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Group 4 complexes of an arene-bridged diamidophosphine ligand for nitrogen activation Maclachlan, Erin Alisa 2006

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Group 4 Complexes of an Arene-Bridged Diamidophosphine Ligand for Nitrogen Activation by ERIN ALISA MACLACHLAN B. Sc., University of Toronto, 1999 M. Sc., Massachusetts Institute of Technology, 2001  A thesis submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (CHEMISTRY)  THE UNIVERSITY OF BRITISH COLUMBIA September 2006 © Erin Alisa MacLachian, 2006  Abstract Molecular nitrogen comprises about 80% of the earth’s atmosphere, but is only used 2 by the Haber 2 and H 3 synthesis from N as a starling material in one industri2l rection: NH 2 complexes of most transition Bosch process. Dinitrogen is generally unreactive, however, N metals and lanthanides are known,. and the challenge remains to discover metal dinitrogen . This thesis describes a new ligand, [NPN]*, its 2 complexes that can functionalize N N . coordination to Zr and Hf, and the use of [NPNJ*Zr complexes to transform 2 2 ([NPNJ* = [{N-(2,4,6Arene-bridged diamidophosphine ligand [NPN]*Li } is synthesized from simple organic compounds and’ PhJ )(2-N-5-Me-C C Me ) 3 H 6 P 2 ) [NPN]*MC1 (M 2 in high yield. Zr and Hf complexes, 2 PhPC1  =  Zr, Hf), are prepared via  [NPN]*MR (R [NPN]*H 2 , SiC1. OrganometaDic 2 3 M(NMe and Me , 4 ) protonolysis from 2  =  [NPN]*MC1 and Grignard or organ9lithium SiMe are prepared from 2 2 CH ) h, 3 CH P Me, 2 [NPN]*ZrR (R reagents. 2  =  SilVIe are light- and heat-sensitive, and’decompose 2 CH ) h, 3 CH P 2  to cyclometalated [NPNCJ *ZrR  ([NPNCJ  *  =  -2,42 H 6 P(Ph) (2-(NC [(2-MesN-5-MeC ) 3 H 6  ] and RH via an intramolecular a-bond metathesis mechanism; -5-MeCH 6-CH CH ) 2 ) 3 ) , is synthesized in high yield from (I12:rI2N 2 {[NPN]*Zr(THF)} A Zr-N 2 complex, )  [NPNI*ZrC1 and 2.2 equiv. of KC . By single crystal X-ray 2 8 in THF under 4 atm of N 2 and is side-on bound to two Zr atoms. Excess Py and 2 has been reduced to N analysis, N R (R 2 PMe , and N ) 2  =  2 complex to furnish Me, Ph) reacts with the Zr-N  R) 2 2 r {Zr[NPN] }, N2) : (II-rI }{ [NPN] *Zr(PMe *  R adducts 2 respectively. The PMe with ,a new  2 to provide react with H  3 to the Py adduct to give N—H bond. A new N—Si bond forms upon addition of PhSiH h){Zr[NPN]}* in high yield. The reaction of 4,4’{[NPN]*Zr(Py)}QIH)OI1]1:1]2NNSiH P 2 dimethylbenzophenone with  the THF  adduct provides  2) with a new N=C bond, and benzophenone imine reacts with the Py NNC(4-MeC ) 4 H 6 2) with two new N—H bonds. rI (I.I11 {[NPN]*Zr(NCPh2)} : H 2 adduct to generate N The dilithium complex of  (Ar  =  ) is prepared in two steps from 4 H 6 4-’PrC  (S) (S = THF, dioxane) is similar to 2 commercially available reagents. PhAr[NPN]Lj [p]*(5) r[NPN]Zr(NMe2) via 4 Ph in solution and in the solid state, and is converted to 2  protonolysis. Future directions for research are also suggested.  11  ‘I able of Contents Abstract.ii Table of Contents  iii  List of Tables  vii  List of Figures  ix  Glossary of Terms  xv  Acknowledgements  xix  Dedication  xxi  Chapter 1: Synthesis and Reactivity of Side-on Bound Dinitrogen 1.1  Introduction  1  1.2  Side-on Coordination of N 2 Prior to 1988  3  1.3  Side-on Coordination of N 2 Since 1988  5  1.4  Side-on N 2 Complexes of the Lanthanides  6  1.5  Side-on N 2 Complexes of the Actinides  11  1.6  Side-on N 2 Complexes of the Transition Metals  12  1.7  Reactivity of Side-on Dinitrogen Complexes  17  1.8  Conclusions and Scope of Thesis  25  1.9  References  28  Chapter 2: Zirconium and Hafnium Complexes of an Arene-Bridged Diamidophosphine Ligand 2.1  Introduction  33  2.2  Results and Discussion  39  2.2.1  Synthesis of a phenyl-bridged diamidophosphine [NPN]’  39  2.2.2  Metathesis approach to [NPNI*  43  2.2.3  Synthesis of group 4 complexes of [NPN]*  47  2.2.4  2 Adducts of [NPN]*ZrCl  53  2.2.5  2 Synthesis and structure of [NPN]*HfC1  56  2.2.6  2 Synthesis and structure of {NPN]*Hfl  60  111  2.3  Conclusions  .62  2.4  Experimental  63  2.4.1  General experimental  63  2.4.2  Starting materials and reagents  64  2.5  79  References  Chapter 3: Zirconium and Hafnium Organometallic Complexes 3.1  Introduction  84  3.2  Results and Discussion  88  3.2.1  2 (M Synthesis of [NPN]*MMe  3.2.2  Ph) {NPN]*M(CH Synthesis and reactivity of 2  92  3.2.3  h)z decomposition [NPNJ*Zr(CH P Kinetics of 2  100  3.2.4  SiMe *M(CH 2 ) Synthesis and reactivity of [NPN] 3  104  3.2.5  2 Attempted hydrogenolysis of [NPN]*MMe  108  =  Zr, Hf)  88  3.3  Conclusions  110  3.4  Experimental  Ill  3.5  3.4.1  General experimental  Ill  3.4.2  Starting materials and reagents  111 120  References  Chapter 4: Synthesis and Structure of Zirconium Dinitrogen Complexes 4.1  Introduction  127  4.2  Results and Discussion  131  4.2.1  (j112:112N 2 {{NPN]*Zr(THF)} Synthesis and structure of )  131  4.2.2  Synthesis and structure of  141  4.2.3  Q.112:12N 2 {[NPN]*Zr} Phosphine adducts of )  147  4.2.4  UV-visible spectroscopy of zirconium dinitrogen complexes  154  4.2.5  Attempted synthesis of a hafnium dinitrogen complex  157  4.3  Conclusions  159  4.4  Experimental  160  4.4.1  160  General experimental  iv  4.4.2 4.5  .161  Starting materials and reagents  169  References  Chapter 5: Reactivity of Zirconium Dinitrogen Complexes 5.1  Introduction  173  5.2  Results and Discussion  177  5.2.1  Reactions of N 2 2 complexes with H  177  5.2.2  Reaction of N 2 complexes with phenylsilane  185  5.2.3  Reaction of 4.1 with 4,4’-dimethylbenzophenone  191  5.2.4  Reaction of 4.1 or 4.2 with (CH CC(=O)H ) 3  199  5.2.5  Reaction of 4.1 or 4.2 with benzophenone 1mm  201  5.2.6  Reaction of N 2 complexes with CO  206  5.2.7  Reaction of N 2 complexes with ethylene  211  5.2.8  Reaction of 4.1 with Ph P=O 3  212  5.3  Conclusions  214  5.4  Experimental  215  5.5  5.4.1  General experimental  215  5.4.2  Starting materials and reagents  216 230  References  Chapter 6: Thesis Overview and Future Work 6.1  Thesis overview  236  6.2  Ongoing and Future Projects  240  6.2.1  Synthesis and characterization of Ph,Mes [NPN]’  6.2.2  Ph.Arp] (Ar Synthesis and characterization of  6.2.3  2 complexes Other reactions of ZrN  240 =  rC 6 P 1 4) 4 H  247 257  6.3  Conclusions  258  6.4  Experimental  259  6.5  5.4.1  General experimental  259  5.4.2  Starting materials and reagents  259 266  References  V  Appendix One: X-ray Crystal Structure Data  268  Appendix Two: Spectroscopic Supporting Information  280  vi  List of Tables  Table 1.1.  Caption  Page  2 in mononuclear and dinuclear General bonding modes of N  2  metal complexes.  Table 1.2  2 complexes and related species for which A selection of side-on N N NMR chemical N-N bond lengths are known; also included are 5  26  shifts along with JR and Raman data, if available.  Table 4.1  2 complexes UV-visible absorption maxima of some Group 4 N 157  in toluene.  Table A1.1.  (THF) 2 Crystal Data and Structure Refinement for [NPN]*Li Py) (2.13). [NPN]*ZrCl ( [NPN]*ZrCl (2.10) and 2 (2.72THF), 2  Table A1.2.  ) 2 Crystal Data and Structure Refmement for [NPNI*Hf(NMe [NPNJ*Hfl (2.17). [NPN]*HfCl (2.15), 2 (2.14), 2  Table A1.3.  269  [NPN]*HfMe (3.2), Crystal Data and Structure Refinement for 2 r (3.4). H oHs) [NPNCJ*Zr( C 2 C  Table A1.4.  270  ) 5 H 6 C 2 Crystal Data and Structure Refinement for [NPNj*Hf(rI1CH SiMe (3.7). 2 *Zr(CH ) (3.5), [NPNC] 3  Table A1.5.  268  271  Crystal Data and Structure Refmement for r N (ji-i } : ) 1i N (4.1), { [NPN]*Zr(Py) 2 (1i } : ) { [NPN]*ZrHF) 2 Ph) 2 2 (4.2), and { [NPN] *Zr(PMe ii-1 {Zr[NPNj } (4.4). (r-N : }) *  vii  272  Table A1.6.  Crystal Data and Structure Refinement for *  ) (ji-H) 2 3 : (JI-1 NNH) T1 {Zr{NPN] } (5.1), } { [NPN] *Zr(PMe h) r {Zr[NPN] } (5.3). : 1 (i-i P NNSiH { [NPN] *Zr(Py) } Qi-H) 2 *  Table A1.7.  Crystal Data and Structure Refinement for {p-r 6 ri : 1 } 2 ) 4 H NNC(4-MeC { [NPN] *Zr} ) 2 2 N (5.5), ri (,t-ri : ) }H { [NPN] *Zr(NCPh 2Q--O)  (5.4),  (JIO) (5.6). {[NPN]*Zr} 2  Table A1.8.  274  Crystal Data and Structure Refinement for  (p.djoxane) 2 PhMesjpN]Lj  2 e M s[NpN]H (6.3). (6.2), Ph  Table A1.9.  Table A1.1O.  273  275  (pdjoxane) 2 Crystal Data and Structure Refinement for PhAr[NpN]Lj  ) (6.6). 2 PrC (6.5), PhAr[NpN1Zr(NMe 1 4) 4 H (Ar = 6  276  Crystallographic Data Collection and Structure Solution Information.  278  viii  List of Figures Caption Figure 2.1.  Dinitrogen complexes prepared in the Fryzuk group with [PNP], ] and [NPN] ancillary ligands. N 2 [P  Figure 2.2.  Page  35  Comparison of two diarnidophospbine ligands: SiMe bridged and arene-bridged —CH — attributes of the 2 . 2 diamidophospbine ligands [NPN]Li 2 and [NPN]*Li  38  Figure 2.3.  Arene-bridged [NP]H and {PNP]H ligands.  42  Figure 2.4.  . D 6 ) in C 2 O 8 H 4 H} and 1 1 P{ 31 Li{ 7 H } NMR spectra of 2.7p-C  45  Figure 2.5.  ORTEP drawing of the solid-state molecular structure of .2THF, 2.72THF. 2 [NPN]*Li  46  Figure 2.6.  H NMR spectrum of 2.9 in C . D 6 300 MHz 1  49  Figure 2.7.  . D 6 300 MHz 1 H NMR spectrum of 2.10 in C  51  Figure 2.8.  ORTEP drawing of the solid-state molecular structure of , 2.10. 2 [NPN]*ZrC1  Figure 2.9.  52  ORTEP drawing of the solid-state molecular structure of (Py), 213. 2 [NPN]*ZrC1  Figure 2.10.  56  ORTEP drawing of the solid-state molecular structure of , 2.14. ) 2 [NPN]*Hf(NMe  58  ix  Figure 2.11.  ORTEP drawing of the solid-state molecular structure of , 2.15. 2 {NPN]*HfC1  Figure 2.12.  59  ORTEP drawing of the solid-state molecular structure of [NPN]*Hfl 217  61  Figure 3.1.  . D 6 300 MHz ‘H NMR spectrum of 3.1 in C  89  Figure 3.2.  ORTEP drawing of the solid-state molecular structure of , 3.2. 2 [NPN]*HfMe  91  Figure 3.3.  400 MHz ‘H NMR spectrum of 3.4 in C . D 6  94  Figure 3.4.  ORTEP drawing of the solid-state molecular structure of [NPNC]*Zr(12CH P 2 h), 3.4.  95  Figure 3.5.  500 MHz ‘H NMR spectrum of 3.5 in C . D 6  97  Figure 3.6.  ORTEP drawing of the solid-state molecular structure of Ph) 3.5. 2 [NPN]*Hf(qhCH ,  Figure 3.7.  98  Eyring plot for the thermal decomposition of Ph) 3.3. 2 [NPN]*Zr(CH ,  Figure 3.8.  101  ORTEP drawing of the solid-state molecular structure of 3 S 2 [NPNC]*Zr(CH ) iMe , 3.7.  107  Figure 4.1.  Zirconium dinitrogen complexes.  128  Figure 4.2.  Reactions of low-valent early transition-metal complexes with N . 2  129  x  Figure 4.3.  . 8 500 MHz ‘H NMR spectrum of 4.1 in THF-d  133  Figure 4.4.  2 in THF-d N Th . 8 N{’H} NMR spectrum of 4.140 MHz 15  136  Figure 4.5.  ORTEP drawing of the solid-state molecular structure of {[P\fJ*ZrHF)} 01  12:192  138  ) 4.1. 2 N  Figure 4.6.  Two views of the stereochemistry around Zr in 4.1.  139  Figure 4.7.  ) 3 H 6 C {[PNP]Zr(O-2,6-Me ( : ) i-i N } i . Structure of 2  140  Figure 4.8.  . D 6 500 MHz ‘H NMR spectrum of 4.2 in C  142  Figure 4.9.  ORTEP drawing of the solid-state molecular structure of 144  4.2.  Figure 4.10.  Two views of the stereochemistry around Zr in 4.2.  145  Figure 4.11.  162 MHz 31 P{’H} NMR spectrum of 4.3 in C . D 6  149  Figure 4.12.  162 MHz 31 P{’H} NMR spectrum of 4.4 in C . D 6  151  Figure 4.13.  ORTEP drawing of the solid-state molecular structure of *  Ph) 2 2 : (ji-r N2) r {Zr[NPN] }, 4.4. { [NPN] *Zr(PMe }-  153  Figure 4.14.  Two views of the stereochemistry around Zr in 4.4.  154  Figure 4.15.  UV-visible absorption spectrum of 4.1 in toluene.  156  Figure 4.16.  UV-visible absorption spectrum of 4.2 in toluene.  156  xi  Figure 4.17.  UV-visible absorption spectrum of 4.4 in toluene.  157  Figure 5.1.  Formation of new N—E bonds from 2 N ([P ( : ) t-r rI N Zr) .  176  Figure 5.2.  8 at 273 K H} NMR spectrum of 5.1 in toluene-d 1 P{ 202 MHz 31  179  Figure 5.3.  H NMR spectrum ZrHZr and NNH resonances in the 500 MHz 1 179  8 at 298 K. of 5.1 in toluene-d  Figure 5.4.  Ball-and-stick model of the solid-state molecular structure of ) (ji-H) (ji-NNH) (Zr[NPN] 3 } { [NPN] *Zr(PMe  *),  5.1.  180  Figure 5.5.  Projection of 5.1 down the Zr2---Zrl axis.  181  Figure 5.6.  . D 6 in C 5 400 MHz 1 H NMR spectrum of 5.3-d  187  Figure 5.7.  ORTEP drawing of the solid-state molecular structure of Ph) {Zr[NPN] }, 5.3. 2 { [NPN] *Zr(Py) } (pt-H) (ji-NNSiH  189  Figure 5.8.  Two views of the N, P, Si, and Zr atoms in 5.3.  190  Figure 5.9.  ORTEP drawing of the solid-state molecular structure  *  : 1 (i-r 2 ) 4 H NNC(4-MeC ), r 5.4. of { [NPN] *Zr} 2(-0) 6  Figure 5.10.  194  Two hydrazonato complexes: [(ri 1 -NNCHPh)2 -MeC Z ) 4 H 5 Q 2 i-ri r] :ri U Cp* M 2 eN_NzCPh (T1 (OTf). (j..t-r 1 -NNCHPh) and )  195  Figure 5.11.  Proposed mechanism for the formation of 5.4 from 4.1.  196  Figure 5.12.  162 MHz 31 H} NMR spectrum of the yellow product (in 1 P{ CC(0)H and 4.2. ) 3 ) obtained from the reaction of (CH D 6 C  xii  200  Figure 5.13.  ORTEP drawing of the solid-state molecular structure of , 5.5. -N r ) 2 H  204  Figure 5.14.  Two views of N, P, and Zr atoms in 5.5.  205  Figure 5.15.  . D 6 500 MHz ‘H NMR spectrum of 5.6 in C  207  Figure 5.16.  Ball-and-stick representation of the solid-state molecular structure of {{NPN]*Zr}QiO) 5.6.  210  Figure 5.17.  Two views of the stereochemistry around Zr in 5.6.  211  Figure 5.18.  162 MHz 31 P{’H} NMR spectrum taken one hour after addition of triphenylphosphine oxide to 4.1 in  Figure 6.1  ORTEP drawing of the solid-state molecular structure of Ph,Mes  Figure 6.2  213  . 6.2(p-C ) 2 0 8 H [NPN] Li 2 (p-dioxane), 4  243  ORTEP drawing of the solid-state molecular structure of PhMCS[-NPNIH  245  6.3.  Figure 6.3  ORTEP representation of crystal packing in 6.3.  246  Figure 6.4  . D 6 P{’H} and 1 31 } NMR spectra of 6.52THF in C Li{ 7 H  248  Figure 6.5  ORTEP drawing of the solid-state molecular structure of PhAr[NpN]  Figure 6.6  ‘-2  . (b-C ) 2 0 3 H , 6.5 4 (p-C ) 2 0 8 H 4  2 in C . D 6 500 MHz ‘H NMR spectrum of Ph.AC{NPN]H  xlii  250  251  Figure 6.7  . D 6 500 MHz 1 H NMR spectrum of 6.6 in C  Figure 6.8  ORTEP drawing of the solid-state molecular structure of ) 6.6. 2 PhAr[NPN]ZrNMe  Figure 6.9  254  H , r P 1 [3,5-(2,6C ) 3 H 6 C 2 r ] 2 P 1 2,6, 3 H 6 [NPN]’ ligands with C 256  and 1 Pr substituents on N.  Figure 6.10  252  N (4-CF ) 4 H 6 C PrP, and 3 Variations on [NPN]’ with CyP, 1 substituents.  256  Figure 6.11  Diamidophosphine ligands with alternative bridging groups.  257  Figure A2.1.  [NPN]*H (2.8) in toluene-d 8 from 300 K H NMR spectra of 2 1  Figure A2.2.  to 370 K in 10 K increments.  282  Plot of ln[3.3] vs. tat 338 K.  283  xiv  Glossary of Terms A  Angstrom (1O° m  Anal.  analysis  Ar  aryl group (unless context indicates argon)  atm  atmosphere  b  broad  Bn  benzyl group (-CH ) 5 H 6 C 2  Bu  (-CH C 2 ) H normal butyl group 3  3u 9  ) 3 tertiary butyl group (-C(CH  °C  degrees Celsius carbon-13  Calcd.  calculated  cm’  reciprocal centimetres (wavenumbers)  COSY  correlated spectroscopy  Cp  cyclopentadienyl group ([C ]) H 5  Cp*  M ([C ] ) e pentamethylcyclopentadienyl group 5  cryst  crystal  d  doublet  D or  deuterium  2D  two-dimensional  6  delta heat  dd  doublet of doublets  ddd  doublet of doublets of doublets  deg (°)  degrees  dens or p  density  DFT  density functional theory  Gt 1  free energy of activation enthalpy of activation  xv  DME  dimethoxyethane 2 C (MeOCH O Me) H n-deuterated entropy of activation  dt  doublet of triplets  e or e  electron(s)  E  element  E  energy  B  entgegen or trans  El  electron impact  ESI  electrospray ionization  ESR or EPR  electron spin resonance or electron paramagnetic resonance  Et  ethyl group 3 CH 2 (-CH )  EtO  ethoxide group 3 CH 2 (-OCH )  0 2 Et  diethyl ether  EtOAc  ethyl acetate  fw  formula weight  g  gram(s)  gof  goodness of fit  h  hour(s)  H 1  proton  H} 1 {  proton decoupled hapticity of order n  HMDSO  hexamethyldisioxane 2 SiJ ) 3 [(CH O  HMQC  heteronuclear multiple quantum coherence  HMSC  heteronuclear single quantum coherence  HOMO  highest occupied molecular orbital  Hz  Hertz, seconds 1  I  nuclear angular momentum quantum number (spin)  I  intensity  JR  infrared  JAB  K  I coupling constant Kelvin  xvi  between nuclei A and B over n bonds  kcal  kilocalories  kE  Boltzmann constant  kJ  kilojoules  Li 7  lithium-7  LUMO  lowest unoccupied molecular orbital  m  mukiplet meta- position of aryl ring  M  metal  M  parent ion bridging, absorption coefficient, or micro  Me  ) 3 methyl group, (-CH  Mes  (CH 2 H 6 (-2,4,6-C 3 mesityl group, )  mg  milligram(s)  MHz  megaHertz  mm.  minute(s)  mL  millilitre(s)  mm  millimetre(s)  mmol  millimole(s)  MO  molecukr orbital  mol  mole(s)  MS  mass spectrometry  (m/  mass-to-charge ratio  N 15  nitrogen-15  v  stretch  nm  nanometre(s)  NMR  nuclear magnetic resonance  NOE  nuclear overhauser effect  NOESY  nuclear overhauser enhancement spectroscopy  [NPNI  Ph) SiMe [PhP(CH N 2  [NPN]  *  PPh] )}2 3 H 6 ) (2-N-5-MeC [{N-(2,4,6-Me H 6 C 3 ortho- position of aryl ring  ORTEP  Oakridge Thermal Ellipsoid Plotting Program  xvii  para- position of aryl ring  phosphorus-31 Ph  phenyl group (-C ) 5 H 6  [PNP]  PiMe [(R S N ) 2 CH ] R  Nd 2 [P  SSiMe {PhP(CH N C P ) 2 iMe Ph] H  ppm  parts per million  Pr 1  isopropyl group (-CH(CH 2 ) 3  Pr  (-CH C 2 ) H normal propyl group 3  Py  Pyridine (C N) H 5  R  alkyl or aryl group  refi  reflections  Rf  retention factor  RR  resonance Raman  rt  room temperature  s  singlet  s  second(s)  Si 29  silicon-29  syst  system  t  time  t  triplet  T  temperature  THF  tetrahydrofuran  TLC  thin layer chromatography  tmeda  tetramethylethylenediamine 2 (IVIe C N ) CH Me H  TMS  tetramethylsilane ((CH Si) 4 ) 3  Tol  tolyl group 3 CH 4 H 6 (-C )  UV-Vis  ultraviolet-visible  V  Volt  V  Volume (of unit cell)  VT  variable temperature  xs  excess  Z  number of formuk units in the unit cell  xviii  =  Me, 1 Pr  Acknowledgements I would like to thank Mike Fryzuk for being an excellent supervisor. His research ideas and patient support were invaluable for the past five years.  I am greatly indebted to past and present members of the Fryzuk group for creating a supportive and fun lab environment, and for all of their help showing me techniques and sharing in the group jobs. I would especially like to thank Howie Jong and Ham Spencer for many productive discussions about chemistry and crystallography, and for making the lab a great place to be. I am very grateful to have worked alongside Lara Morello, a great labmate and friend. Thanks are due to Mike Petrella, Bruce MacKay, Scott Winston, Thorsten von Fehren, and Mike Shaver for many hours showing me the ropes. I have also had the good fortune to supervise many talented undergraduates including Shiva Shoai, Sharonna Greenberg, Nelly Ousatiouk, and Malte Wohifart. Thanks for all of the hard work, enthusiasm, patience and new ideas.  Many thanks are due to the excellent support staff at the Chemistry Department at U.B.C.: Dr. Brian Patrick, our very talented departmental crystallographer, for his patient instruction, Minaz Lakha and Marshall Lapawa and all of the staff at the mass spectrometry/microanalysis facility for their patience and skill with my finicky air-sensitive samples. Thank you to Zorana Danilovic, Maria Ezhova, Marietta Austria, Liane Darge, and Nick Burlirison for their incredible knowledge and assistance with NMR spectroscopy. Thanks very much to the excellent support staff in the mechanical and electronic/computing shop, glassblowing shop, chemistry stores, and in the front office. I am especially indebted to Ken Love for many hours of tireless detective work in front of the Fryzuk lab’s glovebox.  Thanks are due to Peter Legzdins for reading my thesis, and for support through the years. I would also like to acknowledge Peter Wassell for allowing me to teach in the inorganic undergraduate lab  —  it’s been a fun five years! Thanks are also due to Doug  Stephan at the University of Windsor for help with one of the crystal structures, and general supportiveness. I am very grateful to Sharonna Greenberg for editing this entire thesis, and  xix  for her friendship. Thank you to Britta Boden, Tracey Stott, Amanda Gallant, Meghan Dureen, and Carolyn Moorlag for friendship and support. I’m going to miss all of the good cooking!  Thank you to my parents and my brother for being such good role models, and for your generosity, love, and support.  Thank you to Mark for being such a fun and kind husband, and for curing my allergies!  xx  To my parents and Mark...  Chapter One Synthesis and Reactivity of Side-on Bound Dinitrogen  1.1 Introduction.t Transition-metal complexes that incorporate dinitrogen as a ligand have enjoyed a special status in inorganic coordination chemistry. In contrast to isoelectronic carbon monoxide, which is 1 2 is remarkably stable and a poor ligand. reactive and binds strongly to many transition-metal ions, N , was ] 2 N 5 ) 3 2 complex, [Ru(NH Although more is known about CO as a ligand, 2 since the first N discovered in 1965, a great deal has been learned about how N 2 binds to a metal, and the reactivity of coordinated N 2 focused on protonation 3 Early investigations into the reactivity of coordinated N . 2 5 Another ’ 4 in an effort to mimic the conversion of N 2 to ammonia by the enzyme nitrogenase. reaction of interest is the addition of organic and inorganic electrophiles, such as acyl halides or main group halides, to dinitrogen complexes. The displacement of N 2 by better donor ligands is also a well known, albeit unproductive reaction of coordinated dinitrogen. Until relatively recently, research on dinitrogen coordination chemistry has focused on these three types of reactions. 6 In the past decade, the chemistry of coordinated clinitrogen has been reinvigorated by the discovery of new reactions, including N—N bond cleavage, and functionalization of coordinated 7 What has also emerged as significant is the binding mode of the N ’ 1 . 2 N 2 unit to one or more metals, and the extent of activation of coordinated N 2 (Table 1.1). While the end-on bonding mode is the Sm) (Cp* Q I most common for coordinated N , in 1988, the first planar side-on bound N 2 2 complex 2 was communicated. 8 The N 2 unit is only weakly activated in this dinuclear compound, and  A version of this chapter has been published: MacLachian, E. A.; Fryzuk, M. D. O,ganometaluics 2006, 25, 1530.  *  1  its reactivity is limited by the fact that N 2 dissociates from the complex in solution and in the solid state. Since 1988, however, many other side-on bound dinitrogen complexes have been discovered 2 and their reactivity is beginning to be investigated. What is apparent so far is that side-on N complexes show enhanced reactivity compared to end-on N 2 complexes. This chapter will focus on the side-on bound N 2 unit in metal complexes, with some discussion of the side-on—end-on bonding mode of N 2 (E in Table 1.1).  Table 1.1. General bonding modes of N 2 in mononuclear and dinuclear metal complexes. Only connectivity is indicated, along with extremes in N—N bond activation from weak activation (N—N triple bond) to strong activation (N—N double and single bonds). Weak Activation M  N  N  M  N  N  Strong Activation End-on Mononuclear  M  M  N  N  End-on Dinuclear  M  Side-on Dinuclear  A  B  C  D  NN  \M/  2  .  M  E  Side-on End-on Dinuclear  1.2 Side-On Coordination of N 2 Prior to 1988. Orgel was the first to propose the side-on bonding mode of N 2 in 1960, many years before any such complexes existed. 9 In 1970, the side-on bonding mode was invoked when N 3 [(H R N 5 N’ 14 2 )]Br u( ) and N)]Br N 3 [(H R 5 1 N 15 2 u( 4 ) were observed to interconvert over a few hours at room temperature by JR spectroscopy. ° Because isomerization is faster than the dissociation of 1 2 from 2 N Ru the isomerization reaction is intramolecular and proceeds via a mononuclear 5 ) 3 (NH , transition state with N 2 bound side-on to Ru. In 1973, the isolation of triatomic 2 -N in a Co(ri ) matrix containing Co atoms and N 11 A single peak is observed in the JR 2 at 10 K was reported.  2 bound side-on to Co spectrum when N 15 gas is used, indicating that a symmetric species with N 4 ‘ is present. In 1978, a mononuclear side-on N 2 complex was reported on the basis of evidence obtained by EPR spectroscopy.’ 2 2 ZrR(N (R Cp )  =  ZrR(Cl) and 2 2 is prepared from Cp ) 3 CH(SiMe  Na/Hg amalgam in THF under N . There is a quintet in the EPR spectrum of the Zr(III) complex 2 due to coupling to two equivalent ‘ N nuclei (I 4  =  ZrR(’ is prepared analogously and a Cp ) 2 N 1). 5  triplet is observed in its EPR spectrum due to coupling to two equivalent 15 N nuclei (I  =  1/2).  Unfortunately, the solid-state molecular structure of the complex has not been reported, so this result has not been widely acknowledged. The first crystallographically characterized side-on N 2 complex, 2 L 5 H 6 [{(C N 3 ( N , ] OEt) i} i) 1, was reported in 1973; 1 is synthesized from a//-trans-1,5,9-cyclododecatrienenickel, [(CDT)Ni], and PhLi in Et 0 under N 2 13 N . 2 2 is bound side-on to a Ni—Ni bond, and end-on to four Li atoms, and the  N—N  bond is  elongated to  1.35  A. Similarly, 2 )[Na(OEt)] {(C [ N ) 5 H 6 N N (C ai]  (OEt) 6 Li ( 4 , } ) 2 OEt 2, is prepared from PhLi, PhNa, and [(CDT)Ni] under 4 .’ The N—N bond 2 N length is 1.359(18)  A, and N 2 is bound side-on to a Ni—Ni bond, and associated with Na and Li  atoms (see D in Table 1.1). The numbering scheme for compounds in chapter one differs from that used in the remaining chapters. 3  8)  A  2  I (only selected core atoms are indicated for clarity)  An intriguing example of N 2 bound to multiple metals, a component of which has N 2 bound side-on—end-on (E in Table 1.1), was reported in 1982. Upon exposure of solutions of [i-(11’:r1 5 )] 2 4 H 5 C -C (r1 T 3 ) H 5 i  to  2 N  a  tetranuclear  compound,  :r 10 5 -C (i 5 ) 8 H -ri ‘:rl 2 3 (,i -N [(‘q ‘:ri )  15 N 2 is coordinated side-on to one Ti, and end-on to C ] 2 ) 4 T 3 ) H 5 ] [(11’:1 (11 C , i 3, forms.  two Ti atoms, with an N—N bond length of 1.301 (12) A. 16  3  In an early theoretical investigation, side-on bonding of N 2 was predicted to be favourable for group 4 complexes. 17 If two group 4 transition-metal ions (e.g., Zr(H)) donate two electrons each to bridging N , one 2  it  bond, and either a ö bond (if N 2 is coordinated side-on) or a second  it  bond (if  2 is coordinated end-on) will form. If more than two electrons are available from each metal, the N formation of it-bonding interactions will stabilize the complex to a greater extent than the formation  4  of a  bond. The authors challenged synthetic chemists to focus theii: attention on early transition  . 2 metals in the quest for side-on complexes of N 2 is just a part of the larger picture. In the examples described above, side-on bonding of N 2 may be in a larger multinuclear complex, or in some cases the complex could The side-on bound N not be isolated and characterized in the solid state. In 1988, a simple unequivocal example of a side2 complex was reported. For this reason, this date stands as a milestone in dinitrogen on bound N coordination chemistry.  2 Since 1988. 1.3 Side-On Coordination of N 2 complex in which the N—N bond is perpendicular to, In 1988, the ftrst discrete dinuclear N , 4, forms when toluene m) S (Cp* Q 2 112:T12N and coplanar with, the M---M axis was reported. ) m are exposed to N Cp* S 2 under vacuum. In the solid-state molecular ; 4 loses N 2 solutions of 2 structure of 4, the N—N bond length is 1.088(12)  2 (1 .0975(2) A) (see A A, not elongated over free N  m units are perpendicular to each other, and the N Cp* S 2 unit is canted: the in Table 1.1). The 2 2 plane. Although N 2 appears to be N plane is at an angle of 62.9° to the Smi Cp* (centroid) 2 Sm 3 species, as are the chemical neutral in this structure, the Sm—C bond lengths are typical for a Sm 2 with an elongated N— C NMR spectroscopy. To maintain charge neutrality, N shifts observed by 13 N bond would have to be present. The discrepancy between the expected and observed N—N bond  lengths has not been fully rationalized. 1.088(12) A  5  18 Dark 2 was reported. In 1990, the second discrete dinuclear complex with side-on bound N blue 2 ii ({PNPJ N (ii-r ({PNP]ZrCl) : )  =  3 and ]), 5, is prepared from {PNP]ZrC1 iMe2) CH P [(Pr S 2 N  . The N—N bond length is 1.548(7) 2 Na/Hg amalgam in toluene under 4 atm of N  A, longer than the  2 complex (C in Table 1.1). N—N single bond in hydrazine, and the longest measured to date for an N Since 4 and 5 were reported, many other lanthanide, actinide, and transition-metal complexes that 2 complexes display 2 have been discovered. In some cases, side-on N contain side-on bound N interesting new reactions for coordinated dinitrogen. 2 Me  2 Me 5  2 Complexes of the Lanthanides. 1.4 Side-On N Since the report of 4 in 1988, many other lanthanide dinitrogen compounds have been 2 to give 2 reacts with two equivalents of KCp* in Et 0 under N 2 discovered. Tm1 2 bound side19 The low-resolution solid-state molecular structure of 6 shows N , 6, in 55% yield. N ) 2 N core. Side-on N 2 2 complexes have been synthesized with on to two Tm centres in a planar Tm (SiMe H 5 [C ] 2 ) 3  and  ancillary  ] 3 ( 4 H 5 [C ) SiMe  ligands;  m} ii (N—N bond: 1.259(4) N2) i-i (SiMe H 5 {[C T ] ) 3 ( : 2 r1 (N—N bond: 1.236(8) :N2) 2 T1 -  A),  8.19  2 N  is  moderately  activated  in  J im(THF)} (SiMe 4 H 5 {[C ) 3 T ( A), 7, and 2  2 may be more strongly activated in these complexes N  2 is also side-on bound in because Tm(ll) is more reducing (—2.3 V) than Sm(II) (—1.5 V). N ° . 2 (SiMe under N H 5 K[C ] 2 ) 2 and 3 I-1 y} 9, prepared from Dy1 r) N2), (SiMe H 5 {[C D J ) 3 Q : 2 -  6  JMS 1.236(8) A  (TMS  7  =  8  ) 3 SiMe  2 complex required the use of harder ligands than Cp, i.e., The synthesis of a neodymium N , and these ligands also support Tm and Dy dinitrogen complexes. (O2,6tBu ) 3 H 6 C ] and 2 i) 2 S 3 [(Me N 2 to give 2 in THF under N IEHF) or Dy1 3 ( 2 2 react with Tm1 ) 3 Two equivalents of NaN(SiMe i Ln )} e ] i) N 11 Ji-1 n(THF {[(M S 3 N L ( : 2 )  =  Tm, 10, and Dy, 11).21 The two complexes have  analogous solid-state structures with N—N bond lengths of 1.264(7)  A and 1.305(6) A, respectively.  d1HF [(ArO) N 2 complex, blue-green 2 The first example of a Nd-N  N (Ar r) (-ri : 2 )  =  2,6-  2 (N—N bond: 2 and two equivalents of KOAr in THF under N u , 12, is prepared from Nd1 2 B t ) 3 H 6 C 1.242(7)  2 was significant since these species are extremely , Dy 2 , and Nd 2 21 The use of Tm A).  2 reducing and their molecular chemistry had been relatively unexplored. A versatile route to Ln-N 2 to give 8 in THF under N complexes is via reduction of Ln[N(SiMe 1 with one equivalent of KC 2 ) 3 )} e 13, (Ln ] , i) ii N ji-r n(THF {[(M S 3 N L ( : 2 )  =  Tm, Dy, Nd, Gd, Ho, Th, Y, Er, Lu, La) (Equation  1.1).23 The N—N bond lengths range from 1.258(3)  A for Ln  =  Nd, to 1.305(6)  2 ) 3 N(SIMe  10 Ln = Tm 11 Ln=Dy  1.264(7)  A  1.305(6)A  12  7  A for Ln = Dy (11).  2 Ln[N(SiMe } 2 ) 3  +  2 KC 8  2 ) 3 N(SiMe  (M  2 N THF  (1.1) 2 ) 3 “N(SiMe  /  Si) 3 (Me N 2  13  Ln  =  Tm, Dy, Nd, Gd, Ho, Tb, Y, Er, Lu  2 complexes, single 1 has provided many new Ln-N 2 ) 3 Although KG 8 reduction of Ln[N(SiMe S 3 {[(Me N L Q : ) a(THF)} r1 N i-r i) , j an attractive diamagnetic target, could not be crystals of 2 2 complexes could be prepared, however, with a different obtained by this route. Crystalline La-N 24 ancillary ligand.  ), 2 M 5 (C H 4 L a(THF) e ) } Qi-r:rj-N {2  La(THF) 2 2 14, and {Cp* (I1-11 } : ) T1 N , 15, are  La][(IPh) [Cp* B 2 Ph , respectively. The N—N bond Me 5 La(C H 4 ) and ] obtained by KG 8 reduction of 3 in 15 is 1.233(5)  A,  N 5 corresponding to reduction to N , and there is a singlet at 3 569 in the ‘ 2  2 complexes has been recently NMR spectrum. The discovery of these dinuclear side-on Ln-N Me 5 Lu(C H 4 ) to give 2 25 The synthesis and reduction of 3 recounted. M 5 {(C H 4 L ( : ) ji-ri uHF)} N i e ) 26 was recently reported.  1.233(5)  A 15  The second Ln-N 2 compound was reported in 1994. In one pot, 2 Li{{Et [HF) C (ccN H C } ( L 2 ) 4 Sm1 N )] , i 16, is prepared from  C [Et N 2 H } ( , THF) (c-C Li )] {4  (THF) Li metal, SmC1 , 3  and N . In the solid state, N 2 2 is encapsulated in an 4 Li octahedron and the N—N bond length of 2 Sm 1.525(4)  A indicates that N , or hydrazide, is present. 2 27  8  Et Et  L Li)N/L.  2 •2 Li(THF)  \/Li EtEt  16  N complex, [{[(CH) 2 C(cL-C 5 [{(CH) N H 2 ] )} is the ancillary ligand, a labile Sm When 4 CQx5  2 (N—N bond: N H C } 4 0 3 Q ) 2 , Sm[Li(THF)1 (THF) 1-C1)1 1-ii:i-N )1 17, with weakly activated N 1.08(3)  A)  forms  from  the  Sm(II)  reduction  product,  C(c5 ) 2 [{[(CH  2 to regenerate -C1), 18.28 Solutions of 17 readily lose N 3 [Li(THF) Qi [Li(THF)] ] N)] Sm(THF)] 2 2 H C } 4 C(cIL5 ) 2 2 complex, [{[(CH N 3 2 yields the Sm 18, and concentrating solutions of 18 under N N H C S 2 } 4 L 3 ] i](j.t-NLi(THF) (THF), m )J 19. N 2 is bound side-on to three Sm centres and end-on to two Li centres with an N—N bond length of 1.502(5)  29 A.  (THF) •CILi 3  17  When dipyrrolide ancillary ligands are used, N 2 is once again strongly activated by Sm(II). [(cL-C K C 2 N 3 H 4 ] Ph ) reacts with 2 HF) under N SmI 2 to give  C {[Ph N 3 H 4 ] 2 ( (c-C Sm} i)  , 20, in high yield. Diriltrogen is bound side-on to two Sm atoms and end-on to two Sm 2 N)(THF) atoms in an Sm 2 coplanar array, and the N—N bond is 1.412(17) N 4 C(c-C 5 ) [(CH N 3 H 4 ] ) Sm} 2 (THF) [Na(THF)] CrHF) 4 Q ) i-N 2 {2  ° 3 A.  A similar Sm 2 complex, N 4  (N—N bond:  1.371(19)  A),  21, is  prepared in two steps from 1,1 -dlipyrrolylcyclohexane, KR, 3 (I’HF) and Na/naphthalene. SmCl ,  9  C 5 {[(CH) N 3 H ] ( 4 ) 2 Qi-N THF) Sm} (c-C ) (N— Complex 21 can also be prepared by Na reduction of 25 N  bond:  A),  1.392(16)  22,  which  is  prepared  from  S 3 [(I\4e N S 2 m(THF) i) ]  and  1,1-  ’ 2 3 dipyrrolylcyclohexane. N 3 [(Me S S m(THF) i] ) has proven to be a versatile Sm(II) starting material. C(c2 2 gives [{[Et N 3 [(IVIe S S m(THF) i] ) under N C(cL-C [Et N 3 H 4 ] H) with 2 The reaction of 2 2 is bound side-on to two Sm atoms and end-on to two N 3 H C ( 4 ] ) , 2 (THF) THF) Qi-N )]Sm} 23. N Sm atoms with an N—N bond length of 1.415(3)  32 A.  I.  2THF  1.371 (1 9) A  Pr  and  Nd  N 2 H C } 4 M(THF)] )] [Na(THF) ] (M 2 complexes 25 (M  =  complexes  tetrapyrrolide =  Pr) and 26 (M  also  activate  . 2 N  Reduction  of  C(c2 [{[Et  Pr, Nd) with Na/naphthalene under N 2 gives the side-on N 2 =  Nd) upon crystallization. In the solid state, the complexes  contain rI’:1 N cores, and moderately activated N 2 2 (N—N bonds: -bound pyrrole ligands, planar M 5 1.254(7)  A (25),  1.234(8)  A  (26)). Et Et  2 ] 3 [Na(DME)  2 Na(DME) =  25 Et Et  10  Since 1988, side-on binding of N 2 has been found to be ubiquitous for lanthanide complexes. The coordinated N 2 unit varies from unactivated to highly activated, and there will likely be many more reports of N 2 coordination by lanthanides. Research into other aspects of lanthanide 2 to lanthanides has also dinitrogen chemistry also continues. For example, side-on coordination of N 34 been observed by JR spectroscopy using matrix isolation techniques.  1.5 Side-On N 2 Complexes of the Actinides. N] 3 The first actinide dinitrogen complex was reported in 1998. Reduction of [N NIUC1 ([N 3 =  N]U(III), 27, upon sublimation. 3 C [N(CH N ] 3 ) 2 Si93uMe H with K in pentane produces [N  2 binding is reversible, and Under I atm of N , 2 2 jU} 3 {[ Q : N), rI t-1i 28, forms (Equation 1.2). N  27 is regenerated under vacuum. At 1.109(7) A, the N—N bond is essentially unactivated in 28 and UV/visible spectroscopy and magnetic susceptibility measurements show that the complex contains U(III). R N2 2  IIIUN  —-U’  N—U  NIL)  (1.2)  1.1O9(7)A\  27 Although it may seem that the it  28 it  R  =  tBuMeSi  bond of N 2 is a a donor to U in 28, calculations suggest that  back-bonding from U to N 2 is the most important U—N bonding interaction. 36 By DFT, the  it  bond of N 2 is too low in energy to interact with U in the model compound, 2 (NH ) [(NH ) 3 Q UJ i: q ) 2 N r , 29. The bulky [N N] ligand may hinder U f and N 3 2  11  itK  orbital overlap and prevent strong  activation of N ; compared to 28, complex 29 is predicted to have a long N—N bond and short U—N 2 37 bonds. Moderate activation of N 2 by an actinide was reported in 2002.38 The N—N bond is 1.232(10) (Si2Pri))} 4 H 8 {Cp*U(C Q ) 112:rI2N , 30, although N 2 binding is reversible: starting complex A in 2 (Si1Pr is regenerated under vacuum. DFT calculations on the model complex [(r1 4 H 8 Cp*U(C 2 ) 3 5 (7t) 2 Cp)(r ) 6 H 8 ( : ) 2 JI-r U] T N C indicate that U(5f)—*N  t  39 back-bonding is substantial.  Si’I... 3 Pr  30 2 coordinated in the bridging side In contrast to Ln—N 2 complexes, which generally feature N 2 fixation by an on mode, actinide dinitrogen chemistry is diverse. Since the first report of N 41 a mononuclear end-on U-N 2 organouranium complex, ° a heterodinuclear U-N 4 2 compound, 42 and N compound, 2 cleavage by U 43 and Th compounds have been reported.  1.6 Side-On N 2 Complexes of the Transition Metals. Since the discovery 18 of 2 (Ji-r ({PNPJZrCl) : N), rl 5, many transition-metal complexes with side-on N 2 have been reported. Since the early 1990s, there has been speculation on the binding mode of N 2 in nitrogenase. Some have suggested that N 2 binds side-on to Fe in the FeMo cofactor. 45 In 1991, an intriguing pair of N 2 complexes showed how capricious N 2 bonding could be. 46 S 3 {[(Me N ( 1 ) 2 ]TiC1(tmeda)} j.i-r:i N i) (tmeda  =  Me C N ) 2 CH Me H (N—N bond: 1.289(9)  A), 31,  with end-on bound N SLi 3 (Me N i) 2 forms from mixtures of 2 TiC1 and one equivalent of 2 (tmeda)  12  SL1 3 (Me N i) and excess tmeda under under N . When 2 2 TiC1 reacts with 2.5 equivalents of 2 (trneda) , purple [Li(t 2 2 N ] 32, forms (anion shown below). To date, 32 i-i i} ri i) N], ][{[(Me eda) S 3 N T Q : 2 are bound side-on to two metals. The N—N bonds are is unique because two molecules of N 1.379(21)  A.  e  1.379(21)A 3 SiMe  N  NI  ‘  I  3 ‘SiMe  SVN 3 Me SI-......N” 3 Me  3 SiMe  ”N” 1  \j/ I N 3 SMe  3 \_.SIMe  I  3 SIMe  32  47 When 5 2 complexes have been discovered. Since 1990, other [PNP]Zr-N C 1 ( 2 [PNP]ZrCl ) H 2 is , 33, forms, wherein N r N (jt2 ([PNP]ZrCp) : 1 , ) 2 is reduced with Na/Hg amalgam under N coordinated end-on to two Zr centres and the N—N bond length is 1.301(3)  48 N A. 2 may adopt the  end-on bonding mode in 33 because the Cp ligand interacts with the d orbitals required for 6 bonding to N ; in addition, steric factors may be important. In contrast, Na/Hg reduction of 2 2 gives [PNP] 2 )C1 under N 3 H 6 C Zr(O-2,6-Me  N , T (ji-r : ) )}2 3 H 6 C 2 { [PNP] Zr(O-2,6-Me  2 is bound side-on to two Zr atoms with a 1.528(7) solid state, N  A N—N bond.  34. In the  In contrast to 5, the  N core in 34 is not planar, but has a butterfly distortion (D in Table 1.1); the angle between the 2 Zr two ZrN 2 planes is 156°. A peak at 751 cm’ in the KR spectrum of 34 is assigned to the symmetric ]ZrC] N [P 8 reduction of 2 v(N—N) mode, consistent with the presence of a long N—N bond. KG ] N 2 ([P  =  2 generates dark-blue 2 H under N iMe Ph] SSiMe [PhP(CH N C P 2 ) , i ,i-i N ]Zr) N ([P ( : )  2 is bound side-on ] coordinates to each Zr atom, and N N 2 35. In the solid state, one macrocycic [P in a planar Zr N core (N—N bond: 1.43(1) 2  49 A).  13  (Mes on Si omitted)  Side-on N 2 complexes have been implicated as intermediates in N 2 cleavage by a Nb ] 4 [{ptBu-caliX[4]Q ( ) , 2 ][Na(diglyme) J..t-1]l:rl-N Nb} 36, calixarene. The end-on Nb-N 2 complex, ] reacts with Na to give 4 B t {b] ( [ 2 , Na(DME)] u-calix[4J-O I-N) Nb} with two bridging nitrides. ° The 5 side-on Nb-N 2 complex,  (p.-r } : ) N r ] [Na(DME)] (DME), 4 Bu-calix[41-0 t Lb] Nb 2 [{ 4  37, a possible  intermediate in the N—N cleavage reaction, is prepared from 36 and Na. ’ In the solid-state, N 5 2 is perpendicular to a Nb—Nb bond, and the N—N bond length is 1.403(8)  A.  Because the N—N bond  length is similar in 36 and 37, Na has reduced Nb(V) to Nb(IV), and the formation of a Nb—Nb bond has forced N 2 to become side-on bound.  1.403(8) A  37  36  14  2 is known for [NPNITa complexes ([NPN] The side-on—end-on bonding mode of N  =  Qi-H) which reacts 2 ([NPN]Ta) , 2 to provide 4 3 reacts with H Ph) . [NPNITaMe iMe 52 S {PhP(CH N ) ] 2 2 is bound side-on to one with N 2 to give 2 i-i’:r , 38 (Equation 1.3). In 38, N N (ji-H) ([NPN]Ta) Q ) 2 is moderately activated (N—N bond: 1.319(6) Ta and end-on to the other Ta, and N  A).  This  2 is the relatively mild reducing agent that generates reaction is remarkable for two reasons. First, H , Na) or 8 the strongly reducing tetrahyciride dimer. Thus, the use of alkali metal reductants (e.g., KG  53 of strongly reducing metal starting materials (e.g., Sm(II)) is avoided. Second, this is a rare example , although this 2 2 via displacement of H an early transition-metal hydride complex that coordinates N 2 is 54 The JR and RR spectra of 38 confirm that N reaction is known for late transition metals. 55 strongly activated in this complex. Ph P PI>N  *  /  2 )SIMe  MeS(/\/HY’  2 N  (1.3)  ) 2 ( H  2 Me  56 The side-on . 2 In 2001, another early transition-metal hydride was observed to coordinate N 2 complex, 2 Zr-N N r1 Q (rac-BpZr) : ) i-r1 (rac-Bp  39, is  =  2 and H . The 2 2 is prepared from rac-BpZrMe , and rac-BpZrH 2 synthesized from rac-BpZrH 2 and N N core is planar, and the N—N bond length is 1.241(3) 2 Zr  A.  1.241(3) A  Si 2 Me  Si 3 Me  39  15  2 complex was discovered in 2OO3. Two An intermediate in the formation of a Zr-N ZrC1 (Cp” Cp” equivalents of t BuLi add to 2 40, (N—N bond: 1.47(3)  =  , r] ji-r N rì Z [Cp” ( : 2 [1 5 i) C ri ) to yield ) S ,3-(Me 2 ] 3 H  A). Low temperature NMR spectroscopy shows that cyclometalated (Cp”)[l  H 41, is an intermediate in the formation of 40. Related C i)-i ZrH, S (Me 3 H 5 C 2 ] 3--SiMe H ZrH, do not react with C 3 H 5 C ] 3-i-SiMe cyclometalated zirconocenes, such as (Cp*) [1 -(Me Si)-i 2 3 . 2 N 1.377(3)A  1.47(3)A  Sir1I 3 Me  N  N  40  42  3 SiMe  ZrC1 to give Cp* In 1974, the reduction of 2  58 With was reported.  a slight modification to the ancillary ligand, from pentamethyl to tetramethyl Cp, a complex in which 2 coordinates side-on to two Zr atoms is isolated. Thus, the reduction of 2 N e ) with C -rC1 (‘ri M 5 H 4 Z 2 gives 2 Na/Hg amalgam under N e ) , r] ri i-i N C [(r M 5 H 4 Z ( : ) planar Zr N array is 1.377(3) 2  The N—N bond length in the  A. With one additional methyl group per zirconocene, the end-on  2 H 4 )ZrI reduction gives [Cp*(T15CsMe H)Zr(T11 4 dinitrogen complex is obtained; Cp*(r5CsMe N } , ) N ( 2 1 ) ji-i’:ri  4360  The hafnium analogue of 42, 2 e I-1] f] ) was recently N), C rI [(1 M 5 H 4 H Q : -  2 complex characterized in the solid state; 43 is prepared by 61 Complex 43 is the first Hf-N prepared. 2 is strongly activated (N—N bond: 1.423(1 1) the same route used to prepare 42 and N  A).  2 complexes are multinuclear, there is evidence for a metastable Whereas most side-on N mononuclear side-on N 2 complex of Os(II). Photolysis of single crystals of 6 ) N 3 [(H 0 5 ) 2 ] ]{PF s(rl’-N 62 Analysis by X-ray crystallography and JR . 2 ] 6 ) {PF N ] N 3 [(H O 5 2 s(r causes partial formation of )  16  spectroscopy confirms the presence of side-on N . Although the change in the N—N bond length is 2 within error for the structure, the Os—N 1 bond lengths are 0.263(1 7)  A longer than  Os—N(X in the  N NMR starting material, and the N—N stretching frequency is decreased by 187 cm’. 15 ; intramolecular isomerization of 2 spectroscopy has also been used to observe transient side-on N N) (for Cp’ 4 N’ 15 Cp’Re(CO)(L)(  =  Cp, L  =  CO; for Cp’  =  Cp*, L  =  , P(OMe) 3 ) occurs via 3 GO, PMe  ° 1 ] observed by JR spectroscopy. 2 N 5 ) 3 an 2 63 similar to isomerization of [Ru(NH -N intermediate, 1 2 in 64 KG 8 reduction of [NPN]ZrC1 Side-on [NPN]Zr-N 2 complexes were recently reported; 2 is bound side-on to two Zr THF under N 2 gives purple 2 (.t-r1 {[NPN]Zr(THF)} : N), rl 44. N atoms and N 2 is strongly activated; the N—N bond length is 1.503(3)  A.  44  1.7 Reactivity of Side-On Dinitrogen Complexes. Prior to 1997, few reactions were known for side-on N 2 complexes, and most involved the addition of acid to a complex to yield hydrazine. To date, no reactions have been reported for N 2 bound side-on to a lanthanide or actinide; reactivity of side-on N 2 has only been observed in transition-metal complexes. In 1997, the first functionalization reactions of side-on N 2 were reported (Scheme 1.1). Under H , 2 2 N ([P ( : ) ji-11 Tl ]Zr) N (35) transforms to 2 N ( ( : H -H)Qt-11 N Zr) r ), 45•49  Neutron diffraction analysis confirms that new N—H and Zr—H bonds form, and that the N—N  bond length in side-on bound hydrazide (NNH) is 1.39(2)  17  65 A.  In a similar fashion, a new N—Si  46,  bond is produced upon addition of BuSiH 3 to 35. features side-on bound NNSiH 49 Bu with a 1.530(4) A N—N bond. 2  Scheme 1.1.  35 SiBu 3 \\  H/  (Mes on Si omitted)  45  46  The hydrogenation and hydrosilylation of 35 represent new transformations for coordinated dinitrogen that transcend the reaction of end-on N 2 complexes with electrophiles. The formation of an N—H bond in 45 was the first report of this kind of reaction; typically, H 2 displaces N 2 in a dinitrogen complex. DFT calculations on the addition of H 2 and SiH 4 to model complex Z J n ([p i : ) 2 -ii N ti r) ([p ] n 2  =  H] show that the reactions proceed via a-bond 3 [(PH ) 2  66 The addition of a second equivalent of H metathesis. 2 to give 2 n ([p Q : ) H (j.i-H) ]Zr N i-i i is predicted to be spontaneous, although this has not been observed experimentally. 67  18  , N—C bond formation, is observed upon addition of 2 Another new reaction for coordinated N  two equivalents of ArC ECH (Ar  =  Zr) ] N 2 ([P i-CCR)(ji, to 35 to give Q BuC t p) 4 H Ph, p-MeC ,6 4 H 6  N 47, with bridging acetylide and p-Me-styryl-hydrazide (N—N bond ri : i 2 C H=CHAr),  A)  =  1.457(4)  groups (Equation I .4).68 The proposed mechanism involves [2 + 2] cycloaddition of ArCCH  across Zr—N to give a zirconaazacyclobutene intermediate, followed by protonolysis of the Zr—C bond with the second ArCCH; the arylacetylide anion bridges the Zr atoms.  2 H-CC-Ar  (1.4)  (Me’s on Si omitted)  35 (Ar  =  47  ) 4 H 6 Ph, p-MeC , pButC 4 H 6  2 side-on bound to a zu:conocene complex has been Recently, the functionalization of N e ) j..tC [(i M 5 H 4 Z 2 r(H)] , ( 2 59 When 2 observed. e ) 42, is exposed to H , r] ri t-ri N C [(i M 5 H 4 Z ( : ) 1 :N r1 2 H ), 48, is produced with side-on bound hydrazide (N—N bond  =  1.475(3)  A)  and two  2 yields a small amount of ammonia, terminal zirconium hydrides (Scheme 1.2). Heating 48 under H 2 generates 2 whereas heating 48 in the absence of H , e ) 49, in which the r] C [(ri M 5 H 4 Z ( ) ,i-N)(,i-NH N—N bond has been cleaved. This discovery illustrates how a small change to an ancillary ligand can 2 complex. impact not only the extent of activation of coordinated N , but also the reactivity of the N 2 liberates N 58 the hydrogenation of , 2  2 to Whereas the addition of H e ) r} i ,i-i N C {(rj M 5 H 4 Z ( : 2 )  enables  new  N—H  bonds  to  form.  Predictably,  [Cp*(l5  2 to liberate N ° The effect of Cp substituents 6 . 2 , e 43, reacts with H M 5 C H 4 Q 2 ) )Zr(i’-N] -r’:rt’-N 69 on N 2 activation was recounted recently. 19  Scheme 1.2. 1.475(3) A  1 377 3 A  2H2Zk  i2Z  -  }\ N/T— Zr  2 addition to 2 e )(11 )Zr] C J.I[(r H 4 M 5 H 3 ( An investigation into the mechanism of H 2 and 50 with a large negative entropy of , 50, shows the reaction is first order in both H :T1 1 2 ) N 70 The primary kinetic isotope effect indicates that H—H bond breaking is the rateactivation. 2 across Zr—N determining step. Together these observations are consistent with 1,2-addition of H via an ordered transition state with simultaneous Zr—H and N—H bond formation. New N—H bonds also  2 to give e fj ) with H T j.t-T1 N) C [(1 M 5 H 4 H ( : 2 form during the reaction of -  [(ii  e fH] ) r 1 ji-r N M 5 C H 4 H ( : 6 ) 2 H In addition to the hydrogenation of 42, its reactivity with terminal alkynes, amines, ethanol, 71 When two equivalents of a terminal acetylene, R’CCH (R’ = Ph, tBu, and water has been explored. ‘Bu) are added to 42, the hydrazide complex, 2 ) 51, forms. , e r N C .L-11 [(i M 5 H 4 Z ( : ) H r(CCR’)] The production of N—H bonds from a dinitrogen complex and an alkyne is a new reaction, and it stands in contrast to the N—C bond formation observed upon addition of alkynes to 3568 The solid Bu) shows that hydrazide is side-on bound with an N—N bond state molecular structure of 51 (R’ = t length of 1.454(2)  ’ 7 -acetylide coordinates to each Zr. A, and one 1  20  Water adds to 42 to give hydrazine and . (rl M 5 H 4 Z 2 ’ 7 r(OH) C ) In contrast, the addition of e Z 2 [Cp* J.tO).72 rH1 The produces N 2 and (  0 to end-on bound 2 H  addition of excess EtOH to 42 gives hydrazine and . (q M 5 H 4 Z 2 7 r(OEt) C 1 ) When dimethylamine e or  1,1-dimethythydrazine  is  added  2 M 5 C H 4 Z ( : 1 ) 2 H ii’-N r(NR”} Ji-ii e ) (NR”  to =  42,  the  end-on  hydrazide  complex  {(i  ,2 2 NMe NHNMe ) , 52, forms (Scheme 1.3), which also  yields hydrazine upon treatment with EtOH. In these reactions, N 2 in 42 acts as a strong base.  Scheme 1.3. 1 377 3  1.475(3) A  A  )Z1 2 2HNR  \.  R=Ph,Bu,Bu  52  2 = HNMe HNR” , 2 2 NNMe H  The side-on_end-on dinitrogen complex, ) (I-H) ({NPN]Ta) Q 2 I-1’:r N (38), is remarkable in its breadth of reactivity. Some reactions involve only the bridging hydrides; for example, the reaction with propene results in migratory insertion and the formation of a propyl complex with end-on N , 2 53•73  2 in 38 is displaced by phenylacetylene, and 2 N ([NPN]Ta) Q i-  74 Coordinated N (i-ri’:i’-HCCPh), 54, with a bridging bis(i-a1kylidene) is generated. 2 H) 2 in 38 can also act as a nucleophile: benzyl bromide reacts with 38 to give the N-benzyl derivative  21  2 { [NPN]Ta(Br) } Qt-H)  1 N 2 ’ N (CH ) } Ja[NPN]), 5 H 6 C 2  55,73  (N—N bond: 1.353(4)  A).  These  reactions are summarized in Scheme 1.4.  Scheme 1.4  /CHS 2 H C=CH 2 Ph  ) 2 (—N  Nhh-CH B 2 r  P  55  The reactions of 38 with boranes, 75 silanes, 76 and alanes 77 provide even more dramatic transformations. Hydride reagents with the general formula B-H (B-H (HAIR ) 2 ,  SiBunl) 3 and H  add to 38  to give the intermediate  =  9-BBN 2 (HBR ) , DIBAL  (ji-r’:rj 2 ([NPN]TaH)(ji-F -  E)(Ta[NPN]), 56 (Equation 1.5). The solid-state molecular structure of 56 (E 2 N confirms the solution spectroscopic data; for E  =  =  2 or Sil-l BR Bu”) 2  , 56 has only been characterized in solution. 2 AIBu’  Thus, E-H addition across N 2 in 38 is another new transformation of coordinated dinitrogen and represents a starting point for further chemistry.  22  (1.5)  E-H  M /  56  E  Solutions of intermediate 56 yield different products depending on the identity of E. Upon hydroboration of 38 (E  =  H iMe C [(PhNSiMe P S 2 (Ph)CH 14 the {NPN] ligand degrades and H 8 BC ),  75 one equivalent of benzene, from N-Ph 4 58, eventually forms; )](j.i-N)(Ta[NPN]), 1 H 8 ji-N)Ta(=NBC 2 from the bridging hydrides are also produced. In this of [NPN] and B—H, and one equivalent of H transformation, N 2 is cleaved and functionalized. Hydroalumination (E  =  Bu also results in N— 1 A1 ) 2  -N A 1(ji-H)13u) a[NPN]), N bond cleavage and functionalization, and ([NPN]TaH) Qi-H) Qt-ri’ :ii 2 2 77 although [NPNJ does not degrade, one amide donor migrates from Ta to Al, and 59 is produced; one equivalent of isobutene is eliminated. Hydrosilylation (E  =  SiBu”) produces the very 2 H  2 has been cleaved u’) 60.76 In this case N (ji-NSiH ([NPNJTa) B 2 symmetrical disilylinilde species , and functionalized, and the ancillary ligand remains intact. The addition of E—H to 38 is summarized in Scheme 1.5.  23  Scheme 1.5.  (— H)  Bu 3 SiH Ph  S1 2 BuH Ph Ph\N ru  P[ 2 f\.SiMe  2 Me S 2 i’T/ Ta’ N.S1Me Si/ 2 Me Ph  S1, 2 Me  Ph  59  58  BU 2 iH  Ph  60  I’h  2 elimination from intermediate 57. DFT N—N bond cleavage appears to be triggered by H calculations for E  =  3 suggest that the transition state along the path to 57 is a species with a Ta— SiH  Ta bond, such as 61.78 Thus, the Ta—Ta bond contains the electrons required for N—N cleavage.  24  1.8 Conclusions and Scope of Thesis. The side-on bonding mode of N 2 is no longer rare, and there are approximately fifty complexes where the side-on mode has been confirmed using X-ray crystallography (see Table 1.2). In terms of the extent of activation of N , there are no obvious trends. Lanthanide and transition2 metal side-on N 2 complexes show wide variation in the extent of activation as measured by N—N bond distances, although in general, more transition-metal N 2 2 complexes than lanthanide N complexes contain long N—N bonds. What is evident is that more investigations into the reactivity of side-on N 2 are warranted. In the cases described above, it is clear that new reactions have been discovered that seem to correlate with the bonding mode. Whether these reactions can be harnessed to produce useful organonitrogen products catalytically remains to be seen. In this thesis, a new dinitrogen complex with N 2 coordinated in the side-on mode will be described. In chapter two, the synthesis and characterization of a new diamidophosphine ligand is ([p]* presented. [NPN]*  =  )(2-N-5-MeC C [{N-(2,4,6-Me ) 3 H 6 P ) 2 Ph] } is an arene-bridged  analogue of [NPN] previously reported by the Fryzuk group. Complexes of this ligand are expected to be more robust than those of [NPN] because they lack the reactive N—Si bond and the flexible  —  SiMe backbone. In chapter two, the synthesis and characterization of Zr(IV) and Hf(IV) CH — 2 [NPN]*ZrCl is a useful starting material in the complexes of [NPN]* are described. In particular, 2 synthesis  of organometallic  and dinitrogen complexes.  In  chapter three,  the synthesis,  characterization, and reactivity of [NPNI*Hf and [NPN]*Zr organometallic complexes is discussed. [NPN]*ZrCl and KC QIr12:r12N from 2 2 {[NPN]*Zr(THF)} In chapter four, the synthesis of ) 8 in THF is introduced. The synthesis of Py and PMe R (R 2  =  Me, Ph) adducts of the Zr-N 2 complex is  also presented. In chapter five, the reactivity of the side-on bound N 2 complexes with H , PhSiH 2 , 3 4,4’-dimethylbenzophenone, (CH CC (0)H, benzophenone imine, and Ph ) 3 P 0 is discussed. 3  25  Table 1.2. A selection of side-on N 2 complexes and related species for which N-N bond lengths are known; also included are ‘ N NMR chemical shifts along with JR and Raman data if available. 5  Compound  N NMR 15  Bond length  (  (A)  vs. )a 2 MeNO 2 N  293.4b,c  Trans-PhN=NPh NNH H 2 Li} 5 H 6 (C N i) 2 (OEt (1) N ] ) [{ 3 )2 5 H 6 (C ) [Na(OEt [ N ) 5 H 6 N (C ] i] (OEt (2) 4 NaLio(OEt) } ) 2 : 10 -C (Ti 2 5 ) 8 H Ti [(ri ‘:rl 5— ) H 5 5—C ] —Nz) [i 5 2 -T1’ :11 ‘: 3 (,1 )(r 2 4 H 5 C -C T 3 ) H 5 ] i (3) (4)  129.0 689.7  (i-ii [PNP]ZrC1} : ) 1i N (5) {2 H 5 [C T ] 3 ( : ) 2 112_N SilvIe J.t_r1 m} (7) { (SiMe 4 H 5 [C ) 3 T m} ]2 :11 2(i-fl ) N (8) {2 S 3 [(Me N T 2 m(rHF)] i) ] :-N) (10) 2 { } (j.i-t S 3 [(Me N D y(THF)] i) ] } Qt-r :r-N) (11) 2 {2 C [O2,6tBu N 3 ] 2 d(THF) oH -N) (12) 2 { } (-t-tii S 3 [(Me N L uçrHF)] i) ] } (jt-i:r-N) (13-Lu) {2 S 3 [(Me N Y 2 (THF)] i) ] (J.i-fl } : ) 2 ri N (13-Y) {  619.9i  I .0975(2) 1.255g 1.47” 1.35 1.359(18)  2331e  1.301(12)  1282(’ : 2 N 5 1240) (IR)  1.088(12) 1.548(7) 1.259(4) 1.236(8) 1.264(7) 1.305(6) 1.242(7)  557.0  513.3; = 7 Hz 516  S 3 [(Me N L a(THF)J i) ]} (13-La) {2 S 3 [(Me N N d(THF)] i) ]2 (JLr2:r12N (13-Nd) } ) {2 S 3 [(IVIe N G 2 d(THF)J i) ] (j.t-i : N) i (13-Gd) { }2 S 3 [(Me N T b(THF)] i) I2 : }2(Ji-Ti N2) Ti (13-Tb) {2 S 3 [(Me N H 2 o(THF)] i) ] :-N) (13-Ho) 2 { } (.L-T S 3 [QvIe N E r(rHF)] i) ]2 : }20i-Ti N2) fl (13-Er) {2 S 3 [(Me N T 2 m(THF)] i) ] (13-Tm) { } : 2 [(C5Me4J-I)2LaCI’HF)]2(J.I-Ti N2) Ti (14) (J.t-Ti [(CSMe4H)2Lu(THF)1 : ) 2 Ti N (14-Lu)  (15) [(THF)Li { 4 C(ct-C [Et N 2 H } )1 4 (N Sm] L 2 ) i (16) )sC(c-C4-1 [(CH N 2 } )] [{ 4 )çrHf) (17) N 2 C(ct-C 5 ) [(CH N 2 H } )] 2 Sm L 3 ] i (ji-N J 2 ) [Li(THF) 2 [{ 4 (THF) (19) C(cL-C4-1 [jI-Ph N 3 ] Sm} ) 4( J.-11 2:11 2 -N (THF) ) 2 (20) {2 C 5 ) [(CH N 3 H 4 ] 2 (a-C ) Sm} ( 4 ( 2 THF) L{ )2 2 N (THF) (21) [NaHF)] C 5 ) [(CH N 3 H 4 ] Sm} (cL-C )2 (THF) 4 ( 5 . ) ji-N (22) {2 C [Rt N 3 H ] ç 4 ] ) 2 QrHF) (j.i-N Sm} rHF) Qx-C ) (23) [{  26  vNN (cm-i) R = Raman IR = Infrared  1.268(3)  Reference  1441 (p,)h  1111 (P)k  13 14  731 (R)  15, 16 8 18 20 20 21 21 21 23 23  1.525(4) 1.08(3)  23 23 23 23 23 23 23 24 26 24 27 29  1.502(5)  29  1.412(17)  30  1.371(19)  31  1.392(1 6) 1.415(3)  31 32  495.0  1.258(3) 1.278(4) 1.271 (4) 1.264(4) 1.276(5) 1.261 (4) 1.285(4)  521 569.1  1.233(5)  2 (25) ] 3 N [Na(DME) 1i (i-11 {(OEPG)Pr} : 2 ) N ri (ji{(OEPG)Nd} : ) 2 [Na(dioxane) (26) [Na(dioxane)] ] 2 N N 3 [N ( : ) j.i-ri ]U} (28) {2 (SijPr 2 4 {Cp*U(CSH 2 ) 3 jt-r (30) } :(’r-N) ] [{ 2 2 [Li(tmeda) ] (32) i} i) ii-11 z] N 11 S 3 [(Me N T ( : ) N } (34) fl L-1i -CsH ([PNP]Zr(O-2,6-Me ) 3 ( : ) 2  608.1  33 33  1.109(7) 1.232(10) 1.379(21) 1.528(7)  35 38 46 48  1.43(1)  Zr) N (35) 1i ]j.i-ri N ([P ( : 2 )  ]Nb} 2 4 (.I-T1 : 11 [{ [p.tBucalix[4]0 N ) 2 ] [Na(DME)] (DME) (37) 4 i-H) r (38) ,.i-rl N Q ([NPN]Ta) ( : 1 ) 2  r (39) N (j.i-ii (rac-BpZr) : 2 ) r] (40) .iN r Z [Cp” ( : ) 2 i-Ti ) (42) r i N -CsMe 5 [(i H 4 Z Q : ) 2 e f] ) J.i-1i N C 11 [(1 M 5 H 4 H ( : ) 2 [NPN] Zr(THF) : 2Qt-fl 2 N2) { } 1l (44)  a  1.254(7) 1.234(8)  -30.6  1.403(8)  -20.4, 163.6 QJNN = 21.5 Hz)  1.319(6)  621.1 590.5  15 ( : 2 751 N 725) (R) 15 ( : 2 775 N 753) (R)  49 51 52  1165 (R)  56 57 59 61 64  1.241(3) 1.47(3) 1.377(3) 1.423(11) 1.503(3)  . 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A.; Patrick, B. 0.; Albinati, A.; Mason, S. A.; Koetzle, T. F. J. Am.  Chem. Soc. 2001, 123, 3960. Shaver, M. P.; Johnson, S. A.; Fryzuk, M. D. Can. J. Chem. 2005, 83, 652 A) MacKay, B. A.; Johnson, S. A.; Patrick, B. 0.; Fryzuk, M. D. Can.J. Chem. 2005, 83, 315. B) 75 Fryzuk, M. D.; MacKay, B. A.;Johnson, S. A.; Patrick, B. 0. An<gew. Chem. 76  mt. Ed. 2002,41, 3709.  Fryzuk, M. D.; MacKay, B. A.; Patrick, B. 0. J. Am. Chem. Soc. 2003, 125, 3234. MacKay, B. A.; Patrick, B. 0.; Fryzuk, M. D. Organometallics 2005, 24, 3836.  78  Studt, F.; MacKay, B. A.; Fryzuk, M. D.; Tuczek, F. Dalton Trans. 2006, 1137.  32  Chapter IWIO Zirconium and Hafnium Complexes of an Arene-Bridged Diamidophosphine Ligand  2.1 Introduction. At the core of inorganic chemistry is the idea that the structure and reactivity of a metal complex may be controlled by the ancillary ligand. With the appropriate ligand, 1 readily change chemists prepare metal complexes that catalyze organic transformations, oxidation state, 3 attain unusual 2 impart chiral environments for asymmetric synthesis, electronic states, 4 and absorb light for energy transfer. 5 Although it is not yet possible to  predict reactivity based on the choice of ancillary ligand, research into ligand design continues guided by ideas of geometry control, donor atom properties, and substituent effects. The importance of ligand choice was dramatically illustrated in 2004 when Chink et al. reported that the reduction of 2 -rC1 (r) M 5 H 4 Z C e ) under N 2 yields 2 -C [(r1 M 5 H 4 Z 0 ir] e ) 2 bridges two Zr atoms side-on. The activated N 2 in this complex reacts : 1 2 N2) 1 in which N with H 2 to yield 2 6 About [(r1 M 5 H 4 Z ( : ) H ji-r, r(H)] ri N C e ) with two new N-H bonds. three decades earlier, the reduction of 2 -rC1 (1 M Z ) 5 C e was reported to yield the end-on dinuclear complex, [(i 5 ), which releases N 2 2 when it is -r(ri M Z 2 ) C e1 -ii-i ) ( 2 N ] :11 ‘-N exposed to H 7 The difference of one methyl group in the ancillary ligand changed the . 2 extent of activation of N , its coordination mode to Zr, and its reactivity, thus exemplifying 2  A portion of this chapter has been published: MacLachian, E. A.; Fryzuk, M. D. Organometallics 2005, 24, 1112.  33  the challenges chemists face in trying to design ancillary ligands to change a complex in a predictable way. Research in the Fryzuk group has focused on creating multidentate ligands that incorporate amide and phosphine donors. Chelating amidophosphine ligands allow simultaneous coordination by amide donors, which stabilize high-valent, electron-poor metal complexes, and phosphine donors, which stabilize low-valent, electron-rich metal complexes, to a single metal centre. These ligands can facilitate nitrogen activation by early transition metals because they stabilize the metal complex in the presence of strong reducing 8 As described in chapter one, the tridentate anionic [PNP] ligand ([PNP] agents. [N 2 C (SilV1e P R2)] H  R  =  lPr)O  =  stabilizes one of the earliest examples of a side-on N 2  complex: 2 (ji-i1 ({PNP]ZrCl) : ) N r (Figure 2.1) contains the longest intact N—N bond  in  a  metal complex (1.548(7) A). 10 A side-on Zr N complex also forms when macrocycic [P 2 ] N 2 ] N 2 ([P  =  SSil\4e PhP(CH N C P 1 ) 2 iMe Ph] H 1 is the ancifiary ligand: 2 ]Zr) N ([P Q : i-r i  ) has a 1.43(1) A N—N bond, consistent with the presence of an N—N single bond, or an 2 N 2 unit, in the complex (Figure N  2.1).12  In 1997, 2 ]N2) N ([P ( : Zr) ji-i i became the first  transition-metal N 2 complex to react with H 2 to yield new N—H bonds. Previously, the addition of H 2 to an N 2 complex had only been observed to liberate N 2 gas and produce a metal hydride complex.’ 3 This [P ] stabilized complex also reacts with silanes and terminal N 2 acetylenes to yield new N—Si and N—C bonds. 14  34  2 Me  2 Me (t-r ([PNP]ZrCI) : ) 2 N r  ]Zr) N ([P Q : 1 ) 2 N i-  -N 1 : ) (i.t-H) ([NPN]Ta) ( 2 1 .t-ii 2  ] and N 2 Figure 2.1. Dinitrogen complexes prepared in the Fryzuk group with {PNP], [P [NPN] ancillary ligands. In [P ], the silyl methyls have been omitted for clarity. N 2  The Fryzuk group reported the synthesis of a tridentate dianionic ligand [NPNI ([NPN]  =  SiMe [PhP(CH N ) ] 2 Ph) and its Ta complexes in 1998.15 The reaction of  3 with dihydrogen provides the Ta(IV) hydride 4 [NPN]TaMe (ii-H) The 2 ([NPN]Ta) . tetrahydride reacts with N 2 to yield 2 QL-H) ([NPN]Ta) Q : 1 ) rI t-11 N , the first dinuclear complex with N 2 coordinated in the side-on—end-on bonding mode (see Figure 2.1). The addition of boranes, alanes, and silanes to this complex results in the formation of a new N— E (where E  =  B, Si, or Al) bond and cleavage of the N 2 unit. 16 Zr-N 2 complexes of the  [NPN] ligand have also been reported. 17 Although N 2 coordinated to an early transition-metal amidophosphine complex undergoes a variety of transformations, ancillary ligand decomposition often accompanies these reactions. For example, the addition of 9-BBN to 2 (ji-H) ([NPNjTa) ( : 1 ) N ir (9BBN  =  9-borabicyclo[3.3.l]nonane) leads to N—N bond cleavage and the formation of a  new B—N bond. 18 However, [NPN] is degraded in the course of the reaction; benzene is  35  elin-iinated from one of the two phenylamido substituents and the amido N bridges the two Ta centres as a nitride ligand (Scheme 2.1). Scheme 2.1.  Me  2 PhiMe 9-BBN Me2SV S/Tciac 2 Me 4 ..  2 SiMe Ph  h  Ph  , -H H 6 -C 2  2 iMe  It should be noted here that the Fryzuk group has also explored the chemistry of  —  SiMe bridged [NPN] ligands with non-phenyl substituents on N and P, such as CH — 2 mesitylamide (MesN) and cyclohexyiphosphine (CyP), and that decomposition reactions of these ligands are also observed. For brevity, when there are one or two non-phenyl substituents on [NPNJ, they are specified before the square brackets as superscripts in the following order: P substituent, N substituent. In other words, the 2 SiMe bridged —CH — [NPN] ligand with CyP and MesN substituents is abbreviated:  36  CYMes[p  Other undesirable reactions observed for the [NPN] ligand include the formation of a phosphinimide ([NP(=N)Nj) complex from a Ti-N 2 complex, 17 the migration of the N 19 the donor of [NPN] from Ta to Al when DIBAL-H is added to the Ta N complex, 2 formation of cYMeS[NPN1V_NMeS and a cyclic  CY.MCS[PN]  compound (Me[PN]  (ICl) is reduced with KC 2 ° 2 , 8 SiMe CyP(CH N ) 2 Mes) when (cYM[NPNJV) (cYPh[PN1  =  =  CYPh[p]  SiMe CyP(CH N ) 2 Ph) elimination and cY.Ph[NpN]Nb(Cl)(=Nph) formation  CY.Ph[NpNINbC1 is reduced with KG when 2 ’ as well as several other uncharacterized 2 , 8 decomposition reactions of [NPN] metal complexes. Similarly, side-reactions of [PNP] and ] have also been reported. N 2 [P 22 Decomposition of these complexes may result from the  reactivity of the N—Si bond and the flexibility of the 2 SiMe backbone. [PNP], [P —CH — ], N 2 and [NPNI ligands all contain N—Si bonds to facilitate ligand synthesis, and to reduce the basicity of the amido nitrogen donor. Ancillary ligand decomposition is a major barrier to the development of a catalytic cycle based on N 2 functionalization, and for this reason the synthesis of a more robust tridentate diamidophosphine ligand was initiated. This new ligand should mimic the electronic and steric properties of [NPN], but lack the reactive and extremely moisturesensitive N—Si bond. An early analogue of [NPNI contained a 2 CH —CH - linker, C [(PhNCH P ) 2 . 2 Ph] H 3 Although Ta complexes can be prepared with this ligand, attempts to hydrogenate or reduce these complexes give mixtures of products. The seemingly minor substitution of one CH 2 group for SiMe 2 in the backbone of [NPNJ has a dramatic impact on the reactivity of the corresponding metal complexes. One possible explanation is that the reduction of [NPNITa complexes is facilitated by the slightly electron-withdrawing silylamide substituents, whereas the reduction of 2 C [(PhNCH P ) Ph]Ta H complexes is hindered by the presence of the more electron-donating alkylamide substituents. Secondary  37  alkylamines are generally stronger bases than secondary silyl-substituted amines. The PI<a of diisopropylaniine is 36,24 whereas the P’a of bis(trimethylsilyl)amine is 26.25 An arene bridged diamidophospbine ligand may be electronically similar to [NPN], and the amido donors are expected to have similar basicity. The pKa of diphenylarnine is  25.26  In addition,  an arene-bridged diamidophosphine would lack the reactive N—Si bond of [NPN], and should not be readily decomposed by nucleophiles or H 0. An arene-bridged 2 diamidophosphine ligand may also be less flexible than [NPNI, which may hinder the migration of N and P donors that is observed under some conditions. A comparison of  —  SiMe bridged {NPN] and an arene-bridged diamidophosphine ligand is given in Figure CH — 2 2.2. This chapter describes the synthesis of an arene-bridged diamidophosphine ligand and its Zr(IV) and Hf(W) complexes.  2 [N PN]L1  Increased steric bulk at N  2 [NPN]*L1  N-Si bond is reactive and extremely moisture sensitive N-Si & arene backbones are slightly electron withdrawing Arene backbone is rigid P substituents are tunable  Figure 2.2. Comparison of two diamidophosphine ligands: Attributes of the 2 SiMe —CH — . 2 bridged and arene-bridged diamidophosphine ligands [NPN]Li 2 and [NPN]*Li  38  2.2 Results and Discussion. 2.2.1 Synthesis of a phenyl-bridged diamidophosphine [NPN]’. The phenyl-bridged diamidophosphine ligand [NPN]’, ([NPN]’  =  {[N-(4-MeC ) 4 H 6 (2-  ) 4 H 6 NC P 2 ) hP} J can be prepared in three steps from 27 PhP. The 2,2’) 4 H 6 C 2 (2-NH diaminotriphenyiphosphine starting material is synthesized by a Pd-catalyzed P—C coupling reaction from phenyiphosphine (PhPH ) and 2-iodoaniline in the presence of Pd(PPh 2 4 and ) 3 the water-soluble triaryiphosphine GUAP-3 (GUAP-3 Guan or  =  =  [(3-GuanN(H)C P 3 ) 4 H 6 ] 3HC1,  27 ) C(H)(NH ) 2 (NMe ). The N-arylation of 2 (2-NH P ) 4 H 6 C hP with aryliodides via Cu-  Pd-catalyzed  C—N  coupling  is  unsuccessful,  possibly  because  the  chelating  diarninophosphine substrates and products coordinate to the metal catalyst. To decrease the likelihood of catalyst poisoning, 2 (2-NH P ) 4 H 6 C hP was first oxidized by H 0 to provide (22 NH P ) 4 H 6 C 2 hP=O as a beige solid in high yield. The phosphine oxide reacts with 2.2 equivalents of 4-iodotoluene and catalytic 3 CuI(Phen)(PPh to give 6 ) [N-(4-MeC ) 4 H (22 ) 4 H 6 N(H)C P hP=O, ] 2.1, as a beige powder in high yield (Scheme 2.2). There is a singlet at 6 42.4 in the 31 P{’H} NMR spectrum of 2.1, which is in the range expected for a triarylphosphine oxide. The ‘H NMR spectrum of 2.1 shows a singlet at 6 2.26 that is assigned to two equivalent p-CH 3 groups on the NTol substituents, a broad singlet at 6 8.52 assigned to the NH groups, as well as resonances in the aromatic region that are consistent with the proposed C symmetric compound. Overall, this two-step procedure provides the N-arylated diaminophosphine oxide in 85% yield.  • The abbreviations [NPN], [NPN]’, and [NPN]* are used to distinguish three different diamidophosphine ligands. PN] = 2 C [(PhNSiMe P ) , Ph] H [NPNj’ = {[N-(4-MeCH )(24 ) 4 H 6 NC P , 2 Ph} ] and [NPN] = { 2 CH 2 3 [N-(2,4,6-Me ) ) 3 H 6 (2-N-5-MeC P . Ph} ]  39  Scheme 2.2.  2.2 2 NH  2 NH H202  C0 2 K 4 3 cat C:I(phen)(PPh3)  +  2.2  2.1 3 3 NEt  Nl&\zE  :;-” 1 /  2.2 THF, hexanes  2.3  2.4  There are several drawbacks to the Cu-catalyzed route to 2.1 described above. The reaction must be heated at a high temperature for several days before it goes to completion. Moreover, a by-product forms when the reaction is conducted on scales larger than 5 g. The by-product, 6 (2-NC 2 ) [N,N-(4-MeC ) 4 H ] [N-(4-MeC )]PhP= 0, 2.2, results 4 H 6 ) (2-N(H)C 4 H 6 from the reaction of three equivalents of p-CH I with (2-NH 4 H 6 C 3 PhP=O. ) 4 H 6 C 2 Compound 2.2 is isolated as a white microcrystalline solid after it is separated from 2.1 by silica gel chromatography and recrystallized. It was characterized by multinuclear NMR spectroscopy, EI-MS, and microanalysis. The formation of the by-product, and the chromatography required to separate it from 2.1 decrease the yield of the desired diarylated compound to 55% when the reaction is carried out on a 5 g scale.  40  Compound 2.1 is reduced to [NPN]’H , 2.3, using standard phosphine oxide reduction 2 conditions (see Scheme 2.2).29 The reaction is quenched with degassed H 0, and 2.3 is 2 obtained as a translucent white residue in high yield upon work-up. The singlet in the P{’H} NMR spectrum is at 6 —30.9 for 2.3, typical for a triarylphosphine. 31 ° In the 1 3 H NMR spectrum, resonances diagnostic of NH (6 6.36) and ArCH 3 (6 2.06) groups are present, as well as the expected ArH resonances. Finally, addition of two equivalents of BuLi to 2.3 in a mixture of hexanes and THF provides 2 (THF) 2.4, in 53% yield as small yellow [NPN]’Li , crystals (see Scheme 2.2). The 31 H} NMR spectrum of 2.4 is similar to that of 1 P{ (THF) [NPN]Li 1 ; 2 5 a quartet is observed at 6 —33.0 (I( Li) 7  =  3/2,  JPLi =  41 Hz). As expected,  there are a doublet and a singlet in the 7 Li{’H} NMR spectrum of 2 CFHF) [NPNI’Li , indicating that one Li ion is bound to P (6—0.35) and the other is not (6—1.72). By 1 H NMR  spectroscopy, two equivalents of THF are coordinated to 2.4. In addition to the problems noted above for the Cu-catalyzed arylation, there are several other drawbacks to the synthesis of {NPN]’ outlined above. First, the reaction requires four steps from phenylphospbine, which is odious to prepare. The purification of 2.1 is labour intensive and any impurities that remain are difficult to remove after subsequent steps. Also, the presence of small amounts of H 0 and NEt 2 3 remaining after the work-up of 2.3, which are difficult to eliminate completely from the oily residue, are incompatible with the lithiation reaction to give 2.4. Despite many attempts to modify the conditions, multigram quantities of pure 2.4 could not be obtained. It was clear that a new route to arene bridged diamidophosphines was needed. In 2003, Liang and co-workers described the synthesis of arene-bridged [PNP] and [NP] ligand precursors by the reaction of an alkali metal phosphide with an aryl fluoride.  41  This reaction is sometimes referred to as nucleophilic phosphanylation. Steizer and co workers prepared a series of substituted triaryiphosphines in an earlier example of nucleophilic  31 phosphanylation.  P Ph ) 4 ) 3 H 6 C 2 NH(2,6-R C ; R  =  The  [NP]H  aminophosphine  ([NP]H  =  (2-  )NH(2,64 H 6 Me, Pr) is synthesized by heating (2-FC  32 The ) and KPPh 3 H 6 C 2 R 2 in dimethoxyethane (DME) to reflux for several days. aminodiphosphine [PNP]H ([PNP]H  =  PH, (2-R N 2 ) 4 H 6 C R  =  Ph, Pr, 1 Bu, Cy) is prepared  2 (M in a similar manner from (2-FC NH and two equivalents of MPR 2 ) 4 H 6  =  Li, K) (Figure  Following this report, the synthesis of an arene-bridged diaminophosphine by nucleophilic phosphanylation was attempted in the Fryzuk group. Thus, two equivalents of )NH(Ph) in DME are added to a clear red solution formed from the addition of 4 H 6 (2-FC  two equivalents of K to PhPH 2 in DME, and the solution is heated to reflux for several days. In the 31 H} NMR spectra of aliquots taken from the reaction mixture, the peak due to 1 P{ starting material disappears, and several new peaks grow in. To date, attempts to separate the products of this reaction for further characterization have been unsuccessful.  NH 2 ‘PPh [NP]H  [PNP]H  Figure 2.3. Arene-bridged [NPJH and [PNP]H.  In 2004, a second route to arene-bridged aminophosphines was reported. [PNP]H ([PNP]H  =  P-4-MeC (2-Pr N 2 ) 3 H 6 H) is prepared in two steps. First, (4-MeC NH is 2 ) 4 H 6  brominated to yield (2-Br-4-MeC NH. Addition of three equivalents of BuLi and two 2 ) 3 H 6  42  PC1 to the bis(bromoaryl)amine, followed by treatment with deoxygenated 2 equivalents of IPr water yields [PNP]H (Scheme  The synthesis of these proligands and theit Li and  35 transition-metal complexes was recently reviewed.  Scheme 2.3.  PCI 2 1) 3 BuLi, 2 ‘Pr  2 Br —  /<  0 2 2)H  AcOH  [PNP]H  2.2.2 Metathesis approach to [NPNJ  .  As an alternative to the Cu-catalyzed route described above, the synthesis of a diamidophosphine ligand by a metathesis pathway, similar to that used to prepare [PNP]H )(2-Br-42 H 6 C 3 (see Scheme 2.3) was undertaken. The brominated diarylamine, (2,4,6-Me 36 and N-bromosuccinimide )NH, 2.5, can be readily prepared from (Mes)ol)NH 3 H 6 MeC (NBS) in acetonitrile. 37 To determine if 2.5 undergoes complete NH deprotonation and Li/Br exchange in the presence of ‘BuLi, 2.1 equivalents of t1 BuLi are added to a solution of 2.5 and 2.1 equivalents of tmeda (tmeda  =  Me C N ) 2 CH Me H in Et 0 at —35 °C. The 2  product of this reaction, light yellow 6 2 C (2,4,6-Me ) 3 H (2-Li-4-MeC NLi(tmeda), 2.6, has been characterized by ‘H and 13 C {‘H} NMR spectroscopy.  ([p]* To form the diamidophosphine ligand [NPNI*  =  )(2-N-52 H 6 C 3 {[N-(2,4,6-Me  ) 3 H 6 MeC P , 2 Ph} ] or a ligand bridged with a 5-MeC 3 group), 2.5 is lithiated in Et H 6 0 2 solution (no tmeda is used) and reacted in situ with 0.48 equivalents of PhPC1 2 (Scheme 2.4). .(pC 2 [NPN]*Li H 4 sO , 4 Upon work-up, ) 2.7p-C ) 2 O 8 H , is obtained in 85% yield as a yellow  43  powder that is somewhat soluble in toluene and freely soluble in THF. Compound 2.7p) is thermally unstable and can decompose to a brown powder over a few days in an 2 0 8 H 4 C -filled glovebox. Single crystals suitable for X-ray analysis of the THF adduct, 2.72THF, 2 N were grown from a concentrated solution of 2.7(p-C ) in benzene with a few drops of 2 0 8 H 4 THF added. Scheme 2.4.  1. 2 BuLI, 2 Et 0 , NBS  -35°C;rt,3h  JH  2. 0.5 PhPCI , Et 2 0, 2 -35°C;rt,24h  CN 3 CH 0°C 2.5  2.7 S  =  THF or dioxane  Although the formation of 2.7.(p-C ) proceeds in one pot from an easily 2 0 8 H 4 synthesized organic starting material and a commercially available phosphine, PhPC1 , the 2 reaction is quite sensitive to changes in certain reaction conditions. For example, a change in solvent from Et 0 to THF or hexanes gives a mixture of products that does not contain a 2 resonance attributable to 2.7 in its P{ 31 H 1 } NMR spectrum. When more than two equivalents of “BuLi are added, 2.7 cannot be separated from a brown hexanes-soluble impurity. Thus, determining the exact concentration of BuLi in hexanes by titration is  essential. It is also important to add slightly less than 0.5 equivalents of PhPC1 2 dropwise, very slowly, to the solution of lithiated 2.5 at —35 ± 5 °C. Regardless of the scale of the reaction, if the PhPC1 2 addition is carried out over less than 2 h, a low yield of 2.7 is obtained. As yet, it is unclear why the synthesis of 2.7 is so sensitive to the conditions used, or by what mechanism the reaction proceeds.  44  Similar to other [NPN] lithium derivatives, H} NMR spectrum of 2.7(p1 P{ 20 the 31 ’ 15 ) shows a quartet at 6 —35.2 2 0 8 H 4 C  (‘JPL =  Li{ 7 H } NMR spectrum shows a 40 Hz), and the 1  doublet at 6 —0.07 and a singlet at 6 —1.97 (Figure 2.4). The 1 H NMR spectrum of 2.7(p) in C 2 0 8 H 4 C D (with a drop of THF added to increase solubility) is notable because four 6 singlets are observed in the ArCH 3 region (6  2.0). The two ontho-Me groups of each MesN  substituent are inequivalent to each other because of restricted rotation about the N—C 0 bond on the NMR timescale at 298 K. In addition, two singlets are observed for the inequivalent meta C—H groups on each MesN. The other resonances in the aromatic region of the 1 H NMR spectrum are consistent with the proposed C symmetric compound.  -30  -32  -34  -36 (ppm)  -38  -40  6  2  -2 (ppm)  -6  -10  Figure 2.4. 31 H} and 7 1 P{ Li{’H} NMR spectra of 2.7(p-C ) in C 2 0 8 H 4 . D 6  The solid-state molecular structure of 2.72THF (Figure 2.5) as determined by singlecrystal X-ray diffraction shows two distinct Li environments: Lii is coordinated to Ni, N2, and P1 of [NPNj’, and 01 of THF, whereas Li2 is coordinated to Ni and N2, and 02 of the second coordinated THF. The P—Lu bond is 2.510(3)  45  A, the Ui—N  bonds (2.08  A)  are  the same within error, and the Lil—Ol bond is 1.908(3)  A. The Li2—N bonds (2.05 A) are  the same within error, and the Li2—02 bond is 1.932(3) 2.518(4)  A. The Lil---Li2 separation is  A. The stereochemistry at Lii is best described as distorted tetrahedral and the  stereochemistry at Li2 is distorted trigonal. The remaining bond lengths and angles in the [NPN]* ligand are unremarkable. Crystallographic supporting information is in appendix one. Although spectroscopic and X-ray diffraction techniques confirmed the identity of 2.72THF, several attempts to characterize this compound by microanalysis have shown it to be low in carbon. This may be due incomplete combustion, or to the extreme air- and moisture-sensitivity of this material.  .2THF, 2 Figure 2.5. ORTEP drawing of the solid-state molecular structure of [NPN]*Li 2.72THF (ellipsoids drawn at the 50% probability level). All hydrogen atoms, and the carbon atoms of THF have been omitted for clarity. Selected bond lengths  (A) and angles  (°): P1—Lu 2.510(3), NI—Lu 2.0783), N1—Li2 2.046(4), Lil---Li2 2.518(4), 01—Lu 1.908(3), 02—Li2 1.932(3), N2—Li2 2.051(3), N2—Lil 2.076(3), P1—Lil--Li2 77.01(11), N1—Li2—N2 105.76(15), O1—Lil—Li2 144.07(18).  46  The  solid-state and solution data indicate that the structures of 2.7  and  N core in the solid state, 2 5 A diamond-shaped Li [NPN]Li2THF are remarkably similar.’ } NMR spectrum have also been observed 31 H 1 and a quartet due to Li-P coupling in the P{ ° For example, 2 for lithium diamidophospbines with other substituents at N and P. CYMeS[NPN]LiCfHF)  is structurally analogous to 2.7 with similar bond lengths and angles  (N—Lu bonds average to 2.12 A, N—Li2 bonds average to 1.95 A). However, there is only one equivalent of THF coordinated to Li in the complex, and Li-P coupling is not detected at  ambient  temperature  SO 2(C eS[NPN]Li M Ph . 2 H 4 ) quartets between  in  D 6 C  by  [p] 2 e M Ph. .  NMR  spectroscopy  for  this  compound.  2THF all display 3 . 2 CYPh[NPN]Li ), and B 2 0 8 H 4 (t’-C °  P{’H} NMR spectra —30 and —38 in their 31  Hz, respectively). The solid-state molecular structure of  JPL ( 1  = 18.9, 26.6, and 40.1  CrHF) 2 CYPh[NP]]Li  is similar to  that of 2.7.38  2.2.3 Synthesis of group 4 complexes of [NPN]  .  Dichiorozirconium complexes of [NPNI* are prepared in a three-step route from . First, the lithiated ligand is protonated; then the proligand reacts with 2.7(p-C ) 2 O 8 H 4 4 via elimination of Me ) 2 Zr(NMe NH to give the bis(dimethylamido)zirconium complex. 2 [NPN]*ZrC1 To prepare the . Excess Me SiC1 is added to this Zr complex to obtain 2 3 [NPN]*H 2.8, excess Me , proligand 2 NHC1 was stirred with 2.7(p-C 3 O in THF (Scheme 8 H 4 2.5). Taking the reaction mixture to dryness and extracting the product with toluene easily removes LiCl and Me NH from 2.8, which is obtained as an air-stable white powder in high 2 yield. There is a singlet at 6 —31.4 in the 31 P{’H}NMR spectrum of 2.8 in C . The ‘H D 6 NMR spectrum acquired at 298 K shows broad singlets attributable to the oilho-Me and meta  47  CR groups of MesN, as well as resonances for the other ArCH 3 and ArH groups, and a doublet at 6 5.88  J 4 (  =  5 Hz) assigned to NH in the C symmetric compound. The broad  singlets seen for the MesN substituents indicate that rotation about the N—C 0 bond to MesN is hindered. In the variable-temperature ‘H NMR (VT-NMR) experiment, coalescence of the broad Me singlets is observed at 320 K. Thus,  AGTO  39 A is 15.5 ± 0.3 kcal mo]*’.  stacked-plot of the VT-NMR spectra for 2.8 and the calculation of z\G 0 are included in appendix two. , 2.9, is synthesized by adding toluene to a 1:1 mixture of 2.8 and ) 2 [NPN]*Zr(NMe . Upon work-up, 2.9 is obtained as a toluene-soluble yellow powder in high yield 4 ) 2 Zr(NMe (Scheme 2.5). The 31 H} NMR spectrum of 2.9 in C 1 P{ D shows a singlet at 8—11.5, and the 6 ‘H NMR spectrum (Figure 2.6) shows four singlets for the [NPN]* ArCH 3 groups, indicating  that rotation about N—C 50 of MesN does not occur at 298 K on the NMR timescale. There are two NMe 2 resonances at 6 3.06 and 2.31, corresponding to two different amidomethyl environments. Complex 2.9 appears to be a C symmetric trigonal-bipyramidal complex in solution, with one NMe 2 apical and the other equatorial. Addition of THF, Py or PMe 3 to 2.9 in benzene produces no color change or shift in the peak in the 1 ’P{ 3 H } NMR spectrum, which suggests that a sixth neutral donor ligand cannot coordinate to Zr. The ‘H and P{’H} 31  NMR  spectra  of  2.9  are  3 C [PhP(CH N 2 ) SiMe H Zr(NMe ° 4 . ) 2  48  similar  to  those  reported  for  g g b  a  d  dl b C  b  a  CC  d  fd  I  I  I  I  78  7  I  I  I  I  I  I  e  I  I  I  I  1  6  I  I  I  6.0  7O  4  5  3  2  Figure 2.6. 300 MHz ‘H NMR spectrum of 2.9 in C . D 6  , 2.10, is synthesized from 2.9 and excess Me 2 [NPN]*ZrC1 SiC1 in toluene and is 3 isolated in 89% yield as a bright yellow powder (Scheme 2.5). No attempt has been made to observe the expected by-product of the reaction, 2 SiNMe which is likely eliminated from 3 Me , the reaction mixture upon removal of the volatiles under vacuum. A singlet at ö —2.8 is observed in the P{’H} 31 NMR spectrum of 2.10 in C . By 1 D 6 H NMR spectroscopy (Figure 2.7), 2.10 has the expected characteristics of a C, symmetric monomer, although the  (IC1) ([NPN]*ZrCl) , formulation of this complex as a C 2 symmetric dimer in solution, 2 cannot be ruled out based on the available evidence. In the ‘H NMR spectrum of 2.10, there  49  are signals due to four distinct ArCH 3 groups, similar to 2.7 and 2.9, as well as the expected ArH resonances. Scheme 2.5.  3 Me NHCI 3 THF  2.7 S  =  THF or dioxane  Zr(NMe 4 ) 2 toluene  2 ( 4 ZrCI THF) toluene  10 Me SiCI 3 toluene  2.10  2.9  50  aaaa a  f  C C  b bb f  C  e  75  7.0  d  6.5  60  s:o7.5o6.o:o4oJo2.ol.5 (ppm) Figure 2.7. 300 MHz 1 H NMR spectrum of 2.10 in C . D 6  The ORTEP representation of the solid-state molecular structure of 2.10 is shown in Figure 2.8. The stereochemistry around Zr is distorted trigonal bipyramidal with C12 and P1  apical, and NI, N2, and Cli equatorial. [NPN]” coordinates to Zr facially, and the two chlorides are cis to each other. Facial coordination of [NPN]* is not unexpected because the phosphine donor should prevent the ligand from coordinating in a meridional fashion. The P—Zr—NI, P—Zr---N2 angles are noticeably smaller than 90° with the two amido donors appearing to be hinged out of the equatorial plane by the arene bridge of [NPNI*. The Zr—N (average 2.07  A),  Zr—Cl (average to 2.42  A),  Zr—P (2.7229(8)  A),  and other bond lengths in  2.10 are typical. 41 In addition, angles about NI and N2 add to 359.25 and 359.97°, respectively, indicating that the amide N atoms are planar and sp 2 hybridized.  51  cli,  c3o  [NPN]*ZrC1 2.10 , Figure 2.8. ORTEP thawing of the solid-state molecular structure of 2 (ellipsoids at 50% probability). All hydrogen atoms and the proximal Mes substituent (except C have been omitted for clarity. Selected bond lengths  (A)  and angles (°): Zn—Ni  2.060(2), Zrl—N2 2.072(2), Znl—P1 2.7229(8), Zn—Cu 2.4279(8), Znl—C12 2.4099(8), NI— Zrl—N2 113.96(9), Cl1—Zri—C12 96.23(3), N1—Zrl—Pi 72.73(7), N2—Zni—P1 70.38(7), Ni— Zrl—Cll 106.25(7), P1—Znl—Cll 178.63(3), P1—Zrl—C12 85.02(3).  The synthesis of 2.10 from proligand 2.8 is an example of a protonolysis reaction. Although group 4 complexes are often prepared by a metathesis reaction between the Li, Na, or K salt of the ligand and a metal halide complex, such as 2 (THF) this reaction is 4 ZrC1 , sometimes unselective; the desired complex may form in low yield, or be present in a mixture of products from which it cannot be readily separated. Protonolysis, or the reaction of a proligand with a metal amide or alkyl compound to yield a new metal complex, and a volatile amine or alkane by-product, is used to prepare Zr complexes when the metathesis  52  route is 42 unsuccessful. For example, ansa-zirconocene dichloride catalyst precursors for olefm polymerization are synthesized from substituted cyclopentadiene ligands, Zr(NMe , 4 ) 2 and 43 SiC1. When a simple metathesis reaction between 2.7(p-C 3 Me HF) 4 ZrCl ) and 2 2 O 8 H 4 is carried out, the product mixture is dark brown with several peaks in its 31 H} NMR 1 P{ spectrum. Despite extensive effort, the products of this reaction could not be separated.  . 2 2.2.4 Adducts of [NPN] *ZrCI When one or two drops of THF are added to 20 mg of 2.10 in C D in an NMR tube, 6 (THF), 2.11, 2 an instant yellow to red colour change occurs. The red product, [NPN]*ZrCl was only characterized by solution NMR spectroscopy because the compound could not be isolated. Attempts to concentrate solutions of 2.11, or to precipitate 2.11 from THF with pentane, for example, result in the precipitation of 2.10. The singlet in the 31 P {‘H} NMR spectrum of 2.11 in C D is at ö 2.7, shifted downfield relative to the starting material. In the 6 H NMR spectrum, there are two sharp resonances that can be assigned to free THF. As 1 well, there are only four singlets in the ArCH 3 region of the spectrum, and not the eight singlets that would be predicted if 2.11 is a C 1 symmetric complex. Thus, coordinated THF appears to exchange rapidly with excess THF in solution on the NMR timescale, and this fluxionality is responsible for the apparent plane of symmetry in the product. The addition of a slight excess of PMe 3 to 20 mg of 2.10 in C D in an NMR tube also 6 produces an instant yellow to red colour change. As for 2.11, the adduct is not isolable, and 3 ( 2 [NPN]*ZrC1 ) PMe , 2.12, could only be characterized via solution NMR spectroscopy. The singlet due to [NPN]* in the 31 P{’H} NMR spectrum is shifted downfield from 8 —2.8 to 3.4 upon addition of PMe , and there is a broad singlet that integrates as 2P at 6 —50. The 3  53  bound and free PMe 3 average to give the broad singlet at 8 —50 that shifts to 8 —59 upon addition of another drop of PMe 3 to the sample tube, closer to the value expected for free 3 region, and there 3 (8 —62). The 1 PMe H NMR spectrum displays four singlets in the ArCH is no resonance diagnostic of coordinated PMe . These observations suggest that bound and 3 free PMe 3 are exchanging rapidly on the NMR timescale in samples of 2.12. The addition of Py to a toluene solution of 2.10 produces a yellow to red-orange  [NPN]*ZrC1 ( Py), 2.13, is colour change. Upon taking the reaction mixture to dryness, 2 H} NMR spectrum (8 2.7) is shifted 1 P{ isolated. As for 2.11 and 2.12, the singlet in the 31 3 singlets in the ‘H downfield relative to the starting material 2.10. There are four ArCH NMR spectrum, indicative of a plane of symmetry in the six-coordinate complex. If Py coordinates to Zr in the equatorial plane of trigonal-bipyraniidal 2.10, then 2.13 is expected to be a racenric mixture of C, symmetric complexes. The loss of the plane of symmetry would give eight inequivalent ArCH 3 groups that should be observable as eight singlets in the ArCH 3 region of the 1 H and 13 C{ H} NMR spectra. The presence of only four ArCH 1 3 singlets indicates that either a C symmetric product is present in solution, in other words Py coordinates axially and the two chlorides are equatorial, or that 2.13 appears C 5 symmetric because it is fluxional on the NMR timescale at 298 K. The reactions of 2.10 with THF, Py and PMe 3 are summarized in Scheme 2.6.  54  Scheme 2.6.  3 PMe vacuum  2.11  2.12  2.10  Py toluene  2.13  The ORTEP representation of the solid-state molecular structure of 2.13 is shown in Figure 2.9. Two nearly identical molecules of C 1 symmetry are located in the asymmetric unit (only one is presented here), related by a centre of inversion to two complexes of opposite configuration in the unit cell. The geometry around Zr is distorted octahedral with facially coordinated {NPN]*, and the chlorides are cis disposed, with one trans to P and the other cis. As was observed for 2.10, the P—Zr—Ni and P—Zr—N2 angles are less than 90°, at 70.00(4) and 73.45(4)°, respectively. The Zr—N bonds (to [NPN]*) in 2.13 average to 2.14 slightly longer than the Zr—N bonds in 2.10 (average to 2.07 are longer in 2.13 (average to 2.48 N3 bond (2.3889(i6)  A,  A). Similarly, the Zr—Cl bonds  A) than in 2.10 (average to 2.42 A). As expected, the Zr—  A) to Py is longer thanthe Zr—NdO bonds.  55  cli  (Py), 2.13 2 Figure 2.9. ORTEP cfrawing of the solid-state molecular structure of [NPNI*ZrC1  (ellipsoids drawn at the  50%  probability level). Hydrogen atoms and carbon atoms of the  proximal Mes substituent (except C have been omitted for clarity. Selected bond lengths  (A) and angles (°): Zrl—Pl 2.7131(5), Zn—NI 2.1081(15), Zrl—N2 2.1693(16), ZrI—N3 2.3889(16), Zn—Cu 2.4418(5), Zrl—Cl2 2.5257(5), NI—Cl 1.455(2), PI—ZrI—Nl 70.00(4), Pl—ZrI---N2 73.45(4), PI—ZrI—Cll 176.657(18), PI—Zrl—Cl2 82.142(17), Nl—ZnI---N2 97.87(6), Cl1—Zrl—C12 99.062(19), CI—NI—ClO 117.42(15), CI5—P1—C17 109.59(9).  2.2.5 Synthesis and structure of [NPN] *HfC Hafnium complexes of [NPN]* are prepared by the same protonolysis route used to  ) 2 synthesize [NPN]*Zr complexes. [NPNJ*Hf(NMe  2.14, is synthesized from 2.8 and  4 in toluene solution, and is isolated as a pale yellow toluene-soluble powder in ) 2 Hf(NMe  high yield (Scheme 2.7). The NMR spectra of 2.14 are similar to those of its Zr analogue, 2.9. There is a singlet at ö —4.5 in the P{ 31 H 1 } NMR spectrum of 2.14 in C . The 1 D 6 H NMR  56  spectrum features four singlets that are assigned to {NPN]* ArCH 3 groups. Two inequivalent 2 groups are assigned to two singlets in the ‘H NMR spectrum in the ö NMe  2  —  3 range.  Overall, the ‘H and 13 C {‘H} NMR spectra show the expected resonances for a C, symmetric complex. Scheme 2.7.  4 ) 2 Hf(NMe  21 Me S1CI 3 3 Me  2.8 toluene  toluene  2.14  2.15  The ORTEP representation of the solid-state molecular structure of 2.14 is shown in Figure 2.10. The geometry about Hf is distorted trigonal bipyramidal with [NPN]* coordinated facially to Hf. Unsurprisingly, the P—Hf—Ni and P—Hf—N2 angles of 72.89(4)° and 70.71 (4)°, respectively, deviate from  900  because of strain imposed by the arene bridge.  Two inequivalent NMe 2 groups are apparent in the solid state: one NMe 2 is apical and trans to P, and the other is equatorial. The Hf—P and Hf—N bond lengths are unremarkable.  57  , 2 Figure 2.10. ORTEP drawing of the solid-state molecular structure of [NPNJ*Hf(NMe)  2.14 (effipsoids drawn at the 50% probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths  (A) and angles (°): Hf—P1 2.7721(5), Hf—NI 2.1366(17),  Hf—N2 2.1585(16), Hf—N3 2.0632(18), Hf—N4 2.0173(17), Ni—Cl 1.449(3), P1—Hf—NI 72.89(4), P1—Hf—N2 70.71(4), P1—Hf—N3 163.60(6), Pl—Hf—N4 95.11(5), Ni—Hf—N2 120.91(6), N3—Hf—N4 100.92(8), CI—Ni—ClO 117.05(16), C15—P1—C17 107.82(9).  [NPN]*HfC1 2.15, is isolated as a pale yellow powder in quantitative yield from the reaction of 2.14 and excess chlorotrimethylsilane in toluene (see Scheme 2.7). The NMR spectra of 2.15 in C D are analogous to those observed for its Zr congener, 2.10: there is a 6 singlet at  0.1 in the P{ 31 H 1 } NMR spectrum, and four singlets attributable to the ArCH 3  substituents in the 1 H NMR spectrum. The ORTEP drawing of the solid-state molecular structure of 2.15 is shown in Figure 2.11. The geometry around Hf is distorted trigonal  58  bipyramidal, with two chlorides cis-disposed; one is apical and trans to P. The structure resembles that of 2.10 with small differences in bond lengths and angles.  cli  C12  [NPN]*HfCl 2.15 , Figure 2.11. ORTEP drawing of the solid-state molecular structure of 2 (ellipsoids drawn at the 50% probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles (°): Hf—PI 2.7059(9), Hf—NI 2.072(3), Hf—N2 2.076(3), Hf—Cu 2.3903(10), Hf—N4 2.4003(9), Ni—Cl 1.450(4), P1—Hf—Ni 73.75(8), P1— Hf—N2 71.81(9), Pl—Hf—ClI 86.14(3), Pl—Hf—C12 176.49(3), N1—Hf—N2 115.05(11), Cli— Hf—C12 97.36(4), Cl—Ni—dO 115.0(3), C15—Pi—C17 108.5(2).  Similar to 2.10, compound 2.15 coordinates a sixth donor ligand (Equation 2.1). 2.16, is prepared from 2.15 and Py in toluene solution, and is isolated as an orange powder in high yield. There is a singlet at ö 3.2 in the 31 P{ H} NMR spectrum of 1 2.16 in C . As for 2.11, 2.12, and 2.13, the P resonance of 2.16 is shifted downfield from D 6 [NPN]*MCI starting material. Although there are only three resonances in the that of the 2  59  3 region of the 1 ArCH H NMR spectrum, one is broad and integrates to 12H, indicating that two of the ArCH 3 signals are coincident.  Py  (2.1)  toluene  2.15  2.16  When a toluene-d 8 solution of 2.16 is cooled to 220 K, a loss of symmetry in the complex is apparent in the H 1 NMR spectrum. The presence of eight singlets in the ArCH 3 region is diagnostic of a C 1 symmetric complex, and the ArH region also shows the expected resonances for a C 1 symmetric structure. At 360 K, there are three ArCH 3 resonances (again two singlets appear to overlap), and the ArH resonances are consistent with a C symmetric solution structure for 2.16. The apparent plane of symmetry in 2.16 at 298 K in solution is consistent with either intra- or intermolecular exchange of Py.  . 2 2.2.6 Synthesis and structure of [NPNI*Hfl , 2.17, is prepared from 2.15 and excess iodotrimethylsilane 2 [NPN]*Hfl in toluene solution and is isolated in quantitative yield as a yellow powder (Equation 2.2). In C D 6 solution, the 31 P{ H} and 1 1 H NMR spectra closely resemble those of 2.10 and 2.15, and are consistent with a C symmetric trigonal-bipyramidal structure for 2.17. The ORTEP representation of the solid-state molecular structure of 2.17 is shown in Figure 2.12. The geometry at Hf is distorted trigonal bipyramidal, and the bond lengths and angles are  60  unremarkable. In particular, at about 2.77  A, the Hf—I bond lengths agree well with others  reported in the literature. 45  SiI 3 10 Me  (2.2) toluene  2.15  2.17  [NPN]*Hf1 2.17 , Figure 2.12. ORTEP drawing of the solid-state molecular structure of 2 (ellipsoids drawn at the 50% probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths  (A) and angles  (°):  Hfl—P1 2.6994(13), Hfl—N1 2.061 (4), Hfl—  N2 2.068(4), Hfl—I1 2.7924(5), Hfl—12 2.7573(4), P1—Hfl—N1 70.94(12), P1—Hfl—N2 73.56(12), P1—Hfl—I1 177.36(3), P1—Hfl—12 86.03(3), N1—Hfl—N2 112.94(16), I1—Hfl—12 96.605(14).  61  2.3 Conclusions. In this chapter, two new routes to diamidophosphine ligands are reported. Although it was possible to prepare small quantities of 2 HF) using Cu-catalyzed C—N [NPNj’Li coupling to obtain an N,N-diarylated diaminotriphenyiphosphine ligand precursor, the purity and overall yield provided by this route were disappointing. In contrast, the metathesis 4 ( [NPN]*Li ) 2 O 8 pC from (Mes)(2-Br-4method provides a good overall yield of H  )NH, BuLi, and PhPC1 3 H 6 MeC 2 in three simple steps. This reaction has been reproduced [NPNI*Li has been characterized in solution and several times on a large scale (up to 25 g). 2 in the solid state. The metathesis route is used extensively in the Fryzuk group to make early transitionmetal complexes by the reaction of [PNP]Li, 2 ]Li or [NPN]Li N [P , 2 with MCl(THF). Zirconium complexes of [NPN]* cannot be prepared by salt metathesis because multiple metal-containing products form; however, Zr and Hf complexes are prepared in high yield [NPN]*H is synthesized in high yield from [NPN]*Lib by protonolysis. The proligand 2  [NPNI*H and ) and NMe 2 0 8 H 4 C HC1. Zr and Hf complexes of [NPN]* are prepared from 2 3  4 (M ) 2 M(NMe  =  [NPNI*M(NMe with excess Me ) Zr, Hf). The reaction of 2 SiC1 furnishes 3  [NPN]*MC1 Overall, this three-step route provides [NPN]*ZrC1 . 2 the dichloride complexes, 2 4 ( [NPNj*Li ) 2 O 8 pC . Both 2 in 78% and 85% yield, respectively, from H and [NPNI*HfC1  metal dichloride complexes, as well as the hafnium bis(dimethylaniide) complex, have been [NPN]*Hf1 can also be characterized in the solid state by single-crystal X-ray diffraction. 2  [NPN]*HfCl and excess TMSI. prepared in high yield from 2 [NPN]*MC1 coordinate small neutral donor , The trigonal-bipyramidal complexes, 2 ligands such as Py to give racernic mixtures of C 1 symmetric six-coordinate complexes.  62  [NPN]*ZrC1 ( 2 Py) has been characterized crystallographically, and the solid-state molecular structure is  consistent with  the  low  temperature  H 1  NMR  data  obtained for  [NPN]*HfC1 ( 2 Py). In chapter three, [NPNI*ZrC]Q and 2 [NPNI*HfC1 are used as starting [NPN]*MR (M materials for the preparation of organometallic complexes 2  =  Zr, Hf; R  =  3 S 2 CH iMe . The attempted synthesis of Zr and Hf hydride complexes from Me, 2 CH P h, and ) 2 is also described. In chapter four, the preparation of an N [NPN]*MMe 2 complex from , and the attempted preparation of an N 2 [NPNI*ZrC1 {NPNJ*Hf1 is 2 complex from 2 described.  2.4 Experimental. 2.4.1 General experimental. Unless otherwise stated, all manipulations were performed under an atmosphere of dry, oxygen-free N 2 or Ar by means of standard Schlenk or glovebox techniques (Vacuum atmospheres HE-553-2 glovebox equipped with an MO-40-2H purification system and a  —  35 °C freezer). Ar and N 2 were dried and deoxygenated by passing the gases through a column containing molecular sieves and MnO. Hexanes, toluene, tetrahydrofuran, pentane, benzene, and diethyl ether were purchased anhydrous from Aldrich, sparged with N , and 2 passed through columns containing activated alumina and Ridox catalyst. Dioxane was dried over sodium-benzophenone ketyl and distilled. THF-d , C 8 , and C 8 D 7 D were dried over 6 Na/K alloy under partial pressure, trap-to-trap distilled, and freeze-pump-thaw degassed three times. ‘H, 31 P{’H}, and 13 C{’H} NMR spectra were recorded on a Bruker AV-300, Bruker AV-400, or Bruker AMX-500 spectrometer, operating at 300.1, 400.0, and 500.1 MHz for ‘H spectra, respectively. H 1 L 7 i{ } NMR spectra were recorded on the AV-400 or  63  AMX-500. Unless otherwise noted, all spectra were recorded at room temperature. 1 H NMR spectra were referenced to residual protons in the deuterated solvent: C 3 D (6 7.16), CDC1 6 (6 7.24), C 8 (6 2.09), or THF-d D 7 8 (6 3.58). 31 P{’H} NMR spectra were referenced to external P(OMe) 3 (6 141.0 with respect to 85% 4 P0 at 6 0.0). 13 3 H H} NMR spectra are 1 C{ referenced to residual solvent: C D (6 128.0), CDC1 6 3 (6 77.23), or THF-d 8 (6 67.4). 1 Li{ 7 H } NMR spectra were referenced to external LiC1 in 2 0/H at 6 0.0. Chemical shifts (6) D 0 listed are in ppm, and absolute values of the coupling constants are in Hz. Mass spectrometry (EI-MS) and microanalyses (C, H, N) were performed at the Department of Chemistry at the University of British Columbia. Microanalysis of compound 2.17 was performed at CHEMISAR laboratories in Guelph, Ontario.  2.4.2 Starting materials and reagents. SiCl, Me 3 Me SiI, C1 3 SiH, and PhPC1 3 2 (Aldrich) were distilled prior to use. Pyridine, triethylamine and tetramethylethylenediamine (tmeda) were dried over 2 CaH and distilled prior to use. Me NHC1 was suspended in benzene and heated to reflux in a Dean-Stark 3 apparatus  to  remove  ) (Phen 3 CuI(Phen)(PPh  water. =  PPh, ) 4 H 6 C 2 (2-NH ’ 3  4 ) 2 Hf(NMe  and  Zr(NMe 4 4 ) 2 3  ortho-phenanthroline), and (Mes)(Tol)NH 36 were prepared by  literature methods. BuLi Q—1.6 M in hexanes) was titrated against benzoic acid in THF with o-phenanthroline as an indicator. All other compounds were purchased from commercial suppliers and were used as received.  2 ) [N-(4-MeC ) 4 H 6 P (2-N(H)C hPO ] (2.1). In air, (2-NH PPh (1.00 g, 3.42 ) 4 H 6 C 2 rnmol) was dissolved in hexanes (30 mL) and acetone (5 mL). H 0 (30% w/v, 0.5 mL, 4.4 2  64  mmol) was added dropwise to the stirred solution. The beige reaction mixture was taken to dryness, and the pale brown residue so obtained was dissolved in 2 C1 and washed with CH water (3 x 50 ml). The organic layer was separated, dried over 4 SO filtered, and 2 Na , concentrated under vacuum to obtain (2-NH PhP=O as a beige solid (1.03 g, 3.34 ) 4 H 6 C 2 mmol, 98%). 2 (2-NH P ) 4 H 6 C hP=O can be recrystallized from acetone/EtOAc. ‘H NMR (CDC1 , 200 MHz): ö 3  7.6  —  7.3 (m, 7H), 7.23  (t,  2H, 7 Hz), and 6.8  6.5 (m, 4H)  —  (ArH), 4.51 (bs, 4H, NH). P{’H} NMR (CDC1 31 , 81 MHz): ö 3  =  40.8 (s).  Anal. Calcd. for H, 1 C 0 2 N 7 P: 8 C, 70.12; H, 5.56; N, 9.09; Found: C, 69.98; H, 5.62; N, 9.24.  In air, 2 (2-NH P ) 4 H 6 C hPO (1.03 g, 3.34 mmol) was dissolved in xylenes (30 mL) and THF (10 mL), and to this solution was added K 3 C 2 0 (2.00 g, 14.5 mmol), 4-iodotoluene (1.64 g, 7.52 mmol), and CuI(Phen)(PPh ) (0.220 g, 0.35 mmol). The reaction mixture was 3 stirred and heated to reflux for 4 d at 120 °C and appeared as white and orange solids suspended in a brown solution over the course of the reaction. Because no visible changes occurred, the reaction was followed by TLC in 9:1 petroleum ether:EtOAc (R 1  =  0.8). The  reaction mixture was cooled to rt and taken to dryness to obtain a beige residue that was purified by silica gel chromatography (9:1 petroleum ether:EtOAc). Compound 2.1 was isolated as a beige powder (1.42 g, 2.91 mmol, 85% relative to (2-NH PhP). ) 4 H 6 C 2 ‘H NMR (CDC1 , 300 MHz): ö 3  =  8.52 (bs, 2H, NH), 7.67 (dd, 2H,J  =  8 Hz,JH,,  =  7 Hz),  7.51 (t, IH, 7 Hz), 7.44 (m, 2H), 7.29 (m, 4H), 7.03 (d, 4H, 8 Hz), 6.97 (d, 4H, 8 Hz), 6.86 (dd, 2H, JHH  =  8 Hz, JHP  =  7 Hz) and 6.68  31 H 1 P{ } NMR (CDC1 , 121 MHz): 3  =  (t,  2H, 7 Hz) (ArH), 2.26 (s, 6H, 3 ArCH ) .  42.4 (s).  65  C{’H} NMR (CDC1 13 , 75 MHz): 6 3  =  150.9 (d, 5 Hz), 139.0, 133.8, 133.7, 133.6 (d, 2 Hz),  132.4, 132.3, 132.2, 129.9, 128.7 (d, 23 Hz), 121.7, 118.0 (d, 13 Hz), 115.2 (d, 8 Hz), and 113.6 (ArC), 20.9 3 (ArCH ) . El-MS (m/): 488 (100, [M]j, 305 (50, [M  —  (Tol)(Ph)NH]’), 183 (40, [(Tol)(Ph)NHf).  (2-NC 2 ) 6 [N,N-(4-MeC ) 4 H ]6 )(2-N(H)C [N-(4-MeC ) 4 H ] PhP= 0 (2.2). Compound 2.2 was obtained as an impurity when the synthesis of 2.1 was repeated with >5 g of (2PPh. The off-white product was purified by silica gel chromatography (4:1 ) 4 H 6 C 2 NH petroleum ether/EtOAc, Rf  =  0 to yield 2 0.8), followed by recrystallization from EtOH/H  white crystals. H NMR (CDCI 1 , 300 MHz): 6 3  =  7.41 (m, 4H), 7.31-7.07 (m, 9H), 7.03 (d, 2H, 8 Hz), 6.94  (d, 2H, 8 Hz), and 6.71 (bd, 8H) (ArH), 6.54  (t,  1H, 7 Hz, NH), 2.27 (s, 3H) and 2.12 (s, 6H)  (ArCH ) 3 . P{’H} NMR (CDC1 31 , 121 MHz): 6 3 C{ 3 ‘ H 1 } NMR (CDC1 , 75 MHz): 6 3  =  =  34.1 (s). 152.2 (d, 3 Hz), 149.8 (d, 4 Hz), 145.8, 139.3, 135.4 (d,  11 Hz), 133.5 (d, 2 Hz), 133.2 (d, 11 Hz), 132.6 (d, 3 Hz), 132.5, 132.4 (d, 2Hz), 132.0 (d, 10 Hz), 131.4, 131.2 (d, 6 Hz), 131.1  (a, 3 Hz),  130.9, 129.7, 129.2, 128.1 (d, 12 Hz), 124.7 (d,  13 Hz), 123.8, 120.4, 117.4 (d, 7 Hz), 116.4 and 115.0 (ArC), 20.9 and 20.8 3 (ArCH ) . El-MS (m/3: 578 (100, [Mfl. Anal. Calcd. for 2 N C 3 H 0 P: 9 C, 80.95; H, 6.10; N, 4.84; Found: C, 80.63; H, 6.22; N, 5.24. 5  2 H [N-(4-MeC ) 4 H 6 P j(2-N(H)C hP, ] [NPN]’H 2 (2.3). Toluene (30 niL), trichiorosilane (1.2 g, 8.9 mmol), and triethylamine (0.62 g, 6.1 mmol) were added to 2.1 (1.00 g, 2.04 mrnol)  66  under N 2 in a long Schienk tube. The translucent light brown mixture was heated to reflux overnight, whereupon an off-white suspension formed. The reaction mixture was cooled, degassed H 0 (3 mL) was added, and the mixture was taken to dryness to obtain a beige 2 residue. The residue was triturated with toluene (25 mL), and the solution was filtered through Celite. The colourless solution was taken to dryness to obtain a translucent white residue (0.890 g, 1.88 mmol, 92%).  ‘H NMR (C , 300 MHz): ö D 6  =  7.48 (bd, 2H), 7.29 (m, 4H), 7.04 (m, 5H), 6.82 (d, 4H, 8  Hz), 6.76 (d, 4H, 8 Hz), and 6.72 (m, 2H) (ArH), 6.36 (bs, 2H, NH), 2.06 (s, 6H, 3 ArCH ) . 31 H 1 P{ } NMR (C , 121 MHz): ö D 6 C{’H} NMR (C 13 , 75 MHz): ö D 6  —30.9 (s).  =  =  148.5 (bs), 140.4, 135.2 (bs), 134.6, 134.3 (bs), 131.5,  130.8, 130.1, 129.2, 129.1, 122.5, 121.2, 120.5, and 116.6 (ArC), 20.7 (ArCH ). 3  ) (2-N(Li)C 4 H 6 [N-(4-MeC )] 2 4 H 6 PhP2THF, [NPNJ ‘Li2THF (2.4). “BuLi (1.6 M in hexanes, 1.10 mL, 1.75 mmol) was added dropwise to a solution of 2.3 (0.37 g, 0.78 mmol) in hexanes (10 mL) and THF (1 mL) at —35 °C. The yellow clear solution was shaken thoroughly to mix, and was stored overnight at —35 °C. A yellow precipitate formed overnight that was collected on a fit, washed with pentane (3  X  I mL), and dried.  Compound 2.4 was recrystallized from THF/toluene layered with pentane. Small yellow crystals were collected on a frit and dried (0.26 g, 0.41 mmol, 53%).  H NMR (C 1 , 500 MHz): ö D 6  =  7.81 (bt, 2H, 6 Hz), 7.74  7.38 (d, 4H, 8 Hz), 7.13 (m, 8H), 7.02  (t,  (t,  1H, 7 Hz), and 6.67  8H, THF), 2.27 (s, 6H, ArCH ), 0.87 (bs, 8H, THF). 3 P{’H} NMR (C 31 , 202 MHz): D 6  =  —33.0  (q,J =  67  41 Hz).  2H, 7 Hz), 7.66 (t,  (t,  2H, 7 Hz),  2H, 7 Hz) (ArH), 2.96 (bs,  Li{ 7 H 1 } NMR (C , 194 MHz): 6 D 6  =  —0.35 (d, iLi, fLIP  =  41 Hz), —1.72 (s, iLi).  )(2-Br-4-MeC 2 6 C (2,4,6-Me ) 3 H NH (2.5). In a flask shielded from the light and open to the air, N-bromosuccinirnide (3.00 g, 16.9 mmol) was added portion-wise to a stirred pale yellow solution of (Mes)To1)NH (3.80 g, 16.9 mmol) in CH CN (100 mL) at 0 °C over 30 3  mm. The brown suspension was allowed to warm to rt, and a saturated solution of NaHSO 3 (5 mL) was added. The beige reaction mixture was taken to dryness to obtain a beige solid that was dissolved in a minimum amount of petroleum ether and filtered through silica powder about 5 cm deep in a 60-rnL glass frit. The silica was rinsed with petroleum ether until the washings were colourless. Beige crystals were obtained when the filtrate was taken to dryness. The crystals were isolated, washed with petroleum ether (2  X  5 mL), and dried  (4.94 g, 16.2 mniol, 96%). H NMR (CDC1 1 , 300 MHz): 6 3  =  7.33 (s, IH), 6.96 (s, 2H), 6.83 (d, 1H, 8 Hz), and 6.07 (d,  IH, 8 Hz) (ArH), 5.51 (bs, IH, NH), 2.33 (s, 3H), 2.23 (s, 3H), 2.17 (s, 6H) 3 (ArCH ) . c{ 3 ‘ H 1 } NMR (CDC1 , 75 MHz): 6 3  =  141.5, 136.5, 136.0, 135.5, 132.9, 129.4, 129.1, 128.1,  112.6, and 109.4 (ArC), 21.1,20.2, and 18.3 3 (ArCH ) . El-MS (m/: 303 (100, [M]). Anal. Calcd. for H NBr: C 1 6 C, 63.17; H, 5.96; N, 4.60; Found: C, 62.81; H, 5.99; N, 4.72. 8  )(2-Li-4-Me-C 2 C (2,4,6-Me ) 3 H 6 NLitmeda (2.6). A stirred solution of 2.5 (0.790 g, 2.59 mmol) and tmeda (0.80 mL, 0.62 g, 5.3 mniol) in Et 0 (5 mL) was cooled to —35 °C, 2 and rBuLi (3.4 mL, 1.6 M in hexanes, 5.4 mmol) was added dropwise. A light yellow  68  precipitate formed immediately that was collected on a frit, washed with hexanes (5 rnL), and dried (0.680 g, 1.92 mmol, 74%). H NMR (THF-d 1 , 300 MHz): 6 8  6.93 (d, 1H, 2 Hz), 6.74 (s, 2H), 6.38 (dd, 1H, 8 Hz, 2  Hz), and 5.54 (d, IH, 8 Hz) (ArH), 2.31 (s, 4H, tmeda), 2.17 (s, 3H, CH ), 2.15 (s, 12H, 3 tmeda), 2.02 (s, 3H), and 2.00 (s, 6H) (ArCH ). 3 C{’H} NMR (I’HF-d 3 ‘ , 75 MHz): 6 8  =  153.8, 152.1, 133.5, 132.2, 129.4, 129.3, 128.4, 116.4,  113.3, and 111.5 (ArC), 58.8 and 46.2 (tmeda), 21.0, 20.0, and 18.9 (ArCH ). 3 Satisfactory elemental analysis could not be obtained; samples darkened instantly in the modified N -filled glovebox used in the microanalytical facility of the UBC Chemistry Dept. 2  (pC (2.7p-C [NPNj*Li ) 2 O 8 H 4 ). To a stirred solution of 2.5 (4.84 g, 15.9 mmol) in 2 0 8 H 4 0 (100 mL) at —35 °C was added BuLi (1.55 M in hexanes, 20.5 mL, 31.8 mmol) 2 Et dropwise over 15  mm. The clear yellow solution was allowed to warm to rt and stirred for 3  h. The solution was chilled (—35 °(Z), and PhPC1 2 (1.40 g, 7.82 mmol) in EtO (10 mL) was added dropwise over 2  —  3 h at this temperature. The yellow solution became dark orange  throughout the addition. The reaction mixture was warmed slowly to rt and stirred for 24 h to obtain a pale orange suspension that was taken to dryness to obtain an orange foam. Hexanes (30 mL) were added to the foam to obtain a translucent orange solution. 1,4Dioxane (5 mL) was added to the solution to obtain a yellow precipitate that was collected on Celite —3 cm deep in a frit. The precipitate was washed with hexanes and the dark orange filtrate was concentrated and chilled to induce the formation of yellow crystals. The solid trapped on Celite in the frit was eluted through the Celite with a mixture of toluene (50 mL) and THF (0.1 mL) to obtain a yellow filtrate that was taken to dryness. The yellow powder  69  so obtained can be recrystallized from toluene (with a drop of THF to dissolve) layered with hexanes. The combined powder and crystals (4.37 g, 6.65 mmol, 85% isolated yield based on ) were stored at —35 °C because thermal decomposition has been observed. NMR 2 PhPC1 spectroscopy was facilitated by the addition of a drop of THF to the suspension of 2.7(p) in C 2 0 8 H 4 C , and free and 2 0 8 H 4 . Resonances for free (not coordinated to Li) p-C D 6 coordinated THF were observed in the ‘H NMR spectrum. Signals due to coordinated THF H NMR spectrum and cannot be appear as shoulders on the peaks for free THF in the 1 integrated accurately. Elemental analyses of 2.7 (b-C ) were hampered by its sensitivity 2 0 8 H 4 to moist air; the yellow powder darkened instantly upon opening sample vials in the modified glovebox used for microanalysis at U.B.C. Despite many attempts, results that were low in carbon were found. X-ray quality crystals of 2.72THF were obtained by slow evaporation of a benzene solution of 2.7 (p-C ) with a small amount of THF added. 2 0 8 H 4 ‘H NMR (C , 300 MHz): 6 D 6 7.02  (t,  Hz,JHH  =  7.81  (t,  2H, 7 Hz), 7.72 (bd, 2H, 3 Hz), 7.19  (t,  2H, 7 Hz),  1H, 8 Hz), 6.97 (s, 2H), 6.87 (s, 2H), 6.85 (d, 2H, 8 Hz), and 6.52 (dd, 2H, J =  =  6  8 Hz) (ArH), 2.35 (s, 6H), 2.33 (s, 6H), 2.28 (s, 6H), and 2.16 (s, 6H) (ArCH ). 3  H} NMR (C 1 P{ 31 , 121 MHz): 6 D 6  =  —35.2  Li{’H} NMR (C 7 , 155 MHz): 6 D 6  =  —0.07 (d,  “C{’H} NMR 6 (C 75 MHz): 6 , D  =  1 = (q,J  40 Hz).  lLi,JLIP =  40 Hz), —1.97 (s, ILi).  162.1 (d, 28 Hz), 152.0, 140.2, 134.9 (d, 3 Hz), 133.8,  132.3 (d, 14 Hz), 132.2, 132.1, 131.8, 130.8, 129.0, 128.8, 126.8, 122.9, 120.9 (d, 12 Hz), and 117.9 (d, 5 Hz) (ArC), 20.9, 20.7, 20.4, and 20.2 (ArCH ). 3 The data for one representative attempt at microanalysis is reported below. Anal. Calcd. for 2 45 C 5 H L N P O 6 : i C, 77.51; H, 7.78; N, 3.93; Found: C, 74.75; H, 7.59; N, 4.02.  70  LNPNI*HZ (2.8). Trimethylammonium chloride (0.319 g, 3.34 mmol) was added all at once to a stirred yellow solution of 2.7(p-C ) (1.06 g, 1.61 mrnol) in THF (15 mL). After 15 2 O 8 H 4  mm.,  the reaction mixture was a white suspension. After I h, the reaction mixture was taken  to dryness to obtain a white solid that was extracted with warm toluene (20 mL). The toluene suspension was filtered through Celite, the Celite was washed with additional warm toluene (10 mL), and the filtrate was taken to dryness to obtain a white solid. The solid was washed with pentane and dried to yield a white powder (0.872 g, 1.57 mmol, 97%). Compound 2.8 is air-stable as a solid for weeks and in solution for days, although in our laboratory it is stored in the glovebox to keep it water-free. ‘H NMR (C , 300 MHz, 300 K): ö D 6 JHP =  7 Hz), 7.12 (d, 2H, 6 Hz), 7.02  2H), and 6.38 (ad,  2H,JHP =  7.68 (dd, 2H, J  =  7 Hz, JHH  =  7 Hz), 7.29 (d, 2H,  IH, 8 Hz), 6.88 (d, 2H, 7 Hz), 6.78 (bs, 2H), 6.74 (bs,  (t,  5 Hz,JHH  =  =  9 Hz) (ArH), 5.98 (d, 2H,J  =  5 Hz, NH), 2.12 (s,  6H), 2.04 (bs, 6H), 1.98 (s, 6H), and 1.90 (bs, 6H) (ArCH ). 3 H NMR (C 1 , 500 MHz, 273 K): 8 D 7  =  7.63  (t,  2H, 7 Hz), 7.26 (d, 2H, 7 Hz), 7.10 (m, 3H),  6.84 (d, 2H, 7 Hz), 6.75 (s, 2H), 6.69 (s, 2H), and 6.35 (ad, 2H, JHP  =  5 Hz,  J  =  9 Hz)  (ArH), 5.91 (d, 2H, 5 Hz, NH), 2.16 (s, 6H), 2.08 (s, 6H), 2.01 (s, 6H), and 1.93 (s, 6H) ). 3 (ArCH ‘H NMR (C , 300 MHz, 370 K): 6 8 D 7  =  7.59  (t,  2H, 8 Hz), 7.12 (m, 4H), 6.95 (m, IH), 6.82  (d, 2H, 8 Hz), 6.73 (s, 4H), and 6.23 (dd, 2H, JHP JHP  =  =  5 Hz, JHH  =  9 Hz) (ArH), 5.88 (bd, 2H,  5 Hz, NH), 2.12 (s, 6H), 2.01 (s, 6H), and 1.98 (s, 12H) (ArCH ). 3  P{’H} NMR (C 31 , 121 MHz): 6 D 6  =  —31.4 (s).  71  C{’H} NMR (C 13 , 75 MHz): ö D 6  147.7 (d, 16 Hz), 136.5, 135.7 (bs), 135.5 (bs), 135.1,  =  135.0, 134.8, 134.7, 134.5, 131.8, 129.6, 129.1, 129.0, 128.9, 117.9 (d, 7 Hz), and 112.5 (d, 3 Hz) (ArC), 20.6, 20.1, 18.0 (bs), and 17.7 (bs) (ArCH ). 3 JR (KBr): 3360 (m), 3012 (m), 2917 (m), 2854 (m), 1601 (m), 1491 (s), 1389 (m), 1310 (s), 1293 (s), 1268 (m), and 1028 (m) cm . 1 El-MS (m/J: 556 (20, [IVl]), 541 (100, [M  —  Me]).  Anal. Calcd. for N 31 C 4 H P 2 8 : C, 81.98; H, 7.42; N, 5.03; Found: C, 82.04; H, 7.46; N, 4.87.  )z (2.9). Zr(NMe 2 [NPNI*Zr(NMe 4 (0.580 g, 2.17 mmol) and 2.8 (1.21 g, 2.17 mmol) were ) 2 mixed together, and toluene (15 mL) was added to obtain a lemon yellow solution that was stirred for 2 h. The reaction mixture was taken to dryness to obtain a yellow residue. Upon  addition of pentane (5 mL), a light yellow precipitate formed that was collected on a fit and dried (1.43 g, 1.95 mmol, 90%). H NMR (C 1 , 300 MHz): 8 D 6  =  7.60  (t,  2H, 8 Hz, o-PPh), 7.52 (d, 2H, 7 Hz, m-Tol), 7.11 (m,  3H, 7 Hz, m-, p-PPh), 7.02 (s, 2H, m-Mes), 6.97 (s, 2H, m-Mes), 6.93 (d, 2H, 9 Hz, o-Tol), 6.19 (dd, 2H, 8 Hz, m-Tol), 3.06 (s, 6H, N(CH ), 2.42 (s, 6H), and 2.32 (s, 6H) (ArCH 3 ), 3 2.31 (s, 6H, N(CH ), 2.25 (s, 6H), and 2.08 (s, 6H) (ArCH 2 ) 3 ). 3 H} NMR (C 1 P{ 31 , 121 MHz): 6 D 6  =  C{ 3 ‘ H 1 } NMR (CD , 75 MHz): 6 6  —11.5 (s). =  161.5 (d, 31 Hz), 145.2, 144.6, 137.2, 136.4, 135.0,  134.7, 134.3, 133.3, 133.1, 130.3, 130.2, 118.0, 117.6, 115.1, and 115.0 (ArC), 43.6 and 43.5 ), 21.0, 20.4, 19.3, and 19.2 (ArCH 2 ) 3 (N(CH ). 3 El-MS (m/3: 732 (1, [M]), 688 (30, [M  —  ]), 556 (30, [2.8]), 541 (100, [2.8 2 NMe  —  Me]).  Anal. Calcd. for 4 N C 4 H P Zr: 2 C, 68.72; H, 7.00; N, 7.63; Found: C, 68.42; H, 6.99; N, 7.38. 5  72  2 (2.10). To a stirred yellow toluene solution (40 mL) of 2.9 (1.20 g, 1.63 [NPN]*ZrC1 mmol) was added chlorotrimethylsilane (1.77 g, 16.3 mmol) dropwise. The clear yellow solution was stirred overnight, whereupon a yellow precipitate formed. The reaction mixture was taken to dryness to obtain a yellow powder that was collected on a frit, washed with pentane (3  X  5 mL), and dried (1.04 g, 1.45 mmol, 89%). X-ray quality crystals of 2.10 were  grown by slow evaporation of a benzene solution of the compound. H NMR (C 1 , 400 MHz): 6 D 6  =  7.60 (dd, 2H, JHH  =  7 Hz, JHP  =  7 Hz), 7.45 (d, 2H, 8 Hz),  7.05 (m, 3H), 6.91 (s, 2H), 6.84 (d, 2H, 8 Hz), 6.80 (s, 2H), and 6.05 (dd, =  2H,JHH =  , 1 7 Hz,J  ). 3 7 Hz) (ArH), 2.46 (s, 6H), 2.34 (s, 6H), 2.09 (s, 6H), and 1.94 (s, 6H) (ArCH  H} NMR (C 1 P{ 31 , 121 MHz): 6 D 6  =  H} NMR (C 1 C{ 13 , 75 MHz): 6 D 6  —2.8 (s). =  159.9 (d, 32 Hz), 138.5, 138.3, 137.0, 135.3, 134.6,  132.3, 132.2, 131.1, 130.8, 129.6, 125.6, 121.1, 120.6, 114.9, and 114.8 (ArC), 21.1, 20.3, and 19.1 (ArCH ). 3 El-MS (m/: 714 (3, [Mf’), 541 (100, [2.8  —  Me]).  Anal. Calcd. for 2 C 3 H C N P Zr: 8 9 1 C, 63.67; H, 5.48; N, 3.91; Found: C, 63.65; H, 5.80; N, 3.98.  (THF) (2.11). THF (1-2 drops) was added to an NMR tube with 2.10 (20 mg, 2 [NPNJ*ZrC1 28 imol) in C D (0.8 niL) to produce a bright red-orange solution. Attempts to isolate 2.11 6 by precipitation (from toluene/THF solutions layered with pentane at —35 °C) or by concentrating solutions under vacuum gave 2.10. Two sharp resonances due to free THF were observed by ‘H NMR spectroscopy, but signals due to coordinated THF could not be distinguished.  73  H NMR (C 1 , 300 MHz): ö D 6  =  7.75  (t,  2H, 8 Hz), 7.38 (d, 2H, 8 Hz), 7.07 (m, 3H), 6.91 (s,  2H), 6.83 (s, 2H), 6.82 (d, 2H, 8 Hz), and 6.04 (dd, 2H, JHH  =  7 Hz, J  =  6 Hz) (ArH), 2.46  (s, 6H), 2.30 (s, 6H), 2.12 (s, 6H), and 1.95 (s, 6H) (ArCH,). P{’H} NMR (C 1 ‘ , 121 MHz): ö D 6  =  2.7 (s).  (PMe (2.12). PMe, (1-2 drops) was added to an NMR tube with 2.10 (20 2 [NPN]*ZrC1 ) 3 mg, 28 imol) in C D (0.8 niL) to produce a bright red 6  solution.  Attempts to isolate 2.12 by  precipitation (from 3 toluene/PMe solutions layered with pentane at —35 °C) or by concentrating solutions under vacuum gave 2.10. A broad singlet due to free PMe 3 was observed by ‘H and “P{’H} NMR spectroscopy, but a separate peak due to coordinated PMe, could not be distinguished.  ‘H NMR (C , 500 MHz): ö D 6  =  7.78  (t,  2H, 8 Hz), 7.35 (d, 2H, 8 Hz), 7.12 (m, 3H), 6.88 (s,  2H), 6.84 (s, 2H), 6.78 (d, 2H, 8 Hz), and 5.97 (dd, 2H, JHH  =  8 Hz, JHP  =  5 Hz) (ArH), 2.42  (s, 6H), 2.19 (s, 6H), 2.16 (s, 6H), and 1.99 (s, 6H) (ArCH,). P{’H} NMR (C 1 ‘ , 202 MHz): ö D 6  =  3.4 (s).  (Py) (2.13). Pyridine (0.49 2 [NPN]*ZrC1 g, 0.50 mL, 6.2 mmol) was added dropwise to a stirred yellow solution of 2.10 (0.400 g, 0.558 mmol) in toluene (5 mL). The solution turned  red-orange instantly and was stirred for 30 mm. The reaction mixture was taken to dryness to obtain a red-orange powder that was collected on a fit, rinsed with hexanes (5 niL), and dried (0.434 g, 0.545 mmol, 98%). Red single crystals of 2.13 suitable for X-ray diffraction were grown by slow evaporation of a benzene solution of the compound.  74  H NMR (C 1 , 400 MHz): 6 D 6  =  8.38 (d, 2H, 4 Hz, C N), 7.96 (t, 2H, 8 Hz), 7.34 (d, 2H, 8 H 5  Hz), 7.13 (m, 3H), 6.95 (s, 2H), 6.78 (d, 2H, 7 Hz), 6.73 (s, 2H), 6.60 (t, IH, 7 Hz,p-C N), H 5 6.18 (t, 2H, 7 Hz, 5 C N H ), and 6.04 (dd, 2H, JHH  =  8 Hz,  J,  =  6 Hz) (AtH), 2.30 (s, 6H),  2.18 (s, 6H), 2.05 (bs, 6H), and 1.95 (s, 6H) 3 (ArCH ) . P{H} NMR (C 31 , 162 MHz): 6 D 6  =  13 H 1 C{ } NMR (C , 101 MHz): 6 D 6  2.7 (s).  =  151.6, 140.9, 139.2, 139.0, 137.7, 136.3, 134.1, 133.4,  132.9, 132.8, 130.6, 130.5, 130.0, 129.9, 129.7, 129.6, 125.6, 123.2, and 115.7 (d, 9 Hz) (ArC), 21.0, 20.5, 20.1, and 19.6 3 (ArCH ) . El-MS (m/,: 716 (40, [M  —  Pyf’), 556 (10, [2.8f’), 541 (50, [2.8  —  Mefl, 225 (100,  [(I’ol) (Mes)NH] ) Anal. Calcd. for P 2 4 C C 3 HN Zr: 3 l C, 64.89; H, 5.57; N, 5.28; Found: C, 65.20; H, 5.89; N, 5.35.  2 [NPN]*Hf(N ) z Me (2.14). Hf(NMe 4 (2.85 g, 8.03 rnmol) and 2.8 (4.48 g, 8.05 nmiol) ) 2  were mixed together and toluene (50 mL) was added. The lemon yellow solution was stirred for 2 h, and the reaction mixture was taken to dryness. The pale yellow residue so obtained was dissolved in pentane (25 mL), and after about 30 s a pale yellow precipitate formed that was collected on a frit, washed with pentane (5 mL), and dried under vacuum (5.81 g, 7.07 mmol, 88%). X-ray quality crystals of 2.14 were grown by slow evaporation of a benzene solution of the compound. H NMR (C 1 , 500 MHz): 6 D 6  =  7.50 (t, 2H, 8 Hz), 7.44 (d, 2H, 8 Hz), 7.06 (m, 2H), 7.01 (m,  1H), 6.96 (s, 2H), 6.92 (s, 2H), 6.88 (d, 2H, 8 Hz), and 6.15 (dd, 2H,JHH  75  =  8 Hz,JfW  =  6 Hz)  (ArH), 3.02 (s, 6H), 2.38 (s, 6H), 2.33 (s, 6H), 2.28 (s, 6H), 2.18 (s, 6H), and 2.00 (s, 6H) 2 and ArCH ) 3 (N(CH ). 3 H} NMR (C 1 P{ 31 , 202 MHz): 6 D 6  =  C{’H} NMR (C 13 , 75 MHz): 6 D 6  —4.5 (s). =  162.4 (d, 30 Hz), 144.7, 136.6, 135.9, 134.7, 134.5,  134.1, 133.8, 132.9, 132.8, 129.9, 129.8, 129.0, 128.6 (d, 8 Hz), 117.4 (d, 32Hz), and 115.9 (d, 9 Hz) (ArC), 43.2, and 43.0 3 (NCH ) , 20.9, 20.2, 19.2, and 19.1 3 (ArCH ) . El-MS (m/r: 777 (100, [M  —  ]), 733 (40, [M 2 NMe  —  )]j. 2 2(NMe  Anal. Calcd. for N C 4 H P 4 Hf: 2 C, 61.42; H, 6.26; N, 6.82; Found: C, 61.64; H, 6.15; N, 6.57. 5  2 (2.15). To a stirred toluene solution (50 mL) of 2.14 (5.10 6.94 mmol) was [NPN]*HfC1 g, added chlorotrimethylsilane (2.55 g, 23.5 mmol) dropwise. The clear yellow solution was stirred overnight, whereupon a pale yellow precipitate formed. The reaction mixture was taken to dryness and the pale yellow solid so obtained was suspended in pentane (25 mL). The solid was collected on a fit, washed with pentane (3  X  5 mL), and dried under vacuum  to obtain a pale yellow powder (4.97 g, 6.87 mmol, 99%). X-ray quality crystals were grown by slow evaporation of a benzene solution of 2.15. ‘H NMR (C D,, 300 MHz): 6 6  =  7.59 (dd, 2H, J  =  8 Hz, JHH  =  10 Hz), 7.42 (d, 2H, 8 Hz),  7.03 (m, 3H), 6.92 (s, 2H), 6.86 (d, 2H, 8 Hz), 6.82 (s, 2H), and 6.10 (dd, =  2H,JHH =  8 Hz,J  6 Hz) (ArH), 2.48 (s, 6H), 2.41 (s, 6H), 2.10 (s, 6H), and 1.96 (s, 6H) 3 (ArCH ) .  H} NMR (C 1 P{ 31 , 121 MHz): 6 D 6  =  C{’H} NMR (C 3 ‘ , 75 MHz): 6 D 6  =  0.1 (s). 160.9 (d, 30 Hz), 139.0 (d, 5 Hz), 138.3, 137.4, 136.5,  135.5, 134.6, 132.3 (d, 12 Hz), 131.0 (d, 5 Hz), 130.9, 130.8, 130.4 (d, 2 Hz), 129.2 (d, 10 Hz), 120.1, 119.5, and 116.2 (d, 10 Hz) (ArC), 21.1, 20.2, 19.14, and 19.12 3 (ArCH ) .  76  El-MS (m/): 804 (100, [M]j, 541 (40, [2.8  —  MeJ).  Anal. Calcd. for 2 C 3 H C N P Hf: 8 9 1 C, 56.76; H, 4.89; N, 3.48; Found: C, 57.10; H, 5.00; N,  3.68.  (Py) (2.16). Pyridine (0.49 g, 0.50 mL, 6.2 mmol) was added dropwise to a 2 [NPN]*HfCI stirred solution of 2.15 (0.400 g, 0.498 mmol) in toluene (10 mL). The light yellow solution turned yellow-orange instantly and was stirred for 30 mm. at rt. The reaction mixture was  taken to dryness to obtain a pale orange powder that was collected on a frit, rinsed with hexanes, and dried (0.420 g, 0.476 mmol, 95%). ‘H NMR (C , 400 MHz, 300 K): 8 D 6  =  8.31 (d, 2H, 5 Hz), 7.97 (m, 2H), 7.32 (dd, 2H, 8 Hz,  1 Hz), 7.14 (m, 3H), 6.96 (s, 2H), 6.82 (d, 2H, 8 Hz), 6.73 (bs, 2H), 6.60 (t,  2H, 7 Hz), and 6.10 (dd, 2H,JHH  =  8 Hz,J  =  (t,  1H, 7 Hz), 6.15  6 Hz) (ArH), 2.31 (bs, 12H), 2.20 (s, 6H),  and 1.97 (s, 6H) (ArCH ). 3 ‘H NMR (C , 400 MHz, 220 K): 6 8 D 7  =  8.47 (bs, 2H), 7.89 (bs, 2H), 7.38 (d, IH, 8 Hz), 7.32  (d, 1H, 8 Hz), 7.14 (s, 3H), 7.03 (s, 1H), 6.95 (s, IH), 6.92 (s, 1H), 6.77 (d, 1H, 8 Hz), 6.74 (d, 1H, 8 Hz), 6.50 (bt, IH, 7 Hz), 6.36 (s, 1H), 6.12 (bs, 2H), and 6.01 (bs, 2H) (AtH), 3.15 (s, 3H), 2.62 (s, 3H), 2.26 (s, 3H), 2.17 (s, 3H), 2.08 (s, 3H), 2.02 (s, 3H), 1.88 (s, 3H), and 0.84 (s, 3H) (ArCH ). 3 ‘H NMR (C , 400 MHz, 360 K): 8 8 D 7  =  8.46 (bs, 2H), 7.73 (dd, 2H,JHH  =  8 Hz,JHP  =  8 Hz),  7.29 (d, 2H, 8 Hz), 7.14 (m, 3H), 6.91 (bs, IH), 6.88 (s, 2H), 6.79 (d, 2H, 8 Hz), 6.68 (s, 2H), 6.53 (bs, 2H), and 5.97 (dd, 2H,JHH  =  8 Hz,J  2.00 (s, 6H) (ArCH ). 3 P{’H} NMR (C 31 , 162 MHz): 6 D 6  =  3.2 (s).  77  =  6Hz) (ArH), 2.22 (s, 6H), 2.14 (s, 12H),  C{’H} NMR (C 3 ‘ , 101 MHz): ö D 6  =  151.5, 139.0, 138.1, 135.4, 134.3, 133.3 (bs), 133.0,  132.9, 130.4, 130.3, 129.7, 129.5, 129.4, 129.3, 129.1, 128.5, 125.6, 123.4, and 116.9 (bd, 5 Hz) (ArC), 21.4, 21.0, 20.4, and 19.5 (ArCH ). 3 Anal. Calcd. for 2 C 4 H C 3 N P Hf: 3 4 1 C, 58.48; H, 5.02; N, 4.76; Found: C, 58.87; H, 5.40; N, 4.66.  2 (2.17). To a stirred toluene solution (15 mL) of 2.15 (1.75 g, 2.18 mniol) was [NPN]*Hfl added iodotrimethylsilane (3.0 rnL, 2.6 g, 24 mmol) dropwise. The cleat yellow solution was stirred overnight, whereupon a bright yellow precipitate formed. The reaction mixture was taken to dryness to obtain a yellow solid that was suspended in pentane (25 mL), collected on a frit, washed with pentane (3  X  5 mL), and dried under vacuum to obtain a yellow  powder (2.13 g, 2.15 rnmol, 99%). Single crystals of 2.17 were grown by slow evaporation of a benzene solution of the compound. ‘H NMR (C , 500 MHz): 8 D 6 7.11  (t,  2H, 8 Hz), 7.05  (dd, 2H, JHH  =  (t,  8 Hz, J  =  =  7.55 (dd,  2H,JHH =  8 Hz,JPH  =  10 Hz), 7.36 (d, 2H, 8Hz),  IH, 8 Hz), 6.89 (s, 2H), 6.84 (d, 2H, 7 Hz), 6.84 (s, 2H), and 6.09 6 Hz) (ArH), 2.56 (s, 6H), 2.30 (s, 6H), 2.10 (s, 6H), and 1.92 (s,  6H) (ArCH ). 3 H} NMR (C 1 P{ 31 , 202 MHz): 6 D 6  =  C{’H} NMR (C 3 ‘ , 126 MHz): 8 D 6  3.9 (s). =  160.3 (d, 29 Hz), 138.6, 138.3, 137.8, 135.8, 135.4,  134.6, 133.0 (d, 11 Hz), 131.4, 131.2, 131.1, 130.5, 129.0 (d, 10 Hz), 121.3, 121.0, and 116.3 (d, 10 Hz) (ArC), 21.4, 20.7, 20.2, and 20.1 (ArCH ). 3 El-MS (m/: 988 (100, {M]j, 861 (100, [M  —  78  Anal. Calcd. for 2 N C 3 H P I Hf: 8 C, 46.24; H, 3.98; N, 2.84; Found: C, 46.58; H, 4.23; N, 9 2.81.  2.5 References.  1  A) Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100, 3009. B) Chen, Y.; Yekta, S.;  Yudin, A. K. Chem. Rev. 2003, 103, 3155. 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Oganometallics 1995, 14, 5.  83  Chapter Three Zirconium and Hafnium Organometaffic Complexes  3.1 Introduction. Since Ziegler and Natta discovered that mixtures of Ti or Zr halides and organoaluminum reagents catalyze olefin 1 polymerization, interest in group 4 chemistry has continued unabated. 2 A major development in the organometallic chemistry of group 4 has been the creation of homogeneous olefin polymerization catalysts based on titano- and zirconocenes,’ which have been found to be highly active in the presence of co-catalysts such as boranes or methylaluminoxane (MAO). 4 Metallocene catalysts have not only allowed chemists to probe the mechanism of olefin polymerization, 5 but they have also been tailored to yield polymers with narrow molecular weight distributions, 6 to polymerize prochiral olefins stereospecifically, 7 and to give polyolefin products with new structures for advanced 8 In addition, non-metallocene group 4 complexes are being investigated for applications. olefin polymerization. 9 In 1995, Ziegler-Natta catalysis was estimated to provide over 35 million tonnes of polyolefins per year.’° Recent estimates include the production of over 80 million tonnes of polyethylene and 65 million tonnes of polypropylene per year.” In addition to olefin polymerization, metallocene and non-metallocene organo titanium, -zirconium, and -hafnium complexes have been investigated as hydrogenation,’ 2 3 C—C cross-coupling,’ hydroamination,’ 4 silane dehydropolymerization,’ 5 enantioselective organic synthesis, 16 and hydrosilylation 17 catalysts. Small molecule activation, 18 C—F bond  19 C—H bond activation activation, 20 and migratory insertion reactions ’ to yield new organic 2 compounds are other areas of interest to early transition-metal chemists.  84  _  A new reaction for early transition-metal alkyl complexes emerged in the late I 990s 2 gas; a 2 gas, followed by N when a group 4 organometallic complex was reacted with H dinitrogen complex, methane, and hydrogen are the major products of this reaction. The synthesis of N 2 complexes by the hydrogenolysis of early transition-metal alkyl complexes is 2 that is added to the reaction. There are attractive because H 2 is the only reagent besides N 2 following many examples of early transition-metal complexes that bind and activate N ) or sodium amalgam. 8 reduction by an alkali metal reagent, such as potassium graphite (KC  The use of strong reductants to activate N 2 is one of the major barriers to the development of homogeneous catalytic or industrial processes for nitrogen fixation. Among other problems, reducing agents such as KC 8 or Na/Hg amalgam are difficult to work with because they are pyrophoric, are generally incompatible with other reagents required to functionalize N 2 (such as electrophiles), and are difficult to introduce into a catalytic or largescale reaction. The reaction of 2 -C (r1 M 5 H 4 T iR e ) (R  =  Me, Ph) with H 2 gives the red-brown Ti(III)  hydride, 22 2 complex, 2 -iH, (1 M 5 H 4 T 2 C e ) that instantly forms a blue Ti-N -C [(r1 M 5 H 4 T Q 1i] e ) upon exposure to N 2 (Scheme 3.1).23 Dinitrogen is weakly activated in this end-on dinuclear complex: the N—N bond length is 1.170(4) A. Overall, this reaction represents the formation of an N 2 complex from an organometallic complex, H , and N 2 . 2 Scheme 3.1.  2 -  H E 2 2 Ti—H 4 CH  85  Ti—N—N--—-Ti 2 H  24 A Zr-N 2 complex is also prepared by hydrogenolysis of an alkylzirconium complex. 2 (rac-Bp When solutions of (rac-Bp)ZrMe  are exposed  =  (i2 2 gas yields [(rac-Bp)Zr] 2 forms. Exposure of the dihydride to N to H 2 gas, (rac-Bp)ZrH 2 (Scheme 3.2). Again, a group 4 organometallic complex has : 11 ) 2 N i with loss of H activated N 2 without the use of harsh reductants. The N—N bond length of 1.241(3)  A  , unit is present in the complex. 2 suggests a diazenide, or N  Scheme 3.2.  2 H 2 Me 2 Si  Zr \Me  R  =  R’  =  Si 2 2 Me  Zr  4 -CH  TMS  Si 2 Me R  2 compound in Hydrogenolysis of an alkyltantalum complex provides a dinuclear Ta-N which N 2 is coordinated in the side-on—end-on bonding mode. 25 The reaction of 3 ([NPNJ [NPN]TaMe  =  C [(PhNSiMe P ) 2 Ph] H with H 2 gives the Ta(IV) tetrahydride,  (ji-H) which reacts with N 2 ([NPN]Ta) , 4 2 to give 2 QL-H) ([NPN]Ta) Q : 1 ) i-11 ri N . Although this side-on—end-on N 2 complex reacts with boranes, alanes and silanes to generate new nitrogen-element (N—E) bonds, ligand decomposition has stymied efforts to fix nitrogen catalytically with this system. 26 The preceding examples illustrate a rare, but appealing method of synthesizing early transition-metal N 2 complexes: the addition of N 2 to a metal hydride. The reverse reaction,  86  , 2 however, is well known; some early transition-metal complexes react with H 2 to liberate N Zr(111 2 even if the N—N bond is activated in the starting complex. The addition of H 2 to [Cp* ZrH which cannot be induced to coordinate N 2 Cp* 27 It should be . 2 ) N Q : 1 ) 2 r1 N 1-1 ] gives , noted that there are many reports of late transition-metal N 2 complexes synthesized by the elimination of H 28 2 from a metal hydride, but N 2 is only weakly activated in the products. The use of H 2 in the synthesis of N 2 complexes has two main advantages: it can be readily added to a reaction mixture under a variety of conditions, and it is compatible with a range of reagents that functionalize coordinated N , such as silanes, boranes, alanes, and 2 some organic electrophiles. The use of hydrogen as a reductant may someday facilitate the development of catalytic N—E bond-forming reactions. The incompatibility of reductants and electrophiles has been overcome recently in a different manner under carefully designed experimental conditions. 29 Eight equivalents of ammonia are obtained from N 2 in the presence of a bulky Mo catalyst, a weak organic acid ([2,6-Me NHJ [(3,5-(CF H 5 C 2 B], 4 H 6 C 2 ) 3 (Cp* C r). In this system, the electrophile and reducing and a relatively mild reducing agent 2 agent do not react with each other to give H . The choice of electrophile, reductant, and 2 solvent (heptane), and the use of an automated syringe pump proved crucial in this regard. To determine if group 4 organometallic complexes with the [NPN]* ancillary ligand [NPN]*MR (M react with H 2 to give metal hydride complexes, the M(IV) dialkyl complexes, 2 =  Zr, Hf R  =  Me, CH Ph, 3 2 SiMe 2 CH ) , have been prepared and characterized. The reactivity  [NPN]*MMe with H of 2 2 gas, as well as the thermal decomposition of the Zr complexes are described in this chapter.  87  3.2 Results and Discussion. [NPN]*MMe (M 3.2.1 Synthesis of 2  =  Zr, Hf).  ZrMe 3.1, can be prepared as a light- and heat-sensitive hexanes-soluble t [NPN] , 2 {NPN]*ZrC1 (2.10) and 2.2 equivalents of MeMgC1 in yellow powder in high yield from 2 0 (Equation 3.1). There is a singlet at 8 —14.1 in the 31 2 Et P{’H} NMR spectrum of 3.1 in 3 groups, which is . By ‘H and 13 D 6 C C {‘H} NMR spectroscopy, there are four distinct ArCH suggestive of a C symmetric complex, and the peaks in the aromatic regions of both spectra H NMR spectrum (Figure 3.1), the are also consistent with the proposed structure. In the 1 doublet at 6 0.93 ( JHP 3  =  3 group (Met), and the singlet at 8 5 Hz) is assigned to one Zr—CH  0.11 is assigned to the second Zr—CH 3 group (Me ). 5  MeA  and MeB do not interconvert on  the NMR timescale. By HMQC spectroscopy, MeA is assigned to a doublet at 8 45.1 Hz), and Me 5 is assigned to a doublet at 6 41.8  J 2 (  —  =  J 2 (  6  29 Hz) in the ‘ C{’H} NMR 3  spectrum. Unfortunately, NOE difference spectroscopy could not distinguish whether MeA or MeB is trans to P.  2.2 MeMgCI  0 2 Et  M  =  Zr, Hf  88  (3.1)  3 ArCH  3 ZrCH ArH  3 ZrCH  (ppm)  . D 6 Figure 3.1. 300 MHz 1 H NMR spectrum of 3.1 in C  The NMR spectra of 3.1 resemble those of methyizirconium complexes of another NPN]ZrMe ([Ar [Ar NPNJ 2 H NMR spectrum of 2 diamidophosphine ligand. ° In the 1 3  =  3 groups at 6 NSilVIe 3 H 6 C [(2,6-Me C P ) 2 Ph]j H there are two doublets due to the Zr—CH 0.88  J 3 (  =  6.6 Hz) and 6 —0.24  JHP = 3 (  C{’H} NMR spectrum also has two 1.5 Hz). The 13  doublets for the Zr—CH 3 groups at 6 46.4  J = 30.1 2 (  Hz) and 45.0  H: 6 0.88,J, 1 NPNjZrMe were assigned as cis ( [Ar 3 groups in 2 CR =  6.2 Hz) and trans ( H: 6 —0.24, 1  J  =  C: 6 46.4, 3 1.5 Hz; ‘  J= 2 (  6.2 Hz). The Zr—  =  C: 6 45.0,J 6.6 Hz; 13  =  30.1) to phosphorus.  Schrock et al. illuminated the solution- and solid-state structures of alkylzirconium complexes further by preparing monosubstituted [Ar NPN]ZrMe(Cl). The solid-state molecular 2 structure shows that the Me group is equatorial (cis to P), whereas the Cl substituent is apical and trans to P. The Zr—CH 3 group gives rise to a doublet at 6 0.54  89  JHP = 3 (  H 8.8 Hz) in the 1  NMR spectrum of the complex. Although at first glance the apparent mismatch in the  magnitude of  NPN]ZrMe [Ar and J for two methyl substituents coordinated to Zr on 2  31 In particular, the may seem unusual, it is not inconsistent with the Karplus relationship. sign and magnitude of heteronuclear coupling constants in some organometaDic complexes 32 have been rationalized in terms of torsion angles and stereochemistry at the metal centre. Complex 3.1 decomposes in C D solution over several days to give a red-brown 6  P {‘H} NMR spectrum. If a solution of 3.1 is stored solution that shows several peaks in its 31 at 298 K in a sealed J. Young NMR tube, a singlet attributable to methane is observed by ‘H NMR spectroscopy. 33 Although small crystals of 3.1 grow in pentane in the dark at —35 °C, rapid desolvation and decomposition prevent them from being analyzed by X-ray diffraction. Since Hf alkyl complexes are often less thermally sensitive than their Zr 2 has been undertaken. 34 the preparation of [NPN] *HfMe congeners, , 3.2, can be prepared as a pale yellow powder in high yield from 2.15 2 [NPN]*HfMe and 2.2 equivalents of MeMgCl in EtO (see Equation 3.1). The 31 P{’H}, 1 C{’H} H and 13 NMR spectra are very similar to those observed for 3.1, and are consistent with a complex that is a C symmetric monomer in solution with two inequivalent Hf—CH 3 groups that do not interconvert on the NMR timescale. The ‘H NMR spectrum of 3.2 in C D displays two 6 3 resonances: a doublet at ö 0.67 Hf—CH  JHP = 3 (  5 Hz) (Met), and a singlet at ö —0.21 (Me ). 5  By 1 C{ 3 ‘ H } NMR and HMQC spectroscopy, 3.2 has two doublets: MeA is at ö 55.1 Hz), and MeB is at 54.8  J 2 (  =  (= J 2  8  24 Hz). Again NOE difference spectroscopy is unable to  establish whether MeA is cis or trans to P. Although it is likely that MeA is cis to P, and MeB is trans to P in 3.1 and 3.2,30 it may be necessary to characterize 3.1 and 3.2 further, or to  prepare complexes such as [NPN]*MMe(Cl), to obtain additional support for this assignment.  90  The ORTEP representation of the solid-state molecular structure of 3.2 is shown in Figure 3.2. The five-coordinate complex is distorted trigonal bipyramidal at Hf, and the Me groups are axial and equatorial. The Hf—C (C39, C40) bond lengths to methyl groups cis and trans to P are the same, within error, at —2.22  A. Again, the [NPN]* ligand appears to hinge  the anude donors out of the equatorial plane with P—Hf—Ni and P—Hf—N2 angles of 70.10(12) and 72.09(13)°, respectively. The Hf—N, Hf—P, Hf—C bond lengths are similar to others reported in the literature. 35  I I  I [NPN]*HfMe 3.2 , Figure 3.2. ORTEP drawing of the solid-state molecular structure of 2 (effipsoids drawn at the  50%  probability level). All hydrogen atoms have been omitted for  clarity. Selected bond lengths  (A) and angles (°): Hfl—Pl 2.7861(14), Hfl—N1 2.092(4), Hfl—  N2 2.075(4), Hfi—C39 2.211(6), Hfl—C40 2.232(6), P1—Hfl—N1 70.10(12), P1—Hfi--N2 72.09(13), P1—Hfl—C39 86.79(19), P1—Hfi—C40 i78.Oi(18), N1—Hfl—N2 ii6.35(i7), C39— Hfi—C40 95.2(3).  91  . 2 3.2.2 Synthesis and reactivity of LNPNI*M(CHZPh) [NPN]*Zr(CHCH)  [NPN]*ZrCl (2.10) and 2.2 3.3, can be prepared from 2  equivalents of 2 C 5 H 6 C M gC1 H in Et 0, and is isolated as a heat- and light-sensitive yellow 2  [NPN]*H (2.8) and 4 Ph) 2 Zr(CH 3 6 are mixed powder in high yield (Scheme 3.3). When 2 together in C D solution, no new signals appear in the 31 6 H} NMR spectrum. Thus, this 1 P{ route to benzylzirconium complexes cannot be used as an alternative to the Grignard reaction described above. 37  Scheme 3.3.  2.2 BnMgCI 2 [NPN]*ZrCI 0 2 Et 2.10  3.3  The 31 P{’H} NMR spectrum of 3.3 in C D shows a singlet at 6  —7.2. The 1 H NMR  spectrum is consistent with the assignment of 3.3 as a five-coordinate C symmetric complex in solution. Once again, restricted rotation about N—C 0 gives rise to four inequivalent 3 groups, but singlets due to two of the four ArCH ArCH 3 groups overlap. There are two different benzyl groups that do not exchange on the NMR timescale. The benzylic protons appear as a doublet (ö 2.92,  J, 3  =  9 Hz), assigned to CH (A), and a singlet (ö 1.81), assigned 2  CH ) , in the ‘H NMR spectrum. By HMQC spectroscopy, CH to 2 @) appears as a singlet (ö 2 74.6) and CH (A) appears as a doublet (ö 73.0, 2  C {‘H} NMR spectrum. 3 2 = 22 Hz) in the ‘ J  92  Although 3.3 has not been characterized in the solid state, crystals of a derivative of D solutions of 3.3 at room 6 this complex suitable for X-ray diffraction were obtained from C temperature over one week. This derivative can also be prepared on a preparative scale when a toluene solution of 3.3 is stirred in the dark at ambient temperature for two days (see P {‘H} NMR Scheme 3.3). The red-orange product, 3.4, displays a singlet at 3 —5.2 in the 31 . The absence of C symmetry in the product is apparent in its ‘H D 6 spectrum acquired in C NMR spectrum. D are consistent with the formulation 6 C {‘H} NMR spectra of 3.4 in C 3 The ‘H and ‘ h ligand and a cyclometalated CH P of the complex as a C, symmetric monomer with one 2 [p]*  (‘JHH =  There are two doublets, each integrating to IH, at 3 2.28 ( JHH 1  =  7 Hz) and 1.75  H NMR spectrum (Figure 3.3). These resonances are assigned to 7 Hz) in the 1  3 singlets and dliastereotopic benzylic protons. The doublet at 3 2.28 overlaps with two ArCH can be located using ‘H-’H COSY. A second set of diastereotopic benzylic resonances is observed: a doublet of doublets integrating to 1H at 3 2.70 broad doublet integrating to IH at 8 1.85  (‘JHH =  JHH = 1 (  9 Hz,  3, = J  1 Hz) and a  9 Hz). These signals are assigned to the  ) protons of the onho-methy1 metalated [NPNI* ligand. The -4,6-Me Zr(-2-CH N 2 H 6 C observation of seven ArCH 3 singlets in the ‘H and ‘ C{’H} NMR spectra, and two benzylic 3 2 resonances in the ‘ CH C {‘H} NMR spectrum supports the proposed structure for 3.4. The 3 orlho-methyl metalated [NPN]* ligand will be denoted [NPNC]* because it coordinates to N, P, N, and C atoms on [NPN]* ([NPNCI*  =  MeC P(Ph)(2-(N-C 2,4-CH [(2-MesN-5) 3 2 H 6 -  h), has been [NPNC]*Zr(CH P . The proposed structure of 3.4, 2 )] 3 H 6 6-CH)-5-MeC ) confirmed by single-crystal X-ray diffraction analysis.  93  —  — 3 ArCH  Ph 2 ZrCH ArH  \  Mes 2 ZrCH Ph 2 ZrCH  Mes 2 ZrCH  JJJjI 7.0  6.0  1 5.0  2.0  . D 6 Figure 3.3. 400 MHz ‘H NMR spectrum of 3.4 in C  The ORTEP representation of the solid-state molecular structure of 3.4 is shown in Figure 3.4. Complex 3.4 features one 2 -CH ri P h substituent bound to Zr with a Zr—C39— -benzy1 Zr complexes that have Zr— 2 C40 angle of 85.74(1 1)°. This compares well to other T C—C angles in the range of 85 to  1000.38  The Zr—C bond lengths and interatomic distances  are also typical: the Zr—C39 bond length is 2.3027(19) A, and there is a distance of 2.6346(17)  A between Zr and C40. The C39—C40 bond is 1.462(3) A. In addition, the Zr—  , distances (Zr—C41 and Zr—C45), at 2.96 and 3.48 A, respectively, are too long to be 0 C considered bonding interactions. The two Zr—C bond lengths differ because the benzyl ligand is tilted to one side of the complex; the non-cyclometalated MesN substituent of [NPN]* is effectively blocking the other side of 3.4. The C40—C41 and C40—C45 bond lengths (1.410(3), 1.424(3) A) that are slightly longer than the remaining four C—C bond lengths in the phenyl ring, and the similarity of these four remaining C—C bond lengths to  94  2 39 One (2-CH each other, are all consistent with ri -coordination of the benzyl ligand to Zr. 2 )N group is coordinated through N2 and C38 to Zr with bond lengths of H 6 C 2 4,6-Me 2.1230(14) and 2.2807(19)  A,  respectively. The Zr—C38—C35 angle is 93.34(11)°. The  geometry at Zr is best described as distorted square pyramidal with C39 apical and P1, Ni, N2, and C38 basal. It appears that complex 3.3 has lost one equivalent of toluene to yield  3.4. The mechanism of toluene elimination is discussed in the following section.  ‘C38  Figure 3.4. ORTEP drawing of the solid-state molecular structure of [NPNC]*Zr(12 Ph) (3.4) (effipsoids drawn at the 2 CH  50%  probability level). Hydrogen atoms and carbon  atoms of the distal Mes substituent (except C ) have been omitted for clarity. Selected bond 0 lengths  (A)  and angles (°): Zrl—P1 2.7646(5), Zn—Ni 2.1132(14), Zrl—N2 2.1230(14), Zn—  C38 2.2807(19), Zrl—C39 2.3027(19), Zrl---C40 2.6346(17), C39—C40 1.462(3), P1—Zn—NI 71.65(4), P1—Znl—N2 70.21(4), Pi—Zrl—C39 133.09(5), Zri—C39—C40 85.74(11), Zni—C38— C35 93.34(1 1), Ni—Zri—N2 127.13(5).  95  To characterize dibenzyl complexes of group 4 in the solid state, the Hf analogue of 3.3 has been prepared. As with 3.1 and 3.2, the Hf dibenzyl complex is more heat- and light-  H 3.5, is SHS) [NPNI*Hf(C C 2 stable than 3.3, and could be characterized crystallographically. , gC1 H in Et 2 C 5 H 6 C 0, and is isolated as a pale 2 prepared from 2.15 and 2.2 equivalents of M D solution, the benzylic resonances 6 yellow powder in quantitative yield (Equation 3.2). In C appear as doublets at  2.59  J 3 (  =  7.6 Hz) and 1.59  J 3 (  =  H 2 Hz) (Figure 3.5) in the 1  1I resonances appear as CH P } NMR spectrum, the two 2 13 H 1 NMR spectrum. In the C{ doublets at ö 72.3  J 2 (  =  6 Hz) and 66.0  J 2 (  =  20 Hz). Thus, the structure of 3.5 in  h CH P solution is proposed to be five-coordinate and C symmetric with two distinct 2 substituents, one trans and one cis to P.  2.2 BnMgCI 2 [NPNJ*HfCI  (3 2)  0 2 Et 2.15  96  3 ArCH  ArH HtCH 2 Ph  Hf CH 2 Ph  515  5O  . D 6 Figure 3.5. 500 MHz 1 H NMR spectrum of 3.5 in C  The ORTEP representation of the solid-state molecular structure of 3.5 is shown in Figure 3.6. The complex is distorted trigonal bipyramidal at Hf, and has typical Hf—P and Hf—N bond lengths. 35 In the equatorial plane, the Hf—C39 bond length is 2.263(3) A, and the Hf—C39—C40 bond angle is 120.32(18)°. For the axial benzyl ligand trans to P, the Hf—C46 bond is 2.298(3) A, slightly longer than for Hf—C39, and the Hfl—C46—C47 angle is 118.74(1 8)°. The solid-state molecular structure is consistent with the solution data in that it shows two distinct r’-CH Ph groups coordinated to Hf. 2  97  Figure 3.6. ORTEP thawing of the solid-state molecular structure of [NPN]*Hf(tI1 Ph) 3.5 (effipsoids drawn at the 50% probability level). Hydrogen atoms and carbon 2 CH , atoms of the proximal Mes (except C have been omitted for clarity. Selected bond lengths  (A) and angles (°): Hfl—Pl 2.8228(7), Hfl—N1 2.079(2), Hfl—N2 2.1250(19), Hfl—C39 2.263(3), HfI—C46 2.298(3), C39—C40 1.495(4), C46—C47 1.514(4), NI—Cl 1.462(3), P1— HfI—Nl 69.96(6), Pl—HfI-.-N2 71.12(5), Pl—Hfl—C39 87.78(7), Pl—Hfl—C46 175.67(8), Nl—Hfl—N2 115.36(8), C39—Hfl—C46 96.49(10), Hfl—C39—C40 120.32(18)°, Hfl—C46—C47 118.74(1 8)°.  Benzyl ligands are known to coordinate to metals in the ri’-,  2  or r1 -bonding mode. 3  The 1 3 hybridized at the benzylic C, and the M—C(l—C 0 angle is close -bonding mode is sp to the 109.5° predicted for tetrahedral C. A good example of the r’-bonding mode of benzyl is . 4 P 2 Sn(CH h) The Sn—C—C 0 angles in tetxabenzyl tin are all nearly 1110 (110, 110, 112  98  and 114°), and the bonding is analogous to a simple organic compound without any unusual 0 of 40 If there is an interaction between M and C intra- or intermolecular interactions. -coordination mode may be present. For the ri 2 h, then the r CH P 2 -bonding mode, M—C— 2 0 angles of about C  900,  and a shortened M—C, 0 distance are typically observed, although a  41 For example, the solid-state molecular range of bond lengths and angles has been reported. ] ([N P h) 2 (CH P]Zr(CH 2 [N ) 3 structure of P  =  H determined by X-ray Ph] SiNCH 3 [(Me C P 2 )  50 angle of h group is present with a Zr—C—C -CH 2 r crystallography indicates that an P h) has at least three 4 P 2 ° In comparison, Hf(CH 3 0 distance of 2.835(4) A. 95.4(2)° and a Zr—C 50 angles are 88, 92, 93, and -benzyl groups, and the Hf—C—C 2 r  o4OA 101  Thus, there is some  -bonding observed for the benzyl ligand. Although other bonding variety in the degree of 2 3 they are not ligands, 4 ’ modes have been proposed for transition-metal bound benzyl 42 usually cited in discussions of group 4 benzyl complexes. In 3.5, the Hf—Ca—C angles (120.32(18)° and 118.74(18)°) are larger than those h) in the solid state. The Hf—C(x—C 4 P 2 observed for Hf(CH 30 angles are also larger than 3 hybridized C of ‘q’-benzyl, although a range of angles has also would be predicted for an sp Ph)(jLC1)] (M—C(x— 2 -bonding mode.’ For example, in [Cp*Cr(CH 1 been reported for the ‘q h) 0 Py) P 2 Cp*Cr(CH 0 121.4(3)°), and in ( C (M—C(x—C 124.0(6)°, M—C--C 0 119.5(5)°), the large M—Ca—Cxo angles may be explained by the steric influence of the bulky Cp* ligand. One  benzyl  ligand  in  the  complex  N’ h) Zr(CH N [O 9 M P 2  NN’Me] 2 ([O  =  [(2-  e] also features a large M—Ca—C angle (1 18.9(2)°). )CH (CH 2-O-3,5-C 4 5 C N M 2 H 6 ) Although the bis(aminophenolate) ligand is not very bulky, the coordination sphere of the octahechal complex is quite crowded.lTh Thus, the Hf—C(x—C 50 angles observed in 3.5 are within the range of literature values for i’-benzyl complexes, and may be slightly larger than  99  1110  h) because of the steric influence of the bulky mesitylamido 4 P 2 Sn(CH (found for )  substituents on [NPN]* or because of crystal packing.  Ph)z decomposition. 2 3.2.3 Kinetics of [NPN]*Zr(CH h) (3.4) and one equivalent of [NPNC}*Zr(q2CH P The formation of red-orange 2 Ph) (3.3) in C 2 D solution occurs over about two days 6 toluene from yellow [NPNI*Zr(CH with no detectable intermediates (see Scheme 3.3). The reverse of this reaction, formation of 3.3 from 3.4 in the presence of excess toluene is not observed. By monitoring the decomposition of three samples with different concentrations (25.9, 41.4, and 56.9 ± 2 mM) at 298 K over two days by NMR spectroscopy, the reaction was determined to be first order 8 has in 3.3. The decomposition of five 43.1 ± 0.8 mM concentration samples in toluene-d H NMR spectroscopy at 328 K., 338 K, 348 K or 358 K in a pre-heated been followed by 1 H NMR spectrum. The combination of NMR probe, or at 298 K by periodically acquiring a 1 integrals used to calculate the fraction of 3.3 is outlined in appendix two, as is a sample plot of ln[3.3] vs. time (at 338 K) used to determine kQb, and a discussion of the estimation of  errors. The Eyring plot of ln(k/1) vs. 1 /T is shown in Figure 3.7. From the Eyring plot, the activation parameters for the reaction are  =  , and 1 20.8 ± 0.4 kcal mo1  =  —10.3 ± 1.3  45 The negative value for the entropy of activation is consistent with the cal K mol’. 46 formation of an ordered transition state for the intramolecular reaction.  100  -10 —11 -12 -13 -14 -15 -16 -17 2.7  2.8  2.9  3.0  3.1  3.2  3.3  3.4  3 K’) lIT (x10 Ph) 3.3. [NPN]*Zr(CH , Figure 3.7. Eyring plot for the thermal decomposition of 2 Two possible mechanisms for the decomposition of 3.3 are illustrated in Scheme  3•447  In Path A, direct a-bond metathesis via a four-centre—four-electron transition state allows concerted bond forming (C—H of toluene, and Zr—C to [NPNC]*) and breaking (C—H of Ph) to yield 3.4. The second benzyl ligand is not directly involved in 2 NMes, and Zr—C of CH h Zr—CH P Path A. In Path B, toluene is lost via intramolecular ce-H abstraction from one 2 group to give [NPN]*ZrCHPh, a benzylidene intermediate. [NPNI*ZrCHPh accepts a proton from the ortho-CH 3 group on NMes to give cyclometalated 3.4.  101  CH linker in the intermediates, for clarity. —CH — Scheme 3.4. NPN* abbreviated with 2  Path B  Path A  -  5 H 6 C 3 CH  [o:” -  \ 5 H 6 C 3 CH  There are several examples of transition-metal benzyl complexes that form cyclometalated products with loss of toluene. The decomposition may go through a 48 whereas in other cases a a-bond metathesis mechanism is benzylidene intermediate, 9 Sigma-bond metathesis is usually accompanied by a negative entropy of invoked. 4 ’ 47 activation (zS  =  , since the ancillary ligand and benzyl ligand have K ) —10 to —24 cal mo1 1  to adopt an ordered geometry in the transition state for bond making and breaking to  102  46 Of course, ]igand cyclometalation reactions are also known for complexes without occur. ° If C—H activation occurs via a benzylidene or alkylidene intermediate, 5 benzyl substituents. 51 the entropy of activation is usually near zero, typical for cx-hydrogen abstraction processes. 2 For example, pattern. 5 ’ It should be noted, however, that there are many exceptions to this 47 h) ([PNP] [PNP]Y(CH P 2 =  =  e produces cyclometalated [PNP]’Y ([PNP]’ H Me]) [N(SiM C 2 P  e and toluene via a-bond metathesis since the e e Me SiM iM CH CH-)P [M P S N ( ) 2 ]  1t for the 53 The S formation of an alkylidene to C in the backbone of [PNP] is unlikely. reaction is —3 ± 3 cal mol’ 1K’, which is atypically close to zero for a reaction that proceeds via a-bond metathesis. The authors speculate that dissociation of a phosphine donor of [PNP] from the metal centre in the transition state might offset the negative entropy of 53 activation expected for this process. The negative entropy of activation for the decomposition of 3.3 is consistent with the reaction occurring via a-bond metathesis (Path A). To test this proposed mechanism, an isotopic labelling experiment has been performed. Complex 3.3 with perdeuterated benzyl . Et 0 5 and 2.10 in 2 D 6 C 2 groups can be prepared by the reaction of 2.2 equivalents of KCD [NPNJ*Zr(CD 3.3-d is dissolved in C , 2 ) 5 D 6 , transferred to an NMR tube, and D 6 When C ) D 2 C 5 D 6 (C 7 H heated at 55 °C for 3 h, a clear red-orange solution is observed. Toluene-d gives rise to a quintet at 6 2.09 in the ‘H NMR spectrum, which is consistent with the 4 occurring by Path A, since the ‘H is transferred directly from decomposition of 3.3-d, r2 NMes to the leaving toluene. In addition, there is no evidence for [NPNC]*Zr( , in the ‘H NMR spectrum of the product. Thus, the presence of a 6 S)), or 3.4-d CHD(C D 6  4 occurs by Path 7 is confirmed. If decomposition of 3.3-c4 benzy1 on 3.4-d -r perdeuterated 2 B, then 3.4-d 6 would be the expected product because of ‘H transfer from MesN to  103  Zr=C(D)Ph. A fraction of the reaction mixture can be separated from the solvent by GC, and the highest molecular weight peak of this fraction is at m/Z = 99 in the mass spectrum. . The 7 Thus, the results of GC-MS are consistent with the presence of toluene-d 7 lends further support to the a-bond 7 and toluene-d 14 to 3.4-d decomposition of 3.3-d metathesis mechanism proposed for this reaction.  e *M(CH iM [NPN] S . 2 ) 3.2.4 Synthesis and reactivity of 3 2 yields a mixture of products that includes The decomposition of [NPN]*ZrMe methane, as determined by ‘H NMR spectroscopy. Similarly, the evolution of toluene is D solution. To determine if 6 observed by ‘H NMR spectroscopy when 3.3 decomposes in C the cyclometalated [NPNCI* ligand can form via e]irriination of other alkanes from e 3.6, has been prepared and characterized. *Zr(CH iM 3 [NPN] S , 2 , pale yellow ) 2 [NPNI*ZrR SiMe in 2 LiCH Complex 3.6 can be prepared in high yield from 2.10 and 2.2 equivalents of 3  D features resonances 6 0 (Scheme 3.5). The ‘H NMR spectrum of C symmetric 3.6 in C 2 Et iMe groups: a doublet at ö 1.39 3 S 2 assigned to two distinct CH  ([,  =  7 Hz) and a singlet at 6  ) groups at 6 0.10 and —0.08, as well as the expected 3 0.04, and singlets due to two Si(CH P{’H} NMR spectrum of 3.6 shows a singlet at 6 —15.3. 3 resonances. The 31 ArH and ArCH H complexes. 54 iMe 3 Zr—C S The ‘H NMR spectrum compares well to other 2  104  Scheme 3.5.  2 [NPN]*ZrCI  IMe M 3 S 2 2.2 LiCH 0 2 Et  2.10  3.6  Upon stirring a toluene solution of 3.6 at ambient temperature in the dark for three days, a yellow to red-orange colour change occurs. Red-orange 3.7 is obtained in high yield P{’H} NMR spectrum of 3.6 shifts to ö —8.5 (see Scheme 3.5). The singlet observed in the 31 for 3.7, and the ‘H NMR spectrum is indicative of a loss of C, symmetry in the complex. In 3 singlets and one singlet integrating particular, the ‘H NMR spectrum features seven ArCH to 9H at  2 resonances are also . Four diastereotopic CH ) 3 —0.32 attributable to Si(CH  [NPNCI* observed. By analogy with the assignment of 3.4, 3.7 contains the cyclometalated Zr group are a doublet at ö 2.36 ( Mes—CH — ligand. Assigned to the 2 JHH 1 doublet of doublets at  1.56  (‘J,, = 11  11.8 Hz,  JHP =  =  11.8 Hz) and a  4 Hz), each integrating to IH. Assigned  Zr group are two doublets at ö 0.56 and —0.13, each integrating to IH i—CH 2 S 3 Me to the — with  JHH =  2 groups appear as a singlet {’H} NMR spectrum, the two CH ‘ C 11.4 Hz. In the 3  at ö 65.6 and a doublet at 8 64.1  J 2 (  =  3 8 Hz). In addition to the expected ArC and ArCH  C {‘H} NMR spectrum. 3 ) is observed in the ‘ 3 resonances, a singlet at 8 2.38 due to Si(CH The ORTEP representation of the solid-state molecular structure of 3.7 is shown in rI2CH (3.4). The C, h) 2 [NPNC]*Zr( Figure 3.8, and it bears a strong resemblance to P [NPNCI* ligand and one 3 SiMe 2 CH symmetric structure of 3.7 features the cyclometalated ligand bound to Zr. The geometry about Zr is distorted square pyramidal. The Zr—N, Zr—P,  105  and Zr—C bond lengths are similar to those in 3.4, although the Zr—C39 (2.218(2) slightly shorter in 3.7 (Zr—C39 is about 2.30  A) bond is  A in 3.4). The Zr—C39—Si angle is 124.79(1 1)°.  The Zr—C bond and the Zr—C—Si angle are similar to those observed for other group 4 54 The P—Zr—N angles are also both acute at about trimethylsilylmethyl complexes.  700,  as is  observed for the other [NPN]*Zr complexes reported here. D solutions of 3.6 over several days at 6 As expected, tetramethylsilane forms in C room temperature. Also, the formation of 3.7 from 3.6 appears to proceed without [NPNJ*ZrR to P{’H} NMR spectroscopy. The decomposition of 2 intermediates by 31 [NPNC]*ZrR may be a general mode of decomposition for these complexes, provided R does not contain [-hydrogens. 55 An investigation into the mechanism of formation of 3.6 has not been performed.  106  Figure  3.8.  ORTEP  thawing  of  the  3 S 2 [NPNC]*Zr(CH ) iMe , 3.7, (ellipsoids drawn at the  solid-state  molecular  structure  of  50%  probability level). Hydrogen atoms  (A)  and angles (°): Zrl—P1 2.7349(5),  have been omitted for clarity. Selected bond lengths  Zn—Ni 2.1237(15), Zrl—N2 2.1022(15), Zrl—C36 2.270(2), Znl—C39 2.218(2), C39—Sil 1.864(2), C35—C36 1.487(3), P1—Zrl-.--N1 71.77(4), P1—Znl—N2 69.19(4), P1—Znl—C39 118.37(6), P1—Zrl—C36 127.41(6), N1—Zrl—N2 131.71(6), Znl—C39—Sil 124.79(11), Zn— C36—C35 92.05(13).  SiMe 3.8, can be prepared from 2.15 and 2.2 equivalents of [NPNJ*Hf(CH , 2 ) 3 SiMe in Et 2 LiCH 3 0, in the same fashion as 3.6 (Equation 3.3). H NMR spectroscopy of 2 3.8 in C D indicates that the pale yellow complex has two 3 6 SiMe environments: a 2 Hf—CH doublet at 6 0.80  ([HP  =  6 Hz), and a singlet at 6 —0.30 are assigned to the Hf-CH TMS 2  protons, and two singlets are assigned to two distinct Si(CH ) groups at 6 0.10 and —0.10. 3 The P{’H} 31 and 13 H} NMR spectra are also consistent with 3.8 being a five-coordinate 1 C{ C symmetric complex with inequivalent 3 SiMe groups that do not exchange on the 2 CH  107  NMR timescale. Although El-MS was helpful in assigning the structure of 3.4, only peaks  [NPNI*H are seen in the mass spectra of 3.6, 3.7 and 3.8. due to 2 Si 3 Me  (3.3)  2 [NPN]*HfCI 0 2 Et 2.15  3.8  . 2 3.2.5 Attempted hydrogenolysis of [NPN]*MMe 2 in a sealed J. Young NMR D solutions of 3.2 are stored under 1 atm of H 6 When C tube for one month, there is no change in the colour of the solution, and no new signals appear in the 31 H} or 1 1 P{ H NMR spectra of the sample. When a toluene solution of 3.1 or 3.2 is stirred under 4 atm of H , the reaction mixture becomes brown immediately. However, 2 the solution reverts to yellow after about 5 mm., and no further colour changes are observed. There is also no reaction by 31 H} or 1 1 P{ H NMR spectroscopy, since the yellow product obtained upon work-up contains only peaks that can be attributed to starting material in its NMR spectra. The brown species has not been isolated or identified. The reaction of an organometa]lic complex with hydrogen gas to liberate an alkane and yield a metal hydride is also called hydrogenolysis. 56 The hydrogenolysis of late transitionmetal alkyl complexes is exothermic since the bond dissociation enthalpy of M—H is greater than for M—C. 57 The reaction of early transition-metal alkyl complexes with H 2 to yield metal hydrides is typically less exothermic, but can be spontaneous. 24 In addition, the hydrogenolysis of late transition-metal alkyl complexes often occurs by oxidative addition, a route that is not invoked for Zr([V) or Hf(IV) complexes. Instead, for early transition-metal  108  2 adds across the M—C bond via alkyl complexes, a a-bond metathesis mechanism in which H a four-centred transition state may be invoked. This is a preferable explanation for the reactivity of a Zr(IV) alkyl complex because it requires a vacant orbital on the metal centre,  , it may 2 58 If a Zr(IV) alkyl complex does not react with H but does not requite d electrons. ’ The 5 2 to interact with the metal. be because there is no readily accessible orbital for H inaccessibility itself may be due to electronic or steric factors, or a combination of the two. 2 For example, the presence of t-donating ligands, or bulky ancillary ligands, may prevent H ° 6 from approaching the M—C bond. 2 gas does not yield a metal hydride complex. In a The reaction of 3.2 with 4 atm of H related  system,  the  hydrogenolysis  of  ]HfMe N [P 2  ] N 2 ([P  =  SSiMe [PhP(CH N C P ) 2 iMe Ph] H yields 4 ]i-H) N ([P ( 2 , Hf) while a zirconium hydride is not obtained from the reaction of 2 ]ZrMe with H N [P ’ However, since Hf-N 6 . 2 2 complexes are rare, and have only been prepared from Hf diiodides in the presence of strong reducing agents, 61,62 it is unlikely that one would be obtained from the reaction of a Hf hydride with 2 gas. The formation of hydride complexes from 3.1 or 3.2 may be possible by a two-step N {[NPN]*M(CH ) }+ (M route: the synthesis of complexes of the type 3  =  Zr, Hf), followed by  reaction with H 2 in the absence of coordinating solvents or counterions. 63 Although the reactions of 3.3, 3.5, 3.6 or 3.8 with H 2 have not been attempted, the presence of benzyl or trimethylsilymethyl ligands is not likely to increase the reactivity of the complex since the steric crowding at the metal centre should be even greater. Although a Zr or Hf hydride complex has not been prepared by hydrogenolysis of 3.1 or 3.2, there are many other routes to early transition-metal hydrides that have not been attempted. Since the synthesis of metal-hydride precursors for N 2 activation from H 2 under mild conditions is a major goal outlined in this chapter, the use of metal hydride reagents  109  64 to obtain Zr or Hf such as lithium aluminum hydride, or other strong reducing agents hydrides holds limited appeal.  3.3 Conclusions. Zr and Hf alkyl complexes with the [NPN]* ancillary ligand are synthesized as yellow [NPN]*MC1 (M powders in high yield from 2 complexes (M  =  Zr, Hf R  =  =  2 Zr, Hf). By NMR spectroscopy, [NPN]*MR  Ph, 3 2 SiMe are monomeric C symmetric 52 CH ) Me, CH  coordinate species with two distinct alkyl groups that do not interconvert on the NMR [NPN]*HfMe and timescale. In addition, the solid-state molecular structures of 2  Ph) confirm the solution structures. [NPN]*Hf(CH 2 Whereas the Hf alkyl complexes are thermally stable and can be analyzed by X-ray [NPN]*ZrR complexes decompose over several hours to give either a mixture diffraction, 2 of products (R  =  Me), or cyclometalated [NPNC]*ZrR (R  =  Ph, or 3 2 CH SiMe by C—H 2 CH )  activation of the ancillary ligand. The two [NPNC]*ZrR complexes have been characterized in solution and in the solid state as C 1 symmetric five-coordinate complexes. The Ph) to give 2 2 [NPNC]*Zr(r12CH P h) and toluene is first decomposition of {NPN]*Zr(CH Ph) and occurs with AHt 2 [NPN]*Zr(CH order in ,  =  20.8 ± 0.4 kcal mol’, and AS  =  —10.3  1 mol . The negative value for the entropy of activation, and the fact that 1 ± 1.3 cal K [NPNI*Zr(CD yields toluene-d ) 5 D 6 C ) 5 D 6 C 2 decomposition of 2 7 and [NPNC]*Zr(CD indicate that the reaction proceeds via a-bond metathesis. 2 (M Hydrogenolysis of [NPNJ*MMe  =  Zr, Hf) does not yield hydride complexes under  the conditions employed here. In the absence of a hydrogenolysis route to Zr-N 2 complexes, [NPN]*ZrCl (2.10) and alkali metal a more direct route to dinitrogen complexes from 2  110  reducing agents is described in chapter four. The synthesis, characterization, and reactivity of 2 complex are presented in chapters four and five. a Zr-N  3.4 Experimental. 3.4.1 General experimental. Except where noted, experimental procedures follow those outlined in chapter two. GC-MS spectra were recorded on an Agilent series 6890 GC system with a 5973 mass selective detector.  3.4.2 Starting materials and reagents. SiMe was 2 LiCH Hydrogen gas was purchased from Praxair and used as received. 3 purchased from Aldrich as a IM solution in pentane that was taken to dryness, and recrystallized from pentane prior to use. Deuterated benzyl potassium was prepared from , freshly sublimed KOtBu, and BuLi in hexanes solution according to the 8 toluene-d 65 All other compounds were purchased from commercial sources and were used as literature.  received.  2 (3.1). To a stirred suspension of 2.10 (0.300 g, 0.419 mmol) in Et [NPN]*ZrMe 0 (10 mL) 2 at —35 °C in the dark was added methylmagnesium chloride (3.0 M in THF, 0.31 mL, 0.92 mmol) dropwise. The yellow suspension became translucent pale yellow as it warmed to rt, whereupon 1,4-dioxane (0.1 mL) was added. The reaction mixture was taken to dryness, and  hexanes (10 mL) and toluene (5 mL) were added to the yellow solid. The yellow suspension was filtered through Ceite, and the filtrate was taken to dryness to obtain a pale yellow  111  powder. The pale yellow powder was collected on a frit, washed with pentane (5 mL), dried under vacuum, and stored in the dark at —35 °C (0.225 g, 0.332 mmol, 80%). H NMR (C 1 , 500 MHz): ö D 6  =  7.54 (m, 4H), 7.07 (m, 2H), 7.02 (m, 1H), 6.93 (s, 2H), 6.90  (d, 2H, 2 Hz), 6.88 (s, 2H), and 6.12 (t, 2H, J-  = JHH =  7 Hz) (ArH), 2.51 (s, 6H), 2.14 (s,  ), 0.93 (d, 3H, 3 6H), 2.09 (s, 6H), and 2.00 (s, 6H) (ArCH  J  =  5 Hz), and —0.11 (s, 3H)  ). 3 (ZrCH , 202 MHz): D 6 P{’H} NMR (C 31  =  , 126 MHz): ö D 6 C{’H} NMR (C 3 ‘  —14.1 (s).  =  159.4 (d, 33 Hz), 139.4, 138.6, 137.5, 135.3 (d, 5 Hz),  135.1 (d, 3 Hz), 134.4, 132.1 (d, 13 Hz), 130.9, 130.4, 129.2 (d, 4 Hz), 129.1, 129.0, 128.3, ), 3 121.1 (d, 25 Hz), and 114.3 (d, 9 Hz) (ArC), 45.1 (d, 6 Hz), and 41.8 (d, 29 Hz) (ZrCH ). 3 21.1, 20.3, 19.1, and 18.9 (ArCH PZr: C, 71.07; H, 6.71; N, 4.14; Found: C, 71.35; H, 7.06; N, 4.08. 2 N 45 Anal. Calcd. for CH  2 (3.2). In the dark at —35 °C, MeMgC1 (3.0 M in THF, 0.78 mL, 2.34 mmol) [NPN]*HfMe 0 (10 mL). The mixture 2 was added to a stfrred suspension of 2.15 (0.840 g, 1.04 mmol) in Et was translucent pale yellow after 30 mm. at rt. 1 ,4-Dioxane (0.5 mL) was added to the reaction mixture and it was taken to dryness to obtain yellow solids that were extracted with hexanes (30 mL), followed by toluene (10 mL). The extracts were filtered through Celite, and the filtrate was taken to dryness to obtain a pale yellow powder (0.770 g, 1.01 rnmol, 96%). ‘H NMR (C , 500 MHz): ö D 6  =  7.53 (m, 4H), 7.06 (m, 2H), 7.00 (t, 1H, 7 Hz), 6.93 (s, 2H),  6.91 (d, 2H, 7 Hz), 6.90 (s, 2H), and 6.15 (dd, 2H, J  =  6 Hz, JHH  =  8 Hz) (ArH), 2.52 (s,  6H), 2.19 (s. 6H), 2.14 (s, 6H), and 2.00 (s, 6H) (ArCH ), 0.67 (d, 3H, JHP 3 (s, 3H) (HfCH ). 3  112  =  5 Hz), and —0.21  H} NMR (C 1 P{ 31 , 202 MHz): 6 D 6  =  , 126 MHz): 6 D 6 C{’H} NMR (C 13  —8.9 (s).  =  161.1 (d, 32 Hz), 139.1, 137.6, 137.0 (d, 5 Hz), 136.7,  135.1, 134.8, 132.0 (d, 13 Hz), 130.8, 130.4, 129.1, 129.0, 128.3, 120.1, 119.9, and 115.4 (d, , 21.1, 20.2, 19.0, and 18.9 (HfCH ) 10 Hz) (ArC), 55.1 (d, 8 Hz), and 54.8 (d, 24 Hz) 3 . (ArCH ) 3 El-MS (m/: 749 (1, [M  —  Me]j, 733 (2, [M  —  2MeJ), 556 (40, [2.8]j, 541 (100, [2.8  —  Me]j. PHf: C, 62.94; H, 5.94; N, 3.67; Found: C, 62.83; H, 6.26; N, 4.00. 2 N 45 Anal. Calcd. for CH  Ph) (3.3). To a stirred suspension of 2.10 (0.770 g, 1.07 mmol) in Et 2 [NPNI*Zr(CH 0 (15 2 0, 2.40 mL, 2 mL) at —35 °C in the dark was added benzylmagnesium chloride (1.0 M in Et 2.40 mmol) dropwise. The yellow suspension became translucent pale yellow as it warmed to rt, whereupon 1,4-dioxane (0.1 niL) was added. The reaction mixture was taken to dryness to obtain a yellow solid that was extracted with hexanes (10 mL) and toluene (5 mL). The extracts were filtered through Celite, and the filtrate was taken to dryness to obtain a yellow powder that was collected on a flit, washed with pentane (5 mL), dried under vacuum, and stored in the dark at —35 °C (0.795 g, 0.960 mmol, 89%). H NMR (C 1 , 300 MHz): 6 D 6  =  7.60  (t,  2H, 8 Hz), 7.53 (d, 2H, 7 Hz), 7.07 (m, 5H), 6.95 (m,  4H), 6.80 (m, 6H), 6.36 (d, 2H, 7 Hz), 6.33 (d, 2H, 7 Hz), and 6.02 (dd, 2H, J =  8 Hz) (ArH), 2.92 (d, 2H,JHP  =  5 Hz, JHH  , 2.17 (s, 12H), 2.03 (s, 6H), and 1.96 (s, 6H) ZrCH ) 9 Hz, 2  . ZrCH ) , 1.81 (s, 2H, 2 (ArCH ) 3 H} NMR (C 1 P{ 31 , 121 MHz): 6 D 6  =  =  —7.2 (s).  113  C{’H} NMR (C 3 ‘ , 75 MHz): D 6  =  159.1 (d, 31 Hz), 150.4, 146.0, 139.5, 138.9, 138.0, 136.2  (d, 4 Hz), 134.5, 134.3, 132.7, 132.6, 131.3, 131.1, 130.8, 130.4, 129.9 (d, 4 Hz), 129.3, 128.2, 127.2, 126.1, 122.0 (a, 5 Hz), 121.6, 120.6, and 114.3 (d, 9 Hz) (ArC), 74.6, and 73.0 (d, 22 Hz) (ZrCH ), 21.1, 20.3, 19.0, and 18.5 (ArCH 2 ). 3 N C 5 H P Zr: 2 C, 75.41; H, 6.45; N, 3.38; Found: C, 75.06; H, 6.65; N, 3.68. 3 Anal. Calcd. for 2  Ds) (3.3—d 6 C [NPN]*Zr(11CD 2 0 (3 2 ). KCD 14 5 (62 mg, 0.45 mmol) suspended in Et D 6 C 2 0 (5 2 mL) was added dropwise to a stirred suspension of 2.10 (0.145 g, 0.202 mmol) in Et mL) at —35 °C in the dark. The red-orange mixture was stirred at rt for 30 mm., and 1,4dioxane (0.1 mL) was added. The mixture was taken to dryness to obtain a yellow powder. The yellow powder was extracted with C D (1.0 mL), and the yellow extracts were filtered 6 through Celite into an NMR tube. ‘H NMR (C , 400 MHz): ö D 6  =  7.60  (t,  2H, 8 Hz), 7.53 (d, 2H, 7 Hz), 7.10  (m,  2H, 7 Hz), 6.96 (s, 2H), 6.82 (d, 2H, 8 Hz), 6.80 (s, 2H), and 6.02 (dd, 2H,JHP  =  IH), 7.08 (d, 5  Hz,JHH =  8 Hz) (ArH), 2.17 (s, 12H), 2.03 (s, 6H), and 1.96 (s, 6H) (ArCH ). 3 P{’H} NMR (C 31 , 162 MHz): ö D 6  =  —6.8 (s).  Ph) (3.4). Compound 3.3 (0.450 g, 0.540 mmol) was dissolved in 2 [NPNC]*Zr(12CH  toluene (15 mL) and stirred in the dark at rt for 2 d to obtain a clear, red-orange solution. The reaction mixture was taken to dryness to obtain a red solid that was collected on a frit, rinsed with pentane (5 mL), and dried under vacuum (0.390 g, 0.530 mmol, 98%). Crystals of 3.4 suitable for X-ray analysis were grown by slow evaporation of a benzene solution of 3.3.  114  ‘pp) OLZ ‘(Hv) (zil 9  =  f ‘ZH 8  = HHf  ct i  ‘HI ‘PP) 86c  ‘(ilt’ ‘m) 00L-cvL ‘(zH 8 ‘HI ‘p) cL ‘(zH 8 ‘HI ‘p) 19L  ‘(HI ‘m) 9 ‘(ilL ‘m) w9-c69 =  sJT-DD Aq  pu ‘!PD nonp p.jy s uojsudsns pudo  si’  1 3) aJAIN H u 9 9 :(zpç ooi7 ‘  si ujy sspnoio ‘p ppp  (iw ro) HOJ’I pu ‘ir  qm 1NN ‘p ‘Ado3sonDds IJ’IN Aq jduns ‘p uizAjw rJv uorinos  uro-par tjuq  rnqo oi  s “p-çç jo uopnlos 99  tj  ;°  çç v qm JJAIN u’ w piq s oqi pdd Da 9 (a L .L)Jz[DNJN] i’ wo Tur!xoddV p-vc) 1  H JOJ pDp3 JV D :JZdN ’ t’017 ‘N O9 ‘H cIL ‘3 :punoj I8 ‘N 9V9 ‘H IL ‘3 t (÷[uq] ‘001) 16 ‘(+[w  —  8z1 ‘oi) 1179 ‘([u J’\I] ‘) 179 ‘(+[JAII ‘) 17’L :/) —  HDv) £61 Pt ‘L61 ‘V0 ‘cot ‘to ‘V1 ‘911 ‘(vHDz) (zil 8 ‘p) wc9  TJ1  ‘ç99 ‘(3w) (zH 6 ‘p) LiII pu ‘(zH 01 ‘P) ocii ‘t8II ‘çiI ‘L17i1 ‘8ti1  ‘V8i1 ‘98i1 ‘98i1 ‘68i1 ‘V0I ‘t’•OI ‘cici ‘iCI ‘Vi1 ‘0I ‘I ‘LcI O17I ‘(ZH i ‘P) 1c171 ‘Lt’C1 ‘(zH  ‘(ZJ-{  c ‘p)  ‘p) c17I ‘917I ‘99c1 ‘0•9cI ‘i9I ‘9’9I ‘OLI ‘(zH  1 ‘P) WLI ‘86I ‘(ZH Li ‘p) oLcI ‘(zH i ‘p) 9091  =  (s) ç_  1 3) IJ’\IN {Hj u 9 9 :(zj-jj,j 101 ‘ =  9  :(zjj,j  i91  3) I1’IN 1 U 9 ‘ }a {R  R3JZ ‘ZH 6 ‘HI ‘pci) c8I ‘(HDv) (Hc ‘s) ç6 t ‘ZH L ‘HI ‘P) 9LI ‘(sJH  pu ‘(-jç ‘s)  ‘(j-ç ‘s)  1,7O  ‘(ps ‘s) I.Z ‘(Hg ‘s) 9  ‘p) 8ii ‘(i-w ‘s) 6i1 ‘(sp”HH3JZ ‘ZH I ‘p) 86’9 pu ‘(zH9 ‘(zH  = dHf  ‘ZH 8  = HHf  = cIH[ZH  6  ‘(jjç ‘s)  ‘zH  Lii  HH.[HI  =  ‘HI ‘pp) %9 ‘(ZH 9  = dHf  L ‘HI  ‘pp) OLi ‘Q-iw) (zH 8 ‘Hi ‘ZH  8  = HH[  ‘Hi ‘pp) ii•9  8 ‘Hi ‘) 8179 ‘(zH 8 ‘HI ‘p) IW9 ‘(He ‘s) 069 ‘(ZR 8 ‘HI ‘p) 169 ‘(i-it’ ‘w) 00L ‘(i-u ‘w)  9VL ‘(zn 1 ‘ZR 8 ‘HI ‘pp) 617L  ‘(ZR  1 ‘ZR 8 ‘HI ‘pp) 19L  9  =  1 0017 ‘EID) >IJAIN H  (ZJ-{JAJ  IH, 9 Hz, 1 Hz, ZrCHaHbMes), 2.29 (s, 3H), 2.27 (s, 3H), 2.26 (s, 3H), 2.21 (s, 3H), 2.04 (s, , 1.85 (bd, 1H, 9 Hz, ZrCHaHbMes). (ArCH ) 3H), 2.02 (s, 3H), and 1.96 (s, 3H) 3 , 162 MHz): D 6 H} NMR (C 1 P{ 31 GC-MS: 3.48  —  3.59  mm.  —5.3 (s).  =  H]). D 7 (m/,’): 99 (15, [C  [NPN] *Hf(cHPh) (3.5). In the dark at —35 °C, benzylmagnesium chloride (1.0 M in 0, 2.0 mL, 2.0 mmol) was added to a stirred suspension of 2.15 (0.721 g, 0.900 mmol) in 2 Et 0 (10 mL). The solution was translucent pale yellow after 30 2 Et  mm.  at rt, whereupon 1,4-  dioxane (0.5 mL) was added. The pale yellow suspension was taken to dryness to obtain a yellow solid that was extracted with hexanes (20 mL), followed by toluene (10 mL). The yellow extracts were filtered through Celite, and the filtrate was taken to dryness to obtain a pale yellow powder (0.805 g, 0.880 nimol, 98%). X-ray quality crystals were grown by slow evaporation of a benzene solution of the compound. , 500 MHz): 3 D 6 H NMR (C 1 7.02  (t,  Hz,JHH =  (s,  7.52 (m, 2H, 8 Hz), 7.13  2H, 7 Hz), 6.97 (s, 2H), 6.94  1H, 7 Hz), 6.73 8  =  (t,  (t,  (t,  IH, 7 Hz), 7.07 (m, 4H, 8 Hz),  2H, 8 Hz), 6.85 (d, 2H, 7 Hz), 6.82 (s, 2H), 6.76  1H, 7 Hz), 6.49 (d, 2H, 7 Hz), 6.28 (d, 2H, 7 Hz), and 6.06 (dd, 2H,J  8 Hz) (ArH), 2.59 (d, 2H,JHP  =  =  , 75 MHz): 3 D 6 H} NMR (C 1 C{ 13  =  Ph), 2.19 (s, 6H), 2.17 (s, 6H), 2.13 2 7.6 Hz, CH  , and 1.59 (d, (ArCH ) 6H), and 1.96 (s, 6H) 3  H} NMR (C 1 P{ 31 , 121 MHz): 3 D 6  (t,  2H,JHp =  Ph). 2 2 Hz, CH  —5.8 (s). =  160.3 (d, 31 Hz), 150.2, 146.4, 138.9, 138.7, 137.4,  134.7, 134.6, 133.8, 133.6, 132.6 (d, 12 Hz), 131.1, 130.8, 129.7 (d, 4 Hz), 129.4, 129.1, 129.0, 128.5, 127.3, 126.9, 122.1, 121.0, 120.8, and 115.6 (d, 10 Hz) (ArC), 83.2 (d, 6 Hz), and 81.5 . (ArCH ) , 21.1, 20.2, 19.1, and 18.5 3 (HfCH ) (d, 21 Hz) 2 2 C, 68.22; H, 5.84; N, 3.06; Found: C, 67.98; H, 5.93; N, 3.44. 3 Anal. Calcd. for 2 N C 5 H P Hf: 116  SiMe (3.6). To a stirred suspension of 2.10 (0.750 g, 1.05 rnmol) in Et [NPN]*Zr(CH 2 ) 3 0 2 0 (2 mL) 2 SiMe (0.217 g, 2.30 mrnol) in Et 2 LiCH (5 mL) at —35 °C in the dark was added 3 dropwise. The solution became clear pale yellow instantly and was stirred at rt for 30  mm.  1,4-Dioxane (0.5 niL) was added to obtain a pale yellow suspension that was taken to dryness. Toluene (10 niL) was added to the yellow solid, and the suspension was filtered through Celite. The yellow filtrate was taken to dryness to obtain a pale yellow powder. The powder was collected on a fit, washed with pentane (5 mL), and dried under vacuum (0.815 g, 0.994 mmol, 95%). ‘H NMR (C , 500 MHz): 6 D 6 7.03  (t,  =  7.60  (t,  2H, 8 Hz), 7.53 (d, 2H, 7 Hz), 7.10  (t,  1H, 7 Hz), 6.97 (s, 2H), 6.85 (s, 2H), 6.84 (d, 2H, 7 Hz), and 6.06 (dd,  Hz,JHP =  2H, 7 Hz),  2H,JHH =  8  ), 1.39 3 6 Hz) (ArH), 2.57 (s, 6H), 2.17 (s, 6H), 2.11 (s, 6H), and 1.96 (s, 6H) (ArCH  (d, 2H, JHP  =  SiMe 2 CH ) , 0.10 (s, 9H, Si(CH ), 0.04 (s, 2H, 3 ) 3 SiMe 2 CH ) , and —0.08 (s, 7 Hz, 3  9H, Si(CH ). ) 3 P{’H} NMR (C 31 , 202 MHz): 6 D 6  =  —15.3 (s).  S1Me (3.7). A yellow solution of 3.6 (0.350 g, 0.427 mmol) in toluene 2 [NPNC]*Zr(CH ) 3 (10 niL) was stirred for 3 d at rt until the reaction mixture  was clear,  bright red-orange. The  reaction mixture was taken to dryness to obtain an orange powder that was recrystallized from benzene. The red-orange crystals were collected on a frit, rinsed with pentane (5 niL), and dried under vacuum (0.273 g, 0.373 mniol, 87%). Red single crystals of 3.7 were grown by slow evaporation of a benzene solution of the compound. ‘H NMR (C , 500 MHz): 6 D 6  =  7.59 (d, 1H, 8 Hz), 7.56 (d, IH, 8 Hz), 7.49 (dd, 2H, 11 Hz,  7 Hz), 7.05 (m, 3H), 7.02 (d, 1H, 8 Hz), 7.01 (s, 1H), 6.98 (bs, 1H), 6.96 (s, 1H), 6.94 (d, 1H,  117  8 Hz), 6.88 (s, 1H), 6.44 (dd, 1H,JHH =  =  8  Hz,JHP =  6 Hz), and 6.28 (dd, IH,JHH  =  8 Hz,JHP  6 Hz) (ArH), 2.53 (s, 3H), 2.51 (s, 3H), 2.36 (d, 1H, 11.8 Hz, ZrCHaHbAr), 2.25 (s, 3H),  ), 1.56 (bdd, 1H, J 3 2.21 (s, 3H), 2.18 (s, 3H), 2.04 (s, 3H), and 1.99 (s, 3H) (ArCH Hz, J  =  =  11.8  4 Hz, ZtCHaHbAt), 0.56 (d, 1H, 11.4 Hz, ZrCHCHdTMS), —0.13 (d, 1H, 11.4 Hz,  ). ) 3 ZrCHCHdTMS), —0.32 (s, 9H, Si(CH P{’H} NMR (C 31 , 202 MHz): 6 D 6 C{’H} NMR (C 3 ‘ , 126 MHz): 6 D 6  =  =  —8.5 (s). 160.9 (d, 32 Hz), 157.0 (d, 27 Hz), 140.3, 138.3, 137.8,  137.7, 136.6, 136.1, 135.8, 135.2, 135.0, 134.7, 133.8, 133.5, 131.8, 131.7, 130.5, 130.4, 130.2, 129.6, 129.2, 127.7, 116.5, 116.2, 115.5, 115.2, 114.4 (d, 10 Hz), and 113.4 (d, 10 Hz) (Arc), ), 2.38 3 65.6, and 64.1 (d, 8 Hz) (ZrCH R), 21.3, 21.1, 20.4, 20.3, 20.0, 19.6, and 18.7 (ArCH 2 ). ) 3 (Si(CH Anal. Calcd. for 3.71.5(C ): N H 6 C 5 H P 2 SiZr: 1 C, 72.12; H, 6.88; N, 3.30; Found: C, 72.38; 8 H, 6.84; N, 3.51.  SiMe 2 [NPN]*Hf(CH ) 3 z (3.8). To a stirred suspension of 2.15 (0.385 g, 0.479 mmol) in 0 (5 mL) at —35 °C in the dark was added 3 2 Et SiMe (0.099 g, 1.05 mmol) in Et 2 LiCH 0 (2 2 rnL) dropwise. The reaction mixture became clear yellow instantly and was stirred at rt for 30 miii. 1,4-Dioxane (0.5 mL) was added, and the reaction mixture was taken to dryness to obtain a yellow solid that was suspended in toluene (10 rnL). The suspension was filtered through Celite, and the filtrate was taken to dryness to obtain a light yellow powder (0.370 g, 0.408 mmol, 86%). ‘H NMR (C , 500 MHz): 6 D 6  =  7.58  (t,  2H, 8 Hz), 7.51 (d, 2H, 7 Hz), 7.09 (m, 2H), 7.01  IH, 7 Hz), 6.97 (s, 2H), 6.87 (bs, 4H), and 6.10 (dd, 2H,JHII  118  =  8 Hz,J 11  =  (t,  6 Hz) (ArH), 2.58  ), 0.80 (d, 2H, 3 (s, 6H), 2.19 (s, 6H), 2.17 (s, 6H), and 1.97 (s, 6H) (ArCH  J  =  6 Hz,  SiMe 2 CH ) . ), —0.30 (s, 2H, 3 ) 3 SiMe 2 CH ) 3 , 0.10 (s, 9H, Si(CH ), —0.10 (s, 9H, Si(CH ) 3 H} NMR (C 1 P{ 31 , 202 MHz): D 6  =  C{’H} NMR (C 13 , 126 MHz): ö D 6  —7.5 (s). =  160.7 (d, 31 Hz), 140.1, 138.2, 137.4, 136.6, 134.6,  133.1, 133.0, 130.8, 129.3, 129.1, 128.9, 128.8, 120.4, 120.2, and 115.6 (d, 10 Hz) (ArC), 72.3 ), 3.74, and 2.86 3 SiMe 2 (CH ) , 20.9, 20.2, 19.9, and 19.3 (ArCH (d, 6 Hz), and 66.0 (d, 20 Hz) 3 ). ) 3 (Si(CH Anal. Calcd. for 2 4 C 6 H P N H Si 6 1 f: C, 60.87; H, 6.77; N, 3.09; Found: C, 61.00; H, 6.81; N, 3.10.  Thermal Decomposition Studies. The rt decomposition of 3.3 was monitored by NMR spectroscopy to determine the order of the reaction. Complex 3.3 (15.0, 24.0 or 33.0 mg)  was weighed into a 3-mL vial and 0.70 mL of C D was transferred to the vial by syringe. 6 The yellow solution was transferred to an NMR tube and the sample was analyzed periodically over 2 d by 1 H NMR spectroscopy. To determine the rate constant for the reaction at each of five different temperatures, 3.3 (25.0 mg) was weighed into a 3-mL vial and dissolved in 0.70 mL toluene-d . The solution was transferred to an NMR tube and 8 immediately frozen at —10 °C until it could be analyzed. Each sample was placed in the NMR probe heated to 328, 338, 348, or 358 K, and the reaction was followed by 1 H NMR spectroscopy. The first 1 H NMR spectrum was measured two mm. after the sample was inserted into the probe. From the plot of ln[3.3] vs. time, no further time appeared necessary for the sample to reach thermal equilibrium before the first 1 H NMR spectrum was collected. One sample was stored at rt, and monitored periodically over 2 d.  119  [NPN]*MMC with 4 atm H 2 (M Reaction of 2  =  Zr or Hf). In a typical experiment, yellow  3.1 (0.300 g, 0.444 mmol) was dissolved in toluene (10 mL) in a 200-mL Teflon-sealed thickwalled bomb. The solution was degassed by three freeze-pump-thaw cycles and filled with ) behind a blast shield. The solution 2 2 at 77 K. The flask was warmed to rt (4 atm H H became pale brown after the solvent thawed, but after about 5  mm. the reaction mixture was  clear yellow again. The yellow solution was stirred in the dark for 4 h. (For 3.2, the reaction mixture was stirred for 3 d since starting material decomposition was not a concern.) After  , an aliquot of the yellow reaction mixture was analyzed by 2 venting the pressure of H } NMR spectroscopy, and a second aliquot was concentrated under vacuum to obtain 31 H 1 P{ a yellow powder that was analyzed by NMR spectroscopy. Visually, and by NMR spectroscopy, only starting material was present.  . Pale yellow 3.2 (50 mg, 66 iimol) was 2 Reaction of [NPN]*HfMe with 1 atm H 6 dissolved in CD  (-  1 mL), filtered, and transferred to a J. Young NMR tube. The solution  2 was degassed by three freeze-pump-thaw cycles (frozen at —10 °C, thawed under flow of H gas) and sealed (1 atm H2) at rt. The solution was monitored over 4 weeks. There was no H NMR spectra. } or 1 31 H 1 colour change and no new peaks were observed in the P{  3.5 References. ‘A) Ziegler, K. Belgium Patent 553, 362, 1953. B) Natta, G.; Pino, P.; Corradini, P.; Danusso, F.; Mantica, E.; Mazzanti, G.; Moraglio, G. J. Am. Chem. Soc. 1955, 77, 1708. C) Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. 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P.; Winston, S.;  Fryzuk, M. D. Organometallics 2004, 23, 3372. A) Schrock, R. R.; Parshall, G. W. Chem. Rev. 1978, 78, 243. B) Spessard, G. 0.; Miessler, G. L. Organometallic Chemistry; Prentice-Hall, Inc.: Upper Saddle River, New Jersey, 1997, p. 118. 56  A) Lee, H.; Desrosiers, P. J.; Guzei, I.; Rheingold, A. L.; Parkin, G. J. Am. Chem. Soc. 1998,  120, 3255. B) Gell, K. I.; Schwartz, J. J. Am. Chem. Soc. 1978, 100, 3246. ‘  58  Labinger, J.; Bercaw, J. E. Oiganometallics 1988, 7, 926. Gell, K. I.; Posin, B.; Schwartz, J.; Williams, G. M. J. Am. Chem. Soc. 1982, 104, 1846.  125  Lauher, J. W.; Hoffman, R. J. Am. Chem. Soc. 1976, 98, 1729. 59 60  Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. Soc. 1983, 105, 1401.  61  Fryzuk, M.D.; Corkin,J. R.; Patrick, B. 0. Can.J. Chem. 2003, 81, 1376.  62  Bernskoetter, W. H.; Olmos, A. V.; Lobkovsky, E.; Chink, P. J. Organometallics 2006, 25,  1021. Jordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L. Organometallics 1987, 6, 1041. 63 64  Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hilihouse, G. L.; Bercaw, J. E. Organometallics  1985, 4, 97. Kneifel, H.; Bayer, E. Angew. Chem.  mt. Ed. 1973,  126  12, 508.  Chapter Four Synthesis and Structure of Zirconium Dinitrogen Complexes  4.1 Introduction. Molecular nitrogen is unreactive, in part because it has a strong triple bond (945 kJ mol’), a large HOMO-LUMO gap, and it lacks a dipole. 1 In 1965, however, the first dinitrogen complex, , 2 Initially prepared serendipitously 2 ( 5 ) 3 {Ru(NH 1 N] i was reported. from N 0 and O 4 H 2 2 x 3 RuCl H , the complex was later intentionally synthesized from N 2 gas, , C1 and Zn. 5 ) 3 Ru(NH 3 Today, N 2 complexes of most of the transition elements and the lanthanides are known. 4 Diriitrogen coordinated to a transition metal from groups 7 to 10 gate transition metals for the purpose of this discussion) is usually unactivated or only weakly activated, with an N—N bond length similar to that of N 2 gas (1.0975  5 Transition A).  metals from groups 4 to 6 (termed early transition metals here) can activate N 2 strongly because they are more reducing. The N—N bond in ) (j.i-ri ([PNP]ZrC1) : 2 N i is 1.548(7) longer than the N—N single bond in hydrazine (1.47  A,  6 A).  Most late transition-metal dinitrogen complexes are electronically saturated species prepared without strong reducing agents or harsh conditions. For example, 1 ( 5 ) 3 [Re(PMe 1 N)]Cl forms when Re(PMe C1 is dissolved in EtOH in the presence of N 5 ) 3 7 In contrast, . 2 early transition-metal dinitrogen complexes are usually synthesized by reducing a metal halide complex with a strong alkali metal reducing agent. Reduction of [PNP]ZrC1 3 with Na/Hg amalgam provides 2 ) 8 6 Q ([PNP]ZrCl) : ) N 1 , whereas potassium graphite (KC t-rl reduction of 2 ]ZrC1 provides ) N [P N ([P ( : 2 ]Zr) ii (N—N bond: 1.43(1) ji-ii N  127  A)  (Figure  4.1).8  (i2 Recently, the reduction of [NPN]ZrC1 HF) with KC 2 8 to give {[NPNjZr(THF)}  : q 2 N) r (N—N bond: 1.503(3)  A)  has been reported. 9 2 Me Si, N—SiMe 2 i P 2 Pr P Cl—Zr  / )  Cl  -  Na/Hg  /\  Pi  N.  2  2 N  2 Pr’  \,  “Cl  SiN\_.., 2 Me  2  2 Me  CI  Cl 8 KC  2  Ls/i  2 N  8 KC 2  S1 2 Me Me S 2 i  2 N  Figure 4.1. Zirconium dinitrogen complexes (silyl methyl substituents of [P ] omitted). N 2  Early transition-metal N 2 complexes can be synthesized directly from low-valent metal complexes and N . The Nb(III) complex, 3 2 JNbCH reacts with N N 2 [P , 2 to give diamagnetic JNb(CH N {[P ) 3 Q : 1 ) 2 N } i-i i , with an N—N bond length of 1.280(7)  A  (Figure 4.2).’°  Complete cleavage of the N—N triple bond is also achieved from the direct reaction of N 2  128  with a reduced metal complex; two equivalents of [Ar(R)N] Mo(III) (Ar 3  =  ,R 3 H 6 C 2 3,5-Me  =  CH reduce N 2 3 C(CD ) 2 by six electrons to yield two equivalents of 3 [Ar(R)NJ M oEN (Figure 4.2).h1  Early transition-metal hydrides can also activate 2 N ) . Z (Cp” ( : 2 jt’q N r) (Cp”  =  1,3-  -C forms when two equivalents of 93uLi are allowed to react with Cp” ) 3 H (SiMe 2 ) 3 ii 5 ZrC1 2 (Scheme  4.1).12  The initial product of the reaction, ) 3 Z Cp” C ) 2 r(H)(CH H(CH , decomposes  to give a cyclometalated Zr hydride, H -3-(SiM Cp”(1-SiMe C 2 5 ) 3 ZrH, _) C H e that activates . 2 N  Me  2  I  Ph  _—.  Nb  N2 -  LJ-S,  2  R RN.. Ar  / )‘N— Mo—N  N  R 2 N  R  2 R”N......  Ar”  Ar, Ar  Ar = 3,5-Me 3 H 6 C 2 R=3 )(CD C(CH 2 )  (I  R  \Ar  Figure 4.2. Reactions of low-valent early transition-metal complexes with N 2 (silyl methyl substituents of {P ] omitted). N 2  129  ________  Scheme 4.1. 2 SiMe  Si 3 Me  2 •ZcH  4 ‘BuLl SI 3 Me  2  .  M’CI  Me S 3 i S1 3 Me  2  3 S1Me  Zr  \  3 S1Me  N Si 3 Me  3 e Si 3 Me 3 Me  Although many N 2 complexes are known, predicting the conditions that will lead to their formation is a challenge. Ancillary ligand, metal, solvent, and N 2 pressure are important factors in determining whether N 2 activation occurs rather than activation of the solvent, 13 or 4 formation of a reduced product that does not contain N 15 or , 2 the ancillary ligand,’ formation of a mixture of products. Chelating it-acceptor ligands can facilitate synthesis of early transition-metal N 2 complexes because they stabilize reduced species. It is an exciting time in N 2 research since ancillary ligand design is at the core of several [Cp* Z r(rl ( recent major breakthroughs. 16 In 1974, the synthesis of 2 ) from 2 ) 2 ‘-N ii-ri’ ] :rI ‘-N ZrC1 and Na/Hg amalgam was reported. Cp* 2 17 The bridging end-on bound N 2 is slightly activated (N—N bond: 1.182(5)  A), and hydrazine is produced in high yield upon addition of  ZrH and free N 2 HC1 to the complex. The addition of H 2 to the complex provides Cp* 18 In . 2 2004, the synthesis of 2 [(1] M 5 H 4 Z ( : ) Ji-11 r1 N C r] e ) from 2 -rCl (r1 M 5 H 4 Z C e ) and Na/Hg amalgam was reported.’ 9 N 2 in this complex is strongly activated (N—N bond: 1.377(3)  A),  and it reacts with H 2 to yield 2 [(r M 5 H 4 Z ( : ) H ji-rl r(H)] 1i N C e ) with two new N—H  130  bonds. Thus, the use of tetramethylcyclopentadiene rather than pentamethylcyclopentadiene . 2 changed the coordination mode, bond length and reactivity of N 8 reduction of 2 complex by KC In this chapter, the synthesis of a dinuclear Zr-N 2 is described. N [NPN]*ZrC1 2 is coordinated side-on to the two Zr atoms, as revealed by h, PMe P , and 2 3 single crystal X-ray analysis. Coordinated THF can be replaced with Py, PMe h) and in solution. An PMe P and these adducts are characterized in the solid state (Py and 2 attempt to synthesize a Hf-N 2 complex is also presented.  4.2 Results and Discussion. . (t12:12N {[NPN]*Zr(THF)} ) 4.2.1 Synthesis and structure of 2  Deep  blue-green  , 4.1, (Ir12:112N 2 {[NPN}*Zr(THF)} )  can be prepared from  2 (2.10) and 2.2 equivalents of KC [NPN]*ZrCl 8 in THF under 4 atm of N 2 (Equation 4.1). Black crystals of 4.1 are obtained upon work-up in 79% yield. Initially, a Zr-N 2 complex could not be isolated using this method, although there were signs that an N 2 complex formed: the reaction mixture turned bright green and a peak attributable to a dimeric [NPN]*Zr species was apparent in the mass spectrum. There is also evidence that a Zr-N 2 complex forms under other conditions (i.e., 2.2 equivalents KC , THF, 1 atm N 8 , or five 2 equivalents Na/Hg, THF, 4 atm N ), but in all cases, the green reaction mixture transforms 2 to a beige powder during work-up.  131  4.4 KC, N 2  2  (4.1) THF  2.10 4.1  2 complex is possible if the THF used for the reaction is The isolation of a Zr-N rigorously H 0- and 0 2 -free, if the reaction mixture warms slowly to room temperature 2 2 bath: —116 °C), and if the mixture is vigorously stirred and the flask (EtOH/liquid-N periodically inverted over the course of the reaction. If a deep purple or blue-green colour is , then a high yield of 4.1 is 2 observed during the fiist hour after the flask is charged with N generally obtained. It is unclear why 4.1 can be isolated under these conditions, whereas 2 complexes are extremely air decomposition is observed otherwise. It is known that Zr-N 2 in the and moisture sensitive, and that vigorous stirring will increase the concentration of N reaction mixture. Another factor that may have complicated the isolation of 4.1 is its apparent decomposition in the absence of THF. Crystalline samples are dried under vacuum briefly  (- 15 mm.)  prior to analysis because 4.1 becomes an off-white powder when it is stored  under vacuum for prolonged periods. The powder contains a benzene-soluble fraction, and a fraction that is insoluble in benzene, water, THF or DMSO. The benzene-soluble fraction is 2 (2.8), as determined by 1 [NPNI*H H and 31 P{’H} NMR spectroscopy, El-MS and microanalysis. The insoluble white fraction has not been characterized. The mechanism of the decomposition of 4.1 under vacuum remains a mystery.  132  . Both 3 P{’H} NMR spectrum of 4.1 in THF-d There is a singlet at 6 5.0 in the 31 phosphines in the proposed dimeric structure are equivalent. The ‘H NMR spectrum (Figure 3 groups in the C h 2 4.3) shows four singlets between 6 2.2 and 1.7 due to four distinct ArCH symmetric complex, as well as the expected ArH resonances. Singlets due to coordinated THF appear at 6 3.54 and 1.69, and partially overlap with resonances due to free THF in the C{’H} NMR spectrum, the expected arylmethyl and aromatic 3 ‘H NMR spectrum. In the ‘ carbon signals, as well as resonances attributable to free and coordinated THF, are observed. There are two equivalents of THF in the crystal lattice of 4.1 as revealed by ‘H NMR . The results of combustion analysis are also consistent with the D 6 spectroscopy of 4.1 in C formulation 4.12THF. Crystalline samples of 4.F2THF are stable, and can be stored for months at —35 °C. Prior to use, crystalline samples can be dissolved in THF and dried (with careful monitoring) to obtain a green powder that does not contain solvent of crystallization, which is convenient for determining stoichiometry. In the mass spectrum of 4.1, there is a peak at  =  1320 that is assigned to [M  —  2THF]  ArCH3  TH F ArH  THE  • • •  7.5  7.0  6.5  6.0  5.5  • • • •  . • • .  5.0 4.5 (ppm)  • • . •  4.0  . 8 Figure 4.3. 500 MHz ‘H NMR spectrum of 4.1 in THF-d 133  • • . .  3.5  • • • •  3.0  •  2.5  •••  2.0  1.5  Little is known about the mechanism of formation of early transition-metal dinitrogen complexes, although some relevant information can be gleaned from the literature. Potassium graphite (KG ) has a reduction potential sini1ar to potassium metal, although its 8 ° Like elemental potassium, 2 power decreases as electrons are transferred to the substrate. 8 has become a widely used 8 occurs via one-electron transfer steps. KG reduction by KC reducing agent for metal complexes because it is easy to work with on a multi-gram scale, and graphite is the only by-product, in addition to KCI, for example, if metal chlorides are reduced. Cyclic voltarnmetry of 2 ) (R C -rC1 (i R 4 H 5 Z  Chemical  reduction  , H) shows that a 3 Me, Et, SiMe  —1.7 V occurs to yield the Zr(III) species [(re  172 reversible one-electron reduction at E ) rCl R 4 H 5 G Z ’ 2 ]  =  of  TiC1 Gp 2  produces  the  Ti(III)  species,  , which is observed by ESR spectroscopy. Although some Zr(III) and TiC1 2 [Na(THF)J[Cp ] Hf(III)  complexes  are  stable  and  have  been  structurally  characterized,  others  24 A Ti(H) dinitrogen disproportionate to give a mixture of M(H) and M([V) species. complex,  -N8), G i(i 1 h)) SiMe ( 4 H 5 P T (i 2  has  been  25 characterized crystallographically,  2 complexes are unknown, likely due to the stronger whereas discrete mononuclear Zr(TI) N reduction potential of Zr compared to Ti. [NPN]*ZrCl to One proposed route to 4.1 involves the one-electron reduction of 2 . Disproportionation of this Zr(III) anion is [K(THF),L]([NPN]*ZrG1 ) produce a species like 2 [NPN]*ZrGl and a solvated [NPNI*Zr(II) intermediate, such as , expected to give 2 , along with two equivalents of KC1. Although N 2 [NPN]*Zr(THF) 2 is a weaker donor than most solvents or Lewis bases, the formation of strong hard-hard bonding interactions 2 is a thermodynamic driving force for Zr-N between Zr and N 2 complex formation. Since 2 (i.e., N 2 to N the first step in the reduction of N ) occurs at a higher potential than the 2  134  jZr 2 N Zr j, the formation of a formally 4 2 N 2 to 4 subsequent reduction steps (e.g., N (N species. This is one Zr ) dimer may be facile compared to the initial formation of a 2 2 complexes of the early transition possible explanation for the prevalence of dinuclear N ) is expected to be much more Lewis basic 2 metals. In addition, a species such as Zr(N , which may allow the formation of a dinuclear complex. The mechanism of 2 than N dinitrogen activation by reduced Zr species is still unclear, probably because the conditions 2 complexes are somewhat incompatible with required for the synthesis of most Zr-N characterizing intermediates spectroscopically, or monitoring reactions over time. 8 under identical conditions used to When 2.10 is reduced with 2.2 equivalents of KC  , blue-green 4.1 does not form. Instead, the reaction 2 obtain 4.1, but in the absence of N H} NMR 1 P{ mixture turns brown. When an aliquot of the reaction mixture is analyzed by 31 spectroscopy, singlets at ö —14.6 and —15.4 are observed due to the major diamagnetic P containing products, along with minor products such as 2.8, and other unidentified species. No peaks at m/> 556 (2.8) are observed by El-MS. The major products could not be separated from each other for further characterization. 2 can lead to Reduction of early transition-metal halide complexes in the absence of N solvent activation, ancillary ligand activation, or formation of a reduced complex that does not contain N . Solvent activation by reduced species is exemplified by C—O cleavage of 2 27 whereas ancillary ligand 26 or C—H activation of toluene to give an i’-benzy1 complex, THF, J Zr) N 2 2 from activation is exemplified by the formation of dimeric ri -phenyl-bridged ([P 6 ]ZrC’ N [P . 2  The reduction of 3 /PEt mixtures with sodium amalgam gives 4 ZrC1  15 Likewise, ] as a forest green Zr(III) compound with bridging chlorides. 2 ( [ZrC1 ) 3 PEt 3 ({PCP] sodium amalgam reduction of [PCP]ZrC1  135  =  1 ) under ilVIe CH C P [1,3-(Pr S ) 2 5 ] 3 H  28 There is insufficient evidence to determine if any of these reactions . 2 Ar yields {PCP] ZrC1 has occurred for the reduction of 2.10. 4.1ThN is obtained. It should be noted , blue-green 2 2 N 5 When 2.10 is reduced under ‘ 2 gas is used, possibly because a N that ‘ -labelled 4.1 cannot be isolated if a glass bulb of 15 2 N 5 2 from a N 2 is not attained in the flask at room temperature. When 15 pressure of 4 atm of N 2 is isolated in high yield as a black crystalline solid. There N 15 small lecture bottle is used, 4.1is a doublet  JPN = 2 (  , where a 2 N 5 P{’H} NMR spectrum of 4.1-’ 6.7 Hz) at 6 5.0 in the 31  2 at 6 0) in singlet was observed for 4.1. There is also a doublet at 6 116.6 (relative to MeNO H} NMR spectra indicate 1 N{ H} and 15 1 P{ N{’H} NMR spectrum (Figure 4.4). The 31 5 the ‘ 4.1ThN although ‘ N can only be observed to 5 that an AA’XX’ spin system is present in 2  P nucleus ( couple to one 31 JPN 2  P nuclei are magnetically N and 31 0). Since the two 15  inequivalent, N 2 evidently does not rotate about the Zr---Zr axis in 4.1.  122  120  118  114 11.6 (ppm)  112  110  . 8 2 in THF-d N 5 H} NMR spectrum of 4.1-’ 1 N{ Figure 4.4. 40 MHz 15  2 confirms that the N 5 The presence of a signal in the ‘ N {‘H} NMR spectrum of 4.1-’ 5 N source of N 2 gas. At this time, it is difficult to correlate the 15 N 2 in the complex is 15 2 chemical shift in dinitrogen complexes with the coordination mode or extent of N  136  29 The majority 2 complexes. activation. A wide range of such chemical shifts is known for N of side-on N 2 complexes listed in Table 1.2 have 15 N chemical shifts between 6 495 and 621, (jt-H) ([NPN]Ta) Q .tand the chemical shift of hydrazine is 6 690. The 15 N chemical shifts of 2 -N are 6 —20.4 and 163.6. The 6.7 Hz P-N coupling is similar to other ri’:r1 ) 2  JNP  values  observed for 15 2 complexes with phosphine ligands, N ° although the reported values of 2 3 JNP 2 complexes is unreported or N cover a wide range, 31 and in many cases P-N coupling in 15 unobserved. The ORTEP representation of the solid-state molecular structure of 4.1 is shown in Figure 4.5, and the arrangement of P, N, and 0 about Zr is illustrated in Figure 4.6. The dinuclear complex features one THF molecule, and one facially coordinated [NPN per Zr. 2 is bound side-on to both zirconium centres with a slight butterfly or hinge distortion; the N angle between the two ZrN 2 planes is 166°. The two halves of the molecule are related by a two-fold rotation axis that bisects the N—N bond; 4.1 is C 2 symmetric in the solid state. The N—N bond length is 1.503(6)  A, which corresponds to reduction to N , or hydrazide. The 4 2  Zr—N bond lengths to N 2 are slightly different: Zri—N3 is 2.023(3) 2.089(3)  A, and Zrl—N3’ is  A. The Zr—Ni and Zr—N2 bonds are 2.184(3) A and 2.224(3) A, respectively. The  Zr—Pi bond is 2.6777(10)  A, and the Zr—0 bond is 2.371(2) A. The geometry around Zr is  best described as distorted trigonal bipyramidal with 0 and P donors apical and Ni, N2 and the dinitrogen fragment equatorial. As with other complexes of [NPNI*, the P—Zr—NI and P—Zr—N2 angles are acute at 71.84(8), and 73.42(8)°, respectively.  137  Figure  4.5.  ORTEP  drawing  of  the  solid-state  molecular  structure  of  {{NPNj*ZrC ( 2 ) I112:1 FHF)} 4.1 (ellipsoids drawn at the 50% probability level). Carbon 12N , atoms of the proximal Mes substituents (except for C) and all hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles (°): Zrl—P1 2.6777(10), Zn—NI 2.184(3), Znl—N2 2.224(3), Zrl—O1 2.371(2), Znl—N3 2.023(3), Zrl—N3’ 2.089(3), N3--N3’ 1.503(6), P1—Zn—Ni 71.84(8), P1—Znl—N2 73.42(8), N3--Znl—N3’ 42.85(15), Zri—N3’—Zri’ 135.02(15), Oi—Zrl—Pi 154.14(7), Pi—Zr—N3 82.00(8).  138  P1  N2  N2’  01’ P1 N2 N2’ Ni 01 N3  Ni’  01’ Ni’ P1’  Ni 01  Figure 4.6. Two views of the stereochemistry around Zr in 4.1.  2 symmetric in the solid state, but Complex 4.1 is C  h 2 C  symmetric in solution. The  N core that is 2 mirror plane of symmetry in the solution structure encompasses the Zr N is butterfly-distorted in solution, a 2 butterfly-distorted in the solid state. Thus, if Zr 2 from one side of the Zr---Zr axis to the other may be fluxional process that flips N responsible for the apparent mirror plane on the NMR timescale. DFT calculations on a model compound of 2 ,i-i N show that a butterfly-distorted structure r1 ]Zr) N ([P ( : ) (147.8° between ZrN 2 planes) is 11.2 kcal mol’ more stable than the planar structure found in the solid state, 32 and Raman spectroscopy provides evidence that a butterfly-distorted .i)} 3 H 6 C 2 {[PNP]Zr(O-2,6-Me conformation of the compound exists in solution. Like 4.1, Q r ([PNP] : ii 2 ) N  =  2 1) is butterfly-distorted (152.6° between ZrN PiMe [ePr S N 2 ) CH  2 bonds to planes) (Figure 4.7), with two halves of the dinuclear complex equivalent, and N Zr with two different Zr—N bond lengths (2.034(4) and 2.082(4)  33 A).  Also, a singlet is  apparent in the 31 P{’H} NMR spectrum of the complex, implying that if the butterfly  139  2 experience both sides of the Zr---Zr distortion exists in solution, a fluxional process lets N axis.  Figure 4.7. Structure of 2 ) 3 H 6 C {[PNP]Zr(O-2,6-Me ( : ) p-1i ri N } .  Complex 4.1 resembles 2 (t-ri {[NPN]Zr(THF)} : ) ri N , reported by the Fryzuk group in 2005. This dark purple complex forms in high yield from the reaction of 2.2 equivalents  of KC 8 with [NPN]ZrCl(THF) under I or 4 atm of N . Like 4.1, there is a singlet in the 2 P{’H} NMR spectrum (ö —5.6) and the complex appears to have C 31 h symmetry in solution. 2  In the solid state, one [NPN] and one THF ligand coordinate to each Zr, and N 2 is bound side-on to two Zr centres. The N—N bond is 1.503(3)  A,  identical to that of 4.1, and the  other bond lengths and angles are similar between the two structures. The Zr-N -Zr core is 2 planar, not butterfly-distorted, in { [NPN] Zr C HF) } 2 (j..t-r : ) N r . Compared to other side-on bound Zr-N 2 complexes, 4.1 and {[NPN]ZrCfHF)} (ii2 :ri 11 ) 2 N have long N—N bonds, although neither are as long as the N—N bond in  Q {[PNP]ZrCl} : ) 2 N ii -Ti (1.548(7)  A),  which contains the longest intact N—N bond  observed for a metal complex. 34 2 Z (Cp” ( : ) jiN r r) (Cp” similar N—N bond length to 4.1, within error, at 1.47(3)  140  =  12 A.  -T1 2 1,3-(SiMe ) 3 H 5 C has a Other side-on bound Zr-N 2  ]p-i1 N ({[P ( : ) Zr} N r (1.43(1) complexes contain somewhat shorter N—N bonds: 2  8 A)  35 A)  and  [0i M 5 H 4 Z 0 : ) 2 1-r1 r1 N C r] e ) (1.377(3)  19 and A)  (ji-i (rac-BpZr) : ) 2 N r (1.241(3)  are discussed in detail in chapter one.  (.N *Zr(py)} . : ) JJ.. . 4.2.2 Synthesis and structure of { [NPN] 2 Qtr12:r12N 2 {[NPN]*Zr(Py)} , 4.2, can be The pyridine adduct of the Zr N complex, ) 2 H solution (Equation 4.2). The dark evergreen 6 prepared from 4.1 and excess Py in C complex appears to form instantly, and is isolated in high yield as a dark green powder upon work-up. In contrast to 4.1, complex 4.2 can be stored under vacuum for several hours without any noticeable decomposition, possibly because Py is bound more tightly to Zr than THF is. The results of combustion analysis of 4.2 are consistent with the formula given, and a peak corresponding to [M  —  Py] is apparent in the mass spectrum.  (4.2)  4.2 There is a singlet in the 31 P{’H} NMR spectrum of 4.2 in C D at ö 6.0, and the ‘H 6 and ‘ C {‘H} NMR spectra are also consistent with the C symmetric structure proposed. In 3 the 1 H NMR spectrum (Figure 4.8), there are three singlets at  ö 2.0 assigned to ArCH 3  groups; although four singlets should appear based on the symmetry of the complex, the singlet at ö 2.03 integrates to 24H, indicating that two of the ArCH 3 groups have accidental  141  3 magnetic equivalence. In the 13 H} NMR spectrum, the expected four distinct ArCH 1 C{ H and 13 H} NMR spectra contain 1 C{ resonances are apparent. The aromatic regions of the 1 the expected peaks for Py and [NPN]*. ArCH3  ArH and PyH  7.5  7.0  6.5  6.0  5.5  4.5 5.0 (ppm)  4.0  3.5  3.0  2.5  2.0  Figure 4.8. 500 MHz 1 H NMR spectrum of 4.2 in C . D 6  , can be prepared from 4.1 and Py-d 10 4.2-d 5 by the same method used to prepare 4.2. The singlet in the 31 H} NMR spectrum is at 6 6.0, not 1 P{ shifted from that of 4.2. The 1 H NMR spectrum of 4.2-d 10 in C D is nearly identical to that 6 of 4.2, except that the mukiplet at 6 7.12 and the triplet at 6 6.55 are absent, and the multiplet at 6 6.01 integrates to only 4H. Thus, these resonances are assigned to coordinated Py in 4.2. There is a peak assigned to [M  —  ] in the mass spectrum. ‘ 5 Py-d N-labelled 5  , can be prepared from 4.12 N 5 4.2-’ 2 and Py in C N 15 H 6  142  2 that } NMR spectrum of 4.2-N 31 H 1 solution. There is a 1:3:1 triplet at 6 6.0 in the P{ N P nucleus couples to two magnetically inequivalent 15 corresponds to an AXX’ (each 31 nuclei) spin system with  JPN = 2  7 Hz, and 2 JpN’  =  3 Hz. A multiplet appears at 6 118.2 in the  N{ 15 H} NMR spectrum that corresponds to an AA’XX’ spin system with 1 =  3 Hz, and 1 JNN’  =  JNP = 2  7 Hz, 2 JNP’  N P and two 15 2 Hz. As for 4.1, the magnetic inequivalence of the two 31  2 does not freely rotate about the Zr---Zr axis in 4.2. nuclei indicates that N The ORTEP representation of the solid-state molecular structure of 4.2 is shown in Figure 4.9, along with selected bond lengths and angles. Two views of the arrangement of N and P donors around Zr are shown in Figure 4.10. The dinuclear structure is similar to that observed for 4.1. The N—N bond length is 1.481(5) A, about the same as the N—N bond length observed for 4.1, within error. Similar to 4.1, there are two sets of similar length Zr—N bonds: the Zrl—N5 and Zr2—N6 bond lengths average to 2.00 A, and the Zrl—N6 and Zr2— 2 unit is slightly canted: the N—N bond is N5 bond lengths average to 2.09 A. Thus, the N not exactly perpendicular to the Zr---Zr axis. One Py is coordinated to each Zr, and the Zrl—N7 and Zr2—N8 bonds to Py are the same within error at about 2.44 A. These are within the expected range, but are slightly longer than the Zr—N bond to Py in Py) 2.13, which is 2.3889(1 6) [NPN]*ZrC1 ( 2  A, and may be due to the trans influence of the p  donor in 4.2. The bond lengths and angles between [NPN]* and Zr are similar to those in 4.1 and the other [NPN}*Zr complexes reported here. There is a butterfly distortion in the 2 planes meet at a 168° angle. N core: the two ZrN 2 Zr  143  Figure 4.9. ORTEP drawing of the solid-state molecular structure of , 4.2 (ellipsoids drawn at the 50% probability level). Carbon atoms of the proximal r N : ti 2 )  Mes substituents (except C) and all hydrogen atoms have been omitted for clarity. Selected bond lengths  (A)  and angles (°): Zrl—P1 2.6699(12), Zn—Ni 2.203(4), Znl—N2 2.166(4),  Zrl—N5 2.002(4), Zrl—N6 2.092(4), Znl—N7 2.448(4), Zr2—P2 2.6725(12), Zn2—N3 2.172(4), Zr2—N4 2.218(4), Zr2—N5 2.097(4), Zr2—N6 2.011(4), Zr2—N8 2.441(4), N5—N6 1.481(5), N5—Zrl—N6 42.33(14), N6—Zn2—N5 42.19(14), P1—Znl—N7 109.51(14), N7—Znl—N5 119.68(13).  144  156.80(9), N1—Znl—N2  N7 P2 N3  N2  N4 N8 N3 P2 N2  N6 Ni N4  NO  N7  P1  Figure 4.10. Two views of the stereochemistry around Zr in 4.2.  , previously prepared in the r N (jt{[NPNZr(Py)} : 2 Complex 4.2 resembles ) 36 This dark green complex is synthesized from the bright purple THF adduct Fryzuk group. h symmetric in solution and in the solid state. 2 , and appears C 1 N (l.i-ri {[NPN]Zr(THF)} : 2 ) The solid-state molecular structure of the complex confrms that one Py is coordinated to 2 is coordinated side-on to two Zr atoms, as is observed for the THF each Zr and that N adduct. The two Py molecules adopt a trans configuration about the Zr---Zr axis. The N—N bond length is 1.503(2)  A,  2 unit is also canted with respect to the Zr---Zr axis: and the N  Each Zr atom has a 2.0453(14)  . As with 2 A and a 2.0819(1 3) A bond to N of coordinated N  N core is planar. The other bond lengths are 2 the THF adduct of this complex, the Zr similar to those of 4.2. H 6 37 so it is likely to displace THF from 4.1 in C Py is a stronger Lewis base than THF, solution spontaneously. Although both 4.1 and 4.2 are intensely coloured green compounds, an instant blue-green to dark evergreen colour change is apparent when excess Py is added  145  to a benzene solution of 4.1. In addition to the donor strength of Py, the synthesis of 4.2 is facilitated by the low volatility of Py: upon work-up, THF and even the solvent will be {[NPNJ*Zr(Py)}(JI removed before Py. No evidence for an asymmetric complex such as *  N {Zr[NPNI UHF) } is observed, although [NPN] -supported :r1 rj 2 )  { [NPN] Zr(Py) } (ji  36 This asymmetric adduct forms along with the bis-Py N is known. : 2 1 r ) {Zr[NPN](fHF)} and bis-THF adducts upon dissolving the bis-Py adduct in THF. il have another thing in common: they N (Ji-r {[NPNZr(Py)} : 2 Complex 4.2 and ) 2 complex. In contrast, can be readily prepared by the addition of Py to an N N ri (i-r : ) { {PNP] Zr(OAr) } 2  Q-r :11 ‘-Ni’) cannot be prepared directly 2 ZrCp) and ([PNP] 1  from 33 . Instead, these complexes must be prepared by the alkali i N (J1-ri ([PNP]ZrC1) : ) 2 OAr). Thus, the [PNP]ZrCl ( metal reduction of separately prepared precursors, such as 2 2 complexes can be tuned electronically and sterically by the [NPN] and [NPN]* ligated Zr-N simple addition of a donor molecule to a solution of 2 N -r1 and 4.1, T1 Q {[NPN]ZrCfHF)} : ) respectively.  In  addition,  rI N) (,i-r {[PN]Zr(PhCN)} : 2 -  has  been  prepared  and  2 complex, as well 36 and other adducts of the [NPN]-supported N characterized in solution, 2 complex are waiting to be synthesized. as many other adducts of the [NPN]*supported N Qir12:r12N core of 4.1 by replacing THF with other donor 2 {[NPNj*Zr} If tuning the ) ligands is a major goal of this chapter, it should be determined what effect, if any, Py has on the  structure  of the  2 Zr-N  complex.  In  addition  to  comparing  4.1  to  4.2,  N) (B). (.t-r {[NPN]Zr(Py)} 2 N (A) will be compared to : ri (i-r {[NPN]ZrrHF)} : 2 ) } NMR spectra of 4.1 and A shift upfield by 1 ppm for 31 H 1 The singlets observed in the P{ Py adducts 4.2 and B. The N—N bond lengths for all four compounds are the same, within ) bonds are slightly shorter (‘—O.O2 2 error. The Zr—P and Zr—N (to N  146  A)  in A than in B,  whereas these bonds are essentially the same for 4.1 and 4.2. So far, no major differences exist among these four complexes, except for the identity of the donor itself. Thus, a comparison between 4.1 and 4.2 will not be complete until vibrational analysis and supporting DFT calculations are performed. The UV-Visible absorption spectra of 4.1 and 4.2 are provided in section 4.2.4.  4.2.3 Phosphine adducts of {[NPN]*Zr)z(.L12:12Nz). In addition to THF and Py adducts of N complex can be readily prepared. 2 of the Zr  phosphine adducts {Zr[NPN]*},  0 solution (Equation 4.3). Upon 2 3 in Et 4.3, can be prepared from 4.1 and excess PMe 0, a colour change from deep blue-green 2 3 to a solution of 4.1 in Et addition of excess PMe to bright emerald green is observed. Complex 4.3 is isolated as a hexanes-soluble green powder in quantitative yield upon taking the reaction mixture to dryness. As occurs with 4.1, complex 4.3 decomposes under prolonged exposure to vacuum to a beige powder that contains 2.8 and a white insoluble solid. In contrast to 4.1, 4.3 is also unstable in the solid state and can decompose spontaneously at ambient temperature or at —35 °C. Samples of 4.3 are synthesized immediately before use, or are stored for a few days in hexanes solutions 3 at —35 °C. Small crystals of 4.3 can be obtained from with a small amount of added PMe 3 at —35 °C overnight. Unfortunately, single toluene/HMDSO in the presence of PMe crystals suitable for X-ray analysis could not be obtained, due in part to the solubility of the complex in non-polar solvents, and to its tendency to decompose.  147  xs PMe 3 (4.3) 0 2 Et  4.1  4.3  Complexes 4.1 and 4.2 are C h symmetric in solution and each Zr atom is coordinated 2 to one [NPNI* and one THF or Py molecule. In contrast, complex 4.3 appears to be P{’H} NMR spectroscopy. Two doublets at 6 5.1 and —33.1 D by 31 6 asymmetric in C  J= 2 (  44 Hz) and a singlet at 6 2.5, each integrating to 1P, are apparent (Figure 4.11). The downfield signals are due to coordinated [NPN]* and the signal at —33.1 is due to . The 44 Hz coupling is consistent with two-bond P-P coupling of trans 3 coordinated PMe } NMR 31 H 1 38 Thus, the P{ disposed phosphines on an early transition-metal complex. spectrum suggests that one Zr is coordinated to [NPN]*, and the other Zr is coordinated to [NPNI* and PMe 3 groups, a H NMR spectrum, there are eight singlets due to ArCH . In the 1 3 doublet at 6 0.27 ( JPH 2  =  , and ArH resonances 3 6 Hz, 9H) attributable to coordinated PMe  consistent with 4.3 being a C, symmetric dimer. The absence of resonances for free or H and 13 C {‘H} NMR spectra also supports the proposed structure. coordinated THF in the 1  148  10  6  2  -2  -6  -10  -14  -18  -22  -26  -30  44  4  (ppm) . D 6 P{’H} NMR spectrum of 4.3 in C Figure 4.11. 162 MHz 31  0 solution because 2 As with Py adduct 4.2, complex 4.3 appears to form instantly in Et there is a blue-green to emerald green colour change upon addition of the phosphine. The 3 is volatile. If the reaction is carried choice of solvent for this reaction is critical because PMe out in toluene, 4.1 is isolated upon work-up. 3 in Et 0 2 2 and PMe N 15 2 can be readily prepared from 4.1N 15 Isotopically labelled 4.3-  H NMR spectra P{’H} and 1 by the method used to prepare 4.3. At room temperature, the 31 } NMR spectrum shows 15 H 1 D are identical to those of 4.3, whereas the N{ 6 2 in C N 5 of 4.3-’ two broad singlets at  119.3 and 117.9. Since attempts to grow single crystals of 4.3 were  hindered by its high solubility and its tendency to decompose, a different phosphine was chosen  to  prepare  an  asymmetric  adduct  of  . (N 2 {[NPN]*Zr} )  Benzene-soluble  2N {Zr[NPNI*}, 4.4, can be prepared from 4.1 and excess 1)Me h)}Ot112:11 {{NPN1*Zr( P 2 ) h in toluene solution (Equation 4.4). The complex is obtained as an emerald green PMe P 2  149  powder in 82% yield upon work-up. Complex 4.4 can be placed under vacuum for several hours without decomposition, which is necessary for the complete removal of excess h. PMe P 2  (4.4)  4.1  4.4  Similar to 4.3, there are two doublets at 6 7.3 and —22.5  o  (= J 2  46 Hz), and a singlet at  D (Figure 4.12). Again, the doublet at 0 6 1.9 in the 31 H} NMR spectrum of 4.4 in C 1 P{  —  h coordinated to Zr, and the downfield resonances are due to PMe P 22.5 is assigned to 2 3 singlets, a doublet at 6 coordinated [NPNJ’. In the ‘H NMR spectrum there are eight ArCH 0.80  (J  =  h, and peaks in the ArH region consistent P(CH P 2 ) 6 Hz) due to coordinated 3  with the C, symmetric structure proposed for 4.4.  150  I -I  12  8  4  0  -4  -8  -12  -16  -20  -24  -28  (ppm)  ]) 6 C H} NMR spectrum of 4.4 in . 1 P{ Figure 4.12. 162 MHz 31  h by the same PMe P 2 and 2 N 15 2 can be prepared from 4.1N 15 Isotopically labelled 4.4D is similar to 6 2 in C N 5 P{ H} NMR spectrum of 4.4-’ 1 method used to prepare 4.4. The 31 . There is a 3 that of 4.4, but with additional P—N coupling apparent at 253 K in toluene-d doublet of doublets of doublets at 6 7.3  JPN ( = 46 Hz, 2 J 2  6 —1.9, and a doublet of doublets at 6 —22.5  =  4 Hz,  JPN = 2  JPN = 7 Hz). It is unclear why the ( = 46 Hz, 2 J 2  N. There are two AA’XX’ multiplets singlet at 6 —1.9 is not split by 15 Hz,  JPN =  7 Hz), a singlet at  JNN = 2 (  8 Hz,  JPN = 2  4  8 at 253 K at 6 119.0 and 118.0, N{’I-l} NMR spectrum in toluene-d 7 Hz) in the 15  each integrating to iN. The ORTEP representation of the solid-state molecular structure of 4.4 is shown in Figure 4.13, along with selected bond lengths and angles. Two views of the arrangement of N and P donors around Zr are shown in Figure 4.14. As expected from the NMR spectra of the complex, 4.4 is asymmetric; there is one [NPNI* coordinated to each Zr, but Zr2 also  151  h. The N—N bond length is 1.488(2) PMe P has a coordinated 2  A,  the same as that in 4.1,  within error. The Zr—P bond lengths to [NPNI* (Zrl—P1 2.6967(6), Zr2—P2 2.6445(6)  A) are  h is much longer at PMe P similar to those of 4.1 and 4.2, but the Zr2—P3 bond length to 2 2.9139(6)  A.  The Zr2—P3 bond length is similar to other long Zr—P bonds to tertiary  39 Unlike in 4.1 and 4.2, three of the Zr—N bond lengths phosphines reported in the literature. to N 2 are similar (Zrl—N3, Zrl—N4, and Zr2—N3 average to ‘—2.04 A) and the Zr2—N4 bond is longer (2.1153(17)  Ph. As with 4.1 and 4.2, 2 A), possibly due to the steric influence of PMe  1 symmetric 2 planes of 165° in the C there is a butterfly distortion between the two ZrN solid-state structure. P1 and P2 are staggered across the Zr---Zr axis (P1_Zrl—Zr2—P2 torsion angle is 179.9°), whereas P1 and P3 are nearly eclipsed (P1—Zrl—Zr2—P3 torsion N core is either planar, or there is 2 angle is 7.8°). Since 4.4 is C symmetric in solution, the Zr 2 to sample both sides of the Zr---Zr axis on the NMR a fluxional process that allows N  timescale.  152  Figure  4.13.  ORTEP  drawing  of  the  Ph) 2 2 -N { [NPN] *Zr} (i-i:i }) { [NPN] *Zr(PMe  solid-state  molecular  structure  of  4.4 (effipsoids drawn at the 50% probability  level). Carbon atoms of the proximal Mes substituents (except C ) and all hydrogen atoms 0 have been omitted for clarity. Selected bond lengths  (A)  and angles (°): Zrl—P1 2.6967(6),  Zr2—P2 2.6445(6), Zn—NI 2.1370(18), Znl—N2 2.1689(18), Zr2—N5 2.1818(18), Zr2—N6 2.1747(17),  Znl—N3  2.0450(17),  Znl—N4 2.0315(17),  Zr2--N3  2.0371(18),  Zr2—N4  2.1153(17), Zr2—P3 2.9139(6), N3—N4 1.488(2), N3—Zrl—N4 42.83(7), Znl—N3—Zr2 137.18(9), P2—Zr2—P3 166.605(19), P1—Znl—N4 94.18(5), P1—Znl—N3 136.91(5), P1—Zn— Ni 71.28(5), P1—Znl—N2 75.25(5), N1—Zrl—N3 118.84(7), N1—Znl—N4 115.84(7).  153  P2  N2  P3 P1  N6 N5  N4  Ni N3  Ni  N6  Figure 4.14. Two views of the stereochemistry around Zr in 4.4.  The solid-state molecular structure of 4.4 provides some clue as to why only one phosphine donor is coordinated in 4.3 and 4.4. From Figure 4.14, it appears as though the Ph to Zr2 pushes the [NPN]* ligand on Zn away. The new position of 2 coordination of PMe [NPN]* on Zr2 the NMes substituents of .[NPN]* on Zn, and the PPh substituent of Ph from coordinating to Zn. Complex 4.4 2 effectively block a second equivalent of PMe 2 complex characterized in the solid state with different appears to be the first dinuclear Zr-N coordination environments at each Zr.  4.2.4 UV-Visible spectroscopy of zirconium dinitrogen complexes. Complexes 4.1, 4.2, and 4.4 are intensely green coloured compounds in solution and in the solid state. The UV-visible absorption spectrum of blue-green 4.1 in toluene is shown in Figure 4.15. There is one peak at 652 nm 358 nm (e  =  1.0  X  (  =  6.1  X  ) and a second peak at 1 IO L mol’ cm  4 L mol’ cmj. It should be noted that i0  154  8  values are approximate for  these complexes because the dilute solutions become less intensely coloured over several 2 in Teflon-sealed cuvettes as they react with trace hours under N  °2  0 in the solvent. 2 and H  , the peak at i By analogy with the UV-visible absorption spectrum of 32 ]Zr i-ri NN ([P Q : ) 2 4 to 2 MO of N  652 nm is tentatively assigned to a charge-transfer (CT) transition from the a d orbital of Zr(IV), and the peak at 358 nm is assigned to a CT from the  7t’  2 to MO of N  a higher energy d orbital of Zr(W). Similarly, absorption maxima in the UV-visible absorption spectrum of evergreen-coloured 4.2 in toluene solution (Figure 4.16) at 736 nm (6 =  —.  6.1  X  1 cmj and 366 nm iO L mol  (6 =  1.0  X  2 1 cm’) are assigned to N 4 L mol i0  it  Zr(IV) d CT transitions. There is also a shoulder on the high energy CT band at 401 nm  (6 =  6.6  X  3 L mol’ cm’), as well as a smaller peak at 504 nm i0  (6 =  2.2  X  iO L mol’ cm’)  that have not been assigned, but are similar to features observed in the spectrum of Zr) i-ri There are two peaks in the UV-visible absorption spectrum of green ii N). N ([ O : 2 4.4 in toluene solution (Figure 4.17) at 699 nm (c  =  9.7  2 1.1 x I 0 L mot’ cm’) also tentatively assigned to N  X  —+  , and 363 nm cm ) 3 L mol’ 1 i0  (6 =  Zr CT transitions. The UV-visible  absorption spectra of 4.1, 4.2, and 4.4 are similar to other group 4 dinitrogen complexes (Table 4.1).  155  0.9 0.6 0.7 ci) C.) C Cu  -o  0.6 0.5  0 U)  -o  0.4 0.3 0.2 0.1 0  Xmax  730  630  530  430  330  (nm)  Figure 4.15. UV-visible absorption spectrum of 4.1 in toluene.  C Cu  -o  I  0  Co  -o  4:  330  380  430  480  530  Xmax  580  630  680  (nm)  Figure 4.16. UV-visible absorption spectrum of 4.2 in toluene.  156  730  780  0.9 0.8  0.7  CI) 0 C -  0.6  0.5  I—  0 0.4 0.3  0.2 0.1  0 330  380  430  480  580  530  630  680  730  780  max(nrn)  Figure 4.17. UV-visible absorption spectrum of 4.4 in toluene.  2 complexes in toluene. Table 4.1. UV-visible absorption maxima of some Group 4 N 1 cm’) 6 (X iO L mo1 (nm) 6.1, 10 652, 358 6.1, 6.6, 10 736, 401, 366 9.7, 11 699, 363 c 670, 455, 390 c 612, 392 r N (t_q [(rac-Bp)Zr] : 2 c, 3.7 648, 351 6.5, 0.38 886, 553 1 ) e f] N C 11 J1-T [(T M 5 H 4 H ( : 2 e Ref. 34; C: not reported; d: ]j u-C i-4Si(-2-M 2 Me S 3 B t H a: Ref. 31; b: (rac-Bp = 5 Ref. 19; e: Ref. 16B. 2 complex N 4.1 4.2 4.4  max  -  4.2.5 Attempted synthesis of a hafnium dinitrogen complex. When the conditions used to prepare 4.1 are replicated in an attempt to prepare a  [NPN]*Hfl (2.15) and KC , the formation of a 8 hafnium-dinitrogen compound from 2 toluene-soluble brown solid is observed. The brown solid has not been characterized, as it  157  [NPNJ*H (2.8). Only peaks due to 2.8 are apparent by NMR could not be separated from 2 spectroscopy and El-MS. The brown product may be paramagnetic, and higher molecular weight peaks may not be apparent by El-MS because any Hf complexes that are present are thermally sensitive, or not volatile enough for this technique. When 2.15 is stirred with 2 at ambient temperature, a deep redNa/Hg amalgam in toluene solution under I atm of N brown colour forms over four weeks. After one week, signals attributable to multiple P{’H} NMR spectrum, including a small peak at ö 3.5. After products can be seen in the 31 four weeks, the peak at 8 3.5 and a peak due to 2.8 represent the major products of the reaction. Unfortunately, 2.8 could not be removed completely from the red-brown solids. , a slow colour 2 If 2.15 is stirred over Na/Hg amalgam in THF under 4 atm of N } 31 H 1 change from orange to yellow-green is observed over three weeks. According to P{ NMR spectroscopy, the major product is characterized by a singlet at 6 —10.6 (62%). There are also minor products at 6 —3.1 (16%), —6.9 (10%), and —10.5 (12%). Attempts to purify the major product are currently ongoing, however, there is no evidence that the mixture 2 complex. contains a Hf-N 2 2 complexes, the synthesis of Hf-N While there are quite a few examples of Zr-N I f(N H)] [Cp* . 2 complexes remains a challenge. In 1985, the first Hf dinitrogen complex, Q HfI and Na/K alloy in 20% yield. 2 Cp* ° Unfortunately, the product 4 Ni), was prepared from ]Hf1 with N 2 has not been crystallographically characterized. Although the reduction of [P N by EI-MS, and hydrazine is obtained upon addition of HC1 to ]Hf} N {[P ( 2 8 yields ) KG  41 The the product, the complex could not be purified or characterized in the solid state. ) with Na/Hg amalgam yields { e fI -C M 5 H 4 H reduction of (ri 2 ) f} ii ii-i N), -CsMe 5 (ri H 4 H ( : 2  165 in which N 2 is bound side-on to two Hf centres with an N—N bond length of 1.423(1 1) A.  158  , as was observed r N (j.i-r } : ) H )2 e C -f(H) M 5 H 4 H 2 to give { (r 2 This complex reacts with H 2 for the Zr congener. Hafnium cliiodides have been used as starting materials for Hf-N complexes because the analogous hafnium dichioride complexes contain strong Hf—Cl bonds that are unreactive in the presence of strong reducing agents. Hf—I and Zr—I bonds 42 but Zr(IV) complexes are easier to reduce than have similar bond dissociation enthalpies, 43 corresponding Hf(IV) complexes.  4.3 Conclusions. In this chapter, the synthesis of a new arene-bridged zirconium dinitrogen complex,  is reported. The deep blue-green compound has been } NMR 13 H 1 1, and C{ }, H 31 H 1 characterized in solution and in the solid state. By P{ spectroscopies, the dinuclear complex is  h 2 C  symmetric with one THF and one FNPN]*  2 is coordinated to each Zr. The solid-state molecular structure of the complex shows that N coordinated side-on to two Zr atoms with an N—N bond length of 1.503(6)  A. N 2 is formally  , or hydrazide, in the complex. 4 2 N h PMe P , or 2 3 2 complex can be prepared easily by adding Py, PMe Adducts of the Zr-N  HF)} The addition of excess Py to this complex . rj J1r1 {{NPN]*ZrF ( : ) 2 to a solution of N y)} in high yield as a dark green powder. The complex is r r) {[NPN]*Zr(P ( : ) 2 provides N } NMR spectroscopies. The solid-state 13 H 1 H and C{ }, 1 31 H 1 h symmetric in solution by P{ 2 C 2 is coordinated side-on to two Zr atoms, as expected. In molecular structure shows that N  fact, the only major difference between the structure of the THF adduct and that of the Py adduct is the identity of the donor. The N—N bond lengths are the same within error, and 2 planes. both structures show a similar butterfly distortion between the ZrN  159  I11 provides 11 Q {[NPNj*Zr(THF)} : ) 2 Ph to N 2 3 or PMe The addition of excess PMe 2) {Zr[NPN]*} (R r R)}(irI {{NPN}*Zr(PMe : 2 N  =  Me, Ph) as a bright green powder in  R adducts are C symmetric with one Zr atom coordinated 2 high yield. In solution, the PMe . The solid-state t 2 and [NPN] Ph, and the other coordinated to N 2 to N , [NPN]* and PMe 2 Ph is coordinated to 2 Ph adduct confirms that only one PMe 2 molecular structure of the PMe 2 is side-on bound to two Zr atoms. As with the THF and Py the dimeric species, and that N 2 unit adducts, the N—N bond length indicates that an N—N single bond is present, and the N 1 (JI-T1 } : is butterfly-distorted relative to the Zr---Zr axis. The synthesis of {[NPN]*Zr(Py) 2  ) and 2 N  { [NPN] *Z  r {Zr[NPN] : (ji-r N2) (PM Ph) 2  *  }  from  { [NPN] *Z  (J’HF) 2 ri (i-ri } : -  2 complexes with new donor groups. N2) represents a simple, high-yield route to side-on N  4.4 Experimental. 4.4.1 General experimental. 2 General experimental conditions are as given in chapter two. Flasks sealed under N  gas at liquid-nitrogen temperature reach a pressure of 4 atm at  ft.  Only thick-walled Teflon-  sealed Kontes glassware should be used for these procedures. Reaction mixtures should be thawed completely behind a blast shield and handled with great care whenever the flask must /EtOH 2 be removed from behind the shield. Warming solutions slowly to rt in a liquid-N N{’H} NMR spectra were recorded slurry may minimize shock to the flask upon thawing. 15 H NMR spectra on a Bruker AV-400 direct detect spectrometer operating at 400.1 MHz for 1 N-labelled complexes were isolated and 2 at ö 0. 15 and were referenced externally to MeNO . UV-visible spectra were recorded on a Varian/Cary 5000 liv 2 handled under unlabelled N  Vis spectrometer using a 1 cm cuvette. For UV-vis spectra, the compound was dissolved in  160  toluene (dried according to the procedu.re outlined in chapter two, then stirred over sodium filled glovebox, and filtered through Celite), and the solution was -N sand for one hour in an 2 transferred to a Teflon-sealed Kontes UV-Vis cuvette.  4.4.2 Starting materials and reagents. Tetrahydrofuran was purified as usual, stored over purple sodium benzophenone ketyl indicator and degassed by three freeze-pump-thaw cycles prior to use. Pyridine was dried ) was prepared 8 2 prior to use. Potassium graphite (KG 2 and distilled under N over CaH  according to literature methods. Trimethylphosphine and dimethylphenylphosphine were 2 gas N 5 purchased from Strem Chemical Ltd. and used without further purification. ‘ (isotopic purity 98+%, 1 or 2 litres) was purchased from Cambridge Isotopes Ltd. in a small carbon steel lecture bottle and used as received. Mercury was purified according to literature 45 Sodium amalgam was prepared immediately before use in a nitrogen atmosphere, methods. and was washed with toluene until the washings were clear and colourless.  HF)} (4.1). Compound 2.10 (1.00 g, 1.40 mmol) and KC .tT12:T)2N {[NPN]*Zr(T O 2 ) 8 (0.414 g, 3.07 mmol) were added to a 400-mL thick-walled bomb and shaken to mix thoroughly. THF (10 mL) was vacuum-transferred to the mixture at 77 K. The flask was /EtOH slurry 2 2 gas at 77 K, sealed, and warmed slowly to rt in a liquid-N filled with N behind a blast shield. As soon as the mixture had melted, it was stirred vigorously. The flask  was periodically inverted to coat the walls of the flask with the concentrated reaction mixture. The solution turned purple after 2 h, and bright blue-green after 5 h, and was stirred overnight. The suspension was diluted with THF (10 mL), and filtered through Celite. The Geite was washed with additional THF (--‘10 —20 mL). The filtrate was concentrated under  161  vacuum to about 5  —  10 mL The deep blue-green solution was layered with pentane (50 mL)  and chilled to —35 °C. The black crystals that formed were collected on a frit, washed with pentane (5 mL), and dried under vacuum for 15 mm. (0.802 g, 0.548 rnmol, 79%). Storing crystals of 4.1 under vacuum overnight gave a white powder that contained benzene-soluble and -insoluble fractions. Crystals of 4.1 suitable for X-ray analysis were grown in a large Teflon-sealed bomb by vapour diffusion of hexanes into a concentrated benzene/THF solution of the compound in an NMR tube over 3 weeks. H NMR cTHF-d 1 , 500 MHz): 3 8  =  7.42  (t,  4H, 7.5 Hz), 7.22 (m, 6H), 7.08 (d, 4H, 7.5 Hz),  6.82 (s, 4H), 6.73 (s, 4H), 6.64 (d, 4H, 8.5 Hz), and 5.43 (dd, 4H, JHH  =  8 Hz, J,  =  6 Hz)  , (ArCH ) (ArH), 3.54 (bs, THF), 2.18 (s, 12H), 2.07 (s, 12H), 1.94 (s, 12H), and 1.74 (s, 12H) 3 1.69 (bs, THF). } NMR (THF-d, 202 MHz): 6 31 H 1 P{  =  , 126 MHz): 6 3 C{’H} NMR (THF-d 13  5.0 (s).  =  163.1 (d, 11 Hz), 144.7, 137.9, 136.7, 136.4, 134.9,  134.1, 133.8, 130.0, 129.9, 128.9, 128.8, 125.1, 118.2, 117.9, and 113.7 (d, 10 Hz) (ArC), 68.2, . (ArCH ) and 26.4 (THF), 20.9, 20.4, 20.3, and 19.2 3 El-MS (m/: 1432 (1, [M  —  Nr), 1320 (2, [M  —  , 541 (100, [2.8 2THFJ ) t  —  MelD.  r C, 68.71; H, 6.89; N, 5.23; Found: C, 68.34; 10 2 9 C 1 H Z 2 P 4 O 6 N Anal. Calcd. for 4.F2THF: : H, 7.24; N, 4.90. UV-Vis (toluene)  ‘umax  ()  =  358 (1.0  X  10k), 652 (6.1  X  1 cmj. 10) nm (L mol  [NPN]*ZrC1 in the absence of N . Using the procedure outlined for the 2 Reduction of 2 2 (0.350 g, 0.488 synthesis of 4.1, THF (10 mL) was transferred to a mixture of [NPN]*ZrC1 mniol) and KC 8 (0.145 g, 1.07 mmol) at 77 K, and the flask was evacuated and sealed. The  162  reaction mixture was a brown suspension while warming to rt. The mixture was stirred overnight, the pressure was vented, and an aliquot of the reaction mixture was analyzed by } NMR spectroscopy. The reaction mixture was filtered, and the filtrate was P{ 1 ‘ H concentrated and layered with pentane, but no crystals were obtained. After 2 d, the brown P{’H} NMR spectroscopy solution was taken to dryness to obtain a brown powder. 31 indicated the reaction mixture and solid obtained upon work-up had the same composition. , 202 MHz): 6 D 6 {’H} NMR (C ‘ P 1  20.3 (s, 5%), 17.9 (s, ‘-‘5%), —14.6 (s, 30%), —15.4  =  (s, 40%), —31.4 (s, ‘-20%).  2 (0.254 g, 0.173 mmol, N 15 . Complex 4.1(4.1-’ ) 2 N 5  8 (0.133 g, 0.985 mmol) in a 83%) was prepared from 2.10 (0.321 g, 0.448 mmol) and KC 200-nil. Teflon-sealed bomb by the same general method used to prepare 4.1. After vacuumtransferring THF (5 mL) to the flask at 77 K, the sealed, frozen flask was connected to a lecture bottle of 15 2 gas (1 L, 1 N  —  2 atm pressure) via a small transfer bridge. The apparatus  was evacuated and backfilled three times, the flask containing the frozen solution was opened, and the entire apparatus was evacuated and then closed to the Schlenk line. The lecture bottle was slowly opened in the closed system. The flask was warmed to rt in a liquid ) behind a blast shield with vigorous stirring. The ‘H NMR 2 EtOH slurry (4 atm N /N 2 spectrum was the same as for 4.1. , 162 MHz): 6 8 } NMR (THF-d 31 H 1 P{ , 40MHz): 6 8 } NMR (THF-d 15 H 1 N{  El-MS (m/: 1432 (8, [M  —  =  =  5.0 (d, 2 JpN 116.6 (d,  ), 1322 (6, [M N ] 2  —  163  =  2JpN  6.7 Hz). =  6.7 Hz).  2THF]j, 541 (100, [2.8  —  Me]j.  (4.2). To a stirred blue-green suspension of 4.1 (0.815 g, H (15 mL) was added Py (0.98 g, 1.0 rnL, 12 mmol) dropwise. The 6 0.557 mniol) in C solution turned dark evergreen instantly. After 15  mm. the reaction  mixture was taken to  dryness to obtain a dark green powder that was suspended in hexanes, collected on a frit, rinsed with hexanes (5 mL), and dried (0.723 g, 0.489 mmol, 88%). Large black crystals suitable for X-ray analysis were grown by slow evaporation of a benzene solution of the compound in an NMR tube. (C 500 MHz): ö , D ‘H NMR 6  =  7.55 (bm, 4H), 7.45 (d, 4H, 6 Hz), 7.12 (m, 4H, Py), 6.84 (d,  4H, 8 Hz), 6.77 (s, 4H), 6.65 (bs, 6H), 6.55  (t,  2H, 8 Hz, Py), and 6.47 (s, 4H) (ArH), 6.00  . (ArCH ) (m, 8H, ArH and Py), 2.23 (s, 12H), 2.11 (s, 12H), and 2.03 (s, 24H) 3 , 202 MHz): ö D 6 P{’H} NMR (C 31  =  , 126 MHz): ö D 6 {’H} NMR (C ‘ C 3  6.0 (s). =  162.7 (d, 33 Hz), 149.9, 143.9, 137.3, 136.8, 136.0,  134.6, 133.7, 133.2, 133.0, 129.6, 129.5, 128.3, 127.6 (d, 8 Hz), 127.5, 125.6, 125.1, 121.9, and . (ArCH ) 114.0 (d, 10 Hz) (ArC), 20.8, 20.4, 20.1, and 19.3 3 El-MS (m/): 1399 (30, [M  —  Py]j, 1320 (30, [M  —  2Py]), 541 (100, [2.8  —  Me]j.  r C, 69.88; H, 6.00; N, 7.58; Found: C, 70.20; H, 6.31; N, 7.20. 6 8 C 8 H Z 2 P 8 N Anal. Calcd. for : UV-Vis (toluene)  ‘m (E) =  366 (1.0 x 10), 401 (6.6 x 10), 504 (2.2 x 10), 736 (6.1 x 10)  . cm ) nm (L mol’ 1  ) (4.2-drn). Complex 4.2-cl 2 {[NPN]*Zr(Pydg)}z(.LrI2:112N 10 was prepared in the same H 6 5 (0.53 g, 0.50 mL, 6.3 mmol) in C manner as 4.2 from 4.1 (0.290 g, 0.198 mmol) and Py-d P{’H} (5 mL), and was isolated as a moss green powder (0.270 g, 0.181 mmol, 91%). The 31 } NMR spectra are the same as those of 4.2. { 1 C 3 ‘ and H  164  , 500 MHz): ö D 6 H NMR (C 1  =  7.55 (m, 4H), 7.45 (d, 4H, 7 Hz), 6.84 (d, 4H, 8 Hz), 6.77 (s,  4H), 6.65 (bs, 6H), 6.46 (s, 4H), and 6.01 (dd, 4H, JHP  =  6 Hz,  JHH =  8 Hz) (ArH), 2.23 (s,  . (ArCH ) 12H), 2.11 (s, 12H), and 2.03 (s, 24H) 3 El-MS (m/,J: 1404 (10, [M  —  ]j, 1320 (15, [M (Py-d ) 5  —  ]), 541 (100, [2.8 2(Py-d ) 5  —  Me]).  y)} (4.2-’N .L12:11215N {[NPN]*Zr(P O 2 ) 2 was prepared in the same N 15 ). Complex 4.22  2 (0.150 g, 0.102 mmol) and Py (0.24 g, 0.25 mL, 3.0 mrnol) in N 5 manner as 4.2 from 4.1-’ H H (3 mL), and was isolated as a dark green powder (0.129 g, 0.087 mmol, 85%). The 1 6 C NMR spectrum was the same as that of 4.2. , 161 MHz): ö D 6 P{’H} NMR (C 31 , 40 MHz): D 6 } NMR (C 15 H 1 N{ =  =  =  6.0 (AXX’ triplet 2 JPN  =  6 Hz,  118.2 (AA’XX’ multiplet,  JpN’ = 2  JNP = 2  7 Hz,  3 Hz). JNp’ = 2  3 Hz,  JNN’ 1  2 Hz).  El-MS (m/): 1322 (10, [M  —  2Py]j, 541 (100, [2.8  —  Me]).  *} (4.3). Et Me }O.L12:112NZ){Zr[NPN] 3 {[NPN]*Zr(P ) 0 (5 mL) and 4.1 (0.320 g, 0.221 2 3 (0.52 g, mmol) were mixed and chilled to —35 °C. To the stirred solution was added PMe 0 (3 mL), and the mixture turned clear bright green instantly. 2 0.60 mL, 6.9 mmol) in Et After 30 miii. the reaction mixture was taken to dryness to obtain a green powder (0.306 g,  0.219 mmol, 99%). A sample of 4.3 for microanalysis was recrystallized from toluene, with a Si) (HMDSO) at —35 °C. The supernatant 3 (Me 0 few drops of PMe 3 added, layered with 2 liquid was decanted, and the micràcrystaflune solid was rinsed with pentane and dried under vacuum for 5 miii.  165  , 400 MHz): 6 D 6 ‘H NMR (C 2H, 8 Hz), 7.18  (t,  =  7.82 (m, 4H), 7.56 (d, 2H, 8 Hz), 7.37 (d, 2H, 8 Hz), 7.27  IH, 7 Hz), 7.13  (t,  IH, 7 Hz), 7.01  (t,  2H, 7 Hz), 6.94  (d, 4H, 7Hz), 6.77 (s, 2H), 6.74 (s, 2H), 6.66 (s, 2H), 6.13 (dd, and 5.78 (dd, 2H, JHH  =  8 Hz, JHP  =  2H,JHH =  (t,  (t,  2H, 7 Hz), 6.78  8 Hz,JHP  =  6 Hz),  6 Hz) (ArH), 2.31 (s, 6H), 2.23 (s, 6H), 2.17 (s, 6H), 2.11  , 0.27 (d, 9H,J, (ArCH ) (s, 6H), 2.00 (s, 6H), 1.92 (s, 6H), 1.68 (s, 6H), and 1.43 (s, 6H) 3  =  6  . PMe ) Hz, 3 , 162 MHz): 6 D 6 } NMR (C 31 H 1 P{  =  5.1 (d, IP,  J = 44 Hz), 2.5 2  (s, IP), —33.1 (d, IP,  2, = J  . PMe ) 44 Hz, 3 , 101 MHz): 6 D 6 C{’H} NMR (C 13  =  162.8 (d, 29 Hz), 159.6 (d, 25 Hz), 143.0, 141.8, 137.7,  137.1, 135.8, 134.9, 134.3, 134.1, 133.9, 133.6, 133.2, 130.7, 130.0, 129.7, 129.6, 129.3, 129.0, 128.8, 128.7, 128.6, 128.5, 128.1, 127.9, 127.0, 125.7 (d, 5 Hz), 125.6, 118.0, 117.6, 114.7 (d, 9 ), 3 Hz), and 113.5 (d, 11 Hz) (ArC), 21.0, 20.9, 20.5, 20.3, 19.8, 19.7, 17.7, and 16.0 (ArCH . PMe ) 15.4 (d, 13 Hz, 3 r C, 66.27; H, 6.63; N, 5.59; i, 3 9 67 : 8 C 9 H Z 3 P 6 N S 2 9 0 067) 33 4.3(HMDSO Anal. Calcd. for : Found: C, 66.38; H, 6.90; N, 5.22.  )} N 3 5 {Zr[NPNJ :1 (,.L-11 1 ) 2 { [NPN] *Zr(PMe  *}  2 was made N 5 . Compound 4.3-’ (4.3-’ ) 2 N 5  3 (0.26 g, 2 (0.120 g, 82 tmol) and PMe by the same route used to prepare 4.3, from 4.1-N 0 (5 mL). The bright green solution was taken to dryness to 2 0.30 mL, 3.5 mmol) in Et } and ‘H NMR spectra 31 H 1 obtain a bright green powder (0.114 g, 82 imo1, 99%). The P{ were the same as those observed for 4.3. N{’H} NMR (C 15 , 40 MHz): 6 D 6  =  119.3 (bs, iN), 117.9 (bs, iN).  166  (4.4). To a stirred blue-green suspension h (0.250 g, 1.81 mmol). PMe P of 4.1 (0.410 g, 0.280 mmol) in toluene (10 mL) was added 2 The  suspension  turned bright green, and was stirred at rt for 30 mm. to obtain a clear,  emerald green solution. The reaction mixture  was taken  to dryness to obtain a green residue  that was triturated and taken to dryness, first with toluene (5 mL), then with hexanes (3  X  5  mL). The deep green solids obtained were suspended in pentane (5 mL), and the mixture was chilled to —35 °C overnight. The solids were collected on a frit, rinsed with hexanes (5 mL), and dried for 1 h to obtain a bright green powder (0.335 g, 0.229 mmol, 82%). Small crystals of 4.4 suitable for microanalysis were grown by slow evaporation of a benzene/HMDSO solution of the complex. Crystals of 4.4 suitable for X-ray analysis were grown by slow evaporation of a concentrated hexanes solution of the compound. 2H, 9 Hz), 7.74  (t,  2H, 9 Hz), 7.51 (d, 2H, 7 Hz),  7.38 (d, 2H, 8 Hz), 7.25-7.15 (m, 3H), 6.98 (m, 2H), 6.91  (t,  2H, 7 Hz), 6.79-6.65 (m, 16H),  , 400 MHz): ö D 6 H NMR (C 1  6.12 (dd, 2.28  (s,  2H,JHH  6H), 2.19  8 (s,  =  Hz,JHP =  6H), 2.16  , 0.80 (d, 6H, JHP (ArCH ) 6H) 3  =  7.79  (t,  6.5 Hz), and 5.77 (dd, (s,  6H), 1.98  (s,  2H,JHH =  12H), 1.92  (s,  8  Hz,JHP =  6H), 1.67  (s,  6.5 Hz) (ArH),  6H),  and  1.48  (s,  6 Hz).  D, 162 MHz): ö 6 } NMR (C 31 H 1 P{  =  7.3 (d, 1P,  2, = 46 Hz), 1.9 (s, J  IP), —22.5 (d, IP,  2, = J  h). PMe P 46 Hz, 2 , 101 MHz): ö D 6 {’H} NMR (C ‘ C 3  =  162.9 (d, 31 Hz), 159.4 (d, 26 Hz), 141.4, 137.8, 137.5  (d, 4 Hz), 136.1, 135.4, 135.0, 134.7, 134.3, 134.2, 133.9, 133.7, 133.6, 133.5, 133.4, 133.3, 131.7, 131.4, 131.3, 130.8 (d, 8 Hz), 129.7 (d, Hz), 129.2, 129.0, 128.7 (d, 3 Hz), 128.6 (d, 3 Hz), 127.9, 127.4 (d, 7.5 Hz), 127.1 (d, 5 Hz), 125.8 (d, 5 Hz), 118.1, 117.8, 117.6, 117.2, 114.5 (d, 9 Hz), and 113.6 (d, 11 Hz) (ArC), 21.1, 21.0, 20.5, 20.3, 19.5, 19.1, 17.9, and 16.1 . PPh(CH ) 2 ) , 15.6 (d, 13 Hz, 3 (ArCH ) 3  167  El-MS (m/J: 1320 (8, [M  —  h}j, 541 (100, [2.8 PMe P 2  —  Me}).  SO) , C, 66.81; H, 6.91; N, 4.72; i r (C (HMD 2 4.4 ) O 6 N 1 H 99 :C 15 S 5 Z P 3 Anal. Calcd. for : Found: C, 67.21; H, 6.86; N, 4.35. UV-Vis (toluene)  max  (6) =  ). 1 1 cm 363 (1.1 x 10k), 699 (9.7 x 10) nm tL mo1  5 {Zr[NPN] :r (.t-q 1 ) 2 { [NPN] *Zr(PPJ1e )} N  *}  2 (74 mg, 51 . Complex 4.4-N (4.4) 2 N 15  2 (77 mg, 53 jimol) in imol, 97%) was prepared in an analogous fashion to 4.4 from 4.1-’N h (73 mg, 53 jimol). The ‘H NMR spectrum was identical to that PMe P toluene (1 mL) and 2 observed for 4.4. , 162 MHz, 253 K): ö 3 } NMR (toluene-d 31 H 1 P{ JPN  =  7 Hz), —1.9 (s, 1P), —22.5 (dd, IP,  =  7 Hz,  JNP 2  =  7.3 (ddd, IP,  =  46 Hz,  2JpN  =  4 Hz,  JNN 1  =  8 Hz,  JPN = 7 Hz). J2 ,,,, = 46 Hz, 2  , 40 MHz, 253 K): ö 8 {’H} NMR (toluene-d ‘ N 5 JNP  =  =  119.0 (AA’XX’ multiplet, iN,  4 Hz), 118.0 (AA’XX’ multiplet, IN,  ‘JNN  =  8 Hz, 2 JNp  =  7 Hz,  JNP 2  =  4  Hz). El-MS (m/: 1322 (15, [M  —  hfl, 541 (100, [2.8 PMe P 2  —  Me]j.  LNPN]*Hf1 under N . Complex 2.15 (1.33 g, 1.35 mmol) was transferred to 2 Reduction of 2 a Teflon-sealed bomb, and THF (10 mL) was vacuum-transferred into the flask at 77 K. Upon warming to rt, the flask containing the bright orange solution was returned to the glovebox and Na/Hg amalgam (25 g, 0.7%, 7.39 mmol) was added. The flask was evacuated  2 at 77 K. The reaction mixture was allowed to warm slowly to rt in a liquid and filled with N EtOH slurry behind a blast shield. When the solvent had thawed, the solution was /N 2 stirred vigorously. A gradual colour change from bright orange to green was observed over 4  168  weeks of stirring at rt. The pressure was vented, and the THF solution was decanted from the mercury and filtered through Celite. The filtrate was concentrated under vacuum to 5 mL, hexanes (15 mL) were added, and the clear solution was heated to  Ca.  40 °C to obtain a  white precipitate. The slurry was filtered through Celite to eliminate the white precipitate and the clear yellow-green solution was taken to dryness to obtain a dark yellow residue (0.83 g). Attempts to separate the products based on solubility differences in toluene/hexanes solutions at —35 °C, or by slow evaporation of a benzene/HMDSO solution of the mixture failed. , 162 MHz): D 6 } NMR (C 31 H 1 P{  =  —3.1 (s, 16%), —6.9 (s, 10%), —10.5 (s, 12%), —10.6 (s,  62%).  4.5 References. 1  Shaver, M. P.; Fryzuk, M. D. Adv. Sjnth. Cat. 2003, 345, 1061.  llen A. D.; Senoff, C. V. Chem. Commun. 1965, 621. 2 A Harrison, D. E.; Taube, H. J. Am. Chem. Soc. 1967, 89, 5706. ‘  Fryzuk, M. D.;Johnson, S. A. Coord. Chem. Rev. 2000, 200-202, 379. Fryzuk, M. D. Chem. Rec. 2003, 3, 2.  6  Fryzuk, M. D.; Haddad, T. S.; Mylvaganam, M.; McConville, D. H.; Rettig, S. J. J. Am.  Chem. Soc. 1993, 115, 2782. Cbiu, K. W.; Howard, C. G.; Rzepa, H. S.; Sheppard, R. N.; Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. Po/yhedron 1982, 1, 441. 8  Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997, 275, 1445. Morello, L.; Yu, P.; Carmichael, C. D.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2005,  127, 12796.  169  10  Fryzuk, M. D.; Kozak, C. M.; Patrick, B. 0. Inorg. Chim. Acta 2003, 345, 53. Laplaza, C. E.; Curniriins, C. C. Science 1995, 268, 861.  12  Pool, J. A.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2003, 125, 2241.  Love, J. B.; Fryzuk, M. D. Unpublished results. 13 14  Fryzuk, M. D.; Kozak, C. M.; Mehrkhodavandi, P.; Morello, L.; Patrick, B. 0.; Rettig, S. J.  J. Am.  Chem. Soc. 2002, 124, 516.  Wengrovius, J. H.; Schrock, R. R.; Day, C. S. Inorg. Chem. 1981, 20, 1844. A) Yandulov, D.V.; Schrock, R. R. Science 2003, 301, 76. B) Bernskoetter, W. H.; Olmos, A. 16 V.; Lobkovsky, E.; Chink, P. J. Organometallics 2006, 25, 1021. C) Evans, W. J.; Lee, D. S.; Johnston, M. A.; Ziller, J. W. Organometallics 2005, 24, 6393. 17  A) Manniquez, J. M.; Sanner, R. D.; Marsh, R. E.; Bercaw, J. E. J. Am. Chem. Soc. 1976, 98,  3042. B) Manriquez, J. M.; Bercaw, J. E. J. Am. Chem. Soc. 1974, 96, 6229. 18  Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. Soc. 1978,  100, 2716. Pool, J. A.; Lobkovsky, E.; Chink, P. J. Nature 2004, 427, 527. Weitr A.; Rabinovitz, M. Sjnth. Met. 1995, 74, 201. 20 21  Lappert, M. F.; Pickett, C. J.; Riley, P. I.; Yarrow, P. I. W. J. Chem. Soc., Dalton Trans. 1981,  805. Kenworthy, J. G.; Myatt, J.; Todd, P. F. Chem. Commun. 1969, 263. A) Fryzuk, M. D.; Mylvaganam, M.; Zaworotko, M. J.; MacGillivray, L. R. Po/yhedron 1996,  15, 689. B) Ho, J.; Drake, R. J.; Stephan, D. W. J. Am. Chem. Soc. 1993, 115, 3792. C) Bajgur, C. S.; Tikkanen, W. R.; Petersen, J. L. Inorg. Chem. 1985, 24, 2539.  170  A) Blandy, C.; Locke, S. A.; Young, S. J.; Schore, N. E. J. Am. Chem. Soc. 1988, 110, 7540. 24 B) Wielstra, Y.; Gambarotta, S.; Meetsma, A.; de Boer, J. L. Organometallics 1989, 8, 250. C) Wielstra, Y.; Gambarotta, S.; Meetsma, A.; Spek, A. L. Organometallics 1989, 8, 2948. 25  Hanna, T. E.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2004, 126, 14688. B) Hanna,  T. E.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2006, 128, 6018. 26  Grobelny, Z. Ear. J. Org. Chem. 2004, 2973.  27  Bartmann, E. J. Organomet. Chem. 1985, 284, 149. B) Evans, W. J.; Chamberlain, L. R.;  Ulibarri, T. A.; Zifler, J. W. J. Am. Chem. Soc. 1988, 110, 6423. 28  Fryzuk, M. D.; Jafarpour, L.; Rettig, S. J. Organometallics 1999, 18, 4050.  29  Mason, J. Chem. Rev. 1981, 81, 205. B) Donovan-Mtunzi, S.; Richards, R. L.; Mason, J. J.  Chem. Soc., Dalton Trans. 1984, 2429. °  A) Thom, D. L.; Tulip, T. H.; Ibers, J. A. J. Chem. Soc., Dalton Trans. 1979, 2002. B) Klahn,  A. H.; Sutton, D. Organometallics 1989, 8, 198. C) Field, L. D.; Hazari, N.; Li, H. L.; Luck, I. J.  Magn. Reson. Chem. 2003, 41, 709. 31  Bemers-Pnice, S. J.; Morden, K.; Opella, S. J.; Sadler, P. J. Magn. Reson. Chem. 1986, 24, 734.  32  Studt, F.; Morello, L.; Lehnert, N.; Fryzuk, M. D.; Tuczek, F. Chem. Ear. J. 2003, 9, 520. Cohen, J.; Fryzuk, M. D.; Loehr, T. M.; Mylvaganam, M.; Rettig, S. J. Inorg. Chem. 1998, 37,  112. Fryzuk, M. D.; Haddad, T. S.; Rettig, S.J.J. Am. Chem. Soc. 1990, 112,8185. Chink, P. J.; Henling, L. M.; Bercaw, J. E. Otganometallics 2001, 20, 534. 36  Morello, L. Amidophoiphine Complexes ofZirconium and Titaniumfor Dinitrogen Activation. Ph.D.  Thesis; University of British Columbia: Vancouver, 2005. Henrickson, C. H.; Duffy, D.; Eyman, D. P. Inorg. Chem. 1968, 7, 1047.  171  Morello, L.; Love, J. B.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2004, 126, 9480. A) Schrock, R. R.; Seidel, S. W.; Schrodi, Y.; Davis, W. M. Organometallics 1999, 18, 428. B) Fryzuk, M. D.; Duval, P. B.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray, L. R. J. Am. Chem. Soc. 1999, 121, 2478. C) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray, L. R. J. Am. Chem. Soc. 1993, 115, 5336. D) Cayias, J. Z.; Babaian, E. A.; Hrncir, D. C.; Bott, S. G.; Atwood, J. L. J. Chem. Soc., Dalton Trans. 1986, 2743. °  Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hilihouse, G. L.; Bercaw, J. E. Oganometa/lics  1985, 4, 97. ‘  Fryzuk, M.D.; Corkin,J. R.; Patrick, B. 0. Can.J. Chem. 2003, 81, 1376.  42  Schock, L. E.; Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701. Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Oigano-zjrconium and Hafnium  Compound.r, Ellis Hoiwood Ltd.: West Sussex, 1986, p. 21. A) Lalancette, J. M.; Rollin, G.; Dumas, P. Can. J. Chem. 1972, 50, 3058. B) Bergbreiter, D. 44 E.; Killough, J. M. J. Am. Chem. Soc. 1978, 100, 2126. 3?1 ed.; Butterworth Perrin, D. D.; Armarego, W. L. F. Purification ofL2boratoy Chemicals, 45  Heinemann Ltd.: Oxford, 1988.  172  Chapter Five Reactivity of Zirconium Dinitrogen Complexes  5.1 Introduction. The economically and biologically important reaction to convert elemental nitrogen to  ammonia is achieved in one of two ways: by nitrogen-fixing bacteria or by the Haber-Bosch process. Biological nitrogen fixation occurs in bacteria such as Aotobacter vinelandii at the 1 This active site of the nitrogenase enzyme, which contains an Fe, FeMo, or FeV cofactor. reaction proceeds at ambient pressure and temperature, but it requires energy in the form of 2 The mechanism of this reaction is 16 equivalents of MgATP, the cell’s energy carrier. 3 It unknown, and investigations into the structure and function of nitrogenase are ongoing. 3 worldwide per is estimated that nitrogen-fixing bacteria produce 108 million tonnes of NH 3 from the reaction of nitrogen and 4 In industry, the Haber-Bosch process yields NH year. hydrogen gases in the presence of an Fe or Ru catalyst at high temperature (400 °C) and pressure (200 atm). Today, the Haber-Bosch reaction also supplies the world with about 108 5 There is no indication that this process, first implemented tonnes of ammonia per year. industrially in 1913, will be replaced by another method for ammonia synthesis in the near future. 2 complexes were synthesized under mild conditions, chemists sought After the first N 2 at ambient to develop a homogeneous transition-metal-catalyzed route to ammonia from N temperature and pressure. Stoichiometric nitrogen gas, hydrazine, or ammonia may be 2 complex. Alternatively, a hydrazido complex (MN— produced if acid is added to an N ) may be obtained. While it can be difficult to predict what products will form during 2 NH  173  2 in the complex, and the experimental protonation reactions, the extent of activation of N conditions used (e.g., temperature, acid, solvent) can be important. Protonation of cis 6 whereas protonation of trans h) yields nearly two equivalents of ammonia, PMe 4 ( ) W(N P 2 ] (dppe) (M ) 2 {M(N ]  =  Mo, W; dppe  H with HC1 gives trans Ph PCH Ph C P 2 )  Cl (Equation 5.1). In 2003, Schrock and co-workers reported that (Cl)(dppe) 2 [M=NNH ] , a weak organic acid, 2 about eight equivalents of ammonia are produced catalytically from N a reducing agent, and a bulky triamidoamine Mo(HI) catalyst under carefully designed experimental conditions 8 HN/H  2 Ph  2 Ph  N  N  2 Ph  2 Ph  N  2 Ph  2 HCI  CI 2 Ph  2 Ph  CI  (5.1)  2 Ph  N M=Mo,W  Transition-metal dinitrogen complexes are also known to react with electrophilic (dppe) ) 2 [MN organic compounds. N—C bonds form when ailcyl and acyl halides react with ] X (X = [MX(NN(H)C(=O)R)(dppe) ] X or 2 [MX(NN(H)R)(dppe) ] (M = Mo, W) to produce 2  Cl, Br; R = Me, Et, “Pr, 93u, Ph) upon work-up with HCI(aq)• 9 Until recently, the majority of 2 required two steps: protonation of a dinitrogen complex to reactions for coordinated N generate a nucleophilic hydrazido complex, followed by reaction with an electrophile. ] by a condensation reaction to give 2 Aldehydes and ketones react with coordinated [NNH  hydrazonato complexes with new N—C bonds (Equation  5.2).b0  Metal-bound pyrroles,  pyrazoles, pyridines, and indoles can also be synthesized stoichiometrically from hydrazido ’ In some cases, the heterocycle is released 1 complexes and C0 containing electrophiles.  174  from the complex upon addition of a reductant and a proton source to the reaction 12 mixture.  HN/H N  2 Ph  7 l l  2 Ph  R  2 Ph R  ci 2 Ph M  CI =  Mo  L  2 Ph  2 Ph  (5.2)  2 Ph  R = alkyl, aryl R’=:H,alkyl  w  As is discussed in chapter one, new transformations for coordinated dinitrogen have been discovered relatively recently, and many of these involve side-on bound N . New N—H 2 and N—Si bonds form when H 2 and “BuSil-1 3 add to N 2 in ) ] N ([P ( : 2 i.t-T1 Zr) N 1 to yield ] Zr) N 2 ([P (i-H) 2 2 : (II-r1 NNH) r1 (Figure 5.1)  and  ] Zr) N 2 ([P (ji-H) 2 2 : (jiNNSi’Bu), r  respectively  H also adds to ) M 5 [(C H 4 Z ( : 2 ,i-ri 11 N r] e ) to provide ( M 5 [(C H 4 Z 2 r(H)] IIe )  Q ([NPN]Ta) ( : 1 ) ji-r i-H) N to produce 14 : 1 H 2 N z). Boranes, silanes, and alanes add to 2 1  N—B, N—Si, and N—Al bonds, in some cases with concomitant N—N bond cleavage. 15 The formation of N—C bonds is observed upon addition of arylacetylenes (ArCCH) to N]Zr) ([P O n 2 ) N .-ii to yield  ({  (Ar  ,6 4 H 6 MeC BuC (Figure 5. 1).16 t p) 4 H  175  =  Ph, P  2 H-CCAr  (Ar  =  ) 4 H 6 , pButC 4 H 6 Ph, p-MeC  Figure 5.1. Formation of new N—E bonds from  (F  Zr) N (E ri ] N ( : 2 ) j.i-1i  =  H, Si, C) (silyl  J omitted for clarity). N 2 methyl groups of [P  In most cases, when coordinated dinitrogen or hydrazide is functionalized, the new N— E component is not readily released from the transition metal. This is one barrier to the development of catalytic N—E bond-forming processes based on transition-metal dinitrogen Si) when TMSC1, (Me N complexes. Catalytic N—Si bond formation provides a low yield of 3 . Anilines can be prepared h) 17 ( ) ts-[Mo(N P 2 J PMe 2 are mixed in the presence 4 Na, and N 2 under Pd-catalyzed C—N cross-coupling Pr) Li, TMSC1 and N t Ti(O , from aryl chlorides, 4 18 Thus far, few catalytic processes are known for molecular nitrogen, and most conditions. are poorly understood.  176  2 complexes described in chapter four with In this chapter, the reactivity of the Zr-N 2 reacts with H—H, Si—H, C0, C=N, and P0 containing compounds is presented. H (R  =  Me, Ph) to yield a new N—H bond. A  . The (tr)2:112N 2 {[NPNj*Zr(Py)} 3 to ) new N—Si bond is obtained upon addition of PhSiH (L12:r12N provides a 2 {[NPN1*Zr(THF)} reaction of 4,4’-dimethylbenzophenone with ) hydrazonato complex with a new N=C bond, and the reaction of ) with benzophenone imine yields new N—H bonds. 2 N  5.2 Results and Discussion. . 2 2 complexes with H 5.2.1 Reactions of N , the bright green solution becomes 2 When a toluene solution of 4.3 is stirred under H yellow over two to three weeks, and an orange precipitate forms after five weeks. The yellow-orange toluene-soluble product,  ) (ji-H) (i-NNH) {Zr[NPNI* 5.1, 3 }, } { [NPN] *Zr(PMe  2 (1 atm) 3 in toluene solution under H can be prepared in high yield from 4.3 and PMe , 3 2 without added PMe (Equation 5.3). Complex 5.1 can also be synthesized from 4.3 and H but an unidentified brown by-product forms in about 10% yield by this method. Samples of 2 at —35 °C. 5.1 are stable in solution and in the solid state for months under N  2 H  (5.3)  toluene  5.1  4.3  177  } NMR 31 H 1 8 solution. At 298 K, the P{ NMR spectra of 5.1 were acquired in toluene-d 13, —2.5, and —36, which decoalesce at 273  spectrum of 5.1 shows three broad peaks at 6 K to two doublets at 6 13.8 and —34.5  J 2 (  =  56.7 Hz), and a singlet at 8 —2.2 (Figure 5.2).  Because the spectrum is reminiscent of that of starting material 4.3, a dinuclear structure in which one Zr atom is coordinated to [NPN]* (6 —2.2), and the other Zr atom is coordinated 3 (6 —34.5) is proposed for 5.1. The 56.7 Hz P-P coupling to [NPN]* (6 13.8), and PMe constant is typical for a two-bond coupling between trans-disposed phosphines in an early 19 transition-metal complex.  3 region In the 1 H NMR spectrum at 298 K, some of the peaks in the ArH and ArCH are broad; however, a triplet and a broad singlet that each integrate to I H are apparent at 6 4.83  J 2 (  =  ii Hz) and 4.78, respectively. These are assigned to a hydride bridging the two  Zr atoms (ZrHZr), and the hydrogen atom of bridging NNH (Figure 5.3). At 253 K, the  H NMR spectrum are sharper, and 13 singlets are observed at 6 peaks in the 1  2.0 that are  1 symmetry of the 3 groups. Sixteen singlets are expected based on the C assigned to ArCH product, but six of these singlets overlap and integrate to 6H each. A broad singlet at 8 0.09 , and an overlapping triplet at 8 4.84 (ZrHZr), and broad singlet at 3 due to coordinated PMe 6 4.82 (NNH) are also apparent in the spectrum at this temperature. { NMR spectrum at 253 K, the resonances assigned to ZrHZr and NNH In the P} 31 H 1  H appear as two singlets at 6 4.84 and 4.82. Thus, the bridging hydride is a triplet in the 1 P nuclei. One possible explanation NMR spectrum because it couples to two inequivalent 31 is that ZrHZr couples to 31 P nuclei of two [NPN]* ligands, and that the weak Zr—P bond to 3 3 torsion angle causes the coupling between ZrHZr and PMe 3 and/or the H—Zr—PMe PMe to be unobservable.  178  -  20  15  10  5  I  -20  -15  -10  -5  0  -25  -30  -35  -40  (ppm)  8 at 273 K. H} NMR spectrum of 5.1 in toluene-d 1 P{ Figure 5.2. 202 MHz 31  I  I  4.88  I  I  4.80  I  I  I  4.72  (ppm) H NMR spectrum of 5.1 in Figure 5.3. ZrHZr and NNH resonances in the 500 MHz 1 8 at 298 K. toluene-d  The solid-state molecular structure of 5.1 is illustrated in Figure 5.4. Unfortunately, the data are of poor quality, and only the connectivity of the non-hydrogen atoms has been established. The position of the bridging hydride and the hydrogen atom of bridging NNH  179  , and Zr2 is coordinated to 2 cannot be determined. Zn is coordinated to [NPN]* and N [NPN]  ‘,  . It is apparent that P2 and P3 are nearly trans-disposed (‘- 1610), and 2 3 and N PMe  that P1 is bent away from the Zr---Zr axis compared to P2 (Zr---Zn--P angles of 120° and 89°, respectively). Also, there is a much greater butterfly distortion (‘ 109°) between the two 2 planes than is observed for 4.1, 4.2, and 4.4 that is consistent with the presence of a Zr-N bridging hydride between the two Zr atoms. The Zr---Zr distance (‘—‘3.2  A) is similar to that  ° and it is slightly shorter 2 observed in other hydride-bridged dinuclear Zr(IV) complexes, 21 A projection of the N, P, and Zr atoms is shown in Figure 5.5. than in others.  Figure  5.4.  Ball-and-stick  model  of  the  solid-state  molecular  structure  of  ), 5.1. Carbon atoms of the proximal Mes Me }QIH)(,.INNH)(Zr[NPN]* 3 {[NPN]*Zr(P ) subsfltuents (except C) have been omitted for clarity.  180  Ni  P3  N5 N6  P1  P2  Figure 5.5. Projection of 5.1 down the Zr2--.-Zrl axis (only Zr, P, and N atoms included).  D solutions of 5.1 turn green. In 6 , yellow C 2 Over one to two weeks at 298 K under N P{’H} NMR spectrum, peaks due to 5.1 are absent, and singlets at 6 —5.0 (62%), —7.6 the 31 (13%), and —31.4 (19%) appear. There are no signals in the spectrum that can be attributed . The major product at 6 —5.0 has not been identified, but it may 3 to free or coordinated PMe correspond to  a PMe -free complex such 3  as  QIH)QINNH), or to 2 {[NPN]*Zr}  2 , if H O1N 2 {[NPN]*Zr} ) 2 has been eliminated. The peak at 6 —31.4 is due to [NPNJ*H  , solutions of 5.1 remain yellow for weeks 3 (2.8). Fortunately, in the presence of excess PMe H} NMR spectroscopy. 1 P{ at room temperature and no decomposition is detected by 31 . 3 Thus, as with 4.3, decomposition appears to involve loss of PMe 2 gas, toluene-d 8 To confirm that the resonances at 6 4.84 and 4.82 originate from H 2 or D 2 gas in sealed solutions of 4.3 have been stored under H  J.  Young NMR tubes and  2 is complete in six weeks, monitored for several weeks. Whereas the reaction of 4.3 with H }(JI {[NPN1*Zr(PMe ) 2 takes about three months, and a mixture of 3 the reaction with D D)(JINND){Zr[NPNJ*}, 5.1-d and 5.1 is produced. In the 1 H NMR spectrum at 253 K,  the triplet and singlet resonances at 6 4.84 and 4.82 integrate to about 0.02H each relative to  181  one of the ArCH 3 resonances (set to 3H). Thus, the bridging hydride and NNH protons in 2 2 gas. The resonances at 6 4.84 and 4.82 appear in spectra of 5.1-d 5.1 originate with H 2 faster than . Since 4.3 reacts with H 2 because there are trace HD impurities (O.4%) in the D 2 , the formation of 5.1 in this reaction cannot be prevented. Complex 5.1-d 2 it reacts with D 2 (4 3 and D can also be prepared as an orange solid on a larger scale (300 mg) from 4.3, PMe H NMR spectrum in atm). By integration of the resonances at 6 4.84 and 4.82 in the 1 2 and 5.1 are present in a 8 acquired at 253 K, 5.1-d toluene-d  10:1 ratio. A signal attributable  , appears in the mass spectrum of the compound. [5.1-d J to the parent ion, 2 h congener, a PMe P To determine if the hydrogenation of 4.3 can be extended to the 2 2 gas. The green h has been stirred under I atm of H PMe P toluene solution of 4.4 and 2 solution turns yellow after three weeks at room temperature, and a yellow precipitate forms *  after six weeks. Upon work-up,  Ph) (ji-H) (-NNH) {Zr[NPNj 2 }, } { [NPN] *Zr(PMe  5.2, is  isolated as a yellow solid in good yield (Equation 5.4).  (5.4)  4.4  5.2  8 at 298 K shows three Similar to 5.1, the 31 P{’H} NMR spectrum of 5.2 in toluene-d broad singlets at 8 15, —2 and 25. At 253 K, the broad resonances decoalesce and a doublet at 6 14.6  J 2 (  =  57.4 Hz), a broad singlet at 6 —24.6, and a singlet at 6 —2.3 are observed.  Ph coordinated to one Zr, and [NPN]* 2 These signals correspond to [NPN]* and PMe H NMR spectrum at 233 K, the expected coordinated to the other Zr, respectively. In the 1  182  1 symmetric dimer are apparent. In h groups in the C PMe P , and 2 3 signals due to ArH, ArCH addition, a singlet at 6 4.94, and a broad singlet at 6 4.88 are attributable to NNH and ZrHZr protons, respectively. The formation of a new N—H bond upon hydrogenation of 4.4 has been confirmed by *  an isotopic labelling experiment.  Ph) Q.t-H) NH) 2 15 {Zr[NPNJ }, N 15 (} { [NPN] *Zr(pMe  5.2-  h and H PMe P 2 (1 atm) in toluene solution. At 273 K, ,2 2 N 15 can be prepared from 4.42 shows the same peaks as that of 5.2, but the broad N 5 the 31 P{’H} NMR spectrum of 5.2-’ H NMR spectrum acquired at 233 K, singlet at 6 —24.6 is split into a broad doublet. In the 1 h resonances are analogous to those of 5.2, but the peak at PMe P , and 2 3 the ArH, ArCH 6 4.94 is a doublet  JHN = 1 (  72 Hz), and the peak at 6 4.88 is a broad triplet  J = 9.7 Hz). In 2 (  { NMR spectrum, the doublet at 6 4.94 is apparent, but the resonance at 6 4.88 is 31 H 1 the P} N- coupling constant is typical for one-bond coupling, and is 5 ‘ H a singlet. The 72 Hz 1 N{’H} NMR spectrum 5 The 15 2 Zr) ji-H)(jiNH). J ([P ( 2 1 N 15 2 ’ similar to that observed for 13 at 273 K shows a singlet at 6 143.9 and a doublet at 6 29.8 spectrum, a peak due to [M  —  JNP = 2 (  10 Hz). In the mass  h] is apparent. PMe P 2  2 may add to 4.3 or 4.4 by a a-bond metathesis mechanism across the Zr—N bond H via a four-centred transition state: N of dinitrogen acts as a nucleophile and Zr acts as an electrophile in this reaction, which is an example of heterolytic H—H activation. A similar 2 to 13 mechanism has been invoked for the addition of H . ri ]Zr i-i N N ([P Q : ) 2 2 does not react with THF adduct 4.1. When a blue2 adds to 4.3 and 4.4, H Whereas H 2 gas for six weeks at room green toluene solution of 4.1 is stirred under 4 atm of H temperature, there is no colour change, and no new peaks appear in any NMR spectra. 2 for eight weeks, there is a When a toluene solution of 4.2 is stirred under 4 atm of H  183  P{’H} NMR spectroscopy, there is gradual colour change from green to yellow-brown. By 31 . In the ‘H NMR spectrum, no peaks ({NPN]*H ) a mixture of products, including 2.8 2 diagnostic of bridging hydride or NNH protons are observed, and the major products could not be separated from each other. As introduced in chapter one, in 1997, the Fryzuk group reported the first reaction of Zr) is J N 2 ([P Ji-H)(i-NNH) 2 to yield a new N—H bond. Yellow ( an N 2 complex with H 13 A broad singlet at 6 . 2 prepared from blue 2 ]Zr) N under 1 or 4 atm of H rI N-ii ([P ( : ) 5.53 and a multiplet at 6 2.07 observed in the ‘H NMR spectrum are due to EI-NNH and  t  2 gas, these resonances H groups, respectively. When the reaction is conducted under D - the NH resonance is split into a , Zr) 15 ] ([P Q ) 2 2 reacts with N disappear, and when H doublet ( JHN 1  =  71.3 Hz). The ZrHZr resonances for 5.1 and 5.2 are about 3 ppm downfield  Zr) but are within the range ] N 2 ({P i-H)(j.iNNH), compared to the hydride observed for ( of known chemical shifts for hydrides bridging two Zr atoms. The solid-state structure of Zr) determined by neutron diffraction shows that the N—N and N—H ] N 2 ([P 0 .i-H)O1-NNH) bonds in the bridging hydrazide (NNH) are 1.39(2) and 0.93(6) In  contrast  to  , N r1 Zr) Ji-11 J N (E ( : 2 )  A 20 A, respecdvely.  N II-r (T1 ([PNP]ZrCl) : 2 )  and  24 Prior to 1997, attempts to 2 gas. i do not react with H N (ji-i {[NPN]Zr(THF)} : 2 ) generate N—H bonds by the reaction of a dinitrogen complex with hydrogen had been 2 had been observed to react with a dinitrogen complex to unsuccessful, but in some cases H 2 gas. 25 As discussed in chapter one, two new produce a metal hydride complex and liberate N 2 adds to 2 N—H bonds also form when H ) to provide [(ri 5 e r] N C i-ri 11 [(1 M 5 H 4 Z Q : ) , whereas 3 2 yields NH ) Heating this complex under H e 1 N .’ r(H)] I1-r1 M 5 C H 4 Z ( : ) H 2 e in which the N—N bond is C j-N)(jt-NH [( M 5 ( 2 Zr] 42 heating it under vacuum yields )  184  _______  , and 2 2 ) e cleaved. [(i 2 C f(H)1 JI[(q M 5 H 4 H ( ) also reacts with H e f] N C ri i-ri M 5 H 4 H ( : ) 2 complexes 26 Thus, 4.3 and 4.4 join a relatively small number of N N is produced. :r1 ri ) 2 H 2 to provide new N—H bonds. that react with H  5.2.2 Reaction of N 2 complexes with phenylsilane. 3 to a toluene solution of 4.2, a colour Upon addition of 1.1 equivalents of PhSiH change from deep blue-green to yellow-brown occurs. h){Zr[NPN]*}, 5.3, is isolated as an orange-brown toluene-soluble powder in high NNSiH P 2 yield upon work-up (Equation 5.5). In the mass spectrum of 5.3, the highest molecular weight peak can be assigned to [M  —  PyJ. The results of microanalysis are consistent with  the proposed formula plus co-crystallized solvent, as has been observed in ‘H NMR spectra . 8 of crystals of 5.3 dissolved in toluene-d  (5.5)  3 PhS1H  toluene  5.3  4.2  D shows two singlets at 6 The 31 P{’H} NMR spectrum of 5.3 in C 3 2.0 assigned to ArCH  ‘H NMR spectrum shows 13 singlets at  14.9 and —4.3. The groups  (six of the  expected 16 peaks are accidentally coincident), and peaks in the aromatic region consistent  with the proposed C,  symmetric  integrate to IH each and are  structure. Two doublets at 6 5.17 and 3.94 ( JHH 2  assigned  =  9.5 Hz)  to two diastereotopic SiH protons. Small satellites are  185  present that flank the SiH peaks  JHs = 1 (  also a doublet of doublets at 6 8.25  Si 208 Hz, isotopic abundance 29  (2J  =  15 Hz,  JHP = 2  =  4.7%). There is  2 Hz) assigned to a bridging  H1 P 31 at 6 —4.3 according to 31 ( hydride (ZrHZr) that couples strongly to one phosphine P HSQC) and weakly to the second phosphine. There are only a few examples of non metallocene group 4 complexes with bridging hydrides. Most hydrides bridging dinuclear Zr complexes have chemical shifts between 6 2.0 and  6.0.20  The downfield chemical shift seen  for the bridging hydride in 5.3, however, is not unprecedented among group 4 hydride 27 Signals due to bridging hydrides are also often observed downfield of 6 5.0 in complexes. Qi2 (i-H) (6 10.62), and ([NPN]Ta) 2 ([NPNjTa) non-metallocene Ta complexes, such as 4 N (6 :ri 1 H)(-i 2 )  10.85).28  , 16 ArCH D 6 3 singlets and 63 peaks in the In the 1 C{ 3 ‘ H } NMR spectrum of 5.3 in C aromatic region are observed, consistent with the C, symmetric structure proposed. By Si{’H} NMR spectroscopy, a doublet at 6 —34.4 is apparent; the doublet is due to a three29 bond coupling to phosphorus-31  J 3 (  =  10 Hz). The chemical shift and coupling observed  Si{’H} NMR spectroscopy are similar to those of other complexes prepared in our by 29 3 to 2 group. For example, the addition of one equivalent of PhSiI-1 (II-H) ([NPN]Ta) 0 1-rl’:r1 ) induces a series of reactions. The final product, {[NPNITa(H)}(Ji-NSiH 2 N Ph)(J.i2 N) {Ta[NPN] }, and an intermediate in the reaction,  2 { [NPN]Ta(H) } (j.i-H)(j.i-r’ :r1  Si NMR Ph){Ta{NPN]}, have peaks at 6 —39 and —9, respectively, in their 29 2 NNSiH 29 spectra.  To simplify the aromatic region of the ‘H NMR spectrum of 5.3, the Py-d, adduct has h) {Zr[NPN] NNSiH ‘: P been prepared and characterized. { [NPN] *Zr(Pydr) } (j.t-H) (j.i-ri 2  *  }  H NMR spectrum . The 1 3 10 and 1.1 equivalents of PhSiH , can be prepared from 4.2-cl 5 5.3-d  186  D is analogous to that of 5.3, except that the multiplets at 6 6.73 and 5.84 6 of 5.3-c1 in C integrate to only I H and 2H each, respectively, rather than 3H and 5H (Figure 5.6). ArCH3  8.5  6.0  6.5  7.0  7.5  8.0 ArH  SIH  ZrHZr  I  I  I  8.5  8.0  7.5  I  I  I  I  I  3.5  3.0  2.5  2.0  1.5  11111111111  7.0  6.5  6.0  4.5 5.0 (ppm)  5.5  4.0  1.0  . D 6 in C 5 H NMR spectrum of 5.3-d Figure 5.6. 400 MHz 1  . 3 2 and PhSiI-1 2 is obtained from 4.2-N By the same route used to prepare 5.3, 5.3-’N D there is a singlet at 6 6 N-Jabelled compound in C H} NMR spectrum of the 15 1 P{ In the 31 14.9 and a doublet of doublets at 6 —4.2  10 Hz, 3 JPN  JPN = 2 (  is similar to that of 5.3, but the doublet  JHH = 2 (  =  H NMR spectrum 3 Hz). The 1  9.7 Hz) observed for 5.3 appears to be a  N H{ NMR spectrum additional coupling to the 15 1 P} broad multiplet at 6 3.94. In the 31 nuclei is observed for the peak at 6 3.94  (J  =  10 Hz,  JHN =  5 Hz, 3 JHN  =  3 Hz). In the  N} 5 ‘ H 1 { NMR spectrum there are two doublets of doublets at 6 —9.7 and —105.6. The two h group are coupled to each other 5 ’ NSiH rj’:r 1 N 5 P N nuclei of the 2 inequivalent 15 31 3 15 Hz), and each is coupled to P J( NP spectrum, an AMXX’ multiplet  JsN = 1 (  =  7 Hz,  3 Hz, 2 JNP  J 2  187  =  =  6 Hz,  (‘JNN =  H} NMR 1 Si{ 10 Hz). In the 29  J 3  =  3 Hz) is observed for 5.3-  , due to coupling to two different nitrogen-15 nuclei, and to one phosphorus-31 2 N 15 2 30 As for 5.3, the highest molecular weight peak in the mass spectrum of 5.3-N nucleus. corresponds to [M  —  Py].  The ORTEP representation of the solid-state molecular structure of 5.3 is shown in Figure 5.7. Zn in the dinuclear C, symmetric complex is coordinated to [NPN]*, Py and N5 h unit, whereas Zr2 is coordinated to [NPNJ*, and NNSiH P of the side-on—end-on bound 2 h. The bridging hydride, HI, can be located from the -NNSiH 2 1 ji-’:i N5 and N6 of P electron density map and refmes normally. The Zr—P and Zr—N bond lengths to [NPNI* are similar to others reported in this thesis, and are typical for Zr(IV) arnide and phosphine 32 and ’ The Zrl—N7 bond (2.408(3) A) is not unusual for Py coordinated to Zr, 3 complexes. is slightly shorter than the Zr—N bonds to Py in starting material 4.2, which average to 2.44  A. The ZnI—N5 bond is short (1.958(3) A) relative to the Zr2—N5 (2.142(3) A) and Zr2—N6 (2.064(3) A) bonds, reflecting the end-on vs. side-on bonding modes to Zn  and Zr2,  respectively. At 1.407(4) A, the N5—N6 bond is shorter than in the starting material, but can still be considered as a single bond. Also, the N5—N6 bond length is similar to other N—N bonds observed in the Fryzuk group for ri’:i -coordinated dinitrogen and functionalized 2 28 The N6—Sil bond is 1.737(3) A, typical of a N—Si single bond. The ’ 5 dinitrogen units.’  angles around N6 add to ‘—357°, indicating that N6 is nearly planar. Two views of the N, P, Si, and Zr atoms are shown in Figure 5.8.  188  Figure 5.7. ORTEP drawing of the solid-state molecular structure of {[NPN]*Zr(Py)}(ji Ph){Zr[NPNj*}, 5.3, (ellipsoids drawn at the 50% probability level). Carbon 2 H)(INNSiH atoms of the Mes substituents (except C) and all hydrogen atoms (except bridging hydride HI and HI Si, H2Si) have been omitted for clarity. Selected bond lengths  (A)  and angles  (°):  ZrI—PI 2.6853(11), Zr2—P2 2.7311(11), Zn—Ni 2.288(3), Zrl—N2 2.172(3), ZnI—N7 2.408(3), Zr2—N3 2.175(3), Zr2—N4 2.146(3), Zrl—N5 1.958(3), Zr2—N5 2.142(3), Zr2—N6 2.064(3), N5—N6 1.407(4), N6—Sil 1.737(3), Sii—C82 1.867(4), Znl---Zr2 3.2256(6), Ni— ZrI—PI 69.12(8), N2—Znl—P1 74.71(9), N3—Zr2—P2 70.60(8), N4—Zr2—P2 74.01(9), Zn— N5—Zr2 103.68(13), Znl—N5--N6 170.7(2), Zr2—N6—SiI 160.9(2), N6—SiI—C82 113.60(17), Ni—ZnI—N7 100.73(12), N5—N6—Sii 122.3(2).  189  Sil  N2  P1 P2  Figure 5.8. Two views of the N, P, Si, and Zr atoms in 5.3.  iH is synthesi2ed from u) Zr) ji-H)(ji-NNS ] N ([P ( 2 As mentioned in chapter one, B , and is an example of the formation of an N—Si bond 3 n and BuSiH N i-11 ]Zr) N ([P 0 : 2 ) by functionalization of coordinated dinitrogen (see Figure  5.1).13  The ‘H NMR spectrum of  u) shows broad singlets at 6 5.07 and 4.80 due to ii ]Zr) NNSiH i-H)(i-ii N ([P ( : 2 B inequivalent SiFT groups, and a broad quintet at 6 1.53 assigned to the bridging hydride. Whereas product 5.3 has a shorter N—N bond than is observed for starting material 4.2, the iH is 1.530(4) ]Zr) Bu) i-H)(j.i-NNS N ([P ( 2 N—N bond in ’  A,  N (1.43(1) r1 ]Zr) p-i1 N ([P ( : 2 N—N bond in starting material )  significantly longer than the  A).  That the N—N bond in  Zr) t-H)(ji] N 2 ([P 5.3 is shorter than the N—N bond in starting material 4.2, and in ( 2 or Bu) is not surprising; shorter N—N bonds are typically observed when the N NNSiH ’ 2 NNR groups are coordinated in the side-on—end-on mode rather than in the side-on mode. R coordinates side-on—end-on to the two Zr atoms in 5.3. 2 Thus far, it is unclear why NNSiH  190  The presence of one molecule of Py, however, means that both of the Zr atoms are sixcoordinate. 2 introduced in chapter one is the Another reaction between Si—H and coordinated N The N—N bond is cleaved, and a  addition of silanes to  3 react with new N—Si bond is formed in this reaction. Two equivalents of ‘BuSil-I N I-1’:ii (t-H) ([NPN]Ta) Q 2 ) ut) SC B 2 NSiH .  to  yield  the  bis(silylimide)  complex,  i([NPN]Ta) Q 2  j.t{[NPNTa(H)}Qi-H) ( 2 complex to produce 2 3 adds to the Ta-N PhSiH  29 This complex spontaneously ri with a new N—Si bond. NNSil-l : 1 ‘r1 2 P h){Ta[NPNI}, decomposes to give  Ph) {Ta[NPN] }, in which the N—N bond 2 { [NPN]Ta(H) } Qi-N) (ji-NSiH  is cleaved. 2 complex proceeds via 3 with the Ta-N It has been proposed that the reaction of RSiH Si—H addition across one of the Ta—N bonds to yield a new N—Si bond and a terminal tantalum hydride. Complex 5.3 may form by a similar mechanism: Si—H addition across a 3 to produce N— Zr—N bond in 4.2. Dinitrogen complexes 4.1 and 4.4 also react with PhSil-1 Si containing complexes,  h) {Zr[NPN] } -NNSiH ‘:rj P { [NPN] *Zr(THF) } Qi-H) (t-ii 2 *  and  Ph) (ji-H) 2 2 h) {Zr[NPN]* }, respectively. -NNSiH Qi-i’:rj P } { [NPN] *Zr(PMe  5.2.3 Reaction of 4.1 with 4,4’-dimethylbenzophenone. The addition of one equivalent of 4,4’-dimethylbenzophenone to a toluene solution of 4.1 initiates a blue-green to red-brown to orange colour change over 15 nun, at room temperature.  Upon  NNZC(4MeCoH l:ri 2 ) { {NPN] *Zr} 2(!-O) (u-ri 4  work-up,  5.4, is  isolated as a yellow-orange toluene-soluble powder in high yield (Equation 5.6). Although there are no peaks with m/  >  556 ([NPN]*Hz) in the mass spectrum, the results of  191  elemental analysis are consistent with the proposed formula plus co-crystallized benzene as is . 8 observed in ‘H NMR spectra of crystals of 5.4 dissolved in THF-d  (5.6)  4.1  5.4  D there are two singlets at ö —7.7 and 6 In the 31 H} NMR spectrum of 5.4 in C 1 P{ 10.4. In the ‘H NMR spectrum there are eight singlets at ö to ArCH 3 groups of [NPN]K, two singlets at ö  —  2.0, each integrating to 6H, due  2.2 integrating to 3H each due to (p  C=N groups, and ArH resonances consistent with the proposed C symmetric 2 ) 4 H 6 C 3 CH structure. Similarly, the predicted 10 ArCH 3 singlets at ö  20, and 41 peaks attributable to  ArC and CN groups appear in the ‘ C{’H} NMR spectrum. There are no resonances 3 H} NMR spectra. Although 1 characteristic of free or coordinated THF in the ‘H or ‘ C{ 3 strong peaks are apparent in the JR spectrum of 5.4 at about 1500 cm’ that can be attributed to a C=N stretch, several peaks are typically observed in this region for [NPN]*  complexes such as 4.1, and no single peak could be attributed to this ftmnctional group definitively. The ORTEP representation of the solid-state molecular structure of 5.4 is shown in Figure 5.9. Each Zr atom in the dinuclear structure is coordinated to one [NPN]* ligand, and an oxo group, and the NNC(p-MeC 2 fragment bridge the two Zr atoms. The N5—N6 ) 4 H 6 bond length is 1.357(10)  A, which is intermediate between a single and double N—N bond,  192  A).  and shorter than in the starting material 4.1 (1.503(6)  The N—N bond is slightly shorter  Ph in 5.3 at 1.407(4) 2 than that observed for side-on—end-on bound NNSiH  A,  and is within  the range of N—N bond lengths observed for side-on—end-on dinitrogen complexes. As was r is j.L-r N (ji-H) ([NPN1Ta) ( : 1 2 mentioned in chapter one, the N—N bond length in ) 1.319(6)  A.  The N6—C77 bond length is 1.347(12)  A,  consistent with a C—N double bond,  and the N5—N6—C77 angle is 120.6(8)°. The hydrazonato group coordinates to the two Zr atoms in an rI : bonding mode. The Zrl—N5 bond length is 2.016(7) 1  A,  N5 and Zr2—N6 bonds are much longer at 2.241(9) and 2.351(9)  A, whereas the Zr2—  respectively. The Zn—  N5—Zr2 angle is 93.0(3)°, and the Znl—N5—N6 angle is 155.0(6)°. The other bond lengths and angles within the bridging hydrazonato group are unremarkable. The Znl—O1 and Zr2— 01 bonds are the same, within error, and average to  A) is  slightly longer than the Zr2—P2 bond (2.687(3)  -  1.97  A.  The Zrl—P1 bond (2.711(2)  A), whereas the Zn—NI, Znl—N2, Zr2—  N3, and Zr2—N4 bonds are essentially the same length (-2.16  A,  on average). The other  bond lengths and angles are similar to those of the other [NPN]*Zr([V) complexes reported here. -NNCHPh) (pt-ri 2 r] :q jt-r 1 [(‘q Z ) 4 H 5 ( MeC Overall, this structure is reminiscent of 2 NNCHPh), which contains one equivalent of 2 :n1 hydrazonate and is prepared from 1 ,I-r1 NNCHPh, and BuLi (Figure 5.10). An example of a mononuclear 2 -MeC (ri Z ) 4 H 5 , 2 rCl H (r (OTf), U Cp* ( 2 N,N)MeN_NCPh complex with a side-on bound hydrazonate is ) Cp* U (OTf)(Me). This actinide complex has a CNN and 2 2 which is synthesized from Ph C=N double bond (1.32(3)  A)  and an N—N single bond (1.41(3)  A)  (Figure 5.10). While  these complexes are not examples of N 2 activation or functionalization, they provide a useful structural comparison to 5.4.  193  Figure 5.9. ORTEP drawing of the solid-state molecular structure of ( 2 {[N Z t i-O r} PN )(i] 6 ‘ : t ) 2 ) 4 H NNC 1 n (4-M , eC 5.4, (ellipsoids drawn at the  50%  probability level). Carbon atoms  of the proximal Mes substituents (except CJ and all hydrogen atoms have been omitted for  clarity. Selected bond lengths  (A) and angles (°): Zrl—P1 2.711(2), Zr2—P2 2.687(3), Zn—NI  2.166(8), Zrl—N2 2.145(7), Zr2-.-N3 2.189(9), Zr2—N4 2.160(7), Zrl—O1 1.962(6), Zr2—O1 1.982(6), Zrl—N5 2.016(7), Zr2—N5 2.241(9), Zr2—N6 2.351(9), N5—N6 1.357(10), N6—C77 1.347(12), C77—C78 1.460(14), C77—C85 1.475(13), Zn ---Zr2 3.0932(12), Znl—O1--Zr2 103.3(3), Zrl—N5—Zr2 93.0(3), N5—Zr2—N6 34.3(3), N5—Zr2—N6 34.3(3), N5—N6—C77 120.6(8), C77—N5—Zr2 161.7(8), Znl—N5—N6 155.0(6), N5—Znl--P1 161.8(2), N5—Zr2—P 2 149.4(2), N6—Zr2—P2 166.0(2), O1—Zr2—N6 111.2(3).  194  Figure 5.10. Two hydrazonato complexes: 1 -Ji-11 [(ri Z ) 4 H 5 ( 2 MeC r] :r1 -NNCHPh) (u-u 2  ‘  U Cp* M 2 eN_N=CPh (r1 (OTf). NNCHPh) and )  8 can be followed at The reaction of 4.1 with 4,4’-dimethylbenzophenone in toluene-d low temperature by 31 P {‘H} NMR spectroscopy. After mixing the two reagents at 253 K, the singlet at 8 5.0 due to starting material 4.1 decreases in intensity and two singlets integrating to 1P each at 8 —5.9 and —8.4 increase in intensity over 25 mm. at this temperature. About 10 mm. after warming the sample to 273 K, two singlets appear at 6 —7.7 and —10.4 that integrate to 1P each and are assigned to 5.4. The peaks due to 5.4 continue to increase in intensity over 20 miii. at 273 K, and over 15 miii. at 300 K, but the peaks at 6 5.0, —5.9 and  —  8.4 do not disappear. After 24 h at 300 K, the peaks at 6 —5.9 and —8.4 have disappeared, and peaks attributable to 5.4, 4.1, and minor impurities are observed in the 31 H} NMR 1 P{ spectrum. From this evidence it appears that the peaks at 6 —5.9 and —8.4 are due to an intermediate in the formation of 5.4, which may be a dunuclear complex with two inequivalent  phosphines.  One  proposed  195  formulation  is  {[NPN]*Zr}(u  r[O=C(pMeC the ketone adduct of the dinitrogen complex, with one }, 6 N){[NPNj*Z } 2 ) 4 H equivalent of 4,4’-dimethylbenzophenone coordinated. By analogy with the synthesis of h adduct 4.4, one equivalent of the bulky donor ligand replaces two equivalents of PMe P 2 coordinated THF in the starting complex. A mechanism for the formation of 5.4 is proposed in Figure 5.11.  Figure 5.11. Proposed mechanism for the formation of 5.4 from 4.1.  196  Thus far, the only evidence for the mechanism outlined in Figure 5.11 is the P{’H} NMR observation of an intermediate with two inequivalent P atoms by 31 spectroscopy at low temperature. It may be possible to obtain further mechanistic insight by  following the reaction by JR spectroscopy, or by UV-visible absorption spectroscopy. It should also be noted that impurities that also appear to be dinuclear Zr complexes with P{’H} NMR spectrum) form inequivalent phosphines (two equal intensity singlets in the 31 during this reaction if two or three equivalents of the ketone are added to 4.1, or if THF is  used as the solvent. A new N=C bond forms when 4,4’-dimethylbenzophenone reacts with the hyckazido ) fragment in 4.1 to produce the hydrazonato complex 5.4. In organic chemistry, 2 (N hycfrazones are prepared by the condensation reaction of hydrazine with an aldehyde or 6 The direct formation of N=C bonds from dinitrogen complexes and aldehydes or ketone.’ ketones is unusual. One example includes the addition of two equivalents of benzaldehyde to ] { [(calix- [4] -O)Nb] 2 (j.i-i 1; ‘-N 2 ) }, to generate PhHCN— 2 a Nb-N 2 complex, [Na(diglyme) N=CHPh with two new N=C bonds, and two equivalents of the Nb oxo complex, ][(cahx-[4]-O)Nb0]. Another example involves the addition of acetone to 4 [Na(T’HF) 37 (ji-N2) to give 8 ] 2 ) 3 [T’aCl,(PEt CN—NCMe Me . 2 ’ The authors also report the reverse of this reaction: PhHC=NN=CHPh reacts with 3 )(THF) M(CHCMe C 2 1 (M  =  Nb, Ta) to  generate 2 {MC1,(T’HF) ( } ,..t-ii 1:11 ‘-N2).  As mentioned in the introduction, another way to prepare N=C bonds from dinitrogen complexes is by a two-step process. First, a hydrazido complex is prepared by protonation of an N 2 complex; next, the condensation reaction between the hydrazido complex and an aldehyde or ketone furnishes the hydrazonato complex. For example, trans ] [BF 2 [MF(NNCRR’)(dppe) ] (M 4  =  Mo, W; R  197  =  Et, Ph, Me; R’  =  H, Me) forms upon  addition  of  RR’C=O  )(depe),]Br (M 2 {MBr(NNH  to =  . 9 [BF (dppe) 10 ) trans-[MF(NNH ] 2 ] 4 3 ’  Mo, W; depe  =  Similarly,  trans  H reacts with acetaldehyde to Et) PCH Et C 2 P  4 to yield trans Br, which can be reduced by LiAIH trans-[MBr(NN=CHMe)(depe) ] give 2 ° The addition of FcC(0)H or FcC(0)Me (1k 4 [MBr(NNEt)(depe)]Br.  =  Fe(q C (i ) 4 H 5 -  Ph) in the presence of catalytic HC1(aq) yields cis,mer 2 (PMe ] (NNH 3 2 cis,mer-[WC1 ) to ) C ) H 5 h) (R 3 ( [WCI P 2 ] NN=C(Fc)(R))(PMe  =  41 In the presence of the acidic hydride H, Me).  PF to produce trans (dppe) 6 ) trans-[W(OH)(NNH ] CO) acetone adds to 2 12 ( 3 HFeCo , 2 Mo and W hydrazido complexes are transformed into a PF (dppe) 6 ) [W(OH)(NNCMe ] 2 4 . wide range of complexes with coordinated hydrazones. Efforts directed at releasing these organic moieties from the metal complex have mostly been unfruitful. A high yield of h) and acetone in PMe 4 ( ) t-is-[W(N P 2 CN-NCMe can be obtained, however, from ] Me 2 3 H CH i-SH) BF ]Fe} 4 P [{[(Ph C P ) Q 2 ] 3 4 the presence of an unusual proton source, . The synthesis of new N=C bonds from group 6 hydrazido complexes and aldehydes or ketones proceeds via elimination of one equivalent of water. In contrast, group 4 or 5 transition-metal dinitrogen complexes react with aldehydes or ketones to produce stable 2 complex 4.1 is likely driven by the metal-oxo complexes. The formation of 5.4 from N nucleophilicity of coordinated dinitrogen and the oxophilicity of Zr. Although it may be N-NC(4-MeC from 5.4 by adding 2 ) 4 H possible to release an organic compound such as 6 acid or water to the complex, strong Zr—O bonds are expected to form, and it is difficult to envision a catalytic N=C bond forming reaction based on this process.  198  C(O)H. (CH C ) 5.2.4 Reaction of 4.1 or 4.2 with 3 C(=O)H to benzene or toluene (CH C ) The addition of one or two equivalents of 3 solutions of 4.1 or 4.2 produces an instant blue-green to yellow colour change (Scheme 5.1). Upon work-up, a hexanes-soluble yellow powder is obtained that contains multiple products P{’H} C(=O)H, the 31 (CH C ) by NMR spectroscopy. For the product formed from 4.2 and 3 D shows several peaks upfleld of ö 0 that can 6 NMR spectrum of the mixture dissolved in C be assigned to a mixture of at least four complexes with two inequivalent phosphines each (Figure 5.12). When the yellow powder is recrystallized from hexanes, a small amount of a yellow crystalline solid is obtained. Although the crystals still contain a mixture of P{’H} compounds, there is one major product with peaks at ö —10.7 and —14.9 in the 31 . The ‘H NMR spectrum shows singlets at ö D 6 NMR spectrum of the crystals dissolved in C ) 3 4.71 and 0.80 that integrate in a 1:9 ratio, consistent with the presence of an NCHC(CH unit. There are 13 large peaks at  2.0, a feature consistent with the major product being a  QIO)(J.i-NNC(H)C(CH is the 2 {[NPN]*Zr} 3 C, symmetric dimer. If a complex such as ) major product, two diastereomers with different orientations of the H and tBu groups relative to the C=N bond may be present in the mixture (Scheme 5.1). It may be possible to obtain one product selectively from the reaction of an aldehyde with coordinated dinitrogen by modifying the reaction conditions used, or by choosing a different aldehyde. As with ketones, the condensation of an aldehyde with a hydrazido ] reacts with salicylaldehyde 4 complex is well known. For example, [WF(NNH)(dppe) ] [BF 2  to give [WF(NNCHC ]. 4 -2-OH)(dppe) [BF 4 H 6  199  4  0  -4  -8  -20  -16  -12  -24  -28  (ppm)  ) obtained D 6 H} NMR spectrum of the yellow product (in C 1 P{ Figure 5.12. 162 MHz 31 CC(0)H and 4.2. ) 3 from the reaction of (CH  Scheme 5.1.  +  4.1  D 6 C  200  2  5.2.5 Reaction of 4.1 or 4.2 with benzophenone imine. Coordinated diriitrogen in 4.1 reacts with 4,4’-dimethylbenzophenone to yield a hydrazonato complex with a bridging oxo group. In an attempt to find new reactions for 2 with electrophilic organic compounds, the addition of benzophenone imine to {NPN]*ZrN 4.1 and 4.2 was studied. The addition of 2.1 equivalents of benzophenone imine to a toluene solution of 4.1 or 4.2 induces a blue-green to brown colour change. After about 15 reaction mixture becomes  clear red, and a bright red,  mm., the  toluene-soluble powder,  , 5.5, is isolated in high yield upon work-up (Equation (II112:rI2N 2 {[NPN]*Zr(NCPh)} ) 5.7). The same product forms regardless of whether 4.1 or 4.2 is used as the starting material.  C=NH 2 2Ph  (5.7)  toluene  4.2  5.5  , two singlets of equal intensity appear at D 6 In the 31 H} NMR spectrum of 5.5 in C 1 P{ 6 1.2 and —9.2. By analogy with 5.3 and 5.4, the red product is a dimeric complex with two H NMR spectrum acquired at 298 K, the peaks are broad different 31 P environments. In the 1 8 shows 14 peaks at 6 H NMR spectrum of 5.5 in toluene-d and overlapping. At 273 K the 1 3 groups (there are two sets of overlapping peaks), 2.0, attributable to 16 inequivalent ArCH and two doublets ( JHH 3  =  13.7 Hz) at 6 4.45 and 3.51 that each integrate to 1H and  correspond to two inequivalent NH groups. There are also ArH resonances consistent with  201  the proposed C 1 symmetric structure, although this region is complicated by the presence of C{’H} C=N ligands. In the 13 2 many inequivalent protons on the two [NPNI* and two Ph 3 groups, NMR spectrum acquired at 248 K there are 16 peaks that can be assigned to ArCH 1 symmetric complex. In addition, and 72 peaks in the aromatic region, as expected for the C two doublets at  175.4  7 Hz) and 170.5  J, = 3 (  (= J 3  8 Hz) can be assigned to inequivalent  2 nuclei in the complex. N=CPh In the mass spectrum of 5.5, the highest molecular weight peak corresponds to  (NH)(NCPh [{[NPNI*Zr} ) 2 J+ ({M  —  =  )]), and the results of microanalysis 2 (N + HN=CPh  are consistent with the proposed formula, plus co-crystallized solvent. By JR spectroscopy, 4 are observed that can be assigned to v(N-H), and two two peaks at 3390 and 3250 cm 45 It should be 4 are observed that can be assigned to v(C=N). peaks at 1623 and 1615 cm noted that the structure of 5.5 could not be determined with confidence until the results of X-ray analysis were obtained. The ORTEP representation of the solid-state molecular structure of the red product, ) {[NPNj*Zr(NCPh ( 2 I1]2: }2 -N ri ) H , 5.5 is shown in Figure 5.13. Each Zr atom is coordinated to [NPN]*, a ketimido group (Ph CN), and a side-on N 2 H unit bridges the 2 two Zr atoms in the dimer. Two peaks consistent with hydrogen atoms bound to N5 and N6 are apparent in the electron density map of the compound, but are not amenable to refinement. The kethnido fragments contain N=C double bonds (N7—C77 1.273(5) C90 1.279(5)  A, N8—  A), and coordinate to Zr with bond lengths that are shorter than Zr—N bonds  to [NPN]* (Zrl—N7 2.015(3)  A, Zr2—N8 2.007(4) A). The orientation of  [pj*  on Zn  makes one of the ketimido fragments nearly trans to P (P1—Zrl—N7 167°), whereas the ketimido on Zr2 is cis to P of [NPN]* (P2—Zr2—N8 78°). The angles around C77 and C90  202  add to ,3600 and 362°, respectively, suggesting that both C atoms are planar and sp 2 hybridized. At 1.507(4) material 4.2 (1.481(5)  A, the N5—N6 bond is slightly longer than is observed for starting  A), consistent with the presence of an N—N single bond. The N H 2  unit is not coplanar with the Zr atoms: the two ZrN 2 planes meet at a 138° angle. This represents a larger butterfly distortion than is observed for the N 2 complexes 4.1, 4.2, and 4.4, but a smaller butterfly distortion relative to the hydride-bridged dimer, 5.1. The Zr—N bond lengths to the N 2 unit are essentially the same, at about 2.22 Zr—N bonds to N 2 in 4.1, 4.2, and 4.4 (average to 2.05  A, and are longer than the  A). This is not unexpected since a  bridging [N ] unit is present in 5.5, rather than an N H 2 2 unit. The other bond lengths and angles in the complex are unremarkable. Two views of the N, P, and Zr atoms in 5.5 are shown in Figure 5.14. The two phospbines are staggered (P1—Zrl---Zr2—P2 167°) across the Zr---Zr axis, whereas the amides of [NPNI* on each Zr atom are nearly eclipsed (NI—Zn-Zr2—N3 22°, N2—Zrl---Zr2—N4 3°). The two ketiniido N atoms are also nearly eclipsed (N7—Znl ---Zr2—N8 23°).  203  Figure  5.13.  ORTEP  drawing  of  the  solid-state  molecular  structure  of  ) {[NPN]*Zr(NCPh U 2 .t1]2: }2 -N rI H ), 5.5, (ellipsoids drawn at the 50% probability level). Carbon atoms of the Mes substituents (except ) 30 and all hydrogen atoms have been C omitted for clarity. Selected bond lengths  (A) and angles (°): Zrl—P1 2.7718(11), Zr2—P2  2.7222(12), Zn—NI 2.172(3), Zrl—N2 2.179(3), Zrl—N5 2.229(3), Znl—N6 2.224(3), Zrl—N7 2.015(3), Zr2—N3 2.179(3), Zr2--N4 2.203(3), Zr2—N5 2.205(3), Zr2—N6 2.239(3), Zr2—N8 2.007(4), N5—N6 1.507(4), N7—C77 1.273(5), N8—C90 1.279(5), N1—Zrl—N7 112.99(13), N7—Zrl—N2 94.97(12), N7—Znl—N6 98.82(12), N7—Zrl—N5 113.78(12), N7—Zrl--P1 166.52(9), N5—Zrl—P1 78.43(9), N6—Zrl—P1 87.15(9), N8—Zr2—N5 101.49(13), N5—Zr2—P2 160.63(8), N8—Zn2—N4 121.64(13), Zr2—N5—Zrl 123.53(14), Znl—N6—Zr2 122.16(13), C77— N7—Zrl 165.1(3), C90—N8—Zn2 173.1(3).  204  N6 N2  P2  N5  P1 N3  N3  Figure 5.14. Two views of N, P, and Zr atoms in 5.5.  Overall, the reaction of benzophenone imine with 4.2 protonates coordinated N 2 to yield a dinuclear hydrazido complex with two Zr-coordinated ketimido 2 (Ph C =N) ligands. The mechanism of formation of 5.5 from 4.2 has not been explored, however, it may proceed by initial coordination of 2 Ph C =NH to Zr, followed by proton transfer to the nucleophilic coordinated dinitrogen. Another example of a ketimido complex is C T ) 2 ) (NH i(N CHP p , CPh h  which  also  contains  cyclopentadienyl  and  alkylamido  A This complex is prepared from ) 45 ligands. C T 2 S 3 iCECS i(M p iMe e and two equivalents of benzophenone imine, but the protons are transferred to one of the ketirnido ligands to give 2I Although this complex is not an example of N Ti-NHCHPI. 2 activation, it provides a useful structural comparison. Coordinated N 2 in 4.2 acts as a base in the reaction with benzophenone imine. As described in chapter one, side-on bound N 2 acts as a base in the reaction of 2 HNR 2 (NR  =  , N(H)NMe) with 2 NMe [ M 5 H 4 Z ( : 2 N ji T C r] ( e ) ) to yield ( [( M 5 H 4 Z ) 2 r(N C J 1 e ) R 46 : 1 H 2 N ii . New N—H bonds also form upon addition of alkynes, RCECH (R to this Zr-N 2 complex to yield 2 4 [ M 5 H 4 Z Q : ) H r(C 1 ( 1N C EC 6 . 1 1 11 R)1 e )  205  =  Ph, B t u,  2 complexes with Co. 5.2.6 Reaction of N  When toluene solutions of 4.1 or 4.4 are stirred under I atm of CO a colour change QIO) 5.6, is 2 {[NPN]*Zr} from deep green to dark yellow is observed. A yellow powder, , P{’H} NMR spectrum of 5.6 in isolated upon work-up in good yield (Equation 5.8). The 31 D shows one singlet at 6 C  —19.2. With four ArCH 3 singlets, and eight resonances in the  aromatic region, the 1 H NMR spectrum of 5.6 (Figure 5.15) is consistent with the proposed 3 C {‘H} NMR spectrum also shows the expected four ArCH h symmetric complex. The 13 2 C singlets, and 16 aromatic resonances. The molecular ion for 5.6 was detected by EI-MS, and the microanalytical data are consistent with the formula proposed.  (5.8)  4.4  5.6  206  ArCH3  ArH 5’’.O’6.5  O  8.0  7.5  7.0  6.5  6.0  5.5  4.5 5.0 (ppm)  4.0  3.5  3.0  2.5  2.0  . D 6 Figure 5.15. 500 MHz 1 H NMR spectrum of 5.6 in C  The formation of 5.6 under the conditions described above is reproducible. To determine if any carbon-containing products form, the reaction described above was repeated in C D solution. Complex 5.6 can be separated from the yellow-brown supematant 6 liquid by filtration. The 31 P{’H} NMR spectrum of the supernatant liquid shows peaks due to two major products: a singlet due to free PMe Ph, and two doublets present in a 1:1 ratio 2 at  —4.6 (7.5 Hz) and —9.4 (7.5 Hz). The chemical shifts of these resonances are typical for  phosphines of [NPNI* coordinated to Zr, and are tentatively assigned to a dinuclear complex with inequivalent phosphorus-31 nuclei that couple to each other. Such a complex with the [NPN]* ligand is not known to us: all of the dimeric species with inequivalent phospbines, e.g., 5.4, do not show coupling P-P coupling between [NPNI* ligands. For steric reasons, it is unlikely that {[NPN]*}zZr can form. Instead, a complex with a Zr—Zr bond may be present.  207  It has proved difficult to isolate such a complex, or to obtain meaningful information on this product and others that may be present in the supernatant liquid by GC-MS, EI-MS, ESI MS or NMR spectroscopy. When a C D solution of 4.4 is stirred under I atm of 13 6 C0 gas, a blue-green to yellowbrown colour change is observed over three hours. After two days, an aliquot of the clear yellow-brown solution shows a singlet due to free 2 PMe P h (50% by integration), and the two doublets at 6 —4.6 and —9.4  J 2 (  =  7.4 Hz, 30% by integration) as is observed when the  reaction is conducted under unlabelled CO. Two singlets at 6—7.1(14%) and —7.7 (20%) due to two unidentified products, and two singlets that can be assigned to 5.6 (2%) and 2 (2.8) (1%) also appear [NPNI*H in the P{ 31 H 1 } NMR spectrum. It is unclear why such a high yield of 5.6 is obtained when regular CO gas, rather than 3 ‘ C 0 gas is used in this reaction. The formation of 5.6 from  °2  or H 0 impurities in the CO cannot be ruled out at 2  this point, but decomposition reactions have not been observed when other air- and moisture-sensitive Zr complexes are treated with CO from the same cylinders used for this reaction. In addition, only a small volume of CO gas is used in these reactions; it would have to contain a large percentage of 02 to produce the amount of 5.6 observed. In the C{ 13 H 1 } NMR spectrum of the reaction mixture two large doublets are observed at 6 177.5 (5.3 Hz) and 124.5 (8.4 Hz). These peaks do not resonate at chemical shifts expected for zirconium carbonyl compo 47 unds. The reaction of 4.4 with higher purity CO gas, and attempts to characterize the products by mass spectrometry, IR spectroscopy, and other techniques is currently ongoing. The formation of N—C bonds by the reaction of CO with dinitrogen complexes is as yet unknown. The ball-and-stick representation of the solid-state molecular structure of 5.6 is shown in Figure 5.16. It is apparent that 5.6 is a dinuclear C 2 symmetric compound with two 208  bridging oxo groups. Two views of the stereochemistry of N, P, and 0 donors around Zn and Z2 are shown in Figure 5.17. The Zr—P (2.7390(9)  A) and Zr—N (2.13 A on average)  bond lengths are typical for Zr(IV) amidophosphine complexes, 32 and for the other [NPN]*Zr(IV) complexes reported herein. The Zr—O bond lengths average to about 1.98  A,  which is similar to Zr—O bond lengths reported for other dinuclear Zr(TV) compounds with bridging oxygen ligands. Examples of such complexes include [ZrCl Q-OH)(bdmpza)] 2 (bdmpza  =  (Zr—O: 1.96  bis(3,5-dimethylpyrazol-1 -yl)acetate) (Zr_O: 2.09  48 ] A), 2 {Zr[OB(IVIe ( 3 ii-OH) s) } 2’  49 and 2 A), Z (Cp ( t-O) rCl) (Zr—O: 1.945 A). o 5  The Zr---Zr separation in 5.6 is 3.0116(8) two Zr(TV) centres bridged by  2  A, which is consistent with the presence of  ions. If the bridging groups were 0H rather than  2,  Zr  in 5.6 would be in the 3+ oxidation state. Since 5.6 is neutral and diamagnetic, a Zr—Zr bond would be present, and a smaller Zr—-Zr separation would be expected. Examples of Zr—Zr bonded species with bridging  ligands appear to be absent from the literature, however,  Zr—Zr bonded species with bridging C1, Bi, and f ligands are well known. The Zr—Zr bond is typically between 3.1 and 3.2  A for chloride-bridged dinners, although the presence of Zr--  Zr bonds has also been inferred for complexes with longer Zr---Zr distances in the solid state. Thus far, the 3.0  A Zr-—Zr separation observed for 5.6 is typical for an oxo-bridged  Zr(IV) dimer. In contrast to the N 2 complexes described in chapter four, there is only a slight butterfly distortion between the Zr0 2 planes: the two Zr0 2 planes are —178 ° disposed to one another.  209  Figure 5.16. Ball-and-stick representation of the solid-state molecular structure of (tO) 5.6, (ellipsoids drawn at the 50% probability level). Carbon atoms of {[NPN1*Zr} , 2 the Mes substituents (except C ) and all hydrogen atoms have been omitted for clarity. 0 Selected bond lengths  (A)  and angles (°): Zrl—P1 2.7390(9), Zrl—O1 1.9800(19), Zrl—O1’  1.9819(19), Zn—NI 2.144(2), Znl—N2 2.111(2), Zr---Zr 3.0116(8), Znl—O1—Znl’ 98.95(9), OI—Znl—O1’ 80.58(9), P1—Znl—O1 164.13(6), PI—ZnI—OI’ 90.64(6), N1—Zrl—P1 70.01(6), N2—Zrl—P1  74.64(7), N2—Znl—N1  111.67(10), 01—Zn—Ni  123.29(8), 01—Zrl—N2 120.96(9), 01 ‘—Zrl—N2 113.32(9).  210  103.81(8), 01 ‘—Zn—Ni  P1’  N2’  01’  Ni 01 Ni  N2’ N2  01  P1 N2  NI’  Figure 5.17. Two views of the stereochemistry around Zr in 5.6.  5.2.7 Reactivity of 4.1 with ethylene. When a blue-green toluene solution of 4.1 is stirred under I atm of ethylene gas at room temperature for four weeks, the reaction mixture does not appear to change. The H} and 1 1 P{ H NMR spectra indicates that no reaction has absence of any new peaks in the 31 D solutions of 6 occurred. In contrast to the lack of reactivity observed for 4.1, C (i-i : ) N i { [NPN] Zr(THF) } 2  P{ H} 1 react with ethylene to give a white precipitate. By 31  NMR spectroscopy, the purple supernatant liquid only contains the dinitrogen complex, and the white precipitate, although it has not been characterized, may be polyethylene. The reaction of ethylene with a dinitrogen complex to generate an N—C bond is intriguing, albeit unknown. Olefin polymerization catalyzed by dinitrogen complexes, however, is not unprecedented. For example, a heterobimetallic Ti-N 2 complex, ) (W(depe) 2 N Cl) is a highly active catalyst for ethylene/i -hexene copolymerization in the 2 presence of modified methylaluminoxane. 51  211  5.2.8 Reaction of 4.1 with triphenyiphosphine oxide. The addition of one equivalent of triphenyiphosphine oxide to a toluene solution of 4.1 produces an instant blue-green to bright blue colour change. Small teal blue crystals, -N) {Zr[NPNJ }, 2 { [.NJpN}*Zr(0pph) } (-:r *  5.7, are obtained upon work-up (Equation  D shows three singlets at 6 40.4, 4.7, and 0.1, 6 } NMR spectrum of 5.7 in C 31 H 1 5.9). The P{ integrating to IP each (Figure 5.18). The two singlets at 6 4.7 and 0.1 are characteristic of a dinuclear complex with two different [NPN]* coordination environments, whereas the peak 52 Eight at 6 40.4 is at a chemical shift expected for coordinated triphenylphosphine oxide.  5 symmetric complex are apparent in the ‘H NMR 3 groups in the C singlets due to ArCH [NPN]* and Ph PO protons. 3 spectrum, and resonances in the aryl region are consistent with  C {‘H} 3 There are no signals that can be assigned to free or coordinated THF. Similarly, the ‘ 3 NMR spectrum indicates that the complex is C symmetric, since there are eight ArCH singlets and 40 peaks in the aromatic region.  (5.9)  5.7  212  ____  r-Et  (ppm) Figure 5.18. 162 MHz 31 H} NMR spectrum taken one hour after addition of 1 P{ triphenyiphosphine oxide to 4.1 in C . D 6  Unfortunately, crystals of 5.7 suitable for X-ray analysis could not be obtained from hexanes solutions of the blue compound. Upon dissolution of 5.7 in benzene or toluene, the blue solution turns green over 24 h, concomitant with the formation of a mixture of products indicated by 31 P {H} NMR spectroscopy. By analogy with the formation of (JLO) 3 2 -NNC(4-CH 2 (p-ii’:r ) 4 H 6 C ), { [NPN] *Zr}  OtO) 2 NNZPPh 2 l: ) { [NPN] *Zr} (J.t 3  may be present in the green mixture, along with 5.7 and other compounds. After several days at room temperature, there are still many peaks in the 31 P{’H} NMR spectrum of the green solution. The oxophilicity of Zr and the nucleophilicity of coordinated N 2 may drive the formation of a dimer with bridging oxo and phosphininiide groups, and it may be necessary to change the reaction conditions, or the phosphine oxide to obtain a phosphinimide complex selectively. Coordinated N 2 in a Ti-N 2 complex acts as a nucleopbile by attacking the phosphine donor of [NPN] to yield {[NP(N)N]Ti} 2 ([NP(N)N]  213  =  53 Another interesting facet C [hNSiMe P 2 ) 3 (=N)Ph] H) with coordinated phosphinimide. PO does not react with Py adduct 4.2 at 3 of the reaction of Ph PO with 4.1 is the fact that Ph 3 room temperature in C D over two weeks. The strength of Py donation and steric factors 6 may block this reaction.  5.3. Conclusions. In this chapter, the formation of N—H, N—Si, and N=C bonds from dinitrogen {Zr[NPN]*}  2 and complexes is described. The reaction of H  in high yield, with new N—H  provides  and Zr—H bonds. The product was characterized by solution NMR spectroscopy, isotopic labelling experiments, and by a low-resolution solid-state molecular structure. Similarly, *  Ph) (ji-H) 2 2 : (ii-1i NNH) 1 {Zr[NPNI } { [NPNJ *Zr(PMe }  can  be  from  prepared  {Zr[NPN]*} and H 2 in toluene. in  3 reacts with A new N—Si bond forms when PhSiH  in high yield. The C 1  toluene to give  symmetric complex has been characterized in solution by multinuclear NMR spectroscopy, Ph fragment is coordinated side-on— 2 and in the solid state by X-ray analysis. The NNSiH end-on to two Zr atoms, and the N—N bond length is 1.372(14) characterization of labelled  { [NPN]  *(p)  A. Synthesis and *  .NNSiH I 1 P h) {Zr[NPN] } } (.i-H) (u-il 2 also  support  the  and  proposed  structure. The addition of 4,4’-dimethylbenzophenone to provides  -NNC(4-CH ‘:T1 2 ) 4 H 6 C { [NPN] *Zr} 2Q-O) (u-’i 3  214  (,L-ii : 2 ) N i { [NPNj *ZrCrHF) } 1 in high yield. The solid-state  molecular structure indicates that the dimeric compound is C symmetric with bridging oxo C=N—Nj groups coordinated. The N—N 4 H 6 ([(p-MeC ) and side-on—end-on hydrazonato 2 bond is 1.357(10) 1.347(12)  A,  A, intermediate between a single and double bond,  and the C=N bond is  typical for a CN double bond. Benzophenone imine reacts with  N O : ) 11 t-q { [NPN] *Zr(Py) } 2  to yield  ) 2 2 N , Qri : ) i-ri }H { [NPN] *ZtQ=CPh  in which  JI {[NPN]*Zr(THF)} ( P=O to 2 3 coordinated dinitrogen is protonated. The addition of Ph {Zr[NPN]*},  :r1 i ) 2 N initially provides a blue complex, that continues to react in benzene solution to yield a green mixture of products.  The dinitrogen complexes described in chapter four react with a variety of compounds , and 4,4’-dimethylbenzophenone to generate new N—H, N—Si, and 3 , PhSiH 2 including H CC(0)H or ) 3 N=C bonds. Preliminary results indicate that the reactions of 4.1 with (CH PO may be worth pursuing. In addition, when other aldehydes, ketones, phosphine 3 Ph 2 complexes, new and interesting transformations may be oxides, or silanes react with the N 2 complexes with other observed. Clearly, it is worth exploring the reactivity of the N 2 complexes with arylacetylenes, boranes, substrates. In particular, the reactivity of the N ZrH may be profitable, since Cp alanes, CS , C0 2 , or organometallic compounds such as 2 2 4 complexes. 5 ’ 2 29 these compounds have been observed to react with other N  5.4. Experimental. 5.4.1. General experimental. H} NMR spectra 1 N{ General experimental procedures follow those of chapter two. 15 were recorded on a Bruker AV-400 direct detect spectrometer operating at 400.1 MHz for 2 at 6 0. 29 H} NMR spectra 1 Si{ ‘H NMR spectra and were referenced externally to MeNO  215  H NMR spectra were collected on a Bruker AV-400 instrument operating at 400.0 MHz for 1 and were referenced externally to TMS (6 0).  5.4.2. Starting materials and reagents. Hydrogen, carbon monoxide and ethylene gases were obtained from Praxair. C0) were purchased from Cambridge 2 C0 gas (<2% ‘ 3 Deuterium gas (RD 0.4%) and ‘ 0 used as reaction solvents were purified according 2 Isotopes Ltd. Toluene, benzene, and Et to the procedure outlined in chapter two, then stirred over sodium sand, and filtered through CC(=O)H ) 3 3 was degassed by three freeze-pump-thaw cycles. (CH Celite prior to use. PhSiH and benzophenone  mime were stored over activated Linde 4A molecular sieves and  degassed by three freeze-pump-thaw cycles. All other reagents were obtained from commercial sources and used without further purification.  )}(pH)(JJNNH){Zr[NPN]*} (5.1). Complex 4.3 (0.400 g, 0.287 3 {[NPN]*Zr(PMe 3 (0.010 g, 0.132 rnmol) was added. The mmol) was dissolved in toluene (10 mL), and PMe solution was transferred to a Teflon-sealed bomb and degassed by three freeze-pump-thaw cycles. At rt, the flask was filled with I atm of H 2 gas and sealed, and the contents of the flask were stirred vigorously for 6 weeks. Over 2 became light yellow-green, and after 5  —  —  3 weeks, the bright green solution  6 weeks an orange precipitate formed. In the  glovebox, the precipitate was collected on a flit, rinsed with pentane (10 mL), and dried under vacuum for 10 mlii. to obtain a yellow-orange powder (0.224 g, 0.160 nimol, 56%). The filtrate was stored under H 2 (1 atm) in a Teflon-sealed bomb for one week to obtain yellow crystals that were collected on a frit and dried under vacuum (0.105 g, 0.075 nimol, 26%). Samples of 5.1 can be stored in solution or in the solid state at —35 °C for months  216  3 (10 mg per 1 mL without decomposition. At rt, toluene solutions of 5.1 with added PMe toluene) can be stored for weeks without decomposition. Small yellow-orange crystals were grown from toluene/HMDSO at —35 °C. The amount of co-crystallized HMDSO was H NMR spectroscopy performed on crystalline samples consistent with the results of 1 dissolved in C . Orange single crystals suitable for X-ray analysis were grown in an NMR D 6 H solution of the compound with 6 2 by vapour diffusion of pentane into a C tube under H 3 added per I mL of benzene. 10 mg PMe , 400 MHz, 298 K): 6 D 6 H NMR (C 1 4H), 6.91-6.68 (m, 12H), 6.07 (dd,  =  7.98 (bt, 4H, 5 Hz), 7.45-7.25 (m, 4H), 7.14-7.00 (m, 8 Hz,J  IH,JHH =  =  6 Hz), 6.01 (dd, 1H,JHH  =  8 Hz,JHP 1H,  =  6 Hz), 5.86 (bs, 11-I), 5.83 (s, 1H), 5.71 (bs, 1H), and 5.47 (bs, 11-I) (ArH), 4.83  =  11 Hz, ZrHZr), 4.78 (bs, IH, NNH), 2.41 (s, 3H), 2.39 (s, 3H), 2.26 (s, 3H), 2.25 (s, 3H),  (t,  JHP  2.16 (s, 3H), 2.13 (s, 6H), 1.99 (s, 6H), 1.97 (s, 6H), 1.94 (s, 3H), 1.93 (s, 3H), 1.90 (s, 3H), , 0.19 (d, 9H,Jm (ArCH ) 1.88 (s, 3H), and 1.59 (s, 3H) 3 , 500 MHz, 253 K): 6 8 H NMR (toluene-d 1  =  . P(CH ) ) 5 Hz, 3  8.14 (dd, 2H, JHH  =  =  8 Hz, , 11 J  =  8 Hz), 7.62 (d,  1H, 7 Hz), 7.48 (d, 1H, 8 Hz), 7.45 (d, IH, 8 Hz), 7.34 (d, 1H, 9 Hz), 7.18 (m, 4H), 7.06 (m, 2H), 6.99 (m, 4H), 6.86 (d, IH, 8.5 Hz), 6.80 (d, 1H, 8.5 Hz), 6.76 (bs, 3H), 6.72 (s, 1H), 6.67 (s, 2H), 6.57 (d, 2H, 8 Hz), 6.16 (dd, 1H,J =  6 Hz), 5.79 (dd, IH, JHH  Hz) (AtH), 4.84  (t,  IH, 2 JHp  =  =  8 Hz, J,  =  =  8 Hz,JHP  =  6 Hz), 5.94 (dd, 1H,J  6 Hz), and 5.70 (dd, 1H, JHH  =  =  8 Hz,  8 Hz, JHP  =  6  11 Hz, ZrHZr), 4.82 (bs, 1H, NNH), 2.65 (s, 3H), 2.27 (s,  3H), 2.25 (s, 3H), 2.19 (s, 3H), 2.14 (s, 6H), 2.08 (s, 6H), 2.01 (s, 3H), 1.99 (s, 6H), 1.95 (s, ). ) 3 , 0.09 (bs, 9H, P(CH (ArCH ) 31-I’), 1.94 (s, 3H), 1.80 (s, 3H), 1.69 (s, 3H), and 1.64 (s, 3H) 3 , 202 MHz, 273 K): 6 8 } NMR (toluene-d 31 H 1 P{ 34.5 (d, 1P, 2 j  =  =  13.8 (d, IP,  =  56.7 Hz), —2.2 (s, IP),  56.7 Hz).  (N [{[NPN]*Zr} ) El-MS (m/: 1338 (4, 2  +  f’), 541 (100, [2.8 H 0 2  217  —  Me]).  —  3 C, 66.19; H, 6.76; N, 5.58; Anal. 01 67 Si 8 C 1 H 0 O 3 P 6 N : 2 Zr : 133 067 Anal. Calcd. for 5.1.(HMDSO) Found C, 65.98; H, 6.60; N, 5.50.  8 (0.7 mL) was stored at Decomposition of 5.1. A yellow solution of 5.1 (30 mg) in toluene-d  } 31 H 1 2 and gradually became light green. The major peaks in the P{ rt for two weeks under N NMR spectrum and the approximate percentages based on integration are listed below. , 202 MHz): ö 8 } NMR (toluene-d 31 H 1 P{  —5.0 (62%), —7.6 (13%), and —31.4 (19%).  =  )} (-D) (ji.-NND) {Zr[NPN] 3 { [NPN] *Zr(PMe  *)  (5.1- d ). 2  Complex 4.3 (0.300 g, 0.215  3 (0.010 g, 0.132 mmol) was added. The mmol) was dissolved in toluene (5 mL) and PMe solution was transferred to a Teflon-sealed bomb, and was degassed by three freeze-pump2 gas was added to the flask at rt. The solution was stirred vigorously for four thaw cycles. D weeks to obtain a deep green solution with a small amount of a yellow-green precipitate. The 2 pressure) behind 2 at 77 K and allowed to warm to rt (4 atm D flask was then refilled with D a blast shield. After the solution had been stirred vigorously for four weeks, the reaction mixture was a dark-orange suspension. The pressure was vented, and the reaction mixture  was taken to dryness to obtain a dark orange solid. The solid was triturated with hexanes to obtain an orange powder that was collected on a flit, washed with pentane (3  X  5 mL), and  2 and 5.1 was dried under vacuum (0.185 g, 0.132 mmol, 61%). A 10:1 mixture of 5.1-d P {‘H} NMR spectrum was identical to that of 5.1. obtained. The 31 ‘H NMR (toluene-4, 400 MHz, 253 K): 6  =  same as for 5.1 except the resonances at 6 4.84  3 resonances. and 4.82 integrate to 0.IH each rather than 1H relative to one of the ArCH El-MS (m/: 1396 (1, [M]), 541 (100, [2.8  —  Me]).  218  ph)} (ji-H)(i.-NNH) {Zr[NPNI *} 2 { [NPN] lcZr(pMe  (5.2). Complex 4.4 (0.380 g, 0.261  h (0.010 g, 0.073 mmol) were dissolved in toluene (7 mL). The bright PMe P mniol) and 2 green solution was transferred to a Teflon-sealed bomb and degassed by three freeze-pump2 gas, the bomb was sealed, and the thaw cycles. At rt the flask was filled with I atm of H  reaction mixture was stirred vigorously for 6 weeks. Over several weeks, the bright green solution gradually became light yellow-green and an orange precipitate formed. In the glovebox, the reaction mixture was taken to dryness, and pentane (10 mL) was added to obtain a yellow suspension that was chilled to —35 °C. The yellow solid was collected on a frit and dried (0.275 g, 0.188 mmol, 72%). Small yellow crystals were grown from toluene/HMDSO at —35 °C, and the amount of co-crystallized HMDSO was confirmed by . D 6 H NMR spectroscopy of samples of the crystals dissolved in C 1 , 400 MHz, 233 K): ö = 7.99 8 ‘H NMR (toluene-d  (t,  2H, 8 Hz), 7.80  (t,  IH, 8 Hz), 7.49 (d,  1H, 7.5 Hz), 7.41 (d, 1H, 7.5 Hz), 7.32 (d, 1H, 7.5 Hz), 7.27 (d, 1H, 7.5 Hz), 7.09 (m, 2H), 7.05 (s, IH), 6.97 (s, 2H), 6.89 (s, 2H), 6.81 (s, IH), 6.64 (m, IOH), 6.54 (s, 1H), 6.49 (s, 1H), 6.36 (bm, 2H), 6.07 (dd, (t,  2H,JHH  = 8 Hz,JHP = 6 Hz), 5.89 (m, 2H), 5.70  (t,  IH, 7 Hz), 5.48  IH, 7 Hz) (ArH), 4.94 (s, 1H, NNH), 4.88 (bs, IH, ZrHZr), 2.64 (s, 3H), 2.25 (s, 3H),  2.02 (s, 6H), 2.00 (s, 9H), 1.95 (s, 3H), 1.92 (s, 3H), 1.89 (s, 3H), 1.87 (s, 3H), 1.84 (s, 6H), h). (P(CH P 2 ) ), 0.53 (bs, 3H), and 0:33 (bs, 3H) 3 3 1.79 (s, 3H), 1.59 (s, 3H), 1.55 (s, 31-I) (ArCH , 162 MHz, 253 K): 8 = 14.6 (d, 8 } NMR (toluene-d 31 H 1 P{  2, = J  57.4 Hz, IP), —2.3 (s, IP),  —  24.6 (bs, IP). El-MS (m/: 1318 (5, [M  —  h]), (100, [2.8 PMe P 2  —  Mef).  r C, 68.22; H, 6.46; N, 5.55; Anal. 6 7 33 8 C 9 H 0 O 3 P 6 N Z 7 Si : 033) 2 5.2(HMDSO Anal. Calcd. for : Found C, 68.48; H, 6.62; N, 5.90.  219  ph)} (p-H) (p-N 2 NH) {Zr[NPN] *} 15 { [NPN] *Zr(pMe  ). 2 N 5 (5.2-’  Complex  2 N 15 5.2-  2 N 15 (0.163 g, 0.112 mmol, 82%) was prepared in an analogous manner to 5.2 from 4.42 in toluene (5 mL). Ph (0.010 g, 0.073 mmol) and H 2 (0.200 g, 0.137 mmol), PMe , 400 MHz, 233 K) is the same as that of 5.2, but the 8 ‘H NMR spectrum (toluene-d resonance at 8 4.94 is a doublet (IH, triplet (IH,  JHP =  JHN = 1  72 Hz), and the resonance at 8 4.88 is a broad  9.8 Hz).  , 400 MHz, 233 K): 8 8 P} NMR (toluene-d 1 ‘H{’  =  7.99 (d, 2H, 7 Hz), 7.80 (d, IH, 7.5 Hz),  7.49 (s, 1H), 7.41 (s, IH), 7.32 (s, IH), 7.27 (s, IH), 7.09 (m, 2H), 7.05 (s, 1H), 6.97 (s, 2H), 6.89 (s, 2H), 6.81 (s, IH), 6.64 (m, IOH), 6.54 (s, IH), 6.49 (s, 1H), 6.36 (bm, 2H), 6.06 (d, 2H, 8 Hz), 5.89 (d, 2H, 8 Hz), 5.70 (d, 1H, 7 Hz), and 5.48 (d, 1H, 7 Hz) (ArH), 4.94 (d, 1H, JHN =  72 Hz, NNH), 4.88 (bs, 1H, ZrHZr), 2.64 (s, 3H), 2.25 (s, 3H), 2.02 (s, 6H), 2.00 (s,  9H), 1.95 (s, 3H), 1.92 (s, 3H), 1.89 (s, 3H), 1.87 (s, 3H), 1.84 (s, 6H), 1.79 (s, 3H), 1.59 (s, Ph). 2 ) 3 Ph), 0.33 (bs, 3H, P(CH 2 ) 3 3H), and 1.55 (s, 3H) (ArCH ), 0.53 (bs, 3H, P(CH 3 , 162 MHz, 253 K): 8 8 P{’H} NMR (toluene-d 31 24.6 (bd, 1P,  =  14.6 (d, IP,  2, = J  57.4 Hz), —2.3 (s, 1P),  —  2 = 51.5 Hz). J  N{’H} NMR (toluene-d 5 ‘ , 40 MHz, 298 K): 8 8 El-MS (m/: 1320 (12, {M  —  =  143.9 (s), 29.8 (d,  Ph]’), 541 (100, [2.8 2 PMe  —  JNP = 2  10 Hz).  Me]j.  . A solution of 4.1 (0.365 g, 0.249 mmol) in toluene (10 mL) in a 2 Reaction of 4.1 with H thick-walled Teflon-sealed bomb was degassed by three freeze-pump-thaw cycles. At 77 K the flask was filled with H . The solution was warmed slowly to rt behind a blast shield. The 2 deep green solution was stirred for 6 weeks. No change was observed visually or detected by P{’H} NMR spectroscopy. 31  220  Reaction of 4.2 with H . A solution of 4.2 (0.430 g, 0.291 mmol) in toluene (15 mL) was 2 transferred to a thick-walled Teflon-sealed bomb and degassed by three freeze-pump-thaw 2 gas, and allowed to warm slowly to rt behind a cycles. At 77 K, the flask was filled with H blast shield. The solution was stirred vigorously for 8 weeks, and a gradual green to yellow colour change was observed. The pressure was vented, and the yellow reaction mixture was taken to dryness to obtain a yellow hexanes-soluble solid. , 121 MHz): ö D 6 P{’H} NMR (C 31  =  —7.6 (s), —8.0 (s), —21.3 (s), —31.4 (s).  q h) {Zr[NPN] NNSiH : 1 (j.i.P { [NPN] *Zr(Py)} (jt-H) 2  *}  (5.3). To a stirred solution of  4.2 (0.430 g, 0.291 mmol) in toluene (5 mL) at —35 °C was added dropwise a solution of phenylsilane (35 mg, 0.32 mmol) in toluene (2 mL). The reaction mixture was warmed slowly to rt, and it turned orange-brown after 5  mm. After 1 h, the clear orange-brown solution was  taken to dryness to obtain a brown residue. Hexanes (5 mL) were added to precipitate a brown solid that was collected on a frit, washed with pentane (2  X  5 mL), and dried under  vacuum to obtain a light brown powder (0.378 g, 0.248 mmol, 85%). Small crystals of 5.3 suitable for elemental analysis were grown by slow evaporation of a benzene/HMDSO solution of the compound. Samples obtained in this manner contain approximately 1 equivalent of HMDSO and I  —  2 equivalents of benzene of solvation, as determined by ‘H  . Larger single crystals of 5.3 were 8 NMR spectroscopy of the crystals dissolved in toluene-d grown by slow evaporation of a benzene solution of the compound. , 400 MHz): 6 D 6 ‘H NMR (C 1H), 7.86  (t,  =  8.25 (dd, IH,  =15 Hz, 2 JH  =  2 Hz, ZrHZr), 7.92 (bs,  2H, 8 Hz), 7.60 (bd, 1H, 7 Hz), 7.44 (bd, IH, 8 Hz), 7.29 (bd, 2H, 7 Hz), 7.15-  7.02 (m, 7H), 7.00 (s, IH), 6.92 (m, 5H), 6.86-6.77 (m, 6H), 6.73 (d, 3H, 7 Hz), 6.64 (s, 2H),  221  6.58 (s, IH), 6.09 (dd, 1H,JHH IH, J  =  8 Hz, JHP  =  =  8 Hz,JHP  6 Hz), 5.84 (m, 5H), 5.82 (s, 1H), and 5.72 (dd,  =  , (SiH ) 6 Hz) (ArH), 5.17 (d, 1H, 9.5 Hz), and 3.94 (d, 1H, 9.5 Hz) 2  2.57 (s, 3H), 2.47 (s, 3H), 2.22 (s, 3H), 2.16 (s, 91-1), 2.07 (s, 3H), 1.98 (s, 3H), 1.97 (s, 6H), . (ArCH ) 1.92 (s, 3H), 1.89 (s, 3H), 1.69 (s, 3H), 1.68 (s, 3H), 1.53 (s, 3H), and 1.24 (s, 3H) 3 , 162 MHz): D 6 } NMR (C 31 H 1 P{ , 80 MHz): ö D 6 } NMR (C 29 H 1 Si{  =  =  , 101 MHz): ö D 6 C{’H} NMR (C 13  14.9 (s, IP), —4.3 (s, IP). —34.4 (d, =  3= J  10 Hz).  162.7 (d, 27 Hz), 161.8  (a, 29 Hz),  160.6 (d, 31 Hz),  159.6 (d, 23 Hz), 152.6, 147.7, 147.5, 146.9, 146.7, 143.4, 139.6, 138.5, 137.8, 137.6, 137.5, 136.9, 136.6, 136.4, 136.1, 135.8, 135.1, 134.9, 134.7, 134.6, 134.5, 134.4, 134.0, 133.9, 133.8, 133.5, 133.4 (d, 3 Hz), 133.2, 133.0, 132.8, 132.5, 132.0, 131.9, 131.8, 131.6, 131.5, 130.3, 130.1, 129.9, 129.6, 129.5, 129.3, 129.2, 128.8 (d, 3 Hz), 127.3, 126.9 (d, 4 Hz), 125.6, 123.9 (d, 6 Hz), 123.2, 122.8 (d, 31 Hz), 121.9 (d, 32 Hz), 119.9 (d, 40 Hz), 118.9 (d, 26 Hz), 118.1 (d, 7 Hz), 116.5 (d, 8 Hz), 115.2 (d, 11 Hz), 113.7 (d, 20 Hz), 113.6, and 112.7 (d, 19 Hz) (ArC), 21.1, 21.0, 20.94, 20.91, 20.8, 20.6, 20.47, 20.45, 20.37, 20.30, 20.08, 19.81, 18.83, . (ArCH ) 18.61, 18.54, and 17.98 3 El-MS (m/: 1424 (10, [M  —  Py}), 541 (80, [2.8  —  Me]j.  r i C, 68.57; H, 6.66; N, 5.49; 02 18 3 C 1 H Z P 7 ON S 2 5: : 1 ) H 6 Anal. Calcd. for 5.3(HMDSO)(C Anal. Found C, 68.59; H, 6.40; N, 5.60.  { [NPN] *zf(Py  )} (j.i.-H) (.i-11 2 5 d h) {Zr[NPNJ -NNSiH ‘:i P  *}  ). Complex 5.3- d 5 5 (5.3- d  10 (0.120 g, 0.081 nimol), and was prepared by the method used to prepare 5.3 from 4.2-d 3 (10 mg, 0.089 mmol) in toluene (5 mL). PhSiH  222  , 400 MHz): 6 D 6 H NMR (C 1 IH), 7.86  (t,  =  8.25 (dd, IH,  J 2  15 Hz,  JHp = 2  2 Hz, ZrHZr), 7.92 (bs,  2H, 8 Hz), 7.60 (bd, IH, 7 Hz), 7.44 (bd, 1H, 8 Hz), 7.29 (bd, 2H, 7 Hz), 7.15-  (a, 1H, 7 Hz), 6.64 (s, 2H),  7.06 (m, 7H), 7.00 (s, 1H), 6.92 (m, 5H), 6.86-6.77 (m, 6H), 6.73 6.58 (s, 1H), 6.09 (dd, 5.84 (dd, IH,JHH  =  IH,JHH =  8 Hz,J  =  8 Hz,J  =  6 Hz), 5.88 (dd, 1H,J  =  8 Hz,J  6 Hz), 5.82 (s, IR), and 5.72 (dd, IH,JHH  Hz) (ArH), 5.17 (d, IH, 9.5 Hz), and 3.94  =  =  6 Hz),  8 Hz,J  =  6  ), 2.57 (s, 3H), 2.47 (s, 3H), 2 (a, IH, 9.5 Hz) (SiH  2.22 (s, 3H), 2.16 (s, 9H), 2.07 (s, 3H), 1.98 (s, 3H), 1.97 (s, 6H), 1.92 (s, 3H), 1.89 (s, 3H), . (ArCH ) 1.69 (s, 3H), 1.68 (s, 3H), 1.53 (s, 3H), and 1.24 (s, 3H) 3  5 {Zr[NPN] 1 h) S1H : t 1 N 5 N’ P { [NPNJ *Zr(Py)} (-F{) (-‘i 2  *}  2 . Complex 5.3-N (5.3-N ) 2  2 (40 mg, 27 jimol) and N 15 was prepared by the same route used to prepare 5.3, from 4.2phenylsilane (4 mg, 37 jimol) in toluene solution. , 400 MHz): same as for 5.3, but resonance at 6 3.94 is a broad multiplet. D 6 H NMR (C 1 , 400 MHz): 6 D 6 { (C 31 H 1 P}  =  8.25 (s, IH, ZrHZr), 7.92 (bs, IH), 7.86 (d, 2H, 8 Hz), 7.60  (s, IH), 7.44 (s, IH), 7.29 (s, 2H), 7.13-6.77 (m, 19H), 6.73 (d, 3H, 7 Hz), 6.64 (s, 2H), 6.58 (s, 1H), 6.09 (d, IH, 8 Hz), 5.86 (m, 6H), and 5.72 (d, IH, 8 Hz) (ArH), 5.17 (d, IH, 9.5 Hz), and 3.94 (bm, IH,  JHH =  10 Hz,  JHN =  5 Hz, 3 JHN  =  , 2.57 (s, 3H), 2.47 (s, 3H), (SiH ) 3 Hz) 2  2.22 (s, 3H), 2.15 (s, 3Ff), 2.14 (s, 3H), 2.12 (s, 3H), 2.05 (s, 3H), 2.00 (s, 3H), 1.98 (s, 3H), . (ArCH ) 1.97 (s, 6H), 1.92 (s, 3H), 1.89 (s, 3H), 1.69 (s, 31-1), 1.68 (s, 3H), and 1.53 (s, 3H) 3 , 162 MHz): 6 =14.9 (s, IP), —4.2 (dd, IP, 2 D 6 } NMR (C 31 H 1 P{ JPN , 80 MHz): 6 D 6 } NMR (C 29 H 1 Si{  =  , 40 MHz): 6 D 6 } NMR (C 15 H 1 N{  =  15 Hz,  JNP =  —34.4 (ddd, 1 Js —9.7 (dd,  1JNN =  10 Hz).  223  =  5.5 Hz,  =  10 Hz, 3 JPN  =  3 Hz).  J= 2 = 9.5 Hz, 3 J  15 Hz, 2 JNp  =  10 Hz).  3 Hz) —105.6 (dd,  IJNN =  El-MS (m/: 1426 (30, [M  —  Py]j, 541 (40, [2.8  —  ). [C ] H Me]), 78 (100, 6  (5.4). A solution of 4.1 (0.380 g, 0.260 mmol) in toluene (5 mL) was chilled to —35 °C. To this stirred solution was added 4,4’dimethylbenzophenone (57 mg, 0.27 mrnol) in toluene (2 mL) dropwise. The reaction  mixture was allowed to warm to rt, whereupon it became brown after 10 mm. After 30 mm., the reaction mixture was a clear orange solution. After 4 h, the solution was taken to dryness to obtain a dark orange solid. Upon addition of pentane (15 mL), a yellow-orange solid remained, which was isolated on a fit, washed with pentane (2  X  5 mL), and dried to give a  bright yellow-orange powder (0.330 g, 0.216 mmol, 83%). Compound 5.4 was recrystaffized from benzene, and orange single crystals of 5.4 suitable for X-ray analysis were grown by slow evaporation of a benzene solution of the compound. The ratio of 5.4 to benzene in the H NMR spectroscopy of crystals of 5.4 crystals was consistent with that observed by 1 , and by X-ray analysis before solvent suppression. 8 dissolved in THF-d H NMR (C 1 , 400 MHz): ö D 6  =  7.79  (t,  2H, 8 Hz), 7.71  (t,  2H, 8 Hz), 7.40 (d, 2H, 8 Hz),  7.36 (d, 2H, 7 Hz), 7.08 (m, 5H), 6.93 (d, 2H, 8 Hz), 6.88 (d, 2H, 8 Hz), 6.83-6.74 (m, 1IH), 6.70 (s, 2H), 6.62 (d, 2H, 8 Hz), 6.55 (s, 2H), 5.84 (dd, (dd, 2H,JHH  =  8 Hz,J  =  2H,JHH =  8 Hz,J,  =  6 Hz), and 5.81  H , 2.13 3 C 4 H 6 (N—CC 6 Hz) (ArH), 2.22 (s, 3H), and 2.20 (s, 3H) )  (s, 6H), 2.09 (s, 6H), 2.04 (s, 6H), 1.99 (s, 6H), 1.94 (s, 6H), 1.92 (s, 6H), 1.83 (bs, 6H), and . (ArCH ) 1.68 (s, 6H) 3 P{’H} NMR (C 31 , 162 MHz): ö D 6 } NMR (C { 1 C 3 ‘ H , 101 MHz): 6 D 6  =  =  —7.7 (s, 1P), —10.4 (s, IP). 162.1 (d, 30 Hz), 161.0 (d, 25 Hz), 151.7, 143.2, 142.9  (d, 3 Hz), 138.6, 137.9, 137.3, 137.2, 136.84, 136.81, 136.5, 135.9 (d, 14 Hz), 134.6, 134.34, 134.28, 134.04, 133.95, 133.8, 133.6, 133.5, 133.4, 133.3, 132.6 (d, 8 Hz), 132.3, 130.75,  224  130.71, 130.5, 130.4, 130.1, 129.7, 129.3, 129.0, 128.9, 128.5, 128.3, 128.1, 127.9, 127.6, 119.5 (d, 33 Hz), and 115.0 (d, 10 Hz) (ArC and CN), 21.5, 21.4, 21.2, 21.0, 20.3, 20.2, 19.4, 19.19, . (ArCH ) 19.16, and 19.08 3 : C, 73.79; H, 6.25; N, 4.87; Anal. Found C, r 06 07 C 1 H Z 2 P 6 N :O H 6 Anal. Calcd. for 5.42.5C 73.52; H, 6.61; N, 4.49. JR (KBr): 3005 (w), 2952 (w), 2918 (m), 2855 (w), 2723 (w), 2030 (w), 1601 (s), 1509 (s), 1494 (s), 1468 (s), 1436 (m), 1390 (m), 1271 (s), 1242 (s), 1191 (m), 1155 (m), 1087 (m), and  . 1 1057 (m) cm  Low temperature reaction of 4.1 with 4,4’-dimethylbenzophenone. In a 3-mL vial, 4.1  8 (0.8 mL), and the blue-green solution was (10 mg, 6.8 prnol) was dissolved in toluene-d transferred to an NMR tube. In a separate 3-mL vial, 4,4’-dimethylbenzophenone (3 mg, 14 8 (0.1 mL) and transferred very carefully to a melting point jimol) was dissolved in toluene-d capillary tube via syringe. One edge of the open end of the capillary tube was chipped away, and the tube was transferred open-end-up to the NMR tube. The NMR sample was cooled H} NMR spectrum was acquired. The NMR 1 P{ to 253 K in the spectrometer probe, and a 31 tube was then removed from the spectrometer, shaken vigorously to mix for 30 s, and H} NMR spectra were acquired every 5 mm. at 253 K for 1 P{ returned to the cooled probe. 31 30 nun., then every 5  mm. at 273 K for 30 mm., then every 5 mm. at 300 K for 15 mm. A  -filled 2 final 31 H} NMR spectrum was acquired after the sample was stored in an N 1 P{ glovebox at rt for 24 h.  CC(0)H. To a stirred solution of 4.2 (0.489 g, 0.33 1 mmol) ) 3 Reaction of 4.2 with (CH CC(0)H (61 mg, 0.71 ) 3 in toluene (7 mL) at —35 °C was added dropwise a solution of (CH  225  mmol) in toluene (2 mL). The reaction mixture turned brown, then red, then yellow throughout the addition. After 24 h, the yellow solution was taken to dryness to obtain a yellow residue. The residue was triturated with hexanes (15 mL), and the yellow extracts were filtered through Ceite, and taken to dryness to obtain a yellow powder (0.230 g). , 162 MHz): 6 D 6 } NMR (C “P{ H 1  =  —6.5 (s), —6.6 (s), —9.3 (s), —10.7 (s), —13.7 (s), —14.9 (s).  Yellow crystals (60 mg) grew from a hexanes solution of the yellow powder at rt. , 162 MHz): 6 D 6 P{’H} NMR (C 31  =  —6.6 (s, 1P), —10.7 (s, 7P), —13.7 (s, 1P), —14.9 (s, 7P).  Peaks that appear consistent with the major product are noted below: , 400 MHz): 6 D 6 ‘H NMR (C  =  7.67  (t,  2H, 7 Hz), 7.49 (d, IH, 7 Hz), 7.29 (d, IH, 7 Hz),  7.18-6.97 (m, 8H), 6.89-6.73 (m, 12H), 6.66 (s, 2H), 6.24 (dd, 1H,J 6.13  (t,  2H, 7 Hz), and 5.43 (dd,  1H,JHH =  8 Hz,JHP  =  =  8 Hz,J,  =  6Hz),  6 Hz) (ArH), 4.71 (s, IH) (N=CHR),  2.53 (s, 3H), 2.46 (s, 3H), 2.30 (s, 3H), 2.25 (s, 3H), 2.20 (s, 3H), 2.15 (s, 6H), 2.13 (s, 3Ff), , (ArCH ) 2.10 (s, 3H), 2.09 (s, 6H), 2.06 (s, 6H), 1.95 (s, 3H), 1.88 (s, 3H), and 1.68 (s, 3H) 3 . (C(CH ) ) 0.80 (s, 9H) 3  N (5.5). To a stirred solution of 4.2 (0.360 g, 0.244 CPh z) }z(J.Lr)2:T)2 {[NPN]*Zr(N ) 2 H mmol) in toluene (5 mL) was added clropwise a solution of benzophenone imine (93 mg, 0.51 mmol) in toluene (2 mL). The reaction mixture turned brown through the addition, and it was bright red after 5  mm. The reaction mixture was stirred for 24 h, and the clear red  solution was taken to dryness to obtain a red solid that was suspended in pentane (2  X  5  mL), collected on a fit, rinsed with hexanes (5 mL), and dried (0.390 g, 0.232 mmol, 95%). Small crystals of 5.5 were grown by layer diffusion of HMDSO into a solution of the compound in benzene. The amount of co-crystallized solvent observed by microanalysis is . 8 consistent with that observed by ‘H NMR spectroscopy of samples dissolved in toluene-d  226  Single crystals of 5.5 suitable for X-ray analysis were grown by slow evaporation of a benzene solution of the compound. , 400 MHz, 273 K): 6 8 ‘H NMR (toluene-d  =  7.25 (m, 14H), 7.11 (m, 6H), 6.93 (m, IOH),  6.84 (s, 2H), 6.77 (d, 2H, 7.5 Hz), 6.67 (m, 2H), 6.53 (m, 3H), 6.42  (t,  2H, JHP  =  6 Hz), 6.26  (bt, 2H), 6.13 (s, 1H), 6.04 (bs, 1H), 5.97 (bs, 4H), and 5.65 (bt, IH) (ArH), 4.45 (d, IH, 13.7 Hz), and 3.51 (d, 1H, 13.7 Hz) (NH), 2.53 (s, 3H), 2.45 (s, 6H), 2.42 (s, 3H), 2.32 (s, 3H), 2.17 (s, 3H), 2.12 (s, 3H), 2.01 (s, 3H), 1.95 (s, 3H), 1.92 (s, 3H), 1.86 (s, 3H), 1.82 (s, 3H),  . (ArCH ) 1.75 (s, 6H), 1.42 (s, 3H), and 1.14 (s, 31-I) 3 , 162 MHz, 300 K): 6 =1.2 (s, IP), —9.2 (s, IP). D 6 H} NMR (C 1 P{ 31 C{’H} NMR (THF-d 13 , 101 MHz, 248 K): 6 8  =  175.4 (d, 7 Hz), and 170.5 (d, 8 Hz) (C=N),  165.2 (d, 30 Hz), 165.1 (d, 29 Hz), 162.1 (d, 26 Hz), 161.6 (d, 29 Hz), 149.8, 147.8, 146.8, 146.7, 141.7, 140.3, 140.2, 139.7, 139.3, 138.9, 137.5, 137.2, 136.9, 136.3, 136.0, 135.9, 135.6, 135.4, 135.3, 135.2, 134.8, 134.6, 134.4, 133.8, 133.7, 133.3, 133.0, 132.9, 132.7, 132.1, 132.0, 131.9, 131.5, 131.4, 131.2, 130.7, 130.6, 130.5, 130.3, 130.2, 130.1, 130.0, 129.9, 129.6, 129.4, 129.1, 128.9, 128.7, 128.6, 128.2, 128.1 (d, 2 Hz), 127.8, 127.4, 126.9, 126.7 (d, 4 Hz), 126.5 (d, 4 Hz), 121.1, 120.8, 120.7, 120.4, 118.4 (d, 8 Hz), 118.2 (d, 8 Hz), 117.8 (d, 2 Hz), 116.4 (d, 7 Hz), 115.4 (d, 8 Hz), 114.6 (d, 9 Hz), 114.4 (d, 9 Hz), and 112.7 (ArC), 21.9, 21.7, 21.6, . (ArCH ) 21.4, 21.3, 21.2, 20.8, 207, 20.5, 20.3, 19.3, 19.2, 19.1, 18.7, 18.5, and 18.4 3  N (]j, 2 [{[NPNI*Zr} ]+), 1318 (80, ) (NH)(NCPh 2 [{[NPN]*Zr} El-MS (m/J: 1484 (20, ) 541 (100, [2.8  —  Me]).  iO C, 71.51; H, 6.23; N, 6.35; Anal. 05 05 1 C S P 8 N 09 H, : 2 : Zr 05 Anal. Calcd. for 5.5(HMDSO) Found C, 71.54; H, 6.33; N, 6.48.  227  JR (KBr): 3390 (w), 3250 (w), 3051 (m), 3003 (m), 2918 (m), 2854 (m), 1623 (s), 1615 (s), 1574 (s), 1519 (m), 1514 (w), 1504 (m), 1494 (m), 1469 (s), 1393 (m), 1302 (w), 1269 (m), . 1 1241 (s), 1190 (m), 1154 (m), 864 (s), 813 (m), and 696 (s) cm  {[NPN]*Zr}(iO) (5.6). A solution of 4.4 (0.150 g, 0.103 mrnol) in C D (2 mL) in a 406 mL Teflon-sealed bomb was degassed with three freeze-pump-thaw cycles. At rt, the flask was filled with CO gas. The reaction mixture turned yellow after 30 s of shaking. The solution was stirred overnight to obtain a yellow-brown suspension. The solution was then 2 for I h. In the glovebox, the yellow precipitate was collected on a stirred under a flow of N fit, washed with hexanes (2 x 5 mL), and dried (0.106 g, 0.080 mmol, 78%). Single crystals of 5.6 were grown by slow evaporation of a benzene solution of the compound in an NMR tube. , 500 MHz): 6 D 6 ‘H NMR (C (t,  =  7.93  (t,  4H, 8.5 Hz), 7.41 (d, 4H, 6 Hz), 7.15 (m, 4H), 7.03  2H, 8 Hz), 6.78 (s, 4H), 6.77 (d, 4H, 8.5 Hz), 6.67 (s, 4H), and 5.98 (dd, 4H, 8 Hz, 6 Hz)  . (ArCH ) (ArH), 2.30 (s, 12H), 2.23 (s, 12H), 1.97 (s, 12H), and 1.92 (s, 12H) 3 , 202 MHz): 6 D 6 } NMR (C 31 H 1 P{ (C 126 MHz): 6 , D } NMR 6 { 1 C 3 ‘ H  =  =  —19.2 (s). 159.7 (d, Hz), 140.4, 137.6, 136.7, 134.6, 134.4, 134.0,  133.6 (d, Hz), 130.7, 129.8, 129.5, 129.2 (d, Hz), 128.5, 125.6, 119.6 (d, Hz), and 115.0 (ArC), 21.2, 20.8, 19.6, and 18.5 (ArCH ). 3 El-MS (m/: 1322 (60, [IV1]), 541 (100, [2.8— Me]).  r C, 68.95, H, 5.94; N, 4.23; Anal. Found C, 68.60; H, 6 8 C 7 H Z P 2 O 4 N Anal. Calcd. for 5.6: : 5.90; N, 4.63.  228  D (2 mL) in a 406 Reaction of 4.4 with ‘ C0. A solution of 4.4 (0.150 g, 0.103 mmol) in C 3 mL Teflon-sealed bomb was degassed by three freeze-pump-thaw cycles, and refilled with C0 gas at rt (1 atm). The reaction mixture was stirred vigorously and turned yellow-brown 3 ‘ 2 for 1 h. In the glovebox, a after 3 h. After 2 d, the flask was stirred under a flow of N portion of the yellow brown solution was transferred to an NMR tube. , 162 MHz): ö (C D } NMR 6 31 H 1 P{  =  —4.6 (d, 17%, 7.4 Hz), —7.1 (s, 14%), —7.7 (bs, 20%),  —  h). PMe P 9.5 (d, 17%, 7.4 Hz), —19.2 (s, 2.5%, 5.6), —31.4 (s, 0.8%, 2.8), —46.5 (s, 50%, 2 , 162 MHz): (C D } NMR 6 { 1 C 3 ‘ H  =  177.5 (d, 5.3 Hz), 124.5 (d, 8.4 Hz).  Reaction of 4.1 with ethylene. A solution of 4.1 (0.350 g, 0.239 niniol) in toluene (7 niL) in a 100-niL Teflon-sealed bomb was degassed by three freeze-pump-thaw cycles and filled 4 at rt (1 atm). The deep green solution was stirred for I month. No change was H 2 with C H} NMR spectroscopy. 1 P{ observed visually or detected by 31  Reaction of 4.1 with triphenylphosphine oxide. To a stirred solution of 4.1 (85 mg, 0.058 mmol) in toluene (3 niL) at —35 °C was added a solution of triphenyiphosphine oxide (18 mg, 0.065 mmol) in toluene (1 niL) dropwise over 5 miii. The reaction mixture turned bright blue throughout the addition, and was stirred for 30 miii. at rt. The bright blue solution was taken to dryness, and the blue-green solid was triturated with hexanes (10 niL). The blue extracts were filtered through Celite, and the filtrate was allowed to concentrate overnight at rt to obtain small teal blue crystals. The pale blue-green supematant liquid was decanted, and the crystals were dried under vacuum for 30 miii. (39 mg, 0.024 nimol, 42%). , 400 MHz): D 6 H NMR (C 1  =  7.86  (t,  7.43 (d, 2H, 7.5 Hz), 7.28 (m, 3H), 7.22  2H, 8 Hz), 7.53 (d, 2H, 8 Hz), 7.46 (d, 2H, 7.5 Hz), (t,  1H, 7.5 Hz), 7.11 (m, 4H), 6.87 (s, 2H), 6.80 (m,  229  16H), 6.53 (s, 2H), 6.58 Hz,JHP  =  (t,  IH, 7 Hz), 6.37  6 Hz), and 5.82 (dd, 2H,JHH  =  (t,  2H, 7 Hz), 6.33 (s, 2H), 6.14 (dd,  8 Hz,JHP  =  2H,JHH =  8  6 Hz) (ArH), 2.40 (s, 6H), 2.23 (s, 6H),  . (ArCH ) 1.99 (s, 6H), 1.96 (s, 6H), 1.93 (s, 12H), 1.70 (s, 6H), and 1.62 (s, 6H) 3 , 162 MHz): 8 D 6 } NMR (C 31 H 1 P{  =  , 101 MHz): 8 D 6 } NMR (C 13 H 1 C{  40.4 (s, IP), 4.7 (s, IP), 0.1 (s, 1P). =  163.2 (d, 32 Hz), 159.4 (d, 25 Hz), 145.5 (d, 4 Hz),  143.3, 139.3 (d, 28 Hz), 137.2, 136.6, 135.6, 135.1, 134.8, 134.4, 134.3, 134.2, 134.1, 133.8, 133.7, 133.6, 133.5, 133.4, 133.3, 133.1, 132.9, 132.8, 132.7, 132.4, 132.2, 131.5 (d, 3 Hz), 130.2, 129.7, 129.3, 128.9, 128.7, 128.4, 127.8, 125.6, 125.5, 118.3 (d, 34 Hz), 117.5 (d, 29 Hz), 114.3 (d, 8 Hz), and 113.4 (d, 11 Hz) (ArC), 21.1, 20.9, 20.5, 20.3, 19.8, 19.1, 18.5, and . (ArCH ) 15.7 3 D and the blue solution became green over 24 h at rt. 6 The blue crystals were dissolved in C } NMR spectroscopy. 31 H 1 After 24 h at rt, the green solution was analyzed by P{ , 162 MHz): 8 D 6 } NMR (C 31 H 1 P{  =  43.2 (s), 42.4 (s), 40.4 (s), 6.2 (s), 4.7 (s), 0.1 (s), —3.8  (s), —8.9 (s), —12.8 (s), —17.4 (s), —18.1 (s).  5.5  References.  Shah, V. K.; Brill, W. Proc. Nati. Acad. Sci. U.S.A. 1977, 74, 3249. 2  Eady, R. R. Chem. Rev. 1996, 96, 3013. Einsle, 0.; Schmid, B.; Tezcan, F. A.; Andrade, S. L. A.; Yosbida, M.; Howard, J. B.;  Rees, D. C. Science 2002, 297, 1696. B) Yang, T.-C.; Maeser, N. K.; Laryukhin, M.; Lee, H.-I.; Dean, D. R.; Seefeldt, L. C.; Hoffman, B. M. J. Am. Chem. Soc. 2005, 127, 12804. Leigh, G. J. The World’s Greatest F&-, Oxford University Press: New York, 2004, p. 17. 4 Smil, V. Nature 1999, 400, 415.  230  6  A) Chatt, J.; Pearman, A. J.; Richards, R. L. Nature 1975, 253, 39. B) Chatt, J.; Pearman, A.  J.; Richards, R. L. J.  Chem. 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J.; Hollander, F. J.; Bergman, R. G. Oranometallics 1993, 12, 3705. B) Cross, R. 52  J.; Farrugia, L. J.; Newman, P. D.; Peacock, R. D.; Stirling, D. J.  Chem. Soc., Dalton Trans.  1996, 4449. Morello, L.; Yu, P.; Carmichael, C. D.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2005, 127, 12797. A) Spencer, L. P.; MacKay, B. M.; Patrick, B. 0.; Fryzuk, M. D. Proc. NatI. Acad. S 54 USA 2006, in press. B) van Rijt, S.; MacKay, B. M.; Patrick, B. 0.; Fryzuk, M. D.  unpublished results.  235  Chapter Six Thesis Overview and Future Work  6.1 Thesis overview. S) (S [NPN]*Li ( This thesis describes a new arene-bridged diamidophosphine ligand, 2  =  , THF), its coordination to Zr(IV) and Hf(IV), and the application of [NPNJ”Zr 2 0 8 H 4 p-C . At the outset, [NPN]* was designed 2 complexes to the activation and functionalization of N CH bridged [NPN] ligand, but 2 —SiMe to mintic the steric and electronic properties of the — with the reactive and moisture-sensitive N—Si bond replaced by an N—C bond. Remarkably, [NPN]*Li and [NPN]Li 1 Both 2 are nearly identical. the solution and solid-state structures of 2 N core. One major difference 2 compounds feature a P—Li bond and a diamond-shaped Li [NPNI*Li is prepared from air-stable organic compounds, between the two ligands is that 2 and  , 2 PhPC1  whereas  2 [NPN]Li  is  prepared  from  air-  and  moisture-sensitive  . In terms of structure and reactivity, there are 2 1, H and pyrophoric PhPH 2 PhN(H)SiMe C also many similarities between analogous [NPN]*Zr and [NPNIZr complexes. Another compelling similarity between [NPNJ and [NPN]* is that both ligands 2 complexes. support Zr-N  iN r1 0 } : 1 ) { [NPN] Zr(THF) 2  and  { [NPNj *Zr(THF) } 2O’-11-  . The 2 8 reduction of dichiorozirconium complexes in THF under N ) are prepared by KC 2 N solution and solid-state structures of these two complexes, as well as those of the corresponding Py adducts,  i N2) (ii-i1 : { [NPN] Zr(Py) } 2  and  i-ii r N2), Q : { [NPN] *Zf (Py) } 2  3 Phosphine adducts are essentially the same in terms of connectivity and stereochemistry. could not be prepared from 2 ri however, the addition of i-ri N2); ( {[NPNZr(THF)} : -  236  R (R 2 PMe  )}(i {[NPN1*Zr(PMe R (,IrI2:12N gives 2 2 {[NPN]*ZrHF)} Me, Ph) to )  =  N r {Zr[NPN]*} in high yield. This type of dinitrogen complex is unique because the : ri 2 ) two Zr atoms have different coordination environments. From the solid-state molecular h complex, it appears that [NPN]* blocks the coordination of a PMe P structure of the 2 R to these derivatives. The [NPN]Zr and [NPN]*Zr dinitrogen 2 second equivalent of PMe complexes are the first early transition-metal dinitrogen complexes for which the coordination environment at the metal can be altered simply by adding a donor molecule to N and its congeners, ([PNP]Zr(O (jt-i1 ([PNP]ZrCl) : 2 a dinitrogen complex. In contrast, ) , are prepared by reducing -N 1 ) Q-q 1:11 2 2 ) and ([PNP] ZrCp) r N ji-i1 ) 3 H 6 C 2,6-Me ( : 2 ) 4 . 2 separately prepared metal precursors under N 2 complexes of [NPNJ and [NPNJ* can also be compared. The reactivity of the Zr-N OI12:r12N or 2 2 {[NPN]*ZrHF)} When solutions of ) i are N (ji-ri {[NPN]ZrHF)} : ) and  3 For both 2 gas, no reaction takes place. exposed to H  2 provide a mixture of products that could , the reactions with H r N (ji-t {[NPN]Zr(Py)} : 2 ) not  be  separated.  ) {Zr[NPN] 2 N  *  }  Finally,  generates  the  addition  of H 2  to  )}(12:T12 {[NPN]*Zr(PMe R 2 *  ii {Zr[NPN] } : (ji-ri NNH) } (ji-H) 2  { [NPNj  with a  2 complexes new N—H bond. This reaction offers no direct comparison with the [NPN]Zr-N 3 adduct could be synthesized from 2 because no PR t-ri ri N2). 0 {[NPN]ZrCfHF)} : -  However,  it  may  only  be  possible  to  synthesize  )}QI12:12 {[NPN]*Zr(PMe R 2  N2) {Zr[NPN]*} because of the unique properties of the [NPN]* ligand. What is clear is that 2 is not observed when [NPN] is the ancillary ligand, the hydrogenation of side-on bound N but it is observed in one case when {NPN]* is the ancillary ligand. As is described in chapter 2 and a dinitrogen complex has been one, the formation of new N—H bonds from H  237  ]5 N 2 ]2 N 2 observed three other times: ([P (,.i-ri Zr) : ) 2 ri N , (i-ii Zr) : ) H ri N forms from ([P M 5 H 4 M ( i ) H jt-r1 N C (H)] e ) forms from [(ri 2 and [(i 2 M 5 H 4 M ( : ) .t-1i N C ii , e ) ] for M =  R adducts is the fourth example of an 2 6 Thus, the hydrogenation of the PMe Zr and Hf.  N—H bond forming from side-on bound dinitrogen. [NPN]*ZrN and [NPN]Zr-N 2 complexes provides 3 to the 2 The addition of PhSiH (JL 2 another opportunity to compare the reactivities of these two systems. {[NPN1*Zr(Py)} :r1 i ) 2 N  reacts  Ph){Zr[NPN]*} 2 NNSiH  with with  3 PhSiH a  new  to  { [NPN] *Zr(Py) } (pt-H) (ji-T’ :T12  yield  N—Si bond.  In  contrast,  the  reaction  of  3 In 3 provides an intractable mixture of products. (t-ri {[NPNjZr(THF)} : ) 2 ri N with PhSiH chapters one and five, some other examples of the functionalization of coordinated dinitrogen with silanes are described. [NPN]*ZrN and [NPN]Zr-N 2 complexes with ethylene gas offers The reaction of the 2 QL1]2:12N does not react 2 {{NPN]*Zr(IHF)} the final comparison for the two systems. ) with ethylene gas. In contrast, stirring a benzene solution of 2 Q {[NPN]ZrHF)} : ) N ii i-ii under 1 atm of ethylene results in the formation of a white precipitate that may be [NPN]*ZrN or 3 The other reactions that have been carried out using the 2 polyethylene. 2 complexes cannot be compared since different reagents have been used. When [NPN]-ZrN THF, CH 3 CN, 3 Q {[NPN]ZrcfHF)} : ) 2 ri N t-ii is reacted with p-tolylacetylene, allene, BH or ‘BuSiH , mixtures of products are obtained. 3 3 It is unclear whether any of these products form as a result of [NPNJ decomposition. [NPN]*ZrN complexes proceed selectively. For example, Several reactions of the 2  011 : ) i-11 N { [NPN] *Zr(THF) } 2  reacts  with  4,4’-dimethylbenzophenone  to  give  in high yield. Also, only one product forms  238  ir12:rI2NZ) with {[NPN]*Zr} ( from the reaction of the THF or Py adducts of 2 =CPh)} is obtained in , IIrI2:i12N {[NPN]*Zr(N ( ) 2 benzophenone imine. A red complex, H initially generates  =O to Ph P high yield. The addition of 3  =PPh . {Zr[NPNJ*} }(i12:12N 2 {[NPN]*Zr(O ) 3 one product selectively, bright blue ) At this point the following question remains unanswered: is the [NPNI* ligand  superior to [NPN] in terms of supporting new chemistry for coordinated dinitrogen and minimizing non-productive side reactions? So far, no ligand decomposition reactions or unusual donor atom migrations have been observed for complexes of [NPN]*. Further investigations may reveal whether side reactions have been minimized by eliminating the reactive N—Si bond from the backbone of [NPN], or by decreasing the flexibility of this diamidophosphine. The results reported in chapter five represent all of the reactions that have been attempted for the  2 complexes. Based on the numerous {NPN]*ZrN  transformations observed so far, it seems likely that other new and interesting reactions can F)} . I12:rI2N {[NPN]*Zr(H Q 2 be achieved starting from ) In this chapter, the synthesis of a phenyl-bridged diamidophosphine ligand with MesN and ArN (Ar  =  ) substituents (denoted 4 H 6 4-’PrC  PhMesJpJ  and  PhArpNJ)  is presented.  This ligand only differs from [NPN]’ reported in chapter two (section 2.2.1) in the substituents at N, but it is prepared in two steps from commercially available reagents. First, the bromodiarylamine ligand precursor is prepared in one pot from a substituted aniline and 1,2-dibromobenzene by a Pd-catalyzed cross-coupling reaction. Second, as with {NPN]’, the SOZ) and Q,C S[NPN1Lj 4 e M Ph . 2 lithiated ligands, H  5) Ph.ArpN]Li ( 2  (S  =  THF, p-C ), are 2 0 8 H 4  obtained from the bromodiarylamine, two equivalents of BuLi and O.5 equivalents of  239  PhAr[NPN1Zr(NMe is prepared in two steps from ) . 2 2 PhPC1  (rHf) 2 PhAr[PN]Li  by the  . ) 2 protonolysis method used to prepared [NPNI*Zr(NMe  6.2 Ongoing and Future Projects. [NPN]*Lij(pC can ) 2 O 8 H From commercially available compounds, the synthesis of 4 be accomplished in three or four steps, depending on whether p-tolylboronic acid used to 7 An alternative prepare (Mes)(Tol)NH is purchased, or prepared by a Grignard reaction. NH, which can (Ar)(2-BrC ) 4 H approach to an arene-bridged diamidophosphine ligand is via 6 be prepared in one pot from commercially available anilines and l,2-dibromobenzene by Pdcatalyzed cross-coupling. Although very few reports of C—N coupling reactions from 1,24 would H 6 C 2 8 it seemed unlikely that disubstituted 1,2-(ArNH) dibromobenzene are available, form in high yield due to steric congestion, at least for Ar  =  Mes.  [p]j Ph t 4  is  . As was outlined in chapter two, 2 )NH, BuLi, and PhPC1 4 H 6 synthesized from (Ar)(2-BrC phenyl-bridged diamidophosphine ligands are denoted [NPNJ’, and changes to P or N substituents are indicated by superscripts before the square brackets (e.g., with PhP and ArN substituents, a phenyl-bridged ligand is denoted  . PhAr[NPN]Li ) 2  6.2.1 Synthesis and characterization of Ph,Mes NH, 6.1, can be prepared in one pot from 2,4,6)(2-BrC 2 6 C 3 (2,4,6-Me ) 4 H trimethylaniline and 1,2-dibromobenzene, in the presence of 2 mol % (DPPF)PdC1 2 (DPPF =  1,l’-bis(diphenylphosphino)ferrocene), 4 mol % DPPF, and K093u in 1,4-dioxane upon  heating at 80 °C for three days (Equation 6.1). It is isolated as a white crystalline solid in fair yield (53%) upon work-up. Thus far, attempts to improve the yield of this reaction by increasing the amount of catalyst or trimethylaniline, heating the reaction for seven days, or  240  9 Excess (dba) and rac-BINAP) have failed. 2 (Pd by using a different catalyst and ligand 3 dibromobenzene and trimethylaniline can be removed from 6.1 by flash column chromatography, but  filtering  the reaction mixture  through  silica,  followed by  recrystallization, is also an effective method of purification. Compound 6.1 has been C {‘H} NMR spectroscopy, GC-MS, and combustion analysis. 3 characterized by ‘H and ‘ 2 (DPPF)PdCI +  I  1  JH  DPPF, KOtBu  (6.1)  1 ,4-dioxane iX, 3d  2 1H  6.1 es[p M Ph ‘-2  )), 6.2 (p 2 0 8 H 4 hP ] (p-C ) 4 H 6 (2-N(Li)C P )2 2 H 6 C 3 ) ([N-(2,4,6-Me 2 0 8 H 4 (b-C  2 , can be prepared from 6.1, two equivalents of “BuLi and 0.48 equivalents of PhPC1 C ) 2 0 8 H 4 ) (Equation 6.2). Toluene-soluble 2 O 8 H 4 in Et 0 by the same method used to prepare 2.7(p-C 2 D 6 ) is isolated as a yellow solid in high yield. It has been characterized in C 2 O 8 H 4 6.2.(b-C Li{’H} NMR spectroscopy, and in the solid-state by P{’H}, ‘ C{’H}, and 7 3 solution by ‘H, 31 single crystal X-ray diffraction.  0, 2 1. 4 BuLi, Et -35 °C; rt, 3 h 2  (6.2)  0, 2 2. PhPCI , Et 2 -35 °C; rt, 24 h 6.1  S  =  6.2 (CH 5 O 8  ) at 6 —35.2 2 0 8 H 4 P{’H} NMR spectrum of 6.2(p-C There is a quartet in the 31  (‘JPLI =  Li{’H} NMR spectrum. In 41 Hz), and a doublet (6 0.05) and singlet (6 —1.89) appear in the 7 the ‘H NMR spectrum there are three singlets at  241  3 groups. As for 6 2.3 assigned to ArCH  ), the ortho-methyl groups on MesN are inequivalent due to restricted rotation 2 O 8 H 4 2.7(p-C about N—C . Resonances attributable to ArH protons in the C symmetric compound and 0 H} NMR 1 one equivalent of coordinated dioxane are also evident. The peaks in the 13 C{ spectrum are also consistent with the proposed structure. ) is shown in Figure 6.1. The 2 0 8 H 4 The solid-state molecular structure of 6.2(p-C compound forms chains of 6.2 linked by clioxane molecules, and one half of each dioxane coordinated to 6.2 is shown in Figure 6.1. As with 2.72THF, there are two Li environments. Li2 is coordinated to NI, N2 and P1 of [NPN]’, and 01 of dioxane, whereas Lii is  coordinated to NI and N2, and 02 of another molecule of dioxane. The stereochemistry around Lii is distorted tetrahedral, and the stereochemistry around Li2 is distorted trigonal. The bond lengths are essentially the same as those in 2.72THF, within error. The P—Ui bond length is 2.484(8)  A, the Ui—N bond lengths average to about 2.06 A, and the Li2—N  bond lengths average to about 2.02  A. The Lil---Li2 separation is 2.474(12) A. The bond  lengths and angles are similar to those of 2 CH bridged —SiMe — CYPh[PNJLiHF)  and PhPh[NPN]LiCIHF)IAIO  242  çHF) 2 CYMeS[PLi  Figure 6.1. ORTEP drawing of the solid-state molecular structure of  .(t) 2 PhMes[NPyLi  ) (effipsoids drawn at the 50% probability level). Half of each 2 0 8 H 4 dioxane), 6.2(p-C molecule of dioxane coordinated to 6.2 in the 1-D network is shown. All hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles (°): P01—LiOl 2.484(8), NOl—LiOl 2.065(9), N01—Li02 2.014(10), LiOl---Li02 2.474(12), O01—Li02 1.910(9), 02— LiOl 1.892(9), N02—Li02 2.022(9), N02—LiOl 2.056(9), P01—LiOl—Li02 77.4(3), NOl—LiOl— N02 103.7(4), LiOl—N01—Li02 74.7(4), O01—Li02—N01 126.3(5), O01—Li02—N02 122.7(5), 002—LiOl—NOl 123.8(5), 002—LiOl—N02 118.8(4).  The proligand, [NPNJ’H , 6.3, can be prepared from 6.2t-C 2 ) and Me 2 O 8 H 4 NHC1 in 3 THF (Equation 6.3), and is isolated as a white solid in quantitative yield. In C D solution, 6 [NPN]*H (2.8). There is a singlet in the 31 H} NMR spectrum at ö —34.3. 1 P{ 6.3 is similar to 2  In the ‘H NMR spectrum, there is a sharp singlet at two broad singlets at  2.14, due topara-methyl on MesN, and  2.06 and 1.92, due to two on’ho-methyl groups on MesN. There are  243  also two broad singlets at ö 6.77 and 6.72 assigned to meta C—H groups. As with 2.8, H} NMR 1 C{ hindered rotation about N—C 50 broadens resonances on MesN. In the 13 spectrum of 6.3, peaks due to ortho-methyl  (  18.2 and 18.0) and meta carbons  (  135.9 and  H and 13 H} NMR spectra 1 C{ 135.8) are also broad. The other resonances observed in the 1 can all be assigned to groups in the proposed C symmetric diaminophosphine.  (6.3) THF  6.2 S  =  6.3  dioxane  The solid-state molecular structure of 6.3 is shown in Figure 6.2. The P—C bond lengths are the same within error, at 1.83  A,  and the C—P—C angles are 103°, with C16—  P1—C22 slightly shorter at 102.24(10)°, possibly due to crystal packing effects. The bond C N(2,6lPr ) 3 ) 4 H 6 . (2_NC PPh hl oH There is a lengths and angles are similar to those of 2 distance of 3.66  A between C19 on the (C )P group of 6.3 in the asymmetric unit and C20 5 H 6  of the other molecule of 6.3 in the unit cell (Figure 6.3), which is consistent with the presence of weak intermolecular it-It interactions in the solid state. 12  244  Figure 6.2. ORTEP drawing of the solid-state molecular structure of  2 PhMeS[NPN]H  6.3  (ellipsoids drawn at the 50% probability level). All hydrogen atoms except HIN and H2N (located from the electron density map) have been omitted for clarity. Selected bond lengths  (A) and angles (°): NI—Cl 1.436(3), Nl—CI0 1.390(3), Pl—C15 1.835(2), Pl—C16 1.833(2), PI—C22 1.830(2), N2—C27 1.400(3), C15—P—C16 103.11(10), C15—Pl—C22 102.83(9), C16— PI—C22  102.24(10),  ClO—NI—CI  121.10(18), Nl—Cl—C2  123.99(18).  245  119.30(19),  C27—N2—C28  Figure 6.3. ORTEP representation of crystal packing in 6.3. it-stacking interactions may be )P substituents (3.66 A) at the centre of the unit cell. 5 H 6 responsible for close contact of (C  2 C (2.7) and [NPN]*H 4 p 2 [NPN]*Li soa) Phenyl-bridged 6.2 and 6.3 are similar to H  (2.8) by all the methods used to characterize the compounds thus far. The electronic and steric effects of replacing one Me group on the arene backbone with hydrogen are probably minimal, and the synthesis of group 4 complexes of PhMes[NpN] by a protonolysis route is ongoing. Although 6.2 and 2.7 are similar, other modifications to the arene-bridged diamidophosphines may have a greater impact on the structure and reactivity of the ligand and its complexes. It is likely that aniidophospbine ligands could be synthesized with different P or N substituents, and the nature of the backbone could also be altered.  246  6.2.2 Synthesis and characterization of PI1ArLNPN18 (Ar  =  . 4-PrC ) 4 H 6  The synthesis of bromo(diarylamine) ligand precursors from 1,2-dibromobenzene is a convenient new route to diamidophosphine ligands with different amide substituents. For rC 6.4, can be prepared in moderate yield as a colourless NH, P 1 (4) 6 ) 4 (2-BrC example, H PrC 1 4N 4 H 6 , H 1,2-dibromobenzene, and NaOtBu in the presence of oil by refluxing 2 (dba) (1 mol %) and rac-BINAP (2 mol %) in toluene (Equation 6.4). Since 6.4 is a liquid 2 Pd 3 at room temperature, it cannot be purified easily by recrystallization. Instead, 6.4 must be separated from unreacted 1,2-dibromobenzene by column chromatography. As with 6.1, the 8 The compound has been characterized by optimization of the synthesis of 6.4 is ongoing. H and 13 1 H} NMR spectroscopies, EI-MS, and combustion analysis. 1 C{  (dba) 2 Pd 3 u rac-BINAP,NaO B t  (6.4)  +  2 NH  6.4 cy,C 6.5(p-C 4 . Ph.Ar[NPN1Li ) 2 O 8 H ), can be prepared from 6.4, two equivalents 2 O 8 H 4 2 in Et 0 (Equation 6.5). The product is isolated in 2 of BuLi, and 0.48 equivalents of PhPC1 high yield as a yellow solid that is freely soluble in toluene, and somewhat soluble in hexanes. H NMR spectrum can be assigned to protons in the C symmetric The major peaks in the 1 )(24 H 6 complex, and minor peaks are consistent with the presence of about 5% of (4-’PrC )NLi. When 6.5(b-C 4 H 6 LiC ) is recrystallized from hexanes/THF at —35 °C, 6.52THF 2 O 8 H 4 is obtained. In the 1 H NMR spectrum, signals due to coordinated THF appear and there is no peak due to dioxane. In addition, only peaks attributable to the major product are present. The isolated yield of 6.5, however, is decreased upon recrystallization. There is a  247  quartet  (‘JPL =  42 Hz) at 6 —34.8 in the 31 H} NMR spectrum, and a doublet (8 —0.36) and 1 P{  D (Figure 6.4). In 6 singlet (6—1.70) appear in the 1 Li{ 7 H } NMR spectrum of 6.52THF in C the ‘H NMR spectrum, a heptet at 6 2.83 and two doublets at 6 1.26 and 1.25 are assigned to  2 and two inequivalent CH(CH ) 3 CH(CH 2 groups, respectively. Resonances in the aromatic ) 3 region can be assigned to protons in C symmetric 6.5, and there are two resonances consistent with the presence of two equivalents of coordinated THF. In the 13 C {‘H} NMR spectrum, the expected resonances for ArC, CH(CH , CH(CH 2 ) 3 , and coordinated THF 2 ) 3 ) forms in 2 O 8 H 4 appear. Ongoing efforts to optimi2e this reaction indicate that 6.5(p-C 2 slowly to the Et O 2 higher yield and purity by adding exactly 0.50 equivalents of PhPC1 solution of the proposed intermediate, 6 P 1 (4) ) 4 H (2-LiC NLi, rC slowly warming the reaction mixture to room temperature, and fmally, heating the reaction mixture to reflux 3 overnight.’  -30  -32  -34  -36  -38  6  2  -2  (ppm)  (ppm)  Figure 6.4. 31 P{’H} and 1 Li{ 7 H } NMR spectra of 6.52THF in C . D 6  248  -6  -10  1. 4 BuLI, Et 0, 2  I 2  -35°C;rt3h  (6.5)  NH  I  [LJ  PhPCI Et , 0, 2 2. 2 -35°C;rt,24h  6.4 6.5 S  =  THF or dioxane  ) is 2 0 8 H 4 The ORTEP representation of the solid-state molecular structure of 6.5(p-C shown in Figure 6.5. The compound forms a one-dimensional chain of PhAr[p] units bridged by 1,4-dioxane. The P1—Li2 bond length is 2.477(7) A. The N—Lu bond lengths are similar and average to 1.98 A, and the N—Li2 bond lengths are similar, but average to —2.06  A. The 0—Li bond lengths are identical, within error, at about 1.87 A, and the Lil---Li2 separation is 2.418(10) A. The bond lengths are very similar to those of 6.2(p-C ) and 2 0 8 H 4 are slightly shorter than thosç of 2.72THF.  249  Figure 6.5. ORTEP drawing of the solid-state molecular structure of  .Q, 2 PhArNPLi  ), 6.5(p-C 2 0 8 H 4 C ) (ellipsoids drawn at the 50% probability level). All hydrogen atoms 2 O 8 H 4 and the carbon atoms of dioxane have been omitted for clarity. Selected bond lengths and angles (°): P1—Li2 2.477(7), Ni—Lu Lii 1.978(9), 01—Lu  (A)  1.974(9), N1—Li2 2.050(9), N2—Li2 2.079(8), N2—  1.867(8), 02—Li2 1.868(8), Lil---Li2 2.418(10), P1—Lii—Li2 80.9(3),  N1—Li2—N2 102.8(3), Lii—Ni—Li2 73.8(3), Lii—N2—Li2 73.1(3), 01—Lu—Ni 123.4(5), 01—  Lii—N2 126.7(5), 02—Li2—N1 131.3(4), 02—Li2—N2 120.0(4).  2 6.6, can be prepared in two steps from 6.52THF by the same PhAr[NPN1Zr(NMez)  [NPN]*Zr(NMe (2.9) (Scheme 6.1). First, excess Me ) route used to prepare 2 NHCl is added 3  to a THF solution of the lithiated ligand. The yellow suspension turns white instantly, and 2 Ph.Ar[NPN]H  is isolated in quantitative yield as a white translucent residue upon work-up.  There is a singlet at 6 —32.4 in the 31 H} NMR spectrum of’[NPNj’H 1 P{ 2 in 6 ]) The 1 C . H NMR spectrum (Figure 6.6) features a doublet  (J  = 6 Hz) at 6 6.39 assigned to NH, a  heptet at 6 2.66 assigned to CH(CH , and a doublet at 6 1.12 assigned to CH(CH 2 ) 3 , as well 2 ) 3  250  C{ 3 ‘ H } NMR spectrum are also as the expected aromatic protons. The peaks in the 1 consistent with the proposed structure for the proligand.  CH (CH3)2  —ArH—  (ppm) rpN1H in C 4 Ph Figure 6.6. 500 MHz 1 H NMR spectrum of 2 . D 6  PhAr[NPNJH is mixed with equimolar Zr(NMe In the second step, 2 4 in toluene. ) 2 ) 2 PhAr[NpN1Zr(NMe  (6.6) is obtained in high yield as a toluene-soluble yellow powder (see  Scheme 6.1). A singlet is observed at 6 —10.0 in the 31 H} NMR spectrum of 6.6 in C 1 P{ . D 6 In the 1 H NMR spectrum (Figure 6.7), there are singlets due to two inequivalent N(CH 2 ) 3 groups at 6 2.84 and 2.51, and a heptet (6 2.76) and doublet (61.19) due to CH(CH 2 and ) 3  2 groups of the para-isopropyl substituents, as well as the expected ArH peaks for ) 3 CH(CH the C, symmetric complex. Although two doublets are expected for the two inequivalent  2 groups (6 ) 3 CH(CH  1.2), these resonances overlap. Two singlets are observed for the  inequivalent CH(CH 2 groups at 6 24.3 and 24.2 in the ‘ ) 3 C{ 3 H} NMR spectrum. The 1 expected CH(CH 2 (6 34.0), N(CH ) 3 2 (6 41.5, and 40.7), and ArC peaks also appear. ) 3  251  Scheme 6.1.  NHCI 3 xs Me  4 ) 2 Zr(NMe  THF  toluene  6.6  6.5 S  THF, dioxane N(CH3)2  CH(CH3)2  —ArH  CH(CH3)2  1J  5.5  4.5  3.5  .5  (ppm)  Figure 6.7. 500 MHz 1 H NMR spectrum of 6.6 in C . D 6  The ORTEP representation of the solid-state molecular structure of 6.6 is shown in Figure 6.8. Tridentate [NPN]’ coordinates to Zr facially, and the P1—Zn—Ni (72.06(5)°), and P1—Znl—N2 (70.70(5)°) angles are less than  900,  as was observed for [NPN]” complexes  of Zr and Hf. The geometry at Zr can best be described as intermediate between trigonal  252  14 The bond lengths and angles are as expected: the P1— bipyranildal and square pyramidaL Zn bond length is 2.7353(6) about 2.16  A.  A.  The N—Zr bonds to [NPN]’ are the same within error, at  2 approximately trans to P (2.053(2) ) 3 The N3—Zr bond to N(CH  longer than the N4—Zr bond (2.0253(19)  A). The  A)  is slightly  solid-state molecular structure of complex  [NPNJ*Hf(NMe (2.14). The two structures have similar ) 6.6 can be compared to that of 2 5 In 2.14, M—P and M—N bond lengths, and these fall within the range of expected values.’ the P1—Hf—Ni and P1—Hf—N2 angles (72.89(4), and 70.71(4)°) are similar to those in 6.6. The P1—Zr—N3 angle (155.11 (6)°) is slightly mote acute than the P1—Hf—N3 angle (163.60(6)°). The N1—Zr—N2 (125.14(7)°) and N3—Zr—N4 angles (104.44(8)°) are slightly mote obtuse than N1—Hf—N2 (120.91(6)°) and N3—Hf—N4 (100.92(8)°). It will be necessary to prepare other group 4 [NPN]’ complexes to determine if 6.6 differs from 2.14 because the dianiidophosphine ligand is less bulky, or because of other factors (e.g., identity of the metal, crystal packing).  253  , ) 2 Figure 6.8. ORTEP drawing of the solid-state molecular structure of PhAr[NPN]Zt(NMC  6.6 (effipsoids drawn at the 50% probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles (°): P1—ZrOl 2.7353(6), N1—ZrOl 2.1563(19), N2—ZrOl 2.159(2), N3—ZrOl 2.053(2), N4—ZrOl 2.0253(19), P1—ZrOl—N1 72.06(5), P1—ZrOl—N2 70.70(5), N3—ZrOl—N4 104.44(8), N1—ZrOl—N2 125.14(7), P1— ZrOl—N3  155.11(6), P1—ZrOl—N4 100.37(6), N1—ZrOl—N4 115.42(8), N2—ZrOl—N3  98.62(8).  The preparation of PhAr{PNlZrC and its application to nitrogen activation are ongoing projects in the Fryzuk group. The  PhArpJ  ligand may support very different  . For example, the intramolecular cyclometalation reaction that occurs t chemistry than [NPN] 3 S [NPN]*Zr(CH 2 iMe cannot occur for the Ph) and ) 2 spontaneously for [NPN]*Zr(CH ph) because it lacks on’ho-methyl substituents. If 2 proposed complex PhAr[NpZt(CH  254  alkyizirconium complexes of [NPN]’ can be prepared, their reactivity with H 2 should be explored; zirconium hydrides are attractive starting materials for Zr-N 2 complexes. Since [NPNJ and [NPN]* ligands support dinuclear side-on Zr-N 2 complexes, it is likely that a similar N 2 complex can be prepared with [NPN]’. It will be interesting to determine the effect the [NPN]’ ligand has on the structure and reactivity of a Zr-N 2 complex. PhArpN]  is expected to mimic [NPN] more closely than [NPN]* does because both  contain ArN substituents without bulky ortho- or meta-substituents. [NPN]TaMe, reacts with 2 to yield 4 H (j.i-H) which reacts with N 2 ([NPN]Ta) , 2 to give 2 0 {[NPN]Ta} ( ii-ri’:i .i-H) 16 This unusual reaction has proven difficult to replicate when other N substituents on N2). PhAr[NPN]TaMe (Ar = 2,6-Me [NPNJ are present. For example, when 3 ) is stirred under 3 H 6 C 2 4 O 2 IH) does not form.’ , (PhAr[NpN]Ta) 2 H 7 Only one other [NPN] ligand,  CyPhp]  supports a Ta(V) trimethyl complex that yields a Ta(IV) tetrahydride upon reaction with 18 The sensitivity of this reaction to the amide substituent of [NPN] is a compeDing . 2 H reason to prepare a complex such as PhAr[NPN]TaMe, and characterize its reactivity with H . 2 [NPN]* has bulky MesN substituents compared to PhAr[NpNl. There are, however, other aniide substituents that would provide even greater steric bulk. For example, it may be possible to synthesize bulky  (s) PhArpN]Li 2  (Ar = 2 Pr S = p-C t 2,6, 3 H 6 C , THF) 2 0 8 H 4  (Figure 6.9) by a similar route used to prepare 6.5(p-C 02) from 2,6-’Pr 8 H 4 3 and 1,2H 6 C 2 dibromobenzene. If a super-bulky diamidophosphine ligand, such as  2 PhAr[JpN]jj(5)  (Ar =  Pr (Figure 6.9) can be prepared, it may support new reactivity for 1 3,5-(2,6) 3 H 6 C 2 coordinated N . Extremely bulky triamidoamine ligands were recently used to carry out the 2 first catalytic formation of NH 3 from 9 .’ A simpler diamidophosphine ligand, 2 N (5) Ph1PrpN]U 2  (Figure 6.9) is less bulky than [NPN]*, but the ailcyl substituents will  255  increase the basicity of the amides. Thus, the PrN-substituted ligand may not be ideal for the synthesis of dinitrogen complexes, but the ligand may be suited to other applications.  , and ‘Pr substituents [3,5-(2,6-’Pr ] ) 3 H 6 C r 2 2 P 1 2,6, 3 H 6 Figure 6.9. [NPN]’ ligands with C  on N (S  =  THF or dioxane).  Some other variations of {NPNI’ are illustrated in Figure 6.10. The synthesis of ligands such as CYMes[NPN]Li(S)  (S) should be possible if commercially 2 and Me5[NPN]Lj  2 in the metathesis reaction with 6.1. 2 and ‘PrPC1 available CyPC1 2 are used instead of PhPC1 The use of substituted anilines should allow the electronic properties of the ligand to be (S) less basic, whereas 2 N donors will make PhAr[NpN]J.i (4-CF ) 4 H 6 C tuned. For example, 3  N donors will make the amide donor more basic. (4-MeOC ) 4 H 6 ° 2  Figure 6.10. Variations on [NPN]’ with GyP, ‘PrP, and (4-CF )N substituents. 4 H 6 C 3  256  In addition to varying the N and P substituents of a diamidophosphine ligand, the backbone itself may be altered. Although the use of Si—N bonds in the backbone should be avoided, other C—N bridged ligands could be explored. A 2,3-substituted naphthalene-linked diamidophosphine ligand may be a starting point in the design of hemilabile ligands for late transition metals with applications to photochemistry (Figure 6.1 1).21 It should be possible to tune the ligand electronics by adding electron-donating or -withdrawing groups to the linker. PPh2(S)) 2 ) H 6 C 3 For example, it may be possible to prepare ([N-(MesN)-2-N(Li)-5-CF NH and p 4 H 6 C 3 4-CF (Figure 6.11) by the same route used to prepare [NPNj’, from 2 B(OH) It may be possible to synthesize chiral diamidophosphine ligands with alkyl 4 H 6 MeC . 2 linkers (Figure 6.11) for applications to chiral synthesis.  Figure 6.11. Diamidophosphine ligands with alternative bridging groups.  6.2.3 Other reactions of zirconium dinitrogen complexes. The  reactions  of  , 2 H  , 3 PIISiH  CO.  ethylene,  4,4’-dimethylbenzophenone,  benzophenone imine, Ph PO, and Me 3 CC(0)H with Zr-N 3 2 complexes are explored to some extent in this thesis. The addition of other silanes, ketones, phosphine oxides, and aldehydes to the Zr-N 2 complexes may help to shed light on the factors governing these reactions. In addition, the reactions of 4.4 with H , 4.1 with 4,4’-dimethylbenzophenone or 2 PO, or 4.2 with benzophenone iniine may be good candidates for mechanistic study 3 Ph  257  because of the time required for the reaction, the colour changes observed, and the potential to use UV-vis, JR or NMR spectroscopy to follow the formation of products or intermediates. Other reactions that may yield new N-element bonds include the addition of 2 complexes. The ZrH to the Zr-N Cp ) boranes, alanes, or transition metal hydrides (e.g., 2 2 complexes should be attempted because new N—C bonds reaction of alkynes with Zr-N form from the addition of ArCECH to 2 . The addition of aldehydes N ii Ni-i ([P ( : ) ]Zr) or ketones that contain additional functional groups, such as olefins, may yield interesting new products. For example, the addition of dibenzy]ideneacetone (dba) to 4.1 may generate a new C=N bond, followed by reaction of Zr with an olefm group. There are many potentially 2 complexes described in chapter four and organic or interesting reactions between the Zr-N inorganic reagents that have not yet been explored.  6.3 Conclusions. In  this  chapter,  onho-phenylene-bridged  an  diamidophosphine  ligand,  (p.C is described. The bromodiarylamine precursor to this ligand is 4 e M Ph . ) 2 O 8 H s[NpN1Li NH in one pot by a Pd-catalyzed 2 H 6 C 3 synthesized from l,2-dibromobenzene and 2,4,6-Me C—N coupling reaction. By a similar procedure, the bromodiarylamine ligand precursor, (4, rC P 1 ) 6 ) 4 H NH(2-BrC dibromobenzene.  is  prepared  in  one  pot  from  PrC 1 4N 4 H 6 2 H  and  1,2-  From this compound, the less bulky diamidophosphine ligand,  ) 2 PhAT[NPNILi.Q,CHO  (Ar  =  , 6 P 1 4) 4 H rC  is  synthesized.  A  Zr(IV)  complex,  .) is prepared from the lithiated ligand by a two-step protonolysis route. 2 PhArpN1Zr(NMe The Pd-catalyzed C—N coupling route to bromodiarylamine ligand precursors described in this chapter allows arene-bridged diamidophosphine ligands with different substituents at N to be prepared. Thus far, this synthetic strategy has provided two ligands:  258  PrC substituent. The synthesis of 1 4N 4 H one with a bulky MesN substituent, and one with a 6 group 4 complexes of these ligands, and the application of these complexes to the activation and functionalization of molecular nitrogen are ongoing projects in the Fryzuk group.  6.4 Experimental. 6.4.1 General experimental. General experimental conditions are as given in chapter two. GC-MS spectra were recorded on an Agilent series 6890 GC system with a 5973 Mass selective detector.  6.4.2 Starting materials and reagents. 27 were prepared according to , 2 24 3 , 4 ) 2 Zr(NMe (dba) 2 Pd 2 , 5 DPPF, 26 and (DPPF)PdC1 literature methods. Dichlorophenylphosphine, and 2,4,6-trimethylaniline were distilled prior to use. Trimethylamine hydrochloride was suspended in benzene and heated to reflux overnight in a Dean-Stark apparatus to remove water. 1,2-Dibromobenzene was stored over activated Linde 4  A molecular sieves and sparged with N 2 prior to use.  BuLi (—l.6 M in  hexanes) was titrated against benzoic acid in THF with o-phenanthroline as an indicator. All other compounds were purchased from commercial suppliers and used as received.  )(2-BrC 2 C 3 (2,4,6-Me ) 4 H 6 NH (6.1). (DPPF)PdC1 2 (0.620 g, 0.848 mmol) and DPPF (0.939 g, 1.69 mmol) were added to 1,4-dioxane (100 mL). To this mixture was added K093u (6.2 g, 55.4 mmol), 1,2-dibromobenzene (10 g, 42.4 mmol), and 2,4,6trimethylaniline (7.4 g, 54.8 rnmol). The orange-brown mixture was heated to reflux for 3 d,  cooled, and taken to dryness to obtain a brown residue. The residue was suspended in EtOAc (100 mL) and the suspension was filtered through a plug (—5 cm deep) of silica in a  259  120-mL glass frit. The dark yellow filtrate was taken to dryness to obtain a light brown residue. The residue was dissolved in petroleum ether (50 mL), and the solution was transferred by 5-mL aliquots onto a plug (5 cm deep) of silica in a 120-mL glass fit. The silica was then rinsed with 5-mL aliquots of petroleum ether until the yellow product was eluted from the silica. A brown by-product remained on the top layer of silica. The ifitrate was taken to dryness to obtain a yellow residue that was dissolved in EtOH. Dilute hydrochloric acid (0.01 M) was added dropwise to the yellow EtOH solution until the mixture became cloudy. The mixture was heated until it became clear yellow, and was cooled slowly to obtain white flaky crystals. The crystals were collected on a frit, rinsed with petroleum ether (2  X  5 mL), and dried (6.5 g, 22.5 mmol, 53%). To ensure that 6.1 was dry  and acid-free before use, the white crystals were dissolved in EtO and extracted with a O 4 S 2 Na 0 The organic layer was separated, dried over , 3 C 2 K saturated aqueous solution of . ifitered, and taken to dryness to yield white crystals. , 300 MHz): ö = 7.40 (d, 1H, 8 Hz), 6.79 3 ‘H NMR (CDC1  (t,  IH, 8 Hz), 6.77 (s, 2H), 6.37  (t,  IH, 8 Hz), and 6.19 (d, 1H, 7 Hz) (ArH), 5.49 (bs, IH, NI-I), 2.15 (s, 3H), and 2.00 (s, 6H) . (ArCH ) 3 , 75 MHz): 3 = 143.5, 136.0, 132.2, 129.0, 127.6, 127.4, 127.1, 118.2, D 6 C{’H} NMR (C 3 ‘  ). 3 112.1, and 109.0 (ArC), 20.4, and 17.4 (ArCH GC-MS: 17.6  mm  (m/: 291 (100, [M + I-1]).  Br: , C, 62.08; H, 5.56; N, 4.83. Found: C, 62.41; H, 5.47; N, 4.72. 6 H 5 C, Anal. Calcd. for N  es[NpN]Lj.(CHO) (6.2(p-C M Ph )). To a stirred solution of 6.1 (8.7 g, 30.0 2 O 8 H 4 0 (250 mL) at —35 °C was added BuLi (1.6 M, 37.5 mL, 60 mmol) dropwise 2 mmol) in Et  over 15 mm. The clear yellow solution was warmed to  260  ft  and stirred for 3 h. The solution  0 (20 mL) was added dropwise 2 2 (2.58 g, 14.4 mmol) in Et was chilled (—.35 °C), and PhPCI over 2 h at this temperature. The reaction mixture turned dark orange throughout the addition. The orange solution was warmed slowly to rt and stirred for 24 h to obtain an orange-yellow suspension. The suspension was taken to dryness under vacuum to obtain an orange foam. Hexanes (100 mL) was added to the foam to obtain a translucent pale orange solution. Upon addition of I ,4-dioxane (5 mL) a yellow precipitate formed. The yellow suspension was frltered through Celite in a fit, and the yellow solids and Celite were rinsed with hexanes (3 x 10 mL). The yellow solids were then transferred to an Erlenmeyer flask along with some of the Celite. The yellow filtrate was allowed to concentrate overnight in the glovebox atmosphere to obtain small yellow crystals that were collected on a fnt and dried. Meanwhile, the yellow solids mixed with Celite were suspended in toluene (150 mL)  with THF added (2 niL), and the suspension was filtered through Celite (—3 cm deep in a glass fit). The yellow filtrate was taken to dryness to obtain a yellow powder. The combined ) were 2 O 8 H 4 solids (6.60 g, 10.5 mmol, 73%) were stored at —35 °C. Single crystals of 6.2p-C grown by slow evaporation of a concentrated benzene solution of the compound. , 300 MHz): D 6 { NMR (C 31 H 1 P}  7.81 (m, 4H), 7.05  -  6.99 (m, 5H), 6.97 (s, 2H), 6.89 (s,  2H), 6.60 (d, 2H, 8 Hz), and 6.58 (d, 2H, 8 Hz) (ArH), 3.35 (bs, 4H, dioxane), 2.34 (s, 6H), , 1.25 (bs, 4H, dioxane). (ArCH ) 2.32 (s, 6H), and 2.29 (s, 6H) 3 , 121 MHz): 6 D 6 } (C 31 H 1 P{  =  —35.2 (q,  :6 C ) D } (156 MHz, 6 i{ 1 L 7 H  =  0.05 (d, lii,  Ph,Mes  JPb =  41 Hz). =  41 Hz), —1.89 (s, iLi).  [NPN] ‘H 2 (6.3). Trimethylammonium chloride (0.836 g, 8.75 mmol) was added all at  ) (1.10 g, 1.75 mniol) in THF (15 mL). The yellow 2 0 8 H 4 once to a stirred solution of 6.2(p-C suspension immediately became colourless. After 1 h, the white suspension was taken to  261  dryness to obtain white solids. The solids were extracted with hot toluene (20 mL, 50 °C) and the extracts were filtered through Celite in a glass frit. The colourless filtrate was taken to dryness to obtain a white powder that was collected on a fit, washed with cold pentane (3 mL, —35 °C), and dried (0.88 g, 1.7 mmol, 95%). Compound 6.3 is air-stable as a solid for weeks and in solution for days, although in our laboratory it is stored in the glovebox to keep it water-free. Single crystals of 6.3 suitable for X-ray analysis were grown by slow evaporation of a benzene solution of the compound. =  6.77 (bs, 2H), 6.72 (bs, 2H), 6.65  2H, 7 Hz), and 6.37 (d, 2H, 8 Hz) (ArH), 6.11 (s, 2H,  (t,  7.59  2H, 7 Hz), 7.35 (d, 2H), 7.16-6.98 (m, 5H),  , 300 MHz): 3 D 6 H{ NMR (C 1 P} 31  (t,  . (ArCH ) NH), 2.14 (s, 6H), 2.06 (bs, 6H), and 1.92 (bs, 6H) 3 , 121 MHz): 6 D 6 H} NMR (C 1 P{ 31  =  , 300 MHz): 6 D 6 C{ 3 ‘ H 1 } NMR (C  —34.3 (s).  =  149.9 (d, 18 Hz), 136.0, 135.9 (bs), 135.8 (bs), 135.3,  134.9 (4 Hz), 134.6, 134.4, 134.1 (5 Hz), 131.2, 129.6, 129.1, 129.0 (7 Hz), 118.8, 117.8 (d, 6 . (ArCH ) Hz), and 112.3 (ArC), 21.4, 18.2 (bs), and 18.0 (bs) 3  2 glovebox, rac-BINAP (1.74 g, 2.8 mmol) and NH (6.4). In an N )(2-BrC 6 (4-PrC ) 4 H (dba) (1.28 g, 1.4 mn-iol) were suspended in toluene (200 mL) in a 500-mL Teflon-sealed 2 Pd 3 bomb and stirred for 10  Bu t mm. 1,2-Dibromobenzene (35.4 g, 17.9 mL, 0.15 mol) and NaO  (20.2 g, 0.21 mol) were added to the solution, and the flask removed to the Schlenk line. Under N , 4-isopropylaniline (22.4 g, 23.4 mL, 0.17 mol) was added to the reaction. The 2 . The brown reaction 2 puce suspension was stirred and heated at 80 °C for 5 d under N 0 (3 X 200 mL). The organic phase was 2 mixture was cooled, and extracted with H 50 filtered, and concentrated under vacuum to obtain a dark 2 Na , separated, dried with 4  262  purple residue. The residue was purified by flash column chromatography on silica gel (pet ether, Rf = 0.6) to obtain 6.4 as a colourless liquid (27.1 g, 62%). , 500 MHz): ö D 6 ‘H NMR (C 6.85 (d, 2H, 8 Hz), 6.84  (t,  =  7.37 (d, 1H, 8 Hz), 7.07 (d, 1H, 8 Hz), 6.97 (d, 2H, 8 Hz),  1H, 8 Hz), and 6.43  (t,  IH, 8 Hz) (ArH), 5.94 (bs, IH, NH), 2.70  . CH ) (m, IH, 7 Hz, CR), 1.15 (d, 6H, 7 Hz, 3 , 75 MHz): ö 3 C{’H} NMR (CDC1 13  =  143.7, 142.0, 139.0, 132.8, 128.0, 127.3, 121.1, 120.2,  . (CR ) 115.1, and 111.5 (ArC), 33.5 (CR), 24.1 3 6 C, 62.08; H, 5.56; N, 4.83; Found: C, 62.35; H, 5.66; N, 4.70. NBr: 1 H 5 Anal. Calcd. for C, ), 274 (100, [M 4 El-MS (m/: 289 (40, [Mj  —  Me] ‘), 195 (40, [M — (Me + Br)]).  Ph.Ar[NpN]Lj.(,,..CHO) (6.5(p-C )) (Ar 2 0 8 H 4  =  . To a stirred solution of (44-’PrC ) 4 H 6  rC (10.4 g, 35.8 mmol) in EtO (300 mL) at —35 °C was added BuLi P 1 ) 6 ) 4 H NH(2-BrC (1.55 M in hexanes, 46 mL, 71.7 mmol), dropwise over 30  mm. The clear yellow solution  was warmed to room temperature and stirred for 3 h. The solution was chilled (—35 °C) and 0 (50 mL) was added dropwise over 2 h to obtain an 2 2 (3.20 g, 17.9 mmol) in Et PhPC1 orange suspension. The reaction mixture was warmed slowly to room temperature and stirred for 24 h to obtain a yellow suspension. The reaction mixture was taken to dryness under vacuum to obtain a pale yellow foam. Hexanes (75 mL) was added to the foam to obtain a translucent yellow solution. Upon addition of 1,4-dioxane (5 mL) a yellow precipitate formed. The yellow suspension was filtered through Celite (3 cm deep) in a glass frit, and the solids and Celite were washed with hexanes (20 mL). The yellow filtrate was transferred to a second Erlenmeyer flask, and was concentrated and chilled to obtain a yellow crystaffine solid that was collected on a frit. Meanwhile, the yellow solids trapped on Celite in the frit were eluted with toluene (50 mL) into the Erlenmeyer flask. The yellow  263  toluene filtrate was taken to dryness to obtain a yellow powder. This powder was combined with the crystals from the hexanes filtrate and the solids were dried under vacuum (7.4 g, . A portion (4 g) of the powder was recrystallized PhPC1 ) 11.8 mmol, 66% yield based on 2 ) were grown 2 0 8 H 4 from THF/hexanes at —35 °C (1.50 g, 38 %). Single crystals of 6.5 (p-C by slow evaporation of a benzene solution of the compound. NMR data for yellow crystals of 6.52THF grown from THF/hexanes: , 500 MHz): 6 D 6 H NMR (C 1  =  7.79  (t,  2H, 8 Hz), 7.72  7.41 (d, 4H, 8 Hz), 7.17 (d, 4H, 8 Hz), 7.12  (t,  4H), 7.02  (t,  (t,  2H, 7 Hz), 7.65  (t,  1H, 7 Hz) and 6.67  2H, 7 Hz),  (t,  2H, 7 Hz)  , 1.25 (d, 6H, 7 CR ) (ArH), 3.10 (m, 8H, THF), 2.83 (m, 2H, 7 Hz, CR), 1.26 (d, 6H, 7 Hz, 3 , 1.06 (m, 8H, THF). CR ) Hz, 3 , 202 MHz): 6 D 6 P{’H} NMR (C 31  =  —34.8 (q,  , 194 MHz): 6 D 6 Li{’H} NMR (C 7  =  —0.36 (d, iLi,  , 126 MHz): 6 D 6 } NMR (C 13 H 1 C{  =  JpL = 1  42 Hz).  ‘J = 42 Hz), —1.70 (s, ILi).  161.6 (d, 28 Hz), 154.7, 138.8, 137.2, 135.4, 132.6 (d,  14 Hz), 130.3, 128.2, 127.6, 126.8, 126.0, 120.6, 119.3 (d, 5 Hz), and 117.0 (ArC), 67.9 ). 3 C1’HF), 33.8 (CR), 25.2 (THF), 24.66, and 24.69 (CR  f[NPN]Zr(NMe (6.6). Trimethylammonium chloride (0.518 g, 5.42 mmol) was 4 Ph ) 2 2 (1.06 g, 1.69 mmol) in THF (30 mL). 0 8 H 4 added all at once to a stirred solution of 6.5p-C The reaction mixture became an off-white suspension after 15  mm. After 1 h, the reaction  mixture was taken to dryness to obtain white solids. The solids were extracted with hot  toluene (20 mL,  50 °C), and the extracts were filtered through Celite in a glass frit. The  filtrate was taken to dryness to obtain a translucent white residue (0.85 g, 1.61 mrnol, 95%).  264  , 500 MHz): ö D 6 ‘H NMR (C  =  7.50  Hz), 6.82 (d, 4H, 7 Hz), and 6.72  2H, 7 Hz), 7.29 (m, 4H), 7.05 (m, 5H), 6.91 (d, 4H, 7  (t,  2H, 7 Hz) (ArH), 6.39 (d, 2H,J,  (t,  =  6 Hz, NH), 2.66 (m,  ) 3 2H, 7 Hz, CH), 1.13 (d, 12H, 7 Hz), and 1.12 (d, 12H, 7 Hz) (CH , 202 MHz): ö D 6 } NMR (C 31 H 1 P{  =  , 126 MHz): ö D 6 c{’H} NMR (C 3 ‘  —32.4 (s). 160.0, 148.4 (d, 18 Hz), 142.7, 140.8, 135.0, 134.2 (d,  =  19 Hz), 130.7, 129.2, 129.1 (d, 8 Hz), 127.4, 122.5 (d, 6 Hz), 121.2, 120.5, and 116.7 (ArC), . (CH ) 33.8 (CH), 24.2 3 4 (0.430 g, 1.61 nimol) and ) 2 Zr(NMe  2 PhAr[NpN]H  (0.85 g, 1.61 mmol) were mixed  together, and toluene (15 mL) was added. The lemon yellow solution was stirred for 2 h, and the solvent was removed to obtain a yellow residue. The addition of pentane (5 mL) to the residue provided a clear yellow solution. After about 30 s a light yellow precipitate formed that was collected on a frit and dried (1.07 g, 1.52 mmol, 94%). Single crystals of 6.6 suitable for X-ray analysis were grown by slow evaporation of a benzene solution of the compound. , 500 MHz): D 6 ‘H NMR (C 4H), 7.00 (dd, 2H, J 11 (t,  =  =  7.48  6 Hz, JHH  =  (t,  2H, 7 Hz), 7.44  (t,  2H, 8 Hz), 7.17 (m, 7H), 7.07 (m,  8 Hz), 6.75 (dd, 2H, JHH  =  8 Hz, JHP  =  6 Hz), and 6.65  , N(CH ) ), 2.76 (m, 2H, 7 Hz, CH), 2.51 (s, 6H, 3 2 ) 3 2H, 7 Hz) (ArH), 2.84 (s, 6H, N(CH  . CH ) 1.19 (d, 12H, 7 Hz, 3 P{’H} NMR (C 31 , 202 MHz): 8 D 6  =  , 126 MHz): 6 D 6 } NMR (C { 1 C 3 ‘ H  —10.0 (s).  =  163.7 (d, 29 Hz), 149.2, 143.2, 134.9, 133.2, 133.0 (d,  25 Hz), 132.2 (d, 13 Hz), 129.3, 129.0, 127.6, 126.1, 119.3 (d, 5 Hz), 117.7 (d, 8 Hz), and  , 24.3, and 24.2 (CH(CH ) 2 ) ), 34.0 3 2 ) 3 116.4 (d, 34 Hz) (ArC), 41.5, and 40.7 (N(CH . 2 ) 3 (CR ((H  265  6.5. References.  A) Fryzuk, M. D.;Johnson, S. 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Soc. 1995, 117, 1479. 8  A) Tietze, M.; Iglesias, A.; Mensor, E.; Conrad, J.; Klaiber, I.; Beifuss, U. Og. Lett. 2005, 7,  1549. B) Ferreira, I. C. F. R.; Queiroz, M.j. R. P.; Kirsch, G. Tetrahedron 2003, 59, 3737. Wohlfart, M.; MacLachlan, E. A. unpublished results. 9 10  Shaver, M. P.; Thomson, R. K.; Patrick, B. 0.; Fryzuk, M. D. Can. J. Chem. 2003, 81, 1431. Liang, L.-C.; Huang, M.-H.; Hung, C.-H. Ino,. Chem. 2004, 43, 2166.  12  A) Hunter, C. A. Chem. Soc. Rev. 1994, 101. B) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem.  Soc. 1990, 112, 5525. 13  Fiona Hess, personal communication.  266  Addjson A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton 14 Trans. 1984, 1349. Airoldi, C.; Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.; Malik, K. M. A.; Raithby, P. R. J. Chem. Soc., Dalton Trans. 1980, 2010. B) Schrock, R. R.; Seidel, S. W.; Schrodi,  Y.; Davis, W. M. Organometallics 1999, 18, 428. Fryzuk, M. D.;Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998, 120,11024. MacKay, B. A.; Munha, R. unpublished work. 18  Shaver, M. P.; Fryzuk, M. D. Organometallics 2005, 24, 1419. Yandulov, D.V.; Schrock, R. R. Science 2003, 301, 76.  WA) Sykes, A. C.; White, P.; Brookhart, M. Organometallics 2006, 25, 1664. B) Gross, K. C.; Seybold, P. G.; Peralta-Inga, Z.; Murray, J. S.; Politzer, P. J. Org. Chem. 2001, 66, 6919. 21  Matkovich, K. M.; Thorne, L. M.; Wolf M. 0.; Pace, T. C. S.; Bohne, C.; Patrick, B. 0.  Inorg. Chem. 2006, 45, 4610. 22  Ghebreyessus, K.Y.; Gui, N.; Nelson, J. H. Organometallics 2003, 22, 2977.  23  Morello, L.; Love, J. B.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2004, 126, 9480.  24  Diamond, G. M.; Rodewald, S.;Jordan, R. F. Organometallics 1995, 14, 5.  25  Fairlamb, I. J. S.; Kapdi, A. R.; Lee, A. F. Org. Lett. 2004, 6, 4435.  26  Bishop, J. J.; Davison, A.; Katcher, M. L.; Lichtenberg, D. W.; Merril, R. E.; Smart, J. C. J.  Organomet. Chem. 1971, 27, 241. 27  Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.; Hirotsu, K. J. Am. Chem.  Soc. 1984, 106, 158.  267  One X-ray Ci ystal Structure Data (THF) (2.72THF), 2 Table A1.1. Crystal Data and Structure Refinement for [NPN]*Li (Py) (2.13). 2 2 (2.10) and [NPN]*ZrC1 [NPNI*ZrCl compound formula fw colour, habit cryst size, mm cryst syst space group  a,A b, A c,A  cçdeg  1, deg ‘y,deg  3 v,A Z T,°C 3 p, g/cm F(000) radiation jt, cm’ transmission factors 20m,deg total no. of reflns no. ofuniquerefins Rtnerge  no. with I nO(I) no. of parameters R gof residual dens, e/A 3 1 (F R , I>2a(I)) 2  =  2.72THF 6 45 C 5 H P O N 2 Li 712.77 colourless, tablet 0.30 X 0.25 X 0.10 monoclinic /n 1 P2 12.0195(11) 24.292(2) 14.2557(11) 90 102.308(4) 90 4066.7(6) 4 173 1.164 1528 Mo 0.106 0.9688 0.9894 47.748 54955 9577 0.049 6409 486 0.0510 0.1411 1.044 0.720, -0.472 —  Fj  2.102.5C H 6 3 C 5 H P N 2 C1 Zr 911.06 yellow, needle 0.35 X 0.35 X 0.20 monoclinic C2/c 44.638(2) 10.8958(5) 19.4505(9) 90 94.334(2) 90 9433.0(8) 8 173 1.283 3792 Mo 0.417 0.716-0.920 55.96 95472 11331 0.083 8972 541 0.0505 0.1379 1.163 0.920, -0.661  1 ; R (all data) = 0 -I F fl /I F  268  21 0 QDwd F  2.130.33C H 6 C 5 P 3 N Zr 1 44 5 C 45 2 H 815.43 red, tablet 0.25 X 0.12 X 0.08 tnchnic P-I 13.0128(3) 18.6267(4) 19.0488(4) 112.4990(10) 100.0810(10) 92.1610(10) 4171.96(16) 4 173 1.298 1690 Mo 0.464 0.8406 0.9636 56.34 119902 19756 0.061 14529 944 0.0358 0.1007 1.106 0.833, -0.456 —  21 0 _I FI )2/wI F  2)1/2  [NPN]*Hf(NMC (2.14), ) Table A1.2. Crystal Data and Structure Refinement for 2 2 (2.17). [NPNJ*HfC1 (2.15), [NPN]*Hf1  compound formula fw colour, habit cryst size, mm cryst syst space group a,A b,A c,A ct, deg 3,deg y, deg  v, A  Z T,°C 3 p, g/cm F(000) radiation ji, cm Trans. factors 2Omax, deg total no. of reflns no.ofuniquereflns  2.14 2 5 C 4 H H 4 N fP 821.33 pale yellow, needle 0.35 X 0.15 X 0.07 monoclinic /c 1 P2 11.5176(2) 19.3137(4) 17.9531(4) 90 105.0270(10) 90 3857.05(14) 4 173 1.414 1672 Mo 2.78  —  no. with I > nO(J) no. of parameters R R gof residual dens, e/A 3  55.416 80641 9136 0.07 7398 445 0.0296 0.049 1.059 1.172, -0.699  1 (F R 2 I>2CT(1)) =  Fj  Rrnerge  2.152.5C H 6 3 4 C 5 H P N 2 C1 Hf 999.34 pale yellow, plate 0.30 X 0.13 X 0.07 monochnic C2/c 44.7205(16) 11.0406(4) 19.4718(5) 90 94.1910(10) 90 9588.3(5) 8 173 1.385 4056 Mo 2.357 0.5382 0.8529 45.392 72405 10472 0.103 7378 541 0.0357 0.0753 1.018 1.110, -1.004  21 _I FI 0 -I F /I Fj ; R (all data) = (wd F  269  H 6 2.17 1 .5C 7 8 C 4 H P N 2 I Hf 736.09 yellow, prism 0.35 X 0.15 X 0.10 monoclinic /n 1 P2 10.5510(6) 17.2009(9) 24.6184(13) 90 95.214(5) 90 4449.4(4) 6 173 1.648 2148 Mo 3.801 0.4060 0.6838 54.77 16781 9455 0.153 6559 486 0.0367 0.0774 0.907 1.685, -2.085 —  )2/wI  21 0 F  2)1/2  [NPNJ*HfMe (3.2), [NPNC]*Zr(11 2 Table A1.3. Crystal Data and Structure Refinement for 2 ) (3.4). 5 H 6 C 2 CH  compound formula fw colour, habit cryst size, mm cryst syst space group a,A b,A c,A cL, deg 3,deg y, deg  3 v,A Z T,°C 3 p, g/cm F(000) radiation  transmission factors 29,deg total no. of reflns no. ofuniquereflns 1merge  no. withlZnO(I) no. of parameters R gof residual dens, e/A 3 1 (F R , I>2a(I)) 2  =  3.4 C 4 H P 2 N Zr 5 736.02 orange, irregular 0.25 X 0.15 X 0.10 triclinic P-i 11.2260(3) 15.3120(4) 15.5773(4) 64.7420(10) 70.8540(10) 70.5370(10) 2228.39(10) 2 173 1.097 768 Mo 0.311 0.8774-0.9694 55.64 46139 10215 0.058 7857 465 0.0346 0.0892 1.026 0.481, -0.314  3.2C H 6 HfP 2 N 51 CH 841.35 pale yellow, needle 0.50 X 0.35 X 0.05 trichmc P-i 11.6308(11) 12.7965(10) 13.6170(11) 84.039(7) 80.881(7) 87.582(8) 1989.5(3) 2 173 1.404 856 Mo 2.695 0.3305-0.8739 54.15 12008 6580 0.137 5611 461 0.0367 0.0908 1.014 1.568, -1.653  21 -I F1 )2/EwI F 0 21 0 Eli Fj -I F /I Fj ; R (all data) (w(I F =  2)1/2  Residual electron density consistent with disordered solvent was evident, however, no reasonable model could be established. Instead, the program SQUEEZE was used to generate a data set that corrects for the scattering contribution from this disordered solvent.  270  HS) (3.5), 6 C 2 Table A1.4. Crystal Data and Structure Refmement for [NPN]*Hf(r11CH [NPNC] 3 SiMe (3.7). 2 Zr(CH )  compound formula fw colour, habit cryst size, mm cryst syst space group a,A b,A c,A x,deg 13,deg ‘,deg 3 v,A Z T,°C 3 p, g/cm F(000) radiation i, cm 1 transmission factors 2Om,deg totalno.ofreflns no. ofuniquereflns Rmetge no.withln8(I) no. of parameters R R gof residual dens, e/A 3 1 (F R , I>2oI)) 2  =  3.7 C 4 H P 2 N SiZr 2 9 732.11 red, plate 0.50 X 0.40 X 0.08 triclinic P-i 9.22160(10) 11.5343(2) 19.5329(3) 86.9080(10) 78.1770(10) 76.0500(10) 1973.54(5) 2 173 1.232 768 Mo 0.379 0.8609-0.9701 51.932 43622 9436 0.06 7340 434 0.0349 0.0973 1.109 0.495, -0.313  3.5C H 6 C 5 H P 2 N Hf 8 9 993.53 pale yellow, chip 0.35 X 0.12 X 0.05 trichnic P-I 11.268(2) 12.550(2) 17.847(3) 93.0410(10) 93.5840(10) 103.1290(10) 2447.1(7) 2 173 1.348 1016 Mo 2.203 0.590-0.896 46.75 87588 11461 0.087 9139 567 0.0284 0.0599 1.013 0.985, -0.519  21 0 1 -I F /I Fj ; R (all data) (Zw(l F 0 IF =  271  -  21 0 F2I )2/wI F  1,12  (,Iii2:112N 2 {[NPNj*Zr(rHF)} * Table A1.5. Crystal Data and Structure Refinement for ) Ph) O-ri.ri 2 (4.1), [NPN] t Zr(Py) 2 (ii-i } : N i (4.2), and [NPN] *Zr(PMe  {  {  }  ){Zr[NPN]*} (44) 2 N compound formula fw colour, habit cryst size, mm cryst syst space group a,A b, A c,A ct, deg 3, deg y, deg  no. with I? nO(I) no. of parameters R R. gof residual dens, e/A 3  4.F(Sol) 9 C 1 H Z P 3 O 6 N 2 20 8 r 1674.38 black, prism 0.30 X 0.15 X 0.10 trigonal R-3c 27.3381(7) 27.3381 59.1867(16) 90.00 90.00 120.00 38308.2(14) 18 173 1.306 15912 Mo 0.337 0.839-0.967 40.48 210263 7426 0.080 5613 467 0.0481 0.1429 1.043 1.174, -0.522  1 2 R (F I>2a(I)) = ,  Fj  3 v,A  Z T,°C 3 p, g/cm F(000) radiation 1 p., cm transmission factors 2Omax, deg totalno.ofreflns no. of unique reflns Rmerge  4.2 C 8 H Z P 8 N 2 6 8 r 1478 black, prism 0.50 X 0.40 X 0.30 monoclinic /n 1 P2 19.6395(7) 19.7497(8) 27.0757(12) 90.00 91 .7900(1 0) 90.00 10496.8(7) 6 173 0.935 3080 Mo 0.265 0.8580-0.9241 44.892 35075 13279 0.088 9468 899 0.0561 0.1630 1.020 0.971, -0.548  1 ; R.N (all data) = 0 -I F fl /I F  Sol = )) +THF+0.67(C (C 1 H 6 4  See note on Squeeze (fable Al .3)  272  21 0 (wd F  4.4 C 8 H Z 3 P 6 N 2 4 8 r 1456.95 black, rectangular 0.30 X 0.10 X 0.10 monoclinic /c 1 P2 23.7417(8) 15.2378(5) 23.7851(8) 90.00 98.896(2) 90.00 8501.3(5) 5 173 1.138 3036 Mo 0.344 0.812-0.966 53.038 88103 20097 0.063 14389 873 0.0396 0.1045 1.017 0.779, -0.282  21 0 _I F1 )2/EwI F  2)1/2  )}(JIH)(I.i12:112 3 Table A1.6. Crystal Data and Struture Refinement for {[NPN]*Zr(PMe Ph) {Zr[NPN]* }1 (53) 2 NNH) {Zr[NPNJ* } (5.1), { [NPN]*Zr(Py) } (jt-H) (ji-NNSiH compound formula fw colour, habit cryst size, mm cryst syst space group a,A b,A c,A cc deg 3, deg ‘, deg  3 v,A  Z T,°C 3 p, g/cm F(000) radiation ji, cm 1 transmission factors 2O,deg total no. of reflns no. of unique reflris Rmerge  no. with I > nO(1) no. of parameters R R gof residual dens, e/A 3 1 (F R , I>2a(I)) 2  5.1 2 79 Zr C 8 H 3 P 6 N 1397.91 yellow, rod 0.5 X 0.1 X 0.1 triclinic P-I 13.418 19.268 20.788 67.54 75.49 86.02 4806.3 2 173 0.966 1460 Mo 0.302 0.390-0.980 45.537 51485 12606 0.324 7222 811 0.1663 0.4129 1.633 6.601, -2.132  5.3C H 6 C 9 H S P 7 N 2 iZr 3 6 1585.32 red, plate 0.5 x 0.3 X 0.1 triclinic P-i 12.8123(4) 13.1606(5) 25.1766(11) 85.4180(10) 84.5970(1 0) 74.8280(1 0) 4072.3(3) 2 173 1.292 1654 Mo 0.360 0.773-0.982 44.91 43112 10446 0.065 7593 959 0.0413 0.1020 1.002 0.470, -0.344  1 -I F /I Fj ; R (all data) 0 F  =  21 0 (w( F  21 0 F1 )2/wI F  2)1/2  See note on Squeeze (Table Ai.3) Hi (bridging hydride) and HISi, H2Si were located from the electron density map and refined normally. 273  Table A1.7. Crystal Data and Structure Refinement for )2 2 }t (5.4), { [NPN *Zr(NCPh 2 ) 4 H 6 NNC(4MeC Qi-T1 } : ) H ri N (5.5), and (,IO)z (5.6). 2 {[NPN]*Zr} compound formula fw colour, habit cryst size, mm cryst syst space group a, A b, A c,A c, deg f3, deg ‘y, deg  v,A 3 Z T,°C 3 Pcaic, g/cm F(000) radiation ji, cm’ transmission factors 2O,deg total no. of reflns no.ofuniquereflns Rmerge no.withlnO(I) no. of parameters R gof residual dens, e/A 3 1 R  2  I>2o(I)) =  5.4 C 9 H O 6 N Z 2 1 2 P r 1530.09 orange, platelet 0.3 X 0.1 X 0.1 monoclinic 1 P2 13.875(2) 14.394(3) 23.553(4) 90.00 104.983(10) 90.00 4544.0(14) 2 173 1.118 1596 Mo 0.309 0.793-0.970 46.61 30481 13553 0.107 9195 937 0.0712 0.1902 1.004 0.561, -0.503,  5.52C H 6 113 H 14 Z P 8 N r 12 C 1839.48 red, platelet 0.35 x 0.20 x 0.05 monoclinic 1 P2 13.3465(3) 23.3359(6) 16.1975(4) 90.00 107.4220(10) 90.00 4813.3(2) 3 173 1.267 1920 Mo 0.303 0.856-0.985 44.632 29776 6478 0.046 6359 1149 0.0341 0.0762 1.035 0.477, -0.227,  21 0 1 ; R.. (all data) = (w(I F 0 I Fj -I F /I F  See note on Squeeze (fable Al .3) 274  5.6C H 6 C 8 H Z P 4 N O 2 2 4 r 1401.91 yellow, platelet 0.21 x 0.17 x 0.15 monochruc C2/c 22.298(5) 14.064(3) 23.800(5) 90.00 93.884(4) 90.00 7446(3) 4 296 1.250 2920 Mo 0.371 0.881-0.945 46.52 29927 5350 0.049 4612 415 0.0335 0.1125 0.748 0.294, -0.227, 21 0 Fi )2/wI F  2)1/2  Table A1.8. Crystal Data and Structure Refinement for es[pJ M Ph ‘2 (6.3).  compound formula fw colour, habit  çpdioxane) 2 PhMes[NpN1U  6.3 C 3 H P 2 N 6 7 528.65 colourless, prism 0.50 X 0.30 X 0.20  cryst size, mm  6.22C H 6 C 5 H P O N 2 Li 2 5 784.83 yellow, prism 0.50 X 0.30 X 0.20  cryst syst  monoclinic  triclinic  space group  P21/c 17.0576(1 3) 25.018(2) 11.3813(9) 90.00 71.743(5) 90.00 4612.5(6) 5 173 1.130 1672 Mo 0.100 0.837-0.970 53.12 10317 9059 0.071 5871 537 0.0808 0.2087 1.098 0.461, -0.339  P-i 7.9830(8) 13.3300(13) 14.4770(14) 97.374(5) 105.276(5) 91.745(5) 1470.5(3) 2 173 1.194 564 Mo 0.121 0.854-0.976 59.32 11151 7659 0.060 5370 360 0.0541 0.1607 1.031 0.511, -0.451  a, A b, A c,A cc deg 3,deg y, deg  v,A 3 Z T,°C 3 p,g/cm F(000) radiation transmission factors  2O,deg totalno.ofreflns no. ofuniquereflns Rmetge  no. with I nO(I) no. of parameters R R. gof residual dens, e/A 3 1 (F R , I>2a(I)) 2  =  Fj  21 0 1 ; R (all data) = (Ewd F 0 -I F /I F  275  21 0 F1 )2/EwI F  2)1/2  (6.2),  rpdjoxane) 4 Ph ( [NPN]U (Ar = 4Table A1.9. Crystal Data and Structure Refinement for 2 PhAr[p] PrC (6.5), 1 ) 4 H 6 ) (6.6). 2 Zr(NMe  compound formula fw colour, habit cryst size, mm cryst syst space group a,A b,A c,A ct,deg 13, deg y, deg  3 v,A  Z T,°C 3 p,g/cm F(000) radiation cm’ transmission factors 2Om,j,deg total no. of reflns no. of unique reflns Rmg no.withIn9(I) no. of parameters R R. gof residual dens, e/A 3  6.6 PZr 4 N 47 CH 706.01 yellow, irregular 0.50 X 0.20 X 0.15 monoclinic /c 1 P2 19.7201(5) 11.5343(2) 17.3982(5) 90.00 66.3300(10) 90.00 3687.69(17) 4 173 1.272 1480 Mo 0.374 0.816-0.945 45.752 60432 8808 0.072 6212 423 0.0392 0.1260 1.052 1.109, -0.294  6.51.5C H 6 42 C 5 H P O N 2 Li 9 745.78 pale, plate 0.35 X 0.15 X 0.05 tricliruc P-I 11.5372(7) 13.4014(8) 16.1799(9) 107.995(2) 109.297(2) 97.418(2) 2169.8(2) 2 173 1.141 794 Mo 0.103 0.837-0.995 43.012  ,  17773 5573  0.047 2965 509 0.0716 0.1817 1.036 0.315, -0.212  1 F R 2 I>2a(I)) = E Fj  21 FI 0 -I F f /,I Fj ; R., (all data) = (w(j F  )2/w  21 0 F  2)1/2  X-ray Crystal Structure Analysis Selected crystals were coated in oil, mounted on a glass fiber, and placed under an N 2 stream. Measurements for compounds were made on a Bruker X8 Apex diffractometer or a Rigaku AFC-7 diffractometer, both with graphite-monochromated Mo Kct. radiation 0.7 1073  A).  (?  The data were collected at a temperature of —100 ± I °C. Data were collected  276  and integrated using the Bruker SAINT software package. 1 Data were corrected for absorption effects using the multiscan technique (SADABS) 2 and for Lorentz and 3 polarization effects. Neutral atom scattering factors were taken from Cromer and Waber. Anomalous dispersion effects were included in  the values for Af” and I\f” were those  of Creagh and McAuley. 5 The values for the mass attenuation coefficients are those of Creagh and Hubbell. 6 All refinements were performed using the SHELXTL crystallographic software package of Bruker-AXS. The structure was solved by direct methods. All nonhydrogen atoms were refined anisotropically using SHELXL-97. Except where noted, hydrogen atoms were included in fixed positions. Structures were solved and refined using the WinGX software package version 1.64.05.  Crystals for structure 5.6 were sent to the University of Windsor. Data collection and refinement were performed by Greg Welch and Prof. Douglas Stephan in the Department of Chemistry.  277  Table A1.10. Crystallographic Data Collection and Structure Solution Information.  Cornpound 2.72THF 2.10 2.13 2.14 2.15 2.17 3.2 3.4 3.5 3.7 4.1  Code mf# 592 590 599 612 608 648 649 602 607 643 636  Solvent in asym. unit -  2.5C H 6 H 6 0.5C -  2.5C H 6 6 1.5CH H 6 C -  H 6 C -  +THF H 6 C ) 1 H 6 +0.67(C 4  Diffractometer BX8 BX8 BX8 BX8 BX8 RAFC7 RAFC7 BX8 BX8 BX8 BX8  Data Collection BP BP BP BP BP HJ HJ BP BP BP BP  Structure solution BP, EM BP, EM EM EM EM EM EM BP, EM EM EM EM, BP  Special details  5, H H 5, M  =  EM, BP S HJ HJ HJ, EM S HJ HJ,EM S,LR BP EM H, M EM HJ S BP EM GW GW, DS HJ MW, EM HJ MW, EM H BP EM BP EM Rigaku AFC-7 Diffractometer, SSS  =  Dr. Brian Patrick, HJ  =  Howard Jong,  Malte Wohlfahrt; S  =  Squeeze, H  =  Hydrogen atoms of interest located from electron density and stable to refinement, LR  =  4.2 4.4 5.1 5.3 5.4 5.5 5.6 6.2 6.3 6.5 6.6 BX8  =  BX8 657 666 BX8 BX8 665 671 BX8 H 6 C 652 RAFC7 670 H 6 2C BX8 MF3 H 6 C SSS 646 H 6 2C RAFC7 661 RAFC7 629 BX8 627 H 6 1.5C BX8 Bruker Apex X8 Diffractometer, RAFC7 -  -  -  -  -  -  Siemens SMART System CCD Diffractometer; BP GW  =  Greg Welch, DS  =  low resolution structure, M  Prof. Doug Stephan, MW  =  =  =  solvent modeled.  ‘SAINT. Version 6.02. Bruker AXS Inc., Madison, Wisconsin, USA. (1999). 2  SADABS. Bruker Nonius area detector scaling and absorption correction V2.05, Bruker -  AXS Inc., Madison, Wisconsin, USA. ‘  Cromer, D. T.; Waber, J. T. International Tablesfor X-rqy Cystaiographj, Vol. 1T4 The Kynoch  Press: Birmingham, England, 1974, Table 2.2 A.  278  Ibers, J. A.; Hamilton, W. C. Acta Cystaiogr., 1964, 17, 781. Creagh, D. C.; McAuley, W.J. International Tablesfor Cystallgraphj, Vol C; Wilson, A. J. C., ed., Kiuwer Academic Publishers: Boston, 1992, Table 4.2.6.8, pp. 219-222. 6  Creagh, D. C.; Hubbell, J.H. International Tablesfor Cystallographji, Vol C; Wilson, A.J.C, ed.,  Kiuwer Academic Publishers: Boston, 1992, Table 4.2.4.3, pp. 200-206.  279  Appendix Two Spectroscopic Supporting Information 2 (2.8). A2.2 Variable-temperature NMR investigation of [NPN]*H toluene-d at 300 MHz acquired every A stacked plot of the 1 H NMR spectra of 2.8 in 8 10K from 300 to 370 K is shown in Figure A2.1. At 300 K, the two ortho-methyl  H NMR spectra were acquired at 5 K resonances on MesN are broad singlets. 1 increments between 300 K and 340 K, and at 10 K increments between 240K and 300 K, and between 340 K and 370 K. Coalescence is observed at 320 K, and the two ortho methyl resonances are separated by 75 Hz at 273 K. The exchange of the two ortho methyl groups on each MesN substituent of 2.8 due to rotation about the N—C 0 is depicted in Equation A2.1.  (A2.1)  8 Me  The rate constant for the exchange reaction at the coalescence temperature is (Equation A2.2):  k cJ =—=2.22Av (A2.2)  k is the rate constant at the coalescence temperature, T, and iv is the separation between the two peaks at a temperature well below the coalescence temperature. In this case, zv did not increase below 273 K (spectra acquired to 240 1 K). In this experiment, k  = 166.5 ± 2 s_i.  280  L\G:rot is calculated from the Eyring equation (Equation A2.3):  AG = —RT ln(kh / kBTC) (A2.3) R is the gas constant, T is the coalescence temperatuxe, k is the rate constant, h is Planck’s constant, and kB is the Boltzmann constant. Equation A2.3 can be restated (Equation A2.4):  = 4.58T 0 [10.32 + iog[  jJ  cal (A2.4)  The main sources of error in this experiment are those associated with measuring the coalescence temperature; this error will be much greater than the error in determining the peak separation at low temperature. For T, a value of 320 determine  In this experiment,  AGIO  is 15.5  281  ±  ±  0.3 kcal mo1 1  5 K has been used to  370 K 360 K 350 K 340 K 330 K 320 K 310 K 300 K  7  6  5  4  3  ppm  [NPNJ*H (2.8) in toluene-d 8 from 300 K (bottom) to 370 Figure A2.1. ‘H NMR spectra of 2 K (top) in 10 K increments.  Ph) (3.3). [NPN]*Zr(CH A2.2. Kinetics of Decomposition of 2 Ph) (3.3) occurs over 2 [NPNI*Zr(CH At room temperature, the decomposition of 2 [NPNC]*Zr(r2CH P h) (3.4) as a red-orange complex. The decomposition d to yield 2 reaction was followed by ‘H NMR spectroscopy. The decrease in the concentration of 3.3 was taken as the integral measured for ZrCH Ph in 3.3 (6 2.92), divided by the sum of that 2 integral plus two times the integral for CHaHbMes in 3.4 (6 2.70), according to Equation A2.5, where int. is the integral value. Thus, the fraction of 3.3 relative to an initial value of 1.0 was used, rather than the molar concentration. These resonances were chosen because they did not overlap with any other resonances in the spectrum. The values obtained were similar to those from other related combinations of integrals taken from other parts of the spectrum, and their values were standardized to a peak of unchanging concentration.  282  _________________________________  —  d[3.3] dt  Ph(3.3)] 2 kObS[int CH [(mt CH Ph(3.3))+ 2(int CHaHbMes(3.4))1 2 —  ] . 3 —kObS[  =  (A2.5) The thermal decomposition reaction was determined to be first order in 3.3 (spectra not shown) by determining the rate of decomposition for three solutions of different concentration at room temperature. The rate constants (kObS) at five different temperatures (298, 328, 338, 348, and 358 K) were then determined from the plots of ln[3.3] vs. time, for which a representative plot is shown in Figure A2.2 (338 K). In[3.3] vs. time at 328 K 0.0 -0.2  -0.4 -0.6 -0.8 c,  -1.0  C  -1.2 -1.4 -1.6 -1.8 -2.0 0  200  400  600  800  1000  1200  1400  Time (s)  Figure A2.2. Plot of ln[3.3J vs. tat 338 K. From the slope of the line, k 338 1.0 x i0 s.  283  =  1.403  X  iO ±  Thus, the values of kOb, at 5 different temperatures were obtained: 1o s 1  298 k  =  1.80 x I 0 ± 6  223 k  =  4.33 x iO ± 1 x i0 s 1  238 k  =  1.40 x iO ± 1  248 k  =  3.44 x iO ± 2 x iO s 1  258 k  =  7.35 x i0 3 ± 5 x iO s’  X  X  5 s’ iO  The free energy of activation (AG’) is related to the enthalpy of activation (AH) and entropy of activation (AS’) (Equation A2.6).  AG  =  AH  -  TAS  (A2.6) By inserting equation A2.6 into the Eyring equation (A2.3), Equation A2.7 is obtained:  mi(kh1=— AH °  ASt  RT  kBTc)  R  (A2.7) This expression can be simplified to (Equation A2.8):  ARt k log—=1O.32— T 19.14T  +  AS 19.14 (A2.8)  284  From the Eyring plot of ln(kOb/I) vs. I /T (Figure 3.7), the enthalpy (AR’) and entropy (AS’) of activation were determined according to Equation A2.8 from the y-intercept and the slope of the line. Thus:  AH  =  20.8 ± 0.4 kcal mol’, and ASt  =  —10.3 ± 1.3 cal K’ mol’  The two main sources of error in this experiment are due to temperature measurement and integration of resonances in the ‘H NMR spectrum. The error in temperature is estimated to be  ±  1K, and the error is estimated to be  ±  5% for the fractions of 3.3 and 3.4 in solution  based on integration of the 1 H NMR spectrum. The error in kOb was determined statistically.  ‘Friebolin, H. Basic One-and Two-Dimensional NMR Spectroscopy, 3 ed.; Wiley-VCH: Weinheim, 1998, pp. 307-10.  285  

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