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1,3-N,O-Chelated complexes of rhodium and iridium : harnessing metal-ligand cooperativity for bond activation… Drover, Marcus Walter 2016

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1,3-N,O-CHELATED COMPLEXES OF RHODIUM AND IRIDIUM: HARNESSING METAL-LIGAND COOPERATIVITY FOR BOND ACTIVATION PROCESSES  by  Marcus Walter Drover B.Sc.(H), Memorial University of Newfoundland, 2012    A THESIS SUBMITTED IN PARTIAL FULFILLMENT 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)    December 2016  © Marcus Walter Drover, 2016 ii ABSTRACT This thesis explores the use of 1,3-N,O chelating ligands, amidates and phosphoramidates as ligands for rhodium and iridium in the +1 and +3 oxidation states. Toward this end, a series of novel group 9 complexes were prepared, characterized, and employed for cooperative small molecule activation and element-hydrogen (E-H) bond cleavage reactions.  In Chapter 1, amides and phosphoramides are introduced as ligands for late transition metals. In particular, it is highlighted that such ligands have traditionally been used to form early transition metal and lanthanide N,O-chelated complexes, with the late transition metal chemistry being highly underdeveloped.  In Chapter 2, the fundamental reactivity of rhodium(I) complexes having amidate ancillary ligands is presented including catalytic oxygen atom transfer using O2 – the products of such reactions: η2-O2 complexes were characterized using NMR spectroscopy and density functional theory (DFT).   Chapter 3 details the use of 1,3-N,O chelated complexes of monovalent Rh(I) and Ir(I) for the controlled capture of HBCy2, providing six-membered genuine metallaheterocycles bearing a δ-B-H agostic interaction, which can be employed for chemoselective boron transfer reactions. In this chapter, the inclination of this ligand class to change the chemoselectivity of HBCy2 hydroboration toward carbonyl-containing substrates (in the presence of an alkene) is provided.   Chapter 4 examines the preparation of the first unsaturated Cp*Ir(III) (Cp* = C5Me5) phosphoramidate complex for use in element-hydrogen (E-H) bond activation (E = H, C, Si, B). The syntheses of coordinatively unsaturated (E)-vinyloxy Cp*Ir(III)  iii complexes, which are prepared from regioselective 1-alkyne C-H bond activation and O-phosphoramidation is discussed. This regioselectivity is completely inverted from that of free phosphoramidates, which undergo preferential N-alkylation. Finally, we illustrate how aminoborane (H2B=NR2) B-N bond rotation can be accessed using joint metal-ligand stabilization between Ir and a phosphoramidate coligand. All complexes were rigorously characterized using NMR spectroscopy, X-ray diffraction, as well as by DFT.   Chapter 5 surmises a new protocol for rhodium-mediated ethylene amination (nitrogen-carbon bond formation) using diazenes (RN=NR) as the N-atom source. This work provides a “proof-of-principle” for the functionalization of simple C2-synthons using easily handled nitrogen-sources, providing rhoda(III)heterocycles, which undergo [Rh]-N bond protonolysis to provide ethyl-substituted hydrazine complexes.   														  iv PREFACE   All of the work contained herein was performed in consultation with my supervisors, Prof. Laurel L. Schafer and Prof. Jennifer A. Love. Nearly all experimental work was carried out by me, however some of the work was performed collaboratively. All density functional theory (DFT) calculations presented in Chapters 2-4 were performed by Mr. Eric G. Bowes, while Prof. Pierre Kennepohl performed the DFT work presented in Chapter 5. Ligand salt 2.53 (Chapter 2) and the ligand salt used to prepare complex 4.102 (Chapter 4) were prepared by Ms. Cheyenne J. Christopherson using literature procedures. Mr. Daniel W. Beh helped to reproduce some of the results obtained in Chapter 5. Both students were undergraduate researchers under my supervision.   Data presented in Chapter 2 have been reported in Organometallics published by the American Chemical Society as: Drover, M.W.; Schafer, L.L.; Love, J.A. “Amidate-Ligated Complexes of Rhodium(I): A Showcase of Coordination Flexibility.” Organometallics 2015, 34, 1783-1786, as well as in Dalton Transactions published by the Royal Society of Chemistry as: Drover, M.W.; Schafer, L.L.; Love, J.A. “Isocyanate Deinsertion from κ1-O Amidates: Facile Access to Perfluoroaryl Rhodium(I) Complexes.” Dalton Trans. 2015, 44, 19487-19493.   Data presented in Chapter 3 have been reported in Angewandte Chemie International Edition published by Wiley-VCH Verlag as: Drover, M.W.; Schafer, L.L.; Love, J.A. “Capturing HBCy2: Employing N,O-Chelated Complexes of Rhodium(I) and Iridium(I) for Chemoselective Hydroboration.” Angew. Chem., Int. Ed. 2016, 51, 3181-3186.  v  Data presented in Chapter 4 have been reported in Organometallics and Journal of the American Chemical Society by the American Chemical Society as: Drover, M.W.; Johnson, H.C.; Schafer, L.L.; Love, J.A.; Weller, A.S. “Reactivity of an Unsaturated Iridium(III) Phosphoramidate Complex, [Cp*Ir{κ2-N,O}][BArF4].” Organometallics 2015, 34, 3849–3856, and: Drover, M.W.; Love, J.A.; Schafer, L.L. “Achieving Oxygen Regioselectivity in the Anti-Markovnikov Phosphoramidation of 1-Alkynes Using a Cp*Ir(III) Complex.” J. Am. Chem. Soc. 2016, 138, 8396-8399. Data presented in Chapter 4 have also been reported in Chemistry – A European Journal published by Wiley-VCH Verlag as: Drover, M.W.; Bowes, E.G.; Schafer, L.L.; Love, J.A.; Weller, A.S. “Phosphoramidate-Supported Cp*Ir(III) Aminoborane H2B=NR2 Complexes: Synthesis, Structure, and Solution Dynamics.” Chem. –Eur. J. 2016, 22, 6793-6797.   Data presented in Chapter 5 have been reported in Chemistry – A European Journal published by Wiley-VCH Verlag as: Drover, M.W.; Beh, D.W.; Kennepohl, P.; Love, J.A. “3-Rhoda-1,2-diazacyclopentanes: A Series of Novel Metallacycle Complexes Derived From C-N Functionalization of Ethylene.” Chem. -Eur. J. 2014, 20, 13345-13355.           vi  All thesis publications with contributions from Marcus W. Drover from the period of 2012-2016 appear below and are enumerated by date: 13. Drover, M.W.; Love, J.A.; Schafer, L.L. Cooperative Dehydrogenation of Cyclic Amines By a Cp*Ir(III) Phosphoramidate Complex: Isolation of Key Intermediates. In preparation. (Chapter 4)  12.  Drover, M.W.; Love, J.A.; Schafer, L.L. Cooperative C(sp3)-H Bond Activation Induced by Monohydroborane Coordination at an Ir(III)-Phosphoramidate Complex: Toward Controlled Organophosphate Functionalization. Submitted. (Chapter 4)  11.  Drover, M.W.; Love, J.A.; Schafer, L.L. Accessing δ-B-H Coordinated Complexes of Rh(I) and Ir(I) Using Mono- and Dihydroboranes: Stabilization by a Phosphoramidate Coligand. Organometallics 2016 Accepted. (Chapter 3)  10.  Drover, M.W.; Love, J.A.; Schafer, L.L. 1,3-N,O Chelated Complexes of Late Transition Metals. Chem. Soc. Rev. 2016 Accepted. (Chapter 1)  9. Beattie, D.D.; Bowes, E.G.; Drover, M.W.; Love, J.A.; Schafer, L.L. Oxidation State-Dependent Coordination Modes: Accessing an Amidate-Supported Ni(I) δ-bis(C-H) Agostic Complex. Angew. Chem., Int. Ed. 2016 128, 13484-13489. (Chapter 1)  8.  Drover, M.W.; Love, J.A.; Schafer, L.L. Achieving Oxygen Regioselectivity in the Anti-Markovnikov Phosphoramidation of 1-Alkynes Using a Cp*Ir(III) Complex. J. Am. Chem. Soc. 2016, 138, 8396-8399. (Chapter 4) 7.  Drover, M.W.; Bowes, E.G.; Schafer, L.L.; Love, J.A.; Weller, A.S. Phosphoramidate-Supported Cp*Ir(III) Aminoborane H2B=NR2 Complexes: Synthesis, Structure, and Solution Dynamics. Chem. –Eur. J. 2016, 22, 6793-6797. (Chapter 4)  6.  Drover, M.W.; Schafer, L.L.; Love, J.A. Capturing HBCy2: Employing N,O-Chelated Complexes of Rhodium(I) and Iridium(I) for Chemoselective Hydroboration. Angew. Chem., Int. Ed. 2016, 51, 3181-3186. (Chapter 3)  5.  Drover, M.W.; Schafer, L.L.; Love, J.A. Isocyanate Deinsertion from κ1-O Amidates: Facile Access to Perfluoroaryl Rhodium(I) Complexes. Dalton Trans. 2015, 44, 19487-19493. (Chapter 2)  4.  Drover, M.W.; Johnson, H.C.; Schafer, L.L.; Love, J.A.; Weller, A.S. Reactivity of an Unsaturated Iridium(III) Phosphoramidate Complex, [Cp*Ir{κ2-N,O}][BArF4]. Organometallics 2015, 34, 3849–3856. (Chapter 4)  3.  Dauth, A.; Drover, M.W.; Hajiashrafi, T.; Tehrani, A.A.; Love, J.A. Formation  vii of Azarhodacyclobutanes With Varying N-substitution. J. Organomet. Chem. 2015, 791, 192-195. (Chapter 5)  2.  Drover, M.W.; Schafer, L.L.; Love, J.A. Amidate-Ligated Complexes of Rhodium(I): A Showcase of Coordination Flexibility. Organometallics 2015, 34, 1783-1786. (Chapter 2)  1. Drover, M.W.; Beh, D.W.; Kennepohl, P.; Love, J.A. 3-Rhoda-1,2-diazacyclopentanes: A Series of Novel Metallacycle Complexes Derived From C-N Functionalization of Ethylene. Chem. -Eur. J. 2014, 20, 13345-13355. (Chapter 5)                          viii TABLE OF CONTENTS  Abstract ............................................................................................................................. ii Preface ............................................................................................................................... iv Table of Contents ............................................................................................................. viii List of Tables ................................................................................................................... xiv List of Figures .................................................................................................................. xv List of Schemes .............................................................................................................. xxiii List of Charts .................................................................................................................. xxxi List of Symbols and Abbreviations ............................................................................... xxxii List of Compound Numbers ........................................................................................ xxxvii Acknowledgements .......................................................................................................... xli Dedication ........................................................................................................................ xlii CHAPTER 1: Introduction ............................................................................................. ...1 1.1 General Introduction ........................................................................................... ...1 1.2 Overview of 1,3-donating ligands ...................................................................... ...1 1.3 1,3-N,O-Chelated Complexes of Group 8 ............................................................ ...4 1.3.1 Iron ............................................................................................................ ...4 1.3.2 Ruthenium ................................................................................................. ...8 1.3.3 Osmium ..................................................................................................... .13 1.4 1,3-N,O-Chelated Complexes of Group 9 ............................................................ .15 1.4.1 Cobalt ........................................................................................................ .15 1.4.2 Rhodium .................................................................................................... .19 1.4.3 Iridium ....................................................................................................... .23  ix 1.5 1,3-N,O-Chelated Complexes of Group 10 .......................................................... .30 1.5.1 Nickel ........................................................................................................ .30 1.5.2 Palladium ................................................................................................... .37 1.5.3 Platinum .................................................................................................... .41 1.6 1,3-N,O-Chelated Complexes of Group 11 .......................................................... .44 1.6.1 Copper ....................................................................................................... .44 1.6.2 Silver ......................................................................................................... .48 1.6.3 Gold ........................................................................................................... .48 1.7 1,3-N,O-Chelated Complexes of Group 12 .......................................................... .50 1.7.1 Zinc ........................................................................................................... .50 1.7.2 Cadmium and Mercury .............................................................................. .51 1.8 Summary and Outlook ......................................................................................... .51 1.9 Hemilabile Ligands ............................................................................................. .53 1.10 Sigma (σ) Complexes ....................................................................................... .55 1.11 Agostic Complexes ........................................................................................... .56 CHAPTER 2: Amidate-ligated Complexes of Rh(I): Structure, Bonding, and Reactivity .......................................................................................................................................... .58 2.1 Introduction ......................................................................................................... .58 2.2 Synthesis of Rhodium(I) Amidate Complexes ................................................... .61 2.2.1 Generation of Rh(I) Diolefin Precursors .................................................. .63 2.2.2 Reactions of Complexes 2.18/2.20 with PPh3 .......................................... .66 2.2.3 15N NMR Spectroscopy ............................................................................ .68 2.2.4 Reactions of Complexes 2.18/2.20 with PCy3 .......................................... .70  x 2.2.5 Reactions of Complex 2.20 with Phosphites ............................................ .73 2.2.6 Reactions of Complexes 2.21 and 2.22 with Molecular Oxygen (O2) ..... .76 2.2.7 Analysis of O2 Activation Products by Density Functional Theory (DFT)  ........................................................................................................................... .80 2.2.8 Reactions of Complexes 2.18 and 2.20 with an Aryl Isocyanide ............. .83 2.2.9 Reactions of Complexes 2.18 and 2.20 with Carbon Monoxide (CO) ..... .86 2.3 Reaction of Complex 2.22 with Aldehydes ........................................................ .88 2.3.1 Attempts at Aldehyde Hydroacylation ..................................................... .88 2.3.2 Isolation of Decarbonylation By-Products ............................................... .92 2.3.3 Mixed Tischenko Aldehyde Dimerizations .............................................. .94 2.3.4 Reactions with Alkenes and Aldehydes ................................................... .95 2.4 Accessing C6F5- or CF3-Substituted Amidate Complexes ................................. .96 2.4.1 Accessing C6F5- or CF3-Substituted Diolefin Precursors ......................... .97 2.4.2 Reaction of 2.55 with PCy3 ...................................................................... .99 2.4.3 Reaction of 2.55 with an Aryl Isocyanide ............................................... 104 2.4.4 Reactions of PPh3 .................................................................................... 105 2.5 Using 13C NMR Spectroscopy to Identify Rhoda(I)cycle Ring Size ................. 110 2.6 Summary ............................................................................................................ 111 CHAPTER 3: Capturing Boranes: Employing N,O-Chelated Complexes of Rhodium(I) and Iridium(I) for Chemoselective Hydroboration ......................................................... 113 3.1 Introduction ........................................................................................................ 113 3.2 Synthesis of κ2-N,O metalla(I)cyclic precursors ................................................ 115 3.3 Controlling Borane Release ............................................................................... 122  xi 3.4 Assessing Capture Limitations .......................................................................... 126 3.5 Reactivity of B-H Agostic Metalla(I)heterocycles ............................................ 129 3.6 Accessing B-H Agostic Metalla(I)heterocycles of Other Boranes .................... 130 3.6.1 Synthesis and Characterization of 9-BBN Complexes ............................ 131 3.6.2 Synthesis and Characterization of HBMes2 Complexes .......................... 133 3.6.3 Synthesis and Characterization of bis(σ-B-H) Agostic Complexes ........ 136 3.6.4 Reaction of Piers’ borane. ........................................................................ 140 3.6.5 Computational Studies ............................................................................. 142 3.6.6 Accessing π-coordinated Phosphoramidate Complexes .......................... 144 3.7 Summary ............................................................................................................ 149 CHAPTER 4: Synthesis, Structure, and Reactivity of a Coordinatively Unsaturated Cp*Ir(III) Phosphoramidate Complex ............................................................................ 151 4.1 Introduction ........................................................................................................ 151 4.2 Synthesis of a Coordinatively Unsaturated Cp*Ir Phosphoramidate Complex . 153 4.2.1 Reactivity of a Coordinatively Unsaturated Cp*Ir Phosphoramidate Complex with Lewis bases ............................................................................... 157 4.3 C-H Bond Activation using 4.17 ....................................................................... 162 4.3.1 Aryl C(sp2)-H Activation using 4.17 ....................................................... 162 4.3.2 Dehydrogenation of N-heterocycles ........................................................ 164 4.3.3 Amine C(sp3)-H Activation using 4.17 .................................................... 167 4.3.4 Reactivity of 4.17 with Allyl Acetates .................................................... 172 4.3.5 Reactivity of 4.17 with 1-Alkynes ........................................................... 175 4.3.6 Reactions of Isonitriles with Complex 4.69 ............................................ 189  xii 4.4 Reactivity of 4.17 with Ethyl Diazoacetate ....................................................... 191 4.5 Reactivity of 4.17 with Si- and Ge-H Bonds ..................................................... 192 4.6 Reactivity of 4.17 with B-H Bonds ................................................................... 196 4.6.1 Reactivity of 4.17 with a Dihydroborane ................................................ 196 4.6.2 Reactivity of 4.17 with Monohydroboranes ............................................ 198 4.6.3 Reactivity of 4.17 with Amine- and Aminoboranes ................................ 209 4.6.4 Analysis of Aminoborane Adducts using DFT ....................................... 217 4.7 Summary ............................................................................................................ 223 4.8 Using 31P NMR Spectroscopy to Identify Irida(III)Cycle Ring Size ................. 224 CHAPTER 5: 3-Rhoda-1,2-diazacyclopentanes: A Series of Metallacycle Complexes Derived From C-N Functionalization of Ethylene .......................................................... 226 5.1 Introduction ........................................................................................................ 226 5.2 Results and Discussion ...................................................................................... 228 5.2.1 Preparation and Characterization of TPA-Rh Diazacyclopentanes ......... 228 5.2.2 Preparation and Characterization of TPA-Rh Diazabicyclopentanes ...... 233 5.2.3 DFT Computational Analysis .................................................................. 236 5.2.4 15N NMR Spectroscopy ........................................................................... 237 5.2.5 Infrared Spectroscopic and Mass Spectrometric Analysis ...................... 239 5.2.6 Attempted 3-rhoda-1,2-diazacyclopentene Formation ............................ 240 5.2.7 Ring-opening of 5.6 and 5.7 Using p-TsOH ............................................ 243 5.2.8 Deprotection of 5.8 with Trifluoroacetic Acid (TFA) ............................. 244 5.2.9 Mechanistic Analysis for the Deprotection of 5.8 ................................... 247 5.3 [Rh]-O Insertion of C2H4 ................................................................................... 248  xiii 5.4 Ligand Modification .......................................................................................... 251 5.5 Mechanistic Considerations: A Bound Diazene or Olefin Mechanism ............. 252 5.6 Summary ............................................................................................................ 253 CHAPTER 6: Summary and Future Work .................................................................... 254 6.1 Overview ............................................................................................................ 255 6.2 Future Work ....................................................................................................... 257 REFERENCES .............................................................................................................. 260 APPENDIX A. Experimental Details ............................................................................ 283 A.1 General Considerations and Materials .............................................................. 284 A.2 Experimental Data for Chapter 2 ...................................................................... 286 A.3 Experimental Data for Chapter 3 ...................................................................... 308 A.4 Experimental Data for Chapter 4 ...................................................................... 335 A.5 Experimental Data for Chapter 5 ...................................................................... 363 A.6 Experimental Data for Chapter 6 ...................................................................... 378 APPENDIX B. Computational Details .......................................................................... 379 B.1 Computational Data for Chapter 2 .................................................................... 379 B.2 Computational Data for Chapter 3 .................................................................... 387 B.2 Computational Data for Chapter 4 .................................................................... 403 B.2 Computational Data for Chapter 5 .................................................................... 408 APPENDIX C. Tabulated Crystallographic Parameters ................................................ 409 APPENDIX D. Selected NMR Spectra and Data .......................................................... 434 APPENDIX E. Invited Organometallics Cover Image .................................................. 468    xiv LIST OF TABLES  Table 2.1 Scope and Limitation of Aldehyde Dimerization (conversions determined by 1H NMR spectroscopy) .................................................................................................... .91  Table 3.1 13C NMR Chemical shifts for η4-cyclooctadiene (COD) complexes ............ 119 Table 3.2 Controlled HBCy2 reactivity using complexes 3.15 and 3.16  ...................... 124 Table 3.3 Selected spectroscopic and DFT data for [M]··H-B agostic complexes  ....... 144 Table 5.1 1H and 13C NMR spectroscopic data for N-containing metallacycles (400 MHz, 298 K)  ............................................................................................................................ 235  Table 5.2 13C and 15N NMR spectroscopic data for N-containing metallacycles (400 MHz, CDCl3, 298 K)  ..................................................................................................... 239                              xv LIST OF FIGURES Figure 1.1 Solid-state molecular structures of 1.13 and 1.15  ......................................... 10 Figure 1.2 Solid-state molecular structure of 1.45  ......................................................... 19 Figure 1.3 Solid-state molecular structures of 1.61 and 1.62  ........................................ 26 Figure 1.4 Solid-state molecular structure of 1.99 and 1.100  ........................................ 34 Figure 1.5 Solid-state molecular structure of 1.103  ....................................................... 35 Figure 1.6 Solid-state molecular structure of 1.108  ....................................................... 38 Figure 1.7 Solid-state molecular structure of 1.131  ....................................................... 45 Figure 1.8 Solid-state molecular structure of 1.132  ....................................................... 46 Figure 1.9 Solid-state molecular structure of 1.139 and 1.140  ...................................... 51 Figure 2.1 Modes of O2 coordination by transition metal centers  ................................. 58 Figure 2.2 ORTEP depiction of the solid-state molecular structure of [Rh2{µ2-N,O-N(Dipp)C(O)Ph}2(NBD)2] (2.18) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]: Rh(1)-Rh(1′) 2.9861(10), Rh(1)-N(1) 2.1131(11), Rh(1)-O(1) 2.0912(11), O(1)-Rh(1)-N(1) 86.77(5)  .................................... 65  Figure 2.3 ORTEP depiction of the solid-state molecular structures of [Rh{κ2-N,O-N(Dipp)C(O)R}(PPh3)2]; R = Ph (2.21), tBu (2.22) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. (2.21): Rh(1)-N(1) 2.137(3), Rh(1)-O(1) 2.131(3), O(1)-Rh(1)-N(1) 62.04(10). (2.22): Rh(1)-N(1) 2.2023(12), Rh(1)-O(1) 2.1050(10), O(1)-Rh(1)-N(1) 61.16(4)  .................................... 68  Figure 2.4 15N chemical shifts for amidate-ligated complexes 2.23-2.27  ...................... 69 Figure 2.5 ORTEP depiction of the solid-state molecular structure of [Rh{κ2-N,C-N(Xyl)C(O-Rh(η4-NBD)(PCy3))C6H4}] (2.32)  .............................................................. 73  Figure 2.6 31P{1H} NMR spectra for the reaction of 2.21 with O2 (C6D6, 121 MHz, 298 K)  .................................................................................................................................... 78  Figure 2.7 31P{1H} NMR spectra for the reaction of 2.22 with O2 (C6D6, 121 MHz, 298 K)  .................................................................................................................................... 79  Figure 2.8 O2 activation products 2.39-2.41 studied by DFT calculations  .................... 82  xvi Figure 2.9 O2 activation products 2.42-2.44 studied by DFT calculations  .................... 83 Figure 2.10 ORTEP depiction of the solid-state molecular structure of [Rh{κ1-N-N(Dipp)C(O)Ph}(CNXyl)3] (2.46) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. Rh(1)-N(1) 2.120(3), N(1)-C(1) 1.340(5), C(1)-O(1) 1.246(6), Rh(1)-C(2) 1.961(5), C(2)-N(2) 1.161(6), Rh(1)-C(3) 1.894(4), C(3)-N(3) 1.160(6), Rh(1)-C(4) 1.958(5), C(4)-N(4) 1.159(7)  ....................................................... 85  Figure 2.11 ORTEP depiction of the solid-state molecular structure of [Rh2{µ2-N,O-N(Dipp)C(O)tBu}2(CO)4] (2.48) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. Rh(1)-Rh(1′) 2.876(2), Rh(1)-N(1) 2.075(11), Rh(1)-O(1) 2.059(8), C(1)-N(1) 1.345(15), C(1)-O(1) 1.306(12), C(3)-O(3) 1.153(15), O(1)-C(1)-N(1) 117.1(11)  ............................................................................................... 88  Figure 2.12 ORTEP depictions of the solid-state molecular structure of [Rh2{µ2-N,O-N(Dipp)C(O)C6F5}2(NBD)2] (2.55) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. Rh(1)-Rh(1′) 3.0738(5), Rh(1)-N(1) 2.125(2), Rh(1′)-O(1) 2.095(2), O(2)-Rh(1)-N(1) 89.23(8), N(1)-C(1)-O(1) 124.9(2). [Rh2{µ2-N,O-N(Dipp)C(O)CF3}2(NBD)2] (2.56): Rh(1)-Rh(1′) 3.0473(9), Rh(1)-N(1) 2.1309(4), Rh(1′)-O(1) 2.095(2), O(2)-Rh(1)-N(1) 87.77(6), N(1)-C(1)-O(1) 125.75(15)  ............. 99  Figure 2.13 Variable temperature 19F{1H} NMR spectra of E/Z-2.57 (tol-d8, 373 MHz, 298 K)  ............................................................................................................................ 101  Figure 2.14 ORTEP depiction of the solid-state molecular structures of E-2.57 and Z-2.57 (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. E-2.57: Rh(1)-O(1): 2.077(3), Rh(1)-P(1) 2.315(1), O(1)-C(1) 1.292(5), C(1)-N(1) 1.278(6), Rh(1)-O(1)-C(1) 129.8(3), N(1)-C(1)-O(1) 126.2(4), N(1)-C(1)-C(2) 123.4(4), C(1)-N(1)-C(8) 120.2(4), O(1)-C(1)-C(2) 110.4(3). Z-2.57: Rh(2)-O(2) 2.090(3), Rh(2)-P(2) 2.332(1), O(2)-C(46) 1.295(6), C(46)-N(2) 1.286(6) Rh(2)-O(2)-C(46) 131.3(3), N(2)-C(46)-O(2) 129.4(4), N(2)-C(46)-C(47) 111.9(4), C(46)-N(2)-C(53) 121.7(4), O(2)-C(46)-C(47) 118.6(4)  .................................................................. 102  Figure 2.15 ORTEP depiction of the solid-state molecular structure of 2.59 (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å]. Rh(1)-P(1) 2.3485(6), Rh(1)-C(1) 2.074(2)  ....................................................................................................... 104  Figure 2.16 ORTEP depiction of the solid-state molecular structure of Rh(PPh3)3(C6F5) (2.64) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å]. Rh(1)-P(1) 2.2985(8), Rh(1)-P(2) 2.294(1), Rh(1)-P(3) 2.3445(9) and Rh(1)-C(60) 2.082(3).  ......................................................................................................................... 107  Figure 2.17 ORTEP depiction of the solid-state molecular structures of [Rh{κ2-N,O-N(Dipp)C(O)CF3}(PPh3)2] (2.65) (ellipsoids at 50% probability, hydrogens omitted).  xvii Selected bond lengths [Å] and angles [o]: Rh(1)-N(1) 2.1878(15), Rh(1)-O(1) 2.1772(13), O(1)-Rh(1)-N(1) 61.45(5), C(1)-O(1) 1.278(2), C(1)-N(1) 1.301(2)  ............................ 109  Figure 2.18. 13C NMR spectroscopy for the Determination of Amidate Coordination Mode  .............................................................................................................................. 111  Figure 3.1 ORTEP depictions of the solid-state molecular structure of (A) [Ir{κ2-N,O-Xyl(N)P(O)(OEt)2}(η4-COD)] (3.12), and four-membered iridacycle of 3.12  (displacement ellipsoids are shown at the 50% probability, hydrogens omitted for clarity). Selected bond lengths [Å] and angles [o]. Ir(1)-N(1) 2.050(6), Ir(1)-O(1) 2.158(5), P(1)-O(1) 1.508(6), P(1)-N(1) 1.586(7), N(1)-Ir(1)-O(1) 70.3(2), O(1)-P(1)-N(1) 103.1(3). (B) [Ir{κ2-N,H-Xyl(N)P(OHBCy2)(OEt)2}(η4-COD)] (3.16) and six-membered iridacycle of 3.16  (displacement ellipsoids are shown at the 50% probability, hydrogens omitted for clarity). Selected bond lengths [Å] and angles [o]. Ir(1)-N(1) 2.097(2), Ir(1)-H(1) 1.63(2), B(1)-H(1) 1.41(2), B(1)-O(1) 1.519(2), P(1)-O(1) 1.515(1), P(1)-N(1) 1.602(1), B(1)-H(1)-Ir(1) 147(2)  ............................................................................................................ 118  Figure 3.2 DFT-calculated/geometry optimized structures of 3.15 and 3.16  ............... 120 Figure 3.3 ORTEP depiction of the solid-state molecular structure of [κ1-N-Cy2B=N(Xyl)(P(O)(OEt)2)] (3.18)  ................................................................................ 122  Figure 3.4 ORTEP depiction of the solid-state molecular structure of [Rh{µ2-N,O-Xyl(N)P(O)(OEt)2}2(η4-NBD)2]  (3.22)2. (Displacement ellipsoids are shown at the 50% probability). Selected bond lengths [Å] and angles [o].  Rh(1)-N(1) 2.1285, Rh(1)-O(1) 2.1094 P(1)-O(1) 1.5102, P(1)-N(1) 1.6132  .................................................................. 128  Figure 3.5 ORTEP depiction of the solid-state molecular structure of a) [Rh{κ2-N,H Xyl(N)P(OHB(Cy)2)(OEt)2}(η4-NBD)]   (3.23). (Displacement ellipsoids are shown at the 50% probability, displayed hydrogen atoms were located). Selected bond lengths [Å] and angles [o].  Rh(1)-N(1) 2.085(5), Rh(1)-H(1) 1.9403(5), B(1)-H(1) 0.980(7), B(1)-O(1) 1.534(7), P(1)-O(1) 1.510(4), P(1)-N(1) 1.587(5), B(1)-H(1)-Rh(1) 157.7(4)  ..... 128  Figure 3.6 ORTEP depictions of the solid-state molecular structure of A) [Ir(η6-C6H5-C(C6H5)2H)(η4-COD)][BArF4] ([3.25][BArF4]) and B) [Ir(η6-C6H5-NMe2)(η4-COD)][BArF4] ([3.27][BArF4])  ...................................................................................... 130  Figure 3.7 ORTEP depiction of the solid-state molecular structure of [M{κ2-N,H-Xyl(N)P(OHB(C8H14)(OEt)2}(η4-COD)] (3.28). (Displacement ellipsoids are shown at the 50% probability, displayed hydrogen atoms were located). Selected bond lengths [Å] and angles [o]. Rh(1)-N(1) 2.136(3), Rh(1)-H(1) 1.9303(4), B(1)-H(1) 0.980(5), B(1)-O(1) 1.528(5), P(1)-O(1) 1.551(3), P(1)-N(1) 1.600(4), B(1)-H(1)-Rh(1) 147.9(3)  ..... 133  Figure 3.8 ORTEP depiction of the solid-state molecular structure of [Rh{κ2-N,H-Xyl(N)P(OHBMes2)(OEt)2}(η4-COD)] (3.30). (Displacement ellipsoids are shown at the  xviii 50% probability, displayed hydrogen atoms were located). Selected bond lengths [Å] and angles [o].  Rh(1)-N(1) 2.1150(12), Rh(1)-H(1) 1.75(2), B(1)-H(1) 1.32(2), B(1)-O(1) 1.5402(19), P(1)-O(1) 1.5304(10), P(1)-N(1) 1.5919(12), B(1)-H(1)-Rh(1) 134.1(15)  136  Figure 3.9 Variable-temperature 1H NMR spectrum of 3.32 (1H NMR, 400 MHz, 298 K, toluene-d8)  ...................................................................................................................... 138  Figure 3.10 ORTEP depiction of the solid-state molecular structure of [Rh{κ2-N,H-Xyl(N)P(OH2BMes)(OEt)2}(η4-COD)] (3.32). (Displacement ellipsoids are shown at the 50% probability, displayed hydrogen atoms were located). Selected bond lengths [Å] and angles [o].  Rh(1)-N(1) 2.132(1), Rh(1)-H(1) 1.89(3), Rh(1)-H(1)′ 1.88(3), B(1)-H(1) 1.18(2), B(1)-H(1)′ 1.20(2), B(1)-O(1) 1.526(2), P(1)-O(1) 1.537(1), P(1)-N(1) 1.584(2)  ......................................................................................................................................... 139  Figure 3.11 ORTEP depiction of the solid-state molecular structure of [Rh{κ2-N,H-Xyl(N)P(OHB(C6F5)2)(OEt)2}(η4-COD)] (3.34). (Displacement ellipsoids are shown at the 50% probability, displayed hydrogen atoms were located). Selected bond lengths [Å] and angles [o].  Rh(1)-N(1) 2.103(3), Rh(1)-H(1) 1.9516, B(1)-H(1) 0.980, B(1)-O(1) 1.495(4), P(1)-O(1) 1.539(3), P(1)-N(1) 1.591(3), B(1)-H(1)-Rh(1) 150.3  .................. 141  Figure 3.12 1H NMR spectra of 3.36, 3.37, and 3.41 (1H NMR, 400 MHz, 298 K, C6D6). ……………………………………………………………………………………….….145          Figure 3.13 ORTEP depiction of the solid-state molecular structure of [Rh[η5 Xyl(N)P(O··B(C6F5)3(OEt)2}(η4-COD)]  (3.36). (Displacement ellipsoids are shown at the 50% probability, ethoxy alkyl chains (-CH2CH3) omitted for clarity). B(1)-O(1) 1.54(2), P(1)-O(1) 1.54(2), P(1)-N(1) 1.55(1), B(1)-O(1)-P(1) 132.4(9)  ...................... 148  Figure 3.14 ORTEP depiction of the solid-state molecular structure of [κ1-O-Xyl(NH)P(OB(C6F5)3)(OEt)2] (3.41). (Displacement ellipsoids are shown at the 50% probability, ethoxy alkyl chains (-CH2CH3) omitted for clarity). Selected bond lengths [Å] and angles [o]. B(1)-O(1) 1.5412, P(1)-O(1) 1.4975, P(1)-N(1) 1.6240, B(1)-O(1)-P(1) 146  .......................................................................................................................... 149  Figure 4.1 1H NMR spectrum for 4.17  (400 MHz, CD2Cl2, 298 K)  ............................ 155 Figure 4.2 ORTEP depiction of the solid-state molecular structure of [Cp*Ir{κ2-N,O-Xyl(N)P(O)(OEt)2}][BArCl24] (4.17) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArCl24- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-O(1) 2.142(2), Ir(1)-N(1) 1.989(3), P(1)-O(1) 1.523(2), P(1)-N(1) 1.612(3), N(1)-Ir(1)-O(1) 70.8(1), O(1)-P(1)-N(1) 99.6(1)  .................................. 156  Figure 4.3 ORTEP depiction of the solid-state molecular structure of [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(CNtBu)2][BArF4] (4.18) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond  xix lengths [Å] and angles [°]. Ir(1)-N(1) 2.143(5), Ir(1)-C(15) 1.988(5), Ir(1)-C(20) 1.950(5), P(1)-O(1) 1.461(5), P(1)-N(1) 1.618(5), O(1)-P(1)-N(1) 117.1(3)  ................ 159  Figure 4.4 Variable-temperature 31P{1H} NMR spectra for the reaction of MeCN (5 equivs.) with 4.17 (CD2Cl2, 202 MHz)  .......................................................................... 161  Figure 4.5 ORTEP depiction of the solid-state molecular structure of [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(4,4′-tBu-2,2′-bipy)][BArF4] (4.24) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-N(1) 2.168(6), Ir(1)-N(2) 2.087(7), Ir(1)-N(3) 2.089(7), P(1)-O(1) 1.479(6), P(1)-N(1) 1.613(7), O(1)-P(1)-N(1) 116.4(4)  ................ 163  Figure 4.6 ORTEP depictions of the solid-state molecular structure of [Cp*Ir(H)(NH(CH2)2CH2CH)(NH(CH2)2CH2CH2)] (4.38)  (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-N(1) 2.104(4), Ir(1)-N(2)  2.111(9), N(1)-C(1) 1.294(16), N(1)-C(2) 1.498(11) and [Cp*Ir(H)(NH(CH2)3CH2CH)(NH(CH2)3CH2CH2)] (4.39): Ir(1)-N(1) 2.06(2), Ir(1)-N(2) 2.138(9), N(1)-C(1) 1.30(2), N(1)-C(2) 1.48(3) ............................................................. 169  Figure 4.7 ORTEP depictions of the solid-state molecular structure of [Cp*Ir(Cl)(NH(CH2)2CH2CH2)2][Cl]  (4.40):  (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-N(1) 2.1525(3), Ir(1)-N(2) 2.1476(5), Ir(1)-Cl(1) 2.4204(4). [Cp*Ir(Cl)2(NH(CH2)3CH2CH2)] (4.43): Ir(1)-N(1) 2.1530(3), Ir(1)-Cl(1) 2.4216(3). [Cp*Ir(Cl)(NH(CH2)3CH2CH2)2][BArF4] (4.44): Ir(1)-N(1) 2.165(16), Ir(1)-Cl(1) 2.422(4) ................................................................................................................. 171  Figure 4.8 ORTEP depictions of the solid-state molecular structure of [Cp*Ir(η3-CH2CHCHCO2CH3)][BArF4] (4.49) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-O(1) 2.117(9), Ir(1)-C(3) 2.117(14), Ir(1)-C(4) 2.146(13), Ir(1)-C(5) 2.222(14), O(1)-C(2) 1.207(16), C(2)-O(2) 1.301(18), O(2)-C(3) 1.510(19), C(3)-C(4) 1.36(2), C(4)-C(5) 1.45(2). [Cp*Ir(η3-CHPhCHCHCO2CH3)][BArF4] (4.50): Ir(1)-O(1) 2.123(4), Ir(1)-C(3) 2.114(6), Ir(1)-C(4) 2.154(6), Ir(1)-C(5) 2.250(6), O(1)-C(2) 1.238(8), C(2)-O(2) 1.308(9), O(2)-C(3) 1.466(9), C(3)-C(4) 1.428(9), C(4)-C(5) 1.417(9)  .......................................................................................................................... 174  Figure 4.9 1H NMR spectrum for 4.72 (400 MHz, CD2Cl2, 298 K)  ............................. 181  Figure 4.10 ORTEP depictions of the solid-state molecular structure of [Cp*Ir(κ2-N,C-(E)-Xyl(N)P(O-C=C(H)(p-tBuPh))(OEt)2)][BArF4]; 4.70 (top) and [Cp*Ir(κ2-N,C-(E)-Xyl(N)P(O-C=C(H)(nBu))(OEt)2)][BArF4]; 4.72  (bottom)  .......................................... 183   xx Figure 4.11 ORTEP depiction of the solid-state molecular structure of [Cp*Rh{κ2-N,O-Xyl(N)P(O)(OEt)2}][BArF4] (4.74) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Rh(1)-O(1) 2.109(4), Rh(1)-N(1) 2.001(4), P(1)-O(1) 1.526(4), P(1)-N(1) 1.614(4), N(1)-Rh(1)-O(1) 72.0(2), O(1)-P(1)-N(1) 100.7(2)  .............................. 185  Figure 4.12 ORTEP depiction of the solid-state molecular structure of (Z)-Xyl(NH)P=O(CH=CHPh)(OEt) (4.76). Selected bond lengths [Å] and angles [°]. P(1)-O(1) 1.463(2), P(1)-N(1) 1.622(2), O(1)-P(1)-N(1) 114.6(1)  ........................................ 188  Figure 4.13 ORTEP depiction of the solid-state molecular structure of [Cp*Ir(µ-Cl)(CNtBu)]2[BArF4]2 (4.80) (ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [o]. Ir(1)-C(1) 1.969(9), Ir(1)-Ir(1)’ 3.6679(7), C(1)-N(1) 1.143(12), Ir(1)-Cl(1) 2.437(2).  ........ 190  Figure 4.14 ORTEP depictions of the solid-state molecular structure of [Cp*Ir{κ2-N,Si-Xyl(N)P(OSiPh2)(OEt)2}][BArF4] (4.82) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-N(1) 1.992(2), Ir(1)-Si(1) 2.343(1), Si(1)-O(1) 1.758(2) P(1)-O(1) 1.531(3), P(1)-N(1) 1.629(3), N(1)-Ir(1)-Si(1) 85.18(8), O(1)-P(1)-N(1) 108.0(1), Ir(1)-Si(1)-O(1) 102.07(8). [Cp*Ir{κ2-N,Ge-Xyl(N)P(OGePh2)(OEt)2}][BArF4] (4.83) Ir(1)-N(1) 1.993(2), Ir(1)-Ge(1) 2.3990(4), Ge(1)-O(1) 1.928(2) P(1)-O(1) 1.519(2), P(1)-N(1) 1.642(2), N(1)-Ir(1)-Ge(1) 86.28(7), O(1)-P(1)-N(1) 109.7(1), Ir(1)-Ge(1)-O(1) 99.36(6)  ................................................................................................................. 194  Figure 4.15 ORTEP depiction of the solid-state molecular structure of [Cp*2Ir2(µ-H)3] [BArF4] (hydride atoms not located) (4.90)  ................................................................... 198  Figure 4.16 1H NMR spectrum of 4.98 showing the α-Ir-CH group of the two epimers [epimer 1 (*) and epimer 2 (*)] formed during the course of the reaction (400 MHz, CD2Cl2, 298 K); q = quartet  ........................................................................................... 202  Figure 4.17 ORTEP depiction of the solid-state molecular structure of [Cp*Ir{κ2-N,O-Xyl(N)P(O)(OMe)2}][BArF4]; (4.102) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-O(1) 2.120(4), Ir(1)-N(1) 1.999(5), P(1)-O(1) 1.521(4), P(1)-N(1) 1.622(5), N(1)-Ir(1)-O(1) 71.4(2), O(1)-P(1)-N(1) 99.8(2)  .................................. 204  Figure 4.18 1H and 1H{31P} NMR spectra for 4.105 showing the α-Ir-CH2 group (400 MHz, CD2Cl2, 298 K); d = doublet, dd = doublet of doublets  ....................................... 205  Figure 4.19 ORTEP depiction of the solid-state molecular structure of [Cp*2Ir2{µ2-Cl}{µ2-3,5-(CF3)C6H3}2][BArF4]; (4.107) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity). Selected bond lengths [Å] and angles [°]. Ir(1)-C(1) 2.23(1), Ir(1)-Cl(1) 2.469(1), Ir(1)-Ir(1’) 2.702(1)  ........ 208  xxi  Figure 4.20 Potential energy surface (PES) for rotation for H2B=NiPr2 (ΔE = 37.3 kcal·mol-1) calculated using BP86-D3/6-311+G(2d,p)  .................................................. 209  Figure 4.21 ORTEP depiction of the solid-state molecular structure of [Cp*Ir(H)(κ1-N-η1-HB-Xyl(N)P(OBHNCy2)(OEt)2][BArF4] (4.112) (displacement ellipsoids are shown at the 50% probability, hydrogens and BArF4- counterion omitted for clarity, Terminal Ir-H not located). Selected bond lengths [Å] and angles [o]. Ir(1)-H(1) 1.47(3), B(1)-H(1) 1.59(4), Ir(1)-N(1) 2.142(3), Ir(1)-B(1) 2.190(3), P(1)-O(1) 1.555(2), P(1)-N(1) 1.576(2), B(1)-N(2) 1.412(4), B(1)-O(1) 1.427(5), Ir(1)-H(1)-B(1) 91(2). a) view of iridacyclic core b) view along B-N bond  ......................................................................................... 213  Figure 4.22 Variable temperature 1H NMR spectrum for 4.112 (400 MHz, CD2Cl2, 298 K)  ................................................................................................................................... 215  Figure 4.23 DFT-calculated structure of 4.112 with non-coordinating hydrogen atoms omitted for clarity. a) diagram of the iridacyclic core b) diagram of the Ir-H2B core. Interatomic distances correspond to those for 4.112 (top) and 4.111 (bottom, italics)  . 218  Figure 4.24 AIM and NBO analysis of 4.112: a) contour plot of ρ(r) with bond paths shown as black tubes, bcps as red points and rcps as purple points. b) contour plot of ł2r(r) with positive contours shown as solid black lines, negative contours shown as dashed red lines 4.112 c) PNBO overlap N(2)-B(1)-H(2) plane d) N-B π NLMO in the N(2)-B(1)-H(2) plane  ..................................................................................................... 219  Figure 4.25 DFT-calculated potential energy surface and change in B(1)-N(2) bond length for rotation about the B-N bond in 4.112  ............................................................ 221  Figure 4.26 DFT-calculated structure of [4.112-rot]+ with non-coordinating hydrogen atoms omitted for clarity. a) view of the geometry about boron b) N(lp) → B-O(σ*) donation  .......................................................................................................................... 223  Figure 4.27 Irida(III)cycle ring size based on 31P NMR chemical shift  ....................... 225   Figure 5.1 Representative DFT-calculated geometry optimizations for complexes 5.6 (left) and 5.14 (right) using B3LYP/def2-TZVP  ........................................................... 237  Figure 5.2 1H-15N{1H} HMBC of 5.14 (CD2Cl2, 298 K) used for indirect detection of δ(15N). δ(1H) horizontal,   δ(15N) vertical  ...................................................................... 238  Figure 5.3 Modified ligands employed for this study  ................................................... 252  Figure 6.1 ORTEP depiction of the solid-state molecular structure of [Cp*Ru{η6-2,6-Me2C6H3(NH)P(O)(OEt)2}][Cl] (6.1) (displacement ellipsoids are shown at the 30% probability, hydrogens (except NH) and Cl- counterion omitted for clarity). Selected bond  xxii lengths [Å] and angles [o]. P(1)-O(1) 1.468(4), P(1)-N(1) 1.641(4), O(1)-P(1)-N(1) 113.7(2)  .......................................................................................................................... 258                                     xxiii LIST OF SCHEMES  Scheme 1.1 Pathways for H2 cleavage by monoiron monooxygenase  ............................ 5 Scheme 1.2 [Fe]-hydrogenase synthetic mimics  ............................................................. 6 Scheme 1.3 C-O bond formation by a BMM mimic  ....................................................... 6 Scheme 1.4 O2 activation by a µ-N,O [Fe(II)]2 complex  ................................................. 7 Scheme 1.5 N-H bond activation by an Fe(II) complex  .................................................. 7 Scheme 1.6 Survey of ruthenium(II) pyridonate complexes  ........................................... 9 Scheme 1.7 E-H bond activation by a Ru(II) bis(pyridonate) complex  .......................... 9 Scheme 1.8 P-C bond cleavage by a [Ru(II)]4 µ-N,O amidate complex  ........................ 11 Scheme 1.9 Accessing a κ2-N,O Ru(II) complex through treatment with N-methylacetamide  .............................................................................................................. 11  Scheme 1.10 Catalytic cycle for [Ru]-mediated hydroamidation  .................................. 13 Scheme 1.11 Reversible CO2 insertion into an [Os]-H bond  ......................................... 14 Scheme 1.12 Catalytic nitrile hydrolysis by an Os-NHC complex and structure of 1.34 15  Scheme 1.13 Synthesis of [Co(NH3)5(κ1-N-N-NHC(O)Me)]2+ (1.37) via nitrile hydrolysis  .......................................................................................................................................... 16  Scheme 1.14 Generation of the Co(III) κ2-N,O complex 1.40  ....................................... 17 Scheme 1.15 Hydrogen-bond donation enables binding of CNtBu  ............................... 18 Scheme 1.16 Hydrolysis of [CoIII(SMe2N4-(tren))(NCCH3)](PF6) (43)  .......................... 18 Scheme 1.17 Co(III) pyridonate complexes  ................................................................... 19 Scheme 1.18 Survey of Rh pyridonate complexes  ......................................................... 20 Scheme 1.19 Nitrene transfer catalysis (NTC) by [Rh2(espn)2Cl] and structure of 1.52  22 Scheme 1.20 Generation of a µ-N,O amidate Rh(III) complex by hydrolysis  ............... 22  xxiv Scheme 1.21 Oxidation of an Ir(I) pyridonate complex 1.54 using CCl4/hv or Cl2  ....... 23 Scheme 1.22 Iminol hydrogen bonding  .......................................................................... 24 Scheme 1.23 Oxidant-free metal/ligand-assisted dehydrogenation  ............................... 25 Scheme 1.24 Catalytic olefin hydroamidation using Ir  .................................................. 27 Scheme 1.25 κ2-N,O Ir amidate complexes and olefin polymerization  ............................ 28 Scheme 1.26 Pyridylideneamidate Cp*Ir(III) complexes  .............................................. 29 Scheme 1.27 Phosphate hydrolysis at Ir(III)  .................................................................. 29 Scheme 1.28 Comparison of amidate and amide donors in NiSOD  .............................. 30 Scheme 1.29 Square-planar Ni(II) complexes used as bioinorganic mimics  ................. 31 Scheme 1.30 Oxygen-atom transfer by a Ni(II) macrocycle  .......................................... 32 Scheme 1.31 Ni-catalyzed Suzuki-Miyaura cross-coupling using amides  .................... 33  Scheme 1.32 Examining the effect of ligand acyl substituent  ........................................ 34  Scheme 1.33 Accessing a bis(C-H) agostic Ni(I) complex  ............................................ 35  Scheme 1.34 Accessing the first mononuclear Ni κ2-N,O pyridonate complex  ............ 36  Scheme 1.35 Alcohol dehydrogenation by Ni(II) pyridonates  ....................................... 37  Scheme 1.36 Examining reductive elimination trends in Pd amidate complexes  .......... 38  Scheme 1.37 Using ligand design to avoid κ2-N,O amidate coordination  ..................... 39  Scheme 1.38 Design of a novel chiral amidate ligand  ................................................... 40  Scheme 1.39 µ-N,O Pd(II) complexes having a Pd-Pd interaction  ................................ 41  Scheme 1.40 Amide N-H activation by Pt(0)  ................................................................. 42  Scheme 1.41 Nucleophilic alkylation of acetone  ........................................................... 43   Scheme 1.42 Survey of Pt pyridonate complexes  .......................................................... 43    xxv Scheme 1.43 κ1-O to κ1-N geometry change via addition of NaH  ................................. 44  Scheme 1.44 Cu-mediated Goldberg reaction of amides  ............................................... 45  Scheme 1.45 C(sp3)-N alkylation using Cu(I)  ................................................................ 46  Scheme 1.46 Using a Cu pyridonate complex for oxidative coupling  ........................... 47  Scheme 1.47 A tris(κ1-N) pyridonate complex of Cu  .................................................... 48  Scheme 1.48 Cyclo(aurated) amidate complexes for biological applications  ................ 49  Scheme 1.49 Zn-C insertion of RNCO provides µ-N,O amidate complexes  ................. 50  Scheme 1.50 Chelation of Cd using a novel amidate ligand  .......................................... 51  Scheme 1.51 First example of a hemilabile complex  ..................................................... 54  Scheme 1.52 Three classes of hemilability  .................................................................... 54  Scheme 1.53 Selected orbital interactions for a dihydrogen, M-(H2) complex  .............. 55  Scheme 1.54 Isolation of the first dihydrogen complex  ................................................. 55  Scheme 1.55 A selection of transition metal σ-complexes  ............................................ 56  Scheme 1.56 α, β, and γ C-H interactions  ...................................................................... 57  Scheme 2.1 Dioxygen reactivity of [Rh(acac)(CO)(PPh3)]  ........................................... 59  Scheme 2.2 Dioxygen reactivity of [Rh(κ2-N,N-PhN3Ph)(η4-COD)] (2.5)  ................... 60  Scheme 2.3 Dioxygen reactivity of [Rh(κ2-N,N-PhN3Ph)(PMe3)3] (2.8)  ...................... 60  Scheme 2.4 Dioxygen transfer reactivity of [Ir(κ2-N,N-PhNC(NMe2)NPh)(η4-COD)(η2-O2)] (2.13)  ....................................................................................................................... 61  Scheme 2.5 Dirhodium(I)-amidates formed by metallation of Na[N(Dipp)C(O)R]; R = tBu (2.16) or Ph (2.17) with [Rh(NBD)Cl]2  ................................................................... 64  Scheme 2.6 Reactivity of 2.18 and 2.20 with PPh3  ........................................................ 67  Scheme 2.7 Reactivity of 2.18 and 2.20 with PCy3  ........................................................ 71  Scheme 2.8 Intermolecular ortho-metallation generating a dirhodium(I) complex  ....... 72  xxvi Scheme 2.9 Reactivity of 2.20 with P(OEt)3 and P(OPh)3  ............................................. 74  Scheme 2.10 Ortho-metallation in a rhodium tiphenylphosphite hydride complex  ...... 76  Scheme 2.11 O2 activation by Wilkinson’s catalyst, RhCl(PPh3)3  ................................ 76  Scheme 2.12 Reactions of 2.21 and 2.22 with O2  .......................................................... 77  Scheme 2.13 Catalytic Ph3P=O formation using 2.19/2.20 and PPh3/O2  ....................... 80  Scheme 2.14 O2 activation products 2.39-2.44 studied by DFT calculations  ................ 81  Scheme 2.15 Reactivity of 2.18 and 2.20 with CNXyl  .................................................. 84  Scheme 2.16 Reactivity of 2.18 and 2.20 with CO  ........................................................ 87  Scheme 2.17 Aldehyde hydroacylation and intermolecular hydroacylation  .................. 89  Scheme 2.18 Reaction of 2.22 with benzaldehyde  ......................................................... 90  Scheme 2.19 Reaction of 2.22 with pentafluorophenylbenzaldehyde  ........................... 93  Scheme 2.20 Reaction of 2.22 with 2-(diphenylphosphino)benzaldehyde  .................... 94  Scheme 2.21 Reaction of 2.22 with pentafluorophenylbenzaldehyde  ........................... 94  Scheme 2.22 Reaction of 2.22 with p-tolylbenzaldehyde and pentafluorophenylbenzaldehyde  ..................................................................................... 95  Scheme 2.23 Reaction of 2.22 with benzaldehyde and 1-octene  ................................... 96  Scheme 2.24 Routes to perfluoroarylrhodium(I) complexes  ......................................... 97  Scheme 2.25 Dirhodium(I) amidates 2.55 and 2.56 formed by metallation of Na[N(Dipp)C(O)RF] (RF = C6F5 (2.53) or CF3 (2.54)) with 0.5 equiv. [Rh(NBD)Cl]2  . 98  Scheme 2.26 Reactivity of dimer 2.55 with PCy3 and resulting C-C cleavage to give 2.59  ......................................................................................................................................... 100   Scheme 2.27 Reactivity of dimer 2.55 with CNXyl to give 2.61  .................................. 105  Scheme 2.28 Equilibrium between 2.62/2.63 and cleavage to give 2.64  ...................... 106  Scheme 2.29 Salt metathesis to give 2.65  ..................................................................... 108   xxvii Scheme 2.30 Reactivity of Rh(CF3)(PPh3)3 (2.67) to give the difluorocarbene complex, Rh(CF2)(F)(PPh3)2 (2.68)  ............................................................................................... 110  Scheme 3.1 B-H agostic complexes of Fe and Ru  ........................................................ 113  Scheme 3.2 Examples of agostic [M]··H-B complexes  ................................................ 114  Scheme 3.3 Accessing the δ-B-H agostic complexes [M{κ2-N,H-Xyl(N)P(OHBCy2)(OEt)2}(η4-COD)] (M = Rh (3.15), Ir (3.16)). Inset shows 1H and 1H{11B} spectra for 3.15 (400 MHz, C6D6, 298 K) ........................................................ 116  Scheme 3.4 Metal-mediated B-H activation to give the phosphoramidoborane 3.18  ... 121  Scheme 3.5 Proposed routes for stepwise borane functionalization  ............................. 126  Scheme 3.6 Accessing the NBD δ-B-H agostic complex 3.23  ..................................... 127  Scheme 3.7 Reaction of complexes 3.15 and 3.16 with acids  ....................................... 130  Scheme 3.8 Reaction of 9-BBN with complexes 3.11 and 3.12  ................................... 132  Scheme 3.9 Reaction of HBMes2 with complexes 3.11 and 3.12  ................................. 134  Scheme 3.10 Reaction of H2BMes with complexes 3.11 and 3.12  ............................... 137  Scheme 3.11 Reaction of HB(C6F5)2 with complexes 3.11 and 3.12   ........................... 140  Scheme 3.12 Reaction of B(C6F5)3 with complexes 3.11 and 3.12  ............................... 144  Scheme 4.1 A Cp*Ir(III) complex having a dianionic 1,3-bis(N,O-chelating) ligand  .. 152  Scheme 4.2 Preparation of the cationic Ir(III) phosphoramidate complex 4.17  ........... 154  Scheme 4.3 Reaction of 4.17 with isonitriles CNR (R = tBu or Xyl)  ........................... 157  Scheme 4.4 Proposed reactivity of 4.17 with acetonitrile  ............................................. 160  Scheme 4.5 Reaction of 4.17 with substituted pyridines  ............................................... 163  Scheme 4.6 DFT-calculated pathway for α-C-H abstraction of pyrollidine using 4.25  165  Scheme 4.7 Monomer-trimer equilibrium for cyclic imines  ......................................... 165  Scheme 4.8 Preparation of cyclic amido and imine CpRe complexes  .......................... 166   xxviii Scheme 4.9 Preparation of a 2-pyrroline W(II) complex  .............................................. 166  Scheme 4.10 Dehydrogenation of 1,2,3,4-Tetrahydroquinolines by a Cp*Ir Complex  167  Scheme 4.11 Reaction of 4.17 with 2o amines and alcohols  ......................................... 168  Scheme 4.12 Generation of Cp*Ir N-heterocycle complexes  ....................................... 170  Scheme 4.13 Divergent modes of reactivity for allyl acetates  ...................................... 172  Scheme 4.14 White’s C-H acetoxylation using Pd(II)  .................................................. 173 Scheme 4.15 Reaction of 4.17 with allyl acetates  ......................................................... 173  Scheme 4.16 Reaction of 4.17 with allylbenzene  .......................................................... 175  Scheme 4.17 Proposed cooperative H-H bond cleavage in a 2-pyridonate Fe complex  176  Scheme 4.18 Alcohol dehydrogenation using a Cp*Ir(III) κ2-N,O pyridonate complex  ......................................................................................................................................... 176  Scheme 4.19 DFT analysis of the concerted-metallation deprotonation (CMD) mechanism using Pd(OAc)2  ........................................................................................... 177  Scheme 4.20 [Ru]-mediated N-hydroamidation  ............................................................ 178  Scheme 4.21 C-N bond formation using a phosphoramidate nucleophile (products shown after aqueous work-up)  .................................................................................................. 179  Scheme 4.22 Generation of five-membered irida(III)cycles 4.69-4.73  ......................... 181  Scheme 4.23 Reaction of phenylacetylene with 4.74  .................................................... 185  Scheme 4.24 Proposed cycle for catalytic phosphoramidation using 1-alkynes  ........... 186  Scheme 4.25 Protonolysis of 4.69 with CF3CO2H  ........................................................ 187  Scheme 4.26 Reaction of 4.69 with CNR (R = tBu, Xyl)  ............................................. 190  Scheme 4.27 Reaction of 4.17 with ethyl diazoacetate  ................................................. 192  Scheme 4.28 Reaction of 4.17 with H2EPh2 (E = Si or Ge)  .......................................... 193  Scheme 4.29 Geminal activation of H2SiPh2 using Ir(TFB)(κ1-O-O2CCH3)(PR3) (4.84)  ......................................................................................................................................... 195  xxix  Scheme 4.40 Reaction of 4.17 with H2BMes and H2  .................................................... 197  Scheme 4.31 Intramolecular C(sp2)-H bond activation of a coordinated PPh3 ligand by 4.91  ................................................................................................................................. 199  Scheme 4.32 MeCN-promoted reversible C(sp3)-H bond activation  ............................ 200  Scheme 4.33 Generation of the cyclometallated Cp*Ir(III) borane complex 4.98 (* denotes a stereogenic centre)  ......................................................................................... 201  Scheme 4.34 Proposed mechanism to account for observed epimerization in 4.98  ...... 203 Scheme 4.35 Generation of the Cp*Ir(III) cyclometallated borane complexes 4.105 and 4.106 (* denotes stereogenic centre)  .............................................................................. 204  Scheme 4.36 Decomposition product of 4.105 examined by X-ray crystallography  .... 207   Scheme 4.37 B-N bond rotation in a coordinated aminoborane having a pendant NMe2 group  .............................................................................................................................. 212  Scheme 4.38 Generation of the Cp*Ir(III) aminoborane complexes 4.111 and 4.112  .. 212  Scheme 4.39 Generation of the bis(σ-B-H) Ir(III) complex 4.113  ............................... 217  Scheme 5.1 Hydrohydrazination using Co- and Ir-based catalysts  ............................... 227  Scheme 5.2 Formation of the first unsubstituted 2-azarhodacyclobutane 5.4  ............... 227  Scheme 5.3 Formation of the first diazarhodacycles 5.6-5.9 and NMR numbering scheme for complex 5.7  .............................................................................................................. 229  Scheme 5.4 Generation of a 3-zircona-1,2-diazacyclopentene  ..................................... 230  Scheme 5.5 Intramolecular Hydrohydrazination using 5.12  ......................................... 231  Scheme 5.6 Formation of the first 3-rhoda-1,2-diazabicyclo[3.3.0]octane  ................... 234  Scheme 5.7 Formation of Rh-alkyne complexes 5.16-5.18 and attempted reactivity to generate rhodacyclopentenes  ......................................................................................... 240  Scheme 5.8 Ring-opening of 5.6 and 5.7 using p-TsOH and subsequent product decomposition  ................................................................................................................ 243  Scheme 5.9 Formation of 5.23 via deprotection using TFA and subsequent acylation using acyl chloride  ......................................................................................................... 245  xxx  Scheme 5.10 Formation of proposed N,O-chelated complex 5.30 and putative mechanism for its formation  ............................................................................................................. 248  Scheme 5.11 Two postulated mechanisms for the formation of 3-rhoda-1,2-diazacyclopentanes: olefin or diazene bound  ................................................................ 253  Scheme 6.1 Formation of Cp*Ru(II) complexes 6.0 and 6.1  ........................................ 257  Scheme 6.2 Formal C-Nu; Nu = nucleophile bond formation using complex 4.17  ...... 259      xxxi LIST OF CHARTS  Chart 1.1 Overview of 1,3-N,O chelated ligands summarized in this chapter (CBC = covalent bond classification method)  ................................................................................ 2  Chart 4.1 Coordinatively unsaturated complexes of group 8 and 9  ............................. 151  Chart 4.2 Relevant phosphoramidate complexes 4.10-4.14  ......................................... 153  Chart 4.3 Overview of groups 8 and 9 aminoborane complexes  .................................. 211                    xxxii LIST OF ABBREVIATIONS AND ACRONYMS  Å  angstrom (10-10 m) Ac acetyl anal.  analysis AIM atoms in molecules Ar  aryl Bn  benzyl Boc  tert-butoxycarbonyl br  broad c  concentration cal  calorie calcd.  calculated COD  cyclooctadiene COE cyclooctene conv.  conversion Cp  cyclopentadienyl Cp*  pentamethylcyclopentadienyl Cy  cyclohexyl d  doublet D  deuterium δ  chemical shift Da  dalton DCM  dichloromethane  xxxiii DFT  density functional theory ΔG‡ Gibbs free energy of activation ΔH°  standard enthalpy change ΔH‡ enthalpy of activation DEPT  distortionless enhancement by polarization transfer DIPEA  diisopropylethylamine DMA  dimethylacetamide DME  1,2-dimethoxyethane DMSO  dimethylsulfoxide dr  diastereomeric ratio ΔS°  standard entropy change ΔS‡  entropy of activation e  electronic charge ee  enantiomeric excess EI  electron impact equiv.  equivalent(s) ESI  electrospray ionization Et  ethyl e.u.  entropy units (calmol-1K-1) Fw  formula weight gem  geminal HSAB  hard soft acid base HMDS  hexamethyldisilazane (N(SiMe3)2)  xxxiv HRMS  high resolution mass spectrometry iBu  isobutyl iPr  isopropyl IR  infrared nJX,Y  coupling constant between atoms X and Y, n bonds away Ka  acid dissociation constant Keq  equilibrium constant KIE  kinetic isotope effect kn  rate constant L  supporting ligand Ln  ligand set Ln  rare-earth metal m  multiplet M  metal M+  molecular ion µ  absorption coefficient (X-ray crystallography) Me  methyl Mes  mesityl (2,4,6-(CH3)3C6H2) MS  mass spectrometry m/z  mass-to-charge ratio υ frequency NBO  natural bonding orbital NMR  nuclear magnetic resonance  xxxv no.  number NBD norbornadiene ORTEP  Oak Ridge thermal ellipsoid plot Ph  phenyl ppm  parts per million precat.  precatalyst psi  pounds per square inch p-tol  para-tolyl Py  pyridine  q  quartet R  organic substituent reflns  reflections rpm  rotations per minute rt  room temperature s  singlet sept  septet t  triplet tBu  tert-butyl Tc  coalescence temperature tert  tertiary TFA  trifluoroacetic acid THF  tetrahydrofuran TOF  turnover frequency  xxxvi TON turnover number Tp  tris(pyrazolyl)borate Tp*  tris(3,5-dimethylpyrazolyl)borate Ts para-toluenesulfonyl (tosyl) X  halide xyl xylyl (2,6-(CH3)2C6H3)                  xxxvii LIST OF COMPOUND NUMBERS Chapter 2:            RNORN ORh RhR NO Na2.18; R = Ph2.20; R = tBu2.55; R = C6F52.56; R = CF32.19RhNO2.16; R = Ph2.17; R = tBu2.53; R = C6F52.54; R = CF32.21; R = Ph2.22; R = tBu2.62; R = C6F52.65; R = CF3Rh NOPPRRhRNOCy3P2.28; R = Ph2.29; R = tBuRhNOCy3PRh2.32Rh NOPPOROORORR OROR2.34; R = Et2.35; R = PhRh POOPhOPhP(OPh)32.35RhNO PPh3PPh3OOArRRhNOPPh3PPh3OOAr2.39; R = Ph2.42; R = tBu 2.41CNRhNOCN2.45RhXylNCXylNCCNXylRNO2.46; R = Ph2.60;  R = C6F5RNORN ORh RhCOCOOC COR = Ph (2.47)R = tBu (2.48)OCRh NO ROCR = Ph (2.49)R = tBu (2.50)RhPPh3PPh3OCF FFFF2.51RhPPh3PPh3OPPh2 2.52RhNOCy3PF5C6E-2.57Z-2.57RhNOCy3PC6F5RhCy3PFFFFF2.59RhXylNCXylNCCNXylFFFFF2.61RhPh3PPh3PPPh3FFFFF2.64RhPh3PPh3PPPh3NO C6F52.63 xxxviii Chapter 3:                    BHROPNOMO3.15;  M = Rh, R = Cy3.16; M = Ir, R = Cy3.28;  M = Rh, R = 9-BBN3.29; M = Ir, R = 9-BBN3.30;  M = Rh, R = Mes3.31; M = Ir, R = Mes3.34;  M = Rh, R = C6F53.35; M = Ir, R = C6F5BHOPNORhO3.23RBHHOPNOMO3.32;  M = Rh3.33; M = IrOPNEONaOPNEMO3.11;  M = Rh, E = O 3.12; M = Ir, E = O3.13;  M = Rh, E = S 3.14; M = Ir, E = S3.9; E = O 3.10; E = SOPNOO3.18BRhOPNOORhOPNOO(3.22)2B(C6F5)4MNMH PhPh3.26; M = Rh3.27; M = Ir3.24; M = Rh3.25; M = IrB(C6F5)4N POOOMBFFF FFF FFFFC6F53.36; M = Rh 3.37; M = IrHN POOOBFFF FFF FFFFC6F53.40 xxxix Chapter 4:IrNPOOOClBArF4MNPOOO4.16 4.17; M = Ir4.74; M = RhIrBArF4CNRCNR4.18; R = tBu δ(31P) 7.004.19; R = Xyl δ(31P) 7.70NPOOO4.22IrBArF4NCMeNCMeNPOOO IrBArF4NN4.23; R = H 4.24; R = tBuIrMeCNBArF4NNPOOORR4.25BArF4IrNNHHnnH4.38; n = 14.39; n = 2IrNClHIrClNClHNHClIrClNClHIrNClHNHBArF4IrClBArF44.40 4.414.424.434.44NN HHIrOCH3OBArF4R4.49; R = H 4.50; R = PhIrNP OOOBArF4PhH4.51BArF4IrNP OOORH4.69; R = Ph4.71; R = Cy4.70; R = p-tBuPh4.72; R = nBu4.73; R = tBuBArF4 4.75NP OOOHH H4.76N POOOHHHBArF4IrNP OOOH4.78; R  = Xyl 4.79; R  = tBuC N RIrCNtBuClClIrCNtBu(BArF4)24.80BArF4IrNP OOOHOO4.81IrBArF4EPhNP OOOPh4.82; E = Si4.83; E = Ge4.89IrBArF4HHBNP OOO4.98IrNP OO OBBArF4**4.105; R = MesIrNPOOOBArF44.102IrNP OO OBR RBArF4*4.106;  R = CyIrBArF4HBNP OOOCyCy4.111;  R = iPr4.112;  R = CyIrBArF4NP OOOHHB NRR4.113IrBArF4HHBNMeMeNPOOO HMe4.104 xl Chapter 5:                    NN NRhNNNOOOORR+5.6; R = Et 5.7; R = iPr 5.8; R = tBu  5.9; R = BnNN NRhNNNNOOCl-+5.14PhNN NRhN+RR5.16; R = CO2Me 5.17; R = CO2Et 5.18; R = PhCl-NN NRhNN NOOOOR R+ OTs-HCl5.20; R = Et 5.21; R = iPrNN NOTsRhN+ OTs-Cl 5.22NN NRhNNNHH+ Cl-5.23NN NRhNNNOO+ Cl-5.24NN NO2CCF3RhNO2CCF3+ Cl-NN NClRhNCl+ Cl-5.26NN NRhNNONHO5.30+ Cl-5.25 xli ACKNOWLEDGEMENTS  Foremost, I would like to express sincere gratitude to my supervisors, Prof. Laurel L. Schafer and Jennifer A. Love for their patience, enthusiasm, and support. Likewise, I would like to thank members of both research teams for making my PhD at UBC an enjoyable and rewarding experience. I am especially grateful to Addison Desnoyer, Alex Dauth, Dawson Beattie, Eric Bowes, Jason Brandt, and Nicole LaBerge for their advice, support, and review of my work over the years. I also thank Prof. Michael Fryzuk for critique of this thesis. The following funding agencies are also thanking for support of this research: NSERC (PGS-M, CGS-D3, and MSFSS awards), The University of British Columbia (Laird, 4YF, and travel awards) and the government of Canada (Vanier Canada Graduate Scholarship). I would also like to extend thanks to Dr. Maria Ezhova for her help in designing and implementing some of the NMR experiments included herein. I am also grateful to Dr. Brian Patrick for X-ray diffraction training and his assistance in refining many of the structures discussed herein. Scott Ryken, Jacky Yim, and Damon Gilmour are additionally thanked for crystallographic support. Eric G. Bowes and Prof. Pierre Kennepohl are thanked for fruitful DFT collaborations. I would also like to thank Prof. Andrew Weller (U. Oxford) and his group (particularly Amit Kumar, Amparo Prades, and Heather Johnson) for an excellent summer and invaluable research experience.    I have been equally fortunate to have the love and support of great friends throughout my PhD, and I thank you all. I am especially grateful to my mother, Yvonne and partner, Nicole for their constant love and encouragement.  xlii DEDICATION             this thesis is dedicated to my mom  for without her I would not be the man I am today                 1 Chapter 1: Survey of N,O-chelating ligands 1.1 General Introduction This thesis explores the use of 1,3-N,O chelating ligands, amidates and phosphoramidates as ligands for rhodium and iridium in the +1 and +3 oxidation states and represents the first of several collaborate projects between the Schafer and Love groups. The information gleaned from this thesis is applicable to N,O-chelated biomolecules insofar as understanding the role(s) of such ligands is concerned. Likewise, this work presents a novel pathway for the preparation of oragnophosphrous insecticides. 1.2 Overview of 1,3-donating ligands In recent years, the chemistry of 1,3-coordinated transition metal complexes has witnessed a great renaissance. Homobidentate 1,3-O,O chelates such as carboxylate (CO2R-)1-3 or triflate (F3CSO3-)4,5 for example, have found widespread applicability as ligands for metals spanning the periodic table. In a similar vein, metal complexes having homobidentate 1,3-N,N-chelating ligands such as amidinate (RNC(R)NR-),6-8 formamidinate (RNC(H)NR-),9,10 guanidinate (RNC(NR2)NR-),6,8,11 or phosphaguanidinate (RNC(PR2)NR-)12 have also been prepared. Taking a hybrid approach, 1,3-N,O-chelating heterobidentate ligand scaffolds such as amidates (RNC(O)R-), ureates (RNC(O)NR2-), 2-pyridonates (C5H4C(O)N-), phosphoramidates ((RO)2P(O)NR-), and sulfonamidates (RNS(O)OR-) have also been employed for a variety of applications ranging from stoichiometric bond activation, small-molecule activation, and of course, catalysis (Chart 1.1).13 These ligand scaffolds are also omnipresent in nature, employed for proton shuttling as well as element-hydrogen bond activation, to name a few.14 By contrast to early transition metal (TM) systems, late TM complexes having 1,3-N,O chelating ligands are not commonly observed,  2 owing in part to the propensity of the hard oxygen/nitrogen donor set to stabilize high-valent Lewis acidic early TM centres – a factor which is mostly ascribable to elementary Pearson hard/soft acid base concepts (HSAB). Early TM amidate complexes have been recently reviewed.15 These ligands are easily synthesized and tuneable, as their electronic and steric profiles are readily modified through changing the nitrogen and carbon substituents. Such appendages can also be rendered chiral through the introduction of stereogenic centres using readily available amino acids or through the implementation of axial or planar chirality (Chart 1.1c).             Chart 1.1 Overview of 1,3-N,O chelated ligands summarized in this chapter (CBC = covalent bond classification method)16 NHOHNOiPriPrNHO iPriPrNC6H13OHNOPR'RphosphoramidateNONOR'RpyridonateR = NR2 (ureate)R = C, H (amidate)ONRR'Mκ2-N,O µ2-N,Oκ1-O κ1-NMONR'ONR'M MMe- donated 3 1 2 + 11modeLX X X LXCBCRRONR'RE or ZNOSORR' R'sulfonamidateONRR'[M]R'NCO[M] R[M] XR'NHC(O)R[M]iv) NH oxidative additioni) salt metathesisiii) hydrolysisH[M]OHRCNv) insertion[M] XR'NHC(O)Rii) protonolysisNa[R'NC(O)R] -HX- NaXa) 1,3-N,O-Chelating ligandsb) Amidate coordination modesd) Syntheses of amidate-ligated complexesc) Chiral Amidate LigandsPoint Chirality Axial Chirality Planar Chirality 3 The N,O chelating scaffold is characterized as an LX-type ligand, comprising both σ- and π-donor properties, potentially allowing for significant M(d)-N(p) or O(p) π-bonding interactions. This ligand class is also hemilabile – a key attribute allowing for coordinative unsaturation during catalysis. Four main coordination modes have been documented for transition and main group elements spanning the periodic table – κ1-N, κ1-O, κ2-N,O, and µ-N,O (Chart 1.1b), though other arrangements such as µ-N, µ-O, and η6-aryl have also been encountered. It is noteworthy that for κ1-O geometries, two C=N regioisomers are possible; having either (E)- or (Z)-relative orientations. For reasons relating to sterics, few examples of (E)-κ1-O binding modes have been reported. Generally speaking, the N,O coordination mode responds to a combination of metal i) coordinative and/or ii) electronic requirements. For example, the κ1-N coordination (vs. κ2-N,O) mode is less common for early transition metals, while the converse is true for late metals. Other ligand scaffolds, such as pincer-type amidate frameworks, support the formation of specific geometries e.g. κ1-N by way of geometric constraint. In terms of practical synthesis, amidate-ligated complexes can be accessed through one of five possible routes: i) salt metathesis, ii) protonolysis, iii) nitrile hydrolysis, iv) amide N-H bond oxidative addition or v) isocyanate (RNCO) insertion into a M-R bond (Chart 1.1d) – examples of all of these will be discussed herein. By contrast, related ureate, 2-pyridonate, phosphoramidate, and sulfonamidate-ligated complexes are typically prepared through one of i) salt metathesis or ii) protonolysis.  This chapter reviews work on 1,3-N,O-ligated complexes of groups 8-12 with a particular emphasis on literature from 2000 onwards. The term 1,3-N,O is restricted to monoanionic  LX-type ligands with coordinating N- or O-donor atoms, related sulphur- 4 containing systems (e.g. thio derivatives) have been excluded. This chapter is organized by metal triad with a particular emphasis on three core themes 1) synthesis, 2) structure and bonding, and 3) reactivity. It is noteworthy that all crystal structures presented herein have been rendered using the appropriate crystallographic information (.cif) file using Mercury 3.8. 1.3 1,3-N,O-Chelated Complexes of Group 8 For Fe, the chemistry of 1,3-N,O chelates is concerned with the application of such scaffolds as ligands in bioinorganic chemistry e.g. in [Fe]-hydrogenase. For Ru and Os, both mono- and dinuclear complexes are known – some of these have been invoked in catalytic amidation (Ru) or nitrile hydrolysis mechanisms (Os).  1.3.1 Iron N,O-chelates including amidates and 2-pyridonates are considered “nature’s ligands”14 serving as weak-field donors in protein active sites, supporting and in many cases, cooperating with late transition metals (metal-ligand cooperativity; MLC).17 For instance, monoiron monohydrogenase (1.1), whose active site comprises a κ1-N 2-pyridinol ligand serves to reversibly cleave H2 delivering hydride (H-) to N,N-methenyl-tetrahydromethanopterin (MPT+) giving H[MPT] and a proton (H+) equivalent (Scheme 1.1).18 This process is important for the overall reduction of CO2 using H2 to provide methane. In 2004, Hall and co-workers showed that there are two pathways for rupture of the H-H bond by either i) Path A: the 2-pyridinol ortho-hydroxyl group via a Fe-H(δ-)···H(δ+)-O dihydrogen bond or ii) Path B: the Cys176-sulfur (Cys = cysteine) atom. This example reaffirms the importance of such 1,3-N,O chelating ligands in biological systems and in particular asserts their role as intramolecular bases. Such enzymes have inspired the  5 synthesis of related 2-pyridonate iridium(III) and nickel(II) complexes for alcohol dehydrogenation (vide infra).           Scheme 1.1 Pathways for H2 cleavage by monoiron monohydrogenase  Several [Fe]-hydrogenase models have been prepared (Scheme 1.2) including [Fe(CO)2(PPh3)I(κ2-N,O-6-Me-hp)] (1.2) prepared by Hu and co-workers in 2009, which employs a 6-methyl-2-pyridonate ligand as a mimic for the 2-pyridone cofactor.19 Notably, the pyridine C-N and C-O bond lengths (1.351(3) and 1.310(3) Å) are consistent with multiple bond character. In 2011, the same group reported a closely related analogue, 1.3 having thiolate ligands.20 In 2013, Song et al. communicated a related [Fe(II)]2 system 1.4 containing 6-acylmethyl-2-pyridinol and 6-acylmethyl-2-pyridonate  ligands.21  HNN NHNNH2NOCH3HCH3RH+   H2[Fe] HNN NHNNH2NOCH3HCH3RHH+   H+Fe NHOOOSCOOCX(Cys)[Fe]NHNNONH2NOOHOHOPOHOmethenyl-H4MPT+ methylene-H4MPTFe NOOHOSH3CHCOOCH2HFe NOOHOSH3CHCOOCH2Fe NOOHOSH3CHCOOCHFe NOOHOSH3CCOOCH2HPath APath B-H+-H+HFe NOOHOSH3CHCOOCH H‡‡Fe NOOHOSH3CCOOCHHHa) Reversible cleavage of H2 by [Fe]-monohydrogenaseb) Proposed pathways for H-H bond cleavage(1.1) 6     Scheme 1.2 [Fe]-hydrogenase synthetic mimics  Bacterial multicomponent monooxygenases (BMMs) facilitate both O2 and C-H bond activation and consist of two diiron(II) centres having bridging carboxylate ligands. In 2009, Münck et al. showed that a µ-oxodiiron(IV) amidate complex 1.5, formed through electrolysis, can be employed for the C-H bond activation of substrates having bond dissociation energies (DC-H) up to 100 kcal·mol-1 (Scheme 1.3).22 For alcohols, chemoselective O-H bond cleavage was observed generating acetone from t-butanol via β-C-C bond scission.  It is noteworthy that the mechanism for this pathway remains unclear.      Scheme 1.3 C-O bond formation by a BMM mimic   In 2011, MacBeth and co-workers showed that analogous amide complexes could also be used to stabilize adjacent Fe(II) centres (dFe-Fe = 4.138 Å) having bridging (µ2-N,O) and κ1-N amidate binding modes (Scheme 1.4).23 Complex 1.6 was shown to be active for C-O bond formation through intramolecular isopropyl C-H bond activation and O-atom transfer using either O2 or PhIO, culminating in the formation of a new five-membered Fe NOIPPh3OCOCHu, 2009Fe NOSPPh3OCOCHu, 2011R1 R3R2Fe NOOSCOOCHNFeN OOCOCOSong, 20131.2 1.3 1.4NN ONNOOFeNNO NNOOFeOIVIV [FeIIFeIVO(L)2]3+ +  H+HH HOH O O1.5FeFeONX-ray of 1.5 7 ferra(III)cycle 1.7. These examples highlight the innate capacity of an amidate-containing scaffold to support potentially high-valent iron oxo intermediates generating unique models for biological diiron(II) hydroxylase enzymes.	 Scheme 1.4 O2 activation by a µ-N,O [Fe(II)]2 complex  In 1990, the activation of amide N-H bonds by Fe diphosphine complexes was reported by Schaad and Landis. Photochemical activation of cis-Fe(H)2(dmpe)2 (dmpe = 1,2-bis(dimethylphosphino)ethane) with 1.2 equiv. trifluoroacetamide provided the corresponding κ1-N amidate complex 1.8 (Scheme 1.5).24 Although the products were not characterized by X-ray crystallography, a κ1-N geometry was deduced based on multinuclear NMR spectroscopy, which provided a quintet for the hydride (1H NMR spectrum) and a singlet for the dmpe ligand (31P NMR spectrum), though the authors speculated that dynamic processes to give other isomers through Fe-N bond rupture might also be operative.     Scheme 1.5 N-H bond activation by an Fe(II) dihydride complex  FeNNN N OiPrOiPrOFe NNNNOiPrOiPrOKO2 or 2 equiv. PhIO- 2 KOAc, 0.5 KBrH3LiPr FeNNNNOiPrOiPrOO KH, DMFFe(OAc)20.5 equiv. [PPh4]BrPPh4iPriPrPPh4DMFDMF1.6 1.7Fe HPPPPH H2N CF3O+ FePPPPHHNF3CO-H2hv1.8 8 1.3.2 Ruthenium The number of Ru complexes having 1,3-N,O chelating ligands far surpasses that of Fe. As early as 1980 Clegg et al. showed that reaction of [Ru2(OAc)4(PPh3)2] with Na(mhp) (mhp = 6-methyl-2-pyridonate) provided the bis(κ2-N,O) chelated complex, [Ru(κ2-N,O-mhp)2(PPh3)2] (1.9) – one of the first examples where a pyridonate ligand was shown to interact with only one metal atom via a κ2-N,O bonding arrangement (<O-Ru-N = 61.8(2)o) (Scheme 1.6).25 In 1988, Cotton and co-workers reported that reaction of 0.5 equiv. [Ru(η6-p-cymene)Cl2]2 with Na(hp) (hp = 2-pyridonate)  revealed a related κ2-N,O pyridonate complex [Ru(η6-p-cymene)(κ2-N,O-hp)Cl].26 Interestingly, addition of a further equivalent of Ag(hp) provided the bis(pyridonate) complex 1.10 having dual κ1-N and κ2-N,O coordination modes (Scheme 1.6). The 1H NMR spectrum of 1.10 revealed one set of resonances at 303 K, while at 204 K two sets of resonances (one for each hp ligand) were observed, indicating rapid room temperature interconversion between hp ligand binding modes. Tocher et al. showed that related compounds could be accessed by way of protonolysis using [Ru(η6-C6H6)Cl(O2CCF3)] and the corresponding 2-pyridone.27 Mononuclear Ru salts were also observed using an η3:η3-C10H16RuIV framework, giving the pseudo trigonal bipyramidal complex 1.11 (Scheme 1.6).28 In 2000, Kelson et al. showed that the κ1-N binding mode could be accessed using a Ru terpyridine (terpy) ligand scaffold (1.12) (Scheme 1.6).29 This complex could be used for the transfer hydrogenation of ketones, offering turnover numbers of ca. 1000.      9      Scheme 1.6 Survey of ruthenium(II) pyridonate complexes In 2015, Szymczak et al. reported a Ru(II) bis(2′-hydroxy-6′-iminopyridyl)isoindoline complex (1.13) for catalytic nitrile hydroboration (Scheme 1.7, Figure 1.1).30 Stoichiometric studies using 1.13 and H2 or HBPin (Pin = pinacolborane) revealed cooperative element-hydride (E-H) bond activation across the Ru-O bond giving 1.14 or 1.15. Using 5 mol% 1.13, an array of nitriles could be converted to 1o amines through two consecutive hydroboration steps. The ligand ortho-OH groups were deemed critical for this transformation, as variants having ortho-CH3 or para-OH groups were ineffective, indicating the importance of metal-ligand cooperativity (MLC).17 Scheme 1.7 E-H bond activation by a Ru(II) bis(pyridonate) complex NN NRuOH2N ON ORuPPh3PPh3NONOKelson, 2000Cotton, 1988RuClNORTocher, 1992RuNONOClegg, 19801.9 1.10 1.11 1.12O OB PPh3NNNNN OORuHPPh3HBPinPPh3NNNNN OORuPPh3HHHNNNNN OORuPPh3H2- PPh3OOBHNCMeN BPinBPin1.13 1.141.15 10      Figure 1.1 Solid-state molecular structures of 1.13 and 1.15 The chemistry of multiply bonded bimetallic paddlewheel complexes having four µ-N,O-chelating ligands has intrigued chemists for decades. For ruthenium, the bridging trifluoroacetamidate Ru(II)/Ru(III) complex [Ru2-µ2-N,O-(NHC(O)CF3)4]+, first disclosed in 1983, has been studied to a great extent.31 Principally, the redox properties of this molecule indicate that it is resistant to oxidation. Several groups have studied amidate substituent effects in hopes of tailoring the electrochemical properties of such systems – in 1986, Tocher et al. showed that [Ru2-µ2-N,O-(NHC(O)tBu)4]+ having an electron-donating tBu group allows for favourable oxidation, indicating that amidate-substituents may influence electron transfer properties at a transition metal center.32 Moreover, treatment of a related Ru(II)/Ru(III) complex [Ru2-µ2-N,O-(NHC(O)Ph)4]+  (1.16) with triphenylphosphine PPh3 resulted in an unusual P-C bond cleavage reaction resulting in transfer of the aryl group and oxidation giving the [Ru2]6+ complex 1.17 (Scheme 1.8).33 The Ph2POC(Ph)N- ligand bridges both ruthenium(II) centres with an essentially coplanar amidate N-atom [358.4(6)o], in agreement with C=N double bond character. Although amidates are mostly thought to serve as spectator ligands, this example shows how an amidate and Ru centre may act cooperatively to cleave a P-C bond and give new Ru-C and P-O bonds. Later in 1995, Tocher et al. showed that amides provide variable µ2-binding modes in that Ru	P	N	O	 B	Ru	N	P	O	 11 [RuCl2(PPh3)3] reacts with trifluoroacetamide and NEt3 to give the head-to-head (HH) µ-N,O complex, [Ru2-µ2-N,O-(NHC(O)CF3)2(µ2-Cl)(µ2-H)] while use of [RuCl(H)(PPh3)3] provides a mixture of HH and head-to-tail (HT) isomers along with a small amount of [Ru2-µ2-N,O-(NHC(O)CF3)2-µ2-N-(NHC(O)CF3)(µ2-H)(PPh3)4], exhibiting both µ-N,O and µ-N coordination amidate modes.34 Scheme 1.8 P-C bond cleavage by a [Ru(II)]4 µ-N,O amidate complex In 2006, it was reported that the Ru(II) phenyl complex, TpRu(CO)(NCMe)(Ph) (Tp = hydridotris(pyrazolyl)borate) complex reacts with N-methylacetamide to give benzene and the κ2-N,O amidate complex 1.18 for which vCO = 1944 cm-1 (Scheme 1.9).35 Ultimately, this compound was difficult to purify and not cleanly isolated.      Scheme 1.9 Accessing a κ2-N,O Ru(II) complex through treatment with N-methylacetamide The addition of 1-alkynes to amides (hydroamidation) represents a versatile hydrofunctionalization route for the preparation of amides, which have important RuRuPhOHNPhOHNPhONHPhONH+PPh3RuRuPhOHNPhOHNPhONHPhONH+DMSOPh3PPPh3RuRuPh ONPhOHNPhONPhONH+PhPhPPhPhPPhPhIIIIII1.16 1.17N N RuBN NN NHNCMePh HNO+COC6D6, 90 oC- PhHN N RuBN NN NHCONO- MeCN κ2-N,O1.18 12 pharmaceutical, agrochemical, and medicinal applications. This transformation was first reported in 1995 by Watanabe et al. using a mixture of Ru3(CO)12 and PCy3.36 Nearly two decades later, in 2011 Gooßen and co-workers expanded the generality of this transformation using (COD)Ru(met)2 (COD = 1,5-cyclooctadiene, met = methylallyl), PnBu3, and 4-N,N-dimethylaminopyridine (DMAP) (Scheme 1.10).37 The catalytic cycle for this reaction has been studied in detail using density functional theory (DFT) and experiment and invokes several κ1-N amidate-coordinated Ru complexes. Based on an elaborate mechanistic study, the authors propose that the precatalyst (η4-COD)Ru(met)2 first undergoes reductive coupling to give a catalytically-competent Ru(0) complex 1.19 followed by amide N-H bond oxidative addition to give a κ1-N amidate Ru(II) hydride 1.20. Subsequent alkyne coordination (1.21) followed by a 1,2-migratory insertion event gives 1.22. The resulting vinyl complex 1.22 undergoes rearrangement to provide a Ru(IV) hydrido vinylidene species 1.23, which upon intramolecular N-amidation affords a Ru-vinyl hydride 1.24. Reductive elimination from this species releases the functionalized (E)- or (Z)-enamide 1.25 along with the Ru(0) catalyst. Although these intermediates have not been experimentally authenticated, they serve to highlight the coordinative flexibility conferred by an amidate ligand. A general understanding of the coordination modes offered by these ligands undoubtedly helps to provide insight into catalysis involving amides as substrates.     13          Scheme 1.10 Catalytic cycle for [Ru]-mediated hydroamidation  1.3.3 Osmium Osmium amidate complexes were first reported in 1995 by Tocher et al. who showed that [Os(H)2(CO)(PPh3)3]  undergoes protonolysis using trifluoroacetamide to give H2 and the κ1-N amidate complex, [Os(H)(κ1-N-HNC(O)CF3)(CO)(PPh3)3].34 In 2000, Flood et al. showed that a related protonolysis reaction using the cyclometallated Os(II) complex 1.26 and 2-hp provides the κ1-N bonded Os(II) 2-pyridonate complex 1.27 (Scheme 1.11).38 Heating a solution of 1.27 was found to liberate 1 equiv. PMe3, giving fac-1.28, having κ2-N,O coordination. Reaction of fac-28 with CO2 provided the formato complex, fac-1.29 – this reaction was found to be reversible. Insertion reactions of either 1-hexene or ethylene with fac-1.28 were also observed to be reversible. LnRuLnRuR2NO R1H*LnRuR2NO R1H*R3HLnRuR2NO R1HR3H*LnRuR2NO R1HHR3*LnRuR2NOR1HHR3*R2NO R1HR3HL = phosphinesLand/or additivesL LR2NOR1HR3*HR2NOR1H R2NOR1HR3HR3H+2 mol% (COD)Ru(met)26 mol% PnBu34 mol% DMAPPhMe, 100 oC, 15 h1.191.201.211.221.231.241.25 14       Scheme 1.11 Reversible CO2 insertion into an [Os]-H bond The conversion of nitriles to amides typically necessitates the use of harsh conditions including strong base/acid and/or heating. In an effort to remedy this problem, several groups have begun to explore the use of transition metals to achieve catalytic amidation at moderate temperature. In 2012, Esteruelas, Gimeno, et al. reported that an unsaturated Os(II) N-heterocyclic carbene (NHC) complex could be employed for catalytic nitrile hydrolysis (Scheme 1.12).39 In particular, κ2-N,O chelated osma(II)heterocyclic intermediates were cleanly isolated from reaction of the hydroxide complex [Os(η6-p-cymene)(OH)IPr]OTf (1.30) with aceto- or benzonitrile giving [Os(η6-p-cymene)(κ2-N,O-NHC(O)R)IPr]OTf (R = Me (1.33), Ph (1.34)). Although such intermediates have been suggested for a range of late transition metals, well-characterized examples of κ2-N,O chelating amidate complexes have not been widely prepared and to our knowledge, this is the first example of a κ2-N,O amidate complex of a group 8 metal. The κ2-N,O chelating mode is identifiable by characteristic 13C NMR signals at δC = 182.0 (1.33) and 185.5 (1.34) for the central carbon of the NCO fragment.39 Furthermore, the benzonitrile adduct 1.34 was characterized in the solid-state and exhibits a tight <N-Os-O bite angle of 60.31(9)o  as well as short O(1)-C(1) and N(1)-C(1) bond lengths of 1.283(3) and 1.296(4) Å consistent with OsPMe3HPMe2Me3PMe3P CH2NHO+ OsPMe3HMe3PMe3P PMe3NOOsPMe3HMe3PNOMe3P110 oC, C6D6PMe3OsPMe3CO2HMe3PNOMe3P110 oCPhMeCO2fac-1.28fac-1.291.271.26 15 delocalization across the NCO fragment. The proposed catalytic cycle for nitrile hydrolysis is provided in Scheme 1.12.    Scheme 1.12 Catalytic nitrile hydrolysis by an Os-NHC complex and structure of 1.34 1.4 1,3-N,O-Chelated Complexes of Group 9 Like Fe, the chemistry of Co revolves around accessing mimics for biological systems (nitrile hydrolysis). For Rh and Ir, dinuclear complexes having a µ-N,O coordination mode dominate, though recent progress has shown that mononuclear κ1-O, κ1-N and κ2-N,O modes can also be accessed.  1.4.1 Cobalt  Cobalt amidate complexes were reported as early as 1973 by Sargeson et al. who studied the hydrolysis of [Co(NH3)5(NCMe)]3+ to give the κ1-N acetamido complex [Co(NH3)5(κ1-N-NHC(O)Me)]2+ (1.37) (Scheme 1.13).40 Ferguson et al. later determined the structure of 1.37 by single crystal X-ray diffraction, providing evidence for a six-coordinate Co(III) centre.41 The acetamide ligand delivers a moderate trans influence with a Co-N bond length of 1.994(8) Å (trans-N(amidate)) with the mean of the other four Co-N OOsNCOsiPriPriPriPrNNOHOsiPriPriPriPrNNONHRRCNOsiPriPriPriPrNNOHN ROHOsiPriPriPriPrNNN COHRHOONH2R+H2Oκ2-N,Oκ1-NHOR = Me (1.31)R = Ph (1.32)1.30+++R = Me (1.33)R = Ph (1.34)R = Me (1.35)R = Ph (1.36) 16 distances being 1.963(13) Å. For the amide ligand, C(1)-O(1) and C(1)-N(1) bond lengths of 1.267(12) Å and 1.339(12) Å as well as a CO stretching frequency of 1700 cm-1 (cf. 1714 cm-1 for CH3C(O)NH2) are indicative of mild delocalization throughout the N,O chelating ligand.    Scheme 1.13 Synthesis of [Co(NH3)5(κ1-N-N-NHC(O)Me)]2+ (1.37) via nitrile hydrolysis In 1990, Jackson and co-workers surveyed the factors governing κ1-O versus κ1-N coordination for a family of Co(III) amidates: [Co(NH3)5(H2N(CO)R)]3+.42 In that work, the complex [(H3N)5Co(OSO2CF3)5](CF3SO3)2 was shown to react with amides to give the κ1-O derivative  [(H3N)5Co(κ1-O-H2N(CO)R)]3+ in poorly coordinating solvents (e.g. acetone, sulfolane). However, upon addition of base or protic solvent, rearrangement to the thermodynamically favored κ1-N form was triggered. In terms of spectroscopic assignment, the location of the Co-NH (3.7 – 5.2 ppm) signal in the 1H NMR spectrum as well as the NCO (170 to 180 ppm) peak in the 13C NMR spectrum are both diagnostic of κ1-N coordination.42  In the realm of biological nitrile hydrolysis, hydratases (NHases) are enzymes that consist of either Co(III) or Fe(III) centers ligated by two κ1-N amidates as well as other sulfur donors.43 In an effort to uncover the mechanism of hydrolysis by such systems, in 1993, Chin et al. showed that a Co(III) cyclen (cyclen = 1,4,7,10-tetraazacyclododecane) κ2-N,O amidate complex 1.40 could be accessed by way of nitrile hydrolysis (Scheme 1.14).44 NOHNH3NH3CoNH3H3NH3NNCMeNH3NH3CoNH3H3NH3NOH-3+ 2+1.37 17 Importantly, N-methyl substitution of the ligand was found to be pivotal, allowing for access to such a key cobalta(III)heterocycle – one of the first examples of a 3d transition metal bearing a four-membered amidate chelate. Though complex 1.39 was inactive for catalysis, the N-protio complex 1.38 allowed for catalytic nitrile hydrolysis under mild conditions. Treatment of 1.38 with CH313CN and monitoring the reaction by 13C NMR spectroscopy showed consumption of the starting material (δ = 121.0) and formation of acetamide (δ = 178.5). In addition to these, two signals, each at δ = 188.5 and 190.0 were observed, attributable to isomeric N,O-coordinated acetamide complexes having mixed endo/exo exo/endo NH groups, respectively.     Scheme 1.14 Generation of the Co(III) κ2-N,O complex 1.40  In 2006, Ozawa, Masuda, et al. examined the role of the amidate ligand in [Co]-NHase by synthesizing structurally similar complexes of Co(III) (1.41) ligated by an N2S2 bis(κ1-N) amidate ligand (Scheme 1.15).45 From this work, it was found that the carbonyl oxygen atom of the amidate coligand serves as a hydrogen-bond donor, allowing for modification of the Lewis acidity at the Co(III) centre. For example, coordination of the Lewis base, CNtBu occurred only in protic solvents such as H2O or MeOH, whereas 1000-fold excess was required to form the six-coordinate complex 1.42 in acetone. These data suggest that the mechanism of hydration carried out by [Co]-NHase relies on amide intermolecular hydrogen bonding. CoNNCH3CH3NN OHNRHOONH2R R = H R = CH3CoN C R+CoNNRRNNN C RHHHHHOR = H (1.38)R = Me (1.39)1.40endo or exo 18    Scheme 1.15 Hydrogen-bond donation enables binding of CNtBu Well-defined, structurally characterized mimics of NHases are quite rare, especially in instances where both Co(III)-nitrile and Co(III)-amidate intermediates have been isolated. In 2009, Kovacs et al. showed that the cationic cobalt complex, [CoII(SMe2N4-(tren))](PF6) (tren = tris(2-aminoethyl)amine) (1.43) undergoes oxidation using [Cp2Fe][PF6] to give [CoIII(SMe2N4-(tren))(NCCH3)](PF6)2 (1.44) (Scheme 1.16, Figure 1.2).46 Hydroxide addition to 1.44 provides the κ1-N amidate complex, [CoIII(SMe2N4-(tren))(κ1-N-NHC(O)CH3)](PF6) (1.45). X-ray crystallographic analysis revealed the amidate to have a strong trans influence as demonstrated by an increase in Co-N(1) imine bond length from 1.875(2) Å (1.44) to 1.897(4) Å (1.45) as well as an intramolecular hydrogen bonding interaction with the ligand.  Scheme 1.16 Hydrolysis of [CoIII(SMe2N4-(tren))(NCCH3)](PF6) (43) 					CoSNN NH2NH2CoSNNH2NH2NN C CH3 CoSNNHNH2NNHOHCp2FeMeCNHO-H2O/MeCN+ 2+ +κ1-N1.43 1.44 1.45N NO OS SCoH3CH3CCH3CH3N NO OS SCoH3CH3CCH3CH32 CNtBu+CNtBuCNtBuKeqHOR HO R++1.41 1.42HOR 19     Figure 1.2  Solid-state molecular structure of 1.45  In 1996, Winpenny et al. showed that 6-substituted pyridonates Na(6-R-hp) (R = CH3, F) react with Co(OAc)2 in the presence of diimine ligands to reveal complexes 1.46 (R = CH3) and 1.47 (R = F) having κ2-N,O and µ-O pyridonate coordination modes (Scheme 1.17).47 In this work, however, the preference of the diimine ligand is suggested to control the resulting pyridonate coordination mode. This example also highlights a rare example of the µ2-O bonding mode in a late transition metal complex.     Scheme 1.17 Co(III) pyridonate complexes 1.4.2 Rhodium In the 1980s several research groups focused their attention on the use of 2-hp ligands for coordination to Rh(I) and Rh(II) (Scheme 1.18). Amongst these, in 1984 Cotton et al. showed that the dirhodium(II) paddlewheel complex, [Rh2(fhp)4] (fhp = 6-fluoro-2-OCoNCCoNN NONOCoNN ONO FCo NNN OFNFONF1.46 1.47 20 pyridonate) (1.48) could be accessed from RhCl3·3H2O and the sodiated pyridonate ligand Na(fhp).48 The dimethylsulfoxide (DMSO) adduct could be recrystallized with an unusual unidirectional alignment of the four 2-pyridonate ligands having all four fluorine substituents on the same side of the Rh-Rh axis [dRh-Rh = 2.410(1) Å]. Related µ-N,O bridged [Rh(II)]2 amidate complexes have found application in tumour therapy.49 In 1987, Oro et al. showed that reaction of [Rh2(µ-Cl)2(CO)4] with 2-hp and KOH provides the unique tetranuclear complex, [Rh4(µ-OPy)4(µ-CO)2(CO)4] (1.49) - an electronically unsaturated, 60 valence-electron complex.50 Representative bond lengths for one of the pyridonate ligands: C(1)-N(1) = 1.335(11) Å and C(1)-O(1) = 1.283(10) Å are consistent with delocalization across the N,O-chelating ligand. Formation of the related [Rh(I)]2 dimer 1.50 can be accomplished by protonolysis of [Rh(acac)(CO)2]2 (acac = acetylacetonate) with 2-pyridone in CH2Cl2 or by treatment of the olefin derivative [Rh2(µ-Cl)2(η4-COD)2] with excess CO.50 In an interesting result, [Rh2(µ-Cl)2(CO)4] was also found to react with CH3I to give the κ1-N-acetoxypyridone complex [RhI(CO)2(MeCOOC5H4N)].51 Hursthouse and co-workers later reported that addition of the neutral proligand 2-hp to [Rh2(µ-Cl)2(CO)4] gave the κ1-O product, cis-Rh(κ1-O-HOPy)(CO)2(Cl) (1.51).52 Scheme 1.18 Survey of Rh pyridonate complexes NORhRhNODMSOFNOFOro, 1988ClRhOCOCHNOCotton, 1984Rh RhCOCOOC CON OHursthouse, 1988RhRhRhRhNONON ON OOro, 1987NOFN OF= CO1.48 1.49 1.50 1.51 21 In 1989, Carriedo reported the first dirhodium(I) scaffolds having 1,3-N,O chelated amidate ligands.53 Treatment of [Rh2(µ-Cl)2(CO)4] with sodium N-phenylacetamide provided the µ2-N,O bridged complex [Rh2(µ2-N,O-NPhC(O)Me)2(CO)4] that was characterized by microanalysis and IR spectroscopy. Treatment of this complex with 2 equiv. PPh3 resulted in CO evolution providing two isomers of [Rh2(µ2-N,O-NPhC(O)Me)2(CO)2(PPh3)2].  In comparison to Rh(I), the chemistry of 1,3-N,O chelated Rh(II) complexes is considerably more developed. Similar to the dirhodium(II) paddlewheel complexes disclosed over 30 years ago, in 2013, the synthesis of a novel mixed-valence Rh(II)/Rh(III) complex, Rh2(espn)2Cl (espn = α, α, α′, α′-tetramethyl-1,3-benzenedipropanamidate) (1.52) for use in catalytic C-H amination using nitrene transfer catalysis (NTC) was described (Scheme 1.19).54,55 Complex 1.52 is formed by treatment of [Rh2(OAc)4·2MeOH] with H2espn in refluxing CH2Cl2, followed by oxidation using N-chlorosuccinimde (NCS) to give the cis-[2,2] isomer, following chromatographic separation. It is well-accepted that amidate ligands i) bind more strongly to Rh and ii) lower the oxidation potential for access to the Rh(II)/Rh(III) couple when compared to carboxylate ligands. By comparison, the carboxylate complex Rh2(esp)2 (esp = α, α, α′, α′-tetramethyl-1,3-benzenedipropanoate) degrades rapidly during NTC, mainly due to an inability to stabilize the requisite Rh2II,III intermediate, a catalyst resting state.      22       Scheme 1.19 Nitrene transfer catalysis (NTC) by [Rh2(espn)2Cl] and structure of 1.52  Amidate-ligated complexes are also known to support the Rh(IV) oxidation state. In 1996, Kukushkin, Isobe, and co-workers reported that nitrile hydrolysis using [Cp*2Rh2(µ-CH2)2(µ-CO3)] gave the µ-N,O bridged complex, [Cp*2Rh2(µ-CH2)2(µ-N,O-NHC(O)Me)] (1.53) (Scheme 1.20).56 Structural analysis revealed delocalization along the NCO chelate having C-O and C-N bond lengths of 1.29(1) and 1.28(1) Å, respectively.    Scheme 1.20 Generation of a µ-N,O amidate Rh(IV) complex by nitrile hydrolysis 							Rh			Cl	N			O	RhRhOHNHNOHNOONHRhRhOHNHNOHNOONHSO3RNI PhRRO3SNPhIR-HNSO3RH µ2-N,Oµ2-N,O1.52ClClRh RhO OORh RhO NHMeCN, H2O- HCO3-1.53+ 23 1.4.3 Iridium  Binuclear µ2-N,O-chelated complexes of Ir(I) were reported as early as 1985 by Mann, Rodman and co-workers. By analogy to the [Rh(I)]2 systems discussed previously, [Ir2(µ-O(hp’))2(η4-COD)2] (hp = 2-pyridonate or 6-methyl-2-pyridonate) (1.54) could be accessed through salt metathesis [dIr-Ir = 3.216(1) Å].57 Subsequently, four-electron oxidation of 1.54 using Cl2 or CCl4/hv gave [Ir(Cl)2(µ-hp’)(η4-COD)] (1.55) as the major Ir-containing pyridonate complex (Scheme 1.21). In 1995, Tocher reported that a κ1-N amidate complex, [Ir(H)2(PPh3)3(κ1-N-HNC(O)RF)] (RF = CF3 or C2F5) could be accessed by treatment of mer-[Ir(H)3(PPh3)3] with the corresponding amide in boiling toluene.34 The κ1-N and not κ1-O geometry was concluded based on 1H NMR spectroscopy using the hydride chemical shift as an indicator as the strong trans influence of the nitrogen donor causes a 5 ppm upfield shift when compared to the related carboxylate complex [Ir(H)2(PPh3)3(κ1-O-O2CR)].      Scheme 1.21 Oxidation of an Ir(I) pyridonate complex 1.54 using CCl4/hv or Cl2  In 1994, Crabtree et al. reported that amidates could participate in hydrogen bonding through an iminol tautomer.58,59 Coordination of quinolin-8-acetamide to [Ir(PPh3)2(OCMe2)2(H)2][SbF6] (1.55)  provided the κ1-N bonded iminol complex 1.56 (Scheme 1.22). Consistent with this bonding description, X-ray crystallographic analysis revealed a short C-N [1.260(22) Å] and long C-O bond [1.321(23) Å]. Interestingly, 1H NOIr IrN O IrNOClClor Cl2hv, CCl41.54 1.552 24 NMR spectroscopic studies of 1.56/1.57 revealed that the iminol [δ = 9.54 ppm] group was coupled to one of the Ir-H resonances (JH,H = 3 Hz) indicating a hydrogen bonding interaction. In a follow-up report, the authors showed that coordination of benzonitrile (PhCN) resulted in effervescence of H2 along with formation of the κ1-N amidate benzonitrile adduct 1.58. In the absence of an exogenous donor, thermolysis of 1.56/1.57 provided the κ2-N,O bonded complex 1.59 along with H2. This coordination mode was deduced on the basis of IR spectroscopy, which provided a signal at 1476 cm-1 (cf. 1678 cm-1 for the free ligand and 1601 cm-1 for the PhCN adduct 1.58). In addition, complex 1.59 was found to effect Si-H bond cleavage of HSiEt3 providing the silylated iminol complex 1.60. This study shows how a coordinated amidate can be used to advantage in σ-bond metathesis reactions.  Scheme 1.22 Iminol hydrogen bonding  As discussed previously, the hydrogen transfer ability of the 2-pyridone (hp) ligand in monoiron monooxygenase has inspired the synthesis of related Cp*Ir(III) (Cp* = C5Me5-) pyridonate complexes (Scheme 1.23, Figure 1.3). In 2006, Yamaguchi et al. reported that IrPh3PPh3PHH OO NHN O+ IrPh3PPh3PHH NNOHCH2Cl2O2IrPh3PPh3PHH NNOHIrPh3PPhCNH NNOPh3PH2PhCN IrPh3PH NNOΔH2HSiEt3IrPh3PHHPh3P NNOEt3Si+ + ++++1.55 1.561.571.58 1.591.60PPh3 25 Cp*IrCl2(κ1-N-C5H4C(OH)N) was active for the oxidant-free metal/ligand-mediated dehydrogenation of alcohols with turnover numbers (TONs) of up to 2000.60 Intermediate complexes such as the κ2-N,O chelated Cp*IrCl(κ2-N,O-hp) (1.61) derivative were also shown to be active for this transformation. Rauchfuss et al. later studied the mechanism of this reaction, showing that 1.61 reacts with secondary alcohols or H2 to give Cp*Ir(III) hydrides including the binuclear complex [Cp*2Ir2(µ-H)2(µ-N,O-hp)]Cl (1.62).61 The Cp*Ir κ1-N pyridinone hydride 1.63 could also be accessed by treatment of 1.61 with Cp*IrH(H2NCHPhCHPhNTs), which upon deprotonation with NEt3 gave 1.62. In 2009, Yamaguchi and co-workers expanded this reaction to include the formal dehydrogenation-hydrogenation reaction of N-heterocycles using Cp*Ir(5-CF3hp)Cl (5-CF3hp = 5-trifluoromethyl-2-pyridonate).62 Overall, the substitutional lability and Brønsted basicity of a 2-pyridonate ligand were both deemed necessary for reactivity toward hydrogen donors 									   Scheme 1.23 Oxidant-free metal/ligand-assisted dehydrogenation   IrCl NONOHHIr IrCl+ [C5H4NH(OH)]Cl2R RO HHR RO22IrCl NHO2HIrNTsN PhPhCp*H IrNHTsN PhPhCp* NEt31.61 1.621.63H2 26     Figure 1.3 Solid-state molecular structures of 1.61 and 1.62  In 2012, Hartwig et al. reported the intermolecular addition of 1-alkenes and bicycloalkenes to amides using a DTBM-Segphos (DTBM = 3,5-di-tert-butyl-4-methoxy) iridium(I) complex (Scheme 1.24).63 The catalytic resting state was accessed by combination of [Ir2(η2-COE)4Cl2], para-CF3-benzamide, and DTBM Segphos, providing a bis(κ1-N) amidate/amide Ir(III) complex 1.64 – the product of amide N-H bond oxidative addition and amide coordination. Differentiation of the two amide donors (X- vs. L-type) could be made on the basis of a single crystal X-ray diffraction experiment, providing Ir-N contacts of 2.076 Å and 2.117 Å, respectively. The isolated complex was also found to be competent for catalysis providing the corresponding amidation product on exposure to 10 equiv. of norbornene (NBD). For the para-F-benzamide derivative, evidence for reversible amide dissociation (ΔS‡ = 12.4 e.u.) was obtained using 19F NMR spectroscopy. The proposed catalytic cycle invokes amide N-H oxidative bond activation, reversible dissociation of the amide substrate providing a κ1-N or hemilabile κ2-N,O intermediate, followed by reorganization and alkene coordination to give 1.68. Finally, alkene insertion gives 1.69 followed by competitive i) β-hydride elimination to give 1.70 or ii) protonolysis to provide the corresponding N-functionalized product 1.71. 		Ir			Ir			ClN		ClO	N		Cl		O	 27           Scheme 1.24 Catalytic olefin hydroamidation using Ir  The photophysical properties of amidate-ligated Ir(III) complexes have also been examined. In 2011, Zhang, Ding and co-workers showed that iridium(III) bis(ppy) (ppy = 2-phenylpyridine) κ2-N,O amidate complexes [Ir(ppy)2(κ2-N,O-RNC(O)R’)] (1.72-1.75) can be accessed through salt metathesis using the µ-Cl dimer, [(ppy)2Ir(µ-Cl)]2, CH3ONa, and the amide pro-ligand (Scheme 1.25).64,65 For [Ir(ppy)2(κ2-N,O-PhNC(O)CH3)] (1.72) the Ir(1)-N(1) = 2.016(1) Å  and Ir(1)-O(1) = 2.266(7) Å  contacts were found to be long, while the N(1)-Ir(1)-O(1) bite angle [59.8(5)o] was found to be acute. The polymeric iridium(III) derivative 1.76 could also be formed via radical-initiated polymerization of an amide isopropenyl substituent of 1.75 using AIBN (AIBN = azobisisobutyronitrile). The electrochemical properties of this series were studied providing two peaks: one attributable to a Ir(III)/Ir(V) couple and one for reduction of the amide coligand. Intriguingly, density IrOOOOPPClHArArArArNH2OF3CNHOCF3[Ir(η2-COE)2(Cl)]2PP*(S)-DTBM-SegphosNH2OF3C+ + 2PhMeIrHClPPNHC(O)ArIrHClPPHNOArIrHClPP NHC(O)ArIrHClPP NHC(O)ArRIrHClPP NHC(O)ArRRH2NC(O)ArNHC(O)ArRNHC(O)ArR1.671.681.69κ1-N1.66κ2-N,OCoordinationNucleophilic AttackProtonolysis1.65κ1-N- COE1.641.701.71 28 functional theory studies showed that the HOMOs for this series are ca. 48% and 38% iridium d-orbital and ppy-based, while an additional ca. 18% contribution is ascribed to amidate π-bonding. This differs from Ir(ppy)2(acac) where π-bonding contributions from the 1,5-O,O chelating ligand are negligible.        Scheme 1.25 κ2-N,O Ir amidate complexes and olefin polymerization  More recently, in 2016, the Albrecht group reported that a pyridylideneamide Cp*Ir(III) complex 1.77 could be accessed through cyclometallation giving a κ2-N,C amidate geometry (Scheme 1.26).66 Ligand resonance character (neutral (1.78) or mesoioinic (1.79)) was investigated using X-ray crystallography and solution-state NMR spectroscopy where the chemical shift difference between the pyridylidene α and β protons was used as a key diagnostic handle. These complexes were employed for catalytic water oxidation, where the ligand is speculated to facilitate proton and/or electron transfer processes.  IrNNRNOR NHO+ CH2Cl2, r.t.CH3ONaIrNNClCl IrNN0.5R = CH3, Ar = Ph (1.72)R = ipropropenyl, Ar = Ph (1.75)R = Ph, Ar = Ph (1.73)R = Ph, Ar = Naphth (1.74)IrNNNO nAIBN 1.75 only1.76 29 Scheme 1.26 Pyridylideneamidate Cp*Ir(III) complexes  Phosphoramidate ligands are a unique class of 1,3-N,O chelating ligand having a central phosphorous atom. Given that phosphate diesters are key functional components of DNA, these structural units and relatives thereof have found applicability as ligands for transition metals. In 1990, Sargeson et al. studied Co(III) and Ir(III) phosphoramidate complexes by investigating the hydrolysis of [(NH3)5M(BNNP)]2+ (M = Co(III) or Ir(III), BNNP = bis(4-nitrophenyl)phosphate)) in basic media (Scheme 1.27).67 For Ir(III), the major product was the κ1-N bonded phosphoramidate Ir(III) complex 1.85, characterized using 31P NMR spectroscopy. In this work, phosphoramidate coordination to Ir(III) was found to decrease the pKa of the amide NH group in 1.83 allowing for facile deprotonation by OH-. Scheme 1.27 Phosphate hydrolysis at Ir(III) IrClNNOIrNNODMSOPF6IrNNODMSOPF6- KClHHαβK[PF6]1.77 1.78 1.79+ DMSOHO- IrNH2OP-O OEtOC6H4NO2(NH3)4IrH2NPOOEt(NH3)4O-HO-OH- H++ H+Ir NH3OPO OEtOC6H4NO2(NH3)4 Ir NH2-OPO OEtOC6H4NO2(NH3)4IrNH2OPOOEt(NH3)4IrHNPOOEt(NH3)4O-OH1.80 1.81 1.821.831.841.852+ +2++ -OC6H4NO2++ 30 1.5 1,3-N,O-Chelated Complexes of Group 10  Amide ligands are key structural components of [NiFe]-hydrogenases and have thus been studied for coordination to Ni. Cross coupling using a group 10 metal for the assembly of amides has also dominated the chemistry of this group.  1.5.1 Nickel  In 2010, Maroney and co-workers showed that an amidate ligand was found to be a key structural component of nickel superoxide dismutase (NiSOD) – a radical regulator used to catalyze the disproportionation of superoxide radical anion to O2 and H2O2 (Scheme 1.28).68 Computational and experimental work jointly showed that altering the Cys2 (Cys = cysteine) amidate N-donor ligand in WT-NiSOD (1.86; WT = wild type) to a secondary amine group H1*-NiSOD (1.87) has far-reaching implications for function. Previously, DFT calculations predicted that the amidate ligand helps to stabilize the oxidized square-based pyramidal Ni(III) intermediate. For the N-amidate donor ligand, however, the energy of a π-symmetry Ni 3d orbital was calculated to be raised due to a filled π-π interaction manifesting an increase in oxidation potential from ~ 0.29 V vs NHE (WT-NiSOD) to 0.35 V (H1*-NiSOD), inhibiting formation of the oxidized Ni(III) complex and thus turnover to generate H2O2.      Scheme 1.28 Comparison of amidate and amide donors in NiSOD NiS NOH2NHNNSCys6Cys2NiS NHH2NHNNSCys6Cys2HHH1*-NiSODWT-NiSODNi NRRONi NRRH1.86 1.87 31 In a related class of metalloprotein, [NiFe]-hydrogenase, amide ligation has also proven important for the modification of Ni(II)/Ni(III) redox potentials (Scheme 1.29). In an effort to further elucidate factors governing stability of the Ni(III) oxidation state, Holm et al. have studied synthetic mimics using square planar bis(κ1-N) N2X2 (X = O or S) Ni(II) amidate complexes (1.88-1.90).69,70      Scheme 1.29 Square-planar Ni(II) complexes used as bioinorganic mimics  Additionally, high-valent Ni complexes have been implicated in biological oxidation reactions. In 2015, Company et al. showed that a macrocyclic bis(amidate)-ligated Ni(II) complex 1.91 could be employed for oxygen-atom transfer (OAT) using m-chloroperoxybenzoic acid as the oxidant (Scheme 1.30).71 The authors propose that coordination of the acid to give 1.92, followed by homolytic O-O bond cleavage provides a Ni(III) oxyl radical 1.93, which promotes substrate-oxygen (SO) bond formation (substrate = styrene derivative, thioanisole etc.). Although existence of the oxyl intermediate remains contentious, the assignment is supported by experimental extended X-ray absorption fine structure (EXAFS) and resonance Raman spectroscopic measurements. N NO OX XNiX = O or SN NO OS SNiN NO OS SNiRRRRR = H or Me1.88 1.89 1.90 32      Scheme 1.30 Oxygen-atom transfer by a Ni(II) macrocycle  In 2016, Szostak and co-workers showed that amides can be used as electrophilic cross-coupling partners in Ni(0)-catalyzed Suzuki-Miyaura cross-coupling (Scheme 1.31).72 In the context of C(sp2)-C(sp2) bond forming reactions, the use of such robust C-N bonds [~ 18 kcal·mol-1] along with boronic acids for the formation of biaryl scaffolds is a breakthrough. Notably, this Ni(0)-mediated reaction is regioselective for C-N bond oxidative addition and is presumed to occur through nitrogen coordination, disrupting amide n(N) → π*(CO) conjugation through a twisting effect. Stoichiometric experiments using phenyl N-glutarimide (a sterically-distorted amide), cis-NiCl2(PCy3)2, and Na2CO3 evidenced several Ni-containing intermediates including the CO deinsertion product Ni(Cl)(Ph)(κ1-N-C5H6NO2) (1.97; m/z = 281) and the oxidative addition product, Ni(CO3)(COPh)(κ1-N-C5H6NO2)(PCy3) (1.98; m/z = 615).  NN NO ONNiOOClOH+ NN NO ONNiO OArOHNN NO ONNiOHOArOSOSm-CPBA1.921.911.93 S =XX = SMe, CHCH2 33           Scheme 1.31 Ni-catalyzed Suzuki-Miyaura cross-coupling using amides  Of the Ni amidate complexes discussed thus far, only the κ1-N binding mode has been accessed. In 2010, MacBeth et al. showed that modular ligand design is key in differentiating amongst κ1-N or κ1-O binding modes (Scheme 1.32).73 Using 3.1 equiv. KH, NiBr2, and H3LR (H3LR = N(o-PhNHC(O)R)3) (R = iPr, tBu, Ph), the Ni(II) complexes 1.99, 1.100, and 1.101 were accessed. Unlike the related [Fe(II)]2 complex 1.6 (Scheme 1.4) discussed above, for the iPr derivative 1.99, a mononuclear pseudo trigonal-bipyramidal Ni(II) complex results chelated in a tris(κ1-N) fashion. Moreover, switching the iPr substituent to tBu results in decoordination of a third ligand arm giving a bis(κ1-N)/mono(κ1-N) bonded amidate, providing a rare seven-membered nickela(II)cycle (Figure 1.4). In terms of bonding metrics, N(1)-C(1) and O(1)-C(1) bond lengths 1.290(4) and 1.302(3) Å are consistent with delocalization across the κ1-O amidate arm. Finally, use of a Ph-substituted tris(amidate) gives a coordinatively-accessible 16-electron Ni(II) complex, decarbonylationNiNRRAr1OXLNiAr2Ar1OLNiAr2Ar1LAr1 Ar2OAr1 N RRNi(0)Ni(II)COeliminationreductiveC-N oxidativeadditiontransmetallation(HO)2B-NR2, - L(HO)2B-Ar2 NiNPhOOOOOO+  PCy3m/z = 615NiNPhOOm/z = 281ClOAr1 N RRtwistONOOB(OH)2+Ni(PCy3)2Cl2 (5 mol%)4.5 equiv. Na2CO31,4-dioxane, 150 oC, 12 hR1 R2R1 R21.941.951.961.971.98 34 which binds acetonitrile, giving the Lewis base adduct 1.101. This work elegantly shows that the amidate acyl substituent has a marked effect on coordination mode. Further reactivity studies of these complexes showed that the iPr complex reacts cleanly with [Et4N]CN giving a five-coordinate CN- adduct.       Scheme 1.32 Examining the effect of ligand acyl substituent      Figure 1.4 Solid-state molecular structure of 1.99 and 1.100 In 2016, Love, Schafer, and co-workers showed that amidate complexes of Ni(II) and Ni(I) could be accessed (Scheme 1.33).74 Reduction of the Ni(II) κ2-N,O amidate complex 1.102 with Na/Hg provided the Ni(I) complex 1.103, having two C-H agostic 		Ni					Ni	N		O						O			N- 2 KOAc, 0.5 KBrH3LRNiNNNNOiPriPr OiPrO3.1 equiv. KHNiBr20.5 equiv. [PPh4]BrPPh4DMF, CH3CNNiN NNNOtButBuOtBuOPPh4NiNNNNOOONCPPh4H3LiPr H3LtBuH3LPh1.99 1.1001.101 35 interactions with the tert-butyl-substituted amidate. Single crystal X-ray diffraction [Figure 1.5: Ni···H(C) contacts of 2.024(15) and 2.159(15) Å] and density functional theory (DFT) were used to corroborate such interactions. In particular, computational viz. natural bond orbital (NBO) and atoms in molecules (AIM) analyses revealed donation from the β-spin C-H σ-bonding orbital to an sd hybrid on the Ni(I) centre [E(2) = 5.7 kcal·mol-1 (H1) and 5.1 kcal·mol-1 (H2)]. These interactions are non-negligible, providing support for the preparation of the first Ni(I) C-H agostic complex.     Scheme 1.33 Accessing a bis(C-H) agostic Ni(I) complex      Figure 1.5 Solid-state molecular structure of 1.103 The 2-pyridonate ligand scaffold has been shown to provide multinuclear Ni complexes having µ2-, µ3-O or κ1-N binding modes, however in 1998, López et al. reported the first mononuclear nickel(II) complex 1.104 bearing a 2-pyridonate ligand (Scheme 1.34).75 This complex was provided through treatment of 0.5 equiv. [Ni(N3-Ni	N			O	H	Na/HgNOiPrtBuNi ClN NDipp DippMeiPriPriPriPrNiNOMeHHiPrNNHEt2O1.102 1.103 36 mc)(µ-OH)]2(ClO4)2 (N3-mc = 2,4,4-trimethyl-1,5,9-triaazacylcododec-1-ene) with 2-pyridone.      Scheme 1.34 Accessing the first mononuclear Ni κ2-N,O pyridonate complex In 2015, Jones et al. reported the use of related κ2-N,O quinolinate (Q) complexes supported by Tp* (Tp* = tris(3,5-dimethylpyrazolylborate)) ligands for the acceptorless dehydrogenation of alcohols (Scheme 1.35).76 Related systems of Cp*Ir(III) have been discussed previously (Scheme 1.23). Complexes of the type [Tp′Ni(κ2-N,O-Q)] (1.105) could be derived from 0.5 equiv. [Tp’Ni(µ2-OH)]2 along with an appropriately substituted quinolinone proligand. These complexes were employed for alcohol dehydrogenation, providing the corresponding ketone. Intriguingly, related [Tp′Ni(µ2-OH)]2 and Tp′Ni(OAc) complexes showed no reactivity, highlighting the importance of judicious ligand choice. Likewise, use of an 8-hydroxyquinoline ligated-complex provided no desirable conversion, indicating the importance of the 2-hydroxy group. Reversible hydrogenation of other C=O bonds was also observed allowing for the quantitative hydrogenation of PhCHO and PhC(=O)Me using ca. 12 atm of H2 at 120 oC. Moreover, the authors also showed that use of a related 2-pyridonate complex 1.106 culminated in the formation of a bis(ligated) κ2-N,O/κ1-O pyridonate Ni complex that was inactive for catalysis. NiNNNHNO+O2HNiNNNNO-H2O1.1042+ +0.5 37       Scheme 1.35 Alcohol dehydrogenation by Ni(II) pyridonates 1.5.2 Palladium  The Hartwig and Buchwald groups have independently studied the interplay amongst amidate bonding mode and catalytic competency in Pd-mediated amidation reactions. In 2006, Hartwig et al. showed that combination of LnPd(Ph)(X) (Ln = 1,1′-bis(diphenylphosphino)ferrocene; dppf) with 1 equiv. of a potassium amidate salt provides the corresponding κ1-N bonded complex 1.107 (Scheme 1.36).77 For comparative purposes, (FcPtBu2)Pd(Ph)(I) (Fc = ferrocene) having a hindered monodentate phosphine ligand, was used to prepare the related κ2-N,O amidate derivative 1.108 (Figure 1.6). Heating of the κ1-N derivative 1.107 at 100 oC gave N,N-diphenylacetamide (> 90% conversion, 29 h). By comparison, the κ2-N,O amidate complex 1.108 decomposed at 100 oC without release of the corresponding substituted amide product. This study stresses the effect of binding mode on the rate of reductive elimination illustrating that Pd-O bond cleavage has a high barrier to activation.   N NNONiBN NN NHO N N NiBN NN NHCF3NON N NiBN NN NHCF3HNOCF32HNOCF3+Active for alcohol dehydrogenationInactive for alcohol dehydrogenationH1.1051.1060.5equiv. 38 Scheme 1.36 Examining reductive elimination trends in Pd amidate complexes     Figure 1.6 Solid-state molecular structure of 1.108  In 2007, Buchwald and co-workers showed that 4-choroanisole and benzamide could be coupled using Pd2dba3 (dba = dibenzylideneacetone) and a bulky biaryl monophosphine coligand 1.109-1.111 (Scheme 1.37). The ligand employed was found to have a drastic effect on the yield of these reactions, with ligands having methyl groups on the upper aryl ring giving the desired product in 94% yield.78 In-depth computational studies showed that the ortho-methyl group present in 1.111 inhibits rotation of the Pd centre, prohibiting the κ2-N,O amidate binding mode. 		Fe	PPd			O	N	PdONPhPhFePtBu2ΔNOPhPh- Pd0κ2-N,O κ1-NPdNOFePPh2PPh2PhΔ1.1071.108 39         Scheme 1.37 Using ligand design to avoid κ2-N,O amidate coordination  In 2008, Jung and co-workers reported that chiral amidate ligands could be employed as strong chelators for Pd(II).79 Coordination was achieved through treatment of the chiral NHC ligand with Ag2O and [Pd(MeCN)2Cl2] providing the tetracoordinate κ1-N amidate complex 1.112 (Scheme 1.38). Dehydrohalogenation of this complex provided the air and moisture stable [Pd(II)]2 complex 1.113 as a single isomer. Solid-state X-ray analysis revealed short Pd-N bond distances of 1.978(3) Å for 1.112 and 1.980(2) Å for 1.113. Notably, for 1.112, the sum of angles about N was 355.80o, differentiating it from a L-type HN→Pd dative interaction. In terms of reactivity, treatment of 1.113 with PhB(OH)2 gave the phenylpalladated complex 1.114 that could be employed for catalytic oxidative boron Heck couplings using boronic acids and acyclic olefins.    NOHONH2OClO+ Pd2dba3, ligandbase, solventiPriPriPrPR2XXXXX = H, R = iPr (1.109)X = H, R = tBu(1.110)X = CH3, R = tBu (1.111)L = 1.109 1%L = 1.110 9%L = 1.111 94%iPriPriPrP PdtBu tBuNHOiPriPriPrPPdtButBuHNOκ2-N,Oκ1-Nc) Catalytic amidationa) Ligand scope b) DFT-calculated geometriesCatalytically inactiveCatalytically active= CH3 40        Scheme 1.38 Design of a novel chiral amidate ligand  Similar to other d8 square planar complexes, the coordination chemistry of amidate-ligated Pd(II) complexes is dominated by the bridging (µ2-N,O) mode (Scheme 1.39). In 2007, Walmsley et al. showed that [Pd(bpy)(µ-OH)]22+ (bpy = 2,2′-bipyridine) undergoes CH3CN hydration providing a µ-bridged Pd complex [Pd(bpy)(µ2-N,O-CH3C(O)NH)]2(NO3)2H2O (1.115) having intramolecular Pd···Pd and π···π interactions.80 The IR spectrum of this head-to-head (HH) isomer exhibited a C-O stretching frequency at 1583 cm-1 (cf. 1667 cm-1 for CH3C(O)NH2). X-ray crystallography provided evidence for a Pd-Pd interaction [2.8480(8) Å], falling within the generally accepted value (< 3.00 Å). Devoid of stabilizing π···π interactions, the ethylenediamine (en) head-to-tail (HT) amidate-bridged complex [Pd(en)(µ2-N,O-CH3C(O)NH)]2(OTf)2 (1.116) exhibited a Pd-Pd distance of 3.0604(5) Å. This example constitutes one of the few examples that highlights a Pd···Pd interaction between two amidate-ligated Pd(II) centers. NNHNHOOiPrI1.    Ag2O, CH2Cl2     r.t. 16 h2. [Pd(MeCN)2(Cl)2]CH3CNNNNOOiPrPdClK2CO3H2O/CH2Cl2NNN OOiPrPdNNNOOiPrPdDMF-d6, r.t., 16 hPhB(OH)2NNNOOiPrPdB(OH)2κ1-Nbis(κ1-N)H1.1121.1131.114 41     Scheme 1.39 µ-N,O Pd(II) complexes having a Pd-Pd interaction 1.5.3 Platinum In 1992, Schaad and Landis showed that Pt(0) and Pt(II) complexes could be treated with fluorinated amides, providing the corresponding κ1-N amidate complex (Scheme 1.40).81 Photolysis of the oxalate complex, [Pt(C2O4)(PEt3)2] using UV light in the presence of H2NR (R = SO2CF3, COCF3) induces CO2 extrusion along with concomitant release of trans-[Pt(PEt3)2(H)(κ1-N-HNR)] (R = SO2CF3 (1.117), COCF3 (1.118)) via the transient Pt(0) species, Pt0(PEt3)2. When a 15N-labelled amide is employed, the 1H NMR spectrum exhibits a doublet of triplets for the hydride ligand having 195Pt satellites, consistent with a trans-P orientation. An alternative route to such complexes via protonolysis of a Pt-CH3 bond was also reported, providing CH4. The authors additionally showed that cis-[Pt(PEt3)2(CH3)2] reacted with H2NR (R = SO2CF3, COCF3) to give the trans-[Pt(PEt3)2(CH3)(κ1-N-HNR)] complexes. By analogy, (η4-COD)Pt(Me)2 produced the corresponding COD complexes, (η4-COD)Pt(Me)(κ1-N-HNR) along with CH4.     ONNOHPdPdHNNNNµ2-N,OHHONONPdPdHNNNNµ2-N,OHTH2H2H2H2H2+ 2+dPd-Pd = 2.8480(8) dPd-Pd = 3.0604(5)acetone, 5 dMeCN[Pd(µ-OH)(bpy)]22+1.115 1.116 42    Scheme 1.40 Amide N-H activation by Pt(0) Significant work has focused on µ2-N,O bridged Pt amidate complexes, especially in the context of stabilizing the Pt(III) oxidation state giving “platinum blues”. The first platinum blue, [Pt2(NH3)4(hp)2]52+ was structurally characterized in 1979 from cis-Pt(NH3)2(Cl)2 and hp.82 These compounds are so named for their intense blue/purple colour, which results from a transition involving a Pt-Pt σ orbital to a σ* orbital.  In 1996, Matsumoto reported that the µ-bridged [Pt(II)]4 complex [Pt4(NH3)8(µ2-N,O-tBuC(O)NH)4(NO3)](NO3)4 (1.119) reacts with excess HNO3 in acetone giving the axially-coordinated σ-alkyl complex [Pt2(NH3)4(µ2-N,O-tBuC(O)NH)2(CH2C(O)CH3)(NO3)](NO3)2H2O as a mixture of HH (1.121) and HT (1.122) isomers suggested to result from nucleophilic alkylation of acetone (Scheme 1.41).83 For related olefin oxidation reactions mediated by amidate-bridged [Pt(III)]2  complexes, olefin coordination is speculated to occur at the axial site. Crystallographic analysis of the HH isomer provides a rare example of an axially coordinated C(σ)-Pt bond trans to a Pt(III)-Pt(III) bond [dPt-Pt = 2.6892(6) Å]. NMR spectroscopic analysis is consistent with the presence of two isomers, providing four signals in the 195Pt NMR spectrum. Moreover, use of 15N-labelled pivalamide allowed for unambiguous assignment of the Pt centres. In terms of reactivity, treatment of 1.121/1.122 with 10 mM NaOD gives hydroxyacetone, while PtOOPEt3PEt3OO - 2 CO2PtPEt3Et3P NH RFOH PtPEt3Et3P CH3HNH2RFONH2RFO,  hvR = SO2CF3 1.117R = COCF3 1.118 43 treatment with 50 equiv. NaBr provides bromoacetone along with  [Pt2(NH3)4(µ2-N,O-tBuC(O)NH)2]2+.          Scheme 1.41 Nucleophilic alkylation of acetone   The first mononuclear Pt complexes of 2-pyridones (hp) were isolated in 1982 by Hollis and Lippard: mer-[Pt(NH3)2(hp)(Cl)3] (1.123), cis-[Pt(NH3)2(hp)2]2+ (1.124), and cis-[Pt(NH3)2(hp)(Cl)]2+ (1.125) (Scheme 1.42).84 Comparison of the bond metrics between neutral and monoanionic N,O chelate reveals a decrease in C-O bond length of 0.074 Å and increase in C-N bond length of 0.062 Å for the Pt(IV) complex. The <N-C-O bond angle is also 6.2o larger for the Pt(IV) complex.    Scheme 1.42 Survey of Pt pyridonate complexes  PtClNH3ClNH3NOClPtNH3NHOH3NNOH2+PtNH3NH3NHOCl +1.123 1.124 1.125ONNOHPtPtH3NH3NH3NH3N HONNOHPtPtNH3NH3NH3NH3HONO2 4+ONNOHPtPtNH3NH3NH3NH3HONO2NO2OONNOHPtPtNH3NH3NH3NH3HONO2OHHHNONOHPtPtNH3NH3NH3NH3ONO2OHH+HH HT2+2+ 2+µ-N,Oµ-N,Oµ-N,Oµ-N,OOODOBrNaODNaBrOH1.1191.1201.1211.122 44 1.6 1,3-N,O-Chelated Complexes of Group 11 Similar to the Ni triad, Cu-mediated cross coupling for access to N-functionalized amides has occupied a central focus in this group. The chemistry of Au is limited to κ1-N examples, some of which have found application in biological testing.    1.6.1 Copper  A large body of work has been devoted to Cu complexes of pyridine carboxamide ligands – Rajput  and Mukherjee have reviewed these recently.85 For 2-hp ligands, examples of di-, tetra-, hexa-, and heptanuclear Cun complexes have been accessed through either salt elimination or protonolysis.  In 2008, Patten et al. showed that N-substituted-2-(bis-(2-pyridylmethyl))aminoethanamide ligands could be used for coordination to Cu(II) giving κ1-O coordination complexes (R = tBu (1.126), Dipp (1.127)) (Scheme 1.43).86 Deprotonation of these complexes using NaH in THF delivered the neutral κ1-N Cu(II) complexes (R = tBu (1.128), Dipp (1.129)). Analysis by single-crystal X-ray diffraction revealed similar C-N and C-O bond lengths for both complexes.     Scheme 1.43 κ1-O to κ1-N geometry change via addition of NaH  In 2012, Ding and co-workers isolated copper(I) amidates as reactive intermediates in the copper(I)-catalyzed Goldberg reaction (Scheme 1.44).87 Using a NNORHNN CuBrNNNN CuBrTHFNaH- NaBrROR = tBu (1.126)R = Dipp (1.127)+R = tBu (1.128)R = Dipp (1.129) 45 bis(diphenylphosphinoferrocene), dppf copper chloride precursor [(dppf)CuCl]2, κ1-N amidate intermediates were accessed by salt metathesis using NaOCH3 (Figure 1.7). Infrared spectroscopy (IR) was used to assess coordination of the amide precursor giving blue-shifted signals ascribable to the non-coordinated carbonyl group at v(C=O) = 1633 and 1636 cm-1 for 1.130 and 1.131. Single-crystal X-ray diffraction was also used to unequivocally provide the structure of these species. For the CH3-substituted derivative 1.130, a Cu(1)-N(1) bond length of 1.979(3) Å and N(1)-C(41) bond length of 1.319(5) Å are characteristic of the κ1-N amidate chelating mode.      Scheme 1.44 Cu-mediated Goldberg reaction of amides 					   Figure 1.7 Solid-state molecular structure of 1.131 				Fe			Cu						F						O	N	Cl			P	FePPh2PPh2Cu FePh2PPh2PCuClCl F3C NHO R+FePPh2PPh2CuF3CNORFePPh2PPh2Cu IF3C NO RR'R' X+κ1-NR = CH3 (1.130) or Cl (1.131)R' = CH3, X = IR' = H, X = I, Br, ClNaOCH3 46 More challenging copper-catalyzed C(sp3)-N-alkylations have also been reported (Scheme 1.45). In 2014, Peters, Fu and colleagues developed a photo-induced copper-catalyzed monoalkylation of primary amides using C(sp3)-X; X = I, Br electrophiles using 10 mol% CuI and 2 equiv. LiOtBu (Scheme 1.45).88 During catalysis, a copper(I) amidate [LnCu(Nu)] is postulated to serve as a key intermediate. The authors showed that treatment of mesitylcopper(I) with 2-oxazolidone proceeds via protonolysis, liberating 2,4,6-trimethylbenzene and the Cu(I)-oxazolidinyl tetramer (1.132) in 83% isolated yield (Figure 1.8). Importantly, the µ-N,O-chelated Cu(I) salt could be used in-lieu of CuI in the photoinduced methodology       	Scheme 1.45 C(sp3)-N alkylation using Cu(I)       Figure 1.8 Solid-state molecular structure of 1.132 Cu			N	O	ONOCu O NHO+CuCuCuCuONOONOON ODME, r.t.µ2-N,O0.25 equiv.-Me3C6H3ONOCuCuCuCuONOONOON O(1)X+X = Br, IO NO1.1328.0 equiv.CH3CN, DMFr.t.no light: <2%hv (254 nm)X = I (80%)X = Br (73%)(2)1.132 47 In 2011, Fujita, Yamaguchi, et al. showed that biazoles could be conveniently accessed through oxidative homocoupling of azoles (Scheme 1.46).89,90 In this report, the authors showed that substituted imidazoles, oxazoles, and thiazoles could be coupled using CuCl (2 mol%) along with the use of a sodiated 2-pyridonate ligand (4 mol%). Examining the effect of ligand showed that 3- or 4-substituted pyridonates were ineffective for the desired transformation. Although the mechanism has not been studied in detail, the authors speculate that a Cu(I) κ1-N pyridonate complex 1.133 is the active species, requiring hydroxy substitution at the 2-position due to the requirement of ligand-assisted C-H bond activation (MLC). In 2013, the same groups expanded the scope of this catalyst to include oxidative amidation using aromatic and cinnamic aldehydes and 2o amines. In this system, reaction of CuI with piperidine (pip) provided [Cu4(µ3-I)4(pip)4], which in the presence of 5-methylpyridonate, yielded the desired coupling product in the presence of an aldehyde.    Scheme 1.46 Using a Cu pyridonate complex for oxidative coupling   In 2014, Szymczak et al. reported a novel tris(6-hydroxypyrid-2-ylmethyl)amine (H3thpa) ligand for coordination to Cu(I) and Cu(II) (Scheme 1.47).91 The C3v-symmetric Cu(II) scaffold 1.134 could be cleanly accessed from treatment of Cu(SO4)·5H2O, NaBF4, and CsF with H3thpa giving a trigonal bipyramidal complex having secondary F--H NXHR1R2 NXR1R2NXR1R2p-xylene, reflux, 20 hCuCl (1 mol%)Na[5-Me-hp] (2 mol%) (1)N OH3C[Cu]OR1 H R1HNR2+OR1 NR2R1toluene, reflux, 20 hMS, 4 ÅCuI (2-20 mol%)Na[5-Me-hp] (4-20 mol%)(2)proposedcatalyst1.133 48 hydrogen bonding interactions between the three OH groups and F (Cu-F ~ 2.6 Å).92 Reduction of 1.134 using K[Fe(CO)2Cp] (Cp = C5H5-) provides the Cu(II) derivative 1.135, with an outer-sphere fluoride stabilized by hydrogen bonding interactions. For the related Cu(II)-Cl complex, chemical reduction using [Cp2Fe][PF6] results in partial dissociation of the chloride ligand also resulting in capture by three nearby hydrogen bonds.91 These examples highlights how a tris(κ1-N) pyridonate claw can stabilize a metal-bound substrate through hydrogen bonding interactions.    Scheme 1.47 A tris(κ1-N) pyridonate complex of Cu 1.6.2 Silver  Silver salts of 1,3-N,O chelated ligands can be accessed through salt elimination using Ag[NO3] and the sodiated ligand salt, though these species have not been fully characterized. Amidate-ligated Ag complexes have also been proposed as intermediates in Ag-mediated hydroamidation,93 though no isolated examples of this class of compound have been reported.   1.6.3 Gold  Few Au complexes having N,O-chelated ligands have been prepared. In 1985, Bovio and co-workers showed that Au(I) complexes having κ1-N pyridonate ligands could be accessed by treatment of (R3P)AuCl (R = aryl or alkyl) with substituted 2-pyridones and NaOH.94 X-ray analysis of (Ph3P)Au(6-Me-hp) (6-Me-hp = 6-methyl-2-pyridonate) NCuNNNOOOFK[Fe(CO)2Cp]HHH NCuNNNOOOFHHH1.1351.134BF4DME- KBF4- 0.5 [Fe(CO)2Cp]2 49 revealed a Au-N bond distance of 2.077(9) Å and P-Au-N bond angle of 173.4(3)o consistent with a quasi-linear complex. The pyridonate C-O bond length (1.23(2) Å) also suggests that the pyridonate ligand is in the keto-form.  Owing to the ubiquity of amides in biology, amidate-ligated d8 transition metal complexes have attracted great attention as biologically active therapeutics toward a range of bacteria and fungi. Henderson et al. reported treatment of (2-bp)AuCl2 (bp = 2-benzylpyridine) (1.136) with Ag2O and 1,2-diacetamidobenzene in refluxing CH2Cl2 gave cycloaurated complexes having bis(κ1-N) phenylenediamidate ligands (1.138) (Scheme 1.48).95 The Au(III) coordination environment is quasi square planar having Au(1)-N(2) and Au(1)-N(3) bond lengths of 2.089(3) Å and 2.022(3) Å and a N(2)-Au(1)-N(3) bite angle of 79.61(11)o. When the reaction is carried out for a shorter reaction time (2h), the κ1-N aura(III)cyclic 1.137 intermediate may be accessed. In terms of biological activity, the bis(κ1-N) analogue 1.138 showed anti-tumour activity (IC50 = 2434 ng/mL) comparable to cisplatin (IC50 = 2583 ng/mL).       Scheme 1.48 Cyclo(aurated) amidate complexes for biological applications AuNClClHNNHOO+ Ag2OAuNNNOOAuNN HNOOClCH2Cl2bis(κ1-N)κ1-N1.136 1.1371.138 50 1.7 1,3-N,O-Chelated Complexes of Group 12 1.7.1 Zinc The reaction of dialkyl zinc reagents with PhNCO to give anilides was first described in 1936. Thirty years later, Ridley and Coates identified multinuclear Zn amidate complexes as key intermediates in this process.96 More recently, Schulz et al. showed that multinuclear µ2-N,O complexes of Zn can be accessed by treatment of ZnMe2 with RNCO (R = iPr, tBu) providing multinuclear Zn amidate complexes [MeZnOC(Me)NR]n (R = iPr (1.139), tBu (1.140)) with µ-O atoms bridging two adjacent Zn centres (Scheme 1.49, Figure 1.9).97 Intriguingly, the degree of oligiomerization can be controlled by isocyanate R group with insertion of iPrNCO giving a tetrameric Zn structure 1.139 and insertion of the more sterically encumbered tBuNCO giving a trimeric Zn species. IR spectroscopy confirmed consumption of the parent isocyanate with the NCO stretching absorption decreasing from 2245 cm-1 (tBuNCO) and 2251 cm-1  (iPrNCO) to 1577 cm-1 and 1504 cm-1 for 1.139 and 1.140.      Scheme 1.49 Zn-C insertion of RNCO provides µ-N,O amidate complexes 				OZn ONZn ZnMe2iPrNCOtBuNCOZnO ZnONNNOZn OZnOZnNNNµ-N,O µ-N,O1.139 1.140 51     Figure 1.9 Solid-state molecular structure of 1.139 and 1.140 1.7.2 Cadmium and Mercury  As early as 1970, Gould and Sutton reported that MCl2 (M = Hg or Cd) reacted with acetamide, 2-hydroxyisobutyramide, N-phenylglycolamide, and phenyl-lactamide to give mixtures of HgLCl, HgL2 and HgLOH (L = amidate), though the coordination mode of these species was not determined.98,99 Current research focuses on removing these toxic metals through chelation. In 2011, Denat reported a cyclam-based ligand 1.141 bearing an N-sulfonylacetamide pendant arm. Treatment of Cd(NO3)2·4H2O with 1.141 afforded 1.142 having κ1-O amide coordination (Scheme 1.50).100    Scheme 1.50 Chelation of Cd using a novel amidate ligand 1.8 Summary and Outlook The ambident nature of these tuneable ligands allows for stabilization of metals spanning the periodic table, providing an array of reactive and novel bonding modes. In Zn	N				O	 			Zn	N				O	NH NN NHN SOOOPhPh+ Cd(NO3)24H2O MeOH NNNNNSOOO PhPhCdHNO31.141 1.142 52 terms of late transition metals, myriad complexes having the κ1-N binding mode exist, while the κ1-O binding mode seems to be limited to species having bulky ancillary ligands that disfavour the κ1-N binding mode due to steric arguments. Such binding preferences are in line with HSAB – a factor that seems to dominate when predicting binding mode. Importantly, this chapter has showcased that the N,O-chelating bonding mode can easily be diagnosed using NMR spectroscopy to probe the central atom of the 1,3-chelate (e.g. by 13C or 31P NMR spectroscopy), while IR spectroscopy and single crystal X-ray diffraction can also be used to great benefit for the deduction of coordination mode. In the context of judicious N,O-chelating ligand choice, amidates and pyridonates offer tighter bite angles when compared to related sulfonamidates and phosphoramidates - a consequence of a sp3-hybridized P or S atom in the latter when compared with a sp2-hybridized C atom. Although, information relating bite angle to the tendency of such systems to undergo ring opening remain sparse, one might posit that a smaller bite angle allows for facile ring-opening and thus, increased ligand hemilability in solution.  Examples of cooperative small molecule activation as well as element-hydrogen bond cleavage reactions also undoubtedly show great promise in designing N,O-chelated systems for metal-ligand cooperativity. By contrast to symmetrical ligand scaffolds such as 1,3-N,N-donating amidinates and guanidinates, which are also better σ/π-donors, N,O-chelates offer complimentary reactivity via hemilability (due to the weakly donating X=O (X = C, S, or P) group), allowing this appendage to serve as a functional group for the stabilization of element-hydride bonds, for example.  Such synthetic studies will undoubtedly help to inform the role of such ligands in nature during proton shuttling or H2 cleavage, for instance.  In this regard, amidate ligands and related organic N,O-chelating scaffolds remain viable  53 candidates for C-H bond activation through concerted-metallation deprotonation (CMD), whereby tailoring of the NR and CR substituents should allow for facile modification of ligand basicity and thus, reactivity. As the chemistry of N,O-chelated late transition metal complexes continues to advance, it remains clear that new discoveries and advances in this field are poised to position amides, 2-pyridones, etc. as targeted ligands for developments in homogeneous catalysis, small molecule activation, and more. In the succeeding three sections (1.9-1.11), hemilability as well as the synthesis of s- and agostic complexes will be discussed - these topics are central themes discussed throughout this thesis. 1.9 Hemilabile Ligands The 1,3-N,O-chelating heterobidentate ligand scaffolds discussed herein are considered to be hemilabile. Hemilabile ligands were first introduced by Rauchfuss et. al. in 1979 by studying the properties of bidentate phosphine-ether ligands in the coordination sphere of Ru (Scheme 1.51).101 In this work, the authors proposed that the hard oxygen donor atom would readily dissociate, allowing for opening of a vacant coordination site, which could be used for subsequent substrate binding. Hemilabile behaviour is suggested to result in energy differences on the order of 50 kJ·mol-1, allowing for access to both κ2-P,O (1.143) and κ1-P (1.144/1.145) binding modes.       54       Scheme 1.51 First example of a hemilabile complex In 2001, Braunstein and Naud further classified hemilabile behaviour into one of three classes (Scheme 1.52).102 Type 1 relies on the reversible opening of an A-B chelate, type 2 involves reversible interchange between A or B and a third donor site, C and finally, type 3 involves opening of the chelate in the presence of an external reagent, C. In the context of the 1,3-N,O chelates discussed herein, type 1 hemilability is encountered. This ligand behaviour allows for the bonding of exogenous ligands, L or even σ-bonds to generate σ-complexes.           Scheme 1.52 Three classes of hemilability   MABMABType 1MABType 2CMCBAMABType 3 +   C +    BMACRuPh2POPh2POClClRuPh2POPh2POClClvacantcoordination siteRuPh2POPh2POClClLL1.143 1.1441.145 55 1.10 Sigma (σ) Complexes  Sigma (σ) complexes103 are those transition metal complexes having an intermolecular 3-centre-2-electron bond with a pendant E-H (E = H, B, Si, Ge) group. These dative ligands participate in synergistic bonding via donation of electron density from a σ-E-H bond and in turn, receive back-donation from the metal to a σ*-E-H antibonding orbital.        Scheme 1.53 Selected orbital interactions for a dihydrogen, M-(H2) complex  As a consequence of metal back-donation into the E-H σ* orbital, coordination of an E-H bond ultimately results in lengthening, often leading to E-H bond scission – oxidative addition. An example of a σ-complex is Kubas’ complex, [W(PCy3)2(CO)3(η2-H2)] (1.147), first prepared in 1984, which has a bond length of 0.82 Å [by neutron diffraction] compared with 0.74 Å for free H2.104     Scheme 1.54 Isolation of the first dihydrogen complex σ*σMMEWOCOC COPCy3PCy3HHWOCOCCy2PPCy3COH H21.146 1.147 56 Transition metal σ-complexes have been reported for H-H, B-H, C-H, Si-H, Ge-H, Sn-H, and C-C bonds.103 The first σ-complex, [CpMn(CO)2(η2-HSiPh3)] (1.148; Cp = C5H5-) was reported in 1971 by Jetz and Graham having an η2-HSiPh3 ligand.105 In 1996, Hartwig et al. showed that boranes could be similarly coordinated, providing [CpMn(CO)2(η2-HBR2)]  (1.149, R = Bpin, Bcat, Me, Cy).106 Alkane C-H σ-complexes have been similarly observed, though are less common, owing to the low polarization of the C-H bond. An example includes the η2-CH4 complex, [Rh(PONOP)(η2-CH4)] (1.150, PONOP = 2,6-(tBuPO)2C5H3N-), which is stable below -87 oC.107 In 2012, Weller et al. prepared an unusual C-C σ-complex in the solid-state, [Rh(iBu2PCH2CH2PiBu2)(η2:η2-C7H12)][BArF4] (1.151), formed via solid-state hydrogenation of the corresponding norbornadiene (alkene) precursor.108    Scheme 1.55 A selection of transition metal σ-complexes 1.11 Agostic Complexes By contrast to a σ-complex, a transition metal complex having an intramolecular 3-centre-2-electron bond with a pendant C-H bond is termed an agostic (from Ancient Greek “to hold close to oneself”) complex (Scheme 1.56).103 Such interactions are important for the stabilization of low-coordinate complexes. This term has also been extended to include intramolecular interactions of transition metal systems with other E-PiBu2PiBu2RhHHHHOO PPRhtBu2tBu2HCHHHMn+ +OCOC SiHPh3MnOCOC BHR R1.148 1.1501.149 1.151 57 H (E = non-carbon) bonds. Indeed, agostic interactions have also been encountered for non-transition metal centers including main group elements viz. Li, K, Ca, and Al.109,110    Scheme 1.56 α, β, and γ C-H interactions To validate the formation of such species, single X-ray and neutron diffraction techniques are extremely valuable – the latter for cases where the hydrogen atom cannot be reliably located. Infrared (IR) spectroscopy can also be used as a valuable tool, often providing (for a coordinated C-H bond) a reduced vC-H bond frequency. In addition, 1H/13C NMR spectroscopy can also provide compelling evidence for the formulation of an agostic complex, providing shielded 1H NMR resonances with decreased 1JC,H coupling constants (in comparison to the uncoordinated C-H bond). Finally, density functional theory (DFT) and atoms in molecules (AIM)111 can be used as an elegant tool for the support of agostic interactions.112 AIM studies the electron density map of a given molecule, providing a gradient vector field, which shows the location of nuclei (maxima in electron density) and bond critical points (bcps; points of inflection with respect to a coordinate); the existence of a bcp between two nuclei suggests an interaction.      MCH MCCHMC CCHαβγ 58 Chapter 2: Amidate-ligated Complexes of Rh(I): Structure, Bonding, and Reactivity 2.1 Introduction Dioxygen (O2) activation and O-O bond cleavage by homogeneous metal complexes constitutes a green route for access to new E-O (E = C, P) bonds. In vivo, several processes employ O2 as an oxidant including aerobic respiration for the generation of adenosine triphosphate (ATP). Nonetheless, O2 is considered inert toward a variety of organic compounds as the first step in O2 fixation involves a thermodynamically uphill [ΔG = 16.3 kJ·mol-1] one electron reduction. Thus, under ambient conditions, O2 cannot directly oxidize hydrocarbons, amino acids, steroids and other compounds in the absence of a transition metal. In the context of dioxygen activation, the M-O2 unit is strongly influenced by coligands and particulary by those that impart electron density to the metal centre. For the Ir complex, IrX(CO)(PPh3)2(η2-O2) (X = Cl, Br, I), for example the electronegativity of the σ-donor ligand (Cl > Br> I) alters the strength of the Ir-O2 bond, causing the O-O bond to be weaker for X = I > Br > Cl.113   In terms of coordination mode, η2-O2 binding (A, Griffith’s structure)114 is often observed for low-valent late transition metals such as Pt(0), Pd(0), Rh(I), and Ir(I). Additionally, linear (B) and µ-peroxo (C) cooordination modes have also been encountered (Figure 2.1).    Figure 2.1 Modes of O2 Coordination by Transition Metal Centers  M OOMOOM OO MA B CMOO 59  Dioxygen complexes of Rh(I) having substituted carboxylate coligands were reported as early as 1995 by Lis and co-workers who studied the reaction of the hydroformylation catalyst, [Rh(acac)(CO)(PPh3)] (2.1, acac = acetylacetonate) with O2 in the presence of salicylic acid (HOC6H4CO2H) (Scheme 2.1).115 Following protonolysis, the coordinated η2-O2 complex, [Rh(O2)(κ1-O-HOC6H4CO2)(CO)(PPh3)] (2.2) along with H[acac] were identified. Subsequent protonation of the peroxo (O22-) group in 2.2 using salicyclic acid resulted in the formation of a six-coordinate hydrogen dioxide (Rh-O-O-H) complex 2.3, which upon addition of subsequent salicyclic acid provided CO2 – the product of CO oxidation.  									  Scheme 2.1 Dioxygen reactivity of [Rh(acac)(CO)(PPh3)] 	In 2006, Tejel reported that the 1,3-N,N chelated triazenide complex, [Rh(κ2-N,N-PhN3Ph)(η4-COD)] (2.5, COD = 1,5-cyclooctadiene, PhN3Ph = 1,3-diphenyltriazenide) underwent facile oxygenation to give the corresponding 2-rhoda(III)oxetane 2.6.116 Treatment of this dirhodium(I) species with PMe3 provided the C-O functionalized RhOOCOPPh3 RCO2ORhCOPPh3OO2, RCO2H- H[acac]OH= R+ H[acac]RhOOCOPPh3O2HCO2RRhOOO2CRPPh3OH2CO2RRCO2HCO22.1 2.2 2.32.4 60 organic fragment, 4-cycloocten-1-one along with the pentacoordinated Rh(I) complex,  [Rh(κ2-N,N-PhN3Ph)(PMe3)3] (2.8) (Scheme 2.2).													 Scheme 2.2 Dioxygen reactivity of [Rh(κ2-N,N-PhN3Ph)(η4-COD)] (2.5) In an effort to render this process catalytic, later in 2008, the authors studied the mechanism for this transformation (Scheme 2.3).117 In particular, the reactivity of the tris(trimethylphosphine) by-product, [Rh(κ2-N,N-PhN3Ph)(PMe3)3] (2.8) with O2 was investigated. In the absence of an exogenous donor ligand, this complex was shown to provide O=PMe3 quantitatively along with unidentified Rh(I)-containing species. In the presence of exogenous COD ligand however, [Rh(κ2-N,N-PhN3Ph)(PMe3)(η4-COD)] (2.11) and two equiv. O=PMe3 were obtained. Unfortunately, complex 2.11 showed no reactivity toward additional O2, thwarting the possibility of catalysis (Scheme 2.3).		 Scheme 2.3 Dioxygen reactivity of [Rh(κ2-N,N-PhN3Ph)(PMe3)3] (2.8) NNNRhPMe3PMe3PMe3O2- PMe3 N NNRhPMe3PMe3OO N NNRhPMe3OPMe3OPMe3 N NNRhPMe32 O=PMe32.8 2.9 2.10 2.11PMe3 + CODNNNRh O2N NNRhNNNRhOO NNNRhPMe3PMe3Oxs PMe3NNNRhPMe3PMe3PMe3O+2.5 2.6 2.72.822 PMe3 61 In 2012, Rohde reported that a dialkyldiarylguanidinato complex of Ir: [Ir(κ2-N,N-PhNC(NMe2)NPh)(η4-COD)] underwent O2 activation to give the corresponding η2-O2 Ir(III) complex 2.13 (Scheme 2.4).11 Although X-ray data proved unavailable, the mononuclear structure was corroborated on the basis of diffusion NMR experiments (1H-1H DOSY). The Rh analogue 2.12 has also been prepared, though the reactivity of this system has not been studied. The Ir complex, however, is competent for O-atom transfer to PPh3 (1.5 or 10 equiv. with respect to Ir) providing ~ 0.8 equiv. of O=PPh3. Self-decay of 2.13 was also observed after 1 day at 70 oC to give 4-cycloocten-1-one and 2.14. Treatment of 2.13 with excess CO liberates O2 and provides the bis(carbonyl) complex, [Ir(κ2-N,N-PhNC(NMe2)NPh)(CO)2] (2.15). 	        Scheme 2.4 Dioxygen transfer reactivity of [Ir(κ2-N,N-PhNC(NMe2)NPh)(η4-COD)(η2-O2)] (2.13) 2.2 Synthesis of Rhodium(I) Amidate Complexes Over the past few decades, the chemistry of mononuclear low-valent rhodium(I) amidates [N(R)C(O)Rʹ (1-)] has remained largely unexplored. In fact, until recently the NNMM = Rh (2.12)NO ONNIrCOCOM = IrNM = IrC6D6Ph3P=Ounidentified products+ COPPh32 equiv. CODNNIrNO+M = Ir (2.13) 2.152.14 62 only known Rh(I) amidate complexes were the binuclear µ2–N,O Rh(I) systems, [Rh2{µ2-N,O-N(Ph)C(O)Me}2(CO)4], [Rh2{µ2-N,O-N(Ph)C(O)Me}2(CO)2(PPh3)2], and [Rh2{µ2-N,O-N(Ph)C(O)Me}2(CO)2(PPh3)2][PF6] reported by Carriedo over twenty-five years ago.53 Our interest in amidate ligands stems from their inherent hemilability, which offers distinct and variable coordination modes e.g., κ1-O or –N, κ2-N,O or bridging (µ2-N,O); which mode is preferred depends on the steric and electronic requirements of a given metal center. Unlike monodentate ligands, the use of such heterofunctional bidentate ligands allows for access to metal coordinative unsaturation by way of a κ1-E; E = O, N binding mode, for example. Moreover, these ligands offer constricted N-M-O bite-angles (58-63o) potentially allowing for augmented metal accessibility. The use of small-bite angle diphosphine ligands, for example, has been shown necessary to achieve meaningful turnover in Rh-catalyzed hydroacylation.118 Several groups77,119-124 have taken advantage of amidates in the pursuit of active and functional group-tolerant metal catalysts for atom-economical transformations such as hydroamination,119,121 hydroaminoalkylation,120,122 and ring-opening polymerization,123,124 to name a few. To date, however, such catalyst development reports have been focused on systems with early transition metals13,125-130 or lanthanides.131-133 In this chapter, the potential suitability of amidates as ligands for late transition metals is explored, showing that these ligands promote both unique coordination modes and reactivity. It was initially postulated that coupling these unsymmetric, small-bite angle ligands with rhodium(I) could offer hitherto unknown four-membered rhodaheterocycles (with a κ2-N,O coordination geometry), which could later be exploited for application in  63 catalysis. Thus, the goals of this study were three-fold: to 1) broaden the scope of rhodium(I) amidate coordination chemistry beyond the known µ2–N,O geometry, 2) understand how systematic manipulation of auxiliary ligands (through steric and electronic influence) within the Rh(I) coordination sphere affects amidate ligation, and finally, 3) demonstrate that variability in the amidate coordination environment modulates reactivity.  	2.2.1 Generation of Rh(I) Diolefin Precursors  Two amides, HN(Dipp)C(O)R; R = Ph (LH-2.16), tBu (LH-2.17) were chosen for this study based on their difference in steric and electronic properties. The choice of a bulky N-substituted Dipp (Dipp = 2,6-diisopropylphenyl) group was anticipated to encourage the formation of mononuclear Rh(I) complexes, potentially allowing for access to previously unobserved coordination modes. The amide Lewis basicity and steric profile was also varied by altering the carbonyl C-substituent.  Addition of the sodium amidate ligand salt, Na[N(Dipp)C(O)Ph] (2.16) to 0.5 equiv. of [Rh(NBD)Cl]2 in C6H6 immediately afforded a dark red solution, which upon work-up, provided the binuclear complex 2.18 in near quantitative yield (Scheme 2.5). The 1H NMR spectrum in C6D6 at 22 oC showed four doublets of equal intensity centered at δ 0.63, 1.04, 1.13, and 2.27 for the ligand CH3 (Dipp) groups, indicating two inequivalent amidate ligand environments, resulting from hindered rotation about the N-C(Dipp) axis. Furthermore, six methine and two methylene signals (eight in total) corroborated the presence of two unique Rh(I)-η4-NBD environments. Using 13C{1H} NMR spectroscopy, four unique signals of equal intensity for the ligand CH3 (Dipp) groups, and a signal at δ 172.9 for the bridging C1 amidate carbon,134 altogether confirm  64 along with VT 1H NMR spectroscopic measurements, static solution-state µ2-N,O coordination on the NMR timescale (up to 368 K). 					      Scheme 2.5 Dirhodium(I)-amidates formed by metallation of Na[N(Dipp)C(O)R]; R = tBu (2.16) or Ph (2.17) with [Rh(NBD)Cl]2 		X-ray-quality crystals of 2.18 were isolated from a hexanes-layered toluene solution at -35 oC (Figure 2.2). The propensity of related pyridonate,51,135,136 amidinate,137 carboxylate138 and triazenide116 ligands to bridge between two Rh atoms has been reported. Beyond the N,O-chelated moiety, coordination at each Rh(I) centre is completed by two η4-NBD fragments, affording a distorted square planar geometry to each Rh(I) atom. Notably, the distance between Rh(I) atoms is short [2.9861(10) Å], indicating a weak metal-metal interaction. It warrants mentioning that shorter distances ranging from 2.612 to 2.841 Å have been found in binuclear Rh(I) complexes with CO or 1,1-bis(diphenylphosphino)methane ligands.139,140 Separations of 2.916,141 2.975,142 and 2.982 PhNOPhN ORh RhR NO Na0.5C6H6, 22 oC- NaCl0.5 equiv.[Rh(NBD)2Cl]22.182.19RhNO(2.16): R = Ph(2.17): R = tBuNON ORh Rh0.5C6H6, 22 oC- NaCl0.5 equiv. [Rh(NBD)2Cl]2Keq = [2.19]2.20ΔH = -114.8 ± 4.1 kJmol-1ΔS = -372.80 ± 0.01 Jmol-1K-1[2.20]2 65 Å143 have also been observed for related Rh(I)-Rh(I) complexes, where a metal-metal interaction has also been postulated. 							      Figure 2.2 ORTEP depiction of the solid-state molecular structure of [Rh2{µ2-N,O-N(Dipp)C(O)Ph}2(NBD)2] (2.18) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]: Rh(1)-Rh(1′) 2.9861(10), Rh(1)-N(1) 2.1131(11), Rh(1)-O(1) 2.0912(11), O(1)-Rh(1)-N(1) 86.77(5).  Surprisingly, use of Na[N(Dipp)C(O)tBu] (2.17) as the ligand precursor provided a different result. As such, treatment of 2.17 with 0.5 equiv. of [Rh(NBD)Cl]2 in C6H6 gave a dark orange solution, which based on 1H and 13C NMR spectroscopy, yielded two products in a 1:1 ratio: the expected binuclear species, 2.20 along with the targeted mononuclear κ2-N,O-Rh(I) complex, [Rh{κ2-N,O-N(Dipp)C(O)tBu}(NBD)] (2.19). The NMR spectroscopic features of 2.20 are similar to those of 2.18. For the Cs-symmetric Rh(I) complex 2.19, 1H NMR spectroscopy showed two doublets of equal intensity centered at δ 1.76, 1.25 for the ligand CH3 (Dipp) groups, once again highlighting hindered rotation about the N-C(Dipp) axis. Three methine and one methylene signal Rh1 Rh1′ N1 C1 O1  66 (four in total) additionally corroborate the presence of a sole Rh(I)-η4-NBD environment. Using 13C NMR spectroscopy, a signal for the C1 carbon of the amidate ligand was also observed at δ 186.5, which is downfield-shifted from δ 179.9 observed for the C1 atom of 2.20. The equilibrium between 2.19 and 2.20 was studied in tol-d8 from 298 K to 368 K using variable temperature (VT) 1H NMR spectroscopy to calculate the thermodynamic parameters associated with the dimerization of 2.19 using a van’t Hoff plot. Formation of the binuclear Rh2 complex, 2.20 is enthalpically favored by 114.8 ± 4.1 kJmol−1, but disfavored entropically by -372.80 ± 0.01 Jmol−1K−1. The process at 298 K is slightly exergonic with ΔG° = -3.9 kJmol−1 giving Keq(298) ≈ 4.8. A difference in reactivity between ligand salts 2.16 and 2.17 suggests that having two adjacent bulky t-butyl groups is sterically disfavored, culminating in a mixture of monomer (2.19) and dimer (2.20) products. However, as noted for precursor 2.16, neighboring phenyl groups are tolerated, resulting in a sole dimeric Rh(I) product 2.18.         	2.2.2 Reactions of Complexes 2.18/2.20 with PPh3 In an effort to uniquely access mononuclear rhodium(I) amidates through olefin displacement, we examined the reactivity of 2.18 and 2.20 with PPh3 (Scheme 2.6). Treatment of 2.18 or 2.20 with four equiv. of PPh3 was found to give the targeted four-membered rhodaheterocycles, [Rh{κ2-N,O-N(Dipp)C(O)R}(PPh3)2]; R = Ph (2.21), tBu (2.22) via NBD displacement over 15 min in near-quantitative yield. Following work-up, the orange solids 2.21 or 2.22 were obtained; these can also be accessed by salt metathesis between RhCl(PPh3)3 and ligand salts 2.16 or 2.17 over 2 h.    67      Scheme 2.6 Reactivity of 2.18 and 2.20 with PPh3   In the 1H NMR spectrum of both 2.21 and 2.22, two doublets were observed for the amidate CH3 (Dipp) groups at δ 1.01, 1.12 ppm (3JH,H = 6.9 Hz) for 2.21 and δ 1.03, 1.43 ppm (3JH,H = 6.8 Hz) for 2.22, again indicative of hindered rotation about the N-C(Dipp) axis for both complexes. In the 31P{1H} NMR spectrum, two doublets of doublets were observed at δ 48.92, 57.96 (2JP,P = 55.6 Hz, 1JRh,P = 195.7 Hz) for 2.21 and δ 51.24, 56.94 (2JP,P = 55.5 Hz, 1JRh,P = 191.9 Hz) for 2.22. Complementary shifts and coupling constants of δ 41.3, 55.8 (2JP,P = 47 Hz, 1JRh,P = 182 Hz, CD2Cl2) were previously reported for the Rh(I) thioureate complex, [Rh{κ2-N,S-N(Ph)C(S)NMe2}(PPh3)2].144 Related systems, including the Rh(I) formamidinate, [Rh{κ2-N,N-N(Ar)CHN(Ar)}(PPh3)2]; Ar = p-tolyl14 and Rh(I) triazenide, [Rh{κ2-N,N-N(Ar)NN(Ar)}(PPh3)2]; Ar = C6F5145 complexes have also been reported, but no 31P{1H} NMR or crystallographic data were provided. X-ray-quality crystals of 2.21 and 2.22 could be isolated from hexanes at -35 oC (Figure 2.3).  Each structure features a distorted square-planar d8 Rh(I) centre, chelated in a κ2-N,O fashion by the amidate ligand scaffold. As expected, these four-membered rhodaheterocycles bear acute N-Rh-O bite-angles of 62.04(10)o (2.21) and 61.16(4)o (2.22). To our knowledge, this represents a rare 0.5 equiv. 2.18 or 2.20- NBDC6H6, 22 oC(2.21): R = Ph(2.22): R = tBuκ2-N,O2 PPh3 RhCl(PPh3)3C6H6, 22 oC- NaCl, - PPh32.16 or 2.17Rh NOPPR 68 case where X-ray crystallography was employed for the characterization of such κ2-bonded molecular species.          Figure 2.3 ORTEP depiction of the solid-state molecular structures of [Rh{κ2-N,O-N(Dipp)C(O)R}(PPh3)2]; R = Ph (2.21), tBu (2.22) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. (2.21): Rh(1)-N(1) 2.137(3), Rh(1)-O(1) 2.131(3), O(1)-Rh(1)-N(1) 62.04(10). (2.22): Rh(1)-N(1) 2.2023(12), Rh(1)-O(1) 2.1050(10), O(1)-Rh(1)-N(1) 61.16(4).   2.2.3 15N NMR Spectroscopy In an effort to 1) deduce coordination mode based on 15N spectroscopy and 2) determine the identity of the phosphine trans- from each N,O-chelating atom, RhCl(PPh3)3 was treated with 15N-labelled phenylpivalamide 2.23, giving the related rhodaheterocycle, [Rh{κ2-N,O-15N(Ph)C(O)tBu}(PPh3)2] (2.24) (Figure 2.4). This product was characterized using 15N and 31P NMR spectroscopy alone. For the protio C1 O1 N1 Rh1 P1 P2 O1 N1 Rh1 P1   P2 A) Complex 2.21 B) Complex 2.22C1  69 ligand, 15N{1H} NMR spectroscopy (referenced to CH3NO2 at 0 ppm) provided a signal at δN -253, while for the κ2-N,O chelated complex 2.24 a broad doublet of doublets was observed at δN -222 (dd, 1JRh,N = 8 Hz, 2JP,N = 37.7 Hz). By 31P{1H} NMR spectroscopy, however two signals were observed at δP 57.56 (dd, 2JP,P = 54.3 Hz, 1JRh,P = 192.8 Hz) and δP 54.81 (ddd, 2JP,P = 54.3 Hz, 2JP,N = 37.7 Hz, 1JRh,P = 187.9 Hz), indicating the shielded signal to be trans-N. For the related µ-N,O bridged complex, [Rh2{µ2-N,O-15N(Ph)C(O)tBu}2(NBD)2] (2.25) δN was observed to be -208 (1JRh,N = 18 Hz). For previously reported Ta compounds, the κ2-N,O geometry (2.26) gave a signal at δN -180.3, while the κ1-O geometry (2.27) provided a signal at δN -134.8.146 Overall, such indirect detection methods allow for facile determination of δN, though do not seem to be as sensitive as 13C NMR spectroscopy for the unambiguous determination of amidate coordination mode. 	               Figure 2.4 15N chemical shifts for amidate-ligated complexes 2.23-2.27   15N NMR(ppm) -220 -180 -140-260 κ1-Oµ2-N,Oκ2-N,ORh NOPPtBu-222NHtBuO-2531515NON ORh Rh15 15-208Ta NOMe2NMe2NtBu-180NMe2NMe2Ta NOMe2NMe2NtBuNMe2NtBuO-13515 15152.23 2.24 2.252.26 2.27 70 2.2.4 Reactions of Complexes 2.18/2.20 with PCy3 Moving from PPh3 to a more electron-rich, sterically demanding phosphine, PCy3 as auxiliary ligand, resulted in a clear difference in reactivity. Hence, four equiv. of PCy3 were added to C6D6 solutions of 2.18 or 2.20 resulting in orange solutions (Scheme 2.7). For the reaction of 2.18, analysis by 31P{1H} NMR spectroscopy revealed two signals – a doublet at δ 31.67 (1JRh,P = 164.2 Hz) for the κ1-O complex 2.28 and a singlet of equal integration for uncoordinated PCy3, indicating consumption of only two equiv. of PCy3 (one equiv. per Rh centre). When a C6D6 solution of 2.18 was treated with two equiv. of PCy3, one signal at δ 31.67 was observed in the 31P{1H} NMR spectrum. In the 1H NMR spectrum, four resonances attributable to η4-coordinated NBD were also observed e.g., at δ 5.20 (=CH), 3.42 (=CH), 3.35 (-CH), and 1.13 (-CH2) for 2.28, indicating Cs symmetry of the resulting complex. A 1H-31P{1H} HMBC NMR experiment additionally showed correlation of the bound NBD to the coordinated PCy3 ligand, as observed by 31P{1H} NMR spectroscopy validating the formation of a LnRh(η4-NBD)(PCy3) complex. Similar spectroscopic features were observed for 2.29. From all these data, one can conclude κ1-O amidate coordination to Rh(I), giving [Rh{κ1-O-N(Dipp)C(O)R}(NBD)(PCy3)]; R = Ph (2.28), R = tBu (2.29). Complexes 2.28/2.29 can also be isolated by treatment of [Rh(PCy3)(NBD)Cl] with 2.16 or 2.17 in C6H6. Strikingly, the C1 amidate 13C NMR signal for the κ1-O complex 2.28 at δ 166.5 differs significantly from that observed for the µ2-N,O (δ 172.9 for 2.18) and κ2–N,O (δ 178.6 for 2.21) complexes. Analogous changes in 13C NMR signals have been observed for an amidate-ligated zirconocene complex, [Cp2Zr(κ1-O-N(Dipp)C(O)Ph)2] for which the κ1–O and κ2–N,O geometries gave δ 163.3 and 172.1, respectively.127  It is additionally noteworthy that reaction of 2.16  71 or 2.17 with 0.5 equiv. of [RhCl(PCy3)2]2 in C6D6 at 22 oC did not give the desired  [Rh{κ2-N,O-N(Dipp)C(O)R}(PCy3)2] complex. 						    Scheme 2.7 Reactivity of 2.18 and 2.20 with PCy3 	The κ1-O complexes 2.28 and 2.29 were found to be nucleophilic at nitrogen. For example, dissolution of 2.28 in wet C6D6 (not distilled from Na) and analysis by 1H NMR spectroscopy provided signals identical to those observed for the parent complex, with the exception of an additional high-field resonance located at δ 9.81 assigned to an R3NH+ group in 2.30 (the counterion has yet to be identified) (Scheme 2.8). To unequivocally support this proposal, a 1H-15N HMQC experiment modified for single bond correlation (1JN,H) was performed, providing a cross peak at δ -264 (1JN,H = 91 Hz). Notably, these protonated adducts were found to be stable in solution. Conversely, dissolution of the κ1-O complex 2.28 in dried C6D6 (distilled from Na) provided a mixture of unidentifiable products (including protio ligand) after 3 h at 22 oC, while solutions of 2.29 were stable, indicating a ligand-dependent decomposition pathway. In an effort to identify the decomposition product by X-ray analysis, solutions of 2.28 were dissolved in myriad solvent combinations and allowed to cool at – 35 oC, ultimately providing 0.5 equiv. 2.18 or 2.20- NBDC6H6, 22 oC2PCy3RhRNOCy3Pκ1-O PCy3 C6H6, 22 oC(2.28): R = Ph(2.29): R = tBuRhClCy3P2.16 or 2.17C6H6, 22 oC- NaClRh NOCy3PCy3PR1 equiv. 72 material that was unsuitable for analysis. Use of the N-2,6-dimethylphenyl (xylyl) variant 2.31, however, provided orange crystalline material suitable for analysis by single X-ray diffraction. The crystal structure of 2.32 depicts a dirhodium(I) system with one Rh(I) center bonded in a κ1-O fashion by an amidate ligand as well coordinated η4-NBD and PCy3 ligands. Remarkably, the second Rh(I) center, whose coordination environment presumably results from amidate-directed C(sp2)-H bond activation, is bonded to the same amidate ligand in a κ2-N,C fashion, while also maintaining coordination to a η4-NBD ligand. Though it was difficult to characterize the bulk material using NMR spectroscopy or by elemental analysis, this example highlights the propensity of phenyl-substituted amidates to undergo ligand-directed C(sp2)-H bond activation. At this juncture, the role of the amidate coligand in this process remains unknown, though we suggest it acts as an internal base, promoting C(sp2)-H activation in cooperation with the Rh(I) center via a concerted-metallation deprotonation (CMD) or related pathway.2       			Scheme 2.8 Intermolecular ortho-metallation generating a dirhodium(I) complex  RhPhNOCy3PRRRhPhNOCy3PRRHRhNOCy3PRRRhRhNOCy3PRRRhNORRHδ+δ−NHPhRRO+cyclometallationadventitious H2OR = Me (2.32) X-rayR = iPr (2.28)R = Me (2.31)R = iPr (2.30) 73                   Figure 2.5 ORTEP depiction of the solid-state molecular structure of [Rh{κ2-N,C-N(Xyl)C(O-Rh(η4-NBD)(PCy3))C6H4}] (2.32).  2.2.5 Reactions of Complex 2.20 with Phosphites To allow for comparison with the phosphine complexes generated from reaction with PPh3 and PCy3, complex 2.20 was also reacted with the phosphite ligands, P(OR)3; R = Et or Ph (Scheme 2.9). In terms of sterics, these coligands [P(OR)3; R = Et (109o), Ph (128o)] offer cone angles smaller than that of PPh3 (145o) though electronically these ligands are poorer σ-donors/superior π-acids allowing for Rh(I) back-bonding into a low-lying P-O σ* orbital. Thus, four equiv. of P(OEt)3 were added to a C6D6 solution of 2.20 resulting in a bright yellow solution (Scheme 2.9). The κ2-N,O amidate coordination mode in 2.33 was easily deduced on the basis of a 13C{1H} NMR spectroscopy experiment, which provides a downfield shifted resonance at δ 189.6 for the C1 atom of 2.33. Furthermore, two doublets for the N-2,6-diisopropylphenyl group at δ 1.60 and 1.52 Rh1 P1 O1 Rh2 N1  74 are consistent with a Cs-symmetric complex bearing two phosphite ligands. By 31P{1H} NMR spectroscopy, two doublets of doublets were additionally observed at δ 142.67 (1JRh,P = 272.4 Hz, 2JP,P = 106.2 Hz) and 140.73 (1JRh,P = 281.9 Hz, 2JP,P = 106.2 Hz).  								 Scheme 2.9 Reactivity of 2.20 with P(OEt)3 and P(OPh)3 	Use of P(OPh)3 as a potential ligand candidate offered a different reaction outcome. Addition of four equiv. of P(OPh)3 to a C6D6 solution of 2.20 provided a deep orange solution (Scheme 2.9) having spectroscopic features analogous to the κ2-N,O bis(triethyphosphite) derivative 2.33. By 31P{1H} NMR spectroscopy, two doublets of doublets were observed for each P(OPh)3 group at δ 125.16 (dd, 1JRh,P = 288.0 Hz, 2JP,P = 110.3 Hz) and 121.20 (dd, 1JRh,P = 301.3 Hz, 2JP,P = 110.3 Hz). The value of 1JRh,P is related to overlap between Rh(5s) and P(3s) orbitals.147 For the tBu series, strongly σ-donating phosphine ligands were found to give smaller values of 1JRh,P, with those having π-accepting ability giving larger values of 1JRh,P: PCy3 (1JRh,P = 164 Hz), PPh3 (1JRh,P = 192 Hz), P(OEt)3 (1JRh,P = 272/282 Hz), and P(OPh)3 (1JRh,P = 288/301 Hz). Taken tBuNOtBuN ORh Rh0.52 P(OEt)32 P(OPh)3- NBDRh POOPhOPhP(OPh)3NHO+ Rh NOPPOEtOOEtOEtEt OEtOEtRh NOPPOPhOOPhOPhPh OPhOPh+cyclometallationNBD2.202.342.35 2.33 75 together, these data point toward κ2-N,O amidate ligands as being good donor ligands, providing an electron-rich Rh(I) centre, which in turn, prefers coordination of a π-accepting ligand.  Although for PPh3, the magnitude of 1JRh,P for phosphorous trans-N or trans-O is roughly identical, it is expected that for the phosphite complexes 2.33 and 2.34 that the smaller of the two 1JRh,P coupling constants is attributable to the phosphite trans to the nitrogen atom of the amidate ligand, owing to its greater trans influence.  Owing to the conformational flexibility provided by the P(OPh)3 ligand, complex 2.34 was found to decompose in C6D6 or tol-d8 [t1/2 = 6 h], providing protio ligand and a mixture of unidentifiable products, which we suggest is due to ligand-aided C(sp2)-H bond activation (Scheme 2.9). Indeed, treatment of 2.20 with four equiv. of P(OPh)3 without removal of the expelled norbornadiene (NBD), cleanly gives a sole product identified as [Rh{κ2-P,C-P(OPh′)(OPh)2}(P(OPh)3)(NBD)] (2.35) resulting from C(sp2)-H bond activation. Complex 2.35 has been characterized by 1H NMR spectroscopy giving four signals attributable to the coordinated NBD unit at δ 4.23 (=CH), 3.98 (=CH), 3.37 (-CH), and 2.56 (-CH2). By 31P NMR spectroscopy, consumption of 2.34 is corroborated by two new signals at δ 167.51 (dd, 1JRh,P = 223.0 Hz, 2JP,P = 81.0 Hz) and 133.56 (dd, 1JRh,P = 225.5 Hz, 2JP,P = 81.0 Hz). Notably, the 31P NMR signal at δ 167.51 is consistent with a cyclometallated P(OPh)2(OC6H4)′ group. In 1968, Robinson et al. reported that heating HRh(P(OPh)3)4 in n-alkanes results in elimination of H2 giving a related trigonal bipyramidal complex [Rh{κ2-P,C-P(OPh′)(OPh)2}(P(OPh)3)3] (2.36) having two P(OPh)3 moieties in the equatorial plane cf. a norbornadiene molecule as in the case of 2.35.148,149 Comparison of the 31P NMR spectroscopic data reveals good agreement between the two structures (Scheme 2.10).   76  			    Scheme 2.10 Ortho-metallation in a rhodium tiphenylphosphite hydride complex  2.2.6 Reactions of Complexes 2.21 and 2.22 with Molecular Oxygen (O2) Moving forward, we were interested in investigating the reactivity of these phosphine and phosphite complexes with O2 – an environmentally benign oxidant and O-atom source. The O2 reactivity of a related system, Wilkinson’s catalyst, RhCl(PPh3)3, has been reported.150-152 RhCl(PPh3)3 binds one equiv. of O2 giving the η2-peroxo adduct, RhCl(PPh3)3(η2-O2) (2.37), which undergoes subsequent dimerization to give 0.5 equiv. of [RhCl(PPh3)2(O2)]2 (2.38) through loss of one equivalent of PPh3 (Scheme 2.11).150,151 In terms of spectroscopic features, Read reported that the conversion of RhICl(PPh3)3 to RhIIICl(PPh3)3(η2-O2) (2.37) results in an upfield shift of about δ 19.1 in the 31P NMR spectrum and a decrease in the 1JRh,P coupling constant by a factor of 0.75.152    Scheme 2.11 O2 activation by Wilkinson’s catalyst, RhCl(PPh3)3  Rh POOPhOPhP(OPh)3(PhO)3P(PhO)3PACBCHRh(P(OPh)3)4 hexanes- H2Δ Rh POOPhOPhP(OPh)3δA = 167.5, 1JRh,P = 222 HzδB = 133.6, 1JRh,P = 226 Hz2JA,B = 81 HzABδA = 151.6, 1JRh,P = 236 HzδB = 123.6, 1JRh,P = 159 Hz2JA,B = 71 Hz2.36 2.35RhPh3PPh3PPPh3ClRhClPPh3PPh3PPh3OO RhPh3PPh3POO RhPPh3PPh3OOClO2Cl0.5- PPh32.37 2.38 77 In a preliminary screening experiment, a tol-d8 solution of the Rh(I) dimer/monomer mixture 2.19/2.20  was exposed to 3 atm of O2 at 25 °C over one week, resulting in no observable reaction by NMR spectroscopy. However, this lack of reactivity contrasts dramatically with comparative experimentation using complex 2.21 or 2.22 (Scheme 2.12). In this case, treatment of a tol-d8 solution of complex 2.21 or 2.22 with 3 atm of O2 immediately provided a dark red solution upon shaking. The 1H and 31P{1H} NMR spectra for these reactions provided evidence for new LnRh(PPh3)2 complexes, which decomposed rapidly (t1/2 = ca. 5 min) to give free ligand, Ph3P=O, and as yet unidentifiable Rh-containing byproducts.    Scheme 2.12 Reactions of 2.21 and 2.22 with O2   For reaction of 2.21, the 31P{1H} NMR spectrum provides evidence for two new species assigned as cis(O)-P 2.39 and trans-P 2.41 (Figure 2.6), which display upfield-shifted [AB]-type doublet of doublets centered at δ 35.99 (1JRh,P = 31 Hz, 2JP,P = 18 Hz) and δ 34.76 (1JRh,P = 53 Hz, 2JP,P = 18 Hz) (N.B. The values of 1JRh,P are suspiciously low – currently, we are unable to provide a reason for this) as well as a doublet centered at 35.38 (1JRh,P = 114 Hz) for 2.39 and 2.41, respectively. As previously mentioned, a RhNOPPRhNO PPh3PPh3O OArO2, or airC6D6, r.t.+cis(O)-PRhNOPPO2, or airC6D6, r.t.RhNO PPh3PPh3O OArcis(O)-P+NOT OBSERVEDRhNOPPh3PPh3OOAr+trans-PRhNOPPh3PPh3OOAr+trans-PNOT OBSERVED(1)(2)cis(N)-Pcis(N)-PNOT OBSERVED2.21 2.39 2.40 2.412.222.432.42 2.44RhON PPh3PPh3O OArRhON PPh3PPh3O OAr 78 decrease by a factor of 0.16 and 0.27 in 1JRh,P along with an upfield shift of 12.9 and 23.2 ppm in comparison to 2.21 are consistent with the formulation of complex 2.39 as an η2-Rh(III) peroxo complex. In addition, the 1H NMR spectrum exhibited multiple new signals consistent with the presence of both a C1- (2.39) and Cs-symmetric (2.41) Rh complex. For the C1-symmetric complex 2.39, four doublets at δ -0.09, 0.16, 1.64, and 1.78 along with two corresponding heptets at δ 5.15 and 2.56 were observed for the two inequivalent iPr (Dipp) groups. However, for the Cs-symmetric complex 2.41, only two doublets at δ  0.41, and 0.85 along with a corresponding heptet at δ 3.54 were observed in the 1H NMR spectrum for the two equivalent iPr (Dipp) groups. Although the κ2-N,O coordination mode could not be determined by characteristic 13C{1H} NMR spectroscopy for 2.39/2.41 (due to a short life time), it has been used to unambiguously determine the coordination mode for the related complex 2.42 (vide infra).  Figure 2.6 31P{1H} NMR spectra for the reaction of 2.21 with O2 (C6D6, 121 MHz, 298 K) Complex	2.21	Complex	2.39		Complex	2.41		t	=	0	t	=	1	min	t	=	5	min	t	=	10	min	 79 For reaction of 2.22 with O2, a sole product 2.42 is observed in the 31P{1H} NMR spectrum (Figure 2.7) and displays two upfield-shifted doublet of doublets centered at δ 35.57 (1JRh,P = 163 Hz, 2JP,P = 15 Hz) and δ 34.02 (1JRh,P = 141 Hz, 2JP,P = 15 Hz). A decrease by a factor of 0.83 in 1JRh,P along with an upfield shift of 15.7 and 22.9 ppm in comparison to 2.22 are consistent with the formulation of complex 2.42 as an η2-Rh(III) peroxo complex, [RhIII{κ2-N,O-N(Dipp)C(O)tBu}(PPh3)2(η2-O2)] (2.42). In addition, the 1H NMR spectrum exhibited six new signals consistent with a C1-symmetric Rh complex bearing two inequivalent CH3 (Dipp) groups (four doublets at δ -0.21, 0.85, 1.61, and 1.71) and a 1H-13C{1H} HMBC experiment confirmed κ2-N,O coordination (δC = 185.8 for C1).  Figure 2.7 31P{1H} NMR spectra for the reaction of 2.22 with O2 (C6D6, 121 MHz, 298 K) Having established the stoichiometric O2 activation chemistry noted above, we wondered if a catalytic variant of this reaction could be established. When a tol-d8 solution of PPh3 was treated with 5 mol % 2.19/2.20 and O2, the formation of Ph3P=O (37% conversion, 12 h) was observed and monomer 2.19 was found to be regenerated Complex	2.22	Complex	2.42	t	=	0	t	=	2	min	t	=	5	min	 80 following NBD coordination (Scheme 2.13). In this case, decomposition, however, was not entirely precluded and protonated ligand was also observed by 1H NMR spectroscopy. In this instance, κ2–N,O coordination helps to obviate dimerization of the resulting peroxo complex 2.42, and thus, catalytic turnover is accessed (unlike in the case of RhCl(PPh3)3). The reactivity of 2.19/2.20 toward PPh3 and S8 was also screened. In this instance, Ph3P=S formation was analogously observed, regenerating complex 2.19 without substantial ligand decomposition. By comparison, the PCy3 analogue showed no reactivity with O2 while the P(OEt)3- and P(OPh)3-coordinated complexes succumbed to rapid decomposition giving the respective oxides.        Scheme 2.13 Catalytic Ph3P=O formation using 2.19/2.20 and PPh3/O2  2.2.7 Analysis of O2 Activation Products by Density Functional Theory (DFT) In an effort to establish the connectivity and moreover, to assess the degree of O2 activation in these complexes, DFT calculations were performed using the PBE0 hybrid functional and the 6-31G(d,p) basis set for first and second row atoms and LANL2DZ for Rh. For each of the two ligand sets, three unique geometries were considered: 1) cis(O)-P, 2) cis(N)-P and 3) trans-P. It is noteworthy that P refers to PPh3 and that cis(X)-P κ2-N,O2 PPh32 Ph3P=O2 PPh3 2 Ph3P=OO2κ2-N,Oobserved2.19Rh NORh NOPPRhNOPh3PPPh3OONBD NBDκ2-N,O2.222.42 81 refers to the X donor atom of the 1,3-N,O chelating ligand that is cis to PPh3 in the equatorial plane (Scheme 2.14).       Scheme 2.14 O2 activation products 2.39-2.44 studied by DFT calculations We first examined the three possible O2 adducts of [Rh{κ2-N,O-N(Dipp)C(O)Ph}(PPh3)2] (2.21) (Figure 2.8). Each system adopts a κ2-N,O amidate binding mode as suggested by NMR spectroscopic studies along with an η2-O2 unit. In terms of energetics, the three isomers were found to be similar, with the cis(N)-P (2.40) and trans-P (2.41) geometries being 2.9 kcal·mol-1 and -2.1 kcal·mol-1 relative to the cis(O)-P (2.39) isomer. These observations are consistent with experiment where both cis(O)-P 2.39 and trans-P 2.41 are observed.            RhRNO PPh3PPh3O OArcisRhNOPPh3PPh3OOArRtrans-PAr = 2,6-iPr2C6H3RhRON PPh3PPh3O OArcis(O)-P cis(N)-Pcis2.392.42R = PhR = tBu2.402.432.412.44 82 Figure 2.8 O2 activation products 2.39-2.41 studied by DFT calculations We next examined the O2 adducts of [Rh{κ2-N,O-N(Dipp)C(O)tBu}(PPh3)2] (2.22), though despite numerous attempts only two of the specified isomers, 1) cis(O)-P (2.42), and 3) trans-P (2.44) were found to converge (Figure 2.9). Once again each system adopts a κ2-N,O amidate binding mode along with an η2-O2 unit. In terms of energetics, the two isomers were found to be markedly different, with the trans-P (2.44) geometry being +6.1 kcal·mol-1 higher in energy relative to the cis(O)-P (2.42) geometic isomer, likely due to an unfavorable interaction between the bulky tBu amidate and axial PPh3 group. This observation is consistent with experimental data where only cis(O)-P 2.42 is observed. A)	cis-(O)-P	geometry B)	cis-(N)-P	geometryRhPhNO PPh3PPh3O OArRhNOPPh3PPh3OOArPhC)	trans-P	geometryORhOONPPPORhOOORhONPobservedE = 0 kcal/molnot observedErel = +2.1 kcal/molobservedErel = -2.1 kcal/molORhON PPh3PPh3O OPhAr 83  Figure 2.9 O2 activation products 2.42-2.44 studied by DFT calculations  2.2.8 Reactions of Complexes 2.18 and 2.20 with an Aryl Isocyanide The reaction of 2.18 or 2.20 with four equiv. of CNXyl (Xyl = 2,6-Me2C6H3) was found to produce different products depending on the amidate R group employed (Scheme 2.15). Similar to the PPh3 derivative 2.22 discussed above, for the tBu ligand, the κ2-N,O complex, [Rh{κ2-N,O-N(Dipp)C(O)tBu}(CNXyl)2] (2.45) was isolated after 15 min of reaction time in near-quantitative yield. The 13C{1H} NMR spectrum is diagnostic of κ2-N,O coordination providing a signal at δ 192.0, while two signals for the 2,6-diisopropylphenyl group are revealed in the 1H NMR spectrum at δ 1.55 and 1.33. The aryl methyl isonitrile groups also provide two signals at δ 2.11 and 1.82 each of integration 6H; consistent with a Cs-symmetric bis(isonitrile) Rh(I) complex. Solid-state ATR FT-IR analysis of 2.45 also provided three sharp bands at 2096, 2051, and 2013 cm-1 (vCN) cf. 2134 cm-1 for free CNXyl, indicative of π-donation from Rh(I). Surprisingly, treatment of the phenyl-substituted dimer 2.18 with four equiv. of CNXyl did not result in the formation of a κ2-N,O chelated rhoda(I)heterocycle. On first inspection, the 1H NMR A)!cis#(O)#P'geometryRhNO PPh3PPh3O OArRhNOPPh3PPh3OOArC)!trans#P'geometryOobservedE = 0 kcal/molnot observedErel = +6.1 kcal/molNPOPRhOORhNO OP 84 spectrum showed two signals for the aryl methyl isonitrile groups at δ 2.06 and 1.90 of relative intensity 6:12 indicating a Cs-symmetric complex having two unique CNXyl environments for three CNXyl ligands, which results from formation of a tris(isonitrile) κ1-N complex 2.46.   Scheme 2.15 Reactivity of 2.18 and 2.20 with CNXyl   Layering a saturated toluene solution of 2.46 with hexanes at -35 °C provided yellow plates suitable for single crystal X-ray diffraction (Figure 2.10). This analysis revealed a d8 square-planar Rh(I) complex having three isonitrile ligands along with a κ1-N coordinated amidate ligand – this is the only example of a crystallographically characterized κ1-N amidate complex of Rh(I) presented in this thesis. It is noteworthy that in the absence of solid-state molecular data that differentiation between the κ1-N and –O binding modes presents an unsolved challenge. For the three 2,6-dimethylphenylisonitrile coligands, the C≡N bond lengths range from 1.15 to 1.16 Å and show little elongation compared with free isocyanides, which typically range from 1.14 to 1.16 Å. Additionally, the Rh-C≡N and C≡N-C angles are nearly linear having values close to 180o - < Rh-C≡N: 176.7(4)o, 177.8(4)o, 175.8(4)o and < C≡N-C: 172.4(5)o, 173.8(5)o, and 175.8(4)o. More importantly, amidate C(1)-N(1) and C(1)-O(1) bond lengths of 1.340(5) and 1.246(6) Å are consistent with C-N and C=O RNORN ORh Rh0.5 2 CNXyl- NBDCNRhNOCNRhXylNCXylNCCNXylPhNOC6H6, rt3 CNXyl- NBDC6H6, rtR = Ph R = tBuR = Ph (2.18)R = tBu (2.20)2.452.46 85 bonds as anticipated for κ1-N amidate coordination. In terms of metal coordination, the two cis-oriented isonitrile groups have similar Rh(1)-C(2) and Rh(1)-C(4) contacts of 1.961(5) Å and 1.958(5), while the Rh(1)-C(3) bond, which is trans-oriented to the coordinated N-amidate ligand has a shortened bond length of 1.894(4) Å, indicating a moderate trans influence, with a Rh(1)-N(1) bond length of 2.120(3) Å. For a related κ1-N Ir(III) complex of p-trifluoromethylbenzamide, the Ir-N bond length was observed to be 2.076 Å. Likewise, Kovacs46 and Ferguson41 independently reported two unique Co(III) κ1-N acetamidate complexes having significantly shortened Co-N contacts of 1.946(4) and 1.910(8) Å, respectively. By contrast to 2.45, the solid-state ATR FT-IR spectrum of 2.46 provides three signals at 2142, 2116, and 2088 cm-1, indicating that the Ph-substituted amidate ligand is a poorer donor ligand, though admittedly, the amidate coordination modes adopted in each case are markedly different.          Figure 2.10 ORTEP depiction of the solid-state molecular structure of [Rh{κ1-N-N(Dipp)C(O)Ph}(CNXyl)3] (2.46) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. Rh(1)-N(1) 2.120(3), N(1)-C(1) 1.340(5), C(1)-N1 O1 C1 N2 N3 N4 Rh1 C2 C3 C4  86 O(1) 1.246(6), Rh(1)-C(2) 1.961(5), C(2)-N(2) 1.161(6), Rh(1)-C(3) 1.894(4), C(3)-N(3) 1.160(6), Rh(1)-C(4) 1.958(5), C(4)-N(4) 1.159(7).  2.2.9 Reactions of Complexes 2.18 and 2.20 with Carbon Monoxide (CO)  We next ventured to explore the reactivity of 2.18/2.20 with a related π-accepting ligand, CO. As mentioned previously, [Rh2{µ2-N,O-N(Ph)C(O)Me}2(CO)4] was reported by Carriedo et al. in 1989, though only infrared [vCO = 2086, 2062, and 2014 cm-1] and microanalytical data were provided.53 In our hands, the related dimeric bis(carbonyl) adducts were accessible by one of two routes: a) treatment of frozen C6D6 solutions of 2.18/2.20 with ca. 3 atm. of CO and warming to room temperature via olefin displacement or b) from 0.5 equiv. [Rh(µ-Cl)(CO)2]2 and the corresponding sodiated amidate ligand salt 2.16 and 2.17 via salt metathesis (Scheme 2.16). Though related systems having the formula [Rh2{µ2-N,O-N(Dipp)C(O)R}2(CO)4]; R = Ph (2.47), tBu (2.48) were observed, these were not the sole reaction products. A second product: the κ2-N,O chelated bis(carbonyl) complex was also detected by a 1H-13C HMBC experiment using the tBu group of 2.50 as a reporter for the chemical shift of the C1 carbon atom, indirectly providing signals at δ 192.1 and 178.9 for the κ2-N,O (2.50) and µ2-N,O (2.48) isomers. For the phenyl ligand, a mixture of isomers were detected in a 0.4:1 (κ2-N,O(2.49):µ2-N,O(2.47)) ratio (298 K), while for the bulkier tBu variant, a 0.7:1 (κ2-N,O(2.50):µ2-N,O(2.48)) ratio (298 K) was observed. The difference in ratios at 298 K is consistent with the solution-state data encountered for the norbornadiene precursors, where for the bulkier tBu-substituted amidate ligand, a monomer-dimer equilibrium is encountered, while for the Ph-substituted ligand, no such equilibrium is observed. Similar  87 to [Rh2{µ2-N,O-N(Ph)C(O)Me}2(CO)4], the solid-state ATR FT-IR spectrum of mixtures 2.47/2.49 and 2.48/2.50 provides three broad vCO signals at 2120, 2085, and 2051 cm-1 and 2088, 2051, and 2033 cm-1, once again positioning the Ph-substituted amidate as a weaker donor ligand.  Scheme 2.16 Reactivity of 2.18 and 2.20 with CO    For the tBu derivative, 2.48 orange crystals suitable for single crystal X-ray diffraction obtained at -35 °C from a saturated toluene solution, definitively support the preparation of a complex having a µ2-N,O amidate coordination mode (Figure 2.11). Similar to the diolefin complex 2.18 described previously, each Rh(I) centre is coordinated by an η4-NBD ligand and possesses a Rh-Rh distance of 2.876(2) Å. The coordinated C≡O bond lengths are consistent with that observed for free C≡O (1.13 Å) indicating no activation.      RNORN ORh Rh0.5 3 atm CO- NBDRNORN ORh RhCOCOOC CO- 2 NaCl[Rh(Cl)(CO)2]2NONaR +0.5 equiv.OCRh NO ROC2R = Ph (2.49)R = tBu (2.50)R = Ph (2.18)R = tBu (2.20)R = Ph (2.16)R = tBu (2.17)R = Ph (2.47)R = tBu (2.48) 88          Figure 2.11 ORTEP depiction of the solid-state molecular structure of [Rh2{µ2-N,O-N(Dipp)C(O)tBu}2(CO)4] (2.48) (ellipsoids at 50% probability, hydrogens omitted). Selected bond lengths [Å] and angles [o]. Rh(1)-Rh(1′) 2.876(2), Rh(1)-N(1) 2.075(11), Rh(1)-O(1) 2.059(8), C(1)-N(1) 1.345(15), C(1)-O(1) 1.306(12), C(3)-O(3) 1.153(15), O(1)-C(1)-N(1) 117.1(11).  2.3 Reaction of Complex 2.22 with Aldehydes Having established a preliminary understanding of amidate-ligated Rh(I) carbonyls, we next wished to examine the reactivity of the bis(triphenyl)phosphine complex 2.22 with aldehydes, which serve as known CO sources through decarbonylation.  2.3.1 Attempts at Aldehyde Hydroacylation In the context of C-C bond forming reactions, hydroacylation represents a versatile hydrofunctionalization reaction between an aldehyde and carbon-carbon unsaturation to realize the atom-economical synthesis of ketones (Scheme 2.17).153 Both inter- and intramolecular variants of this reaction have been reported, with most requiring the use of a group 9 transition metal catalyst.118,154,155 However, this reaction is wrought with undesirable side reactions including alkene/alkyne isomerization and intermolecular Rh1′  Rh1 N1 C1 O1   C3 O3  89 aldehyde hydroacylation, whereby C-H activation of the aldehyde substrate is followed by insertion of an additional aldehyde equivalent resulting in ester formation (Tischenko reaction) following reductive elimination (Scheme 2.17).156-158          Scheme 2.17 Proposed aldehyde hydroacylation and intermolecular hydroacylation  As a starting point, we first combined complex 2.22 with benzaldehyde (in the absence of alkene), which to our surprise, resulted in consumption of the organic fragment, providing 0.5 equiv. of benzyl benzoate and regeneration of 2.22 (Scheme 2.18). By contrast, Wilkinson’s catalyst, RhCl(PPh3)3 reacts with benzaldehyde to provide the corresponding decarbonylation product, trans-RhCl(CO)(PPh3)2 along with benzene.159 This result highlights the role of the amidate ligand in preventing aldehyde decarbonylation.  R HO [cat]2 R O ROHHIntermolecular Hydroacylation[cat]Aldehyde Hydroacylation (Tischenko Dimerization)R HO R'+ROR' [M]ROR'[M]ROH[M]ROR'[M]ROHR'ROHR'[M]ROORROHROO RHydroacylationTischenkoPathway 90   Scheme 2.18 Reaction of 2.22 with benzaldehyde  Given the success of this screening experiment, we wondered if catalytic turnover could be achieved using complex 2.22. Accordingly 10 mol% of complex 2.22 was combined with a variety of aldehyde substrates containing both electron-donating and –withdrawing groups in C6D6 and allowed to react for 15 h at 22 oC (Table 2.1).             RhNOPPHO+   2.22C6D6, r.t.< 5 minOOHH2.22+0.5 equiv.RhPh3PPh3PPPh3Cl C6H6, 22 oCHO+ RhOCPh3PPPh3Cl+- PPh3(1)(2) 91 Table 2.1 Scope and Limitation of Aldehyde Dimerization (conversions determined by 1H NMR spectroscopy).                 This reaction was found to be tolerant to a variety of aldehydes possessing electron-donating groups (2a-e) including p-CH3-, p-OMe, and 2-naphthaldehyde. Electron-withdrawing substitutents (2g-j) such as p-NO2-, p-Br or pentafluorophenylbenzaldehyde OOHHOOHHOOHHOOHHOOHHBr BrOOHHOOHHO OOOHHF FFFFF FFFFOOHHO2N NO2OOHHPh2PPh2POOHH2a >99% 2b  84% 2c 85%2d 92% 2e 62%2h n.r. 2i n.r.OOHH2j n.r. 2k n.r.2m 7% 2n 7% 2o 3%OOHHAcHN NHAcOOHHMe2N NMe22g n.r.2f n.r.OOHHNN2l 4%RO2R O RO15 h, 25 oC, C6D6HHH 10 mol% [Rh]1 2a-oRh NOPP= [Rh] 92 were not tolerated in this transformation resulting in decomposition of the Rh(I) catalyst (vide infra). In addition, aldehydes containing pendant donor groups such as those present in 2-(diphenylphosphino)- or 2-pyridylbenzaldehyde or aldehydes containing alkyl groups such as cyclohexanecarboxaldehyde or acetaldehyde were not tolerated. Finally, attempts at performing intramolecular Tischenko dimerization using 1,2-benzenedicarboxaldehyde produced the desired lactone 2o in <3% spectroscopic yield. Importantly, control experiments using RhCl(PPh3)3 and benzaldehyde provided no conversion, while use of the sodiated amidate ligand, Na[N(Dipp)C(O)tBu] (10 mol%) and benzaldehyde furnished benzyl benzoate in 33% NMR spectroscopic yield after 15 h at 22 oC, indicating the option of base catalysis.   2.3.2 Isolation of Decarbonylation By-Products  Particularly intriguing was the propensity of electron-poor aldehydes to give decomposed catalyst (by 31P NMR spectroscopy). As such, a C6D6 solution of 2.22 was treated with 1 equiv. of pentafluorobenzaldehyde and monitored by 31P and 19F NMR spectroscopies (Scheme 2.19). In the 31P{1H} NMR spectrum, signals for 2.22 at δ = 51.24 and 56.94 (2JP,P = 55.5 Hz, 1JRh,P = 191.9 Hz) quickly disappeared (< 5 min) and a new signal at δ = 34.7 (1JRh,P = 138.6 Hz) was observed, consistent with the formation of trans-Rh(CO)(C6F5)(PPh3)2 (2.51) This complex was first reported in 1980 by Deacon et al. and was accessed through decarboxylation (CO2 evolution) from the corresponding κ1-O carboxylate complex, Rh(CO)(κ1-O-O2CC6F5)(PPh3)2.160 By 19F NMR spectroscopy, three multiplets at δ = - 139.2, 157.6, and 165.1 additionally corroborate the formation of this carbonyl complex. By 1H NMR spectroscopy, protio ligand was additionally observed. We propose that these products result from 1) aldehyde C-H bond  93 activation providing a Rh-H species (not detected) that undergoes 2) facile deprotonation or reductive elimination, giving amide proligand and finally, 3) decarbonylation to provide the Rh-C6F5 product, which is inactive toward catalysis.   Scheme 2.19 Reaction of 2.22 with pentafluorophenylbenzaldehyde  Another stoichiometric experiment was carried out using a solution of 2.22 and 1 equiv. of the chelating substrate, 2-(diphenylphosphino)benzaldehyde, which is resistant to decarbonylation (Scheme 2.20).161 Once again, signals for the starting material rapidly disappeared to produce a variety of species. After 15 h of reaction time, the C-H activated complex, Rh{κ2-C,P-(COArPPh2)}(PPh3)2] (2.52) was identified as the major phosphine-containing product. By 31P NMR spectroscopy, one signal was observed at δ = 72.54 (ddd, 1JRh,P = 214.6 Hz, 2JP,P = 40.2 Hz, 2JP,P = 17.9 Hz) for the rhoda(I)cyclic phosphorous atom as well as two overlapping multiplets at δ = 19.72 for the coordinated PPh3 ligands. By 1H NMR spectroscopy, protio ligand is additionally observed.      RhNOPPHOFFFFFRhPPh3PPh3OCF FFFFOOHHF FFFFF FFFFnot detected+ ++ NHtBuiPriPrOC6D6, r.t.< 5 min> 95%2.22 2.51 94  Scheme 2.20 Reaction of 2.22 with 2-(diphenylphosphino)benzaldehyde   2.3.3 Mixed Tischenko Aldehyde Dimerizations   In an effort to expand the scope of dimerization carried out by complex 2.22, we wondered if selective homo- or heterocoupling of two unique aldehydes could be performed (Scheme 2.21). Thus, a 1:1 mixture of p-tolylbenzaldehyde and 2-naphthaldehyde was reacted with 10 mol% 2.22. By 1H NMR spectroscopy, no selectivity was witnessed and instead, a statistical mixture of the four expected homo- and heterocoupled products was produced in > 95% conversion (Scheme 2.21).   Scheme 2.21 Reaction of 2.22 with pentafluorophenylbenzaldehyde  Given that electron-deficient aldehydes underwent rapid C-H bond activation followed by decarbonylation, we next wondered if the C-H activated product could be possibly intercepted by an additional equivalent of an aldehyde bearing an electron-donating group. Thus, a 1:1 mixture of pentafluorobenzaldehyde and p-tolylbenzaldehyde RhNOPPHOPPh2not detected+ ++ NHtBuiPriPrOC6D6, r.t.< 5 min> 95%OOHHPh2PPh2PRhPPh3PPh3OPPh22.22 2.52O15h, 25 oC, C6D6H 10 mol% [Rh]OH +OOOOOOOO> 95% conversion10.39 0.730.93 95 was reacted with 10 mol% 2.22 (Scheme 2.22). By 1H NMR spectroscopy, no desired reaction was observed and Rh(CO)(C6F5)(PPh3)2 was observed as the sole organometallic product ( < 5 min). Scheme 2.22 Reaction of 2.22 with p-tolylbenzaldehyde and pentafluorophenylbenzaldehyde  2.3.4 Reactions with Alkenes and Aldehydes   In an effort to generate the hydroacylation product, benzaldehyde and 1-octene were combined in the presence of 10 mol% 2.22, however in this instance rapid aldehyde dimerization (>95% conversion) along with alkene scrambling to give a mixture of internal n-octene products was observed (Scheme 2.23). Furthermore, treatment of complex 2.22 with a range of alkene substrates including substituted styrenes and internal/terminal aliphatic alkenes gave no reaction. However, complex 2.22 was found to isomerize terminal alkenes to the thermodynamically more stable internal alkene – this is highlighted by reaction of allylbenzene with 2.22, which following isomerization provided a mixture of (E/Z)-methylstyrene products (>95% conversion).			  O15h, 25 oC, C6D6HOH +OOOOOOFOO 10 mol% [Rh]FFFFFFFFFFFFF FFFFFFFFFFF 96          Scheme 2.23 Reaction of 2.22 with benzaldehyde and 1-octene  2.4 Accessing C6F5- or CF3-Substituted Amidate Complexes Having developed a preliminary understanding of these novel complexes, including solution behavior and thermal stability, we wondered how changing the electronic nature of the carbonyl substituent from tBu or Ph to an electron-withdrawing group such as CF3 or C6F5 might alter subsequent reactivity and coordination preference. Furthermore, we wished to probe the thermal stability of the resulting complexes in an attempt to potentially access Rh(I)-CF3 or -C6F5 complexes through isocyanate (RNCO) migration. Though analogous CO2 elimination chemistry has been realized using trans-Rh(κ1-O-O2C(C6F5))(PPh3)2(CO) to give trans-Rh(C6F5)(PPh3)2(CO)160 (75%, 7h, 25 oC), the formation of related Rh(I)-CF3 or -C6F5 scaffolds employing isocyanate deinsertion has not yet, to our knowledge, been realized for any amidate-ligated complex. This new methodolog