 3.45 (m, overlapping, C// H ., 1H), 8 3.45 (m, overlapping, CH 1H), 8 4.35 (m, C / / , 1H), A  h  fi  94  g  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  8 6.58 (t, NPh-para, I H ) , 8 6.78 (t, N'Ph-/?ara, I H ) , 8 7.70 (m, NPh-meta, 2H), 8 7.20 (m, overlapping, NPh-ort/ro, 2H), 8 7.20 (m, overlapping, PPh-para, I H ) , 8 7.39 (m, N'Ph-weto, 2H), 8 8.05 (m, A X , Wh-ortho, 2H), 8 8.30 (d, N'Ph-ortfco, 2H). MHz): 8 46.8 (s).  13  31  P { ' H } N M R ( C D , 298 K, 202.5 6  6  C { H } N M R ( C D , 298 K, 125.8 MHz) selected data: 8 22.7 (s, C ), 8 27.7 1  7  8  (s, GO, 8 27.9 (s, C ), 8 33.2 (d, d , V 3  VPC = 2.1 Hz), 8 68.2 (d, C , / 2  2  P C  8  = 6.4 Hz), 8 45.0 (d, C J 2  P C  7>  PC  = 19.2 Hz), 8 46.0 (d, C , 5  = 5.8 Hz), 8 100.5 (s, C ). 6  Reaction of complex 4 with NEt HCI 3  Addition o f NEtyHCl (0.015 g, 0.109 mmol) to a solution o f 4 (0.078 g, 0.108 mol) in toluene (10 mL) resulted in a change in colour from orange to red within two hours. The mixture was filtered to remove insoluble LiCI and the volatile components were removed under vacuum giving a red solid. The ' H and P { ' H } N M R spectra o f the red solid indicate that it is a mixture 31  of the two diastereomers endo-3 and exo-3.  Reaction of complex 4 with NEt DCI 3  A similar procedure to that described above for the reaction with N E t H C l was followed: 3  NEt 'DCl (0.017 g, 0.123 mmol), 4 (0.086 g, 0.119 mmol) and toluene (10 mL). The *H and 3  31  P { H } N M R spectra indicate the formation o f an equilibrium mixture of endo-3-d\ and exo-3-dy 1  in which deuteration at the amino site occurs.  endo- and exo-[NPN(SiMe )]Ru(1-3-T| -5,6-T| -C8Hii) (endo-6 and exo-6) 3  2  3  A ten-fold excess o f chlorotrimethylsilane (0.292 g, 2.69 mmol) was added to an orange solution o f 4 (0.194 g, 0.269 mmol) in toluene (30 mL). Over the period o f 48 hours the solution turns red with the formation o f a white solid (LiCI). The solvent and other volatiles were removed in vacuo. Toluene was added to the remaining solid and the mixture was filtered to remove insoluble by-products. The soluble fraction was dried under vacuum to give a mixture o f endo-6 95  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  and exo-6 as a red solid material (0.17 g, 88 % ) . Attempts to separate the two isomers by rinsing with hexanes or pentane proved unsuccessful. Isomer endo-6: ' H N M R (C6D6, 298 K, 500 MHz): 5 0.12 (s, overlapping, SiC// , 3H), 8 0.15 (s, overlapping, terminal N-SiC# ), 8 0.18 (s, 3  3  overlapping, SiC# ), 8 0.33 (s, SiCr7 , 3H), 8 0.46 (s, SiC7/ , 3H), 8 1.00 to 1.50 (m, overlapping, 3  3  3  Y-CH ), 8 1.47 (m, CHJIc; I H ) , 8 1.52 (m, CH , I H ) , 8 1.85 (m, CR H ; 2  f  d  I H ) , 8 2.10 (m, CHcUc, IH), 8 2.25 (m, CHMv,  I H ) , 8 2.77 (m, CH H , h  I H ) , 8 4.00 (m, CH , I H ) , 8 4.16 (m, CH , I H ) , 8 4.25 (m, CH , b  overlapping, NP/z,  e  and PP/?).  NHP/J  31  I H ) , 8 2.05 (m,  d  a  CRH , h  I H ) , 8 2.90 (m, CH ,  v  g  I H ) , 8 6.80 - 7.45 (m,  P { ' H } N M R ( C D , 298 K, 202.5 MHz): 8 32.9 (s). 7  8  ' ^ { ' H } N M R ( C D , 298 K, 125.8 MHz) selected peaks: 8 25.5 (s, C , ) , 8 28.5 (s, C ), 8 35.0 (s, 7  C ), 4  8 35.6  8  3  8  (s, C ) , 8 61.6  (d, C , , V  7  = 6.3  P C  Hz),  8 61.8  (s, C ) , 8 70.1 5  (s, C ) , 8 107.6 6  (d, C ,  2  2  J  P C  =  10.6 Hz). Isomer exo-6: *H N M R ( C D , 298 K, 500 MHz): 8 0.12 (s, overlapping, terminal N7  8  SiC# ), 8 0.13 (s, overlapping, SiC# , 3H), 8 0.16 (s, overlapping, SiCH ), 8 0.57 (s, SiC# , 3H), 3  3  3  3  8 0.60 (s, SiC7/ , 3H), 8 1.00 to 1.50 (m, overlapping, P - C / / ) , 8 1.43 (m, overlapping, CHf, I H ) , 8 3  2  1.45 (m, C H c / ^ , I H ) , 8 1.75 (m, C H / ^ - , I H ) , 8 2.08 (m, Ctf H >, I H ) , 8 2.12 (m, CHM&; I H ) , 8 d  c  c  2.20 (m, overlapping, CH ///,', I H ) , 8 2.95 (m, C#/,H -, I H ) , 8 3.27 (m, Ctf , I H ) , 8 3.60 (m, h  h  g  C//,,,  I H ) , 8 3.87 (m, CH , I H ) , 8 4.50 (m, CH , I H ) , 8 6.80 - 7.45 (m, overlapping, NP/?, NHPA and b  PP/?).  31  a  P { H } N M R ( C D , 298 K, 202.5 MHz): 8 32.3 (s). 1  7  13  8  C { ' H } N M R ( C D , 298 K, 125.8 7  8  MHz) selected peaks: 8 26.5 (s, C , ) , 8 26.9 (s, C ) , 8 36.2 (s, C ) , 8 36.9 (s, C ) , 8 62.9 (d, C i , 8  V  P C  3  = 5.9 Hz), 8 63.7 (s, C ), 8 69.9 (s, C 5  6  ),  7  8 108.1 (d, C , V 2  Reaction of [NPN]Li (C H 0) with RuCI (PPh ) 2  4  8  2  2  3  P C  4  =11.6 Hz).  3  A colourless solution o f [NPN]Li -(C H 0) (0.412 g, 0.695 mol) in 25 mL o f toluene was 2  4  8  2  added to a brown slurry of RuCl (PPh ) (0.665 g, 0.695 mol) in 25 m L of toluene. After several 2  3  3  hours the solution gradually turns orange with the formation o f a light coloured precipitate. The solid was removed by filtration and the solvent was removed under reduced pressure giving an orange coloured solid.  ' H and P { H } N M R spectroscopy of the crude solid revealed that 3 I  1  numerous products had been produced.  96  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and PzNJ Ligand Sets  [NPNH]RU(1-3-TI :5,6-TI -C8H I)(CO) (7) 3  2  1  In a J-Young valve N M R tube (with a pre-determined volume o f 3.17 mL) was added complex 3 (0.049 g, 0.078 mmol), which was dissolved by adding 1.28 mL o f toluene-^. The contents o f the N M R tube were degassed by performing three freeze-pump-thaw cycles and the N M R tube was then back-filled with CO gas (1.89 mL, 0.078 mmol). Within a few seconds o f rotating the N M R tube the colour o f the solution changed from red to yellow. The N M R data indicated the presence of a single product characterized as [NPNH]Ru(l-3-r| :5,6-ri -C8Hii)(CO) 3  2  (7). ' H N M R ( C D , 298 K, 500 MHz): 8 -0.15, 0.02, 0.47 and 0.56 (s, SiC77 , 12H total), 8 0.98 7  8  3  (m, P C / / , 1H), 8 1.41 (m, overlapping, PCH , 1H), 8 1.45 (m, overlapping, CB.Ji ; 1H), 8 1.61 2  2  d  (m, CH Rd-, 1H), 8 1.80 (m, CH H ; 1H), 8 1.89 and 2.14 (m, PC/7 , 2H), 8 2.29 (m, C/7 H -, 1H), d  C  2  C  C  C  8 2.40 (s, N-/7, 1H), 8 2.62 (m, overlapping, CH , 1H), 8 2.72 (m, overlapping, CU H ; 1H), 8 e  2.76 (m, overlapping, CH n , h  v  h  1H), 8 3.14 (m, CH , 1H), 8 3.23 (m, CH , 1H), 8 3.41 (m, CH , g  a  f  1H), 8 5.26 (m, CH , 1H), 8 6.21 - 7.36 (m, overlapping, NP/?, NHP/z and ?Ph). b  (C D , 298 K, 202.5 MHz): 8 46.0 (s). 7  h  8  13  31  P{'H} NMR  C { ' H } N M R (C D , 298 K, 125.8 MHz) selected peaks: 7  8  8 21.3 (s, Q ) , 8 27.3 (s, C ), 8 32.5 (s, C ), 8 43.9 (s, C ), 8 53.9 (s, C ), 8 69.9 (d, G , J 2  4  3  Hz), 8 101.0 (s, C ), 8 105.1 (d, C , V 6  2  P C  7  5  P C  = 6.72  = 7.63 Hz).  {[PhN(H)SiMe CH2][(C8H i)C(0)N(Ph)SiMe2CH ][Ph]}PRu(CO)4(8) 2  2  1  A solution o f 3 (0.380 g, 0.586 mmol) in 20 m L toluene was added to a glass reaction vessel equipped with a Teflon valve and a ground glass joint. The vessel was evacuated by three freeze-pump-thaw cycles and then one atmosphere o f CO gas was added at room temperature. The colour o f the solution immediately changed in colour from red to yellow-orange. The vessel was sealed and the contents were stirred for 12 hours. The solvent and excess CO gas were removed under reduced pressure until an orange solid remained.  This solid was rinsed with  hexanes, collected and dried under vacuum to give complex 8 (0.383 g, 83 % ) . *H N M R (CeD , 6  298 K, 500 MHz): 8 0.0 - 0.6 (s, br, overlapping, SiC# ), 8 1.4 - 2.0 (m, overlapping, PCH ), 8 3  2  2.2 - 4.0 (m, br overlapping, cyclooctadienyl CH ), 8 5.2 - 5.8 (m, br, cyclooctadienyl CH =CH ), 2  97  2  2  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  8 6.4 - 8.6 (m, br, overlapping, aromatic-//).  31  P { ' H } N M R ( C D , 298 K, 202.5 MHz): 8 20.7 (s, 6  6  br).  X-ray Crystallographic Analyses of Complexes 1, 2, endo-3, 4, 5, 7 and 8  Selected crystallographic data and structure refinement data are provided in Appendix 1.  2.10  References  (1)  Noyori, R.; Ohkuma, T. Angew. Chem. Int. Ed. 2001, 40,40.  (2)  Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics 2001, 20, 1047.  (3)  Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics 2000,19, 2655.  (4)  Ohkuma, T.; Ishii, D.; Takeno, H.; Noyori, R. J. Am. Chem. Soc. 2000,122, 6510.  (5)  Mikami, K.; Korenaga, T.; Terada, M.; Ohkuma, T.; Pham, T.; Noyori, R. Angew. Chem.  Int. Ed. 1999, 38, 495.  (6)  Ohkuma, T.; Koizumi, M.; Doucet, H.; Pham, T.; Kozawa, M.; Kunihiko, M.; Katayama,  E.; Yokozawa, T.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1998,120, 13529.  (7)  Doucet, H.; Ohkuma, T.; Murata, K.; Yokozawa, T.; Kozawa, M.; Katayama, E.; England,  A. F.; Ikariya, T.; Noyori, R. Angew. Chem. Int. Ed. 1998, 37, 1703.  (8)  Ohkuma, T.; Doucet, H.; Pham, T.; Mikami, K.; Korenaga, T.; Terada, M.; Noyori, R. J.  Am. Chem. Soc. 1998,120, 1086.  (9)  Ohkuma, T ; Ooka, H.; Hashiguchi, S.; Ikariya, T ; Noyori, R. J. Am. Chem. Soc. 1995,  //7,2675.  98  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  (10)  Ohkuma, T.; Koizumi, M.; Muniz, K.; Hilt, G.; Kabuto, C ; Noyori, R. J. Am. Chem. Soc.  2002,124, 6508.  (11)  Ohkuma, T.; Ooka, H.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1995,117,10417.  (12)  Xiao, D.; Zhang, X. Angew. Chem. Int. Ed. 2001, 40, 3425.  (13)  Kobayashi, S.; Haruro, I. Chem. Rev. 1999, 99, 1069.  (14)  Kainz, S.; Brinkman, A.; Leitner, W.; Pfaltz, A. J. Am. Chem. Soc. 1999,121, 6421.  (15)  Tararov, V . I.; Kadyrov, R.; Riermeier, T. H.; Holz, J.; Borner, A. Tetrahedron:  Asymmetry 1999, 10, 4009.  (16)  Mao, J.; Baker, D. C. Org. Lett. 1999,1, 841.  (17)  James, B. R. Catalysis Today 1997, 3 7, 209.  (18)  Sablong, R.; Osbom, J. A. Tetrahedron Letters 1996, 37, 4937.  (19)  Sablong, R.; Osbom, J. A. Tetrahedron: Asymmetry 1996, 7, 3059.  (20)  Sablong, R.; Osbom, J. A.; Faller, J. W. J. Organomet. Chem. 1997, 527, 65.  (21)  Uematsu, N.; Fujii, A.; Hashiguchi, S.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1996,  118,4916.  (22)  Fogg, D. E.; James, B. R. Inorganica Chimica Acta 1994, 222, 85.  (23)  Willoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1994,116, 11703.  (24)  Willoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116, 8952.  99  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and /P Nz/ Ligand Sets 2  (25)  Willoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1992,114, 7562.  (26)  Lensink, C ; de Vries, J. G. Tetrahedron: Asymmetry 1992, 3, 235.  (27)  Buriak, J. M.; Osborn, J. A. Organometallics  (28)  Burk, M. J. J. Am. Chem. Soc. 1992,114, 6266.  (29)  Noyori, R. Angew. Chem. Int. Ed. 2002, 41, 2008.  (30)  Knowles, W. S. Angew. Chem. Int. Ed. 2002, 41, 1998.  (31)  Sharpless, K. B. Angew. Chem. Int. Ed. 2002, 41, 2024.  (32)  Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001, 66, 7931.  (33)  Abdur-Rashid, K.; Faatz, M . ; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2001, 123,  1996,15, 3161.  1411.  (34)  Hartmann, R.; Chen, P. Angew. Chem. Int. Ed. 2001, 40, 3581.  (35)  Yamakawa, M.; H., I.; Noyori, R. J. Am. Chem. Soc. 2000,122, 1466.  (36)  Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics  (37)  Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. Organometallics  (38)  Fryzuk, M. D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S. A.; Koetzle, T. K. J.  Am. Chem. Soc.  (39)  1991,121, 155.  1986, 5, 2469.  2001,123, 3960.  Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Chem. Commun. 1996, 2783.  100  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2NJ Ligand Sets  (40)  Giesbrecht, G. R. Amidophosphine Complexes of Electron Poor Metals; University of  British Columbia: Vancouver, 1998.  (41)  Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Organometallics 1998,17, 846.  (42)  Corkin, J. R. Hafnium Complexes Stabilized by a Macrocyclic Ligand; University o f  British Columbia: Vancouver, 2000.  (43)  Leznoff, D. B. Paramagnetic Organometallic Complexes; University of British Columbia:  Vancouver, 1997.  (44)  Johnson, S. A. Ligand Design and The Synthesis of Reactive Organometallic Complexes of  Tantalum for Dinitrogen Activation; University of British Columbia: Vancouver, 2000.  (45)  Kozak, C. M. Activation of Small Molecules by Low Valent Niobium Complexes Stabilized  by a Bis (Amidophosphine) Macrocycle; University of British Columbia: Vancouver, 2002.  (46)  James, B. R.; Markham, L. D.; Wang, D. K. W. Chem. Commun. 1974,439.  (47)  McKinney, R. J.; Knobler, C. B.; Huie, B. T.; Kaesz, H. D. J. Am. Chem. Soc. 1977, 99,  2988.  (48)  Perego, G.; Del Piero, G.; Cesari, M.; Clerici, M. G.; Perrotti, E. J. Organomet. Chem.  1973,54, C51.  (49)  Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry: A Comprehensive Text; 4th  ed.; John Wiley and Sons Inc.: New York, 1980, pp 804-805.  (50)  Cole-Hamilton, D. J.; Wilkinson, G. J. Chem. Soc, Dalton Trans. 1977, 797.  (51)  Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics 1991,10,467.  101  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  (52)  Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97,4221.  (53)  La Placa, S. J.; Ibers, J. A. Inorg. Chem. 1965, 4, 778.  (54)  Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M . Advanced Inorganic  Chemistry: A Comprehensive Text; 6th Ed.; John Wiley and Sons Inc.: Toronto, 1999, pp 29-30.  (55)  Pez, G. P.; Grey, R. A.; Corsi, J. J.Am.  Chem. Soc. 1981,103, 7528.  (56)  Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry: A Comprehensive Text; 4th  Ed.; John Wiley and Sons Inc.: New York, 1980, pp 1199-1202.  (57)  Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc. 1987,109,2803.  (58)  Joesten, M. D.; Schaad, L. J. Hydrogen Bonding; Marcel Dekker, Inc.: New York, 1974.  (59)  Ashworth, T. V.; Nolte, M. J.; Reimann, R. H.; Singleton, E. Chem. Commun. 1977, 937.  (60)  Ashworth, T. V . ; Chalmers, A. A.; Liles, D. C ; Meintjies, E.; Singleton, E.  Organometallics 1987, 6, 1543.  (61)  Wiles, J. A.; Lee, C. E.; McDonald, R.; Bergens, S. H. Organometallics 1996,15, 3782.  (62)  Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C. Metal and Metalloid Amides;  John Wiley and Sons Canada Limited: Toronto, 1980.  (63)  Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1.  (64)  Hartwig, J. F.; Andersen, R. A.; Bergman, R. H. Organometallics 1991,10, 1875.  (65)  Boncella, J. M.; Eve, T. M.; RickMan, B.; Abboud, K. A. Polyhedron 1998,17, 725.  102  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P2N2] Ligand Sets  (66)  Jayaprakash, K. N.; Gunnoe, T. B.; Boyle, P. D. Inorg. Chem. 2001, 40, 6481.  (67)  Rachidi, I. E. I.; Eisentstein, O.; Jean, Y. New. J. Chem. 1990,14, 671.  (68)  Riehl, J. F.; Jean, Y.; Eisenstein, O.; Pelissier, M. Organometallics 1992,11, 729.  (69)  Johnson, T. J.; Folting, K.; Streib, W. E.; Martin, J. D.; Huffman, J. C ; Jackson, S. A.;  Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995, 34, 488.  (70)  Bickford, C. C ; Johnson, T. J.; Davidson, E. R.; Caulton, K. G. Inorg. Chem. 1994, 33,  1080.  (71)  Fryzuk, M. D.; MacNeil, P. A. J. Am. Chem. Soc. 1986,108, 6414.  (72)  Poulton, J. T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein, O.; Caulton, K. G.  Inorg. Chem. 1994, 33, 1476.  (73)  Caulton, K. G. New. J. Chem. 1994,18, 25.  (74)  Dewey, M. A.; Stark, G. A.; Gladysz, J. A. Organometallics 1996,15,4798.  (75)  Perrin, C. L.; Dwyer, T. J. Chem. Rev. 1990, 90, 935.  (76)  Jeener, J.; Meier, B. H.; Bachmann, P.; Ernst, R. R. J. Chem. Phys. 1979, 71,4546.  (77)  VanderLende, D. D.; Abboud, K. A.; Boncella, J. M. Inorg. Chem. 1995, 34, 5319.  (78)  Glassman, T. E.; Vale, M. G.; Schrock, R. R. Organometallics 1991,10, 4046.  (79)  Bennett, M. A.; Bruce, M. I. Comprehensive Organometallic Chemistry; 1 ed.; Wilkinson,  S., G., Stone, F. G. A. and Abel, E. W., Ed.; Permagon Press: Toronto, 1982; Vol. 4, pp 699.  103  References begin on page 98  Chapter 2: Synthesis, Solution Dynamics and Reactivity of Ruthenium(ll) Complexes Incorporating the [NPN] and [P Nz] Ligand Sets 2  (80)  Cobbledick, R. E.; Einstein, F. W. B.; Pomeroy, R. K.; Spetch, E. R. J. Organomet. Chem.  1980,195, 77.  (81)  Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M . Advanced Inorganic  Chemistry: A Comprehensive Text; 6th ed.; John Wiley and Sons Inc.: Toronto, 1999, pp 14-16.  (82)  Fryzuk, M. D.; MacNeil, P. A. Organometallics 1982, / , 1540.  (83)  Fryzuk, M. D.; MacNeil, P. A. J. Am. Chem. Soc. 1984,106, 6993.  (84)  Albers, M. O.; Ashworth, T. V.; Oosthuizen, E. Inorg. Synth. 1989, 26, 68.  (85)  Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. 1970,12, 237.  104  References begin on page 98  Chapter 3: Heterolytic Activation of Dihydrogen (Hi) by Amidophosphine Complexes of Ftuthenium(ll) and Catalytic  Hydrogenation  Sil  Chapter 3 Si2  Heterolytic Activation of Dihydrogen (H) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  3.1  Introduction  (i)  Catalytic Homogeneous Hydrogenation by Transition Metal Complexes  Homogeneously catalyzed hydrogenation by soluble transition metal complexes is an important process in organometallic chemistry that allows for the reduction o f unsaturated organic functionalities.  1-5  One o f the earliest documented examples of the homogeneous catalytic  activation of H dates back to 1938 when copper (I) salts were employed for the catalytic reduction 2  of substrates such as copper (II) and quinoneA  7  About a decade later it was observed that the  reaction o f olefins with carbon monoxide and dihydrogen in the presence o f a cobalt carbonyl complex afforded aldehydes (the oxo-process). Perhaps the most significant advance in this field 8  came in 1966 with the discovery of the complex RhClfPPh)^ (Wilkinson's catalyst) that allowed for the rapid and practical catalytic hydrogenation of alkenes and alkynes under mild conditions (equation 3.1).  9  Subsequent to this finding, related complexes that contained phosphine ligands  105  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  were investigated for their potential for the hydrogenation of unsaturated organic substrates including  neutral  species  [Rh(diene)(PPh ) ] ). +  3  R  \  RuHCl(PPh ) ) 3  3  as  well  as  cationic  complexes  (e.g.  2  2  /  H  (e.g.  H  RhCI(PPh ) 3  H  R \  3  /  H  H  2  H  The mechanism for the catalyzed hydrogenation depicted in equation 3.1 and related systems involves intermediate metal hydrides that are transferred to the substrate via insertion and reductive elimination steps. '  10 11  Consequently, the formation o f metal hydrides from molecular  hydrogen is a crucial step in the catalytic process. The two most common modes for the activation of Eb by transition metals are homolytic and heterolytic cleavage. ' 4 12  (ii)  13  The Activation of Dihydrogen (H ) by Transition Metal Complexes 2  The nature o f the interaction of H  2  with a metal centre is o f significance given the  importance o f the activation o f dihydrogen by transition metal complexes  in catalytic  hydrogenation reactions. A molecule of H can coordinate to a metal centre in a side-on fashion 2  (r| -H ) in which the resulting complex contains an intact dihydrogen ligand. Since the discovery 2  2  of the first transition metal dihydrogen complex, W(H )(CO) (P'Pr ) , in 1984, the chemistry of 14  2  3  3  2  these compounds has developed considerably and the coordination o f dihydrogen has been achieved on both electrophilic and nucleophilic metal centres. 12  associated with the H  2  15  Interestingly, the chemistry  ligand in these two types o f complexes can differ dramatically.  An  investigation into the bonding considerations between a metal centre and an H ligand allows for a 2  better understanding of the properties o f coordinated H moieties. As shown in Figure 3.1, the M2  r ) - H coordination results from a subtle balance between o donation from H to an empty J-orbital 2  2  2  of the metal and back-donation from a filled <5? -metal orbital to a 0*-antibonding orbital o f the H rc  ligand. - " 12  15  2  18  106  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  d(M) * —  C  6  (H-H)  — -  m)  a* -H) (H  Figure 3 . 1 . The bonding scheme for a transition metal T| -H2 complex involving a-donation from H2 and 7i back-bonding from the metal centre.  In complexes that contain nucleophilic metal centres a significant contribution to the bonding is a result of back-donation from the electron-rich metal centre and this leads to a lengthening o f the H-H bond while forming a strong metal-H2 interaction. 12  19  In most cases the  H2 ligand binds very tightly and the resulting complexes are stable with respect to loss o f H as 2  well as displacement o f the H2 moiety by neutral donor ligands. Complexes of this type have been referred to as containing an "elongated" dihydrogen l i g a n d . ' 19  They usually exhibit H-H  23  distances (#HH) intermediate between those of dihydrogen complexes (JHH ^ lA) and distances usually associated with dihydride complexes (dnH ^ 1.5 A ) .  19  Examples o f complexes that have  been shown to posses an elongated dihydrogen ligand include [Cp*Ru(PPh2CH2PPh2)(H2)] (<^HH = +  1.08 A )  2 4  and /ra«5-[Os(H2)Cl(PPh2CH CH2PPh )2] (</HH = 1.22 A ) . 2  +  2  25  Due to the lengthening of the H-H bond and consequent activation of the H2 molecule in these complexes, they have been said to represent an arrested intermediate state in the very important oxidative addition reaction o f H . - 12  19  22  2  Homolytic cleavage o f H2 by transition metal  complexes involves the incorporation o f both atoms of the H2 molecule onto the metal as hydride ligands. An example o f this reactivity is given in equation 3.2, in which the iridium (I) complex IrCl(CO)(PPri3)2  reacts  IrCl(CO)(PPli3)2(H)2.  26  with  H2  reversibly  to  give  the  iridium  (III)  dihydride  This example illustrates how the transition metal must have accessible  higher oxidation states for homolysis to occur as well as the importance of the transition metal to allow for changes in coordination number. In the iridium species the geometry changes from fourcoordinate and square-planar to six-coordinate and octahedral upon homolysis of H2. The  107  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  oxidative addition reaction displayed in the iridium complex is a critically important process in many homogeneous hydrogenation systems.  H PPh  OC  -H,  •Cl  PhoP*  <PPh  OC'.„  3  3  [3.2]  'H  Ph,P'  Cl  The interaction between H2 with electrophilic metal complexes involves predominately cdonation from H2 and the coordinated dihydrogen ligand can become a Br<|)nsted acid. - 12  27  Such  28  complexes have been shown to promote the activation of dihydrogen towards heterolytic cleavage providing a metal hydride and a proton equivalent.  For example, the electrophilic  29-40  monocationic rhenium complex [Re(CO)4(PR.3)] contains 7t-acceptor ligands that enhance 0 +  donation from H2 to the metal at the cost of back-donation, thus enhancing the tendency o f H to 2  undergo heterolysis.  41  The acidity of the coordinated H2 ligand in these types o f complexes can  vary drastically and this is illustrated by the variety of bases that can be used to effect H cleavage. 2  The complex [Re(CN'Bu)3(PCy3)2(H2)]  is weakly acidic and requires strong bases such as alkyl  +  lithium or alkoxides for deprotonation  4 2  The species [CpRu(Me2PCPi2CH2Me2)(H )] , on the +  2  other hand, requires a mild base such as triethylamine for heterolysis, whereas the highly acidic 43  complexes [Cp*Ru(CO)(H )]  +  2  diethyl ether.  and [Os(bpy)(CO)(PPh )(H )] 3  2  2+  have been shown to protonate  44  Intramolecular heterolytic splitting of H2 arises from deprotonation by a basic site on a coligand. This process has been suggested as a key step in the protonation o f alkyl or alkenyl ligands in hydrogenation reactions 45  reactions. 47  48  46  as well as in transition metal catalyzed H/D  exchange  O f particular significance to this work is the intramolecular heterolytic cleavage o f  H2 by amido donors in ruthenium(H) complexes generating ruthenium hydride and amine ligands. This process can be envisioned as occurring via o-bond metathesis as is depicted in Figure 3.2.  12  The ability of a coordinated amido ligand in late transition metal complexes to heterolytically cleave H2 was demonstrated in the Fryzuk group; complexes o f iridium,  49  rhodium  49  and  ruthenium that contain the amidodiphosphine ligand [PNP] have been shown to cleave H2 under 50  mild conditions. As was described in chapter 2 the heterolytic activation o f H2 was proposed to be  108  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  2  a key step in the catalytic reduction of imine and ketone substrates by coordinatively saturated ruthenium(II) complexes.  R  R'  V  "R  N 5  +  N  L Mn  8  R'  L  +  L  nM  R  '-  \  H ft  H  J  LM n  H  Figure 3.2. Depiction of the intramolecular heterolytic cleavage o f H2 by an amido ligand via 0 bond metathesis. Recently, the presence o f hydrogen bonds between a transition metal hydride and a hydrogen bond donor such as an O-H or N-H group (e.g. M-H H-N) has been established. '  48 51-53  This protonic-to-hydridic interaction has the strength (~5 kcal/mol) and directionality o f a conventional hydrogen bond, and consequently can influence structure, " 54  57  reactivity and  selectivity " in solution and in the solid-state. Such proton-hydride interactions are believed to 58  60  be important as intermediates in the base-promoted heterolytic splitting o f dihydrogen as well as 61  the reverse reaction, namely, the protonation o f metal hydrides to give dihydrogen complexes. " 62  3.2  Hydrogenation of [P N ]Ru(ri :r| -C8H 2) (1)  (i)  Reaction of [ P 2 N ] R U ( T I : T | - C 8 H I 2 ) (1) with hydrogen gas  2  2  2  64  2  2  1  2  2  Under an atmosphere o f hydrogen gas a solution o f [P2N2]Ru(r| :r| -C8Hi2) (1) gradually 2  2  lightens from yellow to colourless. The reaction proceeds slowly and is complete within 3 days to give the ruthenium(n) dihydrogen complex [P NNH]Ru(H2)H (10). Monitoring the reaction 2  mixture by H and P { ' H } N M R spectroscopy revealed that an intermediate hydrogenation ]  31  product, 9, is initially formed and is converted to 10 over a period of 3 days. This is portrayed in Scheme 3.1. After four hours at room temperature the P { ' H } N M R spectrum shows that the 31  solution contains a mixture o f three species. The starting material 1 is the major species present  109  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  followed by complex 9; there is only a small amount o f the dihydrogen complex 10 present after 4 hours. After 4 8 hours complex 1 has been consumed and the two ruthenium hydride species 9 and 10 are present in solution in an approximately 1:4 ratio, respectively. Attempts at isolating these two complexes have failed, and consequently, their characterization is based on solution N M R spectroscopy.  Scheme 3.1  (ii)  Spectroscopic identification of the intermediate hydride complex 9  Although the transient hydride complex 9 could not be isolated, various structural characteristics could be gleaned from the spectroscopic data. Prominent in the ' H NMR spectrum of the hydrogenation intermediate is a hydride resonance at 8 - 9 . 6 0 ( J P H = 2 5 . 4 Hz). This signal 2  integrates to one proton per metal centre and is a triplet due to coupling to two equivalent phosphorus-31 nuclei. This is in accordance with the P { H } N M R spectrum, which contains a 3 l  l  singlet at 8 3 0 . 0 . Four silyl methyl proton resonances are observed for the macrocycle, however, the ligand methylene protons could not be assigned as they are obscured by other peaks.  The presence o f a single hydride ligand in 9 suggests that heterolytic cleavage o f H by a 2  ruthenium-amido unit in complex 1 has occurred, thus generating a "[P2NNH]RuH" fragment. The assignment o f the N - / / resonance arising from the resulting amine ligand could not be made due to overlapping peaks in the ' H N M R spectrum.  A n amino proton resonance has been  identified for complex 10 verifying that heterolysis o f H  no  2  does take place.  The heterolytic  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  cleavage o f dihydrogen by complex 1 requires that dissociation o f a bound olefin moiety o f the bidentate cyclooctadiene ligand occurs, thus, creating an open site at the metal centre so that a molecule of H2 can coordinate. This may be one reason why the reaction of 1 with hydrogen gas proceeds slowly.  A possible structure for the intermediate 9 that is consistent with the spectroscopic data is the monomeric ruthenium hydride depicted in Figure 3.3. This species is believed to contain an r] -bound cyclooctadiene ligand and represents the direct product of H2 heterolysis by complex 1. 2  The pseudo-octahedral coordination geometry in 9 contains a mirror plane bisecting the two phosphine ligands. This accounts for the equivalence o f the two phosphorus-31 nuclei as well as the four silyl methyl proton environments that are observed. It is also possible that 9 may exist as a hydride-bridged dimer of formula {[P2NNH]RuH}2. I f this complex was present one would expect to observe free cyclooctadiene, cyclooctene or cyclooctane in solution, however, none of these species were evident in the H N M R spectrum during the formation of 9. !  The structural  characterization of hydrido-olefin ruthenium(II) complexes similar to 9 have been described in the literature. * 65  68  In an attempt to provide further support for the proposed identification of the  intermediate 9, the dihydrogen-hydride complex 10 was treated with an excess of cyclooctadiene. As was anticipated, displacement of an equivalent of H2 in 10 by cyclooctadiene resulted in its conversion to 9 as monitored by ' H and P { ' H } N M R spectroscopy. 31  When the same reaction was performed with an excess of cyclooctene the formation of a new high-field resonance at 5 -10.8 was noted in the ' H N M R spectrum.  This most likely  corresponds to the hydride ligand in a complex similar to 9 only this bearing a coordinated cyclooctene ligand.  This same species was noted (albeit in very small quantities) during the  conversion of 9 to 10 during later stages when the concentration of hydrogen gas in the N M R tube was diminished.  ill  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  Me Si 2  o  v  Me S( 2  NC  Me Si 2  Me Stt 2  9  Figure 3.3. Proposed structure of the intermediate complex 9.  Characterization of complex 10 as a fluxional dihydrogen-hydride complex  (iii)  by variable-temperature NMR spectroscopy and deuterium labelling studies  In the ' H N M R spectrum o f complex 10 a triplet is observed at 8 -11.44 ( J 2  P H  = 13.8 Hz)  that integrates to three protons per metal centre. This feature may be the result o f a dihydrogenhydride complex, [P NNH]Ru(H )H, however, another candidate that satisfies this condition is a 2  2  ruthenium (IV) trihydride species, [P NNH]Ru(H) . 2  3  We favour the formulation o f 10 as the  Ru(H )(H) tautomer since this arrangement is also evident in the structurally related dihydrogen2  hydride complexes A and B that are shown in Figure 3.4.  69  The *H N M R spectra for complexes A  and B contain a high-field triplet near 8 -11.0 ( JPH = ca. 14 Hz) for the three ruthenium-bound 2  hydrogens, and singlets in their P { ' H } N M R spectra between 8 45 - 8 50. These spectral data are 31  identical to those o f 10. Dihydrogen-hydride complexes o f several other late transition metals are also k n o w n . " 70  77  In order to further classify 10 as a dihydrogen-hydride complex the measurement  of the relaxation rate o f the hydride ligands and an analysis o f the effect o f deuterium substitution were undertaken.  112  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  PCy  PCy  3  A  3  B  Figure 3.4. Dihydrogen-hydride complexes o f nithenium(II) that are related to complex 10.  69  The measurement o f the minimum o f the longitudinal relaxation time (T'i(min)) for metalbound hydrogen atoms is one method that has been employed to discriminate between classical hydride  (M-H)  complexes. " 78  80  versus  non-classical  dihydrogen  (M-r| -H2) 2  ligands  in  transition  metal  The basis for this approach is the assumption that dipole-dipole interactions are  almost solely responsible for the relaxation of the N M R signals, and since a dihydrogen ligand has a short H-H distance (compared to a dihydride) it will therefore give rise to a distinctively short T'i(min) relaxation time. In general, the criterion for distinguishing between classical and nonclassical hydrides is based on the distinction o f whether ri(min) is shorter than 80 ms (M(H2)) or greater than 150 ms (M(H)2) at 250 MHz. Since 7i(min) values are proportional to the magnetic field strength these limits correspond to 160 ms and 300 ms, respectively at 500 MHz.  Using an inversion-recovery pulse sequence, the relaxation time (T\) for the metal-bound hydrogen atoms in 10 was determined at a variety of temperatures ranging from 200 to 300 K at 500 MHz. The minimum value o f 62 ms observed at 240 K is qualitatively consistent with the presence o f a dihydrogen ligand in 10, supporting its formulation as a dihydrogen-hydride species.  A quantitative method for determining the H-H distance determined ^ ( m i n ) value has been developed. '  80 81  (C/HH)  from the experimentally  The underlying principle states that if the  relaxation of proton A from dipole interaction with nucleus B can be determined, then the A-B distance can be accurately calculated when both A and B are relatively immobile in the molecule.  82  Dihydrogen complexes, however, have the complication that the H2 ligand can  undergo fast internal rotation which can effect dipolar relaxation. In order to address this problem  113  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  a correction factor of 0.794 is applied to the calculated H - H distance for a rapidly rotating H ligand.  81  2  The equations that are used to calculate dun for slow and fast H2 rotational regimes are:  d H (slow rotation) = 5.81(Zi H)/l>) H  1/6  (H  JHH (fast rotation) = 4.61(ri(HH)/y)  where v is the spectrometer frequency in megahertz, and  ^[(HH)  1/6  [3.3]  A  [3.4]  A  is the minimum T\ value for the H2  ligand and is given in units of seconds.  An accurate determination of the H - H bond length requires that the mutual relaxation rate of the hydrogen atoms in the coordinated H  2  ligand  (RHH,  where  RHH =  I/T'KHH)) be known  explicitly. The rate of dipolar relaxation for a dihydrogen ligand (RHI) is actually the sum o f RHH and the relaxation resulting from other dipoles in the molecule (i? ther): ' 75  76  0  Rm  -  [3.5]  RilW + Mother  Additionally, in the case of a fluxional polyhydride complex the observed relaxation rate is the population weighted average o f all of the hydride sites. Specifically, for a dihydrogen-hydride species the observed relaxation rate i s : 75  76  tfobs =  (2R  m  + Rn)l3  [3.6]  where RH is the relaxation rate o f the hydride ligand. In order to extract the desired RHH value, it is necessary to measure the relaxation rate for the hydride ligand in a related monohydride complex. This relaxation rate will be denoted as /Jobs'. The relaxation value  Robs'  can be used to represent  relaxation contributions in the molecule other than those within the H ligand (i.e. i? b ' ~ Rn + 2  Mother). ' 75  76  0  S  In doing so, equations 3.5 and 3.6 can be combined to yield the following formula for  the relaxation rate of the coordinated H ligand: 2  RHH  =  3(i? bs - i?obs)/2 0  114  [3.7]  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  In order to obtain an accurate determination for the relaxation rate of the dihydrogen ligand in complex 10 a related monohydride complex of the type [P2NNH]RuH(L) (where L is a neutral donor ligand) was required. The monohydride complex [P2NNH]RuH(PPh3) (13), that forms from the addition o f hydrogen gas to [P2NNH]Ru(C6H4PPh2) (2) was a suitable candidate. The details concerning the synthesis and characterization of 13 are found in section 3.3 o f this chapter. The ri(min) value for the Ru-H hydride in 13 was found to be 370 ms at 260 K, corresponding to a relaxation rate of 2.70 s" . The relaxation o f this hydride, however, is also influenced by the ortho1  protons of the c/s-coordinated triphenylphosphine ligand, which come into close contact with the hydride ligand (~ 2 A as determined by X-ray analysis). By a method previously reported, the 80  relaxation contribution due to the ortho-protons is calculated to be approximately 1.03 s" . 1  Consequently, a relaxation rate of 1.67 s"  1  (Robs' —  2.70 s" - 1.03 s" ) can be used as an estimation 1  1  o f the contribution to relaxation of all factors but H-H dipole-dipole relaxation within the dihydrogen ligand in complex 10. 16.1 s"  1  (Robs  =  The observed rate o f dipolar relaxation in complex 10 is  1/0.062 s). Substituting these values into equation 3.7 gives a relaxation rate o f  21.7 s" for the hydrogen atoms of the coordinated H2 ligand. This leads to a calculated H-H 1  distance o f approximately 1.2 A assuming slow rotation of the H2 ligand or 1.0 A assuming fast rotation.  Another characterization tool that has been utilized to provide evidence for the existence of a coordinated dihydrogen ligand in a transition metal complex is the measurement o f the coupling between hydrogen and deuterium in the H D isotopomer ( V H D ) ' ' " ' 1 2  1 9  2 1  2 5  8 3  The HD resonance in  the ' H N M R spectrum becomes a 1:1:1 triplet and is considered to be direct proof of an intact H2 ligand since classical hydrides do not show appreciable spin-spin coupling because no residual HD bond is present. The 'JHD measured in HD gas is 43.2 Hz, but in transition metal dihydrogen complexes this value is reduced and has been found to exist in the range of 5 to 35 H z .  12  Qualitatively^ the smaller couplings that are observed for dihydrogen complexes can be rationalized by a lengthening of the H-D bond upon coordination to a metal centre. It has been proposed that when such couplings fall between 5 and 25 Hz an elongated or stretched dihydrogen ligand is present. '  13 24  The observation o f the inverse relation between H-H distance (dan) and HD  coupling ('/HD) has been quantified and the equation that describes this relationship is given in equation 3.8.  44  115  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  = 1-44 - 0.0168('JH ) A  d  [3.8]  D  HH  For fluxional dihydrogen-polyhydride complexes the use o f deuterium labelling is often critical for the establishment o f an H2 ligand and this is achieved by the observation o f an exchange-averaged spin-spin coupling ( VHD) and/or a perturbation in the chemical shift for the 8  hydride isotopomers. ' ' ' ' " 12  74  75  77  84  88  For a dihydrogen-hydride complex L„M(H)(H2) with rapidly  exchanging hydrogen atoms an average JHD is normally observed upon partial substitution by deuterium. In order to get an estimate o f the H-H distance o f the r) -H2 ligand within such systems 2  the JHD value must be extracted from the experimentally measured "VHD1  T h average H D e  coupling observed in a species with n hydrogen atoms at the metal is the following for an HD„_i isotopomer: '  12 82  a v  7  = « X x,-[^-{ JHD/(n-l)}] 1  H D  [3.9]  1  1  where i * j. Here, %, is the likelihood that the proton occupies site i, and species, equation 3.9 simplifies to './HD  =  = 1. For an HD2  3( JHD). A potential source o f error is neglecting the 3v  two-bond H-D couplings ( JHD) between the hydrogen atoms in the hydride and dihydrogen sites. 2  Some classical hydrides, for example, have been shown to exhibit VHD couplings as large as 3.8 H Z  . 12,82 Exposure o f a solution o f 10 to an atmosphere o f D2 gas results in the incorporation o f  deuterium into the hydride and dihydrogen environments as evidenced by the appearance o f new resonances in the hydride region o f the ' H N M R spectrum. Representative spectra o f the new hydride resonances o f the partially deuterated isotopomers acquired with P decoupling at 300 K 31  are shown in Figure 3.5. After one hour, resonances due to the RU-H3 (10) and RU-H2D (10-Ji) isotopomers are evident with the mono-deuterated species slightly downfield shifted by ca. 20 ppb. Although the two resonances are slightly overlapping the H-D coupling o f 4.5 ± 0.5 Hz in 10-c/i is partially resolved.  Upon prolonged exposure to D2 gas the solution consists almost  exclusively o f the RU-HD2 (lO-t^) isotopomer. The chemical shift o f IO-J2 is downfield shifted with respect to 10 by ca. 30 ppb. The broadness of this peak does not allow for the expected quintet to be completely resolved, nevertheless, an H-D coupling o f 5.0 ± 0.5 Hz could be measured.  This coupling constant represents the exchange-averaged value ("VHD) and gives a  116  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  calculated *JHD of 1 5 . 0 ± 1.5 Hz for the T | - H D ligand.  The magnitude of this coupling is  2  consistent with the presence o f an elongated dihydrogen ligand in complex 10 with an estimated H-H distance o f  1.2 A (from equation 3.8). This value coincides well with the H-H distance  determined from the N M R relaxation data assuming that the coordinated dihydrogen ligand in complex 10 is modelled as slowly rotating. An elongated H moiety may be expected to have a 2  higher rotational barrier due to an increase in metal back-bonding.  -i  1  1  -11.36  1  1  1  11  -11.40  1  |  -11.44 (ppm)  1  1  1  1  -11.48  1  24  1  1  1  r-  -11.52  Figure 3.5. High-field region of the ' H f ? } N M R spectrum o f the isotopomers 10 (H ), 10-Ji 3 1  3  (H D) and l0-d (HD ) ( C D , 500 MHz, 300 K). The upper spectrum was recorded 1 hour after 2  2  2  7  8  the addition o f D gas and the lower spectrum was recorded after 1 6 hours. 2  The estimation of the H-H bond length in complex 10 as determined by the T\ method as well as ' J H D N M R data indicates the presence o f a stretched H ligand in 10. The H-H distance o f 2  1.2 A is similar to the H-H separations that have been determined in structurally related dihydrogen-hydride complexes o f ruthenium(II) (Table 3.1).  A trend that is apparent from  inspection o f the data in Table 3.1 is that the H-H distance increases in going from electron-poor to  117  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  electron-rich complexes. For instance, the species [Ru(PCy )2(CO)2(H )H] (entry 1) contains two 2  3  7C-accepting CO ligands which decreases the delocalization o f electron density from the metal (d ) K  to the H antibonding orbital (a*), thereby limiting the degree o f H-H bond lengthening. At the 2  other extreme, the complexes in entries 4 and 5 contain 7C-donating amide and alkoxide ligands respectively, and the resulting H moieties are elongated. 2  This trend has also been noted for  dihydrogen complexes o f other transition metals particularly when the 7i-accepting or 7C-donating ligands are located trans to the H ligand.  89  2  Table 3.1. Comparison o f H-H distances (C/ H) in some related ruthenium(II) dihydrogen-hydride H  complexes and the method in which they were determined.  Entry 1 2 3 4 5 6  (iv)  Complex tf H [Ru(PCy ) (CO) (H )H] [Ru(PCy ) (bipy)(H )H] [Ru(P Pr ) (py-Ph)(H )H] Ru(PCy ) (py-NH)(H )H Ru(PCy ) (py-0)(H )H [P NNH]Ru(H )H (10) H  +  3  2  2  2  +  3  2  2  i  +  3  2  3  2  3  2  2  2  2  2  2  (A)  -0.9 -1.1 1.08 -1.28 1.30 -1.2  Method JHD JHD 7/i(min) Ti(mm)/J D ^(min) ri(min)/J D  The dynamic behaviour of complex 10 in solution:  H  H  Ref. 74 74 70 69 69 this work  isotopic perturbation of  equilibria and proton-hydride exchange processes via protonic-hydridic bonding interactions  A n examination o f the temperature dependence on the chemical shift and H-D coupling constants for the various isotopomers o f 10 was attempted by performing variable-temperature 'HI^'P} N M R studies. Unfortunately, broadening o f the peaks below 300 K did not allow for a detailed analysis o f the H-D couplings. As mentioned above, the deuterated complexes 10-di and 10-d2 experience slight downfield shifts in their hydride resonances with respect to that o f 10 (A5i ca. 20 ppb and A8 ca. 30 ppb at 300 K). Similar isotopic shifts (downfield or upfield) have been 2  observed upon partial substitution o f deuterium atoms in the hydride positions o f dihydrogen 76,84,88  i polyhydride ' ' 86  a n c  90  91  74-  complexes, and in some instances these isotope shifts have  exhibited a dependence on temperature. The effect o f temperature on the chemical shift o f the H  3  and H D isotopomers of complex 10 is represented graphically in Figure 3.6. In both cases an 2  118  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  upfield shift occurs upon warming a toluene-c?8 solution of each o f the isotopomers. What is also apparent from Figure 3.6 is that an increase in the separation between the two resonances occurs at lower temperatures; at 215 K, for instance, the hydride signal for the isotopomer 10-<i is shifted 2  ca. 90 ppb downfield from 10 as opposed to 30 ppb at 300 K.  E  o. Q.  £ ui  75 o  I  -11.50 4  210  230  250  270  310  290  Temperature (K)  Figure 3.6.  Plot of chemical shift o f the hydride resonance in 10 (orange diamonds) and 10-d  2  (green circles) as a function of observation temperature (from 215 to 300 K).  It has been proposed that large isotope shifts for the hydride resonances that may arise for transition metal polyhydride complexes could be attributed to an isotopic perturbation o f equilibrium.  92-94  One situation could involve an equilibrium that is established between classical  and non-classical tautomers in solution. This behaviour has been used to rationalize the isotope shifts observed in the rhenium polyhydride complex [Re(H) (CO)(PMe Ph) ] 4  species Cp*Os(CO) (H) . 2  2  95  2  3  +87  as well as in the  In the case o f a dihydrogen-hydride structure an equilibrium can be  established in which the isotopes may fractionate between the non-equivalent M-H sites (i.e. the hydride or the dihydrogen environments). This behaviour is demonstrated in Figure 3.7 for the partially deuterated derivatives o f an M ( H ) H fragment. I f the equilibria depicted in Figure 3.7 lie 2  to the left (i.e. deuterium is enriched in the dihydrogen ligand) then a shift in the ' H N M R spectrum towards the hydride resonance would be observed for the H D and H D isotopomers. 2  2  Without a low-temperature "static" spectrum which clearly identifies the hydride and dihydrogen resonances the direction of the observed shift does not provide information as to which side the  119  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  equilibria lie.  However, measurement o f the JHD coupling constants of the H D and H D 2  2  isotopomers can also provide important details about the equilibria. A preference for deuterium to concentrate in the dihydrogen ligand would be evidenced by a JHD(H D) > JHD(HD ); this type of 2  2  behaviour is exhibited by the complex [Ru(PMe3)4(H )H] (10.9 and 10.2 Hz, respectively). +  77  2  Conversely, when JHD(HD ) > JHD(H D) there is a non-statistical distribution of deuterium 2  2  between the dihydrogen and the hydride environments, with a preference for deuterium to occupy the hydride site. The complex [Ru(PCy3) (bipy)(H )H] displays this type o f behaviour (JHD(HD ) +  2  = 6.7 Hz and J H D ( H D ) = 5.5 H z ) . 2  74  2  2  A true isotopic perturbation effect should show a dependence  on temperature due to the Boltzmann equilibrium operating on the isotopic fractionation between the non-equivalent hydride sites.  85  M-  M-  H  D  Figure 3.7. Equilibria for partially deuterated complexes o f an M(H )(H) species. 2  In complex 10 the isotopic shifts that are evident in the partially deuterated derivatives, and in particular, the temperature dependence on the observed chemical shifts are consistent with the occurrence of an isotopic perturbation o f equilibria as shown in Figure 3.7. At 300 K the JHD couplings in the H D and H D isotopomers o f 10 are the same (within experimental error), and 2  2  thus a conclusion as to the whether deuterium preferentially resides in either the hydride or the dihydrogen sites can not be made.  The isotopic perturbation o f equilibria found in complex 10 requires a dynamic process that exchanges the hydrogen atoms between the hydride and dihydrogen environments.  The  observation o f a single hydride resonance in the H N M R spectrum for these two distinct !  environments in 10 (from 180 to 300 K ) indicates that this rearrangement process is rapid on the  120  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  N M R time scale. A low temperature limiting spectrum could not be obtained and broadening of the hydride resonance was apparent upon cooling; no coupling to the P nucleus could be resolved 3 I  below 220 K.  These features can be attributed to efficient dipole-dipole relaxation at lower  temperatures leading to short T\ and T2 values.  96  This result exemplifies the limitation of using 'H  N M R spectroscopy for probing very rapid dynamic processes, and in particular, for cases in which short H-H separations lead to effective dipolar relaxation.  The facile exchange of hydride and dihydrogen environments that occurs in complex 10 has also been observed in related polyhydride species. The free energy of activation (AG*) for site exchange in the complex [(PCy3)2RuH(H2)(bipy)] has been measured to be approximately 5.5 +  kcal mol" (at 120 K ) . 1  As shown in Figure 3.8, this dynamic process is proposed to take place  7 4  via a transient trihydrogen species that forms via a cis-interaction dihydrogen ligands. 12  74  between the hydride and  The c/s-interaction arises due to an electrostatic attraction (a  dipole/induced-dipole interaction) between the negatively charged hydride and a positively charged H-atom of the coordinated H2 ligand.  The M-H bond is especially suited to this  interaction because it is highly localized onto the hydride jr-orbital and is high in energy owing to the elevated electron density on the hydride.  12  The acidity o f coordinated H2 moieties suggests  that these ligands are also well suited for this electrostatic interaction.  121  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  2  c/'s-interaction  Figure 3.8. Exchange o f the ruthenium-bound hydrogen atoms in complex 10 occurring via a transient trihydrogen complex.  Although  the  c/s-effect  allows  for  exchange  between  hydride  and  dihydrogen  environments, complete scrambling of all three H-atoms requires that rotation of the bound H  2  ligand also occurs. In complex 10 the H ligand has been described as slowly rotating with an 2  elongated H-H bond.  The observation of a single hydride resonance at all observation  temperatures (180 to 300 K ) , however, indicates that the rotational motion o f the H ligand must 2  occur fast enough on the N M R time scale to average the magnetic environments of the R u - / / nuclei.  The room-temperature ' H N M R spectrum of complex 10 is representative of a highly symmetrical complex. Two resonances are observed for the silyl methyl protons and two peaks for the methylene protons of the [P NNH] ligand backbone along with one resonance for the 2  ortho-protons, and one for the  meta-  and para-protons of the phosphine phenyl groups.  number of peaks is indicative o f a complex that has C  2v  This  symmetry. While the above dynamic  process can explain the exchange of the ruthenium-bound hydrogen atoms, on its own it does not account for the observed symmetry of complex 10 in solution. Consequently, there must be a second fluxional process that is taking place. Insights into this mechanism were gained when it was noticed that upon exposure of 10 to D gas incorporation of deuterium into the amino proton 2  122  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  site o f the macrocyclic [P NNH] ligand also occurred. This observation suggested that the amino 2  proton was interacting with the hydride ligand in some way that would allow for atom-exchange between these two distinct chemical environments.  H .  Nk...  H:  H  H N H  -Ru<l  •H'  H  H  ligand backbone has been omitted for clarity  Scheme 3.2.  As illustrated in Scheme 3.2, it is proposed that an electrostatic attraction between the hydride and the amine proton in 10 results in the formation of an intramolecular hydrogen bonding interaction. This unique type of hydrogen bond has recently been established and the presence of this interaction has been shown to influence the structure and reactivity of the resulting complexes. '  51 52  For example, proton-hydride bonding is believed to be an important interaction  leading to the protonation of metal hydrides to give dihydrogen complexes. We suggest that this occurs in complex 10 to form an (unobserved) intermediate bis-dihydrogen complex. Stable and isolable bis(H ) complexes o f the type "Ru(H )(H) (PR.3) " are known to e x i s t . 2  2  2  2  97-100  Heterolysis  of one o f the coordinated H ligands in the intermediate species by an amido donor regenerates 10. 2  A related mechanism involving a transient metal-H species has been invoked to rationalize the 2  exchange reactions o f hydrogen and deuterium in an iridium hydride dithiol complex.  47  According to this proposal, complex 10 exists as a rapidly equilibrating mixture o f two enantiomers. The presence of a proton-hydride bonding interaction in 10 may also explain the temperature dependence o f its hydride signal, which shifts from 8 -11.44 at 300 K to 8 -11.20 at 215 K (see Figure 3.6). The high-field shift that occurs upon warming a solution of 10 is in accordance with a stronger proton-hydride bonding interaction at elevated temperatures.  101  Consistent with this finding is the observation that the amino proton resonance in 10 experiences a  123  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  downfield shift towards higher temperatures (ca. 30 ppb between 240 and 300 K). Similar hydride and proton resonance shifts have been observed in other complexes that are known to contain protonic-hydridic bonding interactions. '  54 56  The electrostatic attraction between the hydride and the amino proton in 10 parallels the electrostatic c/s-interaction that exists between the hydride and the dihydrogen ligand.  The  introduction of deuterium into both the N-H and Ru-/f sites suggests that the energy of each of 3  these competing interactions is similar.  Together, these two independent dynamic processes 3 1 1  1  account for the high symmetry of complex 10 in solution as indicated by the H and  P{ H} N M R  data.  (v)  Proposed mechanisms for the formation of complex 10 In the classical mechanisms of olefin hydrogenation, insertion of an olefin into a metal-  hydrogen bond followed by reductive elimination of hydride arid alkyl ligands are regarded as the key steps in the catalytic cycle.  Recent studies concerning the reactivity of metal hydride  complexes with unsaturated substrates, however, have shown that substrate reduction may occur through alternative pathways. For example, olefins could be hydrogenated by alkyl-dihydrogen [M(R)(H )L„] ' 45  2  102  '  103  or olefin-dihydrogen complexes [ M ( o l e f i n ) ( H ) L „ ] . ' 104  In the former  105  2  case, protonation of the alkyl ligand by the coordinated H moiety occurs whereas in the latter, 2  direct transfer of both H-atoms of the dihydrogen ligand to the olefin takes place.  The conversion of complex 9 to 10 under an atmosphere of hydrogen gas is accompanied by the formation of an equivalent of cyclooctane as a reaction by-product.  Two possible  mechanisms for this transformation are given in Scheme 3.3; the intermediates shown in brackets are not observed by ' H and P { H } N M R spectroscopy. In pathway A, following heterolysis of a 31  1  molecule o f H by the starting material 1 to give 9, hydride transfer to the bound olefin and 2  coordination of an H ligand occurs. The next step involves hydrogenolysis of the alkyl bound 2  cyclooctene ligand via protonation by the coordinated H invoked to explain the catalytic activity of RuHCl(PPh ) 3  = Fe, R u )  45  2  106 3  ligand.  Similar reactivity has been  and [MH(H )(P(CH CH PPh ) ] ( M  for the hydrogenation of olefins and acetylenes.  +  2  2  2  2  3  In this system, a molecule of  cyclooctene coordinates to the unsaturated "[P NNH]RuH" species that forms after the protonation 2  124  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  step (structure B) and the process is repeated until cyclooctane (CgH]6) has been eliminated. When there is no longer any free olefin present in solution a molecule o f dihydrogen coordinates to the ruthenium centre, thus forming complex 10.  It has already been mentioned that when the  concentration of H2 in solution is low, small amounts of the intermediate species B are evident in the 'PI N M R spectrum due to competition for coordination at the metal centre between H2 and cyclooctene.  A recent study reports on the hydrogenation o f norbornadiene to norbornene in the complex  RuH(OTf)(NBD)(PPh )2 3  (where  OTf =  triflate  and NBD  =  norbornadiene).  67  Computational details on this system indicated that initial hydride transfer (from Ru-//) from the active species RuH(H2)(NBD)(PPh3)2 followed by proton transfer from the H2 ligand was the energetically favourable pathway. This route resembles the proposed pathway A in Scheme 3.3. It was also determined that the initial hydride transfer step was the rate-limiting step.  This  coincides with the experimental finding that complexes 9 and 10 are the only two species to be observed in the ' H and P { H } N M R spectra during the hydrogenation reaction. I f pathway A is 31  1  the operative mechanistic route for the conversion o f 9 into 10 one reason that hydride insertion may be a slow step is due to its involvement in potential proton-hydride bonding interactions with the amino proton.  In an alternative route (shown as pathway B in Scheme 3.3) hydrogenation of the olefin groups o f the cyclooctadiene ligand may result from the transfer of both hydrogen atoms of an rebound H2 moiety.  It has been reported that protonation of the olefin-hydride complex  Cp*Ru(NBD)H results in the hydrogenation of the NDB ligand presumably via transfer o f protons from a coordinated dihydrogen ligand to the o l e f i n . ' 73  [Cp*Ru(NBD)(H20)]  +  105  Displacement of the aquo ligand in  by H2 shows similar results providing further evidence for olefin  hydrogenation directly from a coordinated H2 ligand. Para-hydrogen induced polarization (PHIP) studies  of  the  photo-catalyzed  hydrogenation  of  the  NBD  ligand  in  the  complex  Mo(H2)(CO)(NBD) offers direct proof for the transfer of both hydrogen atoms o f an t| -H2 to the 2  olefin.  104  Intramolecular protonation o f the hydride ligand in 9 by the amino proton could result in the formation o f an unobserved dihydrogen species, [P2N2]Ru(r| -C8Hi6)(H2) (intermediate C in 2  125  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  Scheme 3.3). There is evidence for the interaction of the amino proton and ruthenium hydride nuclei in complex 10 leading to a transient bis(H2) species, and so it is a reasonable assumption that similar behaviour exists in complex 9. Intramolecular hydrogen transfer from the H2 ligand to the olefin would result in the generation of a ruthenium (IV) alkyl-hydride complex. Reductive elimination of the hydride and alkyl ligands produces a coordinatively unsaturated ruthenium(II) species to which an equivalent of H2 and cyclooctene can coordinate, and the process is repeated until cyclooctane (C8H16) has been eliminated.  At this point a distinction between the two possible mechanistic pathways for the conversion of complex 9 to 10 has not been made and future studies will be required in order to do so. In either case, this system is proposed to involve a coordinated H2 ligand in key proton transfer steps in addition to classical elementary processes such as hydride insertion and reductive elimination.  126  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  (iii) protonation by bound H2 (iv) cyclooctene coordination  [P NNH]R ^^ 2  U  [P NNH]R :  H  2  U  H  Pathway A (i) hydride transfer (ii) H coordination  C8 16 H  2  \ [P NNH]RIK  H  2  X  [P NNH]Ru  :  2  2  10  C8H16  (i) protonation of hydride by amino proton  (v) repeat steps (i) to (iii) (vi) H2 coordination  (v) repeat steps (i) to (iii) C8H16'  Pathway B  (vi) H heterolysis and H coordination 2  2  Scheme 3.3  127  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  3.3  Hydrogenation  of  [P NNH]Ru(C H PPh2) (2) 2  6  4  to  give the  mono-  hydride complex [P NNH]RuH(PPh ) (11) 2  (i)  3  Synthesis and characterization of [P NNH]RuH(PPh ) (11) 2  3  The complex [P2NNH]Ru(C6FLjPPh2) (2) reacts quantitatively with hydrogen gas to form the ruthenium(II) mono-hydride amide species [P2NNH]RuH(PPh3) (11), as shown in equation 3.10, via hydrogenolysis of the orf/zo-metalated triphenylphosphine ligand in 2. Complex 11 has been characterized in the solid-state by a single crystal X-ray diffraction study as well as in solution by ' H and P { ' H } N M R spectroscopy. The molecular structure o f 11 is shown in Figure 31  3.9 and selected bond lengths and angles are highlighted in Table 3.2.  [3.10]  11  2  128  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  Figure 3.9.  ORTEP representation (thermal ellipsoids shown at 50 % probability) of the solid-  state molecular structure o f [P2NNH]RuH(PPli3) (11) as determined by X-ray crystallography. The ruthenium hydride H(50) was located and refined isotropically, the amino proton was not located.  Table 3.2. Selected bond lengths and angles in the complex [P NNH]RuH(PPh ) (11). 2  Atom Ru(l) Ru(l) Ru(D  Atom P(l) P(2) P(3)  Distance (A) 2.3189(6) 2.3302(6) 2.2434(6)  129  Atom Ru(l) Ru(l) Ru( 1)  Atom N(l) N(2) 11(50)  3  Distance (A) 2.381(2) 2.315(2) 1.61(2)  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Atom P(l) P(l) P(2) P(l) P(l) P(2) P(2) P(3)  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom P(2) P(3) P(3) N(l) N(2) N(l) N(2) N(l)  Angle (°) 166.74(2) 94.98(2) 95.93(2) 84.85(4) 86.71(5) 85.26(5) 83.78(5) 172.86(5)  Complexes of Ruthenium(ll) and Catalytic  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom P(3) N(l) P(l) P(2) P(3) N(l) N(2)  Atom N(2) N(2) H(50) H(50) H(50) H(50) H(50)  Hydrogenation  Angle (°) 101.25(5) 85.87(7) 92.3(7) 95.9(7) 86.0(8) 86.9(8) 172.8(8)  The geometry of 11 is best described as distorted octahedral with the two phosphine donors of the macrocyclic ligand approximately trans disposed (166.74(2) °) occupying the axial positions. A mirror plane of symmetry is contained within the equatorial plane of the molecule which bears the amide, amine, hydride and triphenylphosphine ligands resulting in overall C  s  symmetry for complex 11.  The ruthenium-to-phosphorus distances for the [P2NNH] ligand are  elongated with respect to that of the triphenylphosphine ligand, a feature that can be attributed to the strong trans-influence of phosphine donors.  Although the amino hydrogen atom was not  located, the longer R u ( l ) - N ( l ) bond distance of 2.381(2) A (compared to 2.315(2) A for Ru(l)N(2)) indicates that the amine ligand is positioned cis to the hydride.  The solution N M R data is consistent with the solid-state molecular structure of complex 11.  The P { ' H } spectrum, for instance, contains a doublet at 8 35.0 corresponding to the two 3 ,  equivalent phosphines of the [P2NNH] ligand set and a triplet at 8 72.0 for the triphenylphosphine ligand ( V  P P  = ~ 40 Hz).  The resonance for the triphenylphosphine ligand in 11 is located  approximately 80 ppm units downfield from that in complex 2 in accordance with hydrogenolysis of the ort/zo-metalated aryl group.  The C symmetry of complex 11 is reflected in its H N M R spectrum which shows four l  s  resonances each for the silyl methyl and methylene protons of the macrocyclic ligand. The aryl protons of complex 11 are located between 8 6.8 and 8 7.5, and the amino proton is observed as a singlet at 8 1.7.  Unfortunately, neither the ' H N M R nor X-ray data provide any structural  information in regards to the direction in which the amino proton is oriented. Two possibilities exist: it may align towards the amide nitrogen atom (as in 2) or it may point in the direction of the  130  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  hydride ligand (as was shown for complex 10). later) help shed some light on this matter.  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  Reactivity studies with D gas (to be discussed 2  The ruthenium hydride signal in 11 occurs as an  overlapping doublet o f triplets at 8 -15.3; this pattern arises from coupling o f the hydride to the two equivalent phosphorus-31 nuclei o f the [P NNH] ligand ( J?H = 16.6 Hz) and the phosphorus2  2  31 nucleus o f the PPh ligand ( J  = 29.2 Hz). The high-field region o f the H N M R spectrum !  2  3  M  containing the hydride resonance is shown in Figure 3.10.  | 16.6 Hz |  l"l  I  I | I I  I  -15.10  I  |  I  I T T  | I —--1 T  -15.20  | 29.2 Hz  1  j j i | | [ | j | j | | | | • • |—| | I I I —  -15.30  -15.40  T |  11  I I | I I I I | I I '  -15.50  (ppm)  Figure 3.10.' Hydride region o f the 500 MHz ' H N M R spectrum o f [P NNH]RuH(PPh ) (11) 2  3  recorded in benzene-ek at 500 MHz and 298 K.  (ii)  Reaction  of  11 with  deuterium  gas  and evidence  for proton-hydride  exchange  The reaction o f 2 with H gas (1 atmosphere) is complete within a few hours at room 2  temperature; further reactivity was not observed for extended reaction periods or under four atmospheres o f H pressure. This finding is not unexpected given the stability o f 10 towards the 2  heterolytic activation o f H . In addition, the related complexes [PNHP]RuCl(C6H4PPh ) and 2  2  [PNP]Ru(C6H4PPh ) were also shown to react with only one equivalent of H per metal centre.  50  2  2  Exposure o f 11 to an atmosphere o f D gas, however, results in the incorporation o f 2  deuterium into the hydride and amino proton sites generating the species 11-fife- This result is  131  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  compatible with the existence o f a protonic-hydridic interaction in 11 that leads to the formation o f a transient r| -H2 complex (B and C respectively in Scheme 3.4). Exchange of H2 by D2 in the 2  intermediate C results in the simultaneous incorporation of deuterium into the hydride and proton environments. This mechanism is analogous to that postulated for the incorporation of deuterium into the N-H site in complex 10. dimensional E X S Y  1 0 7  '  1 0 8  Further evidence for this behaviour was provided by the two-  spectrum o f complex 11. A cross-peak between the N - / / and Ru-H sites  was observed indicating that these two nuclei are in chemical exchange. Rotation o f the H2 ligand in the intermediate species by 180° allows for this to occur.  B  Scheme 3.4  The presence o f complex A in Scheme 3.4, which contains a hydrogen bond between the amino proton and the amido nitrogen atom, is also possible.  I f it does exist it must be in  equilibrium with B as evidenced by the rapid incorporation o f deuterium in complex 11.  This  implies that the relative strengths of the N H NRu (in A ) and N H HRu (in B) interactions would be approximately equal.  A related study involves the H/D exchange reactions of the iridium  complex [Ir(H) (HNC H4S)2(PCy3)2]BF4, which contains two IrNH H N bonds. 2  5  48  It was proposed  that H/D exchange in this system proceeds via initial intramolecular proton transfer from NH to  132  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  IrH to give a dihydrogen tautomer that exchanges readily with D2 gas. Interestingly, when the reaction of the iridium complex was performed in THF no incorporation of deuterium was observed.  In this case, disruption of the proton-hydride interaction in favour of the stronger  N H O hydrogen bond effectively intercepts the exchange process.  3.4  Catalytic Hydrogenation Studies With [P NNH]Ru(H )H (10) 2  2  and  [P NNH]RuH(PPh ) (11) 2  3  As was described in the Introduction section of Chapter 2, one of the goals of this project was to prepare ruthenium(II) complexes that contain c/s-coordinated hydride and amine ligands via the hydrogenolysis of the ruthenium-amide bonds o f precursor complexes bearing the macrocyclic [P2N2] ligand. Various coordinatively saturated ruthenium(II) complexes that bear amine and hydride ligands in cis positions have been used as effective hydrogenation catalysts for imine substrates operating by the bifunctional mechanism. " 109  111  Our intention was to seek further  evidence for this unique catalytic process, which does not involve substrate coordination to the metal centre, a condition that is of fundamental importance in most catalytic systems.  The  synthesis and isolation of the amino-hydride complexes 10 and 11 allowed us to investigate their potential as precursors for the catalytic hydrogenation of imines and to possibly identify the mode of catalysis. For the purpose of this study, benzylidene aniline (PhNCHPh) was utilized as the imine substrate; this substrate has been employed in other systems and therefore a comparison of catalytic activity would be possible. A summary of the catalytic hydrogenation studies performed with complexes 10 and 11 is given in Table 3.3.  Since the bifunctional mechanism involves substrate "recognition" and outer-sphere coordination due to the polar nature of the substrates involved, it was anticipated that the presence of the electrostatic proton-hydride bonding interactions in complexes 10 and 11 may facilitate the transfer of these two atoms directly to the substrate. In performing stoichiometric reactions of 11 with benzylidene aniline, however, no formation of the hydrogenation product benzylphenyl amine was observed, even when solutions o f the reaction mixture were heated for extended periods. The lack of reactivity of the imine substrate with 11 may be a result of the stability of 11 with respect to the loss of H2. Heating solutions of 11 under static vacuum showed no formation of complex 2,  133  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  the expected product of H2 loss. The reduction of benzylidene aniline (stoichiometric or catalytic) with complex 11 under one to four atmospheres of hydrogen gas pressure was also unsuccessful.  The hydrogenation of benzylidene aniline with complex 10 was also attempted.  Since  complex 11 was unable to transfer its amino proton and hydride to the imine substrate via an outer-sphere interaction it seemed unlikely that this would take place with complex 10.  Transition  metal dihydrogen-hydride complexes have been shown to serve as catalyst precursors for alkene and alkyne hydrogenation.  12  The labile nature of the H2 ligand in these systems provides a site for  substrate coordination and the presence of a hydride ligand allows for a viable catalytic pathway. The coordinated H2 ligand in 10 has been shown to be quite labile. The addition of cyclooctadiene to solutions of 10, for instance, result in the formation of 9 and displacement of H2 by triphenylphosphine generates complex 11.  Due to the lability of the dihydrogen ligand in 10  benzylidene aniline could likewise displace this ligand, coordinate to the metal centre, and possibly undergo catalytic hydrogenation either by pathway A or B in Scheme 3.3. However, even under four atmospheres of hydrogen pressure less than 5 % conversion (as determined by integration of ' H N M R resonances) to benzylphenyl amine resulted when utilizing complex 10 as a precursor.  The catalytic hydrogenation of olefinic substrates (cyclooctadiene, cyclooctene and 1hexene) was successfully accomplished with complex 10 achieving yields greater than 95 % (see Table 3.3).  Complex 11 showed no hydrogenation reactivity towards the same olefin substrates;  the triphenylphosphine ligand in 11 is strongly coordinated to the metal centre not allowing for an open site for substrate binding even under catalytic conditions.  134  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Table 3.3. Catalytic hydrogenation studies utilizing complexes 10 and 11 as precursors.  % Conversion Entry 1 2 3 4  Substrate Benzylidene aniline Cyclooctadiene Cyclooctene 1 -hexene  10 5 95 95 99  11 0 0 0 0  Reactions were carried out at 25°C and 4 atm H pressure in toluene as the solvent for entry 1; entries 3-4 were done in neat substrate. A catalyst loading of 2 mol % was employed in each case. Conversions were determined after 48 h by 'H NMR analysis of the crude reaction mixture 2  3.5  Hydrogenation of exo- and endo-INPNHlRuO-Sir^-S^T^-CsH^) (exo-3 and endo-3)  (i)  Reaction of an equilibrium mixture of exo-3 and endo-3 with hydrogen gas  When a toluene solution containing an equilibrium mixture of the ruthenium amide complexes exo-3 and endo-3 is exposed to an atmosphere of hydrogen gas, three ruthenium hydride products and cyclooctane (CgHi6) are formed as shown in Scheme 3.5. The P { ' H } N M R 3 I  spectrum of the crude product mixture when the reaction is performed under four atmospheres of H2 pressure shows three singlets at 8 47.7, 8 40.2 and 8 32.2 (assigned to 12, 13 and 14, respectively) in the approximate ratio of 2:1:1. These ratios vary depending on the hydrogen gas pressure and the solvent employed. For example, under one atmosphere of hydrogen pressure the hydride complex at 8 47.7 still forms as the major species with a product distribution around 5:1:1. In the following sections we outline the conditions that allow for the separation, purification and characterization of each of these three hydride products.  135  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  2  Ph  x  Ph  Me Si4-N:  Me Si'  2  2  ^-P  MeoSiA— N'  '  ^SiMe PhHN  exo-3  endo-3  H  2  (1-4  atm)  C«H 8 16 n  toluene  <=5  SiMe,  SiMe, .Ph  P h ^ - y " \ H Me Si2  P  /  r  \ Ph P  H ^ J  h M  12  'e  Prf  2  Me  2  14  13  Scheme 3.5  (ii)  Isolation and characterization of [NPN(H)(r|-C H )]RuH (12) 6  5  Addition o f hydrogen gas (1 atm) to a solution o f exo-3 and endo-3 in toluene results in an immediate change in colour from red to orange. The solution was stirred at room temperature for 30 minutes and the solvent was then removed in vacuo until an oily residue remained. Subsequent addition of hexanes caused the deposition o f the orange micro-crystalline solid [NPN(H)(ri 6  C H )]RuH (12) in approximately 50% yield (Scheme 3.5). 6  5  The P { ' H } N M R spectrum o f complex 12 consists o f a singlet at 6 47.7. The 500 MHz 31  *H N M R spectrum contains four peaks for the silyl methyl protons o f the [NPN] ligand backbone  136  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic 2  Hydrogenation  between 8 - 0 . 6 and 8 0.5. The presence o f four different silyl methyl resonances is indicative of an unsymmetrical ligand environment about the metal centre. The ligand methylene protons appear as a broad multiplet centered at 8 1.2. The hydride region o f the spectrum consists o f a doublet due to coupling with the phosphine ligand at 8 - 7 . 7  ( JPH = 47 2  Hz).  A  singlet at 8  1.6  has been  assigned as the amino proton; deuterium labelling o f the N-77 site can be accomplished by the addition o f one equivalent o f base (e.g. LiN(SiMe3)2) to 12 followed by NEt 'DCl to yield the 3  species [NPN(D)(ti -C6H )]RuH (12-di). The most telling feature in the ' H N M R spectrum are the 6  5  peaks observed in the range 8 3 . 5 to 8 5 . 8 ; these have been assigned as the protons o f an r] -coordinated amino phenyl ring. Integration data, a ' H - ' H COSY analysis and proton-proton 6  coupling patterns allowed for the ortho-, meta- and para-positions to be unequivocally identified. The remaining amido-phenyl and phosphine-phenyl signals appear downfield at expected positions between 8 6.6 and 8 7.9.  The solution N M R studies for complex 12 suggest the structure depicted in Scheme 3.5 in which the phenyl ring o f the amino side-arm o f the [NPNH] ligand has coordinated to the ruthenium centre. Elemental analysis supports this formulation as does the solid-state molecular structure, which has been determined by a single crystal X-ray diffraction study. The structure o f 12 is shown in Figure 3.11 and selected bond lengths and angles can be found in Table 3.4. The complex adopts a pseudo-tetrahedral, three legged piano-stool coordination geometry with G symmetry. The ruthenium in complex 12 is a stereogenic centre bound by four different ligands. The N M R data indicate the formation o f only one diastereomer.  Deviations from an ideal  tetrahedral geometry arise due to the constraints o f the chelating [NPNH] donor set. The Ru(l)N ( l ) bond length o f  2.138(2)  A in 12 is similar to the ruthenium-amide bond distance of  2.121(3)  A reported in the related ruthenium(Ii) arene complex (r) -C6Me )Ru(Ph)(PMe3)(NHPh). 6  6  longer, however, than the measured ruthenium-amide distance in endo-3  (2.019(2)  112  It is  A ) ; this is most  likely a consequence o f the coordinative and electronic saturation at the metal centre in 12. The ruthenium-to-carbon distances for the bound amino-phenyl group indicate that it is coordinated in a r| -fashion. 6  137  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H?) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation  H28  Figure 3.11. An ORTEP representation of the solid-state molecular structure o f [NPN(H)(r| 6  C6H5)]RuH (12) as determined by X-ray crystallography with thermal ellipsoids shown at the 50 % probability level. The ruthenium hydride, H ( l ) , and amino proton, H(28), were located and refined isotropically.  Table 3.4. Selected bond lengths and bond angles in the complex [NPN(H)(ri -C6H5)]RuH (12). 6  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Atom P(l) P(l) N(l) 0  Atom Ru(l) Ru(l) Ru(l)  Atom P(l) N(l) C(19) C(20) C(21) C(22) C(23) C(24) Atom N(l) H(l) H(l)  Distance (A) 2.708(6) 2.138(2) 2.307(2) 2.214(2) 2.168(2) 2.245(2) 2.251(2) 2.322(2)  Atom Ru(l) N(2) C(19) C(19) C(20) C(21) C(22) C(23)  H(l) H(28) C(20) C(24) C(21) C(22) C(23) C(24)  Atom  Angle (°) 87.97(6) 75(1) 86(1)  Atom P(l) N(l) H(l)  Atom Ru(l) Ru(l) Ru(l)  Distance (A) 1.50(3) 0.80(3) 1.432(3) 1.403(4) 1.408(4) 1.414(4) 1.403(4) 1.420(4) Atom Cring Cring  Angle (°) 131.16 128.77 129.96  Cring represents the c e n t r o i d o f the c o o r d i n a t e d a r y l r i n g  138  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic 2  (iii)  Hydrogenation  Isolation and characterization of [NPNH ]Ru(H) (Ti -C H ) (13) b  2  2  The complex  [NPNH ]Ru(H) (C H ) 2  2  7  8  (13)  7  8  can be isolated as yellow crystals in  approximately 30% yield by the slow evaporation of the hexanes soluble rinsings from the workup o f compound 12, as described above. In the dihydride complex 13 the amine side-arms o f the [NPNH ] ligand do not coordinate to the metal either via the nitrogen lone pair or through the 2  amino phenyl groups; rather a solvent molecule o f toluene coordinates completing the inner coordination sphere of the metal centre. The activation o f aromatic solvents seems to be general. When the reaction is performed in C6D in an N M R tube a peak at 5 31.9 in the P { ' H } N M R 31  6  spectrum most likely corresponds to a complex similar to 13, only this bearing an ri -bound 6  benzene-^ molecule.  Single crystals o f 13 were obtained and used in an X-ray diffraction study to determine its solid-state molecular structure. This is depicted in Figure 3.12 and a collection o f selected bond lengths and angles are listed in Table 3.5. The solid-state structure clearly shows the coordination of a molecule o f toluene and the pendant amine arms o f the [NPNH ] ligand set. Similar to 2  complex 12, the geometry at ruthenium is pseudo-tetrahedral forming a three legged piano-stool structure. In the solid-state complex 13 exhibits C\ symmetry.  139  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  Figure 3.12. The solid-state molecular structure (ORTEP representation, 50 % thermal ellipsoids) of [NPNH2]Ru(H)2(C7rIg) (13) as determined by X-ray crystallography. The ruthenium hydrides (H(42) and H(43)) as well as the amino hydrogen atoms ( H ( l ) and H(18)) were all refined isotropically.  Table 3.5.  A collection o f selected bond lengths and bond angles in the complex  [NPNH ]Ru(H)2(C H ) (13). 2  7  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  8  Atom P(l) C(25) C(26) C(27) C(28) C(29) C(30)  Distance (A) 2.2665(7) 2.230(3) 2.248(3) 2.268(3) 2.287(3) 2.243(3) 2.226(3)  Atom Ru(l) Ru(l) N(l) N(2) H(l) H(l) H(18)  140  Atom H(42) H(43) H(l) H(18) H(42) H(43) H(43)  Distance (A) 1.61(3) 1.58(4) 0.82(3) 0.66(3) 2.099 2.104 2.251  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  Atom P(l) P(l) H(42) P(l)  Atom Ru(l) Ru(l) Ru(l) Ru(l)  Atom H(42) H(43) H(43) ^ring  Angle (°) 76(1) 82(1) 79(2) 137.47  Atom H(42) H(43) Ru(l) Ru(l)  Atom  Atom Ru(l) Ru(l) H(42) H(43)  Cring Cring H(l) H(l)  Angle (°) 131.44 129.24 111.23 112.23  " Cring represents the centroid of the coordinated toluene molecule  An intriguing structural feature evident in the molecular structure o f 13 is the approach of the amino protons towards the ruthenium hydrides. In particular, the distance between the amino proton H ( l ) with hydrides H(42) and H(43) (ca. 2.1 A in each case) can be attributed to an electrostatic attraction resulting in proton-hydride bonding interactions. This can be considered as an intramolecular three-centre hydrogen bond. The similar H H separations and Ru-H (NH(1)) angles indicate an equivalent bonding interaction of the proton H ( l ) with the two hydrides. The species [ReH (PPh3)3"indole] exhibits a similar three-center interaction via the close intermolecular 5  contacts of the indole proton with the two rhenium hydrides."  3  In this complex, however, the  proton has a stronger interaction with one o f the hydrides over the other as indicated by the shorter proton-hydride distance. The longer intramolecular distance between the amino proton H ( l 8) and the hydride H(43) (2.251 A) in complex implies a weaker bonding interaction between these nuclei.  The room temperature ' H and P { H } N M R data for complex 13 are diagnostic of an rf 31  1  bound toluene ruthenium dihydride species.  In solution, however, 13 displays C symmetry s  implying rapid rotation o f the coordinated toluene molecule and unhindered movement of the pendant amine arms o f the [NPNH2] ligand. This is evident upon inspection of the H N M R [  spectrum, which shows only two resonances for the silyl methyl protons at 8 0.0 and 8 0.3. In addition, the two ruthenium hydrides appear as a doublet (VPH = 43 Hz) at 8 -10.2. A singlet at 8 5.5 that integrates to two protons corresponds to the equivalent amino protons of the dissociated ligand arms.  The aromatic protons o f the coordinated toluene molecule are upfield shifted  between 8 4.8 and 8 5.2 and the toluene methyl protons appear as a singlet at 8 1.9.  Although arene metal dihalide complexes of the type (r| -arene)Ru(PR3)(X)2 (where 6  X=halide)  114  are known to exist, to the best of our knowledge there are no reported examples of  isolated related species in which X = H . The iridium (III) complex [(ti -C6H6)Ir(P Pr3)H2][BF ] has 6  1  4  141  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  recently been reported.  115  In this system the coordinated arene moiety is labile and can be  replaced with other arene derivatives as well as by weakly coordinating acetone-fife ligands. Such complexes have been found to be active catalyst precursors for the hydrogenation of a variety o f unsaturated substrates. The bound toluene molecule in 13, however, does not exhibit the same labile nature. For instance, solutions of 13 in toluene-fife or benzene-fife show no incorporation o f the aromatic N M R solvent; in addition, solutions o f 13 in tetrahydrofuran-fifg indicate no displacement of the coordinated toluene molecule by THF-fifo. The more strongly bound toluene molecule in 13 is also evident by an examination o f the upfield shifted aromatic proton resonances. In the iridium complex the proton resonances of the rf-CeKe ligand are only slightly shifted to 8 6.7. The arene resonances for the toluene molecule in 13, on the other hand, are found between 8 4.8 and 8 5.2. This upfield shift is a result of a decrease in the deshielding of the aromatic protons indicating that the toluene is strongly coordinated in complex 13. This feature most likely explains the lack o f activity o f complex 13 in catalytic hydrogenation studies (to be discussed later).  (iv)  Evidence for proton-hydride bonding in the solution structure of complex 13 from measurement of the minimum Ti values In an attempt to determine whether or not proton-hydride bonding interactions in 13 are  also present in solution, measurement of the Ti(min) relaxation time of the hydride and proton resonances was undertaken. During this study it was noticed that decreasing the temperature o f a toluene-fi/ solution o f 13 resulted in broadening o f both the hydride and proton resonances; below 8  193 K the doublet for the hydride signal could no longer be resolved. Broadening of the signals at lower temperatures can be attributed to efficient dipolar relaxation between closely spaced Ru-H and N-/7 nuclei. This observation suggests that at low temperatures the solution structure of 13 approaches that found in the solid-state with close proton-hydride contacts, however, a G symmetric solution structure was never recognized.  The resonance for the amino protons  experiences a downfield shift from 8 5.6 at 280 K to 8 6.5 at 200 K providing further evidence for proton-hydride bonding interactions in 13.  Perturbation o f the proton resonance is typical for  complexes containing these unconventional hydrogen bonds. ' 56  101  The chemical shift for the  hydride resonance in 13 did not display a significant dependence on temperature.  142  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  Measurement of the minimum relaxation times for the hydride and proton nuclei in complex 13 allowed for an estimation of the average RuH H N distances in solution.  The  hydrides were found to have a short Ti(min) time of 0.366 s at 260 K and 500 MHz (Table 3.6). This corresponds to a relaxation rate of 2.73 s" . When the dipolar relaxation contributions of the 1  cis hydrides, separated by 2.03 A, are accounted for (1.11 s" ), this results in a relaxation rate of 1  1.62 s" due to dipole interactions with the amino protons. This corresponds to a calculated H 1  H  distance of about 1.9 A. In the case of the amino protons the ri(min) value was determined to be 0.386 s. These protons are close to only two dipolar nuclei: the  1 4  N nucleus and the ruthenium  hydrides. In order to obtain an approximation of the relaxation effects due to the N nucleus the 1 4  Ti(mm) value of the N-/7 nuclei in the protonated [NPNH2] ligand (15) was determined. This was found to be 0.614 s at 240 K (relaxation rate = 1.63 s" ). These results suggest that the hydrides 1  are located approximately 2.0 A (relaxation rate contribution of 0.96 s" ) from the amino protons. 1  The relaxation data for the proton and hydride nuclei in complex 13 gave similar RuH HN distances (~ 2.0 and 1.9 A, respectively) indicative o f weak protonic-hydridic bonding interactions in solution.  These estimated distances also correspond well to the proton-hydride separations  evident in the solid-state molecular structure of 13. It is important to point out that since a C\ symmetric structure was never observed in solution the close proton-hydride contacts correspond to an average of all the hydride and proton environments.  Table 3.6.  Ti(min) values measured for the hydride and pendant amino proton nuclei in  complexes 12, 13,14 and 15 in toluene-dg and 500 MHz.  Complex [NPN(H)(ri -C H )]RuH (12) [NPNH ]Ru(H) (C D ) (13) [NPNH (ri -C6H )]RuH2 (14) [NPNH ] (15) 6  6  2  5  2  6  2  2  5  7  8  Ti(min) Ru-ff 0.697 0.366 0.334 -  (s) N-ff 0.386 0.344 0.614  Temperature (K) 250 260 246 240  The H N M R studies (variable temperature and relaxation data) provided evidence for weak proton-hydride bonding interactions in the solution structure of complex 13. Since this bonding scheme has been proposed to lead to hydrogen/deuterium exchange processes in complexes 10 and 11 we investigated the reactivity of complex 13 with D  143  2  gas. Exposure of  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  solutions o f 13 to an atmosphere o f deuterium gas, however, resulted in less than 10 % incorporation into both the ~N-H and Ru-H sites after 24 hours. In a related example, the hydride 1  ligand and the proton on the pyridinium  ring in the complex  2  [Ir//(T| -SC5H4N//)(r| -  SC5H4N)(PPli3)2]BF4 do not undergo any significant exchange with D even though the presence 2  of an JiH HN interaction has been ascertained.  (v)  Isolation and characterization of  116  [NPNH2(TI -C H )]RU(H)2 6  6  5  (14)  Compound 14 forms when the reaction o f 3 with hydrogen gas is performed in toluene as the solvent, however, it is most easily isolated with the use o f a non-aromatic solvent such as pentane, which eliminates the formation o f 13. A change in colour from red to orange-brown is observed with the immediate formation o f an orange insoluble solid when a slurry o f 3 in pentane is exposed to four atmospheres o f hydrogen gas. The orange solid was separated by filtration and was identified as the hydride complex 12 (50% isolated yield) by ' H and ^ P j ' H } N M R spectroscopy. Removal o f the solvent from the soluble fraction o f the reaction mixture results in the isolation o f complex 14 as a brown solid.  The room temperature N M R spectra gave much insight into the structure o f 14 (see Scheme 3.5). The phosphine resonance occurs as a singlet at 8 40.2 in the P { ' H } N M R 31  spectrum. A n unsymmetrical [NPNH ] ligand arrangement can be deduced from the four silyl 2  methyl proton resonances ranging from 8 -0.5 to 8 0.3 in the ' H N M R spectrum.  Peaks  corresponding to a coordinated arene moiety exist between 8 4.7 and 8 5.6; since the reaction was performed in a non-aromatic solvent this is due to coordination o f an amino phenyl group o f the [NPNH2]  ligand. The ortho-, meta- and para-positions were assigned based on integration as well  as ' H - ' H COSY data. The amino proton adjacent to the bound arene moiety exists as a singlet at 8 1.6 (this is the same location in which the amino proton o f 12 is located). The remaining singlet at 8 5.7 consequently corresponds to the amino proton of the dissociated ligand arm, which is in a similar location as the pendant N-H protons in 13. Two doublet o f doublets centered at 8 -9.9 and 8 -10.2 indicates the presence o f two inequivalent hydrides. Figure 3.13 illustrates this region of the ' H N M R spectrum. The magnitude o f coupling between the phosphorus nuclei and the two hydrides was measured to be 40 Hz and 43 Hz, while a coupling constant o f 6 Hz was measured between the two hydrides.  The inequivalency o f the ruthenium hydrides is supported by the  144  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  proposed structure, which has Cl symmetry. Attempts at obtaining X-ray quality crystals for a solid-state structural analysis o f compound 14 resulted in the deposition o f an orange crystalline solid that was determined by N M R data to be complex 12.  43 Hz  40 Hz  A 6 Hz^  JULJIA -9.8  -10.0  -i  1  -10.2  1  r  -10.4  (ppm)  Figure 3.13. High-field region o f the 500 MHz *H N M R spectrum highlighting the hydride resonances o f the complex [NPNH (r| -C6H )]Ru(H) (14) in benzene-^6  2  (vi)  5  2  Proposed mechanism for the formation of the three ruthenium hydride complexes 12,13 and 14 The reaction o f complex 3 with one atmosphere of hydrogen gas proceeds rapidly at room  temperature.  Within seconds the initial red-coloured solutions turn orange indicating that the  reaction is complete.  Because o f this, no intermediate species could be identified and this  precluded a detailed mechanistic study into the reaction o f 3 with H . A plausible pathway can be 2  postulated, however, based on various qualitative observations o f the reaction products. The key intermediate that allows for a rational explanation for the formation o f the three hydride products 12, 13 and 14 from 3 is a coordinatively unsaturated ruthenium monohydride complex, shown as [NPNH]RuH in Scheme 3.6. Although this species must contain an amide, phosphine and hydride  145  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogen 2  ligand no structural information is implied. One reason for this is because the chirality of the phosphine ligand will be inverted depending on which diastereomer of 3 (endo or exo) reacts with H2. The stereochemical outcome o f this effect will be addressed later in this section. The instantaneous reaction of 3 with dihydrogen is most likely a consequence of its coordinative unsaturation. In contrast, the reaction o f the six-coordinate complex 1 with hydrogen gas proceeds over a period of several hours. Upon coordination, the H2 molecule may be cleaved heterolytically transferring a proton equivalent to the 7t-allyl donor o f the cyclooctadienyl ligand, thus affording a ruthenium monohydride cyclooctadiene complex (Scheme 3.6). Since complex 12 is formed during the hydrogenation process and the fact that it contains an intact rutheniumamide bond and one hydride ligand provides direct proof that initial heterolysis o f H2 does not involve the Ru-N unit of 3.  From this point, hydride transfer followed by hydrogenolysis by  another equivalent o f H2 can generate a ruthenium monohydride cyclooctene intermediate; these steps are repeated until cyclooctane (CsPI^) has been eliminated and the unsaturated species "[NPNH]RuH" is formed. This route resembles pathway A in Scheme 3.3 for the conversion of 9 into 10.  146  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  Scheme 3.6  The monohydride complex 12 can form from the "[NPNHJRuH" intermediate simply by coordination of the phenyl group of the pendant amine ligand. It is not unexpected that this donor does not coordinate to the metal centre via the nitrogen lone pair of electrons given the poor Lewis basicity of this group. On the contrary, donation of six-electrons from the aromatic group allows for a stable, 18-electron species to be formed. Coordination of the phenyl group can occur to opposite faces of the metal centre depending on whether the exo or endo diastereomer of 3 undergoes hydrogenation. This would result in the production of 12 as a mixture of enantiomers. Complex 12 is an intriguing species since it is a chiral metal complex that contains a stereogenic metal centre and a chiral phosphine ligand. The two possible enantiomers that may result are SR12 and RS-12, as shown in Figure 3.14. The configurational designations refer to the ruthenium centre and the phosphorus centre, respectively.  147  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (Hi) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Me  SR-12  2  RS-12  Figure 3.14. The two possible enantiomers of complex 12 that may form from the hydrogenation of complex 3. The configurational designations refer to the metal centre and the phosphorus atom, respectively.  Conceptually, complex 14 can be envisioned as forming via the heterolytic cleavage of a molecule of H2 by the amide ligand in complex 12. This, however, is not the mechanism by which it is formed as is shown in Scheme 3.7.  Exposing compound 12 to hydrogen gas (1-4 atm) for  prolonged periods results in the formation of the ruthenium dihydride 14 in very small quantities (< 2%).  This implies that once hydrogenation of the cyclooctadienyl ligand occurs in the  precursor complex 3, and prior to coordination of the amino phenyl ring (which results in the formation of 12), heterolysis of H2 by the remaining ruthenium amide linkage in "[NPNH]RuH" must occur.  This results in a ruthenium dihydride complex with two pendant amine ligands;  coordination of the phenyl group of one of these ligands affords complex 14. The formation of complex 13 would proceed in a similar fashion as 14, however, instead of coordination of an amino phenyl group, an aromatic solvent molecule coordinates. In this case, both diastereomers of 3 will give rise to a single product (since the phosphine ligand and ruthenium centre are no longer chiral).  We wished to determine i f there was preferential coordination of one of the amine ligands in complex 14. For example, does the pendant amine ligand in 3 coordinate to the metal via its phenyl group, does it remain dissociated, or do both situations take place. It was anticipated that hydrogenation of the amino-deuterated complex 3-d\ could allow for a distinction between these possibilities by integration of the ' H N M R signals of the two distinct amino proton environments in complex 14.  148  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  For the purpose o f this study the reaction was performed at four atmospheres of H pressure 2  (to maximize the formation o f 14) in tetrahydrofuran-^g as the solvent (to eliminate the formation of 13).  The N-77 resonance of the phenyl-bound amine ligand integrated to one proton  environment per metal centre suggesting that the pendant (deuterated) side-arm in 3-di ends up as the dissociated ligand arm in 14. It was puzzling, therefore, to observe a resonance at 8 5.7 corresponding to the N - / / proton of the dissociated amine ligand. A n accurate integration o f this signal was difficult because it was overlapping with proton resonances o f the coordinated arene moiety. This finding can be rationalized by a hydrogen/deuterium exchange process that takes place at some point during the hydrogenation o f the cyclooctadienyl ligand.  As portrayed in  Scheme 3.6, the postulated mechanism for this process involves metal-hydride intermediates; it may be possible that the presence of deuteron-hydride bonding interactions in such intermediate species could allow for the exchange to take place. According to this proposal the N-H site in complex 12 should also contain a proton rather than a deuteron under identical reaction conditions, and this was indeed found to be the case. Unfortunately, this procedure did not allow for the determination of whether preferential coordination of one of the amine ligands occurs. I f both ligands are assumed to have an equal opportunity to coordinate to the metal centre through the phenyl ring then an enantiomeric mixture o f complex 14 would be expected.  149  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  endo-3  Scheme 3.7  (vii)  Loss of H from complex 14 to give complex 12 2  As shown in Scheme 3.7, solutions o f 14 slowly evolved hydrogen gas to generate the mono-hydride, mono-amide species 1 2 . This explains the isolation o f 12 during crystallization attempts  of  Similar  14.  reactivity  has been  observed  in  the  complex trans-  Ru(H) (NH2CMe2CMe NH )(R-binap) (binap = binapthyl), which slowly loses H in the solid2  2  2  2  state or in solution to afford the hydridoamide complex Ru(H)(NHCMe CMe NH )(R-binap). 2  The  cationic  complex  2  [RuH(dppm)(ri -C5H4(CH ) NMe H )]BPh4 5  +  2  2  2  110  2  (dppm  diphenylphosphinomethane) containing a pendant protonated amine ligand has also been shown to lose an equivalent o f H resulting in the formation o f a cationic ruthenium amine species (see 2  Scheme 3.8).  117  Unlike complexes 12 and 1 4 both o f these systems exhibit reversible loss and  150  References begin on page 184  Chapter  3: Heterolytic  Activation  of Dihydrogen  (H ) by Amidophosphine 2  Complexes  of Ruthenium(ll)  and Catalytic  Hydrogenation  addition of dihydrogen. This points to the stability o f 12 with respect to hydrogenolysis o f the ruthenium-amide bond. The mechanism for the loss of H in the above two examples is believed 2  to occur via intramolecular proton-hydride bonding interactions; the loss o f dihydrogen then proceeding via an r| -H2 intermediate. 2  60 bar H  Scheme 3.8 It is possible that a similar pathway is responsible for the loss o f H in complex 14 as is 2  shown in Scheme 3.9. Evidence for intramolecular proton-hydride bonding interactions in 14 is given by the short ri(min) relaxation times for the hydride (0.334 s) and proton (0.344 s) nuclei (see Table 3.6). The inequivalent hydride ligands in 14 had very similar Ti(min) values (within 10 ms) indicating that both come into close contact with the ~N-H proton in solution. The reported value in Table 3.6 is the average ri(min) value of the two hydride ligands. I f the internuclear distance between the two hydride ligands in 14 is assumed to be ca. 2.0 A (based on the fact that the two hydrides in 13 are separated by 2.03 A) the RuH "HN distance is calculated to be about 1.9 A. A proton-hydride distance of ca. 2.0 A is calculated based on the relaxation data for the amino protons. The close proton-hydride contacts in 14 could lead to a transient r | - H species that 2  2  loses a molecule of dihydrogen, though such an intermediate has not been identified. Interestingly, the isoelectronic complex 13 is stable with respect to loss of H even though there is 2  evidence for proton-hydride bonding in this complex. An alternative route for the conversion of  151  References  begin on page  184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  complex 14 into 12 could involve the reductive elimination of H followed by oxidative addition 2  of the N-H bond of the pendant amine ligand. This pathway is also outlined in Scheme 3.9.  proton-hydride interaction  reductive-elimination/oxidative-addition  Scheme 3.9 We hypothesized that one way we could identify the method o f H loss in complex 14 was 2  to monitor the decomposition of the labelled complex [NPNDH(r| -C6H5)]Ru(H) (14-Ji), in 6  2  which the amino proton o f the dissociated ligand side-arm is specifically deuterated.  I f the  elimination of H in 14-di proceeds via the reductive elimination mechanism then the resulting 2  complex 12 would be expected to contain a deuterium atom in the hydride position.  On the  contrary, i f H loss occurs via the proton-hydride bonding pathway, then the resulting complex 2  should contain a hydrogen atom at the hydride position. Monitoring the conversion o f 14-0*1 into  152  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  12 by *H N M R spectroscopy would allow for a distinction between the two possible decomposition pathways.  This hypothesis assumes that no scrambling between hydride and  proton environments occurs prior to H2 loss.  With this strategy in mind we desired a synthetic procedure that would allow for the preferential deuteration at the N-H position of the pendant amine ligand without incorporation o f deuterium at the hydride positions. Because of this stipulation the synthesis o f l4-d\ cannot be achieved by the addition o f D2 gas to complex 3 since this would generate a Ru(D)2 fragment with two deuteride ligands. The quantitative and clean formation of l4-d\ has proven to be a challenge and at this point we remain unsuccessful in accomplishing this task. Scheme 3 . 1 0 highlights one strategy that was devised, namely, replacement of the chloride ligand in the complex [NPNHD(r| 6  C H )]RuHCl (16-tfi) by a hydride ligand. 6  5  \4-d^  Scheme 3.10 The addition o f a stoichiometric amount o f NEt3 DCl to a toluene solution o f complex 12 -  results in the formation of a yellow precipitate over a period o f 2 4 hours. The ' H and  31  P{'H)  N M R spectra o f this solid are consistent with the formation of the ruthenium monohydride complex l6-d\ shown in Scheme 3.10. The proposed structure o f 16-d\ is related to the dihydride 14 with a chloride ligand in place of a hydride ligand. Due to its insolubility in aromatic and hydrocarbon solvents N M R characterization o f 16-dy was performed in tetrahydrofuran-cfe- The high-field region o f the ' H N M R spectrum contains a doublet at 8 - 8 . 2 3  ( JPH = 52.2 2  Hz) that  integrates to one proton and corresponds to the ruthenium hydride. The N-H proton of the r| -aryl 6  153  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  coordinated amine ligand is found at 8 3.75. In comparison, this proton resonance is observed at 8 3.85 in complex 12 and 8 3.51 in complex 14 when the H N M R spectra o f these species are J  recorded in THF-d^. These signals show a significant solvent dependence; in benzene-^ this resonance is located at 8 1.6 (for both 12 and 14). The observation o f a downfield shift for this peak may be due to the presence of a hydrogen bond between the amine proton and the oxygen lone pair o f a molecule o f THF. The presence o f four silyl methyl proton resonances and four second-order A B X (X = P ) multiplets for the inequivalent methylene protons of the [NPNHD] 3l  chelating ligand are in accordance with a species that displays C\ symmetry. Peaks associated with the coordinated amino-aryl protons are found between 8 5.4 to 8 5.9, and the remaining amino-phenyl and phosphine-phenyl resonances are located at expected positions between 8 7.1 to 8 7.9. The N-7/ proton resonance o f the pendant amine arm is not observed verifying that deuteration at this site has occurred. In the unlabelled complex (16) this resonance is found at 8 5.7. The phosphine ligand gives rise to a singlet at 8 45.6 in the P { ' H } N M R spectrum. 31  Having prepared 16-Ji the initial attempts at replacing the chloride ligand with a hydride ligand involved the addition of an equimolar amount o f potassium triethylborohydride (KH'BEt3). We anticipated that this would result in the formation o f 14-c/i along with potassium chloride and triethylboron, which could be separated by filtration and evaporation, respectively.  Although  complex \4-d\ did form from this reaction it was only present as a minor species in a mixture o f products. Predominant in this product mixture was the monohydride complex 12. The formation of 12 can be rationalized via deprotonation o f the pendant amine ligand in \6-d\ by KHBEt3. This would result in the elimination o f H D gas and a potassium-amide ligand which could undergo metathesis with the ruthenium chloride to generate 12 and potassium chloride.  The synthesis o f 14-Jj was also attempted by the reaction o f \6-d\ with lithium dimethylamide (LiNMe2). In this situation it was envisioned that metathesis would generate a dimethylamido containing intermediate that could undergo p-hydride elimination to yield 14-d\. In performing this reaction three ruthenium hydride products are formed, none o f which is complex 14-t/i.  Once again the major species present is complex 12, which can form by  deprotonation o f the pendant amine ligand in 16-cA and elimination o f deuterium-labelled dimethylamine (DNMe2). The identity o f the two other products is not known.  154  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  (viii)  Solution epimerization of complex 16 resulting in the formation of a mixture of diastereomers  The reaction between complex 12 and NEt3'DCl initially generates a single species as indicated by the N M R data, however, over a period o f several hours at room temperature the appearance o f a second species is noted. Allowing a THF-os solution to stand for about 24 hours results in an approximately 50:50 ratio o f the two species; this ratio does not change when the solutions are left to stand for extended periods. The new complex gives N M R spectral data that are very similar to the original species that is formed. The P { ' H } resonance is found at 5 43.6 31  slightly shifted from the resonance o f the original species suggesting a similar electronic structure at the metal centre for these two compounds. In the ' H N M R spectrum, a hydride resonance at 8 -8.02 is observed as a doublet (VPH = 55.8 Hz) due to its coupling with the phosphorus-31 nucleus, and a peak at 8 3.65 has been attributed to the N-//proton o f an aryl-bound amine ligand. Evidence for the coordination o f the amino phenyl group is provided by the presence o f upfield shifted resonances between 8 5.2 and 8 6.2. The silyl methyl and methylene environments for this new complex each give rise to four distinct proton resonances indicating an unsymmetrical solution structure.  A summary o f the proposed reactivity o f a racemic mixture o f complex 12 with NEt3 DCl -  is given in Scheme 3.11. As can be seen, this reaction results in the formation o f two complexes, namely RR-\6-d\ and SS-16-di; since these are enantiomers only one species is initially observed in the ' H N M R spectrum. The absolute configurations represent the chirality displayed at the ruthenium and phosphorus centres, respectively.  Inspection o f the structure o f these two  complexes shows that they are chiral-at-metal complexes that also contain chiral phosphine ligands. Complexes o f this type are known to undergo configurational processes; racemization can occur when the metal is the only stereocentre or epimerization when there are additional stereocentres.  118  During prolonged periods in solution it is possible that epimerization at the metal  centre occurs resulting in the formation o f two new complexes SR-16-d] and RS-16-d\. These two new species are enantiomers o f one another, and therefore, are indistinguishable by N M R spectroscopy.  These new species are, however, diastereomers o f their respective equilibrium  partners (i.e. RR- and SR-16-d\ and SS- and RS-\6-d\ are diastereomeric pairs), and this results in the observation o f a second species in solution over several hours.  155  Efforts towards obtaining  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  single crystals for a solid-state molecular structure determination o f these isomers by X-ray crystallography are currently underway.  As is shown in Scheme 3.11, epimerization at the ruthenium centre in RR-16-d\ can generate the isomer SR-16-di. The mechanism for this transformation can proceed by dissociation of the phosphine ligand to yield a trigonal planar ruthenium complex. The presence of the TCdonating chloride ligand can assist in the stabilization of this intermediate.  Phosphine  119  dissociation is known to play a key role in the racemization or epimerization o f other chiral-atmetal complexes. ' 118  120  Rotation about the bound amino phenyl ring and re-coordination o f the  phosphine donor acts to invert the chirality at the metal centre.  Precedent for this type of behaviour can be found in the literature and it has been used to rationalize configurational equilibria processes in structurally related complexes.  O f utmost  relevance to this work is the epimerization that occurs between the pair of diastereomers o f the ruthenium amide complex (r| -C6Me6)-Ru[C6H N(Ph)(CHCH3)](PMe3). 6  4  121  Similar activity is  observed for a diastereomeric mixture o f (Ti -C H )Re(KO)(PPh )(>JHCHPhMe). 5  5  5  3  118  In both o f  these cases, phosphine dissociation leads to a three-coordinate planar species; coordination of the phosphine ligand to either of the diastereotopic faces o f the intermediate generates the observed mixture of isomers.  The only difference for the epimerization of complex 16-Ji is that the  phosphine donor is part of a chelating ligand, and as such requires rotation of the bound phenyl group to allow for phosphine attack at the opposite face. Three-coordinate ruthenium(II) species exhibiting nearly planar geometries have been characterized in the solid-state in complexes of the type (if-C Me5)Ru(PR3)(X) (where R = CH(CH ) 3  5  OSiPh3). > 122  123  2  and X = Cl or R = C H n and X = 6  These findings suggest that isomerization via a planar intermediate as depicted in  Scheme 3.11 is a plausible pathway.  156  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  SR-12  SiMe  Me,Sr-^"^<__:  2  P" /! Prf ^ PhDN'  SiMe  Me Si-  SiMe2  2  H Cl -NDPh  SiMe  2  2  cr "7 H  A  P K \  y .N—Si / Me Ph* D  2  SS-16-d,  /?S-16-d!  "DCI" RS-12  Scheme 3.11  157  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  (ix)  Catalytic hydrogenation studies with complexes  3, 12, 13 and 14, and  speculations into mechanistic details  Exposure o f an equimolar solution o f complex 3 and benzylidene aniline to an atmosphere of hydrogen gas at room temperature results in the quantitative formation o f benzylphenyl amine within 12 hours. The mild conditions that were employed in order to achieve reduction o f the imine substrate were promising and prompted an investigation into the catalytic potential utilizing complex 3 as a catalyst precursor. In doing so, complex 3 was found to effectively catalyze this hydrogenation reaction, as shown in equation 3.11. Optimal results were attained with a substrateto-catalyst loading o f 50:1 utilizing toluene as the solvent and four atmospheres o f hydrogen gas pressure. Conversion to the amine product (99% as determined by integration o f *H N M R signals) occurs within 48 hours.  Ph  \  :  C<  2 mol% 3  ..Ph 'H  4 atm H toluene  Ph  H  N:,  N-  2  /  H  -C  [3.11]  \""Ph H  The results o f this study were encouraging and we next set out to obtain details about the catalytic mechanism for this process. Compared to other systems that are believed to operate via the bifunctional hydrogenation method the reduction o f benzylidene aniline utilizing complex 3 as a precursor proceeds quite slowly.  For example, this same substrate was shown to undergo  complete conversion in less than four hours utilizing RuPi2(PPh3)2(R,R-cydn) and a substrate-tocatalyst ratio o f 500.T!  111  These differences would seem to imply that the concerted transfer o f  hydride and proton nuclei to the imine substrate is probably not the operative mechanism in our system. In order to obtain more information about the mode o f catalysis, as well as possibly identifying what the active species could be, each o f the three ruthenium hydride products was individually tested as a possible catalyst precursor. A summary o f the catalytic studies performed is outlined in Table 3.7.  158  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Table 3.7.  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  A summary of the catalytic studies performed for the hydrogenation of imine and  alkene substrates using complexes 3,12,13 and 14 as precursors.  Entry  Precursor  Substrate  % conversion"  1  3 12 13 14 3 3  Benzylidene aniline Benzylidene aniline Benzylidene aniline Benzylidene aniline 1 -hexene cyclooctene  99  2 3  4 5 6  0 0 0 99 99  Reactions were carried out at 25°C and 4 atm H pressure with a substrate/catalyst loading of 50:1. The imine substrate was dissolved in toluene whereas the olefins were neat samples. Determined by 'H NMR analysis of crude reaction mixture after 48 h. 2  b  Although the catalytic conversion of benzylidene aniline to benzylphenyl amine is possible utilizing complex 3 (entry 1), the possibility of compounds 12, 13 or 14 partaking in the catalytic process can be dismissed as each of these was found to be inactive towards imine hydrogenation (entries 2-4).  This is not surprising considering the coordinatively saturated nature of these  species with tightly bound arene moieties. The inability of the amine arms to coordinate to the metal centre through the nitrogen lone pair of electrons negates the ability to form ruthenium(U) species containing c/s-coordinated amine and hydride ligands, and therefore, capable of effecting catalysis via the bifunctional mechanism. The ease at which the hydride complexes 12, 13 and 14 form renders this a poor catalyst system for hydrogenation processes. In essence, this catalyst system can be said to possess "suicidal" characteristics with the three ruthenium hydride species representing catalytic "dead-ends". The formation of stable rhodium (I) arene complexes has also been shown to have inhibitory effects on rhodium catalyzed asymmetric hydrogenations.  124  The observation that the arene-coordinated ruthenium hydride complexes were inactive towards hydrogenation whereas the starting material 3 did serve as a hydrogenation precursor, suggested that the active species was most likely an unsaturated ruthenium complex. Support for the involvement of a coordinatively unsaturated species as the active complex was given by the addition of an excess of P'P^ to the reaction mixture, which lead to an inhibition of catalysis. The addition of benzylidene aniline directly to complex 3 also showed no reactivity providing further support for the presence of an unsaturated active species. In the proposed mechanism for the  159  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  hydrogenolysis of the cyclooctadienyl ligand in 3 (Scheme 3.6) such an unsaturated intermediate "[NPNHJRuH" is suggested as the key species that allows for the formation of complexes 12, 13 and 14.  It is also possible that this intermediate is the catalytically active species present in  solution. Alternatively, a coordinatively unsaturated ruthenium dihydride could also be the active species. In either case, coordination of the imine substrate to the ruthenium centre followed by hydride migration may initiate the hydrogenation process, which could then proceed in a similar fashion as that depicted in Scheme 3.6. The proposed catalytic mechanism involving substrate coordination to the metal centre suggested that olefins could also undergo catalytic hydrogenation. Indeed, both 1-hexene and cyclooctene were successfully reduced under similar hydrogenation conditions (entries 5 and 6).  At this point the ideas that are presented are speculative and are intended merely to provide some rudimentary insight into this system.  Recent literature reports do lend support to the  possibility that a mono-hydride intermediate such as "[NPNH]RuH" could play a key role in the catalytic hydrogenation process.  Highly active and well-defined mono-cationic ruthenium  hydrogenation catalysts of the type [Ru(bisphosphine)(H)(solvent) ]BF 3  MeOH, E t O H ) our system.  125  "  127  4  (solvent = acetone,  possess some similarities with the proposed active species "[NPNH]RuH" in  As shown in equation 3.12, hydrogenation of the cyclooctatriene ligand in A  generates the active catalyst species B, which contains a chelating bisphosphine ligand and a hydride ligand; the inner coordination sphere is filled by labile solvent molecules. Displacement of a solvent molecule by a substrate molecule can initiate the catalytic process.  In a similar  manner, hydrogenolysis of the cyclooctadienyl ligand in 3 can generate the monohydride intermediate "[NPNH]RuH" (highlighted in Scheme 3.6) bearing a chelating amido-phosphine ligand and a hydride ligand. The presence of the amido donor in the chelating set allows for a neutral complex to be formed.  Coordination of a substrate molecule to a vacant site at the  ruthenium centre can initiate the hydrogenation process as in the cationic complexes.  160  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  [3.12]  B One of the difficulties concerning the hydrogenation of polar substrates such as imines is that coordination to the metal centre through the nitrogen lone pair o f electrons results in r|'binding, thus forming a ©"-complex; this contrasts with the side-on (r| ) bonding mode o f olefins, 2  which generates  ft-complexes. -  128 129  The side-on binding o f a substrate is usually considered an  essential requirement within a catalytic hydrogenation cycle since this results in effective orbital overlap with the metal centre and allows for effective hydride transfer. In the case o f r^-binding by an imine substrate the delivery of the hydride ligand from the metal centre to the imine carbon atom is difficult due to the positioning o f this atom away from the metal centre; r| -bonding can 2  alleviate this apparent geometric restraint. In the Afunctional mechanism the requisite interaction between the M-H bond and the u-face o f a polar substrate is achieved through a ligand-assisted, outer-sphere electrostatic interaction (see Scheme 2 . 1 ) .  130  Having no definitive indication as to the structure o f the catalytically active species in our system (besides evidence that it is an unsaturated complex) we can only speculate as to mechanistic possibilities and intermediates within a catalytic cycle.  The fact that imine  hydrogenation is possible, however, suggests that a side-on bound imine substrate may likely be present at some point.  Assuming that a ruthenium monohydride complex of the type  "[NPNH]RuH" is the active species the amine ligand may play a role in facilitating r| -bonding of 2  the imine substrate; this is portrayed in Figure 3.15.  An inner-sphere hydrogen-bonding  interaction between the amino proton and the imine nitrogen atom can stabilize 7t-complexation o f  161  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  the imine substrate. A similar interaction has been proposed between a coordinated molecule of methanol (the solvent) and the imine substrate in a rhodium (I) system containing chelating diphosphine ligands.  In this example, the use of methanol as a co-solvent was found to be  128  essential for effective conversion and this was rationalized in terms of it facilitating a change from r) - to r| -binding of the imine. A "two-point" cooperative binding o f ketones by a metal and by a 1  2  neighbouring pendant N H group in an iridium complex has also recently been published.  Me  2  Ph  Me .SL  2  131  Ph /  t| -bonding 2  r| -bonding  Figure 3.15. Possible role o f the amine ligand in facilitating r| -bonding of the imine substrate. 2  A mandatory condition for the amine-assisted interaction of the Ru-H bond with the 7t-face of the imine is that the amine ligand itself must coordinate to the metal centre. We have already seen examples which show that the "SiMe N(H)Ph" amine donor is not a good Lewis base; in 2  Chapter 4 we see that H displaces this donor group. I f the amine ligand exhibits labile behaviour 2  during the hydrogenation reaction then this would act to shift the equilibrium in favour o f the n, 1  bonding mode of the imine. This could potentially be one reason for the longer reaction times required to achieve complete conversion in our system.  It is interesting that although the  dihydrogen-hydride complex 10 does contain a coordinated amine ligand and a potential site for substrate coordination it exhibits no catalytic activity towards imine hydrogenation. The reason for this may be a consequence of the trans disposition between the amine ligand and the open coordination site, therefore, not allowing the amine ligand to aid in the side-on binding of the imine substrate.  162  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  3.6  Synthesis of a new [NPN] ligand with variation at the amide positions and its application to ruthenium(ll)  (i)  The need for ligand variation  In the proceeding discussion concerning the hydrogenation o f complex 3 and catalytic hydrogenation studies with 3 serving as a precursor, it is apparent that the presence of phenyl substituents at the amide positions plays a significant role in the resulting reactivity. Our intended goal was to prepare ruthenium(II) complexes containing cw-coordinated amine and hydride ligands and to test the ability of these species to hydrogenate imines, possibly via the bifunctional mechanism. The intrinsic drawbacks o f the chelating ligand system employed (with poor amine basicity and arene coordination), however, hampered such an investigation. These inadequacies initiated an examination into modification o f the amide groups.  In the following section a  discussion concerning our initial efforts into the preparation of a new [NPN] ligand and its reaction with [RuCl2(cod)] will be presented. x  One o f the advantages o f the tridentate [NPN] donor set is the potential for substituent variation, not only at the amide positions, but for the phosphine ligand as w e l l .  132  '  133  This can be  accomplished by changing the amines or phosphines initially used in the synthesis of the [NPN] ligands. For example, utilizing cyclohexylphosphine in lieu of phenylphosphine in the ligand preparation generates a more Lewis basic, cyclohexyl-substituted phosphine donor in the chelating ligand array. In this way, modification o f the steric and electronic properties o f the ligand set, and by extension the resulting metal complexes can be achieved.  In an attempt to eliminate the deficiencies within complex 3 with respect to its hydrogenation reactivity, the replacement of the phenyl groups at the amide positions o f the [NPN] ligand with alkyl substituents was pursued. Our initial variation involved a methyl substituent. We anticipated that the smaller size and electron-donating ability of this group would aid in coordination of the amine donor through the nitrogen lone pair.  163  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  (ii)  Synthesis  and  characterization  Complexes of Ruthenium(ll) and Catalytic  of  Hydrogenation  [PhP(CH SiMe NMe) ]Li C H 0 2  2  ( [NPN]Li C H 0 ) (17) and its reaction with [RuCI (cod)]  2  2  4  8  2  Me  2  4  8  2  2  The new mixed-donor, tridentate ligand ^ I W N J L i ^ H g O z  x  (17) (where  Me  [NPN] =  PhP(CH2SiMe2NMe)2) can be prepared in an analogous fashion as the all phenyl-substituted derivative. The synthetic procedure employed is outlined in Scheme 3.12. The silylated methyl amine, ClCH SiMe NHMe, is formed from the reaction o f MeNHLi with ClCH SiMe Cl. The 2  2  2  2  dropwise addition o f four equivalents o f "BuLi to an ether solution containing a mixture o f two equivalents o f ClCH2SiMe2NHMe and one equivalent o f PI1PH2 gave the expected dilithiated precursor, [NPN]Li2 (18). The room-temperature *H N M R spectrum of the resulting solid (in Me  C6D6) consisted of resonances that could be attributed to silyl methyl, methylene, amido methyl and phosphine phenyl proton environments in accordance with the formation o f 18. A l l o f these resonances were observed as broad peaks indicative o f fluxional solution behaviour for this species. The P { ' H } N M R spectrum o f this solid (C6D6) was also composed o f a broad singlet 31  located at 5 -38.0. The ligand precursor 18 was isolated as a foamy yellow solid and it readily dissolved in hexanes, which made purification troublesome. The addition o f a slight excess o f 1,4dioxane  (C4H8O2)  to a solution o f 18 in hexanes resulted in the deposition o f 17 as a white, micro-  crystalline solid in about 70 % yield.  164  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine  Complexes of Ruthenium(ll) and Catalytic  2  Hydrogenation  2 M e N H HCI 2  4 BuLi n  Me^ 2 MeNHLi  +  2  Me^  JVle  Cl  H  Cl  Cl PhPH 4 "BuLi  M  -Me  2  .SL.  r  Me  2  1,4-dioxane  2  e  S  /Me  K  Ph—P:  • J-l  Me  M  e  2  S = 1,4-dioxane 17  Scheme 3.12  The room temperature *H N M R spectrum o f [ N P N ] L i 2 C H g 0 2 (17) is composed o f well M E  4  resolved peaks and is diagnostic for a mono-dioxane adduct; elemental analysis also supports this ligand composition. The silyl methyl protons appear as two closely spaced singlets near 8 0.1 and the methylene protons o f the backbone are observed as a second-order multiplet centered at 8 0.8. A singlet at 8 2.8 corresponds to the six equivalent methyl amide protons. The resonance for the coordinated dioxane molecule is found at 8 3.6 and three multiplets in the range 8 7.1 to 8 7.5 are due to the ortho-, meta- and /jora-protons o f the phenyl group attached to the phosphine donor. The ' H N M R data suggest a symmetrical solution structure for 17 not unlike other [ N P N ] variants. This would imply that the dioxane molecule undergoes reversible coordination with both lithium centres.  The P { ' H } N M R spectrum for 17 consists o f a singlet at 8 -37.5. This is in contrast with 3 I  the phosphine resonance in the all phenyl [ N P N ] ligand, which is observed as a quartet due to  165  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  coupling o f the P nucleus to a L i nucleus (/ = 3/2, 92.6 % abundance). This implies that the 31  7  phosphine donor in 17 does not coordinate to the lithium cations; the L i { ' H } spectrum of 17 also 7  consists of a singlet. The lack of phosphine coordination is most likely due to the more basic nature of the amido donors bearing methyl groups as opposed to phenyl groups.  This would  render the lithium centres in 17 less Lewis acidic. The presence of only one equivalent of dioxane may also be a result of this.  The reaction of  Me  [NPN]Li "C H80 2  4  2  (17)  with the ruthenium(II) starting material  [RuCl (cod)] was carried out in an identical fashion as with the phenyl-substituted [NPN] ligand. 2  x  This resulted in the isolation of an orange solid whose ' H and P { H } N M R spectra suggested it 31  1  was a paramagnetic compound. The ' H N M R spectrum, for instance, consisted of very broad and shifted peaks, none of which could be attributed to the specific proton environments of the Me  [ N P N ] or cyclooctadienyl ligands. The same orange solid was produced when the reaction was  performed in THF as the solvent in lieu of toluene. At this point the structure of the isolated compound is unknown, although attempts at obtaining single crystals for an X-ray diffraction study are ongoing. What is certain, however, is that the methyl amido analogue of complex 3 has not been produced.  It is possible that P-hydride elimination from the methyl group o f a  coordinated amide donor o c c u r s ,  134-136  leading to the formation of the isolated orange solid. The  use of tertiary butyl groups at the amide position would exclude this potential decomposition pathway. Unfortunately, the synthesis of an [NPN] ligand with these bulky amide donors was unsuccessful. The reaction of the diamidophosphine ligand 17 with other ruthenium(II) starting materials has not been investigated.  3.7 Summary and Conclusions This chapter deals with the reactivity o f the amidophosphine complexes [P N ]Ru(i"| :r| 2  2  2  2  C H i ) (1), [P NNH]Ru(C H PPh ) (2) and [NPNH]Ru(l-3:ri -5,6:ri -C8H, ) (3) with hydrogen 3  8  2  2  6  4  2  2  1  gas, including a discussion of the catalytic hydrogenation of imine and alkene substrates utilizing these species as catalyst precursors. The coordinatively saturated complex 1 reacts with hydrogen gas to produce the ruthenium dihydrogen-hydride species [P NNH]Ru(H )H (10). 2  cleavage of a molecule of H  2  2  The heterolytic  generates the ruthenium amine and hydride moieties.  166  The  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  classification of 10 as a dihydrogen-hydride complex as opposed to a ruthenium (IV) trihydride structure was based on the measurement o f the short 7i(min) value of 62 ms for the hydride nuclei and the observation of an JHD coupling o f about 5 Hz in the partially deuterated isotopomers. 3V  Both the N M R relaxation and the H D coupling data provided an estimated H-H distance o f ca. 1.2 A for the coordinated H ligand in 10. This species undergoes two fluxional processes in 2  solution. In one case, the hydride and dihydrogen environments are readily exchanged. This is proposed to occur through an intermediate trihydrogen species that forms from the electrostatic cw-interaction between these nuclei.  The second process involves an exchange of the amino  proton and hydride sites via a protonic-hydridic bonding interaction. Complex 10 was found to be a precursor for the catalytic hydrogenation o f olefins but not for imines. Displacement o f the H  2  ligand by a substrate molecule most likely initiates the catalytic process.  Complex 2 reacts with hydrogen gas to generate the ruthenium(IT) monohydride complex [P NNH]RuH(PPh3) (11) via hydrogenolysis of the orara-metalated triphenylphosphine ligand in 2  2.  Alternatively, complex 11 can be formed by the addition of triphenylphosphine to 10 by  displacement o f the H ligand. This compound has been characterized in the solid-state by X-ray 2  diffraction and in solution by ' H and P { ' H } N M R spectroscopy.  In both instances a C  31  s  symmetric structure is evident. Under an atmosphere o f deuterium gas, complex 11 was observed to incorporate deuterium at the hydride and amino proton sites. This has been rationalized by the displacement of H  2  in a transient intermediate that forms due to proton-hydride bonding  interactions in 11. In accordance with this proposal, a cross-peak in the two-dimensional EXSY spectrum was observed between the hydride and amino proton environments indicating that these two nuclei are in chemical exchange. Complex 11 was unable to catalyze the hydrogenation o f alkene or imine substrates even under four atmospheres of H pressure. The triphenylphosphine 2  ligand in 11 is strongly coordinated to the metal centre not allowing for an open site for substrate binding.  The reaction o f the mono-amide complex 3 with hydrogen gas results in the formation of three ruthenium hydride species: [NPN(H)(ri -C6H )]RuH (12), [OTNH ]Ru(H) (C H ) (13) and 6  5  [NPNH (TI -C6H5)]RUH 6  2  2  (14).  2  2  7  8  Complex 12 forms via hydrogenolysis of the cyclooctadienyl  ligand in 3 followed by coordination o f the amino phenyl ring o f the [NPNH] ligand side arm. Compounds 13 and 14 undergo further conversion of the ruthenium amide bond into a ruthenium  167  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  hydride and amine side arm resulting from the heterolytic cleavage o f H2. Compounds 12 and 13 have been characterized in solution and in the solid state.  The X-ray determined molecular  structure of 13 shows close hydride and amino proton contacts o f about 2 A ; these interactions are maintained in solution as determined from measurement o f the ri(min) relaxation times o f these nuclei.  Complex 14 was characterized in solution by ' H and P { H } N M R spectroscopy. 3 1  l  Evidence for the presence of proton-hydride bonding in 14 was given from the relaxation data; it is believed that this interaction gives rise to an (unobserved) H2 complex which evolves an equivalent o f dihydrogen to give 12. The coordination o f arene substituents, either amino-phenyl or aromatic solvent molecules (toluene or benzene) generates coordinatively saturated species that are inactive for the hydrogenation o f imine or olefin substrates.  Complex 3, however, is a  precursor for the catalytic hydrogenation o f these substrates. We are currently investigating new systems in which the substituents at the amide position o f the [NPN] ligand have been modified to electron donating, alkyl groups in an attempt to promote coordination of the resulting amine arms to the metal centre via the nitrogen lone pair.  This may lead to the formation o f ruthenium  systems with c/s-coordinated hydride and amine moieties, capable o f performing catalytic hydrogenation operating by the bifunctional mechanism.  3.8  Future Work  (i)  Catalytic  ionic  hydrogenation  utilizing  [NPN(H)(r| -C H5)]RuH (12) 6  6  as  a  precursor  Ionic hydrogenation involves the addition o f a hydride and a proton across an unsaturated organic m o i e t y . ' 10  137  The ability o f transition metal complexes to accomplish this task  stoichiometrically has been known for some time. A mixture o f an organometallic hydride such as CpMoH(CO)3 and a strong acid such as CF3SO3H is capable o f reducing sterically hindered olefins to alkanes via protonation to carbocations followed by hydride transfer from the metal hydride.  138  The reduction o f aldehydes and ketones using mixtures o f CpW(H)(CO)3 and  C F 3 S O 3 H has also been reported.  139  A more recent study reports on the catalytic ionic  hydrogenation o f methyl aryl pyrrolidinium cations by a piano-stool ruthenium hydride complex as shown in equation 3.13.  10  168  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  [3.13]  The proposed catalytic cycle for the ionic hydrogenation mechanism is shown in Scheme 3.13. The first step involves hydride transfer to the iminium cation to generate a cationic metal fragment ( M ) which then reacts with an equivalent of H2. This (unobserved) intermediate then 4  transfers a proton equivalent to generate the ammonium product and the active monohydride complex. The use of chiral chelating phosphine ligands allows for the asymmetric reduction of prochiral immonium substrates, however, the obtained enantiomeric excesses show some room for improvement (typically ~ 30 to 60 % e.e.).  It would be interesting to test the ability of the complex [NPN(H)(ri -C6H5)]RuH (12) in 6  ionic hydrogenation processes.  Similar to the cyclopentadienyl ruthenium complex discussed  above it is a mono-hydride species with a piano-stool structure. A significant difference, however, is the presence of the 7C-donating amido ligand in 12, which could enhance its activity. The ratedetermining step in the hydrogenation mechanism shown in Scheme 3.13 is the initial hydride transfer step, and this is most likely due to the formation of a cationic unsaturated intermediate. Such an intermediate could be stabilized electronically by derealization o f the amido lone pair o f electrons leading to an increase in the catalytic activity. It would also be fascinating to perform asymmetric hydrogenations with 12. Complex 12 is a chiral-at-metal complex that also contains a chiral phosphine donor. This is in contrast to the reported ruthenium complex, which contains a chiral chelating bisphosphine ligand where the chirality is located in the ligand backbone. One problem that could arise is the fact that complex 12 could potentially exist as a racemic mixture (Figure 3.14).  169  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  Scheme 3.13  (ii)  Another strategy towards the synthesis of amino-deuterated complexes of  14 In section 3.5 (vii) o f this chapter we discuss the loss o f H2 from complex 14 to give 12. One possible mechanism for the evolution of H2 is through proton-hydride bonding interactions leading to the formation o f a transient H2 complex; T\ data indicate that there is a close contact between the hydride and proton sites in 14 o f about 2.0 A. An alternate route could involve the reductive elimination o f H2 from the metal centre followed by the oxidative addition o f the N-H bond o f the amine ligand.  A distinction between these two pathways could be achieved by  monitoring the decomposition o f the amino deuterated complex 14-a'i, however, our synthetic efforts have not allowed for a clean and quantitative formation o f this species.  One o f the  complications that we encountered in our initial attempts was deprotonation of the amino proton(s)  170  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  in addition to a metathetical exchange o f chloride and hydride ligands in reactions o f complex 16d\ with K H B E t or LiNMe2. These observations suggested to us another procedure that could 3  possibly allow for the incorporation o f deuterium at both o f the amino proton sites to give l4-d . 2  This is illustrated in Scheme 3.14.  SiMe  SiMe?  2 LiN(SiMe ) 3  -2 HN(SiMe ) 3  2  Ph  /  Ph  Si Me  2  2  )  D  / Ph  2  Si Me  Ph  2  14-d,  14 SiMe  2  2 NEt DCI 3  / - S i Me  Prf  -2 NEt -2 LiCI  3  2  Scheme 3.14  The addition o f two equivalents o f base (e.g. LiN(SiMe3)2) to complex 14 followed by two equivalents o f deuterium chloride may allow for the incorporation o f deuterium into the two N-H sites.  Labelling o f the amino hydrogen by deuterium in complex 12 was accomplished by  employing this reactivity, as was the amino hydrogen atom in complex 3.  Monitoring the  decomposition o f 14-d by H N M R spectroscopy would allow for a discrimination between the !  2  two possible modes of H loss from 14. 2  (iii)  Reaction of [NPN]Li C H 0 (17) with early transition metals Me  2  4  8  2  The reaction o f the diamidophosphine  ligand  [NPN]Li2'C4Hg02 (17) with the  Me  ruthenium(H) starting material [RuCl2(cod)] produced an orange solid that gave rise to very broad x  and shifted peaks in the 'H NMR spectrum, characteristic of a paramagnetic species.  171  It was  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  obvious that the anticipated product [NPNH]Ru(l-3:ri -5,6:r| -C8Hii), analogous to 3, did not Me  3  2  form. It is possible that the presence o f the hydrogen atoms o f the methyl-substituted amide donor permitted other reaction pathways via (3-hydride elimination; this is a common decomposition route for late transition metal amide complexes. Although 17 is not tailored for late transition metals it may be well-suited for the stabilization o f early transition metals.  Figure 3.16. Examples o f [NPN]Zr and [NPN]Ta dinitrogen complexes.  The coordination and functionalization o f dinitrogen by early transition metal complexes stabilized by the [P2N2] and [NPN] ligand sets is a major area of research in our lab.  Highly  activated N2 moieties (as measured by the elongation of the N-N bond upon coordination), reaction with H2 to form N-H bonds, as well as stoichiometric N-C, N-B and N-Si bond forming reactions have all been achieved with these types of c o m p l e x e s .  133  '  140  '  141  Representative examples o f  dinitrogen complexes o f zirconium and tantalum stabilized by the [NPN] ligand are shown in Figure 3.16. Modification o f the electronic and steric properties o f the metal complexes could be expected to influence the reactivity of the coordinated N 2 ligand within these complexes. The methyl substituted [NPN] ligand 17 offers increased Lewis basicity as compared to the phenyl derivative.  As such, one may anticipate an increased activation o f coordinated N 2 moieties in  complexes bearing this ligand, which could translate into an expansion o f the already observed reactivity of this inert molecule.  172  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic  Hydrogenation  With these ideas in mind, the coordination of 17 to zirconium (IV) was undertaken. As shown in equation 3.14, the reaction of 17 with Z r C L ^ H s O ^ yields the diamidophosphine complex [NPN]ZrCl2(C4pi802) (19) in quantitative yield as a white solid. The reaction proceeds Me  cleanly as evidenced by the singlet observed at 8 -6.3 in the P { ' H } N M R spectrum for the crude 3 l  reaction mixture. The ' H N M R spectrum indicates a symmetrical coordination geometry about the zirconium centre. Only one resonance for the methyl amide protons is present and two peaks for the silyl methyl proton environments. The methylene proton resonances consist of a multiplet at 8 1.22 and the phosphine phenyl protons are located between 8 7.10 and 8 7.76. A singlet at 8 3.30 that integrates to eight protons implies the. presence of one equivalent of coordinated 1,4dioxane per metal centre. The only structure consistent with the observed ' H N M R data is that shown in equation 3.14, with the chloride and amide ligands occupying the equatorial plane of a six-coordinate octahedral species, and the phosphine and dioxane ligands at the axial positions. A mirror plane of symmetry bisecting the chloride and amide donors exists resulting in a C  s  symmetric complex.  M e  2  \  »„  .-s  I\  Ph—P:  Li U  Si Me  ZrCI (C H 0) 4  4  8  2  M'  1  Me  [3.14]  2  Me 17  v  |\k,  toluene, 80°C, 24 h  »CI  :-Z<  -Cl  Me Siy  2 LiCI  2  Me Si ^ 2  Ph  S = 1,4-dioxane 19  So far, the reduction of 19 under an atmosphere of N to form a dinitrogen complex has not 2  been attempted. It will be exciting to see i f an N2 complex can be prepared, and i f so, even more exciting to investigate the reactivity of the N2 ligand! The coordination of 17 to other metals including tantalum and niobium has not been examined at this point but would also be worthwhile pursuing in the future.  173  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  3.9  Experimental  (i)  General Procedures  Unless otherwise stated, general procedures were performed according to Section 2.9 (i). ' H N M R T\ relaxation measurements were performed on a Bruker A M X 500 MHz spectrometer using a standard inversion-recovery pulse sequence (180°-T-90°). The T\ values were obtained using the non linear three-parameter fitting routine in the Bruker X W 1 N N M R program with an estimated error o f ± 10 % in each T\ value. The temperature was regulated using a Bruker V T 1000 unit. Toluene-rfg was used as the N M R solvent for these studies. The T\ data including plots of T\ versus Temperature for each complex are provided in Appendix 2.  (ii)  Materials  Complexes 1, 2 and 3 were prepared as described in Chapter 2. Hydrogen gas (purchased from Praxair) and deuterium gas (Cambridge Isotope Laboratories) were employed without further purification.  Cyclooctadiene, cyclooctene, 1-hexene, 1,4-dioxane and ClMe2SiCH2Cl were  purchased from Aldrich and all were distilled prior to use. Benzylidene aniline was purchased from Fisher Chemicals and was recrystallized from hot ethanol and dried under vacuum overnight prior to use. B u L i (Acros Organics), LiNMe2, KH'BEt3 and H N M e f H C l (Aldrich) were used as n  received.  Phenylphosphine  and Z r C U ^ H g O ^  142  1 4 3  were prepared according to reported  literature procedures.  (iii)  Synthesis and Reactivity of Complexes  [ P N N H ] R U H ( T I - C H ) (9) and [ P N N H ] R u ( H ) H (10) 2  2  8  1 2  2  2  A yellow solution o f [P N ]Ru(r| :r| -C8Hi2) (1) (0.052 g, 0.070 mmol) in ~ 1.0 m L o f 2  2  2  2  toluene-^ in a J-Young valve N M R tube was degassed by performing three freeze-pump-thaw cycles. The solution was warmed to room temperature and then exposed to an atmosphere o f hydrogen gas. After four hours, an intermediate species is observed. The suggested composition based on ' H and ^ { ' H } N M R data is ^ N N H J R u H O f - C g H n ) (9). ' H N M R ( C D , 298 K, 500 7  174  8  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  MHz):  8 -9.60 (t, J  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  = 25.4 Hz, Ru-H, I H ) , 8 -0.51, -0.12 (s, SiC# , 12H total), 8 0.63 (s,  2  3  m  overlapping, SiC# , 12H total), 8 1.4 - 3.6 (m, overlapping, N-tf, PCH and 3  2  C #i ), 8  6  8 7.0 - 8.2  (m, overlapping, PC // ). ^ P i ' H } N M R ( C D , 298 K, 202.5 MHz): 8 30.0 (s). Stirring the 6  5  7  8  reaction mixture for 48 hours results in the formation of the complex [P2NNH]Ru(H2)H (10). N M R ( C D , 298 K, 500 MHz): 8 -11.44 (t, J 8  H  = 13.8 Hz, Ru-H 3H), 8 0.36 (s, overlapping,  2  7  !  m  SiCH , 24H total), 8 1.42 (m, PC# , 8H total), 8 2.18 (s, N-7f, I H ) , 8 7.62 - 8.02 (m, P C ^ s , 3  10H).  2  3 1  P { H } N M R (C D , 298 K, 202.5 MHz): 8 35.5 (s). ^ ( m i n ) for Ru-# = 62 ms at 240 K l  7  8  3  in toluene-dg.  Reaction of [P NNH]Ru(H )H (10) with D 2  2  2  An N M R tube containing [P NNH]Ru(H )H (10) (ca. 0.049 mmol) in toluene-fife ( - 1 . 0 2  2  mL) was degassed by three freeze-pump-thaw cycles.  The solution was thawed under an  atmosphere o f D2 gas. After one hour the sealed N M R tube was transferred into an N M R probe. The *H N M R spectrum of the hydride signal had changed from a triplet to a complicated multiplet due to coupling to the P and H nuclei. ' H { P } N M R , hydride region ( C D , 298 K, 500 MHz): 31  2  31  7  8-11.44 (s, overlapping, Ru-# ), 8 -11.43 (t (br), J 2  3  H D  8  = 4.5 Hz, overlapping, Ru-tf D). After 16 2  hours under an atmosphere of D2 gas a new multiplet for the hydride signal was observed in the *H N M R spectrum. ' H { P } NMR, hydride region ( C D , 298 K, 500 MHz): 8 -11.42 (m (br), J 3I  2  7  5.0 Hz, Ru-HD ). 2  8  Temperature dependence of the hydride resonances (Ru-//  3  H D  =  and Ru-ffl)  2  isotopomers, respectively): 298 K (8 -11.44, -11.42), 280 K (8 -11.38, -11.35), 260 K (8 -11.32, 11.28), 240 K (8 -11.27, -11.20), 220 K (8 -11.20, -11.11).  Reaction of [P NNH]Ru(H )H (10) with cyclooctadiene 2  2  In an N M R tube containing a solution of 10 (ca. 0.064 mmol) in toluene-fife (~ 1.0 mL) was added a slight excess o f cyclooctadiene (0.008 g, 0.074 mmol). The ' H and P { ' H } N M R spectra 31  of the reaction mixture indicated the formation o f complex 9.  175  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Reaction of [P NNH]Ru(H )H (10) with P P h 2  2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  3  In an N M R tube containing a solution o f 10 (ca. 0.072 mmol) in toluene-Js (~ 1.0 mL) was added a slight excess o f triphenylphosphine (0.021 g, 0.080 mmol). The *H and P { ' H } N M R 31  spectra o f the reaction mixture indicated the formation of complex 11.  [P NNH]RuH(PPh ) (11) 2  3  A solution o f [P2NNH]Ru(C H PPh2) (2) (0.124 g, 0.138 mmol) in 25 m L toluene was 6  4  added to a glass reaction vessel equipped with a Teflon valve and a ground glass joint. The vessel was evacuated by three freeze-pump-thaw cycles and one atmosphere o f hydrogen gas was added at room temperature. The vessel was sealed and the solution was stirred for two hours. The solvent and excess H gas were then removed under vacuum. The addition o f hexanes caused the 2  deposition o f [P NNH]RuH(PPh ) (11) as an orange solid (0.109 g, 88 % ) . Crystals suitable for an 2  3  X-ray diffraction study were grown by the slow evaporation o f a saturated toluene solution. ' H N M R ( C D , 298 K, 500 MHz): 8 -15.32 (dt ( A M X ) , overlapping, J  = 16.6 Hz, J H  2  6  6  2  2  [F2m]n  [PPh3]  =  29.2 Hz, Ru-H, I H ) , 8 0.12, 0.48, 0.50 and 0.77 (s, SiCH , 24H total), 8 0.92, 1.18, 1.30 and 1.48 3  (m, PCH , 8H total), 8 1.73 (s, N-#, I H ) , 8 6.82 (m, overlapping, PPh-meta and para, 6H), 8 7.51 2  (dd, PPh-ortho, 4H).  31  P { ' H } N M R ( C D , 298 K, 202.5 MHz): 8 35.0 (d, J 2  6  6  P P  = 38 Hz, [P NNH], 2  2P), 8 72.0 (t, JPP = 38 Hz, PPh , IP). ri(min) for Ru-H = 0.370 s at 260 K in toluene-rfV 2  3  [P NND]RuD(PPh ) (11 -d ) 2  3  2  In a J-Young valve N M R tube [P NNH]RuH(PPh ) (11) (0.026 g, 0.029 mmol) was 2  3  dissolved in benzene-afe (~ 1.0 mL). The tube was degassed by two freeze-pump-thaw cycles and warmed to room temperature. A n atmosphere o f D gas was added to the tube that was then 2  sealed. After four hours the ' H N M R spectrum was recorded, and it showed resonances identical to those for 11 (above) except that the N-H and Ru-H signals were no longer present. Integration reveals > 95 % incorporation o f deuterium into these sites after this time period.  176  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  2  [NPN(H)(Ti -C H )]RuH (12) b  6  5  A solution of 3 (0.96g, 1.49 mmol) in toluene (25 mL) was degassed by performing three freeze-pump-thaw cycles.  Upon warming to room temperature an atmosphere of H gas was 2  added to the system resulting in a change in colour from red to orange. The contents were stirred for 30 minutes and then the solvent and excess H were removed under vacuum until an oily 2  residue remained.  The addition of hexanes (25 mL) caused an orange crystalline solid to  precipitate from solution. The solid was collected on a frit, rinsed with hexanes and dried under vacuum (0.42 g, 53 % ) . X-ray quality crystals were obtained by the slow evaporation of a saturated toluene solution of 12. ' H N M R (C D , 298 K, 500 MHz): 8 -7.7 (d, J 2  6  6  P H  = 47 Hz, Ru-H,  1H), 8 -0.6, 0.0, 0.3 and 0.5 (s, SiC// , 12H total), 8 1.2 (m, PC// , 4H), 8 1.6 (s, coordinated 3  2  NHPh, 1H), 8 3.5 (d, coordinated NHPh o-H, 1H), 8 4.8 (m, coordinated NHPh m-H, 1H), 8 5.0 (m, coordinated NHPh o-H,p-H, 2H), 8 5.8 (m, coordinated NHPh m-H, 1H), 8 6.6 (m, NPhp-H, 1H), 8 7.1-7.3 (overlapping m, NPh o-H, m-H and PPh m-H, p-H, 7H), 8 7.9 (dd, PPh o-H, 2H). The amino proton showed a shifted resonance in THF-</ . *H N M R (C D O, 298 K, 500 MHz): 8 8  3.9 (s, coordinated NPh-//, 1H).  3I  4  g  P { ' H } N M R (C D , 298 K, 202.5 MHz): 8 47.7 (s). ^ ( m i n ) 6  6  for Ru-// = 0.697 s at 250 K in toluene-^. Anal. Calcd. for C H N PRuSi : C, 53.60; H, 6.19; 24  33  2  2  N, 5.21. Found: C, 54.00; H, 6.38; N, 5.26.  [ N P N ( D ) ( T I - C H ) ] R U H (12-di) 6  6  5  To a solution of 12 (0.048 g, 0.009 mmol) in toluene (2 mL) was added LiN(SiMe ) 3  2  (0.016 g, 0.009 mmol). The mixture was stirred at room temperature for one hour at which time solid N E t D C l (0.014 g, 0.009 mmol) was added to the reaction mixture. After stirring for one 3  hour the mixture was filtered and the volatiles were removed under vacuum. The ' H and P { ' H } J1  N M R data of the resultant orange solid (\2-d\) is identical to that of 12, except that the N-Z/ signal at 8 1.6 is no longer observed (0.045 g, 94 % ) .  177  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  2  [NPNH ]Ru(H) (C H ) ( 1 3 ) 2  2  7  8  Complex 13 is synthesized in an identical fashion as 12.  It is isolated as a yellow  crystalline solid by the slow evaporation of the hexanes soluble rinsings of the product mixture (0.30 g, 32 % ) . X-ray quality crystals are obtained in this manner as well. H N M R (C D , 298 K, [  6  500 MHz): 5 -10.2 (d, J  6  = 43 Hz, Ru-H, 2H), 8 0.0 and 0.3 (s, SiCH , 12H total), 8 1.6 (m,  z  3  m  PCH , 4H), 8 1.9 (s, coordinated toluene, PhCZfc, 3H), 8 4.8 (m, coordinated toluene, Php-H, 1H), 2  8 5.1 (d, coordinated toluene, Ph o-H, 2H), 8 5.2 (m, coordinated toluene, Ph m-H, 2H), 8 5.5 (s, N-H, 2H), 8 6.8 - 7.3 (m, NPh o-,m-,p-H, PPh m-,p-H, 13H), 8 7.9 (dd, PPh o-H, 2H).  31  P{'H}  (C D ,298 K, 202.5 MHz): 8 32.2 (s). ft (min) for Ru-H = 0.366 s and N-H = 0.386 s at 260 K in 6  6  toluene-tfV  Anal. Calcd. for  C31H43N2PRUS12:  C, 58.92; H, 6.86; N, 4.43. Found: C, 58.64; H,  6.77; N, 4.63.  [NPNH (TI -C H )]RUH 6  2  6  5  2  (14)  Method 1: A slurry of 3 (1.19 g, 1.84 mmol) in pentane (150 mL) was degassed by three free-pump-thaw cycles and stirred under 4 atm o f H for 6 hours. The initial red mixture turned 2  brown with the formation of an orange solid. After removal of H2 in vacuo the orange solid was isolated by filtration and washed with pentane ( 2 x 1 5 mL). The orange solid was identified as complex 12 by ' H and P { H } N M R spectroscopy. 31  1  The dark brown filtrate was reduced in  volume under vacuum (~ 10 mL) allowing complex 14 to be precipitated as a brown solid over a period of 2 hours (0.31 g, 31 % ) . Method 2: In lieu of pentane, THF may also be employed as the solvent. In this case, no precipitation of an orange solid occurs. Removal of the solvent and excess H2 under vacuum generated a brown solid. The *H and P { ' H } N M R spectra indicated a 31  50:50 mixture of complexes 12 and 14. Attempts to separate the two species by rinsing with pentane were not successful. Isolation of 12 and 14 was more successful by employing method 1. ' H N M R ( C D , 298 K, 500 MHz): 8 -10.2 (dd, V 6  V  P H  6  = 40 Hz, V  H H  = 43 Hz, J 2  P H  HH  = 6 Hz, Ru-H , I H ) , 8 -9.9 (dd, a  = 6 Hz, Ru-H , I H ) , 8 -0.5, -0.1, 0.0 and 0.3 (s, S1C//3, 12H total), 8 0.85 - 1.75 b  (m, PCH , 4H), 8 1.6 (s, coordinated NHPh, I H ) , 8 4.6 (d, coordinated NHPh o-H, I H ) , 8 4.8 (d, 2  coordinated NHPh o-H, I H ) , 8 4.9 (m, coordinated NHPh p-H, IH), 8 5.4 (m, coordinated NHPh m-H, I H ) , 8 5.6 (m, coordinated NHPh m-H, I H ) , 8 5.7 (s, NHPh, I H ) , 8 6.6 - 7.2 (m, NHPh o-,  178  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  m-, p-H and PPh m-, p-H, 8H), 8 7.9 (dd, PPh o-H, 2H). The proton of the aryl-coordinated amine ligand displayed a shifted resonance in THF-J .  !  8  coordinated NPh-//, 1H).  31  H N M R ( C D 0 , 298 K, 500 MHz): 8 3.5 (s, 4  8  P { ' H } ( C D , 298 K, 202.5 MHz): 8 40.2 (s). Ti(min) for R u - / / = 6  6  0.334 s and N - / / = 0.344 s at 246 K in toluene-J . Attempts at obtaining single crystals for an X 8  ray diffraction study by the slow evaporation o f a saturated hexanes solution resulted in the deposition o f 12.  Four atmosphere hydrogenation of [ N P N D ] R U ( 1 - 3 : T | - 5 , 6 : T | - C 8 H I I ) (3-di) 3  2  [NPND]Ru(l-3:ri -5,6:ri -C Hii) (3-di) (0.058 g, 0.090 mmol) was dissolved in ~ 1.0 mL 3  2  8  o f THF-c/g and transferred to a thick-walled glass vessel fitted with a Teflon valve and a ground glass joint. The vessel was evacuated with three freeze-pump-thaw cycles, cooled in a liquid N  2  bath and then one atmosphere o f H gas was added. The flask was sealed and thawed, and the 2  mixture was stirred at room temperature for 30 minutes. The excess H gas was removed under 2  vacuum and the contents were placed in an N M R tube. The H N M R spectrum showed the clean J  formation o f a 50:50 mixture o f complexes 12 and 14 in which all o f the amino proton sites contained a hydrogen atom.  H  loss in [NPNH (ii -C6H5)]RuH2 ( 1 4 ) to give [ N P N ( H ) ( T I - C H ) ] R U H ( 1 2 ) 6  6  2  6  2  5  In an N M R tube a solution of 14 dissolved in CeD6 was left to stand for 1 week in the glove box. At this time, the *H and P { ' H } N M R data indicated the presence o f complex 12. 31  [ N P N H ] (15) 2  Toluene (25 mL) was added to a mixture o f [ N P N ] L i ' ( C H 0 ) (0.50 g, 0.84 mmol) and 2  4  8  2  NEt 'HCl (0.26 g, 1.89 mmol) contained in a glass reaction vessel equipped with a Teflon valve 3  and a ground glass joint. The vessel was sealed and heated at 80°C for two days. The solvent and other volatiles were removed under vacuum until a white solid remained. This solid was extracted  179  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine  Complexes of Ruthenium(ll) and Catalytic  2  Hydrogenation  with hexanes (25 mL) and filtered. The hexanes was removed in vacuo leaving [NPNH ] as a 2  viscous, colourless oil (0.34 g, 92 % ) . ' H N M R ( C D , 298 K, 200 MHz): 5 0.01 and 0.18 (s, 6  6  SiC// , 12H total), 5 1.12 (m, PC// , 4 H ) , 5 2.88 (s, N - f l , 2H), 8 6.98 - 8 7.58 (m, overlapping, 3  2  PCetfs, 10H total).  31  P { ' H } N M R ( C D , 298 K, 81 MHz): 8 -41.8 (s). 7i(min) for N-H = 0.614 s 6  6  at 240 K in toluene-</ . 8  [NPNH (ri -C H5)]RuHCI ( 1 6 ) (RR/SS enantiomers) 6  2  6  A slurry o f 12 (0.075 g, 0.14 mmol) and N E t H C l (0.020 g, 0.14 mmol) in 15 m L of 3  toluene contained in a sealed thick-walled glass vessel equipped with a Teflon valve and a stir bar was heated at 80°C for 24 hours. During this time the colour o f the solution changed from orange to yellow and an insoluble yellow precipitate formed. Hexanes (10 mL) was added to the reaction mixture at room temperature ensure complete precipitation and the yellow solid was collected of a frit. It was then washed with hexanes and dried under vacuum to yield [NPNH2(r| -C6H5)]RuHCl 6  (16) (0.078 g, 98 % ) . ' H N M R ( C D 0 , 298 K, 500 MHz): 8 -8.23 (d, J 2  4  8  m  = 52.2 Hz, Ru-//, 1H),  8 -0.48, -0.26, 0.08 and 0.40 (s, SiC// , 12H total), 8 1.35, 1.68, 1.95 and 2.33 (m, A B X , PC// , 4 H 3  2  total), 8 3.75 (s, coordinated NPh-//, 1H), 8 5.41 (m, coordinated NHPh m-H, IK), 8 5.60 (m, overlapping, coordinated NHPh o- and p-H, 3 H total), 8 5.92 (m, coordinated NHPh m-H, 1H), 8 5.72 (s, pendant NPh-//, 1H), 8 7.10 - 7.84 (m, ?Ph and pendant NHPh, 10H total).  31  P{'H}  N M R ( C D 0 , 298 K, 202.5 MHz): 8 45.6 (s). 4  8  [ N P N H ( T I - C H ) ] R U H C I (16) 6  2  6  5  (SR/RS enantiomers)  Leaving a solution o f 16 (RR/SS) in THF-c/ at room temperature over a period of 24 hours 8  gives rise to a second species o f 16 (SR/RS). The two complexes are present in approximately 1:1 ratio as determined by integration analysis. *H N M R ( C D 0 , 298 K, 500 MHz): 8 -8.02 (d, 4  8  J  2  m  = 55.8 Hz, Ru-//, 1H), 8 -0.25, -0.23, 0.25 and 0.48 (s, SiC// , 12H total), 8 1.05, 1.30, 1.82 and 3  1.90 (m, overlapping, PC// , 4 H total), 8 3.65 (s, coordinated NPh-//, 1H), 8 5.20 (m, coordinated 2  NHPh m-H, 1H), 8 5.58 (m, overlapping, coordinated NHPh o-H), 8 5.70 (m, coordinated NHPh  180  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  p-H,  1H), 5 5.72 (s, pendant NPh-H,  I H ) , 8 5.82 (d, coordinated NHPh o-H), 8 6.18 (m,  coordinated NHPh m-H, I H ) , 8 6.63 - 8.60 (m, overlapping, YPh and pendant NHPh).  31  P{'H}  N M R (C DgO, 298 K, 202.5 MHz): 5 43.6 (s). 4  [NPNHD(T| -C H )]RuHCI (16-di) 6  6  5  The mono-deuterated complex 16-d\ was prepared in a manner identical to that used for 16 employing N E t D C l in lieu o f N E t H C l . 3  Amounts used: 12 (0.098 g, 0.18 mmol), N E t D C l  3  3  (0.025 g, 0.18 mmol). Yield: 0.099 g, 94 %. The ' H N M R spectrum was identical to that for 16, except for the peak at 8 5.7, which was no longer observed.  Reaction of  (16-di) with KH BEt  [NPNHD(TI -C H )]RUHCI 6  6  5  3  At room temperature solid KH'BEt (0.012 g, 0.087 mmol) was added to a yellow solution 3  of [NPNHD(r| -C6H5)]RuHCl (16-d\) (0.048 g, 0.084 mmol) in THF-Jg (~ 1.0 mL). After stirring 6  the reaction mixture for one hour the colour changed to orange. At this time the *H and  31  P{ H} ]  N M R spectra were recorded and these indicated a mixture o f products including complexes 12 and 14.  Reaction of [NPNHDft -C H )]RuHCI (16-dO with LiNMe 6  6  5  2  A colourless solution of L i N M e (0.005 g, 0.098 mmol) in THF-cfe (~ 0.5 mL) was added 2  to a yellow solution of [NPNHD(ri -C6H )]RuHCl (16-Ji) (0.054 g, 0.094 mmol) in THF-dg (~ 0.5 6  5  mL).  After one hour the *H and P { ' H } N M R spectra were recorded and these indicated a 31  mixture of products including complex 12.  181  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  2  Me  [ N P N ] l _ i C H 0 (17) 2  4  8  2  A solution of 1.6 M "BuLi in hexanes (50 0 mL, 0.080 mol) was added dropwise to a stirred slurry o f M e N H H C l (2.70 g, 0.040 mol) in 100 mL ether at 0°C. The mixture was then 2  warmed to room temperature and stirred for one hour. Upon cooling to 0°C ClCH SiMe Cl (5.2 2  2  mL, 0.0400 mol) was added dropwise via syringe and the resulting mixture was stirred for one hour at room temperature. After cooling to 0°C once again, PhPH (2.20 g, 0.020 mol) was added 2  via syringe followed by the dropwise addition of "BuLi (50.0 mL, 0.080 mol). The mixture was stirred at room temperature for 18 hours and the solvents were then removed under vacuum generating a foamy yellow solid. This solid was extracted with toluene (30 mL) and filtered through Celite to remove LiCI.  Removal of the toluene in vacuo gives a yellow solid. The  addition of a minimal amount of hexanes to dissolve the yellow solid and then 1,4-dioxane (3.88 g, 0.044 mol) causes  Me  [NPN]Li 'C4H80 2  2  (17) to precipitate from solution as a white, micro-  crystalline solid (4.62 g, 56 % ) . H N M R ( C D , 298 K, 500 MHz): 8 0.1 (s, overlapping, SiC// , !  6  6  3  12H), 8 0.8 (m, PCH , 4H), 8 2.8 (s, N C / / , 6H), 8 3.6 (s, C H 0 , 8H), 8 7.1 (m, PPh p-H, I H ) , 8 3  2  7.3 (m, PPh m-H, 2H), 8 7.5 (m, PPh o-H, 2H). (s).  7  4  31  &  2  P { ' H } N M R ( C D , 298 K, 202.5 MHz): 8 -37.5 6  6  L i { ' H } N M R ( C D , 298 K): 8 2.0 (s). Anal. Calcd. for C , H L i N 0 P S i : 6  6  8  35  2  2  2  2  C, 52.41; H,  8.55; N, 6.79. Found: C, 52.70; H, 8.42; N, 7.00.  Reaction of [NPN]Li C H 0 (17) with [RuCI (cod)] Me  2  4  8  2  2  x  Toluene (30 mL) was added to a mixture of 17 (0.56 g, 1.36 mmol) and [RuCl (cod)] 2  x  (0.38 g, 1.36 mmol) and the mixture was stirred for two days at room temperature. During this time the solution turned orange-brown. The mixture was filtered through Celite and the solvent removed under reduced pressure leaving an oily solid.  The addition of hexanes caused the  deposition of an orange solid. This was collected on a frit, washed with hexanes and dried under vacuum.  The *H N M R spectrum consisted of very broad peaks indicative of a paramagnetic  complex.  182  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  Me  [NPN]ZrCl2(C4H 02) (19) 8  Toluene (30 mL) was added to a mixture o f 17 (0.210 g, 0.509 mmol) and ZrCL'2THF (0.192 g, 0.509 mmol) in a glass vessel equipped with a ground glass joint and a Teflon valve. The solid slurry was heated at 80°C for 18 hours. At room temperature the mixture was filtered through Celite. The toluene was removed under vacuum leaving an oily residue. Addition o f hexanes causes the precipitation o f [NPN]ZrCi2(C4Hg02) (19) as a white, powdered solid (0.194 Me  g, 67 % ) . ' H N M R ( C D , 298 K, 200 MHz): 5 0.01 and 0.02 (s, SiC// , 12H total), 5 1.22 (m, 6  6  3  P C # , 4H), 8 3.30 (s, C 4 W 2 , 8H), 8 3.36 (s, NC77 , 6H), 8 7.10 (m, PPh m- and p-H, 3H), 8 7.76 2  3  (m, PPh o-H, 2H).  31  P { ' H } N M R ( C D , 298 K, 81 MHz): 8 -6.3 (s). 6  6  General procedure for catalytic hydrogenation studies  Benzylidene aniline. A typical procedure is as follows: In a thick-walled glass vessel fitted with a Teflon valve and a ground glass joint was added benzylidene aniline (0.100 g, 0.54 mmol) and ~ 2 % (mole %) o f the catalyst precursor: 3 (7.0 mg), 11 (9.7 mg), 12 (5.8 mg), 13 (6.9 mg) or 14 (5.9 mg). Approximately 10 mL o f toluene was added to dissolve the solids. Degassing was accomplished by three consecutive freeze-pump-thaw cycles, and one atmosphere o f H2 gas was added at -196°C (the flask was immersed in a liquid N bath). The vessel was then sealed, 2  warmed to room temperature and the contents stirred for 48 hours. The solvent and excess H were removed in vacuo until a solid remained.  2  Approximately 1 m L o f C6D6 was added to  dissolve the solid residue and the *H N M R spectrum was obtained. Conversions were determined by integration o f substrate and product peaks. For complex 10: complex 10 was first prepared by the reaction o f 1 (8.1 mg) with hydrogen gas in an N M R tube. The contents of the N M R tube were then transferred to a thick-walled flask (as above) containing benzylidene aniline dissolved in toluene. The procedure was then continued as discussed above.  Olefin substrates. Procedures were performed in a manner identical to that employed for benzylidene aniline except that the reactions were in neat substrate. After 48 hours an aliquot o f the reaction mixture was examined via ' H N M R with a few drops o f C6D6.  183  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  X-ray Crystallographic Analyses of Complexes 11,12 and 13  Selected crystallographic data and structure refinement data are provided in Appendix 1.  3.10 References (1)  Ohkuma, T.; Kitamura, M.; Noyori, R. Asymmetric Hydrogenation; 2nd ed.; Ojima, I., Ed.;  Wiley-VCH, Inc.: Toronto, 2000, pp 1.  (2)  Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic  Chemistry: A Comprehensive Text; 6th ed.; John Wiley and Sons, Inc.: Toronto, 1999, pp 12291242.  (3)  Halpern, J. J. Organomet. Chem. 1980, 200, 133.  (4)  Harmon, R. E.; Gupta, S. K.; Brown, D. J. Chem. Rev. 1973, 73, 21.  (5)  James, B. R. Homogeneous Hydrogenation; Wiley: New York, 1973.  (6)  Calvin, M. Trans. Faraday Soc. 1938, 34, 1181.  (7)  Calvin, M. J. Am. Chem. Soc. 1939, 61, 2230.  (8)  Roelen, O. Angew. Chem. 1948, 60, 62.  (9)  Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J. Chem. Soc. A. 1966, 1711.  (10)  Magee, M . P.; Norton, J. R. J. Am. Chem. Soc. 2001,123, 1778.  (11)  Collman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition Metal  Chemistry; University Science Books: M i l l Valley, 1980, pp 316-402.  184  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  (12)  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Kubas, G. J. Metal Dihydrogen and Sigma-bond Complexes. Structure, Theory and  Reactivity; Fackler, J. P. J.,.Ed.; Kluwer Academic/Plenum Publishers: New York, 2001.  (13)  Jessop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992,727,155.  (14)  Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamin, P. J.; Wasserman, H. J. J. Am. Chem.  Soc. 1984,706,451.  (15)  Heinekey, D. M.; Oldham, J., W. J. Chem. Rev. 1993, 93, 913.  (16)  Morris, R. H.; Schlaf, M. Inorg. Chem. 1994, 33, 1725.  (17)  Kubas, G. J. Acc. Chem. Res. 1988, 21, 120.  (18)  Morris, R. H.; Earl, K. A.; Luck, R. L.; Lazarowych, N. J.; Sella, A. Inorg. Chem. 1987,  26, 261A.  (19)  Law, J. K.; Mellows, H.; Heinekey, D. M. J. Am. Chem. Soc. 2002,124, 1024.  (20)  Esteruelas, M. A.; Garcia-Yebra, C ; Olivan, M.; Onate, E.; Tajada, M. A. Organometallics  2002,27, 1311.  (21)  Law, J. K.; Mellows, H.; Heinekey, D. M. J. Am. Chem. Soc. 2001,123, 2085.  (22)  Earl, K. A.; Jia, G.; Maltby, P. A.; Morris, R. H. J. Am. Chem. Soc. 1991,113, 3027.  (23)  Chin, R. M.; Barrera, J.; Dubois, R. H.; Helberg, L. E.; Sabat, M.; Bartucz, T. Y.; Lough,  A. J.; Morris, R. H.; Harman, W. D. Inorg. Chem. 1997, 36, 3553.  (24)  Klooster, W. T.; Koetzle, T. F.; Jia, G.; Fong, T. P.; Morris, R. H.; Albinati, A. J. Am.  Chem. Soc. 1994,776,7677.  185  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  (25)  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J.; Morris, R. H.; Klooster, W. T.;  Koetzle, T. F.; Srivastava, R. C. J. Am. Chem. Soc. 1996,118, 5396.  (26)  Vaska, L.; DiLuzio, J. W. J. Am. Chem. Soc. 1962, 84, 679.  (27)  Cappellani, E. P.; Drouin, S. D.; Jia, G.; Maltby, P. A.; Morris, R. H.; Schweitzer, C. T. J.  Am. Chem. Soc. 1994,116, 3375.  (28)  Jia, G.; Morris, R. H. J. Am. Chem. Soc. 1991,113, 875.  (29)  Rocchini, E.; Mezzetti, A.; Ruegger, FL; Burckhardt, U.; Gramlich, V.; Del Zotto, A.;  Martinuzzi, P.; Rigo, P. Inorg. Chem. 1997, 36, 711.  (30)  Nishibayashi, Y.; Takei, I.; Hidai, M. Angew. Chem. Int. Ed. 1999, 38, 3047.  (31)  Majumdar, K. K.; Nanishankar, H. V.; Jagirdar, B. R. Eur. J. Inorg. Chem. 2001, 1847.  (32)  Fong, T. P.; Forde, C. E.; Lough, A. J.; Morris, R. H.; Rigo, P.; Rocchini, E.; Stephan, T. J.  Chem. Soc, Dalton Trans. 1999, 4475.  (33)  Schlaf, M.; Lough, A. J.; Maltby, P. A.; Morris, R. H. Organometallics 1996,15, 2270.  (34)  Ng, S. M.; Fang, Y. Q.; Lau, C. P.; Wong, W. T.; Jia, G. Organometallics 1998,17, 2052.  (35)  Jia, G.; Morris, R. H.; Schweitzer, C. T. Inorg. Chem. 1991, 30, 594.  (36)  Chin, B.; Lough, A. J.; Morris, R. H.; Schweitzer, C. T.; D'Agostino, C. Inorg. Chem.  1994,33, 6278.  (37)  Landau, S. E.; Morris, R. H.; Lough, A. J. Inorg. Chem. 1999, 38, 6060.  186  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  (38)  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Bianchini, C ; Marchi, A.; Marvelli, L.; Peruzzini, M.; Romerosa, A.; Rossi, R.; Vacca, A.  Organometallics 1995,14, 3203.  (39)  Jia, G.; Lee, H. M.; Williams, I. D.; Lau, C. P.; Chem, Y. Organometallics 1997,16, 3941.  (40)  Chinn, M. S.; Heinekey, D. M.; Payne, N. G.; Sofield, C. D. Organometallics 1989, 8,  1824.  (41)  Huhmann-Vincent, J.; Scott, B. L.; Kubas, G. J. J. Am. Chem. Soc. 1998,120, 6808.  (42)  Heinekey, D. M.; Voges, M. H.; Barnhart, D. M. J. Am. Chem. Soc. 1996,118, 10792.  (43)  Chinn, M. S.; Heinekey, D. M. J. Am. Chem. Soc. 1990,112, 5166.  (44)  Heinekey, D. M.; Luther, T. A. Inorg. Chem. 1996, 35, 4396.  (45)  Bianchini, C ; Meli, A.; Peruzzini, M.; Frediani, P.; Bohanna, C ; Esteruelas, M. A.; Oro,  L. A. Organometallics 1992,11, 138.  (46)  Liu, S. H.; Lo, S. T.; Wen, T. B.; Zhou, Z. Y.; Lau, C. P.; Jia, G. Organometallics 2001,  20, 667.  (47)  Jessop, P. G.; Morris, R. H. Inorg. Chem. 1993, 32,2236.  (48)  Lough, A. J.; Park, S.; Ramachandran, R.; Morris, R. H. J. Am. Chem. Soc. 1994, 116,  8356.  (49)  Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc. 1987,109,2803.  (50)  Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics 1991,10, 467.  (51)  Custelcean, R.; Jackson, J. E. Chem. Rev. 2001,101, 1963.  ] 87  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  (52)  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Crabtree, R. H.; Siegbahn, P. E. M.; Eisenstein, O.; Rheingold, A. L.; Koetzle, T., F. Acc.  Chem. Res. 1996, 29, 348.  (53)  Lee, J., J. C ; Peris, E.; Rheingold, A. L.; Crabtree, R. H. J. Am. Chem. Soc. 1994, 116,  11014.  (54)  Gusev, D. G.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 1998,120, 13138.  (55)  Abdur-Rashid, K.; Gusev, D. G.; Landau, S. E.; Lough, A. J.; Morris, R. H. J. Am. Chem.  Soc. 1998,720, 11826.  (56)  Abdur-Rashid, K.; Gusev, D. G.; Lough, A. J.; Morris, R. H. Organometallics 2000, 19,  834.  (57)  Landau, S. E.; Groh, K. E.; Lough, A. J.; Morris, R. H. Inorg. Chem. 2002, 41, 2995.  (58)  Chu, H. S.; Lau, C. P.; Wong, K. Y.; Wong, W. T. Organometallics 1998,17, 2768.  (59)  X u , W.; Lough, A. J.; Morris, R. H. Inorg. Chem. 1996, 35, 1549.  (60)  Yao, W.; Crabtree, R. H. Inorg. Chem. 1996, 35, 3007.  (61)  Schlaf, M.; Lough, A. J.; Morris, R. H. Organometallics 1996, 15,4423.  (62)  Grundemann, S.; Ulrich, S.; Limbach, H. H.; Golubev, N. S.; Denisov, G. S.; Epstein, L.  M.; Sabo-Etienne, S.; Chaudret, B. Inorg. Chem. 1999, 38, 2550.  (63)  Ayllon,  J. A.; Sayers,  S. F.; Sabo-Etienne,  S.; Donnadieu,  B.; Chaudret, B.  Organometallics 1999,18, 3981.  (64)  Ayllon, J. A.; Gervaux, C ; Sabo-Etienne, S.; Chaudret, B. Organometallics 1997, 16,  2000.  188  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  (65)  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Bennett, M. A.; Bruce, M. I.; Matheson, T. W. Comprehensive Organometallic Chemistry;  Wilkinson, S. G., Stone, F. G. A. and Abel, E. W., Ed.; Permagon Press: Toronto, 1982; Vol. 4, pp 741-742.  (66)  Liu, S. H.; Yang, S. Y.; Lo, S. T ; X u , Z.; Ng, W. S.; Wen, T. B.; Zhou, Z. Y.; Lin, Z.; Lau,  C. P.; Jia, G. Organometallics 2001, 20, 4161.  (67)  Lo, S. T ; X u , Z.; Wen, T. B.; Ng, W. S.; Liu, S. H.; Zhou, Z. Y.; Lin, Z.; Lau, C. P.; Jia,  G. Organometallics 2000,19, 4523.  (68)  Jalon, F. A.; Otero, A.; Rodriguez, A.; Perez-Manrique, M . J. Organomet. Chem. 1996,  508,69.  •  (69)  Guari, Y.; Sabo-Etienne, S.; Chaudret, B. Organometallics 1996,15, 3471.  (70)  Guari, Y.; Sabo-Etienne, S.; Chaudret, B. J. Am. Chem. Soc. 1998,120,4228.  (71)  Guari, Y.; Ayllon, J. A.; Sabo-Etienne, S.; Chaudret, B.; Hessen, B. Inorg. Chem. 1998, 37,  640.  (72)  Bautista, M.; Earl, K. A.; Morris, R. P L ; Sella, A. J. Am. Chem. Soc. 1987,109, 3780.  (73)  Jia, G.; Lau, C. P. Coord. Chem. Rev. 1999,190-192, 83.  (74)  Heinekey, D. M.; Mellows, H.; Pratum, T. J. Am. Chem. Soc. 2000, 122, 6498.  (75)  Taw, F. L.; Mellows, H.; White, P. S.; Hollander, F. J.; Bergman, R. G.; Brookhart, M . ;  Heinekey, D. M. J. Am. Chem. Soc. 2002,124, 5100.  (76)  Oldham Jr., W. J.; Hinkle, A. S.; Heinekey, D. M. J. Am. Chem. Soc. 1997,119, 11028.  189  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  (77)  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  Gusev, D. G.; Hubener, R.; Burger, P.; Orama, O.; Berke, H. J. Am. Chem. Soc. 1997,119,  3716.  (78)  Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 770,4126.  (79)  Luo, X. L.; Crabtree, R. H. Inorg. Chem. 1990,29, 2788.  (80)  Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R ; Halpern, J. J. Am. Chem. Soc. 1991, 113,  4173.  (81)  Bautista, M. T.; Earl, K. A.; Maltby, P. A.; Morris, R. H.; Schweitzer, C. T.; Sella, A. J.  Am. Chem. Soc. 1988,110, 7031.  (82)  Gusev, D. G.; Kuhlman, R. L.; Renkema, K. B.; Eisenstein, O.; Caulton, K. Inorg. Chem.  1996, 35, 6775.  (83)  Luther, T. A.; Heinekey, D. M. Inorg. Chem. 1998, 37, 127.  (84)  Heinekey, D. M.; Oldham Jr., W. J. J. Am. Chem. Soc. 1994,116, 3137.  (85)  Hamilton, D. G.; Luo, X . L.; Crabtree, R. H. Inorg. Chem. 1989,28, 3198.  (86)  Paneque, M.; Poveda, M. L.; Taboada, S. J. Am. Chem. Soc. 1994,116,4519.  (87)  Luo, X. L.; Crabtree, R. H. J. Am. Chem. Soc. 1990,112, 6912.  (88)  Bampos, N.; Field, L. D. Inorg. Chem. 1990, 29, 587.  (89)  King, W. A.; Scott, B. L.; Eckert, J.; Kubas, G. J. Inorg. Chem. 1999, 38, 1069.  (90)  Gutierrez-Puebla, E.; Monge, A.; Paneque, M.; Poveda, M. L.; Taboada, S.; Trujillo, M.;  Carmona, E. J. Am. Chem. Soc. 1999,121, 346.  190  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  (91)  Heinekey, D. M.; Hinkle, A. S.; Close, J. D. J. Am. Chem. Soc. 1996,118, 5353.  (92)  Saunders, M.; Jaffe, M. H.; Vogel, P. J. Am. Chem. Soc. 1971, 93, 2558.  (93)  Saunders, M.; Kates, M. R. J. Am. Chem. Soc. 1977, 99, 8071.  (94)  Saunders, M.; Telkowski, L.; Kates, M. R. J. Am. Chem. Soc. 1977, 99, 8070.  (95)  Bullock, R. M.; Song, J. S.; Szalda, D. J. Organometallics 1996, 75, 2504.  (96)  Yao, W.; Faller, J. W.; Crabtree, R. H. Inorg. Chim. Acta 1997, 259,11.  (97)  Abdur-Rashid, K.; Gusev, D. G.; Lough, A. J.; Morris, R. H. Organometallics 2000, 19,  1652.  (98)  Sabo-Etienne, S.; Chaudret, B. Coord. Chem. Rev. 1998,178-180, 381.  (99)  Rodriguez, V.; Sabo-Etienne, S.; Chaudret, B.; Thoburn, J.; Ulrich, S.; Limbach, H. H.;  Eckert, J.; Barthelat, J. C ; Hussein, K.; Marsden, C. J. Inorg. Chem. 1998, 37, 3475.  (100) Borowski, A. F.; Sabo-Etienne, S.; Christ, M . L.; Donnadieu, B.; Chaudret, B. Organometallics 1996,15, 1427.  (101)  Shubina, E. S.; Belkova, N. V.; Krylov, A. N.; Vorontsov, E. V.; Epstein, L. M.; Gusev, D.  G.; Niedermann, M.; Berke, H. J. Am. Chem. Soc. 1996, 775, 1105.  (102) Esteruelas, M. A.; Oro, L. A.; Valero, C. Organometallics 1992, 77, 3362.  (103) Esteruelas, M. A.; Oro, L. A. Chem. Rev. 1998, 98, 577.  191  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  (104) Jackson, S. A.; Hodges, P. M.; Poliakoff, M.; Turner, J. J.; Grevels, F. W. J. Am. Chem. Soc. 1990,772, 1221.  (105) Jia, G.; Ng, W. S.; Lau, C. P. Organometallics 1998,17,4538.  (106) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals; 2nd ed.; John Wiley and Sons: New York, 1994, pp 221.  (107) Perrin, C. L.; Dwyer, T. J. Chem. Rev. 1990, 90, 935.  (108)  Jeener, J.; Meier, B. H.; Bachmann, P.; Ernst, R. R. J. Chem. Phys. 1979, 71, 4546.  (109) Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics 2001, 20, 1047.  (110)  Abdur-Rashid, K.; Faatz, M.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2001, 123,  7473.  (111) Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics 2000,19, 2655-2657.  (112) Boncella, J. M.; Eve, T. M.; RickMan, B.; Abboud, K. A. Polyhedron 1998, 77, 725.  (113) Patel, B. P.; Wessel, J.; Yao, W.; Lee, J., J. C ; Peris, E.; Koetzle, T. F.; Yap, G. P. A.; Fortin, J. B.; Ricci, J. S.; Sini, G.; Albinati, A.; Eisenstein, O.; Rheingold, A. L.; Crabtree, R. H. NewJ. Chem. 1997, 27,413.  (114)  Simal, F.; Jan, D.; Demonceau, A.; Noels, A. F. Tetrahedron Lett. 1999, 40, 1653.  (115) Torres, F.; Sola, E.; Martin, M.; Ochs, C ; Picazo, G.; Lopez, J. A.; Lahoz, F. J.; Oro, L. A. Organometallics 2001, 20, 2716.  (116) Park, S.; Lough, A. J.; Morris, R. H. Inorg. Chem. 1996, 35, 3001.  192  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  (117) Chu, H. S.; Lau, C. P.; Wong, K. Y. Organometallics 1998,17, 2768.  (118) Dewey, M. A.; Stark, G. A.; Gladysz, J. A. Organometallics 1996, 15,4798.  (119) Bryndza, H. E.; Dornaille, P. J.; Paciello, R. A.; Bercaw, J. E. Organometallics 1989, 5, 379.  (120) Brunner, H. Adv. Organomet. Chem. 1980,18, 152.  (121) Martin, G. C ; Boncella, J. M.; Wucherer, E. J. Organometallics 1991,10, 2804.  (122) Bickford, C. C.; Johnson, T. J.; Davidson, E. R ; Caulton, K. G. Inorg. Chem. 1994, 33, 1080.  (123) Johnson, T. J.; Folting, K.; Streib, W. E.; Martin, J. D.; Huffman, J. C ; Jackson, S. A.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995, 34, 488.  (124) Heller, D.; Drexler, H.; Spannenberg, A.; Heller, B.; You, J.; Baumann, W. Angew. Chem. Int. Ed. 2002, 41, 111.  (125) Wiles, J. A.; Bergens, S. H. Angew. Chem. Int. Ed. 2001, 40, 914.  (126) Dobbs, D. A.; Vanhessche, K. P. M.; Brazi, E.; Rautenstrauch, V.; Lenoir, J. Y.; Genet, J. P.; Wiles, J.; Bergens, S. H. Angew. Chem. Int. Ed. 2000, 39, 1992.  (127) Rossen, K. Angew. Chem. Int. Ed. 2001, 40, 4611.  (128)  James, B. R. Catalysis Today 1997, 3 7, 209.  (129) Fryzuk, M. D.; Piers, W. E. Organometallics 1990, 9, 986.  \  193  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine 2  Complexes of Ruthenium(ll) and Catalytic Hydrogenation  (130) Noyori, R.; Ohkuma, T. Angew. Chem. Int. Ed. 2001, 40,40.  (131)  Gruet, K.; Crabtree, R. FL; Lee, D. H.; Liable-Sands, L.; Rheingold, A. L. Organometallics  2000,19, 2228.  (132) Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998,120, 11024.  (133) Fryzuk, M. D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S. A.; Koetzle, T. K. J. Am. Chem. Soc. 2001,123, 3960.  (134) Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1.  (135) Hartwig, J. F. J. Am. Chem. Soc. 1996,118, 7010.  (136)  Cetinkaya, B.; Lappert, M. F.; Torroni, S. Chem. Commun. 1979, 599.  (137) Bullock, R. M.; Voges, M. H. J. Am. Chem. Soc. 2000,122, 12594.  (138) Bullock, R. M.; Rappoli, B. J. J. Chem. Soc, Chem. Commun. 1989, 1447.  (139)  Song, J. S.; Szalda, D. J.; Bullock, R. M.; Lawrie, C. J. C ; Rodkin, M. A.; Norton, J. R.  Angew. Chem. Int. Ed. Engl. 1992, 31, 1233.  (140) Johnson, S. A. Ligand Design and The Synthesis ofReactive Organometallic Complexes of Tantalum for Dinitrogen Activation; University o f British Columbia: Vancouver, 2000.  (141) Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997, 275, 1445.  (142) Baudler, M.; Zarkdas, A. Chem. Ber. 1965,104,1034.  194  References begin on page 184  Chapter 3: Heterolytic Activation of Dihydrogen (H ) by Amidophosphine Complexes of Ruthenium(ll) and Catalytic Hydrogenation 2  (143)  Manzer, L. E. Inorganic Synthesis 1982, 21, 135.  195  References begin on page 184  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and Complexes  /P /\y 2  with Ruthenium(ll)  Alkylidene  and  Vinylidene  Chapter 4  Reaction of the Amidophosphine Ligands [NPN] and [P N ] with Ruthenium(ll) Alkylidene and Vinylidene Complexes 2  4.1  Introduction Transition metal catalyzed olefin metathesis is an important method for the formation  of carbon-carbon bonds. ' 1  2  Some o f the diverse applications o f olefin metathesis include the  formation o f heterocycles by ring-closing metathesis ( R C M ) , ' >  3-9  by ring-opening metathesis polymerization ( R O M P ) , ' - - -  and the preparation o f new  1  substituted acyclic development  of  olefins by cross metathesis. ' ' 1  well-defined  ruthenium(II)  (PCy3)2Ci2Ru(CHPh) (A in Figure 4.1)  five-coordinate  13-15  1 4  1 6 - 2 5  10  12  During the last decade the complexes  has  allowed  for  The ruthenium benzylidene complex  is one example o f these complexes that have been  utilized for the olefin metathesis reaction. catalyst, is  4  alkylidene  tremendous progress to be made in this a r e a . ' 1 3  4  3  the synthesis o f polymers  13  Complex A, commonly referred to as Grubbs'  and exhibits a distorted square pyramidal geometry with the  196  References  begin on page 237  2  Chapter 4: Reaction of the Amidophosphine  [P2N2] with Ruthenium(ll)  Ligands [NPN] and Complexes  Alkylidene  and  Vinylidene  mutually trans phosphine and chloride ligands in the plane o f the molecule, and the benzylidene unit at the vertex o f the pyramid.  Both experimental and theoretical studies  implicate phosphine dissociation generating a 14-electron mono-phosphine benzylidene species as the initial step in the catalytic process. Substrate coordination to the vacant site allows for olefin metathesis to proceed via a metallocyclobutane intermediate. mechanism is depicted in Figure 4 . 1 .  Other ruthenium "alkylidene-type" complexes  2 6 - 2 9  have also found success in olefin metathesis processes. (M=C=C) 3 0  3 3  This  and allenylidene ( M = C = C = C ) > 32  34  41  Among these include vinylidene  complexes o f ruthenium(II). The ease o f  synthesis compared to that o f the Grubbs' catalyst is an attractive feature o f the vinylidene and allenylidene metal complexes.  .Ph  Ph  R  ^ C l  3  Cl  Cy P3  ci-**""  + PCy  1  PCy  -PCy  ci*  3  ci-  -RCt  3  .Ph  +  o  l  e  f  i  n  ^"•Cl  Ru'  - olefin  -  C y  3  F ^ ^  |  RU^  Cl*  Cl-  I  r.  R  R  2  Figure 4 . 1 . The mechanism for olefin metathesis utilizing the Grubbs' catalyst ( A ) . A cross metathesis reaction is shown.  The presence o f a labile phosphine donor and the two chloride ligands in the benzylidene complex A suggested that it may be a suitable precursor for the coordination o f the  [P2N2] and [NPN] ligands. This chapter discusses our attempts at isolating ruthenium(II) 197  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  alkylidene complexes containing the [NPN] and [P2N2] ligand sets and utilizing these species in olefin metathesis processes.  Our initial investigations involved the Grubbs' catalyst  (PCy3)2Cl Ru(CHPh) as a starting material, however, due to difficulties that we encountered 2  in the coordination o f the [NPN] and [P2N2] ligands with this complex we examined related vinylidene precursors, (P Pr ) Cl Ru(CCRPh) (R = H or SiMe ). i  3  4.2  2  2  3  Reaction of [NPN]Li (C H 0) 2  4  8  and [P N ]Li (C H 0 ) with  2  2  2  2  4  8  2  (PCy ) CI Ru(CHPh) 3 2  2  The reaction o f the [NPN] and [P2N2] ligands with the alkylidene  complex  (PCy )2Ci2Ru(CHPh) did not give clean formation o f the expected substitution products 3  [NPN](PCy )Ru(CHPh) or [P N ]Ru(CHPh); rather, a mixture o f products resulted as 3  2  indicated by the ' H and  3 1  2  P { ' H } N M R data.  Variation in the solvent employed or the  reaction temperature had no significant effect on the outcome o f the reactions. It is possible that the bulky and basic PCy ligands may not allow for facile substitution to take place, and 3  consequently other avenues for reaction may be more likely. A potential competitive sidereaction could be the deprotonation o f the alkylidene proton to give a ruthenium carbyne (Ru=CPh) complex. intermediate  in the hydrogen-deuterium  (PCy )2Ci2Ru(CHPh). 3  A ruthenium carbyne complex has been suggested as a probable  42  exchange reactions o f the starting  material  Several cationic ruthenium carbyne-hydride species have recently  been isolated from ruthenium vinylidene complexes. ' 43  44  In contrast, metathetical and substitution reactions have been successfully employed with the Grubbs' complex (PCy ) Ci2Ru(CHPh). For example, its reaction w i t h an excess o f 3  2  K O ' B u generates the four coordinate species (PCy )(T3uO) Ru(CHPh), 3  2  45  and the addition o f  K T p (where Tp = tris(pyrazolyl)borate) allows for the preparation o f the neutral sixcoordinate complex Tp(PCy )(Cl)Ru(CHPh) containing the chelating Tp l i g a n d 3  4 6  The  substitution reactions o f Grubbs' complex with bidentate Schiff-base ligands incorporating substituted phenoxy donors was performed after converting the ligands to the corresponding  198  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  thallium salts, as shown in Scheme 4 . 1 .  4 7  Alkylidene  and  Vinylidene  Among the various salts tested the thallium salts  proved to be the most effective, however, the efficiency of the substitution reactions varied depending on the bulk of the substituents on the ligands. For example, while ligands bearing a methyl group at the 6-position o f the phenoxy fragment readily underwent substitution, the reaction o f ligands bearing the bulkier tertiary butyl substituent at the same position gave poor conversion under similar substitution conditions.  Scheme 4.1  These studies show that subtle differences in the electronic and steric properties o f the ligands can influence the outcome o f the substitution reactions. The successful incorporation o f the [NPN] and [ P N ] ligands onto (PCy ) Cl Ru(CHPh) may be possible by employing 2  2  3  2  2  other salts o f these ligands, such as potassium or thallium. This w i l l be addressed in the Future W o r k section o f this chapter (section 4.9).  199  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  4.3  [P2NJ with Ruthenium(ll)  Ligands [NPN] and Complexes  Alkylidene and Vinylidene  Synthesis and Characterization of [NPNH](PPr )Ru(CCPh) i  3  (20)  (i)  Reaction of [NPN]Li (C 4 H 8 0) 2 with (P Pr ) CI Ru(CCHPh) i  2  3  2  2  Initial investigations into the reaction o f the [ N P N ] ligand with the vinylidene complex (P'Pr3)2Cl2Ru(CCHPh) utilized tetrahydrofuran as the solvent. change in colour from purple to dark brown takes place at room temperature.  A n immediate The P { H } 3 1  1  N M R spectrum o f the crude product mixture shows the presence o f two products and triisopropylphosphine.  The same results are obtained when the reaction is performed at  -78 °C and then warmed to room temperature. The major species (ca. 60 %) contains two doublets in the P { ' H } N M R spectrum at 8 45.9 and 5 80.5 ( J 3 1  2  P P  = 48 Hz), and the minor  species contains two doublets at 8 57.1 and 8 76.4 (VPP = 41 H z ) . These similar spectral features suggest that the two products may be structurally related.  The doublet coupling  pattern arises due to the presence o f a coordinated P'Pr ligand and a coordinated [ N P N ] 3  ligand, and the small phosphorus-31 coupling constants indicate a cis arrangement between the phosphine donors in both complexes. The ' H N M R spectrum shows resonances that are commonly observed for metal complexes containing the [NPN] ligand set. The inequivalent silyl methyl and aromatic proton resonances suggest that both species posses low symmetry in solution. I n the ruthenium precursor, the (3-hydrogen atom o f the vinylidene moiety is observed as a well-resolved triplet at 8 4.6 due to coupling with the two equivalent P'Pr3 ligands. I f the substitution product [NPN](P'Pr )Ru(CCHPh) was produced this resonance 3  may be expected to appear as a higher-order multiplet arising from coupling with the two different phosphine ligands.  Although no such resonance is apparent in the ' H N M R  spectrum o f the crude product mixture, two singlets are observed at 8 4.9 (minor species) and 8 5.1 (major species) suggesting that a vinylidene moiety may not be present in the products o f this reaction.  This implies that displacement o f the two chloride ligands and one  equivalent o f P'Pr  3  by the chelating [ N P N ] donor to yield the anticipated complex  [NPN](P Pr3)Ru(CCHPh) did not occur. l  known to be a c i d i c ,  48-50  The [3-hydrogen atom o f the vinylidene unit is  and it is therefore possible that deprotonation by one o f the amido  200  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2NJ with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  donors o f the [NPN] ligand set has occurred. Attempts at separating the two products o f this reaction were unsuccessful due to the similar solubilities o f these species in hydrocarbon solvents, and consequently, further structural elucidation was not possible.  Given the success utilizing toluene as the solvent for the reactions o f the [ N P N ] ligand with the starting material [RuCl (cod)] the above reaction was also attempted in 2  x  toluene. The initial purple coloured solution gradually lightens to a violet colour within 30 minutes at room temperature; after two hours the solution is dark brown, similar to what is observed when the reaction is performed i n THF.  The ' H and P { * H } N M R data o f the 31  crude product show the formation o f a single species (20) and free P Pr3. Interestingly, this l  new species exhibits spectra identical to those o f the minor product when the reaction was performed in THF. Purification o f this complex was accomplished by the slow evaporation o f a hexanes solution, which results i n the deposition o f purple block crystals. The isolated yield o f 20 is low, however, due to the high solubility o f this species i n hexanes.  (ii)  Solid-state and solution characterization of [NPNH](P Pr )Ru(CCPh) (20) i  3  The solid-state infra-red spectrum ( K B r pellet) o f a sample o f powdered crystals o f complex 20 shows significant differences than that o f the precursor vinylidene complex. For example, the vinylidene (C=C) band occurs at 1600 cm" i n (P Pr ) Cl Ru(CCHPh), 1  i  3  2  51  2  however, no such peak is evident in the I R spectrum o f 20. Rather a peak at 2050 cm' is 1  observed consistent with the presence o f a carbon-to-carbon triple bond (C=C).  In  comparison, the spectrum o f the complex [Ru(C=CPh)(PPh3) (r) -C5Me5)] contains v(C=C) 5  2  at 2066 c m " . 1  48  I n addition, a peak at 3194 cm" is indicative o f an N - H stretching mode. 1  Based on the I R data we propose the formulation o f complex 20 as [NPNH](P Pr )Ru(CCPh), 1  3  in which proton transfer from the vinylidene moiety to one o f the amido donors generates an [ N P N H ] chelating array and a c-alkynyl ligand (equation 4.1). Elemental analysis supports this formulation.  201  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine Ligands [NPN] and [P2NJ with Ruthenium(ll) Alkylidene and Vinylidene Complexes  H  Ph—P-MJJ-  N  Me  P h  C  1  T  H  F  -Cl  'Pr P3  K 2  \^  n  Cl-  Ru^  -P'Pr  3  [4.1] Ph  toluene  Me Si/^T 2  Me Si\  -2LiCI -P'Pr  2  \  ^P'Pr  3  3  Th  PR  20  The structure o f 20 was verified by a single crystal X-ray diffraction study.  The  solid-state molecular structure is shown in Figure 4.2 and selected bond lengths and angles are listed in Table 4 . 1 . As seen from the ORTEP drawing, complex 20 has a distorted square pyramidal structure with the phosphine donor o f the chelating [ N P N H ] ligand set at the apical position. The Ru-P distance for this ligand is significantly shorter than that to the P Pr l  ligand (2.1901(6) A vs. 2.3131(6) A).  3  The shorter bond distance is most likely a  consequence o f the vacant site located trans to the chelating phosphine donor.  The solid-  state molecular structure confirms the presence o f a terminal alkynyl ligand in complex 20 as indicated by the short carbon-carbon bond length (1.222(3) A) and the linearity o f the R u ( l ) C(34)-C(35) and C(34)-C(35)-C(36) bonds (ca. 177° and 174°, respectively).  The amino  proton H(58) was located confirming that proton transfer from the vinylidene moiety has occurred.  The ruthenium-amide distance in 20 (2.189(2) A) is longer than that observed in complex 3 (2.019(2) A). Although both complexes are five-coordinate ruthenium(II) species, 20 is square pyramidal whereas 3 adopts a distorted trigonal bipyramidal geometry (or Y shape). As was discussed in chapter 2, the presence o f a single 7t-donating ligand in d  202  6  ML  5  References begin on page 237  Chapter 4: Reaction of the Amidophosphine Ligands [NPN] and [P2N2] with Ruthenium(ll) Alkylidene and Vinylidene Complexes  complexes usually favours a distorted trigonal bipyramidal structure since this allows for multiple bonding between the empty metal J-orbital (d )  and the lone pair o f the n-  xy  donor. * 52  53  This manifests as a shortening o f the M - X bond.  In the case o f a square  pyramidal geometry such a ^-interaction is not possible because all o f the symmetry adapted a'-orbitals are f i l l e d . ' 52  53  In complex 20 there is an intramolecular hydrogen bonding  interaction between the amido nitrogen lone pair and the proton o f the c i s coordinated amine donor.  The N(2) "H(58) separation o f 2.367 A is well within the van der Waals contact  distance o f 2.7 A between nitrogen and hydrogen n u c l e i .  54  Since the amide lone pair  partakes in this interaction it is not available for 7t-bonding with the metal centre and this may be the reason that a distorted trigonal bipyramidal geometry is not observed. Alternatively, a square planar structure may allow for minimized steric interactions. As can be seen in Figure 4.2, the phenyl groups o f the amido and amino donors are oriented towards the open face o f the molecule. In a Y-shaped structure either the alkynyl ligand or the P'Pr^ ligand would be located adjacent to these phenyl substituents, thus, increasing the steric interactions between these groups.  As seen in the ORTEP drawing, the [ N P N H ] phenyl  groups as well as the P'Pr3 methyl groups can shield the vacant site at the metal centre.  203  References begin on page 237  Chapter 4: Reaction of the Amidophosphine Ligands [NPN] and [P2N2] with Ruthenium(ll) Alkylidene and Vinylidene Complexes  Figure 4.2.  ORTEP representation (50% thermal ellipsoids) o f the solid-state molecular  structure o f [NPNH](P Pr )Ru(CCPh) (20) as determined by X-ray diffraction. i  3  The silyl  methyl groups o f the [ N P N H ] ligand and the isopropyl methyl groups o f the P'Pr ligand 3  have been omitted for clarity. The amino proton H(58) was located.  Table 4.1. Selected bond lengths and bond angles i n [NPNH](P Pr )Ru(CCPh) (20). i  3  Atom Ru(l) Ru(l) Ru(l)  Ru(D  Atom P(l) P(2) N(l) N(2)  Distance (A)  Atom  Atom  2.1901(6) 2.3131(6) 2.259(2) 2.189(2)  Ru(l) C(34) N(l) N(2)  C(34) C(35) H(58) H(58)  204  Distance (A) 2.003(2) 1.222(3) 0.842 2.367  References begin on page 237  Chapter 4: Reaction of the Amidophosphine  Atom N(l) N(l) N(l)  N(2) N(2) P(2) P(D  Atom Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) Ru(l)  Atom  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Angle (°) 80.59(7) 93.33(8) 169.79(5) 99.97(5) 173.22(8) 85.48(6) 100.44(2)  N(2) C(34) P(2) P(2) C(34) C(34) P(2)  Atom  Atom  Atom P(l) P(l) P(l) Ru(l) C(34) Ru(l) N(l)  Ru(l) Ru(l) Ru(l) C(34) C(35) N(l) H(58)  Alkylidene  N(2) C(34) C(35) C(36) H(58) N(2)  !  spectroscopy.  Vinylidene  Angle (°) 89.78(5) 87.24(5) 95.80(6) 176.5(2) 174.4(2) 94(2) 119.67  N(l)  Complex 20 has also been characterized in solution by H and  and  3 1  P{'H}  NMR  The ' H N M R spectrum indicates the presence o f a single, non-fluxional  species; furthermore, the number o f peaks that are observed reveals that the complex possesses low symmetry. This is consistent with the solid-state structure, which shows that complex 20 exhibits C\ symmetry, and contains a chiral metal centre as well as chiral amine, amide and phosphine ligands. For example, four silyl methyl proton resonances and four methylene resonances o f the tridentate ligand backbone are observed. A multiplet at 8 2.10 that integrates to three protons has been assigned as the methine hydrogen atoms o f the P'Pr3 ligand and the two diastereotopic methyl groups o f the P'Pr ligand are observed at 8 0.92 3  and 8 1.08. The presence o f a single peak for the methine hydrogen atoms and two peaks for the methyl groups o f the P'Pr ligand indicate that there is free rotation about the ruthenium3  phosphorus bond, but hindered rotation about the phosphorus-carbon bonds within this ligand. The amino proton appears as a singlet at 8 4.95 and the aromatic protons in complex 20 are dispersed between 8 5.75 and 8 8.08. In the ?{ U} 3l  l  N M R spectrum, the P T ^ ligand  exists as a doublet at 8 57.0 and the phosphorus signal for the phosphine donor o f the [ N P N H ] ligand occurs as a doublet at 8 76.5. These assignments were made by performing selective ' H { P } decoupling experiments. 3 1  The magnitude o f coupling between these two  sites (VPP = 41 Hz) implies a cis orientation between the phosphine ligands consistent with that observed in the solid state.  205  References  begin on page 237  Chapter 4: Reaction  (iii)  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  Speculations into the identity of the second species that forms in THF  It is interesting that a simple modification in the synthetic procedure (i.e. changing the solvent from T H F to toluene) would have such a drastic effect on the outcome o f this reaction. The formation o f a single species (20) when the reaction is performed in toluene as opposed to two products in T H F is not easy to rationalize; it is also intriguing that complex 20 forms as the sole product in toluene but would form as the minor species in THF. The characterization o f 20 allows for speculations regarding the identity o f the second species that forms in THF. The similar ' H and P { H } N M R data o f these two compounds suggests 3 1  1  that they are structurally related. It has already been mentioned that 20 is a chiral complex, and it is therefore likely that the unknown species is a diastereomer o f 20. Two examples are shown in Figure 4.3. Isomer A exhibits a distorted trigonal bipyramidal geometry with the P Pr3 ligand in the plane o f the molecule; this is a necessary condition given the small l  coupling (48 Hz) between the two phosphine donors. We have already suggested that such a structure would be unfavourable for steric reasons.  Furthermore, there is no electronic  stabilization since the amido donor is not located opposite the acute angle in the trigonal plane allowing for 71 overlap with the metal d  orbital. 52  xy  53  Similar to complex 20, isomer B  also possesses a square pyramidal structure, however, the alkynyl and amine ligands are now located trans to one another as are the amido and P Pr3 ligands. l  Isomer B could be  envisioned as forming via transfer o f the amino proton to the amido nitrogen atom in complex 20.  We have already established that proton transfer is a common occurrence in  other [P2NNH] and [NPNH] complexes o f ruthenium. In fact, this proposal resembles the mechanism portrayed in Scheme 2.7 for the formation o f complex 2.  In that circumstance  the thermodynamic product also contained trans phosphine and amido donors as well as amine and a-bound carbon ligands. I f complex 20 is the kinetic product o f this reaction it may be possible that proton transfer to yield the thermodynamic product (B) may not proceed in toluene but may be mediated in more polar solvents such as THF. For these reasons we favour isomer B as the second species that forms in T H F although isomer A cannot be ruled out definitively.  206  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  A  Figure 4.3.  Alkylidene  and  Vinylidene  B  Two possible diastereomers o f complex 20.  Isomer A is distorted trigonal  bipyramidal (Y-shape) and isomer B is square pyramidal.  4.4  Reaction of [NPNHHP'PraJRufCCPh) (20) with H Since the reaction between the [NPN]  2  ligand and the vinylidene  precursor  (P'Pr3)2Cl2Ru(CCHPh) did not yield a product containing a Ru=C double bond, olefin metathesis reactivity could not be investigated. The presence o f a ruthenium-amido linkage, however, prompted us to investigate the ability o f complex 20 to heterolytically activate H . 2  Upon exposure of a solution o f 20 to an atmosphere o f hydrogen gas an immediate change in colour from violet to orange takes place. The ' H N M R spectrum shows the formation o f a single, symmetrical ruthenium polyhydride complex. The [NPNH] ligand gives rise to two resonances for the silyl methyl protons and two sets o f multiplets for the methylene protons. There is a single peak for the ortho protons o f the phosphine phenyl group. A broad peak at 8 3.98 that integrates to two proton environments has been assigned as equivalent N - H protons. The presence o f two amino protons implies that heterolysis o f a molecule o f H has 2  occurred. The methyl groups o f the P'Pr3 ligand are also equivalent and occur as a multiplet at 8 0.98. The hydride region o f the H N M R spectrum consists o f a single resonance that !  appears as an overlapping set o f doublets and integrates to six proton equivalents. The *H  207  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine Ligands [NPN] and [P2N2] with Ruthenium(ll) Alkylidene and Vinylidene Complexes  N M R spectrum also shows the presence o f ethyl benzene, a hydrogenation by-product from this reaction. The P { ' H } N M R spectrum contains two doublets at 8 25.0 and 8 86.0 with a 3 1  large coupling o f 225 Hz indicating a trans arrangement o f the two phosphine ligands within the complex.  A portion o f the  3 1  P { H } N M R spectrum that contains these resonances is 1  shown in Figure 4.4.  1  M I I I I I  I  I I  I I I I I I I  100  I  I  I  I I I II I I  I  I  80  1  I I I I I I I  60  ;I  I I I M I  1  40  I  I  I I  I I I I I I I  I  I  I  I I M I I  20  I  I  I II I I I I  I I  I  I I  I I I I I M  I  I  I I I I M I I  0  (ppm)  Figure 4.4.  The P { H } N M R spectrum for the reaction o f 20 with H . The magnitude o f 3 1  1  2  coupling for the two doublets is 225 Hz.  The integration o f six protons for the hydride signal in this new complex suggested the existence o f one or more coordinated dihydrogen ligands. Since only one resonance is observed these rj -bound moieties must be in fast exchange with any classical hydride 2  ligands that may also be present. The two most likely candidates that satisfy these conditions are the ruthenium ( I V ) species [NPNH ](P Pr )Ru(Ti -H2)(H)4, and a ruthenium(II) bis i  2  2  3  dihydrogen complex, [NPNH ](P'Pr3)Ru(r| -H2)2(H)2. 2  2  A survey o f the literature indicates  that although bis dihydrogen complexes are not that common there are several examples o f structurally characterized late transition metal complexes containing two intact dihydrogen  208  References begin on page 237  I  1  I I I I I  Chapter 4: Reaction of the Amidophosphine  moieties;  some  representative  Ligands [NPN] and /P Ay with Ruthenium(ll) Complexes 2  examples  complexes are shown in Figure 4 . 5 . ' 5 5  Alkylidene and  o f octahedral ruthenium(II)  Vinylidene  bis dihydrogen  5 6  R" = Pr or Cy  R = H or Me  J  Figure 4 . 5 . Some examples o f octahedral ruthenium(II) bis dihydrogen complexes.  Based on the many similarities that are observed in the solution N M R data for this new species with known bis dihydrogen complexes we propose that the reaction o f complex 20 with H generates [NPNH ](P Pr3)Ru(Ti -H2)2(H)2 (21), as illustrated in equation 4.2. The i  2  2  2  trans disposed phosphine ligands are in accordance with known complexes, and is verified by the large phosphorus-phosphorus scalar coupling (225 Hz). The observation o f a single "hydride" resonance is a common feature in these types o f complexes and indicates that the dihydrogen and hydride ligands undergo facile exchange within the equatorial plane o f the molecule.  The mechanism for this dynamic process can occur via the formation o f a  transient trihydrogen complex in a similar fashion to that depicted in Figure 3.8 for the exchange o f hydride and dihydrogen environments in complex 10. This fluxional process, in addition to free rotation o f the two phosphine ligands about the Ru-P bonds accounts for the high symmetry for complex 21 that is observed in solution.  L o w temperature spectra o f  complex 21 in toluene-Jg (as low as 180 K ) show no significant deviations from its room temperature spectrum indicating that the dynamic behaviour o f 21 is maintained at low temperatures. As shown in equation 4.2, a "static" complex 21 contains a mirror plane o f  209  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine Ligands [NPN] and [P2N2] with Ruthenium(ll) Alkylidene and Vinylidene Complexes  symmetry lying in the P-Ru-P plane bisecting the H-Ru-H angle, and therefore possesses C  s  symmetry.  Ph Me Si;  \  2  M e 2 S i  VN.  H  -P'Pr.  2  (1  atm) [4.2]  - CH CH Ph  / H Ph  3  2  Ph 21  20  To confirm the presence o f a dihydrogen ligand within complex 21 the minimum o f the longitudinal relaxation time ( f t (min)) for the metal-bound hydrogen atoms was measured.  57-59  Using an inversion-recovery pulse sequence this value was determined to be  51 ms at 220 K and 500 M H z in toluene-Js, consistent with the presence o f at least one coordinated H2 ligand in 21.  This value corresponds well with the fti(min) values that have  been measured in related bis dihydrogen complexes; ' 55  Table 4.2.  56  some examples are highlighted in  Also listed in Table 4.2 are the chemical shift, multiplicity and phosphorus  coupling constants o f the "hydride" ligands as well as the chemical shift o f the phosphine ligands. The most significant difference between complex 21 and the other bis H complexes 2  is the coupling pattern that is observed for the hydride resonance.  In the P'Pr3 and PCy3  complexes for instance, a triplet pattern arises due to coupling with the two equivalent phosphine ligands.  In the case o f 21  the two phosphine ligands are different, and  consequently an overlapping pair o f doublets is observed. By performing selective * H { P } 31  decoupling experiments the magnitude o f coupling to each o f the phosphine ligands was determined. The phosphine donor o f the [ N P N H ] ligand gives rise to a 7.6 Hz coupling, and the  P'Pr3  ligand couples to the Ru-H ligands with a magnitude o f 6.7 Hz.  210  References begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene and Vinylidene  A comparison o f hydride chemical shift (8H), multiplicity (m), VPH and r i ( m i n )  Table 4.2.  values for the hydride ligands as well as phosphine chemical shifts (8p) in complex 21 and related bis dihydrogen complexes.  Complex  8  21 (P Pr ) Ru(H ) (PCy )2Ru(H ) i  3  2  6  3  6  m  (ppm) -7.60 -8.31 -7.90  H  (Hz)  J?H  2  d t t  6.7, 7.6 8.0 7.0  T^min) (ms)  8 (ppm)  51"  86.0, 25.0 88.4 76.5  45  b  28  c  P  " 220 K, 500 M H z , toluene-^ 193 K, 300 M H z , toluene-^ (Ref. 56) 203 K, 250 MHz, toluene-d (Ref. 55) 6  c  %  In general, complexes o f the type (PR )2Ru(ri -H2)2(H)2 are unstable particularly w i t h 2  3  respect to loss o f H  (except for R = C y ) . > 56  2  60  Loss o f H2 from these types o f species  normally results in the formation o f mixed-valent dimeric species o f general formula Ru2H6(PR )4. A t room temperature, solutions o f complex 21 under a dihydrogen atmosphere 3  are unstable and slowly decompose to yield a new species. After four days complex 21 is still the major product in solution, however, a new triplet in the hydride region o f the ' H N M R spectrum is now apparent; this is accompanied by the appearance o f a singlet in the 3 1  P { ' H } N M R spectrum near 8 88.0. The spectral features o f the decomposition product  match the reported literature data for the complex ( P ' P ^ R u f t - t ^ H h ; after two weeks the complex (P Pr )2Ru(r| -H2) (H)2 is the only N M R active species present. The mechanism for 1  2  3  2  this conversion is not known. The fate o f the [NPNH2] ligand is also uncertain as no other decomposition products were evident in the ' H and P { ' H } N M R spectra. 3 1  Exposure o f  solutions o f complex 21 to an atmosphere o f dinitrogen also resulted in its decomposition as noted by a change in colour from orange to brown. The complex (P'Pr )2Ru(ri -H2) (H)2 is 3  2  2  reported to react with N2 to generate a thermally stable dinitrogen-bridged complex {(P Pr )2Ru(H)2(N2)} (u,-N2). ' 1  3  56 60  2  We are currently investigating the reactivity o f complex 21  with D2 gas in order to provide further evidence for the classification o f 21 as a bis dihydrogen dihydride species.  211  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine Ligands [NPN] and [P2N2] with Ruthenium(ll) Alkylidene and Vinylidene Complexes  4.5  Reaction of [P N ]Li (C H 0 ) with (P'PrakClsRuCCCHPh) 2  The reaction  o f the  2  2  [P2N2]  4  8  ligand  (P Pr ) Cl Ru(CCHPh) yields two products. i  3  2  2  2  with The  3 1  the ruthenium  vinylidene  complex  P { ' H } N M R spectrum o f the crude  reaction mixture contains a singlet at 5 25.6 indicating the formation o f a highly symmetrical species. Also present is a doublet and a triplet that integrate in the ratio 2:1 respectively, suggesting the presence of a ruthenium complex bearing the [ P N ] ligand as well as one 2  2  equivalent o f P'Pr . A singlet observed at 8 19.4 in the P { ' H } N M R spectrum corresponds 3 1  3  to free P Pr . The two complexes could be partially separated by rinsing the crude mixture l  3  with hexanes. We propose that the two products formed in this reaction are the vinylidene complex [P N ]Ru(CCHPh) (22), and the terminal alkynyl species [P NNH](P Pr )Ru(CCPh) i  2  2  2  3  (23) as shown in equation 4.3.  H.  Ph  C  +  [4-3]  40%  60%  22  23  212  References begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [PzNJ with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  Complex 22 forms via the replacement o f the two chlorides and two phosphine donors in the starting material by the [P2N2] ligand. The most telling feature in the ' H N M R spectrum o f complex 22 is the triplet located at 8 4.85. This observed pattern arises from coupling with the two equivalent phosphine donors o f the [P2N2] ligand (VPH - 4.2 Hz). This resonance is similar to that observed for the vinylidene hydrogen atom in the starting material, which occurs as a triplet at 8 4.71 with a magnitude o f coupling to the phosphorus nuclei o f 3.6 Hz.  The [P2N2] ligand gives rise to two silyl methyl proton resonances  indicative o f a complex with high symmetry; this is consistent w i t h the singlet that is observed in the  3 1  P { H } N M R spectrum.  The equivalency o f the phosphine donors in  1  complex 22 requires that a mirror plane o f symmetry exists within the trigonal plane o f the molecule. This can arise i f the proton and phenyl groups o f the vinylidene moiety also lie within this plane. The observation o f two silyl methyl signals, however, also requires that a mirror plane exists along the P-Ru-P axis. This may occur i f the proton and phenyl groups o f the vinylidene moiety are aligned perpendicular to the trigonal plane. Therefore, the N M R data suggest that the vinylidene ligand in 22 is fluxional and that facile rotation o f this moiety about the Ru=C=C axis occurs.  This behaviour is also apparent in many  five-coordinate  vinylidene complexes o f the type (PR ) (X)(C1)M(CCHR) (e.g. M = Ru or Os and X = H or 3  Cl).  2  Rotational isomers have been detected at low temperatures for the species  61  (P'Pr3)2(H)(Cl)Os(CCHPh)  62  whereas evidence for the co-existence o f two isomers in the  complex (P Pr ) (H)(Cl)Ru(CCHPh) could not be obtained. i  3  2  63  Theoretical studies on the  model complex (PH )2Ci2Ru(CCH ) indicate a barrier to vinylidene rotation o f 7.3 kcal 3  mol" . 1  61  2  Low temperature N M R studies on complex 22 have not been attempted.  Complex 23 can be envisioned as forming in a similar manner as complex 20, namely, via transfer o f the vinylidene hydrogen atom to one o f the amido donors o f the [P2N ] macrocycle resulting in the formation o f an amine and a terminal alkynyl ligand. In 2  fact, complex 23 may be considered as a coordinatively saturated analogue o f 20 in which one o f the [P2N2] phosphine donors has capped the open face to generate an octahedral structure. The small coupling o f 33 Hz for the resonances in the  3 1  P { ' H } N M R spectrum  implies a cis arrangement between the P'Pr and [P2NNH] phosphine donors. The ' H N M R 3  spectrum contains four singlets for the silyl methyl protons o f the [P2NNH] ligand as well as 213  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene and Vinylidene  four multiplets for the methylene protons within the ligand backbone. The methyl groups o f the P Pr3 ligand occur as a broad multiplet at 8 0.94; the methine protons are located as a l  multiplet at 5 1.66. A singlet at 8 2.12 that integrates to one proton has been assigned as the amino proton in complex 23. The aromatic protons exist at normal positions between 8 7.0 and 8 8.2. The presence o f a mirror plane o f symmetry contained within the equatorial plane accounts for the observation o f four silyl methyl groups and the equivalent phosphine donors o f the [ P N N H ] set. 2  Due to the formation o f a mixture o f complexes 22 and 23 in the reaction o f the [ P N ] ligand with (P Pr )2Cl2Ru(CCFIPh) and the need for separation and purification, 1  2  3  2  further reactivity involving complexes 22 and 23 was not pursued.  The drawback o f the  precursor complex (P'Pr3)2Cl Ru(CCHPh) in its reaction with the [ N P N ] and [P2N2] ligands 2  is that deprotonation o f the acidic vinylidene proton allows for an alternate reaction pathway other than direct halide metathesis and phosphine displacement. In an attempt to circumvent this problem we desired a ruthenium vinylidene starting material that was disubstituted at the terminal position.  A recent literature report discusses the convenient synthesis o f [3-  silylvinylidene ruthenium complexes o f the general formula (PR3)2Ci2Ru{CC(SiMe3)Ph} (where R = Cy or ' P r ) .  The following sections detail the reactions o f the [NPN] and [P2N2]  64  ligands with the P'Pr derivative. 3  This complex was chosen since it allows for a direct  comparison with the parent vinylidene complex.  4.6  Reaction of [NPN]Li (C H 0) 2  4  8  and [P N ]Li (C H 0 ) with  2  2  2  2  4  8  2  (P'PrshCURulCCfSiMeaJPh} (i)  Synthesis and characterization of [P N ]Ru{CC(SiMe )Ph} (24) 2  The mixed-donor  [P N ] 2  2  2  3  ligand reacts cleanly w i t h the vinylidene  precursor  (P Pr )2Cl2Ru{CC(SiMe )Ph} to give the anticipated product [ P N ] R u { C C ( S i M e ) P h } (24) i  3  3  2  2  3  in quantitative yield, as shown in equation 4.4. Toluene solutions containing the two starting  214  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2NJ with Ruthenium(ll) Complexes  Alkylidene  and Vinylidene  materials change in colour from purple to orange over a period o f two hours. The insoluble L i C I by-product is easily removed by filtration. Complex 24 can be isolated as large block crystals by the slow evaporation o f a saturated pentane solution.  Me Siv 3  V"  „.Ph  Ph  C 'Pr P-^_ 3  Me Siy  I ,-*""  C l - ^  2  cl  ^P'Pr  2  toluene 3  2 P'Pr  \\  Me Si\  ....SiMeg  X^">-Ru=G=CXr Me Si  N  2  3  /  [4.4]  ^Ph  Me SQ  2 LiCI  2  Y'".«.  Ph [P N ]Li (C H 0 ) 2  2  The  2  3 1  4  8  2  24  P { ' H } N M R spectrum o f complex 24 contains a singlet at 8 26.5 for the  phosphine donors o f the macrocycle; this is located close to the phosphorus-31 signal in the structurally related species 22 (8 25.6). In the H N M R spectrum a singlet is observed for the !  silyl methyl protons o f the vinylidene moiety indicating free rotation o f this group, while the  [P2N2]  ligand gives rise to four silyl methyl resonances. The equivalency o f the phosphine  donors i n complex 24 coupled with the observation o f four distinct  [P2N2] silyl  methyl  groups suggests that it possesses C symmetry with a mirror plane containing the two amido s  donors and the vinylidene fragment. This is only possible i f the silyl and phenyl substituents o f the vinylidene moiety lie in this plane and do not rotate about the Ru=C C axis. This is i n r::  contrast to complex 22 in which the vinylidene ligand does undergo fast rotation. The larger size o f a trimethylsily group versus a hydrogen atom most likely accounts for this difference. A n unfavourable interaction o f the bulky SiMe group with the phenyl substituents o f the 3  [P2N2]  phosphine donors may keep the vinylidene ligand i n this observed orientation. The  [P2N2]  methylene protons appear as overlapping multiplets between  8 1.25  and  8 1.65,  and  the aromatic protons are located,between 8 7.02 and 8 7.58.  The structure o f complex 24 was confirmed by a single crystal X-ray diffraction study. The solid-state molecular structure o f 24 is shown in Figure 4.6 with selected bond 215  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  lengths and angles collected in Table 4.3. The X-ray structure shows a ruthenium centre surrounded by the [P2N2] macrocycle and a vinylidene ligand. The Ru(l)-C(25)-C(26) angle is almost linear (178.5(2)°) and the C(25) to C(26) distance o f 1.332(4) A is consistent with a carbon-carbon double bond. The trimethylsilyl and phenyl groups of the vinylidene moiety are aligned with the amido donors o f the [P2N2] ligand as predicted from the solution N M R data. It is apparent from the solid-state structure that this arrangement minimizes interactions with the phenyl groups o f the [P2N2] framework. The Ru(l)-C(25) distance o f 1.781(2) A in 24 is longer than that observed in the related  five-coordinate  (P'P^^CbRutCCHPh)  (1.750(4) A) and (PCy ) Cl Ru(CCHPh) (1.761(2) A) complexes, but is shorter than those 64  3  2  2  o f the coordinatively saturated vinylidene ruthenium species [Cp(PPh )2Ru{CC(Me)Ph}] r +  3  (1.863(10) A ) ,  65  and Tp(PPh )ClRu(CCHPh) (1.801(4) A ) . 3  66  This trend most likely reflects  the arrangement o f the vinylidene ligand within the complexes with or without a ligand located in the trans position. The ruthenium amide distances in 24 (ca. 2.07 A) are shorter than those observed in the six-coordinate complexes 1 (ca. 2.22 A) and 2 (ca. 2.26 A). These data reflect the tighter binding o f a ligand that is expected for an electron deficient complex. Both complexes 1 and 2 are 18-electron species, whereas complex 24 has a 16-electron valence count.  216  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Figure 4.6.  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  ORTEP representation (50% thermal ellipsoids) of the solid-state molecular  structure o f [ P N ] R u { C C ( S i M e ) P h } (24) as determined by X-ray diffraction. 2  2  3  The silyl  methyl groups of the [ P N ] ligand have been omitted for clarity. 2  2  Table 4.3. Selected bond lengths and bond angles in [ P N ] R u { C C ( S i M e ) P h } 2  Atom Ru(l) Ru(l) Ru(D  Atom P(l) P(2) N(l)  2  (24).  3  Distance (A)  Atom  Atom  Distance (A)  2.3394(6) 2.3419(6) 2.066(2)  Ru(l) Ru(l) C(25)  N(2) C(25) C(26)  2.075(2) 1.781(2) 1.332(4)  217  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Atom  Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) C(25)  P(l) P(l) P(2) P(2) N(l) Ru(l)  Atom  Atom  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Angle (°) 176.58(2) 88.97(6) 88.54(6) 91.87(8) 112.16(9) 178.5(2)  P(2) N(2) N(l) C(25) C(25) C(26)  Atom  Atom  Atom P(l) P(l) P(2)  Ru(l) Ru(l) Ru(l) Ru(l) Ru(l) C(26)  N(l) N(2) Si(5)  Alkylidene  N(l) C(25) N(2) N(2) C(25) C(25)  and  Vinylidene  Angle (°) ' '89.83(6) 91.54(8) 89.70(6) 128.65(8) 119.18(9) 117.0(2)  Although the structure o f 24 more closely resembles a trigonal bipyramid with the phosphine donors o f the  [P2N2]  ligand at the apical positions, and the amido donors and the  vinylidene ligand lying in the equatorial plane o f the molecule, its geometry may be better described as a highly distorted square pyramid.  To support this claim a brief discussion  concerning the structure and bonding in related vinylidene complexes is in order.  Five-  coordinate  is a  phosphine)  vinylidene have been  complexes  formulated as L2(H)(Cl)Ru(CCHR)  synthesized and these complexes  adopt  (where  a distorted  L  trigonal  bipyramidal geometry with the phosphine donors occupying the apical positions and the Cl, H and vinylidene ligands in the plane o f the m o l e c u l e . ' ' 61  63  67  Furthermore, the angles within  the equatorial plane are inequivalent giving rise to a Y-shape structure with the Cl donor located at the foot o f the Y (i.e. opposite the acute angle). This type o f distortion is typical o f d ML5 complexes that contain a Tt-donating ligand since this allows for effective overlap o f 6  the lone pair o f the 7t-donor with the vacant metal d  xy  orbital. 52  53  This concept has been  previously addressed in chapter 2 (see Figure 2.10). Unlike these complexes, however, the species L2(H)(Cl)Ru(CCHR) also contains a 7t-acceptor ligand, which usually favours a square pyramidal geometry.  Theoretical calculations performed on the model complex  ( P H 3 ) 2 ( H ) ( C l ) R u ( C C H 2 ) have shown that the preference for a distorted trigonal bipyramidal geometry (or Y-structure) originates from a neutral vinylidene being a strong 7t-acceptor in the CpH plane and a weak 7t-donor orthogonal to this p l a n e . 63  2  67  As depicted in Figure 4.7,  two stabilizing interactions occur when the CpPL: vinylidene moiety lies in the Cl-Ru-H plane. The phosphine ligands, which would project in and out o f the page have been omitted for clarity.  The first interaction involves the formation o f a Ru-Cl 7t-bond that is  characteristic o f all Y-shaped d M L 6  5  fragments ( A in Figure 4.7), and the second involves  218  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  9  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  9  back-donation from the filled x -y metal orbital to the vacant p-orbital on C o f the a  9  9  vinylidene ( B ) . I n fact destabilization o f the x -y orbital by its interaction with the Cl p  x  orbital permits for greater overlap between the metal x -y and the empty /j-orbital o f the 2  vinylidene enhancing this re-inter action.  2  63  H  \  A  Figure 4.7.  B  A n illustration o f the two stabilizing bonding interactions i n five-coordinate  vinylidene complexes o f the type L2(H)(Cl)Ru(CCHR), which adapt distorted trigonal bipyramidal (or Y-shaped) structures.  I n A re-donation from the C l lone pair (p ) to the y  empty metal xy orbital occurs. In B back-donation from the filled metal x -y orbital to the 2  vacant /?-orbital on C  a  2  o f the vinylidene occurs. This can only take place i f the CpFf: group  lies in the xy plane.  219  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  Changing the hydride ligand (a strong o-donor) to a chloride ligand (a c and a ndonor) generating complexes o f the type L2Cl2Ru(CCHR) ( L is a phosphine) also results in a change in the coordination geometry at the metal. Theoretical calculations on the model system (PHa^CkRutCCEb) show that these complexes adopt a distorted square pyramidal structure with the vinylidene ligand at the apical position.  61  The terminal CpPL: fragment is  aligned in the Cl-Ru-Cl plane. This arrangement allows for back donation from the filled metal d  xy  orbital to the empty /?-orbital on C o f the vinylidene ligand. The Cl-Ru-Cl angle is a  less than 180° and is a result o f using the in-plane ^-orbital (d ) xy  for metal-vinylidene n-  bonding. By bending away from the vinylidene ligand the two chloride ligands destabilize the d  xy  orbital, thus enhancing its interaction with the vacant p-orbital  strengthening the 7t-interaction.  61  on C  a  and  The vinylidene-metal-chloride angles are found to be  equal and this is probably due to the two chloride ligands competing equally for bonding with the metal centre. These findings are supported by experimental data. The complex (P Pr )2Cl2Ru(CCHPh), 1  3  64  for instance, contains the two phosphine and two chloride donors  in a square plane and the vinylidene ligand at the apical site. The chloride atoms are actually slightly pinched back giving a Cl-Ru-Cl angle close to 160° as are the two phosphine ligands, which are skewed at an angle o f about 170°. The phenyl and hydrogen substituents of the vinylidene ligand lie in the Cl-Ru-Cl plane.  Complex 2 4 is closely related to the L2Cl Ru(CCHR) vinylidene complexes in that 2  both species contain two 7t-donating ligands. For this reason, one may expect that 2 4 would also adopt a distorted square pyramidal geometry. Inspection o f the bond angles about the metal centre in complex 2 4 indicate that no Y-shape is present; in fact, widening o f the N ( l ) R u ( l ) - N ( 2 ) angle above 120° is consistent with a distortion towards a square pyramidal structure. In the case o f complex 2 4 , however, this distortion is limited by the macrocyclic nature o f the [P2N2] ligand. Opening o f the amide bite-angle in 2 4 results in a nearly linear arrangement o f the two phosphine donors (176.58(2)°), and as a consequence, the phenyl substituents o f the phosphine donors come into closer contact with the trimethylsilyl and phenyl groups o f the vinylidene ligand. Minimizing these interactions may also play a role in the widening o f the amide bite-angle (and therefore approaching a square pyramidal  220  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  geometry) in complex 24.  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene and  Vinylidene  A structural feature that complex 24 shares with the precursor  complex (P'Pr3)2Cl2Ru(CCHPh) is that the vinylidene ligand resides in the apical position and that the terminal substituents lie in the same plane as the 7t-donating ligands.  A qualitative representation o f the bonding scheme o f the vinylidene ligand in complex 24 is given in Figure 4.8. This scheme has been adapted from Figure 2.10,  which  describes the effects on the relative energies o f the metal valence x -y and xy c/-orbitals as a 2  d ML 6  5  2  complex distorts towards a square pyramidal geometry. The vinylidene ligand can  coordinate to the metal through G-donation o f its filled sp orbital (on C ) to the vacant x -y 2  y  orbital on the metal. A n empty p  x  2  a  orbital is available for 7t-bonding with the filled xy orbital  on the metal; this synergistic bonding mode assists in the stabilization o f the vinylidene fragment. The remaining p  z  orbital on C is involved in a 7t-bond with Cp o f the vinylidene a  moiety. This terminal position contains a 5p -hydridized carbon atom involving the s, p 2  x  p  y  orbitals.  and  Based on this simplified bonding model the phenyl and trimethylsilyl  substituents o f the vinylidene ligand w i l l be located in the xy plane along with the amido donors o f the [P2N2] ligand (for a ground-state structure). This arrangement is also observed experimentally as is shown in the solid-state molecular structure o f 24.  221  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Ru  Alkylidene  and  Vinylidene  Ru-C re-bond  ——C  Figure 4.8. A qualitative representation o f the bonding scheme for the vinylidene ligand in complex 24.  (ii)  A t t e m p t e d synthesis o f [NPN](P Pr )Ru{CC(SiMe )Ph} i  3  Although  coordination  of  the  [P2N2]  3  ligand  to  the  vinylidene  complex  (P'Pr3) Cl2Ru(CCHPh) was possible, the analogous substitution reaction employing the 2  [NPN] ligand proved unsuccessful.  The ' H and 222  3 1  P{'H}  N M R spectra indicated the References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene and Vinylidene  formation o f a mixture o f unidentified products. It is unclear w h y this reaction has failed and attempts are being made to optimize the reaction conditions to favour the formation o f the substitution product [NPN](P'Pr3)Ru{CC(SiMe3)Ph}. A difference in reactivity between the [P2N2] and [ N P N ] ligands was also observed in their reactions with RuCi2(PPh ) ; whereas 3  2  the reaction w i t h the [ N P N ] ligand gave a mixture o f products the reaction w i t h the [P2N2] ligand yields the complex [P NNH]Ru(C Fl4PPh2) (2). 2  6  4.7  Reactivity studies of [P N ]Ru{CC(SiMe )Ph} (24)  (i)  Reaction of 24 with olefin substrates  2  2  3  Five-coordinate vinylidene ruthenium dichlorides o f the type L2Ci2Ru{CCH(R)} ( L = P'Pr3 or PCy3 and R = B u or Ph) serve as good catalyst precursors for the ring-opening l  metathesis  polymerization  (ROMP)  o f norbornene.  31  Related  complexes  LClRu(CCHPh) ( L = Tp or Cp) that incorporate the tris(pyrazolylborate)  such as (Tp) and  cyclopentadienyl (Cp) ligands also exhibit catalytic activity in this polymerization process.  30  The R O M P o f norbornene and ruthenium vinylidene complexes that catalyze this reaction are shown in Figure 4.9. Although efficiency o f the vinylidene complexes is much lower than that o f the Grubbs' alkylidene complexes, the polymerization rate is sufficient for practical use and the resulting polymers have high molecular weights w i t h polydispersity equivalent to the alkylidene systems.  223  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P NJ Complexes 2  with Ruthenium(ll)  Alkylidene  and Vinylidene  example catalysts:  H  ...-•-ci  R P3  cr  —  PhoP*  <  ci  —PR,  R = 'Pr or Cy  Ph  L = Cp, Cp or Tp  R' = Ph or Bu {  Figure 4.9. The ring-opening metathesis polymerization o f norbornene (highlighted) and vinylidene complexes that are used as catalyst precursors. 30  31  Given the success o f other ruthenium vinylidene complexes for the ROMP o f norbornene, complex 24 was tested for its catalytic potential i n this process. Unfortunately, 24 showed no activity even at elevated temperatures.  Stoichiometric reactions with  norbornene and styrene were also unsuccessful. Structurally, the [P2N2] vinylidene complex 24 more closely resembles the five-coordinate species L2Cl2Ru{CCH(R)}; the major difference is that 24 does not contain monodentate phosphine and chloride ligands but a chelating array o f phosphine and amide ligands. This difference would be expected to have a significant consequence on the reactivity o f complex 24. The catalytic mechanism for square planar L Cl Ru{CCH(R)}complexes can be related to that o f the Grubbs' catalyst with 2  2  phosphine dissociation as the initial step (Figure 4.1). Due to the macrocyclic nature o f the  224  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  [P2N2] ligand, phosphine dissociation to generate a vacant site cis to the vinylidene ligand is an unlikely occurrence, and most likely accounts for the observed lack o f reactivity o f complex 24. Since the amido donors in complex 24 do not lie trans to one another but are pinched back at an angle o f about 130° we envisioned that a substrate molecule could approach the metal centre along one o f the amide-ruthenium-vinylidene (N-Ru-C) angles. Another factor that may contribute to the lack o f reactivity o f complex 24 is the steric bulk o f the disubstituted vinylidene ligand, which can effectively shield the metal centre.  (ii)  Reaction of 24 with H  2  Although complex 24 was stable with respect to the addition o f olefin substrates it was observed to react readily with hydrogen gas.  The addition o f H2 (1 atmosphere) to  solutions o f 24 resulted in a lightening in the colour o f the solution from orange to yellow within an hour to yield the ruthenium hydride complex [P NNH]Ru(H){CC(SiMe )Ph} (25) 2  (Scheme 4.2). The  3 1  3  P { ' H } N M R spectrum o f 25 consists o f a singlet at 8 25.6 indicating  that there are equivalent phosphine environments within the complex.  The hydride  resonance occurs as a triplet at 8 -8.55 with a magnitude o f coupling to the phosphorus-31 nuclei o f 17.8 Hz. This signal integrates to one hydrogen environment per metal centre, and is therefore consistent with the heterolytic cleavage o f a molecule o f H2 across the ruthenium-amide bond in 24.  The amino proton is located at 8 1.80.  The trimethylsilyl  group of the vinylidene ligand gives rise to a singlet and four silyl methyl resonances are observed for the [P2NNH] ligand. This number o f peaks is diagnostic o f a mirror plane o f symmetry that bisects the two phosphine donors o f the macrocycle. Exposure o f solutions o f complex 25 (or 24) to four atmospheres o f H2 pressure resulted in the formation o f the previously characterized dihydrogen-hydride complex [P2NNH]Ru(H2)H (10).  225  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  10 Scheme 4.2  4.8  Summary and Conclusions This chapter discusses our attempts at preparing alkylidene and vinylidene complexes  o f ruthenium that incorporate the [NPN] and [P2N2] ligands. substitution  of  the  chloride  and  phosphine  donors  Our initial studies involved in  the  Grubbs'  complex  (PCy3)2Cl2Ru(CHPh), however, a mixture o f products resulted in these reactions.  Our investigations turned to ruthenium vinylidene complexes as starting materials due to their ease o f preparation. The reaction o f the [NPN] ligand with (P Pr )2Cl Ru(CCHPh) i  3  226  References  2  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and /P /\y with Ruthenium(ll) Complexes  Alkylidene  2  and  Vinylidene  generates the terminal alkynyl complex [NPNH](P Pr3)Ru(CCPh) (20), which forms via 1  deprotonation o f the vinylidene moiety by one o f the basic amido donors o f the [NPN] ligand. Complex 20 has been characterized in the solid-state by X-ray diffraction, infra-red spectroscopy and elemental analysis, and in solution by ' H , spectroscopy.  P { H } and  3 1  1  1 3  C{'H}  NMR  Exposure o f complex 20 to an atmosphere o f hydrogen gas results in the  formation o f the bis dihydrogen complex [NPNH2](P Pr )Ru(ri -H2)2(H)2 (21). I  2  3  A t room  temperature solutions o f 21 slowly decompose to yield the known bis dihydrogen complex (P Pr ) Ru(ri -H2)2(H)2. The reaction o f the [ P N ] ligand with (P Pr ) Cl Ru(CCHPh) gives I  i  2  3  2  2  2  3  2  2  a mixture o f two products, the vinylidene complex [P2N2]Ru(CCHPh) (22) and the terminal alkynyl species [P NNH](P Pr )Ru(CCPh) (23). i  2  3  In order to eliminate deprotonation o f the vinylidene ligand the disubstituted precursor (P Pr )2Cl2Ru{CC(SiMe )Ph) was utilized. 1  3  3  Substitution o f the chloride and  phosphine ligands was successfully accomplished by the addition o f [P2N2]Li2'(C4H80 ) 2  forming [ P N ] R u { C C ( S i M e ) P h } (24). Complex 24 was characterized in the solid-state by 2  2  3  X-ray diffraction. The solution structure o f complex 24, as determined by ' H , P { H } and 3 1  1 3  C { ' H } N M R spectroscopy is consistent with that found in the solid-state.  ]  Unfortunately,  24 demonstrated no reactivity with olefin substrates such as norbornene and styrene. It does react,  however,  with  hydrogen  [P NNH]Ru(H){CC(SiMe )Ph} 2  gas.  The  ruthenium  mono-hydride  complex  (25) forms under one atmosphere of H , whereas the  3  2  dihydrogen-hydride complex [ P N N H ] R u ( H ) H (10) forms when higher pressures o f H2 gas 2  2  are employed. The reaction o f the [NPN] ligand with (P Pr ) Cl Ru{CC(SiMe )Ph} gave a i  3  2  2  3  mixture o f unidentified products.  227  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  4.9  Future Work  (i)  Synthesis of [NPN](MgBr) ( C H 0 ) (26) 2  4  Alkylidene  and  Vinylidene  8  In section 4.2 o f this chapter we discussed the attempted incorporation o f the [NPN] and [P2N2] ligands onto the benzylidene complex (PCy3)2Cl2Ru(CHPh) via substitution o f the chloride and phosphine ligands. The exchange o f halide ligands on late transition metal complexes by anionic donors via salt metathesis is often dependent on the choice o f cation and solvent system employed. For example, the incorporation o f phenoxy-substituted Schiff base ligands onto (PCy ) Cl2Ru(CHPh) was most effective when the thallium salts o f the 3  2  corresponding ligands were utilized (Scheme 4 . 1 ) .  47  One potential side-reaction that may  occur where salt metathesis reactions are used to attach ancillary ligands to a late transition metal is metal reduction, in particular when lithium reagents are employed.  68  This suggested  to us that modification o f the cationic counter ions o f the [NPN] and [P N2] ligands may alter 2  the reactivity o f these mixed-donor chelating sets with ruthenium(II) alkylidene and vinylidene complexes as well as other ruthenium(II) precursors. Scheme 4.3 portrays two possible strategies for the preparation o f other [ N P N ] ligand precursors, namely, [NPN]M2 (where M is a univalent metal) and [ N P N ] M (where M is a divalent metal). As shown in pathway A ,  transmetalation may proceed by the addition o f metal halide to  the  [NPN]Li2'(C4H80)2 ligand with loss o f lithium chloride. Alternatively, an [NPN]M2 ligand can be envisioned as forming via deprotonation o f the amino protons in the neutral ligand [ N P N H ] (15) (B in Scheme 4.3). 2  228  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and /P Ay with Ruthenium(ll) Complexes 2  Alkylidene  and  Vinylidene  Scheme 4.3  Grignard reagents are less reducing than their corresponding lithium reagents; therefore, by analogy, magnesium salts o f amides should be less reducing than lithium amides. The tetrahydrofuran adduct o f the magnesium salt [ P N ] M g " ( C H 0 ) has previously 2  2  4  8  been prepared from the reaction o f [ P N ] L i t C H 0 ) with an excess o f M g B r ' ( O E t ) using 2  tefrahydrofuran as the solvent.  69  2  2  4  8  2  2  2  In an attempt to prepare the related magnesium precursor o f  the [ N P N ] ligand an excess o f M g B r ' ( O E t ) was reacted with [ N P N ] L i - ( C H 0 ) 2  tetrahydrofuran. " [ N P N ] M g " salt.  2  2  4  8  2  in  As shown in equation 4.5, this reaction does not yield the anticipated Instead the tetrahydrofuran adduct [ N P N ] ( M g B r ) - ( C H 0 ) (26) forms  containing two { M g B r }  2  monocations.  +  4  8  This example further illustrates the difference in  reactivity between the [ P N ] and [NPN] ligands that has been noted throughout this thesis. 2  2  The stoichiometric reaction o f [ N P N ] L i ' ( C H 0 ) 2  4  8  2  with M g B r ( O E t ) presumably would 2  2  afford an " [ N P N ] M g " salt analogous to the [ P N ] ligand, however, this reaction has yet to 2  2  be attempted.  229  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  [NPN]Li  2  (THF)  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene and  Vinylidene  2  THF [4.5]  +  - LiBr  exess MgBr (Et 0) 2  2  2  26  The solid-state molecular structure o f complex 2 6 as determined from X-ray crystallography is shown in Figure 4.10, and selected bond lengths and angles are listed in Table 4.4. Complex 2 6 contains a four-membered N2{MgBr}2 core, which is similar to the N 2 L i core observed in the solid-state structure o f the dilithium salt o f the [ N P N ] ligand. One 2  o f the magnesium atoms is coordinated to the phosphine donor and the other is coordinated to a molecule o f tetrahydrofuran; both magnesium centres are four-coordinate. Both amideto-magnesium distances are similar at approximately 2.12 A. The N { M g B r } 2 core is quite 2  symmetrical with N - M g - N angles o f about 92° and M g - N - M g angles close to 87°. The 3 1  P { H } N M R spectrum o f complex 2 6 clearly demonstrates that the lithium cations have 1  been replaced by magnesium; the  3 1  P resonance is observed as a singlet at 8 -47.0.  In  contrast, a quartet is observed at 8 -37.7 (VPU = 38 Hz) in the P { ' H } N M R spectrum o f 3 1  [NPN]Li '(C4HgO) . 2  2  The *H N M R spectrum o f the ligand framework is comprised o f two  silyl methyl resonances, two methylene resonances, and one set o f ortho, meta and para phenyl proton resonances each for the phosphine and amido phenyl groups. This number o f peaks is consistent w i t h a mirror plane o f symmetry within complex 2 6 .  230  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Figure 4.10.  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  ORTEP representation (50% thermal ellipsoids) o f the solid-state molecular  structure o f [NPN](MgBr)2'(C4H80) (26) as determined by X - r a y diffraction.  Table 4.4.  Selected bond lengths and bond angles in [ N P N ] ( M g B r ) ( C H 0 ) (26). -  2  Atom P(l) N(l) N(l) N(2)  Atom Mg(l) Mg(l) Mg(2) Mg(l)  4  8  Distance (A)  Atom  Atom  Distance (A)  2.573(1) 2.127(2) 2.116(2) 2.122(2)  N(2) 0(1)  Mg(2) Mg(2) Br(l) Br(2)  2.120(2) 2.024(2) 2.424(9) 2.418(1)  Mg(l) Mg(2)  231  References  begin on page 237  Chapter 4: Reaction  Atom N(l) P(l) P(l) P(l) N(2) N(l)  Atom Mg(l) Mg(l) Mg(l) Mg(l) Mg(l) Mg(2)  of the Amidophosphine  Atom N(2) Br(l) N(l) N(2) Br(l) N(2)  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Angle (°) 92.34(9) 118.11(4) 89.73(7) 88.66(7) 127.67(8) 92.73(9)  Atom 0(1) O(l) 0(1) N(l) Mg(l) Mg(l)  Atom Mg(2) Mg(2) Mg(2) Mg(2) N(l) N(2)  Alkylidene  Atom Br(2) N(l) N(2) Br(2) Mg(2) Mg(2)  and  Vinylidene  Angle (°) 102.12(6) 111.86(9) 111.85(9) 119.23(7) 87.40(9) 87.42(8)  The reaction o f the ligand precursor 26 with ruthenium(II) starting materials including the benzylidene complex (PCy3)2Cl2Ru(CHPh) have not yet been attempted. The preparation o f other salts o f the [NPN] ligand including potassium and thallium may also be possible via the methods outlined in Scheme 4.3.  4.10 Experimental  (i)  General Procedures  Unless otherwise stated, general procedures were performed according to Section 2.9 (i) .  !  H N M R T\ relaxation measurements were performed on a Bruker A M X 500 M H z  spectrometer using a standard inversion-recovery pulse sequence (180°-x-90°). The T\ values were obtained using the non linear three-parameter fitting routine in the Bruker XwiNNMR program with an estimated error o f ± 10 % in each T\ value. The temperature was regulated using a Bruker V T 1000 unit. Toluene-^ was used as the N M R solvent.  (ii)  Materials  Hydrogen gas (Praxair) and deuterium gas (Cambridge Isotope Laboratories) were employed without further purification.  Norbornene was recrystallized prior to use and  232  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  styrene  was  used  as  Ligands [NPN] and /P Ay with Ruthenium(ll) Complexes 2  received.  The  complexes  Alkylidene  and  Vinylidene  (P Pr3)2Cl2Ru(CCHPh) 1  64  and  (P'Pr3)2Cl2Ru{CC(SiMe3)Ph} were prepared according to published literature procedures. 64  (iii)  Synthesis and Reactivity of Complexes  [NPNH](P Pr )Ru(CCPh) (20) i  3  A solution o f toluene (25 mL) cooled to -78 °C was added dropwise to an intimate mixture o f [NPN]Li -(C H 0)2 (0.996 g, 1.680 mmol) and (P Pr ) Cl Ru(CCHPh) (1.000 g, i  2  4  8  3  2  2  1.680 mmol) also maintained at - 7 8 °C, and the resulting purple slurry was stirred for 10 minutes. The mixture was warmed to room temperature and stirred for a further 30 minutes. During this time the colour lightened to yield an intense violet coloured solution.  The  contents were once again chilled to - 7 8 °C and then cannula transferred to a Schlenk frit containing a layer o f Celite in order to remove insoluble by-products.  The solvent was  evaporated from the filtrate under reduced pressure until an oily residue remained. The solid was dissolved in a minimal amount o f hexanes and the solution allowed to slowly, evaporate in the glove-box to give purple block crystals o f [NPNH](P Pr )Ru(CCPh) (20) i  3  (0.483 g, 36  %) and a brown coloured filtrate. The crystals were washed with hexanes and the rinsings were combined with the original filtrate. X-ray quality crystals were obtained in this manner. A further crop o f crystals can sometimes be obtained by the slow evaporation o f the hexanes soluble fraction. The total isolated yields typically range from 40 to 50 %. ' H N M R ( C D , 6  6  298 K, 500 M H z ) : 8 -0.06, 0.54 and 0.70 (s, SiGrY , 9 H total), 5 0.90 (s, overlapping, SiCtf , 3  3  3H), 8 0.92 (m, overlapping, P C H C H , 9H), 8 1.08 (m, PCHC/f , 9H), 8 1.23, 1.35 and 1.65 3  3  ( m , ?CH , 8H total), 8 2.10 (m, P C # C H , 3H), 8 4.95 (s, N # , I H ) , 8 5.75 to 8.08 (m, 3  2  overlapping, aromatic-tf). ^ P C ' H } N M R ( C D , 298 K, 202.5 M H z ) : 8 57.0 (d, J 2  6  Hz, P'Pr ) and 8 76.5 (d, V 3  P P  6  PP  =  All  = 41.2 Hz, FNPNH]). Infra-red ( K B r ) : v(C=C) at 2050 cm"  1  and v ( N - H ) at 3194 cm" . Anal. Calcd. for C iH58N P RuSi2: C, 61.70; H, 7.32; N, 3.51. 1  4  2  2  Found: C, 62.10; H, 7.48; N , 3.58.  233  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine ~-  [NPNH ](PW )RU(TI -H ) (H) 3  2  2  Alkylidene  and  Vinylidene  (21)  2  2  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  2  A J-Young N M R tube containing a solution o f [NPNH](P Pr )Ru(CCPh) (20) (0.042 i  3  g, 0.053 mmol) dissolved in benzene-t/6 (~ 1 -0 mL) was degassed by performing two freezepump-thaw cycles and then warmed to room temperature.  A n atmosphere o f H2 gas was  added to the N M R tube, which was then flame-sealed. M i x i n g the contents o f the N M R tube resulted in an immediate change in colour from violet to orange yielding the complex [NPNH ](P Pr )Ru(ri -Fi2)2(H)2 (21) as the only N M R active ruthenium species. Solutions o f i  2  2  3  21 gradually lighten to give the known bis dihydrogen complex ( P ' P r ^ i R u ^ M F f e ) .  The  solution N M R data for complex 21: ' H N M R ( C D , 298 K, 500 M H z ) : 8 -7.60 (dd ( A B ) , 6  2  J  P H  = 7.6 Hz [ N P N H ] , Vp  H  6  = 6.7 Hz P P r , R u - / / , 6H), 8 -0.08 and 0.00 (s, S i C / / , 12H 3  3  total), 8 0.98 (m, overlapping, P C H C / / , 9H), 8 1.00 and 1.58 (m, overlapping, P C / / , 8H 3  2  total), 8 1.56 (m, overlapping, P C / / C H , 3H), 8 3.98 (s, N - # , 2H), 8 6.52 to 7.81 (m, 3  overlapping, aromatic-//, 15H total). 2  JPP  3 1  P { ' H } N M R ( C D , 298 K, 202.5 M H z ) : 8 25.0 (d, 6  = 225 Hz, [ N P N H ] ) and 8 86.0 (d,  2  J  P P  6  = 225 Hz, P T ^ ) . 7/i(min) for Ru-H = 51 ms at 6  220 K in toluene-^-  [P N ]Ru(CCHPh) (22) and [PzNNHHP'PrsJRufCCPh) (23) 2  2  Toluene (25 mL) was added to a mixture o f ^ ^ L i f O ^ H g C h ) (0.530 g, 0.835 mmol) and (P Pr ) Cl Ru(CCHPh) (0.496 g, 0.834 mmol) in a Schlenk flask and the contents i  3  2  2  were stirred at room temperature for two hours. The toluene was removed under reduced pressure leaving an oily residue.  The addition o f a minimal amount o f hexanes to this  residue allowed for the separation of a dark precipitate from a dark-brown coloured filtrate. The soluble fraction was removed via pipette, and the precipitate was further rinsed with hexanes until the washings were light brown in colour.  The precipitate was dried under  vacuum to give [P2NNH](P'Pr )Ru(CCPh) (23) as a brown solid in approximately 95 % 3  purity as determined by *H and P { ' H } N M R spectroscopy. Complex 22 and P'Pr were 3 1  3  also present as minor impurities.  Removal o f the hexanes (in vacuo) from the soluble  2 4 3  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  fraction gave a dark-brown oily solid, which the H and P { H } N M R data showed to be 3 1  l  !  [P N ]Ru(CCHPh) (22) (ca. 60 % purity). Also present were complex 23, P'Pr as well as 2  2  3  other unidentified impurities. The solution N M R data for complex 22: ' H N M R (CeD6, 298 K, 500 M H z ) : 5 0.25 and 0.38 (s, S i C / / , 2 4 H total), 5 0.92 to 1.35 ( m , overlapping, ?CH , 3  8 H total), 8 4.85 (t, V H).  3 1  PH  2  = 4.2 Hz, RuCC//Ph, I H ) , 8 6.95 to 8.10 (m, overlapping, aromatic-  P { ' H } N M R ( C D , 298 K, 202.5 M H z ) : 8 25.6 (s, [ P N ] ) . The solution N M R data 6  6  2  2  for complex 23: *H N M R ( C D , 298 K, 500 M H z ) : 8 0.20, 0.42, 0.56 and 0.75 (s, S i C # , 6  6  3  2 4 H total), 8 0.94 ( m , br, P C H C / / , 9H), 8 1.34 and 1.49 ( m , ?CH , 4 H total), 8 1.66 (m, 3  2  PC/7CH , 3H), 8 1.93 and 2.08 ( m , ?CH , 4 H total), 8 2.12 (s, N - / / , I H ) , 8 7.02 to 8.18 ( m , 3  2  overlapping, aromatic-//).  3 1  P { ' H } N M R ( C D , 298 K, 202.5 M H z ) : 8 20.6 (d, J 2  6  Hz, [P2N2], 2P), 8 59.3 (t, J 2  P P  6  P P  = 33  = 33 Hz, P ^ , I P ) .  [P N ]Ru{CC(SiMe )Ph} (24) 2  2  3  A t room temperature toluene (15 m L ) was added to an intimate mixture o f [ P N ] L i - ( C H 0 ) (0.138 g, 0.217 mmol) and (P Pr ) Cl Ru{CC(SiMe )Ph} (0.145 g, 0.217 i  2  2  mmol).  2  4  8  2  3  2  2  3  Over the course o f two hours the colour o f the solution changed from purple to  orange with the formation o f a precipitate. In the glove-box the mixture was filtered and the toluene was removed under reduced pressure. A minimal amount o f pentane solution was added to re-dissolve the solid. The slow evaporation o f the pentane solution resulted in the deposition o f [P N ]Ru{CC(SiMe )Ph} (24) as large block crystals. Yield: (0.163 g, 93 % ) . 2  2  3  Single crystals for an X-ray diffraction study were obtained from the saturated pentane solution. ' H N M R ( C D , 298 K, 500 M H z ) : 8 0.22 (s, CCSC7Z , 9H), 8 0.20, 0.25, 0.36 and 6  6  3  0.44 (s, S i C / / , 2 4 H total), 8 1.25 to 1.65 ( m , overlapping, ?CH , 8H), 8 7.02 to 7.58 ( m , 3  2  overlapping, aromatic-//).  3 1  P { ' H } N M R ( C D , 298 K, 202.5 M H z ) : 8 26.5 (s, [ P N ] ) . 6  6  2  2  Anal. Calcd. for C H56N P RuSi5: C, 52.01; H, 6.98; N , 3.47. Found: C, 52.09; H, 7.22; N , 35  2  2  3.66.  235  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  Reaction of [P N2]Ru{CC(SiMe )Ph} (24) with styrene and norbornene 2  3  In an N M R tube complex 24 (0.036 g, 0.045 mmol) and an excess o f styrene (0.014 g, 0.134 mmol) were dissolved in ~ 1 m L o f toluene-t/g. The contents were mixed and stirred at room-temperature. After 24 hours no change in the reaction mixture was evident upon inspection o f the H and P { ' H } N M R spectroscopy. The sample was heated to 80°C for a !  3 1  further 24 hours but N M R spectroscopy showed that no reaction had taken place. A similar procedure was employed for the reaction o f 24 with norbornene.  [P NNH]Ru(H){CC(SiMe )Ph} (25) 2  3  In a J-Young valve N M R tube, complex 24 (0.044 g, 0.054 mmol) was dissolved in ~ 1 m L o f benzene-^6-  The sample was degassed by performing three freeze-pump-thaw  cycles, warmed to room temperature, and then one atmosphere o f hydrogen gas was vented into the N M R tube. The tube was sealed and the contents were stirred for an hour. The *H and  3 1  P { ' H } N M R spectrum showed the quantitative formation o f 25 with complex 10  present in less than 2 % yield. H N M R ( C D , 298 K, 500 M H z ) : 5 -8.55 (t, J ]  2  6  6  PR  = 17.8 Hz,  R u - / / , 1H), 5 0.00 (s, C C S C / / , 9H), 5 0.10, 0.26, 0.28 and 0.64 (s, SiCifc, 24H total), 8 1.28, 3  1.47, 1.52 and 1.78 (m, P-Gr7 , 8 H total), 8 1.80 (s, overlapping, N - / / , 1H), 8 6.90 to 7.62 ( m , 2  overlapping, aromatic-//).  3 1  P { H } N M R ( C D , 298 K, 202.5 M H z ) : 1  6  6  8 25.6 (s, [ P N ] ) . 2  2  Complex 10 is exclusively formed when the reaction is performed at four atmospheres o f hydrogen pressure as indicated by the *H and P { H } N M R data. 3 l  l  [NPN](MgBr) (C H 0) (26) 2  4  8  To an intimate mixture o f [NPN]Li '(C4H80) (0.65 g, 1.09 mmol) and an excess o f 2  2  MgJ3r (OEt ) (1.00 g, 3.01 mmol) at -78°C was added 20 m L o f tetrahydrofuran. The 2  2  2  solution was warmed to room temperature and stirred for one hour, after which the solvent  236  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Alkylidene and Vinylidene Complexes  was removed under vacuum. The remaining solid was extracted into toluene and filtered. The filtrate was evaporated to dryness, leaving a white powder that was rinsed with hexanes and dried under vacuum to afford [ N P N ] ( M g B r ) ( G H 0 ) (26) in 90 % yield. Single crystals 2  4  8  suitable for an X-ray diffraction study were grown from the slow evaporation o f a saturated toluene solution. ' H N M R ( C D , 298 K, 500 M H z ) : 8 0.05 and 0.52 (s, SiC7/ , 12H total), 6  8 0.64 (m,  THF-OCH2C//2,  6  4H),  3  8 1.12 and  1.97  (m, ?-CH , 2  4H  total), 8 2.58 ( m , T H F -  O C # C H , 4 H ) , 8 6.63 to 7.78 (m, N-phenyl and P-phenyl, 15H total). ^ P f ' H } N M R ( C D , 2  2  6  6  298 K, 202.5 M H z ) : 8 - 4 7 . 0 (s):  X-ray Crystallographic Analyses of Complexes 20, 24 and  26  Selected crystallographic and solution refinement data are provided in Appendix 1.  4.11 References (1)  Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.  (2)  Buchmeiser, M . R. Chem. Rev. 2000,100, 1565.  (3)  Bielawski, C. W.; Louie, J.; Grubbs, R. H. J. Am. Chem. Soc. 2000,122, 12872.  (4)  Dias, E. L.; Grubbs, R. H. Organometallics 1998,17, 2758.  (5)  Jafarpour, L.; Heck, M . P.; Baylon, C ; Lee, H. M.; Mioskowski, C ; Nolan, S. P.  Organometallics 2002, 21, 671.  (6)  Yoa, Q. Angew. Chem. Int. Ed. 2000, 39, 3896.  237  References  begin on page 237  Chapter 4: Reaction  (7)  of the Amidophosphine  Ligands [NPN] and [P2NJ with Ruthenium(ll) Complexes  Alkylidene  and Vinylidene  Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, J., P. J.; Hoveyda, A . H. J. Am. Chem.  Soc. 1999,121,191.  (8)  Ackermann, L.; Furstner, A . ; Weskamp, T.; Kohl, F. J.; Herrmann, W . A .  Tetrahedron Lett. 1999, 40, 4787.  (9)  Scholl, M . ; Trnka, T. M . ; Morgan, J. P.; Grubbs, R. H. Tetrahedron Lett. 1999, 40,  2247.  (10)  Amoroso, D.; Fogg, D. E. Macromolecules 2000, 33, 2815.  (11)  Hansen, S. M . ; Volland, M . A . O.; Rominger, F.; Eisentrager, F.; Hofmann, P.  Angew. Chem. Int. Ed. 1999, 38, 1273.  (12)  Huang, J.; Schanz, H. J.; Stevens, E. D.; Nolan, S. P. Organometallics 1999, 18,  5375.  (13)  Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996,118, 100.  (14)  W u , Z.; Nguyen, S. T.; Grubbs, R. H.; Ziller, J. W . J. Am. Chem. Soc. 1995, 117,  5503.  (15)  Pietraszuk, C.; Marciniec, B.; Fischer, H. Organometallics 2000,19, 913.  (16)  Wilhelm, T. E.; Belderrain, T. R.; Brown, S. N . ; Grubbs, R. H. Organometallics  1997,16, 3867.  (17)  Gandelman, M . ; Rybtchinski, B.; Ashkenazi, N.; Gauvin, R. M . ; Milstein, D. J. Am.  Chem. Soc. 2001,123, 5372.  (18)  Olivan, M.; Caulton, K. G. Inorg. Chem. 1999, 38, 566. 238  References  begin on page 237  Chapter 4: Reaction  (19)  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and Vinylidene  Caolter I I I , J. N.; Spivak, G. J.; Gerard, PL; Clot, E.; Davidson, E. R.; Eisenstein, O.;  Caulton, K. G. J. Am. Chem. Soc. 1998,120, 9388.  (20)  Kingsbury, J. S.; Garber, S. B.; Giftos, J. M.; Gray, B. L.; Okamoto, M . M.; Fairer, R.  A.; Fourkas, J. T.; Hoveyda, A . H. Angew. Chem. Int. Ed. 2001, 40, 4251.  (21)  Belderrain, T. R.; Grubbs, R. H. Organometallics 1997,16, 4001.  (22)  Furstner, A.; Thiel, O. R.; Lehmann, C. W. Organometallics 2002, 21, 331.  (23)  Jafarpour, L.; Nolan, S. P. Organometallics 2000,19, 2055.  (24)  Trnka, T. M.; Morgan, J. P.; Sanford, M . S.; Wilhelm, T. E.; Scholl, M.; Choi, T. L.;  Ding, S.; Day, M . W.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546.  (25)  Jafarpour, L.; Hiller, A . C ; Nolan, S. P. Organometallics 2002, 21, 442.  (26)  Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997,119, 3887.  (27)  Aagaard, O. M.; Meier, R. J.; Buda, F. J. Am. Chem. Soc. 1998,120,1X14.  (28)  Sanford, M . S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc. 2001,123, 749.  (29)  Sanford, M . S.; Love, J. A.; Grubbs, R. H. J. Am. Chem. Soc. 2001,123, 6543.  (30)  Katayama, FL; Yoshida, T.; Ozawa, F. J. Organomet. Chem. 1998, 562, 203.  (31)  Bruneau, C ; Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311.  (32)  Saoud, M.; Romerosa, A.; Peruzzini, M . Organometallics 2000,19, 4005.  239  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine  Ligands [NPN] and [P2NJ with Ruthenium(ll) Complexes  Alkylidene  and Vinylidene  (33)  Del Rio, I.; Van Koten, G. Tetrahedron Lett. 1999, 40, 1401.  (34)  Picquet, M.; Bruneau, C.; Dixneuf, P. H. Chem. Commun. 1998, 2249.  (35)  Furstner, A.; Picquet, M.; Bruneau, C.; Dixneuf, P. H. Chem. Commun. 1998, 1315.  (36)  Furstner, A.; Ackermann, L. Chem. Commun. 1999, 95.  (37)  Furstner, A . ; H i l l , A . F.; Liebl, M . ; Wilton-Ely, J. D. E. T. Chem. Commun. 1999,  601.  (38)  Harlow, K. J.; H i l l , A . F.; Wilton-Ely, J. D. E. T. J. Chem. Soc, Dalton Trans. 1999,  285.  (39)  Jafarpour, L.; Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics 1999,18, 3760.  (40)  Jafarpour, L.; Schanz, H. J.; Stevens, E. D.; Nolan, S. P. Organometallics 1999, 18,  5416.  (41)  Schanz, H. J.; Jafarpour, L.; Stevens, E. D.; Nolan, S. P. Organometallics 1999, 18,  5187.  (42)  Lynn, D. M.; Grubbs, R. H. J. Am. Chem. Soc. 2001,123, 3187.  (43)  Stuer, W.; Wolf, J.; Werner, H.; Schwab, P.; Schulz, M . Angew. Chem. Int. Ed. 1998,  57,3421.  (44)  Gonzalez-Herrero, P.; Weberndorfer, B.; Ilg, K.; Wolf, J.; Werner, H. Angew. Chem.  Int. Ed. 2000, 39, 3266.  240  References  begin on page 237  Chapter 4: Reaction  (45)  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  Sanford, M . S.; Henling, L. M . ; Day, M . W . ; Grubbs, R. H. Angew. Chem. Int. Ed.  2000, 39, 3451.  (46)  Sanford, M . S.; Henling, L. M . ; Grubbs, R. H. Organometallics 1998,17, 5384.  (47)  Chang, S.; Jones I I , L.; Wang, C ; Henling, L. M . ; Grubbs, R. H. Organometallics  1998,77,3460.  (48)  Bruce, M . I.; Hall, B. C ; Zaitseva, N . N.; Skelton, B. W.; White, A . H. J. Chem. Soc,  Dalton Trans. 1998, 1793.  (49)  Touchard, D.; Haquette, P.; Daridor, A.; Romero, A.; Dixneuf, P. H. Organometallics  1998,77,3844.  (50)  Kawata, Y.; Sato, M . Organometallics 1997, 16, 1093.  (51)  Grunwald,  C;  Gevert,  O.; Wolf,  J.; Gonzalez-Herrero,  P.;  Werner,  H.  Organometallics 1996, 75, 1960.  (52)  Rachidi, I. E. I.; Eisentstein, O.; Jean, Y . New. J. Chem. 1990,14, 671.  (53)  Riehl, J. F.; Jean, Y.; Eisenstein, O.; Pelissier, M . Organometallics 1992, 77, 729.  (54)  Joesten, M . D.; Schaad, L. J. Hydrogen Bonding; Marcel Dekker, Inc.: N e w York,  1974.  (55)  Sabo-Etienne, S.; Chaudret, B. Coord. Chem. Rev. 1998,178-180, 381.  (56)  Abdur-Rashid, K.; Gusev, D. G.; Lough, A . J.; Morris, R. H. Organometallics 2000,  19, 1652.  241  References  begin on page 237  Chapter 4: Reaction  of the Amidophosphine  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and Vinylidene  (57)  Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988,110, 4126.  (58)  Luo, X . L.; Crabtree, R. H. Inorg. Chem. 1990, 29, 2788.  (59)  Desrosiers, P. J.; Cai, L.; L i n , Z.; Richards, R.; Halpern, J. J. Am. Chem. Soc. 1991,  773,4173.  (60)  Arligule, T.; Chaudret, B.; Morris, R. H.; Sella, A . Inorg. Chem. 1988, 27, 598.  (61)  Yang, S. H.; Wen, T. B.; Jia, G.; L i n , Z. Organometallics 2000,19, 5477.  (62)  Bourgault, M . ; Castillo, A . ; Esteruelas, M . A.; Onate, E.; Ruiz, N . Organometallics  1997,16, 636.  (63)  Olivan, M.; Clot, E.; Eisenstein, O.; Caulton, K. G. Organometallics 1998, 77, 897.  (64)  Katayama, H.; Ozawa, F. Organometallics 1998,17, 5190.  (65)  Bruce, M . I.; Humphrey, M . G.; Snow, M . R.; Tiekink, E. R. T. J. Organomet. Chem.  1986, 314, 213.  (66)  Slugovc, C ; Mereiter, K.; Zobetz, E.; Schmid, R.; Kirchner, K. Organometallics  1996,15, 5275.  (67)  Olivan, M.; Eisenstein, O.; Caulton, K. G. Organometallics 1997,16, 2227.  (68)  Fryzuk, M . D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1.  242  References  begin on page 237  Chapter 4: Reaction of the Amidophosphine  (69)  Ligands [NPN] and [P2N2] with Ruthenium(ll) Complexes  Alkylidene  and  Vinylidene  Johnson, S. A . Ligand Design and The Synthesis of Reactive Organometallic  Complexes of Tantalum for  Dinitrogen Activation; University o f British  Columbia:  Vancouver, 2000.  243  References  begin on page 237  Appendix 1: X-ray Crystal Structure Data  Appendix 1  X-ray Crystal Structure Data In all cases, suitable crystals were selected and mounted on a glass fiber using ParatoneN oil and freezing to -100 °C (complex 1 was cooled to -85 °C and complex 4 was cooled to -75 °C).  A l l measurements were made on a Rigaku/ADSC CCD area detector with graphite  monochromated M o - K a radiation. program.  1  Data were collected and processed using the d*TREK  The data were corrected for Lorentz and polarization effects. A l l of the structures  were solved by direct methods and expanded using Fourier techniques. 2  atoms were refined anisotropically.  A l l Ru-H  3  The non-hydrogen  and N-77 hydrogen atoms were refined  isotropically, the rest were included in fixed positions. Neutral atom scattering factors were taken from the International Tables for X-ray Crystallography.  4  performed using the teXsan crystallographic software package.  5  A l l calculations were  ORTEP drawings of  complexes 1, 2, endo-3, 4, 7, 8, 11, 12, 13, 20, 24 and 26 are given throughout the thesis along with tables of selected bond lengths and bond angles; an ORTEP drawing of complex 5 is shown in Figure A l .  Crystallographic and structure refinement data for all complexes are given in  Tables A l - A4. A l l of the structures presented in this thesis have been solved by Dr. Brian O. Patrick of the X-ray Crystallography department at the University of British Columbia.  244  Appendix 1: X-ray Crystal Structure Data  Additional information can be obtained from the UBC X-ray lab. A list of the reference names for each of the complexes is given below.  UBC X-ray Reference Name mf472 mf498 mf428 mf437 mf482 mf495 mf466 mf502 mf451 mf456 mf411 mf490 mf477  Complex 1 2  endo-3 4 5 7 8 11 12 13 20 24 26  References (1)  d*TREK Area Detector Software. Version 4.13. Molecular Structure Corporation 1996-  1998.  (2)  Altomare, A.; Burla, M. C ; Cammalli, G.; Cascarano, M.; Giacovazzo, C ; Guagliardi,  A.; Moliterni, A. G. G.; Polidori, G.; Spagna, A. J. Appl. Cryst. 1999, 32, 115-119.  (3)  Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de Gelder, R.; Israel, R.;  Smits, J. M. M. DIRDIF94, Technical Report of the Crystallography Laboratory, University of Nijmegen, The Netherlands 1994. (4)  Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystallography 1974, Vol.  IV, The Kynoch Press, Birmingham, England, Table 2.2 A. (5)  teXsan Crystal Structure Analysis Package, Molecular Structure Corporation 1992.  245  Appendix 1: X-ray Crystal Structure Data  Figure A l .  ORTEP representation (50 % thermal ellipsoids) of the solid-state molecular  structure of {[NPN]Ru(l-3-n :5,6-r) -C8Hn)} {Na.THF} (5) as determined by X-ray diffraction. 3  2  The [NPN] silyl methyl groups have been omitted for clarity and only the ipso carbon atoms of the amido and phosphine phenyl rings are shown.  246  Appendix 1: X-ray Crystal Structure Data  Table A l . Crystallographic Data and Structure Refinement Data for complexes [P N ]Ru(r| :r| 2  2  2  2  C H ) (1), [P NNH]Ru(C H PPh ) (2), e«fi?o-[NPNH]Ru(l-3-ri :5,6--n -C8Hii) (endo-3) and 3  8  12  2  6  4  2  2  {[NPN]Ru(l-3-r| :5,6-ri -C Hi )}{Li.THF} (4). 3  2  8  1  C32H56N2P2SL1.C6  Fw Colour, Habit Crystal size, mm Crystal system Space group a, A b, A  c,A  H Ru 830.34 yellow, platelet 0.50 x 0.20 x 0.05 monoclinic P2/n (#13) 11.113(1) 10.854(1) 17.994(2)'  a, deg P,deg  96.944(3)  M  Y, deg v, A z T,°C  2154.6(3) 2 -85 + 1 1.280  3  Pcalc,  g/cm  3  endo-3  2  1 Formula  C32H N2PRuSi2  19109(1) 8 -100 ± 1 1.296 7824.00 5.61 0.7109-1.0000 50.0  4165.8(2) 4  151583 16723 0.112 13461 (n=2)  13930.4(4) 18 -100 ± 1 1.382 6048.00 6.60 0.7589- 1.0000 55.8 36357 6957 0.060 4940 (n=3)  480 0.046 0.069 0.026 (n=3) 0.032 (n=3)  4  57  5  2  3  43  643.92 red, prism 0.25x0.15x0.10 trigonal R3 (#148) 42.2752(7) 9.0004(3)  no. observations (I > no©) no. of variables R (F , all data) R (F , all data) R(F,I>no(l))  218 0.047 0.095 0.035 (n=2)  1006 0.083 0.158 0.064 (n=2)  391 0.050 0.076 0.028 (n=3)  0.091 (n=2)  0.148 (n=2) 1.10  0.035 (n=3)  1  Rint  2  2  w  R (F,I>na(I)) Gof w  1.00  5  3  2  7  12  884.00 5.77 0.6695- 1.0000 55.8 20052 4799 0.046 3680 (n=2)  Fooo fi (MoKa), cm" correction factors 20™*, deg total no. of reflns no. of unique reflns  4 C 6H oN2PSi LiO Ru.C H 814.10 red, block 0.40x0.30x0.10 orthorhombic P2,2,2, (#19) 9.0674(3) 19.9274(5) 23.055(1)  2[C 2H N P Si4 Ru].C H 1864.67 yellow, chip 0.25 x0.25x0.10 orthorhombic Pbca(#61) 20.3845(8) 21.7255(8) 43.150(2)  -75 ± 1 1.298 1712.00 5.07 0.7804- 1.0000 55.8 31090 9060 0.047 7849(n=3)  0.94  0.88  Rigaku/ADSC C C D diffractometer, R = Z||F | - |F ||/X|F |; R = [S(F -F ) /S(0(F ) ] . 2  2  0  C  247  0  w  o  2  c  8  2  2  o  2  l/2  Appendix 1: X-ray Crystal Structure Data  Table A 2 . Crystallographic Data and Structure Refinement Data for complexes {[NPN]Ru(l-3 ri :5,6-ri -C8H i)}{Na.THF} 3  (5),  2  l  [NPNHJRuCl-S-ri ^^-!! ^,!)^) 3  Me2CH2][(C8H )C(0)N(Ph)SiMe CH2][Ph]}PRu(CO)4 n  C H N NaPSi RuO.C H 814.15 orange, chip 0.25 x0.25 x0.10 triclinic PI (#2) 10.2121(4) 10.3162(3) 22.133(1) 87.707(7) 79.077(6) 64.334(4) 2061.3(2) 36  50  2  7  Fw Colour, Habit Crystal size, mm Crystal system Space group a, A b,A c,A a, deg P,deg 7, dee  v, A z  ?  2  3  1  26max,  deg  total no. of reflns no. of unique reflns Rint  -100 ± 1 1.312 856.00 5.20 0.8093- 1.0000 55.7 18786 8409 0.032 7131 (n=3)  11  C 7H38N 0 Si P Ru 778.93 orange, block 0.25 x0.25 x 0.13 orthorhombic Pbca(#61) 16.0035(5) 18.5094(8) 26.638(2)  2  3  8  2  T, °C Pcalc, g/cm Fooo // (MoKa), cm" correction factors  2  3  8  C 3H43N OPSi Ru 3  671.93 yellow, block 0.35 x 0.10x0.10 monoclinic P2,/n(#14) 9.1968(4) 14.4543(5) 23.979(1)  2  5  2  96.731(2)  no. observations (I > no(I)) 385 no. of variables 480 0.046 0.052 R (F , all data) 0.066 0.082 R (F , all data) 0.026 (n=3) 0.029 (n=3) R (F, I > no(I)) 0.030 (n=3) 0.037 (n=3) R (F,I>na(I)) 0.91 1.48 Gof Rigaku/ADSC CCD diffractometer, R = I||F | - |F ||/Z|F |; R 1  2  2  w  w  2  C  248  C 9H N P RuSi4 4  66  2  3  989.41 orange, irregular 0.40x0.30x0.10 monoclinic P2,/n (#14) 10.3948(4) 15.0228(5) 32.490(1) 98.418(2)  3165.6(2) 4 -100 ± 1 1.410 1400.00 6.51 0.8278- 1.0000 55.8 29377 7258 0.047 5079 (n=3)  0  {[PfiN(H)Si  2  7  5  (7),  (8) and [P NNH]RuH(PPh ) (11).  2  Formula  2  0  7890.6(5) 8 -100 ± 1 1.311 3208.00 5.39 0.8230- 1.0000 55.7 63160 9419 0.075 5240 (n=2)  5019.0(3) 4 -100 ± 1 1.309 2076.00 5.38 0.7056- 1.0000 55.7 44199 11386 0.054 7511(n=3)  461 0.075 0.085 0.035 (n=2) 0.074 (n=2) 0.78  536 0.053 0.075 0.031 (n=3) 0.034 (n=3) 0.97  = [I(F - F ) /i:co(F ) ] 2  w  0  2  c  2  2  0  2  Appendix 1: X-ray Crystal Structure Data  Table A 3 . Crystallographic Data and Structure Refinement Data for complexes [NPN(H)(r| 6  C H )]RuH 6  (12), [NPNH ]Ru(H) (ri -C7H8)  (13), [NPNH](P Pr )Ru(CCPh)  2  (20) and  i  6  5  2  3  [P N ]Ru{CC(SiMe )Ph} (24). 2  2  3  24  12  13  20  b,A c,A  C 4H33N Si2PRu 537.75 orange, platelet 0.35 x 0.15 x 0.04 monoclinic P2,/a(#14) 10.2540(4) 22.2088(8) 11.0383(4)  C ,H N P RuSi 798.11 brown, platelet 0.40 x 0.40 x 0.05 monoclinic P2,/c (#14) 14.8185(4) 14.7405(3) 20.1233(4)  a, deg P,deg  101.362(3)  C H4 N PRuSi2 631.91 yellow, block 0.50 x 0.50 x 0.20 triclinic PI(#2) 10.2259(4) 11.0654(7) 15.8325(9) 89.778(3) 76.184(2)  Formula Fw Colour, Habit Crystal size, mm Crystal system Space group a, A  2  2  ?  T,°C g Cm /  Pcalc,  3  Fooo ju (MoKa), cm"' correction factors 29n,a , deg X  total no. of reflns no. of unique reflns Rint  no. observations (I > no(I)) no. of variables R (F , all data) R (F , all data) 2  2  w  R (F, I > no(I)) R (F,I>no(I)) Gof w  3  20492 6064 0.050 4216(n=3) 299 0.048 0.073 0.027 (n=3) 0.032 (n=3) 0.85  2464.5(1) 4 -100 ± 1 1.449 1112.00 8.13 0.6936-1.0000 57.4  4  2  65.090(2) 1568.3(1) 2 -100 ± 1 1.338 660.00 6.49 0.7021 - 1.0000 55.8 14121 6272 0.036 5184 (n=3)  Y> deg  v, A z  31  58  2  2  2  108.932(2) 4157.8(2) 4 -100 ± 1 1.275 1680.00 5.41 0.7673- 1.0000 55.8  C3 H N P Si Ru 808.29 red, chip 0.35 x 0.35 x 0.15 triclinic PI (#2) 10.3088(1) 10.6551(2) 20.5014(6) 83.512(7) 81.490(7) 66.922(5) 2045.1(1) 2 -100 ± 1 1.312 5  56  2  2  848.00 6.34 0.8153- 1.0000 55.7  34448 9095 0.051 6567 (n=3)  18902 8404 0.035 6847 (n=3)  350 0.054 0.094 0.032 (n=3) 0.044 (n=3)  437 0.053 0.083 0.029 (n=3) 0.037 (n=3)  406 0.052 0.081 0.030 (n=3) 0.039 (n=3)  1.38  1.08  1.35  Rigaku/ADSC C C D diffractometer, R = Z||F | - |F ||/Z|F |; R = [Z(F - F ) /Ico(F ) ] 2  0  2  C  249  0  w  0  2  c  5  2  2  0  2  Appendix 1: X-ray Crystal Structure Data  Table  A4.  Crystallographic  Data  and  Structure  Refinement  Data  for  [ N P N ] ( M g B r ) . ( C H 0 ) (26). 2  4  8  26  C H 9N OSi P Mg2Br  Formula  28  3  2  2  2  Fw Colour, Habit Crystal size, mm Crystal system Space group  clear, chip 0.50x0.20x0.20 orthorhombic Pbca (#61)  A, A  17.7617(6)  A  B,  715.19  16.3058(8)  C,A oc, deg P,deg Y, deg  23.452(1)  v, A z  6792.1(9) 8 -100 ± 1  ?  T,°C g/cm  3  Peak,  F o o o  //(MoKa), cm"' Correction factors 26max, deg  Total no. of reflns No. of unique reflns Rint  1.399 2928.00 25.72 0.7812-1.0000 55.8 59874 8702 0.094 3792(n=3)  No. observations (1 > na(I)) 343 No. of variables R (F , all data) 0.060 R (F , all data) 0.077 0.026 (n=3) R(F,I>no(I)) 0.029 (n=3) R (F,I>no(I)) 0.63 Gof Rigaku/ADSC CCD diffractometer, R = S||F | - |F ||/Z|F |; R = [I(F - F ) /2co(F ) ] . 2  2  w  w  2  0  2  C  250  0  w  0  2  c  2  2  0  2  l/2  compl  Appendix 2: H NMR Longitudinal Relaxation (TJ Measurements 1  Ti versus Terrperature  Appendix 2 300.00  1  H NMR Longitudinal Relaxation (7"i) Measurements  ' H N M R T\ relaxation measurements were performed on a Bruker A M X 500 MHz spectrometer using a standard inversion-recovery pulse sequence (180°-x-90°).  The T\ values  were obtained using the non linear three-parameter fitting routine in the Bruker X W I N N M R program with an estimated error of ± 10 % in each T\ value. The temperature was regulated using a Bruker V T 1000 unit. Toluene-dg was used as the N M R solvent for these studies.  251  Appendix 2: H NMR Longitudinal Relaxation (T,) Measurements 1  Table A5. Temperature and T\ values for the ruthenium hydrides in [P NNH]Ru(H )H (10). 2  2  7*i (ms) Ru-H  Temperature (K) 300  108  280 260 245 240 235 230 220  82 74 65 62 68 75 94  Ti versus Temperature 120.00  40.00 175  200  225  250  275  300  325  350  Temperature (K)  Figure A2. Plot o f T\ versus Temperature for the ruthenium hydrides in [P NNH]Ru(H )H (10). 2  252  2  Appendix 2: H NMR Longitudinal Relaxation (T,) Measurements 1  Table A6. Temperature and Ti values for the ruthenium hydride in [P NNH]RuH(PPh ) (11) 2  h  3  (ms)  Ru-H  Temperature (K) 300  475  270 265 260 255 250 245 240 230  379 375 370 379 396 429 446 606  versus Temperature 700.00 600.00 E  500.00 400.00 300.00 200  225  250  275  300  325  350  Temperature (K)  Figure A3. Plot o f T\ versus Temperature for the ruthenium hydride in [P NNH]RuH(PPh ) (11). 2  253  3  Appendix 2: H NMR Longitudinal Relaxation (T,) Measurements 1  Table A7. Temperature and T\ values for the ruthenium hydride in [NPN(H)(ri -C6H5)]RuH (12). 6  7i (ms) Ru-H  T e m p e r a t u r e (K) 298  1198  275  902  255  724  250  697  246  699  240  715  230  802  7"i v e r s u s T e m p e r a t u r e 1400.00 T — 1250.00 -  •  1100.00 950.00 -  • •  800.00 -  •  650.00 -  • • •  500.00 - 200  220  240  260  280  300  320  T e m p e r a t u r e (K)  Figure A4. Plot o f T\ versus Temperature for the ruthenium hydride in the complex [NPN(H)(r| 6  C H )]RuH (12). 6  5  254  Appendix 2: 'H NMR Longitudinal Relaxation (T,) Measurements  Table A8. Temperature and T\ values for the ruthenium hydride and amino proton in the complex [NPNH ]Ru(H) (r| -C7D ) (13). 6  2  2  8  Ti  (ms)  Temperature (K)  Ru-H  N-H  300 270 265 260 255 250 240  469 381 372 366 382 414 499  632 421 398 386 395 415 479  (a) T, versus Temperature  500.00  Ru-H  400.00  300.00 250  200  350  300  Temperature (K)  (b)  Tf versus Temperature 700.00 N-H _  In  600.00 •  E  ^  500.00 400.00 300.00200  250  300  350  Temperature (K)  Figure A5. Plot o f T\ versus Temperature for (a) the ruthenium hydrides and (b) the amino protons in the complex [NPNH ]Ru(H) (n -C D ) (13). 6  2  2  7  8  255  Appendix 2: H NMR Longitudinal Relaxation (Tt) Measurements 1  Table A 9 . Temperature and T\ values for the ruthenium hydrides and amino proton in the complex [NPNH2(r) -C H5)]RuH2 (14). 6  6  7i (ms) Temperature (K)  H-H  Ru-H  2 9 8  6 5 1  7 4 1  2 7 5  4 5 8  5 0 4  2 5 5  3 6 8  3 5 7  2 5 0  3 5 1  3 5 0  2 4 6  3 3 4  3 4 4  2 4 0  3 5 8  3 5 2  2 3 0  4 6 4  4 2 5  (a) T, versus Temperature  600.00 -E 450.00 -  150.00 -I 210  1  1  1  1  1—  230  250  270  290  310  Temperature (K)  (b) Ti versus Temperature  800.00 i (ms)  700.00 600.00 500.00 400.00 300.00 200.00 200  220  240  260  280  300  320  Temperature (K)  Figure A 6 . Plot o f T\ versus Temperature for (a) the ruthenium hydrides and (b) the amino proton in the complex [NPNrfcOf-CeHs^RuHj (14).  256  Appendix 2: H NMR Longitudinal Relaxation (Ti) Measurements 1  Table A10. Temperature and T\ values for the amino protons in the complex [NPNH ] (15). 2  7i (ms) N-H  Temperature (K) 300  1327  280 260 245 240 235 230  1058 798 666 614 690 732  T! versus Temperature 1450.00 -  •  1300.00 1150.00 % K  •  1000.00 850.00 -  •  700.00 550.00 400.00 - — 200  220  240  260  280  300  320  Temperature (K)  Figure A7. Plot of T\ versus Temperature for the amino protons in the complex [NPNH ] (15). 2  257  Appendix 3: Estimation of Rate Constants for Kinetic  Analyses  Appendix 3  Estimation of Rate Constants for Kinetic Analyses  Rate constants were estimated from line width analysis o f the variabletemperature N M R data using the following equations:  Slow rate o f exchange: &=27t8V Intermediate rate o f exchange: k = 2 K(AV  - Av )  2  Yi  2  0  Coalescence: k-  Vl  2 nAv Y2  0  Fast rate o f exchange: k = (47Ldv )/(5'v) 2  0  where, 5'v is the broadening at half-height (Hz), Av is the peak separation in the absence 0  o f exchange (Hz), and Av is the peak separation during exchange (Hz). error o f ± 5% was applied to each calculated rate constant.  258  A n estimated  Appendix 3: Estimation of Rate Constants for Kinetic  Analyses  Estimated rate constants for the fluxionality of the [P2N2] ligand in the compli [ P N ] R u ( r i : T I - C H ) (10). 2  2  2  2  8  1 2  Temperature = 243 ± 1 K (fast exchange) Av = 194.8 Hz; 8'v = 89.89 Hz; k= 5304 ± 265 s"  1  0  Temperature = 234 ± 1 K (coalescence) Av = 194.8 Hz; £ = 8 6 5 ± 43 s"  1  0  Temperature = 230 ± 1 K (intermediate rate o f exchange) Av =194.8 Hz; Av = 148.5 Hz; k= 560 ± 28 s"  1  0  Temperature = 227 ± 1 K (intermediate rate o f exchange)  Av = 194.8 Hz; Av = 168.8 Hz; k = 433 ± 22 s"  1  0  Temperature = 219 ± 1 K (slow rate o f exchange) 6 ' v = 10.44 Hz; £ = 6 6 ± 3 s"  1  Temperature = 212 ± 1 K (slow rate o f exchange) 8 V = 2.82 H z ; £ = 1 8 ± l s"  1  259  Appendix  3: Estimation  of Rate Constants for Kinetic  Analyses  Estimated rate constants for the inter-conversion of diastereomers exo-3 and endo-3.  Temperature = 285 ± 1 K (slow rate o f exchange) 8V = 4.69 H z ; £ = 3 0 ± 2 s " '  Temperature = 293 ± 1 K (slow rate o f exchange) 5 V = 9.71 Hz; k=6l±3  s"  1  Temperature = 308 ± 1 K (intermediate rate o f exchange) Av = 145.8 Hz; Zlv = 128.3 Hz; k = 308 ± 15 s"  1  0  Temperature = 320 ± 1 K (coalescence) ^ v = 145.8 Hz; £ = 6 4 8 ± 3 2 s"  1  0  260  

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