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Early metal complexes of an iminophosphorane containing ligand framework Wence, Dennis Lee Kole 2016

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EARLY METAL COMPLEXES OF AN IMINOPHOSPHORANE CONTAINING LIGAND FRAMEWORK by DENNIS LEE KOLE WENCE  B.Sc.(H), The University of British Columbia, Okanagan, 2009  A THESIS SUBMITTED IN PARTIAL FULLFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  Doctor of Philosophy in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Chemistry)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  August 2016 © Dennis Lee Kole Wence, 2016 ii  Abstract   A new tridentate, dianionic ligand containing two amido donors and a central iminophosphorane, [NNN]H2, was synthesized as an adaptation from the [tolylNPN*]H2 ligand framework.  The [NNN] system was designed as an extension to the ortho-phenylene bridged [NPN*] frameworks, which have been studied extensively with zirconium and tantalum.  Zirconium amido and chloride complexes stabilized by [NNN] were synthesized via protonolysis routes, and the zirconium dibenzyl complex was synthesized from the halide precursor.  Reduction of the zirconium dichloride species with alkali metal reagents led to cleavage of the iminophosphorane P=N bond.  The LUMO of [NNN]ZrCl2(THF) showed antibonding character of the iminophosphorane P=N, by DFT analysis.  Steric calculations of [NNN]ZrX2 complexes (G Value, %Vbur) showed increased steric hindrance of [NNN] relative to [NPN*] ligands.  A neutral donor substitution competition experiment corroborated the steric calculations.  Tantalum alkyl and alkyne complexes [NNN]TaMe3 and [NNN]Ta(BTA)Cl were synthesized via salt metathesis reactions with the dipotassium salt of [NNN].  Treatment of [NNN]TaMe3 with dihydrogen at elevated temperature led to cleavage of the iminophosphorane P=N bond, likely through reduced tantalum intermediate species.  Treatment of [NNN]Ta(BTA)(benzyl) with dihydrogen did not generate tantalum-hydride species or hydrogenate the alkyne ligand.  Addition of 4-isopropylphenylazide to [NNN]Ta(BTA)Cl led to the tantalum-imido compound [NNN]Ta=N(4-iPrPh)Cl via displacement of the alkyne ligand, BTA. iii   Alternative ligand systems were also examined.  A tetradentate ligand [PNNP]H2 with ortho-phenylene linkers and an ethylene tether was synthesized, and installed on zirconium amido and chloride precursors.  Reduction of [PNNP]ZrCl2 with potassium graphite was unsuccessful in attempt to activate dinitrogen.  A redesigned ligand with a propylene tether could not be synthesized, through several routes.  A tridentate, monoanionic ligand with ortho-phenylene linkers and silylamide functionality was designed based on the [NPN*] and silylamide [PNP] ligands.  The tridentate framework could not be synthesized through several routes, however, a new bidentate ligand with a secondary silylamide ortho to a phosphine group, a first of its class, was synthesized.   iv  Preface   I designed and performed all experiments described in this thesis, in consultation with my supervisor Professor Michael Fryzuk.  X-ray diffraction data of complexes was acquired and solved by Dr. Nathan Halcovitch, Mr. Fraser Pick, and Dr. Vincent Annibale, while I performed refinements on the data.  The density functional theory calculations described in Chapter 3 were performed by Dr. Aleks Zydor and Mr. Fraser Pick, while the steric calculations described in Chapter 3 were performed by the author.  I wrote all sections of this document.   v  Table of Contents  Abstract ..................................................................................................................................... ii Preface ...................................................................................................................................... iv Table of Contents ........................................................................................................................v List of Tables ..............................................................................................................................x List of Figures ........................................................................................................................... xi List of Schemes ........................................................................................................................xvi List of Symbols ........................................................................................................................xxi List of Abbreviations.............................................................................................................. xxii Acknowledgements ................................................................................................................ xxiv 1 Introduction .........................................................................................................................1 1.1 Dinitrogen Activation by Transition Metal Complexes ..................................................1 1.2 Ligand Design in the Fryzuk Group ..............................................................................3 1.3 Ligand Designs Incorporating Iminophosphoranes ........................................................9 1.4 Design of [NNN] Framework ...................................................................................... 13 1.5 Scope of Thesis ........................................................................................................... 15 2 Development of an Iminophosphorane-Containing Ligand Framework.............................. 18 2.1 Introduction ................................................................................................................ 18 2.2 Ligand Design Based on N-Mesityl o-Phenylene [NPN*] Frameworks ....................... 19 vi  2.2.1 Overview of Targeted Iminophosphorane Ligands ............................................... 19 2.2.2 Attempted Staudinger Reactions of N-Mesityl [NPN*] Frameworks .................... 21 2.2.3 Outcomes of the Staudinger Reaction with the N-Mesityl [NPN*] Frameworks ... 25 2.3 Synthesis of the Iminophosphorane-Containing [NNN]H2 Ligand ............................... 25 2.3.1 Redesign of Targeted Iminophosphorane Ligand.................................................. 25 2.3.2 Synthesis of N-Tolyl Substituted o-Phenylene [NPN*] Framework ...................... 26 2.3.3 Staudinger Reaction of the N-Tolyl [NPN*] Framework ...................................... 28 2.4 Conclusion .................................................................................................................. 32 3 Zirconium Complexes of Iminophosphorane-Containing  [NNN] Ligand 2.1 .................... 33 3.1 Introduction ................................................................................................................ 33 3.2 Synthesis of Zr[NNN] Complexes ............................................................................... 34 3.2.1 Amido and Halide Zr[NNN] Complexes .............................................................. 34 3.2.2 Zr[NNN] Organometallic Complexes ................................................................... 42 3.2.3 Reactivity of Zr[NNN] Dichloride and Dibenzyl Complexes ................................ 47 3.3 Reduction Studies of [NNN]ZrCl2 ............................................................................... 49 3.3.1 Background.......................................................................................................... 49 3.3.2 Reduction with KC8 and Na(Hg) .......................................................................... 50 3.3.3 Summary ............................................................................................................. 56 3.4 DFT Analysis of [NNN]ZrCl2(THF) and [tolylNPN*]ZrCl2(THF) ................................. 56 3.5 Steric Analysis of [NNN] Framework on Zirconium ................................................... 62 vii  3.5.1 Overview ............................................................................................................. 62 3.5.2 Solid Angle (G) Calculations of Zirconium [NNN] and [NPN*] Complexes ........ 62 3.5.3 Buried Volume (%Vbur) Calculations of Zirconium [NNN] and [NPN*] Complexes ……………………………………………………………………………………..66 3.5.4 [NNN]ZrCl2(THF) vs. [tolylNPN*]ZrCl2(THF) Neutral Donor Exchange .............. 70 3.6 Conclusion .................................................................................................................. 74 4 Tantalum Complexes of the Iminophosphorane-Containing [NNN] Ligand ....................... 75 4.1 Introduction ................................................................................................................ 75 4.2 Synthesis and Reactivity of [NNN]TaMe3 ................................................................... 77 4.2.1 Synthesis of [NNN]TaMe3 ................................................................................... 77 4.2.2 Hydrogenation Studies of [NNN]TaMe3 .............................................................. 82 4.3 Synthesis and Reactivity of [NNN]Ta Alkyne Complexes ........................................... 90 4.3.1 Overview ............................................................................................................. 90 4.3.2 Synthesis and Reactivity ...................................................................................... 91 4.4 Conclusions .............................................................................................................. 108 5 Alternate Ligand Scaffolds .............................................................................................. 110 5.1 Introduction .............................................................................................................. 110 5.2 Tetradentate [PNNP]H2 Ligand Set ........................................................................... 110 5.2.1 Introduction ....................................................................................................... 110 5.2.2 Synthesis of [PNNP]H2 ...................................................................................... 113 viii  5.2.3 Zirconium Complexes of [PNNP]H2 .................................................................. 116 5.2.4 Summary ........................................................................................................... 123 5.3 Attempted Synthesis of a Propylene-Tethered [prPNNP]H2 Ligand Framework ......... 123 5.3.1 Introduction ....................................................................................................... 123 5.3.2 Attempted Synthesis of [prPNNP]H2 via Aryl-Lithium Salt Metathesis ............... 124 5.3.3 Attempted Synthesis of [prPNNP]H2 via Nickel Template Reactions .................. 132 5.3.4 Summary ........................................................................................................... 137 5.4 Attempted Synthesis of an Ortho-Phenylene Silylamide [PhPSiNP]H Framework ....... 138 5.4.1 Introduction ....................................................................................................... 138 5.4.2 Attempted Synthesis of [PhPSiNP]H .................................................................... 139 5.4.3 Bidentate [PN]H Ortho-Phenylene Silylamine Ligand Class .............................. 145 5.4.4 Summary ........................................................................................................... 147 5.5 Conclusion ................................................................................................................ 148 6 Summary and Future Directions ...................................................................................... 149 6.1 Summary .................................................................................................................. 149 6.2 Conclusions .............................................................................................................. 151 6.3 Future Directions ...................................................................................................... 151 7 Experimental ................................................................................................................... 156 7.1 General Procedures ................................................................................................... 156 7.1.1 Laboratory Equipment and Procedures ............................................................... 156 ix  7.1.2 Solvents ............................................................................................................. 156 7.1.3 Materials ............................................................................................................ 157 7.1.4 Instrumentation and Methods of Analysis .......................................................... 157 7.2 Synthesis of Compounds ........................................................................................... 158 7.2.1 Complexes Pertaining to Chapter 2 .................................................................... 158 7.2.2 Complexes Pertaining to Chapter 3 .................................................................... 160 7.2.3 Complexes Pertaining to Chapter 4 .................................................................... 164 7.2.4 Complexes Pertaining to Chapter 5 .................................................................... 168 References .............................................................................................................................. 177 Appendix ................................................................................................................................ 183    x  List of Tables  Table 3.1:  Selected bond lengths (Å) and angles (deg) for 3.2. ................................................ 40 Table 3.2:  Selected bond lengths (Å) and angles (deg) for 3.3. ................................................ 44 Table 4.1:  Selected bond lengths (Å) and angles (deg) for 4.2. ................................................ 81 Table 4.2:  Selected bond lengths (Å) and angles (deg) for 4.3. ................................................ 94 Table 5.1:  Selected bond lengths (Å) and angles (deg) for 5.2. .............................................. 117 Table 5.2:  Selected bond lengths (Å) and angles (deg) for 5.8. .............................................. 136 Table 5.3:  Selected bond lengths (Å) and angles (deg) for 5.14.............................................. 145    xi  List of Figures  Figure 1.1:  Examples of dinuclear dinitrogen complexes of transition metals. ...........................2 Figure 1.2:  Examples of multidentate silylamidophosphine ligand sets studied by the Fryzuk group, with the silylamide ("classic") linker. ...............................................................................4 Figure 1.3:  [NPNclassic] ligand type with silylamide linker and o-phenylene bridged [NPN*] framework studied by the Fryzuk group. .....................................................................................6 Figure 1.4:  Side-on dinitrogen complexes of zirconium stabilized by the [NPNclassic] and [mesNPN*] ligands.24,33 ................................................................................................................6 Figure 1.5:  [NPN*] ligand system with o-phenylene linker compared to [NNN] ligand with iminophosphorane functionality. .................................................................................................9 Figure 1.6:  Iminophosphorane ligand designs based on the NacNac ligand.54,57,60 .................... 10 Figure 1.7:  Examples of multidentate iminophosphorane-containing ligands that utilize a bulky phosphorane on terminal donor N-atoms, from the Stephan group.63-66 ...................................... 11 Figure 1.8:  Examples of multidentate ligands that incorporate a phosphorane into the ligand framework, with iminophosphorane N-donor atoms, from the Hayes group.52,68,70 ..................... 11 Figure 1.9:  Comparison of internal N-Zr-P ligand angles of [[NPNclassic]ZrTHF]2N2 and [[mesNPN*]ZrTHF]2N2 from solid state data.  Half of each dinuclear complex is omitted for clarity, as they were generated via symmetry operations of the solid state data.24,33 ................... 14 Figure 2.1:  Proposed class of tridentate iminophosphorane-containing ligands based off of [mesNPN*]H2 and [mesNiPrPN*]H2. ............................................................................................. 21 Figure 2.2:  31P{1H} NMR spectra (121.5 MHz) of the reaction of [mesNPN*]H2 and 2,6-dimethylphenylazide in toluene, towards compound A of Figure 2.1. ........................................ 23 xii  Figure 2.3:  31P{1H} NMR spectra in toluene of reaction of [mesNPN*]H2 with excess 4-isopropylphenylazide, towards compound C of Figure 2.1. ........................................................ 24 Figure 2.4:  Redesign of ligand framework [NNN]H2 in order to favour iminophosphorane formation during Staudinger reaction. ....................................................................................... 26 Figure 2.5:  1H NMR spectrum (400 MHz) of 2.1 in C6D6.  Residual solvent signals are denoted by *. .......................................................................................................................................... 30 Figure 2.6:  Hydrogen bonding between amine N-H and iminophosphorane N-atom in compound 2.1 (left), and an enamine-iminophosphorane ligand from literature (right).62 ........... 31 Figure 3.1:  Naming scheme for [NPN*] ligand types............................................................... 34 Figure 3.2:  1H NMR spectrum of 3.1 at 400 MHz in C6D6.  Residual solvent signals and silicone grease are denoted by *. ............................................................................................... 36 Figure 3.3:  ORTEP representation of the solid state structure of 3.2, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms and co-crystallized THF are omitted for clarity. .... 40 Figure 3.4:  ORTEP representation of the solid state structure of 3.3, thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity. ....................................... 44 Figure 3.5:  Representation of the η2-interaction of the axial benzyl ligand of 3.3 in the solid state. ......................................................................................................................................... 45 Figure 3.6:  31P{1H} NMR spectrum at 121 MHz of the reduction product of 3.2 with KC8, acquired in C6D6. ...................................................................................................................... 51 Figure 3.7:  31P{1H} NMR spectrum at 121 MHz in C6D6 of the products of the reaction of 3.4 with excess trimethylammonium chloride.................................................................................. 55 Figure 3.8:  1H NMR spectra at 300 MHz in C6D6 (*) of [tolylNPN*]H2 (top), the reaction of 3.4 with excess trimethylammonium chloride (middle), and 4-isopropylaniline (bottom). ............... 55 xiii  Figure 3.9:  Overlay of wire frame models of solid state structures (green) and geometry optimized calculations (red) of 3.2 and [tolylNPN*]ZrCl2(THF). ................................................. 58 Figure 3.10:  HOMO and LUMO of 3.2. .................................................................................. 59 Figure 3.11:  HOMO and LUMO of [tolylNPN*]ZrCl2(THF). .................................................... 61 Figure 3.12:  Solid-G generated images for 3.2......................................................................... 64 Figure 3.13:  G values of [NNN] and [NPN*] ligands of zirconium complexes. ....................... 65 Figure 3.14:  Solid-G generated images for 3.2 and 3.3. ........................................................... 66 Figure 3.15:  Example of dummy atom "D" creation for use in SambVca input files. ................ 67 Figure 3.16:  Overlay of a sphere of radius ~2.5 Å in comparison to [NNN] and [tolylNPN*] frameworks, for %Vbur evaluation. ............................................................................................ 68 Figure 3.17:  %Vbur of [NNN] compared to [NPN] ligands on zirconium, at varying sphere radii for volume calculations. ............................................................................................................ 69 Figure 3.18:  31P{1H} NMR spectra at 162 MHz of before (top) and 20 minutes after DMAP addition (bottom) to a C6D6 solution of 3.2 and [tolylNPN*]ZrCl2(THF). .................................... 73 Figure 4.1:  1H NMR spectrum of 4.2 in C6D6 at 400 MHz.  Residual solvent, silicone grease, and minor impurity signals denoted by *. .................................................................................. 80 Figure 4.2:  ORTEP representation of the solid state structure of 4.2, thermal ellipsoids are drawn at 50% probability. Hydrogen atoms and co-crystallized hexane are omitted for clarity. . 81 Figure 4.3:  31P{1H} NMR spectra over time at 121 MHz in C6D6 of the reaction of 4.2 with 4 atm of H2(g).  Spectra were acquired at 25 oC. ............................................................................ 83 Figure 4.4:  1H NMR spectra at 300 MHz in C6D6 of 4.2 (top) and the reaction of 4.2 with 4 atm of H2(g) for 7 days at 50 oC (bottom).  Signals from residual solvent impurities and silicone grease are denoted by *. ....................................................................................................................... 84 xiv  Figure 4.5:  2H{1H} NMR spectrum at 61 MHz in C6H6 of the reaction of 4.2 with 4 atm of D2(g) after 7 days at 50 oC. ................................................................................................................. 85 Figure 4.6:  31P{1H} NMR spectra at 162 MHz in benzene of the hydrogenation product of 4.2 (top), and the reaction with trimethylammonium chloride (bottom) to liberate [tolylNPN*]H2 from tantalum. ................................................................................................................................... 87 Figure 4.7:  Comparison of alkyne and alkenediyl resonance structures. ................................... 90 Figure 4.8:  1H NMR spectrum at 400 MHz of 4.3 in C6D6, residual solvent signals and minor impurities are denoted by *. ...................................................................................................... 93 Figure 4.9:  ORTEP representation of the solid state structure of 4.3, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms and co-crystallized ether are omitted for clarity..... 94 Figure 4.10:  Variable temperature 1H NMR spectra at 400 MHz of 4.3 in d8-toluene, of the Si-CH3 region.  Minor impurities are denoted by *......................................................................... 97 Figure 4.11:  1H NMR spectrum of 4.4 at 400 MHz in C6D6.  Residual solvent and BTA signals denoted by *. ............................................................................................................................. 99 Figure 4.12:  31P{1H} NMR spectra at 162 MHz of addition of 4 atm of H2(g) to 4.5 in C6D6 over time. ........................................................................................................................................ 105 Figure 4.13:  31P{1H} NMR spectra at 162 MHz of the reaction of 4.5 with excess 4-isopropylphenyl azide in C6D6. ................................................................................................ 108 Figure 5.1:  General comparison of the [P2N2] macrocycle, [NPN*], and [PNNP] ligand systems. .................................................................................................................................. 112 Figure 5.2:  Literature examples of other ligand frameworks containing PNNP donor arrays.143,145 ............................................................................................................................. 113 xv  Figure 5.3:  Solid-state structure (ORTEP) of 5.1, thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity.  Half of the molecule has been generated by symmetry. .......................................................................................................................... 115 Figure 5.4:  ORTEP representation of the solid-state structure of 5.2, thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity. ..................................... 117 Figure 5.5:  Variable temperature 1H NMR spectra (400 MHz) of 5.2 in d8-toluene, showing ethylene proton signals and dimethylamido signals. ................................................................ 120 Figure 5.6:  Proposed ligand [prPNNP]H2, as a design progression from 5.1. .......................... 124 Figure 5.7:  Solid-state structure (ORTEP) of 5.8, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms, other than those bound to amido donors, are omitted for clarity.  Half of the molecule has been generated by symmetry. ........................................................... 135 Figure 5.8:  Design of [PhPSiNP]H as a progression of the classic amidophosphine [PNP]H framework of the Fryzuk group, and the monoanionic o-phenylene bridged ligand used by the Ozerov group.20,156 .................................................................................................................. 139 Figure 5.9:  Solid-state structure (ORTEP) of 5.14, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms, other than those bound to amine donors, are omitted for clarity.  Half of the molecule has been generated by symmetry, and co-crystallized benzene  is not shown. ........................................................................................................................... 144 Figure 6.1:  Proposed [NSN] and [NON] ligands, compared to [NNN]. .................................. 154    xvi  List of Schemes  Scheme 1.1:  Reaction of [NPNclassic] tantalum side-on end-on dinitrogen complex with 9-BBN, and subsequent ligand rearrangement at the silylamide linker.16 ..................................................5 Scheme 1.2:  Hydrogenolysis of [NPNclassic] and [mesNPN*] stabilized tantalum trimethyl complexes, and further reactivity towards dinitrogen.11,34,35 .........................................................8 Scheme 1.3:  Dinitrogen activation by an iminophosphorane-stabilized iron complex, adapted from literature.62  Dipp = 2,6-diisopropylphenyl. ....................................................................... 12 Scheme 1.4:  Cyclometalation of iminophosphorane aryl groups, Ar = 4-iPrPh and Mes* = 2,4,6-tBuPh.80 ..................................................................................................................................... 13 Scheme 2.1:  General mechanism of the Staudinger reaction. ................................................... 18 Scheme 2.2:  Synthetic route to [mesNPN*]H2, adapted from literature.32................................... 19 Scheme 2.3:  Synthetic route to [mesNiPrPN*]H2.35 ..................................................................... 20 Scheme 2.4:  Synthetic route to [tolylNPN*]H2.82 ....................................................................... 27 Scheme 2.5:  Staudinger reaction to produce 2.1. ...................................................................... 29 Scheme 3.1:  Reduction of a zirconium halide complex with KC8 to activate N2 in a side-on manner by the Fryzuk group, adapted from literature.33 ............................................................. 33 Scheme 3.2:  Protonolysis reaction of 2.1with Zr(NMe2)4 to form 3.1. ...................................... 35 Scheme 3.3:  Reaction of 2.1 with Zr(NMe2)2Cl2(DME) to produce 3.2. ................................... 38 Scheme 3.4:  Reaction of 3.2 with benzylmagnesium chloride to produce the dialkyl  complex 3.3. ............................................................................................................................. 42 xvii  Scheme 3.5:  Reduction of an iron halide complex with an iminophosphorane-containing ligand, to produce an end-on dinitrogen complex, adapted from literature.62  Note that Dipp = 2,6-diisopropylphenyl...................................................................................................................... 49 Scheme 3.6:  Proposed reduction reaction of 3.2 with KC8 to cleave iminophosphorane bond... 52 Scheme 3.7:  Summary of protonation experiments on 3.2 with trimethylammonium chloride, with and without the reducing agent KC8. ................................................................................. 54 Scheme 3.8:  DMAP substitution competition experiment on 3.2 and [tolylNPN*]ZrCl2(THF); product ratios from averaged 1H NMR data. .............................................................................. 72 Scheme 4.1:  Reaction of dinitrogen with the bridging tetrahydride tantalum dimer, to form a side-on and end-on dinitrogen complex.11 ................................................................................. 75 Scheme 4.2:  Formation of tantalum tetrahydride complex using the [mesNPN*] framework, adapted from literature.34,35  TMS = trimethylsilyl, and BTA = bis(trimethylsilyl)acetylene. ..... 76 Scheme 4.3:  Synthesis of 4.1 from 2.1 by deprotonation with KH, and the subsequent salt metathesis reaction with TaMe3Cl2 to produce 4.2. .................................................................... 79 Scheme 4.4:  Protonation experiment with trimethylammonium chloride on the hydrogenation product of 4.2, for analysis by 31P{1H} NMR spectroscopy. ...................................................... 87 Scheme 4.5:  Proposed reductive elimination of methane from a [NNN]Ta-hydride species, during the hydrogenation of 4.2, leading to reduction of the phosphorane and formation of a tantalum-imido complex. ........................................................................................................... 89 Scheme 4.6:  Preparation of tantalum alkyne precursor complexes of type TaCl3(RC≡CR)(DME).124 .......................................................................................................... 91 Scheme 4.7:  Synthesis of 4.3 by the salt metathesis reaction of 4.1 with TaCl3(BTA)(DME). .. 92 Scheme 4.8:  Fluxional behaviour of alkyne ligand of 4.3. ........................................................ 96 xviii  Scheme 4.9:  Synthesis of 4.4 by treatment of 4.3 with 4-isopropylphenyl azide. ...................... 98 Scheme 4.10:  Attempted reactivity of BTA ligand of complex 4.3. ........................................ 101 Scheme 4.11:  Attempted reactivity of chloride ligand of complex 4.3. ................................... 102 Scheme 4.12:  Synthesis of 4.5 by addition of benzylmagnesium chloride to 4.3..................... 103 Scheme 4.13:  Reaction of 4.5 with 4-isopropylphenyl azide to form a tantalum imido complex (not characterized), and the subsequent reaction with a second equivalent of 4-isopropylphenyl azide to form proposed triazenide and amido species (grey shading). ...................................... 107 Scheme 5.1:  Reaction of [[P2N2]Zr]2N2 dimer with H2, adapted from literature.28  Note that Me2 groups on Si are omitted for clarity. ........................................................................................ 111 Scheme 5.2:  Synthetic route to 5.1, based on the synthesis of the NHC-containing ([PCP]H)PF6.130 ...................................................................................................................... 114 Scheme 5.3:  Protonolysis reaction of 5.1 with Zr(NMe2)4 to yield 5.2. ................................... 116 Scheme 5.4:  Synthetic routes to the dichloride complex 5.3, from both 5.1 and 5.2. ............... 121 Scheme 5.5:  Attempted reduction of 5.3 with KC8 under 4 atm N2 led to a mixture of P-containing species. .................................................................................................................. 122 Scheme 5.6:  Formation of an ortho-aryl phosphine bond on N-methylaniline, through a directed ortho metalation pathway by the Cowie group.148 .................................................................... 125 Scheme 5.7:  Proposed synthetic route to installing aryl phosphine groups on [prPNNP]H2 involving an O-lithiocarbamate protecting group. .................................................................... 126 Scheme 5.8:  Unwanted elimination reactions of 1,3-dihalopropane reagents with o-bromoaniline. .......................................................................................................................... 127 Scheme 5.9:  Synthesis of 5.5 via ortho-bromination of 5.4, from commercially available p-toluidine. ................................................................................................................................. 128 xix  Scheme 5.10:  Attempted installation of ortho-phosphine groups on 5.4 and 5.5 through O-lithiocarbamate intermediates. ................................................................................................. 129 Scheme 5.11:  Attempted installation of ortho-phosphine groups on 5.4 by using a diazasilolidine protecting group to form 5.6, and failure to install the same  functionality on 5.5. ................................................................................................................ 132 Scheme 5.12:  Nickel template reaction to install a propylene tether on an ortho-phosphine aniline, adapted from literature.137 ........................................................................................... 133 Scheme 5.13:  Synthesis of 5.7 for Ni template reactions. ....................................................... 134 Scheme 5.14:  Deprotonation of 5.7 to form 5.8. ..................................................................... 135 Scheme 5.15:  Attempted installation of propylene tether on 5.8.  Conditions a:  4 K2CO3, toluene, reflux.  Conditions b:  2 LDA, ether, 25 oC.  Conditions c:  8 KH, THF, 25 oC. .......... 137 Scheme 5.16:  Attempted synthesis of [PhPSiNP]H via salt metathesis pathway of 5.9 and 5.10 with the secondary silylamine tether. ....................................................................................... 140 Scheme 5.17:  Formation of a secondary amine from a chlorosilane and ammonia, adapted from literature.164 ............................................................................................................................. 141 Scheme 5.18:  Formation of a secondary amine through a transamination reaction, adapted from literature.134 ............................................................................................................................. 141 Scheme 5.19:  Synthesis of 5.11 and 5.12 via salt metathesis reactions of the ortho-lithiated phosphines with dichlorodimethylsilane, as well as the conversion to the silylamine  compound 5.13........................................................................................................................ 142 Scheme 5.20:  Synthesis of 5.14 from 5.11, through the formation of a primary amine. .......... 144 Scheme 5.21:  Synthesis of new bidentate ligand 5.15 from 5.11. ........................................... 146 xx  Scheme 6.1:  Potential synthetic routes to proposed ligands [NSN]H2 and [NON]H2, from [NPN*]H2. .............................................................................................................................. 153   xxi  List of Symbols  Å  - Angstrom, 10-10 m Δ  - heat δ  - chemical shift in NMR spectroscopy, in parts per million D  - deuterium (2H) dn  - n-deuterated; d8-toluene indicates 8 H atoms are replaced by D atoms in     toluene ΔG‡rot  - activation energy of rotation ηn  - number of atoms "n" of a ligand bound to a metal hν  - light Hz  - hertz J  - joule K  - Kelvin (temperature unit) nJAB  - scalar coupling of n bonds between nuclei A and B    xxii  List of Abbreviations  Anal. calcd - analysis calculated Ar  - aryl group br  - broad BTA  - bis(trimethylsilyl)acetylene DFT  - density functional theory Dipp  - 2,6-diisopropylphenyl DMAP  - 4-dimethylaminopyridine DME  - 1,2-dimethoxyethane EI-MS  - electron-ionization mass spectrometry HMBC - heteronuclear multiple-bond correlation HOMO - highest occupied molecular orbital HSQC  - heteronuclear single quantum correlation iPr  - isopropyl, -CHMe2 LUMO - lowest unoccupied molecular orbital m/z  - mass to charge ratio Mes  - mesityl, 2,4,6-trimethylphenyl xxiii  n-BuLi  - n-butyllithium NMR  - nuclear magnetic resonance ORTEP - Oak Ridge Thermal Ellipsoid Plot Ph  - phenyl, -C6H5 ppm  - parts per million t-BuLi  - tertiary-butyllithium THF  - tetrahydrofuran TMEDA - tetramethylethylenediamine TMS  - trimethylsilyl, -SiMe3 XRD  - X-ray diffraction xs  - excess   xxiv  Acknowledgements   I would like to thank Dr. Michael Fryzuk for the opportunities I have had working in his laboratory.  Additionally, I would not have understood how to frame a scientific paper or presentation without his feedback and influence.  I would also like to thank the Fryzuk group members:  Joachim, Rui, and Bryan helped me get my feet under me in the early days in the lab, and Nathan, Kyle, Truman, Fraser, Alyssa, Nick, and Amanda kept the lab atmosphere entertaining and collaborative.  As well, I must thank the many post-doctoral researchers:  Thomas, Dominik, Takahiko, Tatsuya, Vince, Aleks, and Rich, who have all brought new ideas and techniques with them.  Everyone has added in some way to this project, from ideas through conversation, to helping with calculations or X-ray crystallography.  I am grateful to the current Fryzuk group members for help with editing this document, and I must especially thank Dr. Rich Burford for his editing and input on several chapters.  I would not have completed this process to my timeline without the effort of Dr. Laurel Schafer, as the departmental reader.  I could not have done this without the support and encouragement from my Dad, Dennis Wence.  He made it possible for me to go through the lengthy education process, through undergraduate and graduate school.  Thank you to Jes, for helping me understand balance, and for the support while I completed my Ph.D.1  1 Introduction 1.1 Dinitrogen Activation by Transition Metal Complexes  The binding and further reactivity of dinitrogen via transition metal complexes is a major research focus of the Fryzuk group.1-5  While ligand design is the central topic of this document, a brief background on dinitrogen activation brings context to the challenge of binding and functionalizing N2, a challenge that has guided several iterations of ligand design.  Dinitrogen is an abundant substance, composing 78% of Earth's atmosphere, yet its inert nature causes difficulty for conversion to nitrogen-containing products.1  The only successful commercial process for dinitrogen fixation is the heterogeneous Haber-Bosch process, which requires high temperatures and pressures, and consumes about 1% of the world's annual energy supply.1,6  Biologically, the iron-molybdenum cofactor of nitrogenase enzymes is able to catalytically convert dinitrogen to ammonia, although this system is complex and further complicated by the protein framework.7  The activation and functionalization of dinitrogen to ammonia or nitrogen-containing materials via transition metal complexes is a long-standing goal in chemistry.3  Dinitrogen is a poor ligand for transition metal complexes due to its large HOMO-LUMO gap and non-polar nature.1  Compared to the isoelectronic molecule carbon monoxide, dinitrogen is both a weaker σ-donor and π-acceptor; carbon monoxide undergoes a variety of chemical reactions while dinitrogen is often used as an inert working gas for sensitive experiments.  The first dinitrogen complex, the ruthenium compound [Ru(NH3)5N2]2+ with dinitrogen bound in an end-on fashion, was reported by Allen and Senoff in 1965.8  From this initial dinitrogen complex, an entire field of inorganic chemistry has developed.1,2,4,9,10 2   Upon coordination, strongly reducing metal complexes can have the ability to reduce the dinitrogen moiety to a formal double bond (N=N)2- or single bond (N-N)4- as determined by X-ray crystallography or RAMAN spectroscopy, which is often referred to as the degree of activation of the N2 unit.  Typically more than one metal centre is involved in early metal dinitrogen complexes for the purpose of multielectron reduction; examples of dinuclear dinitrogen complexes are shown in Figure 1.1.11-14  These examples also illustrate the binding modes of dinitrogen:  terminal and bridging end-on (B), side-on (C), and side-on end-on (A).  Figure 1.1:  Examples of dinuclear dinitrogen complexes of transition metals.11,13,14   A variety of ligand types have shown ability to stabilize dinitrogen complexes, such as the ammine ligands of the Allen and Senoff complex, cyclopentadienyl derivatives as in compound C of Figure 1.1, and mixed-donor multidentate ligands.  The multidentate ligand design strategies used by the Fryzuk group are discussed in the next section.  Often alkali metal reagents such as KC8, Mg, and sodium amalgam (Na(Hg)) are employed for reduction of the metal complex prior to dinitrogen activation; thus, the ligands must be capable of stabilizing the 3  reduced metal species as well as the subsequent dinitrogen complexes.  Additionally, some metal-hydride complexes are capable of activating dinitrogen;2 the side-on end-on dinitrogen compound A in Figure 1.1 is generated via the elimination of H2 from a dinuclear Ta(IV) complex.11,12  Regarding these two methods of dinitrogen activation, Chapter 3 of this thesis investigates the reduction of zirconium complexes, while Chapter 4 reports attempted syntheses of dinuclear tantalum hydride complexes.  Some transition metal complexes with an activated dinitrogen ligand enable the functionalization of dinitrogen, to form element-nitrogen bonds.10,15-18  Additionally, there are homogenous systems that are able to catalyze ammonia production from dinitrogen, in modest turnover, such as compound B of Figure 1.1.14,19  The conversion of dinitrogen to higher-valued nitrogen-containing products, especially in a catalytic manner, is a major goal in the field.  However, fundamental studies of activated dinitrogen complexes and stoichiometric reactivity investigations provide important insight into the development of new catalysts. 1.2 Ligand Design in the Fryzuk Group  Multidentate ligand systems containing both hard and soft donors have been a mainstay of the Fryzuk group research program since the first publication of the amidophosphine [PNP] ligand in 1981.20,21  A family of structurally related amidophosphine ligands has been developed in the Fryzuk group, as shown in Figure 1.2, and their subsequent chemistry has been studied across the periodic table.12,20,22  The work reported in this document involves the development of a multidentate amido-iminophosphorane framework and its subsequent coordination chemistry with the early metals zirconium and tantalum.  This chapter provides the context for the design of this new ligand system relative to our other ligand frameworks. 4    Figure 1.2:  Examples of multidentate silylamidophosphine ligand sets studied by the Fryzuk group, with the silylamide ("classic") linker.  The initial tridentate, monoanionic [PNP] ligand was used as the basis for design of a macrocyclic dianionic ligand, [P2N2]; the [PNP] framework within [P2N2] is highlighted in blue in Figure 1.2.22  Similarly, design of the dianionic [NPNclassic] ligand (red highlighting in Figure 1.2) was derived from the other "half" of [P2N2].12  This family of so-called "classic" silylamide-linked phosphine frameworks of Figure 1.2 has enabled impactful chemistry of early metal complexes, including the activation of dinitrogen and its subsequent reactivity.11,12,15-18,23-31  However, the silylamide functionality within the ligand has also been prone to unwanted reactivity.15,16,23,26,31  An example of ligand rearrangement is shown in Scheme 1.1, where an 5  activated dinitrogen ditantalum complex reacts with 9-borabicyclo[3.3.1]nonane (9-BBN), followed by migration of a silyl group to a bridging nitrogen atom.16  Scheme 1.1:  Reaction of [NPNclassic] tantalum side-on end-on dinitrogen complex with 9-BBN, and subsequent ligand rearrangement at the silylamide linker.16  A more robust o-phenylene bridged framework was developed to facilitate analogous reactivity to the silylamide "classic" systems, but with increased resistance toward ligand decomposition.32  The o-phenylene based framework, shown in Figure 1.3, will be referred to as the [NPN*] family of ligands in this document, with superscript prefixes denoting N-Ar substitutions.  The [mesNPN*] ligand stabilized the activation of dinitrogen in a side-on fashion 6  with zirconium, in a similar manner to the [NPNclassic] ligand.  These two zirconium dinitrogen complexes are shown in Figure 1.4.24,33  Figure 1.3:  [NPNclassic] ligand type with silylamide linker and o-phenylene bridged [NPN*] framework studied by the Fryzuk group.  Figure 1.4:  Side-on dinitrogen complexes of zirconium stabilized by the [NPNclassic] and [mesNPN*] ligands.24,33  While the [NPN*] framework allowed for the study of group 4 dinitrogen complexes akin to those of the [NPNclassic] ligand, differences between the two frameworks caused subsequent tantalum complexes to exhibit unique reactivity towards dinitrogen.11,34,35  As shown in Scheme 1.2, the [NPNclassic]-stabilized tantalum trimethyl complex undergoes hydrogenolysis to form a dinuclear tetrahydride species in a trans orientation.11  This tetrahydride compound 7  spontaneously reacts with dinitrogen to form a side-on end-on bridging complex.11  Similarly, the complex [mesNPN*]TaMe3 undergoes hydrogenolysis to form a ditantalum tetrahydride species, however this compound exists in the cis orientation in the solid-state.34,35  This [NPN*]-stabilized tetrahydride complex is inert towards dinitrogen.34,35  Our group is currently investigating why these two amidophosphine ligand frameworks lead to similar ditantalum tetrahydride complexes, yet display different reactivity with respect to dinitrogen coordination.  There are several literature examples of bridging polyhydride group 5 transition metal complexes, yet few of these show interaction with dinitrogen.36-44   8   Scheme 1.2:  Hydrogenolysis of [NPNclassic] and [mesNPN*] stabilized tantalum trimethyl complexes, and further reactivity towards dinitrogen.11,34,35  As small changes to ligand composition can lead to considerably different reactivity of subsequent complexes, it was our goal to modify the [NPN*] system at the internal neutral phosphine donor and study the impact of the change through comparison to previously investigated [NPN]-stabilized compounds.45  Modification of the phosphine to an iminophosphorane allows the same o-phenylene scaffold to stabilize the tridentate, dianionic ligand, yet alters the ligand geometry.  Figure 1.5 compares the [NPN*] framework to the 9  iminophosphorane-containing [NNN] system.  Note that the [NPN*] ligand forms 5-membered chelate rings, while the [NNN] ligand has an additional N-atom, leading to 6-membered rings.    Figure 1.5:  [NPN*] ligand system with o-phenylene linker compared to [NNN] ligand with iminophosphorane functionality. 1.3 Ligand Designs Incorporating Iminophosphoranes  Iminophosphoranes, R3P=NR', consist of a phosphorane P-atom and an approximately sp2-hybridized N-atom with a highly polarized P=N bond.46  Iminophosphoranes coordinate to metals through the nitrogen lone pair with similar σ-donor capacity to imine (R2C=NR') ligands, but only minor π-acceptor properties.47  There are many examples of metals across the periodic table stabilized by iminophosphorane-containing ligands, including zirconium and tantalum.46,48-56  The incorporation of iminophosphorane functionality into multidentate ligands has been employed for different design strategies.  Iminophosphoranes can be substituted for other functional groups, for example, analogues of β-diketiminato (NacNac) ligands with iminophosphorane rather than imine functionality have been studied by the groups of Piers, Liang, and Fryzuk, as shown in Figure 1.6.54,57-62  Iminophosphoranes have been used in ligand 10  design for their steric properties, such as the tridentate ligands employed by the Stephan group, shown in Figure 1.7, where the terminal PPh3 groups provide bulk.63-66  Novel ligands have also been designed to incorporate the phosphorane into the ligand backbone, such as the tridentate ligands studied by the Hayes group with terminal iminophosphorane functionality, examples of which are shown in Figure 1.8.52,67-72  Additionally, a ligand developed by Cavell and co-workers incorporates iminophosphorane groups to stabilize a carbene functionality on a variety of transition metals.73-75  Figure 1.6:  Iminophosphorane ligand designs based on the NacNac ligand.54,57,60   11   Figure 1.7:  Examples of multidentate iminophosphorane-containing ligands that utilize a bulky phosphorane on terminal donor N-atoms, from the Stephan group.63-66  Figure 1.8:  Examples of multidentate ligands that incorporate a phosphorane into the ligand framework, with iminophosphorane N-donor atoms, from the Hayes group.52,68,70  Many complexes incorporating iminophosphorane-containing ligands have shown catalytic activity, which has recently been reviewed.46  Catalytic applications such as hydrogenation, cross-coupling, and oligomerization have been investigated.46,67,71,76,77  Fundamental stoichiometric reactivity has also been supported by iminophosphorane-containing 12  ligands, such as dinitrogen activation, CO insertion, and metal-hydride formation.54,62,63,78  An example of dinitrogen activation by an iron complex stabilized with an iminophosphorane-containing ligand is shown in Scheme 1.3.62  Scheme 1.3:  Dinitrogen activation by an iminophosphorane-stabilized iron complex, adapted from literature.62  Dipp = 2,6-diisopropylphenyl.  However, cyclometalation reactivity is a common issue with multidentate iminophosphorane-containing ligands, and has been observed for many ligand frameworks and metals.49,52,59,63,69,72,78-80  Cyclometalation is the activation of a ligand's C-H bond to form a C-M bond, typically with elimination of a free molecule such as dihydrogen or an alkane.81  Often, cyclometalation is an undesirable ligand decomposition pathway, and studies have been conducted to develop iminophosphorane-containing ligands resistant to cyclometalation.79,81  An example of cyclometalation at both the phosphorane aryl substituent, and N-aryl substituent from the Hayes group is shown in Scheme 1.4.80 13   Scheme 1.4:  Cyclometalation of iminophosphorane aryl groups, Ar = 4-iPrPh and Mes* = 2,4,6-tBuPh.80 1.4 Design of [NNN] Framework  The o-phenylene bridged [NPN*] framework, shown in Figure 1.3, was designed to increase stability towards the unwanted ligand reactivity that was observed for the silylamide [NPNclassic] framework.32  The aryl backbone was also selected in order to maintain a similar basicity of the amido N-atoms compared to the classic silylamide system.32  However, the rigid o-phenylene backbone restricts ligand geometry compared to the more flexible [NPNclassic] framework.  The comparison of solid-state metrics of the analogous zirconium dinitrogen complexes, illustrated in Figure 1.9, shows that the internal ligand angles N-Zr-P for the [mesNPN*] framework are 71.84(8)o and 73.42(8)o, while the same parameters for [NPNclassic] are 14  76.62(5)o and 77.15(5)o.24,33  The o-phenylene backbone of [mesNPN*] constrains ligand geometry farther from ideal geometry (90o) than [NPNclassic].  Figure 1.9:  Comparison of internal N-Zr-P ligand angles of [[NPNclassic]ZrTHF]2N2 and [[mesNPN*]ZrTHF]2N2 from solid state data.  Half of each dinuclear complex is omitted for clarity, as they were generated via symmetry operations of the solid state data.24,33  A comparison of the dinuclear tantalum tetrahydride species supported by [mesNPN*] and [NPNclassic] is shown in Scheme 1.2.  Based on DFT calculations, we believe that the bulky substitution and restricted geometry of [mesNPN*] forces the cis orientation of the dinuclear complex, compared to the trans orientation of the [NPNclassic]-supported tetrahydride system.  Current computational investigations suggest the necessity of the trans orientation of the dinuclear tetrahydride species for dinitrogen activation.  A similar dianionic, tridentate ligand with increased flexibility compared to the [NPN*] framework could potentially lead to analogous formation of a tantalum tetrahydride species, but with subsequent reactivity toward dinitrogen comparable to what the [NPNclassic] framework enables.  Variations of the [NPN*] framework with alternative amido-aryl substituents have been studied (Ar substituents of Figure 1.5).82  Alternative linker systems such as thiophene- and 15  cyclopentenyl-bridged [NPN] ligands have also been investigated.83,84  We concluded that modification to the central donor of the [NPN*] system was the logical progression to the ligand design.  The inclusion of the iminophosphorane functionality in the [NNN] framework, shown in Figure 1.5, increases the chelate ring size to 6 membered over the 5-membered rings of [NPN*] complexes.  This added donor atom should reduce geometric strain induced by the o-phenylene backbone, which will be reflected through XRD analysis of the resulting [NNN]-metal complexes and their comparison to analogous [NPN*]-stabilized compounds.  Additionally, the iminophosphorane N-Ar' substituent (Figure 1.5) can be varied to further adjust ligand properties.  The substitution of amido N-Ar, and iminophosphorane P-R and N-Ar' groups is discussed in Chapter 2.  The vast majority of multidentate iminophosphorane-containing ligand systems in the literature, as described in Section 1.3, incorporate the iminophosphorane as a flanking donor.  As shown in Scheme 1.4, these systems are prone to cyclometalation.  Attempts to reduce the unwanted reactivity in these systems by adjusting sterics of the phosphorane did not prevent cyclometalation.72  Since in the [NNN] ligand system the iminophosphorane functionality is located in the centre, we intended that the rigidity imposed by the o-phenylene groups would prevent cyclometalation reactivity in early metal alkyl complexes. 1.5 Scope of Thesis  The [NPNclassic] and [NPN*] ligand frameworks, with substituent modifications, have been studied extensively on the early metals zirconium and tantalum.12,23,24,32-35,82,85  The goal of this work is to modify the central phosphine of the [NPN*] framework to an iminophosphorane, and compare the subsequent zirconium and tantalum complexes to the library of analogous compounds synthesized by the Fryzuk group.  Of particular interest is the reduction of zirconium 16  halide compounds toward dinitrogen activation, and the investigation of the formation and reactivity of ditantalum tetrahydride species.  Chapter 2 of this document describes the substituent choices and synthesis of the [NNN] framework.  Challenges of the Staudinger reaction due to ligand bulk are described, which leads to the design and synthesis of the [NNN] ligand that is used for the subsequent chemistry of Chapters 3 and 4.  Chapter 3 focuses on zirconium chemistry of the [NNN] ligand, with amido, chloride, and alkyl complexes presented.  The reduction reactivity of the zirconium dichloride complex is investigated, wherein the sensitivity of the iminophosphorane unit is described.  The steric and electronic properties of zirconium [NNN] complexes are compared to [NPN*] compounds, through G value, %Vbur, and DFT calculations.  Chapter 4 presents tantalum complexes with the [NNN] framework.  Attempted synthesis of a ditantalum tetrahydride compound is presented via tantalum trimethyl and alkyne compounds.  Properties of these tantalum alkyl compounds are compared to analogous [NPNclassic]- and [NPN*]-stabilized tantalum complexes.  Evidence is presented that under certain conditions, the sensitivity of the iminophosphorane unit becomes evident, particularly in the hydrogenation process.  Chapter 5 describes alternate ligand systems that were investigated prior to the [NNN] framework.  This includes a tetradentate [PNNP] framework with o-phenylene linkers, as well as the design and attempted synthesis of a tridentate [PhPSiNP] ligand that includes both o-phenylene linkers and the silylamide functionality. 17   Chapter 6 provides a summary of our investigations and directions for further ligand modifications, based on the findings of this work.   18  2 Development of an Iminophosphorane-Containing Ligand Framework 2.1 Introduction Generation of an iminophosphorane functionality is generally achieved through the Staudinger reaction, which couples an azide with a phosphine through a phosphazide intermediate, as seen in Scheme 2.1.86,87  While this is the common method for iminophosphorane installation in multidentate ligand systems,52,57,58,60,68,69,88,89 there are other synthetic routes available, such as the Kirsanov reaction of a PR3Br2 synthon with the desired amine in the presence of triethylamine.46,64,90  There is also an example of iron-assisted iminophosphorane formation from a coordinated phosphine and an azide, where the resultant iminophosphorane cannot be synthesized under Staudinger conditions.91  Even with these alternative strategies available, synthetic routes for a new tridentate ligand set were based on the Staudinger reaction.  This pathway gives more freedom for modularity of the ancillary ligand as almost any phosphine precursor can be used, and is more convenient than the use of dibromophosphorane PR3Br2 precursors.  Scheme 2.1:  General mechanism of the Staudinger reaction. 19   This chapter describes the design of a new tridentate ligand system with a central iminophosphorane donor and terminal amido groups.  The synthesis of the ligand is performed by the Staudinger reaction of an aryl azide with o-phenylene linker [NPN*]-type ligands that have been previously used by the Fryzuk group.32,35,82 2.2 Ligand Design Based on N-Mesityl o-Phenylene [NPN*] Frameworks 2.2.1 Overview of Targeted Iminophosphorane Ligands As described in Section 1.4, the [mesNPN*]H2 ligand was an excellent starting point for installation of an iminophosphorane functionality.  An optimized synthetic route to [mesNPN*]H2 had been previously developed by Dr. Erin MacLachlan, and is outlined in Scheme 2.2.32  Scheme 2.2:  Synthetic route to [mesNPN*]H2, adapted from literature.32 20   In addition to [mesNPN*]H2, a version of the framework containing an isopropyl-substituted phosphine was synthesized as a modification to the above method, as shown in Scheme 2.3.  This procedure was originally developed by Dr. Kyle Parker while working in the Fryzuk group.35  These two [NPN*] backbone variations were the starting point towards synthesizing a small library of iminophosphorane-containing ligands, by varying the substituents on both the phosphorane and imine.  Scheme 2.3:  Synthetic route to [mesNiPrPN*]H2.35  In order to install the iminophosphorane functionality via the Staudinger reaction with a range of aryl substituents on the nitrogen atom, different azide precursors were synthesized from the corresponding aniline starting materials.92  Aryl azides were chosen due to the variety of substituted anilines available for purchase, as well as their increased stability over lower 21  molecular weight alkyl azides.93  A bulky 2,6-dimethylphenylazide as well as the less sterically demanding 4-isopropylphenylazide were selected for reaction with [mesNPN*]H2 and [mesNiPrPN*]H2, potentially leading to four new iminophosphorane-containing ligands, as outlined in Figure 2.1.  Figure 2.1:  Proposed class of tridentate iminophosphorane-containing ligands based off of [mesNPN*]H2 and [mesNiPrPN*]H2. 2.2.2 Attempted Staudinger Reactions of N-Mesityl [NPN*] Frameworks  The synthesis of compounds A and B of Figure 2.1 were attempted via the treatment of 2,6-dimethylphenylazide with [mesNPN*]H2 and [mesNiPrPN*]H2 in toluene.  When the [mesNPN*]H2 framework was used, an incomplete reaction to form the corresponding phosphazide occurred over several days.  This was evidenced by a signal at δ 35.1 in the 31P{1H} 22  NMR spectrum in toluene.  When the reaction mixture was heated to 120 oC, partial conversion of the phosphazide species to the iminophosphorane was achieved, as evidenced by a signal at δ 12.1 in the 31P{1H} NMR spectrum in toluene.  However, the slow initial reaction between the phosphine moiety and 2,6-dimethylphenylazide never allowed for quantitative conversion to the phosphazide intermediate, and heating did not noticeably improve the reaction rate or the yield.  The 31P{1H} NMR spectra in toluene of the reaction of 2,6-dimethylphenylazide with [mesNPN*]H2 to partially form A are shown in Figure 2.2.  When 2,6-dimethylphenylazide was reacted with [mesNiPrPN*]H2, the formation of the phosphazide species that produces a signal at δ 37.0 in toluene was nearly quantitative after 12 hours, but did not rearrange to the iminophosphorane B through N2 elimination.   23    Figure 2.2:  31P{1H} NMR spectra (121.5 MHz) of the reaction of [mesNPN*]H2 and 2,6-dimethylphenylazide in toluene, towards compound A of Figure 2.1.  Using the same approach, ligands C and D of Figure 2.1 were targeted by the reaction of 4-isopropylphenylazide with [mesNPN*]H2 and [mesNiPrPN*]H2 in benzene or toluene.  With use of the [mesNPN*]H2 framework to form C, an improved reaction rate with the less bulky 4-isopropylphenylazide was observed to form the phosphazide species, as evidenced by a 31P{1H} NMR signal at δ 36.3 in toluene.  However, 10% of the [mesNPN*]H2 starting material was observed after 5 days of reaction by NMR spectroscopy, even with excess azide present.  As well, there was only a 30% conversion of the phosphazide to the iminophosphorane over this same period.  Figure 2.3 shows the 31P{1H} NMR spectra of the reaction of [mesNPN*]H2 and 24  excess 4-isopropylphenylazide.  The reaction of [mesNiPrPN*]H2 with 4-isopropylphenylazide towards D readily formed the phosphazide species at room temperature after 12 hours, which produced a signal at δ 43.5 in the 31P{1H} NMR spectrum.  Unlike the bulkier 2,6-dimethylphenylazide that did not rearrange to the iminophosphorane, a 30% conversion to the iminophosphorane D was observed after 3 days by 31P{1H} NMR spectroscopy (δ 26.1 in toluene), although quantitative conversion was not achieved.  Figure 2.3:  31P{1H} NMR spectra in toluene of reaction of [mesNPN*]H2 with excess 4-isopropylphenylazide, towards compound C of Figure 2.1. 25  2.2.3 Outcomes of the Staudinger Reaction with the N-Mesityl [NPN*] Frameworks  Although it is typical for iminophosphoranes to form at room temperature from phosphazides with the evolution of dinitrogen, slow reaction rates were observed for the phosphazide intermediates en route to the targeted compounds of Figure 2.1.94,95  Due to the 4-membered transition state during the Staudinger reaction, as shown in Scheme 2.1, excessive steric bulk can hinder the elimination of N2 and trap the phosphazide.94  Deng and Xiao found that the treatment of an NPN-type ligand framework of similar bulk to [mesNPN*]H2 with the also bulky 1-azidoadamantane showed no reactivity, which they attributed to steric hindrance.91  We observed that reactions with the more sterically hindered 2,6-dimethylphenylazide resulted in a very slow formation of the phosphazide with [mesNPN*]H2, and no conversion to the iminophosphorane with [mesNiPrPN*]H2.  Literature examples of tridentate ligands with iminophosphorane functionality in the terminal positions readily undergo the entire Staudinger reaction at room temperature.52,69  In addition to steric factors that can impede the 4-membered transition state necessary for iminophosphorane production, trapping of the intermediate phosphazide is also favoured as electron density increases on the phosphorus atom.94  Reactions of the azides with the more electron rich phosphine of [mesNiPrPN*]H2 led to faster formation of the phosphazide species, but poor conversion to the iminophosphorane, unfortunately. 2.3 Synthesis of the Iminophosphorane-Containing [NNN]H2 Ligand 2.3.1 Redesign of Targeted Iminophosphorane Ligand  As described in Section 2.2.3, the bulky N-mesityl containing backbone of [mesNPN*]H2 and [mesNiPrPN*]H2 causes a slow reaction rate with aryl azides, and apparently hinders N2 26  elimination from the phosphazide intermediates.  While the redesign of the targeted tridentate ligand still needs to incorporate two amido donors, and an internal iminophosphorane unit, the logical step is to scale back steric bulk on the amido N-aryl substituents.  As well, avoiding the bulky isopropyl group on the phosphine should favour N2 elimination from the putative phosphazide.94  Therefore, the 4-isopropylphenyl substituted iminophosphorane was chosen as the target to limit steric congestion, while additionally having the benefit of being derived from the simple to purify 4-isopropylphenylazide.  The redesigned ligand, [NNN]H2, is shown in Figure 2.4.  Figure 2.4:  Redesign of ligand framework [NNN]H2 in order to favour iminophosphorane formation during Staudinger reaction. 2.3.2 Synthesis of N-Tolyl Substituted o-Phenylene [NPN*] Framework  The iminophosphorane-containing [NNN]H2 ligand was synthesized from the Staudinger reaction of 4-isopropylphenylazide with [tolylNPN*]H2.  A synthetic procedure for preparing 27  [tolylNPN*]H2 was originally discovered by Prof. Y. Ohki, while working with the Fryzuk group, and further optimized and studied by Dr. Fiona Hess.82  This route is outlined in Scheme 2.4.  Scheme 2.4:  Synthetic route to [tolylNPN*]H2.82  The preparation of [tolylNPN*]H2 shown in Scheme 2.4 has several advantages over the synthetic method for the N-mesityl containing [mesNPN*]H2 framework, in Scheme 2.2.  The secondary amine, di-p-tolylamine, is commercially available, whereas p-tolyl-mesitylamine is synthesized through an aryl amination reaction.32,82,96  As shown in the first step of Scheme 2.4, directed ortho-lithiation is achieved by the addition of two equivalents of n-BuLi in the presence of TMEDA, which both solubilizes the lithium-diarylamide intermediate and increases the basicity of n-BuLi by breaking up alkyllithium aggregates.82,97,98  In contrast, ortho-lithiation of 28  p-tolyl-mesitylamine is carried out through lithium-halogen exchange.32  This requires an additional step in the synthesis before lithiation, that is, ortho-bromination of the secondary arylamine by the use of N-bromosuccinimide (NBS).  It is worth noting that the metathesis reaction of Cl2PPh with the dilithium salts in both Scheme 2.2 and Scheme 2.4 must be performed with care, as P-N bond formation occurs and leads to unwanted side-products.82  A slow addition of a diluted solution of the dichlorophosphine reagent to the cold dilithium salt helps lower the ratio of side-product formed, but its formation cannot be avoided entirely.  However, purification of the intended P-C bound product is possible by precipitation and washing with hexanes. 2.3.3 Staudinger Reaction of the N-Tolyl [NPN*] Framework  Unlike the bulkier N-mesityl containing frameworks [mesNPN*]H2 and [mesNiPrPN*]H2, which proved difficult to form iminophosphorane compounds upon addition of aryl azide reagents as described in Section 2.2.2, [tolylNPN*]H2 readily undergoes clean iminophosphorane formation via the Staudinger reaction at room temperature.  The synthesis of this new [NNN]H2 ligand, 2.1, is shown in Scheme 2.5. 29   Scheme 2.5:  Staudinger reaction to produce 2.1.  When monitored by 31P{1H} NMR spectroscopy in C6D6, over half of the material is converted to the phosphazide intermediate with a signal at δ 34.8 in the first 20 minutes, with very minor conversion to the iminophosphorane product as evidenced by a signal at δ 14.2.  Leaving the reaction to stir overnight in toluene or benzene affords full conversion to 2.1, which was isolated in an 82% yield.  The 31P{1H} NMR spectrum of 2.1 in C6D6 shows a singlet at δ 14.2 representing the phosphorane centre, which is a downfield shift of over 40 ppm compared to the starting phosphine in [tolylNPN*]H2.  The 1H NMR spectrum of 2.1 in C6D6 is shown in Figure 2.5. 30   Figure 2.5:  1H NMR spectrum (400 MHz) of 2.1 in C6D6.  Residual solvent signals are denoted by *.  From the 1H NMR spectrum of 2.1 in C6D6 it was determined that the compound is Cs symmetric in solution, as it contains a mirror plane.  There is one doublet for both sets of isopropyl-CH3 nuclei at δ 1.19, and one set of resonances for each pair of aryl-CH3 nuclei at δ 1.93 and 2.04.  The amine protons produce a singlet that is downfield shifted at δ 9.79, from the value of δ 5.98 in the starting material [tolylNPN*]H2.32  This chemical shift is consistent with literature examples of multidentate ligands that contain both a secondary amine and iminophosphorane functionality.52,54,68  Solid-state structures of this class of compounds in the 31  literature show hydrogen-bonding interactions between the iminophosphorane lone pair and amine proton, which likely leads to the observed chemical shift.52  An enamine-iminophosphorane ligand system used by Fryzuk, Masuda, and co-workers, in Figure 2.6, has shown this hydrogen bonding interaction in the solid-state, which stabilizes the enamine tautomer.62  The downfield 1H NMR shift of the amine protons in 2.1 is characteristic of this interaction.  Figure 2.6 visualizes the hydrogen bonding expected in compound 2.1, in comparison to the enamine-iminophosphorane ligand from literature.62  Figure 2.6:  Hydrogen bonding between amine N-H and iminophosphorane N-atom in compound 2.1 (left), and an enamine-iminophosphorane ligand from literature (right).62  Although crystals of 2.1 suitable for X-ray diffraction studies were not obtained, the presence of an iminophosphorane, not phosphazide, functionality was confirmed by both EI-MS and elemental analysis.  The EI-MS data indicates the parent [M]+ ion at m/z = 633, with a signal at m/z = 541 representing [M - tolyl]+, and another signal at m/z = 527 corresponding to [M - N-tolyl]+, both with the iminophosphorane still intact.  Unfortunately, infrared spectroscopy was not beneficial for identifying the P=N iminophosphorane bond of 2.1 when comparing the 32  appropriate spectral range (1000-1200 cm-1) to the precursor [tolylNPN*]H2, due to the number of additional signals in 2.1.57 2.4 Conclusion  A series of dianionic, tridentate ligands containing an internal iminophosphorane donor were designed as an adaptation from previously studied ligand sets [mesNPN*]H2 and [mesNiPrPN*]H2 within the Fryzuk group.32,35  Slow reaction rates were found for iminophosphorane installation via the Staudinger reaction, for both the phosphazide formation step and iminophosphorane production.  It was determined that steric bulk was hindering both steps of the reaction, consequently ligand redesign was undertaken.  A similar diamine o-phenylene scaffold [tolylNPN*]H2 was used, with reduced bulk on the amine aryl groups.  A triaryl-substituted phosphine was chosen due to lower electron density than an isopropyl-substituted phosphine, to favour N2 elimination from the phosphazide intermediate.  The less sterically hindered azide 4-isopropylphenylazide was chosen, as faster reaction rates were observed in its initial studies with [mesNPN*]H2 and [mesNiPrPN*]H2.  The less bulky [tolylNPN*]H2 framework and azide readily formed the iminophosphorane functionality to produce a novel tridentate, potentially dianionic ligand [NNN]H2 (2.1).   33  3 Zirconium Complexes of Iminophosphorane-Containing  [NNN] Ligand 2.1 3.1 Introduction  The activation of dinitrogen by reduced zirconium complexes is an ongoing research focus within the Fryzuk group.24,28-30,33,82  Typically this is achieved by the reaction of zirconium halide complexes with alkali metal reducing agents (KC8) as shown in Scheme 3.1 with the [NPN*] ligand framework.33  A key question for us was to try to ascertain the effect on dinitrogen activation under these conditions of changing the phosphine of [NPN*] to an iminophosphorane.  Accordingly, the synthesis of the zirconium dichloride complex of the iminophosphorane [NNN] system and study of its reduction properties are outlined in this chapter.  In addition, steric parameters (G value, %Vbur) of [NNN]ZrX2 systems have been calculated from XRD data to compare the effect of installing an iminophosphorane donor to previously studied [NPN] zirconium complexes.  This allows for more extensive discussion of iminophosphorane employment in ligand design.  Scheme 3.1:  Reduction of a zirconium halide complex with KC8 to activate N2 in a side-on manner by the Fryzuk group, adapted from literature.33 34   As there is much comparative discussion between compounds with the [NNN] framework and several [NPN] ligand backbones, please refer to Figure 3.1 for naming conventions used in this chapter.  Note that in general, an asterisk on [NPN*] denotes an o-phenylene backbone, and the prefix refers to the substitution on the amido groups.  Figure 3.1:  Naming scheme for [NPN*] ligand types. 3.2 Synthesis of Zr[NNN] Complexes 3.2.1 Amido and Halide Zr[NNN] Complexes  Zirconium complexes of tri- and tetradentate diamido-containing frameworks can be obtained from either salt metathesis or protonolysis reactions.32,82-84,99,100  However, the analogous o-phenylene [tolylNPN] framework was found to undergo bis-substitution when it was allowed to react as a dilithio-salt with the zirconium precursor ZrCl4(THF)2.82  Due to concerns 35  of similar reactivity with the [NNN] system, and the prior isolation of 2.1 as a protonated species, protonolysis routes to zirconium-[NNN] complexes were pursued.  The neutral protonated ligand 2.1 readily undergoes a reaction with Zr(NMe2)4 at room temperature in toluene to form the yellow diamido complex 3.1 as shown in Scheme 3.2.  The 31P{1H} NMR spectrum of 3.1 displays a singlet at δ 25.3 in C6D6, compared to a shift of δ -10.2 for the analogous complex [tolylNPN]Zr(NMe2)2.82  Other [NPN*]Zr(NMe2)2-type complexes with mesityl- or p-isopropylphenyl-substituted amido groups also have 31P{1H} chemical shifts in the NMR spectra of δ -11.5 and -10.6, respectively.32,82  This indicates that the comparative downfield shift of over 30 ppm for 3.1 is the outlier due to the iminophosphorane functionality.  Scheme 3.2:  Protonolysis reaction of 2.1with Zr(NMe2)4 to form 3.1.  The 1H NMR spectrum for 3.1, shown in Figure 3.2, indicates that the complex is Cs symmetric in solution on the NMR timescale in C6D6.  The mirror plane of symmetry is apparent from one pair of tolyl-CH3 protons of the ligand backbone producing a singlet at δ 1.89, and the other producing a singlet at δ 2.20.  The methyl-CH3 protons of the isopropyl substituent produce a doublet at δ 1.02, coupled to the C-H proton that produces a characteristic septet pattern at δ 36  2.55.  The remaining protons of the ligand system are in aryl environments, making the 6.5-8.0 ppm range of the 1H NMR spectrum cluttered.  As such, most of the information of ligand symmetry and environment is deduced from the tolyl-CH3 and isopropyl-CH3 resonances, which are the main NMR handles of the [NNN] ligand system.  Also note the absence of the amine protons of the precursor 2.1, which have a distinctive downfield shift of δ 9.79.  The spectroscopic assignments made above provide the basis for all subsequent evaluation of [NNN]ZrX2 complexes.  Figure 3.2:  1H NMR spectrum of 3.1 at 400 MHz in C6D6.  Residual solvent signals and silicone grease are denoted by *. 37   The N-CH3 protons of both dimethylamido ligands of 3.1 produce one singlet at δ 2.68 in C6D6.  This contrasts with the previously studied o-phenylene [NPN*]Zr(NMe2)2-type complexes, which display two distinct NMe2 environments in their 1H and 13C NMR spectra.32,82  Although 3.1 likely exists in a trigonal bipyramidal geometry similar to the [NPN*]Zr(NMe2)2 analogues, a fast exchange of axial and equatorial NMe2 groups on the NMR timescale leads to the observed coalescence of the dimethylamido signals in the 1H NMR spectrum and broadened resonance at δ 41.7 (N-CH3) in the 13C NMR spectrum in C6D6.  This indicates that the [NNN] ligand affects the properties of an otherwise similar complex, compared to the [NPN*] ligands.  The diamido compound 3.1 was synthesized as a precursor en route to the targeted zirconium dichloride complex, as the Fryzuk group has had success with treatment of zirconium amides with excess Me3SiCl to generate the corresponding [NPN]ZrCl2 complexes.32,82-84  However, the addition of Me3SiCl to 3.1 in benzene resulted in a mixture of two phosphorus-containing species, as evidenced by 31P{1H} NMR spectroscopy.  A direct route to the dichloride complex 3.2 was discovered through protonolysis of 2.1 with Zr(NMe2)2Cl2(DME) at room temperature, as shown in Scheme 3.3.  It is of note that reaction of the bulkier [mesNPN*]H2 ligand with Zr(NMe2)2Cl2(DME) only led to partial product formation in THF, and no reaction in toluene.82 38   Scheme 3.3:  Reaction of 2.1 with Zr(NMe2)2Cl2(DME) to produce 3.2.  When the protonolysis reaction shown in Scheme 3.3 is performed in non-coordinating solvents such as benzene or toluene, a coordinated dimethylamine group is observed by 1H NMR spectroscopy.  To obtain 3.2 in a pure manner, the reaction was performed in THF, the solvent and dimethylamine byproduct were removed under reduced pressure, and the product was stirred again in excess THF for 30 minutes before concentration in vacuo.  Coordination of dimethylamine was also observed for the analogous [tolylNPN*]ZrCl2 and [iPrNPN*]ZrCl2 systems, where the former was characterized by XRD studies.82  Replacing the dimethylamine 39  donor with THF in these [NPN*]ZrCl2 compounds required heating to 60 oC for full conversion, as up to two weeks were needed for quantitative substitution at room temperature.82  Compound 3.2 produces one signal in the 31P{1H} NMR spectrum at δ 31.7 in C6D6, which is a downfield shift of 6 ppm compared to 3.1.  The 1H NMR signals for the ligand backbone of 3.2 are largely similar to 3.1 other than minor chemical shift changes, which indicates that 3.2 has a mirror plane of symmetry in solution on the NMR timescale, even though the compound is 6-coordinate with a THF donor.  Protons on the ligated THF can be observed as broadened signals in the 1H NMR spectrum, with a minor chemical shift deviation from free THF.  The analogous complexes [tolylNPN*]ZrCl2(THF) and [iPrNPN*]ZrCl2(THF) display similar solution-state symmetry to 3.2.82  Crystals of 3.2 suitable for XRD studies were grown from a 1:1 mixture of THF and hexanes at -35 oC.  The ORTEP representation of 3.2 is shown in Figure 3.3, along with selected bond lengths and angles in Table 3.1. 40   Figure 3.3:  ORTEP representation of the solid state structure of 3.2, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms and co-crystallized THF are omitted for clarity.  Table 3.1:  Selected bond lengths (Å) and angles (deg) for 3.2. Parameter (Å)  Parameter (o) Zr1 - N01 2.1267(13)  N01 - Zr1 - N02 95.49(5) Zr1 - N02 2.1609(13)  N01 - Zr1 - N03 85.74(5) Zr1 - N03 2.2155(13)  N02 - Zr1 - N03 82.12(5) Zr1 - Cl01 2.4741(5)  Cl02 - Zr1 - N03 172.04(3) Zr1 - Cl02 2.4738(6)    Zr1 - O01 2.3035(13)    P01 - N03 1.6319(13)     41   As seen in the solid state molecular structure of 3.2, the complex has a distorted octahedral geometry with the THF donor in an equatorial position.  The analogous complexes [tolylNPN*]ZrCl2(THF) and [iPrNPN*]ZrCl2(THF) have the same asymmetric geometry in the solid state.82  Similarly for these systems, the solution state NMR spectra show symmetric complexes with a mirror plane of symmetry through the ligand backbone.82  There is likely a fast isomerization process of the THF donor in solution on the NMR timescale, which leads to the observed symmetry.  The compound [iPrNPN*]ZrCl2(THF) was previously studied by NMR spectroscopy at temperatures as low as -60 oC, and no changes in symmetry were observed.82  Compound 3.2 has zirconium-amido bond lengths of 2.1267(13) and 2.1609(13) Å for Zr1-N01 and Zr1-N02, respectively.  These are within reported ranges but longer than those found in the comparative [NPN*]ZrCl2-type complexes, which can be as short as 2.066(5) Å for [mesNPN*]ZrCl2 (note that [mesNPN*]ZrCl2 does not have a THF ligand).32,82  The zirconium-iminophosphorane Zr1-N03 bond length of 2.2155(13) Å is significantly shorter than the corresponding Zr-P bond lengths of the [NPN*]ZrCl2 complexes, which are typically ~2.7 Å.  Of particular interest are the internal ligand bite angles, as the addition of the iminophosphorane functionality leads to 6-membered metallacycles compared to the 5-membered metallacycles of [NPN*]ZrCl2 systems.  Compound 3.2 has an N01-Zr1-N02 angle of 95.49(5) o, with amido-iminophosphorane angles of 85.74(5)o and 82.12(5)o for N01-Zr1-N03 and N02-Zr1-N03.  The previously studied octahedral compounds [tolylNPN*]ZrCl2(THF) and [iPrNPN*]ZrCl2(THF) have internal amido angles (N-Zr-N') of 91.32(10) o and 92.93(7) o, while the trigonal bipyramidal complex [mesNPN*]ZrCl2 has a corresponding angle of 113.93(9) o.32,82  This indicates that the o-phenylene linker of the [NPN*] systems is not restricting the internal amido angles relative to [NNN].  However, the amido-iminophosphorane angles of 3.2 are substantially wider than the 42  amido-phosphine angles in any of the [NPN*]ZrCl2-type complexes.  In all three of the studied [NPN*]ZrCl2 systems, the corresponding N01-Zr1-P01 angles fall between 67.70(7) o and 73.94(7) o, which is 10-15o sharper than those of 3.2.32,82  This results in a geometric distortion of the amido ligands away from the equatorial plane in the [NPN*]ZrCl2 complexes, relative to 3.2.  As mentioned in the introduction Section 3.1, the dichloride complex 3.2 was a target for reduction chemistry with the goal of activating dinitrogen.  The reduction properties of this compound will be discussed later in this chapter in Section 3.3. 3.2.2 Zr[NNN] Organometallic Complexes  The dichloride compound 3.2 was reacted with two equivalents of benzylmagnesium chloride to afford the dialkyl complex 3.3, as outlined in Scheme 3.4.  The product was found to be moderately light sensitive, therefore all manipulations of 3.3 were shielded from light with foil whenever possible.  Scheme 3.4:  Reaction of 3.2 with benzylmagnesium chloride to produce the dialkyl complex 3.3. 43   Compound 3.3 produces one singlet at δ 19.7 in the 31P{1H} NMR spectrum in C6D6.  The 1H NMR data indicates that 3.3 has a mirror plane of symmetry through the ligand backbone in the solution state on the NMR timescale, similar to the zirconium amido and chloride complexes previously discussed.  The methylene protons of the benzyl ligands produce one singlet at δ 2.23 in C6D6, which demonstrates the fast exchange of the axial and equatorial benzyl groups on the NMR timescale, similar to the equivalent dimethylamido groups of compound 3.1.  The Zr-methylene carbon signals could not be directly observed in the 13C NMR spectrum in C6D6, but correlated to a signal at δ 74.0 from the 1H-13C HSQC two-dimensional NMR experiment.  An analogous dialkyl zirconium complex, [mesNPN*]Zr(CH3)2, had independent methyl environments in the solution state, indicating that the [NNN] framework influences this fluxional behaviour.32  Crystals of 3.3 suitable for XRD studies were grown from an ether solution at -35 oC.  The ORTEP representation of 3.3 is shown in Figure 3.4, and a summary of selected bond lengths and angles is presented in Table 3.2. 44   Figure 3.4:  ORTEP representation of the solid state structure of 3.3, thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity.  Table 3.2:  Selected bond lengths (Å) and angles (deg) for 3.3. Parameter (Å)  Parameter (o) Zr1 - N01 2.155(3)  N01 - Zr1 - N02 135.26(10) Zr1 - N02 2.174(3)  N01 - Zr1 - N03 77.07(10) Zr1 - N03 2.239(3)  N02 - Zr1 - N03 79.15(9) Zr1 - C44 2.328(4)  N01 - Zr1 - C51 102.45(11) Zr1 - C45 2.750(3)  N02 - Zr1 - C51 118.16(12) Zr1 - C51 2.266(3)  Zr1 - C44 - C45 90.2(2) P01 - N03 1.607(3)    45   In the solid state, compound 3.3 exists in a distorted trigonal bipyramidal geometry with the equatorial benzyl ligand bound η1 and the axial benzyl ligand bound η2 to zirconium.  The sharp Zr1-C44-C45 bond angle of 90.2(2)o and Zr1-C45 distance of 2.750(3) are characteristic of the η2-interaction.101-103  The observed η2-interaction in the solid state differs from the solution state NMR data, where both benzyl ligands are equivalent on the NMR timescale.  A study of a zirconium tribenzyl complex by the Arnold group determined that crystal packing forces may be enough to lead to an η2-interaction of a benzyl ligand in the solid state.104  As both benzyl groups of 3.3 are equivalent in solution on the NMR timescale, not even differentiated as equatorial and axial independently, this observed η2-interaction is likely a result of crystal packing.  A representation of the geometry of 3.3 in the solid state is shown in Figure 3.5.  Figure 3.5:  Representation of the η2-interaction of the axial benzyl ligand of 3.3 in the solid state.  The metal-ligand bond lengths of compound 3.3 are nearly identical to those found in the dichloride complex 3.2.  As well, the iminophosphorane P01-N03 bond distance of 1.607(3) Å is only slightly shorter than the corresponding distance of 1.6319(13) Å found in 3.2.  The major observed differences between the two compounds are found by examining the internal ligand 46  bite angles.  This is due to 3.2 having an octahedral geometry because of the additional THF ligand, while 3.3 exists in a distorted trigonal bipyramidal geometry.  The 135.26(10)o N01-Zr1-N02 angle of 3.3 is much wider than the corresponding 95.49(5)o angle of the octahedral 3.2.  In addition, the amido-iminophosphorane angles N01-Zr1-N03 and N02-Zr1-N03 of 77.07(10)o and 79.15(9)o in 3.3 are notably sharper than the 85.74(5)o and 82.12(5)o angles of 3.2.  This comparison indicates that even with a rigid o-phenylene backbone, the [NNN] framework is quite flexible to accommodate different metal geometries.  When compared to the even more rigid [mesNPN*] framework in the trigonal bipyramidal compound [mesNPN*]ZrCl2, the N01-Zr1-N02 angle of 113.96(9)o is much sharper than that found in 3.3.32  An alternate route to 3.3 of adding two equivalents of benzyl potassium to 3.2 in toluene was attempted, as benzyl potassium is convenient to handle experimentally.  However, complete conversion to the dibenzyl complex was not achieved at room temperature, as a second signal was observed in the 31P{1H} spectrum in proteo-toluene at δ 21.5, which is assigned as the mono-substituted complex.  Decomposition occurred before further conversion to the dialkyl product, hence the Grignard route of Scheme 3.4 remains the preferred synthetic method to produce 3.3.  In an attempt to synthesize a zirconium dimethyl complex, analogous to the previously synthesized [mesNPN*]ZrMe2, two equivalents of methyl lithium were added to 3.2 in THF at -78 oC.32  Although there is one major signal in the 31P{1H} NMR spectrum of the reaction mixture at δ 20.2 in C6D6, there are several minor signals that together represent a substantial portion of material (~40%).  The substance was also prone to decomposition in light and we were unable to purify the material further.  The reaction of two equivalents of Li(CH2SiMe3) with 3.2 in THF at 47  -78 oC led to a mixture of products, and this route towards a trimethylsilylmethylene-zirconium complex was abandoned.  Other Grignard reagents MeMgBr, iPrMgBr, and tBuMgCl were also employed in attempts to synthesize the corresponding dialkyl zirconium complexes.  Analogous reaction conditions to those used for the synthesis of 3.3 were applied, but in all cases multiple species that produced signals in their respective 31P{1H} NMR spectra from δ 20-30 were present.  The reaction of 3.2 with benzyl Grignard remains the only synthetic route to a dialkyl zirconium complex of the [NNN] system. 3.2.3 Reactivity of Zr[NNN] Dichloride and Dibenzyl Complexes  The dibenzyl compound 3.3 is significantly less stable than the dichloride complex 3.2, displaying both light and thermal sensitivity; for example, heating to 60 oC overnight in benzene resulted in nearly complete decomposition to multiple new species as observed by 31P{1H} NMR spectroscopy.  The previously studied dimethyl compound [mesNPN*]ZrMe2 was similarly light and thermally sensitive.32  However, both compounds 3.2 and 3.3 are stable for months when stored as solids at -35 oC under a dry N2 atmosphere in the dark.  Zirconium hydride complexes were also synthetic targets, and attempts to synthesize a dihydride species were made from both the zirconium chloride and benzyl systems.  Several salt metathesis reactions of hydride reagents with 3.2 were attempted, and are briefly summarized in this paragraph.  No reaction was observed between KH and 3.2 in THF at room temperature over the course of days, and addition of 18-crown-6 ether did not lead to hydride formation.  When 3.2 was treated with two equivalents of KHBEt3 in THF, partial conversion to a new species was observed by 31P{1H} NMR spectroscopy, however quantitative conversion was never achieved.  48  As well, there was an absence of Zr-H resonances in the 1H NMR spectrum of the reaction mixture.  Reaction of 3.2 with excess NaBH4 over several days in THF led to a mixture of two inseparable species.  Based on 1H NMR spectroscopy, the lack of observable Zr-H resonances in the δ -10 to +10 region indicated that the formation of zirconium hydrides had failed.  Zirconium hydride complexes can also be formed by hydrogenolysis of zirconium alkyl species.105-107  Hydrogenolysis of a C6D6 solution of 3.3 was attempted in a flame-sealed NMR tube with 4 atm H2(g).  After one week at room temperature the dibenzyl compound had been quantitatively consumed to form several new species, as assessed by 31P{1H} NMR spectroscopy, and no signals characteristic of Zr-H in the 1H NMR spectrum from δ -10 to +10 were observed.  The dibenzyl species is likely to have thermally decomposed over this time, without any definitive interaction with H2.  Separately, the reaction of n-BuSiH3 with 3.3 in benzene led to the formation of multiple new species after 4 days at room temperature, as observed by 31P{1H} NMR spectroscopy.  As before, no signals characteristic of Zr-H species were observed in the 1H NMR spectrum, and this potential route towards hydride complexes was abandoned.  The benzyl ligands of 3.3 were found to be labile towards protonolysis, as addition of aniline to a benzene solution of 3.3 led to production of the bis(phenylamido) species [NNN]Zr(NHPh)2 and toluene, as observed by NMR spectroscopy.  Since the bis(dimethylamido) compound 3.1 was already isolated more directly, as described earlier in Scheme 3.2, this protonolysis route to alternate amido complexes was not further investigated. 49  3.3 Reduction Studies of [NNN]ZrCl2 3.3.1 Background  As mentioned in the introduction Section 3.1, the reduction of early metal halide compounds to form activated dinitrogen complexes is a primary interest of the Fryzuk group.  In addition to the zirconium dinitrogen complex supported by the [mesNPN*] framework, in Scheme 3.1, both the [tolylNPN*] and [iPrNPN*] ligands allowed for formation of side-on dinitrogen complexes of zirconium under similar reaction conditions.33,82  It was intended that the small, but fundamental, change from [tolylNPN*] to [NNN] would lead to similar N2 activation, with distinctive further reactivity towards small molecules (i.e. H2, CO).  The iminophosphorane functionality has shown stability towards N2 activation through metal reduction reactions, as displayed by the reduction of an iron bromide complex with a tridentate ligand framework that contains an iminophosphorane donor illustrated in Scheme 3.5.62  Scheme 3.5:  Reduction of an iron halide complex with an iminophosphorane-containing ligand, to produce an end-on dinitrogen complex, adapted from literature.62  Note that Dipp = 2,6-diisopropylphenyl. 50  3.3.2 Reduction with KC8 and Na(Hg)  The zirconium side-on bridging N2 complexes of [mesNPN*], [tolylNPN*], and [iPrNPN*] frameworks were previously synthesized using similar experimental conditions from the [NPN*]ZrCl2 complexes and 2.2 equivalents of KC8.33,82  The procedure involved pressurizing a thick-walled Teflon-sealable reaction vessel containing the reagents and solvent (THF) at -196 oC to 1 atm of N2(g), and warming to room temperature, resulting in a pressure of ~4 atm N2(g).  Using the described conditions for the treatment of 3.2 with KC8, the resulting reaction mixture contained a major species that produces a signal at δ -8.5 in the 31P{1H} NMR spectrum.  Conveniently, similar results were obtained by simply adding room temperature THF to a mixture of 3.2 and 2.2 equivalents of KC8 under 1 atm N2(g) in the glove box.  Using an alternative reducing agent, sodium amalgam (0.5% sodium in mercury, Na(Hg)), the same species was observed when 2.2 equivalents of Na(Hg) were added to 3.2 in THF at room temperature under 1 atm N2(g).  The 31P{1H} NMR spectrum in C6D6 of the product of the reaction of 3.2 with 2.2 equivalents of KC8 at room temperature in THF is shown in Figure 3.6.   51   Figure 3.6:  31P{1H} NMR spectrum at 121 MHz of the reduction product of 3.2 with KC8, acquired in C6D6.  Reduction reactions of early metal complexes are often very sensitive to experimental conditions, as highlighted in Dr. Hess' work with the [tolylNPN] and [iPrNPN*] zirconium dinitrogen systems.82  Changes in reaction concentration, either too concentrated or dilute, led to increased side product formation.82  It was surprising that similar results could be obtained by reducing 3.2 with either KC8 or Na(Hg), and especially using a variety of solvent concentrations, reaction temperatures (controlled low temperature up to room temperature), and pressures of N2(g).  After many unsuccessful attempts to grow and diffract crystalline samples, we were concerned that reduction of the phosphorane centre may occur rather than reduction of N2.  Reduction of the iminophosphorane centre to a phosphine would potentially lead to the production of the imido complex [tolylNPN*]ZrN(4-iPrPhenyl), 3.4, as illustrated in Scheme 3.6.  Due to the number of aryl protons within the ligand backbone, the isopropyl-CH3 group provides a characteristic 1H NMR handle in the [NNN] ligand.  In the 1H NMR spectra of the previously discussed zirconium amido, chloride, and benzyl complexes, these isopropyl-CH3 protons 52  produce a doublet at δ 1.01-1.02 in C6D6; they are essentially unchanged in electronic environment regardless of the substituents on zirconium.  In the reduction product 3.4, the same protons experience a small downfield shift in the 1H NMR spectrum, to δ 1.27 in C6D6.  Scheme 3.6:  Proposed reduction reaction of 3.2 with KC8 to cleave iminophosphorane bond.  The 31P{1H} NMR chemical shift of 3.4 at δ -8.5 in C6D6 is upfield of any previously observed zirconium compound of the [NNN] ligand, which are from δ 20-30.  Additionally, the previously studied bis amido compound [tolylNPN*]Zr(NMe2)2 produces a similarly shifted signal at δ -10.6 in the 31P{1H} NMR spectrum in C6D6.82  Note that the [tolylNPN*] framework is identical to the ligand backbone of 3.4 after cleavage of the iminophosphorane.  Compound 3.4 may exist in the dimeric form, however, EI-MS did not confirm presence of the dimeric species.  With concerns of ligand involvement during reduction chemistry to potentially produce 3.4, and our inability to obtain a solid state structure of the product, we designed an experiment to remove the resulting ligand framework from the metal complex for NMR analysis.  By adding the proton source trimethylammonium chloride to 3.4, either the intact [NNN]H2 free ligand 2.1 53  or cleaved [tolylNPN*]H2 framework would be liberated from zirconium.  Both of these species are easily identifiable by NMR spectroscopy.  As a control experiment, excess trimethylammonium chloride was added to 3.2 in THF.  The only phosphorus-containing product in the 31P{1H} NMR spectrum was the free ligand, 2.1, indicating that the iminophosphorane functionality can survive the reaction conditions.  When excess trimethylammonium chloride was added to 3.4 in THF, several phosphorus-containing species were present as evidenced by 31P{1H} NMR spectroscopy, however there was no signal corresponding to 2.1.  The major signal in the 31P{1H} NMR spectrum is produced by [tolylNPN*]H2 at δ -29.4, which is corroborated by the 1H NMR experiment.  Additionally, 4-isopropylaniline is identifiable in the 1H NMR spectrum.  We have tentatively assigned the other phosphorus-containing byproducts as primary (δ -143.7) and secondary (δ -56.1, -67.5) phosphines due to the upfield chemical shifts and coupling to 1H nuclei in the non-decoupled 31P NMR spectrum.108  An outline of this experiment is presented in Scheme 3.7, and the 31P{1H} NMR spectrum in C6D6 of the reaction of trimethylammonium chloride with 3.4 is shown in Figure 3.7.  The 1H NMR spectra comparing the products of the reaction of trimethylammonium chloride and 3.4 to [tolylNPN*]H2 and 4-isopropylaniline is shown in Figure 3.8. 54   Scheme 3.7:  Summary of protonation experiments on 3.2 with trimethylammonium chloride, with and without the reducing agent KC8. 55   Figure 3.7:  31P{1H} NMR spectrum at 121 MHz in C6D6 of the products of the reaction of 3.4 with excess trimethylammonium chloride.  Figure 3.8:  1H NMR spectra at 300 MHz in C6D6 (*) of [tolylNPN*]H2 (top), the reaction of 3.4 with excess trimethylammonium chloride (middle), and 4-isopropylaniline (bottom). 56  3.3.3 Summary  The reduction of 3.2 with either KC8 or Na(Hg) leads to the cleavage of the iminophosphorane bond within the [NNN] framework.  The reaction was quite selective for a single product, as shown by the 31P{1H} NMR spectrum in Figure 3.6, and we propose that the imido group migrates to the zirconium centre, while the ligand framework acts as the phosphine-functionalized [tolylNPN*] ligand.  This is corroborated by the consistent integration values in the 1H NMR spectrum between the isopropyl-CH3 protons of the imido ligand, and the tolyl-CH3 protons of the [tolylNPN*] ligand.  Without XRD analysis, the proposed structure 3.4 in Scheme 3.6 is our hypothesis of the reduction product.  It was unanticipated that the reduction of 3.2 leads to ligand decomposition, while the reduction of the analogous zirconium complexes of [mesNPN*], [tolylNPN*], and [iPrNPN*] all produce dinitrogen compounds.  The following section compares the DFT analysis of the frontier orbitals in 3.2 and [tolylNPN*]ZrCl2(THF). 3.4 DFT Analysis of [NNN]ZrCl2(THF) and [tolylNPN*]ZrCl2(THF)  The density functional theory (DFT) calculations in this section were performed by Dr. Aleks Zydor and Mr. Fraser Pick.  DFT Calculations were carried out using the Gaussian 09 package.109  Calculations were performed at the B3PW91 level of theory, using triple-ζ potential (TZP) basis sets and effective core potentials on Zr.110  We are interested in examining what contributions the iminophosphorane group has to the HOMO and LUMO of 3.2, to gain insight into the reduction process that cleaves the phosphorane to generate the putative Zr=NAr unit by reaction with KC8 or Na(Hg).  The frontier 57  orbitals of 3.2 can then be compared to the HOMO and LUMO of [tolylNPN*]ZrCl2(THF), which cleaves zirconium-halide bonds through reaction with KC8 and then reduces dinitrogen.82  Both 3.2 and [tolylNPN*]ZrCl2(THF) were geometry-optimized based on the solid state molecular structures as an initial geometry.  An overlay of the solid state geometry and optimized geometry of these compounds is presented in Figure 3.9.  These images show nearly identical ligand donor-atom positions, with the most deviation at the amido N-aryl groups.  Experimentally, in solution, these N-aryl groups freely rotate on the NMR timescale. 58   Figure 3.9:  Overlay of wire frame models of solid state structures (green) and geometry optimized calculations (red) of 3.2 and [tolylNPN*]ZrCl2(THF). 59   The HOMO and LUMO of 3.2 are presented in Figure 3.10.  In the HOMO, there is no contribution of the iminophosphorane (P atom is yellow, N atoms are dark blue), nor does it contribute to the HOMO-1 orbital (not pictured).  The HOMO is mainly a metal-based orbital that is delocalized into one of the o-phenylene rings of the ligand backbone.  The LUMO of 3.2 shows an interaction between the zirconium dz2 orbital and the iminophosphorane nitrogen, with an interaction that is antibonding in character of the iminophosphorane P=N.  This supports the experimental behaviour of compound 3.2, where populating the LUMO with electron density by adding a reducing agent causes cleavage of the P=N bond.  Figure 3.10:  HOMO and LUMO of 3.2. 60   Similarly, the HOMO and LUMO of [tolylNPN*]ZrCl2(THF) are shown in Figure 3.11.  The HOMO of [tolylNPN*]ZrCl2(THF) is delocalized through the o-phenylene ligand, and there is also a σ-interaction between zirconium and the phosphorus donor atom.  The LUMO of [tolylNPN*]ZrCl2(THF) is based around a zirconium d-orbital, which shows antibonding character to a chloride ligand.  Experimentally, when reduced, [tolylNPN*]ZrCl2(THF) loses both chloride ligands and the [tolylNPN*] framework remains intact.  This behaviour is supported by the calculated LUMO. 61   Figure 3.11:  HOMO and LUMO of [tolylNPN*]ZrCl2(THF).  As shown by the LUMO of 3.2 in Figure 3.10, upon reduction, the complex distributes the extra electron density in a manner that weakens the iminophosphorane bond, regardless of reducing agent or conditions that are used experimentally.  This confirms that the iminophosphorane-containing [NNN] framework is a poor candidate for nitrogen activation on 62  zirconium, and may have fundamental stability issues for reduction chemistry across additional transition metals. 3.5 Steric Analysis of [NNN] Framework on Zirconium 3.5.1 Overview  One of the stated goals of developing the [NNN] system was to alter the internal ligand bite angles and therefore the geometry at the metal centre as compared to previously developed [NPN*] ligands.  The crystal structures of compounds 3.2 and 3.3 have been discussed in comparison to the o-phenylene [NPN*] frameworks with the typical metrics of bond lengths and angles, but using additional steric parameters can provide more insight to how these factors affect the other coordination sites at the metal centre.  Two steric parameters have been evaluated: the solid angle (G) and the buried volume (%Vbur).  A neutral donor substitution reaction on zirconium complexes is also presented, to compare experimental results to trends observed through the calculations.  All calculations in this section were performed by the author. 3.5.2 Solid Angle (G) Calculations of Zirconium [NNN] and [NPN*] Complexes  The G value has been developed by Guzei and Wendt as a means of quantifying the occupancy of the metal coordination sphere by each ligand.111  While other techniques such as the Tolman cone angle take into account sterics at individual donor atoms, the G value quantifies each ligand entirely, as well as the overlap between ligands on the same complex.111,112  This value has been used to evaluate ligand sterics for use in catalysis, as well their influence towards intra- or intermolecular reactivity at the metal centre.113-116 63   The G value can be conceptualized by placing a sphere of arbitrary radius around the metal centre (radius large enough to encapsulate the entire complex), and treating the metal centre as a source of light.  The shadow of each ligand is cast onto the sphere, and the percentage of that shadow relative to the total surface area of the sphere is the G value of that ligand.  The G value represents the shielding of a ligand on the metal centre, that is, the probability of blocking an incoming reagent from the metal centre.111  Guzei and Wendt have made the downloadable program Solid-G available for calculations of G values, which is able to accept coordinates of refined solid state structures.111  All calculations in this section were performed with Solid-G from experimentally determined solid state data gathered by the author, Dr. Erin MacLachlan, and Dr. Fiona Hess.32,82  The visualization output of Solid-G for compound 3.2 is shown in Figure 3.12, from four different angles.  The [NNN] ligand has a blue shadow, while the chloride ligands have green and yellow shadows, and finally a red shadow for THF.  The G value for the [NNN] ligand of 3.2 is determined to be 52.3%.  Similarly, the G values were calculated for the [NPN*] ligands of [tolylNPN*]ZrCl2(THF), [iPrNPN*]ZrCl2(THF), [mesNPN*]ZrCl2, and the [NNN] ligand of 3.3.  This information is summarized in Figure 3.13.  Note that the G value is output to two decimal places from Solid-G, and these summarized G values have been rounded to one decimal place. 64   Figure 3.12:  Solid-G generated images for 3.2.  65   Figure 3.13:  G values of [NNN] and [NPN*] ligands of zirconium complexes.  The most direct comparison between analogous complexes 3.2 and [tolylNPN*]ZrCl2(THF) shows that the iminophosphorane-containing [NNN] backbone has a G value over 5% greater than [tolylNPN*].  The addition of the aryl-substituted iminophosphorane group has a comparable affect on the G value to changing both of the N-aryl groups from p-tolyl to p-isopropyl on the [NPN*] system (comparing B to C).  Of course, the location of the steric increase is then localized to the terminal amido groups, away from other coordination sites at the metal centre, rather than at the central neutral donor of the ligand framework as in [NNN].  While there is another G value increase of 6% when moving from [NNN] and [iPrNPN*] to the [mesNPN*] backbone, a limitation of this technique is apparent.  The compound [mesNPN*]ZrCl2 is trigonal bipyramidal, rather than octahedral, as the previously discussed compounds have a THF ligand.  There is a significant increase in internal amido ligand bite angles of [mesNPN*]ZrCl2 (N-Zr-N is 113.96(9)o) compared to those of [tolylNPN*]ZrCl2(THF) 66  and [iPrNPN*]ZrCl2(THF) (92.93(7)o and 91.32(10)o, respectively).32,82  When examining the distorted trigonal bipyramidal compound 3.3, the G value of [NNN] increases by over 3% due to the same internal N-Zr-N amido bite angle increasing from 95.49(5)o to 135.26(10)o.  A visualization from Solid-G for 3.2 and 3.3 is presented in Figure 3.14, to show how the amido shadows wrap farther around the sphere with a broader internal ligand bite angle in 3.3.  Comparison of G values is therefore most appropriate with compounds of a similar coordination geometry.  Figure 3.14:  Solid-G generated images for 3.2 and 3.3. 3.5.3 Buried Volume (%Vbur) Calculations of Zirconium [NNN] and [NPN*] Complexes  While the G value simplifies the steric shielding of a three dimensional ligand onto a two dimensional surface, the buried volume (%Vbur) summarizes the volume occupied by a ligand as a percentage of the total volume of a sphere, at a specified radius from the metal centre.  The %Vbur value was developed by Cavallo and co-workers as a means of quantifying sterics of N-heterocyclic carbene ligands, as well as other common symmetric ligands such as 67  phosphines.117,118  The technique has since been used for evaluating asymmetric ligands, as well as more specific studies such as assessing catalyst behaviour.115,119,120  The %Vbur has been calculated from the web application SambVca, which was developed by Cavallo and co-workers.117  Coordinates determined experimentally from solid state data were used for all calculations with SambVca.  As all of the evaluated ligands are asymmetric in the solid state, a "dummy atom" had to be created in the solid state data in order to enter information to SambVca in a manner that would set the sphere's centre to the location of the zirconium atom.115  For example, a dummy atom of negligible occupancy was created as a C2 rotation of the ipso-carbon about the zirconium-nitrogen axis of the iminophosphorane, and the dummy atom was only allowed to interact with the nitrogen atom, as shown in Figure 3.15.  The location of the dummy atom was set through a series of bond-length fixing commands, as well as the requirement of belonging to the plane defined by the original atom and the two atoms that define the C2 axis.  Figure 3.15:  Example of dummy atom "D" creation for use in SambVca input files.  There is a significant difference in bond length between the zirconium-iminophosphorane bond, ~2.2 Å, and the zirconium-phosphine bonds of [NPN*] compounds, which are typically ~2.7 Å.32,82  The %Vbur is an interesting measurement, as it can give insight to the steric 68  hindrance of a ligand within any radius of sphere defined by the user.  By varying the radius value, the effect of the shorter Zr-N iminophosphorane bond was evaluated.  A simplified image overlaying a sphere at a radius between the two bond lengths is shown in Figure 3.16.  Figure 3.16:  Overlay of a sphere of radius ~2.5 Å in comparison to [NNN] and [tolylNPN*] frameworks, for %Vbur evaluation.  A comparison of the %Vbur over a radius from 2-5 Å for [NNN] and several [NPN] ligands on zirconium is shown in Figure 3.17.24,32,82  The silylamide-linked [NPNclassic] ligand is included, but note that this data is from the side-on bound dinitrogen dimer, as a solid state structure of the dichloride complex has not been acquired.  Although the %Vbur value of the same ligand may differ when changing complex geometry, the focus of these calculations is the trend within each ligand while altering the calculated sphere radius. 69   Figure 3.17:  %Vbur of [NNN] compared to [NPN] ligands on zirconium, at varying sphere radii for volume calculations.  As evident from the graph, the [NNN] framework is unique amongst those studied in that the %Vbur remains unchanged over a calculated radius range of 2.0-3.1 Å from the metal centre.  Comparatively, each of the other ligands is at a minimum %Vbur value at 2.0 Å (disregarding the long range drop off beyond 4 Å, while the sphere grows larger than the complex).  This is not surprising, as the zirconium-amido and zirconium-iminophosphorane bonds are nearly the same length, so the calculated sphere encapsulates the donor atoms simultaneously.  Conversely, the data for the [tolylNPN*] backbone, which is the closest analogue to [NNN], shows an increase in %Vbur from 2.6-2.8 Å as explained in Figure 3.16.  This is the radius when the calculated sphere is interacting with the phosphine donor of [tolylNPN*]. 70   The bulkiest ligand examined, [mesNPN*], has the largest %Vbur values as expected, but also shows the largest increase in %Vbur as radius increases.  Even with the bulky mesityl groups on the amido donor atoms, the %Vbur value is at a minimum near the metal centre, but increases significantly over [tolylNPN*] which does not have ortho-methyl groups.  The inclusion of the iminophosphorane functionality with its aryl group increases steric shielding away from the metal centre, as found by the G value calculations, its presence also vastly changes the steric environment near the metal centre compared to other o-phenylene and silylamide linked [NPN] frameworks.  This may be a strong factor in the observed solution state equivalence of dimethylamido and benzyl ligands on [NNN]ZrR2 complexes, whereas other [NPN] systems describe unique environments for amido and alkyl ligands.32,82 3.5.4 [NNN]ZrCl2(THF) vs. [tolylNPN*]ZrCl2(THF) Neutral Donor Exchange  With both the G value and %Vbur value indicating more steric hindrance for [NNN] compared to [tolylNPN*], a competition experiment for the exchange of 4-dimethylaminopyridine (DMAP) for THF on the zirconium complexes 3.2 and [tolylNPN*]ZrCl2(THF) was designed.  Based on the larger G value of [NNN], there should be less likelihood of the DMAP donor accessing the metal centre compared to the [tolylNPN*] complex.111  As well, %Vbur indicates continued steric hindrance towards the metal centre for [NNN], in addition to a larger volume occupied over [tolylNPN*].  Although it is uncertain which factor outweighs the other in this experiment, both steric parameters predict that [tolylNPN*]ZrCl2(THF) should undergo faster exchange with DMAP than 3.2.  Note that the rate of DMAP exchange is assumed to be controlled by accessibility to the metal centre, rather than any differences in Lewis acidity at zirconium between 3.2 and [tolylNPN*]ZrCl2(THF). 71   The DMAP adducts on zirconium of both ligand frameworks, [NNN] and [tolylNPN*], were independently synthesized and characterized as compounds 3.5 and 3.6.  The competition experiment, as outlined in Scheme 3.8, was then performed in duplicate in C6D6 and monitored by NMR spectroscopy.  A 1:1 C6D6 solution of 3.2 and [tolylNPN*]ZrCl2(THF) was analyzed by NMR spectroscopy before and 20 minutes after the addition of one equivalent of DMAP, which was prepared as a stock solution in C6D6.  Product ratios did not change between 20 minutes and 100 minutes after addition.  The 31P{1H} NMR spectrum for one of the experiments, before and after addition, is shown in Figure 3.18.  Note that 1H NMR spectroscopy was used for the integration values of aryl C-H signals, and those values showed a 1:1 ratio of the zirconium compounds before addition.   72   Scheme 3.8:  DMAP substitution competition experiment on 3.2 and [tolylNPN*]ZrCl2(THF); product ratios from averaged 1H NMR data. 73   Figure 3.18:  31P{1H} NMR spectra at 162 MHz of before (top) and 20 minutes after DMAP addition (bottom) to a C6D6 solution of 3.2 and [tolylNPN*]ZrCl2(THF).  An average of the integration of aryl C-H signals in the 1H NMR spectra for the two experiments show a 1:0.58 ratio favouring DMAP coordination to the [tolylNPN*] compound, forming 3.6.  This is as predicted from both G value and %Vbur calculations in Sections 3.5.2 and 3.5.3.  While the inclusion of the iminophosphorane functionality in the [NNN] ligand allowed for wider internal ligand angles compared to the [NPN*] frameworks on zirconium, as evidenced by the solid-state data, the added bulk of the iminophosphorane N-Ar functionality causes increased steric shielding of the metal centre. 74  3.6 Conclusion  Straightforward protonolysis synthetic routes were employed to generate zirconium amido and chloride complexes of the [NNN] framework.  The zirconium dibenzyl complex 3.3 was synthesized through a Grignard reaction with the dichloride compound 3.2, although other alkyl complexes could not be synthesized in pure form.  Reduction of the dichloride complex 3.2 with KC8 or Na(Hg) led to cleavage of the iminophosphorane bond, forming an incompletely characterized zirconium imido species.  Through the use of DFT studies, the dichloride complex 3.2 was examined along with [tolylNPN*]ZrCl2(THF), which showed that the iminophosphorane bond is prone to dissociation when populating the LUMO with electron density.  As a result, the [NNN] system was determined to be a poor candidate for reduction chemistry on zirconium.  Steric calculations showed that inclusion of the iminophosphorane functionality with an N-aryl substituent increases the shielding at the metal centre, through an increased G value when compared to the analogous [tolylNPN*] framework on zirconium.  The [NNN] system is also unique compared to [NPN] ligands when comparing %Vbur trends, in that the %Vbur remains constant as approaching the metal centre, rather than decreasing at short radii from the metal.  A DMAP exchange competition experiment corroborated the steric calculations, in that the [tolylNPN*] ligand provides less shielding and allowed for faster exchange with THF on zirconium compared to the [NNN] ligand.  While the [NNN] ligand is able to coordinate to zirconium with less geometric strain than [NPN*], the unique steric environment near the metal centre may lead to the solution-state equivalence of NMe2 and benzyl ligands in 3.1 and 3.3, compared to the analogous [NPN*]ZrX2 systems.   75  4 Tantalum Complexes of the Iminophosphorane-Containing [NNN] Ligand 4.1 Introduction  While a major focus of Chapter 3 was the attempted reduction of diamido-iminophosphorane-zirconium complexes for dinitrogen activation, an alternative way to activate molecular nitrogen is via reaction of N2 with a suitably reducing dinuclear tetrahydride complex (Scheme 4.1).11,12  Starting with the tantalum trimethyl complex [NPNclassic]TaMe3, full hydrogenolysis of the methyl ligands produces the tetrahydride species [[NPNclassic]Ta]2H4 under mild conditions, which subsequently reacts with dinitrogen at atmospheric pressure.  Not only are the reaction conditions more mild than reduction routes toward dinitrogen activation, this methodology marks a step toward a potential catalytic cycle for dinitrogen fixation, where stoichiometric addition of a reducing agent is not required.11  Scheme 4.1:  Reaction of dinitrogen with the bridging tetrahydride tantalum dimer, to form a side-on and end-on dinitrogen complex.11 76   While modification to the [NPNclassic] ligand in Scheme 4.1, such as alteration of the phosphine substituent, has produced similar reactivity with dinitrogen, the silylamide linker is prone to undesired ligand rearrangements.23,26  This has led to studies of the more robust o-phenylene linked [NPN*] frameworks on tantalum, in an attempt to match the same dinitrogen reactivity through a dinuclear tetrahydride intermediate.34,35,82  Although the [mesNPN*] ligand allowed for formation of a ditantalum tetrahydride dimer, as shown in Scheme 4.2, this tetrahydride species was unreactive towards dinitrogen.34,35  Scheme 4.2:  Formation of tantalum tetrahydride complex using the [mesNPN*] framework, adapted from literature.34,35  TMS = trimethylsilyl, and BTA = bis(trimethylsilyl)acetylene. 77   This chapter focuses on the synthesis of tantalum trimethyl and alkyne complexes of the [NNN] framework, and their reactivity towards dihydrogen.  The structures and reactivities are compared to the analogous [mesNPN*]TaR3 complexes, to assess the effect of including the iminophosphorane functionality in the ligand design.  As the tetrahydride route to dinitrogen activation does not require reducing agents, it was expected that the iminophosphorane would be stable to this reaction pathway. 4.2 Synthesis and Reactivity of [NNN]TaMe3 4.2.1 Synthesis of [NNN]TaMe3  The tantalum trimethyl complex [NPNclassic]TaMe3, in Scheme 4.1, was previously synthesized from TaMe3Cl2 using the dilithium salt of the ligand.12  However, following a similar methodology with o-phenylene bridged [NPN*] frameworks led to unwanted side-product formation and the inability to purify the trimethyl compound.35,82  Use of the dipotassium salts of the [NPN*] ligands, rather than dilithium salts, allowed for selective formation of the corresponding [NPN*]TaMe3 compounds.35,82  Similar results to the [NPN*] ligands regarding lithium and potassium salt reactivity with the tantalum precursor TaMe3Cl2 were found with the [NNN] ligand.  When 2.1 was deprotonated with two equivalents of n-BuLi at -78 oC in ether to form the dilithium salt, and then treated with TaMe3Cl2 at -35 oC in THF, a mixture of two phosphorus-containing species was observed by 31P{1H} NMR spectroscopy.  Alternatively, 2.1 was deprotonated with two equivalents of KH in THF at room temperature to form the dipotassium salt, 4.1.  Compound 4.1 is a yellow solid with low solubility in aromatic and hydrocarbon solvents.  Akin to the dipotassium salts of the [NPN*] ligands, 4.1 forms as a THF adduct.34,35,85  The 31P{1H} NMR 78  spectrum of 4.1 contains a singlet at δ 22.0 in C6D6, and the 1H NMR data is severely broadened in C6D6 or CD2Cl2 due to low solubility.  From the 1H NMR data, it was determined that 4.1 loses the mirror plane of symmetry found in the precursor 2.1, as all four tolyl-CH3 groups produce independent signals.  Integration of these tolyl resonances in comparison to THF-CH2 resonances allows for the proper molecular weight determination per synthetic batch, which is typically a ratio of 2 THF per molecule of 4.1.  The tantalum trimethyl complex 4.2 was synthesized by treatment of 4.1 with TaMe3Cl2 in THF at -35 oC.  Compound 4.2 is light sensitive, and must be manipulated in the dark whenever possible.  As well, 4.2 is thermally sensitive and is best stored for extended periods of time in the solid state at low temperature under an N2 atmosphere.  Scheme 4.3 shows the synthesis of 4.2 from the neutral ligand 2.1, via the dipotassium salt 4.1. 79   Scheme 4.3:  Synthesis of 4.1 from 2.1 by deprotonation with KH, and the subsequent salt metathesis reaction with TaMe3Cl2 to produce 4.2.  Compound 4.2 produces a singlet at δ 19.9 in the 31P{1H} NMR spectrum in C6D6.  The 1H NMR spectrum of 4.2 in C6D6, shown in Figure 4.1, indicates a mirror plane of symmetry through the [NNN] ligand backbone in solution.  This is apparent from each pair of tolyl-CH3 groups producing one resonance, and is similar to the symmetry observed for [NNN] on the zirconium complexes discussed in Chapter 3.  Interestingly, all three Ta-CH3 groups are equivalent by 1H NMR spectroscopy and appear as one singlet at δ 1.51, indicating fluxional 80  behaviour at room temperature in solution.  Similar fluxional behaviour was observed for [mesNPN*]TaMe3, as well as the silylamide-bridged [NPNclassic]TaMe3 complex.11,34  Figure 4.1:  1H NMR spectrum of 4.2 in C6D6 at 400 MHz.  Residual solvent, silicone grease, and minor impurity signals denoted by *.  Crystals of 4.2 suitable for XRD studies were grown from a hexanes solution at -35 oC.  The ORTEP representation of 4.2 is shown in Figure 4.2, along with selected bond lengths and angles in Table 4.1. 81   Figure 4.2:  ORTEP representation of the solid state structure of 4.2, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms and co-crystallized hexane are omitted for clarity.  Table 4.1:  Selected bond lengths (Å) and angles (deg) for 4.2. Parameter (Å)  Parameter (o) Ta1 - N01 2.138(4)  N01 - Ta1 - N02 138.98(17) Ta1 - N02 2.055(4)  N01 - Ta1 - N03 81.47(16) Ta1 - N03 2.224(4)  N02 - Ta1 - N03 77.39(17) Ta1 - C44 2.185(6)  C44 - Ta1 - C46 138.0(2) Ta1 - C45 2.218(5)    Ta1 - C46 2.226(5)    P01 - N03 1.601(5)    82   Compound 4.2 displays a distorted trigonal prismatic geometry in the solid state, where one trigonal face consists of N01, N03, and C44, while the second trigonal face is made by N02, C45, and C46.  This shows the asymmetry of 4.2 in the solid state, in contrast to the solution state NMR data.  The Ta-amido bond lengths to the [NNN] ligand, and the Ta-CH3 bond lengths match those of the analogous [mesNPN*]TaMe3 complex.34  Similarly, [mesNPN*]TaMe3 displays a distorted trigonal prismatic geometry in the solid state, while [NPNclassic]TaMe3 is described as a distorted octahedral geometry.12,34  The Ta1-N03 iminophosphorane bond length of 2.224(4) Å is significantly shorter than the analogous tantalum-phosphine bonds of the [NPN] systems, which are 2.6034(14) Å for [mesNPN*]TaMe3 and 2.7713(13) Å in [NPNclassic]TaMe3.12,34  This is similar to the decreased zirconium-iminophosphorane bond lengths observed for [NNN]ZrX2 complexes described in Chapter 3, in comparison to zirconium-phosphine bonds of [NPN]ZrX2 compounds.  Interestingly, there is a short Ta1-P01 distance of 2.9940(13) Å in 4.2, which is within the sum of the van der Waals radii of the two atoms.121  The [NNN] internal ligand angle N01-Ta1-N02 of 138.98(17)o is significantly wider than the analogous 121.59(10)o angle found in [mesNPN*]TaMe3, which is likely due to the 6-membered metallacycles formed within the ligand from the addition of the iminophosphorane donor of [NNN].34 4.2.2 Hydrogenation Studies of [NNN]TaMe3  With the goal of replicating the ditantalum tetrahydride-bridged derivatives stabilized by the [NPNclassic] and [mesNPN*] ligands, 4.2 was exposed to 4 atm pressure of H2(g) in benzene.  Unlike the aforementioned [NPN]TaMe3 complexes, which undergo hydrogenolysis of all three methyl ligands in 24 hr at room temperature, 4.2 is stable to hydrogen for days.11,34  However, when heated to 50 oC, 4.2 was fully consumed over the course of one week.  The major species generated under these conditions is characterized by a signal at δ 16.2 in the 31P{1H} NMR 83  spectrum in C6D6.  The 31P{1H} NMR spectra for the reaction of 4 atm H2(g) with 4.2 at 50 oC over time are shown in Figure 4.3.  Figure 4.3:  31P{1H} NMR spectra over time at 121 MHz in C6D6 of the reaction of 4.2 with 4 atm of H2(g).  Spectra were acquired at 25 oC.  A comparison of 1H NMR spectra in C6D6 of 4.2 with the product of hydrogenation under 4 atm of pressure for 7 days at 50 oC is shown in Figure 4.4.  A flame sealed NMR tube was used for this reaction, effectively containing all gaseous byproducts in the reaction vessel.  Note that the hydrogenation product spectrum represents the same sample/time as the 31P{1H} NMR spectrum labeled "50 oC for 7 days" of Figure 4.3. 84   Figure 4.4:  1H NMR spectra at 300 MHz in C6D6 of 4.2 (top) and the reaction of 4.2 with 4 atm of H2(g) for 7 days at 50 oC (bottom).  Signals from residual solvent impurities and silicone grease are denoted by *.  In the 1H NMR spectrum of the hydrogenation product of 4.2 there are no signals representing methyl ligands on tantalum, which were present in 4.2.  However, there is a signal at δ 0.16 assigned to dissolved CH4, the product of hydrogenolysis of the methyl ligands.  As the produced gaseous methane is in equilibrium with dissolved methane, it is not possible to gain insight to the stoichiometry of the produced gas through integration of this signal.  There are also no signals that are characteristic of a tantalum-methylidene group (Ta=CH2) in the 1H NMR spectrum of the hydrogenation product.122  As well, no signals characteristic of tantalum-hydride ligands were observed from δ 25 to -25 in the 1H NMR spectrum, which are typically observed 85  downfield shifted.12,34  All proton signals from δ 6.0 to 7.5 were correlated to C-H bonds by an 1H-13C HSQC NMR experiment, indicating that these signals are all generated by aryl C-H nuclei.  The conditions for the hydrogenation experiment of 4.2 were repeated in proteo benzene with D2(g).  Monitoring over the course of one week at 50 oC by 31P{1H} NMR spectroscopy indicated similar reaction times and intermediate signals to the H2(g) reaction through comparison to the spectra in Figure 4.3.  The 2H{1H} NMR spectrum in C6H6 after 7 days of reaction between 4.2 and 4 atm of D2(g) at 50 oC is shown in Figure 4.5.  Figure 4.5:  2H{1H} NMR spectrum at 61 MHz in C6H6 of the reaction of 4.2 with 4 atm of D2(g) after 7 days at 50 oC.  The 2H{1H} NMR spectrum of Figure 4.5 indicates that the sole deuterium-containing product of the reaction between 4.2 and D2(g) is methane.  Note that the deuterium signal corresponding to C6H5D is present due to the natural abundance of deuterium in the solvent, proteo benzene.  Although the 31P{1H} NMR spectra acquired between 1 and 6 days of reaction at 50 oC showed the presence of multiple phosphorus-containing intermediates, no additional signals were observed in the 2H{1H} NMR spectra at any point.  The non-decoupled 2H NMR 86  experiment shows splitting of the methane deuterium signal to a broadened quartet, indicating that the produced methane is CH3D, although the complete absence of CH2D2 cannot be claimed.  However, there is no evidence for the production of ethane from the D2 and H2 experiments, or incorporation of deuterium to the aryl groups of the ligand through cyclometalation-type processes.  As cleavage of the iminophosphorane was observed in the reduction chemistry of the [NNN] system on zirconium (see Chapter 3), we were concerned that the iminophosphorane functionality was involved during the hydrogenation reaction of 4.2.  Similar to the protonolysis experiment described in Section 3.3.2 to remove the ligand framework from the metal for analysis by NMR spectroscopy, we designed an experiment to protonate the ligand from tantalum to observe either [NNN]H2 (2.1) or [tolylNPN*]H2 with the loss of 4-isopropylaniline.  When excess trimethylammonium chloride in THF was added to the hydrogenation product of 4.2, as shown in Scheme 4.4, only the phosphine-containing [tolylNPN*]H2 framework was observed by 31P{1H} NMR spectroscopy.  The 31P{1H} NMR spectra of the hydrogenation product of 4.2, and of the P-containing species after protonation with trimethylammonium chloride are shown in Figure 4.6.   87   Scheme 4.4:  Protonation experiment with trimethylammonium chloride on the hydrogenation product of 4.2, for analysis by 31P{1H} NMR spectroscopy.  Figure 4.6:  31P{1H} NMR spectra at 162 MHz in benzene of the hydrogenation product of 4.2 (top), and the reaction with trimethylammonium chloride (bottom) to liberate [tolylNPN*]H2 from tantalum. 88   With confirmation of cleavage of the iminophosphorane during hydrogenation of 4.2, we propose that the hydrogenation product is a Ta(V) species with the [tolylNPN*] framework, an imido ligand from the cleaved iminophosphorane, and an undetermined additional anionic ligand.  As proposed in Scheme 4.5, the reductive elimination of a methyl and hydride ligand would lead to a Ta(III) centre, which could then oxidatively cleave the iminophosphorane.  The solid state molecular structure of 4.2 showed a short distance from tantalum to phosphorus within van der Waals radii, indicating the possibility of this interaction.  However, note that Ta-H nuclei were not observed by NMR experiments in any of the longer-lived intermediate species over the course of the 7 day hydrogenations of 4.2.   89   Scheme 4.5:  Proposed reductive elimination of methane from a [NNN]Ta-hydride species, during the hydrogenation of 4.2, leading to reduction of the phosphorane and formation of a tantalum-imido complex.  Although the hydrogenation product of 4.2 has not been characterized, it is not the intended ditantalum tetrahydride complex.  The same species was also synthesized by the treatment of 4.2 with PhSiH3 over the course of several weeks at room temperature in benzene, as confirmed by NMR spectroscopy.  This supports the proposal that a tantalum-hydride species, synthesized through either hydrogenolysis or addition of a hydride reagent to 4.2, leads to 90  subsequent reductive elimination of methane and cleavage of the iminophosphorane.  The [NNN] system is not suitable for supporting hydrogenolysis of the tantalum trimethyl complex, as the iminophosphorane functionality is a liability in this compound. 4.3 Synthesis and Reactivity of [NNN]Ta Alkyne Complexes 4.3.1 Overview  Tantalum alkyne complexes with the [mesNPN*] framework have been investigated by Dr. Kyle Parker, which included a series of halide, alkyl, and hydride compounds.34,35,85  While the tantalum alkyne nomenclature technically represents a Ta(III) centre with a neutral, two electron donating alkyne ligand, the complexes in this section are best described as a Ta(V) centre bound to an alkenediyl dianion.  A comparison of the neutral alkyne and alkenediyl functionalities is shown in Figure 4.7.123  For the sake of brevity, this ligand type will be referred to as an "alkyne" ligand in this document.  Figure 4.7:  Comparison of alkyne and alkenediyl resonance structures.  This section reports the synthesis of a tantalum alkyne halide complex with the [NNN] framework, analogous to complexes previously studied with the [mesNPN*] ligand, and its subsequent reactivity.  As the [mesNPN*]Ta system allowed for hydrogenation of the alkyne functionality, en route to formation of a dinuclear tantalum tetrahydride complex, hydrogenation studies with the [NNN] ligand were of primary interest.34,35 91  4.3.2 Synthesis and Reactivity  Appropriate tantalum alkyne precursors of the form TaCl3(RC≡CR)(DME), where DME represents 1,2-dimethoxyethane, were prepared through the reaction shown in Scheme 4.6.124,125  3-Hexyne and bis(trimethylsilyl)acetylene (BTA) were chosen for steric variety, and consistency with the work performed by Dr. Parker.35  Scheme 4.6:  Preparation of tantalum alkyne precursor complexes of type TaCl3(RC≡CR)(DME).124  Salt metathesis reactions of the dipotassium salt of [NNN], 4.1, were attempted with both tantalum alkyne precursors.  While the treatment of 4.1 with the 3-hexyne precursor led to an inseparable mixture of two phosphorus-containing species, as evidenced by 31P{1H} NMR spectroscopy, the same reaction conditions with the tantalum-BTA compound cleanly produced complex 4.3.  This reaction is summarized in Scheme 4.7.  Unlike the light and temperature sensitive 4.2, compound 4.3 is light stable and showed no evidence of decomposition by NMR spectroscopy when refluxed in benzene for several days. 92   Scheme 4.7:  Synthesis of 4.3 by the salt metathesis reaction of 4.1 with TaCl3(BTA)(DME).  The 31P{1H} NMR spectrum of compound 4.3 shows a signal at δ 30.3 in C6D6 for the phosphorane, which is coincidentally similar to the chemical shift value of δ 29.7 for the phosphine nuclei in the analogous complex [mesNPN*]Ta(BTA)Cl.85  The 1H NMR spectrum of 4.3, shown in Figure 4.8 from a C6D6 solution, indicates a Cs symmetric compound with a plane of symmetry through the ligand backbone.  The 1H NMR signals for the [NNN] ligand protons are unremarkable compared to those of 4.2, and the zirconium complexes discussed in Chapter 3.  The BTA ligand of 4.3 produces two broad signals, one for each trimethylsilyl environment, each corresponding to 9 protons.  The analogous complex, [mesNPN*]Ta(BTA)Cl, produced two sharp resonances for the BTA unit.35,85  Signals representing the quaternary carbons of the alkyne ligand of 4.3 were not observed in 13C or 1H-13C HMBC NMR spectra. 93   Figure 4.8:  1H NMR spectrum at 400 MHz of 4.3 in C6D6, residual solvent signals and minor impurities are denoted by *.  Crystals of 4.3 suitable for XRD studies were grown from a dilute ether solution at -35 oC.  The ORTEP representation of 4.3 is shown in Figure 4.9, along with selected bond lengths and angles in Table 4.2. 94   Figure 4.9:  ORTEP representation of the solid state structure of 4.3, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms and co-crystallized ether are omitted for clarity.  Table 4.2:  Selected bond lengths (Å) and angles (deg) for 4.3. Parameter (Å)  Parameter (o) Ta1 - N01 2.072(3)  N01 - Ta1 - N02 142.12(10) Ta1 - N02 2.127(3)  N01 - Ta1 - N03 81.19(10) Ta1 - N03 2.166(3)  N02 - Ta1 - N03 81.98(10) Ta1 - C44 2.087(3)  C44 - Ta1 - C45 37.21(13) Ta1 - C45 2.062(3)  N03 - Ta1 - Cl01 151.66(7) Ta1 - Cl01 2.4535(9)  Si01 - C44 - C45 138.2(3) P01 - N03 1.621(3)  Si01 - C44 - C45 138.0(3) C44 - C45 1.324(5)    95   The solid state geometry of 4.3 can be described as distorted trigonal bipyramidal, similar to the analogous complex [mesNPN*]Ta(BTA)Cl.35  The [NNN] ligand is facially bound to tantalum, with the amido N-atoms on the equatorial plane, along with the centroid of the C44-C45 bond.  The bond metrics of the [NNN] ligand in 4.3 have little variation from the previously discussed compound 4.2.  The short Ta1-P01 distance of 2.9354(9) Å in 4.3 is within van der Waals radii of the two atoms, similar to the analogous atoms in 4.2.121  The axially-bound atoms N03 and Cl01 are distorted from idealized linear geometry, with an N03-Ta1-Cl01 angle of 151.66(7)o, which is attributed to steric crowding of the alkyne ligand.35  This is a similar value to the analogous angles found in the [mesNPN*]Ta(alkyne)Cl complexes (alkyne = BTA, 3-hexyne) of 145.59(2)o and 153.63(2)o, where the axial position is occupied by the phosphine atom of [mesNPN*].35  However, the internal [NNN] ligand amido angle of N01-Ta1-N02 in 4.3, 142.12(10)o, is 10 degrees wider than the analogous [mesNPN*]Ta(alkyne)Cl complexes, and can be attributed to the larger 6-membered chelate rings of the [NNN]Ta system.35  The C44-C45 bond distance of 1.324(5) Å for the BTA ligand is consistent with the 1.326(3) Å value found for [mesNPN*]Ta(BTA)Cl.35  This is longer than the typical C≡C triple bond length of ~1.2 Å, indicating the alkenediyl character of the BTA ligand.35,124  Additionally, the nonlinear Si01-C44-C45 and Si01-C44-C45 bond angles of 138.2(3)o and 138.0(3)o, respectively, corroborate the Ta(V)-alkenediyl character of the BTA ligand.  The BTA ligand is unsymmetrically bound, with one trimethylsilyl group near the iminophosphorane moiety and the other near the chloride ligand.  The solid state structure agrees with the solution 1H NMR data that was acquired at 25 oC for 4.3, and shown in Figure 4.8.  Variable temperature NMR experiments were performed on 4.3, to examine the barrier for rotation of the alkyne ligand, which is illustrated in Scheme 4.8.  A selection of 1H NMR 96  spectra of the trimethylsilyl signals of 4.3, from -25 to 35 oC in d8-toluene, is shown in Figure 4.10.  The signals were found to coalesce at 34 oC, and had a separation of 233 Hz at -25 oC.  The ΔG‡rot for the BTA ligand was determined as 59 kJ/mol from these values.  While the analogous complex [mesNPN*]Ta(BTA)Cl did not display fluxional behaviour of the BTA ligand at room temperature , the compound [mesNPN*]Ta(3-hexyne)Cl has a ΔG‡rot value of 68 kJ/mol for the 3-hexyne ligand.35  Scheme 4.8:  Fluxional behaviour of alkyne ligand of 4.3. 97   Figure 4.10:  Variable temperature 1H NMR spectra at 400 MHz of 4.3 in d8-toluene, of the Si-CH3 region.  Minor impurities are denoted by *.  Tantalum imido complexes can be synthesized through the addition of an azide reagent to a low-valent tantalum species, as shown by Bergman and Proulx.126,127  The analogous compound to 4.3, [mesNPN*]Ta(BTA)Cl, was previously found to react with an aryl azide, displacing the alkyne ligand and forming the corresponding tantalum imido complex.35  Similarly, compound 4.3 was treated with 4-isopropylphenyl azide to generate the tantalum imido complex 4.4, as shown in Scheme 4.9. 98   Scheme 4.9:  Synthesis of 4.4 by treatment of 4.3 with 4-isopropylphenyl azide.  Compound 4.4 is characterized by a signal at δ 25.8 in the 31P{1H} NMR spectrum in C6D6, which is 4.5 ppm upfield of the phosphorane signal in 4.3.  Absent in the 1H NMR spectrum of 4.4, shown in Figure 4.11, are the broadened signals characteristic of the fluxional BTA ligand of the precursor 4.3.  Free BTA, which produces a sharp signal at δ 0.16 in C6D6, was present in the reaction mixture and was removed by washing the product with pentane.  Compound 4.4 has a mirror plane of symmetry in the solution state, similar to compounds 4.2 and 4.3.  The signals of the isopropyl group on the imido ligand have only minor chemical shift deviations relative to the analogous isopropyl signals from the iminophosphorane aryl group.  The aryl region of the 1H NMR spectrum is further complicated by the addition of another unique aryl moiety, to those already in the [NNN] framework.  The molecular ion of 4.4 as well as [M - CH3]+ were observed by EI-MS. 99   Figure 4.11:  1H NMR spectrum of 4.4 at 400 MHz in C6D6.  Residual solvent and BTA signals denoted by *.  Further reactivity of the alkyne ligand in 4.3 was investigated, and is briefly summarized in this paragraph and Scheme 4.10.  Cycloaddition reactivity of the alkyne was attempted by treatment of 4.3 with a diene.  Compound 4.3 was inert towards trans,trans-1,4-diphenyl-1,3-butadiene in benzene at reflux.  Diels-Alder reactions can be catalyzed by Lewis acids, thus BEt3 was added to a benzene solution of 4.3 and the diene.128  These conditions led to a mixture of P-containing products as evidenced by 31P{1H} NMR spectroscopy, with the major species' signal at δ 26.0 and minor species (5-15%) at δ 28.3 and 31.6.  The 1H NMR spectrum of the mixture showed a symmetric [NNN] environment for the major species, with a non-fluxional asymmetric 100  alkyne unit.  In an attempt to form a Ta-hydride in situ with a Lewis acid catalyzed cycloaddition, KHBEt3 was added to the mixture of 4.3 and the diene in benzene at 25 oC.  A mixture of three main species that produce 31P{1H} NMR signals at δ 13.6, 20.1, and 32.2 were present (0.2:1.0:0.4 ratio), along with several additional signals for minor P-containing species.  The 1H NMR spectrum of this mixture contained three minor resonances from δ 10-12 in C6D6, possibly correlating to Ta-H signals, and several minor signals from δ 3-5.  This reaction was abandoned due to the complex mixture of products, and no evidence of diene incorporation to the compound.  In an attempt to substitute the alkyne ligand with an imido, compound 4.3 was inert towards azobenzene (Ph-N=N-Ph) in benzene, and generation of the cis-isomer of azobenzene by irradiation of the reaction mixture at 355 nm did not lead to further reactivity.  Hydrogenation of the alkyne of compound 4.3 was attempted, but 4.3 was inert towards 4 atm of H2(g) in benzene, at a temperature of 80 oC.  Hydrogenation of the tantalum-imido functionality of 4.4 was attempted, although compound 4.4 was inert towards 4 atm of H2(g) in benzene at a temperature of 70 oC. 101   Scheme 4.10:  Attempted reactivity of BTA ligand of complex 4.3.  The exchange of the chloride ligand of 4.3 for hydride and alkyl ligands was also attempted via salt metathesis reagents, resulting in the tantalum benzyl species 4.5 as the only isolated complex, which will be described shortly.  Unsuccessful reaction conditions with 4.3 are described hereafter, and summarized in Scheme 4.11.  There was no interaction between a THF solution of 4.3 and KH.  Complex 4.3 was treated with freshly prepared KHBEt3 in toluene at room temperature, analogous reaction conditions that were previously used for the synthesis of 102  [mesNPN*]Ta(BTA)H, which instead resulted in a mixture of 3 major phosphorus-containing species.35,85  The 31P{1H} NMR chemical shifts of these species are identical to the products of the reaction of 4.3, KHBEt3, and trans,trans-1,4-diphenyl-1,3-butadiene that were previously described, with the addition of a minor signal (~10%) at δ 24.1.  In an attempt to synthesize the tantalum-methyl complex, treatment of 4.3 with methyl lithium in THF at -78 oC led to a mixture of no less than 5 phosphorus-containing species, which produced signals in the 31P{1H} NMR spectrum from δ 17 to 36.  The addition of benzyl potassium to 4.3 in THF or toluene at -35 oC en route to the tantalum-benzyl complex resulted in a mixture of no less than 5 phosphorus-containing species, which produced signals from δ 0 to 20 in the 31P{1H} NMR spectrum in benzene.  Scheme 4.11:  Attempted reactivity of chloride ligand of complex 4.3. 103   Treatment of an ether solution of 4.3 with the Grignard reagent benzylmagnesium chloride at -35 oC led to the clean production of the corresponding tantalum benzyl complex 4.5, as shown in Scheme 4.12.  The analogous complex [mesNPN*]Ta(BTA)benzyl was previously synthesized by the salt metathesis reaction of the tantalum chloride precursor with benzyl potassium, conditions that as mentioned above, led to a mixture of P-containing species from 4.3.34,35   Scheme 4.12:  Synthesis of 4.5 by addition of benzylmagnesium chloride to 4.3.  Compound 4.5 produces a signal at δ 25.5 in the 31P{1H} NMR spectrum in C6D6, which is only a minor upfield shift of 0.3 ppm from 4.3.  The 1H NMR spectrum of 4.5 in C6D6 has only minor chemical shift deviations from that of 4.3, indicating a symmetric [NNN] ligand and two fluxional environments for the BTA ligand.  The methylene protons of the benzyl ligand produce a singlet at δ 3.21; the same protons in the compound [mesNPN*]Ta(BTA)benzyl produced a singlet at δ 3.22.35  This indicates that the benzyl ligand is likely in the axial position in 4.5, similar to the geometry determined by XRD studies for [mesNPN*]Ta(BTA)benzyl and of the precursor 4.3.35  Previous studies of the alternate alkyne complex [mesNPN*]Ta(3-104  hexyne)benzyl showed that the benzyl ligand coordinated to an equatorial site on tantalum, which resulted in a 1H NMR chemical shift of δ 2.75 for the methylene protons.35  The identity of 4.5 is confirmed by EI-MS and elemental analysis.  The analogous compound [mesNPN*]Ta(BTA)benzyl was previously treated with H2(g), as shown in Scheme 4.2, to hydrogenate the alkyne ligand to an alkene and form a tantalum hydride by hydrogenolysis of the benzyl ligand.34,35  This isolable intermediate complex undergoes further reaction with hydrogen to produce a dinuclear tantalum tetrahydride compound.35  For comparative studies, a C6D6 solution of 4.5 was sealed under 4 atm of H2(g) and monitored by NMR spectroscopy.  The successful addition of hydrogen was confirmed by the presence of a 1H NMR signal at δ 4.47 representing dissolved H2. While [mesNPN*]Ta(BTA)benzyl reacted with 1 atm H2(g) over 36 hours in benzene to form the corresponding alkene hydride compound, 4.5 was inert to 4 atm of H2(g) over 5 days.  After the initial 5 days, the reaction vessel was heated to 60 oC and monitored over two weeks.  In the first 24 hours three minor signals in the 31P{1H} NMR spectrum appeared at δ 5.0, 8.3, and 15.9.  After 7 days at 60 oC essentially all 4.5 had been consumed, and at least 5 independent phosphorus-containing species were present, as evidenced by 31P{1H} NMR spectroscopy.  After two weeks at 60 oC, the only change to the spectra was the disappearance of the signal at δ 15.9, and new signal at δ 17.1.  Signals characteristic of tantalum hydrides were not observed in the 1H NMR spectra at any time.  Figure 4.12 shows 31P{1H} NMR spectra of the addition of H2(g) to 4.5 over a three week period. 105   Figure 4.12:  31P{1H} NMR spectra at 162 MHz of addition of 4 atm of H2(g) to 4.5 in C6D6 over time.  Preliminary reactivity studies showed that 4.5 reacted with 4-isopropylphenyl azide to displace the BTA ligand and form a tantalum imido species, similar to 4.4.  The reaction was complete within one hour, and generated a single product that produces a signal at δ 20.7 in the 31P{1H} NMR spectrum in C6D6.  The 1H NMR spectrum of the reaction mixture showed the production of BTA as a byproduct at δ 0.16, as well as resonances for the isopropyl group of the newly formed imido ligand, analogous to the reaction to form 4.4.  When a C6D6 solution of 4.5 was exposed to excess 4-isopropylphenyl azide, the imido species formed at room temperature after 1 hour, and two new signals in the 31P{1H} NMR spectrum appeared after 5 days at δ 24.3 and 29.2.  Heating the mixture to 70 oC for an additional 5 days led to quantitative conversion to these two phosphorus-containing species, which remained at a 1.0:0.6 ratio over this time period.  106  The 1H NMR spectrum of this mixture showed that one of the products is Cs symmetric, while the other has an asymmetric [NNN] ligand.  The analogous complex [mesNPN*]Ta(BTA)benzyl was previously treated with 4-isopropylphenylazide to generate the corresponding tantalum imido compound, and inserted a second equivalent of 4-isopropylphenylazide into the tantalum-benzyl bond at 70 oC, to form an asymmetric triazenide complex.35  Scheme 4.13 describes the tantalum imido complex generated by addition of 4-isopropylphenyl azide to 4.5; the orientation of the imido ligand cannot be verified without XRD information, so it is presented in the equatorial position to maintain the geometry of the precursor 4.5.  The analogous tantalum imido compound [mesNPN*]Ta=N(4-iPrPh)benzyl initially formed with the imido ligand in the equatorial position, and underwent thermodynamic rearrangement to the axial position.35  The proposed products from the insertion of a second equivalent of the azide into the tantalum-benzyl bond are also shown in Scheme 4.13, in grey shading.  One of the proposed complexes is an asymmetric triazenide species, and the other is the symmetric tantalum amido product of benzyl insertion to the alkylated N-atom of the azide, and subsequent elimination of N2.  The 31P{1H} NMR spectra of the reaction of 4.5 with excess 4-isopropylphenyl azide in benzene is shown in Figure 4.13.  Further studies are needed to fully characterize the tantalum imido complex, and identify the products of azide insertion. 107   Scheme 4.13:  Reaction of 4.5 with 4-isopropylphenyl azide to form a tantalum imido complex (not characterized), and the subsequent reaction with a second equivalent of 4-isopropylphenyl azide to form proposed triazenide and amido species (grey shading). 108   Figure 4.13:  31P{1H} NMR spectra at 162 MHz of the reaction of 4.5 with excess 4-isopropylphenyl azide in C6D6. 4.4 Conclusions  The tantalum trimethyl complex 4.2 was synthesized through the addition of the dipotassium salt of [NNN], 4.1, to the precursor TaMe3Cl2.  While 4.2 has a similar geometry to the analogous complex [mesNPN*]TaMe3, hydrogenation of 4.2 led to cleavage of the iminophosphorane bond, rather than the formation of a dinuclear tetrahydride species.  Reaction of D2(g) with 4.2 indicated that the only deuterium-containing product of the reaction was methane.  The iminophosphorane functionality of the [NNN] framework was determined to be unstable toward reduced early metal species. 109   The tantalum alkyne complex 4.3 was synthesized, and compared to the previously studied complex [mesNPN*]Ta(BTA)Cl.  Compound 4.3 was found to bind the BTA ligand as an alkenediyl, analogous to [mesNPN*]Ta(BTA)Cl.  The tantalum imido complex 4.4 was synthesized by addition of an aryl azide to 4.3, displacing the BTA ligand.  While we were unable to synthesize a tantalum alkyne hydride complex, the alkyl complex 4.5 was synthesized from 4.3.  Complex 4.5 was inert towards hydrogen at room temperature, and generated an intractable mixture of products at elevated temperature with no evidence of tantalum hydride formation.  Preliminary reactivity of 4.5 indicated the formation of a tantalum alkyl imido compound, similar to the tantalum chloride imido complex 4.4, via addition of an aryl azide and displacement of the BTA ligand.  The [NNN] framework does not support formation of a ditantalum tetrahydride species akin to those stabilized by [NPNclassic] and [mesNPN*].   110  5 Alternate Ligand Scaffolds 5.1 Introduction  This chapter focuses on several ligand designs that were investigated prior to work with the iminophosphorane-containing tridentate [NNN] ligand.  The synthetic strategies proved challenging, and these frameworks were ultimately abandoned with subsequent work moving towards the [NNN] system, which is the focus of Chapters 2-4.  However, the design of these systems required significant effort and time, and reporting of these strategies and results should prove useful for other researchers interested in amidophosphine ligand sets. 5.2 Tetradentate [PNNP]H2 Ligand Set 5.2.1 Introduction  Although many of the ligand frameworks within the Fryzuk design catalogue have involved tridentate, dianionic donor sets,11,32,82-84,129,130 the tetradentate, dianionic [P2N2]H2 macrocycle has also supported impactful transition metal chemistry.18,28,122,131,132  This ligand set enabled the study of zirconium dinitrogen complexes; an example of the Zr[P2N2] dinitrogen dimer and its subsequent reaction with H2 is shown in Scheme 5.1.25,28   111   Scheme 5.1:  Reaction of [[P2N2]Zr]2N2 dimer with H2, adapted from literature.28  Note that Me2 groups on Si are omitted for clarity.  Building from the success of several of the dianionic, multidentate amidophosphine ligand frameworks (see Chapter 1), a new dianionic, tetradentate ligand design was envisioned.  This [PNNP] framework is shown in Figure 5.1, and is compared to the [P2N2] macrocycle, and the o-phenylene bridged [NPN*] ligand.  The [PNNP] system is admittedly a distant design from the [P2N2] macrocycle; other than the diamido and diphosphine donor atoms they bear little resemblance.  However, the early metal reactivity stabilized by the tetradentate macrocycle gave encouragement into further study of tetradentate, dianionic systems.28,29,132  As shown in Scheme 5.1, the dinitrogen complex [[P2N2]Zr]2N2 does not require an additional neutral donor molecule, whereas dinitrogen complexes of tridentate ligand designs are often stabilized by ethereal solvents or other neutral donors.24,28,33,82  The design of the [PNNP] framework incorporates terminal phosphine donors; the coordination and dissociation of a phosphine arm is a possibility to allow for stabilization of early metal complexes, as well as a potential open site for additional reactivity.  This phosphine dissociation behaviour was observed in a tridentate [PNP] ligand 112  framework on zirconium.133  In comparison, the [P2N2] macrocycle features a trans-phosphine orientation, and has an inability for phosphine dissociation due to its macrocyclic nature.100  Figure 5.1:  General comparison of the [P2N2] macrocycle, [NPN*], and [PNNP] ligand systems.  The [P2N2] macrocycle is based on a silylamide backbone, which has been incorporated into several of the so-called "classic" ligand designs within the Fryzuk group.12,20,134  This functionality was included in order to reduce the basicity of the nitrogen donor atoms.32  However, the silylamide bond was prone to cleavage and rearrangement.31,129  This led to a further ligand design based on a rigid o-phenylene backbone, which omits the silylamide functionality and is less prone to ligand decomposition.32  This [NPN*] framework containing o-phenylene linkers is shown in Figure 5.1.  Please refer to Chapter 1 for more detail on ligand design in the Fryzuk group.  The proposed [PNNP] system of Figure 5.1 is designed with o-phenylene linkers, to maintain a rigid backbone and avoid ligand decomposition.  The two central amido groups are tethered with an ethylene linker, again avoiding silylamide functionality.  A PPh2 substituted version of the [PNNP] framework has been reported, however, it was synthesized en route to heterocyclic tridentate ligands.135,136  As well, the propylene linked PPh2 substituted framework 113  has been synthesized and used as a ligand for late transition metals.137  Studies of this ligand have focused on Ni, Pd, Pt, Rh, Cu, Ag, Tc, and Re, including electrochemical and radiochemical research.137-142  The nature of these investigations leaves much unexplored for early transition metal chemistry of [PNNP], with a focus on small molecule activation.  Several classes of tetradentate ligands with a PNNP donor array exist in the literature, such as the benzylamine-bridged framework used by Noyori and coworkers for ruthenium-catalyzed transfer hydrogenation.143  The Morris group has also focused on many PNNP ligand types, including backbones based on benzylideneamine, alkyl, and alkene linkers for iron-catalyzed transfer hydrogenation.144  Examples of these ligand sets are shown in Figure 5.2.  Figure 5.2:  Literature examples of other ligand frameworks containing PNNP donor arrays.143,145 5.2.2 Synthesis of [PNNP]H2  The [PNNP]H2 ligand, 5.1, shares a common backbone to a tridentate NHC-containing [PCP] ligand used for late metal chemistry by the Fryzuk group.130  Scheme 5.2 shows the synthetic route to 5.1, by modification of the method used for synthesis of the [PCP] ligand.  Specifically, the phosphine sulfide species (middle-right complex of Scheme 5.2) is deprotected to generate 5.1, where the published method alternatively installs the NHC via treatment with 114  triethylorthoformate in the presence of NH4PF6.  Installation of a protecting group on phosphorus is necessary to selectively alkylate the aryl amine; unfortunately, the deprotection step required up to a 50-fold excess of Raney nickel per phosphine sulfide, and resulted in a significant loss in yield of 30% isolation.   Scheme 5.2:  Synthetic route to 5.1, based on the synthesis of the NHC-containing ([PCP]H)PF6.130  The 31P{1H} NMR spectrum for 5.1 displays a single resonance at δ -17.1 in C6D6, indicating a symmetric structure.  The 1H NMR data shows the expected two resonances that 115  correspond to two distinct methyl environments on the isopropyl substituents, and one signal for all of the ethylene protons, also confirming a symmetric molecule in the solution state.  X-ray diffraction data was acquired for 5.1, although a twinned crystal resulted in a low-quality data set.  Due to this, bond lengths and angles cannot be discussed in a meaningful way.  However, the data can establish connectivity information for 5.1, and the solid-state structure shows a C2h symmetry, consistent with the NMR data.  The ORTEP representation of XRD data for 5.1 is shown in Figure 5.3.  Figure 5.3:  Solid-state structure (ORTEP) of 5.1, thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity.  Half of the molecule has been generated by symmetry. 116  5.2.3 Zirconium Complexes of [PNNP]H2  Protonolysis reactions of 5.1 with zirconium amido precursors enabled generation of zirconium complexes under mild conditions.  The reaction of 5.1 with Zr[NMe2]4 to produce the zirconium-amido complex 5.2 is shown in Scheme 5.3.  Scheme 5.3:  Protonolysis reaction of 5.1 with Zr(NMe2)4 to yield 5.2.  The 31P{1H} NMR spectrum for 5.2 contains one signal for both phosphorus nuclei at δ 2.3 in C6D6.  The 1H NMR data shows two distinct methyl environments for the isopropyl substituents, and one singlet for all four ethylene protons, similar to the 1H NMR data for the free ligand 5.1.  The methyl protons on both NMe2 ligands appear as one singlet in the 1H NMR spectrum, indicating free rotation of the Zr-N bonds of planar NMe2 ligands at room temperature on the NMR timescale.  Crystals of 5.2 were grown from a solution of THF and pentane, and analyzed by single crystal X-ray diffraction.  The ORTEP representation of 5.2 is shown in Figure 5.4, along with selected bond lengths and angles in Table 5.1. 117   Figure 5.4:  ORTEP representation of the solid-state structure of 5.2, thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity.  Table 5.1:  Selected bond lengths (Å) and angles (deg) for 5.2. Parameter (Å/o)  Parameter (Å/o) Zr1 - N1 2.1959(5)  N1 - Zr1 - N2 73.86(6) Zr1 - N2 2.2032(5)  N3 - Zr1 - N4 124.02(7) Zr1 - N3 2.0791(8)  P1 - Zr1 - P2 161.391(16) Zr1 - N4 2.0715(8)  P1 - Zr1 - N1 67.82(4) Zr1 - P1 2.8758(7)  P2 - Zr1 - N2 67.49(4) Zr1 - P2 2.8622(7)  P1 - Zr1 - N3 85.41(5)    P1 - Zr1 - N4 84.95(5) N1 - N2 - N4 - N3 53.8(3)  P2 - Zr1 - N3 84.37(5) N1 - C01 - C02 - N2 47.5(2)  P2 - Zr1 - N4 87.94(5)  118   Compound 5.2 is chiral in the solid-state; both enantiomers are present in the unit cell.  The solid-state structure of 5.2 indicates a cis-α arrangement of distorted octahedral geometry, where the NMe2 ligands are cis to one another, and both equatorial.  The trans-phosphine donors of the [PNNP] ligand show a 161.391(16)o angle from P1-Zr1-P2, which is significantly distorted from the ideal linear arrangement.  The [PNNP] ligand forms three five-membered metallacycles when bound to zirconium, with sharp internal angles.  The equatorial ethylene-bridged diamido ring contains an N1-Zr1-N2 angle of 73.86(6)o, while both P-Zr-N angles are even sharper at 67.82(4)o and 67.49(4)o.  These constrained rings also impose twisting on the ideal octahedral geometry.  The four equatorial amido donor atoms, from both the [PNNP] framework and NMe2 ligands, show an N1-N2-N3-N4 torsion angle of 53.8(3)o.  This distortion is almost entirely localized to the ethylene tethered diamido portion of the [PNNP] ligand, which has an N1-C01-C02-N2 torsion angle of 47.5(2)o.  The localization of imposed geometric distortion is further observed by the P-Zr-NMe2 angles that range from 84.37(5)o to 87.94(5)o, which are close to the ideal 90o angle when considering the aforementioned nonlinearity of the trans P1-Zr1-P2 donor atoms, and sharp P-Zr-N internal angles of the [PNNP] framework.  The Zr1-N1 and Zr1-N2 bond lengths are nearly identical at 2.1959(5) and 2.2032(5) Å, and agree with literature Zr-amido bond lengths of Zr[P2N2]R2 complexes with varying substituents (R = chloro, alkyl, 2R = imido).100  The Zr1-P1 and Zr1-P2 bond lengths of 2.8758(7) and 2.8622(7) Å are longer than those of the mentioned Zr[P2N2]R2 complexes, which have Zr-P bonds that range from 2.69-2.73 Å.100  However, these bond lengths are still within literature range of other Zr-P species.146  The Zr-NMe2 ligands are sp2-hybridized at nitrogen, with metal-amido bond lengths comparable to literature.82,147  This planar orientation indicates a 119  π-interaction of the amido donors with zirconium, and is confirmed by 1H NMR data that shows all NMe2 groups as equivalent (with free rotation in solution).  Low temperature NMR experiments were performed on 5.2 to compare the molecular geometry between solution and solid-state; a partial window of the 1H NMR spectra is shown in Figure 5.5.  At -80 oC the methyl groups on the NMe2 ligands became inequivalent, indicating the loss of free rotation around the Zr-NMe2 bonds.  The protons on the ethylene linker of the [PNNP] framework become diastereotopic at cold temperature.  Low temperature spectra indicate the presence of only a pseudo rotation axis, as in the solid-state molecular structure of 5.2.   At room temperature there is likely a racemization process that occurs via phosphine dissociation, leading to the observed equivalence of all protons on the ethylene linker of [PNNP].  Phosphine dissociation has been observed for the classic [PNP] ligand on zirconium.133 120   Figure 5.5:  Variable temperature 1H NMR spectra (400 MHz) of 5.2 in d8-toluene, showing ethylene proton signals and dimethylamido signals.  Although initially unexpected, the trans-phosphine arrangement of 5.2 is similar to that of the Zr[P2N2]R2 complexes reported by the Fryzuk group.100  The phosphine donor atoms of these Zr[P2N2]R2 compounds also show significant deviation from linearity, with P-Zr-P angles of 152.52(6)o for the dichloro compound and 159.73(8)o in the dibenzyl compound.  However, the cis-amido N-atoms of the [P2N2] macrocyclic ligand have a far wider internal angle than those of the [PNNP] framework in 5.2, as this N-Zr-N angle was greater than 96o in the Zr[P2N2]R2 compounds.100  Although both 5.2 and the Zr[P2N2]R2 complexes are described as distorted 121  octahedral geometries with trans-phosphine and cis-amido donors, the ligand geometry is significantly varied.  The reduction of zirconium halide complexes with alkali metals is a common method for dinitrogen activation, and as such the dichloro complex Zr[PNNP]Cl2, 5.3, was a synthetic target.28,33,82  Conversion of the bis(dimethylamido) complex 5.2 to the dichloro species 5.3 was achieved by treatment with excess Me3SiCl in toluene, based on literature preparations of similar complexes.32,82  The partially converted mono-substituted zirconium chloro amido compound can remain in the reaction mixture if reaction times are not sufficient.  This species produces two inequivalent coupled signals at δ -4.7 and 17.1 in the 31P{1H} NMR spectrum in C6D6.  However, a cleaner route to 5.3 was the treatment of 5.1 with an alternative zirconium precursor, Zr(NMe2)Cl2(DME).  Both synthetic routes to 5.3 are shown in Scheme 5.4.  Scheme 5.4:  Synthetic routes to the dichloride complex 5.3, from both 5.1 and 5.2. 122   The 31P{1H} NMR spectrum of 5.3 contains one signal at δ 13.5 in C6D6, indicating equivalent phosphine nuclei in solution at room temperature.  The 1H NMR data is similar to that of 5.2; there are two sets of methyl resonances on the isopropyl substituents, and one singlet produced by all four ethylene protons.  Compound 5.3 likely undergoes a fluxional process at room temperature, similar to 5.2, leading to the observed equivalence of the ethylene protons and phosphine nuclei.  Crystals obtained from a concentrated benzene solution did not diffract, and a solid-state structure could not be obtained.  The reduction of 5.3 with KC8 under 4 atm of N2 was attempted, as shown in Scheme 5.5.  Care was taken to use similar conditions that enabled production of the zirconium dinitrogen complex of the [P2N2] ligand set.29  This includes the vacuum transfer of dry THF from sodium and benzophenone into a -196 oC vessel containing the solid reagents, and the subsequent slow thaw to room temperature under dinitrogen.  Unfortunately, the 31P{1H} NMR spectrum showed the presence of more than 5 independent species, with three major signals between δ 5 and 15 in C6D6.  This mixture of products could not be further purified.  Scheme 5.5:  Attempted reduction of 5.3 with KC8 under 4 atm N2 led to a mixture of P-containing species. 123   The protonolysis route to a tantalum amido complex was also attempted, by treatment of 5.1 with the tantalum precursor Ta(NMe2)5.  While the generation of 5.2 and 5.3 occurs over hours at room temperature, there is no reaction between 5.1 and Ta(NMe2)5 over days at elevated temperature in benzene, or in refluxing toluene.  Salt metathesis reactions with tantalum halide starting materials were not investigated. 5.2.4 Summary  A novel tetradentate ligand, 5.1, was synthesized as a modification to the synthetic route used by the Fryzuk group to produce a tridentate, NHC-containing [PCP] donor ligand.130  The ligand 5.1 was installed on zirconium via protonolysis routes with metal-amido starting materials to generate zirconium amido and chloro complexes 5.2 and 5.3, although the analogous reaction with Ta(NMe2)5 was not successful.  The tetradentate [PNNP] ligand coordinates to zirconium with trans-phosphine donors, and imposes a significantly distorted octahedral geometry on the metal centre due to the short N-CH2CH2-N linker in the ligand backbone.  The reduction of the zirconium dichloro compound 5.3 under dinitrogen, analogous to the literature reduction of Zr[P2N2]Cl2 that results in a side-on bound N2 compound, led to a mixture of species.28  As reduction chemistry was a primary goal of this investigation, ligand modifications to reduce geometric strain were the next objective, and are reported in Section 5.3. 5.3 Attempted Synthesis of a Propylene-Tethered [prPNNP]H2 Ligand Framework 5.3.1 Introduction  The solid-state structure of 5.2, discussed in Section 5.2.3, showed that the constrained ring sizes of the [PNNP] framework cause significant distortion of the zirconium complex from ideal octahedral geometry.  Activation of dinitrogen with this [PNNP] ligand was unsuccessful, 124  and the logical progression of this framework is to alter the linker length between amido donors to allow for a less restricted geometry around zirconium, and perhaps better interaction of the amido donors to the metal centre.  The targeted framework, [prPNNP]H2, is shown in Figure 5.6.  Figure 5.6:  Proposed ligand [prPNNP]H2, as a design progression from 5.1. 5.3.2 Attempted Synthesis of [prPNNP]H2 via Aryl-Lithium Salt Metathesis  The reaction conditions outlined in Scheme 5.2 were employed with 1,3-dibromopropane and the protected phosphine sulfide aniline species, in an attempt to install the propylene tether en route to [prPNNP]H2.  Unfortunately, only minor conversion (10-25%) to two new species was observed by 31P{1H} NMR spectroscopy; these species produce signals at δ 62.2 and 62.3 in C6D6, and were not characterized further.  Alternative synthetic routes were investigated involving aryl-phosphine bond formation, on propylene tethered diamine compounds.  The typical route for installing an aryl phosphine bond is through a salt metathesis reaction of the aryl lithium with a chlorophosphine, as previously shown in Scheme 5.2 to produce 5.1.  The aryl lithium precursor can be prepared either by a lithium halogen exchange reaction, or directed ortho metalation, provided there is an appropriate directing group present.  When the targeted ligand contains an amine, care must be taken if there is a lithium amide functionality when attempting to install the aryl phosphine bond, as P-N bond formation occurs 125  as an unwanted side reaction.82  Work by the Cowie group demonstrated how to protect a lithium amide with an O-lithiocarbamate, perform directed ortho metalation with t-BuLi, and selectively form an aryl phosphine bond, as shown in Scheme 5.6.148  The N-methylaniline substrate can be seen to represent "half" of the targeted ligand [prPNNP]H2, and we envisioned that a similar methodology could be used for its synthesis.  The proposed synthetic approach to [prPNNP]H2 is shown in Scheme 5.7.  Scheme 5.6:  Formation of an ortho-aryl phosphine bond on N-methylaniline, through a directed ortho metalation pathway by the Cowie group.148 126   Scheme 5.7:  Proposed synthetic route to installing aryl phosphine groups on [prPNNP]H2 involving an O-lithiocarbamate protecting group.  The Cowie group found that the ortho-lithiation step in Scheme 5.6 required the more basic t-BuLi, as n-BuLi was unreactive under the same conditions.148  Since a proposed intermediate en route to [prPNNP]H2 is a tetraanion, there were concerns about the ortho-lithiation steps proceeding by directed ortho metalation.  An ortho-dibrominated diamine species was also targeted as a precursor, to enable the tetraanion formation by means of lithium halogen exchange if directed ortho metalation proved unsuccessful.  Accordingly, we attempted to install the propylene tether on commercially available o-bromoaniline, using similar reaction conditions 127  to those outlined in Scheme 5.2, substituting 1,3-dibromopropane for 1,2-dibromoethane.130,149  Unfortunately as described in Scheme 5.8, the 1,3-dibromo-, dichloro-, and diiodopropane reagents all led to elimination reactions rather than nucleophilic substitutions from o-bromoaniline in the presence of base.  The resulting allylbromide and allyliodide byproducts were identified by 1H NMR spectroscopy, but allylchloride was not observed as it was removed during purification steps by rotary evaporation, due to its lower boiling point of 45 oC.  Scheme 5.8:  Unwanted elimination reactions of 1,3-dihalopropane reagents with o-bromoaniline.  Drawing from the synthetic route used by the Fryzuk group to prepare the [mesNPN*]H2 ligand (see Section 2.2.1), the ortho-bromine functionality can be installed by N-bromosuccinimide (NBS) provided the para position is blocked.32  Starting with p-toluidine, treatment with 1,3-dibromopropane and KOH led to nucleophilic substitution rather than the elimination reaction; this diamine 5.4 has been previously prepared through a similar route.150  Initial bromination reactions of 5.4 were performed in acetonitrile by addition of two equivalents of NBS at 0 oC, however the reaction was not selective for the targeted dibrominated species, 5.5.  Presence of mono-, di-, tri-, and tetrabrominated diamines were confirmed by EI-MS, and column chromatography was necessary for isolation of 5.5.  We found that the use of ammonium acetate as a catalyst, and careful portionwise addition of NBS under conditions similar to those 128  outlined by the Thomas group, allowed for isolation of 5.5 in higher yield (53% compared to 21%) and only required recrystallization for purification.135,151  The synthesis of the propylene-tethered diamine 5.4, and its selective dibromination to produce 5.5 are shown in Scheme 5.9.  Scheme 5.9:  Synthesis of 5.5 via ortho-bromination of 5.4, from commercially available p-toluidine.  Deprotonation of the amine groups in 5.4 and 5.5 was completed by the addition of two equivalents of n-BuLi in THF, at -78 oC.  Installation of the O-lithiocarbamate protecting groups was achieved by bubbling CO2 into a THF solution of the dilithiated intermediate at room temperature for approximately 15 minutes.  Avoiding water is crucial to this protection step; best results were obtained by passing the CO2 through activated molecular sieves, followed by a cold trap at -78 oC to dry the gas prior to its addition to the reaction mixture.  Monitoring the initial dilithiation step by 1H NMR spectroscopy showed the loss of both amine proton resonances, as 129  well as the appearance of a single broad signal in the 7Li NMR spectrum.  After installation of the O-lithiocarbamate functionalities, the compound's solubility was reduced, which greatly broadens the 1H NMR signals in C6D6.  In the non-brominated compound (R = H of Scheme 5.10), there is an upfield shift from δ 1.03 to 0.65 in C6D6 in the 7Li NMR spectrum after installation of the O-lithiocarbamate groups from the lithium-amide.  The presence of only a single broad peak in the 7Li NMR spectrum indicates a symmetric compound, where both lithium-amide groups have been protected as the O-lithiocarbamate.  Scheme 5.10:  Attempted installation of ortho-phosphine groups on 5.4 and 5.5 through O-lithiocarbamate intermediates.  Scheme 5.10 describes the formation of the O-lithiocarbamate protected intermediates, the procedure is the same for both 5.4 and 5.5.  Attempts to ortho-lithiate this intermediate by directed ortho metalation (R = H) were performed by the addition of two equivalents of t-BuLi at -78 oC.  When attempting lithium halogen exchange on the ortho-brominated species, either two 130  equivalents of n-BuLi or four equivalents of t-BuLi were added at -78 oC.  In all cases, after the addition of two equivalents of ClPiPr2 followed by degassed water to remove the carbamate protecting groups, the major phosphorus-containing products were phosphine oxide species.  The most easily identified compound by 1H and 31P{1H} NMR spectroscopy, and EI-MS was O=PHiPr2.  Further test reactions were carried out with the less costly ClPPh2 reagent, which led to identification of the unwanted byproducts O=PHPh2 and Ph2P-P(O)Ph2.  We were concerned that the ortho-lithiation step was unsuccessful, leaving unreacted chlorophosphine reagents in the reaction mixture until they were quenched upon addition of degassed water to form phosphine oxides.  To test if directed ortho metalation to form the tetraanion was possible, the supposed tetraanionic intermediate of Scheme 5.10 was quenched with D2O (rather than ClPiPr2) to label all lithiated sites.  Although 1H NMR spectroscopy showed the absence of N-H resonances, the ortho-aryl protons were still present and coupled to the meta-protons.  Lithium halogen exchange from 5.5 also proved unsuccessful to form the tetraanion, as EI-MS confirmed the presence of 5.5 after the series of reactions shown in Scheme 5.10 were carried out.  Since formation of the proposed tetraanionic intermediate through the O-lithiocarbamate protection route proved challenging, an alternative silylamine protection route was investigated.  Installation of a silicon heterocycle to form a diazasilolidine would prevent lithium-amide formation, which leads to P-N bound byproducts, and only require a dianionic intermediate before chlorophosphine addition.  The silylamine functionality is stable to alkyllithium reagents, and the protecting group can be removed with tetra-n-butylammonium fluoride (TBAF).152  Initial attempts to install this functionality were through the salt metathesis reaction of SiMe2Cl2 with the lithium-amide dianionic compounds of 5.4 and 5.5 (prepared as shown in Scheme 5.10).  131  Although some conversion to the intended diazasilolidine products was observed by 1H NMR spectroscopy (<50%), this route was not clean.  Instead, a transamination method using SiMe2(NEt2)2 at elevated temperature proved more successful with 5.4 to produce the diazasilolidine compound, 5.6.153  Unfortunately, without the presence of an ortho-directing group, deprotonation of 5.6 with n-BuLi was unsuccessful.  Treatment with the stronger base t-BuLi, and subsequent addition of ClPiPr2 did not achieve reasonable selectivity for the di-ortho-phosphine substituted product.  As proof of concept, TBAF was able to remove the protecting group from 5.6 to regenerate 5.4.  We hoped that lithium halogen exchange on the dibrominated compound would allow for formation of the dilithium salt of the silylamine protected compound.  However, under the same conditions as used for formation of 5.6, the transamination reaction did not proceed on 5.5.  Increased temperatures led to decomposition of the starting materials.  Use of the diazasilolidine functionality and the attempt to install ortho-phosphine groups on the resulting compound 5.6 is summarized in Scheme 5.11. 132   Scheme 5.11:  Attempted installation of ortho-phosphine groups on 5.4 by using a diazasilolidine protecting group to form 5.6, and failure to install the same functionality on 5.5. 5.3.3 Attempted Synthesis of [prPNNP]H2 via Nickel Template Reactions  Due to difficulties in installing aryl phosphine bonds on 5.4 and 5.5 through salt metathesis routes (Section 5.3.2), a nickel template route was also investigated for inserting the propylene tether on the ortho-phosphine substituted aniline compound, 2-(PiPr2)PhNH2.  Synthesis of 2-(PiPr2)PhNH2 was achieved by installing the ortho-phosphine group on phenylisocyanate, through a t-BOC protected intermediate, as shown in Scheme 5.2.130  The nickel template reaction is an elegant solution to protecting the phosphine groups, while bringing the amine functionalities of two anilines in proximity before installing the propylene tether.  This template concept has been used in literature to install a propylene tether on an ortho-diphenylphosphine aniline, as shown in Scheme 5.12.137  We envisioned that a similar method would enable the conversion of 2-(PiPr2)PhNH2 to the targeted ligand [prPNNP]H2. 133   Scheme 5.12:  Nickel template reaction to install a propylene tether on an ortho-phosphine aniline, adapted from literature.137  The initial dicationic nickel complex, 5.7, was synthesized in hot ethanol similar to the literature preparation of the diphenylphosphine-substituted analogue; the reaction is shown in Scheme 5.13.137  The 1H NMR spectrum of 5.7 indicates a symmetric structure, with two distinct environments for the isopropyl-CH3 protons.  The amine protons are not observed in the 1H NMR spectrum in CD3CN.  There is a single broadened signal in the 31P{1H} NMR spectrum at δ 63.5 in CD3CN. 134   Scheme 5.13:  Synthesis of 5.7 for Ni template reactions.  Deprotonation of 5.7 to generate 5.8 was achieved by the addition of excess NEt3 in degassed acetone at room temperature, as shown in Scheme 5.14.  The neutral compound 5.8 is more soluble in benzene than 5.7, and the NMR spectra were much better resolved.  The 1H NMR spectrum of 5.8 similarly indicates a symmetric species, with two separate environments for the isopropyl-CH3 protons.  As well, the amido protons are observable for 5.8 in C6D6, confirming that deprotonation was successful as integration values correlate to one proton per ligand.  Unlike the neutral nickel complex of the diphenylphosphine-substituted analogue in literature, shown in Scheme 5.12, 5.8 does not contain an equivalent of acetone as observed by 1H NMR spectroscopy.137  The EI-MS data for 5.8 shows a parent ion M+ of m/z 474, as expected for the square planar complex.  There is a single well-defined singlet at δ 47.4 in the 31P{1H} NMR spectrum in C6D6.  The analogous reported compound Ni(NHArPPh2)2 produces two signals in the 31P{1H} NMR spectrum at an 85:15 ratio of the cis and trans complexes.137  This indicates that 5.8 forms as one isomer selectively, unlike the diphenylphosphine-containing analogue.  Crystals of 5.8 suitable for X-ray analysis were grown from a concentrated benzene solution, and the solid-state molecular structure shows that the compound exists in the trans arrangement.  The ORTEP representation of 5.8 is shown in Figure 5.7, with selected bond lengths and angles summarized in Table 5.2. 135   Scheme 5.14:  Deprotonation of 5.7 to form 5.8.  Figure 5.7:  Solid-state structure (ORTEP) of 5.8, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms, other than those bound to amido donors, are omitted for clarity.  Half of the molecule has been generated by symmetry.   136  Table 5.2:  Selected bond lengths (Å) and angles (deg) for 5.8.  Parameter (Å/o)   Ni1 - N01 1.8689(11)   Ni1 - P01 2.1976(3)       N01 - Ni1 - P01i 95.16(3)   N01 - Ni1 - N01i 180.00(9)   P01 - Ni1 - P01i 180.000(19)   N01 - Ni1 - P01 84.84(3)    The Ni1-N01 and Ni1-P01 bond lengths in 5.8 (Table 5.2) are equivalent to the Ni-N and Ni-P bond lengths of 1.862(9) and 2.190(3) Å in the analogous diphenylphosphine-substituted complex.137,154  As well, the internal ligand angle of 84.84(3)o for N01-Ni1-P01 is identical to the 84.9(3)o angle of the reported diphenylphosphine-substituted complex.137,154  As previously stated, the literature compound Ni(NHArPPh2)2 was formed in an 85:15 ratio for cis:trans isomers, and there was no published evidence for a trans-effect stabilization leading to the favoured cis isomer.137,154  The increased steric bulk of changing diphenylphosphine groups to diisopropylphosphine substituents is likely responsible for selective formation of the trans isomer in 5.8.  In the literature example of the diphenylphosphine-substituted analogue Ni(NHArPPh2)2OC(CH3)2, the propylene tether was installed using 1,3-bis(toluene-p-sulphonyloxy)propane in the presence of potassium carbonate (Scheme 5.12).137  Alternative reagents 1,3-dichloro- and 1,3-dibromopropane were unreactive, and initial nucleophilic attack was determined to occur at a tosylated carbon.137  The same reaction conditions were used with 5.8 and 1,3-bis(toluene-p-sulphonyloxy)propane, resulting in no interaction in refluxing toluene.  Alternative bases LDA and KH were used (separately) at room temperature, but did not lead to 137  reaction between the amide and tosylated carbon.  Treatment of 5.8 with 1,3-bis(methylsulfonyloxy)propane in the presence of potassium carbonate or LDA was also unsuccessful in achieving nucleophilic attack of a mesylated carbon.  Use of 1,3-diiodopropane in the presence of potassium carbonate led to partial conversion to a mixture of compounds with downfield shifts in the 31P{1H} NMR spectrum, uncharacteristic of the expected range for the intended tethered product.  The failed attempts to install a propylene tether on 5.8 are summarized in Scheme 5.15.  Scheme 5.15:  Attempted installation of propylene tether on 5.8.  Conditions a:  4 K2CO3, toluene, reflux.  Conditions b:  2 LDA, ether, 25 oC.  Conditions c:  8 KH, THF, 25 oC. 5.3.4 Summary  The tetradentate ligand 5.1 was strategically redesigned to include a propylene tether, in order to reduce geometric constraint on resulting metal complexes and provide more idealized metal-amido interactions.  Attempted syntheses of [prPNNP]H2 by installing the ortho-phosphine groups via a tetraanionic intermediate were unsuccessful, as ortho-lithiation of the O-lithiocarbamate protected intermediates could not be achieved under a variety of reaction conditions.  Use of a silylamine protecting group to form the diazasilolidine 5.6 did not allow for 138  directed ortho metalation, and the same protecting group could not be installed on the ortho-brominated precursor 5.5.  The alternative synthetic route of installing the tether on the ortho-phosphine aniline was also investigated through a nickel template synthesis.  Although the neutral nickel complex 5.8 was synthesized, nucleophilic substitution reactions of the amine were not possible due to the trans-arrangement of the ligands.  With these difficulties, further plans of the proposed ligand [prPNNP]H2 were abandoned. 5.4 Attempted Synthesis of an Ortho-Phenylene Silylamide [PhPSiNP]H Framework 5.4.1 Introduction  The silylamide functionality is a common aspect in many of the multidentate amidophosphine ligand sets used by the Fryzuk group since the first [PNP] framework was developed in 1981.20  Although the silylamide group can lead to unwanted ligand decomposition reactivity, as mentioned in Section 5.2.1 and described in Chapter 1, ligands incorporating this functionality have produced impactful transition metal chemistry.11,12,28,30,155  The more rigid and robust o-phenylene backbone has been investigated by the Fryzuk group in multiple [NPN*] type ligands, including the [NNN]H2 ligand (2.1) that is the focus of this thesis.32,82  A novel design concept was envisioned to combine the rigid o-phenylene linker with the silylamide functionality, and therefore maintain a similar amido donor strength to the original class of ligand.  As well, ligand geometry would be varied compared to the tridentate silylamide and o-phenylene systems, as the proposed ligand would produce 6-membered chelate rings with metal centres, as opposed to 5-membered rings.  The envisioned framework [PhPSiNP]H is shown in Figure 5.8, along with its design predecessors: the classic silylamide-containing [PNP]H ligand and a monoanionic tridentate o-phenylene design used by the Ozerov group, similar to the Fryzuk [NPN*] system.20,156  The Liang group is also heavily involved in research involving 139  similar sets of monoanionic o-phenylene bridged PNP-type ligands, and Mayer and co-workers have also used this framework.157-159  To the best of our knowledge, there are no classes of ligands that incorporate a secondary, potentially anionic silylamide functionality ortho to a neutral phosphine donor as shown in [PhPSiNP]H.  Figure 5.8:  Design of [PhPSiNP]H as a progression of the classic amidophosphine [PNP]H framework of the Fryzuk group, and the monoanionic o-phenylene bridged ligand used by the Ozerov group.20,156 5.4.2 Attempted Synthesis of [PhPSiNP]H  Two variations of [PhPSiNP]H were targeted, one with diphenylphosphine groups and the other with diisopropylphosphine groups.  The initial synthetic route was the installation of the secondary amine tether, bis(chlorodimethylsilyl)amine, on the appropriate arylphosphine through a salt metathesis reaction as described in Scheme 5.16.  This silylamine tether was prepared by reaction of hexamethyldisilazane with dichlorodimethylsilane in the presence of aluminum chloride as a catalyst.160  Ortho-brominated arylphosphine reagents 5.9 and 5.10 were 140  synthesized by salt metathesis reactions from 1,2-dibromobenzene and the corresponding ClPR2 reagents, using n-BuLi for lithium halogen exchange.161,162  It is crucial to keep the lithiated arylbromide intermediate at a temperature below -100 oC with a liquid nitrogen and diethyl ether cooling bath, as decomposition pathways occur at temperatures of -90 oC and above.163  Unfortunately, lithiation of 5.9 or 5.10 using n-BuLi and reaction with one-half equivalent of the silylchloride tether did not result in any formation of the targeted ligand, as evidenced by NMR spectroscopy.  Scheme 5.16:  Attempted synthesis of [PhPSiNP]H via salt metathesis pathway of 5.9 and 5.10 with the secondary silylamine tether.  An alternative synthetic route was designed based on a silylamine formation reaction published by Wismar and Wannagat, shown in Scheme 5.17.164  The procedure demonstrates the ability to selectively generate a secondary amine by reaction of excess ammonia gas with chloro(dimethyl)phenylsilane, which is the fundamental backbone of the targeted [PhPSiNP]H framework.  We hoped that the method was robust enough to support the same reactivity with the presence of an ortho-phosphine group.  In addition to this method, the Fryzuk group has also selectively formed a secondary amine through the transamination reaction of a 141  dimethylamidosilane with ammonia, which is generated in situ by the reaction of ammonium chloride with triethylamine.134  This transamination method is described in Scheme 5.18.  Scheme 5.17:  Formation of a secondary amine from a chlorosilane and ammonia, adapted from literature.164  Scheme 5.18:  Formation of a secondary amine through a transamination reaction, adapted from literature.134  The ortho-phosphine substituted chlorosilane complexes 5.11 and 5.12 were synthesized by treating 5.9 and 5.10 with n-BuLi for lithium halogen exchange, followed by addition of dichlorodimethylsilane; 5.11 has been reported, synthesized by a similar method.165  Although Breit and coworkers observed a siloxane impurity of ~10% in their synthesis of 5.11, there was no spectroscopic evidence for its presence by our procedure, as rigorous air- and moisture-sensitive precautions were maintained.165  The dimethylamidosilane-substituted variation of the diphenylphosphine compound, 5.13, was also synthesized by addition of LiNMe2 to 5.11.  The synthetic methods for preparation of 5.11, 5.12, and 5.13 are described in Scheme 5.19. 142   Scheme 5.19:  Synthesis of 5.11 and 5.12 via salt metathesis reactions of the ortho-lithiated phosphines with dichlorodimethylsilane, as well as the conversion to the silylamine compound 5.13.  A variety of reaction conditions were employed in attempt to convert 5.13 to the desired ligand [PhPSiNP]H through a transamination reaction.  There was no interaction between 5.13 and excess NH3(g) at room temperature in THF or at 100 oC in toluene over several days.  Additionally, there was no reaction when 5.13 was stirred with neat NH3(l) over two hours at -78 oC.  Treatment of 5.13 with ammonia that was produced in situ from ammonium chloride and triethylamine was also performed, similar to the conditions shown in Scheme 5.18.  Under these conditions, or when 5.13 was reacted with NH3(g) in the presence of ammonium chloride, partial conversion (~55%) to a new species that produced a signal at δ -10.2 was observed by 31P{1H} NMR spectroscopy, along with minor additional signals (~10%).  It is likely that the chlorosilane 143  was formed from reaction with ammonium chloride, essentially converting 5.13 back to 5.11, which is the reactive species with ammonia.  Reactions of the chlorosilane compounds 5.11 and 5.12 with NH3(g) or in situ generated ammonia were also investigated.  The same outcome resulted from the reaction of 5.11 with either excess NH3(g) in THF, or 3 equivalents of ammonium chloride with 5 equivalents of triethylamine to produce excess ammonia in THF.  In both cases nearly full conversion to a new species was observed by 31P{1H} NMR spectroscopy, which produces a signal at δ -10.2 in C6D6, compared to a signal at δ -11.1 for the starting material 5.11.  This is the same chemical shift as the species produced by reaction of 5.13 with NH3(g) in the presence of ammonium chloride.  Unfortunately the amine proton signal was not observable in the 1H NMR spectrum, which would enable integration to determine if the primary or secondary amine was formed.  Under similar experimental conditions, treatment of 5.12 with NH3(g) led to partial conversion to a new species (~70%) that produces a 31P{1H} NMR signal at δ 1.2 (C6D6), while unreacted 5.12 produced a signal at δ 1.3.  Since we obtained nearly full conversion to the silylamine species from the -PPh2 substituted compound 5.11, we treated the resulting ligand with [Rh(COE)2Cl]2.  Unfortunately, direct evidence for the production of the primary, rather than secondary, amine was found by XRD studies of a resulting rhodium complex.  When this diphenylphosphine-substituted silylamine ligand was added to [Rh(COE)2Cl]2 in C6D6 and monitored by 31P{1H} NMR spectroscopy, two doublets coupled to rhodium were initially observed at δ 48.2 and 56.5.  After 3 days at room temperature, only the doublet at δ 48.2 remained.  Single-crystal XRD studies of this compound show a bis-bidentate rhodium(I) chloride complex, 5.14, as presented in Figure 144  5.9 with selected bond lengths and angles in Table 5.3.  The synthesis of 5.14 through a primary amine intermediate is described in Scheme 5.20.  Scheme 5.20:  Synthesis of 5.14 from 5.11, through the formation of a primary amine.   Figure 5.9:  Solid-state structure (ORTEP) of 5.14, thermal ellipsoids are drawn at 50% probability.  Hydrogen atoms, other than those bound to amine donors, are omitted for clarity.  Half of the molecule has been generated by symmetry, and co-crystallized benzene is not shown. 145   Table 5.3:  Selected bond lengths (Å) and angles (deg) for 5.14.  Parameter (Å/o)   Rh1 - N01 2.142(2)   Rh1 - P01 2.2266(8)       N01 - Rh1 - P01 84.96(8)   N01 - Rh1 - N01i 85.09(15)   P01 - Rh1 - P01i 104.99(4)   N01 - Rh1 - P01i 170.03(7)   Rh1 - N01 - Si01 107.79(11)       P01 - N01 - N01i - P01i 0.9    The solid-state molecular structure of 5.14 shows the selective formation of the cis isomer of the square planar complex.  As isomerization between cis and trans isomers of cationic 16 electron Rh(I) square planar complexes is typically not observed in non-donor solvents, the intermediate species detected by 31P{1H} NMR spectroscopy is likely a mono-substituted rhodium complex.166  The geometry around the amine donor N01 clearly indicates a tetrahedral arrangement, with a Rh01-N01-Si01 angle of 107.79(11)o.  This confirms that the primary silylamine was formed during NH3(g) addition to 5.11, and the amine simply acts as a neutral donor to the resulting rhodium complex 5.14.  With confirmation that the targeted [PhPSiNP]H framework was not obtained through ammonia addition to 5.11, synthesis of an anionic bidentate ligand was undertaken. 5.4.3 Bidentate [PN]H Ortho-Phenylene Silylamine Ligand Class  As mentioned in Section 5.4.1, we are not aware of any reported class of secondary silylamine ligand with an ortho-phosphine donor through a phenylene bridge.  Due to the ease of 146  synthesis of 5.13 via addition of LiNMe2 to the silylchloride precursor 5.11, as described in Scheme 5.19, we were interested in expansion of the synthetic protocol.  Installation of secondary amines enables access to a new class of bidentate ligand, with a potentially anionic amido donor.  As proof of concept, 5.15 was synthesized by treatment of 5.11 with lithium 3,5-dimethylanilide, as shown in Scheme 5.21.  The Fryzuk group has studied late metal complexes of amidophosphine frameworks, with silylamide or cyclopentylidene linkers, including bidentate and tridentate donor systems.21,167-169  The bidentate ligand 5.15 and potential modifications should provide a platform for steric variety, while maintaining similar amido donor properties to the previously studied silylamide ligands.  Scheme 5.21:  Synthesis of new bidentate ligand 5.15 from 5.11.  The 31P{1H} NMR spectrum of 5.15 contains one singlet at δ -9.6 in C6D6, which is in the expected chemical shift range.  The 1H NMR spectrum indicates a symmetric structure with one singlet representing the silyl methyl groups at δ 0.73 in C6D6, and free rotation of the amine-aryl bond, as there is one singlet for both aryl-methyl groups at δ 2.08.  The amine N-H resonance was not observed in the 1H NMR spectrum.  A preliminary reactivity study of 5.15 involved treatment with one half equivalent of [Ir(COD)Cl]2 in hexanes or benzene, which showed complete conversion to a single phosphorus-147  containing species that displays a singlet at δ 17.5 in the 31P{1H} NMR spectrum in C6D6.  Reaction of this iridium(I) complex with excess NEt3 in C6D6 provided partial conversion (~40%) to a new species that produces a singlet at δ 18.4 in the 31P{1H} NMR spectrum, perhaps indicating that conversion to an anionic amido donor under these conditions is possible.  However, treatment of 5.15 with [Rh(COE)2Cl]2 in an attempt to synthesize the analogous complex to 5.14 was unsuccessful, resulting in multiple phosphorus-containing species that couple to rhodium as evidenced by 31P{1H} NMR spectroscopy. 5.4.4 Summary  A novel tridentate ligand framework [PhPSiNP]H was envisioned, containing both the ortho-phenylene linker and silylamine functionality that have been independently common to many ligands in the Fryzuk design catalogue.  Synthetic routes to install the secondary silylamine tether to ortho-lithiated arylphosphines were unsuccessful, and further strategies involved ammonia addition to silylchloride and silylamine functionalities.  However, XRD studies of a resulting rhodium complex, 5.14, showed that the primary silylamine forms selectively from these ammonia reactions rather than the targeted secondary amine.  Since 5.14 demonstrated that the ortho-phenylene silylamine framework has the ability to coordinate to metals in a bidentate fashion, a version of this framework was synthesized specifically as a bidentate ligand.  This neutral bidentate ligand 5.15 showed coordination to Ir(I) under preliminary reaction conditions, and has the ability to be deprotonated to act as an anionic amidophosphine ligand.  Although this bidentate ligand 5.15 was not the primary goal when designing the ortho-phenylene silylamine framework, it does open the synthetic pathway to a series of bidentate ligands which should be easily attainable via reactions of various lithium amides with silylchloride compounds 5.11 and 5.12. 148  5.5 Conclusion  The tetradentate dianionic [PNNP] ligand 5.1 was synthesized and treated with zirconium amido precursor compounds.  Although the ligand was not able to support dinitrogen reduction chemistry of the zirconium dichloride complex 5.3 and research focus was redirected, there are several possibilities for further chemistry with this ligand set.  Zirconium alkyl compounds and other small molecule activation chemistry (H2, CO) have not been investigated.  The deprotonation of 5.1 and subsequent salt metathesis reactions with tantalum precursors TaCl2Me3 and TaCl3(RC≡CR)(DME) has not been explored (see Chapter 4 for analogous chemistry with the [NNN] framework).  These directions leave many options for investigations with the [PNNP] framework.  Unfortunately, modification of this ligand to synthesize an alternate version containing a propylene-tether was unsuccessful, which would have allowed for interesting comparative reactivity studies.  Although we were unable to synthesize the targeted tridentate [PhPSiNP]H framework, a novel bidentate ligand 5.15 that contains a silylamine donor with an ortho-phenylene linker to a phosphine group was designed.  The framework should allow the modular synthesis of a variety of ligands by incorporating different secondary amines, as well as varying the phosphine groups.  While acknowledging that this bidentate ligand was not the initial goal, however, it is now available for future studies, and likely suited for late metal chemistry.    149  6 Summary and Future Directions 6.1 Summary  A new diamido-iminophosphorane ligand, [NNN] (2.1), was designed as a progression of tridentate ligand frameworks that are part of the Fryzuk group research program.  The ligand was based on the o-phenylene linked [NPN*] frameworks, through modification of the central phosphine donor to an iminophosphorane.  The potential modularity of the ancillary ligand (substituents on the amido N-atoms, phosphorane P-atom, and iminophosphorane N-atom), leading to a family of related [NNN] ligands, was a design appeal of the ligand.  Unfortunately, steric bulk of the ancillary ligand caused difficulty with the Staudinger route to generate the iminophosphorane, leading to the less bulky substituents that were chosen for 2.1.  Zirconium amido and chloride complexes of [NNN] were synthesized via protonolysis routes with the appropriate zirconium-amido precursors.   The dibenzyl zirconium complex was synthesized via a Grignard reaction with the dichloride precursor.  Reduction of the dichloride compound 3.2 with alkali metal reagents (KC8, Na(Hg)), led to cleavage of the iminophosphorane.  DFT analysis of the frontier orbitals of 3.2 showed that populating the LUMO with electron density leads to an antibonding interaction of the iminophosphorane P=N.  The LUMO of the analogous complex [tolylNPN*]ZrCl2(THF), which activates N2 upon reduction with KC8, has antibonding character between the Zr centre and chloride ligand, corroborating experimental results.  Steric analysis of the [NNN] ligand on zirconium showed that the inclusion of the iminophosphorane N-Ar group increases steric shielding to the metal centre (G value analysis) compared to [NPN*].  The shorter iminophosphorane N-Zr bond length of 3.2 compared to the P-Zr bond of [NPN]ZrX2 complexes caused a unique trend in %Vbur values across varying sphere radii for [NNN], compared to the [NPN] ligands.  The %Vbur of [NNN] 150  remains constant, rather than decreasing, at short radii from zirconium in 3.2.  The observed solution state equivalence of amido and benzyl ligands in 3.1 and 3.3 may be influenced by the unique steric environment of the [NNN] system.  A DMAP exchange competition experiment between 3.2 and [tolylNPN*]ZrCl2(THF) corroborated the steric calculations, which indicated increased steric shielding of [NNN], thus slower substitution compared to[tolylNPN*].  Tantalum trimethyl and alkyne complexes stabilized by [NNN] were synthesized via reaction of the dipotassium salt of [NNN], 4.1, and the appropriate tantalum halide precursors.  Treatment of the trimethyl compound 4.2 with dihydrogen led to cleavage of the iminophosphorane, whereas the analogous compound [mesNPN*]TaMe3 formed a ditantalum tetrahydride complex under similar conditions.34  Alternatively, the tantalum alkyne complex 4.5 was unreactive towards dihydrogen at room temperature, and an intractable mixture of products resulted from heating the reaction mixture.  The analogous compound stabilized by the [mesNPN*] framework generated a tantalum-hydride alkene compound en route to the dinuclear tetrahydride complex.34  Treatment of the tantalum alkyne complex 4.3 with an aryl azide reagent generated the tantalum imido complex, 4.4.  A new tetradentate [PNNP] ligand 5.1 was synthesized, and was installed on zirconium amido and chloride precursors via protonolysis routes.  Reduction of the dichloride complex 5.3 did not lead to isolation of a dinitrogen compound, and the framework was redesigned to incorporate a propylene, rather than ethylene linker.  Synthesis of the targeted [prPNNP]H2 ligand was attempted via an O-lithiocarbamate protected intermediate, but the tetraanionic intermediate en route to aryl-phosphine bond formation could not be generated.  Alternatively, protection of the amine groups as a diazasilolidine was employed, but the compound 5.6 did not undergo ortho metalation.  A nickel template route was also investigated in attempt to synthesize [prPNNP]H2, 151  unfortunately, the nickel complex 5.8 formed in the trans arrangement, preventing the installation of the propylene tether.  A new tridentate ligand incorporating both o-phenylene linkers and the silylamide functionality, [PhPSiNP]H, was then designed.  Although we were unable to synthesize the targeted tridentate framework, we synthesized a bidentate [PN] ligand, 5.15, with an o-phenylene linker and silylamide functionality.  No ligands of this class exist in the literature. 6.2 Conclusions  Initial design goals of the [NNN] framework were met:  zirconium and tantalum compounds analogous to the library of [NPN]-stabilized early metal complexes were synthesized, the 6-membered chelate rings formed by the inclusion of the iminophosphorane allowed for relaxed ligand geometry compared to [NPN*] frameworks, and cyclometalation decomposition pathways were not observed for [NNN] due to the internal position of the iminophosphorane.  Unfortunately, the iminophosphorane of the [NNN] framework was a liability during the reduction of the zirconium compound 3.2.  Similarly, the iminophosphorane was involved when the tantalum trimethyl complex 4.2 was treated with dihydrogen.  The iminophosphorane functionality in [NNN] is not stable towards reducing early metals, and this system is poorly suited to reduction reactivity studies.  Additionally, the tantalum alkyne complex 4.5 did not react with dihydrogen akin to the [mesNPN*]-stabilized system.  The increased steric hindrance of the [NNN] ligand, due to the iminophosphorane N-Ar unit, may be a disadvantage compared to the analogous [NPN] frameworks. 6.3 Future Directions  The steric studies of the [NNN] ligand in Chapter 3, specifically the %Vbur calculations of Section 3.5.3, showed the unique trend of %Vbur over short sphere radii for [NNN] compared to 152  [NPN] ligands.  We attributed this trend to the shorter metal-iminophosphorane bond, 2.2155(13) Å in 3.2, compared to metal-phosphine bonds of [NPN]ZrX2 complexes that are typically 2.6-2.8 Å.32,82  Additionally, the inclusion of the N-aryl group of the iminophosphorane in [NNN] increases steric shielding of the metal centre compared to [NPN*] ligands, as shown by the G Value calculations in Section 3.5.2.  Modification of the [NPN*] framework to include phosphine sulfide and phosphine oxide functionalities, as proposed in Scheme 6.1, would lead to similar geometries as the [NNN] ligand, but avoid the extra bulk of the N-aryl group.  The Zr-OPR3 bond distance is comparable to the Zr-NP3 bond lengths, while Zr-SPR3 bonds are ~2.7 Å, which is similar to the Zr-PR3 bond lengths of [NPN]ZrX2 systems.55,170  A phosphine sulfide-substituted [NSN] framework should allow for similar geometries to the [NNN] ligand, but with steric characteristics near the metal centre more similar to [NPN*].   153   Scheme 6.1:  Potential synthetic routes to proposed ligands [NSN]H2 and [NON]H2, from [NPN*]H2.  The DFT analysis of compound 3.2 showed antibonding character of the P=N bond in the LUMO, and this bond was cleaved during the reduction of 3.2 with alkali metals.  It may prove useful to study the proposed compounds [NSN]ZrCl2THF and [NON]ZrCl2THF in silico, based on the solid state structure of 3.2, to analyze if the phosphorane centre may be involved during reduction studies prior to synthesizing the proposed ligands.  Several variations of [NSN] and [NON] ligands could be synthesized, provided the oxidation reactions of Scheme 6.1 are successful.  The phosphorane P-R substituent may be phenyl or isopropyl, as [NPN*] frameworks including each of these phosphorus substitutions have been synthesized.  Additionally, a variety of amido N-Ar substituted [NPN*] ligands have 154  been studied.82  While bulky amine N-Ar groups hindered the 4-centered transition state of the Staudinger reaction en route to iminophosphorane generation of [NNN] ligands (Chapter 2), they should not hinder [NSN] and [NON] synthesis.  The proposed ligands [NSN] and [NON] are a logical design progression from the findings of the iminophosphorane-containing [NNN] ligand, and are shown in Figure 6.1.  For solubility and crystallization properties, characteristic resonances for NMR studies, and steric factors, [NSN] and [NON] variations with R = iPr and Ar = p-tolyl are recommended as the first iteration of ligands.  Figure 6.1:  Proposed [NSN] and [NON] ligands, compared to [NNN].  Regarding the [NNN] framework, further studies can be undertaken across the periodic table.  Based on the iron dinitrogen compound supported by an iminophosphorane-containing ligand (Scheme 1.3), late metal complexes may be less capable of cleaving the iminophosphorane.62  There are many examples of group 6-9 metal complexes of dinitrogen that have led to element-nitrogen bond formation, as well as cleavage of dinitrogen; this topic has been recently reviewed.10  Salt metathesis routes towards generating [NNN]-stabilized Fe(III) chloride, Mo(III) chloride, W(III) chloride, and Cr(III) chloride complexes can be attempted with the dipotassium salt of [NNN], 4.1.  Alkali metal reduction of these compounds (KC8, Na(Hg)) 155  under a dinitrogen atmosphere can be performed towards dinitrogen activation.10,171  Additionally, it may be interesting to probe if the internal position of the iminophosphorane donor in [NNN] prevents cyclometalation processes of rare-earth (Lu, Y) alkyl complexes, as no cyclometalation reactivity was observed for [NNN]-supported zirconium and tantalum alkyl species.72,79  Additionally, the tetradentate [PNNP] framework, 5.1, can be studied on tantalum.  Salt metathesis routes to synthesize the tantalum trimethyl compound should be investigated.  The macrocyclic tetradentate [P2N2] ligand, with silylamide linkers, was able to stabilize a dinuclear tetrahydride complex, but this complex did not activate dinitrogen.132  A comparison of the [PNNP]-supported tantalum complex, with a different donor array and potentially labile phosphine donor atoms, may enable unique reactivity.   156  7 Experimental 7.1 General Procedures 7.1.1 Laboratory Equipment and Procedures  Unless specifically noted, all experiments were conducted using standard glovebox (M. Braun equipped with -35 oC freezer) and Schlenk techniques under a dry, oxygen-free N2 atmosphere.  Glassware was oven-dried (200 oC) and cooled under dynamic vacuum.  Molecular sieves were dried under dynamic vacuum at elevated temperature prior to use. 7.1.2 Solvents  Anhydrous THF, diethyl ether (ether), hexanes, benzene, and toluene were purchased from Aldrich in Pure-Pac 1 format, further degassed via sparging with N2, passed through columns of alumina, and stored over activated molecular sieves.  Pentane was refluxed over sodium benzophenone ketyl, distilled under an Ar atmosphere, degassed via freeze-pump-thaw cycles, and stored over activated molecular sieves.  CH2Cl2 was degassed by sparging with N2, and distilled from calcium hydride.  When water, methanol, ethanol, or acetone is specified as degassed, it was via sparging with N2.  C6D6 and d8-THF were vacuum transferred from sodium benzophenone ketyl solutions to vessels containing activated molecular sieves, and degassed via freeze-pump-thaw cycles.  Anhydrous d8-toluene, d5-pyridine, and CD3CN were stored on activated molecular sieves and degassed via freeze-pump-thaw cycles.  Gaseous reagents (H2, D2, NH3) were dried by passage through a trap containing activated molecular sieves; CO2 was passed through activated molecular sieves and a cold trap at -78 oC. 157  7.1.3 Materials  Unless otherwise noted, reagents were obtained from commercial sources and used as received.  Grignard reagents, n-BuLi, t-BuLi, and MeLi were purchased as solutions and used as received.  KH was purchased as a 30% dispersion in mineral oil, washed with pentane, and dried under vacuum.  NEt3 was dried by distillation from calcium hydride.  Para-isopropylaniline was vacuum distilled prior to use.  DMAP was dried under vacuum.  Dichlorodimethylsilane and diethylamine were vacuum distilled and degassed via freeze-pump-thaw cycles.  3,5-dimethylaniline (3,5-xylidine) was distilled onto molecular sieves.  Bis(diethylamino)dimethylsilane was prepared via reaction of dichlorodimethylsilane and diethylamine in ether at room temperature.  Zr(NMe2)2Cl2(DME),172 TaMe3Cl2, Ta(BTA)Cl3DME,125 Ta(3-hexyne)Cl3DME,124 2,6-Me2PhN3,92 MsO(CH2)3OMs,173 TsO(CH2)3OTs,137 (ClSiMe2)2NH,160 [tolylNPN*]H2,82 [mesNPN*]H2,32 [mesNiPrPN*]H2,35 [tolylNPN*]ZrCl2(THF),82 o-C6H4(PSiPr2)(NHCH2CH2NH)(PSPiPr2)o-C6H4,130 o-PiPr2(NH2)Ph,130 and 5.9161 were prepared according to literature procedures; syntheses performed with modification to literature procedures are detailed in Section 7.2.  Use caution when handling azide reagents.174  Avoid halogenated solvents, contact with metals (e.g. spatulas), heat, and impact. 7.1.4 Instrumentation and Methods of Analysis  NMR spectra were acquired on a Bruker Avance 300, Avance 400, Avance III 300, or Avance III HD 400 MHz spectrometer at 25 oC (unless temperature otherwise stated).  1H and 13C NMR chemical shifts were referenced to residual solvent signals relative to TMS (δ 0.0).  31P NMR chemical shifts were referenced to external samples of phosphoric acid (85% in aqueous solution) at δ 0.0. 158   Elemental analyses (EA) were performed using a Carlo Erba Elemental Analyzer 1108 by Mr. Derek Smith, at the Department of Chemistry, University of British Columbia.  Electron ionization mass spectrometry (EI-MS) analysis were performed using a Kratos MS-50 spectrometer by Mr. Marshall Lapawa at the Department of Chemistry, University of British Columbia.  Single crystal X-ray data was collected on a Bruker APEX DUO (with Mo and Cu sources) or a Bruker X8 APEX (Mo source), and integrated using the Bruker SAINT software package.175  All non-hydrogen atoms were refined anisotropically, while hydrogen atoms were refined isotropically.  All hydrogen atoms were placed in calculated positions and assigned to an isotropic displacement parameter, unless specified as located in the difference map.  The XRD data was collected and solved by Dr. Nathan Halcovitch, Mr. Fraser Pick, and Dr. Vincent Annibale, while structures were refined by the author.  Structures were solved and refined using the WinGX software package (version 1.80.05).176  Crystallographic unit cell and refinement information is included in the Appendix. 7.2 Synthesis of Compounds 7.2.1 Complexes Pertaining to Chapter 2 4-iPrPhN3 Method was adapted from literature.92  Preparation was carried out in open air in a fume hood, in the absence of light, using aluminum foil to shield flasks when possible.  Do not use metal tools with azide-containing reagents; plastic scoopulas and glass pipettes are favoured.  Be aware of azide safety and proper disposal prior to using sodium azide or any corresponding azide-containing products.  Do not scale up procedures past safe ranges.  Do not use halogenated 159  solvents.  In a round bottom flask, 4-isopropylanline (2.15 mL, 15.7 mmol) was suspended in water (40 mL) and cooled to 0 oC.  Concentrated HCl (2.60 mL, 31.5 mmol) was added rapid dropwise to the suspension, and the resulting solution was stirred for 30 minutes while remaining in the ice bath.  A pre-cooled (0 oC) solution of NaNO2 (1.09 g, 15.8 mmol) in water (15 mL) was added dropwise over a 10 minute period, to maintain a reaction temperature between 0 and 5 oC.  The reaction was stirred for 10 minutes and a blast shield was assembled around the reaction vessel, prior to the dropwise addition of a solution of sodium azide (1.02 g, 15.7 mmol) in water (10 mL).  The reaction was stirred for 30 minutes at 0 oC, followed by 3 hours at room temperature.  The reaction mixture was extracted with diethyl ether, and dried under vacuum to produce an orange-yellow oil (1.97 g, 12.2 mmol, 78%).  Spectroscopic analysis agreed with previously published data for this compound.52 [NNN]H2 (2.1) A solution of 4-isopropylphenylazide (1.082 g, 6.71 mmol) in toluene (5 mL) was added to a toluene solution (10 mL) of [tolylNPN*]H2 (3.699 g, 6.72 mmol).  The reaction mixture was shielded from light and stirred overnight.  Dinitrogen is produced as a byproduct and may dislodge the reaction vessel’s cap if not vented during the reaction.  The solvent was then removed in vacuo, to afford a light yellow solid (3.495 g, 5.51 mmol, 82%).  31P{1H} NMR (C6D6, 121.5 MHz): δ 14.2.  1H NMR (C6D6, 400 MHz): δ 1.19 (d, 3JHH = 6.8 Hz, iPr-CH3, 6 H), 1.93 (s, CH3, 6 H), 2.04 (s, CH3, 6 H), 2.74 (sept, 3JHH = 6.8 Hz,  iPr-CH, 1 H), 6.84 (m, ArH, 9 H), 6.97 (d, 3JHH = 8.0 Hz, ArH, 4 H), 7.03 (d, 3JHH = 7.9 Hz, ArH, 2 H), 7.30 (m, ArH, 6 H), 7.85 (m, ArH, 2 H), 9.79 (s, NH, 2 H).  13C NMR (C6D6, 100.6 MHz): δ 20.5 (Ar-CH3), 20.8 (Ar-CH3), 24.6 (iPr-CH3), 33.8 (iPr-CH), 113.2 (Cipso), 114.2 (Cipso), 116.8 (d, JPC = 8 Hz, ArC), 120.7 (ArC), 122.9 (d, JPC = 17 Hz, ArC), 127.6 (ArC), 128.6 (d, JPC = 11 Hz, ArC), 130.1 160  (ArC), 131.0 (Cipso), 131.3 (Cipso), 131.7 (ArC), 131.8 (Cipso), 132.9 (d, JPC = 10 Hz, ArC), 133.6 (d, JPC = 11 Hz, ArC), 134.4 (ArC), 139.1 (Cipso), 140.2 (Cipso), 148.8 (Cipso).  EI-MS (m/z): 633 [M]+.  Anal. Calcd for C43H44N3P: C 81.49; H 7.00; N 6.63.  Found: C 81.82; H 7.31; N 6.91. 7.2.2 Complexes Pertaining to Chapter 3 [NNN]Zr(NMe2)2 (3.1) A toluene solution (3 mL) of 2.1 (0.121 g, 0.191 mmol) was added to solid Zr(NMe2)4 (0.051 g, 0.19 mmol) at room temperature, and the resulting orange-red solution was stirred overnight.  The solvent was removed in vacuo, the product was triturated with minimal hexanes, and the yellow solid was dried under vacuum (0.127 g, 0.157 mmol, 82%).  31P{1H} NMR (C6D6, 121.5 MHz): δ 25.3.  1H NMR (C6D6, 400 MHz): δ 1.02 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.89 (s, Ar-CH3, 6 H), 2.20 (s, Ar-CH3, 6 H), 2.55 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 2.68 (s, N-Me2, 12 H), 6.74 (d, 3JHH = 8.1 Hz, Ar-H, 2 H), 6.84 (m, Ar-H, 2 H), 6.89 (m, Ar-H, 2 H), 6.94 (m, Ar-H, 3 H), 7.03 (m, Ar-H, 2 H), 7.14 (s, Ar-H, 2 H), 7.26 (s, Ar-H, 1 H), 7.31 (s, Ar-H, 3 H), 7.33 (s, Ar-H, 2 H), 7.45 (m, Ar-H, 2 H), 2 Ar-H signals likely overlap with C6D6 residual 1H-signal.  13C NMR (C6D6, 100.6 MHz): δ 20.4 (Ar-CH3), 21.0 (Ar-CH3), 24.2 (iPr-CH3), 33.7 (iPr-CH), 41.7 (N-CH3), 106.9 (Cipso), 108.0 (Cipso), 121.1 (d, JPC = 9 Hz, ArC), 124.8 (d, JPC = 13 Hz, Cipso), 126.1 (ArC), 126.3 (d, JPC = 2 Hz, ArC), 127.9 (d, JPC = 8 Hz, ArC), 128.4 (d, JPC = 12 Hz, ArC), 130.6 (ArC), 131.5 (Cipso), 132.1 (ArC), 133.3 (d, JPC = 12 Hz, ArC), 133.6 (d, JPC = 9 Hz, ArC), 135.5 (ArC), 142.4 (d, JPC = 3 Hz, Cipso),145.3 (d, JPC = 7 Hz, Cipso), 149.6 (Cipso), 159.1 (d, JPC = 5 Hz, Cipso).  EI-MS (m/z): 765 [M – NMe2]+.  Anal. Calcd for C47H54N5PZr: C 69.59; H 6.71; N 8.63.  Found: C 69.40; H 6.73; N 8.29.   161  [NNN]ZrCl2(THF) (3.2) A THF (5 mL) solution of 2.1 (0.300 g, 0.473 mmol) was added to solid ZrCl2(NMe2)2(DME) (0.161 g, 0.473 mmol) and the resulting light orange solution was stirred overnight.  The solvent was then removed in vacuo, and the yellow solid was redissolved in THF (3 mL) and stirred for an additional hour to displace remaining HNMe2.  The solvent was again removed under vacuum to give a yellow solid as the 2.5 equivalent THF adduct (0.456 g, 0.468 mmol, 99%).  The product is always isolated as a THF adduct, typically between 2 and 3 equivalents as determined by 1H NMR spectroscopy, and the molecular weight for further reactions is calculated accordingly.  Note that the sample for microanalysis was further dried under vacuum, and the data was found for the di-THF adduct.  Crystals suitable for XRD analysis were grown from a 1:1 THF/hexanes mixture at -35 oC.  31P{1H} NMR (C6D6, 121.5 MHz): δ 31.7.  1H NMR (C6D6, 400 MHz): δ 1.02 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.31 (br s, THF, 10 H), 1.88 (s, CH3, 6 H), 2.12 (s, CH3, 6 H), 2.56 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 3.78 (br s, THF, 10 H), 6.67 (d, 3JHH = 8.1 Hz, Ar-H, 2 H), 6.75-6.96 (m, Ar-H, 10 H), 7.11 (d, 3JHH = 8.1 Hz, Ar-H, 4 H), 7.25-7.37 (m, Ar-H, 5 H), 7.53 (m, Ar-H, 2 H).  13C NMR (C6D6, 100.6 MHz): δ 20.4 (Ar-CH3), 21.2 (iPr-CH3), 24.3 (iPr-CH), 25.5 (THF-CH2), 33.8 (iPr-CH), 70.4 (THF O-CH2), 121.7 (ArC), 124.5 (Cipso), 125.4 (Cipso), 125.8 (br d, ArC), 127.2 (d, JPC = 14 Hz, Cipso), 128.0 (ArC), 128.2 (Cipso), 128.4 (ArC), 130.2 (ArC), 130.6 (br s, ArC), 131.1 (ArC), 132.0 (ArC), 134.3 (br s, ArC), 135.3 (Cipso), 135.5 (d, JPC = 8 Hz, ArC), 144.1 (d, JPC = 4 Hz, Cipso), 147.0 (d, JPC = 7 Hz, Cipso), 161.4 (Cipso).  EI-MS (m/z): 791 [M - THF]+.  Anal. Calcd for C51H58N3O2Cl2PZr: C 65.29; H 6.23; N 4.48.  Found: C 65.18; H 6.41; N 4.51.   162  [NNN]Zr(CH2Ph)2 (3.3) As the product 3.3 is light sensitive, the following procedure was performed with ambient lights turned off, and with aluminum foil covering reaction vessels.  A THF solution (10 mL) of 3.2 (0.518 g, 0.532 mmol) was cooled to -78 oC, and to it MgCl(CH2Ph) (1.1 mL, 1.0 M in diethyl ether, 1.1 mmol) was added.  The reaction mixture was warmed to room temperature and allowed to stir for 2 hours, before removing the solvent under reduced pressure.  The resulting orange solid was extracted with toluene and filtered through Celite.  The solvent was then removed in vacuo to afford the product as an orange-yellow solid (0.396 g, 0.437 mmol, 82%).  Yellow crystals suitable for X-ray analysis were grown from an ether solution at -35 oC.  31P{1H} NMR (C6D6, 121.5 MHz): δ 19.7.  1H NMR (C6D6, 400 MHz): δ 1.01 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.88 (s, CH3, 6 H), 2.17 (s, CH3, 6 H), 2.23 (s, CH2, 4 H), 2.50 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 6.36 (d, 3JHH = 6.7 Hz, Ar-H, 2 H), 6.54 (d, 3JHH = 8.2 Hz, Ar-H, 2 H), 6.79 (dd, 3JHH = 8.3 Hz, JHP = 2.2 Hz, Ar-H, 4 H), 6.86 (m, Ar-H, 2 H), 6.95 (m, Ar-H, 3 H), 6.99-7.03 (m, Ar-H, 6 H), 7.04-7.09 (m, Ar-H, 6 H), 7.14 (m, Ar-H, 2 H), 7.18 (s, Ar-H, 2 H), 7.22 (m, Ar-H, 2 H), 7.29 (d , 3JHP = 14.5 Hz, Ar-H, 2 H).  13C NMR (C6D6, 100.6 MHz): δ 20.4 (Ar-CH3), 21.0 (Ar-CH3), 24.2 (iPr-CH3), 33.8 (iPr-CH), 74.0 (Zr-CH2), 106.3 (Cipso), 107.3 (Cipso), 121.8 (d, JPC = 8 Hz, ArC), 122.0 (ArC), 126.8 (ArC), 127.4 (Cipso), 127.6 (Cipso), 128.1 (ArC), 128.3 (ArC), 128.4 (ArC), 128.5 (ArC), 128.6 (ArC), 131.2 (ArC), 132.6 (br s, ArC), 133.0 (d, JPC = 9 Hz, ArC), 133.3 (Cipso), 133.9 (d, JPC = 12 Hz, ArC), 136.5 (br s, ArC), 142.6 (d, JPC = 7 Hz, Cipso), 144.8 (d, JPC = 3 Hz, Cipso), 145.0 (Cipso), 157.3 (d, JPC = 5 Hz, Cipso).  EI-MS (m/z): 828 [M – C6H5]+.  Anal. Calcd for C57H56N3PZr: C 75.62; H 6.24; N 4.64.  Found: C 70.84; H 6.25; N 4.35.   163  [NNN]ZrCl2(DMAP) (3.5) A toluene solution (3 mL) of 4-dimethylaminopyridine (DMAP) (0.015 g, 0.12 mmol) was added to 3.2 (0.112 g, 0.119 mmol) and stirred for 3 hours.  The solvent was then removed under reduced pressure to afford the product (0.076 g, 0.083 mmol, 70%).  31P{1H} NMR (C6D6, 162.0 MHz): δ 32.1.  1H NMR (C6D6, 400 MHz): δ 0.93 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.91 (s, Ar-CH3, 6 H), 1.98 (s, N-CH3, 6 H), 2.11 (s, Ar-CH3, 6 H), 2.46 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 5.64 (d, 3JHH = 7.5 Hz, DMAP Ar-H, 2 H), 6.57 (d, 3JHH = 7.8 Hz, Ar-H, 2 H), 6.85 (m, Ar-H, 4 H), 6.88-6.98 (m, Ar-H, 6 H), 7.02 (m, Ar-H, 2 H), 7.12 (m, Ar-H, 4 H), 7.28-7.37 (m, Ar-H, 3 H), 7.57 (m, Ar-H, 2 H), 8.96 (d, 3JHH = 7.5 Hz, DMAP Ar-H, 2 H).  13C NMR (C6D6, 100.6 MHz): δ 20.4 (Ar-CH3), 21.2 (Ar-CH3), 24.2 (iPr-CH3), 33.6 (iPr-CH), 38.2 (N-CH3), 105.4 (DMAP ArC), 120.7 (ArC), 125.1 (Cipso), 125.7 (ArC), 126.0 (Cipso), 127.9 (ArC), 128.1 (Cipso), 128.3 (ArC), 128.4 (Cipso), 130.0 (ArC), 130.2 (br d, ArC), 131.6 (ArC), 131.8 (ArC), 134.3 (br d, ArC), 135.2 (Cipso), 135.6 (d, JPC = 8 Hz, ArC), 143.3 (d, JPC = 4 Hz, Cipso), 147.9 (d, JPC = 7 Hz, Cipso), 151.7 (DMAP ArC), 154.5 (Cipso), 161.6 (d, JPC = 4 Hz, Cipso).  EI-MS (m/z): 793 [M – DMAP]+, 756 [M – DMAP – Cl]+, 122 [DMAP]+.  Anal. Calcd for C50H52Cl2N5PZr: C 65.55; H 5.72; N 7.64.  Found: C 65.35; H 6.12; N 7.65. [tolylNPN*]ZrCl2(DMAP) (3.6) A toluene solution (3 mL) of DMAP (0.020 g, 0.16 mmol) was added to solid [tolylNPN*]ZrCl2(THF) (0.120 g, 0.164 mmol).  Additional toluene was added to the resulting yellow suspension (~10 mL total), which was stirred overnight.  The solvent was then removed under reduced pressure to afford the product as a yellow solid (0.104 g, 0.133 mmol, 83%), which is poorly soluble in benzene and dichloromethane.  31P{1H} NMR (C6D6, 121.5 MHz): δ 164  11.9.  1H NMR (CD2Cl2, 400 MHz): δ 2.19 (s, CH3, 6 H), 2.36 (s, CH3, 6 H), 2.97 (s, N-CH3, 6 H), 6.02 (dd, 3JHH = 5.5 Hz, 3JPH = 8.4 Hz, Ar-H, 2 H), 6.25 (d, 3JHH = 7.2 Hz, DMAP Ar-H, 2 H), 6.80 (br, Ar-H, 3 H), 6.94 (m, Ar-H, 2 H), 7.05 (m, Ar-H, 2 H), 7.12 (d, 3JHH = 8.0 Hz, Ar-H, 4 H), 7.44 (m, Ar-H, 4 H), 7.55 (m, Ar-H, 2 H), 8.37 (d, 3JHH = 7.2 Hz, DMAP Ar-H, 2 H).  13C NMR (CD2Cl2, 100.6 MHz): δ 20.3 (Ar-CH3), 21.0 (Ar-CH3), 39.1 (N-CH3), 105.5 (DMAP ArC), 116.4 (d, JPC = 10 Hz, ArC), 128.6 (d, JPC = 9 Hz, ArC), 129.5 (ArC), 129.8 (Cipso), 130.6 (ArC), 132.6 (ArC), 132.9 (ArC), 133.0 (ArC), 133.1 (ArC), 136.3 (Cipso), 150.9 (DMAP ArC).  Additional Cipso signals not observed due to poor compound solubility in non-coordinating deuterated solvents.  EI-MS (m/z): 782 [M]+, 693 [M – tolyl]+, 660 [M – DMAP]+, 121 [DMAP]+.  Anal. Calcd for C41H41N4PZr: C 62.90; H 5.28; N 7.16.  Found: C 61.64; H 6.01; N 6.97. 7.2.3 Complexes Pertaining to Chapter 4 [NNN]K2(THF)x (4.1) A THF solution (3 mL) of 2.1 (0.335 g, 0.529 mmol) was transferred into a vial of solid KH (0.044 g, 1.1 mmol) and stirred overnight.  Be aware that hydrogen gas is produced, and allow the reaction to vent excess pressure for the first 30-60 minutes, depending on scale.  The reaction mixture was then filtered through a glass pad with THF, and dried in vacuo for several hours to afford the product as the di-THF adduct (0.325 g, 0.380 mmol, 72%).  The product is a very insoluble yellow solid, and as such it is difficult to obtain useful NMR data.  There are typically 2-4 equivalents of THF in the isolated product, and the ratio is determined by integration of the 1H NMR spectrum in C6D6 at δ 2.42 or 2.59 (s, Ar-CH3, 3 H), compared to THF at δ 3.57 (m, CH2, 4 H per THF equivalent).  This ratio determines the molecular weight of the isolated species to be used for subsequent reactivity.  31P{1H} NMR (C6D6, 121.5 MHz): δ 22.0. 165  [NNN]TaMe3 (4.2) Reaction performed in the dark, with aluminum foil covering glassware.  The resulting [NNN]TaMe3 compound decomposes under exposure to ambient light, and it is best to store shielded from light at -35 oC.  A THF solution (4 mL) of 4.1 (5 equiv. THF) (0.079 g, 0.074 mmol) was cooled to -35 oC and added to a -35 oC THF solution (3 mL) of TaMe3Cl2 (0.022 g, 0.074 mmol).  The red reaction mixture was allowed to warm to room temperature, and stirred overnight.  The solvent was removed in vacuo, and the solid was extracted with toluene and filtered through Celite.  Removal of toluene under reduced pressure afforded an orange solid (0.066 g, 0.077 mmol, 78%).  Crystals suitable for XRD studies were grown from hexanes at -35 oC.  31P{1H} NMR (C6D6, 121.5 MHz): δ 19.9.  1H NMR (C6D6, 300 MHz): δ 0.98 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.51 (s, Ta-CH3, 9 H), 1.89 (s, CH3, 6 H), 2.12 (s, CH3, 6 H), 2.53 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 6.68 (s, Ar-H, 4 H), 6.75-6.88 (m, Ar-H, 4 H), 7.00 (m, Ar-H, 6 H), 7.03 (s, Ar-H, 2 H), 7.21 (m, Ar-H, 2 H), 7.25-7.30 (m, Ar-H, 5 H).  13C NMR (C6D6, 100.6 MHz): δ 20.5 (Ar-CH3), 21.0 (Ar-CH3), 24.2 (iPr-CH3), 33.6 (iPr-CH), 74.9 (Ta-CH3), 107.3 (Cipso), 108.4 (Cipso), 123.7 (d, JPC = 8 Hz, ArC), 126.6 (ArC), 126.7 (d, JPC = 3 Hz, ArC), 128.4 (ArC), 129.1 (d, JPC = 6 Hz, ArC), 129.1 (d, JPC = 13 Hz, Cipso), 130.3 (ArC), 132.4 (d, JPC = 11 Hz, ArC), 132.5 (d, JPC = 2 Hz, ArC), 133.4 (d, JPC = 9 Hz, ArC), 133.6 (Cipso), 136.7 (d, JPC = 2 Hz, ArC), 144.1 (d, JPC = 3 Hz, Cipso), 145.9 (Cipso), 146.3 (d, JPC = 5 Hz, Cipso), 156.8 (d, JPC = 5 Hz, Cipso).  EI-MS (m/z): 826 [M – 2CH3]+, 812 [M – 3CH3]+, 721 [M – 3CH3 – C7H7]+.  Anal. Calcd for C46H51N3PTa: C 64.41; H 5.99; N 4.90.  Found: C 64.69; H 6.20; N 4.74.   166  [NNN]Ta(BTA)Cl (4.3) Solid 4.1 (8 equiv. THF) (0.465 g, 0.361 mmol) and solid Ta(BTA)Cl3DME (0.198 g, 0.361 mmol) were suspended in toluene (15 mL) and stirred for 3 days.  The red solution was filtered through Celite with additional toluene used for further extraction.  Removal of the solvent under reduced pressure afforded the product as an orange-red solid (0.284 g, 2.79 mmol, 77%).  Orange needle-like crystals suitable for XRD studies were grown from a dilute ether solution at -35 oC.  31P{1H} NMR (C6D6, 121.5 MHz): δ 30.3.  1H NMR (C6D6, 300 MHz): δ -0.30-0.50 (br, Si-CH3, 18 H), 1.04 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.76 (s, CH3, 6 H), 2.18 (s, CH3, 6 H), 2.58 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 6.72-6.80 (m, Ar-H, 4 H), 6.87-6.96 (m, Ar-H, 6 H), 6.95-7.01 (m, Ar-H, 2 H), 7.07 (s, Ar-H, 2 H), 7.10 (s, Ar-H, 2 H), 7.13 (m, Ar-H, 1 H), 7.21 (s, Ar-H, 2 H), 7.23 (s, Ar-H, 2 H), 7.27 (br d, JHP = 14.7 Hz, 2 H).  13C NMR (C6D6, 100.6 MHz): δ 1.2 (Si-CH3), 20.3 (Ar-CH3), 21.0 (Ar-CH3), 24.2 (iPr-CH3), 33.9 (iPr-CH), 99.9 (Cipso), 100.9 (Cipso), 119.5 (d, JPC = 8 Hz, ArC), 126.5 (d, JPC = 3 Hz, ArC), 127.7 (d, JPC = 13 Hz, Cipso), 128.5 (d, JPC = 12 Hz, ArC), 129.0 (ArC), 129.3 (d, JPC = 5 Hz, ArC), 130.4 (ArC), 133.1 (d, JPC = 3 Hz, ArC), 133.9 (Cipso), 134.1 (d, JPC = 10 Hz, ArC), 134.2 (d, JPC = 11 Hz, ArC), 137.5 (ArC), 144.8 (d, JPC = 4 Hz, Cipso), 146.7 (d, JPC = 5 Hz, Cipso), 147.8 (Cipso), 158.1 (d, JPC = 4 Hz, Cipso), TMS-alkyne C-signals not observed.  EI-MS (m/z): 981 [M – Cl]+, 945 [M – SiCH3]+, 847 [M – BTA]+.  Anal. Calcd for C51H60ClN3PSi2Ta: C 60.14; H 5.94; N 4.13.  Found: C 60.21; H 6.08; N 3.73. [NNN]Ta=NPh(4-iPr)Cl (4.4) A toluene solution (5 mL) of 4-isopropylphenylazide (0.030 g, 0.19 mmol) was added to solid 4.3 (0.202 g, 0.182 mmol) and the resulting solution was stirred overnight.  The solvent was then 167  removed in vacuo to afford a dark residue, which was triturated with pentane (5 mL) until a fine yellow precipitate formed.  The yellow product was then isolated on a sintered glass frit and dried under reduced pressure to remove all volatiles (0.104 g, 0.106 mmol, 58%).  31P{1H} NMR (C6D6, 121.5 MHz): δ 25.8.  1H NMR (C6D6, 400 MHz): δ 1.00 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.08 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.82 (s, CH3, 6 H), 2.08 (s, CH3, 6 H), 2.52 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 2.64 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 6.40 (d, 3JHH = 8.2 Hz, Ar-H, 2 H), 6.65 (d, 3JHH = 8.2 Hz, Ar-H, 2 H), 6.77 (m, Ar-H, 2 H), 6.84 (m, Ar-H, 1 H), 6.89 (d, 3JHH = 8.3 Hz, Ar-H, 2 H), 6.98 (m, Ar-H, 4 H), 7.04 (d, 3JHH = 8.2 Hz, Ar-H, 4 H), 7.20 (dd, 3JHH = 8.7 Hz, JHP = 6.0, Ar-H, 2 H), 7.30 (br m, Ar-H, 2 H), 7.34 (m, Ar-H, 2 H), 7.73 (d, 3JHH = 8.2 Hz, Ar-H, 4 H).  13C NMR (C6D6, 100.6 MHz): δ 20.3 (Ar-CH3), 20.9 (Ar-CH3), 24.2 (iPr-CH3), 24.4 (iPr-CH3), 33.7 (iPr-CH), 33.9 (iPr-CH), 101.2 (Cipso), 102.2 (Cipso), 121.2 (d, JPC = 8 Hz, ArC), 125.5 (ArC), 125.6 (ArC), 127.0 (d, JPC = 2 Hz, ArC), 127.2 (d, JPC = 7 Hz, ArC), 127.3 (ArC), 127.7 (Cipso), 128.9 (d, JPC = 13 Hz, ArC), 130.4 (ArC), 133.1 (d, JPC = 10 Hz, ArC), 133.4 (d, JPC = 3 Hz, ArC), 133.5 (d, JPC = 12 Hz, ArC), 133.7 (Cipso), 137.7 (d, JPC = 2 Hz, ArC), 142.9 (Cipso), 144.5 (d, JPC = 3 Hz, Cipso), 146.2 (d, JPC = 5 Hz, Cipso), 147.2 (Cipso), 155.9 (Cipso), 157.7 (d, JPC = 4 Hz, Cipso).  EI-MS (m/z): 980 [M]+, 964 [M - CH3]+.  Anal. Calcd for C52H53N4PTa: C 63.64; H 5.44; N 5.71.  Found: C 52.22; H 4.49; N 5.02. [NNN]Ta(BTA)CH2Ph (4.5) An ether solution (5 mL) of 4.3 (0.185 g, 0.182 mmol) was cooled to -35 oC, and to it was added a diethyl ether solution of MgCl(CH2CH5) (0.19 mL, 1.0 M, 0.19 mmol).  The reaction mixture was allowed to warm to room temperature and stirred overnight, before volatiles were removed in vacuo.  The resulting red residue was extracted with minimal toluene and filtered through a glass pad.  Toluene was removed from the filtrate under reduced pressure, to afford the product 168  as a red solid (0.119 g, 0.111 mmol, 61%).  31P{1H} NMR (C6D6, 121.5 MHz): δ 25.5.  1H NMR (C6D6, 400 MHz): δ -0.39-0.55 (br, Si-CH3, 18 H), 1.01 (d, 3JHH = 6.9 Hz, iPr-CH3, 6 H), 1.82 (s, CH3, 6 H), 2.19 (s, CH3, 6 H), 2.56 (sept, 3JHH = 6.9 Hz, iPr-CH, 1 H), 3.21 (s, CH2, 2 H), 6.51 (t, 3JHH = 7.2 Hz, Ar-H, 1 H), 6.59-6.64 (m, Ar-H, 3 H), 6.67 (m, Ar-H, 2 H), 6.70-6.76 (m, Ar-H, 4 H), 6.79-6.84 (m, Ar-H, 4 H), 6.87 (dd, 3JHH = 7.4 Hz, 3JHP = 3.1 Hz, Ar-H, 2 H), 6.93-7.01 (m, Ar-H, 4 H), 7.05-7.10 (m, Ar-H, 6 H), 7.22 (d, 3JHP = 14.1 Hz, Ar-H, 2 H).  13C NMR (C6D6, 100.6 MHz): δ 1.5 (Si-CH3), 20.5 (Ar-CH3), 20.9 (Ar-CH3), 24.2 (iPr-CH3), 33.9 (iPr-CH), 76.2 (Ta-CH2), 99.8 (Cipso), 100.8 (Cipso), 119.5 (d, JPC = 8 Hz, ArC), 119.8 (ArC), 125.1 (ArC), 126.4 (ArC), 127.1 (ArC), 127.2 (Cipso), 128.7 (ArC), 129.1 (d, JPC = 6 Hz, ArC), 129.7 (d, JPC = 18 Hz, ArC), 130.6 (ArC), 132.6 (ArC), 133.6 (Cipso), 133.7 (d, JPC = 9 Hz, ArC), 134.1 (d, JPC = 11 Hz, ArC), 136.5 (ArC), 144.1 (d, JPC = 4 Hz, Cipso), 146.3 (d, JPC = 6 Hz, Cipso), 149.1 (Cipso), 155.5 (Cipso), 157.4 (d, JPC = 4 Hz, Cipso).  EI-MS (m/z): 998 [M – C6H5]+, 981 [M – C7H7]+.  Anal. Calcd for C58H67N3PSi2Ta: C 64.85; H 6.29; N 3.91.  Found: C 64.79; H 6.04; N 3.89. 7.2.4 Complexes Pertaining to Chapter 5 [PNNP]H2 (5.1) Procedure based on a previous literature preparation.130  A mixture of o-C6H4(PSiPr2)(NHCH2CH2NH)(PSPiPr2)o-C6H4 (1.99 g, 3.91 mmol) and Raney-nickel (22.96 g, 391 mmol) in degassed MeOH (40 mL) was allowed to stir for 4 days.  The solvent was removed under reduced pressure, and the residue extracted with dichloromethane.  After filtration through celite, a yellow solid (0.530 g, 30%) was obtained by concentration in vacuo.  31P{1H} NMR (C6D6, 162 MHz): δ -17.1.  1H NMR (C6D6, 300 MHz): δ 0.92 (dd, 3JHH = 6.9 Hz, 3JPH = 11.9 Hz, CH3, 12 H), 1.08 (dd, 3JHH = 7.1 Hz, 3JPH = 15.5 Hz, CH3, 12 H), 1.93 (m, P-CH-R2, 4 H), 169  3.00 (s, CH2, 4 H), 5.74 (br s, N-H, 2 H), 6.38 (d, 3JHH = 8.0 Hz, 2 H), 6.48 (m, 2 H), 6.71 (t, 3JHH = 7.1 Hz, 2 H), 7.15 (m, 2 H). [PNNP]Zr(NMe2)2 (5.2) A mixture of 5.1 (0.163 g, 0.367 mmol) and Zr(NMe2)4 (0.098 g, 0.37 mmol) were stirred for 24 hours in pentane (5 mL).  The solvent was then removed in vacuo.  Crystals suitable for X-ray analysis were grown from layering pentane and THF.  1H NMR (C6D6, 300 MHz): δ 7.32 (m, 2 H), 6.95 (m, 2 H), 6.69 (m, 2 H), 6.59 (m, 2 H), 3.66 (s, CH2, 4 H), 2.78 (s, NMe2, 12 H), 2.01 (m, P-CH-R2, 4 H), 1.13 (dd, 3JHH = 7.1 Hz, 3JPH = 14.4 Hz, CH3, 12 H), 0.95 (dd, 3JHH = 6.9 Hz, 3JPH = 11.65 Hz, CH3, 12 H).  31P{1H} NMR (C6D6, 121.5 MHz): δ 2.32.  13C NMR (C7D8, 100.6 MHz): δ 132.4, 131.4, 115.2, 112.0 (m), 56.2 (t, JCP = 3.8 Hz, -CH2-), 44.4 (NMe2), 23.1, 19.9 (m), 18.0.  Quaternary carbon signals not observed. [PNNP]ZrCl2 (5.3) Method A (preferred):  Zr(NMe2)2Cl2(DME) (0.014 g, 0.041 mmol) and 5.1 (0.018 g, 0.040 mmol) were dissolved in C6D6 (1 mL).  Monitoring by 31P{1H} NMR spectroscopy indicated a complete reaction after 3 hours.  Solvent was removed in vacuo to afford the product.  Crystals were grown from a benzene solution but did not diffract.  31P{1H} NMR (C6D6, 121.5 MHz): δ 13.5.  1H NMR (C6D6, 300 MHz): δ 7.25 (m, 2 H), 6.90 (m, 2 H), 6.71 (m, 2 H), 6.45 (m, 2 H), 3.78 (s, CH2, 4 H), 2.32 (m, P-CH-R2, 4 H), 1.25 (dd, 3JHH = 6.9 Hz, 3JPH = 15.6 Hz, CH3, 12 H), 1.13 (dd, 3JHH = 7.1 Hz, 3JPH = 12.2 Hz, CH3, 12 H).  Method B:  A mixture of 5.2 (0.084 g, 0.14 mmol) and trimethylsilylchloride (0.14 mL, 1.1 mmol) were stirred for 24 h in THF (2 mL).  No reaction was observed by 31P{1H} NMR spectroscopy, and the THF was subsequently removed under reduced pressure.  The solids were dissolved in toluene (3 mL), and within 20 hours the 170  31P{1H} NMR spectrum indicated product formation.  Note:  there is 10-20% of mono-substituted product present  by 31P{1H} NMR (C6D6, 121.50 MHz): δ 17.80 (d, 2JPP = 60 Hz), -4.00 (d, 2JPP = 60 Hz). 4-tolyl(NH)(CH2)3NH-4-tolyl (5.4) Procedure based on a previous literature preparation of 5.4.149,150  On the benchtop 1,3-dibromopropane (0.76 mL, 7.49 mmol) was added dropwise to p-toluidine (3.19 g, 29.8 mmol) in an oil bath set to 110 oC.  After 2 hours, the reaction was cooled to room temperature, and a solution of KOH (1.05 g, 18.7 mmol, in 3.0 mL H2O) was added.  The organics were extracted with dichloromethane, dried over MgSO4, filtered, and concentrated in vacuo.  Unreacted p-toluidine was removed by vacuum distillation at 60 oC, 0.1 torr.  Some impurities are present in NMR data, but were carried on to the subsequent step.  1H NMR (CDCl3, 300 MHz): δ = 7.04 (d, 3J = 8.2 Hz, 4 H), 6.62 (d, 3J = 8.2 Hz, 4 H), 3.96 (br s, N-H, 2 H), 3.27 (t, 3J = 6.6 Hz, 4 H), 2.28 (s, CH3, 6 H), 1.96 (p, 3J = 6.6 Hz, 2 H).  13C NMR (CDCl3, 100.6 MHz): δ = 145.9 (Cipso-NRH), 129.7, 126.7 (Cipso-CH3), 113.1, 42.5 (N-CH2-R), 29.3 (CH2R2), 20.4 (CH3).  EI MS: m/z = 254 [M]+. 2-Br-4-CH3Ph(NH)(CH2)3-2-Br-4-CH3Ph (5.5) Method A (preferred):  Based on a modification to a literature method.135,151  On the benchtop, 5.4 (1.14 g, 4.48 mmol) was dissolved in acetonitrile (70 mL).  A catalytic loading of NH4OAc (0.07 g, 0.9 mmol) was added to the solution, before shielding the flask from light and cooling to 0 oC.  Two equivalents of N-bromosuccinimide were added in two equal portions, 20 minutes apart (1.60 g, 8.99 mmol), and the reaction was stirred for one hour at 0 oC.  The solvent was removed in vacuo, and the product was extracted with EtOAc, washed with H2O, dried over 171  MgSO4, and filtered.  After removing the EtOAc solvent under reduced pressure, red crystals were obtained by recrystallizing from hot ethanol (0.98 g, 2.4 mmol, 53%).  1H NMR (CDCl3, 400 MHz): δ 7.28 (s, 2 H), 7.00 (d, 3J = 8.2 Hz, 2 H), 6.59 (d, 3J = 8.2 Hz, 2 H), 4.24 (br s, N-H, 2 H), 3.31 (br t, CH2, 4 H), 2.25 (s, CH3, 6 H), 2.02 (p, 3J = 6.5 Hz, CH2, 2 H).  13C NMR (CDCl3, 100.6 MHz): δ 142.8 (Cipso-NRH), 133.0, 129.2, 127.6 (Cipso-CH3), 111.6, 110.0 (Cipso-Br), 42.1 (N-CH2-R), 29.1 (CH2R2), 20.2 (CH3).  EI MS: m/z = 412 [M]+.  Method B:  On the benchtop, N-bromosuccinimide (1.06 g, 5.96 mmol) was added to 5.4 (0.75 g, 2.95 mmol) in 10 mL of acetonitrile at 0 oC, with the exclusion of light.  After stirring for 1 hour, a solution of NaHSO3 (0.62 g, 5.96 mmol) in H2O (10 mL) was added to the reaction.  The vessel was subsequently removed from the ice bath and precautions for avoiding UV exposure withheld.  The mixture was extracted with dichloromethane, washed with H2O, dried over MgSO4, and filtered.  The resulting filtrate was concentrated in vacuo, resulting in a red oil.  Column chromatography (silica gel, hexane-EtOAc, 10:1) afforded a crude fraction containing the dibrominated product, and the pure product was obtained by crystallization from hexanes (0.76 g, 1.8 mmol, 21%). 4-tolylN(CH2)3(SiMe2)N-4-tolyl (5.6) Procedure is based from a literature method for preparation of similar heterocycles.153  A flask containing 5.4 (1.02 g, 4.01 mmol), Si(NEt2)2Me2 (0.98 mL, 4.0 mmol), and ammonium sulphate (0.05 g, 0.4 mmol) was heated to 120 oC with a reflux condenser, overnight under nitrogen gas.  The dark red residue was cooled to room temperature, and exposed to dynamic vacuum to remove any produced diethylamine.  The product was then extracted with toluene, filtered through Celite, and the solvent removed under reduced pressure.  Pure product was obtained as a crystalline yellow solid from a 50:50 THF/pentane solution at -35 oC, and washed with cold 172  pentane (0.253 g, 0.815 mmol, 20%).  1H NMR (C6D6, 400 MHz): δ 0.51 (s, Si-CH3, 6 H), 1.73 (p, 3JHH = 5.5 Hz, CH2, 2 H), 2.21 (s, Ar-CH3, 6 H), 3.18 (t, 3JHH = 5.5 Hz, CH2, 4 H), 6.89 (d, 3JHH = 8.4 Hz, Ar-H, 4 H), 7.03 (d, 3JHH = 8.4 Hz, Ar-H, 4 H).  13C NMR (C6D6, 100.6 MHz): δ 3.2 (Si-CH3), 20.7 (Ar-CH3), 28.5 (-CH2-), 49.3 (N-CH2), 119.5 (ArC), 128.9 (Cipso), 129.7 (ArC), 148.1 (Cipso).  EI-MS (m/z): 310 [M]+. Trans-Ni[o-(PiPr2)NH2Ph]2(NO3)2 (5.7) Based on literature preparation of a similar complex.137  A degassed EtOH solution of o-PiPr2(NH2)Ph (0.51 g, 2.4 mmol) was added to a degassed EtOH solution of Ni(NO3)2(H2O)6 (0.34 g, 1.2 mmol) at room temperature.  The reaction was stirred at 50 oC for 5 hours, cooled to room temperature, and the yellow product was collected on a sintered glass frit (0.43 g, 0.72 mmol, 61%).  31P{1H} NMR (CD3CN, 121.5 MHz): δ 63.5 (br s).  1H NMR (CD3CN, 300 MHz): δ 1.29 (br m, iPr-CH3, 12 H), 1.43 (br m, iPr-CH3, 12 H), 2.72 (br m, iPr-CH, 4 H), 7.36 (br s, 2 H), 7.50 (m, 4 H), 7.67 (br s, 2 H). Trans-Ni[o-(PiPr2)NHPh]2 (5.8) Based on literature preparation of a similar complex.137  Compound 5.7 (0.386 g, 0.642 mmol) was dissolved in degassed acetone, and excess triethylamine (0.50 mL, 3.6 mmol) was added dropwise.  The dark green solution was stirred for 2 hours before solvent was removed in vacuo.  The product was then extracted with toluene and filtered through Celite.  A green solid was obtained by removing the solvent under reduced pressure (0.221 g, 0.465 mmol, 72%).  Crystals suitable for XRD studies were obtained from slow evaporation of a concentrated benzene solution at room temperature.  31P{1H} NMR (C6D6, 121.5 MHz): δ 47.4.  1H NMR (C6D6, 300 MHz): δ 1.16 (dd, 3JHH = 6.8 Hz, 3JPH = 13.6 Hz, iPr-CH3, 12 H), 1.27 (dd, 3JHH = 7.4 Hz, 3JPH = 173  15.3 Hz, iPr-CH3, 12 H), 1.81 (br s, N-H, 2 H), 1.94 (m, iPr-CH, 4 H), 6.35 (m, Ar-H, 2 H), 6.46 (d, 3JHH = 7.0 Hz, Ar-H, 2 H), 7.01 (m, Ar-H, 4 H).  EI-MS (m/z): 474 [M]+. 2-(PiPr2)BrPh (5.10) Synthesis based off of literature preparation of the compound, as well as a modification to the literature preparation that was employed for synthesis of 5.9.161,162  A flask containing 1,2-dibromobenzene (1.0 mL, 8.3 mmol) in a 50:50 mixture of ether and THF (60 mL total) was placed in an ether/liquid N2 bath.  It is crucial that the temperature is maintained between -100 and -110 oC throughout the reaction.  A hexanes solution of n-BuLi (5.2 mL, 1.6 M, 8.3 mmol) was added, and the reaction was stirred for 5 minutes.  A THF solution (5 mL) of ClPiPr2 (1.3 mL, 8.2 mmol) was then added to the lithiated intermediate.  The reaction mixture was stirred for 1 hour at -100 oC before warming to room temperature overnight.  The solvent was removed under reduced pressure, and the product was extracted with hexanes and filtered through Celite.  Hexanes were then removed in vacuo to afford the final product as a liquid (1.807 g, 6.62 mmol, 80%). 2-(PPh2)(SiMe2Cl)Ph (5.11) An ether (40 mL) solution of 5.9 (1.63 g, 4.78 mmol) was cooled to -45 oC, and a hexanes solution of n-BuLi (3.3 mL, 1.6 M, 5.3 mmol) was added dropwise.  The yellow reaction mixture was allowed to warm to room temperature, and stirred for one hour.  The lithiated intermediate was then pre-cooled to -78 oC before addition to a -78 oC toluene (100 mL) solution of excess dichlorodimethylsilane (4.6 mL, 38 mmol).  The reaction mixture was then stirred at room temperature overnight, before removing the solvent and remaining dichlorodimethylsilane under reduced pressure.  The product was then extracted with hexanes and filtered through Celite.  174  Removal of hexanes in vacuo affords the product as a white solid (1.39 g, 3.92 mmol, 82%).  Spectroscopic data is consistent with previously reported data for the compound.165 2-(PiPr2)(SiMe2Cl)Ph (5.12) An ether (40 mL) solution of 5.10 (2.26 g, 8.27 mmol) was cooled to -45 oC, and a hexanes solution of n-BuLi (5.7 mL, 1.6 M, 9.1 mmol) was added dropwise.  The reaction mixture was allowed to warm to room temperature, and stirred for one hour.  The red lithiated intermediate was then pre-cooled to -78 oC before addition to a -78 oC toluene (100 mL) solution of excess dichlorodimethylsilane (8.0 mL, 66 mmol).  The reaction mixture was then stirred at room temperature overnight, before removing the solvent and remaining dichlorodimethylsilane under reduced pressure.  The product was then extracted with hexanes and filtered through Celite.  Removal of hexanes in vacuo afforded the product as a yellow oil (2.05 g, 7.15 mmol, 86%).  31P{1H} NMR (C6D6, 121.5 MHz): δ 1.3.  1H NMR (C6D6, 300 MHz): δ 0.79 (dd, 3JHH = 7.1 Hz, 3JPH = 12.6 Hz, iPr-CH3, 6 H), 0.91 (d, JPH = 3.2 Hz, Si-CH3, 6 H), 1.04 (dd, 3JHH = 6.9 Hz, 3JPH = 14.5 Hz, iPr-CH3, 6 H), 1.82 (m, iPr-CH, 2 H), 7.13-7.19 (m, Ar-H, 2 H), 7.30 (m, Ar-H, 1 H), 8.22 (m, Ar-H, 1 H). 2-(PPh2)(SiMe2NMe2)Ph (5.13) A THF (20 mL) solution of 5.11 (0.599 g, 1.69 mmol) was cooled to -78 oC, and to it was added a THF (10 mL) solution of LiNMe2 (0.098 g, 1.9 mmol).  The reaction mixture was allowed to warm to room temperature and stirred overnight, before removal of the solvent under reduced pressure.  The product was then extracted with hexanes and filtered through Celite.  Hexanes were removed in vacuo to afford an off-white residue; an accurate yield was not obtained due to presence of silicone grease as observed at δ = 0.29 in the 1H NMR spectra.  31P{1H} NMR 175  (C6D6, 121.5 MHz): δ -9.5.  1H NMR (C6D6, 300 MHz): δ 0.57 (d, JPH = 1.1 Hz, Si-CH3, 6 H), 2.34 (s, N-CH3, 6 H), 7.00-7.09 (m, Ar-H, 8 H), 7.32 (m, Ar-H, 5 H), 7.66 (m, Ar-H, 1 H). Cis-[2-PPh2(SiMe2NH2)Ph]2RhCl (5.14) A THF (15 mL) solution of 5.11 (0.277 g, 0.781 mmol) underwent two freeze-pump-thaw cycles in a thick-walled Kontes sealable reaction vessel, and was left under static vacuum.  The solution was cooled to -25 oC in an ethanol/CO2(s) bath, and to it was added NH3(g) (1 atm).  The flask was sealed at -25 oC, allowed to warm to 25 oC slowly, and stirred for 3 days.  White precipitate can be observed over the course of the reaction.  The flask was carefully opened to an N2(g) atmosphere, and the solvent was removed under reduced pressure.  The resulting white residue was extracted with hexanes and filtered through Celite, and the filtrate was concentrated in vacuo to a colourless oil.  Yield and elemental analysis were not obtained, as 100% conversion to the silylamine did not occur.  This material was used directly for the reaction to generate 5.14.  31P{1H} NMR (C6D6, 121.5 MHz): δ = -10.2, with ~20% unreacted silylchloride starting material at δ -11.1.  1H NMR (C6D6, 300 MHz): δ  0.52 (d, JPH = 1.5 Hz, Si-CH3, 6 H), 7.03 (m, Ar-H, 8 H), 7.32-7.37 (m, Ar-H, 5 H), 7.73 (m, Ar-H, 1 H).  A benzene solution (<1 mL) of (Rh[COE2Cl])2 (0.013 g, 0.018 mmol) was added to a benzene solution (1 mL) of the primary amine (0.024 g, 0.037 mmol).  The reaction mixture was left undisturbed, and within 24 hours crystals suitable for XRD analysis had grown.  The 31P{1H} NMR spectrum contained a signal corresponding to the Si-Cl species 5.11 at δ -11.1 (10%), mono-ligated Rh species at δ 56.5 (d, JPRh = 181 Hz) (20%), and 5.14 at δ 48.2 (d, JPRh = 175 Hz) (70%).   176  2-(PPh2)(SiMe2(3,5-Me2Ph)NH)Ph (5.15) A THF (15 mL) solution of 3,5-dimethylaniline (0.10 mL, 0.80 mmol) was cooled to 0 oC, and to it was added a hexanes solution of n-BuLi (0.50 mL, 1.6 M, 0.80 mmol).  The reaction was warmed to room temperature and stirred for 20 minutes, and then cooled to -78 oC.  To this cooled solution was added 5.11 (0.285 g, 0.803 mmol) in THF (5 mL).  The reaction mixture was allowed to warm slowly to room temperature overnight, followed by the removal of THF under reduced pressure.  The resulting residue was then extracted with hexanes and filtered through Celite.  Drying the filtrate in vacuo gave a residue containing the product.  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Crystallogr. 2012, 45, 849.    183  Appendix  Tables of Crystallographic Information  3.2 3.3 Empirical Formula C51H58Cl2N3O2PZr C57H56N3PZr Formula Weight 938.09 905.24 Crystal System Triclinic Monoclinic Space Group P1 P2/m a [Å] 11.5950(16) 10.639(5) b [Å] 11.7413(16) 25.394(5) c [Å] 18.929(3) 17.323(5) α (o) 86.907(3) 90.000(5) β (o) 88.600(3) 90.130(5) γ (o) 60.511(2) 90.000(5) V [Å3] 2239.9(5) 4680(3) ρ [g/cm3] 1.391 1.285 Z 2 4 F (000) 980 1896 μ (mm-1) 0.445 0.310 Temperature (K) 293(2) 293(2) hkl Range -16 16 / -16 16 / -26 26 -12 12 / -30 30 / -20 20 θ Range (o) 1.99 - 30.09 1.42 - 25.04 Measured Reflections 49962 33397 Unique Reflections 13160 8291 Refined Parameters 547 559 Completeness to θ (%) 99.8 99.8 Goodness-of-Fit 1.071 1.026 R1, wR2 (I > 2σ(I)) 0.0337, 0.0866 0.0465, 0.1031 R1, wR2 (all data) 0.0404, 0.0910 0.0705, 0.1128 Res. el. dens. (e-/Å3) 0.766 / -0.414 0.698 / -0.425     184  Tables of Crystallographic Information  4.2 4.3 Empirical Formula C46H51N3PTa C51H60ClN3PSi2Ta Formula Weight 857.82 1018.57 Crystal System Monoclinic Monoclinic Space Group P21/n P21/c a [Å] 15.1275(6) 15.2595(15) b [Å] 17.7022(6) 29.682(3) c [Å] 18.3846(7) 13.0110(12) α (o) 90.000 90.000 β (o) 113.1140(10) 105.231(2) γ (o) 90.000 90.000 V [Å3] 4528.0(3) 5686.1(9) ρ [g/cm3] 1.258 1.190 Z 4 4 F (000) 1744 2080 μ (mm-1) 2.494 2.082 Temperature (K) 293(2) 296(2) hkl Range -18 18 / -18 21 / -21 21 -19 19 / -38 33 / -16 9 θ Range (o) 1.67 - 25.09 1.37 - 27.64 Measured Reflections 33047 59727 Unique Reflections 8026 13170 Refined Parameters 514 646 Completeness to θ (%) 99.7 99.4 Goodness-of-Fit 1.016 1.051 R1, wR2 (I > 2σ(I)) 0.0381, 0.0721 0.0367, 0.0686 R1, wR2 (all data) 0.0766, 0.0831 0.0554, 0.0732 Res. el. dens. (e-/Å3) 0.832 / -0.667 0.685 / -1.017    185  Tables of Crystallographic Information  5.2 5.8 Empirical Formula C30H52N4P2Zr C24H38N2NiP2 Formula Weight 621.92 425.21 Crystal System Monoclinic Monoclinic Space Group P2/m P21/n a [Å] 9.381(5) 7.9611(3) b [Å] 17.549(5) 11.2307(4) c [Å] 19.824(5) 14.3135(5) α (o) 90.000(5) 90.00 β (o) 102.762(5) 102.0290(10) γ (o) 90.000(5) 90.00 V [Å3] 3183(2) 1251.65(8) ρ [g/cm3] 1.298 1.261 Z 4 2 F (000) 1320 508 μ (mm-1) 0.471 0.915 Temperature (K) 293(2) 90(2) hkl Range -11 11 / -20 18 / -23 23 -10 9 / -14 14 / -18 18 θ Range (o) 1.57 - 25.13 2.32 - 27.48 Measured Reflections 22391 11117 Unique Reflections 5665 2873 Refined Parameters 334 141 Completeness to θ (%) 99.5 99.9 Goodness-of-Fit 1.051 1.052 R1, wR2 (I > 2σ(I)) 0.0257, 0.0675 0.0228, 0.0573 R1, wR2 (all data) 0.0304, 0.0708 0.0264, 0.0594 Res. el. dens. (e-/Å3) 0.426 / -0.355 0.368 / -0.217    186  Tables of Crystallographic Information  5.14  Empirical Formula C52H56ClN2P2RhSi2  Formula Weight 965.47  Crystal System Monoclinic  Space Group C2/c  a [Å] 15.614(5)  b [Å] 13.958(5)  c [Å] 21.762(5)  α (o) 90.000(5)  β (o) 99.240(5)  γ (o) 90.000(5)  V [Å3] 4681(2)  ρ [g/cm3] 1.370  Z 4  F (000) 2008  μ (mm-1) 0.579  Temperature (K) 293(2)  hkl Range -18 18 / -16 16 / -25 22  θ Range (o) 1.90 - 25.11  Measured Reflections 28753  Unique Reflections 4175  Refined Parameters 282  Completeness to θ (%) 99.8  Goodness-of-Fit 1.082  R1, wR2 (I > 2σ(I)) 0.0308, 0.0719  R1, wR2 (all data) 0.0378, 0.0758  Res. el. dens. (e-/Å3) 0.835 / -0.372     

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