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Small molecule activation by diamidophosphine complexes of vanadium, niobium and tantalum Shaver, Michael Patrick 2004

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S M A L L M O L E C U L E ACTIVATION BY DIAMIDOPHOSPHINE COMPLEXES OF VANADIUM, NIOBIUM AND T A N T A L U M by M I C H A E L P A T R I C K S H A V E R B . Sc. (Hons.), Mount Al l i son University, 1999 A thesis submitted in partial fulfillment of the requirements for the degree of D O C T O R OF P H I L O S O P H Y in T H E F A C U L T Y OF G R A D U A T E S T U D I E S ( D E P A R T M E N T OF C H E M I S T R Y ) THE UNIVERSITY OF BRITISH COLUMBIA December 2004 © Michael Patrick Shaver, 2004 ABSTRACT A series of diamidophosphine ligand precursors, abbreviated R R [NPN]Li2(S) (where [NPN] = ( R f N S i M e 2 C H 2 ) 2 P R ; R = Ph, Cy; R ' = Ph, Mes, M e ; S = T H F , E t 2 0 , dioxane), were isolated in high yield. These ligands stabilize reactive complexes of the group five metals vanadium, niobium and tantalum. The sensitivity of these ligands to oxygen and water was illustrated by the reaction of C y P h [ N P N ] L i 2 ( O E t 2 ) with H 2 0 to form ( C y P h [ N P N ] L i 3 ) 0 . In this complex, two equivalents of [NPN] sandwich in situ formed L i 2 0 . The metathesis reaction of R R ' [ N P N ] L i 2 ( S ) and V C 1 3 ( T H F ) 3 afforded the chloride-bridged dimers ( R R [NPN]VC1) 2 . Reduction of these vanadium(III) chlorides with KCg produced binuclear vanadium complexes with bridging nitrides. These reactions were complicated by the formation of 1 1 1 1 [NPN]V=NR' and concomitant ligand decomposition. Metathesis of C y P h [ N P N ] L i 2 ( O E t 2 ) and NbCl 3 (dme) (dme = dimethoxyethane) under 1 atm. of N 2 gave C y P h [ N P N ] N b C l ( d m e ) . Under 4 atm. of N 2 , C y P h [ N P N ] N b C l ( d m e ) and ( C y P h [NPN]NbCl) (u . -N 2 ) were produced. Pressure controlled reactivity was also observed in the reaction of p h p h [ N P N ] L i 2 ( T H F ) 2 and NbCl 3 (dme). The complex C y P h [ N P N ] N b C l 2 formed readily from C y P h [ N P N ] L i 2 ( O E t 2 ) and N b C l 4 ( T H F ) 2 . C y P h [ N P N ] N b C l 2 was unstable in solution; A Nb(V) imide, C y P h [ N P N ] N b C l ( = N P h ) , a heterocyclic ring, C y P ( C H 2 S i M e 2 ) 2 N P h , and a paramagnetic impurity formed spontaneously. Similarly, reduction of p h p h [ N P N ] N b C l 2 with K C 8 produced p h p h [ N P N ] N b C l ( = N P h ) . Metathesis of C y P h [ N P N ] L i 2 ( O E t 2 ) with N b C l 2 M e 3 afforded the highly unstable complex C y P h [ N P N ] N b M e 3 . Attempts to hydrogenate this species and isolate a niobium hydride were unsuccessful. In contrast, the analogous tantalum complex, C y P h [ N P N ] T a M e 3 was hydrogenated to produce the bimetallic tetrahydride complex ( C y P h [NPN]Ta) 2 ((a-H) 4 . This complex reacts readily with N 2 to form ( C y P h [NPN]Ta) 2 ( |> H)2(Li-r|2:r|1-N2), in which molecular nitrogen is asymmetrically bound. Isotopic labeling studies suggest ( C y P h [NPN]Ta) 2 (u . -H) 2 is the reactive intermediate that activates molecular nitrogen. 11 Density functional theory was employed to investigate these reactions. B 3 L Y P / L A N L 2 D Z level calculations showed phosphorus donors in optimized structures for niobium analogues of trimethyl complexes ' N P N ' M M e 3 ( ' N P N ' = (CH3NSiH2CH2)2PCH3) do not coordinate. Energetics and Kohn-Sham orbitals of the conversion of ' N P N ' L i 2 ( O M e 2 ) . to ' N P N ' M M e 3 to ( ' N P N ' M ) 2 ( H ) 4 and finally the putative dihydride complex ('NPN'M)2(H)2 are discussed. Reactions of (R P h[NPN]Ta)2(p-H)4 (R = Cy , Ph) with primary and secondary phosphines are examined. Addit ion of one equivalent of HPR'2 (R' = Ph, Cy) to the tetrahydrides gave the tantalum phosphides (RPh[NPN]Ta)2(p-H)3(p-PR'2). Addition of one equivalent of H 2 P R " (R" = Cy, Ad) to ( R P h [NPN]Ta) 2 (p -H) 4 generated the corresponding phosphinidenes (RPh[NPN]Ta)2(p-H)2(p-PR"). Mechanistic insights were offered by several labeling studies. For example, addition of H P C y 2 to the deuterated complex ( P h P h [NPN]Ta) 2 (p -D) 4 produced the isotopomer ( P h P h [NPN]Ta) 2 (p-H)(p-D) 2 (p-PCy2). These results also implicated (RPh[NPN]Ta)2(p-H)2 as a possible intermediate. Attempts to isolate the dihydride intermediate by trapping with P M e 3 promoted the o-metalation of ligand N - P h rings. Activation o f non-phosphine small molecules by (R P h[NPN]Ta)2(p-H)4 complexes is also described. Reaction of the tetrahydride complexes with terminal alkynes gives p-alkyne structures of the form ( R P h [NPN]Ta) 2 (p -H) 2 (p -RCCH) . Addit ion of internal alkynes, however, leads only to complex decomposition. Addit ion of hydrazine to ( C y P h [NPN]Ta ) 2 (p -H) 4 gave ( C y P h [NPN]Ta) 2 (p -H) 2 (p -NH) 2 with two bridging imides. Addition of M e 2 N N H 2 , however, produced M e 2 N H and ( R P h [NPN]Ta) 2 (p -H) 3 (p -N) , with one bridging nitride. i i i T A B L E O F C O N T E N T S A B S T R A C T i i T A B L E O F C O N T E N T S iv LIST OF T A B L E S v i i i L IST OF F I G U R E S x i LIST OF C O M P O U N D S xvi G L O S S A R Y O F T E R M S xxi i A C K N O W L E D G E M E N T S xxvi Chapter One. Promot ing chemistry wi th transition metals stabilized by mixed-donor multi-dentate chelating ligands. 1.1 Multi-dentate ligands in coordination chemistry 1 1.2 M i x e d donor ligands 3 1.3 Amidophosphine ligands 5 1.4 The coordination, cleavage and functionalization of N 2 7 1.4.1 Coordination and activation of molecular nitrogen 7 1.4.2 Dinitrogen cleavage 12 1.4.3 Protonation of coordinated dinitrogen 14 1.4.4 Formation of N-Element bonds from coordinated dinitrogen 17 1.5 Promoting novel transformations: ligand modification 21 1.6 Scope of thesis 23 1.7 References 24 Chapter Two . Diamidophosphine ligand modification. 2.1 Introduction 29 2.2 Synthesis of R R ' [ N P N ] derivatives 33 2.2.1 Synthesis of C y P h [ N P N ] L i 2 ( O E t 2 ) 33 2.2.2 Reaction of 1 with H 2 0 36 2.2.3 Synthesis of other R R ' [ N P N ] lithium salts 39 2.3 Attempted synthesis of cyclic diamidophosphine ligands 44 iv 2.4 Experimental section 46 2.4.1 General considerations 46 2.4.2 Starting materials and reagents 47 2.4.3 Synthesis 47 2.5 References 52 Chapter Three. Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes. 3.1 Introduction 56 3.2 Preparation of V(III) complexes of the [NPN] ancillary ligand 59 3.2.1 Synthesis of ( R R ' [ N P N ] V C l ) n 59 3.2.2 Reduction of ( C y P h [ N P N ] V C l ) 2 : Coordination and cleavage of ... molecular nitrogen 3.2.3 Reduction of ( R R ' [NPN]VC1) 2 complexes: Identification of ligand decomposition products 3.3 Preparation of N b complexes of the [NPN] ancillary ligand 65 3.3.1 Preparation of Nb(III) complexes supported by [NPN]: Formation 65 of Nb(III) chlorides competing with the synthesis of Nb(V) N 2 complexes 3.3.2 Reduction of C y P h [ N P N ] N b C l ( D M E ) 68 3.4 Preparation of Nb(IV) complexes of the [NPN] ancillary ligand 68 3.4.1 Synthesis and decomposition of C y P h [ N P N ] N b C l 2 68 3.4.2 Synthesis and reduction of p h p h [ N P N ] N b C l 2 73 3.4.3 Mechanistic implications of decomposition of [NPN] supported mid-oxidation state complexes of vanadium and niobium 3.5 Experimental section 76 3.5.1 General considerations 76 3.5.2 Starting materials 77 3.5.3 Synthesis 77 3.6 References 83 v Chapter Four. Synthesis, reactivity and DFT calculations on [NPN] supported Nb(V) and Ta(V) complexes 4.1 Introduction 87 4.2 Synthesis and reactivity of niobium trimethyl complexes 88 4.2.1 Synthesis of R R ' [ N P N ] N b M e 3 88 4.2.2 Hydrogena t ionof R R ' [NPN]NbMe 3 89 4.3 Synthesis and reactivity of C y P h [ N P N ] supported Ta(V) complexes 90 4.3.1 Synthesis and characterization of C y P h [ N P N ] T a M e 3 90 4.3.2 Synthesis and characterization of ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 and 93 ( C y P h [NPN]Ta) 2 (p-H) 2 (u- r , 1 : r , 2 -N 2 ) 4.4 Tantalum alkyl , alkylidene and alkylidyne complexes 97 4.4.1 Introduction 97 4.4.2 Preparation of tantalum neopentylidene and neopentylidyne 98 complexes 4.5 A reactive tantalum tetrahydride complex 102 4.6 Density functional theory calculations 104 4.7 Summary 120 4.8 Experimental section 121 4.8.1 General considerations 121 4.8.2 Starting materials and reagents 122 4.8.3 Synthesis 122 4.9 References 127 Chapter Five. Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes 5.1 Introduction 131 5.2 Preparation of tantalum phosphide complexes 134 5.3 Preparation of tantalum phosphinidene complexes 139 5.4 Mechanistic implications 144 5.5 Attempts to trap ( R R ' [NPN]Ta) 2 (p -H) 2 149 5.6 The activation of other E - H bonds 157 vi 5.7 Summary 162 5.8 Experimental section 162 5.8.1 General considerations 162 5.8.2 Starting materials and reagents 162 5.8.3 Synthesis 163 5.9 References 170 Chapter Six. Promoting chemistry with [NPN] supported tantalum complexes 6.1 Introduction 173 6.2 Activation of C=E (E = C, N , O) triple bonds 174 6.2.1 Addit ion o f R C N and C O to 35 174 6.2.2 Addit ion of terminal alkynes to 41 178 6.2.3 Addit ion of diphenylacetylene to 41 182 6.3 Activation of N - N bonds 186 6.3.1 Introduction 186 6.3.2 Addit ion of hydrazine to 35 or 41 188 6.3.3 Addit ion of substituted hydrazines to 35 or 41 192 6.4 Future directions 197 6.5 Experimental 200 6.5.1 General considerations 200 6.5.2 Starting materials and reagents 200 6.5.3 Synthesis 201 6.6 References 204 Appendices. Appendix One: X-ray crystal structure experimental information 207 Appendix Two: Methods, z-matrices, initial parameters and final coordinates . . . . 209 for optimized density functional theory calculations. v i i LIST OF TABLES Table Title Page Table 2.1 Selected Bond Distances (A) and Angles (°) for 35 C y P h [ N P N ] L i 2 ( T H F ) 2 , 3 Table 2.2 Crystallographic Data and details of refinement for 35 C y P h [NPN] L i 2 ( T H F ) 2 , 3 Table 2.3 Selected Bond Distances (A) and Angles (°) for 37 ( C y P h [ N P N ] L i 3 ) 2 0 , 4 Table 2.4 Crystallographic Data and details of refinement for 37 ( C y P h [ N P N ] L i 3 ) 2 0 , 4 Table 2.5 Selected Bond Distances (A) and Angles (°) for 41 C y M e s [ N P N ] L i 2 ( T H F ) , 6 Table 2.6 Crystallographic Data and details of refinement for 41 C y M e s [ N P N ] L i 2 ( T H F ) , 6 Table 2.7 3 1 P and 7 L i N M R spectroscopic data for [NPN] ligand precursors 43 Table 3.1 Selected Bond Distances (A) and Angles (°) for 60 ( C y P h [ N P N ] V C l ) 2 , 14 Table 3.2 Crystallographic Data and details of refinement for 60 ( C y P h [ N P N ] V C l ) 2 , 1 4 Table 3.3 Selected Bond Distances (A) and Angles (°) for 70 C y P h [ N P N ] N b C l ( = N P h ) , 26 Table 3.4 Crystallographic Data and details of refinement for 71 C y P h [ N P N ] N b C l ( = N P h ) , 26 Table 4.1 Selected Bond Distances (A) and Angles (°) for 92 C y P h [ N P N ] T a M e 3 , 34 Table 4.2 Crystallographic Data and details of refinement for 93 C y P h [ N P N ] T a M e 3 , 34 Table 4.3 Selected Bond Distances (A) and Angles (°) for 95 ( C y P h [NPN]Ta) 2 (p -H) 2 (p -n 1 : r , 2 -N 2 ) , 36 Table 4.4 Crystallographic Data and details of refinement for 96 ( C y P h [NPN]Ta) 2 (p -H) 2 (p -n 1 : r , 2 -N 2 ) , 36 v i i i Table 4.5 -Selected Bond Distances (A) and Angles (°) for 101 ' c y p h [ N P N ] T a ( C l ) ( = C H C M e 3 ) , 39 Table 4.6 Crystallographic Data and details of refinement for 101 C y P h [ N P N ] T a ( C l ) ( = C H C M e 3 ) , 39 Table 4.7 Total energy (in Ha) for optimized compounds 108 ( B 3 L Y P / L A N L 2 D Z ) Table 4.8 Selected optimized bond lengths (A) and bond angles (°) for 4B 110 and 4E Table 4.9 Selected optimized bond lengths (A) and bond angles (°) for 4C 110 and 4F Table 4.10 Selected optimized bond lengths (A) and bond angles (°) for 4D 111 and 4G Table 5.1 Selected Bond Distances (A) and Angles (°) for 137 ( p h P h [NPN]Ta) 2 ( |a-H) 3 (^-PCy 2 ) ,42. Table 5.2 Crystallographic Data and details of refinement for 138 ( p h p h [NPN]Ta) 2 (u -H) 3 (u -PCy 2 ) , 42. Table 5.3 Shortest reported Ta-Ta interatomic distances, and selected 139 comparative examples Table 5.4 Selected Bond Distances (A) and Angles (°) for 143 ( P h P h [NPN]Ta) 2 (p . -H) 2 (p-PAd), 48. Table 5.5 Crystallographic Data and details of refinement for 143 ( p h p h [NPN]Ta) 2 (u -H) 2 (u -PAd) , 48. Table 5.6 Selected Bond Distances (A) and Angles (°) for 54. 153 Table 5.7 Crystallographic Data and details of refinement for 54. 154 Table 5.8 Selected Bond Distances (A) and Angles (°) for 55. 156 Table 5.9 Crystallographic Data and details of refinement for 55. 156 Table 6.1 Selected Bond Distances (A) and Angles (°) for 63. 184 Table 6.2 Crystallographic Data and details of refinement for 63. 184 Table 6.3 Selected Bond Distances (A) and Angles (°) for 190 ( p h p h [NPN]Ta) 2 ( | a -NH) 2 (u-H) 2 , 65. ix Table 6.4 Crystallographic Data and details of refinement for 191 ( P h P h [NPN]Ta) 2 ( | a -NH) 2 (p-H) 2 , 65. Table 6.5 Selected Bond Distances (A) and Angles (°) for 193 C y P h [NPN]Ta)(p.-N)((x-H) 3 , 66. Table 6.6 Crystallographic Data and details of refinement for 194 C y P h [NPN]Ta)(p . -N)(p-H) 3 , 66. Table A l Method and Z-matrix for model complex 4A. 209 Table A2 Initial parameters for model complex 4A. 210 Table A3 Final atomic coordinates for the geometry optimization of 4A. 211 Table A4 Method and Z-matrix for model complex 4B. 212 Table A5 Initial parameters for model complex 4B. 213 Table A6 Final atomic coordinates for the geometry optimization of 4B. 214 Table A7 Method and Z-matrix for model complex 4C. 215 Table A8 Initial parameters for model complex 4C. 216 Table A9 Final atomic coordinates for the geometry optimization of 4C. 217 Table A10 Method and Z-matrix for model complex 4D. 218 Table A l l Initial parameters for model complex 4D. 219 Table A12 Final atomic coordinates for the geometry optimization of 4D. 220 Table A13 Method and Z-matrix for model complex 4E. 221 Table A14 Initial parameters for model complex 4E. 222 Table A15 Final atomic coordinates for the geometry optimization of 4E. 223 Table A16 Method and Z-matrix for model complex 4F. 224 Table A17 Initial parameters for model complex 4F. 225 Table A18 Final atomic coordinates for the geometry optimization of 4F. 226 Table A19 Method and Z-matrix for model complex 4G. 227 Table A20 Initial parameters for model complex 4G. 228 Table A21 Final atomic coordinates for the geometry optimization of 4G. 229 Table A22 Gaussianisms. 230 LIST OF FIGURES Figure Title Page Figure 1.1 Visualizing the concepts of ligands, chelation, and denticity. 5 Figure 1.2 Conversion of molecular nitrogen into value added products 8 mediated by a transition metal catalyst. Figure 1.3 Examples of metal complexes exhibiting three different 11 coordination modes for the dinitrogen ligand. The corresponding N - N bond lengths are given. Figure 2.1 O R T E P drawing of C y P h [ N P N ] L i 2 ( T H F ) 2 , 3. S i ly l methyl and 34 T H F carbons have been omitted for clarity. Figure 2.2 O R T E P drawing of ( C y P h [ N P N ] L i 3 ) 2 0 , 4. S i ly l methyl, phenyl 36 and cyclohexyl ring carbons other than ipso or methine carbons have been omitted for clarity. Figure 2.3 O R T E P drawing of C y M e s [ N P N ] L i 2 ( T H F ) , 6. S i ly l methyl and 40 T H F carbons have been omitted for clarity. Figure 3.1 O R T E P drawing of ( C y P h [ N P N ] V C l ) 2 , 14. S i ly l methyl, phenyl 59 and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Figure 3.2 O R T E P drawing of C y P h [ N P N ] N b C l ( = N P h ) , 26. Ligand si lyl 70 methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons omitted for clarity. Figure 3.3 O R T E P drawing of unit cell contents for 72 C y P h [ N P N ] N b C l ( = N P h ) , 26. CI atoms (lime green) are in close contact with the open face of the Nb (dark grey). Figure 4.1 O R T E P drawing of C y P h [ N P N ] T a M e 3 , 34. S i ly l methyl, phenyl 92 and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Figure 4.2 O R T E P drawing of ( C y P h [NPN]Ta) 2 (u -H) 2 (p -n 1 : n 2 - N 2 ) , 36. 95 Si ly l methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. x i Figure 4.3 ORTEP drawing of C y P h[NPN]Ta(Cl)(=CHCMe 3), 39. Silyl 100 methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Figure 4.4 Simplified'NPN'ligand model for DFT calculations. 107 Figure 4.5 Qualitative comparison of the total energy vs. the progress of 109 reaction. Figure 4.6 Depiction of the HOMO of model complex 4B, along with a 112 simplified illustration of the bonding. Figure 4.7 Depictions of the HOMO-1 (top) and HOMO-2 (bottom) of 113 model complex 4B, together with simplified illustrations of the bonding. Figure 4.8 Depictions of the L U M O (top) and LUMO+1 (bottom) of 114 model complex 4B, together with simplified illustrations of the bonding. Figure 4.9 Depictions of the HOMO (top), HOMO-1 (mid) and HOMO-2 115 (bottom) of model complex 4E, together with simplified illustrations of the bonding. Figure 4.10 Depictions of the L U M O (top) and LUMO+1 (bottom) of 116 model complex 4E, together with simplified illustrations of the bonding. Figure 4.11 Depiction of the HOMO (left) and HOMO-1 (right) of model 117 complex 4C showing the Ta-Ta a-bond (HOMO) and Ta-H 8-bonds (HOMO-1). Figure 4.12 Depiction of the L U M O (left) and LUMO+1 (right) of model 117 complex 4C showing the empty orbitals with 8-bonding and a-antibonding symmetries. Figure 4.13 Depiction of the HOMO (left) and HOMO-1 (right) of model 118 complex 4F showing the Ta-Ta a-bond (HOMO) and Ta-H 8-bonds (HOMO-1). xn Figure 4.14 Figure 4.15 Figure 4.16 Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Depiction of the L U M O (left) and L U M O + 1 (right) of model 118 complex 4F showing the empty orbitals with 5-bonding and a-antibonding symmetries. Depiction of the H O M O (left) and H O M O - 1 (right) of model 119 complex 4D showing the Ta-Ta o-bond ( H O M O ) and Ta-Ta Ti-bond (HOMO-1) . Depiction of the L U M O (left) and L U M O + 1 (right) of model 120 complex 4D showing the empty orbitals with a-bonding and 8-antibonding symmetries. ' P l ' H } N M R resonances for ( P h P h [NPN]Ta) 2 (p-H) 3 (p-PCy2), 135 42. P A , the bridging phosphide, couples to P B and Pc, the ligand phosphines. O R T E P drawing of ( p h p h rNPN]Ta) 2 (p -H) 3 (p -PCy 2 ) , 42.. S i ly l 137 methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Hydrides H I , H2 and H3 located in the diffraction pattern and refined isotropically. Hydride resonance in 47 showing coupling to three P nuclei 140 giving rise to a septet. Lorentzian deconvolution is shown. O R T E P drawing of ( p h p h [NPN]Ta) 2 (p -H) 2 (p -PAd) , 48.. S i ly l 142 methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Hydrides H I and H2 located in the diffraction pattern and refined isotropically. Trapping the putative dihydride with tertiary phosphines 149 O R T E P drawing of 54. Si ly l methyl, phenyl and cyclohexyl 152 ring carbons other than ipso and methine carbons have been omitted for clarity. O R T E P drawing of 55. S i ly l methyl and phenyl ring carbons 155 other than ipso carbons have been omitted for clarity. x i i i Figure 6.1 O R T E P drawing of the decomposition product of 183 ( p h P h [NPN]Ta) 2 (p . -H) 4 + PhCCPh , 63. S i ly l methyl and phenyl ring carbons other than ipso positions have been omitted for clarity. Figure 6.2 O R T E P drawing o f ( p h p h [NPN]Ta) 2 (p.-NH) 2 (u.-H)2, 65. S i ly l 190 methyl, phenyl and cyclohexyl ring carbons other than ipso or methine positions have been omitted for clarity. Figure 6.3 O R T E P drawing of ( p h P h [NPN]Ta) 2 (p . -NH) 2 (p-H) 2 , 65. Only 192 the core atoms in the structure are shown. Atoms H1-H4 are included, although isotropic refinement of these atoms was unstable. Figure 6.4 O R T E P drawing of C y P h [NPN]Ta)(p-N)(p. -H) 3 , 66. S i ly l 193 methyl, phenyl and cyclohexyl ring carbons other than ipso or methine positions have been omitted for clarity. Figure 6.5 O R T E P drawing of the structural core of an initial solution 195 (left) and a correct solution (right) from data collection on 66. This structure was solved as a bis(nitride), however N(3) is in fact disordered over the two positions. xiv LIST OF COMPOUNDS The following compounds have been prepared for this dissertation and are included here for quick reference to the main text. xv xvi SiMe Me2 . / I I Ph ™ M e 2 S l Cl—V—P, N<J-SiMe 2 •Si Me2 / l [\ 'CX P — N b — C l y >*ci SiMe2 °. V Si 6 2 P/ hP.h M e 2 P h D h ^ P _ N b = N — N = N b - P . 24 ^ P _ 4 | b - C | Ph4^siSiMez v q f ^ P h " cf 2 gh p . M e 2 S i ? ! L y N . - / h ^ 26 C\ \ f ^Ph P—Nb—Cl P-^Nb—N Cy | Cy ' Ph' I I 20 7 s H Me2 Mes P—~Nb=N N=Nb*-P v . 22 v\_ Vi Ph I l\ > 7 „/ y\ Cl Cl Me2 ph M e 2 S i ^ ^ f C y / / ^ N \ N PhN-^MeT""7 P—Nb—Cl Ph Cl Me2 p h ,si4i>'Vh 2/7—N~N' Me2Si—-(i V* ^Ph 30 / ^ S i P-*~Nb^=N PhN Me2 y I Ph I Cl Me2 ph M e 2 Ph „. C\ V 32 C\ V P-^Nb—Me P-*~Nb—Me Cy l'\ Ph / V Me Me Me Me Me 2S1*0'.< k .- ' '* M „ . e i _ ^PPh xv i i 33 M e 2 Mes M e 2 S L ^ / N . . * M e s / N N P — ~ N b — M e c / l\ Me Me 34 p - ^ T a — M e Cy l'\ Me Me 35 r,L. P h Ph ; M e 2 S i < / T a<^ Tt<<NA S i M e2 V - r ^ \ ^ S i M e z N*4 \ C y ^ Ph Ph n u P h Ph i VN, *H, p<r\ M e 2 S i - ^ N ^ , . . . ^ H ^ . / \ \ 36 M e 2 Si< / K / S N - V S i M e 2 \ ^P'h c y Ph 37 Ph Ph \ M Me 2Si*| ja= cy - C M e 3 38 Ph Ph \ M M e 2 S n T a = C — C M e 3 Ph 39 41 43 Ph Ph \ M e 2 S K N ^ . Cy CMe 3 C H Ph r Me 2Si, T A P < T \ v "N-"\.. SiMe 2 Ph N* ^ Ph Ph Ph Cy, Cy Ph * W \ h B p < n M e 2 S i i l y T a ^ ? T j V , ^ \ S i M e 2 Cy prT y Ph 40 42 Ph CMe 3 Ph \ | Me 2Si*| ^ T a \ Ph Ph Cy Cy Ph \ CI ^ / ' Ph H X N ^ S i M e . Me \ Ph Ph:y Ph Ph Ph Ph _,. Ph \ \ I ?h VN j/ p ^ T l 44 Me2SiT y T a ^ ^ T a \S iMe 2 \ Ph f N ph~y Ph 45 Ph Ph \ M M e 2 S r ^ N ^ Me 2Si Ph Ph „ I Cy / V \ Cy pKy Ph Ph Ph \ VN Cy Ph 46 M e 2 S i , T ^ a ^ T a , i c N SiMe 2 SiMe 2 Ph Ph'y Ph xviii Ph Ph \ M e 2 S K N ^ / \ / - 11 S i M e 2 S i M e 2 Cy i N Ph 48 Ph Ph \ M Ph M e 2 S i J ^ { ^ ^ ^ ^ Ad I R. iT T a ^ — ^ T a J S i M e 2 i ; N \ Ph pKy Ph Ph Ph Ad . I ^ V M e 2 S i f , T a < ^ - ^ T a J S i M e 2 c y p,v Ph Ph = V N .D,, P < T \ 50 * ^ ^ / a ^ \ ^ Cy >Ta ^ \ - S i M e 2 D" » N > r 3 | I V I B 2 [ Ph Ph Ph Cy Cy Ph .^ W Vy J ' N , P ' p ^ r i M e 2 S i f ^ T a ^ T - ^ T a . , , , J s i W l e 2 V ^ / N g / X ^ < S i M e 2 \ c y phy Ph 52 Ph Ph M M e 2 S q Ja-Cy Cy W P D > N ' \ Cy ph~y Ph M e 2 p . h P , h S i ~~~' -N Me2S\-f— \% P — - T a = = T a - — P . . 3 N < . A s i l - T a = / Cy R 3 P N < . 7~SiMe2 / > S i 2 Ph Ph M e 2 54 M e ^ i -Ph / N S i M e 2 / M e 3 P - ^ T a — N * T a i — P ^ -A J. N \ , / •Cy / Cy - S i M e 2 M e ^ i Ph / N M e 3 P - ^ T a ^ l -/ Ph N , T a * - P -'"N N ''' I H / S i M e 2 P h S i M e 2 Ph Si M e 2 r , u P h Ph Ph Cy J H V / S i M e 2 S i < N ^ , \ / \ / ^ \ 56 M e 2 S i < / T a ^ H ^ T \ : " N ^ V J W P \ H N - > \ i Ph cy P h S i M e 2 P h P ^ V N , n Bu C y M e 2 S i - ^ N ^ , | / ~ \ / r < \ \ <r T a v * T a . „ \ - S i M e 2 v " p \ H N - i \ C y N'T ^ P h P h , S i M e 2 58 P h \ P h \ V-N M e 2 s a / a N N ^ \ -R N P h -t T a . , „ ^ ^ - S i M e 2 / .SiMe-> \ Ph ^ Ph Ph xix XX G L O S S A R Y O F T E R M S The following abbreviations, most of which are commonly found in the chemical literature, are used in this thesis. R R ' [ N P N ] , [NPN] R P ( C H 2 S i M e 2 N R ' ) 2 ligand ' N P N ' C H 3 P ( C H 2 S i H 2 N C H 3 ) 2 model ligand R R ' [ N P N ] * R P ( C 6 H 4 N R ' ) 2 ligand R R ' [NP] R P ( C H 2 S i M e 2 ) 2 N R ' c y c l i c [ N P N ] R ( N S i M e 2 C H 2 ) 2 P R ' proposed macrocycle R [PNP] N ( S i M e 2 C H 2 P R 2 ) 2 ligand R [ P 2 N 2 ] R P ( C H 2 S i M e 2 N S i M e 2 C H 2 ) 2 P R ligand [PN 3 ] P h P M e ( C H S i M e 2 N S i M e 2 C H 2 P ( P h ) C H 2 S i M e 2 N S i M e 2 N ) [NN 2 ] M e 2 S i N ( C H 2 C H 2 N S i M e 3 ) 2 ligand [ H I P T N 3 N ] [ (H I P T N C H 2 C H 2 ) 3 N ] 3 " ligand 0 (or deg) degrees °C degrees Celcius *H proton {•H} proton decoupled 1 3 C carbon-13 1-D one dimensional 2-D two dimensional 31p phosphorus-31 { 3 'P} phosphorus-31 decoupled 7 L i lithium-7 9 - B B N 9-borabicyclo[3.3.1]nonane, H B C g H n a, b, c unit cell dimensions; lengths a , p \y unit cell dimensions; angles A Angstrom A d adamantyl Anal . analysis xx i A r aryl (or argon) A r f 3 ,5 - (CF 3 )2 -C 6 H 3 atm atmospheres B e q equivalent isotropic thermal parameter B . M . Bohr magneton br broad Calcd. calculated C C D charge coupled device C O S Y correlated spectroscopy ( N M R experiment) Cp cyclopentadienyl (C5H5) C p * , C p " , C p t t substituted cyclopentadienyl groups cryst crystal Cy cyclohexyl d doublet d o f d doublet of doublets d o f d o f d doublet of doublet of doublets Dca]c calculated density D F T density functional theory diox 1,4-dioxane Dipp 2 , 6 - i P r 2 - C 6 H 3 D M E or dme 1,2-dimethoxyethane cf numbers of ti-electrons dppm diphenylphosphinomethane dmpe dimethylphosphinoethane d x z , d y z , d x y , dZ2, dX2-y2 d orbitals of appropriate symmetry E element, usually referring to s or p block E total energy E P energy as related to electron density Eex energy of correlated electron motion EI-MS electrospray ionization mass spectrometry Et ethyl, - C H 2 C H 3 xx i i E P R electron paramagnetic resonance equiv equivalents eV electron Volt G Gauss G M Gaussian multiplication g grams G C - M S gas chromatography/mass spectrometry G O O F goodness-of-fit h v photon Ha Hartrees H M D S hexamethyldisiloxane HIPT hexaisopropylterphenyl (3,5-(2,4,6- iPr 3-C6H2)2C6H3) H O M O highest occupied molecular orbital H O M O - n M O n orbitals lower in energy than the H O M O H S Q C heteronuclear single quantum coherence H z Hertz, seconds"1 / nuclear spin 'Pr isopropyl substituent IR infrared " J A B n-bond scalar coupling constant between nuclei A and B k rate constant K degrees Kelv in K e q equilibrium constant kJ kiloJoules L general ligand L n a set of n ligands ln natural logarithm L U M O lowest unoccupied molecular orbital L U M O + n M O n orbitals higher in energy than the L U M O Lut HC1 2,6-lutidinium chloride M central metal atom xxi i i M + parent ion m meta m multiplet ( N M R spectroscopy) M e methyl group, -CH3 mle or m/z mass/charge (mass spectrometry unit) Mes mesityl group, -2,4,6-Me3CeH2 M H z Megahertz, one mill ion Hertz mmol millimole M O molecular orbital mol mole M S mass spectrometry n B u normal butyl substituent N M R nuclear magnetic resonance Np neopentyl group, -CH2C(CH3)3 0 ortho O R T E P Oakridge Thermal Ell ipsoid Plotting Program ov overlapping ox. add. oxidative addition p para Ph phenyl group, -C6H5 Pi inorganic phosphate, PO4 3" ppm parts per mil l ion Pr' isopropyl group, -CH(CH 3 )2 py pyridine q quartet R, R' hydrocarbon substituents R 2 coefficient of determination for a linear regression R i , R w residual errors (X-ray crystallography) red. elim. reductive elimination reflns reflections (X-ray crystallography) rt or r.t. room temperature xxiv S solvent or donor atom s singlet SHOP Shell higher olefin process silox OSiC'Bub t triplet (1:2:1 unless otherwise specified) T temperature in Kelvin or °C lBu tertiary butyl group THF tetrahydrofuran TMS trimethylsilyl substituent TJ(eq) equivalent isotropic displacement parameter (one third of the trace of the orthogonalized Uij tensor). UV-VIS ultraviolet/visible V unit cell volume VSEPR valence-shell electron pair repulsion VT variable temperature X halide substituent X-HYDEX hydride location program Z asymmetric units per unit cell a, TI, 8 notations for bonding symmetries s molar extinction coefficient r|n hapticity of order n p n bridging n atoms p (Mo Ka) absorption coefficient (X-ray crystallography) p density p electron density A, wavelength 8 chemical shift in ppm Peff effective magnetic moment xxv A C K N O W L E D G E M E N T S This thesis does not stand on its own. While my name rests as the sole author on the front page, it would have been an impossible without the help of many contributors. I hope I have not overlooked anyone. I wish to thank: Mike "Ichiban " Fryzuk for the immense help in directly supervising me, letting me dirty up his whiteboard, taking time out of a busy golfing schedule to talk chemistry or edit manuscripts, and for "letting" me leave after I solved the Me2NNH2 problem. Working alongside the fine citizens of the Fryzuk group has taught me a lot about both chemistry and human nature. It is amazing how a group of people can change in just five years. I thank all the current members of the group for being a fantastic group. While there are too many fellow graduate students, post-docs and summer students to thank all of them individually, I must especially thank: Erin "Ghoosh" MacLachlan for helping turn this mumbo-jumbo thesis into English, Chris "Carmageddon " Carmichael for crystallography collections and lessons, and Rob "Roshambo " Thomson for rekindling my interest in 24/7 chemistry. I thank the professors and staff of the U B C chemistry department who have helped me throughout this journey. Again, I need to single out several contributors: Laurel Schafer for many an engaging discussion about life in (and out of) the lab, Nick Burlinson for always helping, teaching and trying to keep the 500 running, and Brian Patrick for solving my structures before I learned how to do it myself. I also appreciate the financial support of NSERC (PGS A & B), the Izaak Walton Killam Foundation (Predoctoral Fellowship), the University (Li Tze Fong Memorial Fellowship), and the Department (Laird and McDowell Fellowships). Finally, I wish to thank Lisa Penney. She is the engine that keeps my heart warm, my mouth smiling and my life running. I dedicate this work to her. x x v i Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands 1.1 Multidentate ligands in coordination chemistry In 1787, in Methode de Nomenclature Chimique,x Lavoisier wrote that there are "three things to distinguish in physical science: the series of facts which form the science; the ideas which recall the facts; and the words which express them. The word must suggest the idea; the idea must depict the fact: these are three marks of the same stamp." Science is quite free in the naming of processes, substances, actions and characteristics. Savory, who felt that science was "the natural enemy of language", wrote that "scientists can invent words merely by defining them so that others may know how and when to use them, the only criterion being intelligibility."" Therefore, it is useful to briefly examine some of the terminology used in this Chapter's title to gain a better understanding of the ideas and their intelligibility. Coordination compounds contain a central atom, usually a metal, surrounded by several molecules. 3 These surrounding molecules are said to be coordinated to the metal centre, and they are called ligands4 The term ligand is derived from the Latin roots ligare which means 'to bind' and ligandum meaning to 'that which should be bound'. This Chapter One 1 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands effectively conjures the idea of binding or coordinating these external molecules to the central metal. If a ligand occupies two or more coordination sites, it is called a multidentate or chelating ligand. The Latin root dentis means ' o f or pertaining to a tooth'. In Latin, bidens and tridens refer to items with two or three teeth. To chemists, bidentate or tridentate refer to a ligand coordinating to two or three sites respectively. The term chelate derives from the Greek root chela, which refers to the large claw of a lobster or other crustacean, and suggests the caliper-like action of a claw. 5 In general, chelating ligands form more stable complexes than their monodentate analogs. This chelate effect is explained by the increase in entropy that accompanies the loss of several monodentate ligands when a multidentate ligand binds to a metal. This concept can also be understood qualitatively. The probability of the replacement of a coordinated monodentate ligand with an incoming amine or diamine should be almost equal. The probability of replacement of a second ligand with the other arm of the diamine, however, is much higher than a replacement by a second free amine, as the diamine is already tied to the metal ion and the free end of the molecule is in the immediate vicinity of the metal centre. Transition metals, in general, tend to give up electrons to other elements when they form compounds, and consequently become positively charged. The elements vanadium, niobium and tantalum, for example, can donate up to five electrons forming vanadium(V), niobium(V) and tantalum(V) oxidation states. It should be noted that oxidation states are merely formalisms. Calculations show that the actual positive charge on a metal is usually much less than its formal oxidation state implies. To stabilize these high oxidation states chemists use ligands that not only form strong a-bonds, but release electrons back to the metal (through 7t-bonding), thus reducing the positive charge on the metal. Oxides, fluorides and amides are all effective 7t-donors. L o w oxidation states are stabilized by ligands that accept electrons from the metal (through 7i-backbonding) and in this way increase the positive charge on the metal. These 7T-acid ligands include N O + , C O , C N " and phosphines. Ligands can also be classified into hard and soft bases. Soft acids and bases are highly polarizable, whereas hard acids and bases are not. Ligands that bind to the metal 2 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands with N , O, and F are hard bases, whereas P, S, and I derived ligands are soft bases. Hard-soft acid-base theory6"8 states that the most stable complexes generally result from hard acid-hard base and soft acid-soft base combinations. Early metals are considered hard; they have fewer c/-electrons available for back-donation and are less polarizable than soft late-metals. Qualitatively, an early metal complex w i l l be better stabilized by hard bases, while soft bases improve late metal complex stability. 1.2 Mixed-donor ligands B y combining different donors into a single chelating ligand, a metal complex can be stabilized under different conditions. For example, combining O and S donors into a chelating framework, for instance, could provide a ligand effective at simultaneously stabilizing hard metals in high oxidation states with the oxygen donor and soft metals in low oxidation states with the sulfur donor. Mixed-donor multidentate ligands are used industrially in several processes. A process developed by Shell uses a chelating phosphine-pyridine ligand in the carbonylation of alkynes during the synthesis of methylmethacrylate. 9" 1 1 In this case, the weak palladium-nitrogen bond is broken and the pyridine ring protonated, opening up a coordination site in the metal complex. The bidentate ligand controls the observed chemistry by matching both a strongly and weakly coordinating donor in a single ligand. During the catalytic cycle, shown in Scheme 1.1, the ligand alternates between bidentate and monodentate coordination and complete dissociation. In its protonated form, the pyridine acts as a labile, weakly coordinating ligand and is displaced by C O , methyl acetylene and methanol. Another example of an established industrial process that employs mixed-donor, multidentate catalysts to promote a transformation is S H O P , or Shell higher olefin process.9' 1 2 " 1 4 The oligomerization of ethylene to give linear terminal alkenes produces feedstocks for the synthesis of detergents, plasticizer alcohols and polymerization monomers. Shell uses a nickel catalyst supported by an O, P bidentate ligand in the first step of this process to convert ethylene into linear a-alkenes. Scheme 1.2 shows an example of a nickel precatalyst. Under the reaction conditions, the precursor complex 3 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands generates a nickel-hydride that initiates the oligomerization reaction. The selectivity of the oligomerization reaction is largely controlled by the chelating ligand. MeOH Ph 2 Ph 2 N CO(OMe) CO d [PNH]X Ph 2 \ / C ° X P D \ N OMe [PNH]X < Ph 2 Ph, x P d \ h N COMe [PNH]X Ph 2 Pd. OMe Scheme 1.1 HCCMe [PNH]X 4 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands 1.3 Amidophosphine ligands Work in the Fryzuk laboratory is focused on ligands that exploit the principles of mixed-donor multidentate coordination to stabilize a variety of metals in a variety of oxidation states and degrees of coordinative unsaturation. Conceptually, these ligands employ N and P donor atoms bound to the metal. These donors are tied together, chelating like the claw of a lobster. In this case, evolution has mutated this lobster and given it three or four arms with which to stabilize our metal centre (Figure 1.1). These hybrid ligands combine hard amide donors (NR2~) and soft phosphine donors (PR3). The first such mixed donor ligand was the chelating, anionic amidodiphosphine ligand (N(SiMe 2CH 2PR 2)2)", abbreviated R[PNP] (where R = Me, jPr, T3u, Ph). 1 5 As expected, the pendant phosphine donors are well suited for coordination to low oxidation state late transition metals, assisting the amide donor in binding to the metal.16 Conversely, early metals bind strongly to the amide donor, while the comparatively weak phosphine donor coordinates through the chelate effect.17 Figure 1.1. Visualizing the concepts of ligands, chelation, and denticity. The synthesis of the lithiated ligand precursor R [PNP]Li is readily performed using the commercially available HN(SiMe2CH 2Cl) 2. For phosphines bearing alkyl substituents, the ligand precursor is prepared in a single step using three equivalents of LiPR 2 , two equivalents of which functionalize the chloromethyl sidearms in a metathesis reaction and the third of which deprotonates the amide donor. This ligand is then 5 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands conveniently attached to metal halides with the loss of lithium halide. The R[PNP] ligand synthesis and metal complex formation is shown in Scheme 1.3. M e 2 M e 2 M e 2 M e 2 M e 2 M e 2 Si K 1 ^ - S i 3 i ^ ? 2 J S i — K 1 S i . . . v / S | ^ M ^ S / N \ T H F / N — \ L n M X / N - 2 L i C I ^ L i ^ y - 2 U X R , P ^ M — P R , CI CI - H P R 2 P ^ ^ P ^ 2 R L R 2 R 2 n Scheme 1.3 One drawback to the use of R[PNP] for early metal complexes was the propensity for phosphine dissociation. In several early metal complexes, one arm of the tripodal 18 ligand dissociated, giving a bidentate ligand with a pendant phosphine donor arm. To limit this phosphine dissociation, donor atoms were incorporated into a macrocycle. The synthesis of R[P 2N 2] (R[P2N2] = (RP(CH2SiMe2NSiMe2CH2)2PR)2", R = Ph, Cy) involved linking the two phosphine donors with an additional disilazane moiety, as shown in Scheme 1.4.19 Because of the stereochemical orientations of the two phosphine donors, both syn and anti isomers can form. Judicious control of solvent and temperature selectively produces solely the syn isomer. Although macrocycle synthesis usually requires dilute conditions,20'21 R[P 2N 2] is prepared in high yield via lithium templating. M e 2 M e 2 S i ^ - S i M.e2 M e 2 2 L i H P R ^ 2 ™ * H N ( S i M e 2 C H 2 C I ) 2 / \ E t 2 0 / ^ N ^ " \ 4 B u n L i , E t 2 0 . . . . , H \ *- / H \ 1 ^ P h - P ^ ^ R - P h CI CI P H H P 2 LiCI \ / 1,4-dioxane / \ y  < V ) / \ S = diox V N - S f K K M e 2 M e 2 Scheme 1.4 In designing the R[P 2N 2] ligand set an extra amide donor was added to create a tetradentate macrocycle. This has invariably meant that many transition metal complexes of the diamidodiphosphine ligand are comparatively coordinatively and electronically saturated. These species have increased stability, and mitigated reactivity. To treat this problem, the dianionic diamidophosphine ligand ((PhNSiMe2CH2)2PPh)2", P h P h[NPN] was developed. The ligand synthesis is shown in Scheme 1.5. 6 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands M.e2 2 n BuLi cr OEto NH 5 2 H N ' Ph M e 2 S K Cl H 2 P P h 4 n BuLi THF M e 2 S i / | N S i M e 2 ~* \ , . . . " , I L ' " " . . . K / Scheme 1.5 Of course, application of these amidophosphine ligands to new chemical problems is of the greatest interest. Building new ligand frameworks is only significant if they are useful. There is good news. The three ligands R[PNP], R[P 2N 2] and p h P h[NPN] have shown particular utility in promoting the activation and functionalization of molecular nitrogen. 1.4 The coordination, cleavage and functionalization of N2 1.4.1 Coordination and activation of molecular nitrogen One of the challenges remaining in chemistry is the efficient utilization of molecular nitrogen, or dinitrogen, in the generation of complex nitrogen-containing 22 33 products. " The use of N 2 as a feedstock is appealing for industrial use, as it is abundant, accessible and inexpensive. One can imagine a catalytic cycle in which dinitrogen and appropriate reagents could be combined to provide materials such as amines or N-heterocycles (Figure 1.2). 7 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands I catalytic \ A cycle Jl N 2 + reagents ^^~*" amines, N-heterocycles Figure 1.2. Conversion of molecular nitrogen into value added products mediated by a transition metal catalyst. A barrier preventing the implementation of such a cycle is the inertness of molecular nitrogen. The diatomic dinitrogen molecule is very difficult to activate as reflected by its high ionization potential (15.058 eV), negative electron affinity (-1.8 eV) and high bond dissociation enthalpy (945 kJ mol"1). The inertness of dinitrogen is not just due to its strong triple bond; carbon monoxide, which is isoelectronic with dinitrogen and undergoes a wide variety of chemical reactions,34 has an even greater bond dissociation enthalpy (1076 kJ mol"1). The orbital energies of N 2 provide a rationale for this inertness. A low energy highest occupied molecular orbital (HOMO; -15.6 eV) combined with the high energy lowest unoccupied molecular orbital (LUMO; 7.3 eV) disfavors electron transfer and Lewis acid-base reactions.35'36 It is all of these intrinsic properties together that make N 2 unreactive. Only one commercially successful process utilizes N 2 gas as a reagent. The Haber-Bosch process37"40 involves the reaction of dinitrogen with three equivalents of H 2 gas over a promoted iron or ruthenium41 based catalyst to produce ammonia (Equation 1.1). This reaction is thermodynamically favorable under ambient conditions, but at the high temperatures (400-550 °C) required to give viable reaction rates the gases must be compressed to 100-300 atm to favor ammonia production. By providing a route to fixed nitrogen in the form of ammonia, used widely as fertilizer, Haber won the Nobel Prize in chemistry in 1918. Bosch developed the high-pressure techniques that made industrial ammonia synthesis feasible and was subsequently awarded the Nobel Prize in 1931. metal catalyst N 2 (9) + 3 H 2 (g) 100-300 atm 400-550 °C 2 N H 3 (g) 1.1 8 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands While the necessity of a transition metal-based catalyst in the heterogeneous Haber-Bosch system was known, it was not until 1965, with the synthesis of [Ru(NH3)sN2] 2 +, that interest in the homogeneous coordination chemistry of dinitrogen to transition metals began (Equation 1.2).42' 4 3 The Dewar-Chatt-Duncanson synergistic bonding model rationalizes the activation of a dinitrogen ligand in a transition metal complex. Simplistically, i f dinitrogen is bound end-on to a single metal centre, the filled N 2 nonbonding a orbital forms a dative bond with empty metal dz2 or d x2.y2 orbitals. The filled dxz 5 d y z , or d x y orbitals o f the metal employ back-donation into the vacant n o f N 2 , further stabilizing the metal-N2 complex. This back-donation weakens the N - N bond, effectively activating it towards further reactivity. Unfortunately, the stability of the N2 lone pair, combined with the large H O M O - L U M O gap, minimizes the energy of interaction between metal and dinitrogen orbitals. A s a consequence, dinitrogen is both a poor a-donor and a poor 71-acceptor, especially as compared to isoelectronic C O . Strongly reducing early metals have the opportunity to activate coordinated dinitrogen further than synergistic bonding. B y donating electrons into the N2 unit, the dinitrogen bond order can be reduced; formalisms for reduction to an N = N double bond, (N 2 ) 2 ", or an N - N single bond, (N2)4", have been applied to describe many of these systems. These formalisms must not simply be taken at face value. While no controversies arise in mononuclear systems, in dinuclear dinitrogen complexes the situation is more complex. A n examination of the N - N bond length can correlate to the dinitrogen bond order and generally the greater the bond is lengthened from free N2 (1.0975 A ) , the greater the degree of dinitrogen activation. The Raman stretching frequency v(N-N) is also indicative of activation, since lower frequencies accompany longer N - N bonds. However, these experimental observations must be examined along with the formal oxidation state of the metal centre. In many cases, bond order determinations are subject to interpretation. For instance, in the dinuclear dinitrogen 12+ R u C I 3 x H 2 0 N 2 H 4 H 2 O C l 2 1.2 9 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands alkylidene complex (Cl(PMe3)2(CMe 3CH=)Ta)2(p-N 2), C , the observed N N bond length is 1.298 A. 4 4 This is comparable to the N N double bond in PhN=NPh (1.255 A) and supports the presence of an (N2)2 unit. A s the complex is diamagnetic it can be better described as a Ta(V)-Ta(V) species (rather than Ta(IV)-Ta(IV)), which in turn implies the presence of an (N2)4" unit. The oxidation state and charge o f both metal and nitrogen are merely formalisms that are meant to aid in understanding these systems. These ambiguities are usually limited to strongly activated dinuclear end-on bound dinitrogen complexes. The metal complexes in Figure 1.3 illustrate three common bonding modes for the dinitrogen ligand. In general, N2 bound in a terminal end-on fashion is not extensively activated as in examples A 4 2 ' 4 3 and B . 4 5 This terminal bonding mode is by far the most prevalent, especially in late metal chemistry. Greater activation can be achieved where dinitrogen bridges two late metals, since back-donation from one metal renders it a better Lewis base to a second metal. Dinuclear end-on dinitrogen coordination is a particularly common mode for early transition metal dinitrogen complexes as the formation of strong multiple bonds to nitrogen ligands is facilitated by additional reduction from a second metal-nitrogen bond. This bonding mode is observed in examples C 4 4 and D 4 6 The N N bond lengths in complexes C and D are typical for an N = N double bond. However, the presence of Ta(V) and W(VI) formal oxidation states indicate a (N2)4" unit is present, and for this reason a single bond is drawn. The third common bonding mode is a side-on bound N 2 unit, as in structures E 4 7 and F . 4 8 In this bonding mode filled 7T-N2 orbitals form an M(n, -N2)M unit where one d-orbital of a-symmetry from each metal centre interacts with dinitrogen TI system. This bonding mode is most commonly seen in dinuclear complexes of the early metals, and may be contingent on the lack of a second available d-orbital appropriate for back-donation. Depending on available orbitals and steric congestion, activation can be quite weak, as in complex E , but extensive activation occurs in many of these systems; the exceedingly long N - N bond length of 1.548 A in complex F is an example. 10 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands NH 3M H , H 3 N — R u — N = N A NN = 1.14 A 2+ C l , N P h 2 N P h 2 r^-Po,, I „,>P--, P h 2 N P h 2 !! B NN = 1.12 A P M e 3 Cl". . . . M e 3 C H C J a = N N = T a P M e 3 / ^ C H C M e 3 y ^ C l P M e 3 M e 3 P C NN = 1.298 A E NN = 1.088 A W = N -Me i V Me M e Me Me \ , > M e - N = W D NN = 1.24 A • - S I 6 2 P r ' ,Pv N—SiMe 2 C l ^ / V ^ P . N O n Pr'2 J?—• Z r ^ C I Me 2 Si N . PPr', ' S i - " M e 2 F NN = 1.548 A Figure 1.3. Examples of metal complexes exhibiting three different coordination modes for the dinitrogen ligand. The corresponding N-N bond lengths are given. Dinitrogen complex F is synthesized by reduction of 1Pr[PNP]ZrCl3 with Na/Hg amalgam under N 2 to generate ( lP l{PNP]ZrCl)2(^-r|2:r|2-N2), as shown in Equation 1.3. The N-N bond length is greater than the nitrogen-nitrogen single bond distance of 1.46 A observed in hydrazine. This implies a four electron reduction of the N 2 fragment; the bridging N 2 unit can be treated formally as (N2)4" and each zirconium centre as Zr(IV). Complex F contains the longest N-N bond distance reported in the literature. 11 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands M e 2 F The examples of dinitrogen activation continue to increase. " Dinitrogen complexes of nearly every transition metal and an increasing number of lanthanides and actinides have been isolated. Since N 2 complexes are difficult to prepare, initial studies were aimed at the synthesis of such complexes. Each success was deemed a trophy. N o w chemists are looking further: A more important goal is the transformation of coordinated dinitrogen, implying the need for chemical change within the bound dinitrogen fragment. 1.4.2 Dinitrogen cleavage The industrial conversion of N 2 to ammonia requires the eventual cleavage of dinitrogen. Several recent studies have focused on promoting the cleavage of molecular nitrogen. One important study of the N 2 cleavage process by transition metals was provided by the serendipitous observation that the coordinatively unsaturated molybdenum complex M o [ N ( R ) A r ] 3 (R = C ( C D 3 ) 2 C H 3 ; A r = 3 , 5 - C 6 H 3 M e 2 ) binds and cleaves the dinitrogen triple bond. 4 9 " 5 3 The reaction proceeds through a dinuclear end-on bridged N 2 intermediate, ( [N(R)Ar] 3 Mo) 2 (p-N 2 ) , at -35 °C. Upon warming this product decomposes to the terminal nitride [N(R)Ar] 3 Mo=N. This transformation is shown in Scheme 1.6. A n isoelectronic vanadium diamidoamine complex 5 4 and a niobium calixarene reduced with sodium 5 5 ' 5 6 are two of several recent examples 5 7" 6 1 of N - N cleavage. 12 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands Ar Bu 1 R,, t N„, / V J M o — N Bu N, Ar N ' Ar \ Ar Bu B U ^ N Ar Mo" N II N .Mo. Ar I Bu Bu Bu B U ^ N ^ Ar Mo. Bu I Ar N I Ar Scheme 1 . 6 Dinitrogen bond cleavage has also been promoted by early transition metal amidophosphine complexes. Reduction of ph[P2N2]NbCl with KCs under a N 2 atmosphere gives the paramagnetic dinuclear dinitrogen complex (ph[P2N2]Nb)2(p-N2). Thermolysis of this complex in toluene generates a bridging nitride species where one N atom from the activated N2 inserts into the macrocycle backbone, forming ph[P2N2]Nb(p-N)Nb[PN3] (where [PN3] = PhPMe(CHSiMe 2NSiMe 2CH 2P(Ph)CH2SiMe2NSiMe2N)). 6 2 In this example, shown in Equation 1.4, N2 has not only been cleaved but also functionalized via incorporation into the macrocyclic ring. The formation of new N-P and N-Si bonds degrades the ligand, but shows that functionalization of coordinated nitrogen is possible in these cleavage processes. 13 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands The limitation with developing a viable process coupling nitride formation with the production of useful nitrogen containing materials is the inherent stability of the metal nitrides generated. Reactions of nitrides employ harsh reagents to effect moderate changes. A s well , i f two metal centres reduce dinitrogen by three electrons each, converting N 2 to 2 N 3 " , these metals must subsequently reduced to close a catalytic cycle and regenerate the catalyst; an external source of reducing electrons is preferable. 1.4.3 Protonation of coordinated dinitrogen If synthesis of dinitrogen complexes is arduous, then finding controlled reactivity of the N 2 unit is even more challenging. B y far, the most studied reaction of activated N 2 is protonation. Studies have focused on this reactivity because of the desire to mimic biological nitrogen fixation and to find a less energy intensive industrial synthesis for ammonia. ' ' The scope of these reactions is limited since only NH3, N 2 H 4 and free N 2 can be produced. Many molybdenum N 2 complexes are easy to protonate. Compounds such as the type M ( N 2 ) 2 ( P R 3 ) 4 ( M = M o , W; P R 3 = P M e 2 P h , PMePh 2 ) can yield up to two equivalents of ammonia upon addition of acid. Even with intensive research in the past thirty years, 6 3" 6 6 only a single well-defined homogeneous catalyst capable of reducing and protonating N 2 to NH3 has been found, albeit with very low efficiency. This molybdenum system capable of effecting the conversion of dinitrogen to ammonia was recently reported. 6 7 The highly sterically encumbered molybdenum 14 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands triamidoamine complex [ H I P T N 3 N]MoCl ([H I P TN 3N] = [ ( H I P T NCH 2 CH 2 ) 3 Nf; HIPT = hexaisopropylterphenyl, 3,5-(2,4,6-'Pr3C6H2)2C6H3) performs a diverse set of transformations. Reaction with N H 3 and NaBAr 4 gives the corresponding cationic ammonia complex; reaction with TMS-N 3 affords the corresponding molybdenum nitride. This nitride can be reduced to the Mo=N-H imide by action of HBAr 4. If, however, cobaltocene is chosen as the reductant, and [2,6-lutidinium]BAr4 the proton source, [[H I P TN 3N]Mo(NH 3)]BAr 4 is produced. Addition of three equivalents of CoCp2 and BPh 3 can reform the N 2 complex. These transformations are shown in Scheme 1.7. By tweaking the kinetics of these stepwise reactions, this complex can catalytically convert N 2 to NH 3 . Slow addition of [2,6-lutidinium]BAr'4 (Ar' = 3,5-(CF3)2C6H3) and decamethyl chromocene to the aforementioned molybdenum complex at room temperature under 1 atm. of N 2 gave 4 turnovers of this reaction, producing 8 equivalents of N H 3 . 6 8 Scheme 1.7 The Haber-Bosch process is unlikely to be replaced by this or future homogeneous catalysts. When Bosch converted Haber's bench-top ammonia synthesis to an industrial scale, great capital costs were incurred, but now that the infrastructure is in place, production of ammonia is relatively inexpensive, and also quite efficient.40 While a catalytic cycle that could bypass the high pressures and high temperatures required by 15 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands this process would be beneficial, transforming dinitrogen into more valuable materials is more attractive and likely to find widespread applicability. The diamidodiphosphine ligand P h [P2N 2 ] supports the formation of N-H bonds using a less esoteric source of protons. The complex P h[P2N2]ZrCl2 is readily reduced with potassium graphite (KC 8) under N 2 gas to give the side-on bridged dinitrogen compound (ph[P2N2]Zr)2(p-n2:r)2-N2). Addition of hydrogen gas to this complex produces an N-H bond and a bridging hydride, as shown in Scheme 1.8.69 This reaction can be viewed as the heterolytic activation of H2 gas, with H + bonding to nitrogen, and H" occupying a bridging location between zirconium centres. This reaction is surprising as most dinitrogen complexes either do not react with H2, or react by H 2 displacing the dinitrogen moiety.70"72 Cl Cl A 2 KC ( N 2 THF 8 -2 KCI toluene H 2 Ph. silyl methyls omitted for clarity Scheme 1.8 16 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands 1.4.4 Formation of N-Element bonds from coordinated dinitrogen The side-on bound N 2 complex, ( P h [P2N 2 ]Zr) 2 (p-r | 2 :r | 2-N2), also promotes the activation of silanes and alkynes. Addition of the primary silane nBuSiH3 forms a new nitrogen-silicon bond along with a bridging hydride; an analogous heterolytic cleavage of an S i - H bond has occurred. 7 3 This complex also reacts with phenylacetylene to produce a similar complex, as shown in Scheme 1.9.74 silyl methyls omitted for clarity Scheme 1.9 The above reactions form new N - E bonds (E = S i , C , H). Development of a process to cheaply prepare value-added nitrogenous compounds directly from molecular nitrogen has become the 'holy g ra i l ' 7 5 o f modern dinitrogen activation research. Many 22 32 studies have examined the basic reactivity of activated dinitrogen. " A highlight of this recent research explores N 2 as a synthon for the development of new synthetic strategies, namely the use of in situ prepared titanium dinitrogen complexes to synthesize N -heterocycles. The synthesis of a wide variety of heterocycles, such as indole, quinoline, 17 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands pyrrole, pyrrolizine, and indolizine derivatives was achieved using a mixture o f N2, TiCLt, L i , and TMSC1. These components added to the appropriate reagents in situ can afford the desired transformation. 7 6 In fact, the preparation of these heterocycles has been made catalytic; yields of indole derivatives were over 200% based on T i C U when excess lithium and TMSC1 were used. Interestingly, use o f dry air as the nitrogen source gave nearly the same result as with molecular nitrogen. 7 7 N e w transformations mediated by this system include primary anilines synthesized via transmetalation of arylpalladium complexes with the in situ generated titanium dinitrogen complexes. 7 8 Tetrahydroindole derivatives have been synthesized using much the same route. 7 9 Amides have been synthesized by palladium-catalyzed carbonylation and nitrogenation. Reaction of the titanium dinitrogen fixing system with R X and C O in the presence of a Pd(0) catalyst gives the corresponding amides (RCONH2) in good yields. 8 0 Interestingly, many of these processes have found their way into more complicated syntheses. The synthesis of the natural products monomorine I , 8 1 (±)- lycopodine 7 8 and pumiliotoxine C 8 2 have all been developed from a dinitrogen feedstock. These transformations are summarized in Scheme 1.10. TiCI 4 TMS-CI C 0 2 Me N(TMS) 3 + TiClm{N(TMS} n} 0 1. 10% HCI 2. K 2 C 0 3 3. PhCOCI C0 2 Me O 2. hydrolysis 10% Pd 2(dba) 3 H 2N X Ph H 2N Pumilotoxin C Scheme 1.10 18 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands In the aforementioned reactions, each proton source or chosen reagent can be thought of as an electrophile attacking the nucleophilic N 2 unit. In mononuclear end-on bound systems, polarization of the N 2 fragment induces nucleophilicity. In the dinuclear systems, strong activation reduces molecular nitrogen to the nucleophilic (N 2) 2"or (N 2 ) 4 " fragments. Tantalum complexes of the diamidophosphine ligand P h P h [ N P N ] bind and activate molecular nitrogen. The dinitrogen complex, ( p h p h [NPN]Ta) 2 (p -H) 2 (p -n ' : r i 2 -N 2 ) , 8 3 1 8 4 shown in Figure 1.3, contains an asymmetrically bound N 2 unit that is both highly activated and has an induced polarity. This side-on end-on mode of bonding is unprecedented for bimetallic dinitrogen complexes. This complex can be considered a ditantalum(V) complex with a hydrazido (N 2 ) 4 " ligand. Simple charge considerations assign a positive charge to the bridging nitrogen atom, and a negative charge to the more exposed terminal nitrogen. The high activation and slight polarization induced by this bonding mode promotes novel reactivity. The reaction of 9 - B B N (9-borabicyclo[3.3.1]nonane) with ( P h P h [NPN]Ta) 2 (p -H) 2 (p -r i 1 :Ti 2 -N 2 ) proceeds first via addition of the B - H bond across a Ta-N bond to form ( p h p h [NPN]Ta(H)) (p -H) 2 (p -N 2 -BC 8 Hi4 ) (Ta[NPN]) . Reductive elimination of the two remaining hydride ligands as H 2 provides the final two electrons required to split the N 2 unit. Silicon migration from the ligand to the bridging nitride gives an imide nitride species that loses benzene over time to afford the final product: an imido nitride as shown in Scheme 1.11.8 5 19 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands P h = M e 2 P h ^ • - N M, P < T \ M E . ~« J a 9 -BBN 2 S i < > T f \ ^ o N ^ V S i M e 2 P h - ^ p - ^ , , . ^ P \ \ , / N N ^ S i M 6 2 < ^ h \ > ^ \ I P h S j P h P n M e 2 | B 1£ /Ta[NPN] all compounds characterized by X-ray crystallography H, Ph M e 2 Si / \ V Ph C 6 H 6 M e 2 S i -/ ^ ^ M e 2 / \ V N Ta[NPN] P h ' Ta[NPN] Ph B. Scheme 1.11 The involvement of the silicon atom of the ligand backbone inspired the reaction of primary silanes (RSiH 3 ; R = "Bu, Ph) with the side-on end-on dinitrogen complex. Similar to the reaction with boranes, Si-H addition across the Ta-N bond comprises the first step. Reductive elimination of H 2 splits the N - N bond, and reaction with an additional silane affords ( p h P h |WN]Ta) 2 (u-NSiH 2 R) 2 , a complex with two bridging silylimido units.86 These reactions are shown in Scheme 1.12. 20 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands R Scheme 1.12 1.5 Promoting novel transformations: ligand modification A s in other areas of coordination chemistry, ligand design has been of utmost importance to the development of dinitrogen activation. There are many examples where small changes in ligand design have impressive effects on the chemistry observed. One profound example is dinitrogen activation with zirconium metallocenes. The complex Cp*2ZrCl2 (Cp* = n,5-C5Me5) is reduced with Na/Hg amalgam to afford [Cp*Zr(n,'-N2)]2(p-ri1:Ti1-N2),87 but related zirconocenes including C p " 2 Z r C l 2 and C p t t 2 Z r C l 2 (Cp" = ri5-C5H3-l,3-(SiMe3)2, C p " = n 5 - C 5 H 3 - l , 3 - ( C M e 3 ) 2 ) only undergo one-electron reduction o n QQ to the Zr(III) monochloride under similar conditions. ' Dinitrogen complexes of C p " supported zirconocenes can alternatively be prepared from reductive elimination of isobutene from a zirconocene isobutyl hydride complex, Cp"2Zr(CH2CHMe2)(H) to give (Cp"2Zr)2(p-r|2:r]2-N2).90 B y altering cyclopentadienyl substituents a shift in N 2 coordination from end-on dinuclear to side-on dinuclear is observed. Even more profound is the affect that adjustment of the ligands can have on observed reactivity of zirconium N2 complexes (Scheme 1.13). Addit ion of dihydrogen to [Cp*Zr(n,1-N2)]2(p-Ti1:ri1-N2) promotes rapid loss of N2 and formation of zirconocene 21 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands hydrides. 8 7 However, a new study on the systematic variation of cyclopentadienyl methyl substituents on these zirconium complexes shows acute differences. 9 1 Reduction of (r\-C5Me4H)2ZrCl2 with sodium amalgam under one atmosphere of N 2 produced ((n,5-C 5 Me 4 H)2Zr)2 (p- r | 2 : r| 2 -N2). A s was previously observed, altering the Cp substituents changes the dinitrogen coordination mode. Addition of one atmosphere of H2 gas to a pentane solution of this dinitrogen complex resulted in the formation of two new N - H 5 2 2 bonds and two terminal zirconium hydrides to give ( ( n - C 5 M e 4 H ) 2 Z r H ) 2 ( p - r i " : r i - N 2 H 2 ) . Heating this product promotes loss of H2 and cleavage of the N - N bond to form ((r| 5-C5Me4H)2Zr) 2 (p-NH 2 )(p-N). Treatment with excess anhydrous hydrochloric acid completes the N 2 fixation, yielding two equivalents of N H 4 C I and reforming the zirconocene dichloride. Intriguingly, nitrogen fixation can occur with H2 as the sole source of N - H protons. Warming heptane solutions of the intermediate complex under H2 results in the formation of N H 3 in low yield. These surprising results illustrate the power of ligand modification. (60%) Scheme 1.13 22 References begin on page 24. Chapter One: Promoting chemistry with transition metals stabilized by mixed-donor multidentate chelating ligands 1.6 Scope of thesis This introduction has featured many examples of advances in dinitrogen activation by transition metal amidophosphine complexes. The diamidophosphine donor set, which is a focus of this dissertation, supports the formation of nitrogen-boron and nitrogen-silicon bonds through a side-on end-on activated dinitrogen tantalum complex. Dinitrogen activation remains one of many small molecules of interest throughout this dissertation. This thesis further explores the use of the mixed-donor tridentate diamidophosphine ligand [NPN] in group 5 chemistry. Chapter Two details the synthesis of a series of diamidophosphine ligand derivatives, R R [NPN], RP(CH 2SiMe2NR')2. As in the hydrogenation of zirconocene dinitrogen complexes (Sec. 1.5), small changes to ligand substituents can have a profound effect on the resultant chemistry. The decomposition of these ligand precursors is also investigated. Chapter Three details vanadium and niobium mid-oxidation state complexes supported by the R R [NPN] ligand set. These complexes have the ability to activate and even cleave molecular nitrogen under certain conditions. However, these mid-oxidation state complexes were complicated by ligand decomposition and formation of V(IV) and Nb(V) imido complexes. Studying the stability of these compounds provides new directions for ligand designs and guidelines for controlling reactivity. Chapter Four moves to higher oxidation state Nb(V) and Ta(V) systems using both synthetic experimental and theoretical (density functional) studies. Underlying mechanisms for observed chemical reactions and decomposition reactions are highlighted by DFT studies and give strategies for further activation of small molecules. Chapters Five and Six follow the activation of a series of small molecules by tantalum hydrides. Tantalum phosphides and phosphinidenes are formed from the addition of primary and secondary phosphines to tantalum hydrides, while tantalum imides and nitrides form from the addition of hydrazines to tantalum hydrides. The reactivity of these complexes with various small molecules not only promotes new chemical transformations but also provides the opportunity to examine the mechanisms behind these reactions. 23 References begin on page 24. 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Chapter Two: Diamidophosphine ligand modification Chapter Two D i a m i d o p h o s p h i n e l i g a n d m o d i f i c a t i o n 2.1 Introduction As illustrated in Chapter 1, small modifications in ligand architecture can profoundly affect complex reactivity. Modification of the diamidophosphine ligand R R '[NPN], where R R'[NPN] - [(R'NSiMe2CH2)2PR]2", is achieved through variation of amide and phosphine substituents. Throughout this thesis the abbreviation [NPN] is used, where R refers to the variable substituent of the phosphine donor, and R' refers to the variable substituent on the amide donors. The use of the diamidophosphine ligand prior to this work has focused solely on [NPN]. In the original ligand design steric bulk was avoided for two reasons: dinuclear complexes are more likely to form using less sterically bulky ligands, and less steric shielding of the metal centers should lead to enhanced reactivity. Phenyl was chosen as the substituent in these early studies for its relatively small size. As discussed in Chapter 1, P h P h[NPN] has supported extensive new chemistry.1"7 One of the tenets of inorganic chemistry is that steric hindrance can force low coordination numbers.8 Mixed donor amido ligands with variable N-substituents have been studied as olefin polymerization catalyst with group four metals.9"13 Steric interactions often beneficially control many polymerization processes that occur in these compounds. Bulky ligands may inhibit decomposition, control oligomerization and allow 2 9 References begin on page 52. Chapter Two: Diamidophosphine ligand modification metals to bind substrates selectively.14"16 By analogy, the synthesis of a bulkier [NPN] ligand could prevent decomposition of [NPN]MLn systems and control reactivity. Of course, exceedingly bulky substituents may prevent small molecules from bonding to reactive metal centers, or may prevent two metal centers from activating a substrate cooperatively. Therefore, [NPN] ligands with less bulky substituents may also enhance observed reactivity. Modification of ligand electronics can also control reaction outcomes. Tuning of ligand electronics is an established tool for the discovery and optimization of catalytic asymmetric processes.17"19 In the [NPN] ligand, modification of the phosphine substituent from phenyl to cyclohexyl would increase its nucleophilicity. As cyclohexyl phosphine is a better rj-donor, it would better stabilize reactive transition metal centers. The effects of tuning amidophosphine ligands have been previously studied with R[PNP] (where R[PNP] = [N(SiMe2CH2PR2)2]") and R[P 2N 2] (where R[P 2N 2] = [RP(CH2SiMe 2NSiMe2CH2)2PR] 2") ligand precursors. Zirconium chloride complexes of p h[PNP], for instance, do not form the desired mono(ligand) derivatives, but rather bis(ligand) derivatives. These complexes, ( P h[PNP]) 2ZrCl2, have pendant uncoordinated phosphine arms and the complexes are extremely unreactive.21"23 Conversely, mono(ligand) complexes of R[PNP] derivatives with more basic alkyl phosphines (R = Me, 'Pr, lBu) can be formed in high yield and are quite reactive.24 The mono(ligand) zirconium complexes also display divergent reactivity. Reaction of R[PNP]ZrCl3 with MeMgCl gives R[PNP]ZrMe3 for R = 'Pr and lBu, but leads only to complex decomposition when R = Me. 2 5 These examples are summarized in Scheme 2.1. 30 References begin on page 52. Chapter Two: Diamidophosphine ligand modification M e 2 M e 2 -Si .S i N ZrCL M e 2 " S i , / v V x N S i M e 2 Zr >>V CH 2 PPh 2 R = Ph Ph2P<T I — S i M e 2 R 2 P - L i - P R 2 V - C J s i \ M e 2 C H * P P h 2 ZrCI 4 R = Me, 'Pr, 4Bu M Q - ^ P . R 2 C I M e 2 S i x / N Z r — C l Me 2 Si * \ \ ^ P R 2 C I „ 0 . A P R 2 Me M e 2 S i v \ / M 6 M g C I , \ l — Z r — M e R = i R r ' t B u M e 2 S i f / \ \ ^ P R 2 Me MeMgCI R = Me decomposition Scheme 2.1 There have been investigations into the synthesis of P h[P2N2] complexes of many early transition metals. 2 6" 4 1 Selected comparative studies have been conducted with C y [P 2 N2] , where the phosphine donor has been changed from an aryl phosphine to an alkyl phosphine and the effect on the reactivity observed. Reduction of p h[P2N2]ZrCl2 with potassium graphite amalgam (KCs) under N2 gas gives the dinitrogen compound ( P h [P 2 N 2 ]Zr) 2 (p.-r i 2 : r i 2 -N2). 2 8 In contrast, reduction of C y [ P 2 N 2 ] Z r C l 2 fails to generate dinitrogen complexes, instead producing a paramagnetic Zr(III) complex. 4 2 The complex C y [P2N2]NbCl is monomeric in the solid state, while the phenyl derivative exhibits antiferromagnetic exchange between two d 2 centers, indicating the complex exists as ( P h [P2N 2 ]Nb) 2 (u-Cl)2. 3 6 Reduction of C y [ P 2 N 2 ] N b C l with K C 8 under argon gives only intractable paramagnetic products, whereas reduction of p h [ P 2 N 2 ] N b C l gives a diamagnetic dimer (P h[P2N2]Nb)2 bridged by two n 5 bound phenyl rings linked by a new C - C bond. This chemistry is summarized in Scheme 2.2. 31 References begin on page 52. Chapter Two: Diamidophosphine ligand modification K C 8 Ph ZrCI 4(THF) 2 [P 2N 2 ]ZrCI 2 R = Ph KC [P 2 N 2 ]Z r ' N ' Zr P h [P 2 N 2 ] z. ^ paramagnetic Zr(lll) R = Ph, Cy R = Cy product M e 2 M e 2 N ^ \ / NbCU,(dme) „ K C 8 R P — * - L i L i - * — R R ^ c y [P,N, lNbCI 2 - * - decomposition \f \ R = Cy - N . J> / ^ ^ * S i M e 2 M e 2 M e 2 P h — P v J , i__o i M N \ S i M e 2 /^ ' N ~—"l -SiMe 2 NbCI3(dme) R = Ph ( P h [P 2 N 2 ]NbCI) 2 Me 2Si^ l IN » \ _ _ p h M e 2 S i ^ N P ^ n Me2Si-\ M e 2 S h d Scheme 2.2 Changes in ligand design have a profound affect on reaction behavior. The development of a series of R R [NPN] lithium salts and other amidophosphine ligands for their application to early metal coordination chemistry is the subject for discussion in this chapter. 32 References begin on page 52. Chapter Two: Diamidophosphine ligand modification 2.2 Synthesis of R R [NPN] derivatives 2.2.1 Synthesis of C y P h [ N P N ] L i 2 ( O E t 2 ) The synthesis of the ligand precursor C y P h [NPN]Li 2 (OEt 2 ) , 1, is analogous to the synthesis of P h P h [NPN]Li 2 (THF) 2 , 2, as discussed in Chapter 1. Reaction of a cooled solution (-78 °C) of aniline (C 6 H 5 NH 2 ) and ClS iMe 2 CH 2 Cl with "BuLi formed the silylated aniline, ClCH 2 SiMe 2 NHPh. The reaction of 4 equivalents of "BuLi with 2 equivalents of ClCH 2 SiMe 2 NHPh and 1 equivalent of C y P H 2 in diethyl ether provided 1 in 80% yield. The preparation of the ligand precursor can be improved by conducting it in a single step, where the silylated aniline forms in situ, is warmed to room temperature, and phosphine and "BuLi additions are made at 0°C or -78 °C directly to this reaction mixture. Overall reaction yields were much higher for this 'one-pot' reaction since isolation of the thermally unstable silylamine is avoided. This modified synthesis is shown in Equation 2.1. Overall yields increased from 62% for the two step reaction to 80% for the one step synthesis. The one-pot synthesis of 2 afforded product in 88% yield, as opposed to a 77% overall yield for the two step method. 2 1 Compound 1 was characterized by ' H , 3 1 P , and 7 L i N M R spectroscopies and elemental analysis. Singlet resonances at 8 -34.0 in the 3 1 P{ 1 H} spectrum and 8 -1.1 in the 7 Li{ 1 H} spectrum indicate a lack of 3 1 P - 7 L i coupling. Integration of a triplet at 8 0.58 and a quartet at 8 2.94 in the ' H N M R confirmed that one equivalent of diethyl ether is bound to the dilithium salt. Repeated attempts to grow x-ray quality crystals of 1 were 33 References begin on page 52. Chapter Two: Diamidophosphine ligand modification unsuccessful, however, addition of other donor solvents facilitated crystal growth. Addition of 3 equivalents of THF to a toluene solution of 1 resulted in the precipitation of large off-white crystals of C y P h[NPN]Li 2(THF) 2, 3. A quartet (1:1:1:1) at 8 -35.13 in the ^P^H} spectrum, and two peaks (singlet, 8 -1.21; doublet, 8 -1.03) in the 7 L i {1H} NMR spectrum confirmed that 3 1 P- 7 Li coupling ('.Jfay = 40.1 Hz) exists in this species. To examine the connectivity of this ligand precursor in more depth, the large crystals were subjected to a single crystal X-ray diffraction study. An ORTEP 4 3 depiction of the solid-state molecular structure of 3 as determined by X-ray crystallography is shown in Figure 2.1. Relevant bond lengths and angles are listed in Table 2.1, and crystallographic data are located in Table 2.2. The lithium atoms bridge the two ligand amides. Each lithium is bound to a THF molecule, and the cyclohexyl phosphine is coordinated to one of the bridging lithiums. Figure 2.1. ORTEP drawing of C y P h[NPN]Li 2(THF) 2, 3 (spheroids at 50% probability). Silyl methyl and THF carbons have been omitted for clarity. 34 References begin on page 52. Chapter Two: Diamidophosphine ligand modification Table 2.1 Selected Bond Distances (A) and Angles (°) for C y P h [ N P N ] L i 2 ( T H F ) 2 , 3 Lengths Lengths Angles P(l)-Li(l) 2.556(4) N(2)-Li(2) 2.192(5) Li(2)-N(2)-Li(l) 75.25(19) N(l)-Li(l) 2.068(5) 0(1)-Li(l) 1.923(4) Li(2)-N(l)-Li(l) 77.36(19) N(l)-Li(2) 2.023(5) 0(2)-Li(2) 1.914(5) 0(1)-Li(l)-P(l) 112.5(2) N(2)-Li(l) 1.988(5) Table 2.2 Crystallographic Data and details of refinement for C y P h [ N P N ] L i 2 ( T H F ) 2 , 3 Empirical formula C 3 2 H 5 3 L i 2 N 2 0 2 P S i 2 Crystal system Monoclinic Formula weight 589.79 Space group P2,/a a, b,c{k);pn 15.263(2), 11.844(5), 20.155(3); 103.52(5) V , A 3 3542.5 Total reflections 13765 Z 4 Unique reflections 8070 Dcaic, g cm"3 1.123 Parameters 375 \i (Mo Kcc), cm"1 1.74 R . a 0.0741 T, K 173 ± 1 R w a 0.1854 26 range (°) 2.29 to 27.88 Goodness-of-fit 1.087 "R, = Z | | F 0 | - |FC||/S |F 0 |; R„ = Zw(|F02| - |F C 2 | ) 2 /2>|F 0 2 | 2 ) The observed 3 1 P - 7 L i coupling in the bis(THF) adduct contrasts with spectra acquired for 1, suggesting that the solution behavior of 1 is different than found for 3 in the solid state. While the phosphine may not bind to a lithium atom in solution, a low-temperature (-25°C) 3 1 P { 1 H } N M R spectrum of 1 shows a broadened quartet due to 7 L i coupling ( ' jpL i = 17.4 Hz) . It is likely that the lithium ions undergo rapid exchange in solution at room temperature. A t lower temperatures, this process is slow, and coupling between 7 L i and 3 1 P is observed. In solution, the structure of the dilithio derivatives are likely the same as in the solid state structure of 3, with the phosphine donor bound to one of the lithium centres. While crystals of 3 were readily grown, the monoether adduct 1 is much easier to isolate in high yield and handle under an inert atmosphere. For this reason, 1 was chosen as the ligand precursor to access C y P h [ N P N ] transition metal complexes. 35 References begin on page 52. Chapter Two: Diamidophosphine ligand modification 2.2.2 Reaction of 1 with H 2 0 Ligand precursor 1 is air-sensitive, decomposing quickly upon exposure to air or moisture. Controlled decomposition of 1 with H 2 0 produces a mixture of two products. Analysis of the crude reaction mixture by 3 IP{ 1H} NMR shows two singlets at 5 -36.2 and 8 -28.1, integrating to two and one phosphorus nuclei respectively. Pale yellow single crystals of ( C y P h[NPN]Li 3) 20, 4, were obtained by slow evaporation of a toluene/hexanes solution. An ORTEP 4 3 depiction of the solid-state molecular structure of 4 as determined by X-ray crystallography is shown in Figure 2.2. Figure 2.2. ORTEP drawing (spheroids at 50% probability) of ( C y P h[NPN]Li 3) 20, 4. Silyl methyl, phenyl and cyclohexyl ring carbons other than ipso or methine carbons have been omitted for clarity. Six lithium atoms form a distorted octahedral cage around a central oxygen atom while [NPN] ligands cap two of the octahedral trigonal faces. The complex is centrosymmetric, accounting for the observed symmetry in the 3 1 P NMR spectrum. Each lithium atom on a face is coordinated by one [NPN] donor atom. The amide-lithium bond lengths N(l)-Li(l), N(l)-Li(3), N(2)-Li(2) and N(2)-Li(3) of 2.078(4), 2.039(4), 2.023(5) and 2.052(4) A are very similar. The molecular structure of 3, conversely, contained a 36 References begin on page 52. Chapter Two: Diamidophosphine ligand modification shorter N(2)-Li(l) bond length of 1.988(5) A and a longer N(2)-Li(2) distance of 2.192(5) A. The P(l)-Li(3) bond length of 2.757(4) A is elongated from the P(l)-Li(l) distance of 2.556(4) A in 3. Tables 2.3 and 2.4 contain relevant geometric and crystallographic data. The Li environments cannot be distinguished in solution. 7Li{'H} NMR studies show only a broad singlet at 6-1.7. Table 2.3 Selected Bond Distances (A) and Angles (°) for (C y P h[NPN]Li 3)20, 4 Lengths Lengths/Angles Angles P(l)-Li(2) 2.757(4) 0(1)-Li(l) 1.875(4) Li(l)-0(1)-Li(2) 91.3(2) N(l)-Li(l) 2.078(4) 0(1)-Li(2) 1.857(4) Li(l)-0(1)-Li(3) 76.7(2) N(l)-Li(3) 2.039(4) 0(1)-Li(3) 1.929(4) Li(2)-0(1)-Li(3) 77.8(2) N(2)-Li(2) 2.023(5) 0(1)-Li(l)-N(l) 100.6(2) Li(l)-N(l)-Li(3) 70.0(2) N(2)-Li(3) 2.052(4) 0(1)-Li(2)-N(2) 101.1(2) Li(2)-N(2)-Li(3) 71.4(2) Table 2.4 Crystallographic Data and details of refinement for ( C y P h rNPN ]Li 3 ) 2 0, 4 Empirical formula C 4 8H 7 4Li 6N 4OP 2Si4 Crystal system Triclinic Formula weight 939.07 Space group P i -a, b, c (A) 10.475(1), 11.576(2), 13.119(2) a , / ? ) Y ( ° ) 74.681(3), 78.578(3), 64.226(3) v, A3 1375.3(3) Total reflections l l 773 z 1 Unique reflections 5260 Dcaic, g cm'3 1.134 Parameters 295 \i (Mo Ka), cm"1 2.02 R, a 0.049 T, K 198+1 R w a 0.087 26 range (°) 3.1 to 27.9 Goodness-of-fit 2.05 "R, = Z | | F 0 | - |F C | | / I |F 0 | ; Rw = lw(\F02\ - |FC 2|)2/2>|F0 2|2) The second product formed from the decomposition of 1 in the presence of H2O was found to be C y P h [NPN]H 2 , 5. Isolation of this material and characterization by 'H and P NMR spectroscopies confirmed this assignment. In fact, 5 was a frequently observed decomposition product in many subsequent reactions; a broad N-H resonance at 8 3.2 and a diagnostic P resonance at 8 -28.1 indicated product decomposition. Reaction of 1 with 37 References begin on page 52. Chapter Two: Diamidophosphine ligand modification excess H 2 O gave only the product at 8 -28.1, indicating the formation of 5.The chemical shift of the N - H resonance is variable depending on solvent, temperature and concentration. A possible route to the formation of 4 and 5 is proposed. A molecule of 1 reacts with H 2 O to form C y P h [ N P N ] H 2 and L i 2 0 . This lithium oxide can react with two more equivalents of 1 to form ( C y P h [NPN ]Li3)20 which preferentially crystallized from a toluene/hexanes solution. Addit ion of one equivalent of D 2 O to a concentrated solution of 1 gave a mixture of 4 and C y P h [ N P N ] D 2 . While this mixture proved more difficult to separate, the absence o f the N - H resonance of 5 at 5 3.2 supports this reaction pathway. These decomposition processes are shown in Equations 2.2 and 2.3. 2 2.2 2.3 The L i 6 0 morphology of 4 has been observed in other systems, primarily at the core o f larger lithium aggregates with 7V-silyl allylamines, 4 4 aminofluorosilanes, 4 5 polyimido-phosphonate anions, 4 6 2-aminopyridines, 4 7 and even a sulfoximine-stabilized • 48 dilithiomethane derivative. O f particular interest, however, is the reaction of a dimeric lithium amidinate with Li20 to form (Li[C(NBu t)2(Bu")]VLi20. 4 9 In this example, shown in Scheme 2.3, the authors proposed a partial hydrolysis of L i f B u ^ C N B u 1 ^ ] with trace amounts o f water to form L i O H and Bu n C(NBu t ) [N(H)Bu t ] . The L i O H then can react further to give the hydrolysis product and the Li20 adduct with an LieO core. 38 References begin on page 52. Chapter Two: Diamidophosphine ligand modification B u ' B u n 3. dimerization B u ' N " N B u 1. H 2 0 B u n B u ' N ^ N H B u ' L i O H B u n C N Li N B u 1 l i l l Bu 'N Li N C B u n B u ' N H B u + L U O B u n C B u ' . N B u ' " " C B u n r Bu'N—r -Li L i - \ — N B u ' V \ / \ / L i — O Li /'< / \ l \ Bu'N—">-•. „ L i - / — N B u ' Bu n C<„„ , \ w . - - » C B u n N N B u ' B u ' Scheme 2.3 The complete hydrolysis of 1 would generate L ^ O directly, which could then be entrapped in the lithium amido complex. In support of this mechanism, it was shown that 4 can be prepared via the direct addition of 2 equivalents of 1 to a solution of L i 2 0 in diethyl ether. 2.2.3 Synthesis of other R R '[NPN] lithium salts Synthesis of C y M e s [ N P N ] L i 2 ( T H F ) , 6, and p h M e s [ N P N ] L i 2 ( d i o x a n e ) 2 , 7, proceeded analogously to 1 by metathesis of M e s N H L i with C l C H 2 S i M e 2 C l at -78 °C to form a silylamine that reacts in situ with the desired primary phosphine, R P H 2 , and four equivalents of " B u L i . When C y P H 2 is used, the ligand precursor precipitates as small white crystals of 6 after addition of 1.5 equivalents of T H F to a hexanes solution of the crude product. Similarly, when P h P H 2 is used, a pale yellow microcrystalline solid, 7, is isolated after addition of 2.5 equivalents of dioxane to a concentrated hexanes solution of the crude product. The donor solvent chosen, and the amount used, is determined by the physical properties and isolated yield of the resultant products. Colourless platelet 3 9 References begin on page 52. Chapter Two: Diamidophosphine ligand modification crystals of 6 formed from a saturated 1:1 hexanes/toluene solution at -35 °C. A n O R T E P 4 3 depiction of the solid state molecular structure as determined by X-ray crystallography is shown in Figure 2.3. Figure 2.3. O R T E P drawing (spheroids at 50% probability) of C y M e s [ N P N ] L i 2 ( T H F ) , 6. S i ly l methyl and T H F carbons have been omitted for clarity. Relevant bond lengths and angles are listed in Table 2.5, and crystallographic data are located in Table 2.6. There was some disorder in the crystal. The crystalline lattice contains two different conformations of the ligand within the same unit cell, exhibiting overlapping opposite chair conformations of the cyclohexyl ring, as well as overlapping silyl methyl fragments. Figure 2.3 shows just one of the two conformations. In both conformations, the bond lengths from the amido nitrogen donors N l and N2 to L i l are approximately 0.2 A longer than the corresponding bond lengths from N l and N2 to Li2 . The X-ray data show that 6 has a single T H F molecule coordinated to L i l , facilitating the 40 References begin on page 52. Chapter Two: Diamidophosphine ligand modification asymmetric lithium-amido bonding observed. A s both the coordinated T H F and ligand phosphine work to stabilize L i l , L i 2 is starved for electron density and pulls a larger share of electron density from the bridging amido ligands, manifesting in shorter LI2-N bonds. Table 2.5 Selected Bond Distances (A) and Angles (°) for C y M e s [ N P N ] L i 2 ( T H F ) , 6 Lengths Lengths/Angles Angles P(l)-Li(l) 2.589(4) 0(1)-Li(l) 1.923(4) 0(1)-Li(l)-P(l) 121.74(16) N(l)-Li(l) 2.106(4) Li(l)-N(l)-Li(2) 74.77(15) N(l)-Li(l)-N(2) 98.93(15) N(l)-Li(2) 1.943(4) Li(l)-N(2)-Li(2) 73.74(15) N(l)-Li(2)-N(2) 111.15(18) N(2)-Li(l) 2.133(4) 0(1)-Li(l)-N(l) 115.33(18) 0(1)-Li(l)-N(2) 98.93(15) N(2)-Li(2) 1.964(4) Table 2.6 Crystallographic Data and details of refinement for C y M e s [ N P N ] L i 2 ( T H F ) , 6 Empirical formula Cj^vLizNzOPSiz Crystal system Monoclinic Formula weight 610.86 Space group P2,/a a,b,c(k);fi{°) 19.597(1), 8.9414(4), 21.492(2); 105.846(3) V , A 3 3623.0(4) Total reflections 34076 Z 4 Unique reflections 8455 Dcaic, g cm"3 1.120 Parameters 508 u (Mo Ka) , cm'1 1.69 V 0.045 T, K 173 ± 1 R w 3 0.098 29 range (°) 2.5 to 27.85 Goodness-of-fit 0.87 "R, = ZHFol " \Fe\\/Z.\F0\; R„ = Zw(\F02\ - |F c 2|) 2/Iw|F 0 2| 2) Analysis of bulk and recrystallized samples of 6 by 3 1 P { ' H } , ! H , and 7 L i { 1 H } N M R spectroscopy confirmed the identity of the material. The P{ H} spectrum of 6 shows a singlet at 8 -30.2, downfield shifted by approximately 8 4 from the 8 -34.0 3 1 P shift for 1. 7 L i { ' H } N M R spectra contain a single resonance at 8 -0.8, confirming that no L i - P coupling is observed at room temperature. *H N M R studies suggested a relatively symmetric structure. Mesi tyl methyl proton resonances were coincident; a single resonance at 8 2.20 integrates to 18 H . Coordinated T H F appeared as two broad singlets 41 References begin on page 52. Chapter Two: Diamidophosphine ligand modification at 5 1.13 and 2.96, respectively, integrating to a combined 8 H , or one equivalent of coordinated T H F . Complex 7 was also was characterized by 3 1 P { ' H } , ' H , and 7 L i { ' H } N M R spectroscopy. The 3 1 P { ' H } N M R spectrum contained a quartet at 8 -34.1, shifted 4 upfield from 6 and coupled to one 7 L i nuclei. 7 L i { ' H } N M R spectra gave the expected doublet at 8 -0.8, indicating coupling to the phosphorus nucleus and overlapped a singlet for the other 7 L i nucleus (8 -0.7). The ' H N M R again showed coincident mesityl methyl proton resonances at 8 2.20, integrating to 18 H . A singlet at 8 3.17 integrates to 16 H , confirming the presence of two coordinated dioxane molecules stabilizing the dilithium salt. Samples must be thoroughly dried prior to analysis or use in further synthesis as a slight excess of dioxane not removed under vacuum can misrepresent analysis and stoichiometry. Repeated attempts to grow X-ray quality crystals o f 7 were unsuccessful. The ligand precursors C y M e [NPN]Li 2 (d ioxane ) , 8, and P h M e [NPN]Li 2 (d ioxane ) , 9, were synthesized by an analogous procedure. Precipitation of 8 and 9 were accomplished by adding the requisite amount of dioxane to saturated hexanes solutions of the ligand precursors, although the preparation of X-ray quality crystals was unsuccessful. Synthesis of 8 was verified by 3 I P { ' H } , lU, and 7 L i { ' H } N M R spectroscopy. The 3 I P { 1 H } N M R resonance 8 -36.1 showed no coupling to L i in solution. This was confirmed by the observation of a singlet at 8 -1.1 in the 7 L i { ' H } N M R spectrum. Interestingly, while all previous ligand precursors showed distinct, resolved peaks for the syn and anti si lyl methyl protons, the ' H N M R spectrum of 8 showed a single resonance at 8 0.35 integrating to 12 H . Mult iple methylene proton resonances observed at 8 0.88 and 1.22 suggest, however, that the syn and anti si lyl methyl resonances are merely coincident. Coordinated dioxane is observed as a triplet at 8 3.42. Integration verified the presence of one coordinated dioxane molecule. Similarly, 9 was characterized by 3 1 P { ' H } , ] H , and 7 L i { ! H } N M R spectroscopy. Coupling between the phosphorus and lithium atoms was observed in both the 3 1 P { ' H } and 7 L i { ' H } N M R spectra as a quartet at 8 -37.5 and a doublet at 8 -1.2 respectively. The syn and anti si lyl methyl resonances could only be resolved with high field N M R 42 References begin on page 52. Chapter Two: Diamidophosphine ligand modification spectrometers, appearing at 5 -0.09 and -0.10 respectively. A sharp singlet at 5 3.57, integrating to 16 H, indicated two coordinated dioxane molecules. Table 2.7 summarizes phosphorus and lithium NMR data for the [NPN] dilithium salts described, from which several trends can be noted. First, the amido and phosphine 7 31 substituents have little effect on the observed Li chemical shift. Not surprisingly, the P. chemical shift changes dramatically when comparing alkyl and arylphosphines, with alkylphosphines shifted 5 2.9 further downfield, on average. This is expected, as the difference in chemical shifts between CyPMe2 (5 -42.7)50 and PhPMe2 (5 -47.6)51 is 5 4.9. More surprising is the effect of amido substituents on phosphine chemical shifts. A change from phenyl amido to mesityl amido donors manifests in a downfield shift of 8 3.8 (comparing 6 to 1) or 5 3.6 (comparing 7 to 2). Also of interest is the relationship between the presence or absence of lJpu coupling at room temperature and the coordination sphere of lithium in the ligand precursors. Phosphorus-lithium coupling is observed only in systems with two coordinated donor solvent molecules (2, 3, 7 and 9). In systems where only one donor solvent molecule is present a fluctional process exchanging lithium environments - potentially involving migration of the phosphine and donor solvent from one lithium to another - eliminates observable coupling. Table 2.7 3 1 P and 7 L i NMR spectroscopic data for [NPN] ligand precursors Ligand Precursor 3 1P5(ppm) 7 L i 8 (ppm) 1 J P L i @ r.t. C y P h[NPN]Li 2(OEt 2), 1 -34.0 -1.1 not observed P h P h[NPN]Li 2(THF) 2, 2 -37.7 -1.2,-0.9 37.7 Hz C y P h[NPN]Li 2(THF) 2 , 3 -35.1 -1.2,-1.0 40.1 Hz C y M e s[NPN]Li 2(THF), 6 -30.2 -0.8 not observed p h M e s[NPN]Li 2(diox) 2, 7 -34.1 -0.7, -0.8 18.9 Hz C y M e[NPN]Li 2(diox), 8 -36.1 -1.1 not observed P h M e[NPN]Li 2(diox) 2, 9 -37.5 -1.4,-1.5 26.6 Hz 43 References begin on page 52. Chapter Two: Diamidophosphine ligand modification 2.3 Attempted synthesis of cyclic diamidophosphine ligands The [P2N2] macrocycle benefits greatly from the macrocyclic effect, which limits phosphine dissociation from early metals and promotes complex stability. While macrocycle synthesis usually requires dilute conditions, 5 2" 5 4 the synthesis of [P2N2] is facilitated by lithium templating. A cyclic diamidophosphine ligand may offer similar benefits. Employing a diamine with the established synthesis o f [NPN] ligands could afford access to systems where the amido ligands were joined to close the macrocycle. The resultant complexes would have increased stability from the macrocycle effect, yet still maintain the coordinative unsaturation afforded by the diamidophosphine donor set. A s shown in Scheme 2.4, a lithiated diamine could react with a silylchloride to form a bis(silylamine). Closure of the macrocycle via addition of primary phosphine followed by deprotonation with " B u L i could then afford the desired complexes. Ethylene diamine, propylene diamine, 2,2-dimethyl-1,3-propane diamine, and 3-(aminomethyl)benzyl amine were chosen as candidates to prepare c y c l l c [ N P N ] derivatives. Scheme 2.4 N o synthetic pathway to the proposed bis(silylamine)chlorides has been reported. Previous research has focused on the synthesis of simple bis(silylamines), R 3 SiN (CR2 )nNSiR 3 . 5 5 For instance, C H 2 ( C H 2 N H S i R 3 ) 2 and its dilithium salt have been used extensively as ligands in zirconium coordination chemistry, 5 6" 5 9 as a precursor to bis(amidinates) 6 0 and diazaphosphorinanes,6 1 or as a monomer in the preparation of optically active polyamides. 6 2 44 References begin on page 52. Chapter Two: Diamidophosphine ligand modification The desired bis(silylamine)chlorides were readily synthesized by the procedure proposed in Scheme 2.4. Careful control of reaction temperature and reagent concentrations was crucial. Dropwise addition of a dilute ethereal solution of ethylene diamine at 0 °C to a concentrated solution of C l C H 2 S i M e 2 C l at -78 °C with rapid stirring resulted in the precipitation of a flocculent white solid. Addit ion of " B u L i gave a pale golden yellow solution and fine white precipitate. Filtration of this mixture through celite, followed by removal of solvent, gave a yellow oi l , l , 2 - ( C l C H 2 S i M e 2 N H ) 2 C H 2 C H 2 , 10, in 68% yield. Similarly, the bis(silylamines) C H 2 ( C H 2 N H S i M e 2 C H 2 C l ) 2 , 11, C M e 2 ( C H 2 N H S i M e 2 C H 2 C l ) 2 , 12 , and l , 3 - ( C l C H 2 S i M e 2 N H C H 2 ) 2 C 6 H 4 , 1 3 , were prepared in 78%, 85%) and 57%> yields, respectively, and analyzed by *H N M R . While some thermal sensitivity was observed in isolated silylamine synthons, it was much more pronounced in the bis(silylamine) products. I f oils were not stored at -35 °C, decomposition to form a deep yellow paste would occur in less than 12 h. Product purity was essential to maintaining stability. A sample of 13 that had partially decomposed, for instance, continued to decompose rapidly, even when stored at -35 °C. This sensitivity may have contributed to difficulties in achieving success in the formation of c y c l ' c [ N P N ] macrocycles. Addition of primary phosphines and " B u L i to solutions of the bis(silylamines) does not afford the desired macrocycles, but oligomeric products. For instance, addition of L i 2 P P h to a dilute solution of 12 afforded a sticky orange paste. The pastes had low solubility in common organic solvents, and analysis by 1 31 H and P N M R showed complex spectra with broad resonances. Mass spectral analysis was also complicated, showing multiple products assignable to oligomers of the bis(silylamines) and phosphines. Control of product distribution to give a single macrocycle or oligomer was not realized, even after careful modification of solvent, temperature, reaction time, reagent concentrations and additives. Six ligand precursors have been developed to stabilize early transition metal complexes. C y P h [ N P N ] L i 2 ( E t 2 0 ) , 1, P h P h [ N P N ] L i 2 ( T H F ) 2 , 2, C y M e s [ N P N ] L i 2 ( T H F ) , 6, P h M e s [ N P N ] L i 2 ( T H F ) , 7, C y M e [ N P N ] L i 2 ( d i o x ) , 8, and p h M e [ N P N ] L i 2 ( d i o x ) 2 , 9 w i l l be used in future chapters to investigate the coordination chemistry and reactivity of mid and high oxidation state complexes of vanadium, niobium and tantalum. 45 References begin on page 52. Chapter Two: Diamidophosphine ligand modification 2.4 Experimental section 2.4.1 General considerations Unless otherwise stated, all manipulations were performed under an inert atmosphere of dry, oxygen-free dinitrogen or argon by means of standard Schlenk or glovebox techniques. Three gloveboxes were employed for air-sensitive transformations and storage; a Vacuum Atmospheres HE-553-2 glovebox (equipped with a MO-40-2H purification system and a -60 °C freezer), an MBraun MB150-GII glovebox (equipped with a dual column purification system, cold well and a -35 °C freezer), and an Innovative Technologies System One glovebox (equipped with a GP-1 purification systems, inline access to IT-SPS solvents, and a -35 °C freezer). Where choice of atmosphere affects reaction outcomes, the distinction between dinitrogen and argon use wi l l be made. Anhydrous hexanes and toluene were purchased from Aldr ich , sparged with dinitrogen, and passed through activated alumina and Ridox (or Q-5) catalyst columns prior to use. 6 3 Anhydrous pentane, benzene, tetrahydrofuran and diethyl ether were purchased from Aldr ich , sparged with dinitrogen, and passed through an Innovative Technologies SPS-PureSolv-400-4 apparatus. Water was distilled and thoroughly degassed prior to use. A l l organic solvents were tested with addition of sodium benzophenone ketyl prior to use to ensure absence of oxygen and water. Alternatively, anhydrous diethyl ether was stored over sieves and distilled from sodium benzophenone ketyl under argon. Tetrahydrofuran was refluxed over CaHb prior to distillation from sodium benzophenone ketyl under argon, and pentane was stored over sieves and distilled from sodium benzophenone ketyl solublized by tetraglyme under dry dinitrogen prior to storage over a potassium mirror. Nitrogen gas was dried and deoxygenated by passage through a column containing activated molecular sieves and M n O . Deuterated benzene was dried by heating at reflux with sodium/potassium alloy in a sealed vessel under partial pressure, then trap-to-trap distilled, and freeze-pump-thaw degassed three times. Deuterated tetrahydrofuran and toluene were dried by heating to reflux with molten potassium metal in a sealed vessel under vacuum, then trap-to-trap distilled, and freeze-pump-thaw degassed three times. Unless otherwise stated, ' H , 3 1 P , 46 References begin on page 52. Chapter Two: Diamidophosphine ligand modification ' H { 3 1 P } , ^ P l ' H } , 1 3 C { ' H } , 7 L i { ! H } and two-dimensional N M R spectra were recorded on a Bruker A M X - 5 0 0 instrument with a 5mm B B I probe operating at 500.1 M H z for *H. ' H N M R spectra were referenced to residual protons in deuterated solvent as follows: C 6 D 5 H (8 7.15), C4D7HO (8 3.58), and C7D7H (8 2.09) with respect to tetramethylsilane at 8 0 . 0 . 3 I P N M R spectra were referenced to either external or internal P(OMe)3 (8 141.0 with respect to 85% H3PO4 at 8 0.0). 7 L i N M R spectra were referenced to external L i C l (0.3 M solution in M e O H at 8 0.0). Elemental analyses were performed by M r . P. Borda and M r . M . Lakha and mass spectrometry (EI /MS on a Kratos M S 50 unless otherwise stated) by M r . M . Lapawa, all at the University of British Columbia, Department of Chemistry. Extra care to employ glovebox or glovebag techniques was taken in the elemental analyses of air-sensitive compounds. 6 4 Clusters assigned to specific ions in mass spectra show appropriate isotopic distribution patterns as calculated for the atoms present. -2.4.2 Starting materials and reagents The reagents P h N H 2 , C l S i M e 2 C H 2 C l , M e s N H 2 ( M e s N H 2 = 2,4,6-trimethylaniline), N H 2 ( C H 2 ) 2 N H 2 , N H 2 ( C H 2 ) 3 N H 2 , N H 2 C H 2 C M e 2 C H 2 N H 2 , and 1,3-N H 2 C 6 were purchased from Aldr ich and purified by distillation. M e N H 2 H C l was purchased from Aldr ich and purified by recrystallization from hot methanol and thoroughly dried prior to use. C y P H 2 was purchased from S T R E M and purified by distillation. Solutions of B u " L i (1.6 M in hexanes) were obtained from Acros Organics and used without further purification. P h P H 2 was prepared by a literature method. 6 5 2.4.3 Synthesis Synthesis of C y P h [ N P N ] L i 2 ( E t 2 0 ) , 1 To a -78 °C solution of aniline (14.9 g, 0.16 mol) and C l S i M e 2 C H 2 C l (22.89 g, 0.16 mol) in 100 m L of E t 2 0 was slowly added B u " L i (100 m L , 1.6 M in hexanes). The resulting white suspension was stirred for 2 h at room temperature, then cooled again to -78 °C. To 47 References begin on page 52. Chapter Two: Diamidophosphine ligand modification this mixture was added CyPH 2 (9.29 g, 0.08 mol) followed by dropwise addition of Bu"Li (200 mL, 1.6 M in hexanes). The solution was stirred for 2 h and then thoroughly dried in vacuo. The remaining solids were extracted into 70 mL of toluene and filtered through Celite. The solvent was removed and 20 mL of hexanes was added, to precipitate a white solid from the yellow solution. The solid C y P h[NPN]Li 2(Et 20) was collected via filtration in 80% yield (33.84 g). 'H NMR (C 6D 6 , 25 °C, 500 MHz): £0.45 (s, 12H, SiC// 3), 0.58 (t, 6H, OCH 2C//i), 0.95 (m, 4H, PCr72Si), 0.3 - 1.5 (m, 11H, Cy-H), 2.94 (q, 4H, OC// 2CH 3), 6.48 (m, 2H, NPh p-H), 6.57 (m, 4H, NPh o-H), 7.08 (m, 4H, NPh m-H). ^ P l ' H j . N M R (C 6D 6 , 25 °C, 202.5 MHz): 8 -34.0 (s). 7 L i NMR (C 6D 6 , 25 °C, 194.32 MHz):£-l.l (s). Anal. Calcd for C 2 8 H 4 7 Li 2 N 2 OPSi 2 (%): C, 63.61; H, 8.96; N , 5.30. Found: C, 63.75; H, 9.04; N , 5.49. Synthesis of P h P h[NPN]Li 2(THF) 2, 2 The previously published complex, 2, was synthesized in an analogous reaction to the preparation of 1. PhPH2 (8.81 g, 0.08 mol) was added instead of CyPH 2, and THF was added to a hexanes solution of the crude product, and cooled overnight at -35 °C to afford large off-white crystals of 2 in 88% yield. Characterization by [ H , 3 I P, 7 L i NMR spectroscopy and elemental analysis matched literature values. Synthesis of C y P h[NPN]Li 2(THF) 2 , 3 To a solution of 1 (5.00 g, 9.46 mmol) in toluene (25 mL) was added THF (2.05 g, 28.4 mmol). The mixture was stirred vigorously for 1 min. and then allowed to sit for 24 hours. Slow evaporation of the solvent afforded large off-white crystals and an off-white paste. The materials were dried and analyzed by spectroscopic methods, confirming the isolation of C y P h[NPN]Li 2(THF) 2 , 3, in 85% yield (4.81 g). lU NMR (C 6D 6 , 25 °C, 500 MHz): 5 0.45 (s, 6H, SiC#3), 0.46 (s, 6H, SiGtf3), 0.78-1.90 (m, 11H, Cy-H), 1.12 (br, 8H, OCH 2C// 2), 3.31 (br, 8H, OC// 2CH 2), 6.71 (t, 2H, NPh p-H), 6.93 (d, 4H, NPh o-H), 7.24 (t, 4H, NPh m-H). 3 1P{ 1H} NMR (C 6D 6, 25 °C, 202.5 MHz): £-35.1 (q, 'jpu = 40.1 Hz). 7Li{'H} NMR (C 6D 6 , 25 °C, 194.32 MHz): £-1.03 (d, ILi, V i = 40.1 Hz, N-Z/P-48 References begin on page 52. Chapter Two: Diamidophosphine ligand modification N), -1.21 (s, I L i , N- Iz -N) . Anal . Calcd for C 3 2H53Li 2 N20 2 PSi2 (%): C, 64.19; H , 8.92; N , 4.68. Found: C, 64.45; H , 8.95; N , 4.49. Decomposition of 1 with H 2 0 . Synthesis of ( C y P h [ N P N ] L i 3 ) 2 0 , 4 and C y P h [ N P N ] H 2 , 5 A solution of 1 (5.00 g, 9.46 mmol) in Et20 (20 mL) is prepared in a round bottom flask equipped with a stir bar and stirred vigorously. Addit ion of H 2 0 (56.8 p L , 3.15 mmol) to this solution resulted in a deepening o f the solution colour. Removal of solvent afforded an oily solid. Slow evaporation of a toluene solution of the crude mixture afforded large white crystals of ( C y P h [ N P N ] L i 3 ) 2 0 , 4, and a yellow oily solid analysed as C y P h [ N P N ] H 2 , 5. 4: ' H N M R ( C 6 D 6 , 25 °C, 500 M H z ) : £ 0.29 (s, 24H, S i C / / 3 ) , 0.54-1.71 (m, 28H, Cy-H, P C / / 2 S i M e 2 ) , 2.04 (m, 2H, P - C / / C y ) , 6.69 (m, 8H, NPh- / / ) , 7.14 (m, 12H, NPh- / / ) . 3 1 P { ' H } N M R ( C 6 D 6 , 25 °C, 202.5 M H z ) : £ - 3 6 . 2 (br, s). 7 L i { ' H } N M R ( C 6 D 6 , 25 °C, 194.32 M H z ) : £ -1 .7 (br, s). 5: ' H N M R ( C 6 D 6 , 25 °C, 500 M H z ) : £ 0.08, 0.15 (s, 12H, S i C / / 3 ) , 1.2-1.7 (m, 15H, Cy-H, P C / / 2 S i M e 2 ) , 3.2 (br, 2H , N/Z), 6.46, 6.62, 7.01 (m, 10H, NPh-/ / ) . 3 1 P { ' H } N M R ( C 6 D 6 , 25 °C, 202.5 M H z ) : £ -28 .1 (s). Direct synthesis of ( C y P h [ N P N ] L i 3 ) 2 0 , 4 A solution of 1 (1.00 g, 1.89 mmol) in E t 2 0 (40 mL) was added via cannula to a solution of L i20 (28.3 mg, 0.946 mmol) in Et20 (60 mL) , whereupon the mixture turned a pale yellow. Removal of solvent produced an off-white powder, which was taken up in toluene and filtered through Celite. Removal of toluene afforded a white powder, dried in vacuo to afford 4 in 62% yield. Analysis of 4 matched that reported above. Synthesis of C y M e s [ N P N ] L i 2 ( T H F ) , 6 Complex 6 was synthesized in an analogous reaction to the preparation of 1. MesNH2 (11.640 g, 86.1 mmol), a 1.6 M B u " L i solution (53.8 m L , 86.1 mmol), C l S i M e 2 C H 2 C l (12.320 g, 86.1 mmol), C y P H 2 (5.80 m L , 43.1 mmol) and another addition of 1.6 M B u " L i solution (107.6 m L , 172.2 mmol) afforded crude ligand. Addit ion of 3.5 m L of 49 References begin on page 52. Chapter Two: Diamidophosphine ligand modification THF to a hexanes solution of this crude product caused 6 to precipitate as a white micro-crystalline solid. Filtration isolated the product in 79% yield. X-ray quality crystals were obtained by the slow evaporation of a saturated toluene/hexanes solution. ! H NMR (C 6D 6 , 30°C, 500 MHz): 5 0.21 and 0.35 (s, 12H total, SiCr73), 0.85-1.91 (m, 15H, PC 6 / / , i , PC// 2), 1.13 (m, 4H, OCH 2C// 2), 2.20 (s, 18H, NPh(C//3)3), 2.96 (m, 4H, OC//2CH2), 6.82 (s, 4H, NPh m-H). 3 1P{'H} NMR (C 6D 6 , 25 °C, 202.5 MHz): J-30.2 (s). 7Li{'H} NMR (C 6D 6 , 25 °C, 194.32 MHz): 5 -0.8 (s). Anal. Calcd for C34H57Li2N2OPSi2(%): C, 66.85; H, 9.41; N , 4.59. Found: C, 66.98; H, 9.60; N , 4.39. Synthesis of P h M e s[NPN]Li 2(THF), 7 Complex 7 was synthesized in an analogous reaction to the preparation of 1. MesNH2 (11.640 g, 86.1 mmol), a 1.6 M Bu"Li solution (53.8 mL, 86.1 mmol), ClSiMe 2CH 2Cl (12.320 g, 86.1 mmol), PhPH2 (4.75 mL, 43.1 mmol) and another addition of 1.6 M Bu"Li solution (107.6 mL, 172.2 mmol) afforded crude ligand. Addition of 7.0 mL of dioxane to a hexanes solution of this crude product caused 7 to precipitate as an off-white micro-crystalline solid. Filtration isolated the product in 81%> yield. [ H NMR (CeD6, 30°C, 500 MHz): 5 0.22 and 0.33 (s, 12H total, SiC// 3), 0.89 and 1.28 (m, 4H, ?CH2), 3.17 (s, 16H, OCH2CH20), 2.20 (s, 18H, NPh(C//3)3), 6.80 (s, 4H, NPh m-H), 7.15, 7.24, 7.61 (m, 5H, PPh-//). 3 1P{'H} NMR (C 6D 6, 25 °C, 202.5 MHz): £-34.1 (q, V P L i = 18.9 Hz). 7Li{'H} NMR (C 6D 6 , 25 °C, 194.32 MHz): 3-0.1 (s, ILi), -0.8 (d, xJm = 18.9 Hz). Anal. Calcd for C 3 8H59Li 2N 204PSi2 (%): C, 64.38; H, 8.39; N , 3.95. Found: C, 64.54; H, 8.49; N , 3.86. Synthesis of C y M e[NPN]Li 2(diox), 8 Complex 8 was synthesized in an analogous reaction to the preparation of 1. CH3NH3C1 (2.179 g, 0.0323 mol), a 1.6 M Bu"Li solution (40.3 mL, 0.0645 mol), ClSiMe 2CH 2Cl (4.3 mL, 0.0323 mol), CyPH 2 (2.2 mL, 0.0162 mol) and another addition of 1.6 M Bu"Li solution (40.3 mL, 0.0645 mol) afforded crude ligand. Addition of 1.3 mL of dioxane to a hexanes solution of this crude product caused 8 to precipitate as a white micro-crystalline 50 References begin on page 52. Chapter Two: Diamidophosphine ligand modification solid. Filtration isolated the product in 74% yield. *H NMR (C 6D 6 , 30°C, 500 MHz): 5 0.35 (s, 12H, SiC// 3), 0.88 and 1.22 (m, 4H, VCH2), 1.68, 1.79 and 1.94 (m, 11H, P-Ce^n), 3.02 (s, 6H, NC// 3 ), 3.42 (s, 16H, OCH2CH20). NMR (C 6D 6 , 25 °C, 202.5 MHz): £-36.1 (s). 7Li{ !H} NMR (C 6D 6, 25 °C, 194.32 MHz): £-1.1 (s). Anal. Calcd for C 1 8 H 4 ,L i 2 N 2 0 2 PSi 2 (%): C, 51.65; H, 9.87; N , 6.69. Found: C, 51.93; H, 9.85; N, 6.60. Synthesis of p h M e[NPN]Li 2(diox) 2, 9 Complex 9 was synthesized in an analogous reaction to the preparation of 1. CH3NH3C1 (5.813 g, 0.0861 mol), a 1.6 M Bu"Li solution (107.6 mL, 0.1722 mol), ClSiMe 2CH 2Cl (11.4 mL, 0.0861 mol), PhPH2 (4.7 mL (0.0431 mol) and another addition of 1.6 M Bu"Li solution (107.6 mL, 0.1722 mol) afforded crude ligand. Addition of 3.5 mL of dioxane to a hexanes solution of this crude product caused 4 to precipitate as a pale yellow micro-crystalline solid. Filtration isolated the product in 77% yield. 'H NMR (C 6D 6, 30°C, 500 MHz): 8 -0.09 and -0.10 (s, 12H total, SiC/73), 0.89 and 0.91 (m, 4H, PCH2), 2.83 (s, 6H, NC// 3 ), 3.57 (s, 16H, OCH2CH20), 7.15, 7.22 and 7.49 (m, 5H, PPh-H). 3 1P{ lH} NMR (C 6D 6, 25 °C, 202.5 MHz): £-37.5 (q, Vi = 26.6 Hz). 7Li{'H} NMR (C 6D 6, 25 °C, 194.32 MHz): £-1.4 (s, ILi), -1.5 (d, Vi = 26.6 Hz). Anal. Calcd for C 2 2 H 4 3 Li 2 N 2 0 4 PSi 2 (%): C, 52.78; H, 8.66; N , 5.60. Found: C, 52.52; H, 8.41; N , 5.75. Synthesis of 1,2-(ClCH2SiMe2NH)2CH2CH2, 10, CH 2(CH 2NHSiMe 2CH 2Cl) 2, 11, CMe 2(CH 2NHSiMe 2CH 2Cl) 2,12, and l,3-(ClCH 2SiMe 2NHCH 2) 2C 6H 4 ,13. To a -78 °C solution of ClSiMe 2CH 2Cl (11.44 g, 0.080 mol) in 50 mL Et 2 0 was added a 0 °C solution of the requisite diamine (0.040 mol) in 150 mL Et 20 producing a flocculent white precipitate. These mixtures were maintained at -78 °C, and to it "BuLi (50 mL, 1.6 M in hexanes) was slowly added to give pale golden yellow solutions and a fine white precipitate. The resulting mixtures were warmed to 0 °C and stirred for 30 min. Filtration of these suspensions through Celite-filled schlenk frits, followed by removal of solvent, gave a series of golden yellow oils. These oils were extracted into hexanes, filtered 51 References begin on page 52. Chapter Two: Diamidophosphine ligand modification through Celite and dried in vacuo to afford the bis(silylamines) 10, 11, 12, and 13 in 68%, 78%, 85% and 57% yields respectively. 10: ! H NMR (C 6D 6 , 30°C, 500 MHz): 8 0. 17 (s, 12H, SiC#3), 0.62 (s, 2H, NH), 2.68 (s, 4H, NCrY2CrY2N), 2.85 (s, 4H, ClCrY2SiMe2). 11: *H NMR (C 6D 6 , 30°C, 500 MHz): 8 0.20 (s, 12H, SiCH3), 1.53 (q, 2H, NCH 2 C// 2 CH 2 N), 2.90 (t, 4H, NC// 2 CH 2 C// 2 N), 2.97 (s, 4H, ClC# 2SiMe 2) 3.66 (s, 2H, NH). 12: 'H NMR (C 6D 6 , 30°C, 500 MHz): 8 0.19 (s, 12H, SiC// 3), 0.64 (s, 6H, CC#3), 2.57 (s, 4H, NC// 2 CMe 2 C// 2 N), 2.85 (s, ClC// 2SiMe 2), 3.59 (s, 2H, NH). 13: 'H NMR (C 6D 6, 30°C, 500 MHz): 8 0.21 (s, 12H, SiC// 3), 1.91 (s, 2H, NH), 2.88 (s, 4H, ClC// 2SiMe 2), 3.76 (s, 4H, NCr7 2ArC// 2N), 7.17 (s, 1H, Ar-H), 7.29 (d, 2H, Ar-H), 7 AO (t, 1H, Ar-H). 2.5 References 1. Fryzuk, M . D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S. A.; Koetzle, T. F. J. Am. Chem. Soc. 2001, 123, 3960. 2. Studt, F.; MacKay, B. A.; Fryzuk, M. D.; Tuczek, F. J. Am. Chem. Soc. 2004,126, 280. 3. Fryzuk, M . D.; MacKay, B. A.; Patrick, B. O. J. Am. Chem. Soc. 2003,125, 3234. 4. Fryzuk, M. D.; Petrella, M . J.; Coffin, R. C ; Patrick, B. O. C. R. Chimie 2002, 5, 451. 5. Fryzuk, M . D.; MacKay, B. A.; Johnson, S. A.; Patrick, B. O. Angew. Chem. Int. Ed. 2002, 41, 3709. 6. Fryzuk, M . D.; Yu, P.; Patrick, B. 0. Can. J. Chem. 2001, 79, 1194. 7. Fryzuk, M . D.; Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998,120, 11024. 8. Eller, P. G.; Bradley, D. C ; Hursthouse, M. B.; Meek, D. W. Coord. Chem. Rev. 1977, 24, 1. 9. Gade, L. H. Chem. Commun. 2000, 173. 10. Baumann, R.; Davis, W. M.; Schrock, R. R. J. Am. Chem. Soc. 1997,119, 3830. 11. Baumann, R.; Stumpf, R.; Davis, W. M.; Liang, L. C ; Schrock, R. R. Organometallics 1999,18, 3649. 52 References begin on page 52. Chapter Two: Diamidophosphine ligand modification 12. Cloke, F. G . N . ; Hitchcock, P. B . ; Love, J. B . J. Chem. Soc., Dalton Trans. 1995, 25. 13. Liang, L . C ; Schrock, R. R.; Davis, W. M . ; McConvi l le , D . H . J. Am. Chem. Soc. 1999,121, 5797. 14. Schrock, R. R.; Seidel, S. 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Organometallics 1992,11, 469. 26. Basch, H . ; Musaev, D . G . ; Morokuma, K . ; Fryzuk, M . D . ; Love, J. B . ; Seidel, W . W.; Albinati , A . ; Koetzle, T. F.; Klooster, W . T.; Mason, S. A . ; Eckert, J. J. Am. Chem. Soc. 1999,121, 523. 27. Studt, F.; Morello, L . ; Lehnert, N . ; Fryzuk, M . D . ; Tuczek, F. Chem. Eur. J. 2003, 9, 520. 28. Fryzuk, M . D . ; Love, J. B . ; Rettig, S. J.; Young, V . G . Science 1997, 275, 1445. 29. Fryzuk, M . D . ; Love, J. B . ; Rettig, S. J. Organometallics 1998,17, 846. 30. Fryzuk, M . D . ; Love, J. B . ; Rettig, S. J. Organometallics 1998,17, 846. 31. Fryzuk, M . D. ; Johnson, S. A . ; Rettig, S. J. Organometallics 1999,18, 4059. 32. Fryzuk, M . D . ; Johnson, S. A . ; Rettig, S. J. Organometallics 2000,19, 3931. 53 References begin on page 52. Chapter Two: Diamidophosphine ligand modification 33. Fryzuk, M . D . ; Jafarpour, L . ; Kerton, F. M . ; Love, J. B . ; Rettig, S. J. Angew. Chem. Int. Ed. 2000, 39, 767. 34. Fryzuk, M . D . ; Johnson, S. A . ; Rettig, S. J. J. Am. Chem. Soc. 2001,123, 1602. 35. Fryzuk, M . D . ; Jafarpour, L . ; Kerton, F. M . ; Love, J. B . ; Patrick, B . O.; Rettig, S. J. Organometallics 2001, 20, 1387. 36. Fryzuk, M . D . ; Kozak, C. M . ; Bowdridge, M . R.; Jin, W. ; Tung, D . ; Patrick, B . O.; Rettig, S. J. Organometallics 2001, 20, 3752. 37. Fryzuk, M . D . ; Kozak, C. M . ; Bowdridge, M . R.; Patrick, B . O.; Rettig, S. J. J. Am. Chem. Soc. 2002,124, 8389. 38. Fryzuk, M . D . ; Kozak, C. M . ; Bowdridge, M . R.; Patrick, B . O. Organometallics 2002, 21, 5047. 39. Fryzuk, M . D . ; Kozak, C . M . ; Mehrkhodavandi, P.; Morel lo, L . ; Patrick, B . O.; Rettig, S. J. J. Am. Chem. Soc. 2002,124, 516. 40. Fryzuk, M . D . ; Corkin, J. R.; Patrick, B . O. Can. J. Chem. 2003, 81, 1376. 41. Fryzuk, M . D . ; Kozak, C. M . ; Patrick, B . O. Inorg. Chim. Acta 2003, 245, 53. 42. Fryzuk, M . D . ; Jin, W . Unpublished results. 1998. 43. Farrugia, L . J. J. Appl. Cryst. 1997, 30, 565. 44. Willard, P. G . ; Jacobson, M . A . Org. Lett. 2000, 2, 2753. 45. Jendras, M . ; Klingebiel , U . ; Noltemeyer, M . J. Organomet. Chem. 2002, 646, 134. 46. Briand, G . G . ; Chivers, T.; Krahn, M . ; Parvez, M . Inorg. Chem. 2002, 41, 6808. 47. Jones, C ; Junk, P. C. ; Leary, S. G . ; Smithies, N . A . J. Chem. Soc, Dalton Trans. 2000,3186. 48. Muller, J. F. K . ; Neuburger, M . ; Spingler, B . Angew. Chem. Int. Ed. 1999, 38, 3549. 49. Chivers, T.; Downard, A . ; Yap, G . P. A . J. Chem. Soc, Dalton Trans. 1998, 2603. 50. Gordon, M . D . ; Quin, L . D . J. Am. Chem. Soc 1976, 98, 15. 51. Mann, B . E . ; Masters, C ; Shaw, B . L . J. Chem. Soc. (A) 1971, 1104. 52. Kyba, E . P.; Davis, R. E . ; Hudson, C. W. ; John, A . M . ; Brown, S. B . ; McPhaul , M . J.; Lie , L . K . ; Glover, A . C. J. Am. Chem. Soc. 1981,103, 3868. 53. Coles, S. J.; Edwards, P. G . ; Fleming, J. S.; Hursthouse, M . B . ; Liyanange, S. S. Chem. Commun. 1996, 2783. 54. Caminade, A . M . ; Majoral, J. P. Chem. Rev. 1994, 94, 1183. 54 References begin on page 52. Chapter Two: Diamidophosphine ligand modification 55. Kummer, D . ; Baldeschweiler, J. D . J. Phys. Chem. 1962, 67, 98. 56. LoCoco, M . D . ; Jordan, R. F. Organometallics 2003, 22, 5498. 57. Lee, C. H . ; L a , Y . H . ; Park, J. W . Organometallics 2000, 19, 344. 58. Garcia-Yuste, S.; Hellmann, K . W. ; Gade, L . H . ; Scowen, I. J.; McPartl in, M . Zeit. Natur. B: Chem. Sci. 1999, 54, 1260. 59. Friedrich, S.; Gade, L . H . ; Scowen, I. J.; McPartlin, M . Organometallics 1995,14, 5344. 60. Bambirra, S.; Meetsma, A . ; Hessen, B . ; Teuben, J. H . Organometallics 2001, 20, 782. 61. Kurochkin, V . V . ; Zavalishina, A . I.; Orzhekovskaya, E . I.; Bekker, A . R.; Agranovich, A . G . ; Nifant'ev, E . E . Zhurn. Obsch. Khim. 1987, 57, 311. 62. Bou, J. J.; Rodriguez-Galan, A . ; Munoz-Guerra, S. Macromolecules 1993, 26, 5664. 63. Pangborn, A . B . ; Giardello, M . A . ; Grubbs, R. FL; Rosen, R. K . ; Timmers, F. J. Organometallics 1996,15, 1518. 64. Craig, J. M . ; Brimmer, S. P. Microchem. J. 1995, 52, 376. 65. Baudler, M . ; Zarkdas, A . Chem. Ber. 1965,104, 1034. 55 References begin on page 52. Chapter Three: Synthesis and reactivity of [NPN] supported V(IIl), Nb(HI) and Nb(lV) complexes Chapter Three Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes 3.1 Introduction The preparation of a coordinatively unsaturated molybdenum complex supported by bulky amides was an important breakthrough in dinitrogen chemistry.1"3 The steric bulk of the amido donors in Mo[N(R)Ar ] 3 (R = C ( C D 3 ) 2 C H 3 , A r = 3 ,5-C6H 3 Me 2 ) prevents the formation of a strong metal-metal multiple bond typical of coordinatively unsaturated Mo(III). 4 Dinitrogen is activated and reduced by this system, which eventually cleaves the N=N bond to generate the Mo(VI) nitride complex [N(R)Ar]Mo(=N), as shown in Equation 3.1. While transition metal nitride complexes are usually unreactive due to the strength of the M=N bond, this nitride ligand has been recently incorporated into an organic molecule."^ Bu1-/Bu Bu1 , N / ' - ; V ^ M o — N / Bu ' N 2 Bu 1 • lBu 3.1 2 \ A r A r Ar 56 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(II1), Nb(III) andNb(IV) complexes A diamido amine complex, (Me 3 SiN(CH 2 CH2NSiMe 3 )2V)2 (u . -Cr )2, has also been published as an effective entry point to promoting dinitrogen cleavage. 6 Reduction of the vanadium complex with potassium graphite ( K C g ) results in the binding and cleavage of dinitrogen, to give (Me 3 SiN (CH2CH 2 NSiMe 3 ) 2 V )2 (u . -N )2. Further reduction led to the isolation of the potassium salt K[(Me3SiN(CH2CH2NSiMe 3) 2V) 2(p--N)2]. These reductions are shown in Scheme 3.1. Two niobium systems support N - N bond cleavage. A dinuclear end-on Nb(III) dinitrogen complex, stabilized by the calix[4]arene tetraanion, reacts with benzaldehyde to produce a metal-oxo complex and PhCH=N-N=CHPh. ' This same dinitrogen complex can be reduced with N a metal to cleave dinitrogen and form a dinuclear system with bridging nitrides. 7 A niobium dichloride complex supported by tris(aryloxide) ligands also displays the ability to split dinitrogen. In this case, reduction o f the starting chloride with an excess of L i B H E t 3 under N2 affords N2 bond cleavage. 2 VCI 3 (THF) 3 2 Li 2[NN 2] Me 3 S Me 3 S S iMe ? ^ , S i M e 3 C l — V C ' , v N v S i M e 3 1 [NN2] = Me 2 S iN (CH 2 CH 2 NS iMe 3 ) 2 M e 3 S K 2 K C 8 -N S iMe ? M e 3 S r \ N : > V — N Me 3 S O „ SiMe-i / S i M e 3 K C 8 M e 3 S i ^ > V = N ^ ySMez Me 3 S SiMeq N = V C , > , N v S i M e 3 Me 3 Si M e 3 S r -N Scheme 3.1 There is a rich history of dinitrogen activation by vanadium, niobium and tantalum. Vanadium(II) amidinates and vanadium(III) amides bind N 2 end-on to form 57 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(I1I), Nb(III) andNb(IV) complexes dinuclear complexes. 9 ' 1 0 The reaction of NaHBEt3 with a niobium halide, (Cy2N)2NbCl(ri2-CyN=C(C5Hio)), under N 2 generates an end-on dinuclear dinitrogen complex ( ( C y ^ N ^ s C p - n ' i r i 1 - ^ ) . 1 1 [ (TaCl(=CHMe 3 ) (PMe 3 ) 2 ] 2 (p- r i 1 : r i 1 -N 2 ) is formed from the reduction of T a C l 3 ( = C H C M e 3 ) ( P M e 3 ) 2 with Na /Hg amalgam. 1 2 The end-on dinuclear bonding of N 2 in these complexes is typical for group 5 metal dinitrogen complexes, as discussed in Chapter l . 1 3 " 2 0 These three examples are shown in Scheme 3.2. - J l / -N Pr Pr' \ , i p r N-\ i N—\ K .si V N = N V IPrV r r 'Pr 2 TaCl3(=CHCMe 3)(PMe 3)2 4 Na/Hg I \ N-P M e 3 Pr1 i P r[NNN]V(THF) 2 (Cy 2N) 2Nb(CI)(n 2-N(C 6H 1 0)Cy) 2 NaHBEt 3 P M e 3 M e 3 C H C ^ T l a _ N _ N = T l a ^ C H C M e 3 PMeq P M e ? C y 2 N ^ , N b = N -C y 2 N ^ / C y 2 N NCy 2 | ^ N C y 2 -N=Nb" \ NCy 2 Scheme 3.2 The original premise for studying mid-oxidation state vanadium and niobium complexes supported by the [NPN] ligand was to mimic the N - N bond cleavage reactions shown in Equation 3.1 and Scheme 3.1. These examples use amido ligands; therefore the diamidophosphine ligand seemed appropriate. The reduction of species such as R R ' [ N P N ] V C 1 or R R ' [ N P N ] N b C l would produce vanadium(II) and niobium(II) complexes isoelectronic to these systems. If reductions are conducted under a dinitrogen atmosphere, coordinatively unsaturated dinitrogen complexes of the type [NPN]M) 2 (p -N 2 ) (where M = V , Nb) should form. These fragments should be 58 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nh(IV) complexes isolobal and isoelectronic with the complex ([Ar(R)N] 3 Mo) 2 (p-N2), and may accordingly activate and cleave the N=N bond. 3.2 Preparation of V(III) complexes of the [NPN] ancil lary l igand 3.2.1 Synthesis of (RR [NPN]VC1)„ A convenient and versatile starting material for vanadium(III) chemistry is VC1 3 (THF) 3 . Treatment of a cooled solution of V C 1 3 ( T H F ) 3 in T H F with an E t 2 0 solution of C y P h [ N P N ] L i 2 ( O E t 2 ) , 1, gave a brick-red paramagnetic solid. E I -MS and elemental analysis confirmed an empirical formula of C24H 3 7 ClN 2 PSi2V, corresponding to ( C y P h [ N P N ] V C l ) n , 14. Recrystallization of 14 from a -35 °C layered benzene/HMDS solution gave red block crystals. X-ray analysis of the crystals, isolated in 78% yield, showed that 14 is a chloride-bridged dimer in the solid state, shown as an O R T E P 2 1 drawing in Figure 3.1. Figure 3.1. O R T E P drawing (spheroids at 50% probability) of ( C y P h [ N P N ] V C l ) 2 , 14. Si ly l methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. 59 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(lll), Nb(III) and Nb(lV) complexes Relevant bond lengths and angles and crystallographic data are listed in Tables 3.1 and 3.2, respectively. The V(1)-C1(1) and V(1)-C1(1*) bond lengths of 2.3632(4) A and 2.4913(4) A , respectively, are average for dative-bound chloride dimers 2 2 While 14 appears as the monomer in mass spectrometry studies, it is probable that it exists as a loosely bound dimer in solution, and breaks apart under the harsh ionization conditions of E I - M S . The V - N bond lengths of 1.935(1) and 1.934(1) A are expectedly shorter than the corresponding metal-amide bonds in [NPN] supported tantalum complexes. 2 3 While the V ( l ) - P ( l ) bond length of 2.4323(5) A is not unusual for the broad range of vanadium phosphine complexes, it is quite short for related vanadium chloride dimers (-2.6-2.7 A ) . 2 4 " 2 7 The complex exhibits distorted trigonal bipyramidal geometry with chlorine and phosphine ligands occupying apical positions. Table 3.1 Selected Bond Distances (A) and Angles (°) for ( C y P h [ N P N ] V C l ) 2 , 1 4 Lengths Lengths/Angles Angles V(1)-C1(1) 2.3632(4) V(l)-N(l) 1.935(1) Cl(l)-V(l)-N(2) 127.32(4) V(1)-C1(1*) 2.4913(4) C1(1)-V(1)-C1(1*) 84.68(2) N(l)-V(l)-N(2) 116.17(6) V(l)-P(l) 2.4323(5) Cl(l)-V(l)-N(l) 115.77(4) P(l)-V(l)-N(l) 86.46(4) V(l)-N(2) 1.934(1) Cl(l)-V(l)-P(l) 88.90(2) P(l)-V(l)-N(2) 86.00(4) Table 3.2 Crystallographic Data and details of refinement for ( C y P h [ N P N ] V C l ) 2 , 14 Empirical formula C 2 4H37N 2 PClSi 2 V Crystal system Triclinic Formula weight 1054.22 Space group P-l a, b, c (A) 10.2811(5), 11.4776(4), 13.3016(6) a , # Y ( ° ) 103.948(3), 11.1.556(1), 92.914(3) • v , A 3 1399.8(1) Total reflections 12014 z 1 Unique reflections 5342 D c a i c , g cm"3 1.250 Parameters 280 '• ' '•' u (Mo Ka), cm"1 6.06 R . a 0.047 T, K 173 ± 1 R w a 0.095 29 range (°) 55.8 Goodness-of-fit 1.48 "R, = Z | | F o | - | F C | | / Z | F 0 | ; Rw = Hw(\F02\ - | F c 2 | ) 2 / Z w | F 0 2 | 2 ) 60 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes Metathesis reactions of ligand precursors 2, 6, 7, 8, and 9 with VCl3(THF)3 produced the vanadium chlorides ( P h P h [ N P N ] V C l ) n , 15, ( C y M e s [ N P N ] V C l ) n , 16, ( P h M e s [ N P N ] V C l ) n , 17, ( C y M e [ N P N ] V C l ) n , 18, and ( P h M e [ N P N ] V C l ) n , 19, respectively. Characterization by E I - M S and elemental analysis confirmed the empirical formula in each case. Mass spectra showed a molecular ion corresponding to the monomer (n=l), although complexes may be weakly bound dimers that dissociate in E I - M S . It should be noted that complexes 16 and 17 exhibited substantial fragmentation to form R R [ N P N ] V ( M + - C l , 95%). Elemental analysis confirmed the bulk composition in these cases. A general synthesis is shown in Equation 3.2. 3.2.2 Reduction of ( C y F h [NPN]VCl) 2 : Coordination and cleavage of molecular nitrogen Breaking the strong N - N triple bond is difficult: this transformation requires metal centres that form strong multiple bonds to nitrogen to stabilize intermediate species, and metal centres that are in an appropriate oxidation state to provide a total of six electrons to N 2 (as in Equation 3.1). Reducing equivalents from reactive metal centres can be combined with direct reduction with alkali metals to drive this transformation (as in Scheme 3.1). Reduction of 14 at 4 atm of N 2 with 2.2 equivalents of K C g at -78 °C gave a bright purple solution upon warming to room temperature. In this case, two vanadium(III) centres (4 e") and two alkali metals (2 e") can provide the electrons needed to cleave N 2 . Removal of KC1 and graphite by filtration, followed by recrystallization from pentane gave a deep purple paste, highly soluble in common 61 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(HI) and Nb(IV) complexes organic solvents. EI-MS (200 °C) of the product indicated the formation of a (C y P h[NPN]V)2(N)2 species with a peak at m/z 1010 (C48H74N6Si4P2V2), but repeated attempts to grow x-ray quality crystals failed. EI-MS experiments at higher temperatures (300 °C) gave a molecular ion corresponding to the mononuclear vanadium nitride, C y P h [NPN]V=N (m/z 505, 100%). While the coordination mode of the dinitrogen is unconfirmed in this product, it is likely a bis(nitride) complex. It is unlikely that the purple product contains an intact N 2 moiety, as fragmentation of these complexes primarily involve loss of N2 or no fragmentation, rather than cleavage of the dinitrogen bond.2 8 Crude *H NMR data showed the presence of a paramagnetic impurity, which obscured much of the spectrum, however a highly symmetric product with 2 SiMe resonances was observed. Unfortunately, the paramagnetic impurity prevented characterization by 3 'P or 1 5 N NMR spectroscopies. To confirm that 14 incorporates molecular nitrogen and rule out product formation from complex decomposition, 14 was reduced with 2.2 equivalents of KCs at -78 °C under Ar. The reaction did not produce the characteristic purple colour. Instead, a brown, hexanes insoluble powder was isolated. No vanadium nitride species were observed by EI-MS; the molecular ion corresponded to a C y P h [NPN]V fragment. A similar reduction was performed under an atmosphere of L 5 N2, using the analogous method and charging the vessel with 1.2 atm of 1 5N2. The resulting deep purple product showed a molecular ion corresponding to C4gH74N415N2Si4P2V2, and a peak corresponding to C24H3 7N 2 1 5NSi2PV. Reduction of 14 at 4 atm of N2 with 3.3 equivalents of KCg at -78 °C gave a deep olive green solution upon warming to room temperature. From the solution, a dark green solid was isolated and characterized by EI-MS. A small peak corresponding to K( C y P h[NPN]V=N) 2 and a peak corresponding to C y P h [NPN]V=N (m/z 505, 100%) suggested dinitrogen incorporation. Interestingly, the observed products are both highly coloured - purple and green - and these colour changes match those seen in the isoelectronic diamidoamine vanadium systems.6 Unfortunately, the reduced products could not be purified despite extensive efforts. Attempts to optimize the synthesis of the vanadium nitride by changing solvent, reaction time, N 2 pressure, reducing agent or temperature were unsuccessful. All 62 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(II1), Nb(III) and Nb(IV) complexes reactions were complicated by the formation of an unknown paramagnetic impurity. The reductions are shown in Scheme 3.3. Scheme 3.3 3.2.3 Reduction of ( R R ' [ N P N ]VC1) 2 complexes: Identification of ligand decomposition products Fortunately, the reduction of ( C y M e s [ N P N ] V C l ) n , 16, helped to illustrate the problems associated with reduction o f [NPN] supported vanadium chlorides. Reduction of 16 with 2.2 equivalents of KCg under 1 atm of N 2 at -78 °C did not generate the strong purple coloured product characteristic of the activation of molecular nitrogen by these species. Instead, a tan coloured, pentane insoluble powder and a deep brown pentane soluble paste were isolated. Analysis of the tan powder by E I - M S had a peak 63 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(Ill) and Nb(IV) complexes corresponding to C39H60N3PS12V. This pattern could correspond to a vanadium imide, C y M e s [ N P N ] V = N M e s . Could this originate from molecular nitrogen? If not, how was it generated? To develop a hypothetical mechanism, all decomposition products of the reaction were pursued. Recrystallization of the pentane soluble paste over several weeks at -35 °C gave brown needle crystals of M e s N ( S i M e 2 C H 2 )2PCy, 20. The mesityl ring in 20 is locked; o-methyl protons are magnetically inequivalent, appearing with p-methyl protons at 5 2.28, 2.32, and 2.40. This inequivalence also manifests as two singlets for the mesityl ring protons at 5 6.90 and 7.25. Reduction of 1 6 under A r gave the same isotope pattern at m/z 709. The isolation of the [NP] heterocycle, 20, and the exclusion of N 2 as the nitrogen source both aid in proposing a mechanism. Reaction of ( C y M e s [ N P N ] V C l ) 2 species with K C 8 could generate a V(II)-V(III) intermediate species bridged by the remaining chloride. The amide groups of the [NPN] ligand can also play the role of bridging ligands and can help stabilize this intermediate. A ring closing decomposition of this [NPN] ligand, however, could eliminate an N-Mes moiety and generate the [NP] heterocycle bound to vanadium. This species would then break apart to give the V ( I V ) imide and 20. This proposed mechanism is shown in Scheme 3.4. Attempts to confirm the formation of this imide and provide support for this mechanism by isolating and crystallographically characterizing the imide complex have unfortunately been unsuccessful. The significance of this transformation wi l l be discussed later in the chapter. 64 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(lV) complexes Scheme 3.4 Reductions of 15-19 were conducted with K C g (2.2, 3.3 equiv.) under N 2 (1 atm, 4 atm). In each case, the corresponding V( IV) imide appeared in the mass spectrum. Depending on the conditions and the starting metal complex, peaks corresponding to vanadium nitrides, [NPN]V=N, were also observed. Unfortunately, none of these reductions reproduced even the marginal success observed in the reduction of 14. 3.3 Preparation of Nb complexes of the [NPN] anci l lary ligand 3.3.1 Preparation of Nb(III) complexes supported by [NPN]: Formation of Nb(III) chlorides competing with the synthesis of Nb(V) N 2 complexes 65 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(IU) andNb(IV) complexes A brief foray into the synthesis of niobium(III) complexes supported by the p h P h [ N P N ] ligand has been conducted previously. 2 3 Addit ion o f 2 to N b C l 3 ( D M E ) ( D M E = dimethoxyethane) gave a brown mixture from which X-ray quality crystals of ( p h p h [ N P N ] N b C l ) 2 ( p - N 2 ) , 21, were grown. The scope of this reaction was unstudied, and the potential reactivity of 21 remained unexplored. With two pendant chlorides, the addition o f R P L i 2 or L i 2 S could install molecular bridges across the two niobium centres. The nature of the bridging ligand may affect the coordination mode of the dinitrogen unit. Investigating the reactivity o f 21 could provide new routes to access side-on end-on bound dinitrogen complexes, as shown in Scheme 3.5. Scheme 3.5 Surprisingly, treatment of a cooled solution of NbCl3(DME) with a -78 °C ethereal solution of C y P h [ N P N ] L i 2 ( O E t 2 ) , 1, did not give the expected dinitrogen complex but instead gave a red-brown, paramagnetic solid, C y P h [ N P N ] N b C l ( D M E ) , 22, as confirmed by mass spectrometry and elemental analysis. N o dinitrogen containing species was observable by E I - M S . If the reaction was conducted under 4 atm of N 2 , a mixture of products was observed. The complex ( C y P h [ N P N ] N b C l ) 2 ( / / - N 2 ) , 23, and 22 are generated and observed by E I - M S . Purification of 23 is arduous: Successive 66 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(II1), Nb(III) andNb(IV) complexes precipitation of products from pentane/THF solutions gives moderately pure product. While 22 can be synthesized in near quantitative yield in the above route, 23 can only be isolated in low yields. This observed reactivity is summarized in Scheme 3.6. Cy Me 2 p n [ Me 2 Si Ph P \ i / / V \ SiMe? Me 2 Si NbCU(dme) r Si-1 atm N 2 NbCI3(dme) Me,Si Me 2 Ph Ph 4 atm N 2 Ph NN Af P - * ~ N b — C l o 22 S i e 2 P / h ^ + P — N b = N -di I Cl 23 *I\TN - - N b — •f/V \J 22 Cl -N= Cl •I -Nb / P y P r / P K \ ^ o : S iMe, Si M e 2 Scheme 3.6 Upon further investigation of the reaction of P h P h [ N P N ] L i 2 ( T H F ) 2 with NbCl3(DME) it was seen that this same complex reaction mixture is produced. If the crude product from the reaction is analyzed by E I - M S , both p h P h [ N P N ] N b C l ( D M E ) , 24, and ( P h P h [ N P N ] N b C l ) 2 ( / / - N 2 ) , 21, are present. Again, this is a pressure controlled reaction. Formation of 21 can be increased by conducting the reaction under 4 atm of N 2 . The product distribution is strongly affected by temperature, reagent concentration and reactant and solvent purity, but under no conditions were 21 or 24 produced exclusively. Selective crystallization of the crude mixture gave brown crystals of 21, albeit in low yields. Isolation of 21 on a preparative scale using this method is difficult and not truly feasible. 67 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(HI) and Nb(IV) complexes 3.3.2 Reduction of C y P h [ N P N ] N b C l ( D M E ) While accessing complexes 21 and 23 was complicated by low yields and purity, the synthesis of niobium(III) chlorides provided another route to investigate dinitrogen complexes. C y P h[NPN]NbCl(DME), 22, and p h p h[NPN]NbCl(DME), 24, are isoelectronic with the vanadium(III) chlorides ( R R [NPN]VCl)n. Reduction of these species under N 2 may provide Nb(II) complexes capable of the coordination, activation and cleavage of molecular nitrogen, in analogy to that described previously in Equation 3.1 and Scheme 3.1. NMR spectroscopy indicated the formation of paramagnetic species. EI-MS analysis of the products of these reactions did not suggest incorporation of molecular nitrogen. The analysis showed molecular ions at 533 (M + = C24H37N2NbPSi2) and 527 (M + = C 2 4H 3iN 2NbPSi 2), corresponding to C y P h[NPN]Nb and p h p h[NPN]Nb fragments, respectively. Repeated attempts to crystallize and characterize these products, or to identify other reduction products, have been unsuccessful. 3.4 Preparation of Nb(IV) complexes of the [NPN] anci l lary l igand 3.4.1 Synthesis and decomposition of C y P h [ N P N ] N b C l 2 The niobium dinitrogen complexes (p h p h[NPN]NbCl)2(//-N2), 21, and (C y P h[NPN]NbCl) 2(>N 2), 23, remain a synthetic target of interest. Unfortunately, direct access to these species from niobium(III) starting materials is not feasible. In an attempt to find a higher yield, reproducible synthesis of 21 and 23, the reactivity of R R[NPN] ligand precursors with NbCl4(THF)2 was investigated. It was hoped that a niobium(IV) complex, R R [NPN]NbCl2, could be reduced to a niobium(III) complex free of DME. If the reductions are conducted under a dinitrogen atmosphere, generation of complexes 21 and 23 is expected. This proposed route is shown in Scheme 3.7. 68 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes C y P h[NPN]NbCl 2 , 25, was prepared by reacting C y P h[NPN]Li 2(Et 20) with NbCl4(THF)2 at -78 °C as shown in Equation 3.3. Compound 25 was isolated as a golden brown solid in 72% yield and characterized by EI-MS and elemental analysis. Recrystallization from a layered toluene/hexanes solution at -35 °C gave irregular yellow crystals and a deep brown solution. X-ray analysis of the crystals, isolated in 39% yield, showed that 25 had decomposed to CyPh[NPN]NbCl(=NPh), 26. The molecular structure of 26 is shown as an ORTEP 2 1 drawing in Figure 3.2. Cy / \ ? / \ M e 2 P h V ^ N 7 + NbCI4(THF)2 , 7 8 o c » V / • L i - ^ \ P - ^ N b — C I 5 ' 3 Ph f Ph Cy I Et 2 0 c , 1 25 69 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(1II), Nh(Hl) and Nh(IV) complexes Figure 3.2. O R T E P drawing (spheroids at 50% probability) of C y P h [NPN]NbCl (=NPh) , 26. Ligand silyl methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons omitted for clarity. Relevant bond lengths and angles are listed in Tables 3.3 and 3.4, respectively. The Nb(l)-N(3) bond length for the imido ligand is 1.789(2) A , slightly longer than the average of ~1.76 A . 2 9 The Nb(l)-N(3)-C(25) angle for the imido moiety is close to 29 linear, 167.9(2)°, but is smaller than that observed for other niobium imides. This lack of linearity and lengthened Nb-N unit is somewhat expected. In the presence of amido ligands, which may also act as 7t-donors, 7t-bonding with the imido ligand is lessened; lower 7t-character in the niobium-imide interaction could explain these observations. Table 3.3 Selected Bond Distances (A) and Angles (°) for C y P h [NPN]NbCl (=NPh) , 26 Lengths Angles Angles Nb(l)-N(3) 1.789(2) Nb(l)-N(3)-C(25) 167.9(2) N(2)-Nb(l)-Cl(l) 158.57(6) N(3)-C(25) 1.390(3) N(3)-Nb(I)-Cl(l) 102.85(7) P(l)-Nb(l)-Cl(l) 84.46(2) Nb(l)-Cl(l) 2.5998(6) N(3)-Nb(l)-N(l) 100.04(9) N(l)-Nb(l)-N(2) 105.29(8) Nb(l)-N(l) 2.047(2) N(3)-Nb(l)-N(2) 94.34(9) N(l)-Nb(l)-P(l) 79.29(6) Nb(l)-N(2) 2.041(2) N(3)-Nb(l)-P(l) 172.60(7) N(2)-Nb(l)-P(l) 78.81(6) Nb(l)-P(l) 2.7588(7) N(l)-Nb(l)-Cl(l) 155.95(6) [Nb(l)-Cl(l*)] 2.663(5) References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) andNb(IV) complexes Table 3.4 Crystallographic Data and details of refinement for C y P h [ N P N ] N b C l ( = N P h ) , 26 Empirical formula C3oH42N3PClSi2Nb Crystal system Monoclinic Formula weight 660.19 Space group P2, /« a,b,c(k);j3n 12.7053(7), 17.6956(9), 14.8276(9); 104.540(3) v,A 3 3226.9(3) Total reflections 29601 z 4 Unique reflections 7261 D c a i c , g cm"3 1.359 Parameters 343 u (Mo Koc), cm"1 6.03 R , a 0.054 T, K 173 ± 1 R w a 0.077 29 range (°) 55.7 Goodness-of-fit 1.15 R, = Z | | F 0 | - \FC\\/I,\F0\; R„ = S w ( | F 0 2 | - | F c 2 | ) 2 / S w | F 0 2 | 2 ) The overall complex is distorted square pyramidal with ligands cis to the amide pushed back from the plane resulting in N(3) -Nb( l ) -N( l ) , N(3)-Nb(l)-N(2) and N(3)-N b ( l ) - C l ( l ) angles of 100.04(9)°, 94.34(9)° and 102.85(7)°, respectively. The unit cell contents (shown in Figure 3.3) indicate possible N b - C l interactions, with a chlorine atom from one asymmetric unit in close contact with the open face o f a niobium centre in an adjacent asymmetric unit. While the structure was solved as a monomer, there is certainly a possibility of 26 existing as a weakly bound chloride bridged dimer. 71 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(IH) and Nh(lV) complexes Figure 3.3. O R T E P drawing of unit cell contents for C y P h [NPN]NbCl (=NPh) , 26. C l atoms (lime green) are in close contact with the open face of the Nb (dark grey) as denoted by the red dashed lines. Generation of imide 26 is reproducible and has been confirmed by EI -MS. It is reminiscent of the putative generation of vanadium(IV) imides from the reduction of dinuclear vanadium chlorides in Section 3 . 2 . 2 . Analysis of the crystals by N M R spectroscopy showed that a paramagnetic impurity was present in the bulk sample. Due 7 2 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) andNb(lV) complexes to the high solubility of 26 in common organic solvents, analytically pure sample was not obtained. Analysis of the brown filtrate after solvent removal by E I - M S indicated the generation of CyP(CH2SiMe2)2NPh, 27. This [NP] heterocycle was characterized by N M R spectroscopy. Vanadium(IV) imides were also observed with concomitant production of MesN(SiMe2CH2)2PCy, 20, suggesting a similar mechanism. This decomposition reaction is shown in Equation 3.4. 3.4.2 Synthesis and reduction of nn[NPN]NbCl2 Analogues of 25 were prepared under similar conditions. Addit ion of an ethereal solution of 2 to a cooled solution of N b C l 4 ( T H F ) 2 gives p h p h [ N P N ] N b C l 2 , 28. E I -MS and elemental analysis confirmed the generation of the metathesis product, isolated as a golden brown solid in 72% yield. Complex 28 appears to be more robust. Decomposition to form the niobium imide did not occur, even at elevated temperatures, although no X-ray quality crystals were grown of the niobium dichloride despite repeated attempt's. While 28 does not decompose spontaneously in solution, reduction under N2 to form ( p h P h [ N P N ] N b C l ) 2 0 - N 2 ) , 21, was a challenge. Diethyl ether (50 mL) was vacuum transferred into a vessel containing 28 and 1.1 equivalents of potassium graphite (KCs). The vessel was charged with 4 atm N2 and the reaction contents analyzed after 24 h by E I - M S . There was minimal production of the desired dinitrogen complex, 21. Instead, p h p h [NPN]NbCl ( =NPh) , 29, and P h P ( C H 2 S i M e 2 ) 2 N P h , 30 were observed. Recrystallization of the hexanes soluble fraction gave the [NP] heterocycle 30 which 1 T 1 was characterized by H and P N M R spectroscopies. As with the preparation of 26, a paramagnetic impurity complicated N M R spectroscopy of 29. 73 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) andNb(IV) complexes 3.4.3 Mechanistic implications of decomposition of [NPN] vanadium and niobium mid-oxidation state complexes The decomposition of niobium(IV) complexes, either spontaneously or upon reduction, to give niobium(V) imides prevents the isolation and further study o f the desired complexes of molecular nitrogen. A similar decomposition pathway was observed during the reduction of vanadium(III) complexes. The imide ligand has a unique ability to stabilize high oxidation states while still promoting further reactivity. This ligand can provide a total of three bonds to a metal centre, giving it exceptional coordinative f l ex ib i l i t y . 2 9 ' 3 0 The unique properties of the 31 38 metal-imide bond have shown particular utility in the catalytic metathesis of imines and as supporting ligands for many organic transformations including ring-opening metathesis polymerization. 3 9 ' 4 0 Group 5 imido complexes in particular generate considerable interest. 4 1" 4 6 Mono-imides of group 5 metals can be prepared by a number of routes: through Wittig-like reactions of T a ( C H t B u ) C l 3 ( T H F ) 2 with imines, 1 8 ' 4 7 by reaction of silated alkyamines or arylamines with M C 1 5 species, 4 8 ' 4 9 or by reaction of hexamethyldisilazane with metal halides to afford si lylimides. 5 0 Alternatively, imides can be afforded directly from reaction of the requisite primary amines with metal halides liberating the desired imido complex and H C 1 . 5 1 While S i - N bond cleavage is an established route to group 5 imides, the synthesis of 26 and 29 is not accompanied by S i - 0 or S i - C l bond formation, a major thermodynamic driving force. Interestingly, an unprecedented photochemical scission of a S i - N bond on an arcsa-niobocene arm led to imide formation through oc-silicon 52 abstraction. This reaction can act as an intramolecular model for our proposed decomposition route. The formation of Nb=NPh and V = N R moieties that stabilize the high-oxidation state complexes are the thermodynamic driving forces for this reaction. Variation of the reaction conditions for the transformation of 25 to 26 provided some insight. High dilution minimized the decomposition. Initially, the decomposition reaction was discovered in an attempt to grow crystals of 25 from saturated toluene/hexanes solutions. A ten-fold dilution of this mixture effectively slowed this 74 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes reaction. Also , the isolated yield of either the niobium imide complex or the [NP] heterocycle was always less than 50%. These two factors imply a bimolecular mechanism. Finally, the elimination of radiation sources and ambient light also hindered imide formation. B y keeping reactions in darkened vessels, the decomposition process was slowed. The source of the imide in 26 is from the decomposition of an [NPN] ligand upon cyclization to give the [NP] heterocycle. A proposed mechanism is shown in Scheme 3.8. Just as ( C y P h [ N P N ] V C l ) 2 is a chloride bridged dimer, R R [ N P N ] N b C l 2 can also bridge via pendant chlorides. Although relatively rare, there are examples of amido-bridged complexes of group 5 metals, 5 3" 5 6 suggesting the possible formation of an intermediate bridged not by a chloride, but rather by an N P N amido donor. The photochemical scission of a S i - N bond would generate the [NP] heterocycle, 27, and a new complex bridged by a chloride and imide. Breaking this weakly bound dimer would generate the niobium(V) imide, 26. The decomposition of p h p h [ N P N ] N b C i 2 is not photochemically driven, but results from reduction. In this case, reduction of one niobium centre in an amido-bridged dimer would provide the impetus to form the [NP] heterocycle and heterolytically break the N - S i bond to form 29. Me 2 NPh NbCI 3 species + R = Ph, Cy Scheme 3.8 75 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes The disproportionation (2 Nb(IV) to Nb(V) + Nb(III)) of these mid-oxidation state complexes supported by diamidophosphine ligands stems from the inclusion of weak N - S i bonds in the ligand framework. While trimethylsilyl-substituted amido complexes are much more stable than dialkylamido complexes due to lower nitrogen basicity, 5 7 the N - S i bond is weak. B y providing an amicable electronic environment, and adequate steric protection, silyl-substituted amides give robust metal-amide bonds and can promote novel chemical reactions. This strength as a ligand modification, however, is balanced by the weak N - S i linkage. It is well established that T M S -substituted amido ligands are not robust enough to catalyze demanding reactions such as olefin polymerizations. 5 8 The weakness of the N - S i bond is evident throughout the work discussed in this Chapter in the formation of vanadium and niobium imido complexes derived from the cleavage of [NPN] N - S i bonds. The formation of group 5 imides via this route is also accompanied by an oxidation of the metal centre in question, from V(III) to V ( I V ) in the reduction of complexes 14 to 19, and from Nb(IV) to Nb(V) in the formation of 26 and 29. The remaining three chapters of this dissertation wi l l focus on chemistry promoted by high-oxidation state complexes o f group 5 metals. 3.5 Experimental section 3.5.1 General considerations Unless otherwise stated, general procedures were performed according to Section 2.4.1. Solid state magnetic susceptibility measurements were performed on a Johnson-Matthey MSB-1 Gouy balance at room temperature. For experiments in this section conducted using an A r atmosphere, Schlenk lines and apparatus were evacuated and subsequently purged with A r for 30 minutes. Vessels and solvents were freeze-pump-thaw degassed three times to eliminate remaining N2 gas. 76 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes 3.5.2 Starting materials and reagents Metal chlorides VCI3, N b C l 3 , and N b C L were purchased from S T R E M and used without further purification. V C 1 3 ( T H F ) 3 , 5 9 N b C l 3 ( D M E ) , 6 0 K C 8 , 6 1 and N b C l 4 ( T H F ) 2 6 2 were prepared according to literature procedures. Dimethoxyethane ( D M E ) was purchased from Aldr ich, and distilled under an inert atmosphere prior to use. I 5 N 2 gas was obtained in sealed vessels from Cambridge Isotopes. 3.5.3 Synthesis Synthesis of ( C y P h [ N P N ] VC1) 2 ,14 A n ethereal solution (100 mL) of C y P h [ N P N ] L i 2 ( O E t 2 ) (3.00 g, 4.23 mmol) maintained at -78 °C was added via cannula to a 3:1 mixture of E t 2 0 and T H F (40 mL) containing V C 1 3 ( T H F ) 3 (1.58 g, 4.23 mmol). After the addition, the solution was warmed to r.t. and stirred for 90 min. Upon removal of volatiles, the resultant brick-red powder was dissolved in toluene (100 mL); the solution was filtered through Celite to remove L i C l , and the toluene was removed in vacuo. The brick-red powder, ( C y P h [ N P N ] V C l ) 2 , was washed with pentane and dried under vacuum (75.8%, 1.69 g). Crystals of 14 suitable for X-ray diffraction were grown from a concentrated solution of layered benzene-H M D S . E I - M S m/z (%): 526 ([M+]: C y P h [ N P N ] V C l , 100). Anal . Calcd. For C48H74Cl 2N 4P 2Si4V2 (%): C 54.69, H 7.08, N 5.31; found: C 54.97, H 7.26, N : 5.05. Synthesis of ( P h P h [ N P N ] V C l ) 2 , 15, ( C y M e s [ N P N ] V C l ) 2 , 16, ( p h M e s [ N P N ] V C l ) 2 , 17, ( c y M e [ N P N ] V C l ) 2 , 1 8 , ( P h M e [ N P N ] V C l ) 2 , 1 9 . Compounds 15-19 were prepared analogously to 14. Crude ( p h p h [ N P N ] V C l ) 2 was washed with pentane and dried under vacuum to afford a brick red powder (84.0%). Crude ( C y M e s [ N P N ] V C l ) 2 and ( p h M e s [ N P N ] V C l ) 2 were washed with hexanes and dried under vacuum to afford dark red powders (70.5%, 72.0% yields, respectively). Deep magenta oily solids ( C y M e [ N P N ] V . C l ) 2 and ( p h M e [ N P N ] V C l ) 2 were redissolvedin toluene 77 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) andNb(IV) complexes (50 mL). Addit ion of pentane (25 mL) resulted in the precipitation of magenta powders which were then isolated by filtration and dried under vacuum to afford deep magenta powders (64.2%, 66.9% yield, respectively). 15: E I - M S m/z (%): 520 ([M+]: P h P h [ N P N ] V C l , 100). Anal , calcd. for C 48H 62Cl2N4P2Si4V2 (%): C 55.32, H 6.00, N 5.38; found: C 55.50, H 5.88, N 5.10. 16: E I - M S m/z (%): 610 ([M+]: C y M e s [ N P N ] V C l , 100). Anal , calcd. For C e o H g g C b N ^ S i ^ (%): C 58.95, H 8.08, N 4.58; found: C 58.97, H 8.26, N 4.55. 17: E I - M S m/z (%):. 604 ([M+]: P h M e s [ N P N ] V C l , 100). Anal , calcd. for C 6 o H 8 6 C l 2 N 4 P 2 S i 4 V 2 (%): C 59.54, H 7.16, N 4.63; found: C 59.37, H 7.00, N 4.39. 18: E I - M S m/z (%): 402 ([M+]: C y M e [ N P N ] V C l , 100). Anal , calcd. for C28H 66Cl2N 4P 2Si4V2 (%): C 41.73, H 8.25, N 6.95; found: C 41.90, H 8.02, N 6.85. 19: E I - M S m/z (%): 396 ([M+]: p h M e [ N P N ] V C l , 100). Anal , calcd. For C28H 5 4 Cl2N 4 P 2 Si 4 V2 (%): C 42.36, H 6.86, N 7.06; found: C 42.09, H 6.89, N 6.90. Reduction of 14 with 2.2 K C g under 4 atm N 2 A thick-walled reaction vessel was charged with a magnetic stir bar, 0.218 g (0.413 mmoL) of 14, and 0.056 g (0.909 mmol) of K C s . E12O (50 mL) was vacuum transferred into the flask and frozen at -196 °C. The entire flask was cooled to -196 °C and charged with 1 atm of N2 and sealed with a Kontes valve. The brick-red solution turned deep purple upon warming to r.t. The reaction was stirred for 24 h. Filtration through Celite and removal of solvent gave a waxy purple, pentane soluble solid. E I - M S m/z (%): 505 ([M+]: C y P h [ N P N ] V = N , 100), 491 ( C y P h [ N P N ] V , 22). Reduction of 14 with 3.3 K C g under 4 atm N2 Diethyl ether (50 mL) was vacuum transferred into a thick-walled reaction vessel charged with a magnetic stir bar, 0.218 g (0.413 mmol) of 14, and 0.084 g (1.364 mmol) of K C s and frozen at -196 °C. The vessel was cooled to -196 °C, charged with 1 atm of N2, sealed with a Kontes valve and then warmed to r.t. The brick-red solution changed to olive green and was stirred for an additional 24 h. Filtration through Celite and removal of solvent gave a dark green, pentane-soluble powder. E I - M S m/z (%): 78 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(IH) and Nb(IV) complexes 1049 ([M+]: K ( C y P h [ N P N ] V = N ) 2 , 12), 505 ([M+] - K ( C y P h [ N P N ] V = N ) , 100), 491 ( C y P h [ N P N ] V , 20). Reduction of 16 with 2.2 K C 8 under 1 atm N 2 : Isolation of M e s N ( S i M e 2 C H 2 ) 2 P C y , 20 Diethyl ether (-78 °C, 50 mL) was transferred via cannula into a thick-walled reaction vessel charged with a magnetic stir bar, 0.252 g (0.413 mmol) of 11, and 0.056 g (0.909 mmol) of K C 8 under an atmosphere of N 2 . The vessel was sealed and the contents stirred for 24 h. Filtration through Celite and removal of solvent gave a brown, hexanes-soluble powder. Washing the powder with pentane produced an impure brown solid ( C y M e s [ N P N ] V = N M e s ) and a brown solution, which, upon cooling to -37 °C, afforded brown needle crystals of MesN(S iMe2CH 2 ) 2 PCy, 20. Brown powder: E I -MS m/z (%): 708 ([M+]: C y M e s [ N P N ] V = N M e s , 50), 575 ([M+] - N M e s , 100). 20: *H N M R ( C 6 D 6 , 25 °C, 200 M H z ) 5: 0.05 (s, 6H, S i C / / 3 ) , 0.58 (s, 6H , S iC# 3 ) , 0.85, 1.39, 1.97 (m, 15H total, VCH2 and C6HU) 2.28, 2.32 (s, 6 H total, o-PhC7/ 3), 2.40 (s, 3H, p-PhC/ / 3 ) , 6.90 (s, 1H, m-Ph), 7.25 (s, 1H, m-Ph). 3 1 P { ' H } N M R ( C 6 D 6 , 25 °C, 81 M H z ) 8: -25.8 (s). Anal , calcd. for C 2 i H 3 8 N P S i 2 (%): C 64.40, H 9.78, N 3.58; found: C 64.45, H 9.70, N 3.51. Reduction of 15-19 with 2.2 K C 8 under 4 atm N 2 Diethyl ether (50 mL) was vacuum transferred into thick-walled reaction vessels charged with a magnetic stir bar, 0.5 mmol of one of 15-19, 0.068 g (1.1 mmol) of K C 8 and frozen at -196 °C. The vessels were cooled to -196 °C, charged with 1 atm of N 2 and sealed with a Kontes valve. The flasks were warmed to r.t. and stirred for an additional 24 h. Filtration through Celite and removal of solvent gave oily solids which were analysed by E I - M S . Reduction of 15: E I - M S m/z (%): 576 ([M+]: p h p h [ N P N ] V = N P h , 20), 499 ( p h p h [ N P N ] V = N , 65), 485 ([M+] - N P h , 100). Reduction of 16: E I - M S m/z (%): 708 ([M+]: C y M e s [ N P N ] V = N M e s , 32), 589 ( C y M e s [ N P N ] V = N , 14), 575 ([M+] - N M e s , 100). Reduction of 17: E I - M S m/z (%): 702 ([M+]: p h M e s [ N P N ] V = N M e s , 35), 583 p h M e s [ N P N ] V = N , 48), 569 ([M+] - N M e s , 100). 79 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(1U), Nb(lll) andNb(lV) complexes Reduction of 18: EI-MS m/z (%): 396 ([M+]: C y M e[NPN]V=NMe, 5), 367 ([M+] -NMe, 100). Reduction of 19: EI-MS m/z (%): 390 ([M+]: P h M e[NPN]V=NMe, 7), 361 ([M+] - NMe, 100). Reduction of 14-15,17-19 with 2.2 K C g under 1 atm N 2 Diethyl ether (-78 °C, 50 mL) was transferred via cannula into thick-walled reaction vessels charged with magnetic stir bars, 0.5 mmol of one of 14-15, 17-19, and 0.068 g (1.1 mmol) of KCg under an atmosphere of N 2 . The vessels were sealed and the contents stirred for 24 h. Filtration through Celite and removal of solvent gave brown powders analysed by EI-MS. Reduction of 14: EI-MS m/z (%): 505 ([M+]: CyPh[NPN]V==N, 48), 491 (C y P h[NPN]V, 100). Reduction of 15: EI-MS m/z (%): 576 ([M+]: p h P h[NPN]V=NPh, 20), 485 ([M+] - NPh, 100). Reduction of 17: EI-MS m/z (%): 702 ([M+]: p h M e s[NPN]V=NMes, 35), 569 ([M+] - NMes, 100). Reduction of 18: EI-MS m/z (%): 396 ([M+]: C y M e[NPN]V=NMe, 8), 367 ([M+] - NMe, 100). Reduction of 19: EI-MS m/z (%): 390 ([M+]: p h M e[NPN]V=NMe, 12), 361 ([M+] - NMe, 100). Synthesis of C y P h[NPN]NbCl(DME), 22 ; A cooled solution (-78 °C) of C y P h[NPN]Li 2(OEt 2), (3.000 g, 5.674 mmol) in 50 mL of Et 20 was added to a slurry of NbCl3(DME) (1.642 g, 5.674 mmol) in 20 mL of Et 20 under one atmosphere of N 2 . The solution was warmed to r.t. and turned red brown within 30 min. The solution was evaporated to dryness, the remaining solid extracted into 100 mL hexanes, and the solution filtered through Celite. The solvent was removed and C y P h[NPN]NbCl(DME) was isolated as a red-brown solid (2.43 g, 3.69 mmol) in 65.3% yield. EI-MS m/z (%): 659 ([M+]: C y P h[NPN]NbCl(DME), 100), 568 ([M+] -DME, 46). Anal, calcd. for C 2 8 H 4 iClN 2 Nb0 2 PSi 2 (%): C 51.49, H 6.33, N 4.29; found: C 51.22, H 6.27, N 4.51. peff: 2.78 B.M. 80 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) andNb(lV) complexes Reaction of C y P h[NPN]Li 2(OEt 2) and NbCl3(DME) under 4 atm of N 2 A cooled solution (-78 °C) of C y P h[NPN]Li 2(OEt 2), (3.000 g, 5.674 mmol) in 50 mL of Et 20 was added to a frozen slurry of NbCl3(DME) (1.642 g, 5.674 mmol) in 20 mL of Et 20 at -196 °C in a thick walled vessel. The entire vessel was immediately cooled to -196 °C and sealed with a Kontes valve. Upon warming to r.t. the solution turned brown. Removal of solid, followed by filtration through Celite resulted in the isolation of a brown solid containing 22 and (CyPh[NPN]NbCl)(p.-N2), 23. Attempts to separate the products through recrystallization proved unsuccessful. EI-MS m/z (%): 659 ([M+]: C y P h[NPN]NbCl(DME), 100), 582 (C y P h[NPN]NbClN, 62), 568 ([M+] - DME, 33). Reaction of p h p h[NPN]Li 2(THF) 2 with NbCl3(DME) under 1 atm of N 2 A cooled solution (-78 °C) of p h P h[NPN]Li 2(THF) 2 (1.024 g, 1.727 mmol) in 50 mL of Et 20 was added to a slurry of NbCl3(DME) (0.50 g, 1.73 mmol) in 20 mL of Et 20 under an N 2 atmosphere. The solution turned brown within a few minutes of reaching r.t. The solution was evaporated to dryness, and the remaining solid was extracted into 150 mL of toluene. The solution was filtered through Celite and the solvent removed. The resultant brown powder was washed with pentane and dried under vacuum. A mixture of p h P h[NPN]NbCl(DME), 24, and (phph[NPN]NbCl)2(p.-N2), 21. A low yield of small brown crystals of 21 could be isolated from slow evaporation of a 3:1 benzene/HMDS mixture as ([NPN]NbCl)2(p.-ri1: n 1 -^ ) (C 6H 6). Careful control of crystallization conditions is necessary to reliably separate 24 and 21. EI-MS m/z (%): 653 ([M+]: P h P h[NPN]NbCl(DME), 100), 576 ( p h p h[NPN]NbClN, 54). Synthesis of C y P h[NPN]NbCl 2 , 25 A cooled solution (-78 °C) of C y P h[NPN]Li 2(OEt 2) (3.000 g, 5.674 mmol) in 50 mL of Et 20 was added to a slurry of NbCl4(THF)2.(2.150 g, 5.674 mmol) in 20 mL of Et 20 under one atmosphere of N 2 . The solution turned golden yellow upon stirring for 1 hour at room temperature. The solution was evaporated to dryness, the remaining solid 81 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(1I1), Nb(III) and Nb(IV) complexes extracted into 100 mL toluene, and the solution filtered through Celite. Addition of pentane precipitated a golden yellow solid, C y P h[NPN]NbCl 2 , 25, isolated in 78.9% yield (2.71 g, 4.48 mmol). MS (EI): m/z 603 [M+, C y P h[NPN]NbCl 2]. Anal. Calcd for C 2 4 H 3 iCl 2 N 2 NbPSi 2 : C, 48.17; H, 5.22; CI, 11.85; N , 4.68. Found: C, 48.36; H, 5.11; N, 4.80. Decomposition of 25: Synthesis of CyPh[NPN]NbCl(=NPh), 26, and CyP(CH2SiMe2)2NPh, 27 Recrystallization of C y P h[NPN]NbCl 2 from a toluene/hexanes solution resulted in the deposition of yellow crystals containing CyPh[NPN]NbCl(=NPh), 26, leaving a brown supernatant solution behind containing CyP(CH2SiMe2)2NPh, 27, from which the solvent was removed to give a brown solid. The two fractions both contained a paramagnetic impurity and were analyzed with mass spectrometry and the crystals analyzed by x-ray diffraction. MS (EI) yellow crystals: m/z 659 [M + , CyPh[NPN]NbCl(=NPh)]. MS (EI) brown solid: m/z 349 [M + , CyP(CH2SiMe2)2NPh]. Recrystallization of 27 from toluene/hexanes removed the paramagnetic impurity in this fraction, and allowed characterization by 'H and 3 I P NMR spectroscopy. 'H NMR (C 6D 6, 30°C, 500 MHz): 6 0.27 (s, 12H, SiC// 3), 1.24-1.68 (m, ov, 15 H, PCy-//, ?CH2) 7.06-7.09 (m, 2H, NPh o-H), 7.12-7.15 (m, 1H, NPhp-H), 1AX-1A1 (m, 2H, NPh m-H). 3 1P{'H} NMR (C 6D 6 , 25 °C, 202.5 MHz): £-42.6 (br, s). Synthesis of p h p h[NPN]NbCl 2 , 28 Compound 28 was synthesized analogously to 25. p h p h[NPN]Li 2(THF) 2 (1.500 g, 2.530 mmol) and NbCl4(THF)2 (0.959 g, 2.53 mmol) were used to prepare p h P h[NPN]NbCl 2 isolated in 72.2% yield. MS (EI): m/z 597 [M + , p h P h[NPN]NbCl 2]. Anal. Calcd for C 2 4 H 3 1 Cl 2 N 2 NbPSi 2 : C, 48.17; H, 5.22; N , 4.68. Found: C, 48.46; H, 5.35; N , 4.42. peff : 1.86 B.M. 82 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes Synthesis of phph[NPN]NbCl(=NPh), 29 and PhP(CH2SiMe2)2NPh, 30 To a cooled Kontes flask containing P h P h[NPN]NbCl 2 (0.500 g, 0.835 mmol) and K C 8 (0.124 g, 0.919 mmol) was added 50 mL Et 20 at -78 °C. The flask was then cooled to the neck with liquid N 2 (-196 °C), charged with 1 atm N 2 , sealed and allowed to warm to room temperature. Within two hours of warming to room temperature the solution turned golden brown and a black solid was precipitated. The solution was evaporated to dryness, the remaining solid extracted into 100 mL toluene, and the solution filtered through Celite. Addition of hexanes afforded a yellow solid and a brown supernatant solution from which the solvent was removed giving a brown solid. Analysis of the yellow solid indicated the production of phph[NPN]NbCl(=NPh), 29, along with a paramagnetic impurity while the brown solid contained PhP(CH2SiMe2)2NPh, 30, isolated after recrystallization from a saturated toluene/hexanes solution. MS (EI) yellow solid: m/z 653 [M + , phph[NPN]NbCl(=NPh)]. MS (EI) brown solid: m/z 343 [M + , PhP(CH2SiMe2)2NPh]. ] H NMR (C 6D 6 , 30°C, 500 MHz): 5 0.21 (s, 12H, SiCrY3), 1.42-1.60 (m, 4H, PC// 2), 7.06-7.47 (m, 10H, NPh-//, PPh-/f). 3 1P{'H} NMR (C 6 D 6 , 25 °C, 202.5 MHz): £-47.1 (br, s). 3.6 References 1. LaPlaza, C. E.; Cummins, C. C. Science 1995, 268, 861. 2. LaPlaza, C. E.; Johnson, M . J. A.; Peters, J. C ; Odom, A. L.; Kim, E.; Cummins, C. C ; George, G. N.; Pickering, I. J. J. Am. Chem. Soc. 1996,118, 8623. 3. Cui, Q.; Musaev, D. G.; Svensson, M. ; Sieber, S.; Morokuma, K. J. Am. Chem. Soc. 1995,117, 12366. 4. Hahn, J.; Landis, C. L.; Nasluzov, V. A.; Neyman, K. M. ; Rosch, N . Inorg. Chem. 1997, 36, 3947. 5. Henderickx, H.; Kwakkenbos, G.; Peters, A.; Spoel, J. v. d.; Vries, K. d. Chem. Commun. 2003, 2050. 6. Clentsmith, G. K. B.; Cloke, F. G. H. J. Am. Chem. Soc. 1999,121, 10444. 83 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) andNb(IV) complexes 7. 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Soc. 1997,119, 10104. 17. Buijink, J. K. F.; Meetsma, A.; Teuben, J. H. Organometallics 1993, 12, 2004. 18. Rocklage, S. M. ; Schrock, R. R. J. Am. Chem. Soc. 1982,104, 3077. . 19. Schrock, R. R.; Wesolek, M. ; Liu, A. H.; Wallace, K. C ; Dewan, J. C. Inorg. Chem. 1988, 27, 2050. 20. Berno, P.; Hao, S.; Minhas, R.; Gambarotta, S. J. Am. Chem. Soc. 1994,116, 14X1. 21. Farrugia, L. J. J. Appl. Cryst. 1997, 30, 565. 22. Berno, P.; Moore, M. ; Minhas, R.; Gambarotta, S. Can. J. Chem. 1996, 74, 1930. 23. Fryzuk, M . D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S. A.; Koetzle, T. F. J. Am. Chem. Soc. 2001,123, 3960. 24. Cotton, F. A.; Duraj, S. A.; Roth, W. J. Inorg. Chem. 1984, 23, 4113. 25. Cotton, F. A.; Duraj, S. A.; Falvello, L. R.; Roth, W. J. Inorg. Chem. 1985, 24, 4389. 26. Cotton, F. A.; Lu, J.; Ren, T. Inorg. Chim. Acta 1994, 215, 41. 84 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes 27. Nieman, J. ; Teuben, J. H . Organometallics 1986, 5, 1149. 28. Fryzuk, M . D . ; Kozak, C. M . ; Bowdridge, M . R.; Patrick, B . O.; Rettig, S. J. J. Am. Chem. Soc. 2002,124, 8389. 29. Wigley, D . E . Prog Inorg. Chem. 1994, 42, 239. 30. Gade, L . H . ; Mountford, P. Coord. Chem. Rev. 2001, 216-217, 65. 31. Zuckerman, R. L . ; Krska, S. W. ; Bergman, R. G . J. Am. Chem. Soc. 2000,122, 751. 32. Meyer, K . E . ; Walsh, P. J.; Bergman, R. G . J. Am. Chem. Soc. 1995,117, 974. 33. Meyer, K . E . ; Walsh, P. J.; Bergman, R. G . J. Am. Chem. Soc. 1994,116, 2669. 34. Cantrell, G . K . ; Geib, S. J.; Meyer, T. Y . Organometallics 1999,18, 4250. 35. Cantrell, G . K . ; Meyer, T. Y . J. Am. Chem. Soc. 1998,120, 8035. 36. Cantrell, G . K . ; Meyer, T. Y . Chem. Commun. 1997, 1551. 37. Cantrell, G . K . ; Meyer, T. Y . Organometallics 1997,16, 5381. 38. Bruno, J. W. ; L i , X . J. Organometallics 2000,19, 4672. 39. Schrock, R. R . Acc. Chem. Res. 1990, 23, 158. 40. Britovsek, G . J. P.; Gibson, V . C ; Wass, D . F. Angew. Chem. Int. Ed. 1999, 38, 429. 41. Pugh, S. M . ; Trosch, J. M . ; Skinner, M . E . G . ; Gade, L . H . ; Mountford, P. Organometallics 2001, 20, 3531. 42. Gomes, P. T.; Green, M . L . H . ; Martins, A . M . ; Mountford, P. J. Organomet. Chem. 1997, 541, 121. 43. Antonelli, D . M . ; Gomes, P. T.; Green, M . L . H . ; Martins, A . M . ; Mountford, P. J. Chem. Soc, Dalton Trans. 1997, 2435. 44. Stewart, P. J.; Blake, A . J.; Mountford, P. Inorg. Chem. 1997, 36, 1982. 45. Collier, P. E . ; Pugh, S. M . ; Clark, H . S. C ; Love, J. B . ; Blake, A . J.; Cloke, F. G . N . ; Mountford, P. Inorg. Chem. 2000, 39, 2001. 46. Pugh, S. M . ; Blake, A . J. ; Gade, L . H . ; Mountford, P. Inorg. Chem. 2001, 40, 3992. 47. Rocklage, S. M . ; Schrock, R. R. J. Am. Chem. Soc 1980,102, 7808. 48. Bates, P. A . ; Nielson, A . J.; Waters, J. M . Polyhedron 1985, 8, 1391. 49. Chao, Y . W. ; Wexler, P. A . ; Wigley, D. E . Inorg. Chem. 1989, 28, 3860. 85 References begin on page 83. Chapter Three: Synthesis and reactivity of [NPN] supported V(III), Nb(III) and Nb(IV) complexes 50. Jones, C. M . ; Lerchen, M . E . ; Church, C. J.; Schomber, B . M . ; Doherty, N . M . Inorg. Chem. 1990, 29, 3860. 51. Korolev, A . V . ; Rheingold, A . L . ; Will iams, D . S. Inorg. Chem. 1997, 36, 2647. 52. Herrmann, W . A . ; Baratta, W . J. Organomet. Chem. 1996, 506, 357. 53. Lemenovskii, D . A . ; Konde, S. A . ; Perevalova, E . G . Koord. Khimi. 1986,12, 703. 54. Al-Soudani, A . H . ; Edwards, P. G . ; Hursthouse, M . B . ; Mal ik , K . M . A . J. Chem. Soc., Dalton Trans. 1995, 3, 355. 55. Tayebani, M . ; Feghali, K . ; Gambarotta, S.; Yap, G . Organometallics 1998,17, 4282. 56. Tayebani, M . ; Gambarotta, S.; Yap, G . Organometallics 1998,17, 3639. 57. Dammgen, T J . ; Burger, H . Zeit. Anorg. Allg. Chem. 1977, 429, 173. 58. Schrock, R. R.; Baumann, R.; Reid, S. M . ; Goodman, J. T.; Stumpf, R.; Davis, W. M . Organometallics 1999,18, 3649. 59. Manzer, L . E . Inorg. Synth. 1982, 21, 135. 60. Roskamp, E . J . ; Pedersen, S. F. J. Am. Chem. Soc. 1987, 109, 6551. 61. Berbreiter, D . E . ; Ki l lough, J. M . J. Am. Chem. Soc. 1978,100, 2126. 62. Manzer, L . E . Inorg. Chem. 1977,16, 525. 86 References begin on page 83. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Chapter Four Synthesis, reactivity, and DFT calculations on [NPN] supported Nb(V) and Ta(V) complexes 4.1 I n t r o d u c t i o n Previous research with the [NPN] ligand set has focused on the reactivity 1 , 2 of (P h P h[NPN]Ta)2(|i-H) 2(u.-ri 1:Ti 2-N2). However, the synthesis of this dinitrogen complex is remarkable in its own right. The tantalum hydride complex (PhPh[NPN]Ta)2(p>H)4 spontaneously forms the aforementioned dinitrogen complex upon exposure to molecular nitrogen. Surprisingly, no strong reducing agents, such as Na or K, were used to incorporate and reduce the N 2 fragment to a formally (N 2) 4" moiety. The dinuclear Ta(IV) tetrahydride complex is produced from a d~ Ta(V) complex, P h P h [NPN]TaMe 3 and H 2 . The tetrahydride is a powerful reductant because of electrons stored in the metal-metal bond and hydride ligands. Little effort has been made to fully understand the reactivity of this tetrahydride complex, or to investigate the origin of its reducing power. The trimethyl complex, P h P h [NPN]TaMe 3 , is synthesized from metathesis of P h P h [NPN]Li2(THF) 2 and TaCl 2 Me 3 . TaCl 2Me3 has been used extensively as a reagent to prepare tantalum alkyl and chloro complexes. Examples of enolate,3 substituted Cp, 4 bulky terphenylimido,5 diamidoamine,6 l,8-bis(isopropylamido)napthyl,7 tribenzylidene cS7 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes methane,8 cyclooctatetraene,9 bis(amidinate),10 pyrrolyl,11 borollide,12 porphyrin,13 amido/imido,14 and oxyalkylphosphine15 tantalum complexes have been published since 1990. The reactivity of the corresponding niobium complex, NbC^Mes, has not been 16 17 studied since its discovery in the 1970's. ' This chapter explores the use of NbCbMea as a starting material in place of TaCbMes. Synthetic and theoretical studies of the niobium and tantalum systems will be used to explore the mechanistic aspects of these transformations. 4.2 Synthesis and reactivity of niobium trimethyl complexes 4.2.1 Synthesis of R R ' [ N P N ] N b M e 3 In an attempt to reproduce the success of p h P h[NPN]TaMe 3, the synthesis of analogous niobium complexes was attempted. C y P h[NPN]NbMe3, 31, was prepared by addition of a -78 °C solution of ligand precursor 1 to a cooled solution of NbCl2Me3, as in Equation 4.1. After solvent removal at -10 °C, the resultant brown solid was washed 1 3 1 1 with pentane to give a yellow-orange solid that was characterized by H and P{ H} NMR spectroscopy. The product is extremely photo- and thermo-sensitive. This instability precluded the use of elemental analysis and I 3C{'H} NMR spectroscopy for full characterization. Cy z M e 2 p h S O Ph / ^ ^ L i * ^ \ P - ^ N b — M e 4 , 1 Ph t Ph C y A E t 2 ° Me Me 1 31 The 3 ! P { ' H } spectrum of 31 shows a singlet at 5 10.6. For reference, p h P h[NPN]TaMe 3 displays a singlet at 5 13.5 in its 3 1 P { 'H} spectrum. ' H NMR studies also support the assignment of 31. Two singlets at 8 0.0 and 5 0.3 are assigned to silyl methyl resonances. Cyclohexyl and methylene protons overlap with a 9 H singlet at 5 1.7 assigned to the niobium methyl protons. Protons on the two N-phenyl rings are observed 88 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes between 5 6.9 and 8 7.2. Decomposition of 31 was rapid in solution, but slower in the solid state. In either form, exposure to direct light for >30 min at room temperature led to a visible darkening of the product from yellow to brown. However, the product can be stored as a solid at -35 °C in an opaque container for 60 days without significant 31 1 decomposition. One primary decomposition product seen in P{ H} N M R spectra was C y P h [ N P N ] H 2 , 5. To compare decomposition rates, solutions o f 31 and p h P h [ N P N ] T a M e 3 in C6D6 were prepared in sealed N M R tubes and monitored via 3 1 P N M R spectroscopy. Disappearance of the 3 1 P chemical shift of 31 was complete in 3 h, whereas full decomposition of the tantalum trimethyl complex took 8 days, over 60 times slower. Accurate kinetic data could not be obtained due to the formation of a paramagnetic product. Metathesis reactions with other [NPN] dilithium salts met with varied success. Reaction of 2 with N b C l 2 M e 3 gave P h P h [ N P N ] N b M e 3 , 32, in moderate yield. Again, thermal instability prevented full characterization of the product. Product identification and purity were based solely on simple N M R experiments. Similarly, C y M e s [ N P N ] N b M e 3 , 33, was isolated from the reaction of 6 with N b C l 2 M e 3 . Singlets at 5 6.2 and 8 11.2 were observed in the P{ H} spectrum of 32 and 33 respectively. Niobium methyl resonances appear at 8 1.63 for 32 and 8 2.3 for 33 respectively. The decomposition of these complexes in solution was faster than for 31. Numerous attempts to synthesize p h M e s [ N P N ] N b M e 3 , C y M e [ N P N ] N b M e 3 or p h M e [ N P N ] N b M e 3 were unsuccessful. The decomposition which limited the yield and stability of 31-33 now dominates. These reactions gave dark brown oily solids, and no tractable products could be separated from the crude mixtures. Attempts to control the decomposition by varying reaction conditions, exposing the reaction to UV-l ight or keeping the reactants cold (-35 °C) for the duration of the experiment led to the isolation of protonated ligand precursors, uncharacterizable products and starting materials. 4.2.2 Hydrogenation of R R '[NPN]NbMe 3 It was hoped that hydrogenation of 31-33 would lead to isolable niobium hydrides with greater stability than the trimethyl precursors. These species could conceivably 89 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes activate nitrogen in a similar manner to the tantalum tetrahydride and form new asymmetrically bound dinitrogen complexes. This proposed reaction pathway is shown in Scheme 4.1. Hydrogenation of 31, 32, and 33 was attempted at both 1 atm and 4 atm. The reactions were conducted in the dark at -78 °C. Following addition of H2, the reaction mixtures turned black and a precipitate formed. Analysis of the crude product by EI-MS and NMR spectroscopy indicated the formation of multiple products and absence of starting materials. No hydride resonances were observed in ! H NMR spectra. Attempts to isolate a niobium polyhydride species by changing the concentration of reagents, temperature, exposure to light, pressure of H 2 , solvent, or time of reaction, were unsuccessful. It is likely that the hydrogenation process is too slow and cannot compete with decomposition. The in situ hydrogenation of 31 was also attempted and the reaction monitored by 'H NMR spectroscopy. At no point during the course of the reaction were resonances characteristic of niobium hydrides observed. Scheme 4.1 4.3 Synthesis and reactivity of C y P h [ N P N ] supported Ta(V) complexes The most stable niobium trimethyl complex was C y P h[NPN]NbMe 3, 31. Cyclohexylphosphine is a superior a-donor relative to phenylphosphine, and can better stabilize this reactive organometallic complex. Applying this ligand to tantalum hydride and N 2 complexes may give increased stability and different reactivity. Additionally, 90 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes stabilizing tantalum alkyls with this ligand may attenuate decomposition to improve product yield and purity, as well as illuminate the nature of these decomposition products. 4.3.1 Synthesis and characterization of L y r n [NPN]TaMe 3 The synthesis o f C y P h [NPN]TaMe3, 34, was accomplished by the reaction of 1 with TaMe3Cl2, as shown in Equation 4.2. Complex 34 was isolated as a pale yellow light-sensitive solid in 88% yield. Cy M e 2 S i K S i M e 2 ^ M e 2 S . ^ V N<^Lj""^N + T a C , 2 M e 3 _78°C' V \ A? 4 2 / ' L i ^ \ P — T a — M e 4 Z Ph / P h Cy A E t 2 0 M e M e 1 34 Single crystals of the trimethyl complex 34 were obtained by slow evaporation of a pentane solution. A n O R T E P 1 8 depiction o f the solid-state molecular structure of 34 as determined by X-ray crystallography is shown in Figure 4.1. Relevant bond lengths and angles are listed in Table 4.1, and crystallographic data are located in Table 4.2. The C y P h [ N P N ] ligand is facially bound, with the methyl groups al l cis disposed. The overall geometry is a highly distorted octahedron, with C ( l ) and C(3) bent up and down from the meridional plane, respectively. The Ta( l ) -P( l ) and Ta(l)-N(2) distances of 2.712(3) A and 1.984(10) A, respectively, are both shortened from P h p h [ N P N ] T a M e 3 ( P h P h Ta-P , 2.77 A; P h P h T a - N , 2.03 A) while the Ta( l ) -N( l ) distance of 2.074(10) A remains unchanged ( p h p h T a - N , 2.078 A). The Ta( l ) -C( l ) , Ta(l)-C(2) and Ta(l)-C(3) bond lengths are 2.187(12), 2.233(4) and 2.161(15) A in 34, compared to 2.22, 2.23 and 2.20 A in p h p h [ N P N ] T a M e 3 . 91 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Figure 4.1. ORTEP drawing (spheroids at 50% probability) of C y P h [NPN]TaMe 3 , 34. Silyl methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Table 4.1 Selected Bond Distances (A) and Angles (°) for C y P l l [NPN]TaMe 3 , 34 Lengths Angles Angles Ta(l)-C(l) 2.187(12) N(l)-Ta(l)-C(l) 89.8(5) P(l)-Ta(l)-C(3) 161.8(4) Ta(l)-C(2) 2.233(11) N(l)-Ta(l)-C(2) 153.9(4) C(l)-Ta(l)-C(2) 78.2(5) Ta(l)-C(3) 2.161(15) N(l)-Ta(l)-C(3) 82.9(5) C(l)-Ta(l)-C(3) 113.2(5) Ta(l)-N(l) 2.074(10) N(2)-Ta(l)-C(I) 139.2(5) C(2)-Ta(l)-C(3) 80.8(5) Ta(l)-N(2) 1.984(10) N(2)-Ta(l)-C(2) 93.1(4) N(l)-Ta(I)-N(2) 110.7(4) Ta(l)-P(l) 2.712(3) N(2)-Ta(l)-C(3) 104.3(5) N(l)-Ta(l)-P(l) 81.0(3) P(l)-Ta(I)-C(l) 75.3(3) N(2)-Ta(l)-P(l) 73.8(3) P(l)-Ta(l)-C(2) 117.3(4) 92 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Table 4.2 Crystallographic Data and details of refinement for C y P h[NPN]TaMe 3, 34 Empirical formula C 2 7 H 4 6 N 2 P S i 2 T a Crystal system Triclinic Formula weight 666.76 Space group P-l a, b, c (A) 8.4447(17), 10.8870(26), 15.7396(42) a , / ? , Y ( ° ) 98.960(19), 97.103(8), 99.685(16) v, A3 1392.2(3) Total reflections 7755 z 2 Unique reflections 7705 Dcak, g cm"3 1.590 Parameters 305 u (Mo Ka), cm'1 4.11 R i a 0.0685 T, K 173 ± 1 R w a 0.0841 26 range (°) 59.7 Goodness-of-fit 1.182 R, = I | | F 0 | - \Ft\\/L\F0\; Rw = Zw( |F 0 2 | - \Fc2\f/2Zw\F02\2) 'ff and 3 1 P NMR spectroscopy confirmed the identity of 34. A singlet at 8 1.16 is observed for the tantalum-bound methyls, and two silyl methyl environments at 8 0.03 and 8 0.24 are consistent with a relatively symmetric solution structure, comparable to chemical shifts observed in the analysis of P h P h[NPN]TaMe3. A singlet at 8 16.1 is observed in the P{ H} NMR spectrum of 34. This compares well to the resonance at 8 13.5 for p h P h[NPN]TaMe 3. 4.3.2 Synthesis and characterization of (C y F h[NPN]Ta)2(n-H)4 and (^"[NPNJTaMn-H) 2(P.-T 1 ,:T 1 2-N 2) Upon addition of 4 atm H 2 gas to a degassed Et 20 solution of 34, a colour change from yellow to deep purple was observed after 24 hours. This colour change is reminiscent of the desired reduction to the Ta(IV) hydride. The formation of (CyPh[NPN]Ta)2(u-H)4, 35, was confirmed by NMR spectroscopy and elemental analysis. A single resonance in the 3 1P{'H} NMR spectrum of 35 at 8 29.2 is shifted considerably downfield from the phenyl derivative at 8 21.0. Structure assignment was supported by a 4H singlet at 8 9.9 in the 'H{3 1P} NMR spectrum indicating the presence of four bridging hydrides, two inequivalent silylmethyl resonances totalling 24 protons and the expected 93 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes cyclohexyl, methylene and phenyl resonances. This reaction is shown in Equation 4.3. It is assumed that the hydrides are in bridging positions; confirming their solid state positions would require a neutron diffraction structure. A solution structure with bridging and terminal hydrides in rapid exchange cannot be ruled out entirely. Tetrahydride complex 35 shows similar reactivity towards molecular nitrogen. Reaction of 35 with N 2 resulted in a colour change from deep purple to red. Slow evaporation of a benzene solution of this crude product gave small crystals of ( C y P h [NPN]Ta) 2 (p . -H) 2 (p . - r i 1 :r i 2 -N2) , 36, in good yield. The solid state structure of 36 was 18 * determined by X-ray crystallography and an O R T E P depiction is shown in Figure 4.2. Relevant bond lengths and angles are listed in Table 4.3, and crystallographic data are located in Table 4.4. The N(5)-N(6) distance is 1.318(5) A , consistent with a formal assignment of the bridging moiety as (N 2 ) 4 ' . The Ta(l)-Ta(2) distance is 2.8360(6) A , however the system is formally Ta(V)-Ta(V) and no electrons are available for metal-metal bonding. The end-on Ta(2)-N(5) bond length of 1.892(4) A is consistent with considerable double-bond character. The side-on bonding interactions Ta(l)-N(5) and Ta(l)-N(6) are lengthened from this distance to 2.154(4) A and 1.994(4) A , respectively; the Ta(l)-N(6) interaction also exhibits some double-bond character. The two bridging hydrides were not located, and are not included in Figure 4.2. The bond lengths observed in the solid-state molecular structure of 36 are quite similar to. those observed for the phenyl congener, ( P h P h [NPN]Ta) 2 ( |a-H) 2 (^i-ri 1 : n 2 -N 2 ) . 94 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes Figure 4.2. ORTEP drawing (spheroids at 50% probability) of (CyPh[NPN]Ta)2(p-H)2(p-T|1:T]2-N2), 36. Silyl methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Table 4.3 Selected Bond Distances (A) and Angles (°) for (Cyph[NPN]Ta)2(p-H)2(p-N2), 36 Lengths Angles Angles N(5)-N(6) 1.318(5) Ta(l)-N(6)-Ta(2) 88.77(14) N(5)-Ta(l)-P(2) 73.03(11) Ta(l)-N(6) 1.994(4) N(6)-N(5)-Ta(l) 78.2(2) N(3)-Ta(l)-P(2) 82.25(11) Ta(l)-N(5) 2.154(4) N(l)-Ta(2)-Ta(l) 132.94(11) N(4)-Ta(l)-P(2) 78.47(11) Ta(2)-N(5) 1.892(4) P(l)-Ta(2)-Ta(l) 111.18(3) N(6)-Ta(l)-P(2) 109.77(10) Ta(l)-N(3) 2.056(4) N(l)-Ta(2)-P(l) 84.89(11) N(6)-Ta(l)-Ta(2) 41.83(10) Ta(l)-N(4) 2.080(4) N(2)-Ta(2)-Ta(l) 118.88(11) N(6)-Ta(2)-N(2) 102.46(16) Ta(2)-N(l) 2.068(4) N(5)-Ta(l)-N(3) 109.23(16) N(2)-Ta(2)-N(l) 112.22(15) Ta(2)-N(2) 2.059(4) N(3)-Ta(l)-N(4) 111.10(16) N(5)-Ta(l)-Ta(2) 78.38(11) Ta(l)-P(2) 2.6155(12) N(5)-Ta(l)-N(6) 36.80(15) N(3)-Ta(l)-Ta(2) 109.85(11) Ta(2)-P(l) 2.5985(12) N(3)-Ta(l)-N(6) 112.13(15) N(4)-Ta(l)-Ta(2) 118.03(11) Ta(l)-Ta(2) 2.8360(6) N(4)-Ta(l)-N(6) 136.67(15) P(2)-Ta(l)-Ta(2) 151.31(3) N(6)-Ta(2)-P(l) 159.80(11) N(6)-Ta(2)-N(l) 112.22(15) N(2)-Ta(2)-P(l) 81.57(11) 95 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Table 4.4 Crystallographic Data and details of refinement for ( C y P h [NPN]Ta) 2 (^-H) 2 (p , - r i 1 : r , 2 -N 2 ) , 36 Empirical formula C 2 4 H 3 7 N 3 S i 2 P T a Crystal system Monoclinic Formula weight 1319.50 Space group P2,/c a,b.c{k);p{°) 11.3778(23), 23.5161(47), 20.1422(40); 95.074(30) v, A3 5368.16(145) Total reflections 48065 z 4 Unique reflections 11687 D c a i c , g cm - 3 1.630 Parameters 567 u (Mo Kcc), cm'1 4.26 V 0.0369 T, K 173 ± 1 P v w a 0.0473 29 range (°) 59.7 Goodness-of-fit 1.173 R, = SHFol - \FC\\/T\F0\; Rw = 2>(|F0 2| - \Fc2\f/zZw\F02\2) The assignment of 36 as a side-on end-on bound dinitrogen complex is supported by N M R spectroscopy and elemental analyses. A resonance at 8 10.68 integrated to 2H, indicated the presence of two hydrides. Four silyl methyl resonances at 8 0.10, 0.29, 0.30 and 0.42 support the lack of symmetry expected in 36. Two singlets at 8 16.6 and 8 28.9 in the 3 I P { ' H } spectrum o f 36 are upfield from the phenyl congener (8 7.8 and 8 11.0) and exhibit a similar coupling pattern. The resonances are broadened, and this broadness is not affected by temperature. The peak at 8 28.9 appears as a doublet, coupled to the second 3 1 P environment. The other peak is coupled to an 1 4 N quadrupolar nucleus (1 = 1, 99.6%). This reaction is shown in Equation 4.4. 36 96 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes 4.4 Tantalum alky l , alkylidene and alkylidyne complexes 4.4.1 Introduction The seven-coordinate trimethyl complex Ph[P2N2]TaMe3 can be photolyzed to give the methyl methylidene complex, P h [P2N2]Ta=CH 2 (Me), as shown in Equation 4.5. 1 9 This transformation was discovered serendipitously when solutions of ph[P2N2]TaMe3 were stored under ambient light. Photochemistry is a well-established entry into 20 alkylidene and alkylidyne complexes of the transition metals. niobium or tantalum trimethyl complexes would turn deep brown over time, with niobium complexes decomposing more rapidly than the tantalum congeners. Unfortunately, attempts to isolate an [NPN] stabilized methyl methylidene from decomposition of R R [ N P N ] M M e 3 ( M = Nb , Ta) have been unsuccessful. Controlled thermal or photo-decomposition, or direct photolysis gave the protonated ligand R R [NPN]H2 and other unidentifiable decomposition products. Ph The [NPN] ligand was developed because [P2N2] complexes of group 5 metals showed limited reactivity. B y removing one P donor, an open coordination site is created on the metal which may allow small molecules to bind. Presumably, the open coordination site in ^ [ N P N ] complexes promotes an alternate degradation route and prevents the isolation of a methyl methylidene. Bulkier alkyls could limit this decomposition route by blocking this open site and offering steric control over the reactivity of ^ [ N P N J T a R j complexes. Pioneering work in niobium and tantalum organometallics over 25 years ago, including the isolation of (n 5-C 5H 5)2Ta(CH2)(CH3) 2 1 and ( M e 3 CCH2 ) 3 T a ( C H C M e 3 ) , : 9 7 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes opened the field of high oxidation state alkylidene chemistry and catalytic alkene metathesis. An excellent review of high oxidation state multiple metal-carbon bonds has recently appeared.23 From this previous work, an obvious choice to provide steric bulk to stabilize R R[NPN]TaR3 complexes is the neopentyl group. Extensive research on 22 33 tantalum supported neopentylidene and neopentylidynes has been published. " It is proposed that the complexes Cl 2 TaNp 3 2 2 ' 2 9 ' 3 0 (Np = CH 2CMe 3) and Cl 3 TaNp 2 2 9 ' 3 4 be an entry point into investigating [NPN] tantalum alkylidene and alkylidyne complexes. 4.4.2 Preparation of tantalum neopentylidene and neopentylidyne complexes Addition of C y P h[NPN]Li 2(THF) 2, 1, to TaCl2Np3 promoted a yellow to brown colour change. Removal of an aliquot from the reaction mixture after 24 h showed that no reaction had taken place. Stirring the solution for 5 weeks at room temperature, however, promoted the formation of a bright red, pentane soluble product in moderate yield. This product exhibited a peak at 5 41.9 in the 3 1P{ 1H} NMR spectrum. EI-MS and 'H NMR studies indicated that CyPh[NPN]Ta=C(CMe3), 3 7 , had formed. This was confirmed by the peak at 8 367 in the C NMR spectrum, indicative of a metal alkylidyne. Analysis of the crude reaction mixture indicates that TaCl2Np3 and 1 remain in solution unreacted, and various decomposition products are also present in solution. Small peaks in 3 1 P and l 3 C NMR studies indicated the presence of an alkyl alkylidene intermediate, but this complex could not be isolated. Reactions of niobium and tantalum complexes in this chapter show that complexes supported by the p h P h[NPN] ligand are more labile than those of C y P h [NPN]. It was hoped that changing the phosphine donor would allow easier access to alkylidene and alkylidyne systems. Reaction of 2 with TaCl2Np3 did not produce an immediate reaction. Stirring the reaction for 1 week resulted in a colour change analogous to the production of 3 7 . Analysis of the reaction mixture showed two products, as evidenced by two singlets at 8 16.2 and 8 37.2 in the 3 1P{ 1H} NMR spectrum. After a second week, only one product remained in solution. Further characterization of this product revealed that the resonance at 8 37.2 corresponds with the alkylidyne phPh[NPN]Ta=C(CMe3), 3 8 , isolated in 55% yield as a deep red powder. The product is contaminated with a small 98 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes amount of TaCl2Np3, which can be removed by washing with minimal cold pentane. Analysis of the second product in the reaction mixture indicates it is, in fact, the alkyl 1 "\ alkylidene, as evidenced by a peak at 5 201.5 in the C N M R spectrum. In situ N M R tube reactions of the product mixture reveal the slow conversion of the peak at 8 16.2 to the alkylidyne and neopentane. Attempts to separate the alkyl alkylidene from 38 were unsuccessful. The reactions to form tantalum alkylidynes are shown in Scheme 4.2. Cl M e 3 C H 2 C — T a Cl , . „ » C H 2 C M e 3 * C H 2 C M e 3 RPhi [NPN]Li 2 C M e 4 2 LiCI C M e 3 C H Ph Ph \ M / MezSKlM^ ^ M ^ S i J T a U ^ P ^ C H s C M e g R R = Ph, Cy CMe 4 Ph Ph \ M M e 2 S K N v \ , M e 2 S i y T a = C — C M e 3 \ 37,38 Scheme 4.2 The reactions of 1 and 2 with T a C l 3 N p 2 were attempted in the hopes of isolating a tantalum alkylidene. Reactions were complete after 24 hours, giving bright orange powders. C y P h [ N P N ] T a ( C l ) ( = C H C M e 3 ) , 39, and p h p h [ N P N ] T a ( C l ) ( = C H C M e 3 ) , 40 had formed and were characterized by E I - M S and N M R studies. Products were contaminated with TaCl 3 Np2 and thus isolated in low yields. These reactions are shown in Equation 4.6. Cl C M e 3 C H C H 2 C M e 3 + R P h [ N P N ] L i 2 M e 3 C H 2 C — T a ' Cl •ci C M e 4 2 LiCI Ph Ph \ M e s S K N ^ , ^ Me 2 Sn 'Ta R 4.6 R = Ph, C y 99 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes Orange-red crystals of 39 were grown from a saturated toluene/hexanes solution. An O R T E P 1 8 depiction of the solid state molecular structure of 39 as determined by X -ray crystallography is shown in Figure 4.3. Relevant bond lengths and angles are listed in Table 4.5 and crystallographic data are located in Table 4.6. The Ta(l)-C(25) distance of 1.94 A is consistent with an alkylidene, and is considerably shorter than the Ta -C distances of 2.19, 2.23, and 2.16 A in 34. A single proton on C(25) was located in the diffraction pattern and refined isotropically. The sum of angles surrounding C(25) is 359.6°, supporting planar carbon atom. The Ta(l) -P(l) interatomic distance of 2.58 A is noticeably shorter than in the trimethyl complex (2.71 A). The overall geometry is a distorted trigonal bipyramid, with P(l) and Cl( l ) located in axial positions and bent away from the bulky neopentylidene. Figure 4.3. O R T E P drawing (spheroids at 50% probability) of C y P h [NPN]Ta(Cl ) (=CHCMe 3 ) , 39. Silyl methyl and phenyl ring carbons other than ipso have been omitted for clarity. cn 1 0 0 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Table 4.5 Selected Bond Distances (A) and Angles (°) for CyPh[NPN]Ta(Cl)(=CHCMe3), 39 Lengths Angles Angles Ta(l)-C(25) 1.939(4) N(l)-Ta(l)-C(25) 110.5(1) C(25)-Ta(l)-Cl(l) 104.2(1) C(25)-C(26) 1.517(5) N(l)-Ta(l)-Cl(l) 92.86(9) Ta(l)-C(25)-H(30) 97(3) Ta(l)-N(l) 2.051(3) N(l)-Ta(l)-N(2) 131.9(1) C(26)-C(25)-H(30) 112(3) Ta(l)-N(2) 2.027(3) N(l) :Ta(l)-P(l) 75.21(9) Ta(l)-C(25)-C(26) 150.6(3) Ta(l)-P(l) 2.581(1) N(2)-Ta(l)-C(25) 111.4(1) P(l)-Ta(l)-C(25) 98.3(1) Ta(l)-Cl(l) 2.4102(9) N(2)-Ta(l)-Cl(l) 98.7(1) P(l)-Ta(l)-Cl(l) 157.13(3) C(25)-H(30) 0.90(4) N(2)-Ta(l)-P(l) 76.5(1) Table 4.6 Crystallographic Data and details of refinement for CyPh[NPN]Ta(Cl)(=CHCMe3), 39 Empirical formula C 2 7 H 4 6 N 2 P S i 2 T a Crystal system Monoclinic Formula weight 727.25 Space group P2,/c a,b,c{k)-pO 8.8189(4), 17.1735(8), 21.879(1); 97.300(3) V, A3 3286.8(2) Total reflections 28276 z 4 Unique reflections 7626 D c a i c , gem"3 1.47 Parameters 329 \x (Mo Ka), cm"1 35.6 R i a 0.053 T, K 173 ± 1 R w a 0.073 29 range (°) 55.7 Goodness-of-fit 0.95 R, = ZHFol - |F C | | /Z|F 0 | ; Rw = 2>(|F0 2| - \F*\f/lw\F02\2) Increasing the steric bulk of the alkyl ligands allows for controlled decomposition to form alkylidene and alkylidyne complexes. The low yields of these reactions, along with the time-consuming synthesis of TaCl2Np3 and TaCl 3Np 2 have limited the full investigation of the reactivity of these tantalum complexes. Accessing and assessing the optimized synthesis and reactivity of various RR'[NPN]Ta(R)(=R) and RR'[NPN]Ta(=R) complexes remains an unfinished project. 101 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes 4.5 A reactive tantalum tetrahydride complex If the complexes (R P h[NPN]Ta)2(p-H)4 react with N 2 , they certainly should react with other small molecules. While the chemistry of these hydride complexes with molecular nitrogen has been, and continues to be, a focus of research, the ability of these species to promote other unusual transformations has been ignored. How best can the reactivity of this complex be exploited? Understanding the mechanism of dinitrogen activation would aid in planning future syntheses. The generation of dinitrogen complex 36 from 35 is remarkable, as no strong reducing agents are required. The N 2 unit is strongly activated; the dinitrogen moiety can be formally treated as a (N2)4~ hydrazido fragment. How did this four electron reduction take place? Two electrons are presumably stored in the Ta-Ta bond. The additional two electrons must be obtained by the reductive loss of H 2 in this reaction. Loss of H 2 upon binding of N 2 has been observed previously, but these reactions do not generate strongly activated dinitrogen complexes. What is different about the reactivity of this system? It is proposed that the reactive species that reduces molecular nitrogen is not complex 35, but an intermediate, (CyPh[NPN]Ta)2(p-H)2, that contains a Ta-Ta double bond. Loss of H 2 from 35 would generate a metal-metal double bond that stores the four electrons needed to reduce molecular nitrogen to the observed hydrazido fragment. While this intermediate has not been directly observed, labelling experiments support this proposal. Addition of D 2 to 35 produces a series of isotopomers, (CyPh[NPN]Ta)2(p-H)4, (CyPh[NPN]Ta)2(p-H)3(p-D), (CyPh[NPN]Ta)2(p-H)2(p-D)2, (CyPh[NPN]Ta)2(p-H)(p-D)3, and (CyPh[NPN]Ta)2(p-D)4. Loss of H 2 from 35 would give (CyPh[NPN]Ta)2(p-H)2, to which D 2 , HD, or H 2 could add, effectively creating the observed isotopomers. Isotopic mixing between (CyPh[NPN]Ta)2(p-H)4 and (CyPh[NPN]Ta)2(p-D)4 in Et 2 0 is also observed. These reactions are shown in Scheme 4.3. 102 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Ph Ph Qy VN XXH, P<T\ M e 2 S K N 4 . , ^ H ^ . / \ \ \ cy N' [ Ph Ph + D, isotopic mixing [NPN]Ta^^j-j^>Ta[NPN] H [NPN]Ta^— j^Ta [NPN] [ N P N ] T a ^ - ^ T a [ N P N ] NrT [NPN]Ta^——^Ta[NPN] H [ N P N ] T a ^ ^ T a [ N P N ] [ N P N ] T a ^ ^ ^ . T a [ N P N ] D . A [ N P N ] T a ^ - ^ T a [ N P N ] Scheme 4.3 In investigating the reactivity of 35 and ( P h P h [NPN]Ta)2(p.-H)4, 41, we can exploit the formation of the metal-metal double bond to promote new reactions and provide more evidence for the existence of the putative dihydride. Isolation of 35 and 41 is complicated by their nitrogen-sensitivity. Use of common glovebox workup techniques produces impure products contaminated with the dinitrogen complexes. A n effective route to the isolation of pure 35 and 41 has been developed using a standard Schlenk-line, flushed with A r , for all transformations. Degassed diethyl ether solutions o f tantalum trimethyl complexes in large, thick-walled reaction vessels fitted with teflon valves are charged with 4 atm. of H 2 , producing 35 and 41 in 24 hours. Cannula transfer of these solutions into Schlenk flasks, followed by removal of solvent, gives deep purple powders. Addition of minimal cold pentane, distilled under Ar , to these flasks followed by abrasion of the inner vessel walls precipitated 35 and 41. Filtration through a Schlenk frit, followed by rinsing with minimal cold pentane, and thorough drying in vacuo gives 35 and 41, free of 103 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes impurities, in 80% and 92% isolated yields respectively. Isolated yields for 35 are lower due to its higher solubility in pentane. With the availability of highly pure 35 and 41, we can investigate new reactions with this complex. 4.6 Density functional theory calculations Another method to garner information on reactivity and bonding is density functional theory (DFT) calculations.36 The utility and importance of DFT in modeling compounds of the second- and third-row transition metals that contain metal-metal bonds has been demonstrated. ' While DFT does not provide molecular orbital representations and energies in the same manner as Hartree-Fock calculations, Kohn-Sham orbitals derived from DFT calculations are very similar to those predicted by more stringent methods.39"42 The orbitals of DFT are of great utility to chemists in the analysis of reactivity and structure because orbital energies appear to be empirically related to actual molecular orbital energies. Of import, however, is that the orbitals and eigenvalues derived from DFT calculations are of essentially qualitative and comparative use only. The opportunity for scientists to over-extend the information garnered from density functional theory level calculations is always a danger and results must be taken with a proverbial grain of salt. The appeal of DFT lies in its simplicity. The theory is based on the notion that the total energy, E, of an electronic system is determined by the electron density p or E p . This notion was first suggested by Fermi43 and later proven exact by Kohn and Hohenberg in 1964.44 In the proof, simplified in Equation 4.7, the total energy is written in terms of the energy of n non-interacting electrons and a term E e x that takes into account the correlated motion of these electrons. Ee> = ~ I J> (1 )V V, (r, )d r, + X Jp-^Mr, )drl + - J RA — r i 2 H-dr, dr, + E. While this equation seems daunting at first glance, the computational demands to solve it are much less severe than for traditional ah initio methods. Electron density is attractive for calculations, as it depends only on x, y, and z, as opposed to many particle 104 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes wave functions which depend on 3N or AN variables. A l l that is necessary to perform these calculations is to approximate the exchange-correlation hole function, E e x , which attempts to mimic the repulsive interaction between electrons. This level of theory is termed approximate density functional theory. The hybrid functional B 3 L Y P method 4 5 is used to estimate E e x throughout the calculations in this chapter. Accurate calculations depend on the choice of basis set. A basis set is the set of. atomic orbitals built around the static nuclei. This basis set must be capable of describing the actual wave function well enough to give chemically useful data, but at the same time be solvable within reasonable computation time. The L A N L 2 D Z basis functions and electron core potentials were used in the D F T calculations described herein. 4 6 This level o f theory has been shown to be adequate for modeling complexes containing metal-metal bonds of various orders, although these bonds were consistently slightly longer than observed experimentally. 4 7 The motives behind a D F T investigation of R R ' [ N P N ] M M e 3 and ( R R ' [NPN]M) 2 ( p -H)4 ( M = Nb , Ta) systems are three-fold. First, are the energetics and bonding of tantalum and niobium systems different? It is puzzling that the hydrogenation of the trimethyl complex is so facile in tantalum based systems, yet results only in product decomposition for the niobium systems. There are numerous publications detailing the effect of substituting a group 5 metal centre on orbitals, geometries and electronics calculated with D F T . 4 8 ' 5 9 The over-riding conclusion from these reports is the lack o f observed differences between niobium and tantalum congeners. For instance, in a study of the d 2 d 2 complexes V2O9 ", Nb 2 Cl9 " and Ta 2Cl9 ", the ground-state geometry for the vanadium congener is ferromagnetic, with relatively long V - V separations. The Nb-Nb and Ta-Ta separations were quite similar, with calculations supporting the complete derealization of the metal-based s and dn electrons in a metal-metal double bond. 5 5 Second, do the Kohn-Sham orbitals derived from D F T calculations correlate with observed reactivity and proposed mechanisms? The idea that the ( R R [NPN]M) 2 (p-H )4 complexes lose H 2 to form a metal-metal double bond as a reactive intermediate could be supported or refuted by D F T calculations. A s mentioned above, D F T calculations on metal-metal bonding in V , N b and Ta bimetallic systems 5 5 are known, but hydride studies have been limited to monometallic group 5 systems. 5 3 Finally, from a qualitative 105 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes standpoint, can we model [NPN] systems effectively by D F T ? Results from D F T calculations can be compared to existing structural data to gauge how well calculations o f this level represent transition metal systems of this complexity. Geometry optimizations and D F T calculations were performed using the Gaussian 98 program 6 0 and the aforementioned B 3 L Y P functional and L A N L 2 D Z basis set. Rather than using the [NPN] fragment, a simplified version of the ligand was desired to reduce calculation complexity. Previous calculations on [P2N2] and [NPN] systems 6 1" 6 6 employed a drastic simplification: Amide donors were replaced with NH2 groups, phosphine donors with PH3 and the backbone of the ligands were removed. Sti l l , these modifications gave reasonable outputs when optimized with the appropriate constraints. While care must be taken in D F T calculations of systems with phosphines to incorporate 67 the role of d functions in correlated wave functions to account for extra polarization, the effect of phosphorus atom d-type functions on the calculated M - P bond lengths in related diamidodiphosphine systems was studied systematically and found to have a negligible influence. 6 1 In the calculations presented here, d-polarization functions also had negligible effect on calculation results. Over-simplification of the model complex yields unreasonable results. For example, optimization of (H2N)2(H3P)TaMe3 resulted in phosphine dissociation to give a bis(amide) complex, as shown in Equation 4.8. The more unstable trimethyl and hydride complexes require the chelating ligand framework to prevent phosphine dissociation. Geometry optimization of model complexes (HP(CH2SiH2NH) 2 Ta) 2 (u^H)4 and HP(CH2SiH2NH)aTaMe3 presented a new problem. A s shown in Equation 4.9, the tetrahydride complex does not converge, but rather loses H2 to form a tantalum-trihydride-phosphide complex. Interestingly, a previous density functional study on the coordination and dehydrogenation of PH3 by 23 different transition metal ions in the gas phase found similar reactivity: P H 3 additions to metal ions gave H - M - P species, along /TO with liberation of H2. H 2 N N H 2 V H 3 P — - T a — M e A Me Me geometry optimization H 2 N N H 2 V P H 3 + Me T a — M e Me 106 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes H V 1 9 e o m - / " X S i H 2 H 2 S i k P / a ^ T \ T f e 2 H 2 " ^ T ^ « N / . ^ 7 j ^ T a ^ N \ H 4.. H H H / H " 2 - N ^ H H A working simplified framework for the [NPN] ligand is shown in Figure 4.4. This simplified ligand, 'NPN' ('NPN' = MeP(CH2SiH2NMe)2), retains the basic ligand framework, uses methyl groups on amide and phosphine donors, and a secondary silane backbone instead of a bis(methyl)silyl backbone. no reactive P-H bonds *- CH, ' ' 9 a n d backbone prevents P dissociation ^ \ / Me substituents replace Cy, Ph SiH 2 replaces SiMe 2 y H3C Figure 4.4. Simplified 'NPN' ligand model for DFT calculations. It was hoped that Gaussian 98 DFT calculations would allow us to follow the conversion of 'NPN'Li 2(OMe 2) through three reactions to the putative ('NPN'M)2(p-H)2 species (M = Nb, Ta), as shown in Equations 4.10, 4.11 and 4.12. To determine the qualitative favorability of these reactions, each of the components were analyzed by a geometry-optimized DFT calculation. The small molecule reagents and products of these reactions (LiCl, CH4, OMe 2 and H2) were also optimized and analyzed with Gaussian 98. Previous DFT calculations on L i C l , 6 9 C H 4 , 7 0 H 2 7 1 and MCl 2 Me 3 (M = Nb, Ta)59 agreed well with the present study. The total energies (in Hartrees) for all optimized compounds are listed in Table 4.7. 'NPN'Li2(OMe2) + CI 2MMe 3 *- 'NPN'MMe 3 + 2 LiCl + OMe 2 4.10 2 'NPN'MMe 3 + 5 H 2 ('NPN'M)2(u-H)4 + 6 C H 4 4.11 ( ,NPN ,M)2(p-H)4 »• ('NPN'M)2(u-H)2 + H 2 4.12 107 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Table 4.7. Total energy (in Ha) for optimized compounds ( B 3 L Y P / L A N L 2 D Z ) ' N P N ' L i 2 ( O M e 2 ) , 4A -494.6932851 C l 2 N b M e 3 -206.035812 ' N P N ' T a M e 3 , 4B -502.0993708 C l 2 T a M e 3 -207.5651363 ( 'NPN'Ta) 2 (u -H) 4 , 4C -767.1800936 L i C I -22.5507264 ( 'NPN'Ta) 2 (u -H) 2 , 4D -765.9339573 O M e 2 -155.0054451 ' N P N ' N b M e 3 , 4E -500.5757257 H 2 -1.1744164 ( 'NPN 'Nb) 2 (u -H) 4 , 4F -764.1280637 C H 4 -40.5144688 ( 'NPN 'Nb) 2 (u -H) 2 , 4G -762.906319 Plugging the energies from Table 4.7 into Equation 4.10, the reaction of ' N P N ' L i 2 ( O M e 2 ) , 4A, to form ' N P N ' T a M e 3 , 4B, is endergonic by 0.0522 Ha at this calculation level. Similarly, the reaction of 4A with N b C l 2 M e 3 to form ' N P N ' N b M e 3 , 4E, is slightly less endergonic (0.0465 Ha). Using Equation 4.11, the conversion of 2 equivalents of 4B to ( 'NPN'Ta) 2 (u.-H) 4 , 4C, is quite exergonic (-0.196 Ha). Surprisingly, the conversion of 4E to ( 'NPN 'Nb) 2 (u -H) 4 , 4F (-0.245 Ha) is very exergonic. While this transformation does not occur experimentally, there is, theoretically, no thermodynamic reason for its failure. The loss of H 2 from 4C to give ( 'NPN'Ta) 2 (u.-H) 2 , 4D, is endergonic to a relatively small degree (0.0717 Ha). Conversion o f 4F to ( 'NPN 'Nb) 2 (u -H ) 2 , 4G, is also endergonic (0.0473 Ha). It is apparent that these calculations can only give us a qualitative picture of these reactions. The conversion between the arbitrary 'Hartree' unit and I U P A C units (1 Ha = 2625.5 kJ/mol) would lead us to believe the conversion of 4B to 4C is exergonic by over 500 kJ/mol\ This level of calculations is clearly not sufficient to quantitatively assign thermodynamic parameters, but still can provide a comparative picture of the progress of the reactions, as shown in Figure 4.5. O f note are the relatively small differences in the system energy between tetrahydride and dihydride model complexes. This suggests that the dihydride may be generated from the tetrahydride tantalum complex and act as a reactive intermediate. When comparing the niobium and tantalum systems, the tantalum system is always considerably lower in energy (simply due to the larger number of electrons assigned to tantalum and thus the calculation); the tantalum system also shows larger variations in energy. 108 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes -1407.2 -1407.25 | £ -1407 W o >. a C L U ra o -1407.35 + -1407.4 -1407.45 -1410.25 -1410.3 ~S X E \ -141 CO o >. ta 3 c L U I o -1410.4 -1410.45 -1410.5 2 "NPN'NbMe3 + 4 LiCl + 2 OMe2 + 5 H 2 Jk -1407.237329 — ' — _ •M407.330276 ('NPN'Nb)2(H)2 + H 2 + 6 CH 4 + 4 LiCl + 2 OMe2 2 'NPN'Li2(OMe2) + 2 CI2NbMe3 + 5 H 2 - 1407^81344^ * CNPN'Nb)2(H)4\ + 6 C H 4 N + 4 LiCl + 2 OMe2 •-^407.428672 2 'NPN'TaMe3 + 4 LiCl + 2 OMe2 + 5 H 2 A -1410.284619 •M410.388925 ('NPN'Ta)2(H)2 + H 2 + 6 CH 4 + 4 LiCl + 2 OMe2 2 ,NPN,Li2(OMe2) + 2 CI2TaMe3 + 5 H 2 CNPNTa) 2(H) 4 \ + 6 CH 4 N + 4 LiCl + 2 OMe2 r<1410.480702 Figure 4.5. Qualitative comparison of total energy vs. progress of reaction. This diagram is not meant to represent a traditional reaction profile. Selected optimized bond lengths, bond angles and dihedral angles for the trimethyl model complexes 4 B and 4 E are in Table 4.8. The optimized parameters for the tetrahydride complexes 4 C and 4 F are in Table 4.9, and those for the dihydride model complexes 4D and 4 G are in Table 4.10. While the general features of structures 4 A - F match solid-state structures of related R R [ N P N ] complexes, there are several unexpected deviations of interest. Comparing the metal-phosphine interatomic distances in 4 B and 109 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes 4E is enlightening. The Ta-P distance is 2.94 A , lengthened slightly from the solid state structure, whereas an Nb-P interatomic distance of 4.37 A is observed. Phosphine dissociation still predominates in 4E despite the extended 'NPN' framework, indicating the Nb-P bond is weak. The calculations suggest that a coordination site on niobium opens up via phosphine dissociation; this may promote the rapid decomposition observed in complexes 31, 32, and 33 and prevent the formation of niobium hydrides. Table 4.8. Selected optimized bond lengths (A) and bond angles (°) for 4B and 4E 'NPN'TaMe 3, 4B 'NPN'NbMe 3, 4E Ta-P 2.940 A N-Ta-P 7 7 . 1 1 7 ° Nb-P 4.38332 A N-Nb-P 74.468 ° Ta-N 2.02064 A N-Ta-P 70.551 ° Nb-N 2.02373 A N-Nb-P 73.751 ° Ta-N 2.05522 A N-Ta-N 113.311 ° Nb-N 1.98964 A N-Nb-N 113.872 ° Ta-C 2.20589 A C-Ta-C 112.946 0 Nb-C 2.20458 A C-Nb-C 127.874 ° Ta-C 2.21396 A C-Ta-C 79.090 ° Nb-C 2.21472 A C-Nb-C 77.968 ° Ta-C 2.21871 A C-Ta-C 78.889 0 Nb-C 2.23431 A C-Nb-C 78.527 ° Table 4.9. Selected optimized bond lengths (A) and bond angles (°) for 4C and 4F ('NPN'Ta)2(u-H)4, 4C ('NPN'Nb)2(u-H)4, 4F Tal-Ta2 2.64914 A P-Ta-Ta-P - 1 3 8 . 5 1 0 ° Nbl-Nb2 2.59930 A P-Nb-Nb-P -179.54 ° Tal -P l 2.72848 A Nl-Tal -N2 101.195 ° Nbl -P l 2.65822 A Nl-Nbl -N2 110.457 ° Ta2-P2 2.68712 A N l - T a l - P l 74.368 ° Nb2-P2 2.65804 A N l - N b l - P l 83.768 ° T a l - N l 2.01360 A N2-Tal-Pl 88.097 0 N b l - N l 2.09516 A N2-NM-P1 77.276 ° Tal-N2 2.11473 A N3-Ta2-N4 116.163 ° NM-N2 2.06928 A N3-Nb2-N4 1 0 8 . 8 1 6 ° Ta2-N3 2.03836 A N3-Ta2-P2 81.927 ° Nb2-N3 2.09590 A N3-Nb2-P2 84.589 0 Ta2-N4 2.03760 A N4-Ta2-P2 82.625 ° Nb2-N4 2.07062 A N4-Nb2-P2 76.543 0 T a l - H l 1.83759 A N b l - H l 2.07185 A Ta2-Hl 2.11035 A Nb2-Hl 1.88360 A Tal-H2 2.15249 A Nbl-H2 2.01461 A Ta2-H2 1.88802 A Nb2-H2 1.90574 A Tal-H3 1.79072 A Nbl-H3 1.91106 A Ta2-H3 2.52013 A Nb2-H3 2.01435 A Tal-H4 2.00570 A Nbl-H4 1.89622 A Ta2-H4 1.87075 A Nb2-H4 . 2.04924 A 110 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Table 4.10. Selected optimized bond lengths (A) and bond angles (°) for 4D and 4G ( 'NPN'Ta) 2 (u -H) 2 , 4D • ( 'NPN'Nb) 2 (p--H) 2 , 4G Tal-Ta2 2.61476 A P-Ta-Ta-P - 1 7 9 . 9 8 6 ° Nbl-Nb2 2.83202 A P-Nb-Nb-P 180.000 ° Tal -Pl 2.55074 A Nl-Tal -N2 53.225 ° Nbl -P l 2.51780 A Nl-Nbl -N2 44.949 ° Ta2-P2 2.55078 A N l - T a l - P l 109.198 ° Nb2-P2 2.51780 A N l - N b l - P l 101.891 ° T a l - N l 2.05809 A N2-Tal-Pl 8 1 . 1 5 9 ° N b l - N l 2.04596 A N2-NM-P1 85.150 ° Tal-N2 2.05270 A N3-Ta2-N4 87.840 ° Nbl-N2 2.04082 A N3-Nb2-N4 85.553 ° Ta2-N3 2.05807 A N3-Ta2-P2 1 0 9 . 1 9 8 ° Nb2-N3 2.04080 A N3-Nb2-P2 1 0 1 . 8 9 0 ° Ta2-N4 2.05270 A N4-Ta2-P2 8 1 . 1 5 7 ° Nb2-N4 2.04598 A N4-Nb2-P2 85.150 ° T a l - H l 1.93485 A N b l - H l 1.98874 A Ta2-Hl 1.95611 A Ta2-Hl 1.99172 A Tal-H2 1.95606 A Tal-H2 1.99172 A Ta2-H2 1.93496 A Ta2-H2 1.98873 A The other interesting feature of the geometry optimizations is the asymmetric binding of the hydrides in model complex 4C. Model complexes 4D, 4F, and 4G are symmetric, with little deviation in metal-hydride bond distances and P - M - M - P dihedral angles of - 1 8 0 ° . In contrast, the ' N P N ' ligand is canted in the tantalum tetrahydride; the P-Ta-Ta-P dihedral angle is -138.5° and there is asymmetry in the metal-hydride bonds ( T a l - H l , 1.84 A; T a 2 - H l , 2.11 A for example). The previous proposal of a structure with bridging and terminal hydrides in rapid exchange in 35 gains some credence from this result. However, it is unknown what role this asymmetric binding could play in the reactivity of this complex. The dihydride model complexes 4D and 4G exhibit shortened metal-phosphine bonds. Extra electron density from the phosphorus donors could compensate for the loss o f H 2 . While the Ta-Ta interatomic distance in 4D is decreased by 0.035 A with loss of H 2 , the Nb-Nb bond lengthens by 0.23 A. The short bonds in these systems may derive not from the multiple bond orders, but rather the geometric constraints imposed by the bridging hydride ligands. The Kohn-Sham orbitals calculated following geometric optimization of 4B appear to qualitatively fit the bonding description for 34. The H O M O of 4B is complicated, with significant electron density in a Ta-Me bonding interaction, an anti-bonding Ta-P interaction and a tantalum n-interaction with an amide lone pair. A n 111 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes 72 isosurface of this orbital, created using the orbital depiction software Molden, is shown in Figure 4.6, along with an illustration clarifying these interactions. Figure 4.6. Depiction of the H O M O of model complex 4B, together with a simplified illustration of the bonding. A n isosurface of the next lowest energy orbital (HOMO-1) for 4B is shown in Figure 4.7 (top). This orbital is nearly isoenergetic with the H O M O . The isosurface depicts a strong o-bonding interaction between a d Z2 orbital on tantalum and an orbital on a methyl carbon. A weak TT-interaction between tantalum and one amide donor is evident, as is a weak bonding interaction between a second methyl group and tantalum. A n isosurface of H O M O - 2 for this system is also shown in Figure 4.7 (bottom). It is evident that the electron density in this orbital is delocalized. A weak bonding interaction between tantalum and phosphorus is accompanied by P - C bonding to methylene and methyl substituents. Significant Ta-Me and T a - N bonding is also evident. In summary, the high energy occupied orbitals in 4B include tantalum-methyl o-bonding interactions, tantalum-amide ^-bonding interactions and a weak tantalum-phosphorus bonding interaction. 112 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes Figure 4.7. Depictions of the H O M O - 1 (top) and H O M O - 2 (bottom) of model complex 4B , together with simplified illustrations of the bonding. The L U M O and LUMO+1 orbitals for 4B are both primarily tantalum based. The empty d-orbitals shown in Figure 4.8 are indicative of the susceptibility of the trimethyl complexes to nucleophilic attack. Non-bonding electron density is also present on one amide donor atom. 113 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Figure 4.8. Depictions of the L U M O (top) and LUMO+1 (bottom) of model complex 4B , together with simplified illustrations of the bonding. One of the goals of this D F T study was to investigate the differences between tantalum and niobium systems and correlate that to the observed thermal and photo-sensitivity of the niobium trimethyl complex. The Kohn-Sham orbitals for 4E show definitive variations from the tantalum congener. Isosurfaces for the H O M O , H O M O - 1 and H O M O - 2 of 4 E are shown in Figure 4 .9. The H O M O and H O M O - 1 show a-bonding Ta-Me interactions, and 7t-bonding and anti-bonding Ta-N interactions. It is important to note that no Nb-P interaction is observed. The H O M O - 2 clearly shows the uncoordinated phosphine lone-pair. Again, the open coordination site on niobium could promote faster decomposition and prevent the formation of niobium hydrides. 114 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes Figure 4.9. Depictions of the H O M O (top), H O M O - 1 (mid) and H O M O - 2 (bottom) of model complex 4 E , together with simplified illustrations of the bonding. A s with model complex 4 B , the L U M O and LUMO+1 for 4 E are primarily metal based. The L U M O , shown in Figure 4.10 (top), also has an antibonding niobium amide interaction of 7t-symmetry. The L U M O + 1 , shown in Figure 4.10 (bottom), contains a 115 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes weakly bonding interaction with niobium methyls. As in the tantalum case, the metal complexes appear susceptible to nucleophilic attack. Figure 4.10. Depictions of the L U M O (top) and LUMO+1 (bottom) of model complex 4 E , together with simplified illustrations of the bonding. In an attempt to gauge the reactivity of model complexes 4 B and 4 E , the H O M O -L U M O gaps were calculated. For 4 B , the differential was 0.1802 Ha, whereas for 4 E , a 0.1789 Ha difference was observed. The relative difference in orbital energies is relatively small, but still significant (3.41 kJ/mol). With an open coordination site and a smaller H O M O - L U M O gap, the niobium system is expected to have increased reactivity and instability, as observed in the facile decomposition of complexes 31, 32 and 33. Isosurfaces of the H O M O and H O M O - 1 for the ditantalum tetrahydride model complex 4 C are shown in Figure 4.11. The H O M O of 4 C is the Ta-Ta bonding orbital, as anticipated. There is very little contribution from the bridging hydride Is orbitals in the 116 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes H O M O . The H O M O - 1 resembles a 5-symmetry bonding interaction with the hydride ligands. Calculations on model complexes where the P-Ta-Ta-P was constrained to 180° resulted in poor orbital overlap in the Ta-Ta bond of the H O M O . The asymmetry of hydride bonding is readily apparent. Hydride interactions of sigma-bonding and pi-bonding symmetry also exist in 4C, but occur at much lower energies. The L U M O and LUMO+1 of 4C are both tantalum-based and are of 5-bonding and o-antibonding symmetry respectively. Isosurfaces for these orbitals are shown in Figure 4.12. Figure 4.11. Depiction of the H O M O (left) and H O M O - 1 (right) of model complex 4C showing the Ta-Ta bond ( H O M O ) and Ta-H bonds (HOMO-1) . Figure 4.12. Depiction of the L U M O (left) and LUMO+1 (right) of model complex 4C showing the empty orbitals with 5-bonding and G-antibonding symmetries. 117 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes Orbitals of model complex ( ' N P N ' N b ) 2 ( p - H ) 4 , 4F, show some similarities to the tantalum system described above. The H O M O is, as expected, the metal-metal bond. The HOMO-1 does not, however, involve hydride 5-bonding, as in 4 C , but is ligand based, with most of the electron density residing on the four amide donors. These orbitals are shown in Figure 4.13. The L U M O and LUMO+1 of 4F are quite similar to 4C . Figure 4.14 shows the niobium based 5-bonding and o-antibonding orbitals isosurfaces for the L U M O and LUMO+1 respectively. Figure 4.13. Depiction of the H O M O (left) and H O M O - 1 (right) of model complex 4F showing the Nb-Nb o-bond ( H O M O ) and amide p-orbitals (HOMO-1) . Figure 4.14. Depiction of the L U M O (left) and LUMO+1 (right) of model complex 4F showing the empty orbitals with 5-bonding and a-antibonding symmetries. The orbitals for model dihydride complexes 4D and 4 G are quite similar; only the orbitals for 4D wi l l be discussed. Initially, it was expected that the H O M O for 4D would 118 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nh(V) and Ta(V) complexes show a Ta-Ta 7i-bonding interaction. The H O M O is a Ta-Ta o-interaction. The 7t-bond appears in the H O M O - 1 . The eigenvalues for these orbitals show that they are nearly degenerate, but the single bond is clearly higher in energy. The reason for this unexpected switch in orbital energies is unknown. It is gratifying to observe the proposed Ta=Ta interaction qualitatively in these calculations. The H O M O and H O M O - 1 for 4D are shown in Figure 4.15. Figure 4.15. Depiction of the H O M O (left) and HOMO-1 (right) of model complex 4D showing the Ta-Ta a-bond ( H O M O ) and Ta-Ta 7t-bond (HOMO-1) . The L U M O in 4D is a o-bonding interaction. The orbital overlap for this Ta-Ta bond is very poor, however there is also a weak Ta-P interaction. This implies that this orbital could be tuned by changing the phosphine donor in the ligand backbone. The L U M O - 1 isosurface shows two d-orbitals arranged in 5-antibonding symmetry. Isosurfaces of these unoccupied orbitals of 4D are shown in Figure 4.16. 119 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Figure 4.16. Depiction of the L U M O (left) and LUMO+1 (right) of model complex 4D showing the empty orbitals with o-bonding and 5-antibonding symmetries. Differences in reactivity between tantalum and niobium systems can be examined with the calculated H O M O - L U M O differentials. Comparing the tetrahydrides 4C and 4F showed that the niobium system, 4F, should be more reactive (0.105 Ha for 4C and 0.089 Ha for 4F). These differences are minimal when comparing Ta and Nb dihydride model complexes 4D and 4G. The tantalum congener had a H O M O - L U M O gap of 0.091 Ha, only 0.001 Ha lower than the niobium system. While the decomposition of niobium trimethyl complexes may be accelerated by phosphine dissociation, any niobium hydrides produced would be comparatively less stable, complicating their isolation. Comparing H O M O - L U M O gaps of tetrahydride and dihydride tantalum complexes supports our supposition that the dihydride would show increased reactivity. The smaller H O M O - L U M O gap and the relatively low energy barrier implies that ( [NPN]Ta) 2(u.-H) 2 intermediates could act as reactive intermediates in the activation of nitrogen. 4.7 Summary Synthesis of niobium trimethyl complexes 31, 32, and 33 stabilized by R R [ N P N ] ligands (R = Ph, Cy ; R ' = Ph, Mes) was complicated by rapid thermo- and photo-120 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes decomposition. Attempts to hydrogenate these complexes to form hydrides were unsuccessful. Protonation of the ligand to give R R[NPN]H2 dominated the observed reactivity. D F T calculations indicated that the phosphine donor may not be coordinated to the niobium complexes in solution. This open coordination site could facilitate an unknown decomposition process and prevent isolation of niobium hydrides. The corresponding tantalum trimethyl complexes are comparatively stable. C y P h [NPN]TaMe3, 34, is readily hydrogenated to form ( C y P h[NPN]Ta)2(p-H) 4, 35, and reacts with molecular nitrogen to form the side-on end-on bound N2 complex (CyPh[NPN]Ta)2(p-H)2(p-V:r|2-N2), 36. Attempts to isolate the photo-decomposition products of 31-34 were unsuccessful. B y switching to a bulkier alkyl group, alkylidene and alkylidyne complexes of tantalum stabilized by [NPN] could be isolated. Neopentylidynes 37 and 38 form relatively slowly, proceeding through an alkyl alkylidene intermediate. Tantalum alkylidenes 39 and 40 were isolated from the reaction of the appropriate [NPN] lithium salt with T a C l 3 N p 2 (Np = C H 2 C M e 3 ) . It is proposed that the surprising reactivity of the tetrahydride complexes 35 and 41 is derived from an easily accessible tantalum dihydride with a metal-metal double bond. This species would hold the latent reducing power to activate molecular nitrogen. Isotopic labeling studies and D F T calculations indicate that such a species should be accessible. Exploitation of this Ta=Ta intermediate and promotion of other reactivity, both to develop new synthetic transformations and to provide mechanistic support for the dihydride intermediate, remains to be developed. 4.8 Experimental section 4.8.1 General considerations Unless otherwise stated, general procedures were performed as in Section 2.4.1. The ab initio D F T calculations on the model compounds ' N P N ' M M e 3 , ('NPN'M)2(p-H)4 and ('NPN'M)2(p-H 2) were performed with the hybrid functional B 3 L Y P 4 5 method using the Gaussian 98 package. 6 0 The basis functions and effective core potentials used were those 121 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes in the L A N L 2 D Z basis set. 4 6 N o geometric constraints were set in the optimization of the 72 complexes. Orbital depictions were created using the Molden program. 4.8.2 Starting materials and reagents The compounds NbCl2Me3 7 3 and TaCl2Me374 were prepared according to literature procedures. TaCls and NbCls were purchased from S T R E M and sublimed prior to use. Anhydrous ZnC\2 was purchased from Aldr ich and dried by heating to reflux in excess SOCI2 under an N2 atmosphere. High purity hydrogen gas was purchased from P R A X A I R and used as received. Deuterium gas was purchased from Cambridge Isotopes and used as received. 4.8.3 Synthesis Synthesis of C y P h [ N P N ] N b M e 3 , 31, p h P h [ N P N ] N b M e 3 , 32, and C y M e s [ N P N ] N b M e 3 , 33 The above compounds were synthesized by analogous routes. Given is a procedure for the synthesis of 31. In the dark, a solution of 5.601 g (0.0106 mol) of C y P h [ N P N ] L i 2 ( O E t 2 ) in 150 m L of Et20 maintained at -78 °C was added via cannula to a solution of 2.200 g (0.0106 mol) of N b C l 2 M e 3 in 150 m L of E t 2 0 . The solution was stirred at -78 °C for 1 h, and then warmed to -10 °C, producing an orange solution. Excess Et20 was removed in vacuo while maintaining the temperature at -10 °C. The resulting solid was dissolved in toluene and filtered through Celite. The toluene was removed in vacuo and the solid washed with pentane to afford C y P h [ N P N ] N b M e 3 , 31, in 72% yield (4.42 g). The solid was highly sensitive to light and temperature, and was stored in a darkened vessel at -37 °C. Decomposition prevented obtaining satisfactory elemental analysis. p h P h [ N P N ] N b M e 3 and C y M e s [ N P N ] N b M e 3 were isolated in 68% and 65% yield respectively. 31: ' H N M R ( C 6 D 6 , 25 °C, 500 M H z ) 8: 0.00, 0.34 (s, 12H, S i (C i / 3 ) 3 ) , 0.75-1.42 (m, 15H total, CH2 and C6HU), 1.68 (s, 9H , N b ( C / / 3 ) 3 ) , 6.96-7.12 (m, 10H, N P h - i / j . 3 1 P { ' H } N M R ( C 6 D 6 , 25 °C, 202.5 M H z ) 6: 10.8 (s). 32: ] H N M R ( C 6 D 6 , 25 °C, 500 M H z ) 8: -0.08, 0.35 (s, 12H, Si(C# 3 ) 3 ) , 1.20 (m, 4 H total, CH2), 1.63 (s, 9H , Nb(C# 3 ) 3 ) , 6.80-7.38, 7.60-7.85 (m, 122 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes 15H, N P h - / / , PPh-//) . 3 1 P { ' H } N M R ( C 6 D 6 , 25 °C, 202.5 M H z ) 6: 6.2 (s). 33: *H N M R ( C 6 D 6 , 25 °C, 500 M H z ) 5: 0.21, 0.29 (s, 12H, S i (C / / 3 ) 3 ) , 0.91-2.08 (m, 15H total, CH2 and C 6 / / u ) , 2.10 (s, 6H, o-Ph-C// 3 ) , 2.16 (s, 6H, o-Ph-C// 3 ) , 2.29 (s, 9 H , N b(C / / 3 ) 3 ) , 2.39 (s, 6H, /?-Ph-C/ / 3 ) , 6.82 (s, 2H , m-Ph-H), 7.02 (s, 2H , m-?h-H). 3 1 P { ' H } N M R ( C 6 D 6 , 25 °C, 202.5 M H z ) 5: 11.2 (s). Hydrogenation o f 31-33 A 75 m L ethereal solution of 0.500 g of C y P h [ N P N ] N b M e 3 , 31, P h P h [ N P N ] N b M e 3 , 32, or C y M e s [ N P N ] N b M e 3 , 33, was prepared in a thick-walled reaction vessel fitted with a Kontes valve. The flask and contents were immediately cooled to -78 °C. N 2 was removed by successive freeze-pump-thaw cycles. The solution was then frozen at -196 °C, flushed with H 2 , sealed, and warmed to room temperature. The reaction mixture turned from bright yellow to black over the course of 1 h. Solvent removal yielded a dark black paste in each case. Analysis of the crude product by E I - M S and N M R showed extensive decomposition and the formation of multiple products. N o hydride resonances were observed in ' H N M R spectra. In situ hydrogenation of 31 0.050 mg (0.086 mmol) of C y P h [ N P N ] N b M e 3 was added to a N M R tube fitted with a J-Young valve. The tube was then charged with 2.0 m L of CeD6 and immediately frozen at -196 °C. The tube was evacuated and then refilled with H 2 gas. The reaction was then monitored by ' H N M R at -10 °C. Spectra were collected every 15 minutes. A t no point in the reaction were resonances characteristic of the formation of metal hydrides observed. Synthesis of C y P h [ N P N ] T a M e 3 , 34 A solution of T a M e 3 C l 2 (5.00 g, 16.84 mmol) in 50 m L E t 2 0 was added dropwise to a solution of C y P h [ N P N ] L i 2 ( O E t 2 ) (8.90 g, 16.84 mmol) in 800 m L E t 2 0 at -78°C. The solution was then warmed to room temperature and a white precipitate appeared. The 123 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes solution was evaporated to dryness and the remaining solids extracted into 50 m L toluene and filtered through Celite. The solvent was removed and the solids washed with pentane to afford a yellow solid, C y P h [ N P N ] T a M e 3 , in 85% yield (9.54 g, 14.31 mmol). ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 6 -0.22 (s, 6H, S iC# 3 ) , 0.01 (s, 6H , SiC7/ 3 ) , 0.61 (s, 9H, TaC/ / 3 ) , 0.63-1.75 (m, 15H, C6HU, P C / / 2 S i ) , 6.65-6.80 (m, 6H, NPh) , 6.95-7.05 (m, 4H, NPh). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 16.78 (s). Anal . Calcd for C 2 7 H -4 6 N 2 P S i 2 T a : C, 48.64; H , 6.95; N , 4.20. Found: C, 48.45; H , 6.67; N , 4.60. Preparation of ( C y P h [NPN]Ta) 2 (p -H) 4 , 35 A solution of C y P h [ N P N ] T a M e 3 (2.50 g, 3.75 mmol) in 50 m L E t 2 0 was transferred into a 200 m L thick-walled glass vessel equipped with a Kontes valve, and thoroughly degassed via three freeze-pump-thaw cycles. The vessel was cooled in l iquid nitrogen and H 2 gas added. The vessel was sealed, warmed to room temperature and stirred for 24 hours, over which time the solution turned to deep purple. The solvent was removed in vacuo, and the product extracted into degassed pentane and filtered through Celite. Removal of pentane affords ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 in 97% yield (2.27 g, 1.82 mmol). The product was highly nitrogen sensitive in solution; it is stable under nitrogen in solid form at -35 °C. ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 0.18 (s, 12H, SiC7/ 3 ) , 0.24 (s, 12H, S iC# 3 ) , 0.35-1.90 (m, 30H, CeHu, PC77 2Si), 6.96 (s, 4 H , NPh), 7.18 (s, 8H, NPh) , 7.36 (s, 8H, NPh), 9.90 (s, 4 H , TaHTa). 3 1 P { 1 H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 29.20 (s). Anal . Calcd for C 2 7 H 4 6 N 2 P S i 2 T a : C , 46.22; H , 6.30; N , 4.49. Found: C , 45.89; H , 6.20; N , 4.34. Preparation o f ( C y P h rNPN ]Ta) 2 (p-H) 2 (p-n 1 : n 2 -N 2 ) , 36 A solution of ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 (2.00 g, 1.60 mmol) in 25 m L E t 2 0 was exposed to an atmosphere of N 2 gas for 24 hours, with rapid stirring, resulting in a colour change from purple to red. The solvent was removed and the remaining solid was rinsed with minimal pentane and dried to afford ( C y P h [NPN]Ta) 2 (p -H) 2 (p -n 1 : r i 2 -N 2 ) in 95% yield. ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 6 0.11, 0.30, 0.42 (s, 24H, S i C / / 3 ) , 0.68-2.81 (m, 28H, P-CH2, V-C6Hn), 7.00 (m, 4 H , NPh), 7.08 (m, 8H, NPh), 7.34 (m, 8H, NPh) , 10.71 (s, 2H, 124 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes TattTa). 3 1P{'H} NMR (C 6D 6 , 25°C, 202.5 MHz): 5 15.80 (m), 27.9 (d). Anal. Calcd for C48H76N6P2Si4Ta2: C, 45.28; H, 6.00; N , 6.30. Found: C, 44.99; H, 6.00; N, 6.30. Preparation of CyPh[NPN]Ta=C(CMe3), 37 Diethyl ether (100 mL) was added to an intimate mixture of C y P h[NPN]Li 2(OEt 2) (2.273 g, 4.298 mmol) and TaCl 2Np 3 (2.000 g, 4.298 mmol) and stirred vigorously. The vessel was sealed and the contents stirred for five weeks, promoting a slow colour change from yellow to bright red. Removal of solvent in vacuo gave a bright red paste. Extraction of the product into pentane, followed by filtration through celite, gave CyPh[NPN]Ta==C(CMe3), 3 7 j m S2% yield. 'H NMR (C 6D 6 , 25°C, 500 MHz): 5 0.21 (s, 6H, SiC// 3), 0.39 (s, 6H, SiC// 3), 0.80-1.94 (m, 15H, PC// 2 , PC 6//n), 2.22 (s, 9H, TaC(C(C//3)3)), 6.79 (m, 8H, NPh), 7.13 (m, 2H, NPh). 1 3C{'H} NMR (C 6D 6, 25 °C, selected peaks): 8 367 (s). 3 1P{ 1H} NMR (C 6D 6, 25°C, 202.5 MHz): 8 41.9 (s). MS (EI): m/z 690 [M + , C 2 9H 4 6N 2PSi 2Ta]. Preparation of phPh[NPN]Ta=C(CMe3), 38 Diethyl ether (100 mL) was added to an intimate mixture of p h P h[NPN]Li 2(THF) 2 (2.548 g, 4.298 mmol) and TaCl 2Np 3 (2.000 g, 4.298 mmol) and stirred vigorously. The vessel was sealed and the contents stirred for two weeks, promoting a slow colour change from yellow to bright red. Removal of solvent in vacuo gave a bright red paste. Extraction of the product into pentane, followed by filtration through celite, gave CyPh[NPN]Ta=C(CMe3), 37, in 55.2% yield. *H NMR (C 6D 6 , 25°C, 500 MHz): 8 -0.18, 0.05 (s, 12H, SiC// 3), 0.98-1.08 (m, 4H, PC// 2), 1.80 (s, 9H, TaC(C(C//3)3)), 6.89-8.2 (m, ov, 15H, NPh-//, PPh-//). 1 3C{'H} NMR (C 6D 6, 25 °C, selected peaks): 5 341 (s). 3 1P{'H} NMR (C 6D 6 , 25°C, 202.5 MHz): 8 37.2 (s). MS (EI): m/z 684 [M + , C2 9H4oN2PSi2Ta]. 125 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes Preparation of C y P h [ N P N ] T a ( C l ) ( = C H C M e 3 ) , 39, and p h p h [ N P N ] T a ( C l ) ( = C H C M e 3 ) , 40 Diethyl ether (100 mL ) was added to an intimate mixture of R P h [ N P N ] L i 2 ( S ) (4.656 mmol) and T a C l 3 N p 2 (2.000 g, 4.656 mmol) and stirred vigorously. The vessel was sealed and the contents stirred for 24 hours, promoting a colour change from yellow to orange. Removal of solvent in vacuo gave orange pentane insoluble solids 39 and 40 in 66% and 59% yield respectively. Recrystallization of 39 from a saturated toluene/hexanes solution gave small red chip crystals that were characterized by X-ray crystallography. 39: 0.11, 0.24 (s, 12H, S i C / / 3 ) , 0.88-1.45 (m, ov, 15H, P C / / 2 , P C 6 # n ) , 1.78 (s, 9H, TaCH(C(C/ / 3 ) 3 ) ) , 2.55 (s, 1H, TaC/ / (C(CH 3 ) 3 ) ) , 6.88-7.15 (m, 10H, NPh- / / ) . 1 3 C { ' H } N M R ( C 6 D 6 , 25 °C, selected peaks): 5 203 (s). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 15.6 (s). M S (EI): m/z 726 [ M + , C 2 9 H 4 7 C l N 2 P S i 2 T a ] . 40: ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 6 -0.18, 0.15 (s, 12H, S i C / / 3 ) , 1.04 (m, 4 H , P C / / 2 ) , 2.14 (s, 9H , TaCH(C(C/ / 3 ) 3 ) ) , 3.32 (m, 1H, TaC/ / (C(CH 3 ) 3 ) ) 6.9-7.9 (m, ov, 15H, N P h - / / , PPh-//) . 1 3 C { ' H } N M R ( C 6 D 6 , 25 °C, selected peaks): 5 198 (s). 3 1 P { ! H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 12.2 (s). M S (EI): m/z 720 [ M + , C 2 9 H 4 i C l N 2 P S i 2 T a ] . Procedure for high yield isolation of 35 and ( p h P h [NPN]Ta) 2 (u -H) 4 , 41 A solution of C y P h [ N P N ] T a M e 3 or p h P h [ N P N ] T a M e 3 (2.00 mmol) in 50 m L E t 2 0 was thoroughly degassed by three freeze-pump-thaw cycles and charged with 4 atm. of H 2 . 24 hours of vigorous stirring resulted in a colour change from yellow to purple. Cannula transfer of these solutions under A r into a B24 Schlenk flask was followed by removal of solvent in vacuo. Addit ion o f a minimal amount o f cold pentane, followed by filtration of the resultant suspension through a Schlenk frit gave deep purple powders. Rinsing with a minimal amount of cold pentane, and thorough drying in vacuo gives dinitrogen free ( C y P h [NPN]Ta) 2 (u -H) 4 and ( p h P h [NPN]Ta) 2 (u -H) 4 in 80% and 92% isolated yields respectively. 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W. ; Schlegel, H . B . ; Scuseria, G . E . ; Robb, M . A . ; Cheeseman, J. R. ; Zakarzewski, V . G . ; Montgomery, J . A . ; Stratmann, R. E . ; Burant, J. C ; Dapprich, S.; Mi l l am , J. M . ; Daniels, A . D . ; Kudin , K . N . ; Strain, M . C ; Farkas, O.; Tomasi, J.; Petersson, V . A . ; Ayala , P. Y . ; Cu i , Q.; Morokuma, K . ; Mal ick , D . K . ; Rabuck, A . D. ; Raghavachari, K . ; Foresman, J. B . ; Cioslowski, J.; Ortiz, J. V . ; Stefanov, B . B . ; L u i , G . ; Liashenko, A . ; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L . ; Fox, D . J.; Keith, T.; Al -Laham, M . A . ; Peng, C. Y . ; Nanajakkara, A . ; Gonzalez, C ; Challacombe, M . ; G i l l , P. M . W. ; Johnson, B . G . ; Chen, W. ; Wong, M . W. ; Andres, J. L . ; Head-Gordon, M . ; Repogle, E . S.; Pople, J. A . Gaussian 98, revision a. 7; Gaussian Inc.: Pittsburg, 1998. 129 References begin on page 127. Chapter Four: Synthesis, reactivity and DFT calculations of [NPN] supported Nb(V) and Ta(V) complexes 61. 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J. 2002, 8, 3277. 71. Chin, C . H . ; Mebel , A . M . ; Hwang, D . Y . J. Phys. Chem. A 2004,108, 473. 72. Schaftenaar, G . Molden 3.8; C A O S / C A M M Center, University of Nijmegen: Netherlands, 1991. 73. Fowles, G . W . A . ; Rice, D . A . ; Wilkins, J. D . J. Chem. Soc, Dalton Trans. 1973, 9, 961. 74. Schrock, R. R.; Sharp, P. R. J. Am. Chem. Soc 1978,100, 2389. 130 References begin on page 127. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes 5.1 Introduction It was suspected that the reactive intermediate in the coordination and activation of N2 to form 36 is ( yPh[NPN]Ta)2(p-H)2 - a dihydride tantalum complex with a Ta=Ta double bond generated via reductive elimination of H2 (Equation 5.1). A similar complex has been previously synthesized, as shown in Scheme 5.1. Reduction of (Cl2(PMe3)2Ta)2(p-H)2(p-CI)2 with Na/Hg amalgam gives (Cl2(PMe3)2Ta)2(p-H)2 - a dihydride dinuclear Ta 1 1 1 complex with a metal-metal double bond. Hydrogenation of this species generates (Cl2(PMe3)2Ta)2(p-H)4, a complex isoelectronic to ( [ P i ^ J T a ^ p - H ^ . 1 Chapter Five , \ -S iMe 2 5. ,SiMe 2 131 References begin on page 170. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis of phosphides andphosphinidenes 2 2 5 A related d -d organoditantalum complex with a formal Ta=Ta double bond, (n -C5Me4R)2Ta2(u.-X)4 (R = M e , Et; X = C l , Br), is quite reactive.2"6 For example, the complex reacts to ring-open 3,3-diphenylcyclopropane to give an alkylidene 5 and activates two C - H bonds of allene ligand, 6 as shown in Scheme 5.2. Scheme 5.2 132 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes A related dinuclear iron tetrahydride complex exhibits extensive reactivity towards E - H bond activation. 7 ' 8 Treatment of (r)5-C5Me5)FeCl(NMe2CH2CH2NMe2) with L iAlFLi followed by work-up with H2O gave ((n,5-C5Me5)Fe)2(p-H)4 which undergoes exchange with D2 gas. The iron tetrahydride readily reacts with Pl^SiHb and PI12PH to give silylene and phosphido bridged complexes as shown in Scheme 5.3. Scheme 5.3 The addition of H n P R 3 . n (n = 1, 2) to metal-metal bonds is a relatively unusual route to bridging phosphides. The addition of primary and secondary phosphines to a M = M triple bond ( M = W , M o ) generates bridging phosphide hydride derivatives (Scheme 5.4) reducing the metal-metal bond order to two. 9 ' 1 0 Other reports focus on phosphine addition to polynuclear or cluster metal complexes, generating phosphido bridged complexes o f iron, cobalt, platinum, molybdenum, manganese, tungsten, osmium, and ruthenium. 1 1" 1 9 133 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Scheme 5.4 P - H activation may be achieved by addition of primary and secondary phosphines to the putative ( R P h[NPN]Ta)2(u.-H)2 intermediate. Phosphinidene and phosphide tantalum t 20 21 22 complexes have been supported by BusSiO, phosphine, diphosphine ' and Cp derived ligands. Synthetic strategies include using metathesis, ' ' ' ' oxidative 20 29 * 21 addition of H P R 2 , methane elimination, decomposition of coordinated phosphines or insertion of a P - X bond into a Ta-H followed by deprotonation. 2 6 The synthesis of tantalum phosphido and phosphinidene complexes also includes a terminal tantalum phosphinidene supported by a triamidoamine ligand which promotes phospha-Wittig chemistry. 2 7 ' 2 8 Only two of these publications detail the synthesis of dinuclear tantalum phosphides or phosphinidenes, 2 4 ' 2 5 and these required strong reductants to affect the transformations. Reduction of Cp*TaCl4 with excess L i P H R afforded the bridging phosphinidenes (Cp*TaCl)2(u.-PR)2 which were structurally characterized for R = Cy , l B u , Ph and Mes. These reactions proceeded in low yield due to the formation of R P H 2 and P2H2R2 species and other side products. P - H activation by ( R P h [NPN]Ta) 2 ( | j , -H)4 may provide a route to dinuclear phosphides and phosphinidenes without strong reductants, as wel l as offer mechanistic insight into this reactive tantalum hydride. 5.2 Preparation of tantalum phosphide complexes Addition of dicyclohexylphosphine to an ethereal solution of ( P h P h [NPN]Ta )2 (u-H)4, 41, under A r promotes an immediate colour change from purple to red along with concomitant gas evolution. After solvent removal, a deep red, pentane soluble product o 1 was isolated. P N M R spectroscopy of this product showed three distinct phosphorus 134 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes resonances at 8 10.47, 10.53 and 164.38 respectively, as shown in Figure 5.1. Peak P A is a doublet of doublets coupled to both P B (73.4 Hz) and Pc (10.1 Hz) . P B is a doublet and is assigned trans to P A due to the large coupling constant. It overlaps with a doublet assigned to Pc that exhibits a weaker cis coupling. The resonance at 8 164 is characteristic for a bridging phosphide; for example, while the terminal tantalum phosphide CpCp*TaH2 (PMe 2 ) exhibits a 3 1 P chemical shift o f 8 -81.3, the heterobimetallic complex with a bridging phosphide, Cp2TaH(p-H)(p-PPh2)Fe(CO)3, exhibits a P chemical shift of 8 177.2. Therefore, the product was initially assigned as ( P h P h [NPN]Ta )2 (p-H) 3 (p-PCy 2 ) , 42. 165 0 164 8 164 6 164 4 164 2 164.0 163 8 163 6 163,4 (IT** Figure 5.1. 3 1 P { 1 H } N M R resonances for ( p h p h [NPN]Ta )2 (p-H) 3 (p-PCy 2 ) , 42. P A , the bridging phosphide, couples to P B and P c , the ligand phosphines. A n analysis of the hydride region of the *H N M R spectrum supports this assignment. Two distinct hydride environments at 8 10.5 and 8 8.7, integrating to 1H and 2 H respectively, indicate the presence of three bridging hydrides. The formation of 42 135 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes from 41 is shown in Equation 5.2. The solution colour changes immediately from purple to red upon addition of H P C y 2 to 41. Monitoring the reaction by 3 1 P N M R spectroscopy confirmed that the reaction is complete before the sample can be returned to the spectrometer. Crystals of 42 were grown from a saturated pentane solution and analyzed by X -30 ray crystallography. A n O R T E P depiction of the solid state molecular structure of 42 is shown in Figure 5.2. Relevant bond lengths and angles are listed in Table 5.1 and crystallographic data are located in Table 5.2. Atoms H I , H2, and H3 were located in the diffraction pattern and refined isotropically. To help assert the presence of the bridging hydrides, a second crystallographic refinement was performed, where atoms H I , H2, and H3 were deleted from the solution, and the program X - H Y D E X 3 1 was used to predict the location and number of bridging hydrides. The two studies were in agreement with spectroscopic data; three latent hydrides bridge the two tantalum centres. . \S iMe 2 + HPCy 2 SiMe 2 5.2 Ph 136 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Figure 5.2. O R T E P drawing (spheroids at 50% probability) of C h ™[NPN]Ta) 2 (u-H) 3(u.-PCy 2), 42. Silylmethyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Hydrides H I , H2 and H3 were located in the diffraction pattern and refined isotropically. Table 5.1 Selected Bond Distances ( A ) and Angles (°) for ( P h P h [NPN]Ta) 2 (u -H )3 ( | i -PCy 2 ) , 42. Lengths Angles Angles Ta(l)-N(2) 2.160(4) N(2)-Ta(l)-N(l) 115.00(14) N(3)-Ta(2)-Ta(l) 115.41(10) Ta(l)-N(l) 2.236(4) N(2)-Ta(l)-P(3) 118.46(11) N(4)-Ta(2)-Ta(l) 110.73(10) Ta(l)-P(3) 2.5007(13) N(l)-Ta(l)-P(3) 86.91(10) P(3)-Ta(2)-Ta(l) 60.57(3) Ta(l)-Ta(2) 2.5157(9) N(2)-Ta(l)-Ta(2) 119.40(10) N(3)-Ta(2)-P(2) 85.36(11) Ta(l)-P(l) 2.6031(14) N(l)-Ta(l)-Ta(2) 119.40(10) N(4)-Ta(2)-P(2) 79.60(11) Ta(2)-N(3) 2.114(4) P(3)-Ta(l)-Ta(2) 58.24(3) P(3)-Ta(2)-P(2) 86.68(5) Ta(2)-N(4) 2.185(4) N(2)-Ta(l)-P(l) 83.65(11) Ta(l)-Ta(2)-P(2) 146.30(3) Ta(2)-P(3) 2.4413(14) N(l)-Ta(l)-P(l) 155.88(4) C(55)-P(3)-C(49) 107.3(2) Ta(2)-P(2) 2.5786(13) P(3)-Ta(l)-P(l) 74.10(10) C(55)-P(3)-Ta(2) 114.62(14) P(3)-C(55) 1.925(5) Ta(2)-Ta(l)-P(l) 118.74(3) C(49)-P(3)-Ta(2) 120.06(16) P(3)-C(49) 1.967(5) N(3)-Ta(2)-N(4) 115.72(15) C(55)-P(3)-Ta<l) 124.52(15) P(l)-C(25) 1.790(5) N(3)-Ta(2)-P(3) 117.30(11) C(49)-P(3)-Ta(I) 122.26(16) P(2)-C(43) 1.852(5) N(4)-Ta(2)-P(3) 123.58(11) Ta(2)-P(3)-Ta(l) 61.19(4) 137 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Table 5.2 Crystallographic Data and details of refinement for ( P h F h [NPN]Ta) 2 (p . -H )3 (^PCy 2 ) , 42. Empirical formula C6oH84N4Si4P3Ta2 Formula weight 1443.6 Crystal system Triclinic Space group P-1 a, b, c (A) 13.6335(27), 14.5644(29), 15.7177(31) 91.361(30), 90.161(30), 94.016(30) v,A3 3112.39(20) Total reflections 13906 z 2 Unique reflections 12856 D c a i c , g cm"3 1.54 Parameters 678 u (Mo Ka), cm - 1 3.708 R , a 0.0368 T, K 173 ± 1 R w a 0.0872 29 range (°) 60.2 Goodness-of-fit 1.221 - | F C | | / Z | F 0 | ; * w = 2>(|F 02 | - |FC 2 |) 2/2>|F 0 2 | 2) 12 The molecular structure unambiguously shows the bridging phosphide P(3) bound between Ta( l ) and Ta(2) at distances of 2.4413(14) A and 2.5007(13) A respectively. These lengths are considerably shorter than tantalum phosphine bond lengths, as expected for a bridging phosphide. While considerably longer than bonds to P(3), the interatomic distances between ligand phosphines and tantalum have lengthened from those in complex 41. The distances Ta( l ) -P( l ) and Ta(2)-P(2) are 2.60313(14) A and 2.5786(13) A , respectively, slightly elongated from the Ta-P interatomic distance of 2.568(2) A in 41. The Tal -Ta2 distance in 42 is 2.5157(9) A , shortened from the metal-metal bond length of 2.568(1) A in 41. The tantalum-tantalum distance in 42 is drastically different from the only other crystallographically characterized example of a dinuclear tantalum phosphide. 2 5 ( ( / 7 5 -C 5H4Me)(PPh2)Ta)2(p.-PPh 2)2 has a Ta-Ta bond length of 3.024(2) A . In fact, 42 contains one of the shortest published Ta-Ta single bond distances. Interestingly, all of the crystallographically characterized systems with short Ta-Ta bonds (Table 5.3) contain bridging hydrides. Small bridging ligands bring the two metal centres close together (e.g. halogen-bridged complexes generally have longer Ta-Ta bonds than comparable hydrido-bridged complexes). The complexes with short Ta-Ta bonds also contain at least two phosphine donors. 138 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Table 5.3. Shortest reported Ta-Ta interatomic distances, and selected comparative examples Complex d(Ta-Ta), A (Cl 2 (PMe 3)2Ta) 2 (p-H)4 1 2.511(2) ( P h P h [NPN]Ta) 2 (p -H) 3 (p -PCy) 2 a 2.5157(9) ( (cu)(PMe 3 ) 2 (H)Ta) 2 (p-H) 4 3 2 2.5359(4) ( C l 2 ( P M e 3 ) 2 T a ) 2 ( p - H ) 2 3 3 2.545(1) ( p h p h [ N P N ] T a ) 2 ( p - H ) 4 b 2.568(1) ( [ P 2 N 2 ] T a ) 2 ( p - H ) 4 3 4 2.617(2) (Cl 2 (PMe 3 ) 2 Ta) 2 (p -H) 2 (p -Cl ) 2 3 5 2.621(1) ( ( / 7 5 -C 5 H 4 Me)(PPh 2 )Ta) 2 (p -PPh 2 ) 2 2 5 3.024(2) This work; Unpublished results Other tantalum phosphides were prepared from the addition of various secondary phosphines to the tantalum tetrahydride complexes 35 or 41. Addit ion of H P C y 2 to 35, for example, affords ( C y P h [NPN]Ta) 2 (p -H) 3 (p -PCy 2 ) , 43. The ! H N M R spectrum of 43 is analogous to that of 42. 3 1 P N M R spectroscopy of this derivative, however, shows an upfield shift o f the phosphide resonance from 8 164 to 8 149. Ligand phosphines shift downfield, appearing at 8 16.3 and 18.7 respectively. Addit ion of H P P h 2 to 41 and 35 afford ( p h p h [NPN]Ta) 2 (p -H) 3 (p -PPh 2 ) , 44, and ( C y P h [NPN]Ta) 2 (p -H) 3 (p -PPh 2 ) , 45. A strong upfield shift in the phosphide resonance also occurs for diphenylphosphine derivatives; the phosphide resonances appear at 8 136.3 for 44 and 8 115 for 45. The phosphide chemical shift is related to the [NPN] ligand phosphine. Addition of H P C y 2 to 35 or 41 results in a 8 15 upfield shift in the phosphide resonance comparing 43 to 42. A similar upfield shift of 8 21 is observed upon addition of H P P h 2 to 35 and 41. The C y P h [ N P N ] stabilized metal fragment is a better cr-donor, due to the alkylphosphine donor of [NPN], and the phosphines in these systems are shifted upfield. 5.3 Preparation of tantalum phosphinidene complexes Phosphinidenes can be prepared from primary phosphines by the analogous route used to prepare phosphides from secondary phosphines. Addit ion of cyclohexylphosphine 139 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes to 35 or 41 produced a now familiar purple to red colour change and gas evolution. Initally, it was suspected that a bridging phosphide would form with a p-PH(Cy) linkage. However, on addition of H 2 P C y to 41 the 3 1 P N M R spectra showed three peaks at 8 10.9, 15.0 and 448.9. While the three peaks showed similar coupling patterns to those observed for the tantalum phosphides, the chemical shift of ~8 450 does not correlate to previously studied phosphides. The chemical shift suggests the presence of a phosphinidene. The 3 1 P chemical shifts for the /rans-bis(phosphinidene) tantalum complexes, [Cp*TaCl(p-PR)] 2 are at 5 437.6, 482.0, 403.9 and 390.3 for R = Cy , l B u , Ph and Mes, respectively. 2 4 , 2 5 The observation of a single peak at 5 10.9 integrating to two hydrides in the ' H N M R supports the synthesis of ( P h p h [NPN]Ta) 2 (p -H) 2 (p -PCy) , 46. Further N M R studies and elemental analysis confirmed this structure. Similarly, addition of H 2 P C y to 35 produced ( C y P h [NPN]Ta) 2 (p -H) 2 (p -PCy) , 47. 3 1 P N M R resonances at 8 16.6, 22.1 and 436.4 confirmed the generation of a tantalum phosphinidene complex. The downfield resonance appears as a doublet of doublets, coupling strongly to one ligand phosphine, and weakly to the other. Two equivalent hydrides are observed in the 1 H N M R spectrum at 8 10.4. They appear as a 1:1:1:2:1:1:1 septet, coupling to each of the three phosphorus nuclei, giving an overlapping doublet of doublets of doublets, as shown in Figure 5.3. The high solubility of these phosphinidenes complexes has prevented characterization by X-ray crystallography. The synthesis of complexes 46 and 47 is shown in Equation 5.3. 1111 ll 11 ll M n n 11 I I 11 ll I u || 11 ll 11 u 111; I i 11 u 111 ll u li 11 ll 1 1 1 1 1 1 1 1 ; i; I ll u 11111 IM 111 [i 1 1 1 1 1 MI [ 11 u M )| 111 ll 1 1 1 li 11 ll I n I I 111111 I I 11111| 11 ll 1046 10.44 10.42 1040 10.38 10 36 10,34 (ppmj Figure 5.3. Hydride resonance in 47 showing coupling to three P nuclei giving rise to a septet. Lorentzian deconvolution is shown. ] 40 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes . \S iMe 2 + H 2 PCy ,SiMe 2 - 2 H 2 5.3 R = Ph, 42 R = Cy, 43 Synthesis of phosphinidene tantalum complexes with phenylphosphine proved more difficult. Addit ion o f H2PPI1 to 35 or 41 resulted in ligand protonation to give R P h[NPN]FJ.2, first observed in the decomposition of dilithium ligand precursors with H 2 O . The fate of the tantalum and phosphine remains unknown. Adamantyl groups have long been used to provide a 'round' steric constraint to 36 38 transition metal systems in order to control reactivity. ' A n added benefit to employing adamantyl groups is their proclivity to crystallize from non-polar solvents, due to the fixed adamantane cage. 3 9" 4 1 For this reason, adamantylphosphine was added to solutions of 35 and 41. These reactions gave the corresponding phosphinidene complexes ( P h P h [NPN]Ta) 2 (p -H) 2 (p -PAd) , 48, and ( C y P h [NPN]Ta) 2 (p -H) 2 (p -PAd) , 49, in 90% and 95% yield respectively. N M R spectroscopy of 48 and 49 was similar to 46 and 47. For each phosphinidene, three resonances were observed in 3 1 P { ' H } spectra: 8 7.35, 10.23, and 474.26 for 48 and 5 14.37, 19.80 and 468.35 for 49. A s was observed in phosphide systems, the phosphine substituent in the [NPN] ancillary ligand produces a marked effect in phosphinidene chemical shift. The cyclohexylphosphinidene complex stabilized by the C y P h [ N P N ] ligand appears upfield by 8 12 compared to the P h P h [ N P N ] system. The effect is somewhat muted for adamantyl phosphine: an upfield shift o f 8 6 is observed for cyclohexyl versus phenyl. 141 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Dark red crystals of 48 were crystallized readily from pentanes solutions and were studied by X-ray crystallography. An ORTEP 3 0 depiction of the solid state molecular structure of 48 is shown in Figure 5.4. Relevant bond lengths and angles are listed in Table 5.5 and crystallographic data are located in Table 5.4. The bridging phosphinidene P3 has Tal-P3 and Ta2-P3 bond lengths of 2.3394(9) A and 2.4030(9) A, respectively, significantly shorter than the phosphide complex. P3 is also quite planar; the sum of angles Tal-P3-Ta2, Tal-P3-C48 and Ta2-P3-C48 is 359.59°. The molecular structure clearly supports the assignment of a phosphinidene bridge. Figure 5.4. ORTEP drawing (spheroids at 50% probability) of ( p h P h[NPN]Ta) 2((i-H) 2((i-PAd), 48. Silyl methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. Hydrides HI and H2 located in the diffraction pattern and refined isotropically. 142 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Table 5.4 Crystallographic Data and details of refinement for (phph[NPN]Ta)2(p-H)2(p-PAd), 48. Empirical formula C 58H 9 1N 4Si4P3Ta 2 Formula weight 1411.5 Crystal system Monoclinic Space group P2,/c a,b,c{k);f3n 17.0490(7), 14.5931(5), 25.6519(9); 97.550(1) v, A3 6326.81(9) Total reflections 56050 z 4 Unique reflections 13902 D c a ,c, g cm"3 1.48 Parameters 656 u (Mo Ka), cm"1 3.646 V 0.037 T, K 173 + 1 R w a 0.067 29 range (°) 55.8 Goodness-of-fit 1.173 R, = Z||F0| - \F0\\fL\F0\; Rw = 2>(|F 0 2 | - |F C 2 | ) 2 /2>|F 0 2 | 2 ) Table 5.5 Selected Bond Distances (A) and Angles (°) for (PhPh[NPN]Ta)2(p-H)2(p-PAd), 48. Lengths Angles Angles Ta(l)-N(2) 2.084(3) N(2)-Ta(l)-N(l) 111.38(12) N(4)-Ta(2)-P(3) 117.14(9) Ta(l)-N(l) 2.085(3) N(2)-Ta(l)-P(3) 103.18(9) N(3)-Ta(2)-Ta(l) 117.82(8) Ta(l)-P(3) 2.3394(9) N(l)-Ta(l)-P(3) 101.38(8) N(4)-Ta(2)-Ta(l) 114.65(8) Ta(l)-Ta(2) 2.7532(2) N(2)-Ta(l)-Ta(2) 123.93(8) P(3)-Ta(2)-Ta(l) 53.44(2) Ta(l)-P(l) 2.6479(9) N(l)-Ta(l)-Ta(2) 122.93(8) N(3)-Ta(2)-P(2) 78.75(9) Ta(2)-N(3) 2.094(3) P(3)-Ta(l)-Ta(2) 55.60(2) N(4)-Ta(2)-P(2) 77.21(9) Ta(2)-N(4) 2.080(3) N(2)-Ta(l)-P(l) 81.67(9) P(3)-Ta(2)-P(2) 95.33(3) Ta(2)-P(3) 2.4030(9) N(l)-Ta(l)-P(l) 82.56(8) Ta(l)-Ta(2)-P(2) 148.77(2) Ta(2)-P(2) 2.6069(9) P(3)-Ta(l)-P(l) 171.91(3) Ta(2)-P(3)-C(49) 140.41(11) P(3)-C(49) 1.883(3) Ta(2)-Ta(l)-P(l) 116.33(2) Ta(l)-P(3)-C(49) 148.21(11) P(l)-C(13) 1.853(4) N(3)-Ta(2)-N(4) 113.10(12) Ta(2)-P(3)-Ta(l) 70.96(3) P(2)-C(31) 1.849(4) N(3)-Ta(2)-P(3) 126.57(9) E P(3) angles 359.58 The tantalum to [NPN] phosphine bonds have lengthened again to 2.6069(9) A and 2.6479(9) A. The metal-metal bond has also lengthened considerably, from 2.5157(9) A in 42 to 2.7532(2) A in 48. Presumably, eliminating one bridging hydride from the system also removes some of the geometric constraints that gave structure 42 such a short Ta-Ta bond. Hydride were located by two methods: isotropic refinement of diffraction pattern locations and using X-HYDEX. 3 1 Structures 42 and 48 mark the first structurally 143 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes characterized dinuclear tantalum complexes bridged by a single phosphide or phosphinidene. 5.4 Mechanistic implications Addition of primary and secondary phosphines to the tantalum hydrides 35 and 41 clearly demonstrates that these complexes promote chemistry other than dinitrogen activation. The initial premise behind the H-P additions focussed on exploiting the reactivity of a putative metal-metal double bond formed as a reactive intermediate. Chapter 4 proposed that ( R R [NPN]Ta)2(u.-Hh is the active species promoting dinitrogen activation and hydrophosphination. To support this idea, analysis of the mechanism of P-H addition in the synthesis of the tantalum phosphide and phosphinidene complexes was required. Numerous attempts to monitor reactivity of the tantalum tetrahydride complexes by ultraviolet-visible spectroscopy have met with limited success. At the low concentrations necessary to employ UV-Vis spectroscopy, an unknown decomposition reaction occurs, preventing observation of the kinetic parameters of the desired reaction. To investigate the addition of H nPR 3 . n (n = 1, 2) to (CyPh[NPN]Ta)2(u-H)4, isotopic labelling studies were initiated. Toward this goal, the complex (CyPh[NPN]Ta)2(u.-D)4, 50, was prepared by modifying the synthesis of 35 and employing D 2 gas instead of H 2 gas. Spectroscopic characterization of 50 showed little deviation from spectra for the corresponding hydride complex, save for the disappearance of hydride resonances at 5 9.9. As will be seen, reaction pathways can be supported by integration of the hydride region in 'H NMR spectra following reaction of phosphines with 50. Observed hydrides must originate from the primary or secondary phosphines, and the presence or absence of these peaks can indicate whether D 2 , H 2 or HD is lost during the reaction. Two mechanisms are proposed for the addition of dicyclohexylphosphine to 35 or 50 that differ only in the step where H 2 or D 2 is eliminated. In Mechanism A, P-H addition across the Ta-Ta single bond in 50 would give a phosphide-monohydride-tetradeuteride intermediate, as shown in Scheme 5.5. Loss of either D 2 or HD from this species would generate the final product. Statistically, there are ten different eliminations possible, forming two isotopomers; six of these would eliminate D 2 and leave H in the 144 References begin on page 170. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes resultant product. In other words, there is a 60% possibility that D 2 w i l l be lost instead of H D . This analysis assumes that the re-addition of D 2 or H D does not occur. Mechanism B proposes that D 2 loss precedes P-H addition. Loss of D 2 followed by P-H addition generates the final product. Thus, only D 2 would be lost, forming a dideuteride intermediate with a Ta-Ta double bond. P - H addition would give a single isotopomer: the hydride from the phosphine addition would appear in the final product 100% of the time. P-H addition -1* H PCy 2 A I D T a ^ ^ T a t N P N ] D Mechanism A A ox D -[ N P N ] T a t ^ D ^ T a [ N P N ] D Mechanism B [NPN]Ta P-H addition Scheme 5.5 Experimentally, addition of C y 2 P H to a C6D 6 solution of 50 in an N M R tube fitted with a rubber septum allows for monitoring of this reaction by N M R spectroscopy. The observed spectra are similar to those of 43, save for the hydride region. Careful integration of the two hydride resonances supports the formation of a monohydride-dideuteride complex. Relative to a 3 H silylmethyl proton peak, the peak at 5 8.67 integrates to 0.65H and the peak at 8 10.47 integrates to 0.33H, totalling 0.98H. Similar results were observed for the addition of C y P H 2 to 50 (8 8.56, 0.63H; 8 10.35, 0.33H). In 145 References begin on page 170. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes both cases, the hydride from P-H addition is not lost as HD - the transfer is quantitative. The formation of (C y P h[NPN]Ta)2(H)(D) 2(PCy2), 51, supports Mechanism B. Loss of D 2 generates a Ta=Ta double bond which is the reactive intermediate in this hydrophosphination reaction. To employ complexes 35 and 50 to make mechanistic conclusions, the kinetic isotope effect must be ascertained. For the product distributions to be meaningful, they must be dependent not on the nature of the diatomic species lost, but on the mechanism in action. To examine whether an observable kinetic isotope effect is present in the hydrophosphination reactions, the following experiment was devised, as shown in Scheme 5.6: addition of one equivalent of Cy 2 PH to (C y P h[NPN]Ta) 2(p>H) 4, 35, and ( C y P h[NPN]Ta) 2(u-D) 4 , 50, would give two products, ( C y P h[NPN]Ta) 2(u-H) 3(u-PCy 2), 43, and (C y P h[NPN]Ta)2(|i-D) 2(|i-H)(p.-PCy2), 51. This competition experiment will determine if the hydride and deuteride reagents react at different rates, and thus exhibit a measurable kinetic isotope effect. Equimolar amounts of 35 and 50 are added to an NMR tube containing ferrocene as an internal standard, a solution of HPCy 2 in C6D(, is added via syringe through a rubber septum, and the reaction monitored by NMR spectroscopy. The reaction to form 43 and 51 is much faster than any observed exchange reactions. [NPN]Ta-50 35 Fe as internal standard C y 2 C y 2 X 43 51 where: 3 x + y = # of hydrides observed in product(s) and: x + y = 1 Scheme 5.6 146 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Integration of the hydride resonances at 8 8.67 and 8 10.47 against the ferrocene internal standard totals 2.07 H. With simple algebra, one can now solve for the ratio of 43 and 51 produced during the reaction. If x is the amount of 43 that has formed, and y is the amount of 51 formed, then the sum of the hydride integrations must be 3x + y. As only one equivalent of phosphine was added in to the mixture, x + y = 1. Solving for x and y reveals the products formed in 53.5 % and 46.5 % yield respectively. If complexes 35 and 50 reacted at the same rate, a 50/50 ratio of products should be observed. While a minor kinetic isotope effect is observed, the slight difference does not account for the quantitative transfer of hydride to form phosphides in the previous experiment. With confidence, one can now propose that the formation of tantalum phosphides proceeds through a dideuteride complex, as shown in Mechanism B. Generation of phosphinidene tantalum complexes presents another mechanistic question. For the addition of a primary phosphine to 50, the first step can be assumed to proceed analogously to Mechanism B, again presuming readdition of H 2 , HD or D 2 does not occur. From this monohydride-dideuteride tantalum complex, there are again two possible pathways to tantalum phosphinidenes. The addition of the remaining P-H bond across the latent Ta-Ta single bond would form an intermediate complex with two hydrides, two deuterides and a bridging phosphinidene. Elimination of H 2 , HD or D 2 from this complex would generate the observed tantalum phosphinidene. This potential mechanism is shown in Scheme 5.7 as Mechanism C. In this case, the potential elimination of H 2 (16.7%), HD (66.7%), and D 2 (16.7%) would generate three isotopomers. On average, one hydride would remain in the final product. If Mechanism C is in action, a monohydride-monodeuteride isotopic composition, ( R R [NPN]Ta)2(p-H)(p-D)(p-PCy), would be observed. Alternatively, 1,2-H2 elimination could happen prior to P-H addition, as shown by Mechanism D in Scheme 5.7. The P-H bond and a tantalum hydride or deuteride could eliminate in a concerted fashion to give the observed product. In this case, only loss of H 2 or HD is possible and would lead to the formation of two isotopomers with an average isotopic composition of 0.67 H and 1.33 D. Integration of the hydride region would show 0.67 H if Mechanism D was operating. This mechanism has some support in the literature: A 1,2-H2-elimination has been proposed for the decomposition of (silox)3TaH(PHPh) to (silox)3Ta=PPh.zu In this case, only 1,2-H2-elimination could 147 References begin on page 170. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes occur, as the Ta(V) complex cannot be further oxidized. This would preclude the P-H oxidative addition step proposed in Mechanism C. cy P-H addition [NPN]Ta^C lj|j^Ta[NPN] v 5 J Mechanism C red. elimin. of HH, 2x HD, 2x HD, or D 2 H Cy A 0.67 ?y 0.17 ?y 0.17 ^y / \ A / \ [NPN]Ta- Ta[NPN][NPN]Ta- Ja[NPN] [NPN]Ta- Ja[NPN] \oy \ n f D D H [ N P N F a < ^ p ^ T a [ N P N ] Mechanism D 1,2 elimin. of HH, HD or HD 0.33 f 0.67 f [NPN]Ta£ - J a [NPN][NPN]Ta^ ^.Ja [NPN] D D Scheme 5.7 Experimentally, addition of CyPH 2 to 50 is analogous to the previous isotopic labelling studies. In this case, the spectrum shows only one peak in the hydride region at 5 10.87 that integrates to 0.65 H relative to 3 silylmethyl protons. The product formed in this reaction is a mixture of two isotopomers with an average composition of (CyPh[NPN]Ta)2(p-H)o.67(p-D),.33(M--PCy), 52. Similarity, addition of CyPH 2 to 50 supports these results (5 10.47, 0.69H). If the product contains only two-thirds of a hydride on average, Mechanism D may be operating, presuming a negligible kinetic isotope effect. The concerted 1,2-H2 elimination from Ta-H and P-H bonds generates the phosphinidene complex. 148 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes 5.5 Attempts to trap (RR'[NPN]Ta)2Ca-H)2 Isotopic labeling studies support the presence of the ( R R [NPN]Ta)2(u-H)2 intermediate, as first presented in Chapter 4. This species holds the reducing power to promote dinitrogen activation and hydrophosphination. While the isotopic labelling studies have provided support for this dihydride complex, no direct observation of such an intermediate has been made by low temperature NMR spectroscopy of 35 and 41. One way to directly observe the proposed Ta=Ta double bond would be to 'trap' this species with an appropriate donor. Addition of tertiary phosphines to solutions of 35 or 41 could form a dinuclear tantalum dihydride with a metal-metal double bond supported by two tertiary phosphines, as in Figure 5.5, a complex isoelectronic to (ChCPMes^Ta^d-i-H^.1 Ph* Ph Me 2 Figure 5.5. Trapping the putative dihydride with tertiary phosphines 31 Addition of PPlv? to either 35 or 41 produced no observable reaction. P NMR in situ experiments showed only free triphenylphosphine and unreacted 35 or 41. Heating reactions to 80 °C did not yield the desired complex, rather R P h[NPN]H2 was formed. Similar results were found with the addition of other bulky tertiary phosphines PBul3 and PPr'3 - only free phosphine was observed. The characteristic deep purple color for solutions of 35 and 41 remained unchanged. Addition of an excess of a sterically unencumbered phosphine to 35, however, produced a different result. Addition of 8 equiv. of PMe3 to a toluene solution of 35 produced no immediate colour change. However, cooling this solution to < -78 °C resulted in the solution turning from deep purple to a deep green colour. Upon warming the solution, the color reverted back to purple. The color of the solution could be cycled simply by adjusting the temperature. Ph Ph 149 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Solution N M R spectroscopy of the green compound (^-toluene, -80 °C) were inconclusive. Broad resonances at 8 -30 and 18 in the P{ H} N M R spectrum, integrated against an external standard to be 2P each, lent support for the presence of a bis(trimethylphosphine) adduct of an [NPN] supported binuclear tantalum complex. 1 T 1 t t Analysis of H{ P} spectra indicated a new broad resonance at 8 8.5, integrating to 2 H against S iMe resonances; this peak can be tentatively assigned to the two bridging hydrides supporting the Ta=Ta double bond. Strong resonances for 35 and free PMe3 at 8 29 and -62, respectively, were also present, with the resonance at 8 29 significantly broadened. Attempts to collect spectra at lower temperatures led to solvent freezing and tube breakage. Under the assumption that these two species are in equilibrium, efforts to extract equilibrium constants and thermodynamic data by variable temperature N M R spectroscopy were complicated by decomposition. It can be surmised, however, that K is extremely small at room temperature, and that the forward reaction is endothermic, as low temperatures and large excesses of trimethylphosphine are required to shift the equilibrium concentrations to the products. This proposed equilibrium is shown in Equation 5:4. K [Ta2H4][PMe3]2 A s ( C y P h [NPN]Ta) 2 ((a-H)2(PMe 3)2, 53, is in equilibrium with 35, as shown in Equation 5.4, it was expected that 53 could be isolated by driving the equilibrium to the right by removal of H2. Repeated evacuation of the flask containing 35 and excess P M e 3 did not lead to the isolation of complex 53. Instead, a new chemical transformation was promoted. Upon removal of H2, the solution turned from deep purple to red. Workup of the reaction mixture gave a red solid analyzed by ' H , 3 1 P , ' H / 3 1 ? H S Q C and ' r l / H C O S Y N M R experiments. Three resonances are observed in the 3 1 P { ' H } N M R spectrum; a doublet at 8 -20.2 (P A , 1 P), a singlet at 8 10.5 (P B , 1 P), and a doublet at 8 13.8 ( P c , 1 P). 150 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes The peaks for P A and Pc are assigned to phosphines attached cis to the same Ta centre as they exhibit moderately weak coupling ( Jpp = 18.8 Hz) . Observed coupling constants between [NPN] phosphines trans to one another in Ta-Ta bonded complexes are rare, but can be of the same order of magnitude ( 3 Jpp ~ 10-20 Hz) . In the *H N M R spectrum, resonances assigned to eight S i M e environments overlap with a large resonance (9 H) coupling strongly to PA, as observed in ' H / ^ P H S Q C experiments. With the coupling patterns observed along with *H and 3 1 P chemical shifts, PA is l ikely a coordinated P M e 3 group. Resonances for the cyclohexyl phosphine and methylenes couple to PB and Pc in the ' H / 3 1 P H S Q C spectrum, meaning P B and Pc arise from the [NPN] ancillary ligands. PA, PB and Pc also exhibit coupling to hydridic resonances; PA couples to H A at 8 5.06, PB couples to H B at 8 8.15, and Pc couples to He at 8 11.24. If it is assumed that the three peaks are all tantalum hydrides, the chemical shift of H A indicates it is likely bound terminal. H B and He can be assigned with less certainty, but are most likely bridging hydrides. The presence of three hydridic resonances was initially confusing: the target complex contained only two hydrides, and the desired product had high symmetry. ' H / ' H C O S Y experiments reveal a potential source for the third resonance: four resonances in the aromatic region exhibit the characteristic splitting pattern of orthometalation. Decomposition of complex 53 via orthometalation of one N - P h ring to give new tantalum carbon and tantalum hydride bonds would give a complex in agreement with observed N M R data. The evidence from I D and 2D N M R experiments supports the assignment as c y p h [NPN]Ta( |q-Id) 2 ( f x-N(C 6 H4 )Ta[PN](H)(PMe3X 54. This transformation is shown in Equation 5.5. 151 References begin on page 170. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Red crystals of 54 were grown from slow evaporation of concentrated benzene solutions and were studied by X-ray crystallography. An O R T E P 3 0 depiction of the solid state molecular structure of 54 is shown in Figure 5.6. The structure shows two C y P h [NPN] ligands and a single PMe3 group. An N-Ph ring has indeed undergone C-H activation. Figure 5.6. ORTEP drawing (spheroids at 50% probability) of 54. Silyl methyl, phenyl and cyclohexyl ring carbons other than ipso and methine carbons have been omitted for clarity. 152 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Relevant bond lengths and angles are listed in Table 5.6 and crystallographic data are located in Table 5.7. The Tal-C48 distance of 2.199(4) A is well within the lengths of typical Ta-C bonds. The amido donor attached to this ring appears to be bridging the two tantalum centres. Amido donors N I , N2, and N3 are planar; the sum of angles around each are 359.82°, 359.78° and 359.99° respectively. Conversely, N4 is tripodal. The sum of angles Ta2-N4-Si4, C43-N4-S14, and C43-N4-Ta2 are 326.3°; the amido lone pair is not n-donating to Ta2, but rather facing Tal . While the Ta2-N4 distance of 2.235(3) A is shorter than the Tal-N4 distance of 2.410(3) A , the orientation and distance still supports a bridging amide. Unfortunately, the bridging hydrides could not be found in the 31 • diffraction pattern. Their presence was confirmed with X - H Y D E X . The terminal hydride was located in the diffraction pattern and refined isotropically. HI is located on the same Ta centre as the PMe3 group, between N4, P3 and P2 donors. Electron counting would indicate that complex 54 is a Ta(IV)-Ta(IV) dimer supported by a Ta-Ta single bond. The Tal-Ta2 interatomic distance of 2.6778(3) A agrees with this conclusion. Co-crystallized benzene (1.5 molecules per asymmetric unit) was also refined. The solvent is readily removed from bulk crystalline samples in vacuo, although this results in loss of crystallinity. Table 5.6 Selected Bond Distances (A) and Angles (°) for 54. Lengths Angles Angles Ta(2)-N(3) 2.145(3) N(3)-Ta(2)-N(4) 126.15(12) Ta(l)-N(l)-C(19) 115.6(3) Ta(2)-N(4) 2.235(3) N(3)-Ta(2)-P(2) 79.58(9) Ta(l)-N(l)-Si(l) 129.12(19) Ta(2)-P(2) 2.5796(9) N(4)-Ta(2)-P(2) 82.00(8) C(19)-N(l)-Si(l) 115.1(3) Ta(2)-P(3) 2.5919(9) N(3)-Ta(2)-P(3) 93.67(9) Ta(l)-N(2)-C(13) 126.0(3) Ta(2)-Ta(l) 2.6778(3) N(4)-Ta(2)-P(3) 139.79(9) Ta(l)-N(2)-Sl(2) 122.18(19) Ta(l)-N(2) 2.070(3) P(2)-Ta(2)-P(3) 102.49(4) C(13)-N(2)-Si(2) 111.6(3) Ta(l)-N(l) 2.169(3) N(2)-Ta(l)-N(l) 102.07(13) Ta(2)-N(3)-C(31) 123.7(3) Ta(l)-C(48) 2.199(4) N(2)-Ta(l)-N(4) 163.43(12) Ta(2)-N(3)-Si(3) 127.19(18) Ta(l)-N(4) 2.410(3) N(l)-Ta(l)-N(4) 93.77(12) C(31)-N(3)-Si(3) 109.1(3) Ta(l)-P(l) 2.6318(9) N(2)-Ta(l)-P(l) 85.35(10) Ta(2)-N(4)-C(43) 89.2(2) N(l)-Ta(l)-P(l) 78.30(10) Ta(2)-N(4)-Si(4) 115.10(16) N(4)-Ta(l)-P(l) 93.22(8) C(43)-N(4)-Si(4) 122.0(3) 153 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Table 5.7 Crystallographic Data and details of refinement for 54. Empirical formula C6oH92N4Si4P3Ta2 Crystal system Triclinic Formula weight 1436.55 Space group P-1 a, b, c (A) 11.2799(2), 13.4464(4), 22.9421(7) a,f3,ri°) 81.286(4), 77.613(4), 73.064(4) V , A 3 3236.53(48) Total reflections 25544 z 2 Unique reflections 18249 D c a i c , g cm"3 1.37 Parameters 673 ( i (Mo Ka), cm"1 3.559 R , a 0.0330 T, K 173 ± 1 R w a 0.0705 26 range (°) 55.76 Goodness-of-fit 1.134 R, = ZHFol - \FcWZ.\F„\; *w = 2>(|F02| - |FC 2|)2/2>|F0 2|2) This o-metalated product, 54, can be generated directly from L y r a[NPN]TaMe3. Hydrogenation of the trimethyl complex in the presence of PMe3 yields 54 as the sole product. This contrasts with the hydrogenation of ph[P2N2]TaMe3 in the presence of PMe3, which forms ph[P2N2]Ta(H)3(PMe3), as shown in Equation 5.6.34 Me 2 M e 2 While the formation of 54 needed to be encouraged by the removal of H2 in vacuo, the same transformation of (phph[NPN]Ta)2(u-H)4, 41, with PMe3 proved more facile. Addition of just one equiv. of PMe3 to an ethereal solution of 41 promoted an instantaneous colour change from purple to red. Analysis of the product showed it was similar to the o-metalated complex 54. 3 1P{'H} NMR spectra showed three resonances at 8 -18.25 (d), 6.18 (s), and 10.87 (d) respectively. As in 54, three hydride resonances were observed (8 11.46, 8.41 and 5.29). Integration of the peaks between 8 -0.5 and 0.8 indicated eight silylmethyl resonances and one coordinated PMe3. 2D NMR experiments clearly indicated orthometalation of a ligand phenyl ring, but it was uncertain whether the N-Ph or P-Ph ring had undergone C-H activation. 154 References begin on page 170. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes With difficulty, X-ray quality crystals were grown from the slow evaporation of benzene from a solution of the crude product. Analysis of these crystals by X-ray crystallography confirmed the formation of an analogous C - H activated product to 54, P h P h [NPN]Ta(p-H) 2 (p-N(C 6 H 4 )Ta[PN](H)(PiVle 3 ) , 55. As with 54, co-crystallized benzene (0.5 equiv. per asymmetric unit) is present in the lattice. An O R T E P ' 0 depiction of the solid state molecular structure of 55 is shown in Figure 5.7. Figure 5.7. O R T E P drawing (spheroids at 50% probability) of 55. Silyl methyl and phenyl ring carbons other than ipso carbons have been omitted for clarity. Relevant bond lengths and angles are listed in Table 5.8 and crystallographic data are located in Table 5.9. The structures of 54 and 55 are quite similar. The Ta(l)-C(45) distance in 55 is 2.167(11) A and the Ta(l)-Ta(2) distance is 2.6689(5) A , both differing only slightly from previously observed bond lengths. The Ta(l)-N(3) and Ta(2)-N(3) distances of 2.353(8) A and 2.223(7) A , respectively, indicate a more symmetrical bridging by the amido ligand. This is again supported by the planarity of N(l) , N(2) and N(3) in comparison to N(4); the sum of angles around N(4) are 326.2 °. Unfortunately, 155 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes none of the hydrides were located within the diffraction pattern. Three hydrides were located in the diffraction pattern by X-HYDEX, 3 1 one terminally bound to Ta(2) and two bridging the tantalum centres. Table 5.8 Selected Bond Distances (A) and Angles (°) for 55. Lengths Angles Angles Ta(2)-N(3) 2.140(8) N(3)-Ta(2)-N(4) 126.4(3) Ta(l)-N(l)-C(22) 117.9(6) Ta(2)-N(4) 2.223(7) N(3)-Ta(2)-P(2) 80.1(2) Ta(l)-N(l)-Si(l) 128.3(4) Ta(2)-P(2) 2.570(3) N(4)-Ta(2)-P(2) 81.8(2) C(22)-N(l)-Si(l) 113.6(7) Ta(2)-P(3) 2.593(2) N(3)-Ta(2)-P(3) 92.0(2) Ta(l)-N(2)-C(16) 123.0(5) Ta(2)-Ta(l) 2.6689(5) N(4)-Ta(2)-P(3) 140.8(2) Ta(l)-N(2)-Si(2) 124.8(4) Ta(l)-N(2) 2.079(8) P(2)-Ta(2)-P(3) 99.94(8) C(16)-N(2)-Si(2) 112.1(6) Ta(l)-N(l) 2.145(8) N(2)-Ta(l)-N(l) 103.7(3) Ta(2)-N(3)-C(34) 122.6(9) Ta(l)-C(45) 2.167(11) N(2)-Ta(l)-N(l) 103.7(3) Ta(2)-N(3)-Si(3) 127.5(5) Ta(l)-N(4) 2.353(8) N(2)-Ta(l)-N(4) 156.2(3) C(34)-N(3)-Si(3) 109.9(6) Ta(l)-P(l) 2.618(2) N(l)-Ta(l)-N(4) 97.3(3) Ta(2)-N(4)-C(40) 88.4(5) N(2)-Ta(l)-P(l) 84.0(2) Ta(2)-N(4)-Si(4) 117.1(4) N(l)-Ta(l)-P(l) 79.5(2) C(40)-N(4)-Si(4) 120.0(7) N(4)-Ta(l)-P(l) 88.98(17) Ta(2)-N(4)-Ta(l) 71.3(2) Table 5.9 Crystallographic Data and details of refinement for 55. Empirical formula C 54H 7 2N 4P3Si4Ta 2 Crystal system Monoclinic Formula weight 1345.43 Space group P2i/n a, b,c(A);/3(°) 11.1558(8), 23.4870(16), 22.5891(17); 84.011(4) V , A 3 5886.4(7) Total reflections 19536 Z 4 Unique reflections 11663 D c a i c , g C m " 3 1.517 Parameters 615 \i (Mo Ka), cm"1 3.915 V 0.0554 T, K 173 ± 1 R w a 0.0963 26 range (°) 60.04 Goodness-of-fit 1.038 "R, = H\\F0\ -. |F C | | /S |F 0 |; R„ = 2>(|F 0 2| - |F C 2 | ) 2 /2>|F 0 2 | 2 ) Orthometalation of an N-Ph ring is much easier with 41, a complex with an inferior P rj-donor, than with 35. The proclivity for this reaction to occur is lower when cyclohexylphosphine substituted ligands stabilize the reactive intermediates. Attempts to characterize decomposition products in the absence of PMe3 have been unsuccessful. 156 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Removal of H 2 from dilute solutions of 35 and 41 prompted a purple to brown color change, but analysis of this crude material indicated an uncontrolled decomposition. This observation helps to explain previous observations in the synthesis of (phPh[NPN]Ta)2(p.-H)2(p--r|1:ri2-N2). The yields and purity of this dinitrogen complex dramatically improved when nitrogenation is conducted under a 90/10 N2/H2 mixture instead of an entirely N2 atmosphere. The activation of N2 by 41 is a slow reaction, and is hindered further by the low solubility of molecular nitrogen in diethyl ether or toluene. The presence of H 2 in the system kinetically stabilizes the dihydride species, swinging the equilibrium towards the relatively stable tetrahydride complex 41. With the concentration of Ta=Ta bonds low, the metal complex would be the limiting reagent. The poor solubility of N2 in the reaction solvent is marginalized, and the decomposition reaction is minimized. Also of note, complexes 54 and 55 both contain [NPN] ligands with bridging amide ligands. In Chapter 3, bridging amides were suggested as intermediates in the decomposition of vanadium and niobium [NPN] complexes to form V(IV) and Nb(V) imides. This finding provides some credence to this proposal. 5.6 The activation of other E-H bonds The success of the addition of phosphines to 35 and 41 led directly into the investigation of other E-H addition reactions. The oxidative addition of N-H and S-H bonds is a common route to amide and sulfide complexes of transition metals. For example, the unsaturated tricarbonyl tungsten complex [W2Cp2(u.-CO)(CO)2(u-dppm)][BArf4] (Ar f = 3,5-(CF3)2C6H3) which adds P-H bonds to give bridging phosphides, also adds thiols to give a thiolate-bridged complex.10 Addition of primary and secondary amines or thiols to 35 or 41 does not produce complexes with bridging sulfides, amides or imides, but only RPh[NPN]H2, as shown in Equation 5.7. The extreme reactivity of the tetrahydride complex limits control over these reactions. Addition reactions of primary and secondary phosphines to form phosphides and phosphinidenes are extremely rapid, and the products formed relatively stable. The kinetic lability of the dihydride intermediate was not detrimental to the reaction outcomes in P-H additions, but has proved problematic for the investigation of other E-H additions. 157 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Ph Ph \ 3 - N v x H , P <T\ M e 2 S r ; N ^ , _ ^ H ^ _ / \V R -p. Me 2 Si Ta? M 6 2 S i \ b P / ^ \ T a . „ / N ^ V S i M e 2 E-H \ / S i M e 2 \ H N T ^ Ph Ph .SiMe? NH HN 5.7 E = RS, R 2 N , RHN; R = Ph, Cy, Me, 'Bu, jPr As with amines and thiols, the addition of B-H bonds to 35 or 41 is uncontrolled. The addition of 9-BBN (9-borabicyclo-[3:3:l]-nonane) to 35 produces no fewer than 15 products, as observed by 3 I P NMR spectroscopy. Whereas boranes react with tantalum dinitrogen complexes over weeks to give a series of products,42 the reaction of 9-BBN with 35 is immediate. Attempts to impose thermodynamic control were unsuccessful. Reactions were complete in less than 30 seconds, even at -78 °C. Activation of polar N-H, S-H and B-H bonds is difficult because they are more reactive towards addition than their P-H congeners. Moving to increasingly inert substrates may give isolable products. The addition of silanes to metal-metal bonded systems is appealing, offering the potential to access metal-silane, metal-silylene, and metal-silylyne complexes. Carbon readily forms multiple bonds to many other elements, including transition metals, while silicon is reluctant to participate in multiple bonding.43 Thus, the isolation of doubly and triply bonded silylene and silylyne complexes is still quite rare 4 4 Silylene complexes can be prepared by the abstraction of a group bound to silicon, as in Equation 5.8, or the activation of two Si-H bonds of a silane by first oxidative addition and subsequent a-hydrogen elimination, as in Equation 5.9. It is proposed that addition of silanes to 35 or 41 could access bridging silylenes via double Si-H activation. - X " L n M S i R 2 X ^SiR, L n M R H 2 S i R 2 - RH L n M - S i R 2 H :S iR, H 5.8 5.9 7, 8 The precedent for such a reaction has already been presented in this chapter. The complex (Cp*Fe)2(u.-H)4, activates both P-H and Si-H bonds. The addition of Ph2SiH 2 gives a bridging silylene complex, whereas the addition of lBu2SiH2 gives a bridging silane complex with two agostic Fe-Si-H interactions, as shown previously in 15 g References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Scheme 5.3. S i - H activation can also generate metal-silylynes. Reduction of Cp*(dmpe)(H)Mo=Si(Cl)Mes with L i B ( C 6 F 5 ) 4 gives the complex [Cp*(dmpe)Mo(n 2-HSiMes)][B(C6F 5) 4], with a strong M o - H - S i agostic interaction that imparts considerable silylyne character. 4 4 Agostic N b - S i - H 4 5 " 4 7 and T a - S i - H 4 7 ' 4 8 interactions have been previously observed, as shown in Scheme 5.7. [Cp*(DippN=)TaCl] 2 (p-H) 2 (Dipp = 2 ,6- 'Pr 2 C 6 H 3 ) reacts with ( T H F ) 3 L i S i ( S i M e 3 ) 3 to generate Cp*(DippN=)Ta(H)(Si(SiMe 3 ) 3 ) . This complex is Lewis acidic and reversibly binds halide ions to afford anionic Ta(V) complexes with weak three-centred Ta-Si -H interactions 4 9 Similarity, the addition of H S i C l M e 2 to Cp(DippN=)Ta(PMe 3 ) 2 affords the complex Cp(DippN=)Ta(PMe 3 )(n 2 -H S i M e 2 C l ) . 5 0 Scheme 5.7 159 References begin on page 170. Chapter Five: Addition of phosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes As was hoped, the activation of primary silanes by the tantalum tetrahydride system gives cleaner product distributions. Monitoring the addition of PhSiH3 to 35 by 3 1P{'H} confirms the formation of a single asymmetric product evidenced by singlets at 8 22.5 and 26.6. This bright green compound also has two resonances at 11.93 (2H) and 9.73 (1H) are present in the 'H{ 3 IP} NMR spectrum, each coupling to both ligand phosphines. It is proposed that the complex (CyPh[NPN]Ta)2(p.-H)2(|Li-r|2-HSiPh), 56, has formed, as shown in Equation 5.10. The two protons at 8 11.93 are assigned to bridging hydrides. These hydrides couple to the inequivalent ligand phosphines, giving rise to a doublet of doublets. The peak at 8 9.73 is assigned to a Si-H-M agostic bonding interaction. This resonance couples to naturally abundant 2 9 Si in the sample (Jsm - 160 Hz), showing a pair of of J s i H coupling constants to probe non-classical H-Si interactions has recently been questioned.48 Three resonances at 8 8.8, 14.2 and 140 appear in the 2 9 Si NMR spectra. The peak at 8 140 is extremely broad and poorly resolved from the baseline, although it is tentatively assigned as a bridging silylene. This chemical shift region is common for transition metal silylene resonances. Isotopic labeling studies also support this assignment. Addition of PhSiH3 to the tetradeuteride 50 shows no incorporation of deuterium into the resonance at 8 9.73. The resonance at 8 11.9 is now a complicated multiplet, integrating to 8 0.65. Scheme 5.8 shows that D 2 loss followed by 1,2-H2 elimination would generate a series of isotopomers that supports this assignment. Ph Ph Cy S iMe 2 5.10 satellites flanking the main resonance. While this suggests an r)2-H-Si interaction, the use 160 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Scheme 5.! A product of similar composition is observed with the addition of "BuSiH3 to 35. Resonances at 8 26.71 and 24.67 in the 3 1 P { ' H } N M R spectra, coupled with a hydridic resonance at 8 11.78 in the H{ P} N M R spectra support the assignment of ( C y P h [NPN]Ta) 2 ( |a-H) 2 (p . - r i 2 -HSi n Bu), 57. Observation of a second doublet of doublets at 8 8.89, with 2 9 S i satellites, suggests a similar agostic S i - H - M interaction. Mass spectral and elemental analysis data support the assignment of complexes 56 and 57, but these techniques do not help to assign the structure of the complex. Confirming these assignments without the support of structural data is tenuous. Extensive efforts towards growing crystals of high quality have been unsuccessful to this point, and this remains an unfinished story. 161 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes 5.7 Summary Reactions of primary and secondary phosphines with [NPN] supported tantalum tetrahydride complexes readily accesses bridging phosphido and phosphinidene compounds. The mechanisms of these transformations were studied using isotopic labelling. The conversion of tantalum hydrides to phosphides proceeds first through a Ta=Ta intermediate formed by the reductive elimination of H2, followed by oxidative addition of a P - H bond across the metal-metal double bond. Phosphinidene complexes are generated by a 1,2-H2-elimination following formation of the phosphide-trihydride intermediate. Attempts to trap the proposed intermediate with tertiary phosphines promoted a new transformation. C - H activation of N - P h rings o f [NPN] supporting ligands was promoted, forming new Ta-C and terminal Ta -H bonds supported by a bridging amide ligand. Investigations of the C - H activation of external substrates are continuing. The activation of more reactive N - H , S-H, and B - H bonds promotes complex decomposition, including ligand protonolysis. S i - H activation is more controlled, giving bridging silylene complexes. The confirmation of the structures of these complexes must await formation of suitable crystals for X-ray analysis. 5.8 Experimental section 5.8.1 General considerations Unless otherwise stated, general procedures were performed as in Section 2.4.1. Selected complexes in this chapter do not have acceptable elemental analysis data, likely due to problems with sample handling and the high air-sensitivity and nitrogen-sensitivity of these complexes, despite numerous attempts at obtaining this data. 5.8.2 Starting materials and reagents The compounds H2PPI1 5 1 and H 2 P A d 5 2 ' 5 3 were prepared by literature procedures. H2PAd for test reactions was generously donated by M r . Vince Wright and Dr. Derek Gates. H2PCy, H P C y 2 and HPPh2 were purchased from S T R E M and distilled under N2 162 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes prior to use. Tertiary phosphines P P h 3 , P'Pr 3 , P C y 3 and P M e 3 were purchased from Aldr ich and purified by standard procedures prior to use. Primary and secondary amines CyNH.2, j P r N H 2 , l B u N H 2 , P h N H 2 , P h 2 N H , T ^ N H and M e 2 N H were purchased from Aldr ich and distilled under nitrogen prior to use. Thiols P h S H , C y S H and l B u S H were purchased from S T R E M and distilled under nitrogen prior to use. 9-borabicyclo[3.3.1]nonane was purchased as a 1.0 M hexanes solution from Aldr ich and used as received. Primary silanes H 3 S i P h and H 3 S i n B u were prepared by literature methods. 5 4 5.8.3 Synthesis Preparation of ( P h p h [NPN]Ta) 2 (p -H) 3 (p -PCy 2 ) , 42 The following procedure is representative of the synthesis of compounds 42-45. A solution of ( P h P h [NPN]Ta ) 2 (p -H) 4 (500 mg, 0.405 mmol) in 20 m L E t 2 0 under A r was prepared in a vessel equipped with a Kontes valve. Dicyclohexylphosphine (80.3 mg, 0.405 mmol) was added to the flask via microsyringe, the vessel sealed and its contents stirred for thirty minutes. A colour change from deep purple to red was observed, along with the evolution o f a gas. Removal o f solvent in vacuo left a red, oi ly solid. This solid was triturated with pentane and dried under vacuum to afford ( P h P h [NPN]Ta) 2 (p -H) 3 (p -P C y 2 ) as a red powder in 95% yield (551 mg). Crystals of 42 suitable for X-ray diffraction were grown from slow evaporation of a concentrated solution of 42 in layered benzene/HMDS. *H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8 -0.21 (s, 3H , SiCrY 3 ) , -0.02 (s, 3H, S iC / f 3 ) , 0.07 (s, 3 H , S i C / / 3 ) , 0.17 (s, 3H , S i C / / 3 ) , 0.23 (s, 3 H , S i C / / 3 ) , 0.31 (s, 3H , SiC# 3 ) , 0.88-2.65 (m, 30H, C6HU, P C / / 2 S i ) , 6.65-7.62 (m, 30H, N P h , PPh), 8.67 (m, 2H, TaflTa), 10.47 (m, 1H, Ta#Ta). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 10.47 (d, 2 J P P = 12 Hz) 10.53 (d, 2 J P P = 83 Hz) , 164.38 (d of d, V P P = 12 H z , 83 Hz) . Ana l . Calcd for C 6 oH 8 7N4P 3 Si 4 Ta 2 : C , 50.34; H , 6.13; N , 3.91. Found: C, 50.09; H , 6.20; N , 4.34. 163 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes Preparation of ( C y P h [NPN]Ta) 2 (p -H) 3 (p -PCy 2 ) , 43 This reaction was conducted analogously to the synthesis of 42. ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 (500 mg, 0.401 mmol) and dicyclohexylphosphine (79.49 mg, 0.401 mmol) were employed to afford ( C y P h [NPN]Ta) 2 (p -H) 3 (p -PCy 2 ) in 84% yield (486 mg). ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 -0.02 (s, 3H , S i C / / 3 ) , 0.05 (s, 6 H , S i C / / 3 ) , 0.15 (s, 6H , S i C / / 3 ) , 0.26 (s, 3H, S iC# 3 ) , 0.70-2.38 (m, 52H, 4 C 6//n, 4 PCr7 2 Si) , 6.90-7.50 (m, 20H, NPh), 8.56 (m, 2H, TaOTa), 10.35 (m, 1H, T a M a ) . 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 16.28 (d, 2 J Pp = 4 Hz) , 18.66 (d, 2 J P P = 86 Hz), 149.02 (d of d, V P P = 4 Hz , 86 Hz). Anal . Calcd for C 6oH99N 4P 3Si4Ta 2: C , 49.92; H , 6.91; N , 3.88. Found: C , 49.81; H , 6.67; N , 4.24. Preparation of ( p h P h [NPN]Ta) 2 (p-H) 3 (p-PPh 2 ) , 44 This reaction was conducted analogously to the synthesis of 42. ( P h P h [ N P N ] T a ) 2 ( p - H ) 4 (500 mg, 0.405 mmol) and diphenylphosphine (75.41 mg, 0.405 mmol) were employed to afford ( p h p h [NPN]Ta) 2 (p -H) 3 (p -PPh 2 ) in 94% yield (542 mg). *H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 -0.12 (s, 3 H , S i C / / 3 ) , -0.08 (s, 3H , S i C / / 3 ) , 0.01 (s, 9 H , SiCr7 3 ) , 0.28 (s, 9H, S iC# 3 ) , 0.34 (s, 3H, SiC7/ 3 ) , 0.37 (s, 3H, SiCtf 3 ) , 1.13-1.45 (m, 8H, P C / ^ S i ) , 6.48, 6.60, 6.85, 6.96, 7.10, 7.38, 7.68, 7.75, 7.80 (m, 40H, N P h , PPh, PPh 2 ) 9.31 (m, 2 H , TaflTa), 10.46 (br, 1H, Tai/Ta). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 13.10 (d, 2 J P P = 87 Hz), 14.05 (d, 2 J P p = 12 Hz) , 136.27 (d o f d, V P P = 12 H z , 87 Hz) . Preparation of ( C y P h [NPN]Ta) 2 (p -H) 3 (p -PPh 2 ) , 45 This reaction was conducted analogously to the synthesis o f 42. ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 (500. mg, 0.401 mmol) and diphenylphosphine (74.6 mg, 0.401 mmol) were employed to afford ( C y P h [NPN]Ta) 2 (p -H) 3 (p -PPh 2 ) in 96% yield (554 mg). ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8 0.08 (s, 9H , SiCrY 3 ) , 0.15 (s, 3H, SiCrY 3 ) , 0.21 (s, 6H , SiCr7 3 ), 0.34 (s, 3H, SiC/7 3 ) , 0.70-1.80 (m, 30H, C6HU, P C / / 2 S i ) , 6.80, 7.00, 7.05, 7.18, 7.35, 7.52 (m, 30H, N P h , PPh), 9.15 (m, 2 H , Tai/Ta), 10.20 (s, 1H, Ta/ZTa). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 164 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes 202.5 M H z ) : 6 19.38 (d, V P P = 2 Hz), 21.41 (d, 2JPP = 89 Hz) , 115.39 (d of d, 2J?P = 2 Hz , 89 Hz) . Anal . Calcd for C 6 o H 8 7 N 4 P 3 S i 4 T a 2 : C , 50.34; H , 6.13; N , 3.91. Found: C , 50.00; H , 5.95; N , 4.24. Preparation of ( P h p h [NPN]Ta) 2 (u -H) 2 (u -PCy) , 46 The following procedure is representative o f the synthesis o f compounds 46-49. Cyclohexylphosphine (47.01 mg, 0.405 mmol) was added under A r via microsyringe to a solution of ( p h P h [ N P N ] T a ) 2 ( u - H ) 4 (500.0 mg, 0.405 mmol) in 20 m L E t 2 0 prepared in a vessel equipped with a Kontes valve. A n immediate color change from purple to red was observed along with concomitant gas evolution. The solution was stirred for another 30 minutes to ensure complete reaction, and the solvent was removed. The resulting red solid was dissolved in pentane and then dried under vacuum to afford ( P h P h [NPN]Ta) 2 (u.-H) 2 (u-PCy) (89%, 487 mg). : H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 -0.08 (s, 6H , SiCr7 3), 0.15 (s, 6H, S iC# 3 ) , 0.20 (s, 6H , S i C / / 3 ) , 0.22 (s, 6H , S i C / / 3 ) , 0.96-1.70 (m, 19H, C6Hn, PC/ f 2 Si ) , 6.82, 6.89, 7.05, 7.19, 7.25, 7.32, 7.51, 7.67 (m, 30H, N P h , PPh), 10.87 (m, 2H, TaflTa). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 10.74 (d, 2JPP = 152 Hz) , 15.01 (d, 2 J P P = 17 Hz) , 449.0 (d of d, 2JPP = 17 Hz , 152 Hz). Preparation of ( C y P h [NPN]Ta) 2 (p.-H) 2 (p.-PCy), 47 This reaction was conducted analogously to the synthesis of 46. Cyclohexylphosphine (46.6 mg, 0.401 mmol) and ( C y P h [NPN]Ta) 2 (u -H) 4 (500 mg, 0.401 mmol) were employed to afford ( C y P h [NPN]Ta) 2 (u -H) 2 (u -PCy) (93%, 508 mg). Lorentzian deconvolution was performed on the resonance at 8 10.47 using the mathematical alogarithms found in the W I N N M R software package. ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8-0.18 (s, 6H , S iCf / 3 ) , 0.22 (s, 12H, S i C / / 3 ) , 0.23 (s, 6H , S i C / / 3 ) , 0.65-1.95 (m, 30H, C6HU, P C / / 2 S i ) , 6.85 (m, 2H, NPh), 7.14 (m, 4 H , NPh) , 7.30 (m, 4H, NPh) , 10.47 (m, 2 H , TaftTa). 3 1 P { [ H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 16.58 (d, V P P = 154 Hz) , 22.09 (d, 2JPP = 18 Hz) , 436.38 (d of d, 2JPP = 18 H z , 154 Hz) . Anal . Calcd for C 5 4 H 8 7 N 4 P 3 S i 4 T a 2 : C , 47.71; H , 6.45; N ; 4.12. Found: C , 47.44; H , 6.29; N , 4.27. 165 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Preparation of ( F h P h [NPN]Ta) 2 (u -H) 2 (u -PAd) , 48 This reaction was conducted analogously to the synthesis of 46. Adamantylphosphine (68.1 mg, 0.405 mmol) and ( p h p h [NPN]Ta) 2 (u -H) 4 (500 mg, 0.405 mmol) were employed to afford ( p h p h [NPN]Ta) 2 (u -H) 2 (u -PAd) (88%, 499.9 mg). ! H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 6 -0.11 (s, 6H , S i C / / 3 ) , 0.22 (s, 12H, S i C / / 3 ) , 0.28 (s, 6 H , S i C / / 3 ) 0.95 (s, 6H, PC(C# 2 ) 3 ) , 1.29-1.57 (m, 8H, ?CH2), 1.68 (s, 6H , C H C / / 2 C H ) , 1.75 (s, 3H, C H 2 C / / ( C H 2 ) 2 ) , 6.86 (m, 8H, NPh), 7.09-7.40 (m, 14H, N P h , PPh), 7.77 (m, 4H, PPh), 10.93 (m, 2H, TaflTa). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 7.35 (d, V P P = 162 Hz) , 10.23 (d, 2 J p P = 12 Hz) , 474.26 (d of d, 2JPP = 12 H z , 162 Hz) . Ana l . Calcd for C 5 8 H -7 9 N 4 P 3 S i 4 T a 2 : C , 49.78; H , 5.69; N , 4.00. Found: C, 49.78; H , 5.49; N , 4.14. Preparation of ( C y P h | ^ P N ] T a ) 2 ( u - H ) 2 ( u - P A d ) , 49 This reaction was conducted analogously to the synthesis of 46. Adamantylphosphine (67.5 mg, 0.401 mmol) and ( C y P h [NPN]Ta) 2 (u -H) 4 (500 mg, 0.401 mmol) were employed to afford ( C y P h [NPN]Ta) 2 (u -H) 2 (u -PAd) (97%, 549 mg). Crystals of 49 suitable for X-ray diffraction were grown from slow evaporation of a concentrated solution of 49 in pentane. ! H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8-0.11 (s, 6H , SiCrY 3 ) , 0.25 (s, 6H , S iC# 3 ) , 0.30 (s, 6H, S i C / 6 ) , 0.31 (s, 6H, S i C / / 3 ) 1.08-1.88 (m, 30H, C6HU, PC/fcSi) , 1.39 (s, 6H, P C ( C / / 2 ) 3 ) , 1.78 (s, 6 H , C H C / / 2 C H ) , 2.06 (s, 3H , C H 2 C / / ( C H 2 ) 2 ) , 6.87-6.91 (m, 4 H , NPh), 7.15-7.23 (m, 8H, NPh) , 7.29-7.36 (m, 8H, NPh), 10.61 (m, 2 H , Ta#Ta). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 14.37 (d, 2 J P P = 160 Hz) , 19.80 (s), 468.35 (d, V P P = 160 Hz). Preparation of ( C y P h [NPN]Ta) 2 (u -D) 4 , 50 ( C y P h [NPN]Ta) 2 (u . -D) 4 is prepared analogously to 35, except D 2 gas is added to the diethylether solution of C y P h [ N P N ] T a M e 3 (1.00 g, 1.50 mmol), affording a bright purple solution after 24 hours. The solvent was removed in vacuo, and the product extracted into 166 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes degassed pentane and filtered through Celite. Removal of pentane affords (CyPh[NPN]Ta)2(p-D)4 in 94% yield (0.88 g, 0.705 mmol). The product was highly nitrogen sensitive in solution, however is stable under nitrogen in solid form at -35 °C. 'IT NMR (C 6D 6, 25°C, 500 MHz): 5 0.18 (s, 12H, SiC// 3), 0.24 (s, 12H, SiC7/3), 0.37-1.89 (m, 30H, C6Hn, PC/72Si), 6.95 (s, 4H, NPh), 7.17 (s, 8H, NPh), 7.35 (s, 8H, NPh). 3 1P{'H} NMR (C 6D 6 , 25°C, 202.5 MHz): 5 29.30 (s). Preparation of (phph[NPN]Ta)2(p-D)2(p-H)(p-PCy2), 51 A solution of (phph[NPN]Ta)2(p-D)4 (100 mg, 0.081 mmol) in degassed C 6 D 6 (1 mL) is prepared in a Wilmad 5mm NMR tube fitted with a rubber septum. To this solution, dicyclohexylphosphine (16 mg, 0.081 mmol) in degassed C6D 6 (1 mL) is added via microsyringe through the septum. Mixing of the solutions promotes a color change from purple to red and the reaction is then monitored by f H and 3 1 P NMR spectroscopy. 'H NMR (C 6D 6, 25°C, 500 MHz): 5 -0.21, -0.02, 0.07, 0.17, 0.23, 0.31 (s, 24H, SiCr73's), 0.88-2.65 (m, 30H, C6Hn, PC#2Si), 6.65-7.62 (m, 30H, NPh, PPh), 8.67 (m, 0.65H, TaOTa), 10.47 (m, 0.33H, TaMa). 3 1P{'H} NMR (C 6D 6, 25°C, 202.5 MHz): 8 10.47 (d, V P P = 12 Hz), 10.53 (d, 2JpP = 83 Hz), 164.38 (d of d, 27pP = 12 Hz, 83 Hz). Similar results were observed for the addition of dicyclohexylphoshine to (CyPh[NPN]Ta)2(p-D)4. 'HNMR: 8 8.56 (m, 0.63H, TaOTa), 10.35 (m, 0.33H, TaOTa). Preparation of (phPh[NPN]Ta)2(p-H)0.67(p-D)i.33(p-PCy), 52 A solution of C y P h[NPN]Ta)2(p-D)4 (100 mg, 0.081 mmol) in degassed C 6 D 6 (1 mL) is prepared in a Wilmad 5mm NMR tube fitted with a rubber septum. To this solution, cyclohexylphosphine (9.4 mg, 0.081 mmol) in degassed C^De (1 mL) is added via microsyringe through the septum. Mixing of the solutions promotes a color change from purple to red and the reaction is then monitored by lH and 3 1 P NMR spectroscopy. ! H NMR (C 6D 6 , 25°C, 500 MHz): 8 -0.08, 0.15, 0.20, 0.22 (s, 24H, SiCrY3's), 0.96-1.70 (m, 19H, CeHn, PC// 2Si), 6.82-7.67 (m, 30H, NPh, PPh), 10.87 (m, 0.65H, TarYTa). 3 1P{'H} NMR (C 6D 6, 25°C, 202.5 MHz): 8 10.74 (d, 2 y P P = 152 Hz), 15.01 (d, 2 J P P = 17 Hz), 167 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes 449.0 (d of d, 2 J P p = 17 Hz , 152 Hz). Similar results were observed for the addition of cyclohexylphoshine to ( C y P h [NPN]Ta) 2 (p -D) 4 . ' H N M R : 8 10.47 (m, 0.69H, Tai/Ta). Reaction of ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 with excess P M e 3 A solution of P M e 3 (29.0 mg, 0.381 mmol) in -toluene (1.5 mL) was vacuum transferred into a sealable N M R tube containing ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 (50.0 mg, 0.0381 mmol). The N M R tube was sealed under vacuum and allowed to warm to room temperature briefly, and then cooled back to -78 °C, promoting a colour change from deep purple to dark green. The crude mixture was analyzed by low temperature P{ H} and ' H { 3 1 P } N M R spectroscopy. ' H N M R ( C 6 D 5 C D 3 , -80 °C, 500 M H z , selected resonance): 8.5 (br, 2 H , Ta//Ta). 3 1 P { ' H } N M R ( C 6 D 6 , -80 °C, 202.5 M H z ) : 8: -62 (s, in excess), -30 (br, 2P), 18 (br, 2P), 29 (br, in excess). Synthesis of c y p h [NPN]Ta(p -H) 2 (p -N(C 6 H 4 )Ta [PN] (H) (PMe 3 ) , 54 A solution of P M e 3 (290.0 mg, 3.81 mmol) in E t 2 0 (50 mL) was vacuum transferred into a vessel containing ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 (500.0 mg, 0.381 mmol). The contents of the flask were frozen, and the vessel evacuated and sealed. Al lowing the contents to warm to room temperature, followed by stirring for 1 h promoted a colour change from deep purple to red. Removal of volatiles after 2 h gave a dark red powder, which was dissolved in toluene. Slow evaporation of the toluene solution gave crystals of 54 suitable for X-ray diffraction. Analysis of the product by X-ray diffraction, ' H { 3 1 P } , 3 1 P { 1 H } , ' H / 3 , P H S Q C and ' H / ' H C O S Y spectroscopy confirmed the assignment. ' H { 3 1 P } N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8 -0.34, 0.17, 0.16, 0.03, 0.18, 0.27, 0.53, 0.72 (s, 24H total, S i C / / 3 ) , 0.36 (s, 9H, P (C/ / 3 ) 3 ) , 0.08-1.75 (m, 30H, P C / / 2 , P C 6 / / n ) , 5.06 (d, 1H, Ta//), 6.55-7.63 (m, 19H, NPh- / / ) , 8.15 (s, 1H, Ta//) , 11.24 (d, 1H, Ta//). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 -20.2 (d, 2 J P P = 188 Hz , / > M e 3 ) , 10.5 (s, N P N ) , 13.8 (d, 2 J P P = 18.8 H z , N P N ) . ' H , 3 1 P H S Q C : 3 1 P ( ' H ) 8 -20.2 (0.36, 5.06), 10.5 (0.18, 0.27, 1.09-1.75, 8.15), 13.8 (-0.17, 0.03, 1.09-1.75, 11.24). ' H , ' H C O S Y (selected correlations): 8 7.63 (/?, 7.48), 7.48 (a, 7.63; S, 6.76), 6.76 U3, 7.48; y, 6.55), 6.55 (5, 6.76). Anal . Calcd for C 5 i H 8 5 N 4 P 3 S i 4 T a 2 : C , 46.36; H , 6.48; N , 4.24. Found: C, 46.80; H , 6.81; N , 4.02. 168 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis ofphosphides and phosphinidenes Synthesis of phPh[NPN]Ta(^-H)2(^-N(C6H4)Ta[PN](H)(PMe3), 55 A solution of PMe3 (29.3 mg, 0.385 mmol) in Et 20 (50 mL) was vacuum transferred into a vessel containing (PhPh[NPN]Ta)2(u-H)4 (500.0 mg, 0.385 mmol). Allowing the contents to warm to room temperature promoted an immediate colour change from deep purple to red. Removal of volatiles after 30 min gave a dark red powder, which was dissolved in toluene. Removal of solvent gave 55 in excellent yields. Slow evaporation of a benzene solution of 55 gave crystals suitable for X-ray diffraction. Analysis of the product by X-ray diffraction, 'H{ 3 1P}, 3 I P { I H } , ' H / 3 ^ HSQC and ' H / ' H COSY spectroscopy confirmed the assignment. 'H{3 1P} NMR (C 6D 6, 25°C, 500 MHz): 5 -0.30, -0.12, -0.10, 0.09, 0.23, 0.33, 0.42, 0.58 (s, 24H total, SiC// 3), 0.40 (s, 9H, P(C//3)3), 1.11-2.26 (m, 8H, PC// 2), 5.29 (d, 1H, Ta//), 6.51-7.67 (m, 19H, NPh-//, PPh-//), 8.41 (s, 1H, Ta//), 11.46 (d, 1H, Ta//). 3 1P{ 1H} NMR (C 6D 6 , 25°C, 202.5 MHz): 5 -18.25 (d, V P P = 19.1 Hz, PMe3), 6.18 (s, NPN), 10.87 (d, 2 J P P = 19.1 Hz, NPN). 'H, 3 1P HSQC: 3 1P('H) 8 -18.25 (0.40, 5.29), 6.18 (0.23, 0.33, 1.11-1.58, 8.41), 10.87 (-0.12, 0.09, 1.11-1.58, 11.46). 'H, 'H COSY (selected correlations): 8 7.67 <j3, 7.35), 7.35 (a, 7.67; S, 6.88), 6.88 (j3, 7.35; y, 6.51), 6.51 (S, 6.88). Anal. Calcd for C5iH73N4P3Si4Ta2: C, 46.78; H, 5.62; N , 4.28. Found: C, 47.05; H, 5.99; N , 4.14. Preparation of (CyPh[NPN]Ta)2(^-H)2(^-ri2-HSiPh), 56, and (CyPh[NPN]Ta)2((a-H)2(n-T12-HSinBu), 57. RSiH 3 (0.401 mmol) was added under Ar via microsyringe to a solution of (CyPh[NPN]Ta)2((a-H)4 (500 mg, 0.401 mmol) in 40 mL Et 20 prepared in a vessel equipped with a Kontes valve. A slow color change (1 h) from purple to green was observed along with concomitant gas evolution. The solution was stirred for another 6 hours to ensure complete reaction, and the solvent was removed. The resulting green solid was dissolved in pentane and then dried under vacuum to afford (CyPh[NPN]Ta)2(u.-H)2(u-r|2-HSiPh), 56, when R = Ph, and (CyPh[NPN]Ta)2(p.-H)2(p.-ri2-HSinBu), 57, when R = nBu. 56: lK NMR (C 6D 6 , 25°C, 500 MHz): 8 0.07 (s, 6H, SiC// 3), 0.23 (s, 6H, SiC// 3), 0.30 (s, 6H, SiC// 3), 0.39 (s, 6H, SiC// 3), 0.75-2.18 (m, 30H, C 6 / /n , PC// 2Si), 6.99-7.54 (m, 25H, NPh-//, SiPh-//), 9.73 (d of d, 1 H, Si//Ta, ]JSlH = 60 Hz), 11.93 (m, 169 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes 2H, Taf/Ta). 3 1P{'H} NMR (C 6D 6 , 25°C, 202.5 MHz): 5 22.5 (s), 26.6 (s). 2 9Si{'H} NMR (C 6D 6 , 25°C): 5 8.8 (s), 14.2 (s), 140 (s). 57: ! H NMR (C 6D 6 , 25°C, 500 MHz): 8 0. 01 (s, 6H, S1C//3), 0.10 (s, 6H, SiC// 3), 0.17 (s, 6H, SiC// 3), 0.29 (s, 6H, SiC// 3), 0.18 (m, 9H, SinBu-/f), 0.70-1.30 (m, 30H, C 6#n, PC// 2Si), 6.85-7.68 (m, 20H, NPh), 8.89 (d of d, 1 H, Si/fTa), 11.78 (m, 2H, TaffTa). 3 1P{'H} NMR (C 6D 6 , 25°C, 202.5 MHz): 8 24.67 (s), 26.71 (s). 5.9 References 1. Scioly, A. J.; Luetkens, M . L.; Wilson, R. B.; Huffman, J. C ; Sattelberger, A. P. Polyhedron 1987,6,741. 2. Ting, C ; Baenziger, N . C ; Messerle, L. J, Chem. Soc., Chem. Commun. 1988, 1133. 3. Ting, C ; Messerle, L. J. Am. Chem. Soc. 1989, 111, 3449. 4. Ting, C ; Messerle, L. J. Am. Chem. Soc. 1987,109, 6506. 5. Huang, J.; Lee, T.; Swenson, D.; Messerle, L. Inorg. Chim. Acta 2003, 345, 209. 6. Huang, J.; Luci, J. J.; Lee, T.; Swenson, D. C ; Jensen, J. H.; Messerle, L. J. Am. Chem. Soc. 2003,125, 1688. 7. Ohki, Y.; Kojima, T.; Oshima, M. ; Suzuki, H. Organometallics 2001, 20, 2654. 8. Ohki, Y.; Suzuki, H. Angew. Chem. Int. Ed. 2000, 39, 3120. 9. Garcia, M . E.; Riera, V.; Ruiz, M. A. Organometallics 2002, 21, 5515. 10. Angeles, A. Y.; Garcia, M . E.; Riera, V.; Ruiz, M . A. Organometallics 2004, 23, 433. 11. Arif, A. M . ; Jones, R. A.; Schwab, S. T. J. Organomet. Chem. 1986, 307, 219. 12. Blum, T.; Braunstein, P.; Tiripicchio, A.; Tiripicchio, C. M . Organometallics 1989, 8, 2504. 13. Caffyn, A. J. M. ; Mays, M . J.; Conole, G.; McPartlin, M. ; Powell, H. R. J. Organomet. Chem. 1992, 436, 83. 14. Don, M . J.; Richmond, M . G.; Watson, W. H.; Nagl, A. J. Organomet. Chem. 1989,572,417. 15. Ebsworth, E. A. V.; Mcintosh, A. P.; Schroder, M . J. Organomet. Chem. 1986, 312, C41. 170 References begin on page 170. 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A . ; Fromm, K . ; Blaurock, S.; Jelonek, S.; Hey-Hawkins, E . Polyhedron 1997,16, 721. 26. Nikonov, G . I.; Kuzmina, L . G . ; Mountford, P.; Lemenovskii, D . A . Organometallics 1995,14, 3588. 27. Freundlich, J. S.; Schrock, R. R.; Davis, W . M . J. Am. Chem. Soc. 1996,118, 3643. 28. Cummins, C . C ; Schrock, R. R.; Davis, W . M . Angew. Chem. Int. Ed. 1993, 32, 756. 29. Baker, R. T.; Calabrese, J. C ; Harlow, R. L . ; Will iams, I. D . Organometallics 1993, 72, 830. 30. Farrugia, L . J. J. Appl Cryst. 1997, 30, 565. 31. Orpen, A . G . J. Chem. Soc, Dalton Trans. 1980, 2509. 32. Profilet, R. D . ; Fanwick, P. E . ; Rothwell, I. P. Polyhedron 1992, 77, 1559. 33. Wilson, R. B . ; Sattelberger, A . P.; Huffman, J. C. J. Am. Chem. Soc. 1982,104, 858. 34. Fryzuk, M . D . ; Johnson, S. A . ; Rettig, S. J. Organometallics 2000,19, 3931. 35. Sattelberger, A . P.; Wilson, R. B . ; Huffman, J. C . Inorg. Chem. 1982, 27, 4179. 36. Soo, H . S.; Diaconescu, P. L . ; Cummins, C. C. Organometallics 2004, 23, 498. 171 References begin on page 170. Chapter Five: Addition ofphosphines to tantalum hydrides: Synthesis of phosphides and phosphinidenes 37. Tsang, W . C. P.; Jernelius, J. A . ; Cortez, G . A . ; Weatherhead, G . S.; Schrock, R. R.; Hoveyda, A . H . J. Am. Chem. Soc. 2003,125, 2591. 38. Blaurock, S.; Hey-Hawkins, E . Zeit. Anorg. Allg. Chem. 2002, 628, 2515. 39. Tell ini , V . H . S.; Jover, A . ; Galantini, L . ; Meijida, F.; Tato, J. V . Acta Cryst. 2004, B60, 204. 40. Grubb, T. L . ; Mathias, L . J. J. Poly. Sci. A.: Poly. Chem. 2000, 35, 1743. 41. Gessmann, R.; Petratos, K . ; Hanodrakas, S. J.; Tsitsa, P.; Antoniadou-Vyza, E . Acta Cryst. 1992, C48, 347. 42. Fryzuk, M . D . ; M a c K a y , B . A . ; Johnson, S. A . ; Patrick, B . O. Angew. Chem. Int. Ed. 2002, 41, 3709. 43. Power, P. P. Chem. Rev. 1999, 99, 3463. 44. Mork, B . V . ; Til ley, T. D . Angew. Chem. Int. Ed. 2003, 42, 357. 45. Nikonov, G . I.; Mountford, P.; Dubberley, S. R. Inorg. Chem. 2003, 42, 258. 46. Nikonov, G . I.; Mountford, P.; Kuzmina, L . G . ; Howard, J . A . K . ; Lemenovskii, D . A . ; Roitershtein, D . M . J. Organomet. Chem. 2001, 628, 25. 47. Nikonov, G . I.; Mountford, P.; Green, J. C. ; Cooke, P. A . ; Leech, M . A . ; Blake, A . J.; Howard, J. A . K . ; Lemenovskii, D . A . Eur. J. Inorg. Chem. 2000, 1917. 48. Dubberley, S. R.; Ignatov, S. K . ; Rees, N . H . ; Razuvaev, A . G . ; Mountford, P.; Nikonov, G . I. J. Am. Chem. Soc. 2003,125, 642. 49. Burckhardt, U . ; Casty, G . L . ; Gavenonis, J. ; Til ley, T. D . Organometallics 2002, 21, 3108. 50. Nikonov, G . I.; Mountford, P.; Ignatov, S. K . ; Green, J . C ; Leech, M . A . ; Kuzmina, L . G . ; Razuvaev, A . G . ; Rees, N . H . ; Blake, A . J.; Howard, J. A . K . ; Lemenovskii, D . A . J. Chem. Soc, Dalton Trans. 2001, 2903. 51. Baudler, M . ; Zarkdas, A . Chem. Ber. 1965,104, 1034. 52. Ohashi, A . ; Matsukawa, S.; Imamoto, T. Heterocycles 2000, 52, 905. 53. Setter, H . ; Last, W . D. Chem. Ber. 1969,102, 3364. 54. Finholt, A . E . ; Bond, A . C ; Wilzbach, K . E . ; Schlesinger, H . I. J. Am. Chem. Soc. 1947, 69, 2692. 172 References begin on page 170. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Chapter Six Promoting chemistry with [NPN] supported tantalum complexes 6.1 Introduction The generation of phosphides and phosphinidenes from tantalum hydrides showed that the ditantalum tetrahydride complexes (R P h[NPN]Ta) 2(u-H) 4 ( R = Cy, 35; R = Ph, 4 1 ) can promote not just dinitrogen activation, but other transformations as well. The controlled activation of the triple bond in molecular nitrogen inspires two obvious possibilities. First, can other triply bonded species react similarly? Are asymmetric bonding modes of alkynes, nitriles or carbon monoxide accessible with this system? Second, what activation is possible with N-N bonds of lower order? Will the addition of hydrazine to this system afford interesting activation products? The activation of OsE (E = C, N, O) triple bonds, focusing on the activation of alkynes, and the activation of hydrazine and substituted-hydrazines, with relevance to dinitrogen activation will be discussed in this chapter. As the reactions discussed in each section differ dramatically from each other, separate introductions are included for each type of small molecule investigated. 173 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 6.2 Activation of O E (E = C , N , O) triple bonds 6.2.1 Add i t i on of R C N and C O to ( C y P h [ N P N ] T a ) 2 ( p - H ) 4 , 35 The r\l:r\2 asymmetric bonding mode of molecular nitrogen in 36 is well known for carbon monoxide activation. For example, the reaction of 2 equivalents of Cp2Zr(PPh2)2 with [CpMo(CO)3 ]2 in T H F provides a synthetic route to monophosphido-bridged early/late heterobimetallic complexes. These complexes asymmetrically activate carbon monoxide to give r\{:r\2 bound carbonyl fragments.1 The C - 0 bond in this system lengthens to 1.230(5) A , giving the product shown in Equation 6.1. This reaction 1 2 * represents only one of many examples of n, :r| carbon monoxide binding. R R R V Cp Cp \/ ^ YR Ao A o c o \ c p / i V \ 0 «,, R R The activation of carbon monoxide by metal-metal multiple bonds has also promoted C O bond scission. The W=W core in [ ( t Bu 3 SiO )2ClW] 2 provides the six electrons necessary to cleave the C O triple bond, generating the tungsten carbide [( tBu 3SiO)2(0=)W](p-C)[W(Cl)2(OSi tBu 3)2], as shown in Equation 6.2. 2 A stepwise four-and six-electron reduction of carbon monoxide over a niobium calix[4]arene shows the potential for C O activation with group five metals. In this case, a Nb=Nb double bond reduces C O to an oxyalkylidene (CO bond order of 1) and the addition of sodium as an external reducing agent completes the cleavage reaction. 3 These reactions are shown in Scheme 6.1. 174 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Scheme 6.1 While under-studied compared to carbon monoxide, the organometallic chemistry of nitriles, R C = N , shows similar behavior. For instance, the M n = M n double bond in ((OC) 3 Mn) 2 (p-H) 2 (p-dppm) activates M e C N to give ( (OC) 3 Mn) 2 (p- r i 1 : r ) 2 -NCMe)(p-dppm) with concomitant loss of H 2 . Conversely, benzonitrile inserts into a M n - H bond generating ((OC) 3 Mn) 2 (p-H)(p-N=CHPh)(p-dppm) without H 2 loss, as shown in Scheme 6.2.4' 5 A s with C O , cleavage reactions of R C N can be promoted by transition metal complexes. The reductive cleavage of the C=N bond in nitriles by H 2 is promoted by a f\ 7 sulfide bridged molybdenum complex as shown in Equation 6.3. ' 175 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes The addition of benzonitrile to (™ | J | 1[NPN]Ta)2(p.-H)4, 41, gave a clean transformation to a symmetric product, as evidenced by a singlet at 5 20.5 in the P{ H} N M R spectrum. The product was a highly soluble bright blue solid that decomposed slowly in solution to generate p h p h [ N P N ] H 2 . Attempts to grow single crystals amenable to x-ray diffraction were thwarted by the decomposition process; product assignment was made based on N M R data. 176 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes *H N M R spectra confirmed a highly symmetric structure. The four silyl methyl proton resonances indicated a mirror plane or C 2 axis exists in the product; the core of the tantalum complex must follow this symmetry as well . The aryl resonances in the ' H N M R spectrum revealed phenyl rings in three different environments: four Ph rings assigned to N - P h resonances, two Ph rings attached to ligand phosphines, and one Ph ring presumed to be associated with the activated benzonitrile. No hydride resonances were observed in this blue product by ' H N M R spectroscopy. This differs dramatically from the activation of dinitrogen, primary and secondary phosphines, and silanes. In these cases at least two hydridic protons remain in the final product. The loss of two equivalents of H 2 implies the availability of six electrons to reduce the C - N bond. IR spectroscopy of this product was complicated by overlapping ligand stretches, however no nitrile stretching frequencies were observed. As well , a 1 3 C N M R spectrum of the blue product shows a peak at 8 285.8, suggesting a bridging alkylidyne structure. These three observations support the cleavage of benzonitrile. The product can be assigned as ( p h p h [NPN]Ta) 2 (p-CPh)(p-N) , 58. For this product to maintain the observed symmetry, ligand phosphines must reside 90° out-of-plane from the Ta-N-Ta-C core. This reaction is shown in Equation 6.4. Monitoring this reaction by 3 1 P N M R spectroscopy revealed the formation of an intermediate, characterized by two doublets at 8 21.1 and 25.7 that couple to one another. This intermediate may contain an activated benzonitrile group, prior to C N bond cleavage. Integration and assignment of the ' H N M R spectrum for this intermediate is 177 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes difficult. It is clear, however, that this product contains two bridging hydrides, and five sets of aryl resonances, presumably including one deriving from P h C N . A proposed structure would be ( p h P h[NPN]Ta)2(|a-H)2(|a-NCPh), analogous to the asymmetric activation of N 2 . Unfortunately, attempts to isolate this product have been unsuccessful. The addition of alkylnitriles to tantalum hydrides did not exhibit similar reactivity. Addit ion of " B u C N , M e C N , or l B u C N to 35 or 41 promoted ligand protonation; C y P h [ N P N ] H 2 and P h P h [ N P N ] H 2 were the only isolable products formed. Thermolysis of 58 at 50 °C in toluene for 30 min. promoted a loss of the blue colour and formation of p h p h [ N P N ] H 2 . The origin of protons for these decompositions is unknown. Unfortunately, decomposition also prevented the controlled activation of carbon monoxide. The addition of excess carbon monoxide to 35 or 41 precipitated white solids. Analysis of the solids by elemental analysis revealed minimal carbon, hydrogen and nitrogen content, indicating the formation of tantalum oxides. Attempts to analyze the organic product were unsuccessful. The addition of just one equivalent of carbon 31 1 monoxide to the tantalum hydrides gave eight different products, as shown by P{ H} N M R spectroscopy. 6.2.2 Addition of terminal alkynes to (P h P h[NPN]Ta) 2(u-H) 4, 41 The side-on bound dinitrogen complex ( P h [P 2 N 2 ]Zr ) 2 (u -N 2 ) , where P h[P2N2] is PhP(CH2SiMe2NSiMe2CH2)2PPh, reacts with arylacetylenes to produce a complex containing a carbon nitrogen bond. 8 Previously in the Fryzuk group, phenylacetylene was reacted with ( p h P h[NPN]Ta) 2(|a-H) 2(^-V:n2-N2) in an attempt to add a C - H bond across the Ta=N, functionalizing dinitrogen with carbon analogous to other E - H additions. Instead, phenylacetylene displaces the bound dinitrogen moiety as N2 gas to produce ( P h P h [NPN]Ta) 2 (p . -H) 2 (^-PhCCH), 59, as illustrated in Equation 6.5. 9 Tantalum-carbon bond lengths in this complex are considerably shorter than expected for Ta-C single bonds; this complex can be viewed as a dialkylidene. The reaction to form 59 is unfortunately quite slow, taking up to four days, and isolated yields are moderate. 178 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes ^ S i M e 2 6.5 Interesting activation of alkynes by tantalum systems has been observed previously. The complex Ta2Cl6(SC4H8)3 reacts with diphenylacetylene and pyridine to give the anionic complex [TaCi4(py)(PhCCPh)]".1 0 This complex contains short Ta-C bonds and an elongated C - C bond and is described as a dialkylidene." The activation of ' B u C C ' B u in T H F by T a 2 C l 6 ( S C 4 H 8 ) 3 gives [(THF)Cl 2Ta] 2(p-ri 2:ri 2- tBuCC tBu)(n-Cl)2, a bimetallic system with a side-on side-on bridging coordination mode, deviating only slightly from a perfectly perpendicular orientation. Several p.-alkyne binuclear complexes that deviate greatly from ideal perpendicular orientations. 1 3" 1 6 This has been rationalized as a second order Jahn-Teller effect in most cases, 1 7" 1 9 although in specific cases this asymmetry may arise from a rehybridization of frontier orbitals caused by the ground-state steric influence of the bridging ligand. Complete cleavage of the carbon-carbon triple bond by tantalum complexes has not been previously observed. Carbon-carbon bond cleavage is facilitated by several bimetallic and cluster compounds, including the d -d triply bonded ( t BuO) 3 W=W(O t Bu) 3 . 2 1 " 2 5 More recently, the tungsten hydride complex [(s i lox) 2 WH] 2 , where silox is l B u S i O , reacts with RC=CR' (R = R ' = H , C H 3 ; R = H , R ' = Ph) to give bridging adducts [(silox)2W]2(p.-r)2:r|2-RCCR')((i-H)2.26 Thermolysis of these compounds liberates dihydrogen and produces [(silox)2W]2(u-CR)(u-CR'). This chemistry is shown in Scheme 6.2. 179 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 'BusSiQ. B u 3 S i O v ^ H ^ ' " O S i ' B u , H p S r B ^ RCCR' ' B ^ S i C X 'B^S iC - ' ^OSi 'Bua ^ O S i , B u 3 R' A Bu3SiO///,„„_ Bu 3 SiO'""" '~ f„„ l loOSit Bu 3 ^OSi 'Bus R R = R' = H, C H 3 ; R = H, R' = Ph Scheme 6.2 Addition of alkynes to the tetrahydride 41 produces p-r) 2-bound alkyne complexes in minutes. Addit ion of phenylacetylene to 41 gives high yields of 59 in under five minutes. Addit ion of " P r C s C H and l B u C = C H leads to the isolation of ( p h p h [NPN]Ta) 2 (p -H) 2 (p -HCCPr n ) , 60 and ( p h p h [ N P N ] T a ) 2 ( p - H ) 2 ( p - H C C B u t ) 61, as These products are readily characterized by multinuclear N M R spectroscopy. Each product exhibits two 3 1 P chemical shifts; 5 18.14 and 20.01 for 59, 8 11.91 and 12.48 for 60, and 8 6.10 and 9.17 for 61. Similarly, each has a distinctive hydride region, with two asymmetric, bridging tantalum hydrides. These appear at 11.65 ( A M X Y splitting pattern) and 13.14 ( A M X Y ) for 59. The hydridic resonances in complexes 60 and 61 do not exhibit clear A M X Y patterns, instead appearing as complicated multiplets shown in Equation 6.6. 6.6 180 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes at 5 11.03 and 11.56 for 60 and 8 11.51 and 12.08 for 61. In each case, 1 3 C N M R studies show two resonances at 8 224.2 and 224.3, assignable to the bridging phenylacetylene carbons. Unfortunately, attempts grow single crystals amenable to X-ray crystallography were unsuccessful. Storing solutions of 59 under vacuum leads to the quantitative formation of a The two hydridic resonances at 8 11.65 and 13.14 have disappeared and the alkyne proton has shifted from 8 11.72 to 8 4.95. Only four si lyl methyl resonances are observed. Loss of H 2 could provide the system with the final two electrons required to cleave the C - C bond and generate a bis-alkylidyne complex. 1 3 C N M R experiments reveal that the alkylidene resonances at 8 224.2 and 224.3 in 59 have disappeared. Two new resonances at 8 308.8 and 311.2 support this cleavage process and the formation of ( p h p h [NPN]Ta) 2 (p -CH)(p-CPh) , 62, as shown in Equation 6.7. Attempts to characterize these complexes crystallographically and support the spectroscopic assignment of these structures are ongoing. However, once the structures of these p-bis(alkylidyne) and p-alkyne complexes are confirmed, their reactivity w i l l be a subject of great interest. support the assignment of products as dialkylidenes. For instance, 1 3 C N M R spectra of 59 symmetrical product as evidenced by a singlet at 8 11.5 in the 3 1 P{*H} N M R spectrum. 6.7 181 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 6.2.3 Add i t i on of diphenylacetylene to ( P h P h [NPN]Ta) 2 (p . -H )4, 41 It was hoped that addition of P h C ^ C P h to 41 would generate the symmetrical bis(alkylidyne) ( P h p h [NPN]Ta) 2 (u -CPh) 2 . However, it offered only new complications. The reaction was quite slow, converting from a purple solution to an orange product over 24 hours. Decomposition was evident; the final product is shown in Equation 6.8. 6.8 63 Single crystal x-ray diffraction studies confirmed the formation of 63 (72% yield) as shown in Figure 6.1. Each [NPN] ligand has fractured in a unique way. One ligand has degraded through scission of a N - C bond to give a bridging imide and an n ^phenyl ring. The other ligand has undergone P-C bond cleavage, producing a new terminal T M S -imido group that has lost Ph, and a bridging phosphide. Diphenylacetylene has been incorporated in an r\ -manner and is bound to one tantalum centre. The asymmetric unit also contained a half equivalent of co-crystallized benzene. The bridging imide and phosphide ligands are bound asymmetrically. N(4)-Ta(l) and N(4)-Ta(2) distances are 2.121(4) and 1.961(4) A, respectively, while P( l ) -Ta( l ) and P(l)-Ta(2) interatomic distances of 2.7563(11) and 2.4555(11) A exhibit an even stronger asymmetry. Tantalum carbon distances are typical: Ta(l)-C(19), Ta(2)-C(43) and Ta(2)-C(44) distances are 2.190(4), 2.124(4) and 2.129(4) A, respectively. The C(43)-C(44) distance in the coordinated alkyne is lengthened to 1.313(6) A and can be considered a carbon-carbon double bond. For reference, the molecular structure of Ta(OC6H3Ph2-2,6)2(r|2-182 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes EtCCEt )Cl (PMe 3 ) has a O C distance of 1.291(6) A , and Ta-C distances of 2.045(3) and 2.092(4) A . 2 7 The terminal imido ligand has a much shorter Ta=N bond length than the Ta amides; the Ta(l)-N(2) interatomic distance is 1.782(4) A . These and other selected bond lengths and angles are located in Table 6.1 and crystallographic data can be found in Table 6.2. Figure 6.1. O R T E P drawing (spheroids at 50% probability) of product of ( P h P h [NPN]Ta) 2 (p -H) 4 and PhC=CPh, 63. Si lyl methyl and phenyl ring carbons other than ipso positions have been omitted for clarity. 183 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Table 6.1 Selected Bond Distances (A) and Angles (°) for 63. Lengths Angles Angles Ta(l)-N(l) 2.042(4) Ta(l)-P(l)-Ta(2) 79.38(3) C(19)-Ta(l)-P(l) 126.50(13) Ta(l)-N(2) .1.782(4) Ta(l)-N(4)-Ta(2) 109.57(17) N(4)-Ta(2)-N(3) 123.76(13) Ta(l)-C(19) 2.190(4) Ta(2)-C(43)-C(44) 72.2(2) N(4)-Ta(2)-C(43) 112.13(15) Ta(l)-N(4) 2.121(4) Ta(2)-C(44)-C(43) 71.8(2) N(3)-Ta(2)-C(43) 116.58(14) Ta(l)-P(l) 2.7563(11) N(2)-Ta(l)-N(l) 103.41(16) C(44)-Ta(2)-C(43) 35.97(15) Ta(2)-P(l) 2.4555(11) N(2)-Ta(l)-N(4) 104.13(16) N(4)-Ta(2)-P(l) 91.04(11) Ta(2)-N(4) 1.961(4) N(l)-Ta(l)-N(4) 150.98(14) N(3)-Ta(2)-P(l) 89.24(10) Ta(2)-P(2) 2.6068(11) N(2)-Ta(l)-C(19) 105.43(17) C(43)-Ta(2)-P(l) 118.67(11) Ta(2)-N(3) 2.084(3) N(l)-Ta(l)-C(19) 92.58(15) N(4)-Ta(2)-P(2) 77.36(11) Ta(2)-C(43) 2.124(4) N(4)-Ta(l)-C(19) 88.23(15) N(3)-Ta(2)-P(2) 76.71(10) Ta(2)-C(44) 2.129(4) N(2)-Ta(l)-P(l) 128.07(11) C(43)-Ta(2)-P(2) 89.49(11) C(43)-C(44) 1.313(6) N(l)-Ta(l)-P(l) 76.35(10) P(l)-Ta(2)-P(2) 151.84(3) N(4)-Ta(l)-P(l) 126.50(13) Table 6.2 Crystallographic Data and details of refinement for 63. Empirical formula C 5 9H 7 1 N4P2Si 4 Ta 2 Crystal system Triclinic Formula weight 1372.40 Space group P-l a, b, c (A) 11.424(1), 12.453(2), 23.760(1) 70.66(3), 73.14(3), 72.50(3) v,A3 2972.9 Total reflections 27096 z 2 Unique reflections 12280 D C a i „ g cm"3 1.54 Parameters 649 \i (Mo Ka), cm"' 3.852 R , a 0.0332 T, K 173 ± 1 R w a 0.0657 20 range (°) 55.76 Goodness-of-fit 1.155 "R, = Z | | F 0 | - | F C | | / Z | F 0 | ; * w = Zw(\F02\ - |F C 2 | ) 2 /2>|F 0 2 | 2 ) Proposing a mechanism for this decomposition is challenging (Scheme 6.3). The alkyne is presumably too bulky and cannot react with the dihydride intermediate in the same manner as terminal alkynes. However, it may be able to coordinate to and stabilize the reactive dihydride (I). Cleavage of a phosphorus-methylene bond via addition across the Ta=Ta bond in this species would form a bridging phosphide (II). Reductive elimination of the newly formed Ta-C bond with one of the remaining hydrides would 184 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes generate a TMS-substituted amide (III). Addition of an N - P h bond across the regenerated Ta=Ta double bond would form a terminal imido functionality (IV). Elimination of benzene again regenerates the reactive Ta=Ta double bond (V). A final N - P h oxidative addition and activation of the diphenylacetylene triple bond generates the final product (VI). In this proposal, no hydrides remain in the final product - they are incorporated into the N - T M S ligand and into reductively eliminated benzene. H and P N M R data agree with the product assignment. Integration of the complicated aryl region indicates that seven phenyl ring systems are present in the final complex. Seven silyl methyl resonances are also present, each integrating to 3H, except for a 9 H resonance at 8 0.22. Isotopic labeling studies, tracked via addition of diphenylacetylene to ( p h P h [NPN]Ta)2(u.-D)4, support this mechanism by showing deuterium incorporation into silylmethyl protons. Addition of other internal alkynes also promotes complex decomposition, although no products were isolated and characterized. The formation of 63 is yet another example of the fragile nature of the [NPN] ligand. 185 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Scheme 6 .3 6 . 3 Activation of N-N bonds 6.3.1 Introduction Extensive research has been done on the reaction of hydrazines with transition-metal complexes to elucidate how N - N bonds are cleaved and NH3 is formed. ' Metal hydrazido species may act as intermediates for the biological and industrial fixation of nitrogen. Protonation of metal-bound dinitrogen can lead to the formation of complexes containing diazenido ( N N H ) or hydrazido ( N N H 2 ) ligands, as proposed in the Chatt cycle. The study of the reaction chemistry of hydrazine clarifies details of transition-metal mediated nitrogen reduction. 186 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Cleavage of the N - N bond in hydrazine is facilitated by a number of transition metal systems. The cationic complexes [Cp*MMe3(r) 2-NH2NH 2)] + ( M = W , M o , Re) react with zinc amalgam and 2,6-lutidine hydrochloride to cleave the coordinated hydrazine bond. 3 1 Cleavage of the N - N bond of hydrazine and substituted hydrazines was also achieved using a dinuclear thiolato-bridged complex of molybdenum, Cp2Mo2(u-SMe)3. " The addition of hydrazines to the trinuclear ruthenium polyhydride cluster (Cp*Ru)3((j,-H)3(p.3-H)2 also promotes N - N bond cleavage. The products formed are bis(p.3-imido) complexes, as shown in Equation 6.9, although conditions are quite harsh. 3 5 The addition of 1,1-methylphenylhydrazine to Mo2lr2S 4 and M02RI12S4 clusters affords a terminally bound hydrazine fragment. Addition of 2,6-lutidinium chloride as a proton source, and cobaltocene as an external electron source, to this product promotes N - N bond cleavage and the formation of Af-methylaniline, as shown in Scheme 6.4. 3 6 Addition of hydrazine to 35 or 41 may promote similar transformations without external proton sources and reducing agents. R N H N H 2 (excess) 6.9 P h . Me N Cl HoNNMePh ? ^Cp* N Cl *Cp Scheme 6.4 LutHCI Me TCI cobaltocene \ 7 NH Cp* Ph 187 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 6.3.2 Addi t ion of hydrazine to ( C y P h [NPN]Ta) 2 (p , -H) 4 , 35, or ( P h P h [ N P N ] T a ) 2 ( p - H ) 4 , 41 Addit ion of excess hydrazine ( H 2 N N H 2 ) to either 35 or 41 gave C y P h [ N P N ] H 2 and p h P h [ N P N ] H 2 . In each reaction an insoluble white solid precipitated from the crude mixture. Attempts to characterize this product by E I - M S and N M R spectroscopy have been unsuccessful. Elemental analysis showed a variable composition. Each sample tested showed very low values of carbon and hydrogen and an inconsistent percentage of nitrogen content, implying the possible formation of tantalum nitrides. Addition of one equivalent of hydrazine to 35 under an argon atmosphere resulted in the clean formation of a new product in 82% yield as evidenced by a singlet at 8 3.2 in the 3 1 P { ' H } N M R spectrum. ' H { 3 1 P } N M R spectra show the expected silyl methyl, cyclohexyl, methylene and phenyl resonances, as well as two new signals at 8 15.1 and 3.4, respectively. Both signals integrate to 2 H and couple weakly to one another. One structure that matches this spectroscopic data is ( C y P h [NPN]Ta) 2 (p -NH) 2 (p -H) 2 , 64. This structure has two bridging imides and two bridging hydrides. The bridging N - H protons appear at 8 3.4, and couple to the hydrides at 8 15.1. This structure also maintains the observed symmetry, as N M R studies show equivalent phosphines, hydrides, and silyl methyl resonances. Attempts to confirm this structure by X-ray crystallography were unsuccessful. E I - M S studies also were unable to confirm the dimeric structure due to the harsh ionization conditions. A ' H / I 5 N H S Q C experiment showed strong coupling between the resonance at 8 3.4 and a nitrogen resonance within the structure, suggesting that this proton is nitrogen-bound. This reaction is shown in Equation 6.10. 188 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 6 . 1 0 64 The reaction of one equivalent of hydrazine with the phenyl phosphine congener 4 1 is complicated by the formation of p h P h [ N P N ] H 2 as the major product. A minor product, comprising approximately 30% of the total yield by N M R spectroscopy, appeared at 5 3.1 in the 3 1 P { ' H } N M R spectrum. Integration of ' H { 3 1 P } spectra was difficult, due to impurities, but the chemical shifts of observed resonances were similar to 6 4 , suggesting the formation of ( P h P h [NPN]Ta) 2 (u -NH) 2 (u -H) 2 , 6 5 . L o w yields of small colourless crystals o f the minor product were obtained from rapid cooling of a toluene/hexanes solution of the crude product. The crystals were analyzed by X-ray crystallography. A n O R T E P depiction of the solid state molecular structure of 6 5 is shown in Figure 6.2. Relevant bond lengths and angles are listed in Table 6.4 and crystallographic data are located in Table 6.3. The dihedral angle for Ta(l)-N(l)-Ta(2)-N(2) of -15.6(3)° shows the two bridging nitrogen atoms are bent down from the equatorial plane. The nitrogen atoms N ( l ) and N(2) are symmetrically bound between the two metals, and bond lengths are consistent with bridging imides; for example, the Ta( l ) -N(2) and Ta(2)-N(2) interatomic distances o f 2.027(11) and 2.002(11) A are similar to each other, and also to the average Ta-N bond length of the bis(silylimide) complex ( P h P h [ N P N ] T a ) 2 ( u - N S i n B u ) 2 of 2.008 A. 3 7 189 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Figure 6.2. O R T E P drawing (spheroids at 50% probability) of ( P h P h [NPN]Ta) 2 ( | i -NH) 2 (u\-H)2, 65. Si lyl methyl, phenyl and cyclohexyl ring carbons other than ipso or methine positions have been omitted for clarity. Table 6.3 Selected Bond Distances ( A ) and Angles (°) for 65. Lengths Angles Angles Ta(l)-N(l) 2.076(11) Ta(2)-N(5 -Ta(l) 84.0(5) N(5)-Ta(2)-N(6) 95.2(5) Ta(l)-N(2) 2.054(12) Ta(2)-N(6* -Ta(l) 83.1(5) N(5)-Ta(2)-N(3) 122.6(5) Ta(2)-N(3) 2.062(12) N(5)-Ta(l -N(6) 93.5(5) N(6)-Ta(2)-N(3) 102.9(5) Ta(2)-N(4) 2.066(10) N(5)-Ta(L -N(2) 93.6(5) N(5)-Ta(2)-N(4) 117.7(5) Ta(l)-N(5) 2.010(12) N(6)-Ta(l -N(2) 118.6(5) N(6)-Ta(2)-N(4) 92.5(4) Ta(2)-N(5) 1.982(14) N(5)-Ta(L -N(l) 102.5(5) N(3)-Ta(2)-N(4) 115.4(5) Ta(l)-N(6) 2.027(12) N(6)-Ta(l -N(l) 120.5(5) N(5)-Ta(2)-P(2) 88.3(4) Ta(2)-N(6) 2.002(12) N(2)-Ta(f -N(l) 117.0(5) N(6)-Ta(2)-P(2) 173.7(4) P(l)-Ta(l) 2.615(4) N(5)-Ta(i; -P(l) 174.3(4) N(3)-Ta(2)-P(2) 79.6(3) N(6)-Ta(l ; -P(l) 89.6(4) N(4)-Ta(2)-P(2) 81.2(3) N(2)-Ta(lJ -P(l) 80.7(3) Dihedral N(l)-Ta(i; -P(l) 79.9(3) Ta(l)-N(5)-Ta(2)-N(6) -15.6(3) 190 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Table 6.3 Crystallographic Data and details of refinement for 65. Empirical formula C 4 8 H 6 2 N 6 P 2 S i 4 T a 2 Crystal system Monoclinic Formula weight 1259.24 Space group P2(l)/n a,b,c{k);PO 11.6976(11), 19.4940(11), 23.2595(15); 90.216(4) v,A3 5303.9(7) z 4 Unique reflections 9807 DCaic, gem"3 1.577 Parameters 567 u (Mo Ka), cm"1 4.311 R , a 0.0761 T, K 173 ± 1 R w a 0.1219 29 range (°) 51.36 Goodness-of-fit 1.024 "R, = IIIFol" \Fc\\/i:\F0\; /?w = 2>(|F0 2| - |F c 2 |) 2/Sw|F 0 2 | 2) Attempts to locate hydrogen atoms within the diffraction pattern and employing the X - H Y D E X density mapping protocol gave conflicting results. A s shown in Figure 6.3, four locations were found within the diffraction pattern and assigned as hydrogen atoms. Face-bridging hydrides (H3, H4) are located on the Ta(l)-Ta(2)-N(l) and Ta( l ) -Ta(2)-N(2) faces, giving cause to the bent T a 2 N 2 core, and two N - H locations ( H I , H2) were also found within the diffraction pattern. Exact locations of these hydrogens are uncertain, as isotropic refinements did not converge. The X - H Y D E X mapping program found three potential face-bridging hydride positions but could not locate N - H resonances. Crystal size has prohibited the use of neutron diffraction to confirm hydride locations. Atom connectivity, symmetrical Ta -N bond lengths and N M R evidence supports the peaks observed in the diffraction pattern, pointing towards the formation of bis(imide)bis(hydride) tantalum complexes 64 and 65. 191 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Figure 6.3. O R T E P drawing (spheroids at 5 0 % probability) of ( P W h [ N P N ] T a ) 2 ( p - N H ) 2 ( p - H ) 2 , 6 5 0 n l y m e C Q r e a t o m s i n m e s t r u c t u r e are shown. Atoms H1-H4 are included, although isotropic refinement of these atoms was unstable. 6.3.3 Addi t ion of substituted hydrazines to 35 or 41 With the isolation of ( R P h [NPN]Ta) 2 (p -NH) 2 (p -H) 2 complexes, it was thought that the addition of 1,2-disubstituted hydrazines, such as frvms-l,2-diphenylhydrazine and 7ra/is-l,2-dimethylhydrazine would give stable (**[NPN]Ta) 2 (p-NR) 2 (p-H) 2 complexes. Unfortunately, addition of 1,2-disubstituted hydrazines gave highly complicated product distributions. Moving to 1,1-disubstituted hydrazine promoted a different transformation. Addition of M e 2 N N H 2 to 35 causes a colour change from deep purple to red brown. Analysis of the mixture by 3 1 P { ] H } N M R experiments indicates clean conversion to a new product, evidenced by two singlets at 8 12.8 and 14.8. 'ft N M R spectra showed peaks characteristic of an asymmetric bimolecular complex, including four silyl methyl resonances, and the requisite cyclohexyl, methylene and phenyl peaks. Two hydridic resonances were also observed, at 5 8.4 (integrating to 2 H) and 8 14.3 (integrating to 1 H). Crystals of this product were grown from a saturated toluene/hexanes solution, isolated in 91% yield and analyzed by X-ray crystallography. A n O R T E P depiction of the 192 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes solid state molecular structure of ( y [NPN]Ta)(p-N)(p-H) 3 , 66, is shown in Figure 6.4. Relevant bond lengths and angles are listed in Table 6.6 and crystallographic data are located in Table 6.5. The Ta(l)-N(3) bond length of 1.973(8) A is shorter than either the Ta(l) 2 -N(3) distance of 2.059(7) A , or those bonds in 65, suggesting nitride formation. Figure 6.4. O R T E P drawing (spheroids at 50% probability) of ( C y p h [NPN]Ta)(p-N)(p-H) 3 , 66. Si ly l methyl, phenyl and cyclohexyl ring carbons other than ipso or methine positions have been omitted for clarity. Table 6.5 Crystallographic Data and details of refinement for 66. Empirical formula C4iiH74N6P2Si4Ta2 Crystal system Triclinic Formula weight 635.7 Space group P-l a, b, c (A) 11.3404(4), 1 1.9845(7), 12.2733(7) otfiril 101.223(34), 111.665(32), 108.490(12) V, A 3 1375.18(4) z 2 Unique reflections 5657 DCaic, g cm"3 1.53 Parameters 287 p (Mo Ka), cm"' 4.158 0.026 T,K 173+ 1 0.064 26 range (°) 55.8 Goodness-of-fit 1.101 "Rj = T\\Fa\ - | F c | | / I | F 0 | ; * w = 2>(|/\r| - |/v2l)2/2>|F0 2|2) 193 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Table 6.6 Selected Bond Distances (A) and Angles (°) for C y P h [NPN]Ta) (p -N) (p -H) 3 , 66. " Lengths Angles Angles N(l)-Ta(l) 2.073(3) Ta(l)-N(3)-Ta(l) 2 81.4(3) N(2)-Ta(l)-P(l) 82.41(11) N(2)-Ta(2) 2.070(4) N(3)-Ta(l)-N(2) 94.6(2) N(l)-Ta(l)-P(l) 82.58(12) N(3)-Ta(l) 1.973(8) N(3)-Ta(l)-N(l) 95.1(3) N(3)-Ta(l) 2 2.059(7) N(3)-Ta(l)-P(l) 175.15(19) PO ) -Ta( l ) 2.624(5) N(2)-Ta(l)-N(l) 113.04(13) "Bond distances and angles identical by symmetry transformations are not shown. Initially, the X-ray data indicated the formation of a symmetric bis(nitride) complex with an inversion centre. However, examining the ellipsoids for N(3) revealed that they were extremely large and the solution was incorrect, as shown in Figure 6.5, even though residual error values were quite low. Incorrect assignment of atoms due to disorder is a common danger in crystallographic analyses. 3 8 On further analysis, the structure was determined to be a mono(nitride) complex disordered over two locations. Placing a 5 0 % occupancy on the N3 atom provides the given solution. Four hydrides were located within the diffraction pattern, as is also shown in Figure 6.5. Hydrides H4 and H4 were set at half occupancy to match the disorder in the bridging nitride. The hydride positions were confirmed using the X - H Y D E X mapping program. The structure is, as expected, the mono(nitride) tri(hydride) complex, 66 , and is in agreement with solution N M R studies. 194 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes Figure 6.5. O R T E P drawing (spheroids at 50% probability) of the structural core of an initial solution (left) and a correct solution (right) from data collection on 66. This structure was first solved as a bis(nitride), however N 3 is in fact disordered over the two positions. How does this mononitride form and why do we get a different product with 1,1-dimethylhydrazine? Initial loss of H 2 would generate the Ta=Ta double bond. Reaction of this species with R 2 N N H 2 and cleavage of the N - N bond would generate a bis(amide) complex ( I ) . Oxidative addition of an N - H bond would give an imide-amide-trihydride intermediate (II). For R - H , a 1,2-H 2 elimination from the remaining amide would generate the final product (III). In the reaction with 1,1-dimethylhydrazine, where R = Me, N - H addition cannot occur from this second amide bridge. Instead, reductive elimination of the amide as H N M e 2 would generate an imide-dihydride complex (IV). Oxidative addition of the remaining N - H imide bond would generate the observed nitride trihydride complex (V) . This proposed mechanistic pathway is shown in Scheme 6.5. In support of this mechanism, GC -MS of the headspace above reaction to form complex 66 indicate the presence of H N M e 2 , although it has not been observed in sealed tube N M R experiments, possibly due to its low concentration in solution and high volatility. 195 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes [ N P N ] T a ^ - - ^ T a [ N P N ] H - H , [NPN]Ta Ta [NPN] R 2 N N H 2 ox. add. R2 R 2 N X N R=H - -^>Hix N-H . - ^ H ^ [ N P N ] T a < M H ' ^ T a [ N P N ] - — [ N P N ] T a f c ^ ? T a [ N P N ] 1,2-H2 elim. ox. add. II N H N H 2 [NPN]Ta£ , III H ;:>Ta[NPN] N H R=Me N-H red. elim. [NPN]Ta^——>Ta[NPN] T V N I  |_| N-H ox. add. HNMe, Scheme 6.5 The activation of Me2NNH2 by 35 is particularly intriguing. Not only can this complex cleave the N - N bond in hydrazine, but it also promotes the formation and elimination of a functionalized nitrogen containing product. In the reaction with hydrazine, formation o f a bis(imide) is the thermodynamically favourable product. If one could functionalize one nitrogen atom prior to cleavage, however, the formation of imide shuts down and a nitrogen containing product, in this case Me2NH, is reductively eliminated. Functionalizing one nitrogen atom during dinitrogen activation could promote the release of a value-added nitrogen containing product. It is hoped that this knowledge can soon be applied to molecular nitrogen activating systems. 196 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 6.4 Future directions Throughout this dissertation it was shown that group five complexes stabilized by the diamidophosphine ligands R R [ N P N ] can promote a wide array o f chemical transformations. In this chapter, for instance, the tantalum hydride complexes 35 and 41 were able to promote the asymmetric activation o f alkynes, the cleavage o f nitriles and alkynes, and the cleavage of hydrazine and its derivatives. There is a plethora of small molecule candidates to consider for reactivity studies with this system and the potential reactions are certainly not exhausted by this dissertation. Many o f the complexes prepared in this work have extensive reactivity that remains unexplored. A s first discussed in Chapter 1, the addition of E - H bonds across M = N bonds in ( p h p h[NPN]Ta)2(p.-H)2(p.-r) 1:r)2-N2) gave new nitrogen-element bonds and terminal metal hydrides. Reacting primary silanes or boranes with ( C y P h [NPN]Ta)(u.-N)(u-H) 3 , 66 or ( ^ h rNPN ] T a ) ( ^ -NH) 2 ( ^ -H) 2 (R = Cy , 64; R = Ph, 65) could similarly afford new nitrogen-silicon and nitrogen-boron bonds. Investigating the reactivity of E - H bonds with both the asymmetrically activated alkyne complexes 59-61 and the bis(alkylidyne) complex 62 could promote similar activation. The cleavage of alkynes and formation of new carbon-silicon and carbon-boron bonds has great appeal. These ideas are presented in Scheme 6.6. 197 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes P h -. \ M e 2 S i - ^ N ^ / u \ / \ \ \ \ P h C y 66 P h E-H ? r , u P h P h = N y c\ y H \ p < r \ y ^ T a < ^ H ^ | a VsiMe 2 / l \ _>S iMe 2 \ N H N < 2 \ I i P h C y E p » M e ^ p / 'X M 7 i \ " N P h H R Y-N .1ST P<f\ M e 2 S i ^ T N ^ / \ \ \ R N I H 64, 65 N* \ P h P h If H A r , u P h P h = R M e 2 S i < / a ^ H ^ T t " N - V S l M e 2 7 V ^ f f V \ ^ S i M e * \ R H [ P h P h n L P h P h -. y N *H, P < A M e 2 S i ^ , N ^ M e 2 S \V ' \ R j P h P H H P h 59-61 S i M e 2 / E-H ? o u P h P h -. VN H XVH, P<"\ M e 2 S i ^ P A ^ \"'33i C \ N 'T \ i \ R ^ P h P N H E P h r . u p h P h P h VN Me 2 Si^N^-, \ P h H 62 N T ^ P h P h E-H ? P h y N P h M e 2 S i - ^ N ^ . / P h h P^h M e 2 S i ^ ' ^ T ( - ' ' N ^ S i M e 2 \ sV l P h P h HE P \ Scheme 6.6 Hydrogenation of these complexes presents the possibility o f ejecting a desired value-added product. Addit ion of H 2 to 62, for instance, could generate methane and primary alkanes. Hydrogenation of 64 and 65 could represent a conversion of hydrazine into ammonia. The proposed substituted products in Scheme 6.6 are also intriguing; hydrogenation of these complexes may access highly substituted products. The appeal to these reactions is the potential to regenerate the parent tetrahydride complexes 35 and 41, 198 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes presenting a real opportunity to catalytically access these transformations. These ideas are presented in Scheme 6.7. Scheme 6 . 7 Hindering the expansion and application of many of these chemical transformations has been the instability of the [NPN] ligand. The diamidophosphine ligand set can effectively stabilize highly reactive complexes and intermediates. However, these intermediates are at times so reactive that the ligand itself becomes a target for activation. The formation of vanadium and niobium imides, protonolysis of ligand to form [NPN]H2, P -C , N - C , and N - S i bond cleavage, and o-metalation of ligand substituents in tantalum systems are all examples of these decomposition routes. Diamidophosphine ligand sets are currently being developed with aryl backbones, effectively eliminating the sensitive N - S i linkage. Application of these ligands to mid-199 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes oxidation state vanadium and niobium systems would circumvent observed decomposition. For example, the ligand R P ( C 6 H 4 N R ' ) 2 , or R R ' [ N P N ] * , could form V(III) complexes of the form ( R R [ N P N ] * V C l ) n . Reduction of these complexes under N2 could lead to N 2 cleavage without concomitant decomposition to form vanadium imides. Similarly, reduction of R R [ N P N ] * N b C l 2 species under molecular nitrogen could access bridging N 2 complexes, ( R R ' [NPN]*NbCl ) 2 (p -N 2 ) , rather than R R ' [NPN]NbCl (=NR' ) . Accessing these dinitrogen complexes would be o f great interest. Developing new ligand systems may overcome the tribulations resulting from ligand decomposition. In designing chemical syntheses, it is always a balance between promoting a transformation and preventing unwanted reactions from occurring. The [NPN] ligand set can effectively stabilize reactive group five complexes and encourage novel chemical reactions - as long as it remembers it is only supposed to be a spectator. 6.5 Experimental 6.5.1 General considerations Unless otherwise stated, general procedures were performed as in Section 2.4.1. Selected complexes in this chapter do not have elemental analysis data due to problems with sample handling and the high air-sensitivity and nitrogen-sensitivity of these complexes. 6.5.2 Starting materials and reagents The reagents P h C N , P h C C H , l B u C C H , " P r C C H , P h C C P h , H 2 N N H 2 and Me2NNH2 were purchased from Aldr ich or S T R E M and purified by standard methods prior to use. Carbon monoxide gas was dried and deoxygenated by passage through a column containing activated molecular sieves and M n O prior to use. 200 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 6.5.3 Synthesis Preparation of ( p h P h [NPN]Ta) 2 (p-CPh)(p-N) , 58 A solution o f ( P h P h [ N P N ] T a ) 2 ( p - H ) 4 (500 mg, 0.405 mmol) in 20 m L E t 2 0 under A r was prepared in a vessel equipped with a Kontes valve. Benzonitrile (41.8 mg, 0.405 mol) was added to the flask via microsyringe, the vessel sealed and its contents stirred for 6 hours. A n initial colour change from deep purple to brown was followed by the slow formation of a bright blue solution, along with the evolution of a gas. Removal of solvent in vacuo left an oily deep blue solid. This solid was dissolved in pentane and dried under vacuum to afford ( p h P h [NPN]Ta) 2 (p-CPh)(p-N) in 71% yield. [ H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 -0.35, 0.24 (s, 24H, SiCrY 3 ) , 0.97-1.24 (m, 8H, P C / / 2 S i ) , 6.60-7.78 (m, 35H, N P h - / / , PPh- / / , CPh- / / ) . 1 3 C { ' H } N M R ( C 6 D 6 , 25°C, selected resonances): 8 285.8 (s, Ta-C-Ta) 3 , P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 20.5 (s). Ana l . Calcd for C55H79N5P2Si4Ta2: C , 49.06; H , 5.91; N , 5.20. Found: C , 49.24; H , 5.57; N , 5.26. Preparation of ( P h p h [NPN]Ta) 2 (p -H) 2 (p -PhCCH) , 59, ( P h P h [NPN]Ta) 2 (p -H) 2 (p -"PrCCH) , 60 and ( P h P h [NPN]Ta) 2 (p -H) 2 (p - t BuCCH) 61 A solution of ( p h P h [ N P N ] T a ) 2 ( p - H ) 4 (500 mg, 0.405 mmol) in 20 m L E t 2 0 under A r was prepared in a vessel equipped with a Kontes valve. R C C H (0.405 mol) was added to the flask via microsyringe, the vessel sealed and its contents stirred for 6 hours. A slow colour change from deep purple to brown was observed, along with the evolution of a gas. Removal o f solvent in vacuo left an dark brown solid. This solid was triturated with pentane and dried under vacuum to afford ( p h P h [NPN]Ta) 2 (p -H) 2 (p -PhCCH) , ( p h p h [NPN]Ta) 2 (p -H) 2 (p - n PrCCH) and ( p h P h [N PN ]Ta ) 2 ( p -H ) 2 ( p - t BuCCH ) in 92%, 80% and 88% yields. 59: ! H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8 -0.74, -0.48, -0.24, 0.00, 0.01, 0.09, 0.32, 0.64 (s, 24H, S i C / / 3 ) , 0.87-1.49 (m, 8H, P C / / 2 S i ) , 6.59-7.79 (m, 35H, N P h - / / , PPh-/ / , CPh-/ / ) , 11.65 (d of d of d, 1H, 2 J H H = 16.8 Hz , 2 J H p = 5.5 H z , V H P = 30.0 Hz , TaZ/Ta), 11.72 (d, 1H, 3 J H p = 11.8 Hz , P h C C / / ) , 13.14 (d o f d o f d, 1H, 2JHH = 16.8 Hz , V H P = 5.9 Hz , V H p = 31.8 Hz , TaZ/Ta). " C ^ H } N M R ( C 6 D 6 , 25 °C, selected 201 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes resonances): 5 224.2, 224.3 (TaHCCPh). 3 , P { 1 H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 18.14 (s), 20.01 (s). Ana l . Calcd for C 5 6 H 7 o N 6 P 2 S i 4 T a 2 : C , 50.37; H , 5.28; N , 4.20. Found: C , 50.24; H , 5.50; N , 4.26. 60: lH N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8 -0.20, -0.12, 0.06, 0.10, 0.15, 0.29, 0.31, 0.33 (s, 24H, S i C / / 3 ) , 0.46-1.61 (m, 13H, C H 2 C / / 2 C / / 3 , P C / / 2 S i ) , 3.08 (br, 2 H , T a C C / / 2 ) , 6.51-7.75 (m, 30H, N P h - / / , PPh-//) , 10.84 (d of d, 1H, V H P = 14.5, 20.5 H z , C H 2 C C / / ) , 11.03 (d of d of d, 1H, Ta//Ta), 11.56 (m, 1H, Ta/TTa). 1 3 C { ' H } N M R ( C 6 D 6 , 25 °C, selected resonances): 8 212.9, 214.3 ( T a H C C C ) . 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 11.91 (d, JPP = 4 Hz), 12.48 (d, JPP = 4 Hz). 61: ' H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8 -0.14, -0.11, 0.01, 0.06, 0.18, 0.19, 0.26, 0.34 (s, 24H, S i C / / 3 ) , 0.58-1.70 (m, 8H, P C / / 2 S i ) , 1.45 (s, 9H , C ( C / / 3 ) 3 ) , 6.44-7.89 (m, 30H, N P h - / / , PPh-//), 11.09 (d, 1H, J H p = 12.6 Hz , l B u C C / / ) , 11.51 (m, 1H, Ta/TTa), 12.08 (m, 1H, Ta//Ta). 1 3 C { ' H } N M R ( C 6 D 6 , 25 °C, selected resonances): 8 205.5, 205.3 (TaHCCC) 3 1 P { ! H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 6.10 (s), 9.17 (s). Preparation of ( p h P h [NPN]Ta) 2 (p -CH)(p-CPh) , 62 ( P h P h [NPN]Ta) 2 (p -H) 2 (p -PhCCH) (250 mg) was dissolved in 20 m L E t 2 0 in a vessel equipped with a Kontes valve. The contents o f the flask were frozen, and the vessel evacuated. Al lowing the brown solution to warm to room temperature, and stirring the contents for 12 hours prompted a lightening of the solution colour. Removal of volatiles in vacuo gave a light brown solid. Washing this solid with hexanes afforded ( P h P h [NPN]Ta) 2 (p-CH)(p-CPh) in 75% yield. ] H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 8 0.01, 0.10, 0.21, 0.33 (s, 24H, S i C / / 3 ) , 1.22 (m, 8H, P C / / 2 S i ) , 4.95 (d, 1H, Ta-C/ / ) , 6.62-7.37 (m, 35H, N P h - / / , PPh- / / , CPh- / / ) . ^ C ^ H } N M R ( C 6 D 6 , 25°C, selected resonances): 8 308.8, 311.2 (s, Ta-C-Ta) 3 1 P { 1 H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 8 11.5 (s). Preparation of 63 via addition of P h C C P h to 41 A solution of ( p h p h [ N P N ] T a ) 2 ( p - H ) 4 (500 mg, 0.405 mmol) in 20 m L E t 2 0 under A r was prepared in a vessel equipped with a Kontes valve. Diphenylacetylene (72.2 mg, 0.405 mol) was added to the flask via microsyringe, the vessel sealed and its contents stirred for 202 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes thirty minutes. A slow colour change from deep purple to orange was observed, along with the evolution of a gas. Removal of solvent in vacuo left an orange solid. This solid was triturated with pentane and dried under vacuum to afford 63 as an orange powder in 72% yield. Crystals of this product were grown from a saturated benzene solution. ! H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 -0.72 (s, 3H , S i C / / 3 ) , -0.01 (s, 3 H , S i C / / 3 ) , 0.02 (s, 3H, S1C//3), 0.03 (s, 3H , S i C / / 3 ) , 0.22 (s, 9H, S i (C/ / 3 ) 3 ) , 0.50 (s, 3H , S i C / / 3 ) , 0.84 (s, 3H, S i C / / 3 ) , 1.36-2.10 (m, 6H, P C / / 2 S i ) , 6.69-8.09 (m, 35H, N P h - / / , PPh- / / , TaPh-// , CPh-H). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 13.36 (d, V P P = 141 Hz) , 130.61 (d, V P P = 141 Hz). Anal . Calcd for C 6 o H 8 4 N 4 P 2 S i 4 T a 2 : C , 51.57; H , 6.06; N , 4.01. Found: C, 51.90; H , 6.39; N , 3.70. Preparation of ( C y P h [NPN]Ta) 2 (p.-NH) 2 (p.-H)2, 64 and ( P h P h ^ P N ] T a ) 2 ( u - N H ) 2 ( u - H ) 2 , 65 A solution of ( R P h [NPN]Ta) 2 (u -H) 4 (0.400 mmol) in 20 m L E t 2 0 under A r was prepared in a vessel equipped with a Kontes valve. Hydrazine (0.400 mmol) was added to the flask via microsyringe, the vessel sealed and its contents stirred for thirty minutes. A colour change from deep purple to yellow was observed, along with the evolution of a gas. Removal of solvent in vacuo left a yellow oily solid. This solid was triturated with pentane and dried under vacuum to afford ( R P h [NPN]Ta) 2 (u -NH) 2 (u -H) 2 . When R=Ph, crystals of this product can be grown from a saturated toluene/hexanes solution. 64: ! H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 0.19, 0.47 (s, 24H, S i C / / 3 ) , 1.18-1.70 (m, 30H, 2 C6HU, 4 P C / / 2 S i ) , 3.38 (d, 2 H , JHH = 7 Hz , N - / / ) , 6.81-7.53 (m, 20H, NPh- / / ) , 15.13 (d, 2H , JHH = 7 Hz , TaZ/Ta), 14.33 (m, 1H, Ta//Ta). 3 1 P { 1 H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 3.20 (s). 65: *H N M R ( C 6 D 6 , 25°C, 500 M H z ) : 5 0.19, 0.24 (s, 24H, S i C / / 3 ) , 1.24-1.48 (m, 8H, P C / / 2 S i ) , 4.21 (br, 2 H , NH), 6.95-7.26 (m, 30H, N P h - / / , PPh-//) , 14.83 (br, 2H , Ta//Ta). 3 1 P { ' H } N M R ( C 6 D 6 , 25°C, 202.5 M H z ) : 5 3.17 (s). Preparation of ( C y P h [NPN]Ta) 2 (u-N)(p,-H) 3 , 66 A solution of ( C y P h [ N P N ] T a ) 2 ( u - H ) 4 (500 mg, 0.401 mmol) in 20 m L E t 2 0 under A r was prepared in a vessel equipped with a Kontes valve. 1,1-Dimethylhydrazine (24.1 mg, 203 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 0. 401 mmol) was added to the flask via microsyringe, the vessel sealed and its contents stirred for thirty minutes. A colour change from deep purple to red was observed, along with the evolution of a gas. Removal of solvent in vacuo left a red, oily solid. This solid was triturated with pentane and dried under vacuum to afford (C y P h[NPN]Ta)2(p-N)(p-H)3 as a red powder in 84% yield. Crystals of this product were grown from a saturated benzene solution. ' H N M R (C 6 D 6 , 25°C, 500 MHz): 5 0.08, 0.19, 0.21, 0.24 (s, 24H, SiC// 3 ) , 0.58-1.85 (m, 30H, 2 C6Hlu 4 PCrY2Si), 6.85, 6.95, 7.17, 7.28 (m, 20H, NPh-//), 8.36 (d, 2H, TaZ/Ta), 14.33 (m, 1H, TaflTa). 3 1 P{'H} N M R (C 6 D 6 , 25°C, 202.5 MHz): 5 12.76 (d), 14.78 (d). Anal. Calcd for C52H93N5P2Si4Ta2: C, 47.15; H , 7.08; N , 5.29. Found: C, 47.40; H , 7.37; N , 5.24. 6.6 References 1. Zheng, P. Y . ; Nadasdi, T. T.; Stephan, D. W. Organometallics 1989, 8, 1393. 2. Miller, R. L. ; Wolczanski, P. T. J. Am. Chem. Soc. 1993,115, 10422. 3. CaseIIi, A . ; Solari, E.; Scopelliti, R.; Floriani, C. J. Am. Chem. Soc. 2000,122, 538. 4. Alonso, F. J. G.; Sanz, M . G.; Riera, V. ; Abril, A . A. ; Tiripicchio, A . ; Ugozzoli, F. Organometallics 1992, / / , 801. 5. Liu, X . Y . ; Riera, V . ; Ruiz, M . A. ; Bois, C. Organometallics 2001, 20, 3007. 6. Bernatis, P.; Laurie, J. C. V. ; DuBois, M . R. Organometallics 1990, 9, 1607. 7. Coons, D. E.; Laurie, J. C. V. ; Haltiwanger, R. C ; DuBois, M . R. J. Am. Chem. Soc. 1987,109, 283. 8. Morello, L. ; Love, J. B.; Patrick, B. O.; Fryzuk, M . D. J. Am. Chem. Soc. 2004, 126, 9480. 9. Johnson, S. A . Ligand design and the synthesis of reactive organometallic complexes of tantalum for dinitrogen activation; Department of Chemistry, University of British Columbia: Vancouver, 2001. 10. Cotton, F. A . ; Hall, W. T. Inorg. Chem. 1980,19, 2352. 11. Cotton, F. A . ; Hall, W. T. J. Am. Chem. Soc. 1979,101, 5094. 12. Cotton, F. A. ; Hall, W. T. Inorg. Chem. 1980,19, 2354. 204 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 13. Ahmed, K . J.; Chisholm, M . H . ; Folting, K . ; Huffman, J. C . Organometallics 1986, 5,2171. 14. Aggarwal, R. P.; Connelly, N . G . ; Crepso, M . C ; Dunne, B . J.; Hopkins, P. M . ; Orpen, A . G . J. Chem. Soc, Dalton Trans. 1992, 655. 15. Green, M . L . H . ; Hubert, J. D. ; Mountford, P. J. Chem. Soc, Dalton Trans. 1990, 3793. 16. Feng, Q.; Green, M . L . H . ; Mountford, P. J. Chem. Soc, Dalton Trans. 1992, 2171. 17. Cotton, F. A . ; Feng, X . Inorg. Chem. 1990, 29, 3187. 18. Thorn, D . L . ; Hoffman, R. Inorg. Chem. 1978, 77, 126. 19. Calhorda, M . J.; Hoffmann, R. Organometallics 1986, 5, 2181. 20. Mountford, P. J. Chem. Soc, Dalton Trans. 1994, 1843. 21. Listemann, M . L . ; Schrock, R. R. Organometallics 1985, 4, 74. 22. Schrock, R. R.; Listemann, M . L . ; Sturgeoff, L . G . J. Am. Chem. Soc. 1982,104, 4291. 23. Chisholm, M . H . ; Hoffman, D . M . ; Huffman, J. C. Inorg. Chem. 1983, 22, 2903. 24. Freudenberger, J. H . ; Pedersen, S. F.; Schrock, R. R. Bull. Soc Chim. Fr. 1985, 349. 25. Cotton, F. A . ; Schwotzer, W. ; Shamshoum, E . S. Organometallics 1984, 3, 1770. 26. Chamberlin, R. L . M . ; Rosenfeld, D . C ; Wolczanski, P. T.; Lobkovsky, E . Organometallics 2002, 27, 2724. 27. Mulford, D . R.; Clark, J. R.; Schweiger, S. W. ; Fanwick, P. E . ; Rothwell, I. P. Organometallics 1999, 75, 4448. 28. Heaton, B . T.; Jacob, C ; Page, P. Coord. Chem. Rev. 1996,154, 193. 29. Jahncke, M . ; Neels, A . ; Stoeckli-Evans, H . ; Vale, M . G . ; Suss-Fink, G . J. Organomet. Chem. 1998, 565, 97. 30. Chatt, J.; Heath, G . A . ; Richards, R. L . J. Chem. Soc, Dalton Trans. 1974, 2074. 31. Schrock, R. R.; Glassman, T. E . ; Vale, M . G . ; K o i , M . J. Am. Chem. Soc. 1993, 775, 1760. 32. Schollhammer, P.; Petition, F . Y . ; Poder-Guillou, S.; Saillard, J. Y . ; Talarmin, J.; Muir , K . W . Chem. Commun. 1996, 2633. 205 References begin on page 204. Chapter Six: Promoting chemistry with [NPN] supported tantalum complexes 33. Schollhammer, P.; Guenin, E . ; Petillon, F. Y.; Talarmin, J.; Muir, K. W.; Yufit, D. S. Organometallics 1998,17, 1922. 34. Petillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Inorg. Chem. 1999, 55, 1954. 35. Nakajima, Y.; Suzuki, H. Organometallics 2003, 22, 959. 36. Seino, H.; Masumori, T.; Hidai, M. ; Mizobe, Y. Organometallics 2003, 22, 3424. 37. Fryzuk, M. D.; MacKay, B. A.; Patrick, B. O. J. Am. Chem. Soc. 2003,125, 3234. 38. Harlow, R. J. J. Res. Nat. Inst. Stand. Tech. 1996,101, 327. 206 References begin on page 204. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Appendix One: X- ray crystal structure experimental information In all cases throughout this dissertation, suitable crystals were selected and coated in Paratone-N oi l or an acceptable substitute under an inert atmosphere. Crystals were then mounted on a glass fiber external to the glovebox environment. A l l measurements were made on a R igaku /ADSC C C D area detector with graphite monochromated M o - K a radiation. Crystallographic data and details of structural refinement appear with the structure in question throughout the dissertation. Structures presented in Chapters 2 and 3 were collected and solved with the assistance o f Dr. Brian O. Patrick. Structures presented in Chapters 4, 5 and 6 were collected with the assistance of Christopher D . Carmichael, and solved by the author. In each case the data were collected at a temperature o f -100 ± 1 °C. The data were processed using the d * T R E K program 1 in the CrystalClear software package (v. 1.3.5), and corrected for Lorentz and polarization effects and absorption. Neutral atom scattering factors for al l non-hydrogen atoms were taken from Cromer and Waber. Anomalous dispersion effects were included in Fcalc. 3 The structure was solved by direct methods using SIR92 4 or SIR2002 5 and expanded using Fourier techniques. A l l non-hydrogen atoms were refined anisotropically using S H E L X L - 9 7 . 6 When hydrogen atom locations were important to determine compound composition or connectivity, hydrogen atoms were located and refined isotropically. Otherwise, hydrogen atoms were included in fixed positions. Their positional parameters were calculated with fixed C - H bond distances of 0.99 A for sp 2 C, 0.98 A for sp C, and 0.95 A for aromatic sp C, with U\so set to 1.2 times £/ e q of the 2 3 attached sp or sp C and 1.5 times the £/ e q values o f the attached sp C atoms. Methyl hydrogen torsion angles were determined from electron density. Structure solution and refinements were conducted using the W i n G X software package, version 1.64.05.7 Data files (.cif format) for many of these structures are available on-line at http://www.ccdc.cam.ac.uk/ or at http://www.chem.ubc.ca/faculty/fryzuk/. 207 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and DFT calculation data A . l . References 1. Pflugrath, J. W . Acta Cryst. 1999, D55. 2. Cromer, D . T.; Waber, J. T. International Tables for X-ray Crystallography. 1974, Vol. IV, Kynoch Press. 3. Ibers, J. A . ; Hamilton, W. C. Acta Cryst. 1964,17, 781. 4. Altomare, A . ; Burla, M . C ; Camalli , M . ; Cascarano, G . ; Giacovazzo, C ; Guagliardi, A . ; Polidori, G . J. Appl. Crystallogr. 1993, 26, 343. 5. Burla, M . C ; Camalli , M . ; Carrozzini, G . L . ; Cascarano, G . L . ; Giacovazzo, C ; Polidori, G . ; Spagna, R. J. Appl. Cryst. 2003, 36, 1103. 6. Sheldrick, G . M . Shelx97. Programs for Crystal Structure Analysis. 1997, University of Gottingen, Germany. 7. Farrugia, L . J. J. Appl. Crystallogr. 1999, 32, 837. 208 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Appendix Two: Methods, z-matricies, init ial parameters and f inal coordinates for optimized density functional theory calculations Table A l . Method and Z-matrix for model complex 4A. # GFINPUT B 3 L Y P / L A N L 2 D Z Opt=(maxcy=200) SCF=(maxcy=512) IOP(6/7=3) n p n l i 2 0 1 c n 1 d l s i 2 d2 1 a l c 3 d3 2 a2 1 d h l P 4 d4 3 a3 2 dh2 c 5 d5 4 a4 3 dh3 c 5 d6 4 a5 3 dh4 s i 7 d7 5 a6 4 dh5 n 8 d8 7 a7 5 dh6 c 9 d9 8 a8 7 dh7 l i 9 d l O 8 a9 7 dh8 l i 2 d i l 3 a l O 4 dh9 o 12 d l 2 2 a l l 3 dh lO c 13 d l 3 12 a l 2 2 d h l l c 13 d l 4 12 a l 3 2 d h l 2 h 1 d l 5 2 a l 4 3 d h l 3 h 1 d l 6 2 a l 5 3 d h l 4 h 1 d l 7 2 a l 6 3 d h l 5 h 3 d l 8 4 a l 7 5 d h l 6 h 3 d l 9 4 a l 8 5 d h l 7 h 4 d20 3 a l 9 2 d h l 8 h 4 d21 3 a20 2 d h l 9 h 6 d22 5 a21 4 dh20 h 6 d23 5 a22 " 4 dh21 h 6 d24 5 a23 4 dh22 h 7 d25 5 a24 4 dh23 h 7 d2 6 5 a25 4 dh24 h 8 d27 7 a26 5 dh25 h 8 d28 7 a27 5 dh2 6 h 10 d2 9 9 a28 8 dh27 h 10 d30 9 a29 8 dh28 h 10 d31 9 a30 8 dh2 9 h 14 d32 13 a31 12 dh30 h 14 d33 13 a32 12' dh31 h 14 d34 13 a33 12 dh32 h 15 d35 13 a34 12 dh33 h 15 d36 13 a35 12 dh34 h 15 d37 13 a36 12 dh35 209 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A2. Initial parameters for model complex 4A. d l 1. 39 a l 3 124 82 d2 1. 701 a l 4 109 47 d3 1. 899 a l 5 109 47 d4 1 838 a l 6 109 47 d5 1 857 a l 7 106 5 d6 1 848 a l 8 108 .8 d7 1 894 a l 9 108 . 91 d8 1 71 a20 108 . 9 d9 1 385 a21 108 . 33 d l O 2 068 a22 110 .49 d l l 1 987 a23 111 . 84 d l 2 1 915 a24 108 . 93 d l 3 1 445 a25 108 . 93 d l 4 1 427 a26 106 . 64 d l 5 1 098 a27 106 . 42 d l 6 1 098 a28 109 .47 d l 7 1 098 a29 - 109 .47 d l 8 1 493 a30 109 .47 d l 9 1 493 a31 110 .46 d20 0 97 a32 110 . 47 d21 0 97 a33 106 .3 d22 0 98 a34 110 .78 d23 0 98 a35 110 . 77 d24 0 98 a36 104 . 88 d25 0 97 d h l 9 1 . 9 d2 6 0 97 dh2 3 5 . 4 d27 1 4 93 dh3 179 d28 1 493 dh4 7 1 . 3 d29 1 098 dh5 230 . 9 d30 1 098 dh6 44 . 3 d31 1 098 dh7 185 . 1 d32 0 97 dh8 323 . 6 d33 0 . 97 dh9 257 . 4 d34 0 . 97 d h l O 267 . 7 d35 0 . 97 d h l l 178 . 1 d36 0 . 97 d h l 2 329 .8 d37 0 . 97 d h l 3 0 a l 1 2 3 . 7 5 d h l 4 120 a2 112 . 7 d h l 5 240 a3 1 1 3 . 3 d h l 6 163 .2 a4 102 . 9 " d h l 7 276 . 6 a5 1 0 3 . 2 5 d h l 8 156 .8 a6 1 1 3 . 2 d h l 9 274 a7 1 0 8 . 1 5 dh20 308 . 5 a8 1 2 3 . 1 3 dh21 67 a9 112 . 89 dh22 189 .2 a l O 1 0 6 . 4 6 dh23 352 . 3 a l l 1 3 4 . 0 9 dh2 4 109 . 8 a l 2 1 2 5 . 2 6 dh25 168 . 7 dh26 282 9 dh27 0 dh28 120 dh2 9 240 dh30 3 .4 dh31 243 2 dh32 123 3 dh33 123 dh34 2 .1 dh35 242 6 210 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A3. Final atomic coordinates for the geometry optimization of 4 A . Centre Atomic Atomic Coordinates (Angstroms) Number Number Type X Y z 1 6 0 0 054048 -1 286894 -2 971197 2 7 0 0 501641 -0 577422 -1 732392 3 14 0 2 219700 -0 652928 -1 397932 4 6 0 2 678603 0 495079 0 071086 5 15 0 1 424072 1 918320 0 343776 6 6 0 2 484975 3 186529 1 281569 7 6 0 0 334909 1 225591 1 775962 8 14 0 -1 534478 1 477871 1 458088 9 7 0 -1 873570 0 773324 -0 109568 10 6 0 -3 275066 0 847071 -0 611015 11 3 0 -0 395814 1 134199 -1 367511 12 3 0 -0 928590 -0 951199 -0 406253 13 8 0 -1 305190 -2 623547 0 401089 14 6 0 -2 464796 -2 836325 1 264174 15 6 0 -0 481113 -3 811969 0 192387 16 1 0 0 538220 -0 905453 -3 891066 17 1 0 0 242119 -2 380607 -2 953900 18 1 0 -1 033623 -1 161971 -3 117979 19 1 0 3 070649 -0 237322 -2 569670 20 1 0 2 726217 -2 033174 -1 045769 21 1 0 2 798689 -0 065217 1 008167 22 1 0 3 651406 0 955716 -0 152150 23 1 0 3 019193 2 714334 2 115006 24 1 0 3 211191 3 635927 0 595260 25 1 0 1 837442 3 979843 1 671702 26 1 0 0 549954 0 152559 1 877296 27 1 0 0 639888 1 701102 2 718109 28 1 0 -2 278241 0 848837 2 612455 29 1 0 -1 823737 2 951243 1 583962 30 1 0 -4 010845 0 342210 0 048806 31 1 0 -3 640873 1 884262 -0 742666 32 1 0 -3 357254 0 359464 -1 597078 33 1 0 -2 969493 -1 871333 1 345207 34 1 0 ' -2 143125 -3 173579 2 259728 35 1 0 -3 140800 -3 580535 0 819317 36 1 0 -0 099978 -4 184863 1 153831 37 1 0 0 352135 -3 502866 -0 442352 38 1 0 -1 064446 -4 599004 -0 306531 211 References located on page Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A4. Method and Z-matrix for model complex 4B. # GFINPUT B 3 L Y P / L A N L 2 D Z Opt=(maxcy=200) SCF=(maxcy=512) IOP(6/7=3) tame3g 0 1 t a n 1 n t a 2 n 1 n t a 3 2 n t a n 3 s i 2 s i n 4 1 s i n t a 4 3 d i h 4 s i 3 s i n 5 1 s i n t a 5 2 d i h 5 c 4 c s i 6 2 c s i n 6 1 d i h 6 c 5 c s i 7 3 c s i n 7 1 d i h 7 P 1 p t a 8 2 p t an8 4 d i h 8 c 1 c t a 9 2 c t a n 9 4 d i h 9 h 9 h c l O 1 h c t a l O 2 d i h l O h 9 h e l l 1 h c t a l l 2 d i h l l h 9 h c l 2 1 h c t a l 2 2 d i h l 2 c 1 c t a l 3 2 c t a n l 3 4 d i h l 3 h 13 h c l 4 1 h c t a l 4 2 d i h l 4 h 13 h c l 5 1 h c t a l 5 2 d i h l 5 h 13 h c l 6 1 h c t a l 6 2 d i h l 6 c 1 c t a l 7 2 c t a n l 7 4 d i h l 7 h 17 h c l 8 1 h c t a l 8 2 d i h l 8 h 17 h c l 9 1 h c t a l 9 2 d i h l 9 h 17 hc20 1 h c t a 2 0 2 d i h 2 0 c 2 cn21 1 c n t a 2 1 3 d i h 2 1 h 21 hc22 2 hcn22 1 d i h 2 2 h 21 hc23 2 hcn23 1 d i h 2 3 h 21 hc24 2 hcn24 1 d i h 2 4 c 3 cn25 1 c n t a 2 5 2 d i h 2 5 h 25 hc26 3 hcn26 1 d i h 2 6 h 25 hc27 3 hcn27 1 d i h 2 7 h 25 hc28 3 hcn28 1 d i h 2 8 c 8 cp29 1 c p t a 2 9 2 d i h 2 9 h 29 hc30 8 hcp30 1 d i h 3 0 h 29 hc31 8 hcp31 1 d i h 3 1 h 29 hc32 8 hcp32 1 d i h 3 2 h 4 h s i 3 3 2 h s i n 3 3 1 d i h 3 3 h 4 h s i 3 4 2 h s i n 3 4 1 d i h 3 4 h 5 h s i 3 5 3 h s i n 3 5 1 d i h 3 5 h 5 h s i 3 6 3 h s i n 3 6 1 d i h 3 6 h 6 hc37 4 h c s i 3 7 2 d i h 3 7 h 6 hc38 4 h c s i 3 8 2 d i h 3 8 h 7 hc39 5 h c s i 3 9 3 d i h 3 9 h 7 hc40 5 h c s i 4 0 3 d i h 4 0 212 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A5. Initial parameters for model complex 4B n ta2 2 . 0 6 6 4 6 9 c t a n l 7 140 .204 d i h 3 1 1 7 1 . 802 n t a 3 2 . 040078 d i h l 7 - 1 9 0 . 1 0 1 hc32 1.099157 n t an3 124 .479 h c l 8 1.099157 hcp32 1 1 0 . 9 0 5 s i n 4 1 .775193 h c t a l 8 110 .905 d i h 3 2 - 6 7 . 6 6 6 s i n t a 4 125 .188 d i h l 8 - 1 . 1 0 6 h s i 3 3 1 .492799 d i h 4 1 1 . 3 3 9 h c l 9 1.099157 h s i n 3 3 1 1 2 . 1 3 1 s i n 5 1.792287 h c t a l 9 110 .905 d i h 3 3 149 .814 s i n t a 5 1 3 4 . 6 6 9 d i h l 9 - 1 2 0 . 6 9 4 h s i 3 4 1 .492799 d i h 5 - 8 4 . 3 4 8 hc20 1.099157 h s i n 3 4 1 1 2 . 1 3 1 c s i 6 1 .908015 h c t a 2 0 110 .905 d i h 3 4 - 8 9 . 9 1 3 c s i n 6 1 0 4 . 9 0 1 d i h 2 0 118 .919 h s i 3 5 1 .492799 d i h 6 30 .368 cn21 1.493606 h s i n 3 5 1 1 0 . 1 4 0 c s i 7 1 .897366 c n t a 2 1 118 .950 d i h 3 5 - 1 0 0 . 5 1 2 c s i n 7 107 .232 d i h 2 1 -158 .888 h s i 3 6 1 .492799 d i h 7 2 1 . 3 7 6 hc22 1.099157 h s i n 3 6 110 . 140 p t a8 2 .708000 hcn22 110 .905 d i h 3 6 141 .677 p tan8 74 .468 d i h 2 2 217 .027 hc37 1 .096113 d i h 8 - 4 5 . 7 6 2 hc23 1.099157 h c s i 3 7 111 .749 c t a 9 2 . 2 3 7 6 4 1 hcn23 110 .905 d i h 3 7 138 .334 c t a n 9 8 8 . 4 3 6 d i h 2 3 - 2 3 . 7 2 1 hc38 1 .096113 d i h 9 - 1 2 3 . 4 5 9 hc2 4 1.099157 h c s i 3 8 111 .749 h c l O 1.099157 hcn24 110 .905 d i h 3 8 - 1 0 0 . 3 0 4 h c t a l O 110 . 905 d i h 2 4 9 6 . 0 9 9 hc39 1 .096113 d i h l O 147 . 649 cn25 1.513930 h c s i 3 9 1 1 2 . 1 1 3 h e l l 1. 099157 c n t a 2 5 115 .765 d i h 3 9 1 2 6 . 7 2 3 h c t a l l 110 .905 d i h 2 5 107 .965 hc40 1 .096113 d i h l l 2 6 . 6 1 7 hc26 1.099157 h c s i 4 0 1 1 2 . 1 1 3 h c l 2 1.099157 hcn2 6 110 .905 d i h 4 0 - 1 1 1 . 5 6 0 h c t a l 2 110 .905 d i h 2 6 - 1 3 6 . 5 9 3 d i h l 2 - 9 3 . 8 1 7 hc27 1.099157 c t a l 3 2 . 2 3 3 4 9 9 hcn27 110 .905 c t a n l 3 81 .664 d i h 2 7 - 1 7 . 3 0 0 d i h l 3 1 0 9 . 5 5 9 hc28 1.099157 h c l 4 1 .099157 hcn28 110 .905 h c t a l 4 1 1 0 . 9 0 5 d i h 2 8 - 2 5 7 . 4 2 3 d i h l 4 - 5 7 . 9 7 4 cp2 9 1.879447 h c l 5 1.099157 c p t a 2 9 127 .189 h c t a l 5 110 .905 d i h 2 9 - 6 9 . 8 8 3 d i h l 5 6 1 . 3 4 9 hc30 1.099157 h c l 6 1.099157 hcp30 110 .905 h c t a l 6 110 .905 d i h 3 0 51 .447 d i h l 6 -180 . 058 . hc31 1.099157 c t a l 7 2 .215412 " hcp31 110 .905 213 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A6. Final atomic coordinates for the geometry optimization of 4B. Centre Atomic Atomic Coordinates (Angstroms) Number Number Type X Y z 1 73 0 0 855759 -0 218769 0 235128 2 7 0 0 765315 1 706739 -0 477720 3 7 0 -0 286196 -1 514281 -0 813958 4 14 0 -0 548953 2 273637 -1 543790 5 14 0 -1 864239 -2 322032 -0 554413 6 6 0 -2 180204 1 388668 -1 080677 7 6 0 -3 012675 -1 098665 0 342148 8 15 0 -1 980332 0 475233 0 579716 9 6 0 0 795702 0 590188 2 286450 10 1 0 0 401072 -0 118660 3 027971 11 1 0 0 258608 1 542506 2 380273 12 1 0 1 858226 0 762549 2 538041 13 6 0 2 882457 -0 166198 -0 654460 14 1 0 2 905318 0 357939 -1 622650 15 1 0 3 529186 0 396048 0 041516 16 1 0 3 332659 -1 161251 -0 769561 17 6 0 1 858271 -1 848282 1 358660 18 1 0 2 743004 -1 540200 1 932643 19 1 0 2 164268 -2 656561 0 673032 20 1 0 1 122763 -2 270002 2 069928 21 • 6 0 1 838484 2 714208 -0 235440 22 1 0 1 436816 3 738840 -0 200782 23 1 0 2 327986 2 522716 0 726858 24 1 0 2 613808 2 680660 -1 016256 25 6 0 0 488836 -2 161109 -1 939139 26 1 0 -0 105299 -2 162240 -2 864274 27 1 0 1 417203 -1 620251 -2 143802 28 1 0 0 760050 -3 199398 -1 693113 29 6 0 -2 975692 1 541595 1 784102 30 1 0 -2 503037 2 526784 1 862102 31 1 0 -4 010926 1 662506 1 444863 32 1 0 -2 969074 1 076100 2 775088 33 1 0 -0 700464 3 747129 -1 354887 34 1 0 -0 287613 2 045811 -2 997530 35 1 0 -1 716543 -3 581804 0 229395 36 1 0 -2 416276 -2 690599 -1 889841 37 1 0 -3 018196 2 095722 -1 033558 38 1 0 -2 .423050 0 .640170 -1 843336 39 1 0 -3 .935266 -0 .906462 -0 218274 40 1 0 -3 .290849 -1 .478502 1 .332793 214 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A7. Method and Z-matrix for model complex 4C. # GFINPUT B 3 L Y P / L A N L 2 D Z Opt=(maxcy=200) SCF=(maxcy=512) IOP(6/7=3) t a2h41 0 1 c p 1 pc2 c 2 cp3 1 cpc3 s i 3 s i c 4 2 s i c p 4 1 d i h 4 n 4 n s i 5 3 n s i c 5 2 d i h 5 c 5 cn6 4 c n s i 6 3 d i h 6 s i 1 s i c 7 2 s i c p 7 3 d i h 7 n 7 n s i 8 1 n s i c 8 2 d i h 8 t a 8 t a n 9 7 t a n s i 9 1 d i h 9 t a 9 t a t a l O 8 t a t a n l O 7 d i h l O n 10 n t a l l 9 n t a t a l l 8 d i h l l s i 11 s i n l 2 10 s i n t a l 2 9 d i h l 2 c 12 c s i l 3 11 c s i n l 3 10 d i h l 3 P 13 p c l 4 12 p c s i l 4 11 d i h l 4 c 14 c p l 5 13 c p c l 5 12 d i h l 5 s i 15 s i c l 6 14 s i c p l 6 13 d i h l 6 n 16 n s i l 7 15 n s i c l 7 14 d i h l 7 c 17 c n l 8 16 c n s i l 8 15 d i h l 8 c 8 c n l 9 7 c n s i l 9 1 d i h l 9 c 2 cp20 1 cpc20 7 d i h 2 0 c 14 cp21 10 c p t a 2 1 9 d i h 2 1 c 11 cn22 10 c n t a 2 2 9 d i h 2 2 h 9 h t a 2 3 8 h t a n 2 3 7 d i h 2 3 h 9 h ta24 8 h tan24 7 d i h 2 4 h 9 h t a 2 5 8 h t an25 7 d i h 2 5 h 9 h t a 2 6 8 h t a n 2 6 7 d i h 2 6 h 1 hc27 7 h c s i 2 7 8 d i h 2 7 h 15 hc28 14 hcp28 10 d i h 2 8 h 1 hc29 7 h c s i 2 9 8 d i h 2 9 h 15 hc30 14 hcp30 10 d i h 3 0 h 3 hc31 2 hcp31 1 d i h 3 1 h 13 hc32 14 hcp32 10 d i h 3 2 h 3 hc33 2 hcp33 1 d i h 3 3 h 13 hc34 14 hcp34 10 d i h 3 4 h 7 h s i 3 5 1 h s i c 3 5 2 d i h 3 5 h 16 h s i 3 6 17 h s i n 3 6 10 d i h 3 6 h 7 h s i 3 7 1 h s i c 3 7 2 d i h 3 7 h 16 h s i 3 8 17 h s i n 3 8 10 d i h 3 8 h 4 h s i 3 9 5 h s i n 3 9 9 d i h 3 9 h 12 h s i 4 0 11 h s i n 4 0 10 d i h 4 0 h 4 h s i 4 1 5 h s i n 4 1 9 d i h 4 1 h 12 h s i 4 2 11 h s i n 4 2 10 d i h 4 2 h 19 hc43 8 hcn43 7 d i h 4 3 h 18 hc44 17 hcn44 10 d i h 4 4 h 19 hc45 8 hcn45 7 d i h 4 5 h 18 hc4 6 17 hcn46 10 d i h 4 6 h 19 hc47 8 hcn47 7 d i h 4 7 h 18 hc48 17 hcn48 10 d i h 4 8 h 6 hc49 5 hcn4 9 9 d i h 4 9 h 22 hc50 11 hcn50 10 d i h 5 0 h 6 hc51 5 hcn51 9 d i h 5 1 h 22 hc52 11 hcn52 10 d i h 5 2 h 6 hc53 5 hcn53 9 d i h 5 3 h 22 hc54 11 hcn54 10 d i h 5 4 h 20 hc55 2 hcp55 1 d i h 5 5 h 21 hc56 14 hcp56 10 d i h 5 6 h 20 hc57 2 hcp57 1 d i h 5 7 h 21 hc58 14 hcp58 10 d i h 5 8 h 20 hc59 2 hcp5 9 1 d i h 5 9 h 21 hc60 14 hcp60 10 d i h 6 0 215 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A8. Initial parameters for model complex 4C. pc2 1 .912962 c n s i l 9 117 . 841 d i h 3 5 - 92 .438 hc52 1.102232 cp3 1. 910039 d i h l 9 146 .940 h s i 3 6 1 .494356 hcn52 110 .919 cpc3 1 0 6 . 5 1 1 cp20 1. 880060 h s i n 3 6 114 . 425 d i h 5 2 11 .570 s i c 4 1 .907345 cpc20 104 .776 d i h 3 6 -85 . 971 hc53 1.103893 s i c p 4 108 .688 d i h 2 0 113 .113 h s i 3 7 1 .495952 hcn53 112 .147 d i h 4 9 7 . 7 8 3 cp21 1 .880061 h s i c 3 7 1 0 9 . 7 1 6 d i h 5 3 - 1 3 0 . 7 4 5 n s i 5 1 .774586 c p t a 2 1 123 .858 d i h 3 7 1 5 0 . 7 6 8 hc54 1.103893 n s i c 5 107 .979 d i h 2 1 - 9 . 6 3 8 h s i 3 8 1. 495950 hcn54 112 .147 d i h 5 12 .672 cn22 1. 491548 h s i n 3 8 110 .748 d i h 5 4 130 .746 cn6 1.491548 c n t a 2 2 117 .224 d i h 3 8 152 . 981 hc55 1.094214 c n s i 6 115 .173 d i h 2 2 7 7 . 4 8 6 h s i 3 9 1 .495473 hcp55 108 .731 d i h 6 - 1 7 9 . 4 6 3 h t a 2 3 1.964978 h s i n 3 9 1 1 2 . 6 2 5 d i h 5 5 179 .600 s i c 7 1 .912463 h t a n 2 3 152 .605 d i h 3 9 - 1 2 1 . 577 hc56 1.094215 s i c p 7 1 0 7 . 2 8 9 d i h 2 3 - 3 0 . 5 4 1 h s i 4 0 1.495474 hcp56 108 .731 d i h 7 - 1 3 6 . 3 3 6 h ta24 1.996562 h s i n 4 0 112 . 625 d i h 5 6 5 6 . 9 7 9 n s i 8 1 .769386 h tan24 88 .837 d i h 4 0 1 2 1 . 5 7 9 hc57 1.094006 n s i c 8 106 .048 d i h 2 4 - 1 1 8 . 4 3 8 h s i 4 1 1 .498538 hcp57 109 .133 d i h 8 3 1 . 1 2 0 h t a 2 5 1.966341 h s i n 4 1 110 . 833 d i h 5 7 - 6 1 . 7 9 2 t a n 9 2 . 0 4 9 3 5 6 h t an25 94 .983 d i h 4 1 1 1 9 . 8 7 5 hc58 1.094005 t a n s i 9 1 2 4 . 0 1 6 d i h 2 5 - 5 9 . 3 3 5 h s i 4 2 1 .498538 hcp58 109 .133 d i h 9 - 3 4 . 0 0 9 h t a 2 6 2 .000745 h s i n 4 2 1 1 0 . 8 3 3 d i h 5 8 - 6 1 . 6 2 9 t a t a l O 2 . 799742 h t a n 2 6 140 .031 d i h 4 2 - 1 1 9 . 8 7 3 hc59 1.095852 t a t a n l O 1 2 7 . 4 9 3 d i h 2 6 - 1 5 5 . 6 5 8 hc43 1 .102820 hcp59 110 .576 d i h l O - 9 4 . 4 3 8 hc27 1.097245 hcn4 3 112 .262 d i h 5 9 59 .105 n t a l l 2 .048747 h c s i 2 7 109 .783 d i h 4 3 69 .238 hc60 1.095852 n t a t a l l 127 .285 d i h 2 7 - 8 6 . 5 6 3 hc44 1 .102820 hcp60 110 .576 d i h l l 19 .564 hc28 1.097245 hcn4 4 112 .262 d i h 6 0 177 . 475 s i n l 2 1.774597 hcp28 108 .469 d i h 4 4 1 0 9 . 8 7 1 s i n t a l 2 1 2 7 . 5 9 6 d i h 2 8 - 9 8 . 2 5 4 hc45 1.102674 d i h l 2 - 1 0 3 . 6 2 2 hc29 1.096837 hcn4 5 1 1 0 . 6 3 9 c s i l 3 1 .907333 h c s i 2 9 113 .178 d i h 4 5 - 1 7 1 . 9 7 7 c s i n l 2 1 0 7 . 9 7 9 d i h 2 9 152 .717 hc4 6 1.102674 d i h l 3 0 .556 hc30 1. 096836 hcn4 6 1 1 0 . 6 3 9 p c l 4 1 .910031 hcp30 110 .055 d i h 4 6 - 8 . 9 1 4 p c s i l 4 1 0 8 . 6 8 5 d i h 3 0 143 .818 hc47 1 .102646 d i h l 4 - 1 2 . 6 6 7 hc31 1 .097433 hcn47 1 1 1 . 9 8 1 c p l 5 1 .912972 hcp31 106 .523 d i h 4 7 - 5 2 . 7 2 4 c p c l 5 1 0 6 . 5 1 1 d i h 3 1 -144 . 280 hc48 1 .102645 d i h l 5 - 9 7 . 7 8 7 hc32 1.097434 hcn48 1 1 1 . 9 8 1 s i c ! 6 1.912477 hcp32 106 .523 d i h 4 8 - 1 2 8 . 1 6 8 s i c p l 6 107 .294 d i h 3 2 - 1 0 0 . 3 2 7 hc49 1 .102359 d i h l 6 136 .334 hc33 1.096788 hcn4 9 1 1 1 . 6 9 1 n s i l 7 1.769374 hcp33 111 .185 d i h 4 9 1 0 7 . 4 0 1 n s i c l " 106 .047 d i h 3 3 - 2 7 . 0 3 4 hc50 1 .102359 d i h l 7 - 3 1 . 1 1 7 hc34 1.096790 hcn50 1 1 1 . 6 9 1 c n l 8 1 .489380 hcp34 111 .190 d i h 5 0 - 1 0 7 . 4 0 0 c n s i l 8 117 .843 d i h 3 4 142 .425 hc51 1 .102232 d i h l 8 - 1 4 6 . 9 3 6 h s i 3 5 1.494355 hcn51 110 . 920 c n l 9 1.489378 h s i c 3 5 108 .842 d i h 5 1 - 1 1 . 569 216 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A 9 . Final atomic coordinates for the geometry optimization of 4C. Centre Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z 1 6 0 -4 . 631737 - 1 . 265969 0. 205073 2 15 0 - 3 . 369295 - 0 . 815218 - 1 . 155695 3 6 0 -4 . 116063 0 651928 -2 . 081635 4 14 0 - 3 . 534917 2 217395 - 1 . 156055 5 7 0 - 2 . 525804 1 659143 0. 184573 6 6 0 - 2 . 347172 2 681999 1. 264807 7 14 0 - 3 . 927972 -0 893360 1. 949423 8 7 0 - 2 . 130152 -1 000951 1. 901401 9 73 0 -1 280570 -0 042278 0. 347777 10 73 0 1 301907 0 095285 - 0 . 226529 11 7 0 2 042706 -1 240772 -1 576010 12 14 0 3 757364 -1 734918 -1 714655 13 6 0 4 484858 -1 814688 0 044462 14 15 0 3 587978 -0 534723 1 123133 15 6 0 4 678470 1 018392 1 016209 16 14 0 3 928038 2 159814 -0 316138 17 7 0 2 156332 1 945078 -0 231810 18 6 0 1 387689 3 230453 -0 301436 19 6 0 -1 506859 -1 806227 2 991307 20 6 0 -3 455315 -2 262415 -2 358759 21 6 0 3 846105 -1 157899 2 888746 22 6 0 1 198333 -1 840558 -2 666073 23 1 0 -0 125692 0 638235 -1 336380 24 1 0 0 402049 -0 749685 1 179168 25 1 0 -0 668574 -1 429960 -0 603186 26 1 0 -0 074411 1 227883 0 903316 27 1 0 -5 575139 -0 733769 0 028986 28 1 0 5 725959 0 751499 0 830371 29 1 0 -4 840403 -2 340872 0 121379 30 1 0 4 627333 1 529876 1 986411 31 1 0 -3 723417 0 635259 -3 105689 32 1 0 4 276931 -2 806258 0 467551 33 1 0 -5 208086 0 571245 -2 136499 34 1 0 5 570491 -1 659542 0 069511 35 1 0 -4 432582 -1 942065 2 885167 36 1 0 4 280639 3 578612 -0 023411 37 1 0 -4 428847 0 421861 2 429201 38 1 0 4 517038 1 812011 -1 640685 39 1 0 -2 850715 3 123939 -2 130811 40 1 0 3 832929 -3 083076 -2 349285 41 1 0 -4 714515 2 975622 -0 635731 42 1 0 4 575507 -0 809253 -2 550769 43 1 0 -1 882178 -2 841679 2 996480 44 1 0 1 694056 3 .928241 0 494620 45 1 0 -0 423105 -1 .834788 2 849144 46 1 0 0 321036 3 .030472 -0 196436 47 1 0 -1 710478 -1 .370514 3 982660 48 1 0 1 539368 3 .730284 -1 271744 49 1 0 -1 571445 3 .424400 1 013525 50 1 0 1 282579 -2 .938958 -2 680120 51 1 0 -2 .044965 2 .202418 2 202660 52 1 0 0 .150760 -1 .576850 -2 515753 53 1 0 -3 .287867 3 .223135 1 .463187 54 1 0 1 .505295 -1 .459786 -3 .653813 55 1 0 -2 .808263 -2 .056434 -3 .217765 56 1 0 3 .321907 -2 .111226 3 .012745 57 1 0 -3 .088027 -3 .163170 -1 .856343 58 1 0 3 .419918 -0 .431379 3 .588464 59 1 0 -4 .481897 -2 .425622 -2 .705633 60 1 0 4 .912348 -1 .293122 3 .103463 217 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A10. Method and Z-matrix for model complex 4D. •# GFINPUT B 3 L Y P / L A N L 2 D Z Opt=(maxcy=200) SCF=(maxcy=512) IOP(6/7=3) t a2h2zmat 0 .1 c s i n c P c c s i n t a t a n c c n c P c s i c c s i h h h h h h h h h h h h h h h h h h h h 9 10 s i c 2 n s i 3 cn4 pc5 cp6 cp7 7 s i c 8 8 n s i 9 t a n l O t a t a l l 11 n t a l 2 12 c n l 3 9 c n l 4 11 n t a l 5 15 c n l 6 11 p t a l 7 17 c p l 8 15 s i n l 9 19 c s i 2 0 17 cp21 21 s i c 2 2 10 h t a 2 3 10 h ta24 1 hc25 21 hc26 1 hc27 21 hc28 7 hc29 20 hc30 7 hc31 20 hc32 2 h s i 3 3 22 h s i 3 4 2 h s i 3 5 22 h s i 3 6 8 h s i 3 7 19 h s i 3 8 8 h s i 3 9 19 h s i 4 0 4 hc41 13 hc42 n s i c 3 c n s i 4 p c s i 5 1 cpc6 I cpc7 5 s i c p 8 7 n s i c 9 8 t a n s i l O 9 t a t a n l l 10 n t a t a l 2 I I c n t a l 3 8 c n s i l 4 10 n t a t a l 5 11 c n t a l 6 10 p t a t a l 7 11 c p t a l 8 11 s i n t a l 9 15 c s i n 2 0 11 c p t a 2 1 17 s i c p 2 2 5 h t a p 2 3 5 h tap24 5 hcp25 17 hcp26 5 hcp27 17 hcp28 5 hcp2 9 19 h c s i 3 0 5 hcp31 19 h c s i 3 2 1 h s i c 3 3 21 h s i c 3 4 1 h s i c 3 5 21 h s i c 3 6 7 h s i c 3 7 15 h s i n 3 8 7 h s i c 3 9 15 h s i n 4 0 3 hen41 12 hcn42 1 d i h 4 3 d i h 5 2 d i h 6 2 d i h 7 I d i h 8 5 d i h 9 7 d i h l O 8 d i h l l 9 d i h l 2 10 d i h l 3 7 d i h l 4 5 d i h l 5 10 d i h l 6 5 d i h l 7 10 d i h l 8 10 d i h l 9 I I d i h 2 0 10 d i h 2 1 11 d i h 2 2 1 d i h 2 3 I d i h 2 4 7 d i h 2 5 I I d i h 2 6 7 d i h 2 7 11 d i h 2 8 1 d i h 2 9 15 d i h 3 0 1 d i h 3 1 15 d i h 3 2 5 d i h 3 3 17 d i h 3 4 5 d i h 3 5 17 d i h 3 6 5 d i h 3 7 11 d i h 3 8 5 d i h 3 9 11 d i h 4 0 2 d i h 4 1 11 d i h 4 2 h 4 hc43 3 hcn43 2 d i h 4 3 h 13 hc44 12 hcn44 11 d i h 4 4 h 4 hc45 3 hcn45 2 d i h 4 5 h 13 hc4 6 12 hcn46 11 d i h 4 6 h 14 hc47 9 hcn47 8 d i h 4 7 h 16 hc48 15 hcn48 11 d i h 4 8 h 14 hc49 9 hcn4 9 8 d i h 4 9 h 16 hc50 15 hcn50 11 d i h 5 0 h 14 hc51 9 hcn51 8 d i h 5 1 h 16 hc52 15 hcn52 11 d i h 5 2 h 6 hc53 5 hcp53 1 d i h 5 3 h 18 hc54 17 hcp54 11 d i h 5 4 h 6 hc55 5 hcp55 1 d i h 5 5 h 18 hc56 17 hep56 11 d i h 5 6 h 6 hc57 5 hcp57 1 d i h 5 7 h 18 hc58 17 hcp58 11 d i h 5 8 218 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and DFT calculation data Table A l l . Initial parameters for model complex 4D. s i c 2 1 .918385 s i n t a l 9 120 .916 d i h 3 5 141 .308 hc52 1.103208 n s i 3 1. 788447 d i h l 9 - 6 0 . 9 4 9 h s i 3 6 1 .496595 hcn52 112 .507 • n s i c 3 1 0 9 . 6 4 9 c s i 2 0 1 .929935 h s i c 3 6 108 .348 d i h 5 2 127 .477 cn4 1.493984 c s i n 2 0 106 .482 d i h 3 6 - 1 4 1 . 3 1 1 hc53 1.094504 c n s i 4 1 1 2 . 8 5 3 d i h 2 0 -37 .735 h s i 3 7 1 .488665 hcp53 109 .094 d i h 4 - 1 6 0 . 1 5 1 cp21 1. 903937 h s i c 3 7 1 0 8 . 7 9 6 d i h 5 3 - 1 7 9 . 9 5 1 pc5 1.903937 c p t a 2 1 100 .762 d i h 3 7 1 2 1 . 9 5 3 hc54 1.094503 p c s i 5 109 .355 d i h 2 1 - 1 6 0 . 4 2 1 h s i 3 8 1. 488663 hcp54 109.094 d i h 5 1 6 . 8 0 3 s i c 2 2 1. 918384 h s i n 3 8 1 1 6 . 0 5 5 d i h 5 4 60 .307 cp6 1 .883951 s i c p 2 2 109 .354 d i h 3 8 8 3 . 5 0 9 hc55 1.094580 cpc6 104 .950 d i h 2 2 3 3 . 3 9 0 h s i 3 9 1 .497602 hcp55 108 .961 d i h 6 105 .137 h t a 2 3 1.958099 h s i c 3 9 108 .454 d i h 5 5 - 6 1 . 5 1 8 cp7 •1. 901748 h t a p 2 3 76 .084 d i h 3 9 - 1 2 1 . 474 hc56 1.094580 cpc7 1 0 6 . 6 1 6 d i h 2 3 - 1 6 1 . 5 6 4 h s i 4 0 1 .497600 hcp5 6 108 .961 d i h 7 - 1 4 3 . 0 3 9 h ta24 1.948167 h s i n 4 0 1 0 9 . 4 1 3 d i h 5 6 -58 .126 s i c 8 1.929934 h tap24 127 .327 d i h 4 0 - 1 5 4 . 7 5 3 hc57 1.096161 s i c p 8 1 0 8 . 4 9 6 d i h 2 4 111 .341 hc41 1 .103610 hcp57 110 .819 d i h 8 8 5 . 8 0 6 hc25 1.096147 hcn41 112 .088 d i h 5 7 59 .307 n s i 9 1 .773139 hcp25 107 .170 d i h 4 1 57 .454 hc58 1. 096162 n s i c 9 106 .482 d i h 2 5 - 2 3 . 9 2 2 hc42 1 .103610 hcp58 110 .819 d i h 9 - 3 . 8 1 9 hc2 6 1.096147 hcn42 112 .088 d i h 5 8 -178 . 951 t a n l O 2 . 070746 hcp2 6 107 .170 d i h 4 2 117 .483 t a n s i l O 1 2 0 . 9 2 d i h 2 6 - 8 5 . 7 2 7 hc43 1 .093282 d i h l O 37 .733 hc27 1.097674 hcn43 109 .637 t a t a l l 2 . 6 1 0 6 1 hcp27 110 .960 dih4-3 176 .898 t a t a n l l 122 .88 d i h 2 7 93 .508 hc44 1. 093283 d i h l l 60 .947 hc28 1.097674 hcn44 109 .637 n t a l 2 2 . 0 8 4 3 1 hcp28 110 .961 d i h 4 4 - 1 . 9 6 1 n t a t a ! 2 125 .07 d i h 2 8 156 .843 hc45 1 .104980 d i h l 2 - 5 . 3 4 1 hc29 1.097547 v hcn45 111 .574 c n l 3 1 .493985 hcp2 9 107 .304 d i h 4 5 - 6 3 . 3 2 0 cntal3 127 . 948 d i h 2 9 -155 . 025 hc46 1 .104980 d i h l 3 - 3 8 . 2 6 0 hc30 1.097547 hcn4 6 1 1 1 . 5 7 5 c n l 4 1. 487242 h c s i 3 0 110 .300 d i h 4 6 - 1 2 1 . 7 4 3 c n s i l 4 119 . 949 d i h 3 0 121 .090 hc47 1 .101783 d i h l 4 - 1 3 3 . 4 6 9 hc31 1.097964 hcn47 1 1 1 . 879 n t a l 5 2 .070745 hcp31 110 .313 d i h 4 7 - 7 7 . 4 3 7 n t a t a l 5 122 .88 d i h 3 1 - 3 7 . 7 1 3 hc48 1.101784 d i h l 5 - 9 0 . 7 1 6 hc32 1.097964 hcn48 1 1 1 . 879 c n l 6 1 .487242 h c s i 3 2 112 .395 d i h 4 8 - 1 1 1 . 158 c n t a l 6 1 1 8 . 5 6 3 d i h 3 2 - 1 1 8 . 4 3 9 hc49 1 .102346 d i h l 6 127 .732 h s i 3 3 1 .497119 hcn4 9 110 . 086 p t a l 7 2 .576835 h s i c 3 3 108 . 879 d i h 4 9 163 .467 p t a t a l 7 1 0 5 . 7 9 d i h 3 3 - 1 0 3 . 4 6 0 hc50 1 .102346 d i h l 7 - 1 7 9 . 9 9 9 h s i 3 4 1 .497119 hcn50 1 1 0 . 0 8 6 c p l 8 1 .883951 h s i c 3 4 108 . 879 d i h 5 0 7 . 937 c p t a l E 131 .527 d i h 3 4 103 .457 hc51 1.103208 d i h l 8 - 3 9 . 1 5 1 h s i 3 5 1 .496595 hcn51 112 . 507 s i n l 9 1 .773140 h s i c 3 5 108 .347 d i h 5 1 43 .928 219 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A12. Final atomic coordinates for the geometry optimization-of 4D. Centre Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z 1 6 0 4 . 397149 - 0 . 404266 0. 881823 2 14 0 3. 910176 -2 . 078580 0. 077119 3 7 ' 0 2. 176741 - 2 . 065101 - 0 . 372643 4 6 0 1. 610085 - 3 . 436685 - 0 . 547315 5 15 0 2. 828023 0. 577716 1. 341356 6 6 0 2. 736172 0. 507016 3. 220832 7 6 0 3. 183731 2 . 394603 0. 901575 8 14 0 2 744839 2 652695 - 0 . 959006 9 7 0 2 293280 1 054241 -1 590704 10 73 0 1 204234 -0 252621 -0 441939 11 73 0 -1 204222 0 252729 0 441770 12 7 0 -2 176889 2 065132 0 372274 13 6 0 -1 610261 3 436758 0 546756 14 6 0 2 824624 0 624169 -2 914696 15 7 0 -2 292934 -1 053966 1 591036 16 6 0 -2 824156 -0 623672 2 915000 17 15 0 -2 828264 -0 578066 -1 341127 18 6 0 -2 736476 -0 507969 -3 220627 19 14 0 -2 744432 -2 652571 0 959676 20 6 0 -3 183947 -2 394837 -0 900810 21 6 0 -4 397346 0 404063 -0 881781 22 14 0 -3 910290 2 078591 -0 077578 23 1 0 0 350705 1 381174 0 212721 24 1 0 -0 350879 -1 381033 -0 213048 25 1 0 4 959452 0 203485 0 163509 26 1 0 -4 959633 -0 203486 -0 163284 27 1 0 5 034947 -0 555414 1 762407 28 1 0 -5 035183 0 554990 -1 762374 29 1 0 2 539052 3 016127 1 535963 30 1 0 -2 539544 -3 016551 -1 535294 31 1 0 4 227718 2 648418 1 127648 32 1 0 -4 228034 -2 648616 -1 126463 33 1 0 4 163756 -3 179678 1 057453 34 1 0 -4 163747 3 179391 -1 058281 35 1 0 4 823763 -2 324131 -1 081968 36 1 0 -4 823918 2 324598 1 081383 37 1 0 1 705135 3 712094 -1 070346 38 1 0 -1 704526 -3 711785 1 070859 39 1 0 3 965925 3 142730 -1 673904 40 1 0 -3 965231 -3 142700 1 675004 41 1 0 1 746667 -4 056814 0 354539 42 1 0 -1 746641 4 056676 -0 355275 43 1 0 0 536050 -3 365461 -0 741794 44 1 0 -0 536270 3 365581 0 741487 45 1 0 2 080292 -3 967934 -1 393735 46 1 0 -2 080650 3 968207 1 392950 47 1 0 2 280010 1 097234 -3 747074 48 1 0 -2 279286 -1 096382 3 747413 49 1 0 2 .717519 -0 .465934 -3 028698 50 1 0 -2 .717308 0 .466488 3 028689 51 1 0 3 .893995 0 .864729 -3 .033982 52 1 0 -3 .893445 -0 .864471 3 .034532 53 1 0 1 .850485 1 .056937 3 .553468 54 1 0 -1 .850858 -1 .058101 -3 .553103 55 1 0 2 .633453 -0 .537735 3 .530545 56 1 0 -2 .633653 0 .536668 -3 .530691 57 1 0 3 .634208 0 .942747 3 .673972 58 1 0 -3 .634568 -0 .943759 -3 . 673600 220 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A13. Method and Z-matrix for model complex 4E. # GFINPUT B 3 L Y P / L A N L 2 D Z Opt=(maxcy=200) SCF=(maxcy=512) IOP(6/7=3) nbme3d 0 1 nb n 1 n t a 2 n 1 n t a 3 2 n t a n 3 s i 2 s i n 4 1 s i n t a 4 3 d i h 4 s i 3 s i n 5 1 s i n t a 5 2 d i h 5 c 4 c s i 6 2 c s i n 6 1 d i h 6 c 5 c s i 7 3 c s i n 7 1 d i h 7 P 1 p t a 8 2 p t a n 8 4 d i h 8 c 1 c t a 9 2 c t a n 9 4 d i h 9 h 9 he 10 1 h c t a l O 2 d i h l O h 9 h e l l 1 h c t a l l 2 d i h l l h 9 h c l 2 1 h c t a l 2 2 d i h l 2 c 1 c t a l 3 2 c t a n l 3 4 d i h l 3 h 13 h c l 4 1 h c t a l 4 2 d i h l 4 h 13 h c l 5 1 h c t a l 5 2 d i h l 5 h 13 h c l 6 1 h c t a l 6 2 d i h l 6 c 1 c t a l 7 2 c t a n l 7 4 d i h l 7 h 17 h c l 8 1 h c t a l 8 2 d i h l 8 h 17 h c l 9 1 h c t a l 9 2 d i h l 9 h 17 hc20 1 h c t a 2 0 2 d i h 2 0 c 2 cn21 1 c n t a 2 1 3 d i h 2 1 h 21 hc22 2 hcn22 1 d i h 2 2 h 21 hc23 2 hcn23 1 d i h 2 3 h 21 hc24 2 hcn24 1 d i h 2 4 c 3 cn25 1 c n t a 2 5 2 d i h 2 5 h 25 hc2 6 3 hcn2 6 1 d i h 2 6 h 25 hc27 3 hcn27 1 d i h 2 7 h 25 hc28 3 hcn28 1 d i h 2 8 c 8 cp2 9 1 c p t a 2 9 2 d i h 2 9 h 29 hc30 8 hcp30 1 d i h 3 0 h 29 hc31 8 hcp31 1 d i h 3 1 h 29 hc32 8 hcp32 1 d i h 3 2 h 4 h s i 3 3 2 h s i n 3 3 1 d i h 3 3 h 4 h s i 3 4 2 h s i n 3 4 1 d i h 3 4 h 5 h s i 3 5 3 h s i n 3 5 1 d i h 3 5 h 5 h s i 3 6 3 h s i n 3 6 1 d i h 3 6 h 6 hc37 4 h c s i 3 7 2 d i h 3 7 h 6 hc38 4 h c s i 3 8 2 d i h 3 8 h 7 hc39 5 h c s i 3 9 3 d i h 3 9 h 7 hc40 5 h c s i 4 0 3 d i h 4 0 221 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and DFT calculation data Table A14. Initial parameters for model complex 4E. n ta2 2 . 066469 h c t a l 9 110 .905 d i h 3 5 - 1 0 0 . 5 1 2 n t a 3 2 . 040078 d i h l 9 - 120 .694 h s i 3 6 1 .492799 n t an3 124 . 479 hc20 1.099157 h s i n 3 6 1 1 0 . 1 4 0 ' s i n 4 1 .775193 h c t a 2 0 110 .905 d i h 3 6 141 .677 s i n t a 4 125 .188 d i h 2 0 118 .919 hc37 1 .096113 d i h 4 1 1 . 3 3 9 cn21 1.493606 h c s i 3 7 1 1 1 . 7 4 9 s i n 5 1.792287 c n t a 2 1 118 .950 . d i h 3 7 138 .334 s i n t a 5 1 3 4 . 6 6 9 d i h 2 1 - 158 .888 hc38 1 .096113 d i h 5 -84 .348~ hc22 1.099157 h c s i 3 8 1 1 1 . 7 4 9 c s i 6 1 .908015 hcn22 110 .905 d i h 3 8 - 100 .304 c s i n 6 104 .901 d i h 2 2 217 .027 hc39 1 .096113 d i h 6 30 .368 hc23 1.099157 h c s i 3 9 1 1 2 . 1 1 3 c s i 7 1 .897366 hcn23 110 .905 d i h 3 9 1 2 6 . 7 2 3 c s i n 7 107 .232 d i h 2 3 - 2 3 . 7 2 1 hc40 1 .096113 d i h 7 2 1 . 3 7 6 hc24 1.099157 h c s i 4 0 1 1 2 . 1 1 3 p t a 8 2 .708000 hcn24 110 .905 d i h 4 0 - 1 1 1 . 5 6 0 p t an8 74 .468 d i h 2 4 9 6 . 0 9 9 d i h 8 - 4 5 . 7 6 2 cn25 1.513930 c t a 9 2 .237641 c n t a 2 5 115 .765 c t a n 9 8 8 . 4 3 6 d i h 2 5 107 .965 d i h 9 - 1 2 3 . 4 5 9 hc26 1.099157 h c l O 1.099157 hcn2 6 110 .905 h c t a l O 110 .905 d i h 2 6 --136.593 d i h l O 1 4 7 . 6 4 9 hc27 1. 099157 h e l l 1 .099157 hcn27 110 .905 h c t a l l 110 .905 d i h 2 7 - 1 7 . 3 0 0 d i h l l 26 .617 hc28 1.099157 h c l 2 1 .099157 hcn28 110 .905 h c t a l 2 110 .905 d i h 2 8 --257 . 423 d i h l 2 - 9 3 . 8 1 7 cp2 9 1.879447 c t a l 3 2 . 2 3 3 4 9 9 c p t a 2 9 127 .189 c t a n l 3 81 .664 d i h 2 9 - 6 9 . 8 8 3 d i h l 3 1 0 9 . 5 5 9 hc30 1.099157 h c l 4 1.099157 hcp30 110 .905 h c t a l 4 110 .905 d i h 3 0 51 .447 d i h l 4 - 5 7 . 9 7 4 hc31 1.099157 h c l 5 1.099157 hcp31 110 .905 h c t a l 5 110 .905 d i h 3 1 171 .802 d i h l 5 6 1 . 3 4 9 hc32 1.099157 h c l 6 1 .099157 hcp32 110 .905 h c t a l 6 110 .905 d i h 3 2 - 6 7 . 6 6 6 d i h l 6 - 1 8 0 . 0 5 8 h s i 3 3 1 .492799 c t a l 7 2 . 215412 h s i n 3 3 112 .131 c t a n l 7 140 .204 d i h 3 3 149 .814 d i h l 7 - 1 9 0 . 1 0 1 h s i 3 4 1 .492799 h c l 8 1.099157 h s i n 3 4 112 .131 h c t a l 8 110 .905 d i h 3 4 - 8 9 . 9 1 3 d i h l 8 - 1 . 1 0 6 h s i 3 5 1 .492799 h c l 9 1 .099157 h s i n 3 5 110 .140 222 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and DFT calculation data Table A15 . Final atomic coordinates for the geometry optimization of 4E . Centre Atomic Atomic Coordinates (Angstroms) Number Number Type X Y z 1 41 0 - 1 . 458654 - 0 . 190870 -0 090756 2 7 0 -0 829950 1. 731876 -0 033710 3 7 0 -0 147295 -1 489229 0 653063 4 14 0 0 724212 2 375703 0 586166 5 14 0 1 091041 -2 355927 -0 308829 6 6 0 2 067222 1 084600 0 929515 7 6 0 2 810350 -1 569841 -0 120528 8 15 0 2 853740 0 279375 -0 645784 9 6 0 -1 444336 0 027179 -2 284476 10 1 0 -1 582137 -0 937873 -2 788212 11 1 0 -0 478299 0 466593 -2 574770 12 1 0 -2 251143 0 702141 -2 608448 13 6 0 -3 035283 0 445270 1 328599 14 1 0 -2 585804 1 095245 2 095020 15 1 0 -3 823406 1 009523 0 807973 16 1 0 -3 506998 -0 424632 1 806445 17 6 0 -3 170690 -1 500596 -0 678729 18 1 0 -4 000196 -0 934728 -1 127011 19 1 0 -3 554066 -2 034920 0 205355 20 1 0 -2 824461 -2 244932 -1 413451 21 6 0 -1 722276 2 825613 -0 522844 22 1 0 -1 274236 3 349290 -1 381464 23 1 0 -2 689197 2 424125 -0 845743 24 1 0 -1 925146 3 566301 0 267845 25 6 0 -0 234772 -1 835663 2 106650 26 1 0 0 698954 -1 597333 2 639831 27 1 0 -1 041448 -1 274559 2 595646 28 1 0 -0 445889 -2 906004 2 243932 29 6 0 4 692291 0 643342 -0 280121 30 1 0 4 867485 1 722975 -0 354208 31 1 0 4 982308 0 298699 0 720418 32 1 0 5 316648 0 142118 -1 028473 33 1 0 1 246297 3 362049 -0 405290 34 1 0 0 459152 3 135455 1 847700 35 1 0 0 686074 -2 305387 -1 733642 36 1 0 1 130921 -3 770662 0 .159132 37 1 0 2 868325 1 588482 1 .489814 38 1 0 1 680092 0 291963 1 .578482 39 1 0 3 189540 -1 677447 0 .906182 40 1 0 3 507466 . -2 106253 -0 .781894 223 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A16. Method and Z-matrix for model complex 4F. # GFINPUT B 3 L Y P / L A N L 2 D Z Opt= SCF=(maxcy=512) IOP(6/7=3) (maxcy=200) nb2h4b 0 1 c s i 1 s i c 2 n 2 n s i 3 c 3 cn4 nb 3 t a n 5 P 5 p t a 6 c 6 cp7 nb 5 t a t a 8 P 8 p t a 9 c 9 c p l O n 5 n t a l l c 11 c n l 2 n 8 nta'13 c 13 c n l 4 n 8 n t a l 5 c 15 c n l 6 s i 13 s i n l 7 c 17 c s i l 8 s i 11 s i n l 9 c 19 c s i 2 0 s i 15 s i n 2 1 c 21 c s i 2 2 h 5 h t a 2 3 h 5 h ta24 h 5 h t a 2 5 h 5 h t a 2 6 h 1 hc27 h 18 hc28 h 1 hc2 9 h 18 hc30 h 20 hc31 h 22 hc32 h 20 hc33 h 22 hc34 h 2 h s i 3 5 h 17 h s i 3 6 h 2 h s i 3 7 h 17 h s i 3 8 • h 19 h s i 3 9 h 21 h s i 4 0 h 19 h s i 4 1 n s i c 3 c n s i 4 t a n s i 5 p t a n 6 c p t a 7 t a t a n 8 p t a t a 9 8 c p t a l O 8 n t a t a l l 5 c n t a l 2 5 n t a t a l 3 8 c n t a l 4 5 n t a t a l 5 8 c n t a l 6 8 s i n t a l 7 13 c s i n l 8 5 s i n t a l 9 11 c s i n 2 0 8 s i n t a 2 1 15 c s i n 2 2 8 h t a t a 2 3 8 h t a t a 2 4 8 h t a t a 2 5 8 h t a t a 2 6 hcp27 hcp28 hcp2 9 hcp30 hcp31 hcp32 hcp33 hcp34 h s i n 3 5 13 h s i n 3 6 3 h s i n 3 7 13 h s i n 3 8 11 h s i n 3 9 15 h s i n 4 0 11 h s i n 4 1 d i h 4 d i h 5 d i h 6 d i h 7 d i h 8 d i h 9 d i h l O d i h l l d i h l 2 d i h l 3 d i h l 4 3 d i h l 5 5 d i h l 6 5 d i h l 7 8 d i h l 8 8 d i h l 9 5 d i h 2 0 5 d i h 2 1 8 d i h 2 2 13 d i h 2 3 13 d i h 2 4 13 d i h 2 5 13 d i h 2 6 5 d i h 2 7 8 d i h 2 8 5 d i h 2 9 8 d i h 3 0 5 d i h 3 1 8 d i h 3 2 5 d i h 3 3 8 d i h 3 4 5 d i h 3 5 8 d i h 3 6 5 d i h 3 7 8 d i h 3 8 5 d i h 3 9 8 d i h 4 0 5 d i h 4 1 h 21 h s i 4 2 15 h s i n 4 2 8 d i h 4 2 h 4 hc43 3 hcn43 5 d i h 4 3 h 14 hc44 13 hcn4 4 8 d i h 4 4 h 4 hc45 3 hcn4 5 5 d i h 4 5 h 14 hc4 6 13 hcn4 6 8 d i h 4 6 h 4 hc47 3 hcn47 5 d i h 4 7 h 14 hc48 13 hcn48 8 d i h 4 8 h 12 hc49 11 hcn4 9 5 d i h 4 9 h 16 hc50 15 hcn50 8 d i h 5 0 h 12 hc51 11 hcn51 5 d i h 5 1 h 16 hc52 15 hcn52 8 d i h 5 2 h 12 hc53 11 hcn53 5 d i h 5 3 h 16 hc54 15 hcn54 8 d i h 5 4 h 7 hc55 6 hcp55 5 d i h 5 5 h 10 hc56 9 hcp5 6 8 d i h 5 6 h 7 hc57 6 hcp57 5 d i h 5 7 h 10 hc58 9 hcp58 8 d i h 5 8 h 7 hc59 6 hcp59 5 d i h 5 9 h 10 hc60 9 hcp60 8 "din60 224 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A17. Initial parameters for model complex 4F. s i c 2 1 .912253 s i n t a l 9 127 .124 d i h 3 5 86 .587 hc52 1.104180 n s i 3 1 .771349 d i h l 9 99 .860 h s i 3 6 1. 494702 hcn52 110 .949 n s i c 3 106 .073 c s i 2 0 1 .908239 h s i n 3 6 1 1 4 . 5 0 6 d i h 5 2 13 .663 cn4 1.488467 c s i n 2 0 107 .950 d i h 3 6 - 8 6 . 5 8 7 hc53 1.103377 c n s i 4 118 .340 d i h 2 0 - 1 . 405 h s i 3 7 1. 496344 hcn53 112 .361 d i h 4 1 4 6 . 4 7 3 s i n 2 1 1. 778143 h s i n 3 7 1 1 0 . 7 1 5 d i h 5 3 - 1 3 2 . 7 9 9 t an5 2 . 0 4 5 9 5 6 s i n t a 2 1 127 .124 d i h 3 7 - 1 5 2 . 5 5 3 hc54 1.103377 T a n s i 5 1 2 3 . 9 0 9 d i h 2 1 - 9 9 . 8 6 0 h s i 3 8 1.496344 hcn54 112 .361 d i h 5 - 3 3 . 5 9 1 c s i 2 2 1 .908239 h s i n 3 8 1 1 0 . 7 1 5 d i h 5 4 132 .799 p t a 6 2 .517804 c s i n 2 2 107 .950 d i h 3 8 1 5 2 . 5 5 3 hc55 1.094121 p t a n 6 85 .554 d i h 2 2 1. 405 h s i 3 9 1.495717 hcp55 108 .643 d i h 6 17 .917 h t a 2 3 1.988732 h s i n 3 9 1 1 2 . 5 2 5 d i h 5 5 -57 . 009 cp7 1 .878765 h t a t a 2 3 44 .687 d i h 3 9 - 1 2 2 . 1 0 8 hc56 1. 094121 c p t a 7 124 .310 d i h 2 3 3 6 . 9 3 3 h s i 4 0 1. 495717 hcp5 6 108 . 643 d i h 7 - 1 1 9 . 9 3 6 h ta24 1.991722 h s i n 4 0 112 . 525 d i h 5 6 5 7 . 0 0 9 t a t a 8 2 .832018 h t a t a 2 4 44 .602 d i h 4 0 122 .108 hc57 1.093834 Tatan8 128 .780 d i h 2 4 - 143 .067 h s i 4 1 1.498924 hcp57 109 .148 d i h 8 - 9 0 . 3 2 7 h t a 2 5 1.985160 h s i n 4 1 110 . 611 d i h 5 7 61 .793 p t a 9 2 .517804 h t a t a 2 5 4 4 . 9 1 3 d i h 4 1 1 1 9 . 7 9 1 hc58 1.093834 P t a t a 9 1 0 6 . 9 7 0 d i h 2 5 129 .285 h s i 4 2 1.498924 hcp58 109 .148 d i h 9 - 8 1 . 8 8 2 h t a 2 6 1.999606 h s i n 4 2 1 1 0 . 6 1 1 d i h 5 8 - 6 1 . 7 9 3 c p l O 1 .878765 h t a t a 2 6 44 .502 d i h 4 2 - 1 1 9 . 7 9 1 hc59 1.095747 c p t a l O 124 .310 d i h 2 6 - 5 0 . 7 1 5 hc43 1 .102235 hcp59 110 .546 d i h l O - 9 . 3 4 3 hc27 1.097198 hcn43 1 1 2 . 0 8 9 d i h 5 9 - 1 7 7 . 3 0 1 n t a l l 2 .040802 hcp27 108 .264 d i h 4 3 - 1 0 9 . 9 8 9 hc60 1.095747 n t a t a l l 128 .04 d i h 2 7 98 .095 hc44 1 .102235 hep 60 110 .546 d i h l l 8 2 . 7 3 3 hc28 1.0 97198 hcn44 1 1 2 . 0 8 9 d i h 6 0 177 .301 c n l 2 1 .490391 hcp28 108 .264 d i h 4 4 1 0 9 . 9 8 9 c n t a l 2 116 .697 d i h 2 8 - 9 8 . 0 9 5 hc45 1.104948 d i h l 2 - 8 1 . 7 5 5 hc29 1.097395 hcn45 1 1 0 . 4 7 0 n t a l 3 2 .045956 hcp2 9 109 .997 d i h 4 5 8 .512 n t a t a l 3 128 .78 d i h 2 9 - 144 .179 hc46 1. 104948 d i h l 3 180 .000 hc30 1 .097395 hcn4 6 1 1 0 . 4 7 0 c n l 4 1.488467 hcp30 109 .997 d i h 4 6 - 8 . 5 1 2 c n t a l 4 1 1 7 . 7 5 1 d i h 3 0 144 .179 hc47 1.102848 d i h l 4 - 8 9 . 6 0 9 hc31 1 .098943 hcn47 1 1 2 . 2 2 1 n t a l 5 2 .040802 hcp31 106 .469 d i h 4 7 1 2 7 . 8 0 1 n t a t a l 5 128 .04 d i h 3 1 99 .970 hc48 1.102848 d i h l 5 1 5 . 3 8 5 hc32 1 .098943 hcn48 112 . 221 c n l 6 1 .490391 hcp32 106 .469 d i h 4 8 - 1 2 7 . 8 0 1 c n t a l 6 116 .697 d i h 3 2 - 9 9 . 9 7 0 hc49 1 .101342 d i h l 6 8 1 . 7 5 5 hc33 1.097832 hcn4 9 1 1 1 . 5 2 9 s i n l 7 1 .771349 hcp33 111 .229 d i h 4 9 105 .127 s i n t a l 7 1 2 3 . 9 1 d i h 3 3 - 142 .809 hc50 1 .101342 d i h l 7 90 .327 hc34 1.097832 hcn50 1 1 1 . 5 2 9 c s i l 8 1 .912253 hcp34 111 .229 d i h 5 0 - 1 0 5 . 1 2 7 c s i n l 8 1 0 6 . 0 7 3 d i h 3 4 142 .809 hc51 1 .104180 d i h l 8 3 3 . 5 9 1 h s i 3 5 1.494702 hcn51 1 1 0 . 9 4 9 s i n l 9 1 .778143 h s i n 3 5 114 .506 d i h 5 1 - 1 3 . 6 6 3 225 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A18. Final atomic coordinates for the geometry optimization of 4F. Centre Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z 1 6 0 • 4. 718283 - 0 . 682552 0. 127570 2 14 0 3. 922761 -2 . 227814 - 0 . 659314. 3 7 0 2. 143855 -2 . 020097 - 0 . 755873 4 6 0 1. 476240 - 3 . 313891 - 1 . 097538 5 41 0 1. 240157 - 0 . 205093 - 0 . 335704 6 15 0 3 405324 0 245579 1. 139113 7 6 0 3 768706 -0 200335 2 . 931558 8 41 0 -1 239041 0 190269 0 337804 9 15 0 -3 408557 -0 273904 -1 126073 10 6 • 0 -3 741023 0 100321 -2 940284 11 7 0 2 240196 1 307391 ' -1 386942 12 6 0 1 957808 1 305688 -2 848555 13 7 0 -2 116891 2 038796 0 644826 14 6 0 -1 430983 3 349642 0 866928 15 7 0 -2 234269 -1 285601 1 442804 16 6 0 -1 837142 -1 336556 2 879241 17 14 0 -3 897825 2 249567 0 611299 18 6 0 -4 719916 0 715469 -0 171405 19 14 0 3 106901 2 681197 -0 707271 20 6 0 3 831767 2 081111 0 962891 21 14 0 -3 234868 -2 612227 0 853288 22 6 0 -3 873677 -2 089716 -0 873323 23 1 0 0 304804 1 264954 0 675082 24 1 0 -0 294673 -1 290322 -0 649444 25 1 0 0 408944 -0 610093 1 305338 26 1 0 -0 383100 0 581125 -1 308482 27 1 0 5 052040 -0 001306 -0 663023 28 1 0 -5 107295 0 060934 0 617598 29 1 0 5 587567 -0 938036 0 746634 30 1 0 -5 558037 0 988756 -0 824735 31 1 0 3 360951 2 613221 1 798943 32 1 0 -3 371232 -2 671607 -1 656071 33 1 0 4 915818 2 236587 1 030044 34 1 0 -4 955347 -2 237277 -0 982466 35 1 0 4 246554 -3 426374 0 177082 36 1 0 -4 242573 3 458414 -0 200627 37 1 0 4 532119 -2 470998 -2 001789 38 1 0 -4 466994 2 475740 1 973846 39 1 0 2 283720 3 904677 -0 451761 40 1 0 -2 527466 -3 925522 0 731443 41 1 0 4 210471 3 098029 -1 628368 42 1 0 -4 390776 -2 845841 1 776134 43 1 0 1 588319 -4 054584 -0 287683 44 1 0 -1 577541 4 032287 0 013096 45 1 0 0 408234 -3 148112 -1 256207 46 1 0 -0 358120 3 189896 0 990891 47 1 0 1 896064 -3 756625 -2 018529 48 1 0 -1 .809815 3 .857434 1 771836 49 1 0 1 .156559 2 .012998 -3 .121933 50 1 0 -1 .119280 -2 .148652 3 .086407 51 1 0 1 .633276 0 .307643 -3 .178935 52 1 0 -1 .355071 -0 .396839 3 .184273 53 1 0 2 .859516 1 .555631 -3 .433047 54 1 0 -2 .715915 -1 .468903 3 .533240 55 1 0 3 .036866 0 .292230 3 .579444 56 1 0 -3 .019300 -0 .444611 -3 .556831 57 1 0 3 .672278 -1 .283474 3 .060036 58 1 0 -3 .607567 1 .172662 -3 .116739 59 1 0 4 .779835 0 .113737 3 .214290 60 1 0 -4 .759280 -0 .193777 -3 .218927 226 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and DFT calculation data Table A19. Method and Z-matrix for model complex 4G. # GFINPUT B 3 L Y P / L A N L 2 D Z Opt=(maxcy=200) SCF=(maxcy=512) IOP(6/7=3) nb2h2a 0 1 c p 1 pc2 c 2 cp3 1 cpc3 s i 3 s i c 4 2 s i c p 4 1 d i h 4 n 4 n s i 5 3 n s i c 5 2 d i h 5 c 5 cn6 4 c n s i 6 3 d i h 6 s i 1 s i c 7 2 s i c p 7 3 d i h 7 n 7 n s i 8 1 n s i c 8 . 2 d i h 8 nb 8 nbn9 7 n b n s i 9 1 d i h 9 nb 9 nbnblO 8 nbnbn lO 7 d i h l O n 10 n n b l l 9 n n b n b l l 8 d i h l l s i 11 s i n l 2 10 s i n n b l 2 9 d i h l 2 c 12 c s i l 3 11 c s i n l 3 10 d i h l 3 P 13 p c l 4 12 p c s i l 4 11 d i h l 4 c 14 c p l 5 13 c p c l 5 12 d i h l 5 s i 15 s i c l 6 14 s i c p l 6 13 d i h l 6 n 16 n s i l 7 15 n s i c l 7 14 d i h l 7 c 17 c n l 8 16 c n s i l 8 15 d i h l 8 c 8 c n l 9 7 c n s i l 9 1 d i h l 9 c 2 cp20 1 cpc20 7 d i h 2 0 c 14 cp21 10 cpnb21 9 d i h 2 1 c 11 cn22 10 cnnb22 9 d i h 2 2 h 9 hnb23 8 hnbn23 7 d i h 2 3 h 9 hnb2 4 8 hnbn2 4 7 d i h 2 4 h 1 hc25 7 h c s i 2 5 8 d i h 2 5 h 15 hc26 14 hcp26 10 d i h 2 6 h 1 hc27 7 h c s i 2 7 8 d i h 2 7 h 15 hc28 14 hcp28 10 d i h 2 8 h 19 hc43 8 hcn4 3 7 d i h 4 3 h 3 hc2 9 2 hcp2 9 1 d i h 2 9 h 18 hc44 17 hcn4 4 10 d i h 4 4 h 13 hc30 ' 14 hcp30 10 d i h 3 0 h 19 hc45 8 hcn45 7 d i h 4 5 h 3 hc31 2 hcp31 1 d i h 3 1 h 18 hc4 6 17 hcn4 6 10 d i h 4 6 h 13 hc32 14 hcp32 10 d i h 3 2 h 6 hc47 5 hcn47 9 d i h 4 7 h 7 h s i 3 3 1 h s i c 3 3 2 d i h 3 3 h 22 hc48 11 hcn48 10 d i h 4 8 h 16 h s i 3 4 17 h s i n 3 4 10 d i h 3 4 h 6 hc49 5 hcn4 9 9 d i h 4 9 h 7 h s i 3 5 1 h s i c 3 5 2 d i h 3 5 h 22 hc50 11 hcn50 10 d i h 5 0 h 16 h s i 3 6 17 h s i n 3 6 10 d i h 3 6 h 6 hc51 5 hcn51 9 d i h 5 1 h 4 h s i 3 7 5 h s i n 3 7 9 d i h 3 7 h 22 hc52 11 hcn52 10 d i h 5 2 h 12 h s i 3 8 11 h s i n 3 8 1 0 ' d i h 3 8 h 20 hc53 2 hcp53 1 d i h 5 3 h 4 h s i 3 9 5 h s i n 3 9 9 d i h 3 9 h 21 hc54 14 hcp54 10 d i h 5 4 h 12 h s i 4 0 11 h s i n 4 0 10 d i h 4 0 h 20 hc55 2 hcp55 1 d i h 5 5 h 19 hc41 8 hcn41 7 d i h 4 1 h 21 hc56 14 hcp56 10 d i h 5 6 h 18 hc42 17 hcn42 10 d i h 4 2 h 20 hc57 2 hcp57 1 d i h 5 7 h 21 hc58 14 hcp58 10 d i h 5 8 227 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A20. Initial parameters for model complex 4G. pc2 1.916964 c n s i l 9 118 . 340 d i h 3 5 150 .642 hc52 1.103377 cp3 1 .916352 d i h l 9 146 .473 h s i 3 6 1.496344 hcn52 112 .361 cpc3 105 .335 cp20 1.878765 h s i n 3 6 1 1 0 . 7 1 5 d i h 5 2 132 .799 s i c 4 1 .908240 cpc20 105 .490 d i h 3 6 152 . 553 hc53 1.094120 s i c p 4 108 .833 d i h 2 0 114 . 002 h s i 3 7 1 .495717 hcp53 108 . 643 d i h 4 9 6 . 6 3 0 cp21 1.878765 h s i n 3 7 1 1 2 . 5 2 5 d i h 5 3 178 .519 n s i 5 1 .778143 cpnb21 124 .310 d i h 3 7 - 1 2 2 . 1 0 8 hc54 1.094122 n s i c 5 107 .950 d i h 2 1 - 9 . 3 4 3 h s i 3 8 1 .495717 hcp54 108 .643 d i h 5 1 3 . 3 4 1 cn2 2 1 .490391 h s i n 3 8 1 1 2 . 5 2 5 d i h 5 4 5 7 . 0 0 9 cn6 1 .490391 cnnb2 2 116 .697 d i h 3 8 122 .108 hc55 1.093835 c n s i 6 1 1 6 . 1 6 1 d i h 2 2 8 1 . 7 5 5 h s i 3 9 1.498924 hcp55 109 .148 d i h 6 - 179 .797 hnb23 1.988732 h s i n 3 9 1 1 0 . 6 1 1 d i h 5 5 - 6 2 . 6 7 9 s i c 7 1. 912253 hnbn23 152 .068 d i h 3 9 1 1 9 . 7 9 1 hc56 1.093834 s i c p 7 107 .201 d i h 2 3 - 2 5 . 8 9 4 h s i 4 0 1 .498923 . hcp5 6 109 .148 d i h 7 - 1 3 5 . 3 3 9 hnb2 4 1. 991722 h s i n 4 0 1 1 0 . 6 1 1 d i h 5 6 - 6 1 . 7 9 3 n s i 8 1.771348 hnbn24 90 .481 d i h 4 0 - 1 1 9 . 7 9 1 hc57 1.095746 n s i c 8 106 .073 d i h 2 4 --115 .284 hc41 1 .102235 hcp57 110 .546 d i h 8 3 1 . 021 hc25 1.097198 hcn41 1 1 2 . 0 8 9 d i h 5 7 58 .227 nbn9 2 . 045956 h c s i 2 5 109 . 926 d i h 4 1 6 9 . 9 5 1 hc58 1.095746 n b n s i 9 123 .909 dih.25 - 8 6 . 4 4 2 hc42 1 .102235 hcp58 110 .546 d i h 9 - 3 3 . 5 9 1 hc26 1.097198 hcn42 1 1 2 . 0 8 9 d i h 5 8 177 .301 nbnblO 2 .83202 hcp2 6 108 .264 d i h 4 2 109 . 989 nbnbnlC 128 .780 d i h 2 6 - 9 8 . 0 9 5 hc43 1 .104949 d i h l O - 9 0 . 3 2 7 hc27 1.097395 hcn43 110 . 470 n n b l l 2 .040802 h c s i 2 7 113 .411 d i h 4 3 - 1 7 1 . 5 4 8 nnbnb l ] 128 .037 d i h 2 7 152 .631 hc44 1 .104948 d i h l l 1 5 . 3 8 5 hc28 1.097396 hcn4 4 1 1 0 . 4 7 0 s i n l 2 1 .778143 hcp28 109 .997 d i h 4 4 - 8 . 5 1 2 s i n n b l 2 127 .124 d i h 2 8 144 .179 hc45 1.102848 d i h l 2 - 9 9 . 8 6 0 hc29 1.098943 hcn45 1 1 2 . 2 2 1 c s i l 3 1 .908239 hcp2 9 106 .469 d i h 4 5 - 5 2 . 2 5 9 c s i n l 3 1 0 7 . 9 5 0 d i h 2 9 --145 .468 hc46 1.102848 d i h l 3 1. 405 hc30 1. 098943 hcn4 6 1 1 2 . 2 2 1 p c l 4 1. 916346 hcp30 106 .469 d i h 4 6 - 1 2 7 . 8 0 1 p c s i l 4 108 .833 d i h 3 0 - 9 9 . 9 7 0 hc47 1 .101342 d i h l 4 - 1 3 . 3 4 1 hc31 1.097832 hcn47 1 1 1 . 5 2 9 c p l 5 1 .916967 hcp31 111 .229 d i h 4 7 105 .127 c p c l 5 1 0 5 . 3 3 5 d i h 3 1 - 2 8 . 2 4 7 hc48 1 .101342 d i h l 5 - 9 6 . 6 3 1 hc32 1.097832 hcn4 8 1 1 1 . 5 2 9 s i c l 6 1 .912253 hcp32 111 .229 d i h 4 8 - 1 0 5 . 1 2 7 s i c p l 6 1 0 7 . 2 0 1 d i h 3 2 142 . 809 hc49 1 .104180 d i h l 6 1 3 5 . 3 3 9 h s i 3 3 1 .494703 hcn4 9 1 1 0 . 9 4 9 n s i l 7 1 .771348 h s i c 3 3 108 .947 d i h 4 9 - 1 3 . 6 6 3 n s i c l 7 1 0 6 . 0 7 3 d i h 3 3 - 9 2 . 7 1 0 hc50 1 .104179 d i h l 7 - 3 1 . 0 2 1 h s i 3 4 1.494702 hcn50 1 1 0 . 9 4 9 c n l 8 ' 1 .488467 h s i n 3 4 114 .506 d i h 5 0 1 3 . 6 6 3 c n s i l 8 118 .340 d i h 3 4 - 8 6 . 5 8 7 hc51 1'. 103376 d i h l 8 --146 .473 h s i 3 5 1.496344 hcn51 1 1 2 . 3 6 1 c n l 9 1.488467 h s i c 3 5 109 .712 d i h 5 1 - 1 3 2 . 7 9 9 228 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A 2 1 . Final atomic coordinates for the geometry optimization of 4G. C e n t r e A t o m i c A t o m i c C o o r d i n a t e s ( A n g s t r o m s ) N u m b e r N u m b e r T y p e x' Y Z 1 6 0 4 . 4 2 6 0 6 9 - 0 . 5 2 0 2 0 5 0 . 6 7 1 2 7 5 2 1 5 0 2 . 8 8 9 7 0 4 0 . 4 2 3 8 3 3 1 . 2 8 2 2 9 9 3 6 0 3 . 2 3 7 5 8 3 2 . 2 7 1 5 5 7 0 . 9 9 6 7 4 6 4 1 4 0 2 7 3 3 8 3 0 2 . 7 1 6 9 7 8 - 0 . 8 1 2 2 5 3 5 7 0 2 2 3 1 7 7 4 1 2 0 0 8 1 3 - 1 5 8 2 4 5 0 6 6 0 2 7 3 3 9 8 2 0 8 5 5 3 3 6 - 2 9 3 9 0 3 4 7 1 4 0 3 8 7 6 0 8 3 - 2 1 5 8 7 7 6 - 0 1 6 1 0 7 2 8 7 0 2 1 3 1 8 1 6 - 2 0 8 0 6 5 1 - 0 5 4 8 3 3 6 9 4 1 0 1 1 7 2 8 9 7 - 0 2 3 0 1 7 5 - 0 5 2 4 6 0 2 1 0 4 1 0 - 1 1 7 2 8 7 8 0 2 3 0 1 8 0 0 5 2 4 5 4 3 1 1 7 0 - 2 2 3 1 6 9 6 - 1 2 0 0 8 0 7 1 5 8 2 4 4 9 1 2 1 4 0 - 2 7 3 3 7 4 8 - 2 7 1 6 9 8 6 0 8 1 2 2 7 3 1 3 6 0 - 3 2 3 7 6 3 3 - 2 2 7 1 5 7 1 - 0 9 9 6 6 9 2 1 4 1 5 0 - 2 8 8 9 7 8 0 - 0 4 2 3 8 4 5 - 1 2 8 2 2 7 1 1 5 6 0 - 4 4 2 6 1 1 0 0 5 2 0 1 8 8 - 0 6 7 1 1 5 2 1 6 1 4 0 - 3 8 7 6 0 7 7 2 1 5 8 7 8 8 0 1 6 1 1 0 4 1 7 7 0 - 2 1 3 1 7 9 9 2 0 8 0 6 5 5 0 5 4 8 3 1 6 1 8 6 0 - 1 5 2 1 4 2 3 3 4 2 9 1 6 0 0 7 5 0 7 1 5 1 9 6 0 1 5 2 1 4 4 2 - 3 4 2 9 1 5 4 - 0 7 5 0 7 5 1 2 0 6 0 2 8 8 6 5 1 2 0 1 8 8 9 5 7 3 1 5 1 5 4 9 2 1 6 0 - 2 8 8 6 7 0 9 - 0 1 8 8 9 7 4 - 3 1 5 1 5 2 2 2 2 6 0 - 2 7 3 3 9 1 0 - 0 8 5 5 3 1 8 2 9 3 9 0 2 8 2 3 1 0 0 3 9 6 8 5 5 1 3 6 3 3 9 3 0 3 0 7 5 3 4 2 4 1 0 - 0 3 9 6 8 5 1 - 1 3 6 3 3 8 2 - 0 3 0 7 6 0 6 2 5 1 0 4 9 2 9 2 8 0 0 1 2 0 6 8 9 - 0 0 6 1 9 1 8 2 6 1 0 - 4 9 2 9 2 5 1 - 0 1 2 0 6 9 3 0 0 6 2 1 0 1 2 7 1 0 5 1 2 8 2 5 7 - 0 7 0 2 5 2 9 1 4 9 5 0 3 4 2 8 1 0 - 5 1 2 8 3 7 0 0 7 0 2 4 7 8 - 1 4 9 4 8 5 7 2 9 1 0 2 6 2 3 8 8 7 2 8 3 3 6 8 8 1 7 1 2 2 8 5 3 0 1 0 - 2 6 2 3 9 9 1 - 2 8 3 3 7 0 4 - 1 7 1 2 2 7 5 3 1 1 0 4 2 9 1 6 1 1 2 4 9 7 6 2 6 1 2 0 5 1 7 4 3 2 1 0 - 4 2 9 1 6 7 7 - 2 4 9 7 6 4 0 - 1 2 0 5 0 4 2 3 3 1 0 4 1 3 8 5 5 0 - 3 2 9 2 4 9 0 0 7 8 0 8 2 4 3 4 1 0 - 4 1 3 8 5 6 2 3 2 9 2 4 6 3 - 0 7 8 0 8 3 4 3 5 1 0 4 7 4 5 4 3 2 - 2 3 9 5 0 5 4 - 1 3 5 6 1 4 6 3 6 1 0 - 4 7 4 5 3 8 2 2 3 9 5 1 3 3 1 3 5 6 1 9 7 3 7 1 0 1 7 1 3 0 1 1 3 7 9 9 8 0 6 - 0 7 7 3 0 8 3 3 8 1 0 - 1 7 1 2 8 9 5 - 3 7 9 9 7 7 7 0 7 7 3 0 3 4 3 9 1 0 3 9 3 7 1 5 7 3 2 5 9 8 7 7 - 1 5 1 9 4 1 3 4 0 1 0 - 3 9 3 7 0 1 3 - 3 2 5 9 9 2 8 1 5 1 9 5 0 3 4 1 1 0 1 6 5 1 0 4 7 - 4 0 7 9 9 4 5 0 1 3 1 0 8 1 4 2 1 0 - 1 . 6 5 1 0 3 1 4 . 0 7 9 9 4 2 - 0 1 3 1 1 2 4 4 3 1 0 0 . 4 4 7 9 9 1 - 3 . 3 2 3 5 5 3 - 0 . 9 2 9 1 2 2 4 4 1 0 - 0 . 4 4 7 9 7 0 3 . 3 2 3 5 6 1 0 . 9 2 9 0 8 2 4 5 1 0 1 . 9 6 4 9 5 9 - 3 . 9 4 9 7 7 8 - 1 . 6 1 8 6 3 6 4 6 1 0 - 1 . 9 6 4 9 3 5 3 . 9 4 9 7 9 5 1 . 6 1 8 5 9 6 4 7 1 0 2 . 2 0 6 4 7 6 1 . 4 1 6 0 5 1 - 3 . 7 2 7 2 3 6 4 8 1 0 - 2 . 2 0 6 4 0 9 - 1 . 4 1 6 0 2 7 3 . 7 2 7 2 3 9 4 9 1 0 2 . 5 7 5 2 7 9 - 0 . 2 1 6 8 9 9 - 3 . 1 3 9 7 6 4 5 0 1 0 - 2 . 5 7 5 2 0 7 0 . 2 1 6 9 1 8 3 . 1 3 9 7 5 1 5 1 1 0 3 . 8 1 3 3 7 9 1 . 0 5 2 9 2 5 - 3 . 0 5 2 7 3 6 5 2 1 0 - 3 . 8 1 3 3 0 8 - 1 . 0 5 2 9 0 6 3 . 0 5 2 7 2 8 5 3 1 0 2 . 0 2 2 0 3 8 0 . 7 0 8 8 1 7 3 . 5 7 6 2 4 8 5 4 1 0 - 2 . 0 2 2 2 6 7 - 0 . 7 0 8 8 4 0 - 3 . 5 7 6 2 7 7 5 5 1 0 2 . 7 9 7 0 0 0 - 0 . 8 7 8 6 8 0 3 . 3 7 5 7 0 1 5 6 1 0 - 2 . 7 9 7 2 0 7 0 . 8 7 8 6 6 2 - 3 . 3 7 5 6 8 4 5 7 1 0 3 . 8 0 7 5 4 7 0 . 5 8 4 2 0 8 3 . 5 9 5 4 4 2 5 8 1 0 - 3 . 8 0 7 7 7 7 - 0 . 5 8 4 2 2 1 - 3 . 5 9 5 3 5 2 229 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A22. Gaussianisms. When teaching oneself density functional theory applications using Gaussian 98, great pleasure is gained when, after weeks of frustration, an input structure finally converges. Successful conclusion of a G98 calculation rewards the scientist with a 'Gaussianism'; a short quotation from which one can (at times) gain great insight. For posterity the Gaussianisms obtain through this work are tabulated below in chronological order. GOD DOES NOT PLAY WITH D I C E . — A . EINSTEIN AT THE TOUCH OF LOVE, EVERYONE BECOMES A POET. — PLATO I F I COULD JUST GET IT ON P A P E R . . . L I F E AND INK, THEY RUN OUT AT THE SAME TIME, OR SO SAID MY OLD FRIEND THE SQUID. — JIMMY BUFFETT, 1981 BE CAREFUL NOT TO BECOME TOO GOOD OF A SONGBIRD OR T H E Y ' L L THROW YOU INTO A CAGE. — SNOOPY TO WOODSTOCK YOU ARE IN A MAZE OF TWISTY L I T T L E PASSAGES. THOSE WHO A S P I R E NOT TO GUESS AND D I V I N E , BUT TO DISCOVER AND KNOW, WHO PROPOSE NOT TO DEVISE MIMIC AND FABULOUS WORLDS OF THEIR OWN, BUT TO EXAMINE AND DISSECT THE NATURE OF THIS VERY WORLD I T S E L F , MUST GO TO THE FACTS THEMSELVES FOR EVERYTHING. — FRANCIS BACON, 1620 I F AT FIRST YOU DON'T SUCCEED, TRY, TRY A G A I N . THEN GIVE UP; THERE 'S NO USE BEING A DAMN FOOL ABOUT I T . — W. C . FIELDS THE MOST SERIOUS THREAT TO THE SURVIVAL OF MANKIND IS NOT NOW IGNORANCE I N THE TRADITIONAL SENSE, BUT A MORALLY NEUTRAL, AN I N S E N S I T I V E OR INHIBITED HUMAN I N T E L L I G E N C E . — MARGO JEFFERSON IN NEWSWEEK, SEPT. 2, 197 4 THE DIFFERENCE BETWEEN A NOOSE AND A HALO IS ONLY 12 INCHES. GETTING A SIMPLE ANSWER FROM A PROFESSOR IS L I K E GETTING A THIMBLE OF WATER FROM A FIRE HYDRANT. — PROF. LEN SHAPIRO, NDSU SUCCESS IS COUNTED SWEETEST BY THOSE WHO N E ' E R SUCCEED. TO COMPREHEND NECTAR REQUIRES SOREST NEED. — EMILY DICKINSON THERE IS NO CURE FOR BIRTH AND DEATH SAVE TO ENJOY THE INTERVAL. — GEORGE SANTAYANA 230 References located on page 208. Appendices one and two: X-ray crystal structure experimental information and D F T calculation data Table A22 continued. JUST REMEMBER, WHEN YOU'RE OVER THE H I L L , YOU BEGIN TO PICK UP SPEED. — CHARLES SCHULTZ EXPERIENCE IS THE FRUIT OF THE TREE OF ERRORS. THE LARGE PRINT G I V E T H , AND THE SMALL PRINT TAKETH AWAY. — TOM WAITES BLACK HOLES SUCK. 'TWAS AN EVENING IN NOVEMBER, AS I VERY WELL REMEMBER I WAS STROLLING DOWN THE STREET IN DRUNKEN PRIDE, BUT MY KNEES WERE A L L A ' F L U T T E R SO I LANDED I N THE GUTTER, AND A PIG CAME UP AND LAY DOWN BY MY S I D E . Y E S , I LAY THERE IN THE GUTTER THINKING THOUGHTS I COULD NOT UTTER WHEN A COLLEEN PASSING BY DID SOFTLY SAY, ' Y E CAN TELL A MAN THAT BOOZES BY THE COMPANY THAT HE CHOOSES. ' - AT THAT, THE PIG GOT UP AND WALKED AWAY ! — THE ECONOMIST, AUGUST 23 , 1986 IT IS A QUALITY OF REVOLUTIONS NOT TO GO BY OLD L I N E S OR OLD LAWS, BUT TO BREAK UP BOTH, AND MAKE NEW ONES. — A . LINCOLN (1848) MYSTERY IS THE WISDOM OF BLOCKHEADS — HORACE WALPOLE DISCOVERIES ARE OFTEN MADE BY NOT FOLLOWING INSTRUCTIONS, BY GOING OFF THE MAIN ROAD, BY TRYING THE UNTRIED. — FRANK TYGER A CHEMICAL PHYSICIST MAKES PRECISE MEASUREMENTS ON IMPURE COMPOUNDS. A THEORETICAL PHYSICAL CHEMIST MAKES IMPRECISE MEASUREMENTS ON PURE COMPOUNDS. AN EXPERIMENTAL PHYSICAL CHEMIST MAKES IMPRECISE MEASUREMENTS ON IMPURE COMPOUNDS. THERE IS AN OLD, OLD RECIPE IN MAINE FOR STEWING COOT. PLACE THE BIRD IN A KETTLE OF WATER WITH A RED BUILDING BRICK FREE OF MORTAR AND BLEMISHES. PARBOIL THE COOT AND BRICK TOGETHER FOR THREE HOURS. POUR OFF THE WATER, R E F I L L THE K E T T L E , AND AGAIN PARBOIL FOR THREE HOURS. ONCE AGAIN POUR OFF THE WATER, FOR THE LAST TIME ADD FRESH WATER, AND LET THE COOT AND BRICK SIMMER TOGETHER OVERNIGHT. I N THE MORNING, THROW AWAY THE COOT AND EAT THE B R I C K . IN SO FAR AS QUANTUM MECHANICS IS CORRECT, CHEMICAL QUESTIONS ARE PROBLEMS IN A P P L I E D MATHEMATICS. — EYRING, WALTER, & K I M B A L L , 1944 . . . T H O S E SCIENCES ARE V A I N AND FULL OF ERRORS WHICH ARE NOT BORN FROM EXPERIMENT, THE MOTHER OF CERTAINTY - - LEONARDO DA V I N C I , 1452-1519 231 References located on page 208. 

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