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Metal element multiply bonded group 6 complexes with 1,3-N,O-donor ligands Clarkson, Joseph Mitchell 2018

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Metal Element Multiply Bonded Group 6 Complexes with 1,3-N,O-Donor Ligands by  Joseph Mitchell Clarkson  BSc, University of Missouri-Columbia, 2011  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)  February 2018  © Joseph Mitchell Clarkson, 2018   ii  Abstract  This thesis discusses the synthesis and characterization of group 6 complexes that have metal element multiple bonds and 1,3-N,O-donor ligands. Furthermore, the evaluation of the metal-ligand interactions, including hemilability and metal-ligand cooperativity in E-H bond activation processes (where E=C or N), of the 1,3-N,O-donor ligands that resulted in reactivity of the metal element multiple bonds is reported. The 1,3-N,O-donor ligands in this thesis include amidates and pyridonates. The 1,3-N,O-donor ligands were installed on group 6 metals directly from the 1,3-N,O-proligands or as deprotonated sodium salts of the 1,3-N,O-proligands, by protonolysis or salt metathesis reactions respectively. Complexes such as di(1,3-N,O-chelate)bis(t-butylimido)tungsten and di(1,3-N,O-chelate)bis(dimethylamido)molybdenum, were synthesized by protonolysis reactions in chapters 2 and 4 respectively. In chapter 3 di(1,3-N,O-ligated)(neopentylidene)(oxo)tungsten complexes were synthesized by both protonolysis and salt metathesis reactions. These group 6 complexes with 1,3-N,O-donor ligands were characterized by single crystal X-ray diffraction, and in solution by multinuclear NMR spectroscopies, among other analytical methods. The solid-state molecular structures showed κ2-N,O, κ1-O and µ2-N,O bonding modes, highlighting the flexibility of the 1,3-N,O-donor ligands. Solution NMR spectroscopy showed fluxional 1,3-N,O-donor ligands in all complexes at elevated temperatures, further highlighting the hemilability of these ligands.  Throughout this thesis, pyridonate ligands showed more dynamic hemilability relative to amidate ligands. In chapter 2 pyridonate ligands were observed to have κ2-N,O, κ1-O and µ2-N,O bonding modes in the solid state, whereas amidate ligands where iii  exclusively bound in a κ2-N,O in the solid state. Variable temperature 1H-NMR spectroscopy demonstrated that pyridonate ligands were fluxional at temperatures above -40 °C, whereas amidate ligands were fluxional at elevated temperatures (>60 °C). The steric parameters of 1,3-N,O-donor ligands influence how the ligands prefer to bond to the metal. Furthermore the steric demand also influences the hemilability of the 1,3-N,O-donor ligands. The differences in the electronic parameters between amidate and pyridonate ligands influences their hemilability, where pyridonates exhibit more dynamic hemilability in part due to the aryloxy imine motif. The metal-ligand cooperativity of the hemilabile 1,3-N,O-donor ligands towards E-H bond activations (where E=C or N) is reported in this thesis and applications of these processes are discussed.   iv  Lay Summary  Chemists and the public are urging governments and industries to reduce harmful pollutants emitted during or after the production of consumer products. One way to reduce the release of harmful chemical substances into the environment is to use processes that produce inherently less waste. The Schafer lab has developed chemical processes that generates no significantly less chemical waste than traditional processes. Our fundamental approach to understanding the chemical properties of tungsten and molybdenum aims to develop environmentally friendly processes for the synthesis of consumer products. Undertaking these fundamental studies lays a foundation knowledge that will inspiring new breakthroughs in the future. v  Preface  I designed and performed all experiments in this thesis, in consultation with my supervisor Professor Schafer. In some instances, my peers (including past and present fellow graduate students and postdocs in the chemistry department) and members of my committee assisted in the experimental design. The X-ray diffraction data was collected and integrated by either Dr. Jacky Yim, Mr. Scott Ryken, Mr. Damon Gilmour, Dr. Brian Patrick or Mrs. Anita Lam. In some cases, Dr. Brian Patrick assisted in the refinement of challenging or disordered structures and I completed the final refinements in all cases. All mass spectrometry and elemental analysis were conducted by UBC Mass Spectrometry Centre, except for GC/MS where I ran the samples and managed the instrument. Chapter 3 was an extension of Alex Gatien’s undergraduate honors thesis where we worked collaboratively. However, none of Alex’s synthetic methods or complexes are described in this thesis. Alex Gatien synthesized the N-(2,6-dimethylphenyl)pivalamide proligand used in Chapter 4, and Han Hao synthesized 1,1'-(2,2-dimethylpropane-1,3-diyl)bis(3,3-diisopropylurea) proligand in Chapter 4. Most of chapter 2 has been reported in Inorganic Chemistry published by American Chemistry Society as: Clarkson, J. M.; Schafer, L. L. “Bis(tert-butylimido)bis(N,O-chelate)tungsten(VI) Complexes: Probing Amidate and Pyridonate Hemilability” Inorg. Chem. 2017, 56, 5553. I wrote the manuscript with input and editing from Professor Schafer. vi  Table of Contents  Abstract .............................................................................................................................. ii Lay Summary ................................................................................................................... iv Preface .................................................................................................................................v Table of Contents ............................................................................................................. vi List of Tables .................................................................................................................... xi List of Figures ................................................................................................................. xiii List of Schemes ...............................................................................................................xxv Acknowledgements .................................................................................................... xxxvi Dedication .................................................................................................................. xxxvii Chapter 1: Group 6 complexes with metal element multiple bonds; 1,3-N,O-donor ligands in early transition metal complexes.....................................................................1 1.1 Group 6 metal element multiple bonds ............................................................... 2 1.2 Auxiliary ligands supporting group 6 metal element multiple bonds ................. 8 1.2.1 Alkoxides, aryloxides and siloxides ............................................................... 9 1.2.2 Monoanionic nitrogen donating ligands ....................................................... 11 1.2.3 N,O-Donor ligated complexes that support reactive metal-element multiple bonds ....................................................................................................................... 12 1.2.4 Group 6 complexes with 1,3-N,O-donor ligands and metal element multiple bonds ....................................................................................................................... 14 1.3 1,3-N,O-Chelated complexes that support reactive metal-element multiple bonds ........................................................................................................................... 16 vii  1.4 1,3-N,O-donor auxiliary ligands ....................................................................... 17 1.4.1 Synthesis of complexes with 1,3-N,O-donor ligands.................................... 18 1.4.2 Bonding modes ............................................................................................. 19 1.5 Thesis outline .................................................................................................... 21 Chapter 2: Tungsten bis(t-butylimido) complexes with 1,3-N,O-donor ligands: probing amidate and pyridonate hemilability ...............................................................23 2.1 Objectives ......................................................................................................... 23 2.2 Introduction ....................................................................................................... 23 2.3 Results and discussion ...................................................................................... 29 2.3.1 Ligand design ................................................................................................ 29 2.3.2 Tungsten complex synthesis and characterization ........................................ 31 2.3.3 Computational Ground State Geometry Optimization ................................. 34 2.3.4 Solution phase characterization data ............................................................. 37 2.3.5 Reactivity investigations ............................................................................... 40 2.4 Conclusion ........................................................................................................ 57 2.5 Materials and methods ...................................................................................... 58 2.5.1 General methods and materials ..................................................................... 58 2.5.2 Other NMR spectra ....................................................................................... 79 2.5.3 Theoretical calculations ................................................................................ 80 Chapter 3: Tungsten oxo neopentylidene complexes with 1,3-N,O-donor ligands ....87 3.1 Introduction ....................................................................................................... 87 3.2 Synthesis and characterization of tungsten oxo neopentylidene complexes with 1,3-N,O-donor ligands ................................................................................................ 100 viii  3.2.1 Synthesis and characterization of bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten ........................... 100 3.2.1.1 Synthesis and characterization of bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten via protonolysis route ............................................................................................................. 100 3.2.1.2 Synthesis of bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten via salt metathesis route ............................................................................................................. 107 3.2.2 Synthesis and characterization of other bis(N-(2,6-diisopropylphenyl)amidate)(neopentylidene)(oxo)tungsten complexes ................. 109 3.2.2.1 Synthesis of bis(N-(2,6-diisopropylphenyl)-3,5-bis(trifluoromethyl)benzamidate)(neopentylidene)(oxo)tungsten ...................... 111 3.2.2.2 Synthesis of bis(N-(2,6-diisopropylphenyl)acetamidate)(neopentylidene)(oxo)tungsten ........................ 114 3.2.2.3 Synthesis of bis(N-(2,6-diisopropylphenyl)-2,2,2-trifluoroacetamidate)(neopentylidene)(oxo)tungsten ......................................... 117 3.2.3 Variable temperature NMR studies of bis(N-(2,6-diisopropylphenyl)amidate)(neopentylidene)(oxo)tungsten complexes ................. 122 3.2.4 Synthesis and characterization of tungsten(neopentylidene)(oxo) complexes with N-(3,5-bis(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamidate ligands ......... 126 3.2.5 Synthesis of tungsten(neopentylidene)(oxo) complexes with 6-methylpyridonate ligands ........................................................................................ 138 ix  3.3 Reactivity of 1,3-N,O-ligated tungsten oxo alkylidene complexes with olefins ..   ......................................................................................................................... 140 3.4 Conclusions ..................................................................................................... 142 3.5 Materials and methods .................................................................................... 145 Chapter 4: Trials and advances in group 6 mediated hydroaminoalkylation .........168 4.1 Introduction ..................................................................................................... 168 4.1.1 Nitrogen containing compounds: uses and synthesis.................................. 168 4.1.2 Hydroaminoalkylation ................................................................................ 168 4.1.3 Hydroaminoalkylation outlook ................................................................... 175 4.1.4 Group 6 catalyzed hydroaminoalkylation ................................................... 176 4.2 Results and discussion .................................................................................... 180 4.2.1 Reactivity of 4.10 and 1,3-N,O-donor ligated variants ............................... 181 4.2.2 Hydroaminoalkylation trials with other group 6 complexes ....................... 185 4.2.3 Reactivity of 4.6 and 1,3-N,O-donor ligated variants ................................. 186 4.2.4 Solid-state molecular structures of tungsten oxo complexes with dimethylamido ligands ............................................................................................ 195 4.3 Conclusions ..................................................................................................... 201 4.4 Methods and materials .................................................................................... 203 Chapter 5: Conclusions and future works ...................................................................217 5.1 Summary and conclusions .............................................................................. 217 5.1.1 Chapter 2 ..................................................................................................... 217 5.1.2 Chapter 3 ..................................................................................................... 218 5.1.3 Chapter 4 ..................................................................................................... 220 x  5.2 Future work ..................................................................................................... 222 5.2.1 Chapter 2 ..................................................................................................... 222 5.2.2 Chapter 3 ..................................................................................................... 222 5.2.2.1 Group 6 di(1,3-N,O-chelate)(imido)(alkylidene)metal complexes ..... 222 5.2.2.2 Mono amidate tungsten alkylidene complexes ................................... 223 5.2.2.3 1,3-N,O-donor ligand assisted C-H activation .................................... 225 5.2.3 Chapter 4 ..................................................................................................... 226 5.3 Concluding remarks ........................................................................................ 227 Bibliography ...................................................................................................................229 Appendices ......................................................................................................................239 Appendix A ................................................................................................................. 239 Appendix B ................................................................................................................. 240  xi  List of Tables Table 2-1. Selected bond distances and angles for complexes 2.2-2.5. .............................34 Table 2-2. Tabulated 1H-NMR data taken at 25 °C in toluene-d8, 400 MHz. ...................38 Table 2-3. Reactivity of complexes 2.2-2.5 with the respective proligands HL1-HL4. ....44 Table 2-4. Bond distances and bond angles of complex 2.13. ...........................................56 Table 2-5. Energies of computed isomers (Δ only) of complexes 2.2, 2.3, 2.4, and 2.5 and relative energies. 2.2* and 2.5* with dispersion correction. ..............................................81 Table 2-6. Images of computed isomers of complex 2.2. Image* with dispersion correction. ..........................................................................................................................82 Table 2-7. Images of computed isomers of complex 2.3. ..................................................83 Table 2-8. Images of computed isomers of complex 2.4. ..................................................83 Table 2-9. Images of computed isomers of complex 2.5. Image* with dispersion correction. ..........................................................................................................................84 Table 3-1. Selected 1H-NMR resonances of complexes 3.6, 3.7, 3.8 and 3.9. Resonances reported in ppm (δ). .........................................................................................................124 Table 3-2. Ring closing metathesis of 1,7-octadiene with crude material as catalysts (complexes 3.11 and 3.13 were pure materials). 5 mol. % catalyst loading. Conv. are tabulated as percentages. ..................................................................................................141 Table 4-1. Bond distances and angles of complex 4.13. ..................................................189 Table 4-2. Bond distances and angles of complex 4.20. ..................................................195 Table 4-3. Bond distances and angles of complex 4.21. ..................................................201 Table B-1. Crystallographic parameters of complexes 2.2, 2.3 and 2.4. .........................240 Table B-2. Crystallographic parameters of complexes 2.5, 2.6 and 2.8. .........................241 xii  Table B-3. Crystallographic parameters of complexes 2.9, 2.11 and 2.12. .....................242 Table B-4. Crystallographic parameters of complexes 2.13, 3.6 and 3.7. .......................243 Table B-5. Crystallographic parameters of complexes 3.8, 3.10 and 3.11. .....................244 Table B-6. Crystallographic parameters of complexes 3.12, 4.13 and 4.20. ...................245 Table B-7. Crystallographic parameters of complexes 4.10 and 4.21. ............................246  xiii  List of Figures Figure 1-1. Metal ligand π binding interactions of a metal (M) and a ligand (X). ..............2 Figure 1-2. Metal carbon multiple bonds, X=electron donating group.12 ............................3 Figure 1-3. Metal nitrogen multiple bonds. .........................................................................6 Figure 1-4. Molybdenum nitride complex.26 .......................................................................6 Figure 1-5. Metal oxygen and sulfur multiple bonds. ..........................................................7 Figure 1-6. Selected examples of group 6 complexes with metal element multiple bonds. 7 Figure 1-7. Olefin metathesis catalysts with siloxides ligands.34 ......................................11 Figure 1-8. Structurally characterized mono-metallic group 6 complexes with 1,3-N,O-donor ligands and metal element multiple bonds. .............................................................15 Figure 1-9. Group 4 complexes with metal element multiple bonds supported by 1,3-N,O-chelating ligands.61-62 .........................................................................................................16 Figure 1-10. (from left to right) Amide, 2-pyridone, urea, phosphoramide and sulfonamide proligands. .....................................................................................................17 Figure 1-11. Synthesis of 1,3-N,O-chelate sodium salts by deprotonation of proligands by sodium bis(trimethylsilyl)amide. .......................................................................................19 Figure 1-12. Bonding modes of 1,3-N,O-donor ligands.65 ................................................19 Figure 1-13. Examples of 1,3-N,O-donor ligand bonding modes in the solid state. Substituents on amidate ligands in complex B not shown.68-69 .........................................20 Figure 2-1. Observed binding modes of 1,3-N,O-donor ligands, which highlight ligand hemilability. .......................................................................................................................24 xiv  Figure 2-2. 6-methylpyridonate (HL1) κ2-N,O and κ1-O bonding modes (left), 3-methylpyridonate (HL2) κ2-N,O and κ1-O bonding modes (right). κ1-O demonstrates the aryloxyimine motif of pyridonate ligands..........................................................................29 Figure 2-3. Amidate κ2-N,O and κ1-O bonding modes. HL3, R1=Ph, R2=tBu; HL4 R1=2,6-diisopropylphenyl, R2= Ph. ...................................................................................30 Figure 2-4. Possible stereoisomers of a di(N,O-chelate)bis(t-butylimido)tungsten complex. Simplified point groups assigned by ignoring the C3 axis of t-butyl groups. ....31 Figure 2-5. Solid-state molecular structures of complexes 2.2-2.5, plotted at 50% ellipsoids and hydrogen atoms and disordered atoms omitted for clarity. ........................33 Figure 2-6. Relative energies of C2 N-trans, C2 O-trans and C1 isomers of bis(N,O-chelate)bis(t-butylimido)tungsten(VI) complexes, energies in kcal/mol and each set of isomers is referenced to its corresponding lowest energy isomer. .....................................35 Figure 2-7. Solid-state molecular structure of complex 2.6, plotted at 50% ellipsoids with most hydrogen atoms omitted for clarity (except H1). Selected bond lengths (Å): W1-O1 = 2.099(6), W1-O2 = 2.077(6), W1-O3 = 1.949(6), W1-N1 = 2.270(7), W1-N4 = 1.918(26, W1-N5 = 1.739(7). Selected bond angles (deg): W1-N5-C50 = 166.7(6), W1-N4-C40 = 137.6(5), O1-W1-N1 = 60.6(2), N5-W1-O2 = 171.7(3), N1-W1-N5 = 91.5(3).............................................................................................................................................42 Figure 2-8. Solid-state molecular structure of complex 2.8, plotted at 50% ellipsoids and hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N1 = 1.744(2), W1-N2 = 1.737(3), W1-N3 = 2.120(3), W1-O1 = 2.166(3), W1-Cl1 = 2.3573(8). Selected bond angles (deg): W1-N1-C1 = 163.2(2), W1-N2-C5 = 170.1(3), O1-W1-N1 = 122.3(1), O1-W1-N2 = 123.3(1), N3-W1-Cl1 = 143.96(7), O1-W1-N3 = 60.11(9). .......................46 xv  Figure 2-9. Solid-state molecular structure of complex 2.9, plotted at 50% ellipsoids and most hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N1 = 1.741(10), W1-N2 = 2.014(19), W1-N3 = 1.89(2), W1-O1 = 2.00(2), W1-Cl1 = 2.502(9), W1-Cl1 = 2.480(3). Selected bond angles (deg): W1-N1-C1 = 170(1), W1-N2-C5 = 141(2), O1-W1-N3 = 66.6(9). ...............................................................................................................47 Figure 2-10. Solid-state molecular structure of complex 2.11, plotted at 50% ellipsoids with all hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N102 = 2.227(9), W1-N103 = 2.22(1), W1-N104 = 1.724(8), W1-O101 = 1.938(6), W1-O102 = 2.103(6), W1-O103 = 2.085(6), W1-Cl1 = 2.498(2). Selected bond angles (deg): W1-N104-C101 = 165.8(8), N104-W1-Cl1 = 171.3(2). ...........................................................50 Figure 2-11. Solid-state molecular structure of complex 2.12, plotted at 50% ellipsoids with hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N1 = 1.744(4), W1-N2 = 1.747(3), W1-N3 = 2.135(4), W1-O1 = 2.146(3), W1-Cl1 = 2.346(1). Selected bond angles (deg): W1-N1-C1 = 161.6(3), W1-N2-C5 = 163.8(3), O1-W1-N1 = 123.0(1), O1-W1-N2 = 125.3(1), N3-W1-Cl1 = 144.5(1), O1-W1-N3 = 61.3(1). ...........................52 Figure 2-12. Solid-state molecular structure of 2.8, coordination geometry shown, all other atoms removed for clairity, with the exception of amidate carbon C15. Trigonal bipyramidal view on left, square based pyramid view on right. ........................................53 Figure 2-13. Overlay of solid state structures of 2.8 and 2.12. Complexes were overlaid using Olex overlay command and matching the W, Cl, and O atoms. Overlay of complex 2.8 and 2.12 shows isostructural complexes that have trigonal bipyramidal coordination geometries. .........................................................................................................................54 xvi  Figure 2-14. Solid-state molecular structure of complex 2.13, plotted at 50% ellipsoids with hydrogen atoms omitted for clarity. ...........................................................................55 Figure 2-15. 400 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.2. ...................60 Figure 2-16. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.2. ...................61 Figure 2-17. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.2. ..61 Figure 2-18. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.3. ...................63 Figure 2-19. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.3. ...................63 Figure 2-20. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.3. ..64 Figure 2-21. 400 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.4. ...................65 Figure 2-22. 101 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.4. .................66 Figure 2-23. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.4. ..66 Figure 2-24. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.5. ...................67 Figure 2-25. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.5. ....................68 Figure 2-26. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.5. ..68 Figure 2-27. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.6. ...................69 Figure 2-28. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.6. ...................70 Figure 2-29. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.6. ..70 Figure 2-30. 400 MHz 1H-NMR spectrum in C7D8 at 25 °C of complex 2.7. ...................71 Figure 2-31. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.7. ..72 Figure 2-32. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.8. ...................73 Figure 2-33. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.9. ...................74 Figure 2-34. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.11. .................75 Figure 2-35. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.12. .................76 xvii  Figure 2-36. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.13. .................78 Figure 2-37. 300 MHz 1H-NMR in toluene-d8 of the reaction of complex 2.2 with complex 2.3. .......................................................................................................................79 Figure 2-38. 400 MHz 1H-NMR variable temperature spectra in toluene-d8 of the reaction of complex 2.4 with one equivalent of proligand HL3. At lower temperatures, proligand HL3 precipitates out of solution. .......................................................................................79 Figure 2-39. 400 MHz 1H-NMR variable temperature spectra in toluene-d8 of the reaction of complex 2.5 with one equivalent of proligand HL4. At lower temperatures, proligand HL4 precipitates out of solution. .......................................................................................80 Figure 2-40. Overlay of DFT computed and solid-state molecular structure of complex 2.2. Hydrogen atoms are omitted in both the computed and solid-state molecular structures. Left; overlay of DFT without dispersion correction, Right; overlay of DFT with dispersion correction. .................................................................................................84 Figure 2-41. Overlay of DFT computed and solid-state molecular structure of complex 2.3. Hydrogen atoms are omitted in both the computed and solid-state molecular structures. ...........................................................................................................................85 Figure 2-42. Overlay of DFT computed and solid-state molecular structure of complex 2.4. Hydrogen atoms are omitted in both the computed and solid-state molecular structures. ...........................................................................................................................85 Figure 2-43. Overlay of DFT computed and solid-state molecular structure of complex 2.5. Hydrogen atoms are omitted in both the computed and solid-state molecular structures. Left; overlay of DFT without dispersion correction, Right; overlay of DFT with dispersion correction. .................................................................................................86 xviii  Figure 3-1. i) General olefin metathesis reaction, ii) cross metathesis reaction of 1-pentene, iii) ring closing metathesis of 1,7-octadiene, iv) ring opening metathesis polymerization of norbornene. ...........................................................................................88 Figure 3-2. (left) Bis(carboxylate)(alkylidene)(imido)molybdenum complex, (right) hemilabile 1,3-O,O-donor ligand with PMe3 coordinated in the revealed coordination site. Ar= 2-tBuC6H4. ..................................................................................................................95 Figure 3-3. Solid-state molecular structure of complex 3.6, plotted at 50% ellipsoids with most hydrogen atoms and disordered amidate ligand omitted. Selected bond distances (Å); W1-N2A=2.12(2), W1-O3A=2.28(1), W1-N1=2.138(5), W1-O2=2.280(5), W1-O1=1.684(4), W1-C1=1.934(6), C6-O2=1.289(9), C6-N1=1.329(8), C25A-O3A=1.27(2), C25A-N2A=1.33(2). Selected bond angles (°); O3A-W1-N2A=59.4(6), O2-W1-N1=59.3(2), W1-C1-C2=139.3(5). ..................................................................................103 Figure 3-4. Overlay of the solid-state molecular structures of complexes 2.5 and 3.6, plotted at 50% ellipsoids with most hydrogen atoms and disordered ligands omitted. ...104 Figure 3-5. (left) amide with N-2,6-diisopropylphenyl substituent with tunable amide X substituent, (middle) typical bis(N-2,6-diisopropylphenyl amidate)(L)2 metal complex (L=ligand, M=Ti, Zr, Hf, Mo, W), (right) proposed N-trans bis(amidate)(neopentylidene)(oxo)tungsten complex.70 ..................................................110 Figure 3-6. 1,3-N,O-proligands with N-(2,6-diisopropylphenyl)amides. ........................110 Figure 3-7. Solid-state molecular structure of complex 3.7, plotted at 50% ellipsoids with most hydrogen atoms, green ellipsoids are fluorine atoms. Selected bond distances (Å); W1-N1=2.133(2), W1-O3=2.262(2), W1-N2=2.099(2), W1-O4=2.271(2), W1-O1=1.692(2), W1-C1=1.924(3), C6-O3=1.286(3), C6-N1=1.318(4), C27-O4=1.275(3), xix  C27-N2=1.335(3). Selected bond angles (°); O4-W1-N2=59.88(8), O3-W1-N1=59.19(8), W1-C1-C2=139.9(2). .......................................................................................................114 Figure 3-8. Solid-state molecular structure of complex 3.8, plotted at 50% ellipsoids with most hydrogen atoms and disordered amidate ligand omitted. Selected bond distances (Å); W1-N1=2.093(4), W1-O1=2.277(3), W1-N2=2.131(4), W1-O2=2.263(4), W1-O3=1.692(4), W1-C1=1.901(5), C6-O1=1.273(6), C6-N1=1.322(6), C20-O2=1.286(6), C20-N2=1.320(7). Selected bond angles (°); O1-W1-N1=59.4(1), O2-W1-N1=59.3(1), W1-C1-C2=140.2(4). .......................................................................................................116 Figure 3-9. Solid-state molecular structure of complex 3.10, plotted at 50% ellipsoids with most hydrogen atoms and disordered amidate ligand omitted. Selected bond distances (Å); W1-N1=2.164(3), W1-O1=2.406(4), W1-P1=2.542(1), W1-O2=2.051(3), W1-O3=1.700(4), W1-C1=1.930(7), C6-O1=1.264(6), C6-N1=1.311(7), C20-O2=1.320(6), C20-N2=1.258(6). Selected bond angles (°); O1-W1-N1=57.7(1), W1-C1-C2=142.9(4). ....................................................................................................................118 Figure 3-10. Variable temperature 300 MHz 1H-NMR spectra in C7D8 of complex 3.10, crude material used. .........................................................................................................121 Figure 3-11. Variable temperature 1H-NMR spectra in C7D8 of complexes 3.6, 3.7, 3.8 and 3.10. Spectra are zoomed to the isopropyl methine region. ......................................125 Figure 3-12. Solid-state molecular structure of complex 3.11, plotted at 50% ellipsoids with most hydrogen atoms omitted. Selected bond distances (Å); W1-N1=2.278(2), W1-O1=2.327(2), W1-O2=2.053(2), O2-C16=1.319(3), C16-N2=1.269(3), W1-O3=1.695(2), W1-C1=1.926(2). .............................................................................................................128 xx  Figure 3-13. Variable temperature 400 MHz 1H-NMR and spectra in C7D8 of the crude reaction products of 3.4 and 2 equivalents of NaL8. a) full 1H-NMR spectra δ 0.5-13.0, b) zoom of alkylidene region from δ 10.0-11.7. Ar=3,5-bis(trifluoromethyl)phenyl. .........130 Figure 3-14. Solid-state molecular structure of complex 3.12, plotted at 50% ellipsoids with most hydrogen atoms omitted and phosphine substituents as wire frame for clarity...........................................................................................................................................131 Figure 3-15. Solid-state molecular structure of 3.13, atoms shown as an isotropic ball and stick with model most hydrogen atoms omitted. .............................................................137 Figure 3-16. Overlay of complex 3.11 and 3.13, Labels correspond to complex 3.13. Solid-state molecular structure of complex 3.11, plotted at 50% ellipsoids with most hydrogen atoms omitted. Solid-state molecular structure of 3.13, atoms shown as an isotropic ball and stick with model most hydrogen atoms omitted. ................................138 Figure 3-17. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.6. Dipp=2,6-diisopropylphenyl. ...........................................................................................................148 Figure 3-18. 13C-NMR 75 MHz spectrum in C6D6 of complex 3.6. Dipp=2,6-diisopropylphenyl. ...........................................................................................................148 Figure 3-19. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.6, crude material used. Dipp=2,6-diisopropylphenyl. .........................................................149 Figure 3-20. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.7. Dipp=2,6-diisopropylphenyl, Ar=3,5-bis(trifluoromethyl)phenyl. ..................................................150 Figure 3-21. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.7. Dipp=2,6-diisopropylphenyl, Ar=3,5-bis(trifluoromethyl)phenyl. ..................................................151 xxi  Figure 3-22. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.7, crude material used. Dipp=2,6-diisopropylphenyl. .........................................................152 Figure 3-23. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.8. Dipp=2,6-diisopropylphenyl. ...........................................................................................................153 Figure 3-24. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.8, crude material used. Dipp=2,6- diisopropylphenyl. ........................................................154 Figure 3-25. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.9. Dipp=2,6-diisopropylphenyl. ...........................................................................................................155 Figure 3-26. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.9. Dipp=2,6-diisopropylphenyl. ...........................................................................................................156 Figure 3-27. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.10. Dipp=2,6-diisopropylphenyl. ...........................................................................................................157 Figure 3-28. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.10. Dipp=2,6-diisopropylphenyl. ...........................................................................................................158 Figure 3-29. 31P-NMR 121 MHz spectrum in C6D6 of complex 3.10. Dipp=2,6-diisopropylphenyl. ...........................................................................................................158 Figure 3-30. Variable temperature 282 MHz 19F-NMR spectra in C7D8 of complex 3.10, crude material used. Dipp=2,6-diisopropylphenyl. .........................................................159 Figure 3-31. 1H-NMR 400 MHz spectrum in C7D8 of complex 3.11. Ar=3,5-bis(trifluoromethyl)phenyl. ..............................................................................................160 Figure 3-32. 19F-NMR 282 MHz spectrum in C7D8 of complex 3.11. Ar=3,5-bis(trifluoromethyl)phenyl. ..............................................................................................161 xxii  Figure 3-33. 31P-NMR 162 MHz spectrum in C7D8 of complex 3.11. Ar=3,5-bis(trifluoromethyl)phenyl. ..............................................................................................161 Figure 3-34. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.11, crude material used. Ar=3,5-bis(trifluoromethyl)phenyl. ................................................162 Figure 3-35. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl. ..............................................................................................163 Figure 3-36. 13C-NMR 101 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl. ..............................................................................................164 Figure 3-37. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl. ..............................................................................................164 Figure 3-38. 31P-NMR 121 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl. ..............................................................................................165 Figure 3-39. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.14 in the reaction solvent after filtration. ......................................................................................................166 Figure 3-40. 1H-NMR 300 MHz spectrum in C6D6 of isolated solid material from synthesis of 3.14...............................................................................................................166 Figure 3-41. 1H-NMR spectrum of the RCM catalytic trail with complex as the catalyst...........................................................................................................................................167 Figure 4-1. Recently reported precatalysts for the hydroaminoalkylation reaction. ........175 Figure 4-2. Solid-state molecular structure of complex 4.13, ellipsoids shown at 50% with all hydrogen atoms omitted......................................................................................188 Figure 4-3. Complexes 4.14 and 4.15. .............................................................................190 xxiii  Figure 4-4. Solid-state molecular structure of complex 4.20, ellipsoids shown at 50% with all hydrogen atoms omitted......................................................................................194 Figure 4-5. Solid-state molecular structure of complex 4.10, plotted at 50% ellipsoids with all hydrogen atoms omitted. Selected bond distances (Å); W1-O1=1.708(2), W1-N1=1.9934(14), W1-N2=1.9896(14). ..............................................................................197 Figure 4-6. Hydrogen hydrogen distances shown with a white bond, the distance was ~2.6 Å. .............................................................................................................................198 Figure 4-7. π bonding interaction in 4.10. .......................................................................199 Figure 4-8. Solid-state molecular structure of complex 4.21, plotted at 50% ellipsoids with all hydrogen atoms omitted......................................................................................200 Figure 4-9. 1H-NMR 300 MHz spectrum of complex 4.11 in C6D6. ...............................204 Figure 4-10. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using 4.11 as a potential catalyst. .............................................................................................................205 Figure 4-11. 1H-NMR 400 MHz spectrum of complex 4.11 with B(C6F5)3 in C6D6. .....206 Figure 4-12. 1H-NMR 300 MHz spectrum of complex 4.11 with B(C6F5)3 in C6D6 after hydroaminoalkylation trial. ..............................................................................................207 Figure 4-13. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using W(NtBu)2(NHtBu)2 as a potential catalyst. .....................................................................208 Figure 4-14. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using complex 1 as a potential catalyst. ...................................................................................................209 Figure 4-15. 1H-NMR 400 MHz spectrum of complex 4.13 in C6D6. .............................210 Figure 4-16. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using complex 4.13 as a potential catalyst. ..............................................................................................211 xxiv  Figure 4-17. 1H-NMR 300 MHz spectrum of complex 4.19 in C6D6. .............................212 Figure 4-18. 1H-NMR 400 MHz spectrum of complex 4.18 in C6D6. .............................213 Figure 4-19. 1H-NMR 400 MHz spectrum of complex 4.17 in C6D6. .............................214 Figure 4-20. 1H-NMR 400 MHz spectrum of complex 4.16 in C6D6. .............................215 Figure 4-21. 1H-NMR 400 MHz spectrum of hydroaminoalkylation product in CDCl3.216 Figure 5-1. Proposed group 6 di(1,3-N,O-chelate)(imido)(alkylidene)metal (where metal is Mo or W). Pyr=pyrrolide. ............................................................................................223  xxv  List of Schemes Scheme 1-1. Examples of industrialized group 6 catalyzed reactions.1-2 ........................... 1 Scheme 1-2. Selected example of the synthesis of a carbene ligated complex.16 ............... 4 Scheme 1-3. C-H activation of tetramethylsilane by a tungsten alkylidene complex.20 ..... 4 Scheme 1-4. Cyclic polymers from alkynes initiated by tungsten alkylidene complex.21 . 5 Scheme 1-5. Selected example of the synthesis of a nitrido ligated complex. Ar=3,5-dimethylphenyl.24-25 ............................................................................................................ 6 Scheme 1-6. Selected examples for the synthesis of oxo and sulfido ligated complexes.28 7 Scheme 1-7. Selected examples for the synthesis of alkylidene, alkylidyne and imido ligated complexes. Ar=2,6-diisopropylphenyl.30 ................................................................ 8 Scheme 1-8. Olefin metathesis catalyst undergoing Z-Selective 2+2 reaction and reversion. M=Mo or W, R1=2,6-diisopropylphenyl, R2=n-hexyl, Trip=2,4,6-iPr-C6H2.3110 Scheme 1-9. Aryloxide tungsten complexes that undergo 4 electron reductions of dioxygen and azobenzene.33.............................................................................................. 10 Scheme 1-10. Reactivity of 1.22 (a masked Mo(III) complex).35 .................................... 12 Scheme 1-11. Example of N,O-donor ligated di(oxo)molybdenum complex that undergoes oxygen atom transfer. ...................................................................................... 13 Scheme 1-12. Reaction of nucleophilic alkylidene with CO2.51 ....................................... 14 Scheme 1-13. Synthesis of complex 1.34.59 ..................................................................... 15 Scheme 1-14. Hydroamination of primary amines and terminal alkynes catalyzed by a titanium complex with 1,3-N,O-donor ligands. Catalytically active titanium imido species supported by 1,3-N,O-donor ligands. ................................................................................ 17 xxvi  Scheme 1-15. Synthesis of di(1,3-N,O-chelate)bis(dimethylamido)metal complexes by protonolysis (above) and salt metathesis (below) routes.64 .............................................. 18 Scheme 1-16. Characterized examples of hemilabile amidate complexes.72-73 ................ 21 Scheme 2-1. Hydrofunctionalization of A. Depending upon the 1,3-N,O-donor employed the hydroaminoalkylation (HAA) or the hydroamination (HA) product can be preferentially accessed. This change in product distribution has been proposed to be rationalized by ligand hemilability.66, 102 .......................................................................... 26 Scheme 2-2. Synthesis of 1,3-N,O-donor ligated tungsten complexes via protonolysis reactions (above), and corresponding proligands (below). ............................................... 28 Scheme 2-3. Proposed reaction of lutidinium hydrochloride with bis(amidate) complexes 2.4 and 2.5. Left; addition of HCl to tungsten complex, right; protonolysis of amidate ligand................................................................................................................................. 45 Scheme 2-4. Reaction of complex 2.10 with proligand HL3. The reaction was conducted in benzene-d6 in an NMR tube with a resealable cap. ...................................................... 48 Scheme 2-5. Reaction of 2.2 with lutidinium hydrochloride. ........................................... 50 Scheme 2-6. Synthesis of 2.12 by the reaction of 2.2 with TMSCl. ................................. 51 Scheme 2-7. Synthesis of 2.12 by the reaction of 2.2 with TMSCl. ................................. 54 Scheme 3-1. Synthesis of complex 3.1.18 ......................................................................... 89 Scheme 3-2. Olefin cross metathesis mechanism of the homo-coupling of substituted terminal alkenes, (i) Schrock type catalyst; M=Mo or W, E=O or NR, R= substrate group, X and Y=mono anionic ligands, example of a highly active olefin metathesis catalyst 1.17. Dipp=2,6-diisopropylphenyl. ................................................................................... 91 xxvii  Scheme 3-3. Reductive coupling of neopentylidene ligands to form a ditungsten complex and 1,2-di-tert-butylethylene. ........................................................................................... 92 Scheme 3-4. Reaction of ethylene with a group 6 alkylidene, which initially forms a TBP metallacyclobutane and then isomerizes to a SP metallacyclobutane, which undergoes β-hydride elimination. .......................................................................................................... 93 Scheme 3-5. Stabilization of air and moisture sensitive olefin metathesis catalyst with 2,2´-bipyridine.185 .............................................................................................................. 94 Scheme 3-6. Mechanism of the titanium catalyzed intermolecular hydroamination of primary amines and terminal alkynes, highlighting the hemilability of the 1,3-N,O-donor ligands.101 Dipp = 2,6-diisopropylphenyl. ........................................................................ 97 Scheme 3-7. Hemilabile 1,3-N,O-chelating ligands  bonding mode interconversion and corresponding electron count at the tungsten metal center. Highlighting the necessary generation of unsaturated species capable of participating in the olefin metathesis accepted mechanism. N-trans isomer show as representative complex. .......................... 98 Scheme 3-8. (top) Protonolysis reaction of complex 3.2 with a substituted thiophenol producing complex 3.3, (bottom) Salt metathesis reaction of complex 3.4 with a lithium aryloxide producing complex 3.5.184, 194 ........................................................................... 99 Scheme 3-9. Protonolysis reaction of 3.2 and two equivalents of proligand HL6. Dipp=2,6-diisopropylphenyl, PyrMe2=2,5-dimethylpyrrole. ......................................... 101 Scheme 3-10. Salt metathesis reaction of 3.4 with two equivalents of NaL4. Dipp=2,6-diisopropylphenyl. .......................................................................................................... 107 Scheme 3-11. Optimized synthesis of complex 20. ........................................................ 108 xxviii  Scheme 3-12. Salt metathesis reaction for the synthesis of complexes 3.6, 3.7, 3.8 and 3.9. Ar=3,5-bis(trifluoromethyl)phenyl, Dipp=2,6-diisopropylphenyl. ......................... 111 Scheme 3-13. Synthesis of complex 3.7. Ar=3,5-bis(trifluoromethyl)phenyl, Dipp=2,6-diisopropylphenyl. .......................................................................................................... 112 Scheme 3-14. Synthesis of complex 3.8. Ar=3,5-bis(trifluoromethyl)phenyl, Dipp=2,6-diisopropylphenyl. .......................................................................................................... 115 Scheme 3-15. Salt metathesis reaction of 3.10 and NaL7. Dipp=2,6-diisopropylphenyl.......................................................................................................................................... 117 Scheme 3-16. Reversible phosphine coordination of complex 3.9. Sequestering phosphine with CuBr. ....................................................................................................................... 121 Scheme 3-17. Salt metathesis reaction of 3.4 and two equivalents of NaL8. Ar=3,5-bis(trifluoromethyl)phenyl. ............................................................................................. 126 Scheme 3-18. Decomposition of complex 3.11 to form complex 3.12 and proteoligand HL8. Ar=3,5-bis(trifluoromethyl)phenyl. ....................................................................... 132 Scheme 3-19. Reaction of PMe3 with a bis(carboxylate)(alkylidene)(imido)tungsten complex. .......................................................................................................................... 134 Scheme 3-20. Reaction of 3.2 with two equivalents of HL8. Ar=3,5-bis(trifluoromethyl)phenyl and HPyrMe2=2,5-dimethylpyrrole. .................................... 136 Scheme 3-21. Protonolysis reaction of proligand HL8 and 3.2 in quantitative yield Ar=3,5-bis(trifluoromethyl)phenyl and HPyrMe2=2,5-dimethylpyrrole. ....................... 136 Scheme 3-22. Complex 3.13 does not undergo ligand redistribution of amidate and 2,5-dimethylpyrolide ligands. Ar=3,5-bis(trifluoromethyl)phenyl. ...................................... 137 Scheme 3-23. Salt metathesis reaction of 3.4 and two equivalents of NaL1. ................. 139 xxix  Scheme 3-24. Reductive coupling of alkylidene fragments, forming a double bonded ditungsten complex. ........................................................................................................ 140 Scheme 4-1. General hydroaminoalkylation reaction.97 ................................................. 168 Scheme 4-2. First report of hydroaminoalkylation. Reactions were conducted at 20 atm.90......................................................................................................................................... 169 Scheme 4-3. Hydroaminoalkylation of 1-pentene with dimethylamine, reactions were conducted in sealed tubes.91 ............................................................................................ 170 Scheme 4-4. Hydrogen-Deuterium exchange in the presence of catalytic amounts of metal dimethylamido complexes. Hydrogen-Deuterium exchange reactions were conducted at 160 °C over a 14 hour period with 2 mol% catalyst loading. The W(NMe2)n was a 2:1 mixture of W2(NMe2)6 and W(NMe2)6 respectively.91 ................................... 170 Scheme 4-5. Proposed mechanism of the hydroaminoalkylation reaction.91 ................. 171 Scheme 4-6. α-alkylation of benzylamine mediated by a zirconocene complex.214 ....... 172 Scheme 4-7. Tungsten(VI) C-H activation alpha to nitrogen.238 .................................... 177 Scheme 4-8. Molybdenum(IV) complex that undergoes C-H activation alpha to nitrogen.239 ...................................................................................................................... 178 Scheme 4-9. Molybdaziridine formation from a molybdenum(III) complex.35 ............. 178 Scheme 4-10. Proposed synthetic routes into (1) (1,3-N,O-ligated)tris(dimethylamido)(oxo)tungsten(VI) and (2) di(1,3-N,O-ligated)bis(dimethylamido)molybdenum(IV) complexes. .............................................. 181 Scheme 4-11. Hydroaminoalkylation of 1-octene with 4-methoxy-N-methylaniline. PMP=p-methoxyphenyl. ................................................................................................. 181 xxx  Scheme 4-12. Protonolysis reaction of 4.10 and HL9 proceed to form the proposed complex 4.11. .................................................................................................................. 182 Scheme 4-13. Reaction of complex 4.11 with B(C6F5)3, 1H-NMR spectrum of immediate reaction products, plausible structure of B(C6F5)3 adduct 4.12. ..................................... 184 Scheme 4-14. Hydroaminoalkylation test reactions with tungsten oxo complexes. PMP=p-methoxyphenyl. ................................................................................................. 185 Scheme 4-15. Hydroaminoalkylation trial reactions using various high valent tungsten species as potential catalysts. PMP=p-methoxyphenyl. ................................................. 186 Scheme 4-16. Synthesis of complex 4.13. ...................................................................... 187 Scheme 4-17. Hydroaminoalkylation trial reaction, cat.= complex 4.13. PMP=p-methoxyphenyl. ............................................................................................................... 191 Scheme 4-18. Optimized conditions for the complex 4.13 meditated α-alkylation of 4-methoxy-N-methylaniline with 1-octene, isolated yield of product 61%. PMP=p-methoxyphenyl. ............................................................................................................... 191 Scheme 4-19. Alkene scope α-alkylation trials. PMP=p-methoxyphenyl. ..................... 192 Scheme 4-20. Hydroaminoalkylation test reactions with complexes 4.16, 4.17, 4.18 and 4.19. PMP=p-methoxyphenyl. ........................................................................................ 193 Scheme 5-1. Protonolysis reaction of 3.2 and one equivalent of proligand HL1. Dipp=2,6-diisopropylphenyl. PyrMe2=2,5-dimethylpyrrole. ......................................... 224 Scheme 5-2. Salt metathesis reaction for the synthesis of a mono(amidate) tungsten complex, which produces a mixture of products including the bis(amidate) complex 3.6, desired mono(amidate) complex 5.1 and proligand HL4. Ratios are below the reaction products. Dipp=2,6-diisopropylphenyl. .......................................................................... 224 xxxi  Scheme 5-3. Synthesis of Schrock type alkylidene complexes from bis(t-butylimido)bis(neopentyl)tungsten.124 ............................................................................ 225 Scheme 5-4. Synthesis of a biphenolate imido alkylidene molybdenum complex.267 .... 226 Scheme 5-5. Proposed synthesis of di(1,3-N,O-chelate) imido alkylidene complexes. M=Mo or W. ................................................................................................................... 226                   xxxii  List of Abbreviations Ad   adamantyl α   alpha et al.   and others Å   angstrom Bn   benzyl br   broad cat.   catalyst δ   chemical shift conv.   conversion CM   cross metathesis Cy   cyclohexyl Cp   cyclopentadienyl °   degrees °C   degrees centigrade Δ   delta; coordination isomer DFT   density functional theory Dipp   2,6-diisopropylphenyl 2D   2-dimensional d   doublet; NMR EI   electron impact EA   elemental analysis equiv.   equivalents xxxiii  η   eta; ligand hapticity exs.   excess e.g.   for example GC/MS  gas chromatograph mass spectrometry g   gram h   hours i.e.   in other words iPr   isopropyl κ   kappa; denticity Λ   lambda; coordination isomer L   liter MS   mass spectrometry m/z   mass-to-charge ratio Me   methyl µL   microliter mg   milligram mL   milliliter mmol   millimole min   minute mol   mole µ   mu; denoted bridging metals m   multiplet; NMR NMR   nuclear magnetic resonance xxxiv  δ+   partial positive charge δ-   partial negative charge ppm   parts per million Cp*   pentamethylcyclopentadienyl Ph   phenyl π   pi; as in pi bond Py   pyridine RCM   ring closing metathesis ROMP   ring opening metathesis polymerization RT   room temperature RBF   round bottom flask vide supra  see above vide infra  see below spt   septet; NMR σ   sigma; as in sigma bond s   singlet; NMR SP   square pyramid temp.   temperature tBu   tert-butyl THF   tetrahydrofuran tol   toluene TBP   trigonal bipyramid TMS   trimethylsilyl xxxv  t   triplet; NMR VT   variable temperature xxxvi  Acknowledgements  Firstly, I would like to acknowledge Prof. Laurel Schafer for her support of me and this thesis. Thank you Laurel for mentoring me, you have a way of dissipating doubt from my mind and encouraging me to produce the best work possible.   Thank you to my wife, Monica Clarkson, your support during my thesis was invaluable, I cannot imagine how I would have accomplished this without you. I also would like to thank my family, specifically Doris, Flossie, Rock, Meredith, Emily, Barbara, Justin and Nathan, Andi, Charlie, Susan and family, Erin, Dolores, Richard, Aman and Rebecca, and Michelle for their moral and financial support.   Thank you to all my friends for support throughout my thesis, particularly James and Amy, Scott and Lucie, JM and Nat, Andi and Nicole, Pippa, Travis, Diana, John, Aaron, Jeff and Hannah, Damon, Mitch, Nirmal, and Julia. I want to thank all my past and present group members for their support, input, and assistance throughout my time in graduate school.  I would also like to thank my thesis committee for all their help along the years. I would like to thank the tax payers of Canada (through NSERC and Mitacs), as well as TBF Environmental Incorporated (particularly Mike McLean and Dave Pasin) for their financial support. Thank you to UBC Chemistry shops and services for their excellent work in supporting the research in the department. xxxvii  Dedication This thesis is dedicated to Donald and Florence Jack, and Robert and Doris Clarkson.1  Chapter 1: Group 6 complexes with metal element multiple bonds; 1,3-N,O-donor ligands in early transition metal complexes  The chemistry and properties of group 6 transition metals are exploited in a variety of applications from the industrial production of polyethylene to turning on a light bulb. The Phillips catalyst, which is chromium oxide on a silica surface, has been used to produce approximately 50% of the world’s supply of high density polyethylene (Scheme 1-1).1 The Shell Higher Olefin Process (SHOP) employs a molybdenum olefin metathesis catalyst to produce internal linear olefins (Scheme 1-1), which have been used as precursors for plasticizers and detergents on a scale of over 1 million tons annually.2   Scheme 1-1. Examples of industrialized group 6 catalyzed reactions.1-2 Tungsten filaments have been used in light bulbs since the 1920s. These examples all involve group 6 metal element multiple bonds in some part of their mechanism or production.  The study of metal element multiple bonds has been of interest to chemists for decades. A group 6 metal element multiple bond refers to a chemical bond of bond order > 1 between a group 6 metal (chromium, molybdenum or tungsten) and a non-metal element, typically carbon, nitrogen, oxygen, or sulfur. 2   1.1 Group 6 metal element multiple bonds  Group 6 complexes that bear metal element multiple bonds have been of interest to chemists for decades due to their rich reactivity profiles. The bonding within metal element multiple bonds can be characterized into three general types of π bonding; donation of electrons from a ligand orbital into an empty metal orbital (I, Figure 1-1), back bonding from electrons from a metal orbital into an empty orbital on a ligand (II, Figure 1-1), and a covalent interaction where the π bond has formed from a pairing of electrons, one electron from each of the metal and ligand orbitals (III, Figure 1-1).3 The most common elements incorporated into group 6 metal element multiple bonds have been carbon, nitrogen, oxygen or sulfur bonds.4-6  Figure 1-1. Metal ligand π binding interactions of a metal (M) and a ligand (X).  Metal carbon multiple bonds include metal carbene,7 metal alkylidene8 and metal alkylidyne9 bonds (Figure 1-2), carbyne ligands are also known but will not be discussed further in this thesis.10-11  3   Figure 1-2. Metal carbon multiple bonds, X=electron donating group.12 The neutral donor metal carbene bonds (Fischer carbenes, vide infra) are most common with low valent metal species and the π bonding is best described as π back bonding of electrons in a metal orbital into an empty orbital on the carbene ligand (II, Figure 1-1).12  The neutral donor carbene ligand can only form a double bond if there is sufficient electrons on the metal to π back bond into a ligand orbital. This bond has been described as being polarized by having δ- on the metal atom and δ+ on the carbene carbon.13 Conversely the alkylidene and alkylidyne ligands form double and triple bonds respectively, where the metal has typically been high valent with the metal carbon bond being polarized by having δ+ on the metal atom and δ- on the alkylidene/alkylidyne carbon.13 The alkylidene ligands are dianionic carbon atoms with sp2 hybridization, whereas alkylidyne ligands are trianionic carbon atoms with sp hybridization.   In both cases the unhybridized p orbitals of the carbon atom form the π bonds with the metal center.8 The description of π bonding in group 6 metal element multiple bonds has traditionally been thought of as a C2- bonding to a M2+ where the π bonding would resemble type I (Figure 1-1). However, Covalent Bond Classification describes anionic π donors as a covalent type III bond (Figure 1-1).14 It is important to note that the amount of covalency between a metal and its multiply bonded partner increases as the differences in electronegativity decrease. Thus, the covalency of the metal element multiple bonds can 4  be ranked as carbon > nitrogen > oxygen.15 In this thesis all anionic metal element multiple bonds are considered as type I (Figure 1-1).  The synthesis and reactivity of group 6 metal carbon multiple bonds is briefly discussed here. In 1964 Fischer et al. reported the first metal carbon double bond, which was a tungsten carbene complex 1.1 (Scheme 1-2).16 This complex has been prepared by treating methyl lithium with a tungsten carbonyl complex. Subsequent methylation of the ate complex 1.1 has resulted in the neutral carbene complex 1.2 shown in Scheme 1-2. The reactivity of this class of complexes includes the cyclopropanation of alkenes using chromium, molybdenum and tungsten Fischer carbene complexes.7, 17  Scheme 1-2. Selected example of the synthesis of a carbene ligated complex.16  Alkylidene and alkylidyne ligands are formed by α-hydrogen abstraction processes.18-19 An example of alkylidene formation by Legzdins et al. can be seen in Scheme 1-3, where a bis(neopentyl)tungsten complex (1.3) eliminates neopentane forming a neopentylidene complex (1.4) via an α-hydrogen abstraction.20 This example is interesting since the generated alkylidene species can facilitate a C-H activation reaction of tetramethylsilane and reform a bis(alkyl) tungsten complex (1.5, Scheme 1-3).20  Scheme 1-3. C-H activation of tetramethylsilane by a tungsten alkylidene complex.20 5   In 2016, Veige et al. reported a tungsten alkylidyne complex (1.6, Scheme 1-4) capable of polymerizing alkynes into cyclic polymers.21  In Scheme 1-4 complex 1.6 has been transformed into complex 1.7 upon addition of alkyne. Further insertion into the resulting metallacyclopropene forms a larger metallacycle that is eventually closed into a ring by reductive elimination. This unique reactivity highlights expanded reactivity pathways of group 6 metal carbon multiple bonds brought about by ligand design.21   Scheme 1-4. Cyclic polymers from alkynes initiated by tungsten alkylidene complex.21   Nitrogen donating ligands that form metal ligand multiple bonds include amido, imido and nitrido ligands (Figure 1-3). Amido ligands are monoanionic and can be either sp3 or sp2 hybridized. When sp2 hybridized, amido ligands can form π bond by donation of the nitrogen lone pair in a p orbtial into an appropriate metal orbital (Type I, Figure 1-1). Imido ligands are dianionic and can be either sp2 or sp hybridized.22 When the nitrogen atom has sp hybridization it can form a triple bond (one σ and two π bonds), the π bonds again donate from filled nitrogen p orbitals as Type I shown in Figure 1-1, analogous to the π bonding in the amido ligands. The nitrido ligand is a trianionic ligand that has sp hybridization and can form a triple bond.23 6   Figure 1-3. Metal nitrogen multiple bonds.  One example by Cummins et al. demonstrates the synthesis of a molybdenum(VI) nitrido complex (1.9) by the reaction of a tri(amido)molybdenum(III) complex (1.8) with dinitrogen (Scheme 1-5).24   Scheme 1-5. Selected example of the synthesis of a nitrido ligated complex. Ar=3,5-dimethylphenyl.24-25 A recent example of group 6 metal nitrogen multiple bond reactivity has been reported by Schrock et al., where a molybdenum nitrido complex (1.10, Figure 1-4) is catalytically active for the reduction of dinitrogen to ammonia.26  Figure 1-4. Molybdenum nitride complex.26  Ligands such as alkoxides (OR) and thiolates (SR) can also form π bonds when the donating atoms have sp2 or sp hybridization (Figure 1-5), such interactions are described as type I bonding in Figure 1-1.12 Oxo and the sulfido ligands are analogous to imido ligands and can form double and triple bonds (Figure 1-5).27 7   Figure 1-5. Metal oxygen and sulfur multiple bonds. An effective route into oxo and sulfido complexes has been the reaction of metal chloride starting materials with a silyl ether or silyl thioether (Scheme 1-6).28  Scheme 1-6. Selected examples for the synthesis of oxo and sulfido ligated complexes.28  Interestingly, nature exploits molybdenum oxo and sulfido ligands in atom transfer reactions using molybdenum cofactors in a variety of enzymes to mediate oxygen atom transfer reactions and redox processes in biological systems.29 An example of a molybdenum cofactor (1.11) that contains both terminal oxo and sulfido ligands has been shown in Figure 1-6.  Figure 1-6. Selected examples of group 6 complexes with metal element multiple bonds.  In 1986 Schrock et al. reported a tungsten imido alkylidene complex (1.17, Scheme 1-7), an excellent olefin metathesis catalyst that was capable of catalyzing the metathesis of select substrates at ~1000 turnovers per minute at 25 °C.30 The synthesis of 1.17 is an illustrative example of the formation and transformation of metal element multiple bonds 8  including alkylidene, alkylidyne and imido ligands. First the alkylidyne is formed when alkylating complex 1.12 with 6 equivalents of neopentyl magnesium chloride (Scheme 1-7), and the tris(neopentyl)(neopentylidyne)tungsten complex 1.13 has been formed by α-hydrogen abstraction reactions. Addition of 3 equivalents of HCl to complex 1.13 results in ligand substitution to remove the neopentyl ligands giving complex 1.14 (Scheme 1-7). An amido ligand has been installed by the reaction of 1.14 with a silylamine to form complex 1.15 (Scheme 1-7). The imido ligand is then formed by a tautomerization of the amido alkylidyne complex to an imido alkylidene tungsten complex (1.16) using 10 mol% of triethylamine as a catalyst (Scheme 1-7). Lastly, salt metathesis reactions are used to install the auxiliary ligands which forms the excellent olefin metathesis catalyst complex 1.17 (Scheme 1-7).  Scheme 1-7. Selected examples for the synthesis of alkylidene, alkylidyne and imido ligated complexes. Ar=2,6-diisopropylphenyl.30 1.2 Auxiliary ligands supporting group 6 metal element multiple bonds  Group 6 complexes with metal element multiple bonds are typically supported with auxiliary ligands that will modify electronic properties and control the coordination sphere 9  to inhibit the formation of dimeric or oligomeric species. Common auxiliary ligands that support and often modify reactivity of the metal element multiple bonds have hard oxygen or nitrogen donating atoms to match the hard group 6 metal centers. The sections below highlight three classes of auxiliary ligands commonly employed in complexes bearing metal element multiple bonds; monoanionic oxygen donating ligands (alkoxide, aryloxide and siloxide), monoanionic nitrogen donating ligands (amido), and N,O-donor ligands. These three categories have been selected due to their prevalence in group 6 chemistry exploring metal element multiple bonds. Other common ligands employed with group 6 metal element multiple bonded complexes (such as Cp ligands) are not discussed here.4-6 1.2.1 Alkoxides, aryloxides and siloxides  Monoanionic oxygen donating ligands, including alkoxides, aryloxides and siloxides, have been employed as auxiliary ligands to promote desired reactivity. For example, perfluorinated alkoxide ligands in combination with imido and alkylidene ligands on tungsten and molybdenum metals results in the preparation of excellent olefin metathesis catalysts (e.g. 1.17, Scheme 1-7).30 The perfluorinated ligands are said to enhance reactivity at the metal center by inductively withdrawing electron density. Another example of monoanionic oxygen donating ligands that modify the reactivity of an olefin metathesis catalyst are bulky aryloxide ligands bound to molybdenum and tungsten alkylidene complexes, which are used to access olefin metathesis catalysts that can selectively form Z-alkenes (Scheme 1-8).31 A class of molybdenum and tungsten catalysts called MAP (monoaryloxide-pyrrolide) complexes show excellent Z-selectivity for polymerization of norbornene derivatives and cross metathesis with terminal alkenes.31-32 10   Scheme 1-8. Olefin metathesis catalyst undergoing Z-Selective 2+2 reaction and reversion. M=Mo or W, R1=2,6-diisopropylphenyl, R2=n-hexyl, Trip=2,4,6-iPr-C6H2.31  Aryloxide ligands on a low valent tungsten complex (1.18) have been shown to support the 4 electron reductive cleavage of azobenzene and dioxygen (Scheme 1-9).33 The products of these reactions are di(aryloxide)di(phenylimido)tungsten and di(aryloxide)di(oxo)tungsten complexes respectively. These results highlight the ability of aryloxide ligands to support tungsten complexes in a range of oxidation states.  Scheme 1-9. Aryloxide tungsten complexes that undergo 4 electron reductions of dioxygen and azobenzene.33   Yet another example of monoanionic oxygen donating ligands that have been designed to modify the reactivity a metal complex are the siloxide ligands. Siloxides can be used as auxiliary ligands on molybdenum and tungsten complexes to make competent olefin metathesis catalysts analogous to the aforementioned alkoxide and aryloxide ligands (Figure 1-7).34 These siloxide complexes have been used as homogenous models of 11  heterogenous olefin metathesis catalysts that have been immobilized on silica surfaces (Figure 1-7).34  Figure 1-7. Olefin metathesis catalysts with siloxides ligands.34 1.2.2 Monoanionic nitrogen donating ligands  Monoanionic nitrogen donating ligands are popular auxiliaries that support group 6 complexes with metal element multiple bonds.12 The molybdenum(V) amido complex 1.22 was obtained when Cummins et al. attempted the synthesis of molybdenum(III) complex 1.21.35 One of the amido ligands in complex 1.22 has undergone oxidative addition of a C-H bond on the isopropyl substituent to form the observed molybdaziridine and a molybdenum hydride. Complex 1.22 reacts with dinitrogen to form a bridging nitrido complex (1.23, Scheme 1-10). In this case 1.22 reacts like complex 1.21, which is presumably formed in situ. Further evidence of this reactivity has been observed when 1,2-diphenylacetylene and 1.22 are allowed to react. The alkyne does not insert into the metal hydride nor into the metallaaziridine, instead the η2 alkyne coordinated complex (1.24) forms (Scheme 1-10). This interesting reactivity is only reported with amido ligands in the molybdenum system, and highlights unique reactivity profile of group 6 amido complexes and their ability to support products with metal element multiple bonds. 12   Scheme 1-10. Reactivity of 1.22 (a masked Mo(III) complex).35   Amido ligands are common components of pincer type ligands, and numerous research groups have employed pincer ligands with anionic nitrogen donor groups.36 Most recently Schrock et al. have reported catalytic reduction of dinitrogen employing complex 1.10 (Figure 1-4) as a catalyst.26 Odom et al. has also recently reported a tridentate dipyrrolyl ligand that supports various molybdenum complexes as models for nitrogen reduction chemistry.37 Importantly, the pincer type ligand supports a variety metal-nitrogen double bonds (nitrido, imido and amido), which the complex has been proposed to involve in order to transform dinitrogen into ammonia.37  While the oxygen and nitrogen donating ligands can be excellent auxiliary ligands, many researchers have combined their attributes into N,O-chelating ligands. The use of N,O-chelated group 6 complexes with metal element multiple bonds will be discussed in the next section. 1.2.3 N,O-Donor ligated complexes that support reactive metal-element multiple bonds  By comparison, monoanionic N,O-donor ligands have been less reported with group 6 complexes that have metal element multiple bonds. A majority of previously 13  reported monoanionic N,O-donor ligated complexes with metal element multiple bonds are di(oxo) group 6 species that have been synthesized with the intention of mimicking the various molybdenum cofactor reactivities.38-39 In this vein, many examples of N,O-chelated molybdenum oxo complexes are useful for oxygen atom transfer reactions (Scheme 1-11).40 Recent examples of the monoanionic N,O-donor ligands used for these complexes have been Schiff base,41-42 scorpionate,43 tridentate and tetradentate N,O-donor ligands,44-45 to name a few. Besides oxygen atom transfer reactions some of these complexes are competent as catalysts for the epoxidation of alkenes.41, 46   Scheme 1-11. Example of N,O-donor ligated di(oxo)molybdenum complex that undergoes oxygen atom transfer.  Monoanionic N,O-donor ligands on group 6 complexes have also been reported to support metal carbon multiple bonds. Monoanionic N,O-donor ligands such as 8-quinolate, α-substituted 2-pyridylmethoxide and 2-pyridyl-substituted phenoxides have been reported with alkylidene ligands.47-49 These complexes are competent olefin metathesis catalysts. A recent example of a N,O-donor ligand that modifies the reactivity of an alkylidyne ligand in the same complex has been reported by Veige et al. (complex 1.25, Scheme 1-12).50 Rational ligand design was used to develop a trianionic ONO tridentate pincer type ligand that enhances the nucleophilicity at the alkylidyne carbon. This anticipated reactivity has 14  been demonstrated when complex 1.25 was allowed to react with carbon dioxide and incorporated it into complex 1.26 by forming oxo and ketene fragments (Scheme 1-12).51  Scheme 1-12. Reaction of nucleophilic alkylidene with CO2.51 1.2.4 Group 6 complexes with 1,3-N,O-donor ligands and metal element multiple bonds  A search of the Cambridge Structural Database has shown only seven group 6 mono-metallic complexes containing monoanionic 1,3-N,O-donor ligands and metal element multiple bonds (Figure 1-8). Complexes 1.27,52 1.28,53 1.29,54 1.3155 and 1.3256 are 1,3-N,O-ligated complexes that have formed from isocyanate insertion reactions to give the monoanionic 1,3-N,O-donor ligand. Complex 1.30 has been formed by hydrolysis of an acetonitrile ligand bound to the tungsten center.57 Complex 1.33 has been formed by an addition reaction of acetic anhydride to a phenyl imido ligand to give the 1,3-N,O-donor ligand.58 All of 1,3-N,O-donor ligands in complexes 1.27-1.33 have formed on the group 6 metal and the reactivity of these complexes has not explored further in all cases.  15   Figure 1-8. Structurally characterized mono-metallic group 6 complexes with 1,3-N,O-donor ligands and metal element multiple bonds.  Only one example was found where the 1,3-N,O-donor ligand has not assembled on the metal, and in that case the 1,3-N,O-ligand has been installed via a protonolysis reaction. This complex was the di(pyridonate)bis(t-butylimido)tungsten complex (1.34, Scheme 1-13) reported by Takas and Cavell in 1994.59 Complex 1.34 is a yellow oil, and the solid-state molecular structure of 1.34 was not reported. Like complexes 1.27-1.33 no reactivity of complex 1.34 has been reported.  Scheme 1-13. Synthesis of complex 1.34.59 16  1.3 1,3-N,O-Chelated complexes that support reactive metal-element multiple bonds  1,3-N,O-donor ligands have been shown to be useful auxiliary ligands for group 4 complexes with metal element multiple bonds. Figure 1-9 highlights amidate ligands with specific steric properties to support terminal titanium and zirconium imido ligands. The 1,3-N,O-donor ligands have often been proposed to impart electrophilic character at the metal center due to both the hard nitrogen and oxygen donors combined with poor orbital overlap, and to the tight metal-ligand bite angle with these early transition metals.60  Figure 1-9. Group 4 complexes with metal element multiple bonds supported by 1,3-N,O-chelating ligands.61-62 These terminal imido ligands are important for their reactivity in group 4 catalyzed hydroamination reactions. Scheme 1-14 describes the proposed mechanism of the intermolecular hydroamination of primary amines and alkynes. This mechanism relies on the presence of terminal imido ligands for reactivity. The 1,3-N,O-donor ligands are tunable and coordinatively flexible auxiliary ligands and these features have been used to access a (now) commerically available titanium complex that catalyzes the selective anti-Markovnikov hydroamination of alkynes with primary amines.63 17   Scheme 1-14. Hydroamination of primary amines and terminal alkynes catalyzed by a titanium complex with 1,3-N,O-donor ligands. Catalytically active titanium imido species supported by 1,3-N,O-donor ligands. 1.4 1,3-N,O-donor auxiliary ligands  The 1,3-N,O-donor ligands include amidates, pyridonates, ureates, phosphoramidates and sulfonamidates. The corresponding proligand variants have been shown in Figure 1-10.  Figure 1-10. (from left to right) Amide, 2-pyridone, urea, phosphoramide and sulfonamide proligands. This thesis will focus on only the 1,3-N,O-donor ligands that have a carbon between the nitrogen and the oxygen (amidate, pyridonate and ureate). 18  1.4.1 Synthesis of complexes with 1,3-N,O-donor ligands  The modular synthesis of amide proligands allows for facile access to a variety of steric and electronic properties. The urea proligands can also be tuned easily due to their modular synthesis. Lastly, simple pyridone ligands, such as 3- and 6-methyl substituted pyridones are commerically available. Installing the 1,3-N,O-donor ligands relies on two main synthetic routes, the protonolysis reaction and the salt metathesis reaction (Scheme 1-15).  Scheme 1-15. Synthesis of di(1,3-N,O-chelate)bis(dimethylamido)metal complexes by protonolysis (above) and salt metathesis (below) routes.64 The protonolysis routes have been generally preferred in the synthesis of early transition metal complexes with 1,3-N,O-donor ligands, due to simple reaction conditions and the challenges of removing salt by-product.60, 65 For salt metathesis reactions, the proligands (HL) can be easily deprotonated by sodium bis(trimethylsilyl)amide (Figure 1-11), and the corresponding amidate sodium salts (NaL) can then be used with appropriate metal halide precursors.64 19   Figure 1-11. Synthesis of 1,3-N,O-chelate sodium salts by deprotonation of proligands by sodium bis(trimethylsilyl)amide. 1.4.2 Bonding modes  The 1,3-N,O-donor ligands bond to the metal center with a variety of bonding modes (Figure 1-12).    Figure 1-12. Bonding modes of 1,3-N,O-donor ligands.65 In the κ2-N,O bonding mode the ligand forms a four membered metallacycle with the metal, forcing an acute bite angle of approximately 60° (+/- 3°).60 When bound to early transition metals, the most frequently observed bonding mode in the solid state has been the κ2-N,O chelate mode, followed by κ1-O.60 Bridging µ2-N,O bonding modes have been rarely observed with 1,3-N,O-donor ligands with bulky substituents, however, have been frequently observed with 3-substituted pyridonate ligands.66-67 The κ1-N bonding mode has been rarely observed for early transition metals, with one example being Odom’s nitrido complex 1.33 (Figure 1-8).58 Examples of the bonding modes of 1,3-N,O-donor ligands bound to an early transition metal in the solid state have been shown in Figure 1-13. Complex A shows an example of a κ2-N,O bound 6-methylpyridonate ligand, and also one 20  κ1-O 6-methylpyridonate ligand.68 Complex B shows one µ2-N,O bridging amidate and two κ2-N,O amidate ligands.69  Figure 1-13. Examples of 1,3-N,O-donor ligand bonding modes in the solid state. Substituents on amidate ligands in complex B not shown.68-69  The 1,3-N,O-donor ligands function as hemilabile ligands to allow for interconversion of the bonding modes. The hemilability has been difficult to observe in early transition metal systems, presumably due to rapid interconversion of bonding modes.70 In fact, only a few examples of observed hemilability of the 1,3-N,O-donor ligands has been noted.71-73 Scheme 1-16 highlights two examples from the Schafer group where the hemilability of amidate ligands could be monitored by NMR spectroscopy.72-73 21   Scheme 1-16. Characterized examples of hemilabile amidate complexes.72-73 In the above examples amidate ligand hemilability can be readily observed, however, this has not normally been the case for 1,3-N,O-ligands on early transition metal complexes. Typically, when hemilability of the 1,3-N,O-donor ligands have been proposed, the signatures in the NMR spectra are broadened and difficult to assign.70 Thus, although the hemilability of 1,3-N,O-donor ligands has been an important attribute of the ligands, and we do not yet fully understand the fundamental concepts that govern their dynamic behavior. 1.5 Thesis outline  This thesis aims to pair 1,3-N,O-donor ligands with group 6 complexes that have metal element multiple bonds. It has been hypothesized that 1,3-N,O-donor ligands could be installed on group 6 complexes that have metal element multiple bonds by protonolysis and salt metathesis reactions. Furthermore, the reactivity of the resulting complexes is expected to be unique compared to complexes with other monoanionic donor ligands, due to the 1,3-N,O-donor ligands dynamic hemilabile characteristics. No reactivity studies have been reported for this class of complexes and there are only a handful of known group 6 22  complexes that bear both metal element multiple bonds and 1,3-N,O-donor ligands (Figure 1-8).   This thesis reports synthetic routes into group 6 complexes with metal element multiple bonds. Chapters 2 and 3 demonstrate that 1,3-N,O-donor ligated tungsten complexes with imido, oxo and alkylidene ligands can be readily prepared via protonolysis routes, Chapter 3 demonstrates that 1,3-N,O-donor ligated tungsten oxo alkylidene complexes can be synthesized by salt metathesis reactions. Secondly, evaluation of how the 1,3-N,O-donor ligands bond and interact with this class of complexes has been conducted. Relative hemilability of the 1,3-N,O-donor ligands has been determined, pyridonate ligands demonstrate more dynamic hemilability than amidate ligands. Steric parameters were also shown to be important in observing which bonding modes and coordination geometries are favorable.  Finally, an examination of the reactivity of these complexes has been undertaken. In chapters 2 and 3 1,3-N,O-donor ligated tungsten complexes with metal element multiple bonds undergo reversible N-H bond activations (chapter 2) and olefin metathesis (chapter 3). Chapters 3 and 4 contain data illustrating that the 1,3-N,O-donor ligated complexes are amenable to C-H bond activation reactions. In chapter 3, an amidate assisted C-H activation of a tungsten alkylidene to form a tungsten alkylidyne has been observed. Chapter 4 communicates the first example of a molybdenum mediated α-alkylation of an amine, which also goes through a C-H activation process. Rewardingly, this thesis expands a rare class of complexes, group 6 complexes with metal element multiple bonds and 1,3-N,O-donor ligands, and presents their syntheses, metal ligand interactions and discloses initial reactivity studies. 23  Chapter 2: Tungsten bis(t-butylimido) complexes with 1,3-N,O-donor ligands: probing amidate and pyridonate hemilability 2.1 Objectives  The onset of investigations of group 6 complexes with metal element multiple bonds and 1,3-N,O-donor ligands began with a desire to develop an understanding of the coordination chemistry and metal ligand interactions of 1,3-N,O-donor ligands with group 6 metals. To begin, it was necessary to understand the best ways to synthesize such compounds. Investigating how the 1,3-N,O-donor ligands affect the reactivity of the group 6 complexes was of interest. 2.2 Introduction  The term hemilabile ligand was coined in 1979 when Jeffrey and Rauchfuss reported the metal-ligand interactions of (2-methoxyphenyl)diphenylphosphine coordinated to ruthenium.74 A chelated ligand that readily dissociates an atom of the chelate from the metal center (leaving another part of the chelate still bound to the metal center) which opens a coordination site at the metal center, is said to be a hemilabile ligand. This type of metal-ligand interaction is often described as a hinging action of the chelate, and allows a substrate to bind the newly vacated open coordination site for reactivity such as subsequent catalysis, substrate molecule activation, chemical sensing, stabilization of reactive species, among other applications.75 The Schafer group has shown that 1,3-N,O-donor ligands can adopt different bonding modes and participate in E-H (where E= B, C, N and O) bond activations.76-78 The 1,3-N,O-donor ligands include amidate, pyridonate, ureate, phosphoramidate and sulfonamidate ligands.79 1,3-N,O-donor ligand hemilability 24  is described as a change in bonding mode of the 1,3-N,O-ligand between κ2-N,O, μ2-N,O, κ1-N or κ1-O.  Figure 2-1illustrates the commonly observed bonding modes of the 1,3-N,O-donor ligands.  Figure 2-1. Observed binding modes of 1,3-N,O-donor ligands, which highlight ligand hemilability.  The 1,3-N,O-donor ligands (i.e. amidate and pyridonate) are unique from traditional hemilabile ligands first described by Jeffery and Rauchfuss, in that they do not have a strictly inert donor (P) and a labile donor (O); rather, both the N and O of the 1,3-N,O-ligand can act as either inert or labile donors (i.e. κ1-N or κ1-O can be accessed).74 Solid-state molecular structures where the 1,3-N,O-donor ligand adopts κ2-N,O, κ1-O, κ1-N and μ2-N,O bonding modes have been observed across the periodic table,65 however, the rapid changes in bonding modes make it difficult to observe different coordination environments in solution by NMR spectroscopy. To date, only a few experimental studies have reported the observation of discrete amidate or pyridonate hemilabile coordination environments in solution.71, 73, 80-82 These 1,3-N,O-donor ligands can support high valent early transition metals which are competent catalysts for hydroamination60, 63, 83-89 and hydroaminoalkylation69, 90-94 reactions. These hydrofunctionalization reactions, hydroamination (a C-N bond forming reaction),95-96 and hydroaminoalkylation (a C-C bond forming reaction),97 are catalytic transformations targeting improved atom economy and efficiency in the synthesis of 25  agriculturally and pharmaceutically relevant amine containing fine chemicals.98 For example, in 2003 the Schafer group reported an amidate supported titanium catalyst for the regioselective hydroamination of terminal alkynes with primary amines.63 Notably this commercially available catalyst is capable of realizing anti-Markovnikov selectivity with a broad range of substrates.99-101 The observed exquisite regioselectivity and catalytic efficiency is proposed to be due to the hemilability of the amidate ligand.70, 100  In another example, the Schafer group has taken advantage of the difference between the hemilability of amidates vs. pyridonates to develop catalyst controlled chemoselectivity of intramolecular hydroaminoalkylation with primary aminoalkene substrates (eg, L1, Scheme 2-1)  over intramolecular hydroamination (eg, L2, Scheme 2-1).66 Thus, the variable hemilability of these two classes of 1,3-N,O-donor ligands support divergent catalytic pathways by allowing access to multiple bonding and coordination modes. We proposed that pyridonate ligands have more dynamic hemilability than amidate ligands, and thus are more prone to forming dynamic systems with a diverse array of bonding modes under catalytic reaction conditions.66, 82, 102-103 These differences between pyridonate and amidate ligands have been proposed to stem from differences in steric demand, which in turn impacts the hemilability of the ligand.70, 104 Thus, by understanding trends in ligand hemilability, this feature can be incorporated as a ligand design element for promoting improved or new reactivity. 26   Scheme 2-1. Hydrofunctionalization of A. Depending upon the 1,3-N,O-donor employed the hydroaminoalkylation (HAA) or the hydroamination (HA) product can be preferentially accessed. This change in product distribution has been proposed to be rationalized by ligand hemilability.66, 102  In the aforementioned systems the 1,3-N,O-donors are auxiliary ligands used to modify reactivity at the metal center. In this chapter, we sought a system where the 1,3-N,O-donors would be more reactive than the other ligands on the metal in order to observe structure and reactivity effects of different 1,3-N,O-donor ligands. This approach would allow us to observe effects of temperature, coordination of additional donors and proton-shuttling on 1,3-N,O-donor ligated complexes. To this end, the bis(t-butylimido)X2tungsten(VI) framework (where X is a monoanionic ligand) is an ideal system for such investigations because; 1) the covalent radii of titanium and tungsten are nearly identical,105-106 2) the bis(t-butylimido)tungsten system has nitrogen donating atoms that have significant M-N π bonding, similar to the bis(dimethylamido)bis(1,3-N,O-chelate)titanium(IV) complexes used in the aforementioned catalytic reactions, 3) the bis(t-butylimido)bis(1,3-N,O-chelate)tungsten framework, with its pseudo-octahedral geometry, will mimic the geometric environment of the bis(dimethylamido)bis(1,3-N,O-27  chelate)titanium(IV) complexes, 4) simple protonolysis routes from suitable tungsten(VI) precursors have been devised,59 and 5) theoretical investigations have shown the bonding involved in the bis(t-butylimido)X2tungsten fragment to be isolobal to a group 4 bent metallocene complexes, allowing for interpretations of how the ligands bond with the tungsten metal.107-108   We predicted that while the absolute metal-ligand interactions of new 1,3-N,O-donor ligated tungsten complexes will be different between the known 1,3-N,O-donor ligated titanium systems (i.e. equilibrium constants of a hemilabile 1,3-N,O-donor ligand exchanging from κ2-N,O to κ1-O), the similarities between the two systems would allow for relative trends of 1,3-N,O-donor ligands on high valent early transition metal complexes to be observed. It was predicted that the trends in hemilability of 1,3-N,O-donor ligated tungsten complexes would mirror that of other known early transition metal systems. The reactivity of titanium amidate and pyridonate ligands has suggested that the latter has more dynamic hemilability,66 however, before this project the Schafer group had little experimental evidence of this hypothesis.   The bis(t-butylimido)tungsten fragment has been reported in combination with amido, amidinate, guanidinate, alkoxide, aryloxide, and salen ligands.33, 109-113 To date there are only a handful of monomeric 1,3-N,O-chelated tungsten complexes reported.52-53, 55, 57, 59, 114 Two bis(t-butylimido)di(1,3-N,O-chelate)tungsten complexes have been reported previously, however, neither were structurally characterized nor were their reactivities reported.55, 59 28   Scheme 2-2. Synthesis of 1,3-N,O-donor ligated tungsten complexes via protonolysis reactions (above), and corresponding proligands (below). In this chapter the synthesis of a series of bis(t-butylimido)di(1,3-N,O-chelate)tungsten(VI) complexes (Scheme 2-2) allows for systematic investigations of steric and electronic effects on the hemilability of the 1,3-N,O-donor ligands. Computational investigations and reactivity studies of bis(t-butylimido)di(1,3-N,O-chelate)tungsten complexes illustrate the enhanced hemilability of pyridonate ligands in comparison to amidates. Furthermore, the steric demand of each unique ligand imparts a variable degree of hemilabile character and influences bonding modes. These insights correlate to reported reactivity trends in established 1,3-N,O-donor ligands in hydroamination and hydroaminoalkylation catalytic systems. 29  2.3 Results and discussion 2.3.1 Ligand design  A series of bis(t-butylimido)di(1,3-N,O-chelate)tungsten complexes were prepared to probe characteristic 1,3-N,O-donor ligand hemilability trends. The commercial availability of methyl substituted pyridones and the modular synthesis of amide proligands allows for a variety of steric and electronic parameters to be easily evaluated (HL1-HL4, Scheme 2-2).76   Figure 2-2. 6-methylpyridonate (HL1) κ2-N,O and κ1-O bonding modes (left), 3-methylpyridonate (HL2) κ2-N,O and κ1-O bonding modes (right). κ1-O demonstrates the aryloxyimine motif of pyridonate ligands. The electronic properties of these proligands can be compared by considering their corresponding pKa values. The electronic differences for proligands HL1 and HL2 are expected to be minimal, and the value of unsubstituted pyridone (2-pyridone) with a pKa of 17.0 (in DMSO) is used as a reference.115 The pKa’s of HL3 and HL4 have not been reported.  However, related alkyl ((Ph(H)NC(Me)O, 21.45)  and aryl (Ph(H)NC(Ph)O, 18.77) amides have been reported (in DMSO).116 The relative difference in pKa between the two proligands HL3 and HL4 is expected to be similar. Notably these data show that pyridones are more acidic by at least an order of magnitude than amides.  Although proligands HL1 and HL2 have similar electronic structures, they do have different substituent patterns. We propose that the variable placement of steric bulk affects hemilability (Figure 2-2). Notably proligand HL1 has bulk about the metal center in the 30  κ2-N,O bonding mode, while in the κ1-O bonding mode the methyl group points away from the metal center (Figure 2-2).  In contrast, in proligand HL2, the methyl group points away from the metal center in the κ2-N,O bonding mode, and points towards the metal center while in a κ1-O bonding mode (Figure 2-2). Indeed, the importance of the location of substituents has been noted in catalytic hydroaminoalkylation,66 and has been proposed to stem from differences in pyridonate hemilability. Another important feature of pyridonates is the aromatic system tied into the backbone of the NCO moiety, making the κ1-O binding mode akin to aryloxide type ligands (Figure 2-2). Amides HL3 and HL4 have bulkier groups on the nitrogen (Figure 2-3) compared to pyridones HL1 and HL2. While the increased steric demand of the amidates would offer substantial steric protection, the bulky substituents may also promote hemilability.  Furthermore, for amidate ligands the κ1-O bonding mode can access two isomers, E/Z of the corresponding C=N double bond, demonstrating the further dynamic flexibility of these ligands (Figure 2-3). Comparing HL3 to the more sterically demanding HL4, allows for insights into how changing the steric parameters of 1,3-N,O-chelating ligands effects hemilability.  Figure 2-3. Amidate κ2-N,O and κ1-O bonding modes. HL3, R1=Ph, R2=tBu; HL4 R1=2,6-diisopropylphenyl, R2= Ph. 31  2.3.2 Tungsten complex synthesis and characterization  The simplest synthetic strategy for installing 1,3-N,O-donor ligands on high valent early transition metals has been through protonolysis reactions.70, 104 Thus, protonolysis reactions of bis(t-butylamido)bis(t-butylimido)tungsten (2.1) with proligands HL1-HL4 gave complexes 2.2-2.5, respectively (Scheme 2-2).59 These new complexes can be isolated as analytically pure crystalline yellow solids in good yields ranging from 76 to 95%.  Pyridonate complexes 2.2 and 2.3 are initially isolated as analytically pure viscous oils that crystallize over days. Amidate complexes 2.4 and 2.5 are yellow solids that recrystallize from hexanes. Of the possible coordination isomers (Figure 2-4) C2 symmetric N-trans, C2 symmetric O-trans and C1 isomers have all been observed for related di(1,3-N,O-chelate)bis(dimethylamido)titanium(IV) complexes.70  Figure 2-4. Possible stereoisomers of a di(N,O-chelate)bis(t-butylimido)tungsten complex. Simplified point groups assigned by ignoring the C3 axis of t-butyl groups. Consistent with observations of group 4 complexes, the solid-state molecular structures for complexes 2.2-2.5 (Figure 2-5) are all six coordinate with two κ2-N,O bound 1,3-N,O-chelated ligands with either a pseudo-C2 symmetric N-trans or pseudo-C2 symmetric O-trans coordination geometry (selected bond distances and angles are listed in Table 2-1).70 These complexes exhibit a highly distorted octahedral geometry due to the acute bite angle of the 1,3-N,O-chelated ligands (58.41(7)-60.68(9)°). All the 1,3-N,O-chelated ligands 32  have similar small O-W-N angles (Table 2-1) and are in agreement with the previously reported 1,3-N,O-chelating bite angles (60° +/- 2°).70, 117 The tungsten t-butylimido (W-N) bond distances are also consistent throughout complexes 2.2-2.5, and range from 1.746(2) to 1.761(2) Å, which are elongated when compared to the starting material 2.1 (1.708(11) Å).118 This change in bond length has been expected due to an increase in the coordination number.118 Similar to other reported 6 coordinate bis(t-butylimido)tungsten(VI) complexes, the W-N-C imido bond angles approach 180° and range from 151.0(2)° to 176.1(2)°.112, 119-127 Complex 2.2 has a pseudo-C2 symmetric O-trans coordination environment of the 1,3-N,O-chelated ligands with shorter W1-O1 and W1-O2 bond lengths of 2.063(2) and 2.061(2) Å respectively, and longer W1-N1 and W1-N2 bond lengths of 2.345(2) and 2.357(2) Å respectively. The O1-C1 and O2-C7 bond lengths of 1.329(3) and 1.333(3) Å respectively, indicating minimal multiple bond character between the oxygen and the carbon of the 6-methylpyridonate ligands in complex 2.2.128 This disparity in W-O versus W-N bond distances is indicative of an aryloxyimine bonding motif of the pyridonate ligand.104 Complexes 2.3, 2.4, and 2.5 exhibit a pseudo-C2 symmetric N-trans coordination environment in the solid state. The 1,3-N,O-chelate contacts are consistent across the three complexes and range from 2.236(2) to 2.371(2) Å for the W-O bond lengths and from 2.094(2) to 2.140(3) Å for the W-N bond lengths. Complexes 2.3 and 2.4 have two inequivalent W-N-C imido bond angles in the solid state (176.1(2)°, 151.0(2)° and 175.0(2)°, 162.1(2)° respectively). Although these asymmetric t-butylimido ligands are not observed in the solution phase by NMR spectroscopy, nonequivalent imido bond angles are commonly observed in the solid state.129-131 Amongst early transition metals, this has been the first time that 1,3-N,O-chelates have been observed having substantially 33  shorter M-N bonds over M-O bonds.66, 104, 117 This has been attributed to the strong trans-influence of t-butylimido ligands and the bonding of the 1,3-N,O-donor ligands (vide infra).132  Figure 2-5. Solid-state molecular structures of complexes 2.2-2.5, plotted at 50% ellipsoids and hydrogen atoms and disordered atoms omitted for clarity.     34   Table 2-1. Selected bond distances and angles for complexes 2.2-2.5. Bond Distances (Å) 2.2 2.3 2.4 2.5 W1-O1 2.063(2) W1-O1 2.236(2) W-O1 2.24(1) W1-O1 2.332(2) W1-O2 2.061(2) W1-O2 2.371(2) W-O2 2.339(2) W1-O2 2.290(2) W1-N2 2.357(2) W1-N1 2.140(3) W-N1 2.02(3) W1-N1 2.117(2) W1-N3 1.759(2) W1-N2 2.111(3) W-N2 2.094(2) W1-N2 2.128(2) W1-N4 1.751(2) W1-N3 1.748(3) W-N3 1.752(2) W1-N3 1.760(2) W1-N1 2.345(2) W1-N4 1.761(3) W-N4 1.746(2) W1-N4 1.761(2) O1-C1 1.329(3) O1-C19 1.298(4) O1-C11 1.29(2) O1-C13 1.279(2) N1-C1 1.345(3) N1-C19 1.364(4) N1-C11 1.28(3) N1-C13 1.334(3) O2-C7 1.333(3) O2-C13 1.283(4) O2-C21 1.266(3) O2-C32 1.276(2) N2-C7 1.339(3) N2-C13 1.364(4) N2-C21 1.338(3) N2-C32 1.332(3) Bond Angles (°) 2.2 2.3 2.4 2.5 W1-N3-C13 165.4(2) W1-N3-C1 176.1(2) W1-N3-C31 162.1(2) W1-N39-C39 171.2(2) W1-N4-C17 167.2(2) W1-N4-C5 151.0(2) W1-N4-C41 175.0(2) W1-N43-C43 170.8(2) O1-W1-N1 59.84(8) O1-W1-N1 60.68(9) O1-W1-N1 59.8(9) O1-W1-N1 58.73(6) O2-W1-N2 59.67(8) O2-W1-N2 58.91(9) O2-W1-N2 58.41(7) O2-W2-N2 59.14(6)  2.3.3 Computational Ground State Geometry Optimization Interestingly the two pyridonate complexes, 2.2 and 2.3, do not have the same geometric isomer in the solid state. To further investigate this switch in coordination environment for pyridonate complexes 2.2 and 2.3, computational studies have been 35  undertaken to examine the relative energies of the different stereoisomers that these complexes can adopt. Density functional theory has been employed using the B3LYP functional for optimizations of stereoisomers, followed by a frequency calculation of each optimized isomer in order to compare the relative free energies of the stereoisomers.68 Five possible isomers have been shown in Figure 2-4, however, the C2v and C2h isomers are known to be highly disfavored as they have the two t-butylimido ligands trans to each other,133 therefore only the C2 N-trans, C2 O-trans and C1 isomers have been considered for geometry optimizations. Figure 2-6 shows the relative energies of the different isomers for complexes 2.2-2.4.  Figure 2-6. Relative energies of C2 N-trans, C2 O-trans and C1 isomers of bis(N,O-chelate)bis(t-butylimido)tungsten(VI) complexes, energies in kcal/mol and each set of isomers is referenced to its corresponding lowest energy isomer. The computational modeling of complex 2.5 has been complicated by the fact that only the C2 N-trans isomer yields a six coordinate bis(κ2-N,O-amidate) complex, while 36  most other computed isomers produced five or four coordinate complexes with at least one amidate bound in a κ1-O fashion (Table 2-9). The resulting energies of these four or five coordinate isomers are higher in energy than the C2 N-trans complex. Both Δ and Λ enantiomers where calculated for isomers of complexes 2.2, 2.3 and 2.4, and show the same energy within the error of the calculations (agreeing within 0.8 kcal/mol, in all cases). Complexes 2.2, 2.3, 2.4 and 2.5 were also calculated with the use of dispersion correction (using empiricaldispersion=gd3bj).134-135 The calculations using the dispersion correction have been successful for the isomers of complexes 2.2 and 2.5. Unfortunately, the calculations for complexes 2.3 and 2.4 did not result in the location of local minima, indicating a relatively flat energy landscape. The energies of the calculated isomers when using the dispersion correction for complexes 2.2 and 2.5, did show significantly different values (Table 2-5 in the experimental section 2.4), however the order of the lowest to highest energy isomers remains consistent. The discussion of the computed isomers (below) has been conducted using the calculations without dispersion corrections unless stated otherwise.  The computed structures of complexes 2.2, 2.4 and 2.5 are in good agreement with the solid state molecular structures and overlays of the computed and solid-state molecular structures are shown in the experimental section 2.4. The computational results predict that an O-trans coordination environment is the lowest free energy isomer for both pyridonate complexes 2.2 and 2.3, even though the N-trans coordination environment is observed in the solid state for 2.3. However, the model also predicts that the relative energy differences between the C2 O-trans, C1 and C2 N-trans isomers of complex 2.3 are small (2.7 < kcal/mol), and such similar energies may rationalize how crystal packing forces result in 37  the observed (C2 N-trans) structure for complex 2.3. Furthermore, the small energy difference between the calculated isomers suggested that facile access to multiple geometric isomers is possible, as long as the barrier to isomerization is energetically feasible.   Complexes 2.2 and 2.4 have coordination isomers with more pronounced energy differences between isomers, and in these cases the computationally predicted lowest energy isomer has been consistent with the observed solid-state molecular structure. The computational results point out that steric demand of a 1,3-N,O-donor ligand influences how it coordinates to the metal. Complex 2.3 has reduced steric demand around the metal center due to the structure of the 3-methylpyridonate ligand. Thus, the energy difference between the stereoisomers of 2.3 is less than in complexes 2.2 and 2.4, which have more pronounced steric demand directed toward the metal center. The drastic difference between 2.2 and 2.3 highlight that ligands with similar electronic features do not always have similar ground state coordination environments. These findings suggest that steric demand is a dominating factor in determining the ground state coordination environment of a 1,3-N,O-donor ligated complex. Lastly, when steric demand is removed multiple isomers may be accessible due to coordination isomers being relatively close in energy, such as in complex 2.3. 2.3.4 Solution phase characterization data Room temperature solution 1H- and 13C-NMR spectra for complexes 2.2-2.5 are consistent with C2 symmetric complexes in all cases (1H-NMR data summarized in Table 2-2), however, variable temperature 1H-NMR experiments have been recorded to probe whether fluxionality between geometric isomers could be observed. The observation of 38  solution phase hemilabile 1,3-N,O-chelated ligands, such as κ1 or bridging µ bonding modes would lend support to their relevance in catalysis. Table 2-2. Tabulated 1H-NMR data taken at 25 °C in toluene-d8, 400 MHz.   For 6-methylpyridonate complex 2.2 no changes were observed in the variable temperature 1H-NMR spectrum from -30 to 90 °C.  Only minor changes have been observed from -40 °C to -80 °C. Two of the three aryl signals drift slightly from δ 6.93 and 6.01 at 25 °C and to δ 6.68 and 5.76 at -80 °C respectively. The temperature shifted resonances are also broadened and suggest the dynamic formation of other isomers or aggregate species. However, due to the low abundance and broadened signals, no assignments can definitively be made. Due to the subtle changes in the variable temperature 1H-NMR spectra, complex 2.2 is considered to be highly fluxional in solution. 39   The 3-methylpyridonate complex 2.3 also gives low temperature spectra consistent with fluxionality of the pyridonate ligands in solution. Resolution of three separate broadened pyridonate methyl resonances (δ 1.99, 1.87 and 1.85) as well as three separate t-butylimido resonances (δ 1.58, 1.47 and 1.43) were observed at -70 °C, indicating that interconversion of the isomers above -70 °C is rapid. These observations cannot rule out the possibility of complex 2.3 adopting a bridging ligand motif or the formation of dimeric or aggregate species (vide infra).  For comparison, variable temperature 1H-NMR experiments have also been recorded for bis(amidate) complexes 2.4 and 2.5. The variable temperature 1H-NMR spectra for complex 2.4 showed minimal changes, from 25 °C to -80 °C; two aryl resonances at δ 7.24 and 7.04 broaden and migrate to δ 7.46 and 7.00 respectively. The only other changes in the low temperature spectra were a new set of resonances, with low abundance, that emerged between -20 to -80 °C. The new resonances are broadened and are consistent with the dynamic formation of other isomers or aggregate species. Once again, no definitive assignments can be made. Finally, similar observations have been made for the bulky bis(amidate) complex 2.5. From 25 to 95 °C the isopropyl methyl and methine resonances broadened, suggesting that fluxionality is increased with increasing temperature. From 25 to -60 °C the spectra are consistent with a C2 symmetric complex.   The coordination modes in these complexes has not been clearly demonstrated by 1H-NMR spectroscopy, and the data are best considered to be evidence that all complexes are highly fluxional in solution at catalytically relevant temperatures (>60 C), and the pyridonate ligands in complex 2.2 and 2.3 are fluxional at room temperature. The variable temperature NMR experiments suggest that the pyridonate ligands have more dynamic 40  hemilability compared to the amidate ligands. Thus, we turned our attention to investigating the reactivity of complexes 2.2-2.5 in ligand exchange reactions and reactions with electrophiles to further probe 1,3-N,O-donor ligand hemilability. 2.3.5 Reactivity investigations   Ligand hemilability, resulting in the formation of an open coordination site, would promote facile ligand exchange reactions through an associative mechanism. To this end the 1:1 reaction of 2.2 and 2.3 in toluene-d8 has been monitored by 1H-NMR spectroscopy to probe if pyridonate ligand exchange could be observed. New t-butylimido and methyl pyridonate signals appear at δ 1.41 and 1.87 in a 3:1 ratio, signifying a new bis(t-butylimido)di(1,3-N,O-chelate)tungsten complex. The aryl resonances have also been affected, although overlapping signals complicated their assignment. The aliphatic region also contained resolved resonances for the t-butylimido and pyridonate methyl hydrogens characteristic of both complexes 2.2 and 2.3, at δ 1.44 and 2.09 (overlapping with toluene-d8 resonance) for complex 2.2 and at δ 1.42 and 1.92 for complex 2.3 (Table 2-2).   A plausible explanation for these new resonances is a mixed bis(t-butylimido)(3-methylpyridonate)(6-methylpyridonate)tungsten complex, although no characterization beyond 1H-NMR spectroscopy was not undertaken. This result contrasted with the observation of treating 2.2 with amidate complex 2.4 under identical reaction conditions. No new resonances were observed by 1H-NMR spectroscopy. Furthermore, when complexes 2.4 and 2.5 have been allowed to react and then monitored by 1H-NMR spectroscopy no new products were observed. These results show that pyridonate ligands undergo facile ligand exchange reactions while amidate complexes are resistant to such 41  ligand exchange reactions at ambient temperatures, demonstrating more dynamic hemilability of pyridonate ligands.  It has been shown that amido complexes can be accessed from imido complexes via protonation with a bulky alcohol or a Brønsted acid.55, 59, 109-110, 124, 136-137 The addition of one equivalent of HL1 (as a proton source) to 6-methylpyridonate complex 2.2 in toluene-d8 resulted in no immediately observable reaction at 25 °C. However, variable temperature 1H-NMR spectroscopy studies showed an equilibrium is present, and below -40 °C neither 2.2 nor HL1 can be identified in solution. Below -40 °C multiple resonances have been observed indicating that the exchange of ligand with proligand is rapid and reversible. Although the low temperature 1H-NMR spectrum of the reaction mixture was indicative of more than one single product, recrystallization of the resulting equilibrium mixture from hexanes at -30 °C resulted in precipitation of a mixture of amorphous solids and crystalline material found to be analytically pure tris(6-methylpyridonate)(t-butylamido)(t-butylimido)tungsten(VI) complex 2.6 (Table 2-3, entry 1). Electron impact mass spectrometry (EIMS) of the analytically pure solids showed a [M-HNtBu]+ ion, consistent with the molecular ion of tungsten with three pyridonate ligands and one t-butylimido ligand.   Single crystal X-ray diffraction confirmed the formation of complex 2.6 (Figure 2-7). The solid-state molecular structure is evidence that 6-methylpyridone can protonate a t-butylimido ligand and notably this structure incorporates one κ2-pyridonate and two κ1-pyridonate ligands. The six coordinate complex 2.6 has a distorted octahedral geometry in which the κ2-N,O 6-methylpyridonate adopts an aryloxyimine motif where the W1-O1 (2.099(6) Å bond distance is significantly shorter than the W1-N1 bond length (2.270(7) 42  Å)). The two κ1-O pyridonates have shorter tungsten oxygen bond lengths of 2.077(6) (W1-O2) and 1.949(6) (W1-O3) Å, which are consistent with previously reported bis(aryloxide)bis(imido)tungsten(VI) complexes.138 The t-butylimido ligand has a short W1-N5 bond distance of 1.739(7) Å and a near linear W1-N5-C50 bond angle of 166.7(6)°, while the W1-N4 amido bond distance is 1.918(6) Å, with a W1-N4-C40 bond angle of 137.6(5)°. The hydrogen (H1) (located from residual electron density) of the t-butylamido ligand is orientated towards the nitrogen (N2) of the axial κ1-O pyridonate ligand indicative of hydrogen bonding; suggesting that the reversible protonation of the t-butylimido substituent is assisted by the hemilabile pyridonate ligand as an example of metal-ligand cooperativity in proton transfer.  Figure 2-7. Solid-state molecular structure of complex 2.6, plotted at 50% ellipsoids with most hydrogen atoms omitted for clarity (except H1). Selected bond lengths (Å): W1-O1 = 2.099(6), W1-O2 = 2.077(6), W1-O3 = 1.949(6), W1-N1 = 2.270(7), W1-N4 = 1.918(26, W1-N5 = 1.739(7). Selected bond angles (deg): 43  W1-N5-C50 = 166.7(6), W1-N4-C40 = 137.6(5), O1-W1-N1 = 60.6(2), N5-W1-O2 = 171.7(3), N1-W1-N5 = 91.5(3). The addition of 3-methylpyridonate complex 2.3 and HL2 has been conducted in toluene-d8 and the 1H-NMR spectrum of the mixture at 25 °C demonstrated new broadened resonances in the alkyl and aryl regions, none of which correspond to proligand HL2, indicative of addition of the proligand to complex 2.3 forming a new tris(3-methylpyridonate)tungsten complex 2.7 (Table 2-3, entry 2). Variable temperature 1H-NMR spectra show the broad resonances separate into multiple sharper resonances at lower temperatures, with the t-butylimido singlet at 1.41 δ at 25 °C broadening into 6 singlets at -70 °C. Thus, this complex is fluxional at 25 °C. No solid-state molecular structures could be obtained from recrystallization attempts and only amorphous solids were obtained. Similar to the mass spectrum of complex 2.6, EIMS experiments of the solids obtained yielded a molecular ion corresponding to tris(3-methylpyridonate)(t-butylimido)tungsten [M-HNtBu]+, supporting the formation of complex 2.7. The reactivity of bis(amidate) complexes 2.4 and 2.5 were very different, whereby the addition of one equivalent of HL3 and HL4 to complexes 2.4 and 2.5 respectively (Table 2-3, entries 3 and 4), showed no indication of a reaction as observed by 1H NMR spectroscopy at various temperatures (-40 to 90 °C). Furthermore, EIMS experiments conducted on the isolated solids of these reactions showed only the corresponding precursor bis(amidate)bis(t-butylimido)tungsten complexes and proligands, with no evidence of a tris(amidate) product being formed. 44  Table 2-3. Reactivity of complexes 2.2-2.5 with the respective proligands HL1-HL4.  These observations show that pyridonate complexes 2.2 and 2.3 have increased reactivity and can readily engage in proton-shuttling, presumably due to structural flexibility/hemilability compared to amidate ligands. Further contributing factors include the lower pKa character of amides, and the larger steric parameters of the corresponding amidate ligands which would inhibit the formation of tris(amidate) complexes, although such species have been reported for Ti(IV).139 To explore the effect of an alternative proton source, amidate complexes 2.4 and 2.5 were treated with the Brønsted acid lutidinium hydrochloride (Scheme 2-3). In this case 45  the lutidinium hydrochloride may result in protonation of the t-butylimido ligand with addition of the chloride to the tungsten metal center or may protonate an amidate ligand.  Scheme 2-3. Proposed reaction of lutidinium hydrochloride with bis(amidate) complexes 2.4 and 2.5. Left; addition of HCl to tungsten complex, right; protonolysis of amidate ligand. The addition of lutidinium hydrochloride with amidate complex 2.4 has been conducted at room temperature in toluene. Over a period of 2 hours the poorly soluble lutidinium hydrochloride dissolved and the reaction mixture was stirred for an additional 2 hours. The 1H-NMR spectrum of the resulting crude material showed conversion of complex 2.4 to give three new singlet resonances in the aliphatic region. One t-butyl resonance (δ 1.01) was identified as proligand HL3. The other two resonances at δ 1.26 and 0.92 have been assigned as two t-butylimido ligands and the t-butyl of the amidate (PhNC(tBu)O-) ligand respectively. These resonances are in a 2:1 ratio suggesting the formation of a Cs symmetric mono(N-phenylpivalamidate)bis(t-butylimido)chlorotungsten complex 2.8 (Scheme 2-3, right). Purification of 2.8 has been challenging due to the presence of proligand HL3. However, single crystal X-ray diffraction of colorless crystals formed from a concentrated solution of hexanes, confirmed the Cs symmetric complex 2.8 (Figure 2-8). 46   Figure 2-8. Solid-state molecular structure of complex 2.8, plotted at 50% ellipsoids and hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N1 = 1.744(2), W1-N2 = 1.737(3), W1-N3 = 2.120(3), W1-O1 = 2.166(3), W1-Cl1 = 2.3573(8). Selected bond angles (deg): W1-N1-C1 = 163.2(2), W1-N2-C5 = 170.1(3), O1-W1-N1 = 122.3(1), O1-W1-N2 = 123.3(1), N3-W1-Cl1 = 143.96(7), O1-W1-N3 = 60.11(9). Complex 2.8 exhibits a distorted trigonal bipyramidal coordination geometry.68 The amidate is symmetrically bound with the W-N bond (2.120(3) Å) being shorter than the W-O bond (2.166(3) Å). Notably the W-O has shortened significantly when compared to the W-O bonds in precursor 2.4 (2.24(1) and 2.339(2) Å). The W-N bonds of the t-butylimido ligands in complex 2.8 are 1.744(2) and 1.737(3) Å for W1-N1 and W1-N2 respectively, which are also shorter compared to those of 2.4. The overall of shortening of tungsten ligand bonds is attributed to a reduced coordination number from 6 to 5 and the incorporation of a chloride ligand. The W1-Cl1  bond length of 2.3578(8) Å is consistent with a reported isostructural bis(t-butylimido)chloro(guanidinate)tungsten complex.112 Variable temperature 1H-NMR spectroscopy of the reaction mixture up to 95 °C and down to -40 °C showed no equilibrium between proligand HL3 and complex 2.8, however the 47  amidate resonances shift slightly with temperature. At temperatures below -40 °C proligand HL3 precipitates out of the toluene-d8 solution.  Throughout there has been no spectral evidence suggesting that a bis(amidate)(t-butylamido)chloro(t-butylimido)tungsten complex has formed, rather I propose that the lutidinium hydrochloride protonates the sterically demanding and hemilabile amidate ligand and forms complex 2.8 via elimination of proligand HL3. Alternatively, the lutidinium hydrochloride could protonate an imido ligand of complex 2.8, followed by an N-H activation by a coordinated amidate forming proligand HL3 and complex 2.8. A minor product of the reaction has been shown to be a (t-butylamido) (t-butylimido)dichloro(N-phenylpivalamidate)tungsten(VI) complex (2.9) by single crystal X-ray diffraction (Figure 2-9).   Figure 2-9. Solid-state molecular structure of complex 2.9, plotted at 50% ellipsoids and most hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N1 = 1.741(10), W1-N2 = 2.014(19), W1-N3 = 1.89(2), W1-O1 = 2.00(2), W1-Cl1 = 2.502(9), W1-Cl1 = 2.480(3). Selected bond angles (deg): W1-N1-C1 = 170(1), W1-N2-C5 = 141(2), O1-W1-N3 = 66.6(9). 48  Isolation of analytically pure complex 2.9 has not been possible. As for complex 2.8 the purification of 2.9 has been hindered by proligand (HL3) contamination. In order to discern the reactivity pathway we added a dimeric bis(t-butylamine)bis(t-butylimido)dichlorotungsten complex (2.10) with 1 equivalent of proligand HL3 in an NMR tube (Scheme 2-4).140   Scheme 2-4. Reaction of complex 2.10 with proligand HL3. The reaction was conducted in benzene-d6 in an NMR tube with a resealable cap. Unexpectedly the major product of the reaction is the monochloride amidate complex 2.8 observed by diagnostic 1H-NMR resonances (δ 1.26 and 0.92, vide supra), accompanied by unreacted HL3 and 2.10 as well as small amounts of complex 2.9 (Scheme 2-4).  It should be noted that reactions involving exchanges of tungsten imido, amido, amine and chloride ligands have been observed before on similar systems bearing t-butoxide ligands.  These examples were also reported to be difficult to characterize.141 Interestingly, the major product (complex 2.8, Scheme 2-4) prefers two t-butylimido ligands rather than a mixed imido/amido/amine complex as observed in the tungsten t-butoxide complexes. A plausible explanation for this is that the amidate ligands provide increased steric demand versus a t-butoxide ligand, resulting in complex 2.8 as the preferred amidate product.  Interestingly the addition of lutidinium hydrochloride and amidate complex 2.5 did not proceed analogous to that of 2.4, at room temperature in toluene. The crude reaction 49  mixture of lutidinium hydrochloride and amidate complex 2.5 showed largely unreacted 2.5 (~90%) and upon work up only unreacted complex 2.5 could be re-isolated in reduced yields by filtering through diatomaceous earth with hexanes. The reduced reactivity of complex 2.5 with lutidinium hydrochloride can be attributed to the sterically demanding 2,6-diisopropylphenyl groups on the amidate ligands.  Pyridonate complexes 2.2 and 2.3 have also been treated with lutidinium hydrochloride. When 6-methylpyridonate complex 2.2 was added to one equivalent of lutidinium hydrochloride for 4 hours in toluene, a red orange solid formed upon removal of volatiles (Scheme 2-5). The 1H-NMR spectrum of the crude material suggested that one major product had formed along with unreacted 2.2. Although the crude material showed one major product, it was evident that other products have also formed by examining the 1H-NMR spectrum of the crude material and complex 2.12 (vide infra) could be identified in the crude reaction mixture. Under optimal conditions 2.11 could be isolated in 20% yield with a purity of less than 90% based on 1H-NMR spectrum of the isolated 2.11. A single crystal was obtained by slow evaporation of a concentrated benzene solution of the product. This product has been shown to be chloro(tert-butylimido)((κ1-O)6-methylpyridonate)bis((κ2-N,O)6-methylpyridonate)tungsten(VI) (2.11). 50   Scheme 2-5. Reaction of 2.2 with lutidinium hydrochloride.  The solid-state molecular structure of 2.11 is shown in Figure 2-10.   Figure 2-10. Solid-state molecular structure of complex 2.11, plotted at 50% ellipsoids with all hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N102 = 2.227(9), W1-N103 = 2.22(1), W1-N104 = 1.724(8), W1-O101 = 1.938(6), W1-O102 = 2.103(6), W1-O103 = 2.085(6), W1-Cl1 = 2.498(2). Selected bond angles (deg): W1-N104-C101 = 165.8(8), N104-W1-Cl1 = 171.3(2). The coordination geometry of the complex can be described as a distorted pentagonal bipyramid, where each tungsten bound atom occupies one site. The κ2-N,O pyridonate ligands exhibit an aryloxyimine bonding motif as evidenced by the shorter W-O bond 51  lengths (W1-O102, 2.103(6); W1-O103, 2.085(6)), versus the longer W-N bond lengths (W1-N102, 2.227(9) Å;W1-N103, 2.22(1) Å). The κ1-O pyridonate in 2.11 is analogous to that of complex 2.6. The chloride ligand is trans to the t-butylimido ligand, and exhibits an elongated W-Cl bond length (W1-Cl1, 2.498(2) Å).142 The t-butylimido ligand has a W-N4 bond length of 1.724(8) Å and a W-N104-C101 bond angle of 165.8(8)°.  Complex 2.11 is thought to form via ligand redistribution resulting from the protonation of a tungsten t-butylimido group to release free t-butylamine. Interestingly complex 2.11 has C3 symmetry in solution, as observed in the 1H-NMR spectrum at 25 °C. Two broad singlets of equal integration are observed at δ 2.53 and 1.07, which are attributed to the pyridonate methyl and the t-butylimido groups respectively. The observed broad resonances and observed C3 symmetry are attributed to the dynamic fluxionality of the pyridonate ligands. The 1H-NMR spectrum of the crude solids isolated from the reaction shows unreacted 2.2 and one major product which has been assigned to be 2.11 along with a minor product proposed to be (bis(t-butylimido)chloro(6-methylpyridonate)tungsten(VI)) complex 2.12. To verify this formulation, 2.12 has been synthesized independently by addition reaction of 2.2 with trimethylsilyl chloride (TMSCl), shown in Scheme 2-6.  Scheme 2-6. Synthesis of 2.12 by the reaction of 2.2 with TMSCl. When one equivalent or excess TMSCl has been allowed to react with pyridonate complex 2.2 at 60 °C overnight, complex 2.12 is formed. Removal of the volatiles under 52  vacuum yields dark orange solids and after recrystallization from warm hexanes at -30 °C, crystals suitable for X-ray diffraction could be obtained. The solid-state molecular structure is shown in Figure 2-11. The solution phase 1H-NMR spectrum of complex 2.12 exhibits broad resonances for the t-butylimido and pyridonate methyl signals at δ 1.31 and 1.97 respectively in a 6:1 ratio. These 1H-NMR resonances match that of the proposed minor product resulting from the reaction with lutidinium hydrochloride.  Figure 2-11. Solid-state molecular structure of complex 2.12, plotted at 50% ellipsoids with hydrogen atoms omitted for clarity. Selected bond lengths (Å): W1-N1 = 1.744(4), W1-N2 = 1.747(3), W1-N3 = 2.135(4), W1-O1 = 2.146(3), W1-Cl1 = 2.346(1). Selected bond angles (deg): W1-N1-C1 = 161.6(3), W1-N2-C5 = 163.8(3), O1-W1-N1 = 123.0(1), O1-W1-N2 = 125.3(1), N3-W1-Cl1 = 144.5(1), O1-W1-N3 = 61.3(1).  Complex 2.12 is isostructural to 2.8 and has nearly identical bond metrics for the tungsten ligand contacts (Figure 2-8 and Figure 2-10).85 The structural index parameter τ, used to distinguish the continuous symmetry of complexes between trigonal bipyramidal (TBP) and square pyramidal (SP), gave a value of 0.34 for complex 2.8 which is closer to a SP coordination geometry.143 Closer inspection of the solid state structure reveals complex 2.8 to exhibit a TBP coordination geometry rather than a SP geometry. The tight 53  bite angles of the amidate ligand (60.11(9)°) negates the accuracy of the τ parameter in this complex (Figure 2-12).  Figure 2-12. Solid-state molecular structure of 2.8, coordination geometry shown, all other atoms removed for clairity, with the exception of amidate carbon C15. Trigonal bipyramidal view on left, square based pyramid view on right. The Cs symmetry of complex 2.8 further supports a TBP structure; conversely a SP coordination geometry would be expected to have C1 symmetry. The same analogy can be made for complex 2.12 which is isostructural to 2.8 and has a τ value of 0.34, an overlay of the two solid-state molecular structures is shown in (Figure 2-13). 54   Figure 2-13. Overlay of solid state structures of 2.8 and 2.12. Complexes were overlaid using Olex overlay command and matching the W, Cl, and O atoms. Overlay of complex 2.8 and 2.12 shows isostructural complexes that have trigonal bipyramidal coordination geometries. The reaction of 3-methylpyridonate complex 2.3 with one equivalent of lutidinium hydrochloride at room temperature for 4 hours yields a pale white solid. The 1H-NMR spectrum of the crude reaction mixture shows resonances corresponding to 2.3 and two other products which correspond to the 3-methylpyridonate bridged di((3-methylpyridonate)bis(t-butylimido)chlorotungsten) complex 2.13 (vide infra) and an unknown impurity 2.14. Attempts to isolate complexes 2.13 and 2.14 from the reaction mixture have not been met with success. However, complex 2.13 has been independently synthesized via treatment of 2.3 with TMSCl (Scheme 2-7).   Scheme 2-7. Synthesis of 2.12 by the reaction of 2.2 with TMSCl. 55  In the solid state, complex 2.13 exhibits a dimeric structure (Figure 2-14, selected bond distances and angles are listed in Table 2-4). The nearly C2 symmetric complex has two μ2-N,O-3-methylpyridonate ligands that bridge between two bis(t-butylimido)chlorotungsten fragments. The W1-W2 distance is 3.958(8) Å, which is well beyond the sum of the covalent radii (3.34 Å)105 indicating that there is no bonding interaction between tungsten metal centers. Each tungsten metal center contains two t-butylimido ligands, one chloride, one μ-N-3-methylpyridonate, and one μ-O-3-methylpyridonate. The 5 coordinate tungsten metal centers are best described as distorted square pyramidal, with τ values of 0.14 and 0.16 for W1 and W2 respectively.143  Figure 2-14. Solid-state molecular structure of complex 2.13, plotted at 50% ellipsoids with hydrogen atoms omitted for clarity.     56  Table 2-4. Bond distances and bond angles of complex 2.13. Bond Distances (Å) Bond Angles (°) W1-O1 2.107(3) W2-O2 2.122(3) W1-N1-C1 172.4(3) W2-N3-C9 173.7(3) W1-N6 2.171(3) W2-N5 2.166(3) W1-N2-C5 150.2(3) W2-N4-C13 146.4(3) W1-N2 1.753(4) W2-N4 1.754(3) N6-W1-Cl1 155.45(9) N5-W2-Cl2 156.09(9) W1-N1 1.736(4) W2-N3 1.735(3) O1-W1-N6 80.1(1) O2-W2-N5 79.1(1) W1-Cl1 2.379(1) W2-Cl2 2.386(1) O1-W1-N2 105.6(1) O2-W2-N4 107.5(1) O1-C17 1.319(4) O2-C23 1.307(5) O1-W1-N1 146.9(1) O2-W2-N3 146.3(1) N5-C17 1.338(5) N6-C23 1.345(5) O1-W1-N1 146.9(1) O2-W2-N3 146.3(1) W1-O2 2.872(3) W2-O1 2.794(3) N2-W1-N1 107.3(2) N4-W2-N3 105.8(2)  In sharp contrast, amidate complexes 2.4 and 2.5 did not react with the bulky TMSCl reagent under the same conditions. In these cases, the unreacted amidate complexes 2.4 and 2.5, could be recovered after the reaction.  These results demonstrate the increased reactivity of pyridonate complexes 2.2 and 2.3 to that of amidate complexes 2.4 and 2.5. Both pyridonate complexes 2.2, 2.3 and amidate complexes 2.4, 2.5 are saturated six coordinate complexes in the solid state and have solution phase 1H-NMR spectra suggesting that the 1,3-N,O-donor ligated tungsten complexes behave similarly. However, the strikingly different reactivity patterns of these two classes of complexes clearly demonstrates that pyridonate ligands have diverse reactivity manifolds accessible in comparison to their amidate counter parts. Therefore, it is proposed that the increased ability of the pyridonate ligands to undergo ligand exchange reactions stems from their more dynamic hemilability. Furthermore, pyridonate ligands were shown to adopt bridging interactions which may promote the observed ligand 57  redistribution reactions. No κ1-O bonding modes have been observed in this study for any amidate ligands. Furthermore, no tungsten amidate complexes were shown to have a coordination number above 6, in contrast to pyridonate complexes. This mirrors past reports of titanium amidate and pyridonate complexes, where 7 coordinate tris(pyridonate) complexes have been disclosed, while the coordination numbers of titanium amidate complexes has not exceeded 6 for monometallic species.76 2.4 Conclusion  The new bis(t-butylimido)di(1,3-N,O-chelate)tungsten complexes 2.2-2.5 were synthesized by simple and high yielding protonolysis reactions. Variable temperature 1H-NMR spectroscopic experiments and computational modeling of the different coordination isomers suggest that the 1,3-N,O-donors display fluxional character. The reactivity investigations concluded that pyridonate ligands exhibit a broader scope of coordination modes and hence reactivity, than amidate ligands; this is attributed to the more dynamic hemilability of the pyridonate ligands. The electronic difference between the pyridonate and amidate ligands is in part responsible for the increase in fluxionality of the former, with the pyridonate ligand exhibiting more diverse bonding modes, such as the aryloxyimine motif and bridging bonding modes. Notably pyridonate ligands provide reduced steric protection at the metal center, and this also promotes enhanced reactivity.  These results point toward the benefits of using pyridonate ligands when 1-species are invoked as key reactive intermediates in catalytic cycles where the metal-ligand cooperative effects could be used to advantage.  Most importantly, pyridonate ligands have been shown to engage in hydrogen bonding interactions with metal amido ligands, suggesting that pyridonate ligands can be used to advantage in reactions where proton 58  shuttling is required.  An example of which is the Cp*Ir(III) pyridonate catalysts for ligand-assisted dehydrogenation of alcohols.81-82   Here we also show that pyridonate complexes can readily form dimeric species, a feature that has been used to advantage in the development of our bis(pyridonate)Ti catalyst for chemoselective intramolecular hydroaminoalkylation.66 In contrast, the increased robustness of amidate complexes points toward their preferential application in catalytic reactions where ligand loss or the formation of dimers or aggregate species is postulated to result in catalyst degradation. These observations rationalize why our bulky bis(amidate)Ti complex is an optimized catalyst for hydroamination; a reaction in which bridging imido dimers are known to result in catalyst death.82, 144 Further studies focus on the development of new complexes and catalysts that use these reactivity trends to advantage for E-H bond activations while avoiding complex or catalyst decomposition. 2.5 Materials and methods 2.5.1 General methods and materials  All reactions were conducted under an inert atmosphere of nitrogen, inside a glove box, or using standard Schlenk techniques unless otherwise noted. All chemicals were purchased from commercial sources and used as received unless otherwise noted. Bis(t-butylamido)bis(t-butylimido)tungsten(VI) (2.1) and (t-butylamine)bis(t-butylimido)dichlorotungsten(VI) (2.10) complexes were prepared according to the published procedure .109, 140 Trimethylsilyl chloride was distilled under nitrogen and stored in a Teflon® sealed Schlenk tube. Amide proligands HL3 and HL4 were synthesized from commercially available acid chlorides and primary amines by published procedures.63 Proligands were sublimed or dried under high vacuum overnight. All solvents (excluding 59  deuterated solvents) were passed through an activated alumina tower. Benzene-d6 and toluene-d8 were dried over sodium metal and distilled. NMR spectra were obtained on either a Bruker Avance 300 spectrometer, Bruker Avance 400inv spectrometer, or a Bruker Avance 400dir spectrometer. The spectra shown here have blue peak labels in blue and red integrations. The 1H- and 13C-NMR spectra were referenced to residual solvent signals, benzene-d6, (1H 7.16 ppm, 13C 128.06 ppm) and toluene-d8 (methyl, 1H 2.09 ppm). EI mass spectra were acquired on a Kratos MS-50 spectrometer. Elemental analyses were collected on a Carlo Erba Elemental Analyzer EA 1108 instrument. GC/MS were conducted on an Agilent 7890A GC equipped a 5975C inert XL EI/CI mass detector which is operated in positive CI mode with methane as the reagent gas. Experimental Procedures Synthesis of Lutidinium Hydrochloride 2,6-Dimethylpyridine (1.422 g, 0.01327 mol) was dissolved in 5 mL of hexanes in a 25 mL RBF, open to air. A dropwise addition of 5 mL of a 4 M HCl in a diethyl ether solution was added to the solution of 2,6-dimethylpyridine at 0 °C while stirring. A white solid immediately formed upon addition of the HCl solution. The white solid was isolated by filtration and washed twice with 10 mL of Et2O. The lutidinium hydrochloride was dried under vacuum overnight and then sublimed. The resulting solid was a colorless solid. Yield: 1.773 g, 93%. 1H NMR (DMSO-d6, 300 MHz): δ = 8.33 (t, J=7.9 Hz, 1 H), 7.70 (d, J=7.9 Hz, 2 H), 2.75 ppm (s, 6 H). Synthesis of 2.2 Complex 2.1 (0.4710 g, 1.001 mmol) was dissolved in 6 mL of toluene and then added to a vial charged with 6-methyl-2-pyridone (0.2190 g, 2.007 mmol) and a stir bar. The mixture was capped and stirred for 2 hours, resulting in a translucent yellow solution. The volatiles 60  were then removed under vacuum, and the resulting yellow semisolid was dissolved in 7.5 mL of hexanes and filtered through a 1 cm bed of Celite®. The volatiles were again removed under vacuum to yield a yellow semisolid. The semisolid was dissolved in hexanes and shaken, then dried under vacuum, again yielding a yellow semisolid. The yellow semisolid turned to a crystalline solid after days in a capped vial at room temperature. Yield: 0.5170 g, 95%. 1H NMR (400 MHz, Benzene-d6)  = 6.91 (dd, J = 7.3, 8.2 Hz, 2 H), 6.26 (d, J = 8.5 Hz, 2 H), 6.01 (d, J = 7.3 Hz, 2 H), 2.11 (s, 6 H), 1.48 (s, 18 H); 13C NMR (75 MHz, Benzene-d6)  = 172.1, 153.3, 140.7, 113.2, 107.3, 67.0, 33.2, 21.8; MS(EI) m/z 542 ([M]+), m/z 527 ([M -Me]+), m/z 471 ([M NtBu]+), m/z 414 ([M -NtBu -tBu ]+); Anal. Calcd. For WO2N4C20H30: N, 10.33%; C, 44.29%; H, 5.58%. Found: N, 9.97%; C, 44.53%; H, 5.66%.  Figure 2-15. 400 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.2. 61   Figure 2-16. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.2.  Figure 2-17. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.2. Synthesis of 2.3 62  Complex 2.1 (0.2357 g, 0.5011 mmol) was dissolved in 3 mL of toluene and then added to a vial charged with 3-methyl-2-pyridone (0.1110 g, 1.017 mmol) and a stir bar. The mixture was capped and stirred for 2 hours, resulting in a translucent yellow solution. The volatiles were then removed under vacuum, and the resulting yellow semisolid was dissolved in 4 mL of hexanes and filtered through a bed of Celite®. The volatiles were again removed under vacuum to yield a yellow semisolid which was recrystallized from minimal warm hexanes at -35 °C overnight and afforded a bright yellow powder. The mother liquor was decanted and the solids were dried under vacuum. Yield: 0.2065 g, 76%. 1H NMR (300 MHz, Benzene-d6)  = 7.62 (d, J = 5.6 Hz, 2 H), 6.82 (d, J = 7.0 Hz, 2 H), 6.06 (dd, J = 5.6, 7.0 Hz, 2 H), 1.94 (s, 6 H), 1.44 (s, 18 H); 13C NMR (75 MHz, Benzene-d6)  = 172.9, 141.6, 140.0, 123.0, 112.0, 67.2, 33.2, 15.1; MS(EI) m/z 542 ([M]+), m/z 527 ([M -Me]+), m/z 471 ([M NtBu]+), m/z 414 ([M -NtBu -tBu ]+); Anal. Calcd. For WO2N4C20H30: N, 10.33%; C, 44.29%; H, 5.58%. Found: N, 10.31%; C, 44.60%; H, 5.43%. 63   Figure 2-18. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.3.  Figure 2-19. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.3. 64   Figure 2-20. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.3. Synthesis of 2.4 Complex 2.1 (0.2014 g, 0.4282 mmol) was dissolved in 4 mL of toluene and then added to a vial charged with N-phenylpivalamide (0.1473 g, 0.8310 mmol) and a stir bar. The resulting mixture was capped and stirred for 2 hours, resulting in a translucent yellow solution. The volatiles were then removed under vacuum, to give a pale yellow crystalline solid. The solids were recrystallized from minimal warm hexanes at ambient temperature overnight. Large yellow prisms formed and the mother liquor was decanted and a second batch of crystals formed after the mother liquor was stored in a -35 °C freezer overnight to yield smaller yellow prisms. The yellow crystals were dried under vacuum. Yield: 0.2257 g, 80%. 1H NMR (400 MHz, Benzene-d6):  = 7.26 (d, J=6.1 Hz, 4 H), 7.05 (apparent t, J=7.5 Hz, 4 H), 6.88 (t, J=7.5 Hz, 2 H), 1.16 (br. s, 18 H), 1.15 (br. s, 18 H); 13C NMR 65  (101 MHz, Benzene-d6)  = 188.6, 149.4, 128.8, 127.9, 125.8, 66.5, 42.5, 32.7, 28.6; MS(EI) m/z 678 ([M -Me]+), m/z 663 ([M -Me]+); Anal. Calcd. For WO2N4C30H36: N, 8.25%; C, 53.10%; H, 6.83%. Found: N, 7.97%; C, 53.27%; H, 6.69%.  Figure 2-21. 400 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.4. 66   Figure 2-22. 101 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.4.  Figure 2-23. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.4. Synthesis of 2.5 67  Complex 2.1 (0.2348 g, 0.4992 mmol) was dissolved in 4.5 mL of toluene and then added to a vial charged with N-(2,6-diisopropylphenyl)benzamide (0.2846 g, 1.011 mmol) and a stir bar. The mixture was capped and stirred for 2 hours, resulting in a translucent yellow solution. The volatiles were then removed under vacuum, producing a yellow crystalline solid. The crystalline solids were dissolved in 10 mL hexanes and filtered through a plug of Celite®. The volatiles were removed leaving analytically pure yellow crystalline solids. Yield: 0.3799 g, 86%. 1H NMR (300 MHz, Benzene-d6)  = 7.76 (dd, J = 1.5, 8.3 Hz, 4 H), 7.29 - 7.18 (m, 6 H), 6.94 - 6.79 (m, 6 H), 4.19 (spt, J = 6.9 Hz, 2 H), 3.90 (spt, J = 6.9 Hz, 2 H), 1.74 (d, J = 6.9 Hz, 6 H), 1.44 (d, J = 6.9 Hz, 6 H), 1.20 (s, 18 H), 1.15 (d, J = 6.9 Hz, 6 H), 0.96 (d, J = 6.9 Hz, 6 H); 13C NMR (75 MHz, Benzene-d6)  = 178.5, 145.0, 144.0, 143.7, 134.1, 132.1, 130.4, 127.7, 125.4, 124.0, 67.6, 32.7, 28.5, 28.4, 26.5, 25.4, 24.0, 23.3; MS(EI) m/z 886 ([M]+, %), m/z 871 ([M -Me]+, %) ; Anal. Calcd. For WO2N4C20H30: N, 6.32%; C, 62.30%; H, 7.05%. Found: N, 6.72%; C, 62.67%; H, 7.14%.  Figure 2-24. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.5. 68   Figure 2-25. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.5.  Figure 2-26. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.5. 69  Synthesis of 2.6  Solid complex 2.6 is precipitated from an equilibrium mixture of pyridonate complex 2.2 (0.0500 g, 0.09713 mmol) and proligand HL3 (0.0106 g, 0.09220 mmol) in hexanes at -35 °C. The mother liquor was decanted and the solids were dried under reduced pressure. 1H NMR (300 MHz, Benzene-d6):  = 6.93 (dd, J = 7.4, 8.2 Hz, 2 H), 6.79 (dd, J = 6.9, 9.1 Hz, 1 H), 6.38 (d, J = 9.1 Hz, 1 H), 6.28 (d, J = 8.2 Hz, 2 H), 6.03 (d, J = 7.4 Hz, 2 H), 5.47 (d, J = 6.9 Hz, 1 H), 2.14 (s, 6 H), 2.00 (s, 3 H), 1.47 (s, 18 H); 13C NMR (75 MHz, Benzene-d6):  = 172.0, 167.2, 153.5, 147.5, 141.5, 140.6, 116.6, 113.3, 107.5, 106.3, 66.7, 33.1, 22.0, 19.5; MS(EI) m/z 579 [M -HNtBu]+, m/z 523 [M -HNtBu, -C3H8]+; Anal. Calcd. For WO3N5C26H37: N, 10.75%; C, 47.94%; H, 5.72%. Found: N, 10.64%; C, 48.03%; H, 5.69%.  Figure 2-27. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.6. 70   Figure 2-28. 75 MHz 13C-NMR spectrum in C6D6 at 25 °C of complex 2.6.  Figure 2-29. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.6. 71  Synthesis of 2.7 Precipitation of white and yellow solids from an equilibrium mixture of pyridonate complex 2.3 and proligand HL4 does not produce a single isolable product. EIMS conducted on the precipitated solids showed fragments corresponding to complex 2.3 and a (t-butylimido)tris(3-methyl-2-pyridonate)tungsten(VI) fragment. The 1H-NMR solution phase spectrum suggested fluxional species, which was confirmed by variable temperature 1H-NMR spectroscopy experiments. 1H NMR 25 °C (400 MHz, Toluene-d8)  = 8.43 (br. s.), 8.06 (br. s.), 7.79 (d, J = 4.9 Hz), 7.76 (d, J = 4.9 Hz), 7.40 (d, J = 4.4 Hz), 6.87 (d, J = 7.3 Hz), 6.33 - 6.25 (m), 6.15 (dd, J = 5.4, 6.8 Hz), 6.02 (t, J = 6.1 Hz), 2.56 (br. s.), 1.99 (br. s.), 1.97 (s), 1.93 (s), 1.41 (s), 1.02 (s), 0.99 (s); MS(EI) m/z 579 [M -HNtBu]+, m/z 523 [M –HNtBu, -C3H8]+.  Figure 2-30. 400 MHz 1H-NMR spectrum in C7D8 at 25 °C of complex 2.7. 72   Figure 2-31. 400 MHz 1H-NMR variable temperature spectra in C7D8 of complex 2.7. Synthesis of 2.8 and 2.9 Complex 2.4 (0.0509 g, 0.0750 mmol) was dissolved in 2 ml of toluene and added to a vial containing a suspension of lutidinium hydrochloride (0.0114 g, 0.0794 mmol) in 2 mL of toluene in a glove box. The yellow mixture was then stirred at ambient temperature for 4 hours. The volatiles were removed to yield pale yellow solids. Hexanes (1.5 mL) was used to form a suspension of the crude solids, which was filtered through a 2 cm plug of Celite™, and the volatiles were removed under vacuum. The filtration was conducted again using 1.5 mL of hexanes and again filtering through a 2 cm plug of Celite™, and the volatiles were removed under vacuum. The solids were dissolved in warm hexanes and recrystallized at room temperature, colorless crystals formed overnight, and the mother liquor was decanted and the crystals were dried under vacuum. This first batch of 73  crystalline material yielded small amounts (less than 0.01 g) of predominately complex 2.9, contaminated with complex 2.8 and proligand HL5. The mother liquor was decanted and concentrated then left to recrystallize again for 2 days, yielding colorless crystalline rods which were found to be complex 2.8 (0.0096 g) contaminated with proligand HL5 and small amounts of complex 2.9. The mother liquor was decanted and the crystals were dried in vacuum. Analytically pure material of complex 2.8 or 2.9 could not be obtained, 1H-NMR spectrum of the recrystallized complexes 2.8 and 2.9 are shown below. Spectroscopic assignments for complex 2.8: 1H NMR (300 MHz, Benzene-d6):  = 7.08 - 6.95 (m, 4 H), 6.83 (tt, J = 2.1, 7.2 Hz, 1 H), 1.27 (s, 18 H), 0.91 (s, 9 H); MS(EI) m/z 537 [M]+, m/z 522 [M - Me]+. Spectroscopic assignments for complex 2.9: 1H NMR (300 MHz, BENZENE-d6)  1.02 (s, 9 H) 1.09 (s, 9 H) 1.16 (s, 9 H) 6.92 (tt, J=7.4, 1.3 Hz, 1 H) 7.06 - 7.13 (m, 2 H) 7.59 - 7.65 (m, 2 H) 9.87 (br. s., 1 H).  Figure 2-32. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.8. 74   Figure 2-33. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.9. Synthesis of 2.11 Complex 2.2 (0.0360 g, 0.06638 mmol) was dissolved in 3 ml of toluene and added to a vial containing a solid of lutidinium hydrochloride (0.0093 g, 0.06476 mmol) in a glove box. The mixture was then stirred at ambient temperature for 4 hours, then 3 mL of hexanes was added, and the stirring was halted. Off white solids precipitated, and the mother liquor was decanted. The solids were washed with 2 mL of hexanes twice and then the solids were dried under vacuum. Yield: 0.0087 g (~20% yield). Analytically pure material of complex 2.11 could not be obtained. 1H NMR (300 MHz, Benzene-d6)  = 6.99 (t, J = 7.9 Hz, 3 H), 6.59 - 6.09 (m, 6 H), 2.54 (s, 9 H), 1.09 (s, 9 H); MS(EI) m/z 579 [M -Cl]+, m/z 506 [M -ONC5H6]+, m/z 472 [M -ONC5H6, -Cl]H+, m/z 450 [M -ONC5H6, -C3H8]+, m/z 414 [M -ONC5H6, -Cl, -C3H8]+. 75   Figure 2-34. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.11. Synthesis of 2.12  Complex 2.2 (0.0637 g, 0.118 mmol) was dissolved in 1.5 mL of toluene and was added to a Teflon® sealable reaction flask that was charged with a stir bar. The reaction vessel was then taken out of the glovebox and 1.2 mL of 0.15 M TMSCl (0.020 g, 0.18 mmol) in toluene, was added via syringe to the reaction flask on a Schlenk line. The reaction flask was put in a 60 °C oil bath. The mixture was stirred for 20 hours during which the color changed from a yellow solution to an orange color. The reaction was then removed from the oil bath and allowed to cool to room temperature. The volatiles were then removed under vacuum affording a red solid. The reaction flask was taken back into the glove box and the solids were extracted with hexanes (4-5 mL) and filtered through the a Celite™ plug, then the volatile were removed. The solids were recrystallized from warm hexanes at 76  room temperature overnight producing colorless crystalline solids. The mother liquor was decanted and the solids were washed with cold hexanes, then dried under vacuum. Yield: 0.0157 g. Analytically pure material of complex 2.12 could not be obtained, 1H-NMR spectrum of the recrystallized complex 2.12 is shown in Figure 2-35. 1H NMR (300 MHz, Benzene-d6)  = 6.74 (dd, J = 7.5, 8.7 Hz, 1 H), 5.94 (d, J = 8.7 Hz, 1 H), 5.89 (d, J = 7.5 Hz, 1 H), 1.96 (br. s., 3 H), 1.31 (s, 18 H); MS(EI) m/z 469 [M]+, m/z 454 [M -Me]+, m/z 398 [M -NtBu]+.  Figure 2-35. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.12. Synthesis of 2.13 Complex 2.3 (0.0502 g, 0.0926 mmol) was dissolved in 2 ml of toluene and was added to a Teflon® sealable reaction flask that was charged with a stir bar in the glove box. The reaction vessel was taken out of the glove box and 0.6 mL of TMSCl (0.5 g, 5 mmol) was 77  added via syringe to the flask on a Schlenk line. The reaction flask was then put in a 60 °C oil bath. The mixture was stirred for 20 hours during which the color of the solution remained yellow. The reaction was then removed from the oil bath and allowed to cool to room temperature. The volatiles were then removed under vacuum leaving a yellow solid. The reaction flask was taken back into the glove box and the solids were dissolved in minimal warm toluene and recrystallized at room temperature overnight producing small pale-yellow crystals. The mother liquor was decanted and the solids were dried under vacuum. Yield: 0.0242 g. Analytically pure material of complex 2.13 could not be obtained, 1H-NMR spectrum of the recrystallized complex 2.13 is shown in Figure 2-36. 1H NMR (300 MHz, Benzene-d6)  = 7.22 (br. s., 1 H, overlapping with Benzene-d6), 6.64 (d, J = 7.0 Hz, 1 H), 5.98 (dd, J = 5.1, 7.0 Hz, 2 H), 1.72 (s, 3 H), 1.32 (br. s., 18 H); MS(EI) m/z 469 [M]+, m/z 454 [M -Me]+, m/z 398 [M -NtBu]+. 78   Figure 2-36. 300 MHz 1H-NMR spectrum in C6D6 at 25 °C of complex 2.13. 79  2.5.2 Other NMR spectra  Figure 2-37. 300 MHz 1H-NMR in toluene-d8 of the reaction of complex 2.2 with complex 2.3.  Figure 2-38. 400 MHz 1H-NMR variable temperature spectra in toluene-d8 of the reaction of complex 2.4 with one equivalent of proligand HL3. At lower temperatures, proligand HL3 precipitates out of solution. 80    Figure 2-39. 400 MHz 1H-NMR variable temperature spectra in toluene-d8 of the reaction of complex 2.5 with one equivalent of proligand HL4. At lower temperatures, proligand HL4 precipitates out of solution. 2.5.3 Theoretical calculations  Density-functional calculations were undertaken using a Linux cluster of IBM machines with Intel Xeon processors at the Westgrid facility at the University of British Columbia. The Gaussian’09 package was employed with the B3LYP functional.145-146 The LANL2DZ basis set with the corresponding ECP was used for the tungsten atoms, for all other atoms the 6-31G** basis set was used.147-152 The initial coordinates were imported from the solid-state molecular structures into GaussView and then freely refined as a neutral molecule and S=0. The initial coordinates of the other geometric isomers were 81  adjusted using GaussView and refined analogously. Single point frequency calculations were undertaken to verify local minima.  Table 2-5. Energies of computed isomers (Δ only) of complexes 2.2, 2.3, 2.4, and 2.5 and relative energies. 2.2* and 2.5* with dispersion correction. Complex Absolute Energy (Hartrees) Relative Energy (kcal/mol) Order Coordination 2.2 -1217.256914 8.3 3 N-trans   -1217.270201 0.0 1 O-trans -1217.263088 4.5 2 C1  2.2*  -1217.393502 3.9 3 N-trans  -1217.399762 0.0 1 O-trans -1217.396830 1.8 2 C1 2.3 -1217.260418 2.7 3 N-trans -1217.264766 0.0 1 O-trans -1217.262567 1.4 2 C1 2.4 -1607.754757 0.0 1 N-trans -1607.743986 6.8 3 O-trans -1607.750355 2.8 2 C1 2.5 -2226.862229 0.0 1 N-trans -2226.850762 7.2 3 O-trans -2226.851056 7.0 2 C1 2.5* -2227.178363 0.0 1 N-trans -2227.141987 22.8 3 O-trans -2227.158526 12.4 2 C1  82   Table 2-6. Images of computed isomers of complex 2.2. Image* with dispersion correction. Isomer N-trans C2 O-trans C2 C1 Image    Image*            83  Table 2-7. Images of computed isomers of complex 2.3. Isomer N-trans C2 O-trans C2 C1 Image     Table 2-8. Images of computed isomers of complex 2.4. Isomer N-trans C2 O-trans C2 C1 Image         84  Table 2-9. Images of computed isomers of complex 2.5. Image* with dispersion correction. Isomer N-trans C2 O-trans C2 C1 Image    Image*       Figure 2-40. Overlay of DFT computed and solid-state molecular structure of complex 2.2. Hydrogen atoms are omitted in both the computed and solid-state molecular structures. Left; overlay of DFT without dispersion correction, Right; overlay of DFT with dispersion correction. 85   Figure 2-41. Overlay of DFT computed and solid-state molecular structure of complex 2.3. Hydrogen atoms are omitted in both the computed and solid-state molecular structures.  Figure 2-42. Overlay of DFT computed and solid-state molecular structure of complex 2.4. Hydrogen atoms are omitted in both the computed and solid-state molecular structures. 86   Figure 2-43. Overlay of DFT computed and solid-state molecular structure of complex 2.5. Hydrogen atoms are omitted in both the computed and solid-state molecular structures. Left; overlay of DFT without dispersion correction, Right; overlay of DFT with dispersion correction. 87  Chapter 3: Tungsten oxo neopentylidene complexes with 1,3-N,O-donor ligands 3.1 Introduction Consumer products such as plastics, paints, pharmaceuticals, and common household chemicals all rely on olefins as feedstocks or as intermediates in their production. In particular, alpha olefins are readily accessible due to their industrial production from ethylene.153-154 These alpha olefins can be upgraded to more lucrative fine chemicals or intermediates by a variety of known chemical transformations including hydration,155 halogenation and hydrohalogenation,155 hydrofunctionalization reactions,156 hydroformylation,157 epoxidation,158 polymerization159 and oligomerization160 to name a few. Another important reaction used to interconvert olefins rather than functionalize them has been the olefin metathesis reaction (Figure 3-1).161  Transition metal catalyzed olefin metathesis catalysis161 has found broad ranging synthetic application from the preparation of fine chemicals to large scale industrial manufacturing of materials.162 The Shell Higher Olefin Process (SHOP) is one such example of an olefin cross metathesis (CM) reaction used on industrial scales to produce internal linear olefins (Figure 3-1, equation ii), which are used as precursors for plasticizers and detergents on a scale of over 1 million tons annually.2 In addition, ring closing metathesis (RCM) has been used to synthesize bioactive compounds, often chemo-selectively, in academic and pharmaceutical laboratories (Figure 3-1, equation iii).163 Strained cyclic olefins can undergo ring opening metathesis polymerization (ROMP) reactions producing materials with unique properties (Figure 3-1, equation iv).164 The 88  olefin metathesis reaction has become so prevalent that the Nobel prize has been given to Yves Chauvin, Robert H. Grubbs and Richard R. Schrock in 2005 for their development of olefin metathesis methodology in organic synthesis.165  Figure 3-1. i) General olefin metathesis reaction, ii) cross metathesis reaction of 1-pentene, iii) ring closing metathesis of 1,7-octadiene, iv) ring opening metathesis polymerization of norbornene. The transition metals employed as olefin metathesis catalysts include titanium, vanadium, niobium, tantalum, molybdenum, tungsten, rhenium, ruthenium and osmium.166-168 The most commonly employed metals used for olefin metathesis today are molybdenum, tungsten and ruthenium.166 While the efficiency of the catalyst does depend on the metal used, a critical feature of a given olefin metathesis catalyst is the ancillary ligands bound to the metal. Strategic selection of appropriate ancillary ligands have yielded highly reactive, isolable complexes that contain metal carbon multiple bonds.161, 166 At the 89  heart of olefin metathesis are transition metal catalysts bearing metal carbon multiple bonds called alkylidene ligands. The first reported alkylidene complex was a tris(neopentyl)(neopentylidene)tantalum complex (3.1) reported in 1974 by Richard R. Schrock (Scheme 3-1).18 The synthesis of 3.1 is proposed to form via a pentakis(neopentyl)tantalum intermediate (Scheme 3-1) which undergoes α-hydrogen abstraction forming an alkylidene ligand and neopentane. Alkylidene ligands form via α-hydrogen abstraction, which can occur through thermal or photolytic pathways.18, 169  Scheme 3-1. Synthesis of complex 3.1.18 Tantalum alkylidene complexes have been shown to be competent olefin metathesis catalysts when alkoxide ancillary ligands are combined with the tantalum alkylidene species.170 Great advances in the development of olefin metathesis catalysts have been achieved when tungsten oxo alkylidene complexes were synthesized by transmetallation of a tantalum alkylidene to a tungsten oxo metal center.171 These tungsten alkylidene complexes were independently shown by Schrock and Osborn to have improved catalytic activity for olefin metathesis when activated with a Lewis acid such as AlEt3.171-172 Initially, the tungsten oxo alkylidene catalysts had problematic and unwanted reaction pathways that caused catalyst death, leading Schrock to investigate tungsten imido alkylidene complexes. Subsequently, these complexes have been shown to be some of the most active olefin metathesis catalysts to date.30, 173 These Schrock-type complexes require bulky ancillary ligands to avoid intermolecular reductive coupling of the alkylidene 90  ligands. Another complication with group 6 olefin metathesis catalysts is their inherent sensitivity to air, moisture and protic substrates, which limits their use.174 The general formula for the Schrock type complexes are M(alkylidene)(E)XY; where M=Mo or W, E=O or NR, and X and Y are mono-anionic ligands (Scheme 3-2).175 The Schrock type catalysts (i, Scheme 3-2) are 14-electron unsaturated metal species that show excellent metathesis activity. The importance of an unsaturated complex is evident when considering the mechanism of the olefin metathesis reaction (Scheme 3-2); in which, to allow for olefin coordination (Scheme 3-2, top right and bottom left corners) the metal complex must have an accessible site and be less than an 18 electron complex. If the metal center is electronically saturated the olefin would not be able to bind and metathesis could not proceed. The mechanism of group 6 catalyzed olefin metathesis has been investigated experimentally and theoretically.176-180 The metathesis mechanism begins with olefin coordination to the metal and distortion of the complex to a trigonal bipyramidal (TBP) geometry (Scheme 3-2, II) from the starting tetrahedral geometry (Scheme 3-2, I). The five coordinate TBP intermediate has the Y ligand trans to the ME bond in an axial position, and the incoming olefin coordinates in the equatorial plane with the X and alkylidene ligands. Following olefin coordination is the 2+2 cycloaddition (Scheme 3-2, III) and cycloreversion (Scheme 3-2, IV) to form the metathesized product. The resulting methylidene complex (Scheme 3-2, V) has been inverted compared to the starting complex (Scheme 3-2, I). Productive CM requires another metathesis reaction to take place with the substituted olefin to remake the starting complex I (Scheme 3-2, left side). The CM 91  reaction is driven forward by release of gaseous ethene which results in the homo-coupling of the substituted terminal alkene as shown in Scheme 3-2.       Scheme 3-2. Olefin cross metathesis mechanism of the homo-coupling of substituted terminal alkenes, (i) Schrock type catalyst; M=Mo or W, E=O or NR, R= substrate group, X and Y=mono anionic ligands, example of a highly active olefin metathesis catalyst 1.17. Dipp=2,6-diisopropylphenyl.  The highly active catalyst 1.17 shown in Scheme 3-2 depicts a syn alkylidene, where the R group of the alkylidene points towards the imido ligand, the 1JCH coupling constants of syn alkylidenes range from 105-125 Hz.177 When the R group of the alkylidene is pointed away from the imido substituent it is said to be an anti alkylidene, the 1JCH coupling constants of anti alkylidenes range from 140-150 Hz.177 Schrock type tungsten imido alkylidene complexes have been shown to interconvert between rotamers (syn and anti).177 Tungsten oxo alkylidene complexes are nearly always observed in a syn 92  configuration in the solid state, and rotamers of these complexes have been rarely discussed in previous reports. Experimental and computational investigations suggest that the syn rotamer is more stable by 1-4 kcal/mol, and the stabilization is caused by an α-agostic interaction of the C-H bond and the metal, trans to the ME bond.180-181  The decomposition pathways of group 6 olefin metathesis complexes has also been studied experimentally and theoretically.8 Bimolecular coupling of alkylidene ligands is known a pathway for decomposition of a group 6 olefin metathesis catalysts.8 This pathway of decomposition is frequently proposed with methylidene ligands which readily form bridging complexes.8 Scheme 3-3 highlights an example where coupling of neopentylidene ligands results in reduction of the tungsten metal centers and production of 1,2-di-tert-butylethylene.182  Scheme 3-3. Reductive coupling of neopentylidene ligands to form a ditungsten complex and 1,2-di-tert-butylethylene. Another route for decomposition of group 6 olefin metathesis catalysts is the rearrangement of a TBP metallacyclobutane to a square pyramid (SP) metallacyclobutane complex, followed by β-hydride elimination (Scheme 3-4). While both the TBP and SP metallacyclobutane have been observed in the solid state, computational studies suggest 93  that the SP metallacyclobutane complexes are lower in energy than the TBP metallacyclobutane complexes.178, 183-184  Scheme 3-4. Reaction of ethylene with a group 6 alkylidene, which initially forms a TBP metallacyclobutane and then isomerizes to a SP metallacyclobutane, which undergoes β-hydride elimination.  To overcome the sensitivity of high valent group 6 metals, rational ligand design was used to improve the stability of the group 6 olefin metathesis catalysts. The approach relies on saturating the metal center with neutral donor ligands, thus stabilizing the reactive high valent metal alkylidene complex. Then removal of the donor ligand regenerates the catalytically active olefin metathesis complex. In 2011, Fürstner et al. reported the chelation of 1,10-phenanthroline and 2,2´-bipyridine to a highly active molybdenum olefin metathesis catalyst.185 The resulting adducts were stabilized by the donor ligands and the olefin metathesis was completely shut down, however, their stability towards air and moisture was drastically improved such that the complexes could be stored in aerobic conditions (Scheme 3-5). The highly active catalyst could be regenerated by removing the 1,10-phenanthroline or 2,2´-bipyridine (Bipy) ligands with one equivalent ZnCl2. Although, the catalyst would then be just as sensitive as the initially reported complex.  94   Scheme 3-5. Stabilization of air and moisture sensitive olefin metathesis catalyst with 2,2´-bipyridine.185 Advancements toward improving the functional group tolerance of the group 6 olefin metathesis catalysts were successful when molybdenum alkylidene complexes with N-heterocyclic carbene (NHC) auxiliaries were employed.186 While the molybdenum NHC complexes show good reactivities,187 the catalysts form cationic intermediates and the use of undesired toxic chlorinated solvents is necessary to solubilize these species.  Tremendous advances have been made towards the development of olefin metathesis catalysts, however, the development of new catalysts with increased substrate scopes and excellent catalytic performance is still an area of vigorous research. Applications in organic synthesis and ROMP commonly rely on ruthenium Grubb’s type catalysts due to their stability towards air and moisture,161 however the cost and toxicity of ruthenium presents challenges in its utility. It is increasingly apparent that there will be no “fix all” catalyst, rather a toolbox of catalysts will be needed depending on the desired application.161  Interestingly, there is no precedent for 1,3-N,O-ligated alkylidene metal complexes. There have been select reports of 1,3-O,O-ligated (carboxylate) tungsten alkylidene complexes by Schrock et al. and by Buchmeiser et al., all of which are supported by an imido ancillary.188-190 These complexes were found to be unreactive to olefins, which was 95  proposed to be due to the steric environment and saturation about the metal center.188 The bis(carboxylate)(alkylidene)(imido)tungsten and molybdenum complexes are saturated 18-electron species in the solid state. If the complexes have similar saturated metal centers in solution, the complex would not be able to bind an incoming olefin for productive metathesis (Figure 3-2). However, if the carboxylate ligand is hemilabile this could render the catalyst active. Importantly, Schrock et al. can isolate hemilabile κ1-O carboxylate complexes, but only when a phosphine ligand has been added to the complex. Notably, a phosphine stabilized the 1,3-O,O-ligated complex also does not react with olefins.189  Figure 3-2. (left) Bis(carboxylate)(alkylidene)(imido)molybdenum complex, (right) hemilabile 1,3-O,O-donor ligand with PMe3 coordinated in the revealed coordination site. Ar= 2-tBuC6H4.  The 1,3-N,O-donor and 1,3-O,O-donor ligands have similar bonding properties when coordinated to transition metals,58, 191 but they offer very different steric demands which have been shown to influence overall bonding modes.67 The 1,3-N,O-donor ligands on early transition metals have been characterized as having κ1-O, κ1-N and µ2-N,O bonding modes in the solid state as well as the most prevalent κ2-N,O bonding mode.58, 65, 67, 117, 139, 192-193 These 1,3-N,O-donor ligands are hemilabile and have led us and others to believe that the hemilability of the 1,3-N,O-donor ligands is integral to access reactivity pathways.  96   For example, the commerically available Schafer hydroamination catalyst is a bis(amidate)titanium complex that exploits the hemilability of the 1,3-N,O-donor auxiliaries to achieve unprecedented reactivity and selectivity as a group 4 hydroamination catalyst.66, 70, 99-100 The 1,3-N,O-donor ligands on the titanium catalyst are fluxional, and can adopt κ1-O bonding modes to allow for catalytic turnover.70 1,3-N,O-donor ligands are typically observed in the solid-state with a N-trans geometry if the N-substituent is large with both ligands in a κ2-N,O fashion.63 However, variable temperature NMR spectroscopy shows that the 1,3-N,O-donor ligands are fluxional at the elevated temperatures relevant to catalysis indicating bonding modes other than κ2-N,O are present in solution.70 The mechanism of the group 4 catalyzed hydroamination is shown in Scheme 3-6, which highlights the proposed hemilability of the 1,3-N,O-donor ligands. Notably, hydroamination proceeds via a 2+2 cycloaddition, like olefin metathesis.  97   Scheme 3-6. Mechanism of the titanium catalyzed intermolecular hydroamination of primary amines and terminal alkynes, highlighting the hemilability of the 1,3-N,O-donor ligands.101 Dipp = 2,6-diisopropylphenyl.  Inspired by the success of the aforementioned titanium complex that facilitates the intermolecular hydroamination of primary amines and terminal alkynes, it was hypothesized that 1,3-N,O-donor ligands could be used as ancillary ligands on a Schrock-type olefin metathesis catalyst. Specifically, it has been hypothesized that di(1,3-N,O-chelate)(alkylidene)(oxo)tungsten complexes could generate unsaturated metal species in solution, that are required for productive olefin metathesis catalysis (Scheme 3-7). Such metathesis reactivity would establish the fundamental difference between 1,3-N,O- versus 1,3-O,O-donor ligands. 98   Scheme 3-7. Hemilabile 1,3-N,O-chelating ligands  bonding mode interconversion and corresponding electron count at the tungsten metal center. Highlighting the necessary generation of unsaturated species capable of participating in the olefin metathesis accepted mechanism. N-trans isomer show as representative complex.  The previously reported 1,3-O,O-ligated molybdenum imido alkylidene complexes did not react with olefins presumably due to steric congestion around the metal center.188 Therefore, it has been anticipated that tungsten oxo alkylidene complexes would have less steric demands and could react with olefins. Synthetic routes into Schrock oxo neopentylidene type complexes have been previously developed, and their preparation relies on either W(O)(CHCMe3)(PyrMe2)2PMe2Ph (3.2) or W(O)(CHCMe3)(Cl)2(PMe2Ph)2 (3.4) starting materials (Scheme 3-8).184, 194 Complex 3.2 is employed in protonolysis reactions, while complex 3.4 is used in salt metathesis reactions. Scheme 3-8 depicts recent literature examples of both reaction types. 99   Scheme 3-8. (top) Protonolysis reaction of complex 3.2 with a substituted thiophenol producing complex 3.3, (bottom) Salt metathesis reaction of complex 3.4 with a lithium aryloxide producing complex 3.5.184, 194  The targeted synthesis of tungsten oxo alkylidene complexes with 1,3-N,O-donating ligands will also rely on protonolysis and/or salt metathesis reactions. Scheme 3-7 shows the targeted di(1,3-N,O-chelate)(neopentylidene)(oxo)tungsten complex where I hypothesized that olefins would be able to react with the complex when the hemilabile 1,3-N,O-donor ligands adopt κ1 bonding modes to access an unsaturated complex. To further our studies on di(1,3-N,O-chelate)(neopentylidene)(oxo)tungsten complexes, a series of 1,3-N,O-chelated complexes with amidate ligands has been designed. The modular synthesis of amide proligands would allow for tuning of the resulting amidate ligand electronic and steric features. Evaluating the new complexes by testing their capabilities as olefin metathesis catalysts would allow for testing the relative hemilability of the amidate ligands employed. Thus, a series of complexes could be examined experimentally to ascertain the importance of substituents on the amide proligand, specifically if changing the electronic properties of amidate ligands by varying the 100  substituents on the amide proligand affects hemilability in the resulting complexes. This chapter discusses the synthesis and characterization of the first 1,3-N,O-donor ligated tungsten oxo neopentylidene complexes and their reactivities with 1,7-octadiene. 3.2 Synthesis and characterization of tungsten oxo neopentylidene complexes with 1,3-N,O-donor ligands 3.2.1 Synthesis and characterization of bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten  The proligand HL4 has been chosen as the first amide due its steric parameters and precedent to support metal element multiple bonds in previous work by the Schafer group.61 The steric demand of HL4 was important, as it has been known that tungsten oxo and alkylidene ligands can form dimeric species when there is a lack of steric demand around the metal center.61, 67 The experimental design for synthesis of di(1,3-N,O-chelate)(neopentylidene)(oxo)tungsten complexes has been inspired by literature precedent for protonolysis reactions in the synthesis of Schrock type tungsten oxo alkylidene complexes (Scheme 3-8),194 and our recent success of installing 1,3-N,O-donor ligands on tungsten bis(imido) complexes by protonolysis reactions (Chapter 2).67 3.2.1.1 Synthesis and characterization of bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten via protonolysis route  The protonolysis reaction of 3.2 with two equivalents of HL4 affords a bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten complex 3.6 (Scheme 3-9) as observed in the 1H-NMR spectrum of the isolated material (vide infra). When the reaction has been monitored by 1H-NMR in a J-Young NMR tube, complex 3.6 and HL4 101  have been consumed within the first 30 minutes. Due to the quick consumption of staring materials the reaction conditions were not altered, and a reaction time of 2 hours at room temperature has been employed analogous to that of the protonolysis reaction in Chapter 2 for the synthesis of the di(1,3-N,O-chelate)bis(t-butylimido)tungsten complexes.  Scheme 3-9. Protonolysis reaction of 3.2 and two equivalents of proligand HL6. Dipp=2,6-diisopropylphenyl, PyrMe2=2,5-dimethylpyrrole.  After the 2-hour reaction time the yellow reaction mixture was filtered through diatomaceous earth to remove any insoluble materials, then the volatiles were removed under vacuum leaving a sticky dark yellow semi-solid. The 1H-NMR spectrum of the crude material contained resonances attributed to complex 3.6, dimethylphenylphosphine and 2,5-dimethylpyrrole. The diagnostic resonances for complex 3.6 include; the alkylidene (WCHC(CH3)3) singlet resonance at δ 10.86 (1H) with 1JCH=119.3 Hz indicative of a syn alkylidene, four separate aryl multiplet resonances ranging from δ 7.74-6.82 integrating to a total of 16 hydrogens, four separate isopropyl methine (CArylCH(CH3)2) septet resonances at δ 4.26, 4.18, 3.98 and 3.60 integrating to 1 hydrogen each, eight separate isopropyl methyl (CArylCH(CH3)2) doublet resonances at δ 1.64, 1.61, 1.43, 1.40, 1.12, 1.04, 1.01 and 0.88 each integrating to 3 hydrogens, and one alkylidene (WCHC(CH3)3) t-butyl singlet resonance at δ 1.24 integrating to 1 hydrogen. The neopentylidene tungsten bound carbon (WCHC(CH3)3) was observed at δ 289.0 in the 13C-NMR spectrum, which is within the 102  range of reported complexes.184 The amidate carbons of the NCO motif appear at δ 183.3 and 174.2 in the 13C-NMR spectrum. Importantly the amidate carbons chemical shift suggest that both 1,3-N,O-chelates are bound in a κ2-N,O fashion, due their chemical shift being up field compared to the proligand HL4 (δ 166.1).72-73, 195 The NMR data of 3.6 suggests a C1 symmetric complex, as would be expected for a bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten complex where the amidate ligands are both bound in a κ2-N,O fashion.  Complex 3.6 has also been characterized in the solid state by single crystal X-ray diffraction, and the solid-state molecular structure has been shown in Figure 3-3. One of the N-(2,6-diisopropylphenyl)benzamidate ligands shows disorder over every atom in the 1,3-N,O-chelate ligand. Analogous to the di(N,O-chelate)bis(t-butylimido)tungsten complexes (2.2, 2.3, 2.4 and 2.5, in Chapter 2), 3.6 exhibits a highly distorted octahedral geometry. The complex exhibits two κ2-N,O amidate ligands which matches the solution 1H-NMR data analysis, suggesting that 3.6 has the same structure in solution (at 25 °C) and in the solid state. The two amidate ligands have a N-trans coordination to the tungsten metal center as anticipated due to the steric demand of the 2,6-diisopropylphenyl groups of the amidate ligands.67, 70 The 1,3-N,O-donor ligand bite angles are 59.3(2) and 59.4(6)° for O2-W1-N1 and O3A-W1-N2 respectively, which is within the reported range for κ2-N,O bound ligands.60 The 1,3-N,O-donor ligands have W1-N1 and W1-N2A bond distances of 2.138(5) and 2.12(2) Å respectively, whereas the W1-O2 and W1-O3A are 2.280(5) and 2.28(1) Å respectively. The tungsten oxygen bond distances have been elongated due a trans influence of the oxo and alkylidene ligands, and such elongations were also observed 103  in related di(carboxylate)(imido)(alkylidene)molybdenum complexes.189  The tungsten oxo (W1-O1) and alkylidene (W1-C1 bond distances are 1.684(4) and 1.934(6) Å, which are slightly shorter than previously reported 6 coordinate tungsten oxo alkylidene complexes.  Figure 3-3. Solid-state molecular structure of complex 3.6, plotted at 50% ellipsoids with most hydrogen atoms and disordered amidate ligand omitted. Selected bond distances (Å); W1-N2A=2.12(2), W1-O3A=2.28(1), W1-N1=2.138(5), W1-O2=2.280(5), W1-O1=1.684(4), W1-C1=1.934(6), C6-O2=1.289(9), C6-N1=1.329(8), C25A-O3A=1.27(2), C25A-N2A=1.33(2). Selected bond angles (°); O3A-W1-N2A=59.4(6), O2-W1-N1=59.3(2), W1-C1-C2=139.3(5).   Typical 6 coordinate tungsten oxo alkylidene complexes have tungsten oxo bond distances close to 1.70 Å, and tungsten alkylidene distances of 1.95 Å.34, 196-197 The slight decrease in bond lengths have been attributed to relatively poor donation of the 1,3-N,O-donor ligands to the metal center when compared to the ligands of previously reported complexes, such as siloxides, aryloxides, trispyrazolylborates and chlorides, and neutral donors such as N-heterocyclic carbenes, phosphines and ethereal donor ligands.34, 196-197  The 1,3-N,O-donor ligands are often proposed to impart electrophilic character at 104  the metal center due to the hard nitrogen and oxygen donors combined with poor orbital overlap with metal orbitals,60 which rationalizes the slight shortening of the metal element multiple bonds in complex 3.6. Complex 3.6 (complexes 3.7 and 3.8 as well, vide infra) has tungsten oxo and alkylidene bond distances that better agree with 5 coordinate complexes, where a typical tungsten oxo distance is 1.69 Å and a typical tungsten alkylidene distance is 1.92 Å.184, 194, 198   The solid-state molecular structures of complexes 2.5 (Chapter 2) and 3.6 (complexes 3.7 and 3.8 as well, vide infra) are isostructural. An overlay of the structures is presented in Figure 3-4.  Figure 3-4. Overlay of the solid-state molecular structures of complexes 2.5 and 3.6, plotted at 50% ellipsoids with most hydrogen atoms and disordered ligands omitted.  It is notable that efforts to purify crude 3.6 by recrystallization also resulted in the formation of crystals of proligand HL4. The consistent reappearance of proligand HL4 in the recrystallized material has been puzzling. Furthermore, when the protonolysis reaction (Scheme 3-9) has been monitored by 1H-NMR spectroscopy in a J-Young NMR tube the 105  reaction proceeded to fully consume HL4. Then, with reaction times of 3 hours or longer, HL4 could be observed to form in solution. Interestingly, if the crude solid material of complex 3.6 (which showed no proligand by when analyzed 1H-NMR spectroscopy) was again dissolved in a hydrocarbon solvent, proligand HL4 formation has again been observed. Furthermore, if crude 3.6 which includes dimethylphenylphosphine was kept in an undisturbed sealed NMR tube at room temperature, only small amounts of proligand have been observed over time and a significant amount of 3.6 was still observed after weeks. Alternatively, if 3.6 was stirred vigorously overnight in hydrocarbon solvent a dark solution resulted, and after the volatiles were removed no resonances of 3.6 could be observed in a 1H-NMR spectrum. The continued reactivity of crude 3.6 suggests that it is not stable in solution. Since recrystallization has not been an appropriate purification technique for 3.6, and the crude material contained the desired 3.6 and undesired 2,5-dimethylpyrrole, dimethylphenylphosphine and HL4, alternative methods of purification have been undertaken.  The 2,5-dimethylpyrrole could be removed by leaving the crude material of complex 3.6 under vacuum for 24 hours, however, the dimethylphenyl phosphine could not be full removed. To remove the dimethylphenylphosphine two equivalents of CuBr were added and stirred with crude 3.6 for 15 min. The use of copper salts to scavenge for phosphines has been reported.199 The resulting solution was filtered and then the solids were isolated by removing the volatiles. The 1H-NMR spectrum of the resulting solids showed complex 3.6, proligand HL4 and no free phosphine in solution. However, there were resonances attributed to the phosphine coordinated copper bromide adduct at δ 1.25 (doublet, 2JHP=5.8 Hz) in the 1H-NMR spectrum and δ -37.4 (broad singlet) in the 31P-106  NMR spectrum.34 When reaction times of the CuBr and 3.6 exceeded 2 hours significant decomposition of complex 3.6 resulted.   The use of copper salts as phosphine scavengers has also been known to cause decomposition of tungsten oxo alkylidene complexes.34 The removal of the CuBr phosphine adduct proved to be difficult due to its similar solubility profile as complex 3.6. Neither the CuBr phosphine adduct or proligand HL4 could be completely removed by filtration through diatomaceous earth, therefore basic alumina was used to separate the mixture of materials. Satisfyingly, when the mixture of complex 3.6, proligand HL4 and the CuBr phosphine adduct were dissolved in a minimum amount of toluene and eluted through a 1-2” alumina column in a pipette, the only eluant was a yellow solution containing complex 3.6. The toluene used to elute complex 3.6 through the alumina column must be immediately removed by vacuum to ensure minimal decomposition of complex 3.6 in solution occurs. Rewardingly, the 1H-NMR spectrum of the purified material shows no evidence of remaining proligand HL4 or phosphine compounds, and the yellow/orange solids were analytically pure to give a 29% yield overall. When the analytically pure material was dissolved in C6D6 and monitored over time, the continued reactivity of complex 3.6 has again been witnessed to give proligand HL4 in a sealed NMR tube overnight.  In summary the protonolysis reaction in Scheme 3-9 resulted in the isolation of complex 3.6. Significant effort to must be taken to isolate the purified complex 3.6, and gave a final yield of 29%. These experiments resulted in the repeated observation of proligand formation upon solution phase decomposition of complex 3.6. 107  3.2.1.2 Synthesis of bis(N-(2,6-diisopropylphenyl)benzamidate)(neopentylidene)(oxo)tungsten via salt metathesis route  The synthesis of complex 3.6 via salt metathesis has also been undertaken by allowing complex 3.4 and two equivalents of NaL4 to react (Scheme 3-10). The reaction progress was followed by multinuclear NMR spectroscopy and it was evident from monitoring the reaction that complex 3.4 had been consumed within six hours and the major product was complex 3.6. Once again proligand HL4 and free dimethylphenylphosphine have been observed during the reaction and after work up as determined by a 1H-NMR spectrum of the material. The appearance of proligand HL4 in the crude reaction mixtures from the salt metathesis route to complex 3.6 was not surprising considering due to the continued reactivity of analytically pure 3.6 to give HL4.  Scheme 3-10. Salt metathesis reaction of 3.4 with two equivalents of NaL4. Dipp=2,6-diisopropylphenyl.   To optimize the synthesis of complex 3.6 and potentially diminish the continued reactivity process that results in proligand formation, alteration of the salt metathesis reaction conditions was undertaken. The temperature of the reaction was changed between -78 and 100 °C, yet it has been found that changing the temperature of the reaction produced increased amounts of observed proligand HL4 in the reaction products. Employing ethereal solvents had the same effect; when THF or diethylether have been used 108  as reaction solvents, again an increased amount of proligand HL4 has been observed in the reaction products. When a slight excess of NaL4 has been used in the synthesis of complex 3.6, less side products have been observed, and the excess amidate salt NaL4 could be filtered away in the work-up. The sequence of addition of reagents has also been tested. Whether NaL4 was added slowly to a solution of 3.4 or 3.4 was added slowly to a solution of NaL4, increased amounts of proligand HL4 have been observed in comparison to the experiments where the solids were in the same vial and then adding solvent. Ultimately, the optimal reaction conditions for the synthesis of complex 3.6 by salt metathesis requires the addition of toluene solvent to a vial containing both solid 3.4 (1.0 equivalent) and NaL4 (2.05 equivalents), followed by stirring the reaction at room temperature for a period of 6 to 24 hours (Scheme 3-11).   Scheme 3-11. Optimized synthesis of complex 20. The optimized salt metathesis reaction for the synthesis of complex 3.6 produced a yellow crude semi-solid in a good yield (84% or greater of crude material). The crude material of complex 3.6 via salt metathesis route could be purified once again by column chromatography using alumina to obtain approximately the same yields as in the protonolysis reactions (29%).  Complex 3.6 is the first example of an alkylidene complex bearing 1,3-N,O-donor ligands. The synthesis of 3.6 has been accomplished by both protonolysis and salt 109  metathesis routes. The salt metathesis route has been the preferred route to complex 3.6 because the 2,5-dimethylpyrrole biproduct in the protonolysis route is difficult to remove. Furthermore, the starting material 3.4 is easier to synthesize and in larger quantities than the alternative 3.2. 3.2.2 Synthesis and characterization of other bis(N-(2,6-diisopropylphenyl)amidate)(neopentylidene)(oxo)tungsten complexes  The synthesis of other bis(N-(2,6-diisopropylphenyl)amidate)(neopentylidene)(oxo)tungsten complexes has been undertaken to; 1) expand the breadth of metal alkylidene complexes with 1,3-N,O-donor ligands, 2) further investigate the continued reactivity of complex 3.6 which results in proligand HL4 formation, and 3) to evaluate electronic parameters of the 1,3-N,O-donor ligands by varying the electronics of  amide proligands. Three alternative amide proligands have been designed, where the steric demand remained similar in all the proligands, but the electronic parameters of the amide were tuned. The bulky N-2,6-diisopropylphenyl group was used as the N-substituent throughout the amides, while the substituent on the carbonyl (X in Figure 3-5) of the NCO motif was varied (Figure 3-6). Complexes bearing bis(amidate) ligands that have the N-2,6-diisopropylphenyl substituents consistently give C2 symmetric N-trans geometries (Figure 3-5, middle) like complexes 2.5 (Chapter 2) and 3.6. Thus, the use of this substituent eliminates one variable with respect to isomerization. 110   Figure 3-5. (left) amide with N-2,6-diisopropylphenyl substituent with tunable amide X substituent, (middle) typical bis(N-2,6-diisopropylphenyl amidate)(L)2 metal complex (L=ligand, M=Ti, Zr, Hf, Mo, W), (right) proposed N-trans bis(amidate)(neopentylidene)(oxo)tungsten complex.70 The X substituent in the amide has been modified to allow for evaluation of electronic effects by examining the complexes physical properties and the reactivities of the complexes in RCM metathesis reactions (vide infra). The amides chosen were N-(2,6-diisopropylphenyl)-3,5-bis(trifluoromethyl)benzamide (HL5), N-(2,6-diisopropylphenyl)acetamide (HL6), and N-(2,6-diisopropylphenyl)-2,2,2-trifluoroacetamide (HL7) and have been shown in Figure 3-6.  Figure 3-6. 1,3-N,O-proligands with N-(2,6-diisopropylphenyl)amides. The inductive electron withdrawing ability of trifluoro methyl groups is used in amide HL5 to alter the electronics of the proligand compared to HL4. Minimal differences between the steric demand of the methyl and CF3 groups in HL6 and HL7, while the inductive withdrawing nature of the CF3 group in HL7 will differ significantly from methyl group in 111  HL6. Developing trends in coordination of amidate ligands with respect to the electronics of the ligand is important since the ligands can have a dramatic effect on the reactivity of that complex.  The same synthetic protocols used in the synthesis of complex 3.6 were successfully employed in the synthesis of complexes bis(amidate)(neopentylidene)(oxo)tungsten complexes 3.7, 3.8 and 3.9 (Scheme 3-12). The protonolysis and salt metathesis reactions were both able to produce the bis(amidate)(neopentylidene)(oxo)tungsten complexes, and in all cases the salt metathesis reactions were preferred (vide supra).    Scheme 3-12. Salt metathesis reaction for the synthesis of complexes 3.6, 3.7, 3.8 and 3.9. Ar=3,5-bis(trifluoromethyl)phenyl, Dipp=2,6-diisopropylphenyl. 3.2.2.1 Synthesis of bis(N-(2,6-diisopropylphenyl)-3,5-bis(trifluoromethyl)benzamidate)(neopentylidene)(oxo)tungsten  The salt metathesis reaction of 3.4 with 2.05 equivalents of NaL5 was stirred for 6 hours then filtered through diatomaceous earth to remove NaCl(s) and any other insoluble 112  materials, finally the volatiles were removed under vacuum leaving a sticky dark yellow semi-solid (Scheme 3-13).  Scheme 3-13. Synthesis of complex 3.7. Ar=3,5-bis(trifluoromethyl)phenyl, Dipp=2,6-diisopropylphenyl. The 1H-NMR spectrum of the crude material contained resonances attributed to a bis(N-(2,6-diisopropylphenyl)-3,5-bis(trifluoromethyl)benzamidate)(neopentylidene)(oxo)tungsten complex (3.7), dimethylphenylphosphine and proligand HL5. The diagnostic resonances for complex 3.7 are; the alkylidene (WCHC(CH3)3) singlet resonance at δ 11.05 with 1JCH=118.7 Hz indicative of a syn alkylidene, several aryl multiplet resonances ranging from δ 8.11-6.99 integrating to a total of 12 hydrogens, three separate isopropyl methine (CArylCH(CH3)2) septet resonances at δ 4.06, 3.76 and 3.35, eight separate isopropyl methyl (CArylCH(CH3)2) doublet resonances at δ 1.54, 1.53, 1.34, 1.29, 1.04, 0.99, 0.92 and 0.68, and one alkylidene (WCHC(CH3)3) t-butyl singlet resonance at δ 1.18. In the 19F-NMR spectrum there are two signals attributed to complex 3.7 at δ -63.67 and -63.76, indicating the free rotation of 3,5-bis(trifluoromethyl)phenyl group. The NMR data of 3.7 is consistent with a C1 symmetric complex analogous to complex 3.6.  The dark yellow semi-solid became crystalline over the course of days in a sealed vial in the glovebox at ambient temperature and the crystals of complex 3.7 were of sufficient quality for single crystal X-ray diffraction. The solid-state molecular structure 113  has been shown in Figure 3-7. Analogous to the di(N,O-chelate)bis(t-butylimido)tungsten complexes (2.2, 2.3, 2.4 and 2.5, in Chapter 2), 3.7 exhibits a highly distorted octahedral geometry. The complex exhibits two κ2-N,O amidate ligands which matches the solution 1H-NMR data analysis, suggesting that 3.7 has the same structure in solution (at 25 °C) and in the solid state. The two amidate ligands have a N-trans coordination to the tungsten metal as anticipated.67, 70 The 1,3-N,O-donor ligand bite angles are 59.88(8) and 59.19(8)° for O4-W1-N2 and O3-W1-N1 respectively, which are similar to those reported for the non-bis(3,5-trifluoromethylphenyl) substituted amidates.60 The 1,3-N,O-donor ligands have W1-N1 and W1-N2 bond distances of 2.133(2) and 2.099(2) Å respectively, whereas the W1-O3 and W1-O4 are 2.262(2) and 2.271(2) Å respectively, consistent with elongated tungsten oxygen bond lengths due a trans influence of the oxo and alkylidene ligands.189 The tungsten oxo (W1-O1) and alkylidene (W1-C1) bond distances are 1.692(2) and 1.924(3) Å respectively, which are slightly shorter than previously reported 6 coordinate tungsten oxo alkylidene complexes.34, 196-197 114   Figure 3-7. Solid-state molecular structure of complex 3.7, plotted at 50% ellipsoids with most hydrogen atoms, green ellipsoids are fluorine atoms. Selected bond distances (Å); W1-N1=2.133(2), W1-O3=2.262(2), W1-N2=2.099(2), W1-O4=2.271(2), W1-O1=1.692(2), W1-C1=1.924(3), C6-O3=1.286(3), C6-N1=1.318(4), C27-O4=1.275(3), C27-N2=1.335(3). Selected bond angles (°); O4-W1-N2=59.88(8), O3-W1-N1=59.19(8), W1-C1-C2=139.9(2). 3.2.2.2 Synthesis of bis(N-(2,6-diisopropylphenyl)acetamidate)(neopentylidene)(oxo)tungsten  A salt metathesis reaction of 3.4 with 2.05 equivalents of NaL6 was stirred for 6 hours then filtered through diatomaceous earth to remove NaCl(s) and any other insoluble materials. The volatiles were then removed under vacuum leaving a sticky pale yellow semi-solid (Scheme 3-14). 115   Scheme 3-14. Synthesis of complex 3.8. Ar=3,5-bis(trifluoromethyl)phenyl, Dipp=2,6-diisopropylphenyl.  The 1H-NMR spectrum of the crude material contained resonances attributed to a bis(N-(2,6-diisopropylphenyl)acetamidate)(neopentylidene)(oxo)tungsten complex (3.8), dimethylphenylphosphine and 2,5-dimethylpyrrole. The diagnostic resonances for complex 3.8 are; the alkylidene (WCHC(CH3)3) singlet resonance at δ 10.61 with 1JCH=118.1 Hz indicative of a syn alkylidene, one aryl multiplet with overlapping resonances centered at δ 7.06 that integrate to 6 hydrogens, four separate isopropyl methine (CArylCH(CH3)2) septet resonances at δ 3.99, 3.93, 3.66 and 3.32, eight separate isopropyl methyl (CArylCH(CH3)2) doublet resonances at δ 1.56, 1.55, 1.34, 1.33, 1.32, 1.20, 1.06 and 0.89, and one alkylidene (WCHC(CH3)3) t-butyl singlet resonance at δ 1.17. Two distinct methyl groups of the N-(2,6-disopropylphenyl)acetamidate ligands are observed as singlets at δ 1.64 and 1.50 in the 1H-NMR spectrum. Just as in complexes 3.6 and 3.7, the NMR data of 3.8 suggests a C1 symmetric complex.  Crystals suitable for single crystal X-ray diffraction of complex 3.8 have been obtained from to the crude pale yellow semi-solid product. The solid-state molecular structure has been shown in Figure 3-8. Analogous to the di(N,O-chelate)bis(t-butylimido)tungsten complexes (2.2, 2.3, 2.4 and 2.5, in Chapter 2) and complexes 3.6 and 3.7 in this chapter, 3.8 exhibits a highly distorted octahedral geometry. The complex exhibits two κ2-N,O amidate ligands which again matches the solution 1H-NMR 116  spectroscopic data analysis. As expected the two amidate ligands have a N-trans coordination to the tungsten metal.67, 70 The 1,3-N,O-donor ligand bite angles are 59.4(1) and 59.3(1)° for O1-W1-N1 and O2-W1-N2 respectively.60 The 1,3-N,O-donor ligands have W1-N1 and W1-N2 bond distances of 2.093(4) and 2.131(4) Å respectively, whereas the W1-O1 and W1-O2 are 2.277(3) and 2.263(4) Å respectively. The tungsten oxygen bond distances are elongated due a trans influence of the oxo and alkylidene ligands, and again, such elongations were also observed in related di(carboxylate)(imido)(alkylidene)molybdenum complexes.189  The tungsten oxo (W1-O3) and alkylidene (W1-C1) bond distances are 1.692(4) and 1.901(5) Å, which are shorter than previously reported 6 coordinate tungsten oxo alkylidene complexes, presumably due to the relatively poor electron donation of amidate ligands.34, 196-197   Figure 3-8. Solid-state molecular structure of complex 3.8, plotted at 50% ellipsoids with most hydrogen atoms and disordered amidate ligand omitted. Selected bond distances (Å); W1-N1=2.093(4), W1-O1=2.277(3), W1-N2=2.131(4), W1-O2=2.263(4), W1-O3=1.692(4), W1-C1=1.901(5), C6-O1=1.273(6), C6-N1=1.322(6), C20-O2=1.286(6), C20-N2=1.320(7). Selected bond angles (°); O1-W1-N1=59.4(1), O2-W1-N1=59.3(1), W1-C1-C2=140.2(4). 117  3.2.2.3 Synthesis of bis(N-(2,6-diisopropylphenyl)-2,2,2-trifluoroacetamidate)(neopentylidene)(oxo)tungsten  Moving on to the synthesis of tungsten alkylidene complexes with proligand HL7, the salt metathesis reaction of 3.4 with 2.05 equivalents of NaL7 was undertaken (Scheme 3-15). The bis(N-(2,6-diisopropylphenyl)-2,2,2-trifluoroacetamidate)(neopentylidene)(oxo)(dimethylphenylphosphine)tungsten complex (3.10).  Scheme 3-15. Salt metathesis reaction of 3.10 and NaL7. Dipp=2,6-diisopropylphenyl. The crude material was isolated by filtering off the NaCl(s) biproduct and any other insoluble materials then removing all volatiles under vacuum to leave a dark orange semi-solid. Like complexes 3.7 and 3.8, crystalline material formed from the semi-solid directly in a capped vile in the glove box at ambient temperatures. The solid-state molecular structure of 3.10 has been shown in Figure 3-9, and the six-coordinate complex has a distorted octahedral coordination geometry. Complex 3.10 has one κ2-N,O amidate, one κ1-O amidate, a neopentylidene, an oxo ligand and a coordinated dimethylphenylphosphine. The κ1-O amidate leaves an open coordination site for the dimethylphenylphosphine coordination. The κ1-O ligand in complex 3.10 highlights the hemilability of amidate ligands. This hemilability models the initial hypothesis proposed in Scheme 3-7; the hemilability of the 1,3-N,O-donor ligands would allow for coordination 118  of a donor ligand. Thus the solid-state molecular structure of 3.10 serves as a proof of concept to the hypothesis that 1,3-N,O-donor ligands can exploit their hemilability characteristics to reveal coordination sites for binding of substrates.   Figure 3-9. Solid-state molecular structure of complex 3.10, plotted at 50% ellipsoids with most hydrogen atoms and disordered amidate ligand omitted. Selected bond distances (Å); W1-N1=2.164(3), W1-O1=2.406(4), W1-P1=2.542(1), W1-O2=2.051(3), W1-O3=1.700(4), W1-C1=1.930(7), C6-O1=1.264(6), C6-N1=1.311(7), C20-O2=1.320(6), C20-N2=1.258(6). Selected bond angles (°); O1-W1-N1=57.7(1), W1-C1-C2=142.9(4).  The κ1-O amidate has a W1-O2 bond distance of 2.051(3) Å, which is within the normal range for a κ1-O ligand which is trans to a tungsten element multiple bond.67 The κ1-O amidate has a O2-C20 bond distance of 1.320(6) Å indicative of a carbon oxygen single bond, and a C20-N2 bond distance of 1.258(6) Å indicative of a carbon nitrogen 119  double bond.128 Consistent with an alkoxy imine motif in the solid state. Furthermore, the κ1-O amidate has an E configuration of the imine which has been rarely observed, as the Z configuration is thermodynamically preferred.80, 139, 200 The κ2-N,O amidate has a W1-N1 bond distance of 2.164(3) Å, and a W1-O1 bond distance of 2.406(4) Å, indicating a strong trans influence from the tungsten alkylidene ligand.3 The tungsten alkylidene has a syn orientation with a (W1-C1) bond distance of 1.930(7) Å. The W1-O3 tungsten oxo bond distance is 1.700(4) Å. The elongated tungsten oxo bond agrees with previously reported 6 coordinate tungsten alkylidene complexes.34, 196-197   The 1H-NMR spectrum of crude complex 3.10 at 25 °C shows two alkylidene resonances at δ 11.20 and 11.95 (broad), presumably corresponding to the phosphine free (complex 3.9) and phosphine (complex 3.10) adduct in approximately a 1:6. The alkyl region of the crude material shows; resonances for free dimethylphenylphosphine, resonances of proligand HL7, nine broad doublets (ranging from δ 1.75-1.17) corresponding to the methyls of the isopropyl groups and of the coordinated dimethylphenylphosphine, four broad and ill-defined septets of the ligated amidates CH(Me)2 hydrogen atoms (ranging from δ 3.94-2.55) and two tBu resonances of the neopentylidene ligands at δ 0.79 and 1.00. The amidate ligand resonances in the 1H-NMR spectrum are broad at 25 °C, indicative of fluxional behavior of the ligands.   Complex 3.9 shows reversible coordination of dimethylphenylphosphine in solution as observed by variable temperature 1H-NMR spectroscopy (Figure 3-10). At increased temperatures (95 °C) the phosphine free complex 3.9 is dominate (vide infra), compared to 25 °C where 3.10 is more prevalent. The coordinated phosphine in 3.10 has diagnostic doublet resonances at δ 1.78 (2JHP=9.7 Hz, 3H) and 1.66 (2JHP=9.7 Hz, 3H), and 120  as the temperature was increased these resonances diminished and resonances for free dimethylphenylphosphine increase. The reversible phosphine coordination has also been observed in the 19F-NMR spectrum which shows 5 signals, two of the signals are broad (complex 3.10, δ -68.45 and -70.69) and the other 3 are sharp. One of the sharp resonances corresponds to proligand HL7 at δ -75.41, the other two sharp resonances correspond to complex 3.9 at δ -70.02 and -71.36. As the temperature was increased all the 19F-NMR signals (except the resonance for proligand HL7) became a single broad resonance at δ -70.91. The 31P-NMR shows a broad resonance at δ 10.59 and free dimethylphenylphosphine at δ -46.1 at 25 °C, and at elevated temperatures the broad resonance diminishes and only free dimethylphenylphosphine is observed at 95 °C. At elevated temperatures complex 3.9 is favored over 3.10, as evidenced by the ratios (approximately 9:1) of alkylidene resonances in the 1H-NMR spectrum at 95 °C (Figure 3-10). The amidate ligands show fluxional character at elevated temperatures as well, at 95 °C the isopropyl methine resonances have coalesced into a single broad resonance at δ 3.43 in the 1H-NMR spectrum. Unfortunately, evaluation of equilibrium between 3.9 and dimethylphenyl, and 3.10 has been complicated due to excess dimethylphenylphosphine remaining in the crude material. 121   Figure 3-10. Variable temperature 300 MHz 1H-NMR spectra in C7D8 of complex 3.10, crude material used.  The phosphine free complex 3.9 was assigned by reacting the crude material with two equivalents of CuBr for 1 hour in toluene followed by removing the volatiles and triturating with hexanes and then followed by triturating with pentane, which filtered away most of the resulting CuBr phosphine adduct (Scheme 3-16).   Scheme 3-16. Reversible phosphine coordination of complex 3.9. Sequestering phosphine with CuBr. 122  The 1H-NMR showed only one alkylidene resonance at δ 11.19 with coupling constant of 1JCH=119.0 Hz, signifying a syn alkylidene.8 Overlapping aryl multiplet resonances in the 1H-NMR are centered at δ 7.03 integrating to 6 hydrogens. The isopropyl methine resonances are slightly broadened septets at δ 3.79, 3.65, 3.41 and 3.15. The 1H-NMR also contains eight doublets corresponding to the isopropyl methyl groups at δ 1.49, 1.45, 1.33 (overlapping with PhMe2PCuBr resonances, 3H), 1.26 (two overlapping), 1.15 (two overlapping) and 0.97. Multinuclear NMR spectroscopy also showed no indication of 3.10, the 19F-NMR spectrum had two sharp singlet resonances at δ -70.02 and -71.36 confirming complex 3.9, and the 31P-NMR was void of the characteristic peak for 3.10 at δ 10.59. Although the only tungsten complex that has been identified in the NMR spectra was 3.9, there were remaining impurities observed including proligand HL7 and the copper dimethylphenylphosphine adduct in the material. The 1H- and 19F-NMR spectra suggest a C1 symmetric complex in solution. A solid-state molecular structure of complex 3.9 has not been obtained however, the EI mass spectrometry showed a tungsten isotope pattern of 744 m/z corresponding to complex 3.9 minus the alkylidene fragment, which was common for the amidate complexes in this chapter. 3.2.3 Variable temperature NMR studies of bis(N-(2,6-diisopropylphenyl)amidate)(neopentylidene)(oxo)tungsten complexes  The solid-state molecular structures of complexes 3.6, 3.7 and 3.8 have N-trans amidate ligands, consistent with previously reported bis(amidate) complexes that have N-2,6-diisopropylphenyl substituents, and the data suggests that complex 3.9 is isostructural.70 Complexes 3.6, 3.7 and 3.8 have solid-state molecular structures reminiscent of the bis(amidate)bis(imido)tungsten complex 2.5 from chapter 2 and they 123  also have similar bond metrics to the related bis(carboxylate)(imido)(neopentylidene) molybdenum complexes.189 Specifically, the 1,3-donor ligands have asymmetric bonding of the donor atoms, where the donor atoms trans to the tungsten element multiple bonds have been elongated due to a trans influence. All complexes have neopentylidene ligands with a syn orientation in the solid state.   Complexes 3.6-3.9 exhibit similar features in the 1H-NMR spectra at 25 °C in solution, and suggest a C1 symmetric complex. The methyl and methine groups of the N-2,6-diisopropylphenyl substituents are all unique in the 1H-NMR spectrum, eight doublets corresponding to the methyl groups of the isopropyl substituents, and four septets of the isopropyl methine hydrogens. The diagnostic resonances have been summarized in Table 3-1. The alkylidene resonances of complexes 3.6-3.9 range from δ 10.61 to 11.19 with 1JCH coupling constants from 118.1 to 119.3 Hz, indicating that the neopentylidene ligands are all in a syn orientation in solution. The chemical shift of the alkylidene hydrogen shifts down field in complexes with increased electron withdrawing groups on the amidate NCO backbone, where 3.9 > 3.7 > 3.6 > 3.8 (Table 3-1). In principle, one should observe tungsten 2JWH satellites, however none have been observed for the complexes in this chapter. Literature precedence for 2JWH satellites, which are typically around 13 Hz +/- 3 Hz,194, 201 varies from complex to complex and have not been reported for all complexes.194, 201 The absence of observable coupling to tungsten is puzzling, and is potentially related to the dynamic processes of these complexes.  124  Table 3-1. Selected 1H-NMR resonances of complexes 3.6, 3.7, 3.8 and 3.9. Resonances reported in ppm (δ).   These complexes are formally 18 electron complexes in the solid-state and in solution. The similarities between complexes 3.6-3.9 in solution at 25 °C are not surprising as they are isostructural. Complex 3.10 was an outlier when compared to complexes 3.6-3.8. When complex 3.9 was isolated and analyzed in solution by 1H-NMR spectroscopy, it also agreed with complexes 3.6-3.8. Complex 3.10 displayed fluctional behavior suggesting that complexes 3.6-3.8 may also display ligand hemilability at elevated temperatures. Another feature complexes 3.6-3.9 share is the observation of proligands and dimethylphenylphosphine in their crude reaction products. The crude materials of complexes 3.6-3.9 have been used for the variable temperature NMR studies. To further investigate the similarities and differences between complexes 3.6-3.9, variable temperature NMR spectroscopy have been undertaken.   The 2,6-diisopropylphenyl group resonances in the 1H-NMR spectrum are very informative to analyze if the ligands have fluxional character in solution. When the amidate ligands are loosely coordinated higher symmetry amidate ligand resonances would result, 125  compared to the low symmetry conformations observed in the solid state and in solution at 25 °C. Variable temperature NMR spectroscopy has been conducted on complexes 3.6, 3.7 and 3.8 to test if the amidate ligands have fluxional character in solution. The full spectra have been shown in section 3.5 of this chapter. To illustrate the observed fluxional behavior for complexes 3.6, 3.7 and 3.8, a cross section of the isopropyl methine resonances has been shown in Figure 3-11. These spectra show that at high temperatures the amidates are all highly fluxional. In all cases the four isopropyl methine septets begin to broaden at 55 °C and then coalesce to a single peak at 95 °C. In comparison the methine resonances of complex 3.10 coalesce at 65 °C (Figure 3-10). Notably the amidate ligands in complexes 3.10/3.9 were fluxional at 25 °C already due to reversible coordination of dimethylphenylphosphine. Complexes 3.6, 3.7 and 3.8 do not show reversible phosphine coordination in the variable temperature NMR spectra.  Figure 3-11. Variable temperature 1H-NMR spectra in C7D8 of complexes 3.6, 3.7, 3.8 and 3.10. Spectra are zoomed to the isopropyl methine region. 126  Such highly fluxional amidate ligands have been hypothesized to be important in realizing olefin metathesis with these 18 electron di(amidate)(neopentylidene)(oxo)tungsten complexes due to the in situ generation of unsaturated tungsten metal centers (Scheme 3-7). 3.2.4 Synthesis and characterization of tungsten(neopentylidene)(oxo) complexes with N-(3,5-bis(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamidate ligands  Based on the literature precedence of employing ancillary ligands with electron withdrawing groups by Schrock et al.,8 a 1,3-N,O-donor ligand with electron withdrawing groups have been incorporated into both the N-substituted and the X-substituent of the NCO amidate back bone (Figure 3-5). Thus, proligand N-(3,5-bis(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamide (HL8) has been prepared (Scheme 3-17). The salt metathesis reaction of 3.4 with two equivalents of NaL8 has been conducted, and the major product of the reaction was found to be a bis(N-(3,5-bis(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamide)(neopentylidene)(oxo)(dimethylphenylphosphine)tungsten complex (3.11) (Scheme 3-17).   Scheme 3-17. Salt metathesis reaction of 3.4 and two equivalents of NaL8. Ar=3,5-bis(trifluoromethyl)phenyl. The major product of complex 3.11 has been found to be fluxional due to the presence of broad resonances observed in the multinuclear NMR spectra. In addition, the mixture included some unidentified impurities and proligand HL8. The crude reaction mixture 127  resulted in an orange semi-solid after a work-up of filtering through diatomaceous earth and removing volatiles under vacuum.   Recrystallization of the solids from toluene/hexanes at -30 °C produced orange crystals of complex 3.11 that have been suitable for single crystal X-ray diffraction (Figure 3-12). Complex 3.11 is a 6 coordinate complex and has a distorted octahedral coordination geometry with one κ2-N,O amidate and one κ1-O amidate. The κ1-O amidate opens a coordination site for phosphine coordination. The κ1-O amidate has a W1-O2 bond distance of 2.053(2) Å, a O2-C16 bond distance of 1.319(3) Å, and a C16-N2 bond distance of 1.269(3) Å. The κ1-O amidate forms an alkoxy imine motif in the solid state, the κ1-O amidate has the more typical Z configuration of the imine. The κ2-N,O amidate has a W1-N1 bond distance of 2.278(2) Å, and a W1-O1 bond distance of 2.327(2) Å, both indicating a trans influence from the tungsten alkylidene ligand.3 The tungsten alkylidene has a syn orientation with a W1-C1 bond distance of 1.926(2) Å. The W1-O3 tungsten oxo bond distance is 1.695(2) Å. The syn orientation of the neopentylidene and all the bond distances of complex 3.11 agree well with other six coordinate tungsten oxo alkylidene complexes.34, 196-197  128   Figure 3-12. Solid-state molecular structure of complex 3.11, plotted at 50% ellipsoids with most hydrogen atoms omitted. Selected bond distances (Å); W1-N1=2.278(2), W1-O1=2.327(2), W1-O2=2.053(2), O2-C16=1.319(3), C16-N2=1.269(3), W1-O3=1.695(2), W1-C1=1.926(2).  The 1H-NMR spectrum of the material recrystallized from toluene/hexanes (complex 3.11) in toluene-d8 exhibits broad resonances and contains two resonances in the alkylidene region at δ 10.50(1.0H) and 10.96(0.27H) (relative integration in parentheses). There is one relatively sharp singlet in the 1H-NMR spectrum at δ 0.97 assigned as the t-butyl group of the neopentylidene ligand. The alkylidene carbon resonance has been found at δ 306.4 as a doublet with 2JCP=13.1 Hz. The alkyl region exhibits broadened resonances, however, there are two doublets coupled to a 31P-nuclei at δ 1.14(3H) and 1.32(3H) (2JHP=10.6 Hz for both) which are assigned to a dimethylphenylphosphine ligand. The 31P-129  NMR exhibits a broad singlet at δ 15.44 with tungsten satellites (1JPW=392 Hz), confirming a tungsten bound phosphine ligand. The 19F-NMR displayed two sets of resonances for amidate L8, indicating a bis amidate complex with C1 symmetry as seen in the solid-state molecular structure. For complex 3.11 the multinuclear NMR spectra showed many small unidentified resonances in all regions of the spectra, indicating small impurities or isomers of complex 3.11 are present. Elemental analysis of the crystals confirmed the purity of complex 3.11, suggesting that the small unidentified resonances have been due to isomers of complex 3.11.  Variable temperature spectroscopy of the crude reaction mixture indicates fluxional species in solution, indicative of the hemilabile amidate ligands (Figure 3-13). In addition to small unidentified resonances, proligand HL8 and free dimethylphenylphosphine has also been present in the crude reaction mixture. The broad resonance at δ 10.50 decreases in integration and appears as a doublet (3JHP=3.5 Hz) at temperatures below 0 °C, thus attributed to a neopentylidene (WCHCMe3) coupled to a dimethylphenylphosphine ligand bound to tungsten. The resonance at δ 10.96 gradually increases in intensity as the temperature is lowered, and splits into two broad resonances at δ 10.75 and 10.69 when cooled to -60 °C (Figure 3-13). The resonances in the aryl and alkyl region also shift indicating possible complex isomerization. 130   Figure 3-13. Variable temperature 400 MHz 1H-NMR and spectra in C7D8 of the crude reaction products of 3.4 and 2 equivalents of NaL8. a) full 1H-NMR spectra δ 0.5-13.0, b) zoom of alkylidene region from δ 10.0-11.7. Ar=3,5-bis(trifluoromethyl)phenyl.  As had been seen previously, it was evident that complex 3.11 continues to react in solution as seen by the disappearance of the resonances assigned to complex 3.11 in the 1H-NMR spectrum, and the appearance of HL8 and free dimethylphenylphosphine over time. The source of the evolution of HL8 became evident when the yellow crystals obtained from recrystallized sample of crude product has been shown to be complex 3.12 by X-ray diffraction (Figure 3-14). 131   Figure 3-14. Solid-state molecular structure of complex 3.12, plotted at 50% ellipsoids with most hydrogen atoms omitted and phosphine substituents as wire frame for clarity.  Notably dimeric complex 3.12 has only three amidate ligands and a terminal alkylidyne, resulting in presumably upon HL8 elimination (Scheme 3-18). Complex 3.12 has undergone an C-H activation process from a tungsten neopentylidene ligand to form the neopentylidyne ligand observed (Scheme 3-18). The Schafer group has previously shown that N-H, B-H and C-H bonds can be activated by hemilabile 1,3-N,O-donor ligands.67, 97, 202-203 132   Scheme 3-18. Decomposition of complex 3.11 to form complex 3.12 and proteoligand HL8. Ar=3,5-bis(trifluoromethyl)phenyl.  Complex 3.12 has a unique structure in the solid state, with two tungsten atoms that are bridged by two µ2-N,O amidates and one µ-oxo ligand.204 Both tungsten centers have a dimethylphenylphosphine ligand. One tungsten center has a κ2-N,O amidate and a neopentylidyne, while the other tungsten metal center has a terminal oxo and a neopentylidene. The κ2-N,O amidate has W1-O1 and W1-N1 bond distances of 2.192(3) and 2.263(3) Å respectively, and a bite angle of 58.2(1)°. The neopentylidyne has a W1-C1 bond length of 1.777(5) Å, and a W1-C1-C2 angle of 171.6(3)°. The W1-O2 and W1-O3 bond distances of the µ2-N,O ligands are 2.128(3) and 2.265(3) Å respectively, with the W1-O3 bond is elongated due to a trans influence of the neopentylidyne ligand.132 The W2-N2 and W2-N3 bond distances of the µ2-N,O are 2.594(3) and 2.227(3) Å respectively. The W2-N2 distance is longer than the sum of the covalent radii of tungsten and nitrogen by 0.26 Å,105 and is a weak interaction due to the steric demands close to N2 of the amidate which forces elongation of the W2-N2 coordination. The W2-O5 terminal oxo bond distance is 1.734(3) Å, and the W2-C6 bond distance of the syn neopentylidene is 1.933(4) Å and the W2-C6-C7 angle is 139.5(3)°. The bridging oxo ligand has W-O bond distances of 1.966(2) and 1.907(3) Å for W1-O4 and W2-O4 respectively and a W1-O4-W2 angle of 145.2(1)°. One tungsten center (W1) is best described as a distorted pentagonal 133  bipyramidal coordination geometry, and the other tungsten center (W2) is best described as a distorted octahedral coordination geometry. This C1 symmetric complex has a unique structure in the solid state and shows the hemilabile character of the amidate ligands by the multiple bonding modes observed.   Due to the propensity of both oxo and amidate ligands to adopt bridging bonding modes it is likely that two equivalents of complex 3.11 have reacted to form a dimeric complex, followed by sterically induced loss of proligand HL8 as a result of C-H activation at the alkylidene to yield complex 3.12. Phosphine coordination  and/or ligand redistribution would influence the production of complex 3.12.189 The C-H activation of an alkylidene to form an alkylidyne has been proposed in a related bis(carboxylate)(arylimido)(alkylidene)molybdenum complex, where it is said to react to a bis(carboxylate)(arylamido)(alkylidyne)molybdenum upon coordination of PMe3, however the reaction products were not fully characterized due to difficulties isolating pure material.189 The C-H activated product of the alkylidene ligand has been proposed to be a tautomer alkylidyne amido complex where the alkylidene hydrogen has been transferred to the nitrogen of the imido group (Scheme 3-19). The authors note the appearance of a broad resonance at δ 10.44, and attribute it to the proposed side product, based on literature precedence of NH(Cl2C6H3) amido groups.205 134   Scheme 3-19. Reaction of PMe3 with a bis(carboxylate)(alkylidene)(imido)tungsten complex. In the case of 3.12 the intermolecular deprotonation of a tungsten alkylidene by NaL8 can be ruled out. Recall that analytically pure complex 3.11 was observed to decompose to presumably complex 3.12 and proligand HL8 over time when monitored by NMR spectroscopy in a sealed tube. In a J-Young NMR tube complex 3.11 takes days to react and produce proligand HL8, however, a stirred solution of complex 3.11 will completely react in hours.  Knowing that the addition of phosphine to a complex, such as 3.11, could promote dimerization by inducing a κ1-bonding mode of the amidate ligand and subsequent alkylidyne formation, B(C6F5)3 was added to sequester free dimethylphenylphosphine in the reaction of 3.4 with two equivalents of NaL8. The CuBr could not be used here due to decomposition problems when in solution with the tungsten oxo alkylidene complexes.34 The reaction with B(C6F5)3 has been conducted in a J-Young NMR tube to allow for reaction monitoring. The reaction produced the same signatures of that of the salt metathesis reaction without B(C6F5)3 according to the 1H-, 19F- and 31P-NMR spectra. However, the PhMe2PB(C6F5)3 adduct has been  observed and no other coordinated B(C6F5)3 species could be characterized.206 When the same salt metathesis reaction with B(C6F5)3 was scaled up and conducted in a glovebox, complex 3.11 could be isolated in 135  70% yield by recrystallization at -30 °C from a toluene solution layered with pentane. This improved synthetic method could shorten the reaction time to 3 hours and the yield was increased when compared to the original synthesis.  It is important to note that if two equivalents of B(C6F5)3 are used, the reaction outcome is different and no resonances in the alkylidene region are observed. Thus, at least one equivalent of phosphine ligand is needed to stabilize the reactive amidate complex 3.11. Analytically pure complex 3.11 will decompose in solution over time, as evidenced by monitoring with NMR spectroscopy to observe the formation of proligand HL8 and free dimethylphenyl phosphine. The decomposition is presumably due to dimerization and ligand redistribution.  Traditionally, the Schafer group has had more success in synthesizing early transition metal 1,3-N,O-chelated complexes by protonolysis synthetic routes rather than salt metathesis.64 Using 3.2 as the precursor, protonolysis reactions towards the synthesis of complex 3.11 has also been undertaken. Interestingly, when two equivalents of HL8 have been allowed to react with 3.2 there was an immediate and clean production of a (N-(3,5-bis(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamidate)(2,5-dimethylpyrrolide)(neopentylidene)(oxo)(dimethylphenylphosphine)tungsten complex (3.13), however, over time resonances for complex 3.11 appear and that of 3.13 and proligand HL8 diminish (Scheme 3-20). 136   Scheme 3-20. Reaction of 3.2 with two equivalents of HL8. Ar=3,5-bis(trifluoromethyl)phenyl and HPyrMe2=2,5-dimethylpyrrole.  Using a protonolysis reaction, one equivalent of proligand HL8 was treated with 3.2,194 producing complex 3.13 (Scheme 3-21) as the only product, as evident by full consumption of 3.2 and the appearance of a single new alkylidene resonance at δ 10.73 (doublet 3JHP=3.6 Hz) when the reaction is monitored by 1H-NMR spectroscopy. The orange powder (complex 3.13) can be obtained in a 97% yield as a pure solid after leaving the crude material under high vacuum for more than 24 hours to ensure removal of the 2,5-dimethylpyrrole biproduct (Scheme 3-21).  Scheme 3-21. Protonolysis reaction of proligand HL8 and 3.2 in quantitative yield Ar=3,5-bis(trifluoromethyl)phenyl and HPyrMe2=2,5-dimethylpyrrole. The orange powder was recrystallized from warm pentanes to yield single crystals suitable for X-ray diffraction. The solid-state molecular structure of complex 3.13 is shown in Figure 3-15, while the data was not of sufficient quality to resolve accurate bond metrics the connectivity and distorted octahedral molecular geometry were found. 137   Figure 3-15. Solid-state molecular structure of 3.13, atoms shown as an isotropic ball and stick with model most hydrogen atoms omitted. Complex 3.13 does not undergo ligand redistribution of amidate and 2,5-dimethylpyrrolide ligands in solution (Scheme 3-22), unlike complex 3.11.  Scheme 3-22. Complex 3.13 does not undergo ligand redistribution of amidate and 2,5-dimethylpyrolide ligands. Ar=3,5-bis(trifluoromethyl)phenyl. Complex 3.11 and 3.13 are isostructural, as confirmed by an overlay of the solid-state molecular structures (Figure 3-16). Due to the differences in stability towards ligand redistribution for complex 3.13 compared to complex 3.11, the enhanced reactivity of complex 3.11 can be attributed to the hemilabile ligands. 138   Figure 3-16. Overlay of complex 3.11 and 3.13, Labels correspond to complex 3.13. Solid-state molecular structure of complex 3.11, plotted at 50% ellipsoids with most hydrogen atoms omitted. Solid-state molecular structure of 3.13, atoms shown as an isotropic ball and stick with model most hydrogen atoms omitted.  Ultimately, complex 3.11 could be successfully synthesized by both salt metathesis and protonolysis reactions, where the former has been preferred due to shorter reaction times, while the protonolysis reaction of 3.11 and HL8 is sluggish. The continued reactivity of complex 3.11 in solution is attributed to an amidate assisted C-H activation process that resulted in the isolation of complex 3.12. There is no current procedure to selectively form complex 3.12 and there are other decomposition products present have yet to be identified. 3.2.5 Synthesis of tungsten(neopentylidene)(oxo) complexes with 6-methylpyridonate ligands  The synthesis of tungsten oxo neopentylidene complex with a pyridonate 1,3-N,O-donor ligand has also been explored. The pyridone HL1 has been used due to its 139  substitution at the 6 position, as 3-subtituted pyridones have been shown to readily access undesirable bridging complexes.66-67 The salt metathesis reaction of two equivalents of NaL1 and 3.4 has been undertaken (Scheme 3-23).  Scheme 3-23. Salt metathesis reaction of 3.4 and two equivalents of NaL1. The reaction mixture was initially bright yellow/green in color, which faded to brown as the reaction proceeded. After the reaction has been completed the solution was filtered through diatomaceous earth and the volatiles were removed under vacuum. The resulting brown solids showed no indication of the desired bis(pyridonate)(neopentylidene)(oxo)tungsten complex by NMR spectroscopy. Reducing the reaction temperature to -40 °C gave the same results. When the reaction was conducted in a J-Young NMR tube to monitor the reaction via NMR spectroscopy, it was apparent that the proposed bis(pyridonate)(neopentylidene)(oxo)tungsten complex had formed, however, when the product had been isolated by removing the solvent under vacuum, the resulting solids showed no signs of the species that had been observed during the reaction.   Since the desired pyridonate complex could not be isolated out of solution, 1H-NMR spectra have been taken as the reaction proceeded in a J-Young NMR tube. After 3 hours the starting complex 3.4 had been fully consumed and only resonances for the proposed bis(pyridonate)(neopentylidene)(oxo)tungsten complex, dimethylphenylphosphine, proligand HL1, and small amounts of 1,2-di(tert-butyl)ethene 140  were observed. The neopentylidene WCHC(CH3)3 has been observed as a broad singlet at δ 11.23, and the WCHC(CH3)3 was at δ 1.38. The methyl groups of 6-methylpyridonate ligands are a single broad resonance at δ 2.08, and the aryl resonances are at δ 6.78, 6.11 and 6.02.     As shown in chapter 2, the relatively small pyridonate ligands have more dynamic hemilability compared to amidate ligands, which can allow for bridging or aggregate species to form.67 it is also known that group 6 alkylidene complexes can react with themselves intermolecularly to form a reduced di-tungsten species and coupled alkylidene ligands to form an alkene (Scheme 3-24).8   Scheme 3-24. Reductive coupling of alkylidene fragments, forming a double bonded ditungsten complex. Here we are likely observing such decomposition due to the appearance of 1,2-di(tert-butyl)ethene (observed at δ 5.48 in the 1H-NMR spectrum) in the reaction mixture. 3.3 Reactivity of 1,3-N,O-ligated tungsten oxo alkylidene complexes with olefins  To test the differences in reactivity with olefins of the amidate complexes synthesized in this chapter, RCM trials using 1,7-octadiene as the substrate and 5 mol% of the tungsten amidate complex have been undertaken (Table 3-2). The substrate 1,7-octadiene has been completely converted to ethylene and cyclohexene by a RCM reaction under similar conditions in 1 hour.207 Comparing the relative efficiencies of ring closing metathesis activities between complexes 3.6-3.8, 3.10, 3.11 and 3.13  was proposed to be impacted by ligand electronic including the relative hemilability of the amidate ligands. 141  Recall, as proposed, more dynamic hemilability would generate unsaturated metal species and lead to productive metathesis, would also increase the reactivity of the olefin metathesis catalyst (Scheme 3-7).  Two temperatures have been used for the catalytic trials, room temperature and 80 °C. The reactions were conducted for 3 hours. The catalytic trials were conducted in small vials (4 mL) capped with a tight-fitting Teflon® cap, the reactions have been setup in a glovebox then taken out and stirred for 3 hours. The reactions have been quenched with benzaldehyde then analyzed by 1H-NMR spectroscopy with trimethoxy benzene as an internal standard. The results from the catalytic trials are summarized in Table 3-2.  Table 3-2. Ring closing metathesis of 1,7-octadiene with crude material as catalysts (complexes 3.11 and 3.13 were pure materials). 5 mol. % catalyst loading. Conv. are tabulated as percentages.   The tungsten amidate complexes showed very little activity at room temperature, from <1-5% conversion. This was not surprising for complexes 3.6-3.8, which have both amidate ligands bound in a κ2-N,O bonding mode, and thus a formally saturated metal center. Complexes 3.10, 3.11 and 3.13 are known to be fluxional at room temperature transiently generating unsaturated metal centers, however their conversions have been shown to b less than 2%. The reactions that have been heated to 80 °C showed poor to moderate conversion of the 1,7-octadiene substrate to cyclohexene, with yields ranging from 5-52%. Complex 3.8 showed the highest activity with 52% conversion in 3 hours. All 142  the other complexes showed substantially lower conversion ranging from 14-5% (Table 3-2). The order of activity towards the RCM reactions of 1,7-octadiene with 5 mol% of catalyst has been 3.8 > 3.6 > 3.7 > 3.10 > 3.13 > 3.11. The trend between complexes 3.6, 3.7, 3.10, 3.11 and 3.13 is minimal since the range of conversions is 14-5%. Although these new tungsten oxo alkylidene complexes show limited ability catalytically, the fact that they are active for olefin metathesis catalysis is an improvement over the related 1,3-O,O-ligated molybdenum complexes that do not react with olefins at all.189 The low catalytic activated has been attributed to catalyst decomposition, since it has been known that this class of 1,3-N,O-chelated complexes continue to react in solution.   Interestingly, there has been little difference when purified complex 3.6 has been used as a catalyst versus crude complex 3.6, the former having a yield of 15% and the latter a yield of 12%. Signifying that the residual dimethylphenylphosphine does not substantially hinder the olefin metathesis reaction. When 10 mol% of B(C6F5)3 has been used as an additive with 5 mol% of complex 3.6 in a catalytic trial the metathesis reactivity drastically increased reaching full conversion in less than 3 hours at room temperature (the reaction was conducted in a J-Young NMR tube with the head space removed). The B(C6F5)3 reagent is known to activate the tungsten oxo bond of a tungsten oxo alkylidene complex and enhance the olefin metathesis activity of the tungsten catalyst.208 3.4 Conclusions  The synthesis of the first 1,3-N,O-donor ligated tungsten alkylidene complexes has been achieved. In most cases, full characterization of the 1,3-N,O-chelated tungsten complexes proved difficult due solution phase decomposition. Only complexes 3.6, 3.11, and 3.13 have been subjected to combustion analysis, however, complexes 3.7, 3.8 and 143  3.10 have been analyzed by high resolution EIMS, single crystal X-ray diffraction and solution NMR spectroscopy. The success of the 1,3-N,O-donor ligands with N-2,6-diisopropylphenyl substituents shows how ligand design can influence the coordination mode of the 1,3-N,O-ligand, with bulky groups consistently giving N-trans coordination geometries for bis(amidate) complexes. The bulky groups help prevent intermolecular coupling of neopentylidene fragments, which causes reduction of the tungsten complex and has been known as a catalyst deactivation pathway.8 The variable temperature NMR spectroscopy shows that the amidate ligands are highly fluxional at elevated temperatures, however the trends in the variable temperature NMR studies were not mirrored in the olefin metathesis trials.  The unexpected dimeric Complex 3.12 shed light into a C-H activation process that we propose is responsible for the observation of proligand formation when the 1,3-N,O-ligated complexes continue to react in solution. Although the details of the mechanism are still unknown, alkylidyne formation has been observed. The amidate assisted C-H activation route highlights the hemilability of the 1,3-N,O-ligated ligands. Similar bond activation have been observed for late transition metal 1,3-N,O-ligated complexes but this is the first example of a 1,3-N,O-donor ligand on an early transition metal complex that has been involved in α-hydrogen abstraction. Harnessing the C-H activation decomposition route towards selective activation of alkylidene ligands to make alkylidyne ligands (and the reverse) is a potential route for the interconversion of such species.  Developing trends of the 1,3-N,O-donor ligands by comparing relative efficiencies of di(amidate)(neopentylidene)(oxo)tungsten complexes to catalyze the RCM of 1,7-octadiene was complicated by the continued reactivity of the 144  di(amidate)(neopentylidene)(oxo)tungsten complexes. The unexpected continued reactivity observed when di(amidate)(neopentylidene)(oxo)tungsten complexes were in solution, causes the decomposition of the alkylidene complex. Importantly, the decomposition of the catalytically active alkylidene complexes will halt the olefin metathesis reactivity. Thus, decomposition of the di(amidate)(neopentylidene)(oxo)tungsten complexes would lead to decreased conversion of the olefin substrate. Furthermore, the conversions observed in the RCM trials are all low and span a narrow range (5-14% at 80 °C), except for complex 3.8 which showed moderate reactivity (52% at 80 °C). For these reasons no trends in reactivity could be elucidated. However, one explanation that agrees with the RCM trials is that complex 3.8 decomposes slower than the other complexes tested. This would explain a higher yield of metathesis product because complex 3.8 have more time to catalyze the olefin metathesis reaction. The relative rates of proligand formation (accompanied by alkylidene decomposition) by the 1,3-N,O-donor ligands were not measured.  When trifluoromethyl groups substituents employed in the backbone of the NCO amidate ligands, such as in complexes 3.9/3.10 and 3.11, the resulting amidate complexes demonstrated phosphine coordination and κ1-O bound amidates in the solid-state molecular structures. The electron withdrawing nature of the trifluoromethyl groups in these systems has seemingly changed the dynamic of the 1,3-N,O-donor amidate ligands to preferentially form hemilabile κ1-O species to allow for phosphine coordination; unlike complexes that do not have strong electron withdrawing groups (such as complexes 3.6, 3.7 and 3.8). This could be due the electronics of the amidate ligands that have strongly electron withdrawing group such as trifluoromethyl groups in the amidate NCO backbone. Future investigations 145  employing these amidate ligands are needed to uncover if hemilability of amidate ligands can be influenced by the electronic parameters of strong electron withdrawing groups in the amidate NCO backbone.   The unexpected C-H activation of the tungsten alkylidene ligand renders the bis(amidate)(neopentylidene)(oxo)tungsten complexes difficult to obtain as analytically pure materials and to manipulate thereafter. Complex 3.8 has been the only complex to demonstrate significant reactivity, although the productivity of complex 3.8 is dwarfed by that of previously reported olefin metathesis complexes.209 Comparing the amidate complexes from this chapter to previously reported carboxylate molybdenum imido alkylidene complexes shows increased reactivity with olefins of the former. Beyond olefin metathesis, these complexes display an interesting C-H activation pathway that has the potential for selectively forming an alkylidene or alkylidyne species. 3.5 Materials and methods  All reactions were conducted under an inert atmosphere of nitrogen, inside a glove box, or using standard Schlenk techniques unless otherwise noted. All chemicals were purchased from commercial sources and used as received unless otherwise noted. Hexanes, toluene and diethyl ether were passed through an activated alumina tower and dried further with molecular sieves if necessary. THF, pentane, benzene-d6 and toluene-d8 were dried over sodium metal and distilled. NMR spectra were obtained on either a Bruker Avance 300 spectrometer, Bruker Avance 400inv spectrometer, or a Bruker Avance 400dir spectrometer. The spectra shown here have blue peak labels in blue and red integrations. The 1H- and 13C-NMR spectra were referenced to residual solvent signals, benzene-d6, (1H 7.16 ppm, 13C 128.06 ppm) and toluene-d8 (methyl, 1H 2.09 ppm). The 19F- and 31P-NMR 146  spectra were refenced to CFCl3 (0 ppm) and H3PO4 (0 ppm) respectively. Neutral alumina was dried by heating in a round bottom Schlenk over a flow of dry N2 gas, after water had stopped distilling off from the alumina the Schlenk was removed from heat and further dried under vacuum. EI mass spectra were acquired on a Kratos MS-50 spectrometer. Elemental analyses were collected on a Carlo Erba Elemental Analyzer EA 1108 instrument. GC/MS were conducted on an Agilent 7890A GC equipped a 5975C inert XL EI/CI mass detector which is operated in positive CI mode with methane as the reagent gas. Amide proligands HL4,63 HL5,193 HL6,210 HL7,210 and HL8,211 have been prepared by literature methods. Proligand HL1 was purchased from commercial sources. All proligands were dried under vacuum overnight or sublimed to remove traces of H2O. Complexes W(O)(CHCMe3)Cl2(PMe2Ph)2 and W(O)(CHCMe3)(PyrMe2)2(PMe2Ph) were synthesized by literature methods.184, 194 Synthesis of complex 3.6 The amidate salt NaL4 (0.0586 g, 0.193 mmol) and 3.4 (0.0600 g, 0.0972 mmol) were added to a vial in the glove box with a stir bar, then 3 mL of toluene was added and the reaction was stirred overnight. The yellow solution was filtered through diatomaceous earth and then the volatiles were removed leaving a yellow semi-solid. The yellow semi-solid was triturated without filtering with 3 mL of hexanes. Crude yield 71.2 mg (89%). The crude material contained complex 1, small amounts of proligand and dimethylphenylphosphine. Recrystallization of the crude mixture from a toluene/hexanes solution at -30 °C yielded material that contained complex 3.6 and proligand HL4 and dimethylphenylphosphine. Another reaction was purified by dissolving the crude material 147  in a minimum amount of toluene and eluting through a column of dried alumina (~1-2”). The column was eluted with toluene and a yellow solution eluted first and was the only colored solution to elute form the column. The yellow solution was immediately put under vacuum to remove volatiles which yielded analytically pure complex 3.6 in a 29% yield. 1H NMR (300 MHz, BENZENE-d6)  0.88 (d, J=6.7 Hz, 3 H), 1.01 (d, J=6.7 Hz, 3 H), 1.04 (d, J=6.7 Hz, 3 H), 1.12 (d, J=6.9 Hz, 3 H), 1.24 (s, 9 H), 1.40 (d, J=6.9 Hz, 3 H), 1.43 (d, J=6.9 Hz, 3 H), 1.61 (d, J=6.7 Hz, 3 H), 1.64 (d, J=6.9 Hz, 3 H), 3.60 (spt, J=6.7 Hz, 1 H), 3.98 (spt, J=6.7 Hz, 1 H), , 4.18 (spt, J=6.9 Hz, 1 H), 4.26 (spt, J=6.9 Hz, 1 H), 6.82 (m, 6 H), 7.10 (m, 3 H), 7.21 (m, 3 H), 7.74 (m, 4 H), 10.86 (s, 1 H, 1JCH=119.3 Hz); 13C NMR (75 MHz, BENZENE-d6)  21.77 (s), 23.78 (s), 23.89 (s), 24.22 (s), 24.69 (s), 24.93 (s), 25.10 (s), 25.26 (s), 26.50 (s), 28.64 (s), 28.71 (s), 28.81 (s), 29.62 (s), 33.39 (s), 43.57 (s), 124.09 (s), 124.75 (s), 125.05 (s), 125.12 (s), 126.03 (s), 127.90 (s), 128.90 (s), 129.16 (s), 129.67 (s), 130.25 (s), 130.65 (s), 131.88 (s), 132.15 (s), 132.88 (s), 133.20 (s), 133.58 (s), 140.69 (s), 143.18 (s), 143.30 (s), 144.32 (s), 144.41 (s), 144.98 (s), 147.31 (s), 174.17 (s), 183.28 (s), 289.04 (s); MS(EI) m/z 830 ([M]+), m/z 760 ([M -CCMe3]+); HRMS(EI); ([M]+) calc. 828.36167, found 828.36127. Anal. Calcd. For WO3N2C43H54: N, 3.37%; C, 62.17%; H, 6.55%. Found: N, 3.39%; C, 62.29%; H, 6.53%. 148   Figure 3-17. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.6. Dipp=2,6-diisopropylphenyl.  Figure 3-18. 13C-NMR 75 MHz spectrum in C6D6 of complex 3.6. Dipp=2,6-diisopropylphenyl. 149   Figure 3-19. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.6, crude material used. Dipp=2,6-diisopropylphenyl. Synthesis of complex 3.7 The amidate salt NaL5 (0.0924 g, 0.210 mmol) and 3.4 (0.0620 g, 0.100 mmol) were added to a vial in the glove box with a stir bar, then 3 mL of toluene was added, and the reaction was stirred overnight. The yellow solution was filtered through diatomaceous earth and then the volatiles were removed leaving a yellow semi-solid. The yellow semi-solid was triturated without filtering with 3 mL of hexanes. The semi-solid material contained complex 3.7, small amounts of proligand and dimethylphenylphosphine, and over the course of weeks turned to crystalline material suitable for X-ray diffraction. 1H NMR (300 MHz, BENZENE-d6)  0.68 (d, J=6.7 Hz, 3 H), 0.92 (d, J=6.7 Hz, 3 H), 0.99 (d, J=6.7 Hz, 3 H), 1.04 (d, J=7.0 Hz, 3 H), 1.18 (s, 9 H), 1.29 (d, J=7.0 Hz, 3 H), 1.34 (d, J=6.7 Hz, 3 H), 1.53 (d, J=6.7 Hz, 3 H), 1.54 (d, J=6.7 Hz, 3 H), 3.35 (spt, J=7.0 Hz, 1 H), 3.76 (spt, 150  J=6.7 Hz, 1 H), 4.06 (spt, J=6.7 Hz, 2 H), 6.99 (s, 1 H), 7.10 (m, 5 H), 7.54 (s, 1 H), 7.57 (s, 1 H), 8.04 (s, 2 H), 8.11 (s, 2 H), 11.05 (s, 1 H, 1JCH=118.7 Hz); 19F NMR (282 MHz, BENZENE-d6)  -63.8 (s), -63.7 (s); MS(EI) m/z 1102 ([M]+), m/z 1032 ([M -CCMe3]+); HRMS(EI); ([M]+) calc. 1100.31121, found 1100.31299.  Figure 3-20. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.7. Dipp=2,6-diisopropylphenyl, Ar=3,5-bis(trifluoromethyl)phenyl. 151   Figure 3-21. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.7. Dipp=2,6-diisopropylphenyl, Ar=3,5-bis(trifluoromethyl)phenyl. 152   Figure 3-22. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.7, crude material used. Dipp=2,6-diisopropylphenyl. Synthesis of complex 3.8 The amidate salt NaL6 (0.0500 g, 0.207 mmol) and 3.4 (0.0617 g, 0.100 mmol) were added to a vial in the glovebox with a stir bar, then 3 mL of toluene was added, and the reaction was stirred for 6 hours. The yellow solution was filtered through diatomaceous earth and then the volatiles were removed leaving a yellow semi-solid. The yellow semi-solid was triturated without filtering with 3 mL of hexanes. The semi-solid material contained complex 3.8, small amounts of proligand and dimethylphenylphosphine. 1H NMR (300 MHz, BENZENE-d6)  0.89 (d, J=6.7 Hz, 3 H), 1.06 (d, J=6.7 Hz, 3 H), 1.17 (s, 9 H), 1.20 (d, J=6.7 Hz, 3 H), 1.34 (d, J=6.7 Hz, 3 H), 1.33 (d, J=6.7 Hz, 3 H), 1.32 (d, J=6.7 Hz, 3 153  H), 1.50 (s, 3 H), 1.56 (d, J=6.7 Hz, 3 H), 1.55 (d, J=6.7 Hz, 3 H), 1.64 (s, 3 H), 3.32 (spt, J=6.7 Hz, 1 H), 3.66 (spt, J=6.7 Hz, 1 H), 3.93 (spt, J=6.7 Hz, 1 H), 3.99 (spt, J=6.7 Hz, 1 H), 7.06 (m, 6 H), 10.61 (s, 1 H, 1JCH=118.1 Hz); MS(EI) m/z 706 ([M]+), m/z 636 ([M -CCMe3]+); HRMS(EI), ([M]+) calc. 704.33037, found 704.32981.  Figure 3-23. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.8. Dipp=2,6-diisopropylphenyl. 154   Figure 3-24. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.8, crude material used. Dipp=2,6- diisopropylphenyl. Synthesis of complex 3.9 The amidate salt NaL7 (0.0410 g, 0.139 mmol) and 3.4 (0.0399 g, 0.0647 mmol) were added to a vial in the glovebox with a stir bar, then 3 mL of toluene was added, and the reaction was stirred for 6 hours. The yellow solution was filtered through diatomaceous earth and then the volatiles were removed leaving a yellow semi-solid. The yellow semi-solid was triturated without filtering with 4 mL of pentane. The semi-solid material contained complex 3.9, small amounts of proligand and a (dimethylphenylphosphine)CuBr complex. The crude yield was 0.0473 g. 1H NMR (300 MHz, BENZENE-d6)  0.97 (d, J=6.6 Hz, 3 H), 1.00 (s, 9 H), 1.15 (overlapping d, apparent t, 6 H), 1.26 (overlapping d, 155  apparent t, J=4.9 Hz, 6 H), 1.33 (d, 3 H, overlapping with PhMe2PCuBr doublets), 1.45 (d, J=6.4 Hz, 3 H), 1.49 (d, J=6.4 Hz, 3 H), 3.15 (spt, J=6.4, Hz, 2 H), 3.41 (spt, J=6.6 Hz, 1 H), 3.65 (spt, J=6.3 Hz, 1 H), 3.79 (spt, J=6.3 Hz, 1 H), 7.03 (m, 6 H), 11.19 (s, 1 H, 1JCH=119.0 Hz); 19F NMR (282 MHz, BENZENE-d6)  ppm -71.36 (s), -70.02 (s).  1H-NMR 300 MHz, C6D6  Figure 3-25. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.9. Dipp=2,6-diisopropylphenyl. 156   Figure 3-26. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.9. Dipp=2,6-diisopropylphenyl. Synthesis of complex 3.10 The amidate salt NaL7 (0.0611 g, 0.207 mmol) and 3.4 (0.0619 g, 0.100 mmol) were added to a vial in the glovebox with a stir bar, then 3 mL of toluene was added, and the reaction was stirred for 6 hours. The yellow solution was filtered through diatomaceous earth and then the volatiles were removed leaving a yellow semi-solid. The yellow semi-solid was triturated without filtering with 3 mL of hexanes. The semi-solid material contained complex 3.10, small amounts of proligand and dimethylphenylphosphine. 1H NMR (300 MHz, BENZENE-d6)  0.79 (s), 0.98 (m), 1.06 (d, J=3.2 Hz), 1.17 (d, J=6.2 Hz), 1.25 (d, J=6.5 Hz), 1.34 (d, J=5.0 Hz), 1.41 (d, J=6.5 Hz), 1.47 (d, J=6.2 Hz), 1.52 (d, J=6.2 Hz), 1.65 (d, J=10.0 Hz), 1.76 (d, J=10.0 Hz), 2.55 (br. s.), 2.79 (s), 3.41 (m), 3.62 (m), 3.94 (m), 6.89 (m), 6.97 (s), 7.07 (s), 7.37 (s), 7.46 (d, J=7.9 Hz), 11.20 (s), 11.95 (br. s.); 19F 157  NMR (282 MHz, BENZENE-d6)  -75.41 (s), -71.35 (s), -70.67 (br. s.), -70.00 (s), -68.40 (br. s.); 31P NMR (121 MHz, BENZENE-d6)  -45.92 (s), 10.53 (br. s.); MS(EI) m/z 744 ([M -CCMe3]+); HRMS(EI), ([M -CCMe3]+) calc. 742.19559, found 742.19601.  Figure 3-27. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.10. Dipp=2,6-diisopropylphenyl. 158   Figure 3-28. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.10. Dipp=2,6-diisopropylphenyl.    Figure 3-29. 31P-NMR 121 MHz spectrum in C6D6 of complex 3.10. Dipp=2,6-diisopropylphenyl. 159    Figure 3-30. Variable temperature 282 MHz 19F-NMR spectra in C7D8 of complex 3.10, crude material used. Dipp=2,6-diisopropylphenyl.  Synthesis of Complex 3.11 JC7-063 Complex 3.4 (0.0387 mmol, 0.0239 mg), B(C6F5)3 (0.0371 mmol, 0.0190 g) and amidate salt NaL8 (0.0792 mmol, 0.0275 g) were added to the same vial. Toluene (2 mL) was added the vial containing the solids and the mixture was stirred for 3 hours. The reaction mixture was then filtered through a 1.5 centimeter plug of diatomaceous earth, then the volatiles were removed to leave a yellow solid. The solids were dissolved in ~1.5 mL of toluene and then ~1.5 mL of pentane was added and solution was put in a -30 °C freezer to recrystallize. Overnight orange crystals precipitated. Yield 0.0252 g (57%). The elemental analysis matched the asymmetric unit of the solid-state molecular structure of complex 160  3.11, which was the tungsten complex with a solvent toluene molecule. 1H NMR (400 MHz, Tol)  0.97 (s, 9 H), 1.15 (d, J=10.6 Hz, 3 H), 1.33 (d, J=10.6 Hz, 3 H), 6.90 (br. s., 3 H), 7.57 (m, 5 H), 10.49 (br. s., 1 H). 19F NMR (282 MHz, Tol)  -72.82 (br. s.), -68.60 (br. s.), -63.39 (br. s.), -63.25 (br. s.); 31P NMR (162 MHz, Tol)  15.44 (br. s. satellites 1JPW=392 Hz); Anal. Calcd. For WPF18O3N2C33H27: N, 2.44%; C, 41.83%; H, 3.07%. Found: N, 2.36%; C, 41.62%; H, 2.93%. The 13C-NMR spectrum did not show all expected resonances due to the poor solubility of complex 3.11 in C7D8, however some resonances were observed. See Results and Discussion section.  Figure 3-31. 1H-NMR 400 MHz spectrum in C7D8 of complex 3.11. Ar=3,5-bis(trifluoromethyl)phenyl. 161   Figure 3-32. 19F-NMR 282 MHz spectrum in C7D8 of complex 3.11. Ar=3,5-bis(trifluoromethyl)phenyl.  Figure 3-33. 31P-NMR 162 MHz spectrum in C7D8 of complex 3.11. Ar=3,5-bis(trifluoromethyl)phenyl. 162   Figure 3-34. Variable temperature 400 MHz 1H-NMR spectra in C7D8 of complex 3.11, crude material used. Ar=3,5-bis(trifluoromethyl)phenyl. Synthesis of complex 3.13 JC7-037 Complex 3.3 (0.0823 mmol, 0.0491 g) was added as a solid to a vial containing HL8 (0.0803 mmol, 0.0261 g). Toluene (3 mL) was added to the solids and the mixture was stirred for 2 hours. The volatiles were removed leaving an orange semi solid. The solids were triturated without filtering twice using pentane, which resulted in an orange powder after the volatiles were removed by vacuum overnight. The 1H, 19F and 31P-NMR spectra of the crude solids shows only complex 3.13. The orange solids were analytically pure and gave a yield of 0.0643 g, 97%. Recrystallization of the solids from warm pentane produced crystalline material for X-ray diffraction. 1H NMR (300 MHz, BENZENE-d6) δ 1.14 (s, 9 H), 1.42 (d, 2JHP=9.5 Hz, 6 H), 2.14 (br. s., 3 H), 2.53 (br. s., 3 H), 6.21 - 6.31 (br. s., 1 H), 163  6.40 (br. s., 1 H), 6.38 (s, 2 H), 7.03 - 7.14 (m, 5 H), 7.51 (s, 1 H), 10.73 (d, 3JHP=3.6 Hz, 1 H, 1JCH=120.3 Hz). 13C NMR (101 MHz, BENZENE-d6) δ 15.0 (d, 1JCP=32.5 Hz), 16.7 (d, 1JCP=30.5 Hz), 18.1 (s), 18.5 (s), 32.4 (s), 45.2 (d, 3JCP=2.0 Hz), 109.8 (br. s.), 110.8 (br. s.), 118.7 (q, 1JCF=288.4 Hz), 119.2 (spt, 3JCF=4.0 Hz), 123.7 (q, 1JCF=273.7 Hz), 125.1 (m), 129.7 (d, 2JCP=8.9 Hz), 130.2 (d, 3JCP=8.9 Hz), 131.7 (q, 2JCF=33.5 Hz), 131.3 (d, 4JCP=3.0 Hz), 134.1 (d, 1JCP=39.4 Hz), 134.4 (br. s.), 134.9 (br. s.), 158.0 (qd, 2JCF =35.0, 3JCP=2.0 Hz), 299.5 (d, 2JCP=11.8 Hz, satellites 1JCW=173.3 Hz). 19F NMR (282 MHz, BENZENE-d6) δ -67.43 (s), -62.71 (s). 31P NMR (121 MHz, BENZENE-d6)  10.5 (s, satellites 1JPW=312.7 Hz). MS(EI) m/z 688 [M -PMe2Ph]+. Anal. Calcd. For WPF9O2N2C29H32: N, 3.39%; C, 42.15%; H, 3.90%. Found: N, 3.21%; C, 42.18%; H, 3.61%.   Figure 3-35. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl.  164   Figure 3-36. 13C-NMR 101 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl.   Figure 3-37. 19F-NMR 282 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl. 165   Figure 3-38. 31P-NMR 121 MHz spectrum in C6D6 of complex 3.13. Ar=3,5-bis(trifluoromethyl)phenyl. Synthesis of complex 3.14 Solid 3.4 (0.0107 g, 0.0173 mmol) and NaL1 (0.0069 g, 0.0562 mmol) were loaded into a J-Young NMR tube and ~0.7 mL of C6D6 was added. The NMR tube was placed in an apparatus that continuously inverted the tube to encourage mixing. After 3 hours, a 1H-NMR spectrum was acquired, and showed full consumption of the starting 3.4 complex. Resonances for dimethylphenylphosphine are broadened and shifted from free phosphine (δ 1.09 vs 1.07(free)), indicating reversible bonding to the proposed bis(pyridonate)(neopentylidene)(oxo)tungsten complex.  The 1H-NMR was assigned as listed below. Upon isolating the solid by removing volatiles in vacuum, the signal attributed to the proposed bis(pyridonate)(neopentylidene)(oxo)tungsten complex disappear. 1H NMR (300 MHz, BENZENE-d6)  1.38 (s), 2.08 (br. s.), 6.02 (d, J=7.3 Hz), 6.11 (d, J=7.9 Hz), 6.87 (t, J=7.8 Hz), 11.23 (br. s.). 166   Figure 3-39. 1H-NMR 300 MHz spectrum in C6D6 of complex 3.14 in the reaction solvent after filtration.  Figure 3-40. 1H-NMR 300 MHz spectrum in C6D6 of isolated solid material from synthesis of 3.14. Typical catalytic trial for the ring closing metathesis of 1,7-octadiene 167  Complex 3.8 (0.0070 g, 0.00991 mmol) was added to a small vial containing a stir bar and 300 µL of C6D6 and 1,7-octadiene (30 µL (0.0220 g), 0.2 mmol) were added to the small vial via micro syringe. The vials were capped with an air tight cap and the vial was taken out of the glove box and immediately put in a prewarmed 80 °C oil bath for 3 hours. After 3 hours the vial was removed from the oil bath and the cap was unscrewed and 300 µL of a solution of C6D6 with internal standard (1,3,5-trimethoxybenzene) was added and the resulting solution was transferred to a NMR tube and a 1H-NMR spectrum was acquired right immediately. The conversion was obtained by integrating the disappearance of the 1,7-octadiene substrate.  Figure 3-41. 1H-NMR spectrum of the RCM catalytic trail with complex as the catalyst. 168  Chapter 4: Trials and advances in group 6 mediated hydroaminoalkylation 4.1 Introduction 4.1.1 Nitrogen containing compounds: uses and synthesis  A desirable way to synthesize amines has been via hydrofunctionalization reactions because they are atom economic,156 meaning that 100% of the atoms in the substrates are incorporated into the product.212 This contrasts with traditional methods for synthesizing amines which often use wasteful stoichiometric reagents.98 An example of a hydrofunctionalization reaction that is capable of synthesizing amines is hydroaminoalkylation (Scheme 4-1).97  Scheme 4-1. General hydroaminoalkylation reaction.97 The hydroaminoalkylation reaction forms a carbon carbon bond alpha to a nitrogen atom. Hydroaminoalkylation has been reported with primary, secondary and tertiary amines.97, 213 4.1.2 Hydroaminoalkylation  The first report of hydroaminoalkylation was in 1980 by Clerici and Maspero, and it reported the hydroaminoalkylation of ethene, propene, and 1-hexene with either dimethyl or diethylamine (Scheme 4-2).90 This first example of a hydroaminoalkylation reaction required a catalyst and high temperatures of 160 °C, as well as a 24 hour reaction time. Even with the harsh reaction conditions, a yield of 18% of the alkylated product has been 169  formed. When the temperature has been increased to 200 °C and the reaction conducted for 150 hours, the yield maximum was 38% for the pentakis(dimethylamido)tantalum catalyst. In all cases the branched product has been observed as the only product.  Scheme 4-2. First report of hydroaminoalkylation. Reactions were conducted at 20 atm.90 The catalysts tested were Ti(NMe2)4, V(NMe2)4, Zr(NMe2)4, Nb(NMe2)5, Mo(NMe2)4, Sn(NMe2)4 and Ta(NMe2)5. The Ti(NMe2)4, V(NMe2)4, Mo(NMe2)4 and Sn(NMe2)4 complexes showed either zero or trace product formation.   In 1983 Nugent et al. reported similar reactivity to the initial report by Clerici and Maspero and proposed a mechanism for the reaction.91 The report demonstrated the hydroaminoalkylation of 1-pentene with dimethylamine. The catalysts tested by Nugent et al. were Ti(NMe2)4, Zr(NMe2)4, Hf(NMe2)4, Nb(NMe2)5, Sn(NMe2)4, Ta(NMe2)5 and a tungsten catalyst that had a 2:1 mixture of W2(NMe2)6:W(NMe2)6. Only three of the complexes tested showed catalytic activity, the three complexes were Ta(NMe2)5 Nb(NMe2)5 and W2(NMe2)6:W(NMe2)6, and produced exclusively the branched product in 1, 9 and 14 % yields respectively (Scheme 4-3). 170   Scheme 4-3. Hydroaminoalkylation of 1-pentene with dimethylamine, reactions were conducted in sealed tubes.91  To probe the mechanism of this reaction Nugent et al. allowed N-deutero dimethylamine and the dimethylamido metal complexes react at catalytic conditions and it has been found that deuterium has been transferred to the methyl groups of the dimethylamine. Four of the complexes showed significant hydrogen deuterium exchange ranging from 26-67% exchanged (Scheme 4-4). Their proposal was that a reversible metallaaziridine was forming and the N-deutero dimethylamine protonated the metal carbon bond of the metallaaziridine to form the observed reaction products (Scheme 4-4).  Scheme 4-4. Hydrogen-Deuterium exchange in the presence of catalytic amounts of metal dimethylamido complexes. Hydrogen-Deuterium exchange reactions were conducted at 160 °C over a 14 hour period with 2 mol% catalyst loading. The W(NMe2)n was a 2:1 mixture of W2(NMe2)6 and W(NMe2)6 respectively.91  171   The proposed mechanism for hydroaminoalkylation has been shown in Scheme 4-5.  Scheme 4-5. Proposed mechanism of the hydroaminoalkylation reaction.91  The first step in the mechanism is the formation of the metallaaziridine intermediate ii, subsequent alkene insertion into the metal carbon bond results in the formation of intermediate iii. From intermediate iii, the product is released after two protonolysis reactions, and the reformation of intermediate ii restarts the catalytic cycle.91 Although the catalytic variant of the hydroaminoalkylation with early transition metals did not reappear until 2007, the stoichiometric α-alkylation of amines has been developed by Buchwald et al.214 172   Scheme 4-6. α-alkylation of benzylamine mediated by a zirconocene complex.214 The α-alkylation of benzylamine has been accomplished with a zirconocene complex. The benzyl amine was not alkylated without first protecting the nitrogen with a trimethylsilyl group, followed by transmetallation via salt metathesis of the lithiated TMS protected benzylamdne and a chloro(bis(cyclopentylidenyl))methylzirconium complex. The mixed alkyl amido intermediate 4.2 then eliminates methane to form a THF supported metallaaziridine complex (4.3, Scheme 4-6). Alkene insertion into the zirconium carbon bond of the metallaaziridine then forms complex 4.4, and the product is isolated by a work up with excess methanol, which releases the product from the metal center and removes the TMS protecting group (Scheme 4-6). Importantly complexes 4.3 and 4.4 could be isolated as analytically pure compounds and the structure of 4.3 has been confirmed by X-ray diffraction analysis.214 These structures strongly support the mechanism first outlined by Nugent et al.  In 2007 Herzon and Hartwig reported an improved substrate scope for the hydroaminoalkylation reaction by using N-methyl-aniline as the nitrogen containing substrate and pentakis(dimethylamido)tantalum (Ta(NMe2)5) as the catalyst.92 The C-H 173  bonds on the methyl group of the N-methyl-aniline substrates are more reactive than corresponding dialkylamines used in the pioneering work from Clerici and Maspero, and Nugent et al.90-91 The scope of the hydroaminoalkylation has thus been expanded to a variety of substituted N-methyl-aniline derivatives and terminal alkenes, although the reaction temperatures remained high (165 °C) and reaction times long (27-67 hours).92 Notably no alkylamines were compatible with the hydroaminoalkylation reaction using this tantalum catalyst.   In 2008 Herzon and Hartwig employed a (hexachloro)(tetrakis(dimethylamido))ditantalum ([TaCl3(NMe2)2]2) catalyst that has been capable of facilitating hydroaminoalkylation of select dialkylamines.215 The dialkylamines underwent hydroaminoalkylation with 1-octene over a period of 24-36 hours at 150 °C with [TaCl3(NMe2)2]2 as the catalyst. Furthermore, the [TaCl3(NMe2)2]2 catalyst facilitated the hydroaminoalkylation of 1-octene with N-methylaniline at 90 °C,215 which was substantially lower than the previous report of 165 °C.92 The enhanced catalytic activity of [TaCl3(NMe2)2]2 for the hydroaminoalkylation has been attributed to a more electropositive tantalum due to the replacement of three amido ligands in Ta(NMe2)5 with three chloride ligands in [TaCl3(NMe2)2]2. The yields and scope have been drastically improved from the first reports of catalytic hydroaminoalkylation. Even though these systems were a tremendous advancement, the reaction still struggled with high reaction temperatures and long reaction times.   The 2007 and 2008 reports form Herzon and Hartwig inspired other groups to contribute to the hydroaminoalkylation field. As in the first reports of hydroaminoalkylation, research into a variety of metal catalysts has been undertaken. Most 174  of the subsequent reports on hydroaminoalkylation have used group 4 and 5 transition metals. Achievements have been made in the area by extending the substrate scope and decreasing the reaction temperature. Selected early transition metal hydroaminoalkylation precatalysts are shown in Figure 4-1. The research groups of Schafer,93 Hultzsch216-217 and Zi218 contributed with enantioselective variants of the hydroaminoalkylation reaction using niobium and tantalum. Group 3 and 4 metal complexes have been reported as precatalysts for hydroaminoalkylation.66, 213, 219-225 The group 3 precatalysts afford the catalytic α-alkylation of tertiary amines with alkenes.213, 223 Employing alkyl ligands on the precatalysts led to reduced reaction temperatures,226-228 and in the case of a tantalum phosphoramidate alkyl complex the reaction proceeded at room temperature.94 The substrate scope could be expanded when 1,3-N,O-donor ligands were used as auxiliaries ligands with titanium and tantalum.93, 102, 229-230 Others have focused on using late transition metals to afford α-alkylated amine products, however these transformations do not follow the same mechanism as the early transition metal variants and will not be discussed further.231-237 175   Figure 4-1. Recently reported precatalysts for the hydroaminoalkylation reaction. 4.1.3 Hydroaminoalkylation outlook  The advancements of the hydroaminoalkylation reaction in terms of substrate scope and turnover numbers since 1980 have made this reaction accessible to use as a methodology to build nitrogen containing molecules. The advantages of this methodology include high atom economy, inexpensive and accessible starting materials and regioselective catalysis. However, the methodology struggles with the sensitivity of the early transition metal catalyst, narrow substrate scope (aprotic solvents or functional 176  groups, internal olefins), long reaction times (approximately 24 hours) and high reaction temperatures (up to 165 °C for some substrates). Catalyst development resulted in lowering reaction temperatures to room temperature,94 and ligand design resulted in broadening the substrate scope.93, 102, 230 There is no general catalyst that works well for all substrates, thus catalyst development plays a crucial role in the currently unrealized potential of the hydroaminoalkylation reaction. The advancements of the hydroaminoalkylation reaction in the past decade have sprung to metals in groups 3, 4 and 5, and furthering the methodology of this reaction has encouraged the Schafer lab to investigate group 6 complexes as potential hydroaminoalkylation catalysts. 4.1.4 Group 6 catalyzed hydroaminoalkylation  The hydroaminoalkylation reaction has prospered due to catalyst development in group 3, 4 and 5 metal catalysts. The catalyst development has been inspired by the initial reports from Clerici and Maspero, and Nugent et al, as well as recent reports. One area where no further investigation has been reported on is the use of group 6 metals as catalysts for the hydroaminoalkylation reaction. To date, the only report of the α-alkylation of amines mediated by a group 6 complex is the 1983 report by Nugent et al., where dimethylamine and 1-pentene underwent hydroaminoalkylation with a catalyst described as a 2:1 mixture of W2(NMe2)6:W(NMe2)6.91 However, there have been a few examples of C-H activations alpha to a nitrogen, and even one structurally characterized molybdaziridine. The existence of group 6 metallaaziridines complexes is encouraging because the metallaaziridine species are key intermediates in the hydroaminoalkylation mechanism.97 177   A C-H activation on a carbon alpha to a nitrogen atom was observed when W(NPh)Cl4(OEt2) and half an equivalent of Zn(C6H3(CH2NMe2)2-2,6)2 were allowed to react in dichloromethane to form complex 4.5 (Scheme 4-7).238 The authors note the C-H activation was unexpected, however, the results demonstrates that C-H activation alpha to a nitrogen is possible on a W(VI) metal center that bears a metal element multiple bond. Importantly, the 1H-NMR spectrum highlights the diagnostic diastereotopic doublet on the C-H activated carbon, where two doublets are observed at δ 4.79 and 4.06 with 2JHH=13.6 Hz.238  Scheme 4-7. Tungsten(VI) C-H activation alpha to nitrogen.238  Another example of metallaaziridine formation was observed when 4 equivalents of 3,5-dimethylpyrazole and one equivalent of tetrakis(dimethylamido)molybdenum complex (4.6) are allowed to react shown in Scheme 4-8. The authors propose that the C-H activation happens via molybdaziridine formation as shown in Scheme 4-8, where a 3,5-dimethylpyrazolato ligand assists in the C-H activation that forms the metallaaziridine and eliminates free 3,5-dimethylpyrazole.239 The free 3,5-dimethylpyrazole can then protonate the nitrogen of the molybdaziridine forming the observed complex 4.7. This suggests that a Mo(IV) species could mediate the α-alkylation of amines, because the metallaaziridine is a key step in the proposed mechanism (Scheme 4-5). 178   Scheme 4-8. Molybdenum(IV) complex that undergoes C-H activation alpha to nitrogen.239  A structurally characterized example of a molybdenum metallaaziridine has been reported by Cummins et al. in 1999.35 When Cummins et al. targeted the synthesis of a tri(amido)molybdenum(III) complex (4.8, Scheme 4-9), they found that they had isolated a molybdenum(V) (4.9, Scheme 4-9) instead. One of the amido ligands in complex 4.8 has undergone oxidative addition of a C-H bond on the isopropyl substituent forming the observed molybdaziridine and a molybdenum hydride (4.9, Scheme 4-9). Complex 4.9 is observed in the solid state, however, the reactivity of 4.9 in solution is most consistent with the reactivity of the molybdenum(III) complex 4.8 (Scheme 1-10).35 Insertion into either the molybdenum hydride or the molybdaziridine has not been reported.  Scheme 4-9. Molybdaziridine formation from a molybdenum(III) complex.35  To expand the breadth of group 6 complexes capable of mediating the hydroaminoalkylation reaction, known group 6 complexes that contain dimethylamido 179  ligands were desired. The high valent tetrakis(dimethylamido)(oxo)tungsten complex (4.10) was envisioned as a potential catalyst for the hydroaminoalkylation reaction. The synthesis of complex 4.10 has been reported by Berg and Sharp in 1987, however the reactivity studies have not been disclosed.240 Another group 6 complex that contains dimethylamido ligands is tetrakis(dimethylamido)molybdenum (4.6), which was first reported in 1971 by Bradley and Chisholm.241   These two starting materials were targeted due to observed C-H activation on a carbon alpha to a nitrogen atom with related W(VI) and Mo(IV) complexes.238-239 Furthermore, employing both 4.6 and 4.10 as potential hydroaminoalkylation catalysts will allow for comparisons of d0 tungsten (VI) complexes versus d2 molybdennum (IV) complexes. It has been hypothesized that high valent group 6 complexes would be competent catalysts for the hydroaminoalkylation reaction due to the reported propensity to form a reversible metallaaziridine in the 1983 report from Nugent et al. (Scheme 4-4).91 Recall that addition of 1,3-N,O-donor ligands to high valent homoleptic dimethylamido complexes of group 4 and 5 metals (Ti, Zr, Nb and Ta) increases their reactivity the towards hydroaminoalkylation reaction.66, 93, 104 Thus, it has been hypothesized that addition of 1,3-N,O-donor ligands in the group 6 would yield competent catalysts for the hydroaminoalkylation reaction.   This chapter discloses efforts to develop group 6 complexes can realize the α-alkylation of amines. Group 6 complexes with 1,3-N,O-donor auxiliary ligands have been synthesized by protonolysis reactions. A di(amidate)bis(dimethylamido)molybdenum(IV) has been shown to mediate the α-alkylation of 4-methoxy-N-methylaniline. While no group 180  6 complex was found to catalyze the hydroaminoalkylation reaction, the first example of molybdenum mediated α-alkylation of an amine has been achieved. 4.2 Results and discussion  When an amidate ligand replaced a dimethylamido ligand in Ta(NMe2)5 to form a Ta(amidate)(NMe2)4 complex, the reactivity of the resulting complex towards hydroaminoalkylation was improved.93 Extending this approach to select group 6 complexes was logical in developing new group 6 complexes capable of mediating the hydroaminoalkylation reaction. Starting from group 6 starting materials that contain dimethylamido ligands, protonolysis reactions have been used to install 1,3-N,O-donor ligands (Scheme 4-10). For example using 4.6 results in the formation of di(1,3-N,O-ligated)bis(dimethylamido)molybdenum complexes (Scheme 4-10). The di(1,3-N,O-ligated)bis(dimethylamido)molybdenum complexes have been desired due to their similarity to group 4 di(1,3-N,O-ligated)bis(dimethylamido)metal complexes, which are competent hydrofunctionalization catalysts.63, 66, 70, 144 Another appropriate group 6 starting material is 4.10, where the substitution of one dimethyl amido ligand with a 1,3-N,O-donor ligand results in (1,3-N,O-ligated)tris(dimethylamido)(oxo)tungsten complex (Scheme 4-10). 181   Scheme 4-10. Proposed synthetic routes into (1) (1,3-N,O-ligated)tris(dimethylamido)(oxo)tungsten(VI) and (2) di(1,3-N,O-ligated)bis(dimethylamido)molybdenum(IV) complexes.  In both proposed complexes (Scheme 4-10) there are two amido ligands which can undergo transamination reactions with amine substrate. Two coordination sites are needed to form the metallaaziridine intermediate, which is a key step in the hydroaminoalkylation catalytic cycle (Scheme 4-5). Once the desired complexes have been obtained, a test catalytic reaction was conducted. The substrates used for the catalytic test reactions are 4-methoxy-N-methylaniline and 1-octene (Scheme 4-11). These substrates are popular because they have been observed to give excellent reactivity for this reaction.192   Scheme 4-11. Hydroaminoalkylation of 1-octene with 4-methoxy-N-methylaniline. PMP=p-methoxyphenyl. 4.2.1 Reactivity of 4.10 and 1,3-N,O-donor ligated variants  Tetrakis(dimethylamido)(oxo)tungsten has been reported in 1987 by Berg and Sharp.240 Since the initial report on the synthesis of 4.10 no reactivity investigations have been disclosed. Protonolysis reactions with 1,3-N,O-proligands and 4.10 were undertaken. Due to the success of the previously reported tantalum systems with N-(2,6-182  diisopropylphenyl)pivalamide (HL9), a protonolysis reaction of one equivalent of HL9 with 4.10 has been attempted first (Scheme 4-12).93   The protonolysis reaction of 4.10 and HL9 produces an orange solid after a work up of filtration through diatomaceous earth and removal of volatiles under vacuum. The 1H-NMR spectrum in a C6D6 solution is consistent with the Cs symmetric structure proposed for complex 4.11 shown in Scheme 4-12.  The amidate resonances include a multiplet centered at δ 7.09 integrating to three aryl-hydrogens, a methine isopropyl septet at δ 3.41 integrating to two hydrogens, two doublets for the methyl groups of the isopropyl substituents at δ 1.30 and 1.25 both integrating to six hydrogens, and one t-butyl singlet at δ 1.04 integrating to nine hydrogens. Complex 4.11 could be further characterized by EIMS, where a diagnostic tungsten isotope pattern was found at 548 m/z, signifying complex 4.11 minus one dimethylamido ligand. Analogous to the di(1,3-N,O-chelate)(neopentylidene)(oxo)tungsten complexes in chapter 3, anytime complex 4.11 is manipulated in solution or left under vacuum for extended periods of time, 4.11 continues to react and proligand HL9 is observed. Complex 4.11 also decomposes when heated at 70 °C in a C6D6 solution, proligand and free dimethylamine can be observed along with multiple other products. No crystalline material of complex 4.11 or any of its decomposition products could be obtained.  Scheme 4-12. Protonolysis reaction of 4.10 and HL9 proceed to form the proposed complex 4.11. 183   To induce electrophilic character at the tungsten center and encourage tungstaziridine formation in complex 4.11, it has been proposed that B(C6F5)3 would coordinate to the tungsten oxo ligand and impart electrophilic character at the tungsten center.208 Complex 4.11 and B(C6F5)3 were added to a J-Young tube and allowed to react in a C6D6 solution. An immediate reaction occurred as evidenced by complete consumption of complex 4.11 and appearance of multiple species in the 1H-NMR spectrum. Excitingly, two doublets that resemble resonances for diastereotopic protons of a metallaaziridine are among the signals in the 1H-NMR spectrum. Satisfyingly, 2D NMR experiments assign both 1H doublets to the same carbon atom and the doublets are coupled with a 2JHH=10.2 Hz. Tentative assignment of a tungstaziridine such as the plausible structure for complex 4.12 in Scheme 4-13 is made, however, the reaction product could not be confidently assigned due to impure material. Furthermore, no crystalline species have been obtained from recrystallization of the reaction products.   184   Scheme 4-13. Reaction of complex 4.11 with B(C6F5)3, 1H-NMR spectrum of immediate reaction products, plausible structure of B(C6F5)3 adduct 4.12.  Although complexes 4.11 and 4.12 proved to be difficult to work with and have not been fully characterized, trial hydroaminoalkylation reactions have been undertaken (Scheme 4-14). The reactions have been carried out with 4.10 and complex 4.11, both with and without a B(C6F5)3 additive, however, no hydroaminoalkylation product was observed and unreacted substrates have been observed after 20 hours, as determined by 1H-NMR spectroscopy.      185   Scheme 4-14. Hydroaminoalkylation test reactions with tungsten oxo complexes. PMP=p-methoxyphenyl. 4.2.2 Hydroaminoalkylation trials with other group 6 complexes  Inspired by the α-alkylation of benzylamine reported by Buchwald et al., where zirconocene complexes meditated the alkylation via zirconaziridine species (Scheme 4-6), some isolobal species to the group 4 bent metallocene systems have been examined. Tungsten bis(t-butylimido) complexes are isolobal to the group 4 bent metallocene complexes, thus it has been hypothesized that the chemistry first reported by Buchwald in 1989 might be extended to group 6 systems. Scheme 4-15 highlights three complexes to test as potential hydroaminoalkylation catalysts. The test reactions did not yield the desired hydroaminoalkylation product, and the unreacted substrates where observed after the reaction, as determined by 1H-NMR spectroscopy.    186   Scheme 4-15. Hydroaminoalkylation trial reactions using various high valent tungsten species as potential catalysts. PMP=p-methoxyphenyl. Continuing the investigations on group 6 complexes as potential catalysts for the hydroaminoalkylation reaction the starting material 4.6 has been investigated. 4.2.3 Reactivity of 4.6 and 1,3-N,O-donor ligated variants  Clerici and Maspero first reported the use of 4.6 as a potential catalyst for the hydroaminoalkylation reaction,90 and they reported only traces of product formation. It has been envisioned that combining the Mo(IV) core with amidate ligands would improve the reactivity for hydroaminoalkylation. The synthesis of di(amidate)bis(dimethylamido)molybdenum complexes has been undertaken. Installing nitrogen and oxygen donor ligands onto a molybdenum complex with dimethylamido ligands has been accomplished by protonolysis reactions previously.37, 239, 242-247 The protonolysis reaction of two equivalents of the proligand HL9  with one equivalent of 4.6 resulted in the formation of a bis(N-(2,6-diisopropylphenyl)pivalamidate)bis(dimethylamido)molybdenum complex (4.13, Scheme 4-16).     187   Scheme 4-16. Synthesis of complex 4.13. After a workup of filtering through diatomaceous earth, dark red solids are isolated by removing all volatiles under vacuum. Complex 4.13 readily recrystallizes from a concentrated solution of hexanes at -30 °C, producing analytically pure 4.13 in an 83% yield.   The solid-state molecular structure of complex 4.13 is shown in Figure 4-2. The bis(N-(2,6-diisopropylphenyl)pivalamidate)bis(dimethylamido)molybdenum complex has two κ2-N,O amidate ligands and can be described as having a highly distorted octahedral coordination environment and the complex has overall pseudo C2 symmetry. The dimethylamido-molybdenum bond distances are 1.957(1) and 1.961(1) Å for Mo1-N1 and Mo1-N2 respectively. The dimethylamido-molybdenum distances in complex 4.13 fall within the reported range (1.914(3)-2.004(7) Å) of previously reported molybdenum-dimethylamido bond distances, furthermore, all these reports note π bonding of the dimethyl amido ligand with the molybdenum(IV) metal.37, 239, 243, 246, 248-250 The dihedral angles of the axial nitrogens of the amidate ligands to the methyl group of the dimethyl amido ligands are 25.9(1)° and 24.9(1)° for N3-Mo1-N1-C1 and N4-Mo1-N2-C4 respectively, this torsion is attributed to the steric demand of the amidate ligands. The amidate bite angles are 60.22(4) and 60.18(4) for O1-Mo1-N3 and O2-Mo1-N4 188  respectively, which agree with literature values for κ2-N,O amidate ligands.60 Selected bond distances and angles are shown in Table 4-1.   Figure 4-2. Solid-state molecular structure of complex 4.13, ellipsoids shown at 50% with all hydrogen atoms omitted.       189  Table 4-1. Bond distances and angles of complex 4.13. Bond Distances (Å) Bond Angles (°) Mo1-N1 1.957(1) O2-Mo1-O1 81.15(4) Mo1-N2 1.961(1) O1-Mo1-N3 60.22(4) Mo1-N3 2.185(2) O2-Mo1-N4 60.18(4) Mo1-N4 2.192(1) O2-Mo1-N1 155.61(5) Mo1-O1 2.168(1) N4-Mo1-N1 97.94(5) Mo1-O2 2.168(1) N1-Mo-N2 104.88(6) C22-O2 1.293(2) N3-Mo1-N4 148.91(5) C5-O1 1.294(2) C4-N2-C3 111.1(1) N3-C5 1.326(2) C1-N1-C2 111.1(1) N4-C22 1.324(2) N3-Mo1-N1 100.68(5)   The 1H-NMR spectrum of complex 4.13 shows ten broadened featureless resonances ranging from δ 0.12 to 8.00 at 25 °C in C6D6 indicating paramagnetic character. Eleven resonances were expected for the C2 symmetric complex, it is anticipated that the eleventh resonance is overlapping with another resonance. Magnetic susceptibility measurements of complex 4.13 in a C6D6 solution found µeff=2.14 µB (Evans method), which is in between the value of 1 (1.78 µB) and 2 (2.87 µB) unpaired electrons.251-252 The molybdenum atom is expected to have two valence electrons in either a high spin (unpaired electrons S=3, triplet state) or low spin (paired electrons S=1, singlet state) state. A previously reported related Mo(IV) complex (4.14, Figure 4-3) by Schrock et al. show similar 1H-NMR spectra, where the 1H-NMR resonances broadened and were featureless within the standard 1H-NMR window (~0.00 to ~12.50 ppm).253 Furthermore, Odom et al. 190  report a Mo(IV) complex (4.15, Figure 4-3) with a magnetic moment of 1.18 µB which is well below the expected magnetic moment of 2.87 µB for a triplet state. Notably, as a solid 4.15 exhibits no paramagnetism and the authors demonstrate that 4.15 has a singlet ground state with an accessible triplet state that results from a thermally induced spin crossover, which is responsible for the discrepancy of the magnetic moment.37 Such a thermally induced spin crossover could be responsible for the peculiar magnetic moment observed for complex 4.13. The magnetic properties of 4.13 were not explored further.  Figure 4-3. Complexes 4.14 and 4.15.  To test the thermal stability of complex 4.13 an NMR sample was prepared in sealed J-Young tube and the sample was put in a preheated oil bath. Complex 4.13 showed thermal stability in a C6D6 solution up to a temperature of 110 °C. At 110 °C for 24 hours it was evident from the 1H-NMR spectrum that decomposition of 4.13 had begun, although qualitatively a majority of 4.13 remained.  The hydroaminoalkylation test reaction has been undertaken in a sealed J-Young NMR tube using 10 mol% of 4.13 as the potential catalyst and heating 4.13 with 4-methoxy-N-methylaniline and 1-octene for 20 hours at 110 °C (Scheme 4-17). After the reaction has been stopped, by removing the NMR tube from the 110 °C oil bath, the results of the heating have been observed by 1H-NMR spectroscopy. It was evident that neither substrate had been fully consumed, however a small amount of hydroaminoalkylation 191  product had formed (~10%) along with some olefin isomerization products. GC/MS confirmed the presence of the hydroaminoalkylation product as well as isomerized octene products. The remaining unreacted substrates were also observed.       Scheme 4-17. Hydroaminoalkylation trial reaction, cat.= complex 4.13. PMP=p-methoxyphenyl.  To increase the amount of product formed hydroaminoalkylation trials with higher catalyst loadings were employed. From these trials it was evident that the percent of product formation never exceeded the catalyst mole percent, revealing that the α-alkylation of 4-methoxy-N-methylaniline with 1-octene is meditated by complex 4.13 stoichiometrically rather than catalytically. The optimized conditions for the molybdenum meditated α-alkylation of 4-methoxy-N-methylaniline with 1-octene were four equivalents of substrates to one equivalent of complex 4.13 (Scheme 4-18), which produced a 61% isolated yield (with respect to molybdenum) of the α-alkylation product after work up and isolation by flash chromatography. When complex 4.13, 4-methoxy-N-methylaniline and 1-octene were reacted in a 1:1:1 ratio, only 18% of the α-alkylated product could be isolated.  Scheme 4-18. Optimized conditions for the complex 4.13 meditated α-alkylation of 4-methoxy-N-methylaniline with 1-octene, isolated yield of product 61%. PMP=p-methoxyphenyl.  Heating the hydroaminoalkylation trial reactions further to 165 °C for prolonged periods (48 hours, Scheme 4-17) did not result in catalytic hydroaminoalkylation, 192  prolonged heating only resulted in increased amounts of isomerized 1-octene. The isolated α-alkylation product meditated by complex 4.13 has been shown to be the branched product analogous to previously reported early transition metal catalyzed hydroaminoalkylation reactions. This suggests that a molybdaziridine formed with the 4-methoxy-N-aniline substrate, 1-octene insertion forms exclusively the branched product and the resulting alkylated amine is released by protonolysis reactions. A molybdaziridine has been hypothesized previously as an intermediate in route to complex 4.7 in Scheme 4-8. Due to the paramagnetic nature of complex 4.13, performing mechanistic studies by monitoring with NMR spectroscopy was not feasible.  To test if the alkene isomerization was inhibiting the α-alkylation process a small alkene scope has been explored, the alkenes examined were neohexene, trimethyl(vinyl)silane and styrene (Scheme 4-19), however none of these alkenes resulted in alkylation of 4-methoxy-N-methylaniline in the presence of complex 4.13.  Scheme 4-19. Alkene scope α-alkylation trials. PMP=p-methoxyphenyl.  Other di(1,3-N,O-chelate)bis(dimethylamido)molybdenum complexes were synthesized to test how the ligand parameters of the 1,3-N,O-donor affect the molybdenum meditated α-alkylation of 4-methoxy-N-methylaniline (Scheme 4-20). Complexes 4.16, 4.17, 4.18 and 4.19 were synthesized analogous to complex 4.13, protonolysis reactions 193  with appropriate proligands and Mo(NMe2)4 afford the complexes. None of the complexes in Scheme 4-20 could meditate the α-alkylation of 4-methoxy-N-methylaniline with 1-octene, however alkene isomerization was observed when complexes 4.16, 4.17 and 4.19 were used. The crude materials have been used for the hydroaminoalkylation test reactions, and complexes 4.16, 4.17 and 4.18 were not fully characterized.   Scheme 4-20. Hydroaminoalkylation test reactions with complexes 4.16, 4.17, 4.18 and 4.19. PMP=p-methoxyphenyl.  During the hydroaminoalkylation test with complex 4.18, single crystals had formed on the walls of the J-Young NMR tube after the reaction was removed from the heated oil bath. Single crystal X-ray diffraction showed the material to be complex 4.20. The solid-state molecular structure of complex 4.20 is shown in Figure 4-4. The dimolybdenum complex is bridged by two dimethyl amido ligands and a molybdenum-molybdenum multiple bond. In the solid-state molecular structure, the molybdenum atoms are in the 3+ oxidation rather than 4+ in which they began (from 4.6 or presumably in complex 4.18 di(pyridonate)bis(dimethylamido)molybdenum). The molybdenum molybdenum bond is 2.4829(5) Å which is within the range for triple bonds that have 194  bridging ligands like complex 4.20.254-259 The bridging dimethylamido has a Mo1-N3 bond distance of 2.097(2) Å. The 6-methylpyridonate bond distances of Mo1-O1 and Mo1-O2 are 2.112(1) and 2.131(1) Å, and Mo1-N1 and Mo1-N2 are 2.247(2) and 2.237(2) Å. These parameters as well as pyridonate ring bond distances agree well with previously reported early transition metal complexes with di(6-methylpyridonate) ligands and indicate mono-ionic ligands with no delocalized radical in the pyridonate ligand.67, 117   Figure 4-4. Solid-state molecular structure of complex 4.20, ellipsoids shown at 50% with all hydrogen atoms omitted.       195  Table 4-2. Bond distances and angles of complex 4.20.  Bond Distances (Å) Mo1-O1 2.112(1) O1-C1 1.305(3) O2-C7 1.313(4) Mo1-N1 2.247(2) N1-C1 1.366(3) N2-C7 1.356(4) Mo1-O2 2.131(1) C1-C2 1.407(4) C7-C8 1.416(3) Mo1-N2 2.237(2) C2-C3 1.379(4) C8-C9 1.372(6) Mo1-N3 2.097(2) C3-C4 1.402(4) C9-C10 1.401(5) Mo1-Mo1 2.4829(5) C4-C5 1.387(4) C10-C11 1.393(4)   N1-C5 1.347(3) N2-C11 1.347(4)   The formation of the molybdenum(III) complex 4.20 demonstrates that redox activity is possible in these systems in the reaction conditions. Furthermore, since no α-alkylation or alkene isomerization was observed when using complex 4.18, and 4.18 was not observable after the hydroaminoalkylation trial reaction, formation of complex 4.20 or other molybdenum molybdenum bonded spices could be the rationalization for an absence of reactivity of the substrates. The α-alkylation of 4-methoxy-N-methylaniline with 1-octene meditated is the only example of group 6 hydroaminoalkylation since Nugent et al. first report in 1983. Continued interest in realizing another example of group 6 catalyzed hydroaminoalkylation catalysts inspired me to investigate other group 6 systems for this reaction. 4.2.4 Solid-state molecular structures of tungsten oxo complexes with dimethylamido ligands  The solid-state molecular structure of 4.10 has not been reported in the disclosure of its synthesis, thus when 4.10 was synthesized for reactivity investigations, single crystal 196  X-ray diffraction analysis was also undertaken. The solid state molecular structure of complex 4.10 is shown in Figure 4-5. The complex resides on a crystallographic 2-fold axis and the tungsten and oxygen bond lies on the plane of the axis, thus only two dimethylamido ligands are observed in the asymmetric unit. The complex has a square-pyramidal coordination geometry and has C4 symmetry in the solid state. The basal plane, defined by the four dimethylamido ligands, sits 0.4981(12) Å below the tungsten atom. The N1-W1-N1 and N2-W1-N2 bond angles are 152.16(10)° and 149.89(10)° respectively. These two angles are the two largest in the complex and results in a τ value of 0.04 confirming the square-pyramidal structural assigment.260-261 The deviation from a perfect square pyramid is typical of these types of complexes and is plausibly due to steric hinderance of the methyl groups with the apical oxygen atom.240 The W1-O1 bond length is 1.708(2) Å, which is like other square-pyramidal complexes with terminal tungsten oxo ligands.262 The W1-N1 and W1-N2 bond lengths are 1.9934(14) and 1.9896(14) Å respectively and agree with the tungsten amido distances in the related W(NPh)(NMe2)4 complex.240 The sum of the angle around atoms N1 and N2 are 359.03 and 358.92 respectively indicating sp2 hybridization. These tungsten amido bond distances are indicative of amido bonds that compete for π bonding, such as in complexes like W(NMe2)6, where there are more π donating ligands (six filled amido Np orbitals) than π accepting orbitals available (tungsten dxy, dxz and dyz orbitals).263 197   Figure 4-5. Solid-state molecular structure of complex 4.10, plotted at 50% ellipsoids with all hydrogen atoms omitted. Selected bond distances (Å); W1-O1=1.708(2), W1-N1=1.9934(14), W1-N2=1.9896(14). The dimethylamido ligands adopt an unusual configuration where the dimethyl amido ligands are twisted between having dihedral angles of 47.4° and 49.2° for O1-W1-N1-C2 and O1-W1-N2-C4 respectively. The packing of the asymmetric units of complex 4.10 showed rather short intermolecular contacts of the dimethylamido ligands. The contacts between hydrogen atoms of the analogous dimethylamido ligands is as short as 2.6 Å, as seen in Figure 4-6. The torsion observed in 4.10 could also stem from the tight packing of molecules in the solid state. 198   Figure 4-6. Hydrogen hydrogen distances shown with a white bond, the distance was ~2.6 Å.  Complexes of this type, with π donating ligands such as amido ligands usually have dihedral angles close to 0° to allow for optimal π bonding with the vacant tungsten dxy orbital. This peculiarity promoted us to investigate complex 4.10 further and DFT calculations were undertaken to understand the unusual configuration of the amido ligands in complex 4.10. In the bonding analysis of complex 4.10 only π bonding interactions will be discussed (Figure 4-7). As expected, the DFT calculations show two π bonds with the oxo ligand; the π bonds are degenerate and consist of the oxo px donation into the tungsten dxz and the oxo py donation into the tungsten dyz. The dimethylamido ligands form four ligand group orbitals from their Np orbitals and donate into the vacant dxy tungsten orbital. The highest occupied molecular orbitals are three nearly degenerate ligand group orbitals that contain the non-bonding lone pairs of the dimethylamido ligands.  199   Figure 4-7. π bonding interaction in 4.10.  In the process of obtaining a solid state molecular structure of 4.10 another complex was identified by X-ray diffraction. The unexpected complex was a lithium pentakis(dimethylamido)(oxo)tungsten trimer ate complex (4.21) shown in Figure 4-8. The three tungsten atoms are bridged by a six-membered alternating lithium oxygen core. The trimer complex has C3h symmetry in the solid state, where each of the tungsten centers has an octahedral coordination environment and each metal center has the same bond metrics with each of the analogous five dimethylamido and oxo ligands. The discussion of the bond metrics of complex 4.21 will focus on only the atoms around W1 since all the tungsten centers are equal. The W1-O1 ligand bond length is 1.846(5) Å, which is between a single and double bond.33, 264 The oxo ligand is also bound to two lithium atoms with O1-Li1 and O1-Li3 distances of 1.87(2) and 1.82(1) Å respectively. The W1-N1 to W1-N4 bond distances range from 2.002(8)-2.042(7) Å, and indicate π bonding with the tungsten 200  metal.263 The W1-N5 bond distance of 2.138(7) Å is slightly elongated due to coordination to both tungsten and lithium, and indicates limited π bonding interactions.248  Figure 4-8. Solid-state molecular structure of complex 4.21, plotted at 50% ellipsoids with all hydrogen atoms omitted.           201  Table 4-3. Bond distances and angles of complex 4.21. Bond Distances (Å) W1-O1 1.843(5) W2-O2 1.850(5) W3-O3 1.846(5) W1-N1 2.002(8) W2-N6 2.013(7) W3-N11 2.009(7) W1-N2 2.023(8) W2-N7 2.017(7) W3-N12 2.040(7) W1-N3 2.009(7) W2-N8 2.005(7) W3-N13 2.015(7) W1-N4 2.042(7) W2-N9 2.052(7) W3-N14 2.043(7) W1-N5 2.138(7) W2-N10 2.133(5) W3-N15 2.142(7) O1-Li1 1.87(2) O2-Li2 1.86(2) O3-Li3 1.85(1) O1-Li3 1.82(1) O2-Li1 1.81(1) O3-Li2 1.83(2) Bond Angles (°) N1-W1-N2 176.7(3) N7-W2-N6 175.7(3) N12-W3-N11 176.5(3) N3-W1-N5 174.4(3) N10-W2-N8 174.9(3) N13-W3-N15 174.9(3) O1-W1-N1 88.9(3) O2-W2-N6 88.4(3) O3-W3-N11 88.9(3) O1-W1-N2 88.4(3) O2-W2-N7 88.3(3) O3-W3-N12 88.7(3) O1-W1-N3 97.9(3) O2-W2-N8 97.9(3) O3-W3-N13 98.1(3) O1-W1-N4 174.5(3) O2-W2-N9 174.5(3) O3-W3-N14 174.0(3) O1-W1-N5 87.7(3) O2-W2-N10 87.2(2) O3-W3-N15 86.9(3)  The formation of complex 4.21 is proposed to be from the addition of LiNMe2 to 4.10. However, the 1H-NMR of 4.10 showed only trace impurities, therefore 4.21 is not expected to be a major component of the material. 4.3 Conclusions  This chapter targeted the development of novel group 6 hydroaminoalkylation catalysts. It was shown that a di(amidate)bis(dimethylamido)molybdenum(IV) could 202  mediate the α-alkylation of an amine, however, all efforts to realize a catalytic variant were unsuccessful. The high valent tungsten oxo complexes in this chapter showed no indications of being capable of mediating the α-alkylation of amines.  Protonolysis reactions of 4.6 with 1,3-N,O-donor ligands provided a simple and high yielding route into complex 4.13. Complex 4.13 has been the first molybdenum complex capable of mediating the α-alkylation of an amine. The α-alkylated product was shown to be the branched isomer, analogous to the products from most other early transition metal complexes capable of catalyzing the hydroaminoalkylation reaction. No mechanistic studies have been undertaken to understand why this molybdenum system will not turnover.  Of note is the rationalization that a molybdaziridine is being formed transiently in this system. The molybdenum mediated α-alkylation of an amine supports that there is potential for realizing a group 6 hydroaminoalkylation catalyst in the future.  1,3-N,O-donor ligands could not be conclusively installed by protonolysis reactions with complex 4.10. Evidence of a tungstaziridine was found upon addition of B(C6F5)3 to the ill characterized 4.11, however, rigorous characterization has not been possible. The solid-state molecular structure of complex 4.10 has been collected and demonstrated that it has C4 symmetry in the solid state. Furthermore, a solid-state molecular structure of complex 4.21 suggested that complex 4.10 can add a lithium dimethylamide ligand forming a trimeric structure. No hydroaminoalkylation was observed with these tungsten oxo complexes nor could any 1,3-N,O-ligated tungsten oxo complexes be fully characterized. The tungsten oxo dimethylamido complexes proved to be difficult to handle. 203  4.4 Methods and materials  All reactions were conducted under an inert atmosphere of nitrogen, inside a glove box, or using standard Schlenk techniques unless otherwise noted. All chemicals were purchased from commercial sources and used as received unless otherwise noted. Hexanes, toluene and diethyl ether were passed through an activated alumina tower and dried further with molecular sieves if necessary. THF, pentane, benzene-d6 and toluene-d8 were dried over sodium metal and distilled. NMR spectra were obtained on either a Bruker Avance 300 spectrometer, Bruker Avance 400inv spectrometer, or a Bruker Avance 400dir spectrometer. The spectra shown here have blue peak labels in blue and red integrations. The 1H- and 13C-NMR spectra were referenced to residual solvent signals, benzene-d6, (1H 7.16 ppm, 13C 128.06 ppm) and toluene-d8 (methyl, 1H 2.09 ppm).  EI mass spectra were acquired on a Kratos MS-50 spectrometer. Elemental analyses were collected on a Carlo Erba Elemental Analyzer EA 1108 instrument. GC/MS were conducted on an Agilent 7890A GC equipped a 5975C inert XL EI/CI mass detector which is operated in positive CI mode with methane as the reagent gas. The proligands HL4,63 HL9,93 N-(2,6-dimethylphenyl)pivalamide,265 1,1'-(2,2-dimethylpropane-1,3-diyl)bis(3,3-diisopropylurea) were synthesized by literature methods.88 Proligand HL1 was purchased from commercial sources. Complexes 4.6 and 4.10 were synthesized by reported procedures.240-241 Synthesis of 4.11 Complex 4.10 (0.0920 g, 0.245 mmol) and N-(2,6-diisopropylphenyl)pivalamide (0.0634 g, 0.243 mmol) were added to a vial in the glovebox, then 2 mL of toluene was added and the reaction was stirred at room temperature for 24 hours. The volatiles were removed 204  under vacuum, which left a dark semi-solid. The solids were dissolved in 3 mL of hexanes and filtered through diatomaceous earth and the volatiles were again removed under vacuum. The solids were triturated without filtering twice using hexanes which left an orange powder. The complex was not pure by 1H-NMR spectroscopy and the crude yield was 86% (0.1230 g). 1H NMR (300 MHz, BENZENE-d6)  ppm 1.04 (s, 9 H), 1.25 (d, J=6.9 Hz, 6 H), 1.30 (d, J=6.9 Hz, 6 H), 3.41 (spt, J=6.9 Hz, 2 H), 3.49 (s, 6 H), 3.59 (s, 12 H), 7.09 (m, 3 H); MS(EI) m/z 548 ([M-NMe2]+).  Figure 4-9. 1H-NMR 300 MHz spectrum of complex 4.11 in C6D6. Hydroaminoalkylation trial with 4.11 The substrates 4-methoxy-N-methylaniline (0.0196 g, 0.142 mmol) and 1-octene (0.0210 mg, 0.187 mmol) were dissolved in 0.5 mL of C7D8 and added to J-Young NMR tube, solid 4.11 (0.0169 g, 0.0285 mmol) was then added to the NMR tube. The NMR tube was capped 205  and heated at 110 °C for 22 hours in an oil bath. The 1H-NMR spectrum after heating shows no hydroaminoalkylation product.  Figure 4-10. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using 4.11 as a potential catalyst. Reaction of B(C6F5)3 with 4.11 Complex 4.11 (0.0120 g, 0.0203 mmol) was dissolved in 1 mL of C6D6 and then transferred to a vial containing B(C6F5)3 (0.0097 g, 0.0190 mmol). The orange solution turned red upon addition and the B(C6F5)3 dissolved. The solution was put in a J-Young tube. The 1H-NMR spectrum of the reaction is shown in Figure 4-11. To this solution 4-methoxy-N-methylaniline (0.010 g, 0.0729 mmol) and 1-octene (0.0227 g, 0.202 mmol) were added, the reaction was heated at 70 °C for 20 hours to test for hydroaminoalkylation reactivity. 206  After heating no product was observed and the substrates were unreacted as determined by 1H-NMR spectroscopy (Figure 4-12).  Figure 4-11. 1H-NMR 400 MHz spectrum of complex 4.11 with B(C6F5)3 in C6D6. 207    Figure 4-12. 1H-NMR 300 MHz spectrum of complex 4.11 with B(C6F5)3 in C6D6 after hydroaminoalkylation trial. Hydroaminoalkylation trial with 2.1 The substrates 4-methoxy-N-methylaniline (0.0681 g, 0.497 mmol) and 1-octene (0.117 mL, 0.744 mmol) were dissolved in 0.5 mL of C7D8 and added to J-Young NMR tube, solid 2.1 (0.0095 g, 0.0202 mmol) was then added to the NMR tube. The NMR tube was capped and heated at 130 °C for 22 hours in an oil bath. The 1H-NMR spectrum after heating shows no hydroaminoalkylation product. 208   Figure 4-13. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using W(NtBu)2(NHtBu)2 as a potential catalyst. Hydroaminoalkylation trial with 1.34 The substrates 4-methoxy-N-methylaniline (0.0690 g, 0.503 mmol) and 1-octene (0.117 mL, 0.744 mmol) were dissolved in 0.5 mL of C7D8 and added to J-Young NMR tube, solid complex 1.34 (0.0120 g, 0.0233 mmol) was then added to the NMR tube. The NMR tube was capped and heated at 130 °C for 20 hours in an oil bath. The 1H-NMR spectrum after heating shows no hydroaminoalkylation product.  209   Figure 4-14. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using complex 1 as a potential catalyst. Synthesis of complex 4.13 Complex 4.6 (0.0504g, 0.184 mmol) was dissolved in 2 mL of toluene and added to solid proligand HL9 (0.0961g, 0.368 mmol) all at once. The reaction mixture was then stirred at room temperature for 4 hours, and the color of the reaction mixture changed from purple to dark red. The volatiles were removed under vacuum to leave dark red crystalline solids. The solids were dissolved in 2 mL of hexanes and then filtered through diatomaceous earth, then the volatiles were removed to leave dark red crystalline solids. The solids were dissolved in minimal warm hexanes and stored at -30 °C to recrystallize. The resulting dark red crystals were analytically pure. Yield 0.1073 g, 83%. 1H NMR (400 MHz, BENZENE-d6)  ppm 0.21 (br. s.), 0.58 (br. s.), 2.24 (br. s.), 2.45 (br. s.), 3.17 (br. s.), 4.36 (br. s.), 210  4.97 (br. s.), 5.52 (br. s.), 7.36 (br. s.), 8.00 (br. s.). MS(EI) m/z 706 [M]+Anal. Calcd. For MoO2N4C38H64: N, 7.95%; C, 64.75%; H, 9.15%. Found: N, 7.68%; C, 65.00%; H, 9.30%. Evans method magnetic suseceptibility µeff= 2.14 µB.  Figure 4-15. 1H-NMR 400 MHz spectrum of complex 4.13 in C6D6. Hydroaminoalkylation trial reaction using complex 4.13 as a potential catalyst Complex 4.13 (0.0341 g, 0.0484 mmol), 4-methoxy-N-methylaniline (0.0688 g, 0.502 mmol) and 1-octene (0.0657 g, 0.585 mmol) were dissolved in 0.5 mL of C7D8 and added to J-Young NMR tube. The reaction was heated to 110 °C in an oil bath for 15 hours, the 1H-NMR spectrum of the reaction mixture showed small amounts of the hydroaminoalkylation product. 211   Figure 4-16. 1H-NMR 300 MHz in C7D8 of the hydroaminoalkylation trial using complex 4.13 as a potential catalyst. Synthesis of complex 4.19 Complex 4.6 (0.2007 g, 0.7371 mmol) was dissolved in 6 mL of hexanes and added to solid proligand 1,1'-(2,2-dimethylpropane-1,3-diyl)bis(3,3-diisopropylurea) (0.2571 g, 0.7211 mmol) all at once. The reaction mixture was gently heated with a heat gun to encourage the proligand to dissolve, then stirred at room temperature. After 4 hours of stirring the color of the reaction mixture changed from purple to brown. The volatiles were removed under vacuum to leave a brown powder. The solids were mostly dissolved in 4.5 mL of hexanes and then filtered through diatomaceous earth, then the volatiles were removed to leave a brown powder. The solids were dissolved in minimal warm hexanes and stored at -30 °C to recrystallize. Yield 0.2623 g, 68%. 1H NMR (300 MHz, BENZENE-212  d6)  ppm -61.71 (br. s.), -0.74 (br. s.), 0.86 (br. s.), 11.80 (br. s.), 20.58 (br. s.). MS(EI) m/z 540 [M]+. Anal. Calcd. For MoO2N4C38H64: N, 15.60%; C, 51.29%; H, 9.36%. Found: N, 15.65%; C, 51.06%; H, 9.57%. Evans method magnetic suseceptibility µeff= 2.71 µB.  Figure 4-17. 1H-NMR 300 MHz spectrum of complex 4.19 in C6D6. Synthesis of complex 4.18 Complex 4.6 (0.0506 g, 0.186 mmol) was dissolved in 1.5 mL of toluene and added all at once to vial containing proligand HL1 (0.0399 g, 0.366 mmol). The reaction was stirred at room temperature for 3 hours and the color of the solution changed from purple to dark red. The volatiles were removed under vacuum and the solids were triturated with 3 mL of hexanes without filtering. The volatiles were removed to leave a dark red powder. The crude material was used for hydroaminoalkylation trials. 1H NMR (400 MHz, BENZENE-213  d6)  ppm -27.57 (br. s.), -21.79 (br. s.), 15.33 (br. s.), 20.23 (br. s.), 24.32 (br. s.). MS(EI) m/z 402 [M]+.  Figure 4-18. 1H-NMR 400 MHz spectrum of complex 4.18 in C6D6. Synthesis of complex 4.17 Complex 4.6 (0.0506 g, 0.186 mmol) was dissolved in 2 mL of toluene then transferred to a vial containing proligand N-(2,6-dimethylphenyl)pivalamide (0.0760 g, 0.370 mmol). The reaction was stirred for 3 hours and the color changed from purple to dark red. The volatiles were removed to give a dark red brown crystalline solid. The crude material was used for the hydroaminoalkylation trials. 1H NMR (400 MHz, BENZENE-d6)  ppm 1.10 (s), 1.69 (br. s.), 2.06 (s), 4.74 (br. s.), 5.58 (d, J=6.2 Hz), 6.46 (t, J=6.0 Hz), 7.43 (d, J=7.3 Hz), 7.75 (br. s.). 214   Figure 4-19. 1H-NMR 400 MHz spectrum of complex 4.17 in C6D6. Synthesis of complex 4.16 Complex 4.6 (0.1005 g, 0.3691 mmol) was dissolved in 4 mL of toluene and then added to a vial containing proligand HL4 (0.2043 g, 0.7260 mmol) all at once. The reaction was stirred for 3 hours and the reaction remained purple throughout the course of the reaction. The volatiles were removed to leave a purple crystalline solid. 1H NMR (400 MHz, BENZENE-d6)  ppm -2.99 (br. s.), -1.39 (br. s.), 1.19 (br. s.), 1.37 (br. s.), 1.65 (br. s.), 2.59 (br. s.), 3.33 (br. s.), 5.69 (br. s.), 6.22 (br. s.), 7.03 (br. s.), 7.22 (br. s.), 10.47 (br. s.). 215   Figure 4-20. 1H-NMR 400 MHz spectrum of complex 4.16 in C6D6. Complex 4.13 mediated α-alkylation of an amine Complex 4.13 (0.0346 g, 0.0491 mmol), 4-methoxy-N-methylaniline (0.0323 g, 0.235 mmol) and 1-octene (0.0269 g, 0.239 mmol) were dissolved in 0.5 mL of C7D8 and added to J-Young NMR tube. The NMR tube was capped, and the reaction was heated to 110 °C in an oil bath for 48 hours, the 1H-NMR spectrum of the reaction mixture showed the hydroaminoalkylation product. The hydroaminoalkylation product was isolated by column chromatography in a 61% yield (0.0074 g, based on complex 27). 1H NMR (400 MHz, CHLOROFORM-d)  ppm 0.89 (t, J=6.7 Hz, 3 H), 0.97 (d, J=6.3 Hz, 3 H), 1.28 (m, 10 H), 2.85 (dd, J=9.5, 7.6 Hz, 1 H), 3.01 (br. dd, J=9.5, 7.6 Hz, 1 H), 6.60 (d, J=8.9 Hz, 2 H), 6.79 (d, J=8.9 Hz, 2 H). GC/MS(CI) m/z 250 [H+M]+.  216   Figure 4-21. 1H-NMR 400 MHz spectrum of hydroaminoalkylation product in CDCl3. The molybdenum mediated α-alkylation of an amine trial reactions with complexes 4.16, 4.17, 4.18 and 4.19 were conducted analgous to the reaction with 4.13 (vide supra). In all cases not product was observed by 1H-NMR spectroscopy and GC/MS. 217  Chapter 5: Conclusions and future works 5.1 Summary and conclusions  This thesis describes the successful synthesis and characterization of 1,3-N,O-ligated group 6 complexes that have metal element multiple bonds. It has been shown that the 1,3-N,O-donor ligands can support reactive group 6 metal element multiple bonds in chapters 2 and 3. It has also been shown that these complexes are susceptible to metal-ligand cooperativity for E-H bond activation processes and this reactivity can be challenging to control. In other reactivity investigations, the first example of a molybdenum complex capable of mediating the α-alkylation of an amine was accomplished. The insights in this thesis lay the ground work for future investigations of group 6 complexes with 1,3-N,O-donor ligands. A more detailed summary of the achievements of each chapter are provided below. 5.1.1 Chapter 2  Investigations of group 6 complexes with metal element multiple bonds and 1,3-N,O-donor ligands started with new bis(t-butylimido)di(1,3-N,O-chelate)tungsten complexes 2.2-2.5 that have been synthesized by simple and high yielding protonolysis reactions. To gain insights in to the nature of the metal ligand interactions variable temperature 1H-NMR spectroscopic experiments and computational modeling of the different coordination isomers suggest that the 1,3-N,O-donor ligands display fluxional character typical of hemilabile ligands. A difference in the electronic parameters between the pyridonate and amidate ligands is partially responsible for the more dynamic hemilability, due to the pyridonate ligand exhibiting more diverse bonding modes (aryloxyimine motif and bridging bonding modes). The 3-substitued pyridonate ligands 218  can readily form dimeric species. Amidate complexes avoid the formation of dimers or aggregate species, which can be advantageous when trying to avoid intermolecular in catalyst degradation due to the formation of multi-metallic species.  The reactivity investigations concluded that pyridonate ligands exhibit a broader scope of coordination modes and hence reactivity, than amidate ligands; this is attributed to more dynamic hemilability of the pyridonate ligands. Notably pyridonate ligands provide reduced steric protection at the metal center, and this also promotes enhanced reactivity.  Importantly, pyridonate ligands have been shown to engage in hydrogen bonding interactions with ligands, suggesting that pyridonate ligands can be used to advantage in reactions where proton shuttling is required. Chapter 2 demonstrated the more dynamic hemilability of pyridonate ligands versus amidate ligands, this trend has also been observed throughout the chapters 3 and 4. 5.1.2 Chapter 3  In chapter 3 the synthesis of the first examples of tungsten alkylidene complexes with 1,3-N,O-donor ligands has been achieved. Using bulky 2,6-diisopropylphenyl substituents on the nitrogen atom of the 1,3-N,O-donor ligands has been important to obtain N-trans coordination geometries for bis(amidate) complexes, such as complexes 3.6-3.9. Variable temperature NMR spectroscopy shows that the amidate ligands are highly fluxional at elevated temperatures for all complexes. Less bulky ligands formed phosphine adducts such as in complexes 3.11 and 2.13, and when the smaller 6-methylpyridonate ligand has been installed rapid complex decomposition has been observed. Thus the strategic selection of ligands has been important to produce isolable tungsten neopentylidene complexes with 1,3-N,O-donor ligands.  219   The solid-state molecular structure of dimeric complex 3.12 resulted from an unexpected C-H activation process that ultimately yielded the formation of proligand in situ. Notably, the formation of such free proligand has been routinely observed whenever such 1,3-N,O-ligated complexes were stored in solution. Details of the C-H activation process were not identified, however, the transformation of an alkylidene to an alkylidyne has been confirmed by single crystal X-ray analysis. The amidate assisted C-H activation route presumably proceeds via the hemilability of the 1,3-N,O-ligated ligands. Similar bond activations have been observed for late transition metal 1,3-N,O-ligated complexes, but this is the first example of a 1,3-N,O-donor ligand that has been involved in α-hydrogen abstraction to yield another carbon multiple bond and subsequent complex unidentified complex degradation products.   The unexpected continued reactivity observed when di(amidate)(neopentylidene)(oxo)tungsten complexes were in solution, caused the decomposition of alkylidene complexes. Thus, investigating substituent effects of the 1,3-N,O-donor ligands by comparing reactivities of di(amidate)(neopentylidene)(oxo)tungsten complexes RCM catalysis of 1,7-octadiene was complicated by unwanted degradation. Importantly, the decomposition of the catalytically active alkylidene complexes halts the olefin metathesis reactivity, leading to decreased conversion of the olefin substrate. The conversions observed in the RCM trials were all low (5-14% at 80 °C), except for complex 3.8 which showed moderate reactivity (52% at 80 °C). this may be attributed to the facile decomposition observed for this class of alkylidene complexes and thus, no ligand induced trends in reactivity could be elucidated. However, one point that suggests that catalyst degradation is an overwhelming factor in evaluating these systems in the RCM is the 220  qualitative observation that complex 3.8 decomposes more slowly than the other complexes tested. The quantitative relative rates of proligand formation (accompanied by alkylidene decomposition) with the different 1,3-N,O-donor ligands were not measured.  Interestingly, carboxylate molybdenum imido alkylidene complexes have been reported to be unreactive towards olefins metathesis, whereas the (amidate)(neopentylidene)(oxo)tungsten complexes in this chapter do react with olefins, albeit in a limited way. The carboxylate molybdenum imido alkylidene complexes are not reported to decompose to carboxylic acid and molybdenum alkylidyne analogous to the tungsten amidate complexes reported in this thesis. However, Schrock et al. do highlight the conversion of di(carboxylate)(imido)(neopentylidene)(trimethylphosphine)molybdenum complex to a proposed di(carboxylate)(amido)(neopentylidyne)(trimethylphosphine)molybdenum complex. The C-H activation processes in both of these 1,3-donor ligands (amidate and carboxylate) highlights the potential of these classes of ligands to be used productively in other E-H (where E=B, C, N, etc.) bond activations moving forward. 5.1.3 Chapter 4  Chapter 4 describes the development of novel group 6 complexes capable of mediating the α-alkylation of amines. Two group 6 starting materials have been used (4.6 and 4.10), and 1,3-N,O-donor ligands have been installed as auxiliary ligands. These two starting materials have been used because they contained dimethylamido ligands, which are common reactive ligands for early transition metal hydroaminoalkylation catalysts.97 Furthermore, I wanted to compare reactivities of a group 6 d0 and d2 system. Notably, a d2 system never been reported as a catalyst for the hydroaminoalkylation reaction. 221  Rewardingly a di(amidate)bis(dimethylamido)molybdenum(IV) complex could mediate the α-alkylation of an amine, however, all efforts to realize a catalytic variant have been unsuccessful. When 4.10 or 4.11 have been tested as potential catalysts for the hydroaminoalkylation reaction the bulk of the substrates were observed unchanged after the trial reaction was completed.   The high valent tungsten oxo complexes in chapter 4 showed no indications of being capable of the α-alkylation of amines, and have been difficult to characterize. Attempts to isolate and rigorously characterize tungsten complexes with 1,3-N,O-donor ligands derived from 4.10 were not meet with success. Although when crude reaction products have been used for reactivity investigations, evidence of the formation of a tungstaziridine could be observed in the 1H-NMR spectrum. The hydroaminoalkylation trials have not been successful with the high valent tungsten oxo complexes, suggesting that these complexes were not capable of the α-alkylation of amines.   Protonolysis reactions of the d2 precursor 4.6 with 1,3-N,O-donor ligands provided a simple and high yielding route into di(amidate) complex 4.13. Complex 4.13 is the first molybdenum complex capable of mediating the α-alkylation of an amine, albeit in stoichiometric amounts. The α-alkylated product has been shown to be the branched isomer, analogous to the products from most other early transition metal catalyzed hydroaminoalkylation reactions. No mechanistic studies have been undertaken to understand why the molybdenum system could not turnover catalytically to produce the α-alkylated product. However, given the observed branched product formation it is likely that a molybdaziridine is involved in this system. The molybdenum mediated α-alkylation of 222  an amine supports that there is potential for realizing a group 6 hydroaminoalkylation catalyst in the future. 5.2 Future work 5.2.1 Chapter 2  To gain insight into the hemilabile processes in these complexes variable temperature 13C-NMR studies would be important to try and see the various bonding modes of the 1,3-N,O-donor ligands. The 13C-NMR resonance of the NCO motif is sensitive to the bonding mode of amidate ligands,78 particularly if the amidate is either κ1-O (up field from proligand) or κ2-N,O and µ2-N,O (down field from proligand). Thus, monitoring the amidate carbon resonances as a function of temperature could give insights into how the amidate ligand is bonding to the metal center at elevated temperatures relevant to other catalytic 1,3-N,O-ligated systems. 5.2.2 Chapter 3 5.2.2.1 Group 6 di(1,3-N,O-chelate)(imido)(alkylidene)metal complexes  The unexpected amidate assisted C-H activation process that causes decomposition of the di(amidate)(neopentylidene)(oxo)tungsten complexes limited the use of 1.3-N,O-donor ligands as auxiliaries towards the catalytic olefin metathesis reaction. To further access the 1,3-N,O-donor ligands as auxiliaries, group 6 di(1,3-N,O-chelate)(imido)(alkylidene)metal (where metal is Mo or W, Figure 5-1)) could be synthesized to test if the C-H activation process would extend to these proposed complexes. As has been shown in this thesis, 1,3-N,O-donor ligands can be installed on group 6 alkylidene complexes by both protonolysis and salt metathesis reactions. 223   Figure 5-1. Proposed group 6 di(1,3-N,O-chelate)(imido)(alkylidene)metal (where metal is Mo or W). Pyr=pyrrolide. 5.2.2.2 Mono amidate tungsten alkylidene complexes  Olefin metathesis catalysts with pyrrolide and aryloxide ligands have been shown to be good olefin metathesis catalysts, and in some variations can metathesize olefins to give Z-selectivity.31-32, 266 To further investigate the use of 1,3-N,O-donor ligands as auxiliaries to support group 6 olefin metathesis catalysts I propose to replace pyrrolide or aryloxide ligands with 1,3-N,O-donors (Figure 5-1). The group 6 Z-selective catalysts rely on employing bulky auxiliary ligands to induce the stereoselectivity. Thus, with the easily tunable amidate ligand framework, a large variety of ligands could be synthesized and installed to further develop stereoselective group 6 olefin metathesis catalysts.  Initial efforts in synthesizing mono amidate tungsten oxo alkylidene complexes with L1 by protonolysis routes have not been not successful. When 3.2 and one equivalent of HL4 are allowed to react, complex 3.6 and 3.2 are observed as the reaction products (Scheme 5-1). An (amidate)(2,5-dimethylpyrollide)(neopentylidene)(oxo)tungsten complex has not been accessible from a protonolysis reaction, unlike the synthesis of complex 3.13. 224   Scheme 5-1. Protonolysis reaction of 3.2 and one equivalent of proligand HL1. Dipp=2,6-diisopropylphenyl. PyrMe2=2,5-dimethylpyrrole.  The synthesis of an (amidate)(chloro)(neopentylidene)(oxo)tungsten complex (5.1) was attempted when 3.4 was stirred with only one equivalent of amidate salt NaL6 and the reaction products included a mixture of 5.1, 2.6, 3.4 and proligand HL4 in a 1:0.4:0.6:0.4 ratio respectively (Scheme 5-2).  Scheme 5-2. Salt metathesis reaction for the synthesis of a mono(amidate) tungsten complex, which produces a mixture of products including the bis(amidate) complex 3.6, desired mono(amidate) complex 5.1 and proligand HL4. Ratios are below the reaction products. Dipp=2,6-diisopropylphenyl.  Complex 5.1 could not be isolated as a pure complex, however the 1H- and 31P-NMR signals were consistent with a (amidate)(chloro)(dimethylphenylphosphine)(neopentylidene)(oxo)tungsten species. The 1H-NMR spectrum in C6D6 of the reaction products of 5.1 with one equivalent of NaL4 shows a doublet at δ 12.26 with 3JHP=2.0 Hz and 1JCH=117.4 Hz, indicating the alkylidene is coupled to a coordinated phosphine ligand and the alkylidene is in the syn configuration. The tBu group of the neopentylidene ligand is at δ 0.99. The mono(amidate) complex 5.1 exhibits two septets at δ 3.80 and 4.64, and four doublets at δ 0.79, 1.20, 1.43 and 1.57. 225  The coordinated phosphine has two diagnostic doublets in the 1H-NMR spectrum at δ 1.78 and 1.81, and a singlet with tungsten satellites in the 31P-NMR spectrum at δ 7.0 (sat. 1JPW=354.7 Hz). Although the synthesis and isolation of mono amidate complexes with L4 was unsuccessful for tungsten oxo neopentylidene complexes, using an imido with a bulky substituent in place of the oxo ligand may allow for the isolation of mono amidate complexes. 5.2.2.3 1,3-N,O-donor ligand assisted C-H activation  The α-hydrogen abstraction process that forms metal carbon multiple bonds is important in the generation of olefin metathesis catalysts.19 Recently, a synthetic route has been reported where (t-butylimido)di(chloro)(neopentylidene)di(pyridine)tungsten complex (5.3) is synthesized from the reaction of three equivalents of pyridine hydrochloride and bis(t-butylimido)bis(neopentyl)tungsten (5.2) as shown in Scheme 5-3.124 Complex 5.3 must be further functionalized by salt metathesis reactions to yield Schrock type olefin metathesis catalysts.124  Scheme 5-3. Synthesis of Schrock type alkylidene complexes from bis(t-butylimido)bis(neopentyl)tungsten.124  A few examples by Schrock et al. have demonstrated that select proligands can act in place of the pyridine hydrochloride to generate an alkylidene ligand, relieving the need for the multiple step synthesis of the desired alkylidene complexes. For example, the reaction of a 226  diprotic biphenol (L12) with a di(alkyl)di(imido)molybdenum complex produced a biphenolate imido alkylidene molybdenum complex (Scheme 5-4).267  Scheme 5-4. Synthesis of a biphenolate imido alkylidene molybdenum complex.267 I proposed that 1,3-N,O-proligand may also realize the direct synthesis of a Schrock type complex from the reaction of  di(alkyl)di(imido)metal group 6 complex with two equivalents of 1,3-N,O-proligand.  Scheme 5-5. Proposed synthesis of di(1,3-N,O-chelate) imido alkylidene complexes. M=Mo or W. 5.2.3 Chapter 4  Complex 4.13 was the first molybdenum complex that could mediate the α-alkylation of an amine, albeit stoichiometrically. To further investigate the reactivity profile of 4.13 I propose to test if it can mediate other types of hydrofunctionalization reactions such as hydroamination,268 hydroalkylation,269 hydrophoshination,270 etc. In group 5 hydroaminoalkylation catalysts, changing from dimethylamido ligands to alkyl ligands improved the efficiency of the group 5 systems.94, 226-228 Thus, exchanging the 227  dimethyl amido ligands in 4.13 with alkyl ligands could potentially increase the efficiency of the reaction and possibly even realize a catalytic variant.   Further investigation of the physical properties of complex 4.13, such as the magnetic properties have been of interest. Variable temperature susceptibility measurements would be important in understanding the unusual magnetic moment µeff=2.14 µB in complex 4.13. Investigating the redox properties by electrochemical methods would also be important to realizing the full reactivity potential of complex 4.13.     To continue to broaden the scope of hydroaminoalkylation catalysts other group 6 starting materials could be employed. Many potential starting materials could be selected from known group 6 complexes. For example, W(NPh)(NMe2)4,240 W(NMe2)Cl3,271 Mo(Acac)2Cl2,272 and group 6 complexes with metal metal bonds such as W2(NMe2)6,249, 273-274 to name a few. These starting materials could be tested on their own or variants with auxiliary ligands (1,3-N,O-chelates for example) could be synthesized and tested. 5.3 Concluding remarks  In this thesis the synthesis and reactivity of some new group 6 complexes with 1,3-N,O-donor ligands have been documented for the first time. These group 6 complexes with 1,3-N,O-donor ligands have been synthesized by protonolysis and salt metathesis routes, and were showed to produce the desired complexes in good yields. The metal ligand interactions discussed in this thesis depict the 1,3-N,O-donor ligands as fluxional auxiliaries that are able to access a variety of bonding modes and coordination geometries. Reactivity investigations in this thesis highlight the capability of 1,3-N,O-donor ligands to participate in metal ligand cooperativity for E-H (where E=C and N) bond activations at the group 6 metal. In conclusion, the findings of this thesis will aid the design of new of 228  group 6 complexes and other early transition metal complexes that bear 1,3-N,O-donor ligands. 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W., J. Am. Chem. Soc. 1978, 100, 153. 274. Akiyama, M.; Chisholm, M. H.; Cotton, F. A.; Extine, M. W.; Haitko, D. A.; Little, D.; Fanwick, P. E., Inorg. Chem. 1979, 18, 2266. 239  Appendices Appendix A   Diffraction data were collected on either a Bruker X8 Apex or Bruker Apex DUO diffractometer. Data collection was undertaken using COSMO and the cell determination and integration were carried out using SAINT. CELL_NOW was used to determine twinned data sets. Data collections, cell determinations and integrations were undertaken at the X-ray Crystallography facility by either Dr. Brian Patrick, Dr. Jacky Yim, Mr. Scott Ryken or Mr. Damon Gilmour. Refinement of integrated data was conducted using OLEX2 package using SHELXL and the Least Squares method. All refined models were subjected to Checkcif and any alerts were addressed.              240  Appendix B   Table B-1. Crystallographic parameters of complexes 2.2, 2.3 and 2.4. complex 2.2 2.3 2.4 formula C20H30N4O2W C20H30N4O2W C30H46N4O2W Fw (g/mol) 542.33 542.33 678.56 space group (#) Cc P21/c P21/n a (Å) 11.596(2) 9.1515(12) 10.1188(4) b (Å) 14.728(3) 27.314(4) 18.2455(7) c (Å) 13.227(2) 8.6675(11) 17.9297(7) α (°) 90 90 90 β (°) 91.174(4) 90.664(3) 102.740(2) γ (°) 90 90 90 V (Å3) 2258.5(7) 2166.4(5) 3228.7(2) Z 4 4 4 ρcalcd (g cm-1) 1.595 1.663 1.396 temperature (K) 100 100 100 μ(Mo Kα (mm-1)) 5.135 5.353 3.607 wR2 (all data) 0.0278 0.0501 0.053 R1 (I > 2σ(I)) 0.0136 0.0280 0.025      241  Table B-2. Crystallographic parameters of complexes 2.5, 2.6 and 2.8. complex 2.5 2.6 2.8 formula C46H62N4O2W C26H37N5O3W C19H32ClN3OW Fw (g/mol) 886.84 651.45 537.77 space group (#) P21/n C2/c P21/n a (Å) 21.377(6) 34.268(4) 11.5734(3) b (Å) 17.045(5) 7.783(1) 11.4154(3) c (Å) 26.136(8) 20.807(3) 16.9672(5) α (°) 90 90 90 β (°) 113.803(6) 99.746(7) 99.751(2) γ (°) 90 90 90 V (Å3) 8713(4) 5469.3(12) 2209.24(11) Z 8 8 4 ρcalcd (g cm-1) 1.352 1.582 1.617 temperature (K) 100 90 100 μ(Mo Kα (mm-1)) 2.691 4.259 5.361 wR2 (all data) 0.0436 0.1288 0.0575 R1 (I > 2σ(I)) 0.0203 0.0653 0.0294       242  Table B-3. Crystallographic parameters of complexes 2.9, 2.11 and 2.12. complex 2.9 2.11 2.12 formula C19H33Cl2N3OW C22H27ClN4O3W C14H24ClN3OW Fw (g/mol) 574.23 614.77 469.66 space group (#) C2/c P-1 Pccn a (Å) 16.957(3) 14.820(3) 23.1329(10) b (Å) 9.7705(16) 15.097(4) 11.6036(5) c (Å) 28.168(4) 21.625(5) 13.2922(6) α (°) 90 77.615(8) 90 β (°) 97.323(4) 89.775(7) 90 γ (°) 90 89.515(9) 90 V (Å3) 4628.8(13) 4725.3(19) 3568.0(3) Z 8 8 8 ρcalcd (g cm-1) 1.648 1.728 1.749 temperature (K) 100 100 100 μ(Mo Kα (mm-1)) 5.234 5.032 6.625 wR2 (all data) 0.0566 0.0973 0.0470 R1 (I > 2σ(I)) 0.1388 0.0441 0.0220       243  Table B-4. Crystallographic parameters of complexes 2.13, 3.6 and 3.7. complex 2.13 3.6 3.7 formula C28H48Cl2N6O2W2 C43H54N2O3W C47H50N2O3F12W Fw (g/mol) 939.32 830.73 1102.74 space group (#) P21/n C2/c P-1 a (Å) 8.7929(10) 23.579(3) 13.456(2) b (Å) 23.397(3) 11.4635(14) 15.935(3) c (Å) 17.054(2) 30.219(4) 23.691(4) α (°) 90 90 86.825(4) β (°) 99.824(2) 107.242(2) 74.630(3) γ (°) 90 90 85.070(4) V (Å3) 3457.2(7) 7800.9(16) 4877.5(15 Z 4 8 4 ρcalcd (g cm-1) 1.805 1.415 1.502 temperature (K) 100 100 100 μ(Mo Kα (mm-1)) 6.837 3.001 2.454 wR2 (all data) 0.0585 0.1306 0.0579 R1 (I > 2σ(I)) 0.0311 0.0474 0.0274       244  Table B-5. Crystallographic parameters of complexes 3.8, 3.10 and 3.11. complex 3.8 3.10 3.11 formula C33H50N2O3W C41H55N2O3F6PW C40H35N2O3F18PW Fw (g/mol) 706.60 952.69 1148.52 space group (#) P21/c P21/c P21/c a (Å) 32.228(5) 12.9661(18) 16.0268(7) b (Å) 12.221(2) 17.255(2) 14.5320(6) c (Å) 17.062(3) 19.819(3) 19.2525(9) α (°) 90 90 90 β (°) 99.252(4) 108.586(3) 104.751(2) γ (°) 90 90 90 V (Å3) 6632.6(19) 4203.0(10) 4336.2(3) Z 8 4 4 ρcalcd (g cm-1) 1.415 1.506 1.759 temperature (K) 100 100 100 μ(Mo Kα (mm-1)) 3.516 2.851 2.819 wR2 (all data) 0.1013 0.0913 0.0505 R1 (I > 2σ(I)) 0.0294 0.0423 0.0222       245  Table B-6. Crystallographic parameters of complexes 3.12, 4.13 and 4.20. complex 3.12 4.13 4.20 formula C63H58N3O5F27P2W2 C38H64N2O2Mo C28H36N6O4Mo Fw (g/mol) 1879.76 704.87 712.51 space group (#) P21/c P-1 P-1 a (Å) 27.267(2) 9.6127(11) 7.5856(11) b (Å) 20.7386(17) 13.3490(15) 8.9844(12) c (Å) 26.799(2) 17.345(2) 11.7841(17) α (°) 90 69.600(2) 91.017(3) β (°) 110.908(2) 84.013(2) 107.001(3) γ (°) 90 70.147(2) 108.712(3) V (Å3) 14156.6(19) 1962.9(4) 721.88(18) Z 8 2 1 ρcalcd (g cm-1) 1.764 1.193 1.639 temperature (K) 100 100 100 μ(Mo Kα (mm-1)) 3.413 0.369 0.913 wR2 (all data) 0.0840 0.0699 0.0901 R1 (I > 2σ(I)) 0.0382 0.0302 0.0360        246  Table B-7. Crystallographic parameters of complexes 4.10 and 4.21. complex 4.10 4.21 formula C8H24N4OW C36H104Li3N15O3W3 Fw (g/mol) 376.16 1367.71 space group (#) C2/c P212121 a (Å) 15.760(2) 9.5884(3) b (Å) 5.2960(7) 24.2620(8) c (Å) 15.755(2) 24.5019(9) α (°) 90 90 β (°) 108.515(2) 90 γ (°) 90 90 V (Å3) 12.46.9(3) 5700.0(3) Z 4 4 ρcalcd (g cm-1) 2.004 1.594 temperature (K) 100 100 μ(Mo Kα (mm-1)) 9.245 6.083 wR2 (all data) 0.0316 0.0731 R1 (I > 2σ(I)) 0.0128 0.0400       

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