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o-Phenylene bridged diamidophosphine complexes of groups 4 and 5 metals for dinitrogen activation Hess, Fiona Millicent 2014

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o-Phenylene Bridged Diamidophosphine Complexes of Groups 4 and 5  Metals for Dinitrogen Activation by Fiona Millicent Hess B. Sc., University of Cape Town, 1995 B. Sc.(HONS), University of Cape Town, 1996 M. Sc., University of Cape Town, 1999  A thesis submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSHOPHY in The Faculty of Graduate and Postdoctoral Studies (CHEMISTRY)   THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) November 2014 © Fiona Millicent Hess, 2014  ii  Abstract  A series of diamidophosphine donor sets (ipropNPN, tolNPN and phNPN) was prepared, whereby the arylamido groups have no ortho substituents. This allowed for the Buchwald-Hartwig arylamination to be replaced by a directed ortho metalation (DOM) process, sourcing commercial diarylamines. Amido and chloro complexes of Zr, Ti, Hf and Ta with these new diamidophosphine donor sets were prepared. Reduction of the zirconium dichlorides with KC8 under N2 gave the side-on dinitrogen complexes [ipropNPNZr(THF)]2(µ-η2:η2-N2) and [tolNPNZr(THF)]2(µ-η2:η2-N2) and of titanium dichloride gave the end-on complex [tolNPNTi(THF)]2(µ-η1:η1-N2). Compared to previously reported sterically encumbered [mesNPNZr(THF)]2(µ-η2:η2-N2), the zirconium complexes were more stable, with longer N-N bonds, less labile THF ligands and shorter Zr-O bond lengths. THF adduct displacement thus occurred less readily; for phosphine donors, displacement was at both zirconium centres i.e. [ipropNPNZr(PPhMe2)]2(µ-η2:η2-N2), compared to the mesNPN analogue with an open site at one of the zirconium centres i.e. [mesNPNZr(PPhMe2)](µ-η2:η2-N2)[mesNPNZr]. For titanium, four different pyridine adduct species where observed in solution, but only one species was isolated wherein each THF was displaced by two pyridine molecules i.e. [tolNPNTi(Py)2]2(µ-η1:η1-N2). These new dinitrogen complexes were found to be unreactive with H2; for zirconium, the lack of an open site at one of the metal centres may explain lack of reactivity, and for titanium, the end-on dinitrogen bonding mode is not amenable to hydrogenolysis. The potassium salt of tolNPN with TaMe3Cl2 gave the trimethyl species tolNPNTaMe3, but [tolNPNTaMe4][Li(THF)4] was isolated from tolNPNTaCl3 with MeLi. Tantalum hydrides from trimethyl species and H2 were unstable and did not form dinitrogen complexes, but mass spectra of tantalum trichlorides with KHBEt3 and N2 indicated dinitrogen hydrides [NPNTaH]2(N2) and further reaction with BEt3. Reduction of tantalum trichlorides with KC8 under N2 gave mass spectra of dinitrogen complexes [NPNTaCl]2(N2), with no crystals isolated. iii  Preface  This dissertation is the original intellectual product of the author, F. Hess, except for the following contributions: Chapter 2: The [ipropNPNLi2ˑdiox]n [2.6] ligand was originally prepared by E. MacLachlan and the directed ortho metalation (DOM) process was first introduced by Y. Ohki. The x-ray crystal structure for [ipropNPNLi2ˑdiox]n [2.6] was solved by E. MacLachlan and for [tolNPNLi2ˑ0.5TMEDAˑDME]2 by Y. Ohki. Chapter 3:  The x-ray crystal structure for ipropNPNZr(NMe2)2 [3.7] was solved by E. MacLachlan and for tolNPNZrCl2(HNMe2) [3.4] and tolNPNZr(NMe2)2 [3.8] by Y.Ohki. Chapter 4: The x-ray crystal structure for iprop-PNPNTaMe3 was solved by D. Nied. Chapter 5: The zirconium dinitrogen complex [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3] was initially prepared by Y. Ohki. The zirconium dinitrogen complex [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] was presented orally at the 236th ACS National Meeting, Philadelphia, August 17-21 2008, INOR-004. The zirconium [5.1] / [5.3] and titanium [5.16] / [5.17] / [5.18] dinitrogen complexes were presented orally at the 239th ACS National Meeting, San Francisco, March 21-25 2010, INOR-1366 and the 93rd CSC Canadian Chemistry Conference and Exhibition, May 29 - June 25 2010.    iv  Table of Contents Abstract ........................................................................................................................................... ii Preface ............................................................................................................................................ iii Table of Contents ........................................................................................................................... iv List of Tables.................................................................................................................................. ix List of Figures ............................................................................................................................... xii Glossary of Terms ...................................................................................................................... xxiii List of Compounds ...................................................................................................................... xxx Acknowledgements .................................................................................................................. xxxvi Dedication ............................................................................................................................... xxxvii Chapter 1: Introduction ................................................................................................................... 1 1.1. Historical Context ........................................................................................................... 1 1.2. Dinitrogen Complexes .................................................................................................... 7 1.2.1. Zirconium N2 Chemistry ......................................................................................... 8 1.2.2. Hafnium N2 Chemistry .......................................................................................... 11 1.2.3. Titanium N2 Chemistry ......................................................................................... 12 1.2.4. Tantalum N2 Chemistry ......................................................................................... 16 1.3. Project Objectives ......................................................................................................... 19 Chapter 2: Ligand Synthesis ......................................................................................................... 24 2.1. Buchwald-Hartwig Arylamination ................................................................................ 30 2.1.1. Synthesis of  ipropArBrArNH [2.1] ........................................................................... 30 2.2. Directed Ortho-Metallation (DOM) Reaction ............................................................... 34 2.2.1. Synthesis of [tolArLiArNLiˑTMEDA]2[2.2] and [phArLiArNLiˑ1.5TMEDA]2[2.3] 34 2.3. Lithiated NPN Ligands ................................................................................................. 39 2.3.1. Synthesis of  [ipropNPNLi2ˑdiox]n [2.6] ................................................................... 39 2.3.2. Synthesis of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and [phNPNLi2ˑ1.5TMEDA]2 [2.8] .. 45 2.4. Protonated NPN Ligands ............................................................................................... 52 v  2.5. Conclusions ................................................................................................................... 54 Chapter 3: Group 4 Diamido-Phosphine Complexes .................................................................... 55 3.1. Zirconium Diamido-Phosphine Complexes .................................................................. 55 3.1.1. Salt Metathesis Route ............................................................................................ 55 3.1.2. Protonolysis Route ................................................................................................ 59 Synthesis of ipropNPNZrCl2(HNMe2) [3.3] and tolNPNZrCl2(HNMe2) [3.4]...................... 60 Synthesis of ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] ............................... 64 Synthesis of ipropNPNZr(NMe2)2 [3.7] and tolNPNZr(NMe2)2 [3.8] ................................... 68 Synthesis of [ipropNPNZrCl2]2 [3.9] and [tolNPNZrCl2]2 [3.10] .......................................... 70 3.2. Titanium Diamido-Phosphine Complexes .................................................................... 78 Synthesis of ipropNPNTiCl2(HNMe2) [3.11] and tolNPNTiCl2(HNMe2) [3.12] .................. 79 Synthesis of ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14] ............................ 81 Synthesis of ipropNPNTi(NMe2)2 [3.15] and  tolNPNTi(NMe2)2 [3.16] .............................. 85 Synthesis of ipropNPNTiCl2 [3.17] and tolNPNTiCl2 [3.18] ................................................ 87 3.3. Hafnium Diamido-Phosphine Complexes ..................................................................... 89 Synthesis of ipropNPNHf(NMe2)2 [3.19] ............................................................................. 89 Synthesis of [ipropNPNHfCl2]2 [3.20] ................................................................................. 91 Synthesis of  ipropNPNHfCl2(THF) [3.21] .......................................................................... 94 3.4. Conclusions ................................................................................................................... 97 Chapter 4: Tantalum Diamido-Phosphine Complexes .................................................................. 98 4.1. Tantalum Chloride Complexes ...................................................................................... 99 4.1.1. Synthesis of Tantalum Amido Complexes .......................................................... 100 4.1.2. Synthesis of Tantalum Trichloro Complexes ...................................................... 104 4.2. Tantalum Alkyl Complexes ........................................................................................ 109 4.2.1. Salt Metathesis with TaCl2Me3 ........................................................................... 110 4.2.2. Salt Metathesis with tolNPNTaCl3 [4.5] ............................................................... 115 Summary ......................................................................................................................... 120 vi  4.3. Tantalum Dinitrogen Complexes ................................................................................ 121 4.3.1. Hydride Route ..................................................................................................... 121 Hydrogenation of ipropNPNTaMe3 [4.8] ........................................................................... 121 Reactions with KHBEt3 and N2 ....................................................................................... 121 4.3.2. Reduction Route .................................................................................................. 125 Reduction with 2 KC8 and N2 .......................................................................................... 125 Reduction with 3.5 KC8 and N2 ....................................................................................... 126 4.4. Summary ..................................................................................................................... 127 Chapter 5: Group 4 Dinitrogen Complexes ................................................................................. 129 5.1. Zirconium Dinitrogen Complexes ............................................................................... 129 5.1.1. Synthesis of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] and [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3] . ............................................................................................................................. 129 5.2. Reduction of ipropNPNHfCl2(THF) [3.21] with KC8 and N2 ........................................ 143 5.3. Zirconium Dinitrogen Adducts ................................................................................... 144 5.3.1. Nitrogen Atom Donors ........................................................................................ 145 5.3.1.1. Pyridine ....................................................................................................... 145 5.3.1.2. 4,4’-Bipyridine ............................................................................................ 149 5.3.2. Phosphorus Atom Donors ................................................................................... 152 5.3.2.1. PMe3 and PPhMe3 ....................................................................................... 153 5.3.3. Sulphur Atom Donors ......................................................................................... 158 5.3.3.1. THT ............................................................................................................. 158 5.4. Titanium Dinitrogen Complexes ................................................................................. 163 5.4.1. Synthesis of [ipropNPNTi(THF)]2N2 [5.17] and [tolNPNTi(THF)]2N2 [5.15] ........ 163 5.5. Titanium Dinitrogen Adducts ...................................................................................... 171 5.5.1. Nitrogen Atom Donors ........................................................................................ 171 5.5.1.1. Pyridine ....................................................................................................... 171 5.6. Titanium Hydrides for Alternative Dinitrogen Activation Route ............................... 178 vii  5.7. Summary ..................................................................................................................... 180 Chapter 6: Group 4 Dinitrogen Complex Reactivity................................................................... 183 6.1. Reactivity of Zirconium Dinitrogen Complexes ......................................................... 183 6.1.1. Reaction with Dihydrogen .................................................................................. 183 6.1.2. Reaction with Isocyanide .................................................................................... 187 6.1.3. Reaction with Phenylsilane ................................................................................. 194 6.1.4. Reaction with Ethylene ....................................................................................... 196 6.1.5. Reaction with Carbon Monoxide ........................................................................ 198 6.1.6. Reaction with 4 ,4’-Dimethylbenzophenone ....................................................... 201 6.1.7. Reaction with Carbon Dioxide ............................................................................ 203 6.1.8. Reaction with (Trimethylsilyl)diazomethane ...................................................... 204 6.2. Titanium Dinitrogen Complex Reactivity ................................................................... 205 6.2.1. Reaction with Dihydrogen .................................................................................. 205 6.2.2. Reaction with Carbon Monoxide ........................................................................ 206 6.2.3. Reaction with Ethylene ....................................................................................... 206 Chapter 7: Conclusions and Future Directions ........................................................................... 208 7.1. Summary ..................................................................................................................... 208 7.2. Future Ligand Designs ................................................................................................ 212 7.3. naphNPN and 2,6-iPr2NPN Donor Sets ............................................................................. 214 7.3.1. Synthesis of naphArBrArNH [7.1] and 2,6-iPr2ArBrArNH [7.2] ................................. 214 7.3.2. Synthesis of [2,6-iPr2ArLiArNLi]n [7.3] and [2,6-iPr2ArLiArNLiˑ2THF]2 [7.3a] ........ 216 7.3.3. Synthesis of [naphArLiArNLiˑ2Et2O]2 [7.4] and [naphArLiArNLiˑ2THF]2 [7.5] ...... 222 7.3.4. Synthesis of [naphNPNLi2ˑdiox]n [7.6] .................................................................. 223 7.3.5. Synthesis of [2,6-iPr2NPNLi2ˑdiox]n [7.7] .............................................................. 226 7.3.6. Synthesis of naphNPNH2 [7.8] and 2,6-iPr2NPNH2 [7.9] .......................................... 229 7.4. Final Thoughts ............................................................................................................ 230 Chapter 8: Experimental ............................................................................................................. 231 viii  8.1. General Experimental .................................................................................................. 231 8.2. Starting Materials and Reagents .................................................................................. 232 8.3. Synthetic Methods ....................................................................................................... 233 References ................................................................................................................................... 368 Appendix A: Supporting NMR Spectroscopic Information ........................................................ 388 A. DOSY 31P{1H} NMR Data for [ipropNPNZrCl2]2 [3.9] at -40 °C ..................................... 388 A.1. DOSY 31P{1H} NMR Data for tolNPNTaCl3 [4.5] at -60 °C ....................................... 392 A.2. Variable Temperature 31P{1H} NMR Data for NPNTaCl3 Complexes....................... 394 A.2.1. ipropNPNTaCl3 [4.4].............................................................................................. 395 A.2.2. tolNPNTaCl3 [4.5] ................................................................................................ 395 A.2.3. PhNPNTaCl3 [4.6] ................................................................................................ 396 Appendix B: X-ray Crystal Structure Data ................................................................................. 397 B.1. X-ray Crystal Structure Analysis ................................................................................ 397 B.2. X-ray Crystal Structures .............................................................................................. 398     ix  List of Tables Table 1 : Pre-column GC-MS data for Pd2(dba)3/rac-BINAP catalyst, 0.7 mol% Pd and Pd/rac-BINAP (1:1.5). .............................................................................................................................. 31 Table 2 : Selected bond lengths (Å) and angles (°) for [tolArLiArNLiˑTMEDA]2 [2.2] ................. 37 Table 3 : Comparative bond lengths (Å) and angles (°) for the ipropNPNLi2 and mesNPNLi2 donor sets.97 ............................................................................................................................................. 40 Table 4 : Comparative bond lengths (Å) and angles (°) for the tolNPNLi2 donor set. ................... 50 Table 5 : Comparative bond lengths (Å) and angles (°) for tolNPNH2 [2.11] and phNPNH2[2.12] 54 Table 6 : Selected bond lengths (Å) and angles (°) for [tolNPN]2Zr [3.2] ..................................... 58 Table 7 : Selected bond lengths (Å) and angles (°) for tolNPNZrCl2(HNMe2) [3.4]261 and mesNPNZrCl2(Py)97 ........................................................................................................................ 64 Table 8 : Selected bond lengths (Å) and angles (°) for ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6]261 ............................................................................................................. 67 Table 9 : Selected bond lengths (Å) and angles (°) for ipropNPNZr(NMe2)2 [3.7] and tolNPNZr(NMe2)2 [3.8]261 .............................................................................................................. 70 Table 10 : Selected bond lengths (Å) and angles (°) for [ipropNPNZrCl2]2 [3.9] and mesNPNZrCl297, 214 ................................................................................................................................................... 73 Table 11 : Selected bond lengths (Å) and angles (°) for ipropNPNTi(NMe2)2 [3.15] ..................... 86 Table 12 : Selected bond lengths (Å) and angles (°) for tolNPNTiCl2 [3.18] and SiNPNTiCl2137 .. 88 Table 13 : Selected bond lengths (Å) and angles (°) for ipropNPNHf(NMe2)2 [3.19] and mesNPNHf(NMe2)297 ...................................................................................................................... 90 Table 14 : Selected bond lengths (Å) and angles (°) for [ipropNPNHfCl2]2 [3.20] and mesNPNHfCl297 ............................................................................................................................... 92 Table 15 : Selected bond lengths (Å) and angles (°) for ipropNPNHfCl2(THF) [3.21] ................... 97 Table 16 : Selected bond lengths (Å) and angles (°) for tolNPNTa(NMe2)3 [4.2] ....................... 103 Table 17: Comparative bond lengths (Å) and angles (°) for related SiNPN and P2N2 tantalum complexes. ................................................................................................................................... 103 Table 18 : Selected bond lengths (Å) and angles (°) for PhNPNTaCl3 [4.6] ................................ 105 Table 19 : 31P{1H} NMR data for NPNTaCl3 complexes at -70 °C. ........................................... 106 Table 20 : Selected bond lengths (Å) and angles (°) for iprop-PNPNTaMe3 .................................. 114 Table 21 : Selected bond lengths (Å) and angles (°) for [tolNPNTaMe4][Li(THF)4] [4.14] with comparative Ta-Me bond lengths (Å) ......................................................................................... 117 Table 22: Inter-ligand bond angle analysis for seven coordinate geometries of [tolNPNTaMe4][Li(THF)4] [4.14] ................................................................................................ 118 x  Table 23 : Selected bond lengths (Å) and angles (°) for [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] compared to [mesNPNZr(THF)]2(µ-η2:η2-N2), [SiNPNZr(THF)]2(µ-η2:η2-N2) and[CY5NPNDMPZr(THF)]2(µ-η2:η2-N2) ....................................................................................... 137 Table 24 : 1H and 13C{1H} NMR Data for the Py ligand in [5.4] and [5.5] in C6D6 ................... 147 Table 25 : Selected bond lengths (Å) and angles (°) for [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15] compared to [PNPTiCl)]2(µ-η1:η1-N2)182 and [P2N2Ti]2(µ-η1:η1-N2)137 ...................................... 166 Table 26 : Selected bond lengths (Å) and angles (°) for trans-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19] ..................................................................................................................................................... 174 Table 27 : 31P{1H} and 15N{1H} NMR data for reactions of xylylNC and tBuNC with [5.1], [5.2] and [5.3] ...................................................................................................................................... 187 Table 28 : Screening studies with zirconium dinitrogen complexes ........................................... 212 Table 29 : Selected bond lengths (Å) and angles (°) for 2,6-iPr2ArBrArNH [7.2] and naphArBrArNH [7.1] ............................................................................................................................................. 216 Table 30 : GC-MS data for lithiation of 2,6-iPr2ArBrArNH [7.2] .................................................. 216 Table 31 : Selected bond lengths (Å) and angles (°) for [2,6-iPr2ArLiArNLiˑ2THF]2 [7.3a] .......... 221 Table 32 : 31P{1H} NMR spectroscopic data for the thermal / light decomposition study of ipropNPNTaMe3 [4.8]. ................................................................................................................... 294 Table 33: Fryzuk Research Group x-ray data processing code (mf#) ......................................... 398 Table 34: Crystal Data and Structure Refinement for [tolArLiArNLiˑTMEDA]2 [2.2], [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and [tolNPNLi2ˑ0.5TMEDAˑDME]2 ........................................... 399 Table 35: Crystal Data and Structure Refinement for tolNPNH2 [2.11], phNPNH2 [2.12] and [tolNPN]2Zr [3.2] .......................................................................................................................... 400 Table 36: Crystal Data and Structure Refinement for tolNPNZrCl2(HNMe2) [3.4], ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] .............................................................. 401 Table 37: Crystal Data and Structure Refinement for ipropNPNZr(NMe2)2 [3.7], tolNPNZr(NMe2)2 [3.8] and [ipropNPNZrCl2]2 [3.9] ................................................................................................... 402 Table 38: Crystal Data and Structure Refinement for ipropNPNTi(NMe2)2 [3.15], tolNPNTiCl2 [3.18] and ipropNPNHf(NMe2)2 [3.19] .......................................................................................... 403 Table 39: Crystal Data and Structure Refinement for [ipropNPNHfCl2]2 [3.20], ipropNPNHfCl2(THF) [3.21] and tolNPNTa(NMe2)3 [4.2] ............................................................. 404 Table 40: Crystal Data and Structure Refinement for PhNPNTaCl3 [4.6], iprop-PNPNTaMe3 and [tolNPNTaMe4][Li(THF)4] [4.14] ................................................................................................ 405 Table 41: Crystal Data and Structure Refinement for [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1], [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15] and trans-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19] ................ 406 xi  Table 42: Crystal Data and Structure Refinement for naphArBrArNH [7.1], 2,6-iPr2ArBrArNH [7.2] and [2,6-iPr2ArLiArNLiˑ2THF]2 [7.3a] .......................................................................................... 407    xii  List of Figures Figure 1: Chatt cycle for mononuclear molybdenum complexes (Mo0-MoVI)26 ............................. 3 Figure 2: Schrock’s [HIPTN3N]Mo(N2) catalyst, HIPT = hexa-iso-propyl-terphenyl45, 51 ............. 4 Figure 3: Idealised catalytic cycle for the combination of dinitrogen with substrates .................... 5 Figure 4: Activated dinitrogen bonding modes for dinuclear complexes ....................................... 7 Figure 5: Steric effect of ligand on N2 bonding modes ................................................................... 8 Figure 6: Selected examples of zirconium dinitrogen complexes ................................................... 9 Figure 7: Dinitrogen bonding modes for titanium dinitrogen complexes ..................................... 13 Figure 8: End-on dinitrogen [PNPTiCl]2(µ-η1:η1-N2)182 and [P2N2Ti]2(µ-η1:η1-N2)137  complexes ....................................................................................................................................................... 15 Figure 9: Dinitrogen bonding modes for titanium dinitrogen complexes ..................................... 15 Figure 10: Tantalum dinitrogen alkylidene complexes obtained by reduction of precursor chlorides72-75 .................................................................................................................................. 16 Figure 11: Tantalum dinitrogen cyclopentadienyl complexes obtained by reduction of precursor chlorides76-78, 183, 184 ........................................................................................................................ 17 Figure 12: Tantalum SiNPN dinitrogen complexes obtained by the hydride route ....................... 18 Figure 13: SiNPN vs. o-phenylene NPN ligand ............................................................................. 19 Figure 14: Reactivity of mesNPN containing zirconium dinitrogen complexes97 .......................... 20 Figure 15: SiNPN vs. o-phenylene NPN ligand ............................................................................. 21 Figure 16: Donor variation for the PNP, P2N2 and NPN donor sets ............................................. 24 Figure 17: Variation in organic groups of phosphine donors ........................................................ 25 Figure 18: NPN donor sets with different backbones ................................................................... 26 Figure 19: Summary of NPN donor sets with reduced steric bulk at the amido units .................. 26 Figure 20: Synthesis of mesNPN precursors ................................................................................... 27 Figure 21: General DOM mechanism ........................................................................................... 29 Figure 22: Synthesis of ipropArBrArNH [2.1] under Pd2dba3/rac-BINAP/toluene catalytic conditions. ..................................................................................................................................... 31 Figure 23: Potential formation of o-(ipropArNH)2C6H4 .................................................................. 32 Figure 24: Potential formation of ipropArN(C6H4Br)2..................................................................... 32 Figure 25: 7Li{1H} (top) and 1H NMR (bottom) spectra of [tolArLiArNLiˑTMEDA]2 [2.2] in C6D6 and THF-d8 .................................................................................................................................... 35 Figure 26: Synthesis of [tolArLiArNLiˑTMEDA]2 [2.2] and [phArLiArNLiˑ1.5TMEDA]2 [2.3] ..... 36 Figure 27: ORTEP representation of the solid state molecular structure of [tolArLiArNLiˑTMEDA]2 [2.2] ....................................................................................................... 37 xiii  Figure 28: Synthesis of tolArDArND [2.4] and phArDArND [2.5] ................................................... 38 Figure 29: 2H NMR spectrum of tolArDArND [2.4] in C6H6.......................................................... 38 Figure 30: Synthesis of [ipropNPNLi2ˑdiox]n [2.6] .......................................................................... 39 Figure 31: ORTEP representation of the solid-state molecular structure of [ipropNPNLi2ˑdiox]n [2.6]97 ............................................................................................................................................ 41 Figure 32: 1H NMR spectra for the ipropNPNLi2 donor set: 1,4-dioxane, mixed 1,4-dioxane/THF and THF adducts ........................................................................................................................... 42 Figure 33: Chain and monomeric forms of the ipropNPNLi2 donor set .......................................... 42 Figure 34: 31P{1H} NMR spectra for the ipropNPNLi2 donor set: 1,4-dioxane, mixed 1,4-dioxane/THF and THF adducts ..................................................................................................... 44 Figure 35: 7Li{1H} NMR spectra for the ipropNPNLi2 donor set: 1,4-dioxane, mixed 1,4-dioxane/THF and THF adducts ..................................................................................................... 44 Figure 36: Synthesis of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] ................................................................ 45 Figure 37: 31P{1H} NMR spectra of the tolNPNLi2 donor set: TMEDA, mixed TMEDA/THF and THF adducts .................................................................................................................................. 46 Figure 38: 7Li{1H} NMR spectra of the tolNPNLi2 donor set: TMEDA, mixed TMEDA/THF and THF adducts .................................................................................................................................. 46 Figure 39: 1H NMR spectra of the tolNPNLi2 donor set: TMEDA, mixed TMEDA/THF and THF adducts .......................................................................................................................................... 48 Figure 40: Structural forms of the tolNPNLi2 donor set ................................................................. 48 Figure 41: ORTEP representation of the solid state molecular structure of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and tolNPNLi2ˑ0.5TMEDAˑ1DME261............................................ 49 Figure 42: 31P{1H NMR) NMR spectrum of tolNPNPPh [2.9] ...................................................... 51 Figure 43: Synthesis of tolNPNPPh [2.9] ....................................................................................... 52 Figure 44: Synthesis of ipropNPNH2 [2.10], tolNPNH2 [2.11] and phNPNH2 [2.12] ........................ 53 Figure 45: ORTEP representations of the solid state molecular structures of tolNPNH2 [2.11] and phNPNH2 [2.12] ............................................................................................................................. 53 Figure 46: Salt metathesis and protonolysis routes for zirconium complexes .............................. 55 Figure 47: Formation of [ipropNPN]2Zr [3.1] and [tolNPN]2Zr [3.2] ............................................... 56 Figure 48: 31P{1H} (top) and 1H NMR (bottom) spectra of [ipropNPN]2Zr [3.1] in C6D6 .............. 57 Figure 49: ORTEP representation of the solid state molecular structure of [tolNPN]2Zr [3.2] ...... 58 Figure 50: Reaction of SiNPNLi2ˑ2THF, mesNPNLi2·diox and [ipropNPNLi2·diox]n [2.6] with ZrCl4(THF)2 .................................................................................................................................. 59 Figure 51: Protonolysis with ZrCl2(NMe2)2(DME) or Zr(NMe2)4 ................................................ 60 xiv  Figure 52: 31P{1H} (top) and 1H NMR (bottom) spectra of tolNPNZrCl2(HNMe2) [3.4] in C6D6 . 61 Figure 53: Proton transfer for tolNPNZrCl2(HNMe2) [3.4] ............................................................ 61 Figure 54: Possible origin of the minor impurity trichloride ipropNPN(H)ZrCl3 ............................ 62 Figure 55: Isomers of NPNZrCl2(HNMe2) ................................................................................... 63 Figure 56: ORTEP representation of the solid state molecular structure of tolNPNZrCl2(HNMe2) [3.4] ............................................................................................................................................... 63 Figure 57: Isomers of NPNZrCl2(THF) ........................................................................................ 65 Figure 58: 31P{1H} (top), partial 13C{1H} (middle) and 1H NMR (bottom) spectra of ipropNPNZrCl2(THF) [3.5] in C6D6 ................................................................................................. 66 Figure 59: ORTEP representations of the solid state molecular structures of ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] ................................................................................................. 67 Figure 60: Protonolysis of tolNPNH2 [2.11] with ZrCl2(NMe2)2(DME) in THF at 60 °C ............. 68 Figure 61: 31P{1H} (top) and 1H NMR (bottom) spectra of tolNPNZr(NMe2)2 [3.8] ..................... 69 Figure 62: ORTEP representation of the solid state molecular structure of ipropNPNZr(NMe2)2 [3.7] and tolNPNZr(NMe2)2 [3.8] ................................................................................................... 69 Figure 63: 31P{1H} NMR spectra of ipropNPNZr(NMe2)2 [3.7] (bottom) and after 2, 5 and 7 equiv of TMSCl (middle three) and ipropNPNZrCl2(THF) [3.5] after excess THF (top) in C6D6 at 25 °C ....................................................................................................................................................... 71 Figure 64: 31P{1H} (top) and 1H NMR (bottom) spectra of [ipropNPNZrCl2]2 [3.9] and [tolNPNZrCl2]2 [3.10] in C6D6 at 25 °C ......................................................................................... 72 Figure 65: ORTEP representation of the solid state molecular structure of [ipropNPNZrCl2]2 [3.9] ....................................................................................................................................................... 73 Figure 66: 31P{1H} NMR spectra of [tolPNZrCl2]2 [3.10] in toluene-d8 at 93 and -71 °C ............. 74 Figure 67: 31P{1H} NMR spectra of [ipropNPNZrCl2]2 [3.9] in toluene-d8 from 93 to -60 °C (δ 4.54 at 25 °C used as reference for spectra at other temperatures) ....................................................... 75 Figure 68: 31P{1H} NMR spectra of different samples [ipropNPNZrCl2]2 [3.9] in toluene-d8 at -60 °C .................................................................................................................................................. 75 Figure 69: 1H NMR spectrum of [ipropNPNZrCl2]2 [3.9] in toluene-d8 at  -60 °C, 25 °C and 93 °C ....................................................................................................................................................... 76 Figure 70: Chloro-bridged isomers for [NPNZrCl2]2, [3.9] and [3.10] ......................................... 77 Figure 71: Protonolysis with TiCl2(NMe2)2 or Ti(NMe2)4 ............................................................ 79 Figure 72: Possible isomers for NPNTiCl2(HNMe2) [3.11] and [3.12] ........................................ 79 Figure 73: 31P{1H} NMR spectrum of tolNPNTiCl2(HNMe2) [3.12] ............................................. 80 Figure 74: 1H NMR spectrum of tolNPNTiCl2(HNMe2) [3.12] ..................................................... 80 xv  Figure 75: 1H NMR spectrum of tolNPNTiCl2(THF) [3.14] in C6D6 ............................................. 81 Figure 76: 31P{1H} NMR spectra of ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14] in C6D6 ............................................................................................................................................... 82 Figure 77: 1H NMR of  ipropNPNTiCl2(THF) [3.13] before and after THF spike in C6D6 ............. 82 Figure 78: Possible isomeric structures for ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14] ............................................................................................................................................. 83 Figure 79: 31P{1H} (top) and 1H NMR (bottom) spectra of ipropNPNTiCl2(HNMe2)/(THF) [3.11]/[3.13] .................................................................................................................................. 83 Figure 80: Equilibrium structures for ipropNPNTiCl2(THF) [3.13] and ipropNPNTiCl2(HNMe2) [3.11] ............................................................................................................................................. 84 Figure 81: 31P{1H} NMR spectrum of ipropNPNTi(NMe2)2 [3.15] ................................................. 85 Figure 82: Partial 13C{1H} (top) and 1H NMR (bottom) spectra of ipropNPNTi(NMe2)2 [3.15] .... 85 Figure 83: ORTEP representation of the solid state molecular structure of ipropNPNTi(NMe2)2 [3.15] ............................................................................................................................................. 86 Figure 84: 31P{1H} NMR spectra of ipropNPNTi(NMe2)2 [3.15] (bottom) and + 2, 4 and 6 equiv of TMSCl in C6D6.............................................................................................................................. 87 Figure 85: ORTEP representation of the solid state molecular structure of tolNPNTiCl2 [3.18] ... 88 Figure 86: Protonolysis of ipropNPNH2 [2.10] with Hf(NMe2)4 ..................................................... 89 Figure 87: ORTEP representation of the solid state molecular structure of ipropNPNHf(NMe2)2 [3.19] ............................................................................................................................................. 90 Figure 88: 31P{1H} (top) and 1H NMR (bottom) spectrum of [ipropNPNHfCl2]2 [3.20] in C6D6 at 25 °C .................................................................................................................................................. 91 Figure 89: ORTEP representation of the solid state molecular structure of [ipropPNHfCl2]2 [3.20] ....................................................................................................................................................... 92 Figure 90: 31P{1H} NMR spectra of [ipropNPNHfCl2]2 [3.20] in toluene-d8 from 93 to -81 °C (δ 7.89 at 93 °C used as reference for spectra at other temperatures) ............................................... 93 Figure 91: 1H NMR spectra of [ipropNPNHfCl2]2 [3.20] in toluene-d8 at 25 °C and -71 °C ........... 94 Figure 92: 31P{1H} (top) and 1H NMR (bottom) spectra of ipropNPNHfCl2(THF) [3.21] in C6D6 . 95 Figure 93: Partial 13C{1H} NMR spectrum of ipropNPNHfCl2(THF) [3.21] in C6D6 ..................... 95 Figure 94: Isomers of ipropNPNHfCl2(THF) [3.21] ........................................................................ 95 Figure 95: ORTEP representation of the solid state molecular structure of ipropNPNHfCl2(THF) [3.21] ............................................................................................................................................. 96 Figure 96: Schematic representation of target NPN tantalum complexes ..................................... 98 Figure 97: Salt metathesis and protonolysis routes for tantalum complexes ................................ 99 xvi  Figure 98: Protonolysis route for synthesis of NPNTaCl3 complexes [4.4], [4.5] and [4.6] ....... 100 Figure 99: 1H (top) and 31P{1H} NMR (bottom) spectra of tolNPNTa(NMe2)3 [4.2] in C6D6, “hex” in the 1H NMR spectrum refers to residual hexanes ................................................................... 101 Figure 100: Partial 13C{1H} NMR spectrum of tolNPNTa(NMe2)3 [4.2] in C6D6 ........................ 102 Figure 101: ORTEP representation of the solid state molecular structure of tolNPNTa(NMe2)3 [4.2] ............................................................................................................................................. 102 Figure 102: 1H (top) and 31P{1H} NMR (bottom) spectra for tolNPNTaCl3 [4.5] in C6D6 at room temperature .................................................................................................................................. 104 Figure 103: ORTEP representation of the solid sate molecular structure for PhNPNTaCl3[4.6] . 105 Figure 104: 31P{1H} NMR spectra for tolNPNTaCl3 [4.5] in toluene-d8 and THF-d8 at -70 °C. . 107 Figure 105: Partial 1H NMR spectra for tolNPNTaCl3 [4.5] in toluene-d8 and THF-d8 at -70 °C. ..................................................................................................................................................... 107 Figure 106: Implausible equilibria for solvated NPNTaCl3 complexes ...................................... 108 Figure 107: Possible configurational isomers for solvated NPNTaCl3 complexes ..................... 109 Figure 108: Synthesis of tolNPNTaMe3 [4.7]............................................................................... 110 Figure 109: 1H (top) and 31P{1H] NMR (bottom) spectra for tolNPNTaMe3 [4.7] in C6D6 ......... 110 Figure 110: 1H-31P HMBC NMR spectrum for tolNPNTaMe3 [4.7] in C6D6 ............................... 111 Figure 111: 31P{1H} NMR spectra for reaction of [ipropNPNLi2ˑdiox]n [2.6] with TaMe3Cl2 in toluene-d8 (successive spectra offset by δ 2 units, 0 min = time the sample was placed inside the spectrometer at -80 °C) ............................................................................................................... 112 Figure 112: 1H NMR spectrum for reaction of [ipropNPNLi2ˑdiox]n [2.6]with TaMe3Cl2 in toluene-d8 at -80 °C, CH-iprop = methine, Me-iprop = methyl of the isopropyl group ........................... 113 Figure 113: o-Phenylene bridged NPNTaMe3 complexes .......................................................... 113 Figure 114: ORTEP representation of the solid state molecular structure for iprop-PNPNTaMe3 . 114 Figure 115: 31P{1H} NMR spectra of tolNPNTaCl3 [4.5] + 1, 2, 3 and 4 equiv of MeLi at room temperature in toluene-d8. ........................................................................................................... 115 Figure 116: 1H NMR spectrum for species tol4MeLi in toluene-d8 after 4 equiv of MeLi. ........... 116 Figure 117: ORTEP representation of the solid state molecular structure for [tolNPNTaMe4][Li(THF)4] [4.14]. ............................................................................................... 117 Figure 118: Possible seven-coordinate geometries for the [tolNPNTaMe4]- anion of [4.14]. Pentagonal bipyramid: Me1, Me2 axial and Me3, Me4, N, N, P pentagonal. Capped octahedron: Me1, P axial and Me3, Me4, N, N equatorial of octahedron with Me2 cap of trigonal face Me1, N, N. Capped trigonal prism: Me1, Me3, Me4 and Me2, N, N trigonal bases with P cap of xvii  quadrilateral face Me3, Me4, N, N. 4:3 Piano stool: Me1, Me2, Me3, Me4  tetragonal base and N, N, P trigonal cap. ......................................................................................................................... 119 Figure 119: Potential tantalum methyl species for the salt metathesis of tolNPNTaCl3 [4.5] with MeLi ............................................................................................................................................ 120 Figure 120: Partial 31P{1H} (top) and partial 1H NMR (bottom) spectra for ipropNPNTaCl3 [4.4] + KHBEt3 (Ar) + N2 in C6D6 .......................................................................................................... 122 Figure 121: Potential species indicated by mass spectral data .................................................... 123 Figure 122: 31P{1H} (top) and partial 1H NMR (bottom) spectra for tolNPNTaCl3 [4.5] + KHBEt3 + N2 in C6D6 ................................................................................................................................ 123 Figure 123: Schematic of potential reactions of NPNTaCl3 with KHBEt3 under Ar and N2 ...... 124 Figure 124: 31P{1H} NMR spectrum for reaction of tolNPNTaCl3 [4.5] with 2.2 KC8 under N2 in C6D6 ............................................................................................................................................. 125 Figure 125:  Reduction of NPNTaCl3 complexes with 2.2 KC8 under N2 .................................. 126 Figure 126: 31P{1H} NMR spectra for tolNPNTaCl3 [4.5] + 3.5 KC8 under N2 in C6D6 ............. 127 Figure 127: Synthesis of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] and [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3] ............................................................................................................................................. 129 Figure 128: 31P{1H} (bottom) and 1H NMR (top) spectra of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] ..................................................................................................................................................... 130 Figure 129: 31P{1H} (bottom) and 1H NMR (top) spectra of [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3] ..................................................................................................................................................... 131 Figure 130: Potential mechanism for the formation of zirconium dinitrogen complexes ........... 132 Figure 131: Experimental set-up of the glass liner for the Parr reactor with the KC8 ampoule .. 134 Figure 132: ORTEP representation of the solid state molecular structure of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] ......................................................................................... 136 Figure 133: 31P{1H} and 15N{1H} NMR spectra for [ipropNPNZr(THF)]2(µ-η2:η2-15N2) [5.2] in C6D6 ............................................................................................................................................. 139 Figure 134: Infrared spectra for [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] and [ipropNPNZr(THF)]2(µ-η2:η2-15N2) [5.2] ........................................................................................................................... 140 Figure 135: Theoretical vibrational modes for a Zr2N2 core141 ................................................... 141 Figure 136: UV-Vis spectra for [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] ...................................... 142 Figure 137: Reduction of ipropNPNHfCl2(THF) [3.21] with KC8 and N2 .................................... 144 Figure 138: Comparison of zirconium dinitrogen complexes P2N2 (silyl methyls omitted for clarity) with NPN(Ln) .................................................................................................................. 145 xviii  Figure 139:  ORTEP representations of the solid state molecular structures of related [SiNPNZr(Py)]2(µ-η2:η2-N2)137 and [mesNPNZr(Py)]2(µ-η2:η2-N2)92, 97 complexes ...................... 146 Figure 140: Synthesis of [tolNPNZr(Py)]2(µ-η2:η2-N2) [5.4] and [tolNPNZr(Py-d5)]2(µ-η2:η2-N2) [5.5] ............................................................................................................................................. 146 Figure 141: [tolNPNZr(Py)]2(µ-η2:η2-N2) [5.4] with excess pyridine .......................................... 147 Figure 142: 31P{1H} NMR (top) spectrum of [5.4] and  partial 1H NMR  spectra of [5.4] (middle) and [5.5] (bottom) in C6D6 .......................................................................................................... 148 Figure 143: Partial 1H NMR spectra with variation in free pyridine for [tolNPNZr(Py)]2(µ-η2:η2-N2) [5.4] in C6D6 ......................................................................................................................... 148 Figure 144: 31P{1H} NMR (bottom) and partial 1H NMR (top) spectra of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] after 1 and 2 equiv of 4,4’-bipyridine in C6D6 .................................................... 150 Figure 145: Reaction of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] with one and two equiv of 4,4’-bipyridine .................................................................................................................................... 150 Figure 146: Chain vs. Dimer structure for [ipropNPNZr(4,4’-bipy)]2(µ-η2:η2-N2) [5.6] ............... 152 Figure 147: Reaction of [mesNPNZr(THF)]2(µ-η2:η2-N2) with PMe3 and PPhMe2...................... 152 Figure 148: Reaction of the zirconium dinitrogen THF adducts [5.1] and [5.3] with PMe3 and PPhMe2 ........................................................................................................................................ 153 Figure 149: 31P{1H} (a, b and c-1) and 1H NMR (c-2) spectra of mixtures of [ipropNPNZr(THF)](µ-η2:η2-N2)[ipropNPNZr(PMe3)] [5.7] and [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1]in C6D6 ................................................................................................................................. 155 Figure 150: 31P{1H} spectra of [ipropNPNZr(PMe3)]2(µ-η2:η2-N2) [5.8] (top), [tolNPNZr(PMe3)]2(µ-η2:η2-N2) [5.9] (middle) and [ipropNPNZr(PPhMe2)]2(µ-η2:η2-N2) [5.10] (bottom) ..................... 156 Figure 151: 31P{1H} NMR spectra of [tolNPNZr(PPhMe2)]2(µ-η2:η2-N2) [5.11] at 25 and -25 °C in C6D6 ............................................................................................................................................. 157 Figure 152: 1H NMR spectra of [tolNPNZr(PMe3)]2(µ-η2:η2-N2) [5.9] (top) and [ipropNPNZr(PPhMe2)]2(µ-η2:η2-N2) [5.10] (bottom), with excess free phosphine in C6D6 ......... 157 Figure 153: 31P{1H} (bottom) and 1H NMR (top) spectra of exchanging [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3] and [tolNPNZr(THT)]2(µ-η2:η2-N2) [5.14] in C6D6.............................................. 159 Figure 154: Exchange between THF ([5.3] and [5.1]) and potential THT ([5.14] and [5.12]) adducts ........................................................................................................................................ 160 Figure 155: 31P{1H} (bottom) and 1H NMR (top) spectra of 30 equiv of THT with [ipropNPNZr(PMe3)]2(µ-η2:η2-N2) [5.8] + trace THF in C6D6 ...................................................... 160 Figure 156: 31P{1H} (bottom) and 1H NMR (top) spectra of [tolNPNZr(THT)]2(µ-η2:η2-N2) [5.14] in C6D6 ........................................................................................................................................ 161 xix  Figure 157: Phosphine displacement with neat THT, in situ from [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3] ............................................................................................................................................. 162 Figure 158: Synthesis of [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15] .................................................. 163 Figure 159: 31P{1H} (bottom) and 1H NMR (top) spectra of [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15] in C6D6 ........................................................................................................................................ 164 Figure 160: 31P{1H} (bottom) and 1H NMR (top) spectra of crude brown solid after THF centrifuge in C6D6 ....................................................................................................................... 165 Figure 161: ORTEP representation of solid state molecular structure of [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15]332 ........................................................................................................................ 165 Figure 162: 31P{1H} (bottom) and 1H NMR (top) spectra of crude brown solid for ipropNPNTiCl2 [3.17] reduction in C6D6 .............................................................................................................. 167 Figure 163: Potential phosphinimide formation during the reduction of NPNTiCl2 [3.17] and [3.18] ........................................................................................................................................... 168 Figure 164: 31P{1H} NMR spectra of [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15] + species a before (bottom) and after THF spike (top) in C6D6 ................................................................................ 169 Figure 165: 31P{1H} (bottom) and 1H NMR (top) spectra of species a in C6D6 .......................... 169 Figure 166: Formation of [tolNPNTi(THF)2]2(µ-η1:η1-N2) [5.16] ............................................... 170 Figure 167: 31P{1H} NMR spectra after pyridine addition to [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15] in C6D6 ........................................................................................................................................ 171 Figure 168: Synthesis of trans-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19] from [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15] ........................................................................................................................... 172 Figure 169: Potential pyridine adducts observed in the C6D6 solution with two or four Py per titanium centre ............................................................................................................................. 173 Figure 170: ORTEP representation of solid state molecular structure of trans-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19]332 ........................................................................................................................ 174 Figure 171: 31P{1H} NMR spectra of trans-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19] (bottom) and with a 20 µL Py-d5 spike (top) in C6D6 ............................................................................................... 175 Figure 172: 1H NMR spectra of trans-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19] (bottom) and with a 20 µL Py-d5 spike (top) and with a 20 µL Py spike (middle) in C6D6 ............................................. 177 Figure 173: Synthesis of [tolNPNTi(2,2’-bipy)]2(µ-η1:η1-N2) [5.20] ........................................... 177 Figure 174: 31P{1H} (bottom) and 1H NMR (top) spectra of [tolNPNTi(2,2’-bipy)]2(µ-η1:η1-N2) [5.20] in C6D6 .............................................................................................................................. 178 Figure 175: Synthesis of [tolNPNTiH2]2 [5.21] ............................................................................ 179 xx  Figure 176: 31P{1H} (bottom), partial 1H (middle two) and partial 1H{31P} NMR (top) spectra of [tolNPNTiH2]2 [5.21] in C6D6 ....................................................................................................... 180 Figure 177: Hydrogenation with P2N2 (silyl methyls omitted for clarity) and NPN amido-phosphine N2 complexes ............................................................................................................. 184 Figure 178: Failed hydrogenations with NPN(Ln) zirconium N2 complexes .............................. 185 Figure 179: Reaction of 2:2 dinitrogen complexes NPN(Ln), [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3] and [tolNPNZr(PMe3)]2(µ-η2:η2-N2) [5.9] with molecular hydrogen ........................................... 186 Figure 180: 31P{1H} (top) and 1H NMR (bottom) spectra of complex [5.1] + 2 equiv of xylylNC (species a) in C6D6, x denotes residual toluene and n-hexane solvents ....................................... 188 Figure 181: 31P{1H} (top) and 15N{1H} NMR (bottom) spectra of complex [5.2] + 2 equiv of xylylNC (species a-1) in C6D6..................................................................................................... 189 Figure 182: Proposed reaction of complexes [5.1], [5.2] and [5.3] with 2 equiv of xylylNC or tBuNC. Note: (i) the N-N bond is depicted intact, as insufficient data to evaluate if N-N cleavage occurred, (ii) isocyanide insertion is depicted as N-inside, but may be N-outside354 and (iii) the P atoms of the ligands are depicted in a trans arrangement (as in the precursors), but could be cis. ..................................................................................................................................................... 190 Figure 183: 31P{1H} (top) and 1H NMR (bottom) spectra of complex [5.1] + 2 equiv of tBuNC (species  c) in C6D6 ...................................................................................................................... 191 Figure 184: 31P{1H} NMR spectra of complex [5.2] with 1, 2, 3 and 4 xylylNC (species a-1 and e-1) (top) and 1H NMR spectrum with 4 xylylNC (species e-1) (bottom) in C6D6 ..................... 192 Figure 185: 31P{1H} and partial 15N{1H} NMR spectra of complex [5.2] with 4 xylylNC (species e-1) in C6D6 ................................................................................................................................. 193 Figure 186: Hydrosilylation with P2N2 and SiNPN dinitrogen complexes .................................. 194 Figure 187: Hydrosilylation with the mesNPN containing dinitrogen complex ........................... 195 Figure 188: 31P{1H} NMR spectrum of [ipropNPNZr(THF]2(µ-η2:η2-N2) [5.1] + PhSiH3 in C6D6 ..................................................................................................................................................... 195 Figure 189: Hydrosilylation with [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] with PhSiH3 ............... 196 Figure 190: 31P{1H} (top) and 1H NMR (bottom) of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] after 1 atm H2C=CH2 .............................................................................................................................. 197 Figure 191: Partial 1H NMR of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] after 1atm H2C=CH2 in C6D6 ............................................................................................................................................. 197 Figure 192: Theoretical products for reaction of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] with large excess CO .................................................................................................................................... 198 xxi  Figure 193: Theoretical products for reaction of [ipropNPNZr(THF]2(µ-η2:η2-N2) [5.1] with 1 equiv of CO ................................................................................................................................. 199 Figure 194: 31P{1H} NMR spectra of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] after 1 atm CO in C6D6 ............................................................................................................................................. 200 Figure 195: 31P{1H} spectrum of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1]  after 1 equiv of CO ... 201 Figure 196: Theoretical products for reaction of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] with Ar2C=O ....................................................................................................................................... 202 Figure 197: 31P{1H} NMR spectrum of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] after 1 equiv of Ar2C=O in C6D6 .......................................................................................................................... 203 Figure 198: Theoretical products for [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] with 1 equiv of N2CHSiMe3 ................................................................................................................................. 204 Figure 199: 31P{1H} NMR spectrum of [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1] + 1 equiv of N2CHSiMe3 in C6D6 .................................................................................................................... 205 Figure 200:31P{1H} (bottom) and partial 1H NMR (top) spectra for [tolNPNTi]2(H2C=CH2) [5.22] in C6D6 ........................................................................................................................................ 207 Figure 201: NPN donor set variation of arylamido groups ......................................................... 212 Figure 202: Potential reactivity of bulky NPN zirconium N2 complexes with dihydrogen ........ 213 Figure 203: Potential NPN ligand design for side-on titanium N2 complexes ............................ 214 Figure 204: Synthesis of naphArBrArNH [7.1] and 2,6-iPr2ArBrArNH [7.2] ..................................... 215 Figure 205: Solid state molecular structures of 2,6-iPr2ArBrArNH [7.2] and naphArBrArNH [7.1] . 216 Figure 206: Lithiation of 2,6-iPr2ArBrArNH [7.2] ......................................................................... 217 Figure 207: Synthesis of [2,6-iPr2ArLiArNLi]n [7.3] and [2,6-iPr2ArLiArNLiˑ2THF]2 [7.3a] ............. 217 Figure 208: 7Li{1H} (bottom) and 1H NMR (top) of [2,6-iPr2ArLiArNLi]n [7.3] in C6D6 .............. 218 Figure 209: 7Li{1H} (bottom) and 1H NMR (top) of [2,6-iPr2ArLiArNLiˑ2THF]2 [7.3a] in THF-d8 ..................................................................................................................................................... 219 Figure 210: Solid state molecular structure of dimeric [2,6-iPr2ArLiArNLiˑ2THF]2 [7.3a] in two different orientations, with the carbon atoms of the THF adducts omitted for clarity ................ 220 Figure 211: Synthesis of [naphArLiArNLiˑ2Et2O]2 [7.4] and [naphArLiArNLiˑ2THF]2 [7.5] .......... 222 Figure 212: Synthesis of [naphNPNLi2ˑdiox]n [7.6] ...................................................................... 223 Figure 213: 31P{1H} NMR spectrum of [naphNPNLi2ˑdiox]n [7.6] in toluene-d8 .......................... 224 Figure 214: 7Li{1H} NMR spectrum of [naphNPNLi2ˑdiox]n [7.6] in toluene-d8.......................... 224 Figure 215: Structural forms for [naphNPNLi2ˑdiox]n [7.6],  [naphNPNLi2ˑ1.5diox]n [7.6a] and [naphNPNLi2ˑdioxˑ2THF]n [7.6b] .................................................................................................. 225 Figure 216: 31P{1H} NMR spectrum of [naphNPNLi2ˑdioxˑ2THF]n [7.6b] in C6D6 ..................... 226 xxii  Figure 217: Potential P-Li coupled P-N and P-C side-products for one-pot reaction (a) ........... 227 Figure 218: Synthesis of [2,6-iPr2NPNLi2ˑdiox]n [7.7], [2,6-iPr2NPNLi2ˑ1.5diox]n [7.7a], 2,6-iPr2NPNLi2ˑ2Et2O [7.7b] or 2,6-iPr2NPNLi2ˑ3Et2O [7.7c] ............................................................... 228 Figure 219: 31P{1H} NMR spectra of crude reaction mixtures for [2,6-iPr2NPNLi2ˑdiox]n [7.7] in C6D6 ............................................................................................................................................. 228 Figure 220: Synthesis of naphNPNH2 [7.8] ................................................................................... 229 Figure 221: Synthesis of 2,6-iPr2NPNH2 [7.9] ................................................................................ 229 Figure 222: DOSY 31P{1H} NMR spectrum and diffusion coefficients (D) for [ipropNPNZrCl2]2 [3.9] in toluene-d8 at -40 °C ........................................................................................................ 388 Figure 223: Diffusion coefficients (D) from DOSY 31P{1H} NMR spectrum of tolNPNTaCl3 [4.5] in toluene-d8 at -60 °C ................................................................................................................. 392 Figure 224: Variable temperature 31P{1H} NMR spectra for ipropNPNTaCl3 [4.4] in C7D8 from 25 °C to -70 °C ................................................................................................................................. 395 Figure 225: Variable temperature 31P{1H} NMR spectra for tolNPNTaCl3 [4.5] in C7D8 from 25 °C to -69 °C ................................................................................................................................. 396 Figure 226: Variable temperature 31P{1H} NMR spectra for PhNPNTaCl3 [4.6] in C7D8 from 25 °C to -69 °C ................................................................................................................................. 396    xxiii  Glossary of Terms  °C   degrees Celsius ca   approximately Å   Ångström (10-10 m) N2, N≡N  dinitrogen PhN=NPh  diazobenzene N22-, (N=N)2-  diazenido N24-, (N-N)4-  hydrazido NH3   ammonia H2   dihydrogen Ar   argon CDCl3   deuterated chloroform C6D6   deuterated benzene C7D8   deuterated toluene THF-d8   deuterated tetrahydrofuran THF   tetrahydrofuran 1H   proton 31P   phosphorus-31 {1H}   proton decoupled NMR   nuclear magnetic resonance MHz   megahertz 13C   carbon-13 7Li   lithium-7 2H   deuterium 15N   nitrogen-15 	   delta η1-N2   terminal end-on-bound N2 µ-η1:η1-N2  bridging end-on-bound N2 µ-η2:η2-N2  bridging side-on-bound N2 µ-η1:η2-N2  bridging side-on-end-on-bound N2 ppm   parts per million Hz   Hertz, seconds-1 kcalmol-1  kilocalorie per mole r.t.   room temperature xxiv  %   percentage, fraction or ratio with 100 denominator GC   gas chromatography UV-Vis   Ultraviolet-Visible LMCT   Ligand-to-Metal Charge Transfer equiv   equivalent(s) av   average d   doublet nJAB   │coupling constant│between nuclei A and B over n bonds CH3   methyl group hep   heptet CH   methine group CH2   methylene ArH   phenyl proton Cipso   ipso-carbon  ArC   aromatic carbon Anal.   analysis  Calcd.    calculated EI   electron impact MS   mass spectrometry m/z   mass-to-charge ratio [M]+   parent ion hr   hour(s) min   minute(s) R.T.   retention time conc.   concentration ppt   precipitate bs   broad singlet t   triplet qt   quartet s   singlet m   multiplet DOM   directed ortho-metalation DMG   direct metalation group ORTEP   Oak Ridge thermal ellipsoid plot xxv  KAAP   KBR Advanced Ammonia Process (KBR = Kellogg, Brown & Root) D2O   deuterium oxide diox   1,4-dioxane C6H6   benzene P(OPh)3  triphenyl phosphate H3PO4   phosphoric acid MeNO2   nitromethane NH4NO3  ammonium nitrate LiCl   lithium chloride D2O   deuterium oxide H2O   water CO2   carbon dioxide CaH2   calcium hydride C   carbon H   hydrogen or proton N   nitrogen S   sulphur P   phosphorus Fe   iron Mo   molybdenum Ru   ruthenium Cr   chromium Si   silicon Al   aliminium B   boron Me3SiI   iodotrimethylsilane dba   trans, trans-dibenzylidene acetone PdCl2   palladium dichloride Pd   palladium rac-BINAP  rac-2,2'-bis(diphenylphosphino)-1,1'-binaphthalene DPPF   1,1'-bis(diphenylphosphino)ferrocene Pd2dba2   tris(dibenzylideneacetone)dipalladium(0) PdCl2(CH3CN)2  dichloro-bis(acetonitrile)palladium(II) PdCl2(DPPF)  dichloro(1,1'-bis(diphenylphosphino)ferrocene)palladium(II) xxvi  CH3CN   acetonitrile NatOBu  sodium tertiary butoxide o-C6H4Br2  1,2-dibromobenzene C6H4BrI  1-bromo-2-iodobenzene KtOBu   potassium tertiary butoxide Br2   bromine TMEDA  N,N,N',N'-tetramethylethylenediamine Et2O   diethylether Bu2O   dibutylether PPhCl2   p,p-dichlorophenylphosphine NMe3.HCl  trimethylamine hydrochloride tol2NH   di-p-tolylamine Ph2NH   diphenylamine phNPNPPh  bis-(N-phenyl-2-(phenylamine)-phenylphosphine- P- phenyl-phosphonous diamide DME   dimethoxyethane PiPr2Cl   diisopropylchlorophosphine PR2Cl   dialkylchlorophosphine or diarylchlorophosphine PtBu3   tri-tert-butylphosphine PCy3   tricyclohexylphosphine PMe3   trimethylphosphine PPhMe2  dimethylphenylphosphine naphArNH2  1-naphthylamine 4-iPrArNH2  4-isopropylaniline 4-iPrArNHLi  4-isopropylphenylamidolithium 2,6-iPr2ArNH2  2,6-diisopropylaniline Cp*   η5-C5Me5, pentamethylcyclopentadienyl Cp   cyclopentadienyl η5-C5Me4H  tetramethylcyclopentadienyl mesNPNLi2  bis-(N-mesityl-2-(4-methylphenyl)amidolithium)-phenylphosphine SiNPNLi2 bis-(N-phenyl-(N-dimethyl-methylenesilane)amidolithium)-phenylphosphine ipropNPNLi2  bis-(N-4-isopropyl-phenyl-2-phenylamidolithium)-phenyl phosphine xxvii  Ph,mesNPNLi2  bis-(N-mesityl-2-phenylamidolithium)-phenylphosphine  tolNPNLi2  bis-[bis-(N-tolyl-2-(4-methylphenyl)amidolithium)-phenyl phosphine phNPNLi2   bis-[bis-(N-phenyl-2-phenylamidolithium)-phenylphosphine naphNPNLi2  bis-(N-1-naphthyl-2-phenylamidolithium)-phenylphosphine  2,6-iPr2NPNLi2  bis-(N-2,6-diisopropyl-phenyl-2-phenylamidolithium)-phenylphosphine mesArBrArNH  N-mesityl-2-bromo-4-methylaniline mesArBr-PhArNH  N-mesityl-2-bromo-4-aniline NBS   N-bromosuccinimide o-(PhNH)2C6H4  N,N'-bis-phenyl-1,6-benzenediamine o-(ipropArNH)2C6H4 N,N'-bis-4-isopropyl-phenyl-1,6-benzenediamine ipropArArNH  N-(4-isopropylphenyl)-aniline ipropArN(C6H4Br)2 2-bromo-N-(2-bromophenyl)-N-phenyl-benzenamine ipropArLiArNLi  bis-(N-4-isopropyl-phenyl-2-lithiophenylamidolithium) [(tol-LiAr)2NLiˑTMEDA]n poly-(bis-(2-lithio-4-methyl-phenyl)-amido  lithiumˑTMEDA) SiNPNLi2ˑ2THF bis-(N-phenyl-(N-dimethyl-methylenesilane)amidolithium)-phenylphosphineˑ2THF ipropNPNLi2ˑ2THF bis-(N-4-isopropyl-phenyl-2-phenylamidolithium)-phenyl phosphineˑ2THF  ipropNPNLi2ˑ4THF bis-(N-4-isopropyl-phenyl-2-phenylamidolithium)-phenyl phosphineˑ4THF [ipropNPNLi2ˑ2THFˑdiox]n poly-[bis-(N-4-isopropyl-phenyl-2-phenylamidolithium)-phenyl phosphineˑ2THFˑ1,4-dioxane] tolNPNZrCl2(Et2O) dichloro-(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine) (diethylether) zirconium(IV) o-C6H4BrF  1-bromo-2-fluoro-benzene n-BuLi   n-butyllithium tert-BuLi  tert-butyllithium naphArClArNH  N-1-naphthyl-2-chloroaniline DPEPhos  bis-(2-(diphenylphosphino)phenyl)ether naphArHArNH  N-(1-naphthyl)-aniline mesNPNH2  bis-(N-mesityl-2-(4-methyl-phenylamine))-phenylphosphine Ph,mesNPNH2  bis-(N-mesityl-2-(phenylamine))-phenylphosphine xxviii  [Ph,mesNPNLi2ˑdiox]n poly-[bis-(N-mesityl-2-phenylamidolithium)-phenylphosphineˑ1,4-dioxane] MesBr   2-bromo-1,3,5-trimethylbenzene PCy3   tricyclohexylphosphine PPh3   triphenylphosphine PNP   diphosphine amido P2N2   diphosphine diamido NPN   phosphine diamido NPN(P)  diphosphine diamido NPN(O)  phosphine diamido alkoxy Ar2NH   diarylamine [Ar2NLi]n  poly-[diarylamidolithium] [Ar2NLiˑTMEDA]2 bis-(diarylamidolithiumˑN,N,N',N'-tetramethylethylenediamine) Ph-naphArNH2  2-phenylnaphthalen-1-amine Ph-naphArBrArNH  N-(2-bromophenyl)-2-phenylnaphthalen-1-amine ZrCl4(THF)2  tetrachloro-bis(tetrahydrofuran)zirconium(IV) ZrCl4   tetrachlorozirconium(IV) Zr(NMe2)4   tetrakis(dimethylamino)zirconium(IV) ZrCl2(NMe2)2(DME) dichloro-bis-(dimethylamino)(1,2-dimethoxyethane)zirconium(IV) TMSCl   chlorotrimethylsilane KC8   potassium graphite PtBu3   tris-tert-butylphosphine dmpe   1,2-Bis(dimethylphosphino)ethane THT   tetrahydrothiophene xylylNC  2,6-dimethylphenylisocyanide tBuNC   tert-butylisocyanide PhSiH3   phenylsilane TiCl4   tetrachlorotitanium(IV) Ti(NMe2)4   tetrakis(dimethylamino)titanium(IV) Hf(NMe2)4  tetrakis(dimethylamino)hafnium(IV) [TaCl5]2   pentachlorotantalum(V) Ta(NMe2)5  pentakis(dimethylamino)tantalum(V) [TaCl3(PMe3)2]2 Trichloro-bis-(trimethylphosphine) tantalum(III) dimer xxix  [ipropNPNTaCl(PMe3)]2 Chloro[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine]( trimethylphenylphosphine) tantalum (III) dimer [ipropNPNTaCl]2 Chloro[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine] tantalum (III) dimer [ipropNPNTaCl]x Chloro[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine] tantalum (III) if x =1, or dimer (if x = 2), etc. [ipropNPNTaCl4] Tetrachloro[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine]tantalum(V) anion [ipropNPNTaCl2] Dichloro[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine] tantalum(V) cation [tolNPNTaCl4]  Tetrachloro[(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenyl    phosphine]tantalum(V) anion [tolNPNTaCl2]  Dichloro[(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine] tantalum(V) cation SiNP(C)NTa(NMe2)2 [(N-phenyl-(N-dimethyl-methylenesilane-phenylphosphino))-( N-phenyl-(N-dimethyl-silane)-methane]-bis-(dimethylamido)tantalum (V) [{ipropNPNTaMe2}2]Cl2  bis-[Dimethyl-[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine] tantalum (V)] dichloride  (or species uipr) [{tolNPNTaMe2}2]Cl2   bis-[Dimethyl-[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V)] dichloride (or species utol) tolNPNTaBn3  Tribenzyl-[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine] tantalum (V) KHBEt3  potassium triethylborohydride KH   potassium hydride  xxx  List of Compounds  ipropArBrArNH [2.1]: N-4-isopropyl-phenyl-2-bromoaniline [tolArLiArNLi·TMEDA]2 [2.2]: bis-(N-4-methyl-phenyl-(2-lithio-4-methyl-phenyl)-amido  lithiumˑTMEDA) [phArLiArNLi·1.5TMEDA]2 [2.3]: bis-[N-phenyl-(2-lithio-phenyl)amidolithiumˑ1.5TMEDA] tolArDArND [2.4]: N-4-methyl-phenyl-(2-deuterio-4-methyl-phenyl)-deuterioamine phArDArND [2.5]: N-phenyl-(2-deuterio-phenyl)-deuterioamine [ipropNPNLi2·diox]n [2.6]: poly-[bis-(N-4-isopropyl-phenyl-2-phenylamidolithium)-phenyl phosphineˑdioxane]  [tolNPNLi2·1.5TMEDA]2 [2.7]: bis-[bis-(N-tolyl-2-(4-methylphenyl)amidolithium)-phenyl phosphineˑ1.5 TMEDA] [phNPNLi2·1.5TMEDA]2 [2.8]: bis-[bis-(N-phenyl-2-phenylamidolithium)-phenylphosphine ˑ1.5TMEDA] tolNPNPPh [2.9]: bis-(N-tolyl-2-(4-methyl-phenylamine))-phenylphosphine- P- phenyl -phosphonous diamide ipropNPNH2 [2.10]: bis-(N-4-isopropyl-phenyl-2-phenylamine)-phenylphosphine  tolNPNH2 [2.11]: bis-(N-tolyl-2-(4-methyl-phenylamine))-phenylphosphine phNPNH2 [2.12]: bis-(N-phenyl-2-(phenylamine))-phenylphosphine [ipropNPN]2Zr [3.1]: bis-[bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine] zirconium(IV) [tolNPN]2Zr [3.2]: bis-[bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine]zirconium(IV) ipropNPNZrCl2(HNMe2) [3.3]: Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine)(dimethylamine) zirconium(IV) tolNPNZrCl2(HNMe2) [3.4]: Dichloro-(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine)(dimethylamine) zirconium(IV) ipropNPNZrCl2(THF) [3.5]: Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl  phosphine)(tetrahydrofuran) zirconium(IV) tolNPNZrCl2(THF) [3.6]: Dichloro-(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine) (tetrahydrofuran) zirconium(IV) ipropNPNZr(NMe2)2 [3.7]: (bis-(N-4-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine)-  bis-(dimethylamido) zirconium (IV) tolNPNZr(NMe2)2 [3.8]: (bis-(N-4-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine)- bis-(dimethylamido) zirconium (IV) [ipropNPNZrCl2]2 [3.9]: bis-[Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl xxxi   phosphine) zirconium(IV)] [tolNPNZrCl2]2 [3.10]: bis-[Dichloro-(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenyl  phosphine] zirconium(IV)] ipropNPNTiCl2(HNMe2) [3.11]: Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl  phosphine)(dimethylamine) titanium (IV) tolNPNTiCl2(HNMe2) [3.12]: Dichloro-(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenyl  phosphine)(dimethylamine) titanium (IV) ipropNPNTiCl2(THF) [3.13]: Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl  phosphine)(tetrahydrofuran) titanium (IV) tolNPNTiCl2(THF) [3.14]: Dichloro-(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine)  (tetrahydrofuran) titanium (IV) ipropNPNTi(NMe2)2 [3.15]: (bis-(N-4-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine)-  bis-(dimethylamido) titanium (IV) tolNPNTi(NMe2)2 [3.16]: (bis-(N-4-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine)-  bis-(dimethylamido) zirconium (IV) ipropNPNTiCl2 [3.17]: Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine)  titanium (IV) tolNPNTiCl2 [3.18]: Dichloro-(bis-(N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine)  titanium (IV) ipropNPNHf(NMe2)2 [3.19]: (bis-(N-4-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine)-  bis-(dimethylamido) hafnium (IV) [ipropNPNHfCl2]2 [3.20]: bis-[Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl  phosphine) hafnium(IV)] ipropNPNHfCl2(THF) [3.21]: Dichloro-(bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine)(tetrahydrofuran) hafnium (IV) ipropNPNTa(NMe2)3 [4.1]: [(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine]-tris-(dimethylamido)tantalum (V) tolNPNTa(NMe2)3 [4.2]: [(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine]-tris-(dimethylamido)tantalum (V) PhNPNTa(NMe2)3 [4.3]: [(bis-N-bis-phenylamido)-phenylphosphine]-tris-(dimethylamido)tantalum (V) ipropNPNTaCl3 [4.4]: Trichloro-[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine] tantalum (V) tolNPNTaCl3 [4.5]: Trichloro-[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl xxxii  phosphine] tantalum (V) PhNPNTaCl3 [4.6]: Trichloro-[(bis-N-bis-phenylamido)-phenylphosphine] tantalum (V) tolNPNTaMe3 [4.7]: Trimethyl-[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V) ipropNPNTaMe3 [4.8]: Trimethyl-[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine] tantalum (V)  tolNPNTaMe4Li(Et2O) [4.13]: Tetramethyl-[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V) lithium diethylether (or species tol4MeLi) [tolNPNTaMe4][Li(THF)4] [4.14]: Tetramethyl-[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V) lithium tetrakis-tetrahydrofuran tolNPNTaMe4Li(THF) [4.15]: Tetramethyl-[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V) lithium tetrahydrofuran (or species tol4MeLi) [ipropNPNTaH]2(N2) [4.17]: Bis-{[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine] tantalum (V) hydride}(dinitrogen) [ipropNPNTaH]2(NBEt3)2(N2)2 [4.17a]: Bis-{[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine] tantalum (V) hydride}(hexaethyl-diboron-µ-η1:η1-N,N’-hydrazine)(bis-dinitrogen) [tolNPNTaH]2(N2) [4.18]: Bis-{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V) hydride}(dinitrogen) [tolNPNTaH]2(NBEt3)2(N2)2 [4.18a]: Bis-{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V) hydride} (hexaethyl-diboron-µ-η1:η1-N,N’-hydrazine)(bis-dinitrogen) [ipropNPNTaCl]2(N2) [4.19]: Bis-{[(bis-N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine] tantalum (V) chloride}(dinitrogen) [tolNPNTaCl]2(N2) [4.20]: Bis-{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] tantalum (V) chloride}(dinitrogen) [ipropNPNZr(THF)]2(µ-η2:η2-N2) [5.1]: Bis{[bis-(N-4-isopropyl-phenyl-2-phenylamido)- phenylphosphine](tetrahydrofuran) zirconium(IV)}(µ-η2:η2-dinitrogen) [ipropNPNZr(THF)]2(µ-η2:η2-15N2) [5.2]: Bis{[bis-(N-4-isopropyl-phenyl-2-phenylamido)- phenylphosphine](tetrahydrofuran) zirconium(IV)}(µ-η2:η2-dinitrogen-15) [tolNPNZr(THF)]2(µ-η2:η2-N2) [5.3]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine](tetrahydrofuran) zirconium(IV)}(µ-η2:η2-dinitrogen) [tolNPNZr(Py)]2(µ-η2:η2-N2) [5.4]: bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl xxxiii  phosphine](pyridine) zirconium(IV)}(µ-η2:η2-dinitrogen) [tolNPNZr(Py-d5)]2(µ-η2:η2-N2) [5.5]: bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine](pyridine-d5) zirconium(IV)}(µ-η2:η2-dinitrogen) [ipropNPNZr(4,4’-bipy)]2(µ-η2:η2-N2) [5.6]: bis{[bis-(N-4-isopropyl-phenyl-2- phenylamido)-phenylphosphine](4,4'-bipyridine)zirconium(IV)}(µ-η2:η2-dinitrogen) {[ipropNPNZr]2(4,4’-bipy)(µ-η2:η2-N2)}n [5.6a]: poly-{bis{[bis-(N-4-isopropyl-phenyl-2- phenylamido)-phenylphosphine]zirconium(IV)}(4,4'-bipyridine)(µ-η2:η2-dinitrogen)} [ipropNPNZr(THF)](µ-η2:η2-N2)[ipropNPNZr(PMe3)] [5.7]: {[bis-(N-4-isopropyl-phenyl-2- phenylamido)-phenylphosphine](tetrahydrofuran) zirconium(IV)}{[bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine](trimethylphosphine) zirconium(IV)}(µ-η2:η2-dinitrogen) [ipropNPNZr(PMe3)]2(µ-η2:η2-N2) [5.8]: Bis{[bis-(N-4-isopropyl-phenyl-2-phenylamido)- phenylphosphine](trimethylphosphine) zirconium(IV)}(µ-η2:η2-dinitrogen) [tolNPNZr(PMe3)]2(µ-η2:η2-N2) [5.9]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine](trimethylphosphine) zirconium(IV)}(µ-η2:η2-dinitrogen) [ipropNPNZr(PPMe2)]2(µ-η2:η2-N2) [5.10]: Bis{[bis-(N-4-isopropyl-phenyl-2-phenylamido)- phenylphosphine](dimethylphenylphosphine) zirconium(IV)}(µ-η2:η2-dinitrogen) [tolNPNZr(PPhMe2)]2(µ-η2:η2-N2) [5.11]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine]( dimethylphenylphosphine) zirconium(IV)}(µ-η2:η2-dinitrogen) [ipropNPNZr(THT)]2(µ-η2:η2-N2) [5.12]: Bis{[bis-(N-4-isopropyl-phenyl-2-phenylamido)- phenylphosphine](tetrahydrothiophene) zirconium(IV)}(µ-η2:η2-dinitrogen) [tolNPNZr(THT)]2(µ-η2:η2-N2) [5.14]: Bis{[bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenyl phosphine](tetrahydrothiophene) zirconium(IV)}(µ-η2:η2-dinitrogen) [tolNPNTi(THF)]2(µ-η1:η1-N2) [5.15]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine](tetrahydrofuran) titanium(IV)}(µ-η1:η1-dinitrogen) [tolNPNTi(THF)2]2(µ-η1:η1-N2) [5.16]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido) phenylphosphine](bis-tetrahydrofuran) titanium(IV)}(µ-η1:η1-dinitrogen) [ipropNPNTi(THF)]2(µ-η1:η1-N2) [5.17]: Bis{[ bis-(N-4-isopropyl-phenyl-2-phenylamido)- phenylphosphine](tetrahydrofuran) titanium(IV)}(µ-η1:η1-dinitrogen) cis-[tolNPNTi(Py)]2(µ-η1:η1-N2) [5.18]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine]cis-(pyridine) titanium(IV)}(µ-η1:η1-dinitrogen) trans-[tolNPNTi(Py)]2(µ-η1:η1-N2) [5.18a]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine]trans-(pyridine) titanium(IV)}(µ-η1:η1-dinitrogen) trans-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl xxxiv  phosphine]trans-(bis-pyridine) titanium(IV)}(µ-η1:η1-dinitrogen) cis-[tolNPNTi(Py)2]2(µ-η1:η1-N2) [5.19a]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine]cis-(bis-pyridine) titanium(IV)}(µ-η1:η1-dinitrogen)  trans-[tolNPNTi(Py-d5)2]2(µ-η1:η1-N2) [5.19b]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine]trans-(bis-pyridine-deuterium) titanium(IV)}(µ-η1:η1-dinitrogen) [tolNPNTi(2,2’-bipy)]2(µ-η1:η1-N2) [5.20]: Bis{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine]( 2,2'-bipyridine) titanium(IV)}(µ-η1:η1-dinitrogen) [tolNPNTiH2]2 [5.21]: Bis-{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenyl phosphine] titanium (IV) hydride} [ipropNPNZr(THF)](xylylNC-N2)[ipropNPNZr(xylylNC)] [6.1]: {[bis-(N-4-isopropyl-phenyl-2- phenylamido)-phenylphosphine](tetrahydrofuran) zirconium(IV)}{[bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine](2,6-dimethylphenylisocyanide) zirconium(IV)}(N-(2,6-dimethylphenyl)methanimine-hydrazide) [ipropNPNZr(THF)](xylylNC-15N2)[ipropNPNZr(xylylNC)] [6.2]: {[bis-(N-4-isopropyl-phenyl-2- phenylamido)-phenylphosphine](tetrahydrofuran) zirconium(IV)}{[bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine](2,6-dimethylphenylisocyanide) zirconium(IV)}(N-(2,6-dimethylphenyl)methanimine-hydrazide-15N) [tolNPNZr(THF)](xylylNC-N2)[tolNPNZr(xylylCN)] [6.3]: {[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine](tetrahydrofuran) zirconium(IV)}{[ (bis-N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine](2,6-dimethylphenylisocyanide) zirconium(IV)}(N-(2,6-dimethylphenyl)methanimine-hydrazide) [ipropNPNZr(THF)](tBuNC-N2)[ipropNPNZr(tBuNC)] [6.4]: {[bis-(N-4-isopropyl-phenyl-2- phenylamido)-phenylphosphine](tetrahydrofuran) zirconium(IV)}{[bis-(N-4-isopropyl-phenyl-2-phenylamido)-phenylphosphine](tert-butylisocyanide) zirconium(IV)}(N-(tert-butyl)methanimine-hydrazide) [tolNPNZr(THF)](tBuNC-N2)[tolNPNZr(tBuNC)] [6.5]: {[(bis-N-tolyl-2-(4-methyl)-phenyl amido)-phenylphosphine](tetrahydrofuran) zirconium(IV)}{[(bis-N-tolyl-2-(4-methyl)-phenylamido)-phenylphosphine](tert-butylisocyanide) zirconium(IV)}(N-(tert-butyl)methanimine-hydrazide) naphArBrArNH [7.1]: N-1-Naphthyl-2-bromoaniline 2,6-iPr2ArBrArNH [7.2]: N-2,6-Diisopropylphenyl-2-bromoaniline [2,6-iPr2ArLiArNLi]n [7.3]: poly-{bis-(N-2,6-diisopropyl-phenyl-2-lithiophenylamidolithium)} [2,6-iPr2ArLiArNLiˑ2THF]2 [7.3a]: Di-{bis-(N-2,6-diisopropyl-phenyl-2-lithiophenylamidolithium)ˑbis-tetrahydrofuran} xxxv  [naphArLiArNLiˑ2Et2O]2 [7.4]: Di-{bis-(N-2-napthyl-2-lithiophenylamidolithium)ˑbis-diethyl  ether} [naphArLiArNLiˑ2THF]2 [7.5]: Di-{bis-(N-2-napthyl-2-lithiophenylamidolithium)ˑbis-tetrahydro furan} [naphNPNLi2ˑdiox]n [7.6]: poly-{bis-(N-1-naphthyl-2-phenylamidolithium)-phenylphosphineˑ dioxane} [naphNPNLi2ˑ1.5diox]n [7.6a]: poly{di-[bis-(N-1-naphthyl-2-phenylamidolithium)-phenyl phosphine]ˑtris-dioxane} [naphNPNLi2ˑdioxˑ2THF]n [7.6b]: poly-{bis-(N-1-naphthyl-2-phenylamidolithium)-phenyl phosphineˑdioxaneˑbis-tetrahydrofuran} [2,6-iPr2NPNLi2ˑdiox]n  [7.7]: poly-{bis-(N-2,6-diisopropyl-phenyl-2-phenylamidolithium)-phenyl phosphineˑdioxane} [2,6-iPr2NPNLi2ˑ1.5diox]n  [7.7a]: poly-{di-[bis-(N-2,6-diisopropyl-phenyl-2-phenylamido lithium)-phenylphosphine]ˑtris-dioxane} 2,6-iPr2NPNLi2ˑ2Et2O  [7.7b]: bis-(N-2,6-diisopropyl-phenyl-2-phenylamidolithium)-phenyl phosphineˑbis-diethylether 2,6-iPr2NPNLi2ˑ3Et2O  [7.7c]: bis-(N-2,6-diisopropyl-phenyl-2-phenylamidolithium)-phenyl phosphineˑtris-diethylether naphNPNH2 [7.8]: bis-(N-1-naphthyl-2-phenylamine)-phenylphosphine 2,6-iPr2NPNH2  [7.9]: bis-(N-2,6-diisopropyl-phenyl-2-phenylamine)-phenylphosphine  xxxvi  Acknowledgements Within this allotted space, I am unable to give thanks in a fair and equitable way to all those persons who have helped me in so many ways through the different stages of my journey of scientific and personal discovery to the final completion of this thesis document.  I will thus limit myself to those of direct relevance to the production, interpretation and presentation of this body of work. To my research supervisor, Prof. Michael Fryzuk, for his unwavering support and guidance for the lifetime of the project and to Prof. Laurel Schafer, whose crucial assistance at two important pivotal occasions was invaluable.  To the Fryzuk Group Research Members for advice on laboratory matters and friendly scientific discourse and the Technical, Mechanical and Analytic Support Services at the UBC Chemistry Department.   xxxvii  Dedication A major navigational prize of the 18th century was the location of the southern continent Antarctica. This goal inspired Captain James Cook’s expeditions of discovery in the Pacific Ocean. Towards the end of his first voyage from 1768 to 1771 on the ship Endeavor, he navigated the east coast of New Holland (a.k.a. Australia) through the treacherous Great Barrier Reef.  Below is an excerpt from his diary days before he passed through the Endeavour Strait  between the mainland and Prince of Wales, in the process proving that New Guinea and New Holland were not a continuous landmass.  “...our depth of water in the Channell was from 30 to 7 fathom very erregular soundings and foul ground until we had got quite within the Reef where we anchor’d in 19 fathom a Corally & Shelly bottom happy once more to encounter those shoals which but two days ago our utmost wishes were crowned by geting clear of, such are the Vicissitudes attending this kind of service and must always attend an unknown Navigation: Was it not for the pleasure which naturly results to a Man from being the first discoverer, even was it nothing more than sands and Shoals, this service would be insupportable especially in far distant parts, like this, short of Provisions and almost every other necessary. The world will hardly admit of an excuse for a man leaving a Coast unexplored he has once discover’d, if dangers are his excuse he is than charged with Timorousness and want of Perseverance and at once pronounced the unfitest man in the world to be employ’d as a discoverer; if on the other hand he boldy incounters all the dangers and obstacles he meets and is unfortunate enough not to succeed he is than charged with Temerity and want of conduct...” On repairing his ship at Batavia before his return trip to Europe, he had the following to say about the condition of the keel of Endeavour “... so that it was a Matter of Surprise to every one who saw her bottom how we had kept her above water; and yet in these conditions we had xxxviii  saild some hundreds of Leagues in as dangerous a Navigation as in any part of the world, happy in being ignorant of the continual danger we were in.” These insights from Captain Cook should resonate with anyone pursuing new journeys of scientific discovery. First and foremost, one has to create a vision and thereafter have the excitement and resolution to follow through with requisite scientific rigour, mindful always of the fact that even negative results can lead to the advancement of knowledge. The personal delight in contributing towards concepts and discoveries greater than the individual, with potential gargantuan scientific consequences should be muted by the humbleness displayed in a quote by Sir Isaac Newton “If I have seen further it is by standing on the shoulders of giants”.    1  Chapter 1: Introduction 1.1. Historical Context Nitrogen is essential for life and the conversion of N2 to ammonia is a crucial step in the nitrogen cycle.1-3  Atmospheric nitrogen can enter into the cycle via biological fixation (nitrogenase enzymes), lightning mediated oxidation and industrial fixation.  Earlier competing industrial nitrogen fixation technologies such as the Birkelan-Eyde process (also known as Norwegian Arc), the Frank-Caro cyanamide process and by-product ammonia recovery from coke ovens all proved inferior to the Haber-Bosch process.3-5 The Haber-Bosch process, whereby ammonia is produced from nitrogen and hydrogen gasses was developed by Fritz Haber in 1905-19096-8 and commercialised by Carl Bosch for BASF, with the first plant being built in Oppau in 1913.5 Haber received the Nobel Prize in 1918 for his invention, and later in 1931 Bosch (joint with Friedrich Bergius) received the Nobel Prize for his contributions towards the development of industrial chemical high pressure methods. Although the Haber-Bosch process is highly efficient, it is energy intensive due to the high temperatures (400-500 °C) and pressures (130 to 300 atm) of operation.4, 9, 10 The predominant solid state pre-catalyst is composed of iron oxide (magnetite or wustite) with traces of oxide promoters  (Al, Mg, Si, Ca and K). More recently, catalysts with ruthenium on graphite or boron nitride allow for slightly lower operating pressures (KAAP process).4, 11 To this day, ammonia production via the Haber-Bosch process remains the only economically viable industrial process,9, 12 with an annual global production estimated at over 100 to 130 million metric tons.13-15 Ammonium salts, nitrates and urea for fertilizer utilization accounts for the largest ammonia consumption, with an estimated annual 70 million metric tons3 and approximately 87% of US domestic ammonia use in 2010 was for fertilizers.15 Ammonia and nitric acid (derived from ammonia via the Ostwald process16, 17) are essential building blocks for nitrogen-containing chemical classes such as amines, amides and nitriles, which are precursors to 2  compounds with applications in diverse industries such explosives,18, 19 pharmaceuticals20 and synthetic fibres.21   As with industrial fixation, the biological fixation process needs the intervention of a transition metal catalyst, located within the MoFe protein of the nitrogenase enzymes complex.10, 22-33 Vanadium and ‘iron-only’ variations of dinitrogenase proteins also exist and the V and Fe ions are thought to occupy similar positions to the Mo atom.27, 34-36 The high energy requirement for the conversion is reflected in the large number of adenosine triphosphate (ATP) molecules consumed by the Fe protein (dinitrogenase reductase) during the natural process (16 ATP ~ 468.6 kJ.mol-1).10, 28, 37 Biotic ammonia production is higher than industrial fixation with an estimated annual production of 170 million metric tons.10, 38  In contrast to the heterogeneous solid-gas Haber-Bosch process, biological fixation takes place in a homogeneous aqueous medium at mild temperatures (290 K) and pressures (0. 8 atm).  The FeMo cofactor (7Fe-9S-Mo-C-homocitrate) within the MoFe protein has been associated with substrate binding5, 26, 33 and the Thorneley-Lowe model5 depicts increasingly more oxidised electronic states of the MoFe cofactor from the most reduced (E0) to the most oxidised (E7), as a series of 8 electrons and 8 protons are sequentially added to N2 to liberate 2 NH3 + H2.26, 29, 31, 39 It is of considerable interest to develop a low temperature and pressure alternative for the Haber-Bosch process. While steady-state assays40 of natural nitrogenases are able to replicate catalytic conversion of N2 to NH3, strategies focusing on biosynthesis of the MoFe protein41, 42 or biomimetic transition metal clusters31, 43-45 have yielded no successful results.  In a more traditional chemical approach, the isolation of the first discreet N2 complex [Ru(NH3)5(N2)]2+ in 196546-48 paved the way for the development in 1976 of the Chatt cycle (Figure 1), which is a hypothetical model for nitrogenase action with mononuclear dinitrogen complexes.26, 30 3   Figure 1: Chatt cycle for mononuclear molybdenum complexes (Mo0-MoVI)26  While the rationale for this approach is not based on direct mimicry of nitrogenase,27, 49 many researchers use the metals implicated in nitrogenase enzymes as a starting point, thus accounting for focussed investigations of molybdenum50-54 (or tungsten55-58), iron59-63 (or ruthenium53) and vanadium64-66 (or niobium67-71 and tantalum72-81) containing systems, and with sulphur-binding thiolate ligands.61, 62, 82, 83 The first homogeneous transition metal complex to generate NH3 via fixation of N2, however, was a titanium complex reported by Vol’pin and Shur in 196484-87 and this served to cement group 4 metals as suitable dinitrogen activator candidates. A landmark breakthrough was achieved by Schrock et al (Figure 2) with the first homogeneous mononuclear catalyst exhibiting four turnovers of NH3 with respect to one molybdenum atom at room temperature and pressure.51 The oxidation states in the Schrock system (MoIII-MoVI) are not as reduced as proposed in the Chatt cycle (Mo0-MoVI) and the reductant CrCp2* performs an equivalent role as the nitrogenase reductase (Fe protein) in the natural process. 4   Figure 2: Schrock’s [HIPTN3N]Mo(N2) catalyst, HIPT = hexa-iso-propyl-terphenyl45, 51  Unfortunately, while catalytic, the highly favoured competitive reaction of electrons with protons is a likely factor inhibiting the Schrock system from achieving the higher turnover levels requisite for industrially viable processes. Subsequently, a molybdenum complex with a PNP pincer ligand developed by Nishibayashi et al50 and a iron complex with a tripodal phosphine borane ligand developed by Peters et al88, 89 has been reported to catalyse ammonia generation from nitrogen in the presence of a protic source and a reductant, but conversions were still too low for industrial consideration. The development of a homogeneous equivalent of the Haber-Bosch process remains a lofty prize for chemists. Since the first partial hydrogenation reported for a zirconium dinitrogen complex with a P2N2 macrocycle by Fryzuk and workers in 1997,90 a handful of dinitrogen 5  complexes have shown reactivity with hydrogen gas, in some cases associated with the liberation of ammonia, but none of these systems have demonstrated catalytic ability (see chapter six for more discussion).63, 90-101 The substituted cyclopendadienyl trinuclear titanium complexes reported recently by Shima and co-workers are unique in that molecular hydrogen is first converted into a metal hydride complex before activating N2 and forming N-H bonds.100   Figure 3: Idealised catalytic cycle for the combination of dinitrogen with substrates Another desirable goal of N2 fixation studies in homogeneous solution chemistry would be to move “beyond nature” and directly combine dinitrogen with substrates without intermediate ammonia production.27, 54 A catalytic process (Figure 3) for the transformation of dinitrogen into functionalised nitrogen compounds would require the following, namely;  (i) activation of the dinitrogen molecule  (ii) formation of new N-element bonds  (iii) cleavage of the N-N bond  (iv) liberation of the product with the new N-element  (v) regeneration of the activated dinitrogen metal complex.  Transition metal dinitrogen complexes are often labile and the coordinated dinitrogen unit typically undergoes displacement, however, under certain conditions, it should be possible to 6  functionalise the coordinated dinitrogen before it can be displaced. The nature of the ligand Ln plays a crucial role, as at earlier stages of the catalytic cycle strong LnM-nitrogen bonds are needed to avoid displacement, however, at later stages weaker LnM-nitrogen bonds are needed to ensure reaction with substrates and the liberation of products. The steric and electronic interactions between Ln and the metal centres need to be robust and able to respond to the varying LnM-nitrogen conditions. As activated dinitrogen complexes can be formed from metal hydrides,68, 80, 100, 102 this provides a mechanism for catalyst regeneration, whereby the introduction of a hydride source to the nitrogen-substrate bound product liberates the protonated final product and generates the associated metal hydride. For ammonia production, the ability of a recently reported trinuclear titanium polyhydride complex100 to simultaneously activate N2 and form new N-H bonds via molecular hydrogen as a proton source may represent the groundwork towards the development of a homogeneous catalysts analogue to the heterogeneous Haber-Bosch process. New N-C bonds can be accessed from N2 complexes via condensation reactions of protonated N2 complexes with aldehydes or ketones or via reaction with electrophilic reagents (i.e. organohalides) or via cycloaddition of alkynes across the metal-N bond.27, 54, 79, 103, 104 N2 compounds also react with isocyanates105 and CO2106 to form new C-N bonds. New N-Si bonds can be formed by reaction with Me3SiI58 or via hydrosilylation107-109 with silanes. Similarly, new N-B and N-Al bonds are formed via hydroboration110, 111 and hydroalumination.112  The complete cleavage of N2 can occur immediately on complex formation,52, 113, 114 or during further reduction or heating of the N2 complex.93, 115-117 One of the elusive challenges that remain is to develop strategies to liberate the functionalised nitrogen products with concomitant regeneration of the activated dinitrogen species. The first noteworthy example is the catalytic formation of silylamines in 1972,118 with Hidai and co-workers reporting a discreet molybdenum dinitrogen complex in 1989 capable of a turnover number of 25 mol / Mo atoms.119 This result was greatly improved upon by Nishibayashi to 226 mol / Mo atoms, using a molybdenum dinitrogen complex 7  with ferrocenyl linked phosphine ligands.120 Dinitrogen complexes from iron carbonyl and ferrocenes can also catalyse this transformation under ambient conditions, but the active catalytic species has yet to be isolated.121 Numerous other organo-nitrogen compounds have been formed from N2 via in situ generated titanium dinitrogen complexes.122 1.2. Dinitrogen Complexes The bonding of N2 to transition metals is explained using the Dewar-Chatt-Duncanson model.123, 124 The activated N2 unit may bind in a side-on, end-on or hybrid side-on/end-on fashion (Figure 4) and mono, di and polynuclear complexes can be formed. Note that in an idealised catalytic cycle (Figure 3), the activated dinitrogen is depicted as side-on rather than end-on, as the lone pair in the side-on mode is more available and is considered more conducive to further reactivity with substrates.125 The degree of back-donation on activation can be correlated with the degree of elongation of the N-N bond length obtained via X-ray diffraction data.   Figure 4: Activated dinitrogen bonding modes for dinuclear complexes For weak activation, the N-N bond length is similar to that of free N≡N (1.10 Å), for moderate activation the N-N bond length is similar to PhN=NPh (1.26 Å) and for strong activation the N-N bond length is similar to that of hydrazine (1.47 Å). The formal oxidation state of the N2 unit varies accordingly, with the moderately activated diazenido (N=N)-2 unit, strongly activated hydrazido (N-N)-4 unit and the completely cleaved bridging or terminal nitride 8  (=N-)3- / (≡N)3-. Spectroscopy can be helpful to distinguish between the end-on and side-on N-N binding modes.126 Again, the nature of the ligand can have a profound effect on the type of N2 bonding observed, as is illustrated in the below-mentioned series of cyclopentadienyl titanium complexes (Figure 5). For pentamethyl-substitution, a dinuclear complex with one end-on unit is reported;127 increasing the steric bulk of one group to iso-propyl results in a mononuclear complex with two end-on N2 ligands.128 Reducing the steric bulk by removing two methyl groups leads to a side-on dinuclear complex instead.129  Figure 5: Steric effect of ligand on N2 bonding modes 1.2.1. Zirconium N2 Chemistry  The first report of a zirconium dinitrogen complex was made by Bercaw and Manriquez 130, 131 in 1974 for a end-on bridged dinuclear zirconocene (A in Figure 6). This bright green complex contained two additional terminal side-on dinitrogen ligands and the two different bonding modes were confirmed later with x-ray crystallography.132 Since then a wide variety of zirconium dinitrogen complexes have been reported, mostly containing substituted cyclopentadienyl, amide or phosphorus ligands (Figure 6). Mixed heterobimetallic zirconium and tungsten containing complexes were also prepared, which coordinated dinitrogen in a bridging end-on fashion.133, 134 The first side-on zirconium dinitrogen complex, which contained a planar Zr2N2 core, was reported for an amidodiphosphine complex [PNPZrCl]2(µ-η2:η2-N2) by Fryzuk et al in 1990 (F).135 Changing the anionic chloride donor to an aryloxy group resulted in a butterfly 9  distortion of the Zr2N2 core (G)136 and when the donor was changed to cyclopentadienyl group a bridging side-on bonding mode was observed (D).75 Resonance Raman spectroscopy was shown to be a useful for discriminating between the side-on and end-on modes.126 Of the Fryzuk groups side-on diamidophosphine (NPN) zirconium dinitrogen complexes, [SiNPNZr(THF)]2(µ-η2:η2-N2),137, 138 [SiNPNZr(Py)]2(µ-η2:η2-N2),137, 138 and [CY5NPNDMPZr(THF)]2(µ-η2:η2-N2)139, 140 have planar Zr2N2 cores and [mesNPNZr(THF)]2(µ-η2:η2-N2), [mesNPNZr(Py)]2(µ-η2:η2-N2) and [mesNPNZr(PPhMe2)](µ-η2:η2-N2)[mesNPNZr]92, 97 complexes display a butterfly distortion. Vibrational spectroscopic studies have been conducted of this butterfly distortion of the planar Zr2N2 core complexes.136, 141    Figure 6: Selected examples of zirconium dinitrogen complexes  Subtle changes to the substitution of cyclopentadienyl groups were found to lead to dramatic changes in the dinitrogen bonding mode. For example, removing one of the methyl groups from the pentamethylcyclopentadienyl moiety led to the coordination of one planar bridging side-on dinitrogen group (E).93, 94 The ansa-zirconocene with tert-butyl and methyl 10  substituents display a butterfly distorted Zr2N2 core,142 whereas tert-butyl and TMS substituents result in a planar Zr2N2 core.143 The mixed pentamethylcyclopentadienyl / guanidinate side-on zirconium dinitrogen complexes (L) also exhibit a distortion from linearity.144 The bis-indenyl dinitrogen complex results in a side-on mode with two weakly coordinated sodium chlorides (C),98 however, with a mixed indenyl  / pentamethylcyclopentadienyl system, a side-on end-on mode was observed (H).145 The formation of the side-on, end-on mode observed for complex (H) is strongly dependant on method of preparation and requires the reduction of the precursor dichloride in the presence of dinitrogen. If, however, the mixed indenyl  / pentamethylcyclopentadienyl sandwich complex was isolated by reduction of the self-same dichloride under argon, subsequent exposure to dinitrogen led to the isolation of a non-linear end-on bridged complex (K).145  While crystal structures of mononuclear zirconium dinitrogen complexes have not yet been reported, a presence of a bis-dinitrogen binuclear intermediate (J) is postulated during the splitting of water by the tris-dinitrogen zirconocene (A).146 Pentamethyl zirconocene with a bulky alkyl (-CH(SiMe3)2) ligand was reported to form a brown ‘side-on’ dinitrogen complex (I).147 Even more interesting, low temperature (-30 °C) re-crystallisation of this brown mononuclear zirconocene dinitrogen led to the purple dinuclear end-on dinitrogen zirconocene (B).147Conversion of the brown mononuclear complex (I) to the purple dinuclear one (B) was also observed on prolonged exposure to reduced pressure. This purple dinuclear complex (B) was also not characterised crystallographically, but is surmised to have a similar structure to the related titanocene dinitrogen complex with an aryl ligand characterised by Teuben et al.148 The green side-on dinitrogen complexes [(Cp-Me5)(Cp-1,2-Me2,4-R)Zr]2(µ-η2:η2-N2) with R =  Me or Ph were isolated as isomeric syn:anti mixtures, with preference given to the anti isomers.96 Isomeric exchange between these isomers is confirmed with increasing temperature above 50 °C, with a mechanism involving inter-conversion between an end-on and side-on dinitrogen ligand. The 11  forest green side-on dinitrogen zirconocene (E) was also observed to undergo transformation in excess dinitrogen to an intense purple complex, which is favoured at lower temperatures. Electronic and infrared spectra of the purple solutions suggest that the bridged dinitrogen unit was side-on, with two additional terminal side-on dinitrogen ligands, similar to the structure reported for A.96  Reduced zirconium species have a high affinity for reducing dinitrogen, forming strongly activated dinitrogen transition metal complexes with some of the longest N-N bonds having been reported for the butterfly distorted side-on mixed cyclopentadienyl / amidinate144 and planar side-on amidodiphosphine (PNP),135  diamidophosphine (NNP)149 and diamidodiphosphine (P2N2)90, 150 zirconium complexes, with bond lengths of 1.518(2) Å, 1.548(7) Å, 1.576(9) Å and 1.465(19) Å, respectively. 1.2.2. Hafnium N2 Chemistry  Hafnium and zirconium have similar covalent radii and display similar chemical behaviour,151 but fewer dinitrogen complexes with hafnium have been reported, in part due to the hafnium dichlorides being more difficult to reduce.152 To date, a few cyclopentadienyl based hafnium dinitrogen complexes have been prepared, via reduction of either the precursor chlorides or iodides.99, 134, 144 The dinitrogen ligand was postulated to be end-on for a dinuclear hafnocene complex153 and characterised end-on in the case of the mixed tungsten / hafnium dinuclear complex.134 Varying the substitution on the cyclopentadienyl group led to the side-on dinitrogen dinuclear hafnocene dinitrogen complexes99 and recently mixed cyclopentadienyl / guanidinate and cyclopentadienyl / amidinate dinitrogen complexes144 were reported. The side-on dinuclear hafnocene dinitrogen complexes proved to be highly activated and reactive with H2,99 CO,154-156 CO2,106, 157 methyl triflate158 and phenyl isocyanate105 substrates. While no solid state molecular structure was obtained, a mass spectrum confirmed the formation of a [P2N2Hf]2(N2) complex, as well as [P2N2Hf]2 and P2N2Hf(C7H8) side-products with Hf-arene bonds.159  12  1.2.3. Titanium N2 Chemistry  Titanium dinitrogen complexes form an integral part of the early history and development of transition metal dinitrogen complexes. The first reports of the ability of transition metals to fix dinitrogen and facilitate conversion with appropriate substrates into functionalised nitrogen containing compounds was made by Vol’pin and Shur in 196484-86, 160 for the observation of ammonia by exposing in situ reduced titanocene species ‘Cp2Ti’ to dinitrogen and quenching with dilute acid. This discovery fueled the speculation that a putative ‘Cp2Ti(N2)’ species was involved in this transformation. One year later in 1965 the first transition metal dinitrogen complex was serendipitously reported by Allen and Senoff161 while studying ruthenium ammonia complexes.   The first reports of the isolation of titanocene-based dinitrogen complexes were made by Shilov et al,162 van Tamelen at al163 and Brintzinger et al164 between 1969 to 1971 and a titanium (II) dimer [Cp2Ti]2, implicated in the genesis of these complexes, was isolated by Bercaw and Britzinger in 1971.164 Elucidation of the solid state molecular structure of the dinitrogen complexes proved evasive and the topic of extensive debate until crystals obtained for [Cp*2Ti]2(µ-η1:η1-N2) in 1976 by Bercaw et al165 revealed that the dinitrogen was bound end-on between two titanium atoms with N-N bond lengths of 1.155(14) Å and 1.165(14) Å  (see C in Figure 7). A notable contribution was also made by Pez and workers, who in 1976 isolated a cyclopentadienyl-based titatium (II) dimer166 and a tetrameric titanium dinitrogen complex.167 The side-on, end-on bound dinitrogen unit to three of the titanium centres of the tetramer was crystallographically characterised in 1982 (G).168 Since then numerous end-on titanocene dinitrogen complexes have been isolated,127, 129, 148, 169-171 as well as other end-on dinitrogen titanium complexes with amido,172 guanidinate,173 benzamidinate,174 pyridine 175and multidentate NON176 and NNP149 ligand systems.  The N-N bond for the cyclopentadienyl based end-on dinitrogen titanium complexes are generally classed 13  as moderately activated with bond lengths in the range of 1.15-1.20 Å, whereas the non-titanocene based dinitrogen complexes tend to be more strongly activated with N-N bond lengths ranging from1.25 to 1.30 Å.177 This trend is also present in the side-on bridged dinitrogen complexes, where a titanocene side-on dinitrogen complex (E) is moderately activated with a N-N length of 1.22 Å129 and a titanium side-on bis-dinitrogen amido based complex (F) is strongly activated (1.38 Å).172 Cyclopentadienyl chloro titanium centres have been reported to formed heterobimetallic bridged end-on dinitrogen structures with phosphine chloro tungsten centres.133 Complete cleavage and funtionalisation of the N-N bond during reduction has also been reported for titanium complexes with pyrrolide178 and NPN137, 138 ligand systems.   Figure 7: Dinitrogen bonding modes for titanium dinitrogen complexes The chemistry of the titanocene dinitrogen complexes has been comprehensively review recently and classified according to the mode of dinitrogen coordination.179, 180 A wide variety of different dinitrogen bonding modes have been elucidated, from mono-181 and bis-dinitrogen128 mononuclear complexes (A and B in Figure 7) to dinuclear end-on (C) or side-on bridged (E)129 and mixed terminal / end-on bridged (D).129, 180 The size and number of substituents on the cyclopentadienyl ring play a major role in determining the observed structural diversity. The 14  dinuclear side-on bridging mode is preferred with the sterically least hindered η5-C5H2-1,2,4-Me3 ligand.129 With the more bulky η5-C5Me4R, R = H, Me, Et, Ar and -(SiMe2)0.5127, 129, 132, 180 the dinuclear end-on bridged mode is observed, and in the case of R = Et, additional terminal side-on dinitrogen can coordinate.180 It may be that the size of the substituent may play a larger role in promoting an end-on rather than side-on bonding mode compared with increasing substitution of the cyclopentadienyl ligand, as the 1,3 di-substituted η5-C5H3-1,3-(SiMe3)2169 and ansa (η5-C5H2-2-SiMe3-4-tBu)2-SiMe2129 ligands also exhibit an end-on bonding mode.  As the R group for the η5-C5Me4R ligands become more bulky, bridging of the dinitrogen unit no longer occurs and for R = iPr, two terminal end-on dinitrogen ligands are coordinated to a single titanium centre,128 with only one terminal dinitrogen unit when R = SiMe2Ph.181 Electronic effects of the substituted cyclopentadienyl complement the steric effects, where the smallest, least substituted and hence more electrophilic titanocenes form more highly activated bridging dinitrogen complexes, with decreasing electrophilitity leading to weakly activated monomeric species.179  The Fryzuk group’s mixed amidophosphine ligands attached to titanium metal centres are also capable of activating dinitrogen. Brown end-on bridged [PNPTiCl]2(µ-η1:η1-N2)182 and [P2N2Ti]2(µ-η1:η1-N2)137 complexes were obtained with N-N bond lengths of 1.275(7) Å and 1.255(7) Å, respectively, which falls into the range of a strongly activated N24- unit (Figure 8).  15  Figure 8: End-on dinitrogen [PNPTiCl]2(µ-η1:η1-N2)182 and [P2N2Ti]2(µ-η1:η1-N2)137  complexes However, the reduction of SiNPNTiCl2 with KC8 under N2 led to the formation of a bridged phosphinimide titanium complex.137, 138 A corresponding reaction with 15N2 confirmed that the source of the nitrogen of the phosphinimide was an activated dinitrogen molecule, which implies that facile cleavage of coordinated dinitrogen occurred, with the associated formation of phosphorus-nitrogen bonds.   Figure 9: Dinitrogen bonding modes for titanium dinitrogen complexes The forest green phosphinimide complex {[SiN(P=N)N]Ti}2 was shown to transform into an olive green intermediate with an upfield shifted  31P{1H} NMR spectral signal. It was not possible to isolate this intermediate, but its identity was speculated to be the dinitrogen complex [SiNPNTi]2(N2).  While this phosphinimide complex represents a novel P=N functionalisation, the SiNPN ligand is unfortunately transformed during the process. The new o-phenylene bridged NPN ligands synthesized for this project (ipropNPN and tolNPN) have a more rigid back-bone, which may inhibit phosphinimide formation and stabilise a dinitrogen complex.  16  1.2.4. Tantalum N2 Chemistry  The first group 5 dinitrogen complexes were formed by reduction of a neopentylidene tantalum bis(trimethylphosphine)trichloride with sodium mercury amalgam in the presence of N2.72-74 The activated bridging N2 unit was coordinated in an end-on bonding mode (Figure 10). Reduction of alkylidene tantalum complexes SiPNPTaCl2(=CHR), R = tBu, Ph with sodium mercury amalgam and N2 were later also reported to form end-on bridged N2 complexes (Figure 10).75   Figure 10: Tantalum dinitrogen alkylidene complexes obtained by reduction of precursor chlorides72-75 Reduction of substituted cyclopentadienyl76, 77 and mixed pentamethylcyclopentadienyl-guanidinate78 tantalum chloride complexes under N2 also leads to end-on bridged N2 complexes (Figure 11). Further reaction with H2 and PhSiH3 was reported for the mixed pentamethylcyclopentadienyl-guanidinate system,78 as well as complete cleavage of N2 to form a bridging nitrido complex.78  The tetrachloride [Cp*TaCl2]2(N2) has proved to be a convenient salt metathesis precursor for the mixed pentamethylcyclopentadienyl-amidate system.183 In one case a Ta(III) dimer [Cp*TaCl2]276, 184  was implicitly identified as an intermediate formed during the reduction process. A Ta(III) hydroxide was also reported to be the active species in the reduction 17  of N2 to yield hydrazine.185 Alternative routes for the preparation of tantalum N2 complexes exist, where the nitrogen sources were hydrazine76 or substituted hydrazines71, 186-189 and not molecular N2. Heterobimetallic tantalum-tungsten N2 complexes have also been prepared by reaction of a pre-activated tungsten N2 complex with Cp*TaCl4.133  Figure 11: Tantalum dinitrogen cyclopentadienyl complexes obtained by reduction of precursor chlorides76-78, 183, 184 Dinitrogen activation can also be achieved in specific cases from transition metal hydrides.190 For example, silica-grafted single site organometallic tantalum hydrides have been reported to completely cleave N2.191 The seminal [SiNPNTaH]2(N2) complex was formed from a precursor tetrahydride [SiNPNTaH2]2 (Figure 12), where the side-on, end-on bonding mode for a bridging N2 unit was described for the first time.79-81 A wide range of reactivity was displayed with this complex, namely:  i) reaction with alkyl halides79 and 1,2-cumulenes192 to form new N-C bonds 18  ii) hydroboration110, 111 to form new N-B bonds  iii) hydrosilylation107-109 to form new N-Si bonds  iv) hydroalumination112 to form new N-Al bonds  v) reaction with Schwartz’s reagent to form new N-Zr bonds and fully cleave the N-N bond115 vi) formation of aluminum, gallium and boron Lewis adducts193 vii) reaction with propene194 to form Ta-alkyl N2 complexes with conversion to end-on bonding mode viii) displacement of N2 when reacted with phenylacetylene195 or carbon disulphide196  Figure 12: Tantalum SiNPN dinitrogen complexes obtained by the hydride route Despite the rich new types of chemical reactivity discovered for this novel [SiNPNTaH]2(N2) complex, numerous types of ligand degradation pathways have also been reported. For example, the reaction of the hydroalumination product of [SiNPNTaH]2(N2) with diisobutylaluminum hydride reacts further to fully cleave the N2 bond, but the amide of the ligand decoordinates from Ta and migrates to the Al centre.112 Similarly, reaction with Schwartz’s reagent Cp2Zr(Cl)H leads to complete cleavage of N2, but the P atom of the ligand decoordinates and forms a phosphinimide with one of the cleaved N atoms.115 C-H activation has been reported for the phenyl ring of the P atom in the reaction with butylsilane108  and loss of H2 after 19  hydroboration with 9-borabicyclononane (9-BBN) leads to cleavage of N2, with associated scission of the ligand’s Si-N bond and migration of the Si atom to the cleaved N atom.110, 111   Figure 13: SiNPN vs. o-phenylene NPN ligand These facile SiNPN ligand rearrangements hamper further development of this research area, mostly due to the labile N-Si bond and the flexible backbone. Replacing P-CH2-SiMe2-N with an o-phenylene bridge  (Figure 13) would eliminate this problem, making the ligand more rigid while maintaining the relative amine basicity.197 1.3. Project Objectives  Previous Fryzuk Group researchers observed some interesting chemical reactivity for the side-on dinitrogen zirconium complexes containing the o-phenylene-bridged mesNPN ligand (Figure 14).92, 97 For example, displacement of the labile THF solvent with more bulky phosphine ligands led to the formation of dinuclear dinitrogen complexes where one of the zirconium centres had an open coordination site, which may provide a ready reactive centre with substrates. These zirconium dinitrogen complexes reacted with substrates such as dihydrogen, a silane, an aldehyde, a ketone, an immine, ethylene, carbon monoxide and a phosphine oxide. In some cases new nitrogen-hydrogen, nitrogen-silicon and nitrogen-carbon bonds were created. In other cases zirconium oxides were obtained with inconclusive results regarding the fate of the activated nitrogen atoms.  20   Figure 14: Reactivity of mesNPN containing zirconium dinitrogen complexes97 The overall objective of this project is to investigate the effect of reduced steric bulk in the ortho position of the aromatic amine of this arene-bridged NPN donor set and to probe reactivity studies with the expected zirconium dinitrogen complexes. The mesityl group (mesNPN) would be replaced by 4-isopropyl phenyl (ipropNPN), p-tolyl (tolNPN) and phenyl (phNPN) groups, thereby reducing the steric bulk and providing a range of similar complexes with potentially different solubility, and perhaps different reactivity. A secondary aim of the project is to expand the Fryzuk group’s o-phenylene-bridged NPN donor set into other group 4 metals (titanium and hafnium) and group 5 metals (tantalum). One of the intrinsic problems with group 4 (Ti, Zr, Hf) dinitrogen complexes is that only 4 electrons can be supplied at a time, making it impossible to cleave the N2 bond. For nitride formation with the NPN donor set, group 5 and higher transition metals are needed, based purely on reducing power. 21   Figure 15: SiNPN vs. o-phenylene NPN ligand For future work, a project was initiated to increase the steric bulk at the ortho position of the aromatic amine with 2,6-diisopropyl phenyl (di-ipropNPN) or naphthyl (naphNPN), as this may encourage the formation of activated dinitrogen complexes with open sites at one or both of the zirconium centres. In chapter 2, the synthesis of the ipropNPN donor set is described, modelled on the previously reported mesNPN donor set, with a modification for the synthesis of the intermediate o-bromo-diarylamine using a Buchwald-Hartwig arylamination. A new method starting with commercially available diarylamines is introduced for the synthesis of the tolNPN and phNPN donor sets, using a directed ortho metalation (DOM) process, which is specific to arylamido groups that have no ortho substituents.  In chapter 3, the synthesis of zirconium, titanium and hafnium amido and dichloro complexes containing ipropNPN and tolNPN ligands is described. For zirconium, complexation was evaluated via salt metathesis with ZrCl4(THF)2 and protonolysis with Zr(NMe2)4 and ZrCl2(NMe2)2DME and for titanium with Ti(NMe2)4 or TiCl2(NMe2).  22  In chapter 4, the synthesis of tantalum trichloro complexes containing ipropNPN, tolNPN and PhNPN ligands is described via protonolysis with Ta(NMe2)5 followed by reaction with TMSCl. The trimethyl species tolNPNTaMe3 [4.7] was isolated by reaction of the potassium salt of the tolNPN ligand and TaMe3Cl2. The ionic species [tolNPNTaMe4][Li(THF)4] was isolated on reaction of the trichloride with MeLi, indicating tolNPNTaMe3 [4.7] reacts further with MeLi.  The synthesis of tantalum hydrides was attempted by reacting tantalum trimethyl species with H2 and tantalum trichlorides with KHBEt3. In situ introduction of N2 was performed for both of these above-mentioned hydride routes in attempts to isolate tantalum dinitrogen complexes, as well as reduction of tantalum trichlorides with KC8 under N2. In Chapter 5, reduction with KC8 under N2 was investigated for the zirconium, hafnium and titanium dichloride complexes prepared in chapter 3, with the aim of forming activated dinitrogen complexes. Reaction of titanium dichloride with KHBEt3 under N2 was also evaluated. In Chapter 6, screening tests (predominantly 31P{1H} NMR experiments) were conducted with the new zirconium and titanium dinitrogen complexes to evaluate potential for reactivity of the activated dinitrogen ligand. The former complex was reacted with dihydrogen, organo isocyanide, phenylsilane, ethylene, carbon monoxide, 4,4’-dimethylbenzophenone, carbon dioxide and (trimethylsilyl)-diazomethane and the latter with dihydrogen, ethylene and carbon monoxide.  In Chapter 7, the pertinent findings from this study dealing with the synthesis of the new sterically less hindered o-phenylene-bridged ipropNPN, tolNPN and PhNPN donor sets and complexes with zirconium, hafnium, titanium and tantalum are summarised, as well as the new zirconium and titanium dinitrogen complexes. Preliminary results for the synthesis of naphNPN and 2,6-iPr2NPN donor sets is presented.  23  For the overall project, it was found that reducing the steric bulk of the amido substituents led to more strongly activated zirconium side-on dinitrogen complexes, with less labile THF adducts. This inhibited displacement with other neutral donors, or formation of open coordination sites at the zirconium centres and reaction with molecular hydrogen did not occur. Future projects should focus on increasing the steric bulk of the amido substituents instead. The more rigid o-phenylene-bridge resulted in the isolation of stable end-on titanium dinitrogen complexes, which had not been possible with the flexible SiNPN donor set. These complexes displayed no reactivity with molecular hydrogen and other small molecules such as CO, and future ligand design should focus on being able to achieve side-on dinitrogen binding. Hafnium complexes with these ligands failed to reduce dinitrogen. For tantalum, the alkyl / hydride route for accessing dinitrogen complexes failed; neither was it possible to isolate the dinitrogen complexes formed via reduction or hydrogenation of precursor trichlorides.   24  Chapter 2: Ligand Synthesis  The Fryzuk suite of mixed ‘hard’ amido and ‘soft’ phosphine ligand donor sets (PNP, P2N2 and NPN in Figure 16) provide a flexible platform for variation in ligand design. For example, the amido donor in the PNP donor set has been replaced by a cyclopentadienyl198 donor (A) and an N-heterocyclic carbene donor with a saturated backbone199, 200 (C). In the NPN donor set, it was replaced by an aryloxy201 donor (G).   Figure 16: Donor variation for the PNP, P2N2 and NPN donor sets The neutral phosphine donor was replaced by amine202-204 (B and E), arsine205, 206 (D) and an N-heterocyclic carbene with an unsaturated backbone207 (F). Another degree of variance is the organic fragments bonded to the donor groups. Phosphine donors with methyl208, 209 (I) in Figure 17), i-propyl135, 209 (H), t-butyl209 (J), cyclohexyl116, 210 (L) and phenyl80, 211, 212 (K) groups have been employed. 25  The organic spacer between the donor groups can be varied to contain two (B, D and G) or three (A, C and F) or a mixture of two and three (E) atoms. The methylene and SiMe2 groups introduce flexibility into the backbone (A, B, D and E), whereas the o-phenylene and N-heterocyclic carbene groups impart planarity to provide a more rigid structure (C, F and G). The number of atoms in the spacer would affect the bite angles between the ligand donor atoms and the metal centre and the spacer flexibility could affect the range of reactivity possible for the metal complexes.   Figure 17: Variation in organic groups of phosphine donors For the NPN donor set (Figure 18), the degree of aromaticity in the backbone was further varied via the introduction of a thiophene213 (denoted SNPN) and a cyclopentenyl139, 140 (denoted CY5NPN) bridge. Despite extensive new reactivity observed with the SiNPN based group 4 and 5 dinitrogen complexes (see discussion in Chapter 1), further investigations were often hampered by ligand rearrangement, mostly due to the labile N-Si bond and the flexible backbone. Replacing -CH2-SiMe2- with an o-phenylene bridge (mesNPN)92, 97, 214 may mitigate this problem, making the ligand more rigid while maintaining the relative amine basicity. The pKa of diphenylamine (25)215 and bis(trimethylsilyl)amine (26)216 are similar, whereas secondary alkylamines (36) are more basic.216 26   Figure 18: NPN donor sets with different backbones In donor sets that contain terminal amido groups, i.e. the NPN donor set, the terminal organic fragment can also be varied. The SiNPN donor set with flexible spacers contain terminal phenyl groups, whereas the mesNPN, SNPN and CY5NPN donor sets contain sterically hindered mesityl,92, 213, 214 2,6-dimethylphenyl and 2,6-diisopropylphenyl139, 140 groups (Figure 18).  Figure 19: Summary of NPN donor sets with reduced steric bulk at the amido units For this project, the key aim in ligand design was to reduce the steric bulk at the ortho position of the terminal aryl amido group for the o-phenylene bridged NPN donor set, which would reduce steric crowding in the vicinity of the metal centre. This could be achieved by replacement of the N-mesityl group with N-4-isopropylphenyl (ipropNPN), N-4-methylphenyl 27  (tolNPN), and N-phenyl (phNPN) (Figure 19). The ipropNPN, tolNPN and phNPN ligands are expected to have similar chemical characteristics, but with decreasing relative solubilities.  The initial synthesis of the mesNPN donor set involved the formation of an intermediate ortho-brominated diarylamine (mesArBrArNH) in a two-step process via a copper-catalysed C-N coupling, followed by bromination with NBS (see route A in Figure 20).97, 214 A modification of the original method allows for the one-step synthesis of mesArBr-PhArNH in a 53% yield via a Buchwald-Hartwig arylamination (see route B in Figure 20), using a palladium catalyst (2.0 mol% Pd) with a bidentate phosphine ligand Pd/DPPF (1:3).97     Figure 20: Synthesis of mesNPN precursors 28  Preliminary work on the ipropNPN donor set demonstrated that ipropArBrArNH [2.1] (Figure 22) could be prepared in 62% yield using a palladium catalyst (1.7 mol% Pd) with a bidentate phosphine ligand Pd/rac-BINAP (1:3).97 These reactions were conducted at 80 °C to 85 °C over three to five days. While the effectiveness and versatility of mono-bromo-aryl substrates in the Buchwald-Hartwig reaction is well established, 217, 218 there is less precedent using dihalo-arenes. Other reasonable examples include the reaction of C6H4BrI with aniline to form N-(2-Br-C6H4)-(C6H5)NH219 and of o-C6H4Br2 with o-nitroaniline to form N-(2-Br-C6H4)-(2-NO2-C6H4)NH.220 However, o-C6H4Br2 has also been reported to react with aniline at both halogen centres to form o-(PhNH)2C6H4 221, 222 and it can react with mono- and diarylanilines to form carbazoles.223, 224  Mono-halo-arenes and halogenated anilines may also be used as substrates, for example 2-chloroaniline reacts with iodo- or bromoaryl substrates to give ortho-chlorinated diarylamines.224 However, under certain conditions carbazoles can be obtained from 2-chloroaniline and aryl bromides.225 In arylaminations involving mono-halo-arenes and halo-substituted anilines, it is desirable that the halogen on the arene be more reactive than on the aniline (I > Br > F)226, as demonstrated in the synthesis of the amido PNP pincer ligand precursors.227 Difficulties can be encountered when the same halogen is present on both the arene and the aniline, for example the reaction of o-bromo-aniline with MesBr is reported not to form the desired mesArBrArNH in the presence of a palladium catalyst.228 The type of ligand used during these palladium-catalysed reactions is of crucial importance. Bidentate diphosphines such as rac-BINAP220, 228  and DPEPhos224 favour ortho-halogenated diarylamines. However, the aforementioned o-(PhNH)2C6H4 and carbazole products were obtained when bulky mono-phosphine donors (PtBu3 and PCy3) were used.  The synthetic utility for making these new o-phenylene bridged diamidophosphine ligand precursors would be greatly enhanced if one could avoid the Buchwald-Hartwig arylamination 29  step altogether (with associated column chromatography purification). An alternative method, where the phosphorous atom is first attached to the arene backbone by reacting PhPCl2 with o-Li-C6H4F,229 followed by aromatic nucleophilic substitution of the appropriate primary lithium amide, was briefly evaluated. However, this was abandoned as there were indications that the in situ generated o-Li-C6H4F became involved in side reactions.230 It would be attractive to start with a commercially available secondary diaryl amine instead, and to this purpose, the directed ortho metalation (DOM), also known as heteroatom-facilitated o-lithiation, was investigated.231-239 Reactions typically associated with aromatic benzene rings involve electrophilic substitution such as the Friedel-Crafts reaction as this is promoted by the delocalised pi-electron system. DOM reactions, however, involve nucleophilic substitution, which is disfavoured due to the inherent difficulty in removing a proton from the self-same pi-electron system.   Figure 21: General DOM mechanism The DOM reaction involves the initial coordination of an organometallic compound, usually RLi, to the lone pair of the directing metalation group (DMG) (Figure 21).232-234 DMGs typically contain oxygen, sulphur or nitrogen, decreasing in their ability to act as ortho-directors. The proton ortho to the DMG is deprotonated to form the ortho-lithiated species. This species can then be further reacted with the desired electrophile. The reaction is almost exclusively ortho-directing, but meta-directed examples have been reported. 240, 241  The application of the DOM reaction to amines is well established.232, 235, 242, 243 The first equivalent of n-BuLi is expected to react quickly with the N-H proton of the diarylamine 30  (Ar2NH) to form an insoluble [Ar2NLi]n ladder aggregate.244 Addition of TMEDA serves two functions; firstly, it would solubilise the [Ar2NLi]n aggregate by disrupting the Li-N network to form a dimeric [Ar2NLiˑTMEDA]2 species,245-247 and secondly, it would increase the basicity of the amido DMG group to promote coordination of the second n-BuLi.233 After deprotonation and ortho-lithiation, a dimeric [Aro-LiArNLiˑ2TMEDA]2 structure was observed with two TMEDA molecules per Ar o-LiArNLi units.246 The utility of the DOM reaction has potential to extend beyond a more efficient NPN ligand synthesis. Experimental evidence indicates that addition of 3 equiv of n-BuLi to tol2NH with TMEDA gives the trilithio-diarylamide [(tol-LiAr)2NLiˑTMEDA]n in high yield. This may replace the less efficient bromination step during the synthesis of a new class of diphosphine amido (PNP) ligands 227, 248 that has proven to be highly efficient catalysts in carbon-carbon bond-forming reactions.249, 250  2.1. Buchwald-Hartwig Arylamination 2.1.1. Synthesis of  ipropArBrArNH [2.1] ipropArBrArNH [2.1] was obtained via the Buchwald-Hartwig arylamination in yields ranging from 26 - 37%, using a Pd/rac-BINAP (1:1.5) catalyst at 80 °C in toluene for 1 day (Figure 22). The lower catalyst loading (0.7 mol% Pd) and shorter reaction times were deemed to be sufficient, and is consistent with typical literature procedures.224 No significant increase in yield was observed for 3 days compared to 1 day. GC-MS analysis of the pre-column mixture did, however, indicate a higher 51% yield (Table 1, (i)), hence losses were incurred during inefficient column work-up procedures. 31   Figure 22: Synthesis of ipropArBrArNH [2.1] under Pd2dba3/rac-BINAP/toluene catalytic conditions. The GC-MS analysis of all reaction mixtures indicated a large amount of unreacted 4-iPrArNH/o-C6H4Br2 as well as a ca 4% ipropArArNH (Table 1). When a reaction with 1.8 mol% Pd, Pd/DPPF (1:3) was monitored over a 5 day period, the pre-column GC-MS yield decreased from 52.2% to 28.3, and the ipropArArNH side-product increased to 15.8%, with a larger amount of unidentified material. This suggests a catalyst decomposition pathway may exist where one or more products are more reactive than the reactants. ipropArArNH may be explained by protonation of a four-membered C2NPd-palladacycle251 formed by base-catalysed oxidative addition of  Pd(BINAP) or Pd(DPPF) to ipropArBrArNH [2.1].  Table 1 : Pre-column GC-MS data for Pd2(dba)3/rac-BINAP catalyst, 0.7 mol% Pd and Pd/rac-BINAP (1:1.5).   Relative concentrations (wt%) R.T. (min) [M]+ (m/z) M (i) (ii) (iii) 11.3 234 135 o-C6H4Br2 4-iPrArNH      51.4(a)     51.6(a)    40.1(a) 16.6 211 ipropArArNH 3.9 4.1 3.8 18.0 291 ipropArBrArNH   41.6   37.8     22.11 22.6 344 o-(ipropArNH)2C6H4 1.2 - - - - unidentified 1.8 6.5   33.3 (i) 4-iPrArNH2/o-C6H4Br2/NatOBu (1:0.9:1.3),  (ii) 4-iPrArNH2/o-C6H4Br2/NatOBu (1:0.5:1.3),  (iii) 4-iPrArNH2/o-C6H4Br2/KtOBu (1:2.1:1.2), (a) combined o-C6H4Br2 + 4-iPrArNH2   Certain reaction conditions for the synthesis of ipropArBrArNH [2.1] were varied, all at a reaction temperature of 80 °C: (i) Effect of ligand (rac-BINAP vs DPPF): When the ligand was changed from  rac-BINAP to Pd/DPPF (1:3) with a slightly higher catalyst loading of 1.8 mol% Pd, the pre-column GC-MS 32  data indicates a 52.2% yield (isolated yield 33%), which shows no observable improvement over the Pd2(dba)3/rac-BINAP catalyst system (Table 1, (i)).  BrBrNH2+NHPd2(dba)3rac-BINAPtoluenereflux2 NatOBu2NH(ipropArNH)2C6H4 Figure 23: Potential formation of o-(ipropArNH)2C6H4 (ii) Effect of increased 4-iPrArNH: Increasing the amount of 4-iPrArNH could favour formation of the bis-diarylamine side-product, o-(ipropArNH)2C6H4 (Figure 23).  There are no significant changes in the composition of the pre-column mixture (Table 1, (ii) compared to (i)); most notably only a trace amount of o-(ipropArNH)2C6H4 is observed to form. This agrees with literature evidence that a bulky mono-phosphine ligand such as PtBu3 is required to promote coordination of a second 4-iPrArNH molecule to form the bis-arylamine species.221 (iii) Effect of increased o-C6H4Br2: Another possible side-reaction may be the formation of ipropArN(o-C6H4Br)2 due to competition between the primary and secondary amine (Figure 24). However, no [M]+ of 971 m/z is ever observed for this reaction, even when o-C6H4Br2 is doubled (see Table 1, (iii)).  BrBr+ NHBrPd2(dba)3rac-BINAPtoluenerefluxKtOBu NBrBripropArN(C6H4Br)22 Figure 24: Potential formation of ipropArN(C6H4Br)2 33  (iv) Effect of bases: The lower yield and greater amount of unidentified material observed for data in Table 1, (iii) is not due to increased o-C6H4Br2 and could be attributed to changing the base from NatOBu to KtOBu. As reported previously, NatOBu is the base of choice. (v) Effect of increased catalyst loading: After reaction for 3 days, a second aliquot of Pd2(dba)3/rac-BINAP was added, maintaining Pd/rac-BINAP (1:1.5). However, after further reaction for 2 days, no additional benefit could be observed, with the final isolated yield being 37%. (vi) Effect of increased Pd/rac-BINAP ratio: When the Pd/rac-BINAP ratio was increased from 1:1.5 to 1:3, together with an increased catalyst loading, a lower isolated yield of 21% was obtained. Mechanistic studies of the Pd2dba3/rac-BINAP system have revealed that in solution a mixture of mono- and bis-BINAP complexes exists, viz. Pd(BINAP)(dba), Pd(BINAP)2(dba) and Pd(BINAP)2, with the bis-BINAP species predominating. 252 The active catalyst Pd(BINAP) is formed from Pd(BINAP)2 / Pd(BINAP)2(dba) in a pre-equilibrium step.  It may be that the equilibrium was shifted too far towards the bis-BINAP complexes. It was later found that increasing the oil bath temperature from 80 °C to 130-140 °C with a Pd/DPPF (1:3) catalyst and a higher loading (6 mol% Pd) led to a significantly increased pre-column GC-MS yield of 82% with a shorter reaction time of 7 hrs. This agrees with what was reported for the reaction of N-2,4,6-trimethylphenylamine with o-dibromobenzene.228 The main disadvantage of this method remains the column purification step, which impedes the ability to scale-up the reaction. Further increase in yield may be possible by changing to a higher boiling solvent such as Bu2O, but it would be more difficult to remove the solvent during subsequent work-up procedures. 34  2.2. Directed Ortho-Metallation (DOM) Reaction 2.2.1. Synthesis of [tolArLiArNLiˑTMEDA]2[2.2] and [phArLiArNLiˑ1.5TMEDA]2[2.3] Tol2NH and Ph2NH react with two equiv of n-BuLi and TMEDA in n-hexanes to give the white solids [tolArLiArNLiˑTMEDA]2 [2.2] and [phArLiArNLiˑ1.5TMEDA]2 [2.3] (Figure 26). High yields of 75% to 90% were obtained, irrespective if one or two equiv of TMEDA were used. The 7Li{1H} NMR spectrum of [tolArLiArNLiˑTMEDA]2 [2.2] displays a peak at δ 0.73 in C6D6 (Figure 25), but no signal could be observed for [phArLiArNLiˑ1.5TMEDA]2 [2.3] as it is only sparingly soluble in C6D6. The 1H NMR spectrum of the isolated solid [tolArLiArNLiˑTMEDA]2 [2.2] in C6D6 has a single peak at δ 1.76 for coordinated TMEDA (δ 2.04 for CH3 and δ 2.18 for CH2 for free TMEDA) (Figure 25) with relative integration indicating only one TMEDA per tolArLiArNLi, which is corroborated by a solid state molecular structure (see later discussion). The 7Li{1H} NMR spectrum of [2.2] exhibits a more shielded signal at δ -1.16 in THF-d8 compared to C6D6 (Figure 25), which suggests that the THF solvated species may have increased basicity. In THF-d8 (Figure 25), the TMEDA in [2.2] displays two peaks at δ 2.16 for CH3 and δ 2.101 for CH2 indicating free TMEDA. The residual THF signals at δ 1.73 and δ 3.58 suggest exchange between completely solvated (coordinated) THF and large excess THF solvent (free THF at δ 1.73 and δ 3.58). A dimeric [tolArLiArNLiˑ2THF]2 species may be formed on solvation of [tolArLiArNLiˑTMEDA]2 [2.2] in THF (Figure 26). As lithium ions in solvated lithium amide structures may have two THF ligands,245 solvated species with a molecular formulae [tolArLiArNLiˑ4THF]n may also be possible, wherein the dimer structure could possibly disaggregate into monomers.  35   Figure 25: 7Li{1H} (top) and 1H NMR (bottom) spectra of [tolArLiArNLiˑTMEDA]2 [2.2] in C6D6 and THF-d8 The 7Li{1H} NMR spectrum of solvated [phArLiArNLiˑ1.5TMEDA]2 [2.3] displays a singlet at δ -0.91 in THF-d8. Relative integration of free TMEDA in the 1H NMR spectrum of solvated [2.3] in THF-d8 indicates 1.5 TMEDA per phArLiArNLi unit and elemental analysis of this solid also confirms 1.5 TMEDA. A possible hybrid structure is proposed for [phArLiArNLiˑ1.5TMEDA]2 [2.3] between dimeric [phArLiArNLiˑTMEDA]2 and monomeric phArLiArNLiˑ2TMEDA resonance structures (Figure 26). Lithium ions in solvated lithium amide structures may have two donor ligands, i.e., bidentate TMEDA.246 As the cyclic ether tetrahydropyran performed better than TMEDA in the DOM of phenol,236 a reaction was conducted with 1,4-dioxane instead of TMEDA. However, no ortho-lithiated product was observed, which emphasizes the importance of being able to depolymerise the [Ar2NLi]n aggregate.244 36   Figure 26: Synthesis of [tolArLiArNLiˑTMEDA]2 [2.2] and [phArLiArNLiˑ1.5TMEDA]2 [2.3] The solid state molecular structure of [tolArLiArNLiˑTMEDA]2 [2.2] was obtained (Figure 27).  Each dimeric [tolArLiArNLiˑTMEDA]2 unit has a core containing four lithium, four carbon and two nitrogen atoms. Two of the lithiums (Li1 and ‘Li1) are three-coordinate and the other two (Li8 and ‘Li8) are five-coordinate. The four lithium atoms form a rhombus with an average LiˑˑˑLi distance of 2.277 Å (Table 2), which is shorter than the sum of the van der Waals radii between two lithium atoms (3.64 Å). The diagonal Li8ˑˑˑ‘Li8 distance of 2.1176(6) Å may also represent a non-bonding close contact. One of the nitrogen atoms of the TMEDA is bonded to a three-coordinate lithium N19-Li1 2.032(3) Å and the other to a five-coordinate lithium N19a-Li8 2.052(3) Å. The amido nitrogen atoms are bonded to two lithium atoms, one three- and one five-coordinate i.e. N8-Li1 (2.006(3) Å) and N8-‘Li8 (1.985(3) Å), with neither of these lithium atoms bonded to the same TMEDA molecule. These bond lengths compare well with those reported for other lithium amides.245, 246, 253 37     Figure 27: ORTEP representation of the solid state molecular structure of [tolArLiArNLiˑTMEDA]2 [2.2] The C2-‘Li1, C2-Li8 and C2-’Li8 bond lengths for the ortho-carbon are 2.169(4), 2.601(3) and 2.666(3) Å, which compares with average Li-C bond lengths of 2.67 Å reported for a ferrocenyllithium and other aryllithium compounds.246, 254-259 The C7-‘Li8 bond length for the ipso-carbon adjacent to the nitrogen atom is longer at 2.238(3) Å, but still shorter than the weak LiˑˑˑC intermolecular association reported for Ph(naphthyl)NLiˑTMEDA at 3.12 and 3.15 Å.246  Table 2 : Selected bond lengths (Å) and angles (°) for [tolArLiArNLiˑTMEDA]2 [2.2] [tolArLiArNLiˑTMEDA]2 Li1ˑˑˑ ‘Li8 2.282(4) N19-Li1-Li8     103.61(15) ‘Li1ˑˑˑ ‘Li8 2.271(4) N19-Li1-‘Li8     164.70(18) Li1-N8 2.006(3)  N19-Li1-N8     117.93(16) Li1-N19 2.032(3)  N19-Li1-C2     131.71(16) Li1-C2 2.169(4)    Li8ˑˑˑLi1 2.271(4)  N19a-Li8-Li1    97.04(14) Li8ˑˑˑ ‘Li1 2.282(4)  N19a-Li8-‘Li1       152.118(17) Li8-‘N8 1.985(3)  N19a-Li8-‘N8     117.89(16) Li8-N19a 2.052(3)  N19a-Li8-C2     121.74(15) Li8-C2 2.601(3) N19a-Li8-‘C2     126.69(15) Li8-‘C2 2.666(3)  N19a-Li8-‘C7     122.08(14) Li8ˑˑˑC7 2.238(3)  N19a-Li8-‘Li8 150.9(2) Li8ˑˑˑ‘Li8   2.1176(6)    Li8-N8-‘Li1  76.93(13) ‘Li8-Li8-N8 87.61(14) Li1-Li8-N8    124.82(16) ‘Li1-Li8-N8 51.92(11) Li1-Li8-‘Li1    109.03(14) Li1-Li8-‘Li8 54.69(12) Li8-Li1-‘Li8  70.97(14) ‘Li1-Li8-‘Li8 54.34(12)  38  Compounds [tolArLiArNLiˑTMEDA]2 [2.2] and [phArLiArNLiˑ1.5TMEDA]2 [2.3] were deuterolyzed with D2O in THF (Figure 28) and parent ions were observed at 199 m/z and 171 m/z in their respective electron impact mass spectra.    Figure 28: Synthesis of tolArDArND [2.4] and phArDArND [2.5] The 2H NMR spectrum of tolArDArND [2.4] in benzene displays two peaks in a 1:1 ratio at δ 4.91 (N-D) and δ 6.85 (Ar-D) (Figure 29) and of phArDArND [2.5] at δ 4.97 (N-D) and δ 6.85 (Ar-D).   Figure 29: 2H NMR spectrum of tolArDArND [2.4] in C6H6 39  2.3. Lithiated NPN Ligands 2.3.1. Synthesis of  [ipropNPNLi2ˑdiox]n [2.6] The synthesis of [ipropNPNLi2ˑdiox]n [2.6] was reported in a preliminary study, together with the solid state molecular structure.97 However, NMR spectroscopic data was only given for the THF adduct ipropNPNLi2ˑ2THF. [ipropNPNLi2ˑdiox]n [2.6] is obtained from ipropArBrArNH [2.1] in a two-step one-pot process (Figure 30). In the first step, [2.1] reacts with n-BuLi in Et2O to form an aryllithium lithioamido intermediate (ipropArLiArNLi). Although ipropArLiArNLi is not isolated, the solid state molecular structure of analogous [2,6diipropArLiArNLiˑ2THF]2 [7.3a] reported in chapter 7 suggests a dimer with two solvent molecules per  ipropArLiArNLi unit. It is imperative that exactly two equiv of n-BuLi are used in order to avoid undesired side reactions in the subsequent PPhCl2 quenching step.   Figure 30: Synthesis of [ipropNPNLi2ˑdiox]n [2.6] The second step involves quenching the aryllithium moiety with the electrophile PhPCl2. The PPhCl2 was added as a dilute ethereal solution (0.04 to 0.25 M) with a controlled addition rate of 1-2 cm3/min. The reaction temperature should ideally be maintained between -30 to -40 °C during the PPhCl2 addition; while lower temperatures than -40 °C are acceptable, higher temperatures are to be avoided (vide infra). The final product [ipropNPNLi2ˑdiox]n [2.6] is isolated in 78 - 93% yields as the 1,4-dioxane adduct, which is an improvement on the previously 40  reported yield of 66%.97  Deviation from these reaction conditions leads to a greater concentration of side-products, which form a tar-like residue that inhibits precipitation of [ipropNPNLi2ˑdiox]n [2.6]. Heating the crude material to 60 °C helps to dissolve these tarry side-products and allows the isolation of pure [2.6] as a fluffy yellow powder. Compound [2.6] is stable indefinitely at room temperature in the absence of air or moisture, both in solution and as a solid.  The solid-state molecular structure of [ipropNPNLi2ˑdiox]n [2.6] (Figure 31)97 shows that one 1,4-dioxane molecule bridges two ipropNPNLi2 units, forming a one-dimensional chain. The Li22 is coordinated to P1 in a distorted tetrahedral geometry and the other Li23 atom has a distorted trigonal geometry. The Li22-Li23 distance of 2.217(10) Å for the N2Li2 diamond core is shorter than the sum of the van der Waals radii between two lithium atoms (3.64 Å). The bond lengths and angles are similar to those reported for the [Ph,mesNPNLi2ˑdiox]n chain structure97 and monomeric mesNPNLi2ˑ2THF97, 214 (Table 3). Table 3 : Comparative bond lengths (Å) and angles (°) for the ipropNPNLi2 and mesNPNLi2 donor sets.97  [ipropNPNLi2ˑdiox]n [Ph,mesNPNLi2ˑdiox]n mesNPNLi2ˑ2THF P1-Li22   2.278(7)    2.284(8)   2.410(3)  Li22-O27   1.868(8)    1.892(9)   1.908(3)  L23-O24   1.867(8)    1.910(9)   1.932(3)  N8-Li22   2.050(9)    2.056(9)   2.078(3)  N8-Li23   1.974(9)    2.022(9)   2.046(4)  N8a-Li22   2.079(8)    2.065(9)   2.076(3)  N8a-Li23   1.978(9)      2.014(10)   2.051(3)  Li22ˑˑˑLi23     2.217(10)      2.274(12)   2.418(4)  N8-Li22-N8a     102.11(3)    103.7(4)      103.71(15)  N8-Li23-N8a   109.5(4)    106.7(3)      105.76(15)  Li22-N8-Li23 73.1(3)  74.8(2)    75.26(13)  Li22-N8a-Li23 73.8(3)  74.7(4)    75.21(13)  P1-Li22-N8 81.0(3)  81.1(2)    80.56(11)  P1-Li22-N8a 81.3(3)  81.8(2)    81.55(11)  P1-Li22-O27   125.0(4)    136.6(3)      138.07(16)  P1-Li22-Li23 80.9(3)  77.4(3)    77.01(11)  O24-Li23-N8   131.3(4)    122.9(5)      123.57(16)  O24-Li23-N8a   120.0(4)    126.3(5)      126.96(17)  O27-Li22-N8   123.4(5)    118.8(4)      115.48(16)  O27-Li22-N8a   126.7(5)    123.8(5)      126.13(16)   41   Figure 31: ORTEP representation of the solid-state molecular structure of [ipropNPNLi2ˑdiox]n [2.6]97 The Li22-O27 and Li23-O24 bond lengths are shorter for [ipropNPNLi2ˑdiox]n [2.6] than [Ph,mesNPNLi2ˑdiox]n and mesNPNLi2ˑ2THF. The less bulky 4-iso-ipropyl amido group thus enhances coordination of the oxygen donor, leading to a more strongly bound 1,4-dioxane.  The P1-Li22 bond length is longer for mesNPNLi2ˑ2THF compared to [Ph,mesNPNLi2ˑdiox]n and [ipropNPNLi2ˑdiox]n [2.6], and the THF adduct would be expected to have a weaker P-Li bond. In the previously reported synthesis of the THF adduct ipropNPNLi2ˑ2THF, values for bound THF were observed at δ 3.10 and δ 1.06 in the  1H NMR spectrum (δ 3.58 and δ 1.73 for free THF).97 ipropNPNLi2ˑ2THF is expected to have a monomeric structure similar to what was observed in the solid state molecular structure of  mesNPNLi2ˑ2THF,97, 214  where the P-Li coupling is maintained (Figure 33). The signal for 1,4-dioxane in the 1H NMR spectrum of [ipropNPNLi2ˑdiox]n [2.6] in C6D6 is at δ 3.09 (free 1,4-dioxane at δ 3.53) and the relative 42  integration of the peak indicates that only one molecule of 1,4-dioxane is present (Figure 32), which is consistent with the previously reported solid state molecular structure.97   Figure 32: 1H NMR spectra for the ipropNPNLi2 donor set: 1,4-dioxane, mixed 1,4-dioxane/THF and THF adducts  ipropNPNLi2.2THF ipropNPNLi2.4THF7Li{1H} = 0.93(s), 2.22 (d, 1JLiP = 43 Hz)31P{1H} = -31.62 (q, 1JLiP = 42 Hz)7Li{1H} = -1.70(s), -0.36 (d, 1JLiP = 42 Hz)31P{1H} = -34.8 (q, 1JLiP = 42 Hz)7Li{1H} = 3.49(s)31P{1H} = -33.21(s)PNNLiLiS'S'S'S'S' = THFPNNLiLiS'S'S' = THF[ipropNPNLi2.diox]n [2.6]PNNLiLiSSS = dioxn [ipropNPNLi2.2THF.diox]nPNNLiLiSSS'S'S' = THFS = diox7Li{1H} = 1.19(s), 2.47 (d, 1JLiP = 41 Hz)31P{1H} = -31.94(q, 1JLiP = 41 Hz)n Figure 33: Chain and monomeric forms of the ipropNPNLi2 donor set 43  When two equiv of THF are added to [ipropNPNLi2ˑdiox]n [2.6] in C6D6, both the 1,4-dioxane and THF remain bound to lithium (Figure 32), forming a mixed THF/1,4-dioxane adduct, [ipropNPNLi2ˑ2THFˑdiox]n. The 1H NMR spectrum in THF-d8 spiked with THF has a peak for 1,4-dioxane at δ 3.58 and THF peaks at δ 3.64 and δ 1.80 (Figure 32). This indicates that 1,4-dioxane is no longer bound and that the THF is weakly coordinated or exchange occurs between bound THF and a large excess free THF. A monomeric ipropNPNLi2ˑ4THF species may be formed in excess THF (Figure 33), similar in structure to that reported for dimeric N-lithiocarbazole.260 The 31P{1H} NMR spectrum of [ipropNPNLi2ˑdiox]n [2.6] in C6D6 displays a quartet at δ -31.62 (1JPLi = 42 Hz) and the 7Li{1H} NMR spectrum shows a singlet at δ 0.93 and a doublet at δ 2.62 (1JLiP = 43 Hz) (Figure 34 and Figure 35). The quartet in the 31P{1H} NMR spectrum and the doublet in the 7Li{1H} NMR spectrum are due to coupling of one of the Li atoms (Li22) to the P atom (P1). These values are similar to what was obtained for ipropNPNLi2ˑ2THF and other NPNLi2 derivatives.79, 80, 97, 114, 214  As the peaks in the 7Li{1H} NMR spectrum for [ipropNPNLi2ˑdiox]n [2.6] are shifted δ 2.7 downfield compared to ipropNPNLi2ˑ2THF97 in C6D6 (Figure 35), the oxygen of the monomeric species (THF adduct) may be more strongly bound to Li than in the chain structure (1,4-dioxane adduct). The peaks in the 31P{1H} NMR spectrum of ipropNPNLi2ˑ2THF97 have also shifted 3.18 ppm upfield (Figure 34), indicating that the P atom is more weakly bound, reminiscent of the longer Li-P bond length obtained for mesNPNLi2ˑ2THF. The Li22-Li23 distance of 2.217(10) Å for the N2Li2 diamond core is shorter than the sum of the Van Der Waals Radii for two lithium atoms (3.64 Å). The bond lengths and angles are similar to those reported for the [Ph,mesNPNLi2ˑdiox]n chain structure[22] and monomeric mesNPNLi2ˑ2THF[22, 23] (Table 3).  44    Figure 34: 31P{1H} NMR spectra for the ipropNPNLi2 donor set: 1,4-dioxane, mixed 1,4-dioxane/THF and THF adducts  Figure 35: 7Li{1H} NMR spectra for the ipropNPNLi2 donor set: 1,4-dioxane, mixed 1,4-dioxane/THF and THF adducts 45  For the mixed THF/1,4-dioxane adduct, [ipropNPNLi2ˑ2THFˑdiox]n, the 31P{1H} and  7Li{1H} NMR spectra are indistinguishable from [ipropNPNLi2ˑdiox]n [2.6] and the P-Li coupling has remained intact (Figure 34 and Figure 35). When [ipropNPNLi2ˑdiox]n [2.6] is dissolved in THF-d8, the 31P{1H} NMR spectrum displays a singlet at δ -33.21 and the 7Li{1H} NMR spectrum shows a singlet at δ 3.49 (Figure 34 and Figure 35), indicating that for ipropNPNLi2ˑ4THF the coupling between the P donor and Li is disrupted (Figure 33). The 7Li{1H} NMR spectral peak for ipropNPNLi2ˑ4THF in THF-d8 is shifted significantly downfield (Figure 35) which is in agreement with the more weakly bound THF and lack of P-Li coupling. 2.3.2. Synthesis of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and [phNPNLi2ˑ1.5TMEDA]2 [2.8] To generate the tolNPN and phNPN donor sets, PPhCl2 is added slowly at low temperature to [tolArLiArNLiˑTMEDA]2 [2.2] or [phArLiArNLiˑ1.5TMEDA]2 [2.3] in THF (Figure 36).   Figure 36: Synthesis of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] Upon work-up, [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and [phNPNLi2ˑ1.5TMEDA]2 [2.8] can be obtained in moderate yields as fluffy yellow powders, which are stable indefinitely at room temperature in the absence of air and moisture, both as a solid and in solution. The solid-state molecular structure of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] confirms a structure with two tolNPNLi2 units and 1.5 TMEDA per tolNPNLi2 unit (Figure 41). It was not possible to obtain acceptable 46  elemental analysis for [tolNPNLi2ˑ1.5TMEDA]2 [2.7] or [phNPNLi2ˑ1.5TMEDA]2 [2.8] and it may be that the degree of TMEDA coordination can vary, resulting in different structures. Loss of 0.5 equiv of TMEDA may lead to the formation of [tolNPNLi2ˑTMEDA]n chains or even more condensed structures.  Figure 37: 31P{1H} NMR spectra of the tolNPNLi2 donor set: TMEDA, mixed TMEDA/THF and THF adducts  Figure 38: 7Li{1H} NMR spectra of the tolNPNLi2 donor set: TMEDA, mixed TMEDA/THF and THF adducts 47  The 31P{1H} NMR spectra of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] (Figure 37) and [phNPNLi2ˑ1.5TMEDA]2 [2.8] in C6D6 have broad singlets at δ -31.66 and δ -31.96, respectively, which may be masking any Li-P coupling. The 7Li{1H} NMR spectrum of [2.7] shows a broad singlet at δ 0.29 which may also be masking any Li-P coupling (Figure 38). For [2.8], the 7Li{1H} NMR spectrum does exhibit a singlet at δ 0.09 and a doublet at δ 1.67 (1JLiP = 40 Hz), confirming Li-P coupling. The 1H NMR spectrum of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] in C6D6 (Figure 39) shows a very broad peak for TMEDA at δ 1.92 (free TMEDA at δ 2.18 for CH2 and δ 2.04 CH3) that overlaps the tolyl region; unfortunately, poor solubility makes NMR spectroscopic characterisation difficult. Similarly, the TMEDA signals in the 1H NMR spectrum of [2.8] in C6D6 appear as a broad peak at δ 1.63, and two sharp peaks at δ 1.57 and δ 1.47.  These broad peaks in the 7Li{1H} NMR, 31P{1H} NMR and 1H NMR spectra of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and [phNPNLi2ˑ1.5TMEDA]2 [2.8] are not due to an impurity, as when the samples are spiked with THF, typical spectra are obtained for [tolNPNLi2ˑ4THF]2 or [tolNPNLi2ˑ0.5TMEDAˑ2THF]2 (Figure 37, Figure 38 and Figure 39). Clearly, Li / TMEDA exchange or a more complex Li coordination model may exist for [2.7] and [2.8] in C6D6 than the solid state molecular structure of [2.7] in Figure 41 would suggest. The 31P{1H} NMR spectrum of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] in C6D6 + 4THF (Figure 37) shows a quartet at δ -32.8 (1JPLi = 41 Hz) and the 7Li{1H} NMR spectrum (Figure 38) displays a singlet at δ 0.49 and a doublet at δ 2.06 (1JLiP = 41 Hz). These values are indistinguishable from those obtained for [ipropNPNLi2ˑdiox]n [2.6]. 48   Figure 39: 1H NMR spectra of the tolNPNLi2 donor set: TMEDA, mixed TMEDA/THF and THF adducts    Figure 40: Structural forms of the tolNPNLi2 donor set 49  Similarly, [phNPNLi2ˑ1.5TMEDA]2 [2.8] in C6D6 + 8THF displays a quartet at δ -32.16 (1JPLi = 40 Hz) in the 31P{1H} NMR spectrum and a singlet at δ 0.35 and a doublet at δ 2.00 (1JLiP = 42 Hz) in the 7Li{1H} NMR spectrum, indicating that the P-Li coupling remains intact. The 1H NMR spectra of [2.7] and [2.8] of these samples suggest that both TMEDA and THF are bound to the Li centres, potentially forming [tolNPNLi2ˑ0.5TMEDAˑ2THF]2 and [phNPNLi2ˑ0.5TMEDAˑ2THF]2 (Figure 40), similar to the solid state molecular structure of [tolNPNLi2ˑ0.5TMEDAˑDME]2 (Figure 41).261  Figure 41: ORTEP representation of the solid state molecular structure of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and tolNPNLi2ˑ0.5TMEDAˑ1DME261 50  In THF-d8 the Li-P coupling of solvated [2.7] and [2.8] is disrupted, with singlets at δ -33.21 (Figure 37) and δ -32.61 in the 31P{1H} NMR spectrum, respectively, and at δ 0.52 (Figure 38) and δ -1.46 in the 7Li{1H} NMR spectrum. Their 1H NMR spectra in THF-d8 indicate that TMEDA is free and the THF is either weakly coordinated or exchanging between bound THF and the large excess of free THF. The P atom and TMEDA are most likely de-coordinated from lithium, which is solvated with THF, forming monomeric tolNPNLi2ˑ4THF or phNPNLi2ˑ4THF structures (Figure 40). Table 4 : Comparative bond lengths (Å) and angles (°) for the tolNPNLi2 donor set.   [tolNPNLi2ˑ1.5TMEDA]2  [tolNPNLi2ˑDMEˑ0.5TMEDA]2261 P1-Li21 2.272(7)  P1-Li21 2.296(13)  Li22-N23 2.078(7)  Li22-O23 2.016(15)  Li22ˑˑˑN23a 2.430(8)  Li22-O23a 2.059(16)  Li21-N26 2.065(7)  Li21-N26 2.52(14) N8-Li21 2.069(8)  N8-Li21 2.89(13) N8-Li22 2.169(7)  N8-Li22 2.081(16) N8a-Li21 2.046(7)  N8a-Li21 2.52(14) N8a-Li22 2.082(8)  N8a-Li22 2.82(15) Li21ˑˑˑLi22 2.723(9)  Li21ˑˑˑLi22 2.750(18) N8-Li21-N8a 102.1(3)  N8-Li21-N8a 99.4(6) N8-Li22-N8a 97.7(3)  N8-Li22-N8a 100.4(6) Li21-N8-Li22 76.5(3)  Li21-N8-Li22 78.2(5) Li21-N8a-Li22 78.9(3)  Li21-N8a-Li22 77.9(6) P1-Li21-N8 80.7(2)  P1-Li21-N8 79.8(4) P1-Li21-N8a 81.3(2)  P1-Li21-N8a 81.1(5) P1-Li21-N26 121.2(3)  P1-Li21-N26 116.0(6) P1-Li21-Li22 89.0(3)  P1-Li21-Li22 86.9(5) N23-Li22-N8 108.0(3)  O23-Li22-N8 111.2(7) N23-Li22-N8a 137.1(4)  O23-Li22-N8a 124.7(8) N23a-Li22-N8 137.5(3)  O23a-Li22-N8 126.2(7) N23a-Li22-N8a 103.1(3)  O23a-Li22-N8a 114.6(7) N26-Li21-N8 120.5(3)  N26-Li21-N8 122.6(7) N26-Li21-N8a 133.4(4)  N26-Li21-N8a 136.4(7)  X-ray analysis of single crystals of [tolNPNLi2ˑ1.5TMEDA]2 [2.7] reveals two tolNPNLi2 units with one bridging and one non-bridging TMEDA (Figure 41). The Li-N bonds lengths for N8, N8a, N23 and N26 range from 2.046(7) to 2.169(7) Å (Table 4) and are comparable to typical reported Li-N bond lengths of 1.9 to 2.10 Å.245, 246, 253 The other nitrogen atom N23a of the non-bridging TMEDA is located too far away from Li22 at 2.430(8) Å to be covalently bonded, but may be weakly interacting. It is unclear why one of the TMEDA molecules bridges and the 51  other does not. In an analogous system with DME instead of THF, a solid state molecular structure was obtained showing that the bridging TMEDA between the two tolNPNLi2 units remains, with the other lithium atom bonded to the bidentate DME (Figure 41).261 The structural parameters for [tolNPNLi2ˑ0.5TMEDAˑDME]2 (Table 4) show no marked differences compared to  [tolNPNLi2ˑ1.5TMEDA]2 [2.7].   Figure 42: 31P{1H NMR) NMR spectrum of tolNPNPPh [2.9] The lower yields obtained when PPhCl2 quenches the TMEDA adduct precursors [tolArLiArNLiˑTMEDA]2 [2.2] and [phArLiArNLiˑ1.5TMEDA]2 [2.3] compared to the 1,4-dioxane adduct may be correlated with the observation of a prominent side-product. For the reaction of [tolArLiArNLiˑTMEDA]2 [2.2] with PPhCl2, the crude reaction mixture for [2.7] displayed, amongst others, peaks at δ -5.7 and δ 93.8 in a 1:1 ratio for this side-product in the 31P{1H} NMR spectrum. In Et2O solvent, these peaks dominate and tolNPNPPh [2.9] was isolated (Figure 42). The P-N bonds of [2.9] are susceptible to hydrolysis and [2.9] reacts slowly with excess H2O to form tolNPNH2 [2.11] (Figure 43). The incorporation of the ortho C2 carbon in the Li2N2C4 core of [tolArLiArNLiˑTMEDA]2 [2.2] may inhibit C-P bond formation. Exploratory reactions with the trilithio-diarylamide [(tol-LiAr)2NLiˑTMEDA]n species indicated only one C-P bond formation in combination with P-N bond formation, even when quenching with three equiv of PiPr2Cl.  52   Figure 43: Synthesis of tolNPNPPh [2.9] The formation of tolNPNPPh [2.9] would be favoured by a combination of enhanced N-P bond formation relative to C-P bond formation and a stoichiometric excess of PPhCl2. Due to the possibility of more than one TMEDA molecule per dilithio-diarylamide unit, if the TMEDA content of the [tolArLiArNLiˑTMEDA]2 [2.2] or [phArLiArNLiˑ1.5TMEDA]2 [2.3] reactants are not accurately ascertained prior to PPhCl2 addition, conditions for excess PPhCl2 may be attained. As [tolArLiArNLiˑTMEDA]2 [2.2] is less soluble in Et2O than THF, the less solvated Et2O adduct may further disfavour C-P bond formation. 2.4. Protonated NPN Ligands Protonation of [ipropNPNLi2ˑdiox]n [2.6], [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and [phNPNLi2ˑ1.5TMEDA]2 [2.8] with excess NMe3ˑHCl gives ipropNPNH2 [2.10], tolNPNH2 [2.11] and phNPNH2 [2.12] in yields up to 90% (Figure 44). The reaction can be performed in either THF or toluene. Although an excess NMe3ˑHCl is used, two equiv are sufficient. H2O can also be used as the source of protons.  The 31P{1H} NMR spectra of [2.10], [2.11] and [2.12] display signals at δ -31.35, δ -29.39 and δ -30.80. These values are not significantly different from those obtained for the lithiated version of the ligands. The 1H NMR spectra exhibit a characteristic doublet at δ 6.38 53  (4JHP = 6 Hz), δ 6.21 (4JPH = 5 Hz) and δ 6.30 (4JPH = 5 Hz) for the N-H proton of [2.10], [2.11] and [2.12], respectively.   Figure 44: Synthesis of ipropNPNH2 [2.10], tolNPNH2 [2.11] and phNPNH2 [2.12] ipropNPNH2 [2.10] is a translucent oil and it is more convenient to weigh its precursor, the solid dilithio derivative [2.6]. Thus [2.10] is often not isolated, but prepared in situ and reacted further with the desired precursor metal dimethyamido complex (see Chapter 3 and Chapter 4). tolNPNH2 [2.11] and phNPNH2 [2.12] are white solids that are isolated prior to protonolysis with the metal dimethyamido complexes. Single crystals and solid state molecular structures of tolNPNH2 [2.11] and phNPNH2 [2.12]261 were obtained (Figure 45) and the P-C and N-C bond lengths and C-P-C and C-N-C bond angles (Table 5) are not significantly different from those reported for PPh3,262 HNPh2263 and  Ph,mesNPNH297.   Figure 45: ORTEP representations of the solid state molecular structures of tolNPNH2 [2.11] and phNPNH2 [2.12] 54  Table 5 : Comparative bond lengths (Å) and angles (°) for tolNPNH2 [2.11] and phNPNH2[2.12]   tolNPNH2  phNPNH2261 P1-C2   1.805(10)  P1-C2 1.843(2)  P1-C2a 1.815(9)  P1-C2a 1.833(2)  P1-C17   1.820(12)  P1-C17 1.835(2)  N8-C7   1.399(12)  N8-C7 1.409(3) N8a-C7a   1.423(12)  N8a-C7a 1.403(3) N8-C9   1.369(14)  N8-C9 1.410(3) N8a-C9a    1.370(12)  N8a-C9a 1.411(3) C2-P1-C17  104.6(5)  C2-P1-C17     102.39(11) C2a-P1-C17 98.2(5)  C2a-P1-C17     103.42(10) C2-P1-C2a   101.6(4)  C2-P1-C2a     101.73(10) C7-N8-C9   128.0(9)  C7-N8-C9 125.5(2) C7a-N8a-C9a   125.7(9)  C7a-N8a-C9a 127.0(2)  2.5. Conclusions A modification for the synthesis of the new ipropNPN donor set was presented, whereby an o-bromo-diarylamine intermediate was prepared using a Buchwald-Hartwig arylamination of o-dibromo-benzene. It was found that increasing the external temperature of the oil-bath from 80 °C to 130-140 °C significantly improved the yield, however, a short-coming of this method is the chromatographic work-up necessitated  by the remaining unreacted o-dibromobenzene. The tolNPN and phNPN donor sets were prepared using a directed ortho metalation (DOM) method specific to arylamido groups that have no ortho substituents, starting with commercially available diarylamines. While column chromatography is eliminated, the Li2N2C4 cores of the ortho-lithiated diaryl lithium amide intermediates [tolArLiArNLiˑTMEDA]2 [2.2] and [phArLiArNLiˑ1.5TMEDA]2 [2.3] possess aryl-lithium associations, inhibiting C-P and favouring N-P bond formation during the PPhCl2 quenching. The moderate yields obtained for [tolNPNLi2ˑ1.5TMEDA]2 [2.7] and [phNPNLi2ˑ1.5TMEDA]2 [2.8] are offset by the fact that the synthesis of [tolArLiArNLiˑTMEDA]2 [2.2] and [phArLiArNLiˑTMEDA]2 [2.3] are nearly quantitative and can be prepared in large scale.   55  Chapter 3: Group 4 Diamido-Phosphine Complexes The use of group 4 metal halides as precursors for the formation of dinitrogen complexes is well established.154, 178, 179, 264 This chapter deals with the synthesis and characterisation of zirconium, titanium and hafnium chloro complexes with the new o-phenylene-bridged ligand systems, ipropNPN and tolNPN, the syntheses of which were described in the previous chapter.  3.1. Zirconium Diamido-Phosphine Complexes Two different routes were investigated for the synthesis of the zirconium dichloro complexes. Given that the ligand precursors are isolated as dilithio salts (see Chapter 2), the salt metathesis route is most attractive as it only requires reaction of this lithiated form with zirconium tetrachloride ZrCl4(THF)2 (Figure 46). The protonolysis route is multi-step and requires reaction of the protonated form of the ligand with tetrakis(-dimethylamido)zirconium(IV) Zr(NMe2)4. Starting with zirconium dichloride bis(-dimethylamido) complex ZrCl2(NMe2)2(DME) instead can eliminate the subsequent TMSCl chlorination step from the latter route (Figure 46).  Figure 46: Salt metathesis and protonolysis routes for zirconium complexes 3.1.1. Salt Metathesis Route  Addition of one equiv of [ipropNPNLi2·diox]n [2.6] to a toluene solution of ZrCl4(THF)2 at room temperature forms [ipropNPN]2Zr [3.1], which displays a singlet in the 31P{1H} NMR 56  spectrum at δ 19.58; none of the expected dichloride complex was observed. Reaction with two equiv of [2.6] gives the same result. Likewise [tolNPN]2Zr [3.2] is obtained from reaction of Zr(NMe2)4 with two equiv of tolNPNH2 [2.11], as evidenced by a peak at δ 16.03 in the 31P{1H} NMR spectrum. [ipropNPN]2Zr [3.1] is also formed by reaction of two equiv of [ipropNPNLi2·diox]n [2.6] with one equiv of [ipropNPNZrCl2]2 [3.9].   Figure 47: Formation of [ipropNPN]2Zr [3.1] and [tolNPN]2Zr [3.2] If the reaction of one equiv of each of [ipropNPNLi2·diox]n [2.6] and ZrCl4(THF)2 is allowed to continue, a mixture of 77% [ipropNPN]2Zr [3.1] and 23% ipropNPNZrCl2(THF) [3.5] can be observed after 24 days. In order to confirm that ipropNPNZrCl2(THF) [3.5] forms via conproportionation of [ipropNPN]2Zr [3.1] with ZrCl4(THF)2, one equiv of both solids were dissolved in toluene-d8 at room temperature and the reaction monitored via 31P{1H} NMR spectroscopy. After 6 days, 14% ipropNPNZrCl2(THF) [3.5] was observed, which increased to 28% after 18 days. 57  Single peaks in the 31P{1H} NMR spectra of [ipropNPN]2Zr [3.1] and [tolNPN]2Zr [3.2] may indicate that the two NPN ligands are symmetrically bonded to the central Zr atom in solution, with either trans- or cis-disposed phosphorus donors. The 1H and 13C{1H} NMR spectra however, show considerable complexity, suggestive of chiral structures and therefore cis-disposed phosphines (Figure 48).  Figure 48: 31P{1H} (top) and 1H NMR (bottom) spectra of [ipropNPN]2Zr [3.1] in C6D6 In the solid state both tolNPN ligands of [tolNPN]2Zr [3.2] are coordinated in a facial manner and the geometry about the Zr centre is best described as trigonal prismatic, with the P1, N8 and N8a atoms forming one basal plane and the P1a, N8b and N8c atoms the other (Figure 49). Overall this molecule is chiral (C2 point group) and the two P atoms (P1 and P1a) are in a cis configuration. The Zr1-P1 bond length 2.6977(11) Å agrees well with the average Zr-P bond lengths reported for mesNPN containing zirconium complexes97, 125, 214 and is significantly longer than the Zr1-P1a bond length of 2.4455(10) Å (Table 2).  58   Figure 49: ORTEP representation of the solid state molecular structure of [tolNPN]2Zr [3.2] For both of the NPN Ligands, one of the Zr-amido bond lengths are significantly shorter at 1.869(3) Å for Zr1-N8 and 2.038(3) Å for Zr1-N8b and the other are longer at 2.464(4) Å for Zr1-N8a and 2.407(4) Å for Zr1-N8c (Table 2). While they all fall within the range of Zr-N bond lengths reported for zirconium complexes with the mesNPN ligand,97, 125, 214 there is no explanation for why there is such a wide range from Zr-imido (Zr1-N8) to Zr-amine (Zr-N8a and Zr-N8c) bond character. The average P-Zr-N ligand bite angle of 73.9° is typical, but the average N-Zr-N ligand bite angle of 89.7° is smaller than those observed for monodentate mesNPN zirconium complexes mesNPNZrCl2 (113.96(9)°) and mesNPNZrCl2(Py) (97.87(6)°). This may be due to reduced steric bulk at the ortho position of the arylamido groups of the tolNPN ligand compared to mesNPN. Table 6 : Selected bond lengths (Å) and angles (°) for [tolNPN]2Zr [3.2] [tolNPN]2Zr [3.2] Zr1-P1 2.6977(11) P1-Zr1-P1a 76.29(3) Zr1-P1a 2.4455(10) P1-Zr1-N8 72.44(11) Zr1-N8 1.869(3)  P1-Zr1-N8a 70.57(8) Zr1-N8a 2.464(4)  P1a-Zr1-N8b 82.98(10) Zr1-N8b 2.038(3)  P1a-Zr1-N8c 69.53(8) Zr1-N8c 2.407(4)  N8-Zr1-N8b 127.84(15) P1-Zr1-N8b 159.22(10)  N8-Zr1-N8a 92.03(15) P1a-Zr1-N8 145.00(11)  N8b-Zr1-N8c 87.33(13) N8a-Zr1-N8c 154.04(12)    59  With the bulkier o-phenylene bridged mesNPN precursor ligand,97 salt metathesis generated a mixture of products (Figure 50); interestingly, metathesis using the classic SiNPN ligand yields the dichloride SiNPNZrCl2(THF) in toluene at 60 °C (Figure 50).137, 138 While there is no evidence for bis-(ligand) complex formation in this latter reaction, the higher reaction temperature may facilitate a facile disproportionation of a potential [SiNPN]2Zr intermediate and ZrCl4(THF).  Zr NPSiSiN0.5 ZrCl4(THF)2ZrCl4(THF)2ZrCl4(THF)2toluenetoluene, 60 oCtoluene, r.t.Mixture ofproducts0.5 ZrCl4(THF)2toluene, r.t.ONSiNSiPLiLiN NPOOLiLiN NPOOLiLiSiNPNLi2.2THF[ipropNPNLi2.diox]n [2.6][mesNPNLi2.diox]nSiNPNZrCl2(THF)ipropNPNZrCl2(THF) [3.5][ipropNPN]2Zr [3.1]nnZr NPNClClONPNZrNPNClOCl Figure 50: Reaction of SiNPNLi2ˑ2THF, mesNPNLi2·diox and [ipropNPNLi2·diox]n [2.6] with ZrCl4(THF)2 Increasing the reaction temperature for the salt metathesis with [ipropNPNLi2ˑdiox]n [2.6] may speed up the conversion to ipropNPNZrCl2(THF) [3.5], however, this route was abandoned for the alternative protonolysis method. 3.1.2. Protonolysis Route  Protonolysis involves reaction of the protonated form of the NPN ligand with zirconium 60   dimethylamido precursors, liberating dimethylamine. Two different precursors, namely Zr(NMe2)4 and ZrCl2(NMe2)2(DME), were investigated (Figure 51).   Figure 51: Protonolysis with ZrCl2(NMe2)2(DME) or Zr(NMe2)4  Both routes led to the isolation of the desired zirconium mono(ligand) dichloride complexes, however, as will be discussed below, the route starting with Zr(NMe2)4 is preferred. Synthesis of ipropNPNZrCl2(HNMe2) [3.3] and tolNPNZrCl2(HNMe2) [3.4] The reaction of mesNPNH2 with Zr(NMe2)4 is well established,97, 214 but no reaction was observed when mesNPNH2 was reacted with ZrCl2(NMe2)(DME) at room temperature in toluene. A modest conversion to 14% mesNPNZrCl2 was observed in THF. Reaction of ipropNPNH2 [2.10] and tolNPNH2 [2.11] with ZrCl2(NMe2)2(DME) in toluene at room temperature gave the orange solids ipropNPNZrCl2(HNMe2) [3.3] and tolNPNZrCl2(HNMe2) [3.4], respectively. The less bulky ipropNPN and tolNPN ligands appear to favours HNMe2 adduct formation.   The 31P{1H} NMR spectra display singlets at δ 9.06 and δ 8.20 for [3.3] and [3.4] (Figure 52), respectively. In the 1H NMR spectra [3.3] and [3.4] display broad peaks at δ 2.57 and δ 2.39 (N-H) and doublets at δ 2.08 and δ 2.01 (N-CH3), respectively, which indicates coordinated HNMe2 (Figure 52). The 13C{1H} NMR spectra display peaks at δ 41.8 and δ 42.2 (N-CH3). The 61  elemental analysis suggests that some HNMe2 may be liberated under prolonged reduced pressure from ipropNPNZrCl2(HNMe2) [3.3].  Figure 52: 31P{1H} (top) and 1H NMR (bottom) spectra of tolNPNZrCl2(HNMe2) [3.4] in C6D6 The mass spectrum for tolNPNZrCl2(HNMe2) [3.4] shows the expected fragment ion [M - HNMe2]+ at 660 m/z. There is a small peak at 704 m/z that could correspond to the parent M+ ion. This is unusual as neutral donors such as THF and HNMe2 can be liberated at the early stages of analysis and as a result, fragment ions are observed as the most abundant ions in the mass spectrum. However, it is possible that proton transfer occurs from HNMe2 to the tolNPN ligand during analysis to generate a tautomeric form of the complex (Figure 53).  Figure 53: Proton transfer for tolNPNZrCl2(HNMe2) [3.4]  62  In addition to the fragment ion [M - HNMe2]+ for ipropNPNZrCl2(HNMe2) [3.3], the mass spectrum also shows trace amounts of an ion at 724 m/z, which may be due to the presence of a zirconium trichloride species ipropNPN(H)ZrCl3 (Figure 54) perhaps formed by the reaction of ipropNPNH2 [2.10] with ZrCl3(NMe2), which may be an impurity formed during the synthesis of ZrCl2(NMe2)2(DME). These minor species were not observable by 31P{1H} NMR spectroscopy.   Figure 54: Possible origin of the minor impurity trichloride ipropNPN(H)ZrCl3  The NPN ligand is usually coordinated in a facial conformation, which could result in two isomers for ipropNPNZrCl2(HNMe2) [3.3] and tolNPNZrCl2(HNMe2) [3.4] (Figure 55). The chlorides are arranged cis relative to each in both possibilities, with both chlorides cis and HNMe2 trans to the P atom in one case and in the other case one of the chlorides and HNMe2 is cis and the other chloride trans relative to the P atom. The latter case implies a chiral structure, which would require two different R and R’ environments for substituents of the NPN ligand. The 31P{1H} NMR spectra of [3.3] and [3.4] display a singlet resonance, which indicates that in solution either only one of the two aforementioned isomers is formed or both isomers are exchanging fast on the NMR timescale. Because one set of R and R’ environments is observed in the 1H NMR spectra, either (i) the exclusive occurrence of the trans isomer is indicated in solution; (ii) an equilibrium (which may be slow) shifted significantly towards the left such that the concentration of the cis isomer is below NMR detection limits or (iii) fast exchange between appreciable concentrations of both isomers. 63   Figure 55: Isomers of NPNZrCl2(HNMe2)  The solid state molecular structure of tolNPNZrCl2(HNMe2) [3.4] was determined from single crystals grown by slow evaporation from a benzene solution at room temperature.261 The geometry around the Zr atom is octahedral and the tolNPN ligand is bound facially, with one of the chlorides (Cl1) trans to the P1 atom and the other chloride (Cl2) cis (Figure 56). This cis isomeric form corresponds to that observed for the solid state molecular structure of mesNPNZrCl2(Py).97 The P1-Zr1-Cl1 angle is more linear at 170.63(3)° than N8-Zr1-Cl2 and N8a-Zr1-N21 (Table 7).   Figure 56: ORTEP representation of the solid state molecular structure of tolNPNZrCl2(HNMe2) [3.4] The zirconium amido (Zr1-N8, Zr1-N8a), phosphine (Zr1-P1) and chloride (Zr1-Cl1, Zr1-Cl2) bond lengths (Table 7) agree well with previously reported mesNPNZrCl2(Py)97 and other NPN-containing zirconium dichloride complexes.97, 139, 140, 213, 214 The Zr1-N21 bond length of 2.438(3) Å for the neutral donor HNMe2 is longer than for the zirconium amido bond lengths. As with the bis-(ligand) [tolNPN]2Zr [3.2], the N8-Zr1-N8a ligand bite angle for tolNPNZrCl2(HNMe2) [3.4] with the less bulky tolyl arylamido group is smaller at 91.71(9)° than 64  the corresponding mesNPNZrCl2(Py) complex at 97.97(6)°. No intramolecular hydrogen bonding was observed between the HNMe2 and Cl groups, with N-HˑˑˑCl distances (av 2.94 Å) being longer than sum of the van der Waals radii for nitrogen and hydrogen (2.75 Å).  Table 7 : Selected bond lengths (Å) and angles (°) for tolNPNZrCl2(HNMe2) [3.4]261 and mesNPNZrCl2(Py)97  tolNPNZrCl2(HNMe2) [3.4]261 mesNPNZrCl2(Py)97  Zr1-P1    2.7631(8)   2.7131(5) Zr1-N8  2.139(2)     2.1695(16) Zr1-N8a  2.098(2)     2.1082(15) Zr1-N21  2.438(3)     2.3889(16) Zr1-Cl1    2.4484(9)   2.4419(5) Zr1-Cl2    2.4938(9)   2.5257(5) P1-Zr1-Cl1   170.63(3)      176.657(18) N8-Zr1-Cl2   150.54(7)  151.42(4) N8a-Zr1-N21   160.99(9)  155.53(6) P1-Zr1-N8 67.54(6) 67.54(6) P1-Zr1-N8a 73.59(7) 73.45(4) P1-Zr1-N21 88.01(7) 88.36(4) P1-Zr1-Cl2 85.76(3)    82.143(17) Cl1-Zr1-N8  107.56(7)  104.55(4) Cl1-Zr1-N8a  115.11(7)  113.11(5) Cl1-Zr1-N21 83.57(7) 88.83(4) Cl1-Zr1-Cl2 96.96(3)     99.060(19) N8-Zr1-N8a 91.71(9) 97.87(6) N8-Zr1-N21  85.47(10) 86.23(6) Cl2-Zr1-N8a 92.44(7) 87.27(4) Cl2-Zr1-N21 81.22(7) 78.30(4)  The fact that the cis isomer is isolated in the solid state, but not apparently observed in solution may be explained by either (i) fast exchange between both isomers or (ii) an equilibrium shifted significantly towards the trans isomer such that the concentration of the cis isomer is below NMR detection limits.  Synthesis of ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] The orange-yellow solids ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] were obtained by addition of THF to the dimethylamine adducts [3.3] and [3.4] or to dichloro dimers [3.9] and [3.10] (see later discussion). Displacement of dimethylamine is sluggish at room temperature in neat THF. Monitoring via 31P{1H} NMR spectroscopy, 28% conversion to [3.5] occurred after 5 min, increasing to 62% overnight, with complete conversion after ca 2 weeks; and placement of the system under reduced pressure did not improve matters. For [3.6], 44% unreacted tolNPNZrCl2(HNMe2) [3.4] remained after 21 hrs. In hot THF (60 °C), conversions of 65  [3.3] and [3.4] to their respective THF adducts [3.5] and [3.6] occurred within one to six hours, in agreement with the previously reported formation of [3.6], where the THF solution was also heated.261 31P{1H} NMR spectra of ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] display singlets at δ 6.48 (Figure 58) and 6.07, respectively. The 1H NMR spectra respectively of [3.5] and [3.6] have signals at δ 3.87 and 1.03 (Figure 58), and at δ 3.83 and 1.10, attributable to coordinated THF. In the corresponding 13C{1H} NMR spectra, there are signals at δ 74.4 and 25.1 (Figure 58), and at δ 72.9 and 25.2 that are assigned to the THF carbons of [3.5] and [3.6], respectively.  Figure 57: Isomers of NPNZrCl2(THF)  As with ipropNPNZrCl2(HNMe2) [3.3] and tolNPNZrCl2(HNMe2) [3.4], two isomers are possible for ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] (Figure 57), but only one set of R and R’ signals were observed in their respective 1H NMR spectra. Single crystals of both ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6]261 verify that in the solid state the isomer with the THF cis to the P atom was obtained (Figure 59). Again, a similar argument to the one used for tolNPNZrCl2(HNMe2) [3.4] can be invoked to explain the incongruence between the cis solid state structure and the inferred trans solution structure. Upon cooling a toluene-d8 solution of ipropNPNZrCl2(THF) to -60 °C, no changes where observed in the 31P{1H} NMR and 1H NMR spectra. 66   Figure 58: 31P{1H} (top), partial 13C{1H} (middle) and 1H NMR (bottom) spectra of ipropNPNZrCl2(THF) [3.5] in C6D6 Both ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] display distorted octahedral geometries, with the P1-Zr1-Cl1 and N8-Zr1-O1 angles for [3.5] being less linear than for [3.6] (Table 8). The zirconium chloride bond lengths (Zr1-Cl1 and Zr1-Cl2) for [3.5] and [3.6] (Table 8) are all similar to those obtained for mesNPNZrCl2,97 mesNPNZrCl2(Py)97 and tolNPNZrCl2(HNMe2) [3.4] (Table 7). So too are the Zr1-P1, Zr1-N8 and Zr1-N8a bond lengths and angles (Table 8). The Zr1-O1 bond lengths of [3.5] and [3.6] (Table 8) are shorter compared to those obtained for [SiNPNZr(THF)]2(N2)137, 138 at 2.305(1) Å and [mesNPNZr(THF)]2(N2) at 2.371(2) Å.92, 97 67    Figure 59: ORTEP representations of the solid state molecular structures of ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] Table 8 : Selected bond lengths (Å) and angles (°) for ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6]261   ipropNPNZrCl2(THF) [3.5]  tolNPNZrCl2(THF) [3.6]261   Zr1-P1   2.6945(6)    2.7316(10) Zr1-N8a     2.1540(17) 2.128(3) Zr1-N8     2.0853(17) 2.088(3) Zr1-O1     2.2862(14) 2.254(2) Zr1-Cl1   2.4469(6)     2.4098(10) Zr1-Cl2   2.4653(6)     2.4596(10) P1-Zr1-Cl1   168.92(2)  174.02(3) N8a-Zr1-Cl2   149.27(5)  149.42(7) N8-Zr1-O1   155.55(6)    161.70(10) P1-Zr1-N8a 70.54(5) 67.70(7) P1-Zr1-N8 72.79(5) 73.94(7) P1-Zr1-O1 82.80(4) 87.82(7) P1-Zr1-Cl2 82.00(2) 86.80(3) Cl1-Zr1-N8a  113.12(5)  106.32(7) Cl1-Zr1-N8  116.61(5)  106.80(8) Cl1-Zr1-O1 87.53(4) 91.19(7) Cl1-Zr1-Cl2 91.53(2) 98.91(4) N8a-Zr1-N8 92.93(7)   91.32(10) N8a-Zr1-O1 79.96(6) 80.18(9) Cl2-Zr1-N8 91.82(5) 97.75(8) Cl2-Zr1-O1 83.25(4) 82.33(7)  Protonolysis of tolNPNH2 [2.11] with ZrCl2(NMe2)2(DME) in THF instead of toluene may avoid HNMe2 formation and lead directly to the THF adduct; however, reaction at 60 °C gave a mixture that contained amongst others tolNPNZrCl2(THF) [3.6], tolNPNZr(NMe2)2 [3.8] and unreacted tolNPNH2 [2.11]. Possible explanations for [3.8] is a conproportionation between tolNPNZrCl2(THF) [3.6] and ZrCl2(NMe2)2(DME), or ZrCl2(NMe2)(DME) may be in equilibrium with ZrClx(NMe2)4-x species i.e. x = 0 and 4 (Figure 60). 68  While reaction of the protonated NPN ligands with ZrCl2(NMe2)2(DME) may utilise less steps compared to Zr(NMe2)4, traces of ZrCl3(NMe2) in ZrCl2(NMe2)2(DME) led to the occasional observation of the zirconium trichloride species ipropNPN(H)ZrCl3 (see earlier discussion). A different method for the synthesis of ZrCl2(NMe2)2(DME) from Zr(NMe2)4, TMSCl and DME265 instead of reaction of ZrCl4 with Zr(NMe2)4266 may be considered in future.  Figure 60: Protonolysis of tolNPNH2 [2.11] with ZrCl2(NMe2)2(DME) in THF at 60 °C Synthesis of ipropNPNZr(NMe2)2 [3.7] and tolNPNZr(NMe2)2 [3.8] Reaction of one equiv of ipropNPNH2 [2.10] or tolNPNH2 [2.11] with Zr(NMe2)4 in toluene at room temperature gave the lemon yellow solids ipropNPNZr(NMe2)2 [3.7] or tolNPNZr(NMe2)2 [3.8] in high yield. Their 31P{1H} NMR spectra display singlets at δ -10.60 and δ -10.16, similar to mesNPNZr(NMe2)297, 214 at δ -11.5. There are two different methyl environments for the NMe2 groups, with peaks at δ 2.48 / 2.80 and δ 2.56 / 2.87 in their 1H NMR spectra (Figure 61) and at δ 40.7 / 41.5  and δ 40.8 / 41.6 in their 31C{1H} NMR spectra, for [3.7] and [3.8] respectively. This agrees with what has been observed for mesNPNZr(NMe2)297, 214 and other NPNZr(NMe2)2213, 267 complexes. 69   Figure 61: 31P{1H} (top) and 1H NMR (bottom) spectra of tolNPNZr(NMe2)2 [3.8] Single crystals of ipropNPNZr(NMe2)2 [3.7]97 [3.7] and tolNPNZr(NMe2)2 [3.8]261 were obtained and their solid state molecular structures  display a distorted trigonal bipyramidal geometry around the zirconium centre (Figure 62), as observed in other NPNZr(NMe2)2 complexes. 139, 140   Figure 62: ORTEP representation of the solid state molecular structure of ipropNPNZr(NMe2)2 [3.7] and tolNPNZr(NMe2)2 [3.8] 70  The ipropNPN and tolNPN ligands are bonded facially with one NMe2 (N24a) and the P atom forming the apexes and the other NMe2 (N24) and the two N atoms of the ligand (N24 and N24a) in the trigonal plane. The Zr-NMe2 bond lengths for ipropNPNZr(NMe2)2 [3.7] and tolNPNZr(NMe2)2 [3.8] (Table 9) are typical of zirconium amido complexes139, 140, 213, 268, 269 and the two different NMe2 environments observed in solution are clearly reflected in the solid state. The P1-Zr1-N8 and P1-Zr1-N8a bite angles for the five-coordinate [3.7] and [3.8] complexes are similar to the octahedral ipropNPN and tolNPN zirconium complexes discussed in this chapter (Table 2, Table 7 and Table 8), but the N8-Zr1-N8a bite angles of 125.17(8)° and 123.16(17)° are much larger. Table 9 : Selected bond lengths (Å) and angles (°) for ipropNPNZr(NMe2)2 [3.7] and tolNPNZr(NMe2)2 [3.8]261   ipropNPNZr(NMe2)2 [3.7]97  tolNPNZr(NMe2)2 [3.8]261   Zr1-P1   2.7355(7)   2.7509(6) Zr1-N8 2.158(2)     2.1570(18) Zr1-N8a 2.157(2)     2.1376(18)  Zr1-N24 2.027(2)     2.0153(18)  Zr1-N24a 2.053(2)     2.0418(19) P1-Zr1-N8 70.71(6) 70.39(5) P1-Zr1-N8a 72.06(6) 72.10(5) P1-Zr1-N24  100.36(6) 99.50(6) P1-Zr1-N24a  155.07(6)  154.11(6) N24-Zr1-N8  109.76(9)  111.11(7) N24-Zr1-N8a  115.41(8)  115.97(8) N24a-Zr1-N8 98.60(9) 98.75(7) N24a-Zr1-N8a 98.62(8) 96.89(8) N8-Zr1-N8a 125.17(8) 123.16(7) N24-Zr1-N24a 104.49(9) 106.37(8)  Synthesis of [ipropNPNZrCl2]2 [3.9] and [tolNPNZrCl2]2 [3.10] Monitoring the addition of TMSCl to ipropNPNZr(NMe2)2 [3.7] with 31P{1H} NMR spectroscopy, an intermediate with a sharp peak at δ 0.09 is observed after 2 equiv of TMSCl (Figure 63); ca 7 equiv of TMSCl are required for complete conversion to [ipropNPNZrCl2]2 [3.9], and also observed for [tolNPNZrCl2]2 [3.10]. More often, the dimeric complexes with bridging dichlorides [3.9] and [3.10] were not isolated; after addition of TMSCl the toluene solvent was replaced with THF at room temperature, giving ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6]. 71   Figure 63: 31P{1H} NMR spectra of ipropNPNZr(NMe2)2 [3.7] (bottom) and after 2, 5 and 7 equiv of TMSCl (middle three) and ipropNPNZrCl2(THF) [3.5] after excess THF (top) in C6D6 at 25 °C  These bridging dichloride complexes [3.9] and [3.10] are not very soluble in benzene, improving marginally in toluene. Their 31P{1H} NMR spectra at room temperature in C6D6 exhibit very broad peaks at δ 11.23 and δ 9.95, respectively, with spurious sharp peaks observed at δ 4.54, δ 33.90 and δ 7.54 (Figure 64). The corresponding 1H NMR spectra indicates that no impurities, other than solvent, are present in the samples (Figure 64) and elemental analysis results also reflect sample purity. It was not possible with either EI-MS or MALDI-TOF mass spectrometry to obtain the parent ions [M]+ for [ipropNPNZrCl2]2 [3.9] and [tolNPNZrCl2]2 [3.10]. For [3.9], the largest fragment ion was observed at 688 m/z indicating survival of the monomer [M - ipropNPNZrCl2]+. For [3.10], a larger fragment ion corresponding to [M - ZrCl4]+ was observed at 1087 m/z, as well as the monomer fragment ion [M - tolNPNZrCl2]+ at 660 m/z. mesNPNZrCl2,97, 214 CY5NPNZrCl2139, 140 and thiophene-based SNPNZrCl2213 are monomers in the solid state. However, a NPNZrCl2 complex with a -CH2CH2- backbone267 has been 72  postulated to be dimeric, along with confirmed chloro-bridged solid state structures reported for a Zr(III) dimeric derivative [NPN(P)ZrCl2]2,149 and a zirconium trichloride phosphine dimer.270  Figure 64: 31P{1H} (top) and 1H NMR (bottom) spectra of [ipropNPNZrCl2]2 [3.9] and [tolNPNZrCl2]2 [3.10] in C6D6 at 25 °C Single crystals of [ipropNPNZrCl2]2 [3.9] reveal a chloro-bridged dimer (Figure 65). The coordination environment around the Zr atom can best be described as distorted octahedral, with the P1-Zr1-Cl2, N8-Zr1-Cl2’ and N8a-Zr1-Cl1 angles deviating significantly from 180° (Table 10). The terminal chlorides of the opposing Zr centres are situated trans to each other and the ipropNPN ligands are facially bound such that the phosphorus atom (P1) on one zirconium atom (Zr1) is orientated trans to the other P1’ atom attached to the Zr1’ atom.  73   Figure 65: ORTEP representation of the solid state molecular structure of [ipropNPNZrCl2]2 [3.9] The terminal chlorides (Cl1, Cl1’) have shorter bonds to zirconium than the bridging chlorides (Cl2, Cl2’) and both types have longer Zr-Cl bond lengths than reported for CY5NPNZrCl2,139, 140 mesNPNZrCl2 (Table 10),97, 214 tolNPNZrCl2(HNMe2) [3.4], ipropNPNZrCl2(THF) [3.5] and tolNPNZrCl2(THF) [3.6] (Table 7 and Table 8). The Zr-Cl terminal bonds in [ZrCl3(PBu3)2]2 are also shorter than the bridged Zr-Cl bonds,270 though the inverse was observed for [NPN(P)ZrCl2]2.149 Table 10 : Selected bond lengths (Å) and angles (°) for [ipropNPNZrCl2]2 [3.9] and mesNPNZrCl297, 214  [ipropNPNZrCl2]2 [3.9]  mesNPNZrCl297, 214  Zr1-P1    2.6661(9)     2.7228(8) Zr1-N8a      2.1400(16)   2.071(2)  Zr1-N8      2.1219(17)   2.060(2) Zr1-Cl1    2.5037(8)      2.4098(8)  Zr1-Cl2     2.6278(10)     2.4279(8)  Zr1-Cl2’     2.6506(10)  P1-Zr1-Cl2      152.840(17)    178.63(3) N8a-Zr1-Cl1  145.23(4)  N8-Zr1-Cl2’  152.14(4)  P1-Zr1-N8a 70.36(5)  70.38(7) P1-Zr1-N8 71.57(4)  72.73(7) P1-Zr1-Cl1 75.71(4)  85.02(3) P1-Zr1-Cl2’    81.348(19)  Cl2-Zr1-N8a  124.41(5)   109.43(7) Cl2-Zr1-N8  124.72(4)   106.25(7) Cl2-Zr1-Cl1 84.34(3)  96.24(3) Cl2-Zr1-Cl2’    78.259(19)  N8a-Zr1-N8 92.83(6)   113.97(9) Cl1-Zr1-N8 83.42(4)   111.40(7) Cl2’-Zr1-N8a 83.94(4)   117.49(7) Cl1-Zr1-Cl2’ 83.69(2)  Zr1-Cl2-Zr1’      101.741(19)   74  In order to further explore the solution behaviour of these dichloride complexes, variable temperature NMR experiments were conducted. When [tolNPNZrCl2]2 [3.10] is heated to 93 °C there is a single sharp peak at δ 6.86 in the 31P{1H} NMR spectrum (Figure 66). When the temperature is lowered to -71 °C, four peaks are observed at δ 14.05, δ 7.54, δ 5.14 and further downfield at δ 33.85.   Figure 66: 31P{1H} NMR spectra of [tolPNZrCl2]2 [3.10] in toluene-d8 at 93 and -71 °C For [ipropNPNZrCl2]2 [3.9], on heating to 93 °C a broader peak is observed at δ 7.80 with a small peak at δ 4.54 (Figure 67). As the sample cools, the peak at δ 7.80 continues to broaden even more at room temperature, gradually shifting downfield and a third peak is observed at δ 7.29. With further cooling down to -60 °C, the broad peak sharpens and shifts to δ 12.90, and together with δ 7.29 and δ 4.54, these signals mirrors those observed for [3.10] at low temperature (Figure 66). Unlike [tolNPNZrCl2]2 [3.10] (Figure 66), more than one signal is observed at ca δ 33 for [ipropNPNZrCl2]2 [3.9] at low temperature, which starts growing in below 7 °C (Figure 67). When the experiment was repeated with a different sample [ipropNPNZrCl2]2 [3.9], the peak at δ 7.29 was not observed at low temperatures (Figure 68). We were unable to rationalise this temperature dependent behaviour other than to suggest that different diasteriomeric forms with bridging chlorides may be forming at low temperatures, as discussed below. 75  [ipropNPNZrCl2]2 [3.9] and [tolNPNZrCl2]2 [3.10] compounds both displayed complex solution behaviour compared to monomeric mesNPNZrCl2. An authentic sample of mesNPNZrCl2 was cooled down to -50 °C in toluene-d8, with no changes observed for the single sharp peak at δ -1.86 the 31P{1H} NMR spectrum.   Figure 67: 31P{1H} NMR spectra of [ipropNPNZrCl2]2 [3.9] in toluene-d8 from 93 to -60 °C (δ 4.54 at 25 °C used as reference for spectra at other temperatures)  Figure 68: 31P{1H} NMR spectra of different samples [ipropNPNZrCl2]2 [3.9] in toluene-d8 at -60 °C  Changes are also observed for the 1H NMR spectra, as illustrated for [ipropNPNZrCl2]2 [3.9] at -60 °C, 25 °C and 93 °C (Figure 69). On cooling to -60 °C, new peaks are observed in the phenyl region at δ 8.45, 8.19 (downfield) and δ 5.98, 5.88, 5.65 and 5.28 (upfield). At least seven 76  different methine signals are observed, indicating multiple i-propyl environments, with one signal significantly downfield at δ 3.69 (Figure 69).   Figure 69: 1H NMR spectrum of [ipropNPNZrCl2]2 [3.9] in toluene-d8 at  -60 °C, 25 °C and 93 °C To rationalize the observation of multiple species in solution at low temperatures, different dinuclear chloro-bridged species can be envisioned (Figure 70). Isomer A depicts the solid state molecular structure of [ipropNPNZrCl2]2 [3.9] (Figure 65) and Isomer C correlates with the solid state molecular structure obtained for the hafnium congener [ipropNPNHfCl2]2 [3.20] (see later discussion and Figure 89). The possibility cannot be discounted that the N atoms of the ipropNPN / tolNPN ligands may also form bridging amido structures,271 although these are not explicitly shown below. Furthermore, monomeric ipropNPNZrCl2 / tolNPNZrCl2 species may be in equilibrium with the proposed dimers. It may be that the dimers dissociate to generate monomers that recombine to give the isomeric forms proposed in Figure 70.  77   Figure 70: Chloro-bridged isomers for [NPNZrCl2]2, [3.9] and [3.10] Diffusion ordered NMR spectroscopy (DOSY)272, 273 is a technique that can be used to determine the diffusion coefficients of dissolved species and hence particle size. More specifically, according to the Stokes-Einstein equation, the spherical radius of a particle (r) in a liquid is inversely proportional to the diffusion coefficient (D).   = 6	 Thus the D values for dimers are expected to be half that obtained for a monomer. A DOSY 31P{1H} NMR experiment was conducted for a sample of [ipropNPNZrCl2]2 [3.9] at -40 °C in order to investigate the particle size of the isomeric species observed. It was not possible to attain the rigorous experimental conditions required to determine the absolute diffusion coefficient values, and analysis was further hampered by low solubility and broad peaks. However, a qualitative comparison between the peaks could still be made, as all the particles can be evaluated during a single experiment. The D values obtained for the six peaks at δ 34.4, δ 33.3, δ 31.0, δ 12.0, δ 7.7 and δ 4.8 were determined to be 5.99, 7.12, 7.72, 6.55, 7.16 and 8.11 x 10-9 m2s-1, respectively (see Appendix A).  78  Assuming that the smallest D value represents a dimer, doubling this value gave 5.99 x 2 = 11.98 x 10-9 m2s-1, which is significantly larger than the largest D value obtained in this experiment. This suggests that none of the species present can be correlated to a monomer. The D values obtained are consistent with the presence of species of similar size to the dimer in solution, however, uncertainty remains as the equation is based on the assumption of spherical particles. Repeating this experiment spiking with mesNPNZrCl2 may in future provide a better reference D value for a monomer. However, if the monomer is present in very small concentrations but undergoes fast exchange, then the DOSY experiment will not be affected.  These DOSY NMR experiments with the zirconium dichlorides failed to provide conclusive evidence for the presences of a monomeric species. However, if an experiment mixing a solution of [ipropNPNZrCl2]2 [3.9] with [tolNPNZrCl2]2 [3.10] was shown to produce a mixed dimer such as [ipropNPN(Cl)Zr(µ-Cl)2Zr(Cl)NPNtol], more credence could be placed on a mechanism whereby a dimer dissociates into monomers before recombining into a different dimer. 3.2. Titanium Diamido-Phosphine Complexes The protonolysis method using both TiCl2(NMe2) and Ti(NMe2)4 was investigated (Figure 71) and the most notable difference from the zirconium system is that dimeric chloride-bridged structures were not observed.  79   Figure 71: Protonolysis with TiCl2(NMe2)2 or Ti(NMe2)4 Synthesis of ipropNPNTiCl2(HNMe2) [3.11] and tolNPNTiCl2(HNMe2) [3.12] The purplish-black solids ipropNPNTiCl2(HNMe2) [3.11] and tolNPNTiCl2(HNMe2) [3.12] were obtained from ipropNPNH2 [2.10] or tolNPNH2 [2.11] and TiCl2(NMe2)2 in toluene at room temperature. As with zirconium, two isomers are possible for [3.11] and [3.12] (Figure 72). The observance of one set of R and R’ signals in their respective 1H NMR spectra suggests a similar scenario for the cis and trans isomers as outlined for the zirconium congeners. Unfortunately single crystals were not obtained in order to determine the preferred isomer in the solid state.  Figure 72: Possible isomers for NPNTiCl2(HNMe2) [3.11] and [3.12] 80  Their 31P{1H} NMR spectra display singlets at δ 27.83 and δ 26.35 (see Figure 73 for [3.12]) and their 1H NMR (see Figure 74 for [3.12]) and 13C{1H} NMR spectra display characteristic signals for coordinated HNMe2.   Figure 73: 31P{1H} NMR spectrum of tolNPNTiCl2(HNMe2) [3.12]   Figure 74: 1H NMR spectrum of tolNPNTiCl2(HNMe2) [3.12] Relative integration of the broad N-H peaks in the 1H NMR spectra for [3.11] and [3.12] indicates less than 1 equiv of coordinated HNMe2, some of which may have been liberated while drying the sample under reduced pressure. 81  Synthesis of ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14] Unlike the zirconium system (see earlier discussion), it was possible to cleanly obtain tolNPNTiCl2(THF) [3.14] by reacting tolNPNH2 [2.11] with TiCl2(NMe2)2 in THF at 60 °C in 97% isolated yield (Figure 71). While not directly tested, the facile conversion of HNMe2 adducts of titanium dichloride to THF adducts is implicit from the aforementioned reaction. Reaction of SiNPNLi2ˑ2THF with TiCl4(THF)2 in toluene at room temperature yields SiNPNTiCl2 with no evidence for THF adduct formation.137 However, ipropNPNTiCl2 [3.17] and tolNPNTiCl2 [3.18] react with THF at room temperature to form THF adducts that can be isolated as purple-black solids of formula ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14], respectively. In solution, [3.13] and [3.14] display a sharp singlet in their 31P{1H} NMR spectra at δ 30.34 and δ 24.04 (Figure 76), respectively, and the 1H NMR spectra display THF peaks at δ 1.37 and δ 3.72 for [3.13] (Figure 77) and δ 1.35 and δ 3.65 for [3.14] (Figure 75).   Figure 75: 1H NMR spectrum of tolNPNTiCl2(THF) [3.14] in C6D6 Given close agreement between the 31P{1H} NMR δ values for the ipropNPN and tolNPN containing zirconium adducts of THF and HNMe2, as well as the titanium HNMe2 adducts, it is unusual that ipropNPNTiCl2(THF) [3.13] has a value shifted significantly downfield compared to tolNPNTiCl2(THF) [3.14]. 82   Figure 76: 31P{1H} NMR spectra of ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14] in C6D6 For ipropNPNTiCl2(THF) [3.13], partial 0.25 equiv of THF coordination is suggested by the relative integration of the 1H NMR spectrum (Figure 77). Loss of THF may have occurred while drying the sample in vacuo. Two methine CH signals were also observed for this sample of [3.13], indicating two distinct iso-propyl environments of the ligand (Figure 77). As both signals remain after the sample was spiked with excess THF (Figure 77), the possibility of an equilibrium co-existence of [3.13] with a solvent-free tolNPNTiCl2 [3.18] species can be eliminated.   Figure 77: 1H NMR of  ipropNPNTiCl2(THF) [3.13] before and after THF spike in C6D6 As with the zirconium congeners, ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14] can exist in two different isomeric forms (Figure 78).  83   Figure 78: Possible isomeric structures for ipropNPNTiCl2(THF) [3.13] and tolNPNTiCl2(THF) [3.14] For [3.14], the observation of a single set of p-tolyl methyl signals in solution allows the previously developed cis / trans arguments to apply. However, for [3.13], the observation of two different 4-isopropyl signals suggests that the chiral isomer with the THF group cis to the P atom may be dominant in solution (though the presence of an amine impurity cannot be discounted). Unfortunately single crystals for [3.13] and [3.14] were not obtained to verify structures formed in the solid state.   Figure 79: 31P{1H} (top) and 1H NMR (bottom) spectra of ipropNPNTiCl2(HNMe2)/(THF) [3.11]/[3.13] 84  Under certain conditions a mixture of coordinated THF and HNMe2 [3.11] / [3.13] was obtained (Figure 79). The 31P{1H} NMR spectrum has a single broad peak at δ 25.83 which is upfield relative to both pure [3.11] and [3.13]. The 1H NMR spectrum indicates partial coordination of both THF and HNMe2 (Figure 79), with peaks at δ 3.75 and 1.29 (THF) and δ 2.89 and 2.15 (N-H and N-CH3). The occurrence of only one 4-isopropyl suggests that the more symmetric isomers with THF and HNMe2 trans to the P atom were formed (Figure 80).   Figure 80: Equilibrium structures for ipropNPNTiCl2(THF) [3.13] and ipropNPNTiCl2(HNMe2) [3.11] In an attempt to grow single crystals of [3.11] / [3.13] from THF / n-hexanes, an example of crystal picking led to the identification of TiCl3(NMe2)(THF)2 being present in the sample. A mass spectrum of the sample also confirmed the presence of an ion corresponding to [TiCl3(NMe2)]+. It is possible that this was generated during the reaction of TiCl4 with Ti(NMe2)4. Despite the fact that elemental analysis for TiCl2(NMe2)2 indicated sample purity and only one peak was observed at δ 2.97 in the 1H NMR spectrum, the mass spectrum did indicate a peak at 198 m/z (10%) for [TiCl3(NMe2)]+ in addition to the parent ion at 206 m/z (65%). For [3.12], elemental analysis suggests that some TiCl3(NMe2) may also be present. So, while protonolysis of TiCl2(NMe2)2 by the NPNH2 ligands in warm THF represents an efficient one-step process for the formation of the titanium dichloride species, the method for the synthesis of TiCl2(NMe2)2 requires care to avoid the presence of titanium trichloride impurities. 85  Synthesis of ipropNPNTi(NMe2)2 [3.15] and  tolNPNTi(NMe2)2 [3.16] Reaction of ipropNPNH2 [2.10] or tolNPNH2 [2.11] with Ti(NMe2)4 in toluene at room temperature gave the brick red solids ipropNPNTi(NMe2)2 [3.15] and tolNPNTi(NMe2)2 [3.16], with singlets observed in their 31P{1H} NMR spectra at δ -2.05 (Figure 81) and δ -2.35, respectively.   Figure 81: 31P{1H} NMR spectrum of ipropNPNTi(NMe2)2 [3.15]  Their 1H and 13C{1H} NMR spectra display characteristic signals indicative of two different coordinated NMe2 environments (Figure 82).   Figure 82: Partial 13C{1H} (top) and 1H NMR (bottom) spectra of ipropNPNTi(NMe2)2 [3.15] The solid state molecular structure for ipropNPNTi(NMe2)2 [3.15] was determined from single crystals grown by slow evaporation from a benzene solution (Figure 83) and confirms two 86  different environments for the NMe2 groups, one cis (N24) and one trans (N24a) to the P atom of the NPN ligand. This corresponds to what was observed in the zirconium complexes [3.7] and [3.8] (Figure 62).   Figure 83: ORTEP representation of the solid state molecular structure of ipropNPNTi(NMe2)2 [3.15] Similarly, the geometry about the Ti centre can be described as distorted trigonal bipyramidal, with an axial P1-Ti1-N24a angle of 159.80(9)°. The ligand is arranged facially with the two N8 and N8a ligand atoms in the trigonal plane, together with one of the NMe2 (N24) groups. The ligand Ti1-P1, Ti1-N8 and Ti1-N8a bond lengths (Table 11) are comparable to those observed for SiNPNTiCl2,137 [(P2N2)Ti]2(N2),137 [(PNP)TiCl]2(N2)182 and other (NN)TiCl(NR2)274 and (NNN)TiLn275 complexes. The NMe2 bond lengths Ti1-N24 and Ti1-N24a are 1.880(3) Å and 1.921(3) Å and compare well with other titanium dimethylamido complexes.269, 275-277  Table 11 : Selected bond lengths (Å) and angles (°) for ipropNPNTi(NMe2)2 [3.15] ipropNPNTi(NMe2)2 [3.15]  Ti1-P1     2.5939(11) N24-C22 1.454(4) Ti1-N8 2.033(3) N24-C23 1.452(4) Ti1-N8a 2.028(3) N24a-C22a 1.443(4) Ti1-N24 1.880(3) N24a-C24a 1.460(4) Ti1-N24a 1.921(3) Ti1-N24-C22 124.0(3) P1-Ti1-N8 74.83(8) Ti1-N24-C23 124.7(2) P1-Ti1-N8a 73.99(8) Ti1-N24a-C22a 127.9(2) P1-Ti1-N24 98.42(9) Ti1-N24a-C23a 121.1(2) P1-Ti1-N24a  159.80(9) C22-N24-C23 111.2(3) N24-Ti1-N8    115.93(13) C22a-N24a-C23a 110.1(3) N24-Ti1-N8a    108.20(12)   N24a-Ti1-N8  97.49(12)   N24a-Ti1-N8a  98.01(11)   N8-Ti1-N8a   128.66(12)   N24-Ti1-N24a   101.72(12)   87  The Ti-N-C bond angles for one amido groups (N24) are the same, but differ by 6.8° for the other amido group (N24a) (Table 11). This structural feature most likely persists in solution, as evidenced by the 13C{1H} NMR spectra, wherein a singlet is observed for the carbons (C22 and C23) on the N24 amido group and two singlets for carbons (C22a and C23a) on the N24a amido group (Figure 82). Synthesis of ipropNPNTiCl2 [3.17] and tolNPNTiCl2 [3.18] After addition of 2 equiv of TMSCl to ipropNPNTi(NMe2)2 [3.15], a 68% conversion to ipropNPNTiCl2 [3.17] was observed via 31P{1H} NMR spectroscopy, with an unidentified intermediate visible at δ 17.35 (Figure 84). The conversion is almost complete after 4 equiv of TMSCl, with only 7% unreacted [3.15]. Reaction of ipropNPNTi(NMe2)2 [3.15] and tolNPNTi(NMe2)2 [3.16] with ca 6 equiv of TMSCl in toluene gave ipropNPNTiCl2 [3.17] and tolNPNTiCl2 [3.18] in 80% and 99% yields, respectively, both as purple solids. Their 31P{1H} NMR spectra display peaks at δ 24.85 and δ 24.41, respectively.   Figure 84: 31P{1H} NMR spectra of ipropNPNTi(NMe2)2 [3.15] (bottom) and + 2, 4 and 6 equiv of TMSCl in C6D6 When a solution of [3.18] in toluene-d8 is cooled down to -70 °C, no change is observed in the 31P{1H} NMR spectrum. The solid state molecular structure of tolNPNTiCl2 [3.18], 88  obtained by x-ray crystallographic analysis of single crystals grown via vapour diffusion of n-hexanes into a toluene solution in the freezer, confirms a monomeric structure (Figure 85).   Figure 85: ORTEP representation of the solid state molecular structure of tolNPNTiCl2 [3.18] The geometry about the Ti centre mirrors that observed for ipropNPNTi(NMe2)2 [3.15] as distorted trigonal bipyramidal, with an axial P1-Ti1-Cl1 angle of 162.05(2)° (Table 12) that is slightly larger than [3.15] at 159.80(9)°, but significant more bent than mesNPNZrCl2 complex at 178.63(3)° 97, 214 or SiNPNTiCl2 at 176.08(5)°137. Compared to the classical SiNPN ligand containing SiNPNTiCl2 complex (Table 12), tolNPNTiCl2 [3.18] has a shorter Ti1-P1 bond length, smaller P1-Ti1-N8 / P1-Ti1-N8a bite angles and a wider N8-Ti1-N8a bite angle.  Table 12 : Selected bond lengths (Å) and angles (°) for tolNPNTiCl2 [3.18] and SiNPNTiCl2137  tolNPNTiCl2 [3.18]  SiNPNTiCl2137  Ti1-P1   2.5809(6)      2.6084(12) Ti1-N8a     1.9519(15)  1.936(4)  Ti1-N8     1.9586(15)  1.914(3) Ti1-Cl1   2.2968(5)       2.2937(12)  Ti1-Cl2   2.2545(6)      2.2874(12)  P1-Ti1-Cl1   162.05(2)    176.08(5) P1-Ti1-Cl2 93.70(2)  87.80(4) P1-Ti1-N8a 73.87(5)    75.85(11) P1-Ti1-N8 74.96(5)    80.64(10) Cl1-Ti1-N8a 96.94(5)     100.45(12) Cl1-Ti1-N8 99.72(5)     100.11(11) Cl1-Ti1-Cl2 104.18(2)  95.21(5) N8a-Ti1-N8 126.34(6)     116.45(14) Cl2-Ti1-N8 110.61(5)     117.58(11) Cl2-Ti1-N8a 113.95(5)     119.42(11)  89  The Ti-Cl1 and Ti1-Cl2 bond lengths of 2.2545(6) Å and 2.2968(5) Å and the ligand-metal bond lengths of Ti1-P1, Ti1-N8 and Ti1-N8a (Table 12) are comparable to those observed for SiNPNTiCl2,137 [(PNP)TiCl]2(N2)182 and (NN)TiCl(NR2)274 complexes. 3.3. Hafnium Diamido-Phosphine Complexes The hafnium dichloride complexes were accessed using the protonolysis method with Hf(NMe2)4 and ipropNPNH2 [2.10] and as with zirconium, the hafnium dichlorides were dimeric (Figure 86).  Synthesis of ipropNPNHf(NMe2)2 [3.19] The lemon yellow solid ipropNPNHf(NMe2)2 [3.19] was obtained in 57% yield from the reaction of ipropNPNH2 [2.10] with Hf(NMe2)4 in toluene at room temperature. The 31P{1H} NMR spectrum displayed a singlet at δ -3.12, and as expected, two unique environments are indicated for the NMe2 groups, with peaks at δ 2.56 and δ 2.90 in the 1H NMR spectra and at δ 40.5 and δ 41.1 in the 13C{1H} NMR spectrum.   Figure 86: Protonolysis of ipropNPNH2 [2.10] with Hf(NMe2)4  The solid state molecular structure of [3.19] was obtained via x-ray crystallographic analysis of single crystals grown by vapour diffusion of n-hexanes into a toluene solution at -30 90  °C (Figure 87). A distorted trigonal bipyramidal geometry was observed for the atoms bonding to the hafnium centre, as was reported for the zirconium [3.7] and [3.8] (Figure 62) and titanium [3.15] congeners (Figure 83) and mesNPNZr(NMe2)2.97   Figure 87: ORTEP representation of the solid state molecular structure of ipropNPNHf(NMe2)2 [3.19] The apexes are defined by the P1 and N24a atoms and the N8, N8a and N24 atoms form the trigonal plane. The Hf1-P1, Hf1-N8 and Hf-N8a bond lengths and hafnium-amido Hf1-N24 and Hf1-N24a bond lengths (Table 13) compare well with those obtained for other NPN97 and PNP209 hafnium complexes and the axial P1-Hf1-N24a angle at 155.76(9)° is more distorted compared mesNPNHf(NMe2)2 (Table 13). As with the other group 4 ipropNPN / tolNPN containing complexes, the N8-Hf1-N8a bite angle for [3.19] at 125.86(11)° is larger than for mesNPNHf(NMe2)2. Table 13 : Selected bond lengths (Å) and angles (°) for ipropNPNHf(NMe2)2 [3.19] and mesNPNHf(NMe2)297  ipropNPNHf(NMe2)2 [3.19] mesNPNHf(NMe2)297 Hf1-P1      2.7089(10)    2.7717(9) Hf1-N8   2.136(3)  2.156(3) Hf1-N8a   2.132(3)  2.137(3) Hf1-N24   2.007(3)  2.019(3) Hf1-N24a   2.037(3)  2.066(3) P1-Hf1-N8   71.15(8)  70.74(8) P1-Hf1-N8a   72.79(9)  73.01(8) P1-Hf1-N24    100.52(9)    95.16(10) P1-Hf1-N24a    155.76(9)     163.71(12) N24-Hf1-N8      110.03(12)     119.44(12) N24-Hf1-N8a      115.21(12)     108.79(13) N24a-Hf1-N8    98.77(12)    98.05(12) N24a-Hf1-N8a    97.95(12)     104.70(13) N8-Hf1-N8a     125.86(11)     120.89(11) N24-Hf1-N24a     103.67(12)     100.75(15) 91  Synthesis of [ipropNPNHfCl2]2 [3.20] ipropNPNHf(NMe2)2 [3.19] reacts with ca 6 equiv of TMSCl to give the yellow solid [ipropNPNHfCl2]2 [3.20] in 62% yield; a single sharp peak at δ 3.80 at room temperature in the 31P{1H} NMR spectrum (Figure 88) is observed. This is in contrast to the broad peaks observed for the zirconium congeners [3.9] and [3.10] (Figure 64). Single crystals of [ipropNPNHfCl2]2 [3.20] were grown from a saturated toluene solution at -30 °C and the solid state molecular structure (as with zirconium) reveals a dimeric structure (Figure 89), in contrast to penta-coordinate monomeric mesNPNHfCl2.97 Due to the similar covalent radii of Zr (175 ± 7 x 10-12 m) and Hf (175 ± 10 x 10-12 m)278 and their relative positions in the periodic table, similar chemical behaviour is often observed. However, the solid state molecular structure obtained for [ipropNPNHfCl2]2 [3.20] has a different isomeric form with the terminal chloride atoms (Cl1 and Cl1’) trans to the P1 atom compared to the zirconium congener [ipropNPNZrCl2]2 [3.9] (Figure 65), where the terminal Cl1 and Cl1’ atoms are cis to the P atom.   Figure 88: 31P{1H} (top) and 1H NMR (bottom) spectrum of [ipropNPNHfCl2]2 [3.20] in C6D6 at 25 °C  92   Figure 89: ORTEP representation of the solid state molecular structure of [ipropPNHfCl2]2 [3.20] The Hf1-P1, Hf1-N8 and Hf-N8a bond lengths 2.7487(12) Å, 2.062(4) Å and 2.080(4) Å (Table 14) are typical97, 209 and the terminal chloride bond length Hf1-Cl1 of 2.3923(12) Å is similar to those obtained for mesNPNHfCl297 and PNPHfCl3.209 The bridging chloride bond lengths Hf1-Cl2 and Hf1-Cl2’ of 2.5403(12) Å and 2.6335(11) Å are longer than those for the terminal chloride (Hf1-Cl1) as well as those in mesNPNHfCl2.97  Table 14 : Selected bond lengths (Å) and angles (°) for [ipropNPNHfCl2]2 [3.20] and mesNPNHfCl297  [ipropNPNHfCl2]2 [3.20]  mesNPNHfCl297  Hf1-P1      2.7487(12)  2.709(3) Hf1-N8a  2.062(4)    2.082(10)  Hf1-N8  2.080(4)    2.078(10) Hf1-Cl2     2.5403(12)   2.393(4)  Hf1-Cl1     2.3923(12)  2.402(3)  Hf1-Cl2’     2.6335(11)  P1-Hf1-Cl1   176.40(4)      176.60(11) N8a-Hf1-Cl2     149.41(11)  N8-Hf1-Cl2’     164.24(12)  P1-Hf1-N8a   68.03(11) 72.0(3) P1-Hf1-N8   75.57(11) 73.7(3) P1-Hf1-Cl2 86.50(4)     86.12(11) P1-Hf1-Cl2’ 95.19(4)  Cl1-Hf1-N8a    112.81(11)   118.1(3) Cl1-Hf1-N8    100.84(11)   112.3(3) Cl1-Hf1-Cl2 93.68(4)     97.27(12) Cl1-Hf1-Cl2’ 88.36(4)  N8a-Hf1-N8    100.36(15)   115.3(4) Cl2-Hf1-N8   88.76(12)   112.3(3) Cl2’-Hf1-N8a   87.57(11)   118.1(3) Cl2-Hf1-Cl2’ 77.82(4)  Hf1-Cl2-Hf1’   102.18(4)   93  The three trans angles for octahedral [ipropNPNHfCl2]2 [3.20] (Table 14) are less distorted compared to [ipropNPNZrCl2]2 [3.9] (Table 10) and the hafnium atom is more weakly bonded to phosphorus (P1) and more strongly bonded to the terminal (Cl1) and bridged (Cl2, Cl2’) chloride atoms compared to the isomer isolated for [ipropNPNZrCl2]2 [3.9] (comparing bond lengths in Table 10 to Table 14). In order to probe the solution behaviour of [ipropNPNHfCl2]2 [3.20] for the occurrence of other isomeric forms, variable temperature NMR spectroscopy was employed. When [ipropNPNHfCl2]2 [3.20] in toluene-d8 was cooled down from 93° to -81°, the peak at δ 5.39 in the 31P{1H} NMR spectra gradually sharpens and shifts upfield to δ 0.08 (Figure 90).  Figure 90: 31P{1H} NMR spectra of [ipropNPNHfCl2]2 [3.20] in toluene-d8 from 93 to -81 °C (δ 7.89 at 93 °C used as reference for spectra at other temperatures) The two smaller peaks observed at δ 7.89 and δ 7.30 may be considered to be impurities, as they were not observed in a pure sample of [3.20] at room temperature (see Figure 88). Some differences are also noted for the P-Ph peaks in the 1H NMR spectrum of [3.20] at low temperature (Figure 91).  94   Figure 91: 1H NMR spectra of [ipropNPNHfCl2]2 [3.20] in toluene-d8 at 25 °C and -71 °C  It is noteworthy that one of the signals observed for the zirconium congener isomers [ipropNPNZrCl2]2 [3.9] at δ 7.80 (Figure 67) and [tolNPNZrCl2]2 [3.10] at δ 6.86 [3.10] (Figure 66) has a gradual downfield shift with decreasing temperature, contrasting the upfield shift observed for [ipropNPNHfCl2]2 [3.20] (Figure 90). Compared to [ipropNPNZrCl2]2 [3.9], the solution behaviour for [ipropNPNHfCl2]2 [3.20] appears less complex and it may be that the heavier, slightly smaller hafnium atom slows down the ability of the hafnium dichloride dimer [3.20] to dissociate into a monomer and re-associate into different isomeric forms compared to the zirconium congeners [3.9] and [3.10] (see DOSY NMR discussion on pgs 78-79).  Synthesis of  ipropNPNHfCl2(THF) [3.21]   ipropNPNHfCl2(THF) [3.21] is formed by dissolution of [ipropNPNHfCl2]2 [3.20] in THF at room temperature, typically directly after TMSCl addition to ipropNPNHf(NMe2)2 [3.19]. The yellow solid was isolated in 76% yield; in solution the 31P{1H} NMR spectrum displays a single sharp peak at δ 5.44 and the 1H NMR spectrum shows broad coordinated THF peaks at δ 3.92 and δ 0.93 (Figure 92).   95   Figure 92: 31P{1H} (top) and 1H NMR (bottom) spectra of ipropNPNHfCl2(THF) [3.21] in C6D6   Figure 93: Partial 13C{1H} NMR spectrum of ipropNPNHfCl2(THF) [3.21] in C6D6 The 13C{1H} NMR spectrum displays a sharp singlet at δ 25.1 and a broad singlet at δ 74.5 for coordinated THF (Figure 93). As with the corresponding zirconium (Figure 57) and titanium (Figure 78) systems, two different isomers can be expected for [3.21] (Figure 94).     Figure 94: Isomers of ipropNPNHfCl2(THF) [3.21] 96  As only one methine signal is observed for the isopropyl groups, the more symmetric isomer with THF trans to the P atom is likely formed in solution. The broad THF resonance at δ 74.5 in the 13C{1H} NMR spectrum of [3.21] may indicate some fluxionality, but low temperature solution NMR spectroscopic experiments were not conducted to further elucidate the solution behaviour of [3.21]. Single crystals of ipropNPNHfCl2(THF) [3.21] were obtained via vapour diffusion of n-hexanes into a toluene solution in the freezer. The solid state molecular structure for [3.21] (Figure 95) is similar to those determined for zirconium complexes [3.5] and [3.6], where the chiral isomer having THF cis to the P atom of the ligand is observed.  Figure 95: ORTEP representation of the solid state molecular structure of ipropNPNHfCl2(THF) [3.21] Complex [3.21] has distorted octahedral geometry, with the N8-Hf1-Cl2 and N8a-Hf1-O1 trans angles of 153.65(15)° and 161.6(2)° more distorted than the P1-Hf1-Cl1 angle of 178.08(6)°. The Hf1-P1, Hf1-N8, Hf1-N8a, Hf1-Cl1 and Hf1-Cl2 bond lengths (Table 15) are comparable with the other hafnium complexes mentioned in this chapter and the Hf1-O1 bond length of 2.210(5) Å is typical for THF ligands bonded to hafnium.279, 280    97  Table 15 : Selected bond lengths (Å) and angles (°) for ipropNPNHfCl2(THF) [3.21]  ipropNPNHfCl2(THF) [3.21]  Hf1-P1     2.6821(17) Hf1-N8 2.131(5) Hf1-N8a 2.084(5) Hf1-O1 2.210(5)  Hf1-Cl1    2.3955(18)  Hf1-Cl2    2.4428(19) P1-Hf1-Cl1  178.08(6) N8-Hf1-Cl2    153.65(15) N8a-Hf1-O1 161.6(2) P1-Hf1-N8   74.37(15) P1-Hf1-N8a    71.21(14) P1-Hf1-O1    90.36(15) P1-Hf1-Cl2  82.98(6) Cl1-Hf1-N8      104.27(15) Cl1-Hf1-N8a      107.62(15) Cl1-Hf1-O1     90.82(15) Cl1-Hf1-Cl2   98.66(7) N8-Hf1-N8a 92.2(2) N8-Hf1-O1 83.4(2) Cl2-Hf1-N8a     93.12(15) Cl2-Hf1-O1     83.50(15) 3.4. Conclusions Salt metathesis and protonolysis routes were evaluated for the complexation of the NPN donor set with group 4 metals. In the case of zirconium, the salt metathesis route proceeded via a two step mechanism. Due to the lack of substituents in the ortho position of the amido moieties of the ipropNPN and tolNPN ligands, a facile bis-(ligand) complex formation was followed by a sluggish conproportionation with ZrCl4(THF)2. Protonolysis proved to be the superior method, with tetrakis(dimethylamido) metal(IV) complexes being the preferred precursors; dichloride bis(dimethylamido) metal(IV) complexes are also effective, but care should be employed to avoid trichloride impurities and HNMe2 adducts are not always easily displaced by THF. The titanium(IV) dichlorides are monomers in the solid state but the zirconium(IV) and hafnium(IV) dichlorides form chloro-bridged dimers, with complex solution behaviour. Again, the dimer formation may be facilitated by the lack of steric bulk at the ortho position of the amido moieties, as the analogous mesNPN containing  zirconium(IV) and hafnium(IV) dichlorides do not form dimers in the solid state, and do not readily coordinate a solvent molecule to form octahedral complexes.  98  Chapter 4: Tantalum Diamido-Phosphine Complexes From the discussion of group 5 dinitrogen complexes in chapter 1, one could access tantalum dinitrogen complexes via reduction of precursor chloride complexes or hydrogenation of precursor alkyl (methyl) complexes in the presence of N2 (Figure 96). In addition, Kawaguchi and co-workers68, 70 demonstrated that the reaction of a tripodal triaryloxide niobium trichloride complex with KHBEt3 completely cleaved the N2 bond to form a niobium nitride complex, via a niobium tetrahydride intermediate. Thus tantalum hydride complexes could conceivably be accessed from NPN tantalum trichloride complexes via reduction of the trichloride in the presence of H2 or reaction of the trichloride with hydride reagents (Figure 96).   Figure 96: Schematic representation of target NPN tantalum complexes The hydrogenation route is well established for SiNPN tantalum trimethyl complexes,79, 80 and although the reduction of SiPNP tantalum-alkylidene chloride complexes under N2 was successful,75 all subsequent attempts to form tantalum trichloride complexes with the related P2N2, SiNPN or mesNPN Fryzuk donor sets have thus far failed.  The main aim of this study is to investigate the potential for the sterically less hindered ipropNPN, tolNPN and PhNPN o-phenylene bridged ligands developed in this project (see chapter 2) to form tantalum chloride, alkyl, hydride and ultimately N2 complexes. 99  4.1. Tantalum Chloride Complexes  Salt metathesis and protonolysis routes were investigated for obtaining tantalum chloride complexes, utilising lithium salts or protonated forms of the NPN ligand, respectively (Figure 46). Tantalum(V) trichlorides or tantalum(III) chlorides could be accessed via salt metathesis, with tantalum pentachloride [TaCl5]2 or [TaCl3(PMe3)2]2 precursors, respectively (Figure 46).74, 281 Although NPN tantalum chloride formation was observed in both cases, difficulties were encountered and these routes were abandoned. Tantalum trichloride complexes may be accessed by reaction of [TaCl5]2 with protonated ligands, liberating HCl(g),282 but this route was not investigated.  Figure 97: Salt metathesis and protonolysis routes for tantalum complexes Protonolysis of TaCl3(NMe2)2(THF) with ipropNPNH2 [2.10] did form the expected tantalum(V) trichloride complex ipropNPNTaCl3 [4.4] (Figure 98), but only as a minor species in a mixture of other inseparable side-products.  100   Figure 98: Protonolysis route for synthesis of NPNTaCl3 complexes [4.4], [4.5] and [4.6] Protonolysis with Ta(NMe2)5 proved superior to TaCl3(NMe2)2(THF) as no unwanted side-products were obtained, but is sluggish, requiring high reaction temperatures. This became the preferred mode for accessing the NPN tantalum chloride complexes. It should be noted that this route is not general for all variations of the NPN donor set. When this promising new protonolysis route was explored for SiNPNH2 with Ta(NMe2)5 in toluene at 145 °C, a SiNP(C)NTa(NMe2)2 species283 was obtained  instead of the expected SiNPNTa(NMe2)3 complex. This result serves to emphasize the difficulties encountered in trying to obtain tantalum trichloride complexes with the SiNPN ligand, which has eluded synthetic attempts since the SiNPN ligand was first generated in 1998.80 4.1.1. Synthesis of Tantalum Amido Complexes Orange ipropNPNTa(NMe2)3 [4.1], yellow-orange tolNPNTa(NMe2)3 [4.2], and yellow PhNPNTa(NMe2)3 [4.3] were obtained by reaction of the corresponding protonated ligands ipropNPNH2 [2.10], tolNPNH2 [2.11], and phNPNH2 [2.12] with Ta(NMe2)5 in toluene under reduced pressure at temperatures of 125 °C to 145 °C over ca 1 to 2 days (Figure 98). The 101  solution 31P{1H} NMR spectra of these isolated solids display singlets at δ 13.00, δ 12.48, and δ 13.04, respectively (see Figure 99 for [4.2]).    Figure 99: 1H (top) and 31P{1H} NMR (bottom) spectra of tolNPNTa(NMe2)3 [4.2] in C6D6, “hex” in the 1H NMR spectrum refers to residual hexanes The 1H NMR spectra reveal that two of the NMe2 groups have identical environments with singlets at δ 3.44, 3.32, and 3.29, respectively, for [4.1], [4.2], and [4.3] and the other NMe2 group appears upfield with singlets at 3.28, 3.22, and 3.14 (Figure 99). The 13C{1H} NMR spectra display two different NMe2 environments; doublets at δ 48.3 (3JPC = 3 Hz), δ 48.3 (3JPC = 2 Hz), and δ 48.2 (3JPC = 3 Hz), respectively, for [4.1], [4.2], and [4.3] and less well-resolved doublets upfield at δ 47.7 (3JPC = 1 Hz), δ 48.0 (3JPC = 1 Hz), and δ 47.8 (3JPC = 2 Hz), respectively, with smaller 3JPC couplings (Figure 100). 1H-13C HMBC spectra correlate the downfield doublets with larger 3JPC couplings in the 13C{1H} NMR spectra to the downfield singlets in the 1H NMR spectra representing the two identical amido groups. 102   Figure 100: Partial 13C{1H} NMR spectrum of tolNPNTa(NMe2)3 [4.2] in C6D6 Suitable single crystals of tolNPNTa(NMe2)3 [4.2] were obtained and the solid state molecular structure reveals an octahedral geometry about the central tantalum atom with distorted P1-Ta1-N22, N8-Ta1-N21 and N8a-Ta1-N21a angles av 161° (Table 10). The tolNPN ligand is facially bound (Figure 101). As alluded to in the NMR spectroscopic data discussion, two of the NMe2 groups (N21 and N21a) have similar environments with larger cis 3JPC couplings. The other NMe2 group (N22) is trans to the P atom of the ligand (P1) with a smaller 3JPC coupling.  Figure 101: ORTEP representation of the solid state molecular structure of tolNPNTa(NMe2)3 [4.2] The Ta1-N21, Ta1-N21a, and Ta1-N22 bond lengths of 2.009(5) Å, 1.990(6) Å, and 1.991(5) Å for the NMe2 groups (Table 10) are very similar to those reported for Ta(NMe2)5  at 1.965(5) - 2.038(8) Å,284, 285 Ta(NEt2)5 at 1.917(9) - 2.238(9) Å286 and other tantalum(V) 103  complexes containing NMe2 groups, ranging from 1.94(2) to 2.09(2).287-292 The Ta1-P1, Ta1-N8 and Ta1-N8a bond lengths of tolNPNTa(NMe2)3 [4.2] (Table 10) fall within the range of bond lengths reported for P2N2TaMe3,293 SiNPNTaMe379, 80 and [SiNPNTaH]2N279, 80 complexes (Table 1). Table 16 : Selected bond lengths (Å) and angles (°) for tolNPNTa(NMe2)3 [4.2]  tolNPNTa(NMe2)3 [4.2]  Ta1-P1       2.6643(17) P1-Ta1-N8     73.94(13) Ta1-N8   2.191(5) P1-Ta1-N8a     68.89(14) Ta1-N8a   2.157(5) P1-Ta1-N21     89.82(16) Ta1-N21   2.009(5)  P1-Ta1-N21a     92.99(16) Ta1-N21a   1.990(6) N22-Ta1-N8 99.0(2) Ta1-N22   1.991(5) N22-Ta1-N8a 93.0(2)   N22-Ta1-N21 98.7(2) N8-Ta1-N8a     91.14(19) N22-Ta1-N21a   105.2(2) N8-Ta1-N21a 85.3(2) P1-Ta1-N22       160.00(17) N21-Ta1-N8a 89.6(2) N8-Ta1-N21   162.2(2) N21-Ta1-N21a 88.4(2) N8a-Ta1-N21a   161.8(2)  When comparing the P-Ta-N bite angles of the new o-phenylene bridged tolNPN ligand (Table 10) with tantalum complexes containing the silyl-methylene bridged SiNPN and P2N2 ligands (Table 1), one of the angles (P1-Ta1-N8) is within the observed range of 70.3(1) - 86.2(2)° and the other (P1-Ta1-N8a) is smaller at 68.89(14)°. The N8-Ta1-N8a bite angle for tolNPNTa(NMe2)3 [4.2] at 91.14(19)° is significantly smaller compared to the complexes with the SiNPN ligand as well as the P2N2 macro-cycle (Table 1). Smaller ligand bite angles are to be expected with the more the rigid o-phenylene backbone. Table 17: Comparative bond lengths (Å) and angles (°) for related SiNPN and P2N2 tantalum complexes.  SiNPNTaMe379 P2N2TaMe3293 [SiNPNTaH]2N279 Ta1-P1       2.7713(13)    2.6180(8)    2.573(5)      2.6088(9)    2.596(5)  Ta1-N8   2.025(4)  2.141(3)    2.079(4)       2.031(4)  Ta1-N8a   2.078(4)  2.210(2)    2.069(4)       2.049(4)  P1-Ta1-N8     81.72(11) 84.58(7) 78.8(2)   73.86(7) 77.5(2) P1-Ta1-N8a 70.3(1) 74.60(7) 86.2(2)   78.39(7) 76.3(2) N8-Ta1-N8a   113.0(2) 96.39(9)   108.2(2)      107.2(2) 104  4.1.2. Synthesis of Tantalum Trichloro Complexes The synthesis of dark brown tantalum trichloride complexes ipropNPNTaCl3 [4.4], tolNPNTaCl3 [4.5] and PhNPNTaCl3 [4.6] required reaction with an excess of ca 100 equiv of TMSCl in toluene heated to 140 °C for at least 2 days. A high yield is achievable for this reaction, as was seen for tolNPNTaCl3 [4.5] with 86%. However, the presence of impurities required multiple re-crystallisation events to effect complete removal, leading to lower yields for ipropNPNTaCl3 [4.4] and PhNPNTaCl3 [4.6], respectively.    Figure 102: 1H (top) and 31P{1H} NMR (bottom) spectra for tolNPNTaCl3 [4.5] in C6D6 at room temperature The 31P{1H} NMR spectra in C6D6 at room temperature for [4.4], [4.5] and [4.6] display broad peaks at δ 37.82, δ 36.77 and δ 36.04, respectively (Figure 102). Their corresponding 1H NMR spectra at room temperature  display broad peaks in the phenyl region (Figure 102) an