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Electronic structure and single electron reactivity in organochromium complexes Zhou, Wen 2013

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ELECTRONIC STRUCTURE AND SINGLE ELECTRON REACTIVITY IN ORGANOCHROMIUM COMPLEXES  by  Wen Zhou  B.Sc., The University of British Columbia, 2008  A THESIS SUBMITTED IN PARTIAL FULEILLMENT OF THE REQUIRMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY  in  THE COLLEGE OF GRADUATE STUDIES (Chemistry)  THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan)    April 2013 © Wen Zhou, 2013 ii  Abstract      The stoichiometric and catalytic reactivity of transition metal complexes can be controlled by varying the steric and electronic properties of their ancillary ligands. The paramagnetic nature of some organometallic compounds of the first-row transition metals hinders the use of NMR spectroscopy for characterization and reactivity screening. Despite this barrier, there is increasing interest in developing catalysts based on these earth-abundant elements, since they often display reactivity patterns complementary to more established precious metal catalysts. Understanding how the electronic properties of ancillary ligands can be used to control the radical reactivity of paramagnetic first-row metal complexes is a critical prerequisite for rational catalyst design.      This thesis describes the synthesis and reactivity of new, well-defined paramagnetic organometallic molecules that contain the metal chromium. Many of the complexes contain a cyclopentadienyl (Cp) group as one ancillary ligand. The compounds in chapter 2 also have a β- diketiminate (nacnac) ligand with two different N aryl substituents. These CpCr(nacnac) complexes are used to catalyze a radical C(sp 3 )-P bond-forming reaction. In chapter 3, CpCr(N- heterocyclic carbene) complexes are prepared and used to catalyze the homocoupling of aryl Grignard reagents. In chapter 4, the synthesis and reactivity of Cr complexes with ligand-based diimine radicals are explored. In chapter 5, reactive imido complexes are prepared by reaction of organic azides with CpCr(phenylenediamido) compounds. The new complexes are characterized by single-crystal X-ray diffraction, UV-vis spectroscopy, magnetic moment measurements, and elemental analysis. iii  Preface      The majority of the results presented in Chapter 2 have been published and some figures were reproduced with permission from: Zhou, W.; Tang, L.; Patrick, B. O.; Smith, K. M. Organometallics 2011, 30, 603−610 (© 2011 American Chemical Society) and Zhou, W.; MacLeod, K. C.; Patrick, B. O.; Smith, K. M. Organometallics 2012, 31, 7324−7327 (© 2012 American Chemical Society). Preliminary synthesis of compounds 2.1a-d, 2.1e, and 2.1f were performed by the following Smith group researchers: Dr. Lming Tang (postdoctoral), Julia L. Conway (undergraduate), Joshua J. Smith (undergraduate). X-ray data collection was performed by Dr. Brian O. Patrick and Anita Lam at the University of British Columbia, Vancouver.      The majority of the results presented in Chapter 4 have been published and some figures were reproduced with permission from: W, Zhou.; A, N, Desnoyer.; B, O, Patrick.; K, M, Smith.; Inorganic Chemistry 2013, Inorg. Chem., 2013, 52, 2271-2273 (© 2013 American Chemical Society) and W, Zhou.; L, Chiang.; B, Patrick.; T, Storr.; K, M, Smith. Dalton Transactions, 2012, 41, 7920-7930 (© 2012 Royal Society of Chemistry). Preliminary synthesis of compound 4.3 was performed by Addison Desnoyer, an undergraduate Smith group researcher. X-ray data collection was performed by Dr. Brian O. Patrick and Anita Lam at the University of British Columbia, Vancouver.    iv  Table of Contents: Abstract………………………………………………………………………………….……… ii Preface………………………………………………………………………………….………. iii Table of Contents……………………………………………………………………….……… iv List of Figures…………………………………………………………………………….……. vi List of Tables…………………………………………………………………………….…….. xii List of Abbreviations………...……………………………………………………………….. xiv Acknowledgements…………………………………………………………………………… xvi Dedication..……….………………...………………………………………………………… xvii Chapter 1: Electronic Effects in Paramagnetic Organochromium Complexes..…………… 1 Chapter 2: Synthesis and Reactivity of Mixed-aryl β-diketiminate Cr(II) and Cr(III) complexes………………………………………………………………………………………... 5           2.1     Synthesis of Mixed-aryl β-diketiminate Cr(III) Iodo  Complexes…………………. 7           2.2     Synthesis of Mixed-aryl β-diketiminate Cr(III) Methyl Complexes……………….. 7           2.3     Synthesis of Mixed-aryl β-diketiminate Cr(III) Chloro Complexes……………….. 9           2.4     X-Ray Crystal Structures of Cr(III) Methyl and Chloro Complexes……………... 10           2.5     Rationale for Nacnac Ligand Effects on Alkyl Halide Oxidative Addition………. 11           2.6     Synthesis of Mixed-aryl β-diketiminate Cr(III) Alkyl Complexes………………... 12           2.7     Ligand Effects in Mixed-aryl β-diketiminate Cr Catalyzed C-P Bond Formation... 16           2.8     Synthesis of Mixed-aryl Anilido Imine Cr(II)/(III) Complexes……………...…… 20           2.9     Experimental Section……………………………………………………………… 23 Chapter 3: Synthesis and Reactivity of Cyclopentadienyl  Chromium Complexes Containing an N-heterocyclic Carbene Ligand……………………………………………... 37           3.1     Synthesis of CpCr(NHC)(R), Cr(II)  Complexes.………………………………… 39           3.2     Synthesis of CpCr( i Pr-NHC)(Ar)2, Cr(III)  Complexes…….…………………….. 43           3.3     Photolysis of CpCr( i Pr-NHC)(X)2, Cr(III)  Complexes……….………………….. 46           3.4     Stoichiometric Reactivity of CpCr(NHC)(Ar)2, Cr(III)  Complexes……….…….. 47           3.5     Homocoupling of ArMgX Catalyzed by CpCr( i Pr-NHC)(Cl), Cr(III)  Complexes. 51           3.6     Experimental Section…………………………………………………………….... 54 v  Chapter 4: Synthesis and Reactivity of Chromium Complexes with Diimine, Pyridine- imine and Bipyridine Ligand-based radicals……..…………………………………………. 60           4.1     Reactions of bipyridine with Cr(II) Procursors…………………………………… 63           4.2     Synthesis of Cr(III) and Cr(II) Diimine  Complexes……………………………… 69           4.3     Synthesis of Pyridine-imine Cr(II)/Cr(III) X Complexes………………………..... 73           4.4     Synthesis of Pyridine-imine Cr(III) Alkoxide Complex………………………….. 76           4.5     Synthesis of Pyridine-imine Cr(III) Methyl Complex…………………………….. 76           4.6     Synthesis of Diimine Complexes with Cr-O and Cr-N Multiple Bonds………….. 78           4.7     Experimental Section………….…………………………………………………... 84 Chapter 5: Synthesis and Reactivity of Chromium Complexes with Phenylenediamido Ligand-based radicals………………………………………………………………………… 93           5.1     Synthesis of CpCr(II) and Cr(III) Complexes with the (Me3SiN)2C6H4 ligand…... 94           5.2     Synthesis of a Cr(V) Adamantyl Imido Complex………………………………… 97           5.3     Synthesis of CpCr[(Me3SiN)2C6H4](NAr) Aryl Imido Complexes……………….. 99           5.4     Synthesis of CpCr[(Me3CCH2N)2C6H4] Complexes…………………………….. 101           5.5     Synthesis of CpCr[(PhN)2C6H4] Complexes…………………………………….. 108           5.6     Radical Reactivity of CpCr[(RN)2C6H4] Complexes……………………………. 110           5.7     Experimental Section………………….…………………………………………. 115 Chapter 6: Conclusion...……………………………….…………………………………….. 124 References…………………………………………………………………………………….. 126 Appendices…………………………..………………………………………………………... 136            Appendix A. Supplementary X-ray Data…….………………………………………… 136            Appendix B. 1 H NMR and UV-vis Spectra.…………………………………………… 146 vi  List of Figures: Figure 1.1. Mechanism for Single Electron Oxidative Addition of Alkyl Halides with Chromium(II) Reagents.. .............................................................................................. 2 Figure 1.2. Redox active diimine, bipyridine, and pyridine imine LX ligands. ............................. 3 Figure 1.3. CpCr(phenylenediamido) complexes derived from 2,6-xylyl isocyanide. .................. 4 Figure 2.1. Mixed-aryl (2.1a-d) and symmetric bis(2,6 = R2) (2.1e,f) CpCr(nacnac) complexes. 5 Figure 2.2. Mixed-aryl β-diketiminate Cr(II) and Cr(III) complexes (Y = OMe a, CH3 b, H c, CF3 d). ........................................................................................................................... 6 Figure 2.3. Thermal ellipsoid diagram (50%) of Cr(III) iodo complexes, Y= OMe (2.3a (a)), Y=Me (2.3b (b)). .......................................................................................................... 7 Figure 2.4. Thermal ellipsoid diagram (50%) of Cr(III) methyl complexes, Y= OMe (2.3a (a)), Y = Me (2.3b (b)), Y = H (2.3c (c)), Y = CF3 (2.3d (d)).. ........................................... 8 Figure 2.5. Thermal ellipsoid diagram (50%) of Cr(III) chloro complex, Y= OMe (2.4a (a)), Y = Me (2.4b (b)), Y = H (2.4c (c)), Y = CF3 (2.4d (d)).. ......................................... 10 Figure 2.6. Relative Steric Repulsion in CpCr(LX) and CpCr(LX)(X) Complexes with Symmetric and Mixed-Aryl β-diketiminate Ligands. ................................................. 12 Figure 2.7. Synthesis of CpCr[DppNC(Me)CHC(Me)NTol](X) complex (X = Br 2.5, OTs 2.6, Cy 2.7) ......................................................................................................... 13 Figure 2.8. Thermal ellipsoid diagram (50%) of Cr(II) complex 2.6… ....................................... 13 Figure 2.9. Thermal ellipsoid diagram (50%) of Cr(III) cyclohexyl (2.7 (a)), benzyl (2.8 (b)) complexes. .................................................................................................................. 15 Figure 2.10. 31 P NMR of stoichiometric reaction of 2.7 (14.5 mg, 0.0265 mmol) and Ph2PCl (5 µL, 0.027mmol) after 20 h in room temperature.. ............................................... 17 Figure 2.11. Hypothesis for the reaction mechanism of C(sp 3 )-P bond-forming reaction. .......... 17 vii  Figure 2.12. Two catalysts for C-P bond formation reaction, symmetric Cr(II), 2.1f and asymmetric Cr(II), 2.1b.. ......................................................................................... 20 Figure 2.13. Thermal ellipsoid diagram (50%) of Cr(II) complex 2.9… ..................................... 21 Figure 3.1. Hypothetical CpCr(L) catalyzed Kumada Cross-Coupling reaction.......................... 37 Figure 3.2. Synthesis of CpCr( i Pr-NHC)(X), Cr(II) complexes, where X = Cl (3.1), = Mes (3.3) and CpCr( i Pr-NHC)(X)(R), Cr(III) complexes, where X, R = Cl (3.2), X, R = I, Mes (3.4)........................................................................................................... 38 Figure 3.3. Synthesis of CpCr( i Pr-NHC)(R), Cr(II) complexes, where R = Me (3.5), N(SMe3)2 (3.6), Ph (3.7), and CH2CMe2Ph (3.8). ...................................................... 40 Figure 3.4. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)(Me), Cr(II) methyl 3.5 complex. ...................................................................................................................... 41 Figure 3.5. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)[N(SiMe3)2], Cr(III) amide 3.6 complex.. ........................................................................................ 42 Figure 3.6. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)(Ph), Cr(II) Phenyl 3.7 complex. ...................................................................................................................... 42 Figure 3.7. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)(CH2CMe2Ph), Cr(II) alkyl 3.8 complex. ................................................................................................................ 43 Figure 3.8. Synthesis of CpCr( i Pr-NHC)(Ph)2, Cr(III) 3.9 Complexes. ....................................... 44 Figure 3.9. Thermal ellipsoid diagrams (50%) of CpCr( i Pr-NHC)(Ar)2, Cr(III) di-alkyl complexes, (3.9 (a)) and (3.10 (b)). ............................................................................ 45 Figure 3.10. Photolysis of CpCr( i Pr-NHC)(Cl)2, Cr(III)  Complex 3.2 with NREt3 + Cl -  (R = H, Et). Thermal ellipsoid diagram (50%) of [HNEt3 + ][CpCrCl3 - ], Cr(III) compound [HNEt3][3.11]. ......................................................................................................... 47 Figure 3.11. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)[2-(CPh)2], 3.12 complex.. . 49 Figure 3.12. Stoichiometric reaction for C-C bond homo-coupling ............................................. 51 viii  Figure 3.13. Hypothesis for the reaction mechanism of the catalyzed C-C bond homo-coupling reaction. .......................................................................................... 52 Figure 4.1. Comparison of Cr nacnac and Diimine Complexes ................................................... 60 Figure 4.2. MO diagram of diimine π system ............................................................................... 61 Figure 4.3. The reactions of Cr( t Bu-acac)2 with diimine and bipyridine. Thermal ellipsoid diagrams (50%) of octahedral Cr( t Bu-acac)2[(XylNCMe)2],  4.3. ............................. 63 Figure 4.4. Thermal ellipsoid diagram (50%) of (-5-Cp)(-1-Cp)Cr(bpy) complex 4.4. ............ 64 Figure 4.5. Thermal ellipsoid diagram (50%) of Cr(II) bis-amide complex 4.5. The complex crystallizes with two independent molecules in the asymmetric unit. ........................ 65 Figure 4.6. UV-vis spectrum of Cr(bpy)[N(SiMe3)2]2, Cr(II) complex 4.5 (6.14 x 10 -4  M in Et2O). .......................................................................................................................... 66 Figure 4.7. Thermal ellipsoid diagram (50%) of Cr(III) bis-alkoxide complex 4.6. .................... 67 Figure 4.8. Synthesis of Cr( i Pr-NHC)(  t Bu-bpy)2, 4.7 .................................................................. 68 Figure 4.9. Thermal ellipsoid diagram (50%) of Cr( i Pr-NHC)( t Bu-bpy)2 complex 4.7... ............ 69 Figure 4.10. Thermal ellipsoid diagrams (50%) of Cr(III) chloride complexes, (4.8a (a)) and (4.8b (b)). ................................................................................................................. 70 Figure 4.11. Thermal ellipsoid diagram (50%) of Cr(II) complex 4.1… ..................................... 71 Figure 4.12. UV-vis spectrum of complex 4.1 in hexane. ............................................................ 71 Figure 4.13. Thermal ellipsoid diagrams (50%) of Cr(III) alkoxide complexes, (4.9a (a)) and (4.9b (b)). ................................................................................................................. 73 Figure 4.14. UV-vis spectrum of complex 4.10 in hexane. .......................................................... 74 Figure 4.15. Thermal ellipsoid diagram (50%) of Cr(II) complex 4.10.. ..................................... 75 Figure 4.16. Improved synthesis of pyridine-imine Cr(II) and Cr(III) complexes ....................... 76 Figure 4.17. Thermal ellipsoid diagram (50%) of Cr(III) Iodo complex 4.12. ............................ 76 ix  Figure 4.18. Thermal ellipsoid diagrams (50%) of Cr(III) alkoxide (4.13 (a)) and amide (4.14 (b)) complexes. ............................................................................................... 77 Figure 4.19. Thermal ellipsoid diagram (50%) of Cr(III) methyl complex 4.15. ........................ 78 Figure 4.20. Diimine Complexes with Cr-O and Cr-N Multiple Bonds ...................................... 79 Figure 4.21. Thermal ellipsoid diagram (50%) of Cr(III) hydroxide complex 4.16.. .................. 80 Figure 4.22. Synthesis of diimine Cr(III) fluoride complex 4.17, reduction of 4.17 by Gomberg’s dimer . ................................................................................................... 80 Figure 4.23. Thermal ellipsoid diagram (50%) of Cr(III) fluoride complex 4.17. ....................... 81 Figure 4.24. Synthesis of diimine Cr(III) azide 4.18, and Cr(V) nitrido 4.19 complexes. ........... 81 Figure 4.25. Thermal ellipsoid diagrams (50%) of Cr(III) azide (4.18 (a)) and nitrido (4.19 (b)) complexes. ............................................................................................... 82 Figure 4.26. 1 H NMR for CpCr[(DppNCH)2](N) (4.19) nitrido Complex in C6D6 solvent. ........ 82 Figure 5.1. Molecular orbital for ligand-based radicals, N-C bond lengths for phenylenediamido ligands. ......................................................................................... 93 Figure 5.2. Synthesis of CpCr[(Me3SiN)2C6H4], Cr(II) Complex 5.1 and CpCr[(Me3SiN)2C6H4](THF), Cr(III) Complex 5.2 ................................................... 95 Figure 5.3. Thermal ellipsoid diagram (50%) of Cr(III) complex 5.2. ......................................... 95 Figure 5.4. UV-vis absorption spectra of complex 5.1 (red line) in hexane [1.6*10 -4  M] and complex 5.2 (black line) in THF [1.6*10 -4  M]. .......................................................... 96 Figure 5.5. Synthesis of CpCr[(NSiMe3)2C6H4](I), Cr(III) Complex 5.3 and CpCr[(NSiMe3)2C6H4]Cl, Cr(III) Complex 5.4 .......................................................... 97 Figure 5.6. Electronic Structures of CpCr[(Me3SiN)2C6H4](NR’) complexes. ............................ 98 Figure 5.7. Thermal ellipsoid diagram (50%) of CpCr[(Me3SiN)2C6H4](NAd), Cr(V) 5.5 imido complex. ........................................................................................................... 99 x  Figure 5.8 Thermal ellipsoid diagram (50%) of CpCr[(Me3SiN)2C6H4](NR’), Cr(V) imido complexes, R’= phenyl (5.6). R’= P-tol (5.7), and R’= mesityl (5.8).. .................... 100 Figure 5.9. Synthesis of CpCr[(Me3CCH2N)2C6H4], Cr(II) Complex 5.9 ................................. 101 Figure 5.10. Synthesis of CpCr( i Pr-NHC)[(Me3CCH2N)2C6H4], Cr(III) Complex 5.10, and CpCr[(Me3CCH2N)2C6H4](CH2PPh3) complex 5.11. ............................................ 102 Figure 5.11. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)[(Me3CCH2N)2C6H4], Cr(III) complex 5.10 and CpCr[(Me3CCH2N)2C6H4](CH2PPh3), Cr(V) complex 5.11.. ........................................................................................................ 103 Figure 5.12. Synthesis of CpCr[(Me3CCH2N)2C6H4](I), Cr(III) Complex 5.12 and CpCr[(Me3CCH2N)2C6H4]Cl, Cr(III) Complex 5.13 ............................................. 103 Figure 5.13. Thermal ellipsoid diagram (50%) of CpCr[(Me3CCH2N)2C6H4](Cl), Cr(III) complex 5.13. ......................................................................................................... 104 Figure 5.14. Thermal ellipsoid diagram (50%) of CpCr[(Me3CCH2N)2C6H4](NAd), Cr(V) complex 5.14. ......................................................................................................... 105 Figure 5.15. Thermal ellipsoid diagram (50%) of Cr[(Me3CCH2N)2C6H4](NAd)2, Cr(V) complex 5.15. ......................................................................................................... 106 Figure 5.16. Thermal ellipsoid diagram (50%) of {CpCr[(Me3CCH2N)2C6H4]}2(µ-O), Cr(III) complex 5.16. ............................................................................................. 107 Figure 5.17. Thermal ellipsoid diagram (50%) of [Mg]{CpCr[(RN)2C6H4](CH2SiMe3)}2, Cr(III) complex 5.17.. ............................................................................................ 109 Figure 5.18. Thermal ellipsoid diagram (50%) of CpCr[(Ph)2C6H4](Cl), Cr(III) complex 5.19. ....................................................................................................................... 110 Figure 5.19. Thermal ellipsoid diagram (50%) of CpCr[(NSiMe3)2C6H4](OMes*), Cr(III) alkoxide complex 5.20. .......................................................................................... 111 Figure 5.20. Thermal ellipsoid diagram (50%) of CpCr[(Me3CCH2N)2C6H4](NHTS), Cr(III) complex 5.22. ............................................................................................. 112 xi  Figure 5.21. Catalyzing cyclized organic product benzosultams by using CpCr[(R)2C6H4], Cr(II) Complexes. .................................................................................................. 113 Figure 5.22. Thermal ellipsoid diagram (50%) of CpCr[(Me3SiN)2C6H4](NHTrisyl), Cr(III) complex 5.23. ......................................................................................................... 114 Figure B.1. 1 H NMR (400 MHz, C6D6) spectrum 5.15……………………….…………….….146 Figure B.2. 1 H NMR (400 MHz, CDCl3) spectrum of organic product benzosultam…….…....147 Figure B.3. UV-vis absorption spectra of complex 5.18 in hexane [2.37 x 10 -4  M]….…….…..148      xii  List of Tables: Table 2.1. Cr–X Bond Lengths (Å) in CpCr[DppNC(Me)CHC(Me)NC6H4Y](X) Complexes (X =  CH3 (2.3a-d), or Cl (2.4a-d)). ............................................................................ 10 Table 2.2. Cr–NAr Bond Lengths (Å) in CpCr[DppNC(Me)CHC(Me)NC6H4Y](X) Complexes (X = CH3 (2.3a-d), or Cl (2.4a-d)). .......................................................... 11 Table 2.3. Dihedral angle between Cr and nacnac ligand in Cr(II) and Cr(III) complexes. ........ 14 Table 2.4. Chromium-Catalyzed Synthesis of Ph2PCy. ............................................................... 18 Table 3.1. Cr–C(NHC) Bond Lengths (Å) in CpCr(iPr-NHC)(R) Complexes (R =  CH3 (3.5), or Ph (3.7)) and CpCr( i Pr-NHC)(R2) Complexes (R =  Ph (3.9), or Tol (3.10)) and .. 46 Table 3.2. The results of photolysis reaction of CpCr( i Pr-NHC)(Cl)2, Cr(III)  Complex 3.2 with [NREt3]Cl (R = H, Et) ......................................................................................... 47 Table 3.3. Chromium-Catalyzed Synthesis of Ar-Ar. .................................................................. 58 Table 5.1. Cr=NR’ and ligand CN Bond Lengths (Å) in CpCr[(Me3SiN)2C6H4](NR’) Complexes (R’= adamantyl (5.5), R’= phenyl (5.6). R’= tol (5.7), and R’= mesityl (5.8).). ........................................................................................................................ 100 Table A. 1. Crystal data and refinement parameters for X-ray structures of 2.2a, 2.2b, 2.3a, 2.3b, 2.3c, and 2.3d…………….……………………………………..………….. 136 Table A. 2. Crystal data and refinement parameters for X-ray structures of 2.4a, 2.4b, 2,4c, 2.4d, 2.6, and 2.7……………….…………..…………………………………….. 137 Table A. 3. Crystal data and refinement parameters for X-ray structures of 2.8, 2.9, 3.5, 3.6, 3.7, and 3.8…………………….…………………………………………………. 138 Table A. 4. Crystal data and refinement parameters for X-ray structures of 3.9, 3.10, 3.12, 4.1, 4.4, and 4.5........................................................................................................ 139 Table A. 5. Crystal data and refinement parameters for X-ray structures of 4.6, 4.7, 4.8a, 4.8b, 4.9a, and 4.9b………………………………...………….…………………. 140 xiii  Table A. 6. Crystal data and refinement parameters for X-ray structures of 4.10, 4.12, 4.13, 4.14, 4.15, and 4.16……………………………………………………………….. 141 Table A. 7. Crystal data and refinement parameters for X-ray structures of 4.17, 4.18, 4.19, 5.2, 5.5, and 5.6……..……………………….……………………………………. 142 Table A. 8. Crystal data and refinement parameters for X-ray structures of 5.7, 5.8, 5.10, 5.12, 5.14, and 5.15……………………………………………………………….. 143 Table A. 9. Crystal data and refinement parameters for X-ray structures of 5.16, 5.17, 5.18, 5.19, 5.21, and 5.23.................................................................................................. 144 Table A. 10. Crystal data and refinement parameters for X-ray structures of 5.24………….... 145 xiv  List of Abbreviations δ                                    chemical shift ε                                    extinction coefficient Ad                                 adamantyl acac                              acetylacetonate Ar                                  aryl BDE                               bond dissociation energy bpy                                2,2’-Bipyridine BTMSA                         bistrimethylsilylacetylene t Bu                                 tert-butyl DBU                              1,8-diazabicyclo[5.4.0]unec-7-ene Et2O                               diethyl ether Cp                                  cyclopentadienyl, C5H5 Cp*                                1,2,3,4,5-pentamethylcyclopentadienyl, C5Me5 Cy                                  cyclohexyl DMAP                           4-dimethylaminopyridine Dpp                                2,6-diisopropylphenyl Et                                    ethyl 1 H                                   proton HAT                               hydrogen atom transfer HOMO                           highest occupied molecular orbital IR                                   infrared spectroscopy LUMO                           lowest unoccupied molecular orbital MAO                              methylaluminoxane Me                                  methyl Mes                                mesityl, 2,4,6-trimethylphenyl 14 N                                 nitrogen N3R                                organoazides nacnac                            β-diketiminate NHC                               N-heterocyclic carbene NMR                               nuclear magnetic resonance NTs                                 N-(tolylsulfonyl)imino xv  16 O                                  oxygen OTf                                 trifluoromethanesulfonate OMes*                           2,4,6-tri(tert-butyl)phenoxy OTs                                 p-toluenesulfonate 31 P                                   phosphorus PCy3                                tricyclohexylphosphine Ph                                    phenyl ppm                                 parts per million i Pr                                    isopropyl py                                    pyridine SFU                                 Simon Fraser University SOMO                             singly occupied molecular orbital TBP                                 trigonal bipyramid TD-DFT                          time dependent-density functional theory THF                                 tetrahydrofuran TMSCl                            trimethylsilyl chloride Tol                                   p-tolyl Trisyl                               2,4,6-Triisopropylbenzenesulfonyl UPEI                                University of Prince Edward Island UV-vis                             Ultraviolet–visible spectroscopy Xyl                                   xylyl, 2,6-dimethylphenyl xvi  Acknowledgements      First and foremost, I would like to express my heartfelt gratitude to my supervisor Professor Kevin M. Smith, for the continuous support of my Ph.D study and research, for his patience, motivation, enthusiasm, and immense knowledge. I could not have asked for a better role model and mentor for my graduate study. I would like to thank Professor Stephen McNeil and Dr. James Bailey for taking the time to be on my supervisory committee and for providing ideas, positive encouragement, and direction throughout my research. I would also thank Professor Paul Shipley for the help with NMR experiments, and Dr Brian Patrick for his patience in dealing with X-ray crystallography.      Thanks to my colleagues and the staff of the department for generating a constructive working atmosphere. In particular, I enjoyed the company of the past and present members of the Smith and McNeil lab groups.      And last, but not least, I would like to thank my family for their endless support and understanding. In particular, I am grateful to my wife Sapphire, who has been a constant source of strength and inspiration of my life. xvii    To My Parents 1   Chapter 1: Electronic Effects in Paramagnetic Organochromium Complexes.      For decades, the synthesis and reactivity of well-defined, monomeric organometallic transition metal complexes has been an area of active research for inorganic chemists. These homogeneous d-block compounds are often made up of reactive ligands and ancillary ligands. The ancillary ligands do not directly participate in the stoichiometric or catalytic reactions mediated by the metal center. Nevertheless, understanding how the ancillary ligands control metal reactivity through steric and electronic effects is a critical prerequisite for rational catalyst design. 1       Many important types of chemical reactions are catalyzed by organometallic complexes of second and third row transition metals. For catalytic reactions, such as cross-coupling (Pd) or olefin metathesis (Ru, Mo, or W), 2,3,4  nuclear magnetic resonance (NMR) has been the primary tool used to evaluate the influence of ancillary ligands on catalytic activity. Recently there have been increased efforts to develop earth-abundant first row transition metal complexes for both small molecule activation and catalysis. Since many of these complexes are paramagnetic, NMR is less useful for characterizing first row metal compounds or for screening their reactivity. 5  Instead, single-crystal X-ray diffraction has become increasingly important for both confirming the identity of new first row metal complexes and providing valuable structural information that may be correlated with their observed reactivity. 6       The unpaired d-electrons in paramagnetic first row transition metal complexes may also interact with other unpaired electrons. The unusual reactivity observed for cross-coupling catalysts based on first row metals can often be attributed to the generation of carbon-based radicals as a key step in productive catalytic processes. 7  Redox-active ancillary ligands can have an unpaired electron in a ligand-based π-antibonding orbital.8 The distinctive reactivity of many 3d complexes with metal-ligand multiple bonds may also be due to the radical character of oxyl or imidyl ligands. 9  Understanding how all of these unpaired electrons interact with each other would permit the development of first row metal catalysts with unique and useful reactivity profiles for a range of potential applications.  2  Step 1     X2Cr     +     R-X X2Cr-X     +     R Step 2     X2Cr     +     R X2Cr-R overall    2 X2Cr     +     R-X X2Cr-X     +     X2Cr-R Figure 1.1. Mechanism for Single Electron Oxidative Addition of Alkyl Halides with Chromium(II) Reagents.      Figure 1.1 shows a specific example of a radical reaction mediated by a first row transition metal. For over half a century, 10  paramagnetic Cr(II) complexes have been known to react with organic halides in an inner-sphere halogen atom abstraction reaction to form a Cr(III) halide and a carbon-based radical (step 1). In a subsequent fast step, the organic radical is trapped by a second equivalent of Cr(II) to form a Cr(III) organometallic species. 11  While this reaction forms the basis for the stoichiometric, catalytic, and enantioselective coupling of organic halides and aldehydes using chromium reagents, 12  relatively little research has been conducted using well- defined organochromium complexes to examine ancillary ligand steric and electronic effects in this reactivity. 13       For the past 10 years, researchers in the Smith group have developed synthetic routes to CpCr(LX) complexes of Cr(II) and Cr(III) to explore metal-mediated radical reactivity. 6  Cp refers to the 5-cyclopentadienyl ligand. Using the nomenclature developed by Green for neutral (L) and anionic (X) donor atoms, LX denotes a bidentate, monoanionic ligand. 14  In his 2012 Ph.D. thesis, Cory MacLeod investigated steric effects in CpCr(LX) chemistry, particulary how interactions between bulky β-diketiminate (or “nacnac”) LX ligands and large alkyl groups led to reversible Cr(III)-R homolysis in CpCr(LX)(R) complexes. 15  This thesis extends this research to examine electronic effects on the characteristic radical reactivity of paramagnetic organochromium complexes.      Chapter 2 looks at the synthesis and reactivity of CpCr(LX) complexes with mixed-aryl nacnac LX ligands. Compared to the previously-used symmetric bis(2,6-disubstituted) N-aryl nacnac complexes, the new mixed-aryl compounds show increased rates of RX oxidative addition and a remarkably stable Cr(III) cyclohexyl complex. 16  The reactivity differences between mixed-aryl and symmetric CpCr(nacnac) complexes are explored in a Cr-catalyzed radical C(sp 3 )-P bond-forming reaction. 17       In chapter 3, the CpCr(LX) framework is replaced with CpCr(NHC)(X), where X is an anionic halide, alkyl, aryl or amido ligand, and NHC is an N-heterocyclic carbene ligand. By 3  using a strongly donating σ-donor NHC ligand in combination with Cp, CpCr(NHC)(R)2 complexes with two Cr(III)-alkyl bonds can be prepared, a requirement for any monometallic cross-coupling catalyst. By studying the synthesis and reactivity of the CpCr(NHC)(Ar)2 derivatives, a Cr-catalyzed homocoupling of ArMgX reagents was developed. The mechanistic steps that currently preclude this system from being employed in more desirable cross-coupling reactions have also been identified.      In chapter 4, CpCr(LX) complexes are investigated where the negative charge of the LX ligand is due to an unpaired electron in a ligand-based π-antibonding orbital (Figure 1.2).8 Related redox-active ligands such as pyridine diimines have been recently used in first row metal complexes with the goal of suppressing single electron reactivity. 18  The studies described in chapter 4 were initiated to see if the redox activity of bipyridine, pyridine imine, and diimine ligands could be used to enhance the characteristic radical reactivity of paramagnetic organochromium complexes.   Figure 1.2. Redox active diimine, bipyridine, and pyridine imine LX ligands.       In chapter 5, the reactivity of phenylenediamido chromium complexes is explored. This work complements the diimine chemistry in the previous chapter, as the radical monoanionic phenylenediamido LX ligand is obtained by single electron oxidation of the [(RN)2C6H4] 2-  X2 precursor, rather than by single electron reduction of a neutral L2 diimine. 8  The phenylene backbone was also expected to be less prone to the unwanted alkylation reactions that were observed for imine-containing ligands in chapter 4. 19  As shown in Figure 1.3, a related complex had been isolated by Wilkinson and co-workers when excess 2,6-xylyl isocyanide was used to attempt to trap a Cr=NAr imido intermediate. 20  The CpCr(phenylenediamido) complexes proved to be excellent precursors to chromium imido complexes when treated with N3R’ reagents, where R’ = adamantyl, aryl, or SO2Ar. By varying the (RN)2C6H4 substituents (R = Me3Si, Me3CCH2, or Ph), the influence of the electronic properties of the phenylenediamido ligand on 4  the reactivity of the imido ligand could be evaluated. This work culminated in an active chromium catalyst for the radical intramolecular N-H amination of trisyl azide to the corresponding benzosultam. 21    Figure 1.3. CpCr(phenylenediamido) complexes derived from 2,6-xylyl isocyanide.                5  Chapter 2: Synthesis and Reactivity of Mixed-aryl β-diketiminate Cr(II) and Cr(III) complexes      The ease with which the steric and electronic properties of the β-diketiminate or “nacnac” ligand can be varied has contributed to its widespread use over the past decade. 22  This chapter examines electronic effects in the reactivity of CpCr[DppNC(Me)CHC(Me)NC6H4Y] complexes 2.1a-d, where Y = OCH3 (a), CH3 (b), H (c), or CF3 (d), as shown in Figure 2.1. These mixed- aryl complexes were based on 2.1e, the Cr(II) complex previously reported by Smith group that has the most popular β-diketiminate ligand with two 2,6-iPr2C6H3 N-aryl substituents. 23  Decreasing the size of the ortho substituents in 2.1e from i Pr to Me results in bis(xylyl) complex 2.1f, which was a precursor to Cr(III) compounds that showed improved crystallinity. Changing the ortho substituents in the symmetric nacnac complexes influenced the Cr(III)-R bond homolysis by changing the steric hindrance. 24  However, no clear impact was observed on the rates of single electron oxidative addition of iodomethane.  Cr N N Y 2.1a-d Cr N N 2.1e Cr N N 2.1f  Figure 2.1. Mixed-aryl (2.1a-d) and symmetric bis(2,6 = R2) (2.1e,f) CpCr(nacnac) complexes.       The Cr(II) complexes 2.1a-d were first prepared in 2006 by Dr. Liming Tang while she was a postdoctoral research assistant in the Smith group at UPEI. The X-ray structures of complexes 2.1a, 2.1b, and 2.1d all had the C6H4Y group oriented perpendicular to the Cr[(NCMe)2CH] plane. Despite this orientation, there was a modest yet distinct correlation between the electronic parameters of the Y substituents 25  and the rates of MeI oxidative addition, with ρ = -0.36. The presence of electron-donating substituents presumably increases the rate of oxidative addition of iodomethane by stabilizing the Cr(III) iodo product with respect to the Cr(II) reactant. Surprisingly, even the least reactive mixed-aryl complex, 2.1d, had a rate constant that was an order of magnitude larger than those previously determined for 2.1e and 2.1f.       When I began this project in May 2008, the first goal was to independently synthesize the Cr(III)-X (X = I, CH3, Cl) complexes shown in Figure 2.2. It was anticipated that obtaining single crystals suitable for X-ray diffraction might be more difficult, since the 6  CpCr[DppNC(Me)CHC(Me)NC6H4Y]X complexes are lower symmetry than either the Cr(II) mixed-N(aryl) precursors 2.1a-d or the Cr(III) complexes with symmetric bis-(Dpp) on bis-(Xyl) groups. It was thought that if crystal structures were obtained, they might help explain why altering the 4Y position influences the rate of oxidative addition of MeI, while changing the size of the ortho groups in the bis(2,6-R2) compounds had no clear effect. The structures might also help explain why all of the Dpp/4Y complexes were an order of magnitude faster for the reaction of MeI compared to the symmetric bis(orthodisubstituted) nacnac complexes.  Cr N N I Y Cr N N Y 2.1a-d Cr N N Cl Y Cr N N Me Y 2.2a-d 2.3a-d 2.4a-d Figure 2.2. Mixed-aryl β-diketiminate Cr(II) and Cr(III) complexes (Y = OMe a, CH3 b, H c, CF3 d).      The structures obtained indicated that Dpp/4Y complexes were significantly less sterically congested than the Cr(III) complexes from either 2.1e or 2.1f. The reduced steric hindrance of the Dpp/4Y ligands allowed for the synthesis of CpCr[DppNC(Me)CHC(Me)NTol](C6H11) by salt metathesis. This permitted the stoichiometric reactivity of Cr(III)-R homolysis to be studied using a well-defined secondary alkyl complex. Although attempts to use chromium cyclohexyl complex for intermolecular radical C-H activation of toluene were unsuccessful, it was used to synthesize Ph2P-Cy from various Ph2P-Z precursors (Z = PPh2, Cl, H). This reactivity was subsequently extended to catalytic reactions, using CyX (X = Br or Cl) as the cyclohexyl source, and PbX2 activated Mn as the stoichiometric reductant. The complementary catalytic reactivity of 2.1b and 2.1f can be attributed to the reactivity differences imparted by modifying the β- diketiminate ligand. 7       Initial studies were also performed using the anilido imine ligand. The stepwise synthetic route to these ligands lends itself well to preparing mixed-aryl ligands, and the less-hindered aldimine backbone should further enhance the reactivity trends observed for 2.1a-d. The Cr(II) complexes were prepared and preliminary reactions with iodobenzene were explored.  2.1 Synthesis of Mixed-aryl β-diketiminate Cr(III) Iodo  Complexes.      Single-electron oxidation of well-defined Cr(II) precursors with iodine is a common route to synthesize Cr(III) iodo complexes. 26,27  Reaction of Cr(II) 2.1a-d with I2 did give the expected iodo complexes 2.2a-d (eq 2.1), although the mixed-aryl β-diketiminate compounds did not crystallize as readily as  the more symmetric CpCr[(ArNCMe)2CH](I) analogues. 28  Complex 2.2c (Y = H) in particular displayed a tendency to precipitate as a powder rather than form crystals. The lower yields for compounds 2.2a-d are presumed to be due to the difficulties in recrystallizing these chiral-at-metal complexes, rather than some inherent problem with the synthetic route in eq 2.1 or a lack of stability of the Cr(III) iodo species. The X-ray crystal structure of 2.2a and 2.2b are shown in Figure 2.3. Cr N N I Y Cr N N Y 2.1a-d 2.2a-d 1/2 I2 Et2O (2.1)   Figure 2.3. Thermal ellipsoid diagram (50%) of Cr(III) iodo complexes, Y= OMe (2.3a (a)), Y=Me (2.3b (b)).  2.2 Synthesis of Mixed-aryl β-diketiminate Cr(III) Methyl Complexes.      The optimal choice of RMgX and Cr(III) precursor to prepare CpCr[(ArNCMe)2CH](R) complexes by salt metathesis depends on the steric demands of the NAr and R groups.  23,24,27,29,  8  Both the Cr(III) iodo and Cr(III) chloro mixed-aryl β-diketiminate complexes reacted readily with MeMgI. However, synthesis of Cr(III) methyl compounds 2.3a-d directly from the corresponding Cr(II) precursors, as shown in eq 2.2, capitalized on the ease of synthesis of 2.1a- d. Addition of iodomethane to CpCr[(DppNC(Me)CHC(Me)NC6H4Y] produced a mixture of Cr(III) iodo and Cr(III) methyl species, which was converted to 2.3a-d by subsequent addition of MeMgI.  Complexes 2.3b and 2.3d were also prepared by reaction of the appropriate Cr(II) complex with MeI and SmI2. 30  As was observed for CpCr[(DppNCMe)2CH](CH3), 28  the high solubility of the Cr(III) methyl complexes limited the yield of products 2.3b-d as crystalline solids (Figure 2.4).  The comparatively high yield of 2.3a may be due to a slight reduction in lipophilicity imparted by the polar methoxy substituent. Cr N N Me Y Cr N N Y 2.1a-d 2.3a-d 1) 1/2 MeI 2) 1/2 MeMgI Et2O (2.2)   Figure 2.4. Thermal ellipsoid diagram (50%) of Cr(III) methyl complexes, Y= OMe (2.3a (a)), Y = Me (2.3b (b)), Y = H (2.3c (c)), Y = CF3 (2.3d (d)). In complex 2.3d, the fluorine atoms of the CF3 group are disordered and were modeled in two orientations; only one is shown.    9  2.3 Synthesis of Mixed-aryl β-diketiminate Cr(III) Chloro Complexes.      In light of the problems encountered in recrystallization of the Cr(III) iodo complex 2.2a-d, routes were investigated to prepare Cr(III) chloro compounds as potential precursors for the independent synthesis of 2.3a-d by salt metathesis. Although the symmetric CpCr[(DppNCMe)2CH](Cl) could be prepared by oxidation of the Cr(II) precursor with PbCl2, it was not readily accessible by salt metathesis reactions from CpCrCl2(THF). 28  This observation was confirmed by Jin and co-workers, although this route served well for their preparation of CpCr[(PhNCMe)2CH](Cl) and related β-ketoiminate complexes. 31  For CpCr[(XylNCMe)2CH]- (Cl), sequential reaction of CrCl3 with deprotonated β-diketiminate followed by NaCp had proved optimal. 29       Rather than CrCl3, isolated CpCrCl2(THF) was used to prepare CpCr[(DppNC(Me)CHC(Me)NC6H4Y](Cl) (2.4a-d) complexes (eq 2.3). Schaper and co- workers demonstrated that the attempts to prepare bis(β-diketiminate) Cr(III) complexes by reaction of Li[(XylNCMe)2CH] with CrCl3(THF) yielded only the monosubstituted compound. 32  Although inadvertent formation of Cr(LX)2Cl complexes by salt metathesis is not a problem even for the smallest symmetric 2,6-disubstituted β-diketoiminate ligand, it was an issue for synthesis of Cr[(PhNCMe)2CH]X2 derivatives. 33,34  Adding the mixed-aryl β-diketoiminate to a well-defined Cr(III) precursor that already has a cyclopentadienyl ligand presumably helps avoid such difficulties in the synthesis of 2.4a-d. Cr N N Cl Y Cr N HN Y 2.4a-d THF (2.3)OCl Cl + Li  10   Figure 2.5. Thermal ellipsoid diagram (50%) of Cr(III) chloro complex, Y= OMe (2.4a (a)), Y = Me (2.4b (b)), Y = H (2.4c (c)), Y = CF3 (2.4d (d)). Complex 2.4a crystallizes with disordered solvent in the lattice. The PLATON/SQUEEZE program was used to generate a second, solvent- free data set. In complex 2.4d, the Cp ring was disordered and modeled in two orientations; only one is shown.  2.4 X-Ray Crystal Structures of Cr(III) Methyl and Chloro Complexes. Table 2.1. Cr–X Bond Lengths (Å) in CpCr[DppNC(Me)CHC(Me)NC6H4Y](X) Complexes (X =  CH3 (2.3a-d), or Cl (2.4a-d)). Cr–X Y = OMe Y = CH3 Y = H Y = CF3 Cr–CH3 2.3a 2.0563(15) 2.3b 2.0608(17) 2.3c 2.0799(18) 2.3d 2.052(2) Cr–Cl 2.4a 2.3046(4) 2.4b 2.3173(10) 2.4c 2.2984(5) 2.4d 2.2947(2)      X-ray crystal structures were obtained for all four mixed-aryl β-diketiminate complexes as both the Cr(III) methyl and Cr(III) chloro species. The thermal ellipsoid diagrams for complexs 2.3a-d and 2.4a-d are shown in Figures 2.4 and 2.5, respectively, and the Cr-X (X = Cl, CH3) bond lengths are collected in Table 2.1. In the symmetric CpCr[(ArNCMe)2CH](R) alkyl complexes, the Cr–CH3 species had shorter bonds (between 2.0645(17) and 2.076(2) Å) 27,28  than were found for substituted primary alkyl Cr-CH2R complexes (typically between 2.10 and 2.13 Å). 24  The mixed-aryl Cr(III) methyl complexes 2.3a-d follow the same trend, with two compounds (2.3a,d) having Cr-CH3 bond lengths less than 2.06 Å. However, there is no clear 11  connection between the Cr-CH3 or Cr-Cl bond lengths in Table 2.1 and the electronic properties of the NC6H4Y substituents for 2.3a-d or 2.4a-d. Table 2.2. Cr–NAr Bond Lengths (Å) in CpCr[DppNC(Me)CHC(Me)NC6H4Y](X) Complexes (X = CH3 (2.3a-d), or Cl (2.4a-d)). Cr–NAr Y = OMe Y = CH3 Y = H Y = CF3 Dpp 2.3a 2.0262(12) 2.3b 2.0254(12) 2.3c 2.0391(13) 2.3d 2.0274(19) C6H4Y 2.3a 2.0128(12) 2.3b 2.0175(14) 2.3c 2.0109(13) 2.3d 2.0177(19) Dpp 2.4a 2.0274(12) 2.4b 2.134(3) 2.4c 2.0285(11) 2.4d 2.024(2) C6H4Y 2.4a 2.0067(12) 2.4b 2.011(3) 2.4c 1.9993(12) 2.4d 2.000(2)      The differing steric demands of the N(Dpp) and N(C6H4Y) groups are shown in the Cr-N bond lengths for 2.3a-d and 2.4a-d (Table 2.2). With the exception of the anomalously long Cr- N(Dpp) bond of 2.134(3) Å in 2.4b, the Cr-N(Dpp) bond lengths are similar to those observed for the corresponding symmetric CpCr[(ArNCMe)2CH]X complexes. 24,29  In all cases, the Cr- N(C6H4Y) bond is significantly shorter, presumably reflecting the reduced steric requirements of the smaller aryl group. Once again, however, no correlation between the electronic properties of the Y group and the Cr-N(C6H4Y) bond length could be discerned.  2.5 Rationale for Nacnac Ligand Effects on Alkyl Halide Oxidative Addition.      While the X-ray crystal structures discussed in section 2.4 do not vary systematically as the Y substituent is altered, they can be used to explain the reactivity differences between mixed-aryl complexes 2.1a-d and bis-(2,6-R2) compounds 2.1e and 2.1f. The significant increase in the rate constants measured for all four mixed-aryl Cr(II) complexes in comparison to the previously reported symmetric nacnac analogues appears to be an unanticipated steric consequence of removing the ortho substituents to enhance electronic effects. 28      Figure 2.6 illustrates the difference in steric demands between open Cr(II) and crowded Cr(III)-X complexes for the symmetric ortho-disubstituted nacnac system. The steric demands of the N(2,6-R2C6H3) groups are more acutely felt in CpCr(nacnac)(X) than in CpCr(nacnac), resulting in the relative destabilization of the Cr(III) product. For the mixed-aryl nacnac system, this relative destabilization of Cr(III)-X is lessened due to reduced steric repulsion. Increasing the relative stability of CpCr(nacnac)(X) results in a lower barrier for inner-sphere halogen atom abstraction, corresponding to the observed enhancement in the rate of oxidative addition of MeI for 2.1a-d. 12    Figure 2.6. Relative Steric Repulsion in CpCr(LX) and CpCr(LX)(X) Complexes with Symmetric and Mixed-Aryl β-diketiminate Ligands.  2.6 Synthesis of Mixed-aryl β-diketiminate Cr(III) Alkyl Complexes.      Compared to the symmetric bis(orthodisubstituted) CpCr(nacnac) complexes, CpCr[DppNC(Me)CHC(Me)NTol] has both enhanced rates of single-electron oxidative addition of iodomethane and a less sterically-congested coordination site. We were interested in the reaction of mixed N-aryl CpCr(nacnac) complexes with cyclohexyl bromide (CyBr) and other secondary alkyl halides. As in the oxidative addition of iodomethane reaction, routes to independently synthesize the Cr(III)-X complexes had to be developed. The Cr(III) bromo 2.5 was synthesized by single electron oxidation of  CpCr[DppNC(Me)CHC(Me)Tol] 2.1b with PbBr2 as shown in Figure 2.7. 35  Oxidation of 2.1b with silver p-toluenesulfonate afforded the Cr(III) tosylate, 2.6, which was structurally charaterized by X-ray diffraction (Figure 2.8). The tosylate complex 2.6 is more readily crystallized than bromo 2.5, and both 2.5 and 2.6 are air stable as solids.  13  N N Cr Cr N N N N Cr O CH3 S O O N N Cr Br AgOTs THF PbBr2  THF Cy2Mg  Et2O 2.1b 2.5 2.6 2.7  Figure 2.7. Synthesis of CpCr[DppNC(Me)CHC(Me)NTol](X) complex (X = Br 2.5, OTs 2.6, Cy 2.7)  Figure 2.8. Thermal ellipsoid diagram (50%) of Cr(II) complex 2.6. Complex 2.6, the Cp ring appears to be disordered and was modeled in two orientations with restraints employed to maintain a regular Cp geometry.      As discussed in section 2.3, the Cr(III)-methyl complexes 2.4a-d could be synthesized directly from the corresponding Cr(III) iodo or chloro precursors with MeMgI. Like related sterically demanding CpCr(nacnac)(R) compounds, 24,29  Cr(III)-cyclohexyl complex 2.7 was best prepared from tosylate 2.6 and the halide-free Cy2Mg dialkyl magnesium reagents, although it could also be synthesized in lower yields from Cr(II) complex 2.1b, CyI and SmI2. 30a  Previous attempts to prepare related CpCr(III)-cyclohexyl complexes with symmetric bis(2,6-R2) nacnac ligands did not result in crystals suitable for X-ray diffraction. 14       The X-ray crystal structure of complex 2.7 as shown in Figure 2.9(a), the successful synthesis 2.7 can be attributed to the reduced steric demand of the mixed-aryl nacnac ligand. Although the Cr-C(cyclohexyl) bond length of 2.106(3) Å is longer than the Cr-CH3 bond (2.061(2) Å) of the corresponding Cr(III) methyl complex 2.3b, 36  it is in the range of 2.10 to 2.13 Å previously observed for primary alkyl ligands in CpCr(III) complexes bearing symmetric 2,6-disubstituted β-diketiminate ligands. The steric strain imposed by the secondary alkyl ligand in 2.7 is evident in the distortions of the N-aryl substituents away from the cyclohexyl group, and the relatively long Cr-N(Dpp) and Cr-N(tol) bonds, 2.057(2) Å and 2.024(2) Å, respectively. The UV-vis spectrum of 2.7 in hexanes displays the strong absorbance band at 553 nm characteristic of CpCr[(ArNCMe)2CH](R) complexes. 24  Table 2.3. Dihedral angle between Cr and nacnac ligand in Cr(II) and Cr(III) complexes. Dihedral angle (º) R = Cl R = Me R = Cyclohexyl Cr(III)-R 2.4b 155.49 2.3b 153.06 2.7 147.18 Cr(II) 2.1b 179.44 2.1f 180.00 The differences in steric demands between open Cr(II) and crowded Cr(III)-X/R complexes can be assessed by measuring the dihedral angle between the Cr center and the plane of the nacnac ligand as shown in Table 2.3. Increasing the relative steric repulsion of the complex can push the metal out off the nacnac ligand plane. The steric bulk of the secondary cyclohexyl group results in the most bent dihedral angle of 147.18 º. The primary alkyl complexes and Cr(III) chloride have similar dihedral angles of 153.06 º and 155.49 º. For the Cr(II) complexes, the Cr center is not significantly displaces from the plane of the nacnac ligand in either the symmetric complex 2.1f or the asymmetric 2.1b.  15  N N Cr I O (PhCH2)MgCl N N Cr O 2.8 (2.4) 2.2a Et2O   Figure 2.9. Thermal ellipsoid diagram (50%) of Cr(III) cyclohexyl (2.7 (a)), benzyl (2.8 (b)) complexes.      The conversion of CpCr[(XylNCMe)2CH](CH2CMe3) in toluene to the corresponding Cr(III)- benzyl complex was an early indication of the Cr-R homolysis reactivity of sterically hindered Cr(III) alkyl complexes. In contrast, Cr(III) cyclohexyl 2.7 slowly converted to Cr(II) 2.1b in toluene without evidence of Cr(III)-benzyl formation by UV-vis spectroscopy. To assess the stability of the desired product of toluene C-H activation, a Cr(III) benzyl complex was synthesized by salt metathesis. As shown in Figure 2.9b, X-ray quality crystals were obtained of CpCr[DppNC(Me)CHC(Me)NC6H4(OMe)](CH2Ph), 2.8. As previously noted for the mixed-aryl Cr(III) methyl complexes, the increased crystallinity of lipophilic alkyl complexes with this particular mixed-aryl ligand may be due to the polarity of the OMe substituent. The Cr(III)- CH2Ph bond length in 2.8 is 2.124(3) Å, longer than the Cr-R bonds in related methyl or cyclohexyl complexes but in the range previously obtained for Cr(III) benzyl compounds with bis(2,6-R2) nacnac ligands. 24  In the crystal structure, the benzyl aryl substituent was oriented towards the less sterically demanding NC6H4OMe group. Since the Cr(III) benzyl complexes are evidently stable, the failure to generate these species from Cr(III) cyclohexyl 2.7 in toluene is tentatively attributed to the inherent barrier for hydrogen atom abstraction of hydrocarbon C-H bonds by carbon-based radicals. We therefore investigated 2.7 for radical C(sp 3 )-P bond formation, including the use of cylcohexyl radicals generated from 2.7 to abstract a hydrogen atom from Ph2PH. 16   2.7 Ligand Effects in Mixed-aryl β-diketiminate Cr Catalyzed C-P Bond Formation.      Transition-metal catalyzed carbon–phosphorus bond-forming reactions have largely focused on C(sp 2 )–P processes.37  Recent work by the groups of Oshima and Studer have demonstrated the utility of radical C–P formation using tin and silyl reagents.38,39  New catalytic routes to ArnPR3–n directly from secondary or tertiary organic halides are of potential interest, in part due to continuing advances in applications of ArPR2 ligands with bulky, electron-donating substituents. 40   The titanium-mediated radical synthesis of Ph2PCy from P2Ph4 and cyclohexyl bromide was recently developed by Cossairt and Cummins using stoichiometric Ti[N(3,5- Me2C6H3)tBu]3. 41   Although the three-coordinate Ti(III) reagent is a powerful single-electron reductant, 42  the Ti(IV) bromo product of halogen atom abstraction from CyBr is only slowly reduced back to the active Ti(III) species even using Na/Hg amalgam, effectively precluding a catalytic reaction. 41       The reactivity of Cr(III) cyclohexyl 2.7 in stoichiometric reactions with Ph2PY sources at room temperature in benzene was evaluated by 31 P NMR, with PPh3 added as an internal standard (eq 2.5). Reaction of CpCr[DppNC(Me)CHC(Me)NTol](Cy) with Ph2PCl resulted in the formation of Ph2PCy in 94% yield ( 31 P NMR Shown in Figure 2.10). Similarly, treatment of 2.7 with P2Ph4 and CyBr resulted in generation of Ph2PCy in 96% yield ( 31 P NMR). The corresponding reaction of 2.7 with CyBr and Ph2PH resulted in a lower yield (30%) of Ph2PCy. However, treatment of Ph2PH with 2.2 equiv of CyBr and 2.7 equiv of the Cr(II) complex 2.1b produced 69% Ph2PCy by 31 P NMR.  N N Cr Ph2PCl P P2Ph4 + CyBr Ph2PH + CyBr 2.7 (2.5)  17    Figure 2.10. 31 P NMR of stoichiometric reaction of 2.7 (14.5 mg, 0.0265 mmol) and Ph2PCl (5 µL, 0.027mmol) after 20 h in room temperature.  Figure 2.11. Hypothesis for the reaction mechanism of C(sp 3 )-P bond-forming reaction.      Our working hypothesis for the reaction mechanism of these various C(sp 3 )-P bond-forming processes is outlined in Figure 2.11. In the absence of oxidants, small amounts of Cr(II) complex 2.1b can trap the radicals generated by the Cr-C bond homolysis of 2.7, preventing the bimolecular reaction between two cyclohexyl radicals (step 1). However, Ph2PCl reacts rapidly with 2.1b to form Cr(III) chloro 2.4b and P2Ph4 (steps 2 and 3). The consumption of the Cr(II) radical trap favors the production of cyclohexyl radicals, which then react with P2Ph4 (step 4). 38,39  Similarly, bromine atom abstraction from CyBr by Cr(II) generates Cr(III) bromide 2.5 (step 5), also resulting in the rapid reaction of Cy• with available P2Ph4 (step 4). The Cr(II) 18  complex 2.1b does not react with P2Ph4, and attempts to prepare a Cr(III)-PPh2 complex via salt metathesis reactions of KPPh2 with 2.5 or 2.6 were unsuccessful. The reaction of Cr(II) complex 2.1b with substoichiometric Ph2PCl also produced only the Cr(III) chloride 2.4b, P2Ph4, and unreacted 2.1b, indicating that if any Cr(III)-PPh2 species is generated, it is unstable with respect to 2.1b and P2Ph4.      The key step in the overall reaction of 2.7 or 2.1b with CyBr and Ph2PH is the rapid intermolecular hydrogen atom abstraction process shown in step 6, 43  which generates Ph2P• radical and cyclohexane. While the steps proposed in Figure 2.11 remain speculative in the absence of mechanistic studies, the range of Ph2PY substrates that can be employed to produce Ph2PCy from Cr(III) cyclohexyl complex 2.7 attests to the flexibility of metal-mediated radical routes to C(sp 3 )-P bond formation. Table 2.4. Chromium-Catalyzed Synthesis of Ph2PCy.  entry Cr cat. CyX Ph2PY additive time temp yield b  1  2.1b  CyBr  Ph2PCl  PbBr2  28 h  25 ºC  79% 2  2.1be  CyBr  Ph2PCl  PbBr2  28 h  25 ºC  73% 3  2.1b  CyBr  P2Ph4  PbBr2  28 h  25 ºC  70% 4  2.1b  CyBr d  Ph2PH  PbBr2  28 h  25 ºC  70% 5  2.1f  CyBr  Ph2PCl  PbBr2  28 h  25 ºC  92% 6  2.1f CyBr  P2Ph4  PbBr2  28 h  25 ºC  96% 7  2.1f CyBr d  Ph2PH  PbBr2  28 h  25 ºC  83% 8  2.1b CyBr  Ph2PCl  PbBr2  12 h  55 ºC  66% 9  none  CyBr  P2Ph4  PbBr2  24 h  25 ºC  NA 10  Cp2Cr  CyBr  Ph2PCl  PbBr2  24 h  25 ºC  47% 11  ligandsf  CyBr  Ph2PCl  PbBr2  24 h  25 ºC  32% 12  CrCl3  CyBr  Ph2PCl  PbBr2  28 h  25 ºC  NA 13  SmI2  CyBr  Ph2PCl  PbBr2  28 h  25 ºC  NA 14  2.1b  CyCl  P2Ph4  PbCl2  24 h  55 ºC  42% 15  2.1b CyCl  P2Ph4  PbCl2  48 h  55 ºC  61% 16  2.1b CyCl  P2Ph4  PbCl2  72 h  55 ºC  80% 17  2.1f CyCl  P2Ph4  PbCl2  72 h  55 ºC  29% 19  18  2.1f CyCl  P2Ph4  PbCl2  216 h  55 ºC  77% 19  2.1f  CyCl  P2Ph4  PbCl2  312 h  55 ºC  81%  a  1 mol% catalyst was used for entries 1–8, 10; 10 mol% catalyst was used for entries 11–13 and 14–19. b Catalytic PbX2 (1 mol% to 3 mol%) was added to activate Mn. c  The yields were determined by 31 P NMR. d  2.4 equiv CyBr were used with the Ph2PH substrate. e  Reaction performed in a foil-wrapped vessel to exclude light. f  To investigate the possible catalytic role of managanese species generated by transmetallation of Cp and/or nacnac ligands from chromium, the reaction was performed without Cr but with 10 mol% of both NaCp and Li[DppNC(Me)CHC(Me)NTol] added.      The stoichiometric reactions in Figure 2.11 can be rendered catalytic by the use of PbBr2- activated Mn powder 44  at ambient temperature and 1 mol% of the mixed N-aryl Cr(II) complex 2.1b, resulting in a 79% yield of Ph2PCy from Ph2PCl after 28 h (Table 2.4, entry 1). Comparable yields were obtained with catalyst 2.1b when the reaction was protected from ambient light or when P2Ph4 and Ph2PH were used as precursors (entries 2-4). In all cases, bipyridine was added at the completion of the reaction in order to displace Ph2PCy from the paramagnetic MnBr2 byproduct. 45 , 46 , 47  The catalytic activity of the CpCr[(XylNCMe)2CH] symmetric Cr(II) complex 2.1f was assessed under the same reaction conditions. Although we have been unable to characterize the corresponding Cr(III) cyclohexyl complex by X-ray crystallography, due to its instability, the catalytic use of the bulkier 2,6-Me2C6H3 disubstituted ligand led to an unexpected increase in the yields of Ph2PCy from each phosphorus substrate (entries 5-7). A much lower yield of 47% was obtained when 1 mol % Cp2Cr was used as the catalyst, and no Ph2PCy was observed by 31 P NMR when the reaction was conducted without chromium catalyst or when 10 mol % SmI2 or CrCl3 was used. Interestingly, 32 mol % Ph2PCy was obtained without Cr when 10 mol % of both NaCp and Li[DppNC(Me)CHC(Me)NTol] were added, suggesting that with the proper ancillary ligands a Mn-based catalyst may also be viable for this reaction. Although related Ph2PR complexes prepared by radical addition to P2Ph4 have been amenable to oxidation with H2O2 and purification by column chromatography, 39  our initial attempts to isolate our product via this procedure were not successful.      Less-reactive secondary alkyl chlorides continue to pose a challenge as substrates for transition-metal catalyst reactions. 48,49  Although the reaction requires higher catalyst loading (10 mol% 2.7), higher reaction temperature (55 °C) and longer reaction times (72 h), Ph2PCy can be produced in 80% 31 P NMR yield from P2Ph4 and CyCl (entry 16). Interestingly, under these reaction conditions, the symmetric Cr(II) complex 2.1f gives only 29% yield along with the 59% 20  unreacted P2Ph4 after 72 h (entry 17), with 81% yield only being achieved after 13 days at 55 °C (entry 19)  Cr N N Cr N N Weaker Cr(III)-Cy bond Better catalyst for CyBr Faster R-X oxidative addition Better catalyst for CyCl 2.1f 2.1b  Figure 2.12. Two catalysts for C-P bond formation reaction, symmetric Cr(II), 2.1f and asymmetric Cr(II), 2.1b.      As summarized in Figure 2.12, the observed variations in catalytic activity between 2.1b and 2.1f can be attributed to the reactivity differences imparted by modifying the β-diketiminate ligand. With the more reactive cyclohexyl bromide substrate, the higher yields obtained with catalyst 2.1f are presumably due to the weaker Cr-Cy bond in the more hindered Cr(III) secondary alkyl complex, favoring the formation of Ph2PCy as shown in Figure 2.10, step 4. However, as was previously observed in the catalytic radical cyclization of chloroacetals, 50  Cr(II) complex 2.1f only reluctantly reacts with unactivated C(sp 3 )-Cl bonds. Due to its decreased steric requirements, 2.1b is much more reactive than 2.1f for the single-electron oxidative addition of alkyl halides. 16  This increased propensity for oxidative addition accounts for the relatively high activity of 2.1b with the more challenging cyclohexyl chloride substrate.  2.8 Synthesis of Mixed-aryl Anilido Imine Cr(II)/(III) Complexes.      Anilido imine ligands 51  were initially developed as bidentate, monoanionic ligands that would be less prone to decomposition than nacnac. The stepwise construction of anilido imine ligands makes the preparation of mixed N-aryl derivatives particularly easy. 52  Once again, one bulky Dpp substituent was retained to afford steric protection, while the second aryl group did not have ortho substituents. Cr + THF cat. DBU Cr N NN HN 2.9 (2.6)  21       Protonolysis reaction of Cp2Cr is a useful route to new well-defined monomeric monocyclopentadienyl chromium derivatives. The synthesis of CpCr[DppNCH(C6H4)NTol] (2.9) (Tol = 4-MeC6H4) was achieved by conducting the protonolysis at room temp with 22 mol% DBU as catalytic base (eq 2.6). The first Cr(III) anilido imine complex were recently reported by Xu, Mu and co-workers. 53  Single crystal X-ray diffraction of 2.9 showed a similar structure to analogous mixed aryl β-diketiminate CpCr(II) complexes (Figure 2.13). Cr–NAr bond lengths (Å) in CpCr[DppNCH(C6H4)NTol] complex are (2.016(3), 2.002(2) Å). The side of Cr-N(Dpp) bond is longer than other side of Cr-N(C6H4Y) bond due to steric effect. However, a comparison to the mixed-aryl β-diketiminate chromium complex 2.1b show that both Cr-N bond lengths in CpCr[DppNCH(C6H4)NTol] complex are shorter than the Cr-N bonds in β-diketiminate derivative (2.02-2.03 Å). This is attributed to the smaller ligand backbone of the anilido imine ligand, which leads to a decrease in the effective steric bulk of the N-aryl substituents. 16   Figure 2.13. Thermal ellipsoid diagram (50%) of Cr(II) complex 2.9.      The CpCr[DppNCH(C6H4)NTol](I) complex 2.10 can be prepared by the reaction of [Cp2Cr] + I -  with DppNCH(C6H4)NHTol as shown in eq 2.7. Selective protonolysis of just one cyclopentadienyl ring is more readily achieved using the cationic Cr(III) [Cp2Cr] + X -  precursor 54  than from neutral Cr(II) Cp2Cr. 55  Reaction of [Cp2Cr] + X -  with neutral β-diketones, salicylaldimines and β-diketoimines has been shown to be a convenient synthetic route to CpCr(LX)(X) complexes without resorting to salt metathesis.  22  N NCr + THF cat. DBU Cr N HN 2.10 I I Dpp Tol (2.7)       As expected, the decreased steric demand of 2.9 compared to 2.1b results in enhanced reactivity with alkyl halides. Preliminary reactions of 2.9 with one-half equivalent of iodobenzene at room temperature shows consumption of Cr(II) and formation of Cr(III) iodo complex 2.19 by UV-vis spectroscopy (eq 2.8). Cr N N 2.9 + I N N Cr 2.10 I 2 Dpp Tol (2.8)  23  2.9 Experimental Section:      General Considerations. All reactions were carried out under nitrogen using standard Schlenk and glove box techniques. Hexanes, pentane, Et2O, CH2Cl2 and THF were purified by passage through activated alumina and deoxygenizer columns from Glass Contour Co. (Laguna Beach, CA, USA). Celite (Aldrich) was dried overnight at 120 ˚C before being evacuated and then stored under nitrogen. Iodine was purified by sublimation before use. n-BuLi (1.6 M in hexanes), NaCp (2.0 M in THF), CrCl2, CrCl3 (anhydrous), iodomethane (2.0 M in MTBE), 1,4- dioxane (anhydrous), SmI2 (0.1 M in THF), methylmagnesium iodide (3.0 M in Et2O), DBU (1,8-diazabicyclo[5.4.0]undec-7-ene, 98%, Aldrich), chlorodiphenylphosphine, potassium diphenylphosphide (0.5M, in THF), diphenylphosphine, triphenylphosphine, samarium diiodide (0.1 M in THF), lead(II) bromide (98% powder), lead(II) chloride (98% powder), silver p- toluenesulfonate, 2,2’-bipyridine, manganese (99% powder), and trimethylsilyl chloride were purchased from Aldrich and used as received. Cyclohexyl bromide and cyclohexyl chloride were degassed by three freeze-vacuum-thaw cycles and stored under nitrogen prior to use. Benzene was dried over sodium/benzophenone, purified by vacuum distillation, degassed by three freeze- vacuum-thaw cycles and stored under nitrogen. Tetraphenyldiphosphine was prepared by reaction of Ph2PCl with Ph2PK in toluene, and was recrystallized from Et2O/toluene. The β- diketiminate ligands were prepared according to the literature procedure. 56,36 CpCrCl2(THF) was prepared by treatment of Cp2Cr with excess anhydrous HCl (1.0 M in Et2O) in THF at 0 ºC. 57  The Cr(II) β-diketiminate compounds 2.1a, 2.1c, and 2.1d were prepared as described in the literature. 56       Mg(C6H11)2·x(1,4-dioxane) was prepared by reaction of CyMgCl (Aldrich, 2.0 M in Et2O) with 1,4-dioxane (anhydrous, Aldrich), and titrated to determine the 1,4-dioxane content according to the literature procedures. 58 Compounds CpCr[(XylNCMe)2CH](Br), 50  CpCr[(XylNCMe)2CH], 36  and CpCr[(XylNCMe)2CH](OTs) 29  were prepared according to the literature procedures.  31 P NMR spectra were recorded on a Varian Mercury Plus 400 spectrometer in C6H6 solvent with chemical shifts referenced to external PPh3 (-4.9 ppm) in C6D6 solvent. The 31 P NMR spectra for the stichiometric and catalytic reactions conducted in this chapter were included in the Supporting Information of reference. 17  UV-vis spectroscopic data was collected on a Varian Cary 100 Bio UV–Visible spectrophotometer in pentane or hexanes solution in a specially constructed cell for air sensitive samples: a Kontes Hi-Vac Valve with PTFE plug was attached 24  by a professional glassblower to a Hellma 10 mm path length quartz absorption cell with a quartz-to-glass graded seal. Elemental analyses were performed by Guelph Chemical Laboratories, Guelph, ON, Canada or by the UBC Department of Chemistry microanalytical services.      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4Me] (2.1b). A solution of NaCp (1.9 ml, 2.0 M in THF, 3.8 mmol) was added dropwise to a suspension of CrCl2 (418 mg, 3.40 mmol) in 25 ml THF, and the resulting mixture was stirred at room temperature for 2 h. In a separate reaction vessel, a solution of n-BuLi (2.4 ml, 1.6 M in hexanes, 3.8 mmol) was added dropwise to a –30 ºC solution of DppNHC(Me)CHC(Me)NC6H4Me (1.18 g, 3.38 mmol) in 15 ml THF, and the yellow solution was allowed to warm to room temperature and was stirred for 1 h. The ligand solution was then added to the Cr(II) reaction. After stirring for an additional 20 h, the solvent was removed in vacuo, the residue was extracted with 36 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 2.1b (1.28 g, 81.0%) was isolated in three crops over several days. Anal. Calcd. For C29H36N2Cr: C, 74.97; H, 7.81; N, 6.01. Found: C, 71.59; H, 6.15; N, 8.71. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 306 (10300), 428 (5800), 557 (1080).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4(OMe)](I) (2.2a). To a solution of 2.1a (100 mg, 0.208 mmol) in 5 ml Et2O was added a solution of I2 (27.9 mg, 0.110 mmol) in 3 ml Et2O. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml Et2O, filtered through Celite and the solution was cooled to -30 ºC. 2.2a (50.0 mg, 40.0%) was isolated after 2 days. Anal. Calcd. for C29H36N2OCrI: C, 57.34; H, 5.97; N, 4.61. Found: C, 57.62; H, 6.04; N, 4.82. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 432 (5500).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4Me](I) (2.2b). To a solution of 2.1b (200 mg, 0.431 mmol) in 10 ml Et2O was added a solution of I2 (60.1 mg, 0.237 mmol) in 4 ml Et2O. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 5 ml Et2O, filtered through Celite and the solution was cooled to -30 ºC. 2.2b (103 mg, 40%) was isolated after 2 days. Anal. Calcd. for C29H36N2CrI: C, 58.89; H, 6.13; N, 4.74. Found: C, 58.55; H, 6.37; N, 5.04. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 433 (6300), 579 (700).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H5](I) (2.2c). To a solution of 2.1c (100 mg, 0.222 mmol) in 3 ml Et2O was added a solution of I2 (24.0 mg, 0.0946 mmol) in 4 ml Et2O. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 10 ml Et2O, filtered through Celite and the solution was cooled to -30 ºC. 2.2c (10 mg, 8.0%) was isolated 25  after several days. Anal. Calcd. for C28H34N2CrI: C, 58.24; H, 5.93; N, 4.85. Found: C, 57.85; H, 6.20; N, 4.82. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 431 (4200), 577 (620).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4CF3](I) (2.2d). To a solution of 2.1d (115 mg, 0.222 mmol) in 6 ml Et2O was added a solution of I2 (45.0 mg, 0.18 mmol) in 4 ml Et2O. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml Et2O, filtered through Celite and the solution was cooled to -30 ºC. 2.2d (48.3 mg, 34.0%) was isolated after several days. Anal. Calcd. for C29H33N2F3CrI: C, 53.96; H, 5.15; N, 4.34. Found: C, 54.04; H, 5.44; N, 4.21. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 431 (5600).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4(OMe)](CH3) (2.3a). To a solution of 2.1a (200 mg, 0.416 mmol) in Et2O was added a solution of MeI (0.12 ml, 2.0 M in MTBE, 0.24 mmol). After the solution been stirred for 1 h, MeMgI (0.10 ml, 3.0 M in Et2O, 0.33 mmol) was added, causing the solution to become dark purple. After stirring for 20 h, excess 1, 4-dioxane (0.3 ml, 3.3 mmol) was added and the reaction was stirred for an additional 2 h. The solvent was removed in vacuo, the residue was extracted with 15 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 2.3a (170 mg, 82.0%) was isolated after 2 days. Anal. Calcd. for C30H39N2OCr: C, 72.70; H, 7.32; N, 5.65. Found: C, 72.50; H, 7.66; N, 5.52. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 417 (4600), 542 (1300).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4Me](CH3) (2.3b) Method A: To a solution of 2.1b (250 mg, 0.538 mmol) in 15 ml Et2O was added a solution of MeI (0.15 ml, 2.0 M in MTBE, 0.30 mmol). After the solution been stirred for 1 h, MeMgI (0.10 ml, 3.0 M in Et2O, 0.30 mmol) was added, causing the solution to become dark purple. After stirring for 20 h, excess 1, 4-dioxane (0.3 ml, 3.3 mmol) was added and the reaction was stirred for an additional 2 h. The solvent was removed in vacuo, the residue was extracted with 10 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 2.3b (67.0 mg, 26.0%) was isolated after several days.      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4Me](CH3) (2.3b) Method B: To a solution of 2.1b (86.0 mg, 0.185 mmol) in 10 ml THF was added a solution of MeI (0.10 ml, 2.0 M in MTBE, 0.20 mmol), followed by a solution of SmI2 (2.2 ml, 0.1 M in THF, 0.22 mmol). After the reaction had stirred for 3 h, the solvent was removed in vacuo, the residue was extracted with 5 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 2.3b (39.0 mg, 44.0%) was isolated after several days. Anal. Calcd. for C30H39N2Cr: C, 75.13; H, 8.20; 26  N, 5.84. Found: C, 74.98; H, 8.44; N, 5.49. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 417 (5700), 541 (1700).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H5](CH3) (2.3c). To a solution of 2.1c (200 mg, 0.444 mmol) in Et2O was added a solution of MeI (0.13 ml, 2.0 M in MTBE, 0.26 mmol). After the solution been stirred for 1 h, MeMgI (0.10 ml, 3.0 M in Et2O, 0.33 mmol) was added, causing the solution to become dark purple. After stirring for 20 h, excess 1, 4-dioxane (0.30 ml, 3.3 mmol) was added and the reaction was stirred for an additional 2 h. The solvent was removed in vacuo, the residue was extracted with 6 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 2.3c (50.0 mg, 24.0%) was isolated after several days. Anal. Calcd. for C29H37N2Cr: C, 74.81; H, 8.01; N, 6.02. Found: C, 75.20; H, 7.63; N, 6.21. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 417 (5100), 541 (1500).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4CF3](CH3) (2.3d) Method A: To a solution of 2.1d (200 mg, 0.386 mmol) in 15 ml Et2O was added a solution of MeI (0.11 ml, 2.0 M in MTBE, 0.22 mmol). After the solution been stirred for 1 h, MeMgI (0.10 ml, 3.0 M in Et2O, 0.33 mmol) was added, causing the solution to become dark purple. After stirring for 20 h, excess 1, 4-dioxane (0.30 ml, 3.3 mmol) was added and the reaction was stirred for an additional 2 h. The solvent was removed in vacuo, the residue was extracted with 7 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 2.3d (63.0 mg, 31.0%) was isolated after several days.      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4CF3](CH3) (2.3d) Method B: To a solution of 2.1d (70.0 mg, 0.135 mmol) in 10 ml THF was added a solution of MeI (0.075 ml, 2.0 M in MTBE, 0.15 mmol), followed by a solution of SmI2 (1.5 ml, 0.1 M in THF, 0.15 mmol). After the reaction had stirred for 3 h, the solvent was removed in vacuo, the residue was extracted with 5 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 2.3d (37.0 mg, 52.0%) was isolated after several days. Anal. Calcd. for C30H36N2F3Cr: C, 67.53; H, 6.80; N, 5.25. Found: C, 67.37; H, 7.06; N, 5.51. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 417 (5600), 542 (1600).       Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4(OMe)](Cl) (2.4a). A solution of n- BuLi (0.40 ml, 1.6 M in hexanes, 0.64 mmol) was added dropwise to a –78 ºC solution of DppNHC(Me)CHC(Me)NC6H4(OMe) (0.223 g, 0.612 mmol) in 15 ml THF, and the yellow solution was allowed to warm to room temperature and was stirred for 1 h. A solution of CpCrCl2(THF) (150 mg, 0.576 mmol) in 15 ml THF was added and the reaction was stirred at 27  room temperature for an additional 20 h. The solvent was removed in vacuo, the residue was extracted with a total of 10 ml hexanes and 10 ml CH2Cl2, filtered through Celite and the solution was cooled to -30 ºC. 2.4a (158 mg, 53.0%) was isolated after several days. Anal. Calcd. for C29H36N2OCrCl: C, 67.50; H, 7.03; N, 5.43. Found: C, 67.23; H, 7.33; N, 5.25. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 421 (8300), 582 (810).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4Me](Cl) (2.4b). A solution of n-BuLi (2.06 ml, 1.6 M in hexanes, 3.30 mmol) was added dropwise to a –78 ºC solution of DppNHC(Me)CHC(Me)NC6H4Me (1.15 g, 3.43 mmol) in THF, and the yellow solution was allowed to warm to room temperature and was stirred for 1 h. A solution of CpCrCl2(THF) (781 mg, 3.00 mmol) in THF was added and the reaction was stirred at room temperature for an additional 20 h. The solvent was removed in vacuo, the residue was extracted with a total of 10 ml hexanes and 5 ml CH2Cl2, filtered through Celite and the solution was cooled to -30 ºC. 2.4b (555 mg, 37%) was isolated after several days. Anal. Calcd. for C29H36N2CrCl: C, 69.66; H, 7.26; N, 5.60. Found: C, 69.30; H, 6.95; N, 5.33. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 421 (5100), 585 (480).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H5](Cl) (2.4c). A solution of n-BuLi (0.40 ml, 1.6 M in hexanes, 0.63 mmol) was added dropwise to a –78 ºC solution of DppNHC(Me)CHC(Me)NC6H5 (0.194 g, 0.581 mmol) in 15 ml THF, and the yellow solution was allowed to warm to room temperature and was stirred for 1 h. A solution of CpCrCl2(THF) (150 mg, 0.576 mmol) in 15 ml THF was added and the reaction was stirred at room temperature for an additional 20 h. The solvent was removed in vacuo, the residue was extracted with a total of 10 ml hexanes and 10 ml CH2Cl2, filtered through Celite and the solution was cooled to -30 ºC. 2.4c (69.0 mg, 25.0%) was isolated after several days. Anal. Calcd. for C28H34N2CrCl: C, 69.20; H, 7.05; N, 5.76. Found: C, 69.53; H, 7.39; N, 5.81. UV-vis (hexanes; λmax, nm (ε, M-1 cm-1)): 420 (6100), 585 (570).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4CF3](Cl) (2.4d). A solution of n- BuLi (0.40 ml, 1.6 M in hexanes, 0.63 mmol) was added dropwise to a –78 ºC solution of DppNHC(Me)CHC(Me)NC6H4CF3 (0.237 g, 0.588 mmol) in 10 ml THF, and the yellow solution was allowed to warm to room temperature and was stirred for 1 h. A solution of CpCrCl2(THF) (150 mg, 0.576 mmol) in 10 ml THF was added and the reaction was stirred at room temperature for an additional 20 h. The solvent was removed in vacuo, the residue was extracted with a total of 30 ml Et2O, filtered through Celite and the solution was cooled to -30 ºC. 28  2.4d (59 mg, 19%) was isolated after several days. Anal. Calcd. for C29H33N2F3CrCl: C, 62.87; H, 6.00; N, 5.06. Found: C, 62.50; H, 6.29; N, 5.33. UV-vis (hexanes; λmax, nm (ε, M-1 cm1)): 420 (3700), 584 (430).      Synthesis of CpCr[DppNC(Me)CHC(Me)NTol](Br) (2.5). To a solution of 2.1b (195 mg, 0.421 mmol) in 15 ml THF, PbBr2 (88.6 mg, 0.241 mmol) was added, causing the solution to become dark green. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 12 ml toluene, and then the dark green extracts were filtered through Celite and cooled to -30 °C to yield 2.5 (97.0 mg, 42.3%) in three different fractions. µeff = 3.85 µB (Evans, C6D6).Anal. Calcd for C29H36N2CrBr: C, 63.97; H, 6.66; N, 5.14. Found: C, 62.44; H, 6.39; N, 4.88. UV-vis (hexanes; λmax, nm (ε, M -1  cm -1 )): 426 (7100), 578 (560).       Synthesis of CpCr[DppNC(Me)CHC(Me)NTol](OTs) (2.6). 2.1b (465 mg, 1.00 mmol) and AgOTs (307 mg, 1.10 mmol) were combined as solids in a 100 ml Schlenk flask. After 30 ml of THF was added, the resulting dark green solution (red to transmitted light) was stirred for 20 h. The solvent was removed in vacuo, the residue was extracted with a 2:1 mixture of hexanes and CH2Cl2 and filtered through Celite. The resulting dark green solution was concentrated in vacuo and cool to –30 ºC to yield black crystals of 2.6 (458 mg, 72%) in two crops. µeff = 3.87 µB (Evans, C6D6). Anal. Calcd for C36H43N2CrSO3: C, 68.00; H, 6.82; N, 4.40. Found: C, 67.89; H, 7.18; N, 4.32. UV-vis (hexanes; λmax, nm (ε, M -1  cm -1 )): 417 (6400), 559 (430). Alternatively, 2.6 can be prepared from Cr(III) chloride complex 2.4b as follows. To a solution of 2.4b (555 mg, 1.10 mmol) in 20 ml THF, solid AgOTs (341 mg, 1.22 mmol) was added, causing the solution to become a dark green. After stirring for an additional 20 h, the solvent was removed in vacuo, the residue was extracted with 10 ml hexanes and 5ml CH2Cl2, and then the dark green extracts were filtered through Celite. The resulting dark green solution was concentrated in vacuo and cool to -30 ºC to yield black crystals of 2.6 (609 mg, 87%) in two crops.      Synthesis of CpCr[DppNC(Me)CHC(Me)NTol](Cy), (2.7). To a solution of 2.1b (102.5 mg, 0.221 mmol) in 20 ml THF, AgOTs (64.8 mg, 0.232 mmol) was added and stirred at room temperature for 20 h, during which time the colour changed to dark green. After filtration to remove the Ag byproduct, Mg(C6H11)2·1.1(1,4-dioxane) (30.9 mg, 0.108 mmol) was added, causing the solution to become dark purple. After stirring for an additional 20h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexanes, and the dark purple extracts were filtered through Celite and cooled to -30 °C to yield 2.7 (88.4 mg, 73.2%) isolated in five 29  different fractions. µeff = 3.95 µB (Evans, C6D6). Anal. Calcd for C35H47N2Cr: C, 76.75; H, 8.65; N, 5.11. Found: C, 75.86; H, 8.24; N, 5.62. UV-Vis (hexanes; λmax, nm (ε, M -1  cm -1 )): 397 (5800), 553 (1150).      Synthesis of CpCr[DppNC(Me)CHC(Me)NC6H4(OMe)](CH2Ph), (2.8). To a solution of 2.1a (130 mg, 0.271 mmol) in 5 ml ether, I2 (39.05 mg, 0.154 mmol) was added and stirred at room temperature for 2 h, during which time the colour changed to dark green. PhCH2MgCl (0.3 ml, 0.300 mmol) was added, causing the solution to become dark blue. After stirring for an additional 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexanes, and the dark blue extracts were filtered through Celite and cooled to -30 °C to yield 2.8 (71.5 mg, 40.6%) isolated in two different fractions. µeff = 3.89 µB (Evans, C6D6). Anal. Calcd for C36H43N2OCr: C, 75.63; H, 7.58; N, 4.90. Found: C, 75.60; H, 7.63; N, 5.02. UV-Vis (hexanes; λmax, nm (ε, M -1  cm -1 )): 408 (7500), 560 (1400). Synthesis of CpCr(TolNC6H4CHNDpp) (2.9). To a solution of Cp2Cr (109.6 mg, 0.602 mmol) in 7.5 ml THF, the aniline imine TolNHC6H4CHNDpp (251.42 mg, 0.680 mmol) and a catalytic amount of DBU (20 µl, 0.134 mmol) were added.  The resulting dark red solution was stirred for 20 h, after which the solvent was removed in vacuo.  The residue was extracted with 3 ml hexanes, filtered through Celite, and cooled to -35 °C.  Black crystals of 2.9 were isolated in two different fractions (131.0 mg, 44.8%).  Anal. Calcd for C31H34N2Cr: C, 76.52; H, 7.04; N, 5.76. Found: C, 76.14; H, 7.34; N, 5.80.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 373 (6400), 493 (3600). Synthesis of CpCr(TolNC6H4CHNDpp)(I) (2.10). To a orange-red solution of Cp2Cr (123 mg, 0.676 mmol) in Et2O, I2 (105 mg, 0.406 mmol) was added and stirring at room temperature for 5 min, immediate colour change from orange-red to yellow with precipitate. The TolNC6H4CHNDpp (211.14mg, 0.749mmol) was added after. The solution was left to stir for 20 h. The solvent was removed in vacuo, the residue was extracted with 10 ml of hexane and 5 ml of CH2Cl2 then filtered through the Celite, and cooled to -35 °C. Black crystals of 2.10 were isolated in three different fractions (156.8mg, 44.21%). UV-vis (Hexane; λmax, nm): 365, 517. Stoichiometric C–P bond-forming reactions with 2.7 a) Stoichiometric reaction of 2.7 with Ph2PCl. To a solution of CpCr[DppNC(Me)CHC(Me)NTol](Cy) (2.7) (14.5 mg, 0.0265 mmol) in an NMR tube with C6H6 (1 ml), Ph2PCl (5 µL, 0.027 mmol) was added and allowed to react at room temperature for 20 h, during which time the colour changed from dark purple to dark green. PPh3 standard (100 μL of a 0.275 M solution in benzene) was added to the tube prior to 31 P 30  NMR analysis. Ph2PCy (-3.4 ppm) was present in 94% yield, determined by comparison of relative integration values obtained after determination of the T1 relaxation. b) Stoichiometric reaction of 2.7 with P2Ph4 and CyBr. To a solution of CpCr[DppNC(Me)CHC(Me)NTol](Cy) (2.7) (8.9 mg, 0.0162 mmol) and P2Ph4 (5.2 mg, 0.014 mmol) in an NMR tube with C6H6 (1 ml), CyBr (2 µL, 0.0164 mmol) was added and allowed to react at room temperature for 20 h, during which time the colour changed from dark purple to dark green. PPh3 standard (100 μL of a 0.275 M solution in benzene) was added to the tube prior to 31 P NMR analysis. Ph2PCy (-3.4 ppm) was present in 96% yield, determined by comparison of relative integration values obtained after determination of the T1 relaxation. c) Stoichiometric reaction of 2.7 with Ph2PH and CyBr. To a solution of CpCr[DppNC(Me)CHC(Me)NTol](Cy) (2.7) (15.9 mg, 0.0289 mmol) in 0.5 ml C6H6, Ph2PH (7.5 µL, 0.043 mmol) and CyBr (11.6 µL, 0.095 mmol) were added and stirred at room temperature for 42 h. The solution was filtered into an NMR tube and PPh3 standard (150 μL of a 0.275 M solution in benzene) was added to the tube prior to 31P NMR analysis. Ph2PCy (-3.4 ppm) was present in 30% yield. d) Stoichiometric reaction of 2.1b with Ph2PH and CyBr. To a solution of CpCr[DppNC(Me)CHC(Me)NTol] (2.1b) (52.3 mg, 0.113 mmol) in 1 ml C6H6, Ph2PH (7.5 µL, 0.043 mmol) and CyBr (11.6 µL, 0.095 mmol) were added and allowed to stir at room temperature for 45 h. The solution was filtered into an NMR tube and PPh3 standard (150 μL of a 0.275 M solution in benzene) was added prior to 31P NMR analysis. Ph2PCy (-3.4 ppm) was present in 69% yield. Catalytic-in-Cr C–P bond-forming reactions      Entry 1: Catalytic reaction with 1 mol % 2.1b, Ph2PCl and CyBr. To a solution of CpCr[DppNC(Me)CHC(Me)NTol] (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%). CyBr (42 μL, 0.344 mmol), Mn powder (82.4 mg, 1.50 mmol), PbBr2 (1.2 mg, 0.0033 mmol), and Ph2PCl (51.0 μL, 0.276 mmol) were added. After stirring for 28 h, bipyridine (92.1 mg, 0.590 mmol) was added and the mixture was stirred for an additional 5 min. The solvent was removed in vacuo, the residue was extracted with benzene and filtered through Celite into a 10 ml volumetric flask. The flask was filled to the line with additional C6H6, and a 1.00 ml aliquot was transferred into an NMR tube. A 100 μL aliquot of a 0.275 M PPh3 standard solution in benzene was added to the tube prior to removal from the glovebox for 31 P NMR analysis. Ph2PCy (-3.4 ppm) was present in 79% yield, determined by comparison of relative 31  integration values obtained after determination of the T1 relaxation. Also present was P2Ph4 (12%) and Ph2PH (6%).      Entry 2: Dark catalytic reaction from (1 mol %) 2.1b, Ph2PCl and CyBr. The procedure described in Entry 1 was repeated with the following reactants (the reaction was conducted in a foil-wrapped vessel to exclude light): CpCr[DppNC(Me)CHC(Me)NTol] (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%), CyBr (42 μL, 0.344 mmol), Mn powder (72.2 mg, 1.40 mmol), PbBr2 (1.6 mg, 0.0044 mmol), Ph2PCl (51.0 μL, 0.276 mmol), bipyridine (76.5 mg, 0.490 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 73% yield.      Entry 3: Catalytic reaction with 1 mol % 2.1b, P2Ph4 and CyBr. The procedure described in Entry 1 was repeated with the following reactants: CpCr[DppNC(Me)CHC(Me)NTol] (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%), CyBr (42 μL, 0.344 mmol), Mn powder (69.4 mg, 1.26 mmol), PbBr2 (2.5 mg, 0.0068 mmol), and P2Ph4 (50.8 mg, 0.137 mmol), bipyridine (83.1 mg, 0.532 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 70% yield. Also present was P2Ph4 (13%) and Ph2PH (11%).      Entry 4: Catalytic reaction with 1 mol % 2.1b, Ph2PH and CyBr. The procedure described in Entry 1 was repeated with the following reactants: CpCr[DppNC(Me)CHC(Me)NTol] (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%), CyBr (80 μL, 0.655 mmol), Mn powder (81.0 mg, 1.47 mmol), PbBr2 (1.8 mg, 0.0049 mmol), Ph2PH (48.0 μL, 0.276 mmol), bipyridine (90.8 mg, 0.581 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 70% yield. Also present was P2Ph4 (14%) and Ph2PH (12%).      Entry 5: Catalytic reaction from (1 mol %) 2.1f, Ph2PCl and CyBr. The procedure described in Entry 1 was repeated with the following reactants: CpCr[(XylNCMe)2CH] (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%), CyBr (42 μL, 0.344 mmol), Mn powder (84.2 mg, 1.53 mmol), PbBr2 (1.5 mg, 0.0041 mmol), Ph2PCl (51.0 μL, 0.276 mmol), bipyridine (92.5 mg, 0.592 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 92% yield.      Entry 6: Catalytic reaction with 1 mol % 2.1f, P2Ph4 and CyBr. The procedure described in Entry 1 was repeated with the following reactants: CpCr[(XylNCMe)2CH] (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%), 32  CyBr (42 μL, 0.344 mmol), Mn powder (87.5 mg, 1.59 mmol), PbBr2 (2.7 mg, 0.0074 mmol), P2Ph4 (50.8 mg, 0.137 mmol), bipyridine (82.5 mg, 0.528 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 96% yield.      Entry 7: Catalytic reaction with (1 mol %) 2.1f, Ph2PH and CyBr. The procedure described in Entry 1 was repeated with the following reactants: CpCr[(XylNCMe)2CH] (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%), CyBr (80 μL, 0.655 mmol), Mn powder (88.8 mg, 1.61 mmol), PbBr2 (2.2 mg, 0.0060 mmol), Ph2PH (48.0 μL, 0.276 mmol), bipyridine (85.2 mg, 0.545 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 83% yield. Also present was P2Ph4 (13%).      Entry 8: Catalytic reaction with (1 mol %) 2.1b, Ph2PCl and CyBr (55 ºC 12h). To a solution of CpCr[DppNC(Me)CHC(Me)NTol] (1.6 mg, 0.0034 mmol, 1 mol%) and CyBr (42 μL, 0.344 mmol) in 3 ml THF (0.1 M), Mn powder (68.7 mg, 1.25 mmol), PbBr2 (3.4 mg, 0.0093 mmol), and Ph2PCl (50.5 μL, 0.273 mmol) were added. After stirring for 12 h under 55 ºC, bipyridine (79.4 mg, 0.508 mmol) was added and the mixture was stirred for an additional 5 min. The solvent was removed under reduced pressure, the residue extracted with benzene, and filtered over Celite into a 10 ml volumetric flask, which was filled to the line. A 1.0 ml aliquot was transferred to an NMR tube, and 100 μL of a 0.275 M PPh3 standard solution in benzene was added to the tube prior to 31 P NMR analysis. Ph2PCy (-3.4 ppm) was present in 66% yield, determined by comparison of relative integration values obtained after determination of the T1 relaxation.      Entry 9: Control reaction without added Cr catalyst. To a solution of Mn powder (6.6 mg, 0.12 mmol), PbBr2 (1.25 mg, 0.0034 mmol), and P2Ph4 (8.7 mg, 0.0235 mmol) in 1.0 ml THF, CyBr (7 μL, 0.0573 mmol) was added. After stirring for 24 h, the solvent was removed under reduced pressure, the residue extracted with C6D6, and filtered over Celite into an NMR tube. Only the P2Ph4 peak (-14.4ppm) was evident in the 31 P NMR spectrum.      Entry 10: Control reaction with Cp2Cr. The procedure described in Entry 1 was repeated with a reaction time of 24 h and the following reactants: Cp2Cr (1.0 ml of a 2.75 × 10 -3  M solution in THF, 0.00275 mmol, 1 mol%), CyBr (42 μL, 0.344 mmol), Mn powder (79.4 mg, 1.44 mmol), PbBr2 (1.5 mg, 0.0041 mmol), Ph2PCl 33  (51.0 μL, 0.276 mmol), bipyridine (73.4 mg, 0.470 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 47% yield.      Entry 11: Control reaction with 10 mol% ligands and no added Cr catalyst. The procedure described in Entry 1 was with a reaction time of 24 h and the following reactants: Li[DppNC(Me)CHC(Me)NTol] (9.8 mg, 0.0287 mmol, 10 mol%), NaCp (4.8 mg, 0.0269 mmol, 10 mol%), CyBr (42 μL, 0.344 mmol), Mn powder (91.5 mg, 1.66 mmol), PbBr2 (1.7 mg, 0.0046 mmol), Ph2PCl (51.0 μL, 0.276 mmol), bipyridine (79.6 mg, 0.510 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 32% yield. Also present was P2Ph4 (16%).      Entry 12: Control reaction with CrCl3. To a suspension of CrCl3 (4.32 mg, 0.0273 mmol, 10 mol%), Mn powder (92.5 mg, 1.68 mmol), and PbBr2 (2.2 mg, 0.0060 mmol) in 3 ml THF (0.1 M), CyBr (42 μL, 0.344 mmol) and Ph2PCl (51.0 μL, 0.276 mmol) were added. After stirring for 28 h, bipyridine (83.6 mg, 0.535 mmol) was added and the mixture was stirred for an additional 5 min. The solvent was removed under reduced pressure, the residue extracted with benzene, and filtered over Celite into a 10 ml volumetric flask, which was filled to the line. A 1.00 ml aliquot was transferred to an NMR tube, and 100 μL of a 0.275 M PPh3 standard solution in benzene was added to the tube prior to 31 P NMR analysis. Only the P2Ph4 peak (-14.4ppm) was evident in 80% yield, determined by comparison of relative integration values obtained after determination of the T1 relaxation. In another control experiment, Ph2PCl (50 μL, 0.271 mmol) was added to a suspension of Mn powder (118.7 mg, 2.158 mmol) in 2 ml THF. After stirring for 18 h, the solvent was removed in vacuo, the residue was extracted with C6D6 and filtered through Celite into an NMR tube. Only the P2Ph4 peak (-14.4ppm) was evident in the 31 P NMR spectrum.      Entry 13: Control reaction with SmI2. To a suspension of SmI2 (0.275 ml of a 0.1 M solution in THF, 0.0275 mmol, 10 mol%), Mn powder (73.2 mg, 1.33 mmol), and PbBr2 (1.7 mg, 0.0046 mmol) in 3 ml THF (0.1 M), CyBr (42 μL, 0.344 mmol) and Ph2PCl (51.0 μL, 0.276 mmol) were added. After stirring for 28 h, bipyridine (80.1 mg, 0.513 mmol) was added and the mixture was stirred for an additional 5 min. The solvent was removed in vacuo, the residue extracted with benzene, and filtered through Celite into a 10 ml volumetric flask, which was filled to the line. A 1.00 ml aliquot was transferred to an NMR tube, and 100 μL of a 0.275 M PPh3 standard solution in benzene was added to the tube prior to 31 P NMR analysis. Only the P2Ph4 peak (-14.4ppm) was evident in 34  86% yield, determined by comparison of relative integration values obtained after determination of the T1 relaxation.      Entry 14: Catalytic reaction with 2.1b, P2Ph4 and CyCl (55 ºC 24 h). To a solution of CpCr[DppNC(Me)CHC(Me)NTol] (12.4 mg 0.0267 mmol) and CyCl (42 μL, 0.354 mmol) in 3 ml THF (0.1 M), Mn powder (93.2 mg, 1.69 mmol), PbCl2 (1.7 mg, 0.0061 mmol), and P2Ph4 (50.8 mg, 0.137 mmol) were added. After stirring for 24 h at 55 ºC, bipyridine (93.2 mg, 0.597 mmol) was added and the mixture was stirred for an additional 5 min. The solvent was removed under reduced pressure, the residue extracted with benzene, and filtered through Celite into a 10 ml volumetric flask which was filled to the line. A 1.00 ml aliquot was transferred to an NMR tube, and 100 μL of a 0.275 M PPh3 standard solution in benzene was added to the tube prior to 31 P NMR analysis. Ph2PCy (-3.4 ppm) was present in 42% yield as well as the starting material P2Ph4 (-14.4 ppm) in 34%, determined by comparison of relative integration values obtained after determination of the T1 relaxation.      Entry 15: Catalytic reaction with 2.1b, P2Ph4 and CyCl (55 ºC 48 h). The procedure described in Entry 13 was repeated with the following reactants: CpCr[DppNC(Me)CHC(Me)NTol] (12.4 mg 0.0267 mmol), CyCl (42 μL, 0.354 mmol), Mn powder (88.2 mg, 1.60 mmol), PbCl2 (1.5 mg, 0.0054 mmol) and P2Ph4 (50.8 mg, 0.137 mmol) were used. After stirring for 48 h at 55 ºC, bipyridine (84.6 mg, 0.542 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene). Ph2PCy (-3.4 ppm) was present in 61% yield yield as well as the starting material P2Ph4 (14%).      Entry 16: Catalytic reaction with 2.1b, P2Ph4 and CyCl (55 ºC 72 h). The procedure described in Entry 13 was repeated with the following reactants: CpCr[DppNC(Me)CHC(Me)NTol] (12.4 mg 0.0267 mmol), CyCl (42 μL, 0.354 mmol), Mn powder (93.3 mg, 1.70 mmol), PbCl2 (1.1 mg, 0.0040 mmol) and P2Ph4 (50.8 mg, 0.137 mmol). After stirring for 72 h at 55 ºC, bipyridine (90.3 mg, 0.578 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene) were added. Ph2PCy (-3.4 ppm) was present in 80% yield.      Entry 17: Catalytic reaction with 2.1f, P2Ph4 and CyCl (55 ºC, 72 h). The procedure described in Entry 13 was repeated with the following reactants: CpCr[(XylNCMe)2CH] (11.6 mg 0.0275 mmol), CyCl (42 μL, 0.354 mmol), Mn powder (102.4 mg, 1.86 mmol), PbCl2 (1.7 mg, 0.0061 mmol) and P2Ph4 (50.8 mg, 0.137 mmol) were used. After stirring for 72 h at 55 ºC, bipyridine (82.5 mg, 0.528 mmol) and PPh3 standard (100 μL of 35  a 0.275 M solution in benzene) were added. Ph2PCy (-3.4 ppm) was present in 29% yield as well as the starting material P2Ph4 (59%).      Entry 18: Catalytic reaction with 2.1f, P2Ph4 and CyCl (55 ºC, 216 h). The procedure described in Entry 13 was repeated with the following reactants: CpCr[(XylNCMe)2CH] (11.6 mg 0.0275 mmol), CyCl (42 μL, 0.354 mmol), Mn powder (85.2 mg, 1.55 mmol), PbCl2 (1.5 mg, 0.0054 mmol) and P2Ph4 (50.8 mg, 0.137 mmol) were used. After stirring for 216 h at 55 ºC, bipyridine (87.5 mg, 0.560 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene) were added. Ph2PCy (-3.4 ppm) was present in 77% yield as well as the starting material P2Ph4 (12%) and Ph2PH (6%).      Entry 19: Catalytic reaction with 2.1f, P2Ph4 and CyCl (55 ºC, 312 h). The procedure described in Entry 13 was repeated with the following reactants: CpCr[(XylNCMe)2CH] (11.6 mg 0.0275 mmol), CyCl (42 μL, 0.354 mmol), Mn powder (85.4 mg, 1.55 mmol), PbCl2 (1.5 mg, 0.0054 mmol) and P2Ph4 (50.8 mg, 0.137 mmol) were used. After stirring for 312 h at 55 ºC, bipyridine (85.1 mg, 0.545 mmol) and PPh3 standard (100 μL of a 0.275 M solution in benzene) were added. Ph2PCy (-3.4 ppm) was present in 81% yield as well as the starting material P2Ph4 (14%).      Structure details: Single crystals were mounted on a glass fibers and measurements were made on a Bruker X8 APEX II diffractometer with graphite-monochromated Mo Kα radiation. The data was collected at a temperature of -100 ± 1 ˚C in a series of φ and ω scans in 0.50˚ oscillations. Data was collected and integrated using the Bruker SAINT software package6 and were corrected for absorption effects using the multi-scan technique (SADABS). 59  The data was corrected for Lorentz and polarization effects and the structure was solved by direct methods. 60  In complex 2.2b, the N(1)-C(17) fragment is disordered and was modeled in two orientations in roughly equal proportions. In complex 2.3d, the fluorine atoms of the CF3 group are disordered and were modeled in two orientations. Complex 2.4a crystallizes with disordered solvent in the lattice. No reasonable model of the solvent could be obtained; therefore, the PLATON/SQUEEZE program 61  was used to generate a second, solvent-free data set. In complex 2.4d, the Cp ring was disordered and subsequently modeled in two orientations. All non- hydrogen atoms were refined anisotropically except for C25, C26, C27, C28, and C29. The complex 2.6, the Cp ring appears to be disordered and was modeled in two orientations with restraints employed to maintain a regular Cp geometry. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in calculated positions but not refined. All 36  refinements were performed using the SHELXTL crystallographic software package of Bruker- AXS. 62  The molecular drawings were generated by the use of ORTEP-310 and POV-Ray. 37  Chapter 3: Synthesis and Reactivity of Cyclopentadienyl  Chromium Complexes Containing an N-heterocyclic Carbene Ligand      Cross-coupling catalysts based on first-row transition metals have demonstrated reactivity that is complementary to established palladium catalysts. 7a, 63  The synthesis of well-defined complexes has provided useful mechanistic details for the cross-coupling reactions of iron, 64  cobalt, 65  and nickel 66  catalysts. Almost 100 years ago, it was reported that biphenyl was generated in high yields when PhMgBr was treated with stoichiometric CrCl3. 67  While this discovery was recently noted as a significant early step towards modern catalytic reactions, 2 chromium complexes have received very little attention as potential cross-coupling catalysts.      Octahedral Cr(III) aryl complexes are known to form Cr(I) 6-arene species via a reductive elimination reaction that is typically preceded by ligand loss. 67,68  Substituted CpCr(6-arene) complexes constitute a relatively well-explored class of Cr(I) compounds. 69,70  The Cr(III)-Ph complexes are less prone to Cr-R homolysis due to the high energy of the phenyl radical. The inert nature of Cr(III)-Ph complexes make them useful for mechanistic studies. Even if the initial systems are too inert to provide useful catalytic activity, investigation of the individual reaction steps may suggest ways that ancillary ligands might be systematically varied to increase the rates of any turnover-limiting steps.  Cr L X Cr L R RMgX MgX2 Cr R Cr R L Cr L R Cr L X Ph-XPh-R  Figure 3.1. Hypothetical CpCr(L) catalyzed Kumada Cross-Coupling reaction 38       Figure 3.1 shows a hypothetical Kumada cross-coupling reaction catalyzed by CpCr(L) complexes. Alkylation of a CpCr(L)(Ph)(X) complex with an RMgX Grignard generates a Cr(III) bis(hydrocarbyl) compound. Loss of the neutral L ligand leads to reductive elimination of the 13-electron Cr(III) intermediate. Recoordination of the L group displaces the 6-arene interaction, facilitating the exchange of product for ArX substrate and subsequent oxidative addition. Cr NN Cl + Cr Cl N N Cr N N PhMgCl (3.1) H       N-heterocyclic carbenes have recently seen use as ancillary ligands in cross-coupling reactions catalyzed by first-row transition metals. 71  The synthetic route to relevant CpCr(L)(Ar)(X) complexes was based on the preparation of CpCr(Mes-NHC)(Ph), where Mes- NHC is the 2,4,6-Me3C6H2 substituted N-heterocyclic carbene shown in Equation 3.1. Tilset and co-workers prepared CpCr(Mes-NHC)Cl by protonolysis of Cp2Cr, and then alkylated with PhMgCl. 72  As shown in Figure 3.2, this work was extended by the Smith group to prepare Cr(II) and Cr(III) mesityl complexes. 26   CrCr N NCr Cl N N Cr Cl N N Cl Cr N N I 3.1 3.3 3.2 3.4  Figure 3.2. Synthesis of CpCr( i Pr-NHC)(X), Cr(II) complexes, where X = Cl (3.1), = Mes (3.3) and CpCr( i Pr-NHC)(X)(R), Cr(III) complexes, where X, R = Cl (3.2), X, R = I, Mes (3.4) 39       The reaction of 1,3-diisopropylimidazolium chloride with Cp2Cr forms the desired CpCr( i Pr- NHC)(Cl) Cr(II) complex 3.1. This complex has been used to yield the Mes complex 3.3 upon subsequent alkylation with MesMgCl and the dichloro complex 3.2 by PbCl2 or CHCl3 oxidation (Figure 3.2). The 1 H NMR spectrum (C6D6) of this type of complex shows broad peaks characteristic of a paramagnetic material. The downfield shifted imidazolin-2-ylidene ring protons and the upfield shifted i Pr methyl groups of the i Pr-NHC complexes are perhaps the most diagnostically useful resonances observed. For example, the 1 H NMR spectrum of 3.1 in C6D6, (400 MHz), shows two broad peaks at 17 ppm (12H, i Pr-CH3), and -11 ppm (2H, C2H2).      In this chapter, CpCr( i Pr-NHC)(Cl), 3.1, is used to synthesize both Cr(II) CpCr( i Pr-NHC)(R) and Cr(III) CpCr( i Pr-NHC)(Ar)2 complexes. The use of photolysis to induce NHC loss from CpCr( i Pr-NHC)(X)2 complexes is examined, and the stoichiometric reactivity of Cr(III) bis(aryl) compounds is investigated. While the cross-coupling reactivity proposed in Figure 3.1 remains to be achieved, the reactivity issues that appear to prevent it have been identified, and a Cr- catalyzed photolytic homocoupling reaction of ArMgX reagents has been developed.  3.1 Synthesis of CpCr(NHC)R, Cr(II)  Complexes.      Chromium alkyl complexes are widely used in ethylene polymerization and oligomerization reactions. 73  The important class of N-heterocyclic carbene ligands have also been used in these projects. Chelating-NHC chromium complexes have been reported by Theopold that were found to polymerize ethylene when activated by MAO or alkylaluminum reagents. 74  In our lab, the Cr(II) alkyl, CpCr( i Pr-NHC)(Me) 3.5 complex can be prepared by the alkylation reaction of MeMgI with Cr(II) precursor 3.1 (Figure 3.3). This alkyl complex shows high solubility in non- polar solvent hexane and the Cr(III) methyl complexes had low yield of products as crystalline solids (Figure 3.4). 40  Cr Cl N N 3.1 MeMgI NaN(SiMe3)2 PhMgCl Cr Me N N Cr N N N Si Si Cr N N 3.5 3.7 3.6 1/2 Mg(CH2CMe2Ph)2 Cr N N 3.8 Figure 3.3. Synthesis of CpCr( i Pr-NHC)(R), Cr(II) complexes, where R = Me (3.5), N(SMe3)2 (3.6), Ph (3.7), and CH2CMe2Ph (3.8).      An X-ray crystal structure was obtained for complex 3.5, which confirm its monomeric, two- legged piano stool geometry (Figure 3.4). The Cr-NHC and Cr-Me bond lengths in 3.5 are 2.1044(10) Å and 2.10066(12) Å, respectively, which are close to the corresponding Cr-NHC and Cr-C(Mes) bond lengths of 2.1245(13) Å and 2.0995(13) Å, respectively, found in the Cr(III) mesityl complex 3.3. The solution magnetic susceptibility of 3.5 (Evans method, 298K, µeff = 4.34 µB) is low but still in good agreement with that expected for a Cr(II) species with four unpaired electrons. The 1 H NMR spectrum of this complex shows two broad peaks at 18 ppm (12H, i Pr-CH3), and -8.5 ppm (2H, C2H2)).  41   Figure 3.4. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)(Me), Cr(II) methyl 3.5 complex, one of the isopropyl group of this compound was disordered and subsequently modeled in two orientations.      The salt metathesis reaction between CpCr( i Pr-NHC)(Cl), complex 3.1 and NaN(SiMe3)2 resulted in a dark pink solution, and crystallization from hexane solvent gave X-ray quality crystals of CpCr( i Pr-NHC)[N(SiMe3)2] (3.6) as shown in Figure 3.5. The complex crystallizes with two independent molecules in the asymmetric unit. The Cr-C( i Pr-NHC) bond length of 2.141(2) Å is longer than in Cr(II) methyl 3.5 or Cr(II) mesityl 3.3 because of the steric bulk of the bis-trimethylsilyl amide group. The Cr-N(amide) bond length of 2.0302(18)Å is similar to related Cr(bpy)[N(SiMe3)2]2 complex 4.3 (2.055(15) Å) but longer than Cr[N(SiMe3)2]2I2 (1.836 Å). 75  The solution magnetic susceptibility of 3.5 (Evans method, 298K, µeff = 4.69 µB) is in good agreement with that expected for a Cr(II) species with four unpaired electrons. 1 H NMR spectrum of this complex shows three broad peaks at 38ppm (18H, SiMe3), 14ppm (12H, i Pr- CH3), and -12ppm (2H, C2H2)).  42   Figure 3.5. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)[N(SiMe3)2], Cr(III) amide 3.6 complex, this complex crystallizes with two independent molecules in the asymmetric unit.       Reaction of Cr(II) chloro 3.1 with PhMgCl gave CpCr( i Pr-NHC)(Ph) complex 3.7, which was also characterized using X-ray crystallography (Figure 3.6), The Cr-C( i Pr-NHC) bond length of 2.0976(10) Å and the Cr-C(Ph) bond length of 2.0731(10) Å, both are shorter than related Cr(II) mesityl 3.3 (Cr-C( i Pr-NHC), 2.1245(13) Å and Cr-C(Mes), 2.0995(13) Å) and Tilset CpCr(Mes-NHC)(Ph) complex (Cr-C(Mes-NHC), 2.1232(13) Å and Cr-C(Ph), 2.089(2) Å) 26  due to the small CpCr( i Pr-NHC)Ph framework. The solution magnetic susceptibility of 3.7 (Evans method, 298K, µeff = 4.83 µB) is in good agreement with that expected for a Cr(II) species with four unpaired electrons. 1 H NMR spectrum of this complex shows three broad peaks at 23.5 ppm (3H, Ph), 19 ppm (12H, i Pr-CH3), and -9.5 ppm (2H, C2H2)).   Figure 3.6. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)(Ph), Cr(II) Phenyl 3.7 complex. 43       The bulky alkyl complex 3.8 can be readily prepared from the reaction of the Cp( i Pr-NHC)Cl, Cr(II) complex 3.1 with half equivalent of Mg(CH2CMe2Ph)2 reagent in THF. The resulting complex 3.8 were crystallized in non-polar Et2O solvent and showed very high yield. The same Cr(II) complex was also isolated when Cr(II) phenyl complex 3.7 was treated sequentially with AgOTf and Mg(CH2CMe2Ph)2, although the mechanism for the formation of 3.8 from this reaction remains unknown.   Figure 3.7. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)(CH2CMe2Ph), Cr(II) alkyl 3.8 complex.      The X-ray crystal structure that was obtained for complex 3.8 confirmed its monomeric, two- legged piano stool geometry (Figure 3.7). In the CpCr( i Pr-NHC)(CH2CMe2Ph) alkyl complex, the Cr-C( i Pr-NHC) bond is length of 2.096(2) Å, similar to the related Cr(II) methyl 3.5 complex. On the other hand, the Cr-C (neophenyl) bond length of 2.128(2) Å in 3.8 is longer than the related Cr(II) methyl 3.5 complex. The solution magnetic susceptibility of 3.8 (Evans method, 298k, µeff = 4.83 µB) is in good agreement with that expected for a Cr(II) species with four unpaired electrons. 1 H NMR spectrum of this complex shows two broad peaks at 20 ppm (12H, i Pr-CH3), 16 ppm (5H, alkyl), and -8 ppm (2H, C2H2)).  3.2 Synthesis of CpCr( i Pr-NHC)(Ar)2, Cr(III)  Complexes.       CpCr( i Pr-NHC)(Ph)2, 3.9, can be prepared in a two-step one-pot synthesis by reacting the Cr(II) chloride complex 3.1 sequentially with Ph2Mg(dioxane)x, followed by one-half equivalent of I2 in THF. As shown in Figure 3.8, the initial Cr(II) phenyl complex 3.7 reacts with PhMgCl to generate the proposed anionic intermediate [CpCr( i Pr-NHC)(Ph)2] - [MgX] + , A. Related anionic 44  aryl complexes of Cr(II) and Cr(III) are known. 76  If the proposed structure is correct, A would be expected to have a low-spin Cr(II) d 4  configuration, a very unusual electronic structure that is only observed for complexes with multiple strong field ligands. 77  Single-electron oxidation with iodine yields the neutral Cr(III) diphenyl complex 3.9. As expected based on this mechanism, 3.9 can also be prepared from CpCr( i Pr-NHC)(Ph) with one-half equivalent of PhMg(dioxane)x followed by iodine. The corresponding di(p-tolyl) complex 3.10 can be prepared by the same procedure using Mg(C6H4CH3)2(dioxane)x. Attempts to prepare either 3.9 or 3.10 by alkylation of the Cr(III) dichloro complex 3.2 were unsuccessful, leading to mixtures of products. A similar Cr(III) complex (LX)Cr(Ph)(Cl), where LX = dimethylindenyl-functionalized N-heterocyclic carbene ligand, was reported by Danopoulos and Hanton. Alkylation of this complex with excess MgPh2 was also unsuccessful, resulting in recovery of the starting materials. 73    Figure 3.8. Synthesis of CpCr( i Pr-NHC)(Ph)2, Cr(III) 3.9 Complexes.       Preliminary reactions indicate that alkyl and aryl halides can also be used as single electron oxidants to convert A to neutral CpCr( i Pr-NHC)(Ar)2 complexes. Treatment of a stock solution of in situ generated [CpCr( i Pr-NHC)(Tol)2] - [MgX] +  with different RX reagents gave a qualitatitive order of t BuBr > PhI > PhBr > 4-(MeO)C6H4Br > t BuCl for the relative rates of generation of neutral Cr(III) di(p-tolyl) complex 3.10. This order is consistent with the expected abilities of these organic halides to act as outer-sphere single electron transfer agents. 78  45    Figure 3.9. Thermal ellipsoid diagrams (50%) of CpCr( i Pr-NHC)(Ar)2, Cr(III) di-alkyl complexes, (3.9 (a)) and (3.10 (b)). The complex 3.10 crystallizes with two independent molecules in the asymmetric unit.      The molecular structures of 3.9 and 3.10 were determined by single crystal X-ray diffraction as shown in Figure 3.9. The Cr-C( i Pr-NHC) bond length of 3.9 and 3.10 were 2.1163(12) Å and 2.1135(18) Å respectively. The Cr-C(Ph) bond length of complex 3.9 were 2.1007(12) Å and 2.0767(13), the Cr-C(Tol) bond length of complex 3.10 were 2.0976(17) Å and 2.0768(18). An interesting point of this type of Cr(III) di-aryl complexes is that one of the Cr-C(Ar) bond is longer than the other Cr-C bond by 0.02 Å, which was also observed for CpCr(C6H4CH2NMe2)(Tol), a Cr(III) bis(aryl) complex (2.075(1)Å and 2.040(1)Å). In the solid state geometry, the two phenyl groups are in different positions due to their rotation, with the aryl group lying in approximately the same plane as the NHC ligand having the longer Cr-C bond, presumably due to steric repulsion. The Cr-C bonds in complexes 3.9 and 3.10 are longer than the related CpCr( i Pr-NHC)(Ph) Cr(II) complex 3.7 due to the increased steric repulsion, but are shorter than the Cr-Mes bond in 3.3 and the Cr-Ph bond in Tilset’s CpCr(Mes-NHC)(Ph) complex. 72  The solution magnetic susceptibility of 3.9 and 3.10 (Evans method, 298k, µeff = 3.44 µB and 3.24 µB) are both low but still consistent with a Cr(III) species with three unpaired electrons.   46  Table 3.1. Cr–C(NHC) Bond Lengths (Å) in CpCr(iPr-NHC)(R) Complexes (R =  CH3 (3.5), or Ph (3.7)) and CpCr( i Pr-NHC)(R2) Complexes (R =  Ph (3.9), or Tol (3.10)) and Cr–C (Å) R = Mesityl R =  CH3 R = CH2CMe2Ph R = Ph R =Tol Cr(II) 3.3 2.0995(13) 3.5 2.1066(12) 3.8 2.128(2) 3.7 2.0731(10) Cr(III)    3.9 2.1007(12)       2.0767(13) 3.10 2.0976(17)         2.0768(18) The differences in steric demands between CpCr(NHC)R and CpCr(NHC)R2 complexes can be determined by the Cr-C(NHC) bond lengths as shown in Table 3.1. The sterically hindered Cr(III) di-aryl complex 3.9 has Cr-C(NHC) bond lengths of 2.1007(12) Å and 2.0767(13) Å. These are longer than the corresponded less sterically hindered Cr(II) phenyl complexes 3.7, which has Cr- C(NHC) bond length of 2.0731(10) Å. For the Cr(II) complexes, The sterically hindered Cr(II) neophenyl complex 3.8 also has longer Cr-C(NHC) bond length of 2.128(2) Å, compared to other less sterically hindered Cr(II) aryl and alkyl complexes 3.3 and 3.5, which have Cr-C(NHC) bond lengths of  2.0995(13) Å and 2.1066(12) Å.  3.3 Photolysis of CpCr( i Pr-NHC)(X)2, Cr(III)  Complexes.      The evident stability of CpCr( i Pr-NHC)(Ar)2 complexes 3.9 and 3.10 prompted the investigation of photolysis reactions of CpCr( i Pr-NHC)(X)2 compounds. The X = Cl complex 3.2 proved useful for these studies, as light-induced dissociation of the NHC ligand in THF would generate CpCr(THF)Cl2, a stable complex with a distinctive UV-vis spectrum and known ligand substitution reactivity. For instance, even in THF, CpCr(THF)Cl2 reacts with [RNEt3]Cl (R = H, Et) to produce anionic [CpCrCl3] -  3.11, which was first reported by Fischer in 1963. 79  The crystal structure of 3.11 with a [HNEt3] +  counter cation is shown in Figure 3.10. Crystals of [HNEt3][CpCrCl3] were obtained from a reaction of CpCr(THF)Cl2 with NEt3 and PyCH2NHMes in an unsuccessful attempt to prepare CpCr(PyCH2NMes)(Cl) (see section 4.3).       47  Table 3.2. The results of photolysis reaction of CpCr( i Pr-NHC)(Cl)2, Cr(III)  Complex 3.2 with [NREt3]Cl (R = H, Et) entry Reactant Light Product(s) 1 [NEt4]Cl dark CpCr(NHC)(Cl)2 2 [HNEt3]Cl dark CpCr(NHC)(Cl)2 3 [NEt4]Cl 150W CpCr(NHC)(Cl)2 and [CpCrCl3] -  4 [HNEt3]Cl 150W [CpCrCl3] -       The results of the photolysis reactions are shown in Table 3.2. When samples were protected from light, UV-vis spectroscopy indicated that CpCr( i Pr-NHC)(Cl)2 did not react with 2 equivalents of either [NEt4]Cl or [HNEt3]Cl in THF over 20 hours. However, when the same reactions were performed under the light of a 150 W bulb, the reaction with [NEt4]Cl generated a mixture of NHC dichloro starting material 3.2 and trichloro anion 3.11, while [HNEt3]Cl produced just anion 3.11 and no unreacted starting material.   Figure 3.10. Photolysis of CpCr( i Pr-NHC)(Cl)2, Cr(III)  Complex 3.2 with NREt3 + Cl -  (R = H, Et). Thermal ellipsoid diagram (50%) of [HNEt3 + ][CpCrCl3 - ], Cr(III) compound [HNEt3][3.11]. 48       These results are rationalized by the reactions shown in Figure 3.10. Without photolysis, the Cr-NHC bond remains intact and no CpCr(THF)Cl2 is generated. Photolysis induces cleavage of the Cr-NHC bond, a reaction that is expected to be reversible. Jolly and coworkers previously prepared a Cr(III) NHC complex related to 3.2 by treatment of CpCr(THF)Cl2 with 1,3,4,5- tetramethylimidazol-2-ylidene in THF. 80  In the presence of two equivalents of [NEt4]Cl, the observed mixture of 3.2 and 3.11 after photolysis is attributed to competition between Cl -  and NHC for the Cr center. When [HNEt3]Cl is used, however, the neutral NHC is consumed by protonation with triethylammonium, driving the reaction to completion.  3.4 Stoichiometric Reactivity of CpCr(NHC)(Ar)2, Cr(III)  Complexes.      The photolysis reactions of CpCr( i Pr-NHC)(Cl)2 help explain the products observed when CpCr( i Pr-NHC)(Ph)2 is exposed to light. Exposure of Cr(II) diphenyl complex 3.9 in C6H6 to a 150 W light bulb for 20 h results in formation of CpCr( i Pr-NHC)(Ph), 3.7, identified by UV-vis, and biphenyl, identified by 1 H NMR (equation 3.2). The same reaction with Cr(III) ditolyl complex 3.10 in C6H6 generates 4,4’-dimethylbiphenyl and a new organochromium complex tentatively identified as CpCr( i Pr-NHC)(C6H4Me) by the similarilty of its UV-vis spectrum to the Cr(II) phenyl compound 3.7 (equation 3.2).       The absence of C6H5-C6H4Me product in the photolysis of 3.10 in C6H6 suggest the reaction does not proceed via photolytic homolysis of the Cr(III)-C6H4Me bond, since the p-tolyl radical would be expected to react with the C6H6 solvent. 78  Based on the CpCr( i Pr-NHC)Cl2 photolysis reactions discussed in Section 3.3 and the previously established mechanism for reductive elimination from Cr(III)-aryl complexes, our current hypothesis is that the first step is light- induced dissociation of the NHC ligand. This is followed by reductive elimination of Ar-Ar to form CpCr(I), presumably stabilized by an 6-arene interaction.69 This Cr(I) complex then subsequently reacts with the free NHC ligand and a second equivalent of CpCr( i Pr-NHC)(Ar)2. Aryl ligand transfer from Cr(III) diaryl to Cr(I) leads to two equivalents of the CpCr( i Pr- NHC)(Ar), Cr(II) complex in a comproportionation reaction. However, in contrast to the reactivity of the dissociated CpCrPh2 intermediate, Theopold reported a related yet stable five 49  coordinate (L2)CrPh3 complex, where L2 = bis(carbene). The strongly σ-donating chelating carbene ligand presumably stabilizes the five coordinate triphenyl Cr(III) complex with respect to reductive elimination. 81    Figure 3.11. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)[2-(CPh)2], 3.12 complex. The complex crystallizes with two independent molecules in the asymmetric unit.      In order to test the feasibility of the comproportionation step, a well-defined complex that could serve as a reactive source of the Cr(I) CpCr(NHC) fragment was required. As shown in equation 3.3, reduction of Cr(II) chloro 3.1 with magnesium in the presence of PhC≡CPh gives CpCr( i Pr-NHC)[2-(CPh)2], 3.12, which was characterized by X-ray crystallography (Figure 3.11). This reaction was inspired by the synthesis of Cp2Ti(BTMSA) from Cp2TiCl2, Mg, and Me3SiC≡CSiMe3 (bistrimethylsilylacetylene, or BTMSA). 82  Although Cp2Ti(BTMSA) complex has a structure more consistent with Ti(IV) bound to a [(CSiMe3)2] 2-  dianionic ligand, it readily loses the neutral alkyne and so has been widely used as a source of Cp2Ti(II). The structure of CpCr( i Pr-NHC)[2-(CPh)2], 3.12, has relatively short Cr-C(alkyne) bond lengths of 1.991(2) and 2.026(2) Å, and an elongated alkyne C-C bond length of 1.316(3) Å. These bond lengths indicate a stronger Cr-alkyne bond than in Cp*Cr(NDpp)[2-(CPh)2] with Cr-C(alkyne) bond lengths of 2.002(4) and 2.011(4), and a PhC-CPh bond length of 1.295(5). 20  The magnetic moment of 3.12 50  is µeff = 4.62 µB by Evans method, which is higher than expected for the three unpaired electrons predicted for either an intermediate spin Cr(I) alkyne complex or a Cr(III) compound.        CpCr( i Pr-NHC)[2-(CPh)2], 3.12, reacts rapidly with either CDCl3 or PbCl2 to form CpCr( i Pr- NHC)Cl2 by UV-vis spectroscopy, demonstrating that 3.12 can serve as a well-defined source of the CpCr( i Pr-NHC) fragment. As shown in equation 3.4, the alkyne complex also reacts rapidly with Cr(III) dichloro complex 3.1 to give CpCr( i Pr-NHC)Cl by comproprtionation. The corresponding reaction of 3.12 and CpCr( i Pr-NHC)(Ph)2 does not proceed at room temperature, but does give Cr(II) phenyl 3.9 upon heating (equation 3.5). The improved rate of CpCr( i Pr- NHC)X formation from CpCr( i Pr-NHC)[2-(CPh)2] and CpCr( i Pr-NHC)X2 for X = Cl compared to X = Ph is presumably due to the greater ease of formation of a chloro-bridged bimetallic intermediate in the comproportionation reaction. 83   51   Figure 3.12. Stoichiometric reaction for C-C bond homo-coupling      Reductive elimination from CpCr(C6H4CH2NMe2)(C6H4Me) was recently achieved by treatment with AgOTs. 84  Figure 3.12 shows related oxidatively-induced reductive elimination reactions of Cr(III) diaryl complexes 3.9 and 3.10. The clean formation of Ar-Ar products by reaction with CDCl3 in C6D6 is further evidence that these C-C bond forming reactions do not proceed via aryl-radicals, since chloroform readily undergoes both H-atom and Cl-atom abstraction reactions with aryl radicals. UV-vis spectroscopy demonstrated that the product of CDCl3 oxidation was Cr(III) dichloro complex 3.2. Similarly, Cr(III) diaryl complexes 3.9 or 3.10 react overnight with I2 in C6H6 to give the Ar-Ar products and an organochromium complex tentatively identified as CpCr( i Pr-NHC)(I)2 by comparison of its UV-vis spectra with that of the previously reported Cr(III) diiodo complex CpCr(Me-NHC)(I)2. 26   3.5 Homocoupling of ArMgX Catalyzed by CpCr( i Pr-NHC)(Cl), Cr(III)  Complexes.      Both photolysis and oxidation were used in Section 3.4 to induce reductive elimination of Ar- Ar from Cr(III) diaryl complexes 3.9 and 3.10. However, oxidants such as I2 or CDCl3 are not suitable for cross-coupling or homocoupling reactions with ArMgX due to their incompatibility with Grignard reagents. 85  Photolytic reaction conditions were therefore explored for reactions involving CpCr( i Pr-NHC) catalysts and TolMgBr reagents.      Recent work by Nakamura and co-workers has used FeCl3 to catalyze the homocoupling of RMgX to R-R using 1,2-dichloroalkanes as the stoichiometric oxidant. 86  We found that reaction of TolMgBr with 1,2-dichlorobutane and 10 mol% of CpCr( i Pr-NHC)(Cl), 3.1, under the light of a 150 W bulb gave the diaryl product in 86.5% isolated yield. 52    Figure 3.13. Hypothesis for the reaction mechanism of the catalyzed C-C bond homo-coupling reaction.      The proposed mechanism is shown in Figure 3.13. The Cr(II) chloro complex 3.1 reacts with TolMgBr to give first the Cr(II) aryl, then the anionic Cr(II) diaryl species, which is oxidized with 1,2-dichlorobutane to the neutral Cr(III) ditolyl complex 3.10. Photolysis of Cr(III) ditolyl induces NHC loss and reductive elimination. The Ar-Ar product is released from Cr by recoordination of the NHC ligand, followed by either oxidation with 1,2-dichlorobutane to Cr(II) chloro 3.1, or comproportionation with the neutral Cr(III) ditolyl compound, 3.10. However, instead of the anionic Cr diaryl species, the alternative intermediate can be anionic CpCrPh2 with Mg(NHC)(X) as counter ion. This complex also can reductive eliminate the Ar-Ar product then re-coordinate the NHC ligand.      As described in the experimental section, other organic halides such as t BuCl or ArI can be used in place of C4H8Cl2 as the stoichiometric oxidant in the catalytic reaction. Either Cr(II) chloro 3.1 and Cr(III) ditolyl 3.10 can be used as catalyst precursors. Both TolMgBr and halide- free Tol2Mg reagents were equally effective, but no Ar-Ar product is generated under the reaction conditions in the absence of chromium catalyst. 53       Consistent with the mechanism proposed in Figure 3.13, attempts to obtain cross-coupling products by use of TolMgBr and PhI still resulted in formation of the ditolyl organic product. Further studies will be required in order to improve the catalytic activity, remove the need for photolytic conditions, and extend this process to more useful cross-coupling reactions. 54  3.6 Experimental Section:      General Considerations: All reactions were carried out under nitrogen using standard Schlenk and glove box techniques.  Solvents were dried by using the method of Grubbs. Celite (Aldrich) was dried overnight at 120 °C before being evacuated and then stored under nitrogen. Iodine was purified by sublimation, PbCl2 (Aldrich, 98%) was dried at 120 ºC prior to use. NaCp (2.0M in Et2O), CrCl2 (99% anhydrous), CrCl3 (anhydrous), NaN(SiMe3)2, 1,4-dioxane (anhydrous), MeMgI (3.0 M in Et2O), PhMgCl (2.0 M in Et2O), TolMgBr (0.5 M in Et2O), PhCCPh (98%), HNEt3Cl, NEt4Cl and 1,2-dichorobutane (98%) were purchased from Aldrich and used as received.  Compounds 3.1, 3.2, 3.3, 3.4, 26  CpCr2, 87  CpCr(THF)Cl2, 88  and 1,3- diisopropylimidazolium chloride ( i Pr-NHC·HCl), 89  were prepared according to literature procedures. 1,3-diisopropylimidazolium chloride was also washed with acetone and dried prior to use. 72  The dialkyl magnesium reagents: Mg(CH2CMe2Ph)2 ∙ x(1,4-dioxane), Mg(Ph)2 ∙ x(1,4- dioxane), and Mg(Tol)2 ∙ x(1,4-dioxane) were also prepared according to the literature procedures. 58b,c      UV-vis spectroscopic data were collected on a Varian Cary 100 Bio UV-visible or a Shimadzu UV 2550 UV-vis spectrophotometer in hexanes solution in a specially constructed cell for air-sensitive samples: a Kontes Hi-Vac Valve with PTFE plug was attached by a professional glassblower to a Hellma 10 mm path length quartz absorption cell with a quartz-to-glass graded seal. Elemental analyses were performed by Guelph Chemical Laboratories, Guelph, ON, Canada or by the UBC Department of Chemistry microanalytical services. 1 H NMR spectra were recorded on a Varian Mercury Plus 400 spectrometer in CDCl3 with chemical shifts referenced to the solvent peak.      Synthesis of CpCr( i Pr-NHC)(Me) (3.5). To a solution of CpCr( i Pr-NHC)(Cl) (29.8 mg, 0.0978 mmol) in 10 ml THF, MeMgI (0.04 ml, 3.0 M in Et2O, 0.1 mmol) was slowly added and led to a rapid colour change from purple to dark brown. After stirring at room temperature for 20 h, 1,4-dioxane (0.12 ml, 1.7 mmol) was added, resulting in the immediate formation of a large quantity of white precipitate. After stirring for an additional 1 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexanes then filtered through Celite, and cooled to – 35 °C. Dark brown crystals of 3.5 were isolated in one fraction (17.5 mg, 62.9%). (Evans, C6D6): µeff = 4.34 µB. 1 H NMR (C6D6, 400 MHz): δ 18 (12H, i Pr-CH3), -8.5 (2H, C2H2)). Anal. Calcd for C15H24N2Cr: C, 63.36; H, 8.51; N, 9.85. Found: C, 61.19; H, 8.52; N, 9.50. UV-vis (Hexane; λmax, nm (ε, M -1 cm -1 )): 372 (890), 405 (640), 487 (360). 55       Synthesis of CpCr( i Pr-NHC)[N(SiMe3)2] (3.6). To a solution of CpCr( i Pr-NHC)(Cl) (49.5 mg, 0.162 mmol) in 15 ml THF, NaN(SiMe3)2 (33.6 mg, 0.183 mmol) was added and led to a rapid colour change from purple to pink. After stirring at room temperature for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexane then filtered through Celite, and cooled to –35 °C. Dark brown crystals of 3.6 were isolated in four fractions (50.1 mg, 71.8%). (Evans, C6D6): µeff = 4.69 µB.  1 H NMR (C6D6, 400 MHz): δ 38 (18H, SiMe3), 14 (12H, i Pr-CH3), -12 (2H, C2H2)). Anal. Calcd for C20H39N3CrSi2: C, 55.90; H, 9.15; N, 9.77. Found: C, 55.52; H, 9.50; N, 9.69. UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 504 (290).      Synthesis of CpCr( i Pr-NHC)(Ph) (3.7). To a solution of CpCr( i Pr-NHC)(Cl) (50.1 mg, 0.160 mmol) in 10 ml THF, PhMgCl (0.1 ml, 2.0 M in Et2O, 0.10 mmol) was slowly added and led to a rapid colour change from purple to orange brown. After stirring at room temperature for 20 h, 1,4-dioxane (0.20 ml, 2.3 mmol) was added, resulting in the immediate formation of a large quantity of white precipitate. After stirring for an additional 1 h, the solvent was removed in vacuo, the residue was extracted with 3 ml Et2O then filtered through Celite, and cooled to 35 °C. Dark brown crystals of 3.7 were isolated in three fractions (52.9 mg, 93.1%). (Evans, C6D6): µeff = 4.83 µB 1 H NMR (C6D6, 400 MHz): δ23.5 (3H, Ph), 19 (12H, i Pr-CH3), -9.5 (2H, C2H2)). Anal. Calcd for C20H26N2Cr: C, 69.34; H, 7.56; N, 8.08. Found: C, 66.12; H, 7.27; N, 7.93. UV-vis (Et2O; λmax, nm (ε, M -1 cm -1 )): 362 (1700), 444 (290).      Attempted synthesis of CpCr( i Pr-NHC)(Ph)(CH2CMe2Ph). To a solution of CpCr( i Pr- NHC)(Ph) (20.7 mg, 0.060 mmol) in 20 ml Et2O, AgOTf (19.2 mg, 0.075 mmol) was added and stirring for 4 h. The suspension was filtered through Celite, and the insoluble residue was washed with additional 10 ml Et2O. The Mg(CH2CMe2Ph)2 ∙ 1.85 (1,4-dioxane) (24.2 mg, 0.064 mmol) was added to the Cr(III) reaction, causing the solution to become brown yellow. After stirring 20 hr, the solvent was removed in vacuo, the residue was extracted with 3 ml hexanes, filtered through Celite and the solution was cooled to –35 ºC. 3.8 (5.6 mg, 23.2%) was crystallized, as characterized by X-ray crystallography.      Synthesis of CpCr( i Pr-NHC)(CH2CMe2Ph) (3.8). To a solution of CpCr( i Pr-NHC)(Cl) (50.1 mg, 0.16 mmol) in 10 ml THF, (CH2CMe2Ph)2Mg∙ 1.85 (1,4-dioxane)  (36.4 mg, 0.10 mmol) was slowly added and led to a rapid colour change from purple to brown yellow. After stirring at room temperature for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml Et2O then filtered through Celite, and cooled to –35 °C. Dark brown crystals of 3.8 were isolated in three fractions (54.0 mg, 81.8%). (Evans, C6D6): µeff = 4.83 µB.  1 H NMR 56  (C6D6, 400 MHz): δ20 (12H, i Pr-CH3), 16 (5H, alkyl), -8 (2H, C2H2)). Anal. Calcd for C24H34N2Cr: C, 71.61; H, 8.51; N, 6.96. Found: C, 71.21; H, 8.38; N, 6.81. UV-vis (Et2O; λmax, nm (ε, M-1cm-1)): 355 (1300), 465 (310).      Synthesis of CpCr( i Pr-NHC)(Ph)2 (3.9). To a solution of CpCr( i Pr-NHC)(Cl) (50.6 mg, 0.17 mmol) in 10 ml THF, The (Ph)2Mg∙ 2.74 (1,4-dioxane) (76.8 mg, 0.18 mmol) was added with stirring for 20 h, during which time the colour changed to dark brown yellow. I2 (23.2 mg, 0.09 mmol) was added to the reaction, causing the solution to become orange yellow. After stirring 20 hr, the solvent was removed in vacuo, the residue was extracted with 6 ml Et2O, filtered through Celite and the solution was cooled to –35 ºC. Yellow crystals 3.9 were isolated in three fractions (35.2 mg, 50.6%). (Evans, C6D6): µeff = 3.44 µB. 1 H NMR (C6D6, 400 MHz): δ9 (12H, iPr-CH3), -8.4 (2H, C2H2). Anal. Calcd for C26H31N2Cr: C, 73.73; H, 7.38; N, 6.61. Found: C, 65.94; H, 6.94; N, 5.38. UV-vis (Et2O; λmax, nm (ε, M -1 cm -1 )): 366 (870), 408 (800), 491 (480).      Synthesis of CpCr( i Pr-NHC)(Tol)2 (3.10). To a solution of CpCr( i Pr-NHC)(Cl) (49.8 mg, 0.163 mmol) in 10 ml THF, The Mg(Tol)2 ∙ 1.70 (1,4-dioxane) (64.2 mg, 0.182 mmol) was added and stirred for 20 h, during which time the colour changed to dark brown yellow. I2 (23.1 mg, 0.09 mmol) was added to the reaction, causing the solution to become orange yellow. After stirring 20 hr, the solvent was removed in vacuo, the residue was extracted with 6 ml Et2O, filtered through Celite and the solution was cooled to –35 ºC. Yellow crystals 3.10 were isolated in three fractions (48.3 mg, 67.6%). (Evans, C6D6): µeff = 3.24 µB. 1 H NMR (C6D6, 400 MHz): µeff = δ 10.5 (12H, i Pr-CH3), -13 (2H, C2H2). Anal. Calcd for C28H35N2Cr: C, 74.47; H, 7.81; N, 6.20. Found: C, 58.76; H, 6.74; N, 4.05. UV-vis (Et2O; λmax, nm (ε, M -1 cm -1 )): 385 (860), 505 (400).      Synthesis of CpCr( i Pr-NHC)(Tol)2 (3.10) with different oxidants. To a solution of CpCr( i Pr-NHC)(Cl) (10.0 ml of 4.49 x 10 -3 M solution in THF), The Mg(Tol)2 ∙ 1.70 (1,4- dioxane) (18.4 mg, 0.0520 mmol) was added and stirring for 20 h, during which time the colour changed to dark brown yellow. Different oxidants (PhI, PhBr, 4-(MeO)C6H4Br, t BuBr, and t BuCl) were added separately to five of 1 ml THF solution, causing the solution to become orange yellow. UV-vis of 3.10 was used to see the relative rates of completion, which gives the order ( t BuBr > PhI > PhBr > 4-(MeO)C6H4Br > t BuCl).      Synthesis of [HNEt3 + ][CpCrCl3 - ], [HNEt3 + ][3.11] Method A: To a solution of CpCr(THF)Cl2 (10.2 mg, 0.0392 mmol) in 3 ml of THF, HNEt3 + Cl -  (6.2 mg, 0.045 mmol) was 57  added and stirred for 20 h, during which time solution colour become dark purple-blue. The solution was characterized by UV-vis (THF; λmax, nm): 668, 523, as compound [HNEt3 + ][3.11].      Method B: To a solution of CpCr( i Pr-NHC)(Cl)2 (10.1 mg, 0.0297 mmol) in 10 ml of THF, HNEt3 + Cl -  (8.72 mg, 0.063 mmol) was added and transferred to an air-tight UV-visible cell then placed in front of a 150 W bulb for 20 h, during which time solution colour become dark purple blue. The solution was characterized by UV-vis (THF; λmax, nm): 668, 523, as compound [HNEt3] + [3.11].      Same reaction was prepared without photolysis, however no reaction occured      Synthesis of [NEt4]  +  [CpCrCl3]  - , [NEt4]  +  [3.11]  -  Method A: To a solution of CpCr(THF)Cl2 (2.6 mg, 0.01 mmol) in 3 ml of THF, NEt4 + Cl -  (3.3 mg, 0.020 mmol) was added and stirred for 20 h, during which time solution colour become dark purple blue. The solution was characterized by UV-vis (THF; λmax, nm): 530, 682, as compound [NEt4]  +  [3.11]  - .      Method B: To a solution of CpCr( i Pr-NHC)(Cl)2 (3.4 mg, 0.01 mmol) in 10 ml of THF, NEt4 + Cl -  (3.3 mg, 0.02 mmol) was added and transferred to an air-tight UV-visible cell then placed in front of a 150 W bulb for 20 h, during which time solution colour still purple. The solution were characterized by UV-vis (THF; λmax, nm): 579, 669, as mixture of CpCr(iPr- NHC)Cl2 and compound [NEt4]  +  [3.11]  - .      Same reaction were prepared without photolysis, however no reaction occurs      Synthesis of CpCr( i Pr-NHC)2-(CPh)2 (3.12). To a solution of CpCr( i Pr-NHC)(Cl) (50.1 mg, 0.164 mmol) in 10 ml THF, Mg (7.2 mg, 0.296 mmol) and PhCCPh (33.6 mg, 0.197 mmol) were added. After stirring at room temperature for 20 h, the solution colour changed to dark red. The solvent was then removed in vacuo, the residue was extracted with 3 ml Et2O then filtered through Celite, and cooled to –35 °C. Dark red crystals of 3.11 were isolated in two fractions (26.4 mg, 36.62%). (Evans, C6D6): µeff = 4.62 µB. 1 H NMR (C6D6, 400 MHz): δ 17 (12H, i Pr- CH3), -14.8 (2H, C2H2). Anal. Calcd for C28H31N2Cr: C, 75.14; H, 6.98; N, 6.26. Found: C, 73.54; H, 6.72; N, 6.11. UV-vis (Et2O; λmax, nm (ε, M -1 cm -1 )): 453 (940), 541 (780).      Stoichiometric C-C bond-forming reactions with 3.9 or 3.10      Method A by photolysis: Placed a solution of CpCr( i Pr-NHC)(Tol)2 (9.3 mg, 0.21 mmol) in 4 ml C6H6 in an air-tight UV-visible cell then placed in front of a 150 W bulb for 20 h, during which time solution colour become yellow. The solvent was then removed in vacuo, the residue was extracted with 1 ml C6D6, The solution was then transferred to an air-tight J. Young NMR tube. Bi-toluene product was characterized by 1 H NMR (C6D6, 400 MHz): δ 7 (m, 8H, Ar-H), 2 58  (s, 6H, CH3). The solution was characterized by UV-vis (THF; λmax, nm): 444, as CpCr( i Pr- NHC)Tol, Cr(II) compound.      Method B by oxidization: To a solution of CpCr( i Pr-NHC)(Tol)2 (10.1 mg, 0.22 mmol) in 1 ml C6D6, CDCl3 (1.8 µL, 0.022 mmol) was added and stirred at room temperature for 20 h. The solution was then transferred to an air-tight J. Young NMR tube. Bi-toluene product was characterized by 1 H NMR (C6D6, 400 MHz): δ 7 (m, 8H, Ar-H), 2 (s, 6H, CH3). The solution was characterized by UV-vis (THF; λmax, nm): 581, it is same as CpCr(Me-NHC)(Cl)2, Cr(III) compound.      Method C by oxidization: To a solution of CpCr( i Pr-NHC)(Tol)2 (9.6 mg, 0.21 mmol) in 1 ml C6D6, I2 (7.8 mg, 0.0307 mmol) was added and stirred at room temperature for 20 h. The solution was then transferred to an air-tight J. Young NMR tube. Bi-toluene product was characterized by 1 H NMR (C6D6, 400 MHz): δ 7 (m, 8H, Ar-H), 2 (s, 6H, CH3). The solution was characterized by UV-vis (THF; λmax, nm): 360, it is same as CpCr(Me-NHC)(I)2, Cr(III) compound.      Catalytic-in-Cr C–C bond-forming reactions Table 3.3. Chromium-Catalyzed Synthesis of Ar-Ar. ArMgX   +   Alkyl halides 10 mol % Cr cat. THF Ar-Ar  entry Cr cat. MgX Alkyl halide yield A 3.1 TolMgBr 1,2-dichlorobutane 86.5% B 3.10 Tol2Mg Me3CCl 86.8% C 3.10 2 TolMgBr Tol-I 73.2% D 3.1 TolMgBr Ph-I 61.2% E none TolMgBr Tol-I 0%  a) Catalytic reaction with 10 mol % 3.1, TolMgBr and 1,2-dichorobutane.      To a solution of CpCr( i Pr-NHC)(Cl) (9.9 mg, 0.033 mmol, 10 mol%) in 3 ml of C6H6, TolMgBr (1.45 ml, 0.5 M in Et2O, 0.72 mmol) and 1,2-dichorobutane (82 µL, 0.72 mmol) were added and transferred to an air-tight UV-visible cell then placed in front of a 150 W bulb for 80 h, during which time solution colour become yellow. The solvent was then removed in vacuo, 59  the residue colour become dark-purple and was extracted with 10 ml hexane then filtered through a silica column. The solvent was removed in vacuo again. White crystals of bi-toluene (57.1 mg, 86.5%) were isolated. b) Catalytic reaction with 10 mol % 3.10, Tol2Mg and Me3CCl.      The procedure described in a) was repeated with the following reactants: CpCr( i Pr- NHC)(Tol)2 (9.6 mg, 0.021 mmol, 10 mol%), Mg(Tol)2 ∙ 1.70 (1,4-dioxane) (88.4 mg, 0.251 mmol) and Me3CCl (25 µL, 0.226 mmol). White crystals of bi-toluene (21.2 mg, 86.8%) were isolated. c) Catalytic reaction with 10 mol % 3.1, TolMgBr and Tol-I.      The procedure described in a) was repeated with the following reactants: CpCr( i Pr-NHC)(Cl) (10.6 mg, 0.035 mmol, 10 mol%), TolMgBr (1.45 ml, 0.5 M in Et2O, 0.73 mmol) and Tol-I (78.7 mg, 0.36 mmol). White crystals of bi-toluene (55.9 mg, 84.0%) were isolated. d) Catalytic reaction with 10 mol % 3.1, TolMgBr and Ph-I.      The procedure described in a) was repeated with the following reactants: CpCr( i Pr-NHC)(Cl) (9.8 mg, 0.032 mmol, 20 mol%), TolMgBr (0.72 ml, 0.5 M in Et2O, 0.36 mmol) and Ph-I (36.5 µL, 0.33 mmol). White crystals of bi-toluene (20.1 mg, 61.2%) were isolated. e) Catalytic reaction with no catalyst, TolMgBr and Tol-I.      The procedure described in a) was repeated with the following reactants: TolMgBr and Tol-I were used. However, no product isolated or observed in 1 H-NMR spectrum.       3.6 X-ray Crystallography. Protocols were identical to those reported in Chapter 2. One of the isopropyl groups of compound 3.5 was disordered and subsequently modeled in two orientations. Compound 3.9, 3.10, and 3.12 crystallize with two independent molecules in the asymmetric unit. Compound 3.12 was calculated with the SHELXL instruction 'ACTA 50'. 60  Chapter 4: Synthesis and Reactivity of Chromium Complexes with Diimine, Pyridine-imine and Bipyridine Ligand-based radicals      In Chapter 2, the rates of oxidative addition of organic halides were shown to increase when the steric bulk of the CpCr(nacnac) fragment was decreased by modifying the N-aryl substituents. Another strategy to reduce the steric hindrance of the bidentate monoanionic ligand would be to decrease its bite angle by moving to the diimine ligand framework. In figure 4.1 complexes two pairs of paramagnetic chromium complexes with β-diketiminate and diimine ligands. In 1998, Theopold and co-workers reported the synthesis and structure of Cr[(PhNCMe)2CH](THF)2(Cl)2, A which has a N-Cr-N angle of 91.7º. 90  Although the structure of the Xyl-substituted variant was not included in the subsequent communication of its synthesis, its bite angle is expected to be quite similar. In 2008, the closely related Cr(III) complex Cr[(XylNCMe)2](THF)2(Cl)2, B was reported. 91  While the overall geometry at the Cr center closely resembled the nacnac complex, the N-C-N angle in the diimine compound was only 79.68(6)º presumably due to the removal of the methane CH group from the ligand backbone. The N-aryl substituents in the diimine complex are almost co-planar, in contrast to the nacnac ligand whose N-aryl groups form a V- shape surrounding the metal. As will be shown in this chapter, the same structural pattern is evident for CpCr(nacnac) and CpCr(diimine) complexes, such as 2.1e and 4.1, respectively.   Figure 4.1. Comparison of Cr nacnac and Diimine Complexes      Despite their structural similarities, however, the β-diketiminate and diimine ligands in Figure 4.1 have very different electronic structures. The nacnac ligands are obtained by a condensation 61  reaction of acetylacetone with substituted anilines, and obtain their negative charge by deprotonation. The negative charge on the diimine ligand is not due to loss of H + , but comes from single electron transfer to the LUMO π* ligand orbital. As shown in Figure 4.2, diimines are “redox active ligands” that can bind to metals as neutral (L2) spin-paired molecules or as monoanionic (LX) ligand-based radicals. 8  When coordinated to octahedral Cr(III) centers, the unpaired electron in the diimine LUMO π* orbital is usually strongly antiferromagnetically coupled to the unpaired d-electrons on the metal. Since the LUMO is π-bonding with respect to the C-C bond in the ligand backbone, the monoanionic LX ligand has a C-C bond order of 1.5. X-ray structures can readily distinguish between neutral L2, monoanionic LX, and dianionic X2 forms of diimine or bipyridine ligands by the ligand backbone C-C distance. The characteristic values for L2, LX and X2 states for diimine and bipyridine ligands are shown in Figure 4.2. 92    Figure 4.2. MO diagram of diimine π system 62        Before the reactivity of paramagnetic chromium diimine complexes like 4.1 with alkyl halides can be explored, strategies to synthesize these mixed-ligand compounds have to developed. Over 30 years ago, tom Dieck prepared a neutral chromium bis(α-diimine) complex as a pre-catalyst for isoprene dimerization by reaction of Cr(acac)3 with two equivalents of the neutral diimine and three equivalents of sodium metal. 93  Most of the recent syntheses of chromium α-diimine complexes follow this route, reacting the neutral α-diimine with a reducing metal and a suitable chromium precursor, typically CrCl2, CrCl3, or CrCl3(THF)3. 94  In 2008, Wieghardt and co-workers prepared an octahedral Cr(III) complex with a single diimine radical LX ligand by sequential reaction of the neutral diimine (DppNCMe)2 with first Na and then with Cr(acac)3. 95  However, the strategy of ligand reduction follow by salt metathesis proved not to be a general route to neutral Cr(acac)2(diimine) complexes, as the use of loss sterically demanding N-aryl substituents led to loss of all three acac ligands and isolation of the Cr(II) bis(LX) complex. 95       An alternative synthetic strategy was employed by Theopold and co-workers to prepare the Cr(III) diimine complex B shown in Figure 4.1. Direct reaction of neutral (XylNCMe)2 with CrCl2 in THF results in single electron transfer from Cr(II) to the diimine LUMO π* to give the radical anionic diimine LX ligand antiferromagnetically coupled to the Cr(III) center. 91  In a preliminary reaction to explore this strategy, I reacted (XylNCMe)2 with Cr( t Bu-acac)2  ( t Bu- acac = 2,2,6,6-tetramethylheptan-3,5-dionate), a Cr(II) precursor that is soluble in Et2O, unlike the polymeric Cu( t Bu-acac)2. As shown in Figure 4.3, the X-ray crystal structure of the Cr(III) octahedral complex Cr( t Bu-acac)2[(XylNCMe)2], 4.2, was highly disordered due to co- crystallization of the enantiomers of the chiral-at-Cr complex, a phenomenon that has been recently observed for related octahedral t Bu-acac complexes. 96  This initial reaction was followed up by Addison Desnoyer in his Honours B.Sc. thesis project in 2010-2011, reacting Cr( t Bu- acac)2 with bipyridine, and other pyridine-imine ligands to offer complexes such as 4.3. 97   63   Figure 4.3. The reactions of Cr( t Bu-acac)2 with diimine and bipyridine. Thermal ellipsoid diagrams (50%) of octahedral Cr( t Bu-acac)2[(XylNCMe)2],  4.2.      In this chapter, the reactions of bipyridine, pyridine imine, and diimine ligands with CrX2 precursors are explored in order to evaluate the strengths and limitations of this synthetic strategy. The single-electron transfer reactivity of complexes like 4.1 then are investigated to determine if the characteristic Cr(II)/Cr(III) chemistry shown for CpCr(nacnac) complexes like 2.1e is even feasible in the presence of ligand-based anionic diimine LX radicals.  4.1 Reactions of bipyridine with Cr(II) Precursors.      Direct addition of neutral 2,2’-bipyridine (bpy) to chromocene at room temperature in THF provides the Cr(III), Cp2Cr(bpy) complex 4.4 (Equation 4.1). Unlike its highly reactive heavier group 6 congeners, chromocene typically only forms weak bonds with neutral donor ligands due to the relative stability of the S = 1 state for Cp2Cr. 98  The stability of Cp2Cr(bpy) complex 4.4 can be attributed to single electron transfer from Cr(II) to bpy to generate an inert Cr(III) center that is antiferromagnetically coupled to a bipyridine radical anion, thus retaining the overall S = 1 state with µeff = 2.92 µB in solution (Evans, C6D6). 64        As shown in Figure 4.4, complex 4.4 has an (5-Cp)(1-Cp)Cr(bpy) structure99 with Cpy-Cpy (1.425(2) Å) and Cr-N (1.9825(13) Å and 1.9684(12) Å) bond lengths consistent with the bipyridine ligand in the radical anionic oxidation level. The disparate binding modes of the cyclopentadienyl rings in 4.4 are similar to those observed for neutral (5-Cp)(3-Cp)V(bpy), a complex demonstrated to have a bpy radical anion in an extensive computational study of the electronic structures of organometallic bipyridine complexes. The geometric parameters of 4.4 also resemble those observed for Cp*Cr(bpy)(CH2Ph), an S = 1 complex prepared by Theopold and co-workers by bpy-induced alkyl radical loss from Cp*Cr(III) bis(benzyl) precursors. 100    Figure 4.4. Thermal ellipsoid diagram (50%) of (-5-Cp)(-1-Cp)Cr(bpy) complex 4.4.      The reaction of Cr[N(SiMe3)2]2(THF)2 with bipyridine results in the dark purple complex Cr[N(SiMe3)2]2(bpy), 4.5, (Equation 4.2) which has two intense absorbances at 509 nm and 372 nm in Et2O, each with ɛ ≈ 1300 M –1 cm –1 (Figure 4.6). 101  In contrast to the S = 1 spin state observed for 4.3, and 4.4, complex 4.5 has µeff = 4.62 µB in solution (Evans, C6D6) consistent with an S = 2 spin state. As shown in Figure 4.5, Cr[N(SiMe3)2]2(bpy) exhibits a distorted square planar geometry in the solid state, with Npy–Npy–NSi–NSi dihedral angles of 20.0º and 20.7º for the two independent molecules of 4.5 in the unit cell. The relatively long Cpy–Cpy (1.481(3) Å 65  and 1.485(3) Å) and Cr–Npy (between 2.14 and 2.16 Å) distances are consistent with a neutral bipyridine ligand. 102    Figure 4.5. Thermal ellipsoid diagram (50%) of Cr(II) bis-amide complex 4.5. The complex crystallizes with two independent molecules in the asymmetric unit.      For Cr[N(SiMe3)2]2(bpy), the absence of single electron transfer from Cr(II) upon bipyridine coordination can be accounted for using concepts from ligand field theory. Due to the steric bulk of the N(SiMe3)2 ligands, 4.5 is stable as a monomeric complex with coordination number of four. This allows the compound to adopt the electronically favorable (albeit sterically distorted) square planar geometry shown in Figure 4.5 while retaining a high spin Cr(II) S = 2 spin state. 103  The same electronic structure is observed for Cr(Mes)2(bpy), where Mes (mesityl) = 2,4,6- Me3C6H2, which also has a slightly-distorted square planar geometry, an S = 2 spin state, and a neutral bipyridine ligand. 104  This is in contrast to octahedral complexes such as 4.2 and 4.3, where electron transfer to the bpy LUMO π* is energetically favorable compared to either the high spin (S = 2, t2g 3  eg 1 ) or low spin (S = 1, t2g 4  eg 0 ) electron configurations for Cr(II). Although both Cr[N(SiMe3)2]2(bpy) and Cr(Mes)2(bpy) would be expected to have very electron-rich Cr(II) centers, neither complex exhibits any structural evidence for the bipyridine acting as a π-acceptor ligand.  66   Figure 4.6. UV-vis spectrum of Cr(bpy)[N(SiMe3)2]2, Cr(II) complex 4.5 (6.14 x 10 -4  M in Et2O).       After I had synthesized the bpy complexes 4.4 and 4.5, their utility as protonolysis precursors was evaluated by Addison Desnoyer. In his preliminary experiments, Addison noted that Cp2Cr(bpy) 4.4 reacted more quickly with 2,2,6,6-tetramethylheptane-3,5-dione than Cr[N(SiMe3)2]2(bpy) 4.5. This reactivity trend is the opposite of that observed for the corresponding bpy-free complexes, since Cr[N(SiMe3)2]2(THF)2 reacts rapidly with alcohols, while the synthesis of [CpCr(µ-OtBu)]2 from Cp2Cr and t BuOH requires hours of refluxing in toluene. Attempts to synthesize CpCr(bpy)(OCH i Pr2) by reaction of Cp2Cr with bpy and 2,4- dimethylpent-3-ol instead resulted in Cr[OCH( i Pr)2]2(bpy)2, 4.6 (equation 4.3). Complex 4.6 was also readily prepared by the reaction of Cr[N(SiMe3)2]2(THF)2 with two equivalents each of bpy and HOCH i Pr2, as shown in equation 4.4.      The X-ray crystal structure of 4.6 clearly shows that the two bipyridine ligands in Cr[OCHiPr2]2(bpy)2 are each in different oxidation levels. One bpy has the Cpy-Cpy (1.425(2) Å) and Cr-N (2.0040(15) Å and 2.0525(15) Å) bond lengths conststent with a radical anion, while 67  the second is neutral, with longer Cpy-Cpy (1.474(3) Å) and longer Cr-N (2.0928(15) Å and 2.1276(15) Å). A similar pattern was observed recently by Wieghardt and co-workers for Cr( t Bu-bpy)2(I)2, who noted that other [Cr(bpy)3] 2+  and Cr(bpy)2(X)2 derivatives previously described as examples of low-spin Cr(II) undoubtedly have S = 1 configurations that instead are the result of antiferromagnetic coupling of Cr(III) with the unpaired electron of a bpy radical anion. 77  Interestingly, the structure of a related Mo(O i Pr)2(bpy)2 complexes has two radical bpy anions with Cpy-Cpy of 1.425(4) Å and 1.424(4) Å, and so is Mo(IV) d 2 . 105     Figure 4.7. Thermal ellipsoid diagram (50%) of Cr(III) bis-alkoxide complex 4.6.      As shown in Figure 4.8, the intended product of a reaction of CpCr( i Pr-NHC)Cl, 3.1, with Na( t Bu-bpy) was CpCr( i Pr-NHC)( t Bu-bpy). Instead, loss of NaCp produced Cr( i Pr-NHC)( t Bu- bpy)2, 4.7 (Figure 4.9). The overall geometry of 4.7 is trigonal bipyramidal, with a bpy N atom at each axial site and the i Pr-NHC ligand equatorial. Since complex 4.7 crystallizes with one-half molecule residing on a two-fold axis of rotation, the two t Bu-bpy ligands are identical. The Cpy- Cpy bond length of 1.405(2) Å is between the ranges observed for radical monoanionic LX (1.43 68  Å) and dianionic X2 (1.38 Å) bpy ligands. This could be interpreted as 4.7 being a Cr(III) complex, with the three total electrons being delocalized evenly over both t Bu-bpy ligands. Alternatively, 4.7 may have a static Cr(NHC)(LX)(X2) electronic structure as shown in Figure 4.8, but the crystallographically-imposed symmetry results in the apparent equivalence of the two t Bu-bpy ligands with a Cpy-Cpy bond length between that expected for LX and X2 forms. A similarly ambiguous structure was recently reported by Theopold and Wieghardt for Cr(bpy)2(O2CMe)2, a complex closely related to 4.6 but with identical bpy ligands. 106  This is consistent with the magnetic moment of 2.64 µB (Evans), corresponding to the S = 1 spin state of Cr(III) coupled to the single unpaired electron on the two bpy ligands.   Figure 4.8. Synthesis of Cr( i Pr-NHC)(  t Bu-bpy)2, 4.7 69   Figure 4.9. Thermal ellipsoid diagram (50%) of Cr( i Pr-NHC)( t Bu-bpy)2 complex 4.7. This Complex crystallizes with one half-molecule residing on a two-fold axis of rotation. One of the t- butyl groups in the complex 4.7 is disordered and was subsequently modeled in two orientations.  4.2 Synthesis of Cr(III) and Cr(II) Diimine  Complexes.      Three new CpCr(α-diimine)(Cl) complexes were prepared by the two step synthetic route illustrated in equation 4.5. Octahedral Cr(III) intermediates bearing ligand centered radicals were generated as previously reported by Theopold and co-workers, 91  by adding a neutral diimine ligand to a suspension of CrCl2 in THF. Treatment of the brown dichloro intermediates with NaCp followed by recrystallization from hexanes gave the CpCr[(ArNCR)2](Cl) complexes (4.8a: Ar = 2,6- i Pr2C6H3 (Dpp), R = H; 4.8b: Ar = 2,6-Me2C6H3 (Xyl), R = Me; 4.8c: Ar = 2,4,6- Me3C6H2 (Mes), R =Me) in moderate yields as shown in equation 4.5.  70   Figure 4.10. Thermal ellipsoid diagrams (50%) of Cr(III) chloride complexes, (4.8a (a)) and (4.8b (b)).      The UV-vis spectra of complexes 4.8a-c were similar to the corresponding Cr(III) chloro complexes with β-diketiminate ligands, CpCr[(ArNCMe)2CH](Cl) with Ar = Dpp, 23 Xyl, 29  or Mes, 28  consisting of a high intensity peak between 430 nm and 410 nm, and a lower intensity peak at ~575 nm. However, complexes 4.8b and 4.8c also exhibit an additional low intensity peak at ~650 nm not observed in the β-diketiminate complexes.      The molecular structures of 4.8a and 4.8b were determined by single crystal X-ray diffraction, and are shown in Figure 4.10. The X-ray structures display bond lengths for the diimine ligands and structural parameters at the Cr centers consistent with radical anionic ligands bound to Cr(III). The structures of 4.8a and 4.8b are analogous to the related Cr(III) β-diketiminate species, although the decreased bite angles in 4.8a and 4.8b and the absence of backbone methyl groups in 4.8a both lead to reduced steric conflict between the bulky N-aryl substituents and the chloro ligand. Significantly, the α-diimine C-C bond lengths (1.387 Å for 4.8a and 1.397 Å for 4.8b) and C-N bond lengths (between 1.339 Å and 1.349 Å for both complexes) are all in the narrow ranges reported by Theopold and co-workers for anionic radical diimine ligands bound to Cr(II) and Cr(III). 91  The magnetic moments observed for complexes 4.8a and 4.8b are between 2.72 and 2.95 µB, consistent with Cr(III) antiferromagnetically coupled to a diimine radical anion.      Chemical reduction of 4.8a could potentially reduce either the metal center from Cr(III) to Cr(II), the radical anionic ligand to the spin-paired dianionic enediamide, or both. As shown in equation 4.6, reaction of CpCr[(DppNCH)2](Cl) with Zn in THF followed by recrystallization from hexanes gives CpCr[(DppNCH)2], 4.1, which has a magnetic moment of 3.78 µB (Evans). 71     Figure 4.11. Thermal ellipsoid diagram (50%) of Cr(II) complex 4.1.  Only one of the six independent molecules in the unit cell is shown.        The X-ray crystal structure of 4.1 (Figure 4.11) is quite similar to the known CpCr(II) β- diketiminate complex CpCr[(DppNCH)2CH]. The six independent molecules of 4.1 in the unit cell have average C-C (1.358 Å) and C-N (1.361 Å) bond lengths that are again consistent with a radical diimine ligand. 101  The UV-vis spectrum of 4.1 displays a very strong absorbance at 649 nm that is not observed in related CpCr(II) β-diketiminate compounds (Figure 4.12). This prominent feature is convenient for spectroscopic monitoring of single-electron Figure 4.12. UV-vis spectrum of complex 4.1 in hexane. 72  transfer reactions such as the chemical oxidation with PbCl2 that cleanly converts 4.1 back to the Cr(III) chloride 4.8a. The conservation of the ligand-based diimine radical as the oxidation state of the chromium is altered has previously been noted, 101  and is in contrast to the reactivity observed for iron-bound pyridinediimine where redox processes can involve both the metal and the ligand. 107       In Chapter 2, protonolysis reactions of Cp2Cr were used to prepare defined monomeric monocyclopentadienyl chromium derivatives. 26  Although chromocene reacts with t BuOH at elevated temperatures to give [CpCr(µ-OCMe3)]2, 55  the stable Cr2(OR)2 core remains intact even upon oxidation to Cr(III). 108  This renders [CpCr(µ-OCMe3)]2 unsuitable as a precursor to monomeric Cr-OR complexes. The synthesis of CpCr[(DppNCH)2](OCR2R’) 4.9a (R = Me, R’ = Ph) and 4.9b (R = i Pr, R’ = H) as shown in equation 4.7 was initially attempted to intercept a monomeric CpCr(OR) intermediate in the protonolysis of Cp2Cr. The optimized protonolysis reaction to give 4.9a and 4.9b proceeds in good yields at room temperature, but the precise mechanism remains unclear. The accelerating effect observed upon addition of a catalytic amount of base, as seen in other protonolysis reactions, 109  suggests initial attack of an anionic ligand at Cp2Cr to aid in cyclopentadienyl ligand displacement. 110  A similar effect may also be responsible for the halide-specific synthesis of CpM(L)X complexes by reaction of Cp2M with substituted imidazolium halides (M = Ni, Cr), 26,72,111  phosphonium chlorides (M = Ni), 112  or DBU·HCl (M = Cr; DBU = 1,8-diazabicyclo-[5.4.0]undec-7-ene). 26  73   Figure 4.13. Thermal ellipsoid diagrams (50%) of Cr(III) alkoxide complexes, (4.9a (a)) and (4.9b (b)).      The structures of the Cr(III) alkoxide complexes 4.9a and 4.9b were determined by X-ray diffraction and are shown in Figure 4.13. As in Cr(III) chloride 4.8a, the average C-C (1.386 Å) and C-N (1.343 Å) bond lengths of the α-diimine groups are consistent with a radical anionic ligand. 2  Interestingly, Cr(II) complex 4.1 does not react with dicumyl peroxide at room temp to give 4.9a, presumably due to the steric bulk of the NDpp substituents hindering the inner sphere electron transfer process.      Reversible transfer of hydrogen from multidentate ancillary ligands to bound substrates has been recently recognized as a valuable ligand design feature. 113  A bound secondary alkoxide ligand, Cr-OCHR2, could potentially transfer a hydrogen to one of the diimine carbon atoms in the ligand-based radical to generate a ketone and a non-radical amido imine ligand. Commercially available 2,4-dimethyl-3-pentanol is less sterically hindered than related alkoxide ligands recently employed in mid-valent chromium chemistry, 114  and the use of bulky and electron-donating R = i Pr substituents is expected to favour the H˙ transfer process both sterically and electronically. The Cr-OCH i Pr2 ligand in 4.9b was found to be disordered over two positions. In neither conformation was any interaction of the secondary alkoxide C–H bond with the ligand radical evident.  4.3 Synthesis of Pyridine-imine Cr(II)/Cr(III) X Complexes. 74       To explore the potential for intramolecular H-atom transfer further, a route to an authentic CpCr(II) complex with a redox innocent amido imine ligand was sought. Related pyridine amido ligands have been demonstrated to lead to highly selective Cr-based ethylene trimerization catalysts. 115  The attempted synthesis of CpCr(PyCH2NMes) (C) shown in equation 4.8 followed the route previously used for CpCr[(ArNCMe)2CH] complexes, by treating CrCl2 sequentially with first NaCp, and then the deprotonated ligand. 28        The crystalline product isolated from this reaction unexpectedly displayed a very intense peak at 704 nm (Figure 4.14), similar to that observed for the Cr(II) radical diimine complex 4.1. A single crystal X-ray structure was obtained that confirmed the overall connectivity, although there was extensive disorder in the structure. Despite the disorder and poor data quality, the structure was more consistent with the radical complex resulting from loss of a ligand H atom, CpCr(PyCHNMes), 4.10, than the initial target pyridine amido complex C.  Figure 4.14. UV-vis spectrum of complex 4.10 in hexane. 75   Figure 4.15. Thermal ellipsoid diagram (50%) of Cr(II) complex 4.10, the complex was crystallizes with two independent molecules in the asymmetric unit. All non-hydrogen atoms in compound 4.10 were refined anisotropically except for C1, C2, C3, C4, C6, C8, C24, C27, C28, C29, C41 and N3.      Radical pyridine-imine ligands have recently been investigated for first-row transition metals, 116  and for s-block and p-block elements. 117  An improved synthetic route to CpCr- (PyCHNMes), 4.10, is shown in Figure 4.16, consisting of Mn reduction of CpCrCl2(THF) in the presence of the neutral pyridine-imine ligand. The corresponding Cr(III) Cl complex 4.11 is obtained by sequential treatment of CrCl2 with PyCHNMes and NaCp. Oxidation of 4.10 with one-half equiv of I2 gives the Cr(III) iodide complex 4.12, which was structurally characterized by X-ray diffraction, as shown in Figure 4.17. Compared to the neutral pyridine-imine ligand, the relatively long imine C-N bond (1.344(2) Å) and short C-C bond (1.406(2) Å) in complex 4.12 are consistent with a singly reduced radical ligand. 116  As was observed with the α-diimine complexes, single electron transfer reactions of these complexes lead to Cr-based redox chemistry while the radical ligand retains its unpaired electron, antiferromagnetically coupled to the paramagnetic metal center.   76   Figure 4.16. Improved synthesis of pyridine-imine Cr(II) and Cr(III) complexes   Figure 4.17. Thermal ellipsoid diagram (50%) of Cr(III) Iodo complex 4.12.  4.4 Synthesis of Pyridine-imine Cr(III) Alkoxide Complex.      As shown in equation 4.09, the Cr(III) alkoxide complex CpCr(PyCHNMes)(OCMe2Ph), 4.13, was prepared by protonolysis of chromocene, analogous to the synthesis of 4.9. The X-ray crystal structure of 4.13 (Figure 4.18) revealed a typical Cr(III) half-sandwich CpCr(LX)X geometry. The key imine C-N (1.339(2) Å) and C-C (1.404(2) Å) bond lengths are once again indicative of a radical anionic ligand.      Initial attempts to prepare 4.13 in the absence of base by thermolysis at 80 ºC instead gave the thermal decomposition product (CpCr)2(µ-NMes)(µ- 2: κ2-MesNCHPy), 4.14, whose X-ray crystal structure is shown in Figure 4.18b. The mechanism for the formation of this bridging 77  imido 4.14 complex is unclear, but suggests that the pyridine imine ligand leads to decreased thermal stability compared to the β-diketiminate complexes in Chapter 2.   Figure 4.18. Thermal ellipsoid diagrams (50%) of Cr(III) alkoxide (4.13 (a)) and amide (4.14 (b)) complexes.  4.5 Synthesis of Pyridine-imine Cr(III) Methyl Complex.      Further indication of the unwanted reactivity of the pyridine imine is provided by the reaction 4.10 with iodomethane and MeMgI (equation 4.10). As described in Chapter 2, oxidation of CpCr(LX) compounds with MeI should give a mixture of Cr(III) iodo and Cr(III) methyl complexes, which is then converted to just the Cr(III) methyl product by alkylation with the methyl Grignard reagent. As shown in Figure 4.19, the product of this two-step process was alkylation of both the Cr(III) center and the ancillary ligand to form CpCr(PyCH(Me)NMes)(CH3), 4.15. Unintended alkylation of pyridine imine and related ligands can proceed by a variety of different mechanisms. Theopold and co-workers also recently observed ligand alkylation while investigating Cr(diimine) complexes. 118  The phenylenediamido complexes described in Chapter 5 were intended to be more robust than the diimine or pyridine imine compounds. 78    Figure 4.19. Thermal ellipsoid diagram (50%) of Cr(III) methyl complex 4.15.  4.6 Synthesis of Diimine Complexes with Cr-O and Cr-N Multiple Bonds.      Well-defined first row metal complexes with M-O or M-N metal ligand multiple bonds are of interest for numerous applications, including hydrogen atom abstraction, cyclization, azidation and hydroamination reactions. It is often assumed that the degree of radical character on the oxygen or nitrogen atom is an important factor in modulating this type of reactivity. 119  Recent Smith group PhD student Cory MacLeod investigated the reactivity of chromium oxo species generated by oxidation of CpCr[(ArNCMe)2CH] Cr(II) complexes with pyridine N-oxide, O2, or air. 8,  The presumed S = 1 CpCr[(ArNCMe)2CH](O) intermediate can be considered as a Cr(IV) complex with a dianionic oxo ligand, or as a Cr(III) species with an oxyl radical monoanion, as shown in Figure 4.20. The observed reactivity of the CpCr[(ArNCMe)2CH](O) complex for intermolecular and intramolecular H-atom abstraction, as well as the reversible reaction with the Cr(II) CpCr[(ArNCMe)2CH] precursor to form a Cr(III), µ-oxo dimer is consistent with at least partial radical character on the oxo ligand.      It was anticipated that replacing the nacnac ligand with (DppNCH)2 might permit the redox- active diimine to control the radical character of the oxo or nitride ligand. Oxygen atom transfer to CpCr[(DppNCH)2] would be expected to generate a S = ½ complex that could have either of the two electronic configurations shown, among other possibilities. Similarly, a neutral CpCr[(DppNCH)2](N) complex should be diamagnetic, with either a d 0  Cr(VI) center and a 79  dianionic enediamido X2 ligand, or with a radical monoanionic LX ligand antiferromagnetically coupled to the single d-electron of Cr(V).   Figure 4.20. Diimine Complexes with Cr-O and Cr-N Multiple Bonds      As shown in equation 4.11, reaction of CpCr[(DppNCH)2] 4.1 with pyridine N-oxide in THF gave a dark green solution, from which black crystals of 4.16 could be obtained after recrystallization from hexanes. Based on the magnetic moment (µeff = 2.66 µB, Evans) and the Cr-O bond length, (1.8261(17) Å), and the diimine C-C bond length (1.389(3) Å), 4.16 is a Cr(III) hydroxide complex with an S = 1 spin state and a monoanionic diimine ligand radical. The hydroxide is presumably obtained from hydrogen atom abstraction from an unknown source. Hydroxide 4.16 reacts with Me3SiCl to form the Cr(III) chloro complex 4.8a. 80    Figure 4.21. Thermal ellipsoid diagram (50%) of Cr(III) hydroxide complex 4.16, the complex was crystallized on a mirror plane, with one half-molecule in the asymmetric unit.       Oxidation of Cr(III) complex 4.1 with AgF or [Cp2Fe]BF4 produces CpCr[(DppNCH)2](F), 4.17 (Figure 4.22). Compared to the CpCr[(DppNCH)2](X) complexes where X = Cl, Br, or I, Cr(III), fluoro 4.17 displays increased solubility in non-polar solvents such as hexanes. The UV- vis spectrum of 4.17 displays a strong absorption band at 403 nm and two weak bands at 559 and 620 nm. The X-ray crystal structure displays a Cr-F bond length of 1.9348(13) Å, and the short Cr-N bonds (1.9627(11) Å) and diimine C-C bond (1.392(2) Å) consistent with a radical anionic ligand (Figure 4.23).   Figure 4.22. Synthesis of diimine Cr(III) fluoride complex 4.17, reduction of 4.17 by Gomberg’s dimer. 81   Figure 4.23. Thermal ellipsoid diagram (50%) of Cr(III) fluoride complex 4.17, the complex was crystallizes on a mirror plane, with one half-molecule in the asymmetric unit.      Like the Cr(III)-OH complex, reaction of CpCr[(DppNCH)2](F) with Me3SiCl results in Cr(III) chloro complex 4.8. Complex 4.17 can be cleanly reduced back to the Cr(II) precursor by treatment with Na, excess PhSiH3, or excess (Ph3C)2, Gomberg’s dimer.      As shown in Figure 4.24, Cr(III) fluoro 4.17 is also a precursor to Cr(III) azido compound 4.18 by treatment with TMSN3 for two days at 50ºC. This is an improvement over the initial synthetic route to CpCr[(DppNCH)2](N3), from Cr(III) chloro 4.8a and NaN3, which required 14 days at 50 ºC.   Figure 4.24. Synthesis of diimine Cr(III) azide 4.18, and Cr(V) nitrido 4.19 complexes. 82   Figure 4.25. Thermal ellipsoid diagrams (50%) of Cr(III) azide (4.18 (a)) and nitrido (4.19 (b)) complexes. The complex 4.18 crystallizes with 25% of CpCr[(DppNCH)2](Cl) molecule in the asymmetric unit, the complex 4.19 crystallize with 6% of CpCr[(DppNCH)2](N3) molecule in the asymmetric unit.      Photolysis reaction of compound 4.18 with a 150 W tungsten light bulb resulted in a colour change from dark green to purple. The resulting UV-vis spectrum of the crude reaction mixture contained a strong absorption band at 406 nm and two weak bands at 488 and 549 nm, which is different than the starting material. Crystallization of this product provided X-ray quality crystals of CpCr[(DppNCH)2](N), 4.19 nitrido complex. Compound 4.19 is air stable in both solid state and solution and is diamagnetic. The 1 H-NMR spectra of 4.19 in C6D6 is shown in Figure 4.26. The Cp singlet is at 5.4 ppm, the CH of the diimine backbone are at 6.4 ppm, and a multiplet for the Dpp aromatic protons are observed between 7.0 and 7.1 ppm. There are four sets of doublets for the i Pr methyl groups between 1.1 and 1.5 ppm, while the i Pr methine signal is at 2.7 ppm.  Figure 4.26. 1 H NMR for CpCr[(DppNCH)2](N) (4.19) nitrido Complex in C6D6 solvent. 83        As previously observed for CpCr(nacnac)(X) complexes, the efficient intermolecular packing of CpCr[(DppNCH)2](X) complexes leads to complexes that crystallize readily but are prone to co-crystallize with any unreacted starting material that may be present. This is a problem for both Cr azide 4.18, which co-crystallizes with 25% of CpCr[(DppNCH)2](Cl) (Figure 4.23a), and Cr nitride 4.19, which co-crystallizes with 6% of CpCr[(DppNCH)2](N3) (Figure 4.23b). The presence of Cr(III)-N3 in 4.19 is likely responsible for the Cr≡N bond length of 1.662(2) Å, 120  which is longer than the lengths of around 1.56 Å typically observed for Cr≡N bonds.121 A similar example was reported by Schrock and co-workers, in their synthesis of Cr(V) chloro, azide and Cr(VI) nitride complexes with sterically demanding terphenyl-substituted triamidoamine ligands. 122  In Schrock’s case, the Cr-N3 complex co-crystallized in a 65:35 ratio with the Cr-Cl precursor, and the Cr(N) co-crystallized in a 50:50 ration with the Cr-N3, with all three compounds crystallizing in the same space group with nearly identical structural parameters. The bond length of 1.64 Å determined for Schrock’s Cr≡N complex was also considered to be influenced by the presence of Cr-N3 in the unit cell. 122  Based on the diimine C- C bond length of 1.404(3) Å, the diamagnetic S = 0 spin state of 4.19 is attributed to the anionic diimine radical being antiferromagnetically coupled to the single unpaired d-electron on the Cr(V) d 1  center. 84  4.7 Experimental Section:      General Considerations: All reactions were carried out under nitrogen using standard Schlenk and glove box techniques.  Solvents were dried by using the method of Grubbs. Celite (Aldrich) was dried overnight at 120 °C before being evacuated and then stored under nitrogen. Iodine was purified by sublimation, and 2,4-dimethyl-3-pentanol (99%, Aldrich), DBU (1,8- diazabicyclo[5.4.0]undec-7-ene, 98%, Aldrich) and TMSN3 were freeze-pump-thaw degassed before use.  p-Toluenesulfonic acid monohydrate, 2-phenyl-2-propanol (97%), CrCl2 (99% anhydrous), CrCl3 (anhydrous), Zn (99% powder), Mn (99% powder), NaN(SiMe3)2, n-BuLi (1.6M in hexanes), NaCp (2.0M in THF), pyridine N-oxide (95%), AgF (99% powder), NaN3, 2,2′-bipyridine, and 1,4-dioxane (anhydrous) were purchased from Aldrich and used as received. (ArNCR)2, 123  PyCHNMes, 118  PyCH2NHMes, 124  TolNHC6H4CHNDpp, 125  CpCr2, 126  CpCr(THF)- Cl2. 127  Gomberg’s dimer (CPh3)2, 128  Cp2Fe + BF4, 129  and Cr[N(SiMe3)2]2(THF)2 114a, 130 were prepared according to the literature procedures.      UV-vis spectroscopic data were collected on a Varian Cary 100 Bio UV-visible or a Shimadzu UV 2550 UV-vis spectrophotometer in hexanes solution in a specially constructed cell for air-sensitive samples: a Kontes Hi-Vac Valve with PTFE plug was attached by a professional glassblower to a Hellma 10 mm path length quartz absorption cell with a quartz-to-glass graded seal. Elemental analyses were performed by Guelph Chemical Laboratories, Guelph, ON, Canada or by the UBC Department of Chemistry microanalytical services.      Synthesis of CpCr[(DppNCH)2] (4.1). To a solution of CpCr[(DppNCH)2]Cl (101.6 mg, 0.206 mmol) in 15 ml THF, Zn (26.3 mg, 0.402 mmol) was added and stirred at room temperature for 20 h, during which the colour changed from green to blue. The solvent was removed in vacuo, the residue was extracted with 1 ml hexanes then filtered through Celite, and cooled to -35 °C.  Dark green crystals of 4.1 were isolated in one fraction (55.4 mg, 58.7%). (Evans, C6D6): µeff = 3.78 µB.  Anal. Calcd for C31H41N2Cr: C, 75.42; H, 8.37; N, 5.67. Found: C, 75.55; H, 8.43; N, 5.70.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 406 (5500), 532 (1700), 649 (4800).      Synthesis of Cr[(XylNCMe)2]( t Bu-acac)2 (4.2). To a solution Cr( t Bu-acac)2 (98.1 mg, 0.234 mmol) in 15 ml Et2O, diimine [XylNCMe]2 (72.5 mg, 0.248 mmol) was added.  The resulting dark red solution was stirred for 20 h, after which the solvent was removed in vacuo. The residue was extracted with 7.5 ml of hexane, filtered through Celite, and cooled to -35 °C. Dark crystals 85  of 4.2 were isolated in two different fractions (133.2 mg, 79.9%). UV-vis (hexane; λmax, nm): 346, 458, 551, 664.      Synthesis of CpCr(bpy)1-Cp (4.4). To a solution of Cp2Cr (50.0 mg, 0..275 mmol) in 10 ml THF, 2,2’-bipyridine (48.5 mg, 0.311 mmol) was added.  The resulting dark red solution was stirred for 20 h, after which the solvent was removed in vacuo. The residue was extracted with 6 ml of Et2O, filtered through Celite, and cooled to -35 °C. Dark green crystals of 4.4 were isolated in three different fractions (62.7 mg, 67.5%).  (Evans, C6D6): µeff = 2.92 µB.  Anal. Calcd for C20H18N2Cr: C, 71.01; H, 5.36.; N, 8.28. Found: C, 70.56; H, 5.35; N, 8.21. Near-IR (Et2O; λmax, nm (ε, M-1cm-1)): 339 (3100), 448 (800), 650 (400), 996 (400). UV-vis (Et2O; λmax, nm (ε, M - 1 cm -1 )): 337 (3400), 444 (340).      Synthesis of Cr(bpy)[N(SiMe3)2]2 (4.5). To a solution of Cr[N(SiMe3)2](THF)2 (309.6 mg, 0.608 mmol) in 20 ml Et2O, 2,2’-bipyridine (97.4 mg, 0.624 mmol) was added. The resulting purple red solution was stirred for 20 h, after which the solvent was removed in vacuo. The residue was extracted with 5 ml hexanes and 5 ml Et2O, filtered through Celite, and cooled to 35 °C. Dark black crystals of 4.5 were isolated in two different fractions (143.9 mg, 45.4%). (Evans, C6D6): µeff = 4.62 µB. Anal. Calcd for C22H44N4Si4Cr: C, 49.96; H, 8.38.; N, 10.59. Found: C, 49.59; H, 8.30; N, 10.70. UV-vis (Et2O; λmax, nm (ε, M -1 cm -1 )): 372 (1300), 509 (1350).      Synthesis of Cr(bpy)2(OCH i Pr2)2 (4.6). To a solution of Cr[N(SiMe3)2](THF)2 (250 mg, 0.491 mmol) in 20 ml Et2O, 2,2’-bipyridine (164 mg, 1.05 mmol) was added. After stirring for 30 min, HOCH i Pr2 (150 µl, 1.07 mmol) was added. The resulting dark green solution was stirred for 20 h, after which the solvent was removed in vacuo. The residue was extracted with 10 ml hexanes and 10 ml Et2O, filtered through Celite, and cooled to -35 °C. Dark black crystals of 4.6 were isolated in two different fractions (245.6 mg, 84.1%). (Evans, C6D6): µeff = 2.67 µB. Anal. Calcd for C34H46N4CrO2: C, 68.66; H, 7.80.; N, 9.42. Found: C, 68.56; H, 7.89; N, 9.40. UV-vis (Et2O; λmax, nm (ε, M -1 cm -1 )): 352 (6200), 444 (2900), 665 (1600).      Synthesis of Cr( t Bu-bpy)2( i Pr-NHC) (4.7). To a solution of 4,4’-di-tert-butyl-2,2’-dipyridyl (92.7 mg, 0.345 mmol) in 3 ml of THF, Na (11.5 mg, 0.5 mmol) was added, resulting in an instant colour change to a dark purple. After stirring at room temperature for 2 h, the ligand solution was then added to the solution of CpCr( i Pr-NHC)Cl (3.1) (50.2 mg, 0.165 mmol) in 10 ml THF. The resulting dark brown red solution was stirred for 20 h, after which the solvent was removed in vacuo, the residue was extracted with 6 ml Et2O, filtered through Celite, and cooled 86  to -35 °C. Black crystals of 4.7 were isolated three fractions (28.5 mg, 23.45%). (Evans, C6D6): µeff = 3.49 µB. Anal. Calcd for C45H64N6Cr: C, 72.94; H, 8.71; N, 11.34. Found: C, 69.53; H, 9.10; N, 10.63. UV-vis (Et2O; λmax, nm): 328, 450, 536, 613, 710, 741.      Synthesis of CpCr[(DppNCH)2](Cl) (4.8a). To a suspension of CrCl2 (1.324 g, 10.76 mmol) in 30 ml THF, diimine (DppNCH)2 (3.79 g, 10.0 mmol) was added and stirred at room temperature for 20 h, during which time the colour changed from green to red.  NaCp (5.5 ml, 2.0 M in THF, 11.0 mmol) was then added, causing the solution to become dark green.  After stirring for an additional 20 h, the solvent was removed in vacuo, the residue was extracted with 80 ml hexanes, and the dark green extracts were filtered through Celite, and cooled to -35 °C. Black crystals of 4.8a were isolated in two different fractions (2.322 g, 43.5%). (Evans, C6D6): µeff = 2.75 µB.  Anal. Calcd for C31H41N2CrCl: C, 70.37; H, 7.81; N, 5.29. Found: C, 70.84; H, 7.98; N, 5.24.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 412 (8700), 567 (1300).      Synthesis of CpCr[(XylNCMe)2](Cl) (4.8b). To a suspension of CrCl2 (171 mg, 1.39 mmol) in 20 ml THF, diimine (XylNCMe)2 (405.7 mg, 1.387 mmol) was added and stirred at room temperature for 20 h, during which time the colour changed from green to red.  NaCp (0.80 ml, 2.0 M in THF, 1.6 mmol) was then added, causing the solution to become dark green.  After stirring for an additional 20 h, the solvent was removed in vacuo, the residue was extracted with 9 ml hexanes, and then the dark green extracts were filtered through Celite and cooled to -35 °C. Black crystals of 4.8b were isolated in three different fractions (351.3 mg, 56.8%).  (Evans, C6D6): µeff = 2.72 µB.  Anal. Calcd for C25H29N2CrCl: C, 67.48; H, 6.57; N, 6.29. Found: C, 68.06; H, 6.77; N, 6.13.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 430 (6200), 580 (1000), 643 (900).      Synthesis of CpCr[(MesNCMe)2](Cl) (4.8c). To a suspension of CrCl2 (151.2 mg, 1.229 mmol) in 20 ml THF, diimine (MesNCMe)2 (404 mg, 1.26 mmol) was added and stirred at room temperature for 20 h, during which time the colour changed from green to red.  NaCp (0.70 ml, 2.0 M in THF, 1.4 mmol) was then added, causing the solution to become dark green.  After stirring for an additional 20 h, the solvent was removed in vacuo, the residue was extracted with 7.5 ml hexanes, and then the dark green extracts were filtered through Celite and cooled to 35 °C. Black crystals of 4.8c were isolated in four different fractions (293.9 mg, 50.5%). (Evans, C6D6): µeff = 2.95 µB.  Anal. Calcd for C27H33N2CrCl: C, 68.56; H, 7.03; N, 5.92. Found: C, 69.18; H, 7.17; N, 6.00.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 420 (5500), 572 (900), 650 (1100). 87       Synthesis of CpCr[(DppNCH)2](OCMe2Ph) (4.9a). To a solution of Cp2Cr (50.5 mg, 0.277 mmol) in 5 ml THF, diimine (DppNCH) 2 (116 mg, 0.308 mmol) was added. After stirring for 1 h, HOCMe2Ph (44.3 mg, 0.325 mmol) and a catalytic amount of NaN(SiMe3)2 (< 5 mg, < 10 mol%) were dissolved in 3 ml THF and added to the Cp2Cr solution.  The resulting solution was stirred for 20 h, after which the solvent was removed from the dark green solution in vacuo.  The residue was extracted with 3 ml of hexanes, filtered through Celite, and cooled to -35 °C. Dark green crystals of 4.9a were isolated in three different fractions (113.8 mg, 65.4%).  (Evans, C6D6): 2.65 µB.  Anal. Calcd for C40H52N2CrO: C, 76.40; H, 8.33.; N, 4.45. Found: C, 76.14; H, 8.50; N, 4.44.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 437 (5700), 584 (800), 688 (600).      Synthesis of CpCr[(DppNCH)2](OCH i Pr2) (4.9b). To a solution of Cp2Cr (48.2 mg, 0.265 mmol) in 7.5 ml THF, diimine (DppNCH) 2 (116 mg, 0.309 mmol) was added. After stirring for 30 min, HOCH i Pr2 (45 µl, 0.32 mmol) and a catalytic amount of NaN(SiMe3)2 (< 5 mg, < 10 mol%) were dissolved in 3 ml of THF and added to the Cp2Cr solution.  The resulting solution was stirred for 20 h, after which the solvent was removed from the dark green solution in vacuo. The residue was extracted with 3 ml hexanes, filtered through Celite, and cooled to -35 °C. Dark green crystals of 4.9b were isolated in three different fractions (82.8 mg, 51.3%).  Anal. Calcd for C38H56N2CrO: C, 74.96; H, 9.27.; N, 4.60. Found: C, 75.23; H, 9.44; N, 4.73.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 444 (5500), 568 (900), 702 (1000).      Attempted synthesis of CpCr(PyCH2NMes). A solution of NaCp (1.1 ml, 2.0 M in THF, 2.2 mmol) was added dropwise to a suspension of CrCl2 (248 mg, 2.02 mmol) in 20 ml THF, and the resulting mixture was stirred at room temp for 2 h. In a separate reaction vessel, a solution of n-BuLi (1.4 ml, 1.6 M in hexanes, 2.24 mmol) was added dropwise to a -30 ºC solution of PyCH2NMes (459 g, 2.03 mmol) in 10 ml THF, and the yellow solution was allowed to warm to room temperature and was stirred for 1 h. The ligand solution was then added to the Cr(II) reaction, causing the solution to become dark black. After stirring 20 h, the solvent was removed in vacuo, the residue was extracted with 9 ml hexanes, filtered through Celite and the solution was cooled to -30 ºC. 4.10 (473 mg, 69.1%) was crystallized, as characterized by X-ray crystallography.      Synthesis of CpCr(PyCHNMes) (4.10). To a solution of CpCr(THF)Cl2 (85.2 mg, 0.327 mmol) in 15 ml THF, a solution of the pyridine imine PyCHNMes (90.6 mg, 0.404 mmol) in 3 ml of THF and Mn (430 mg, 7.83 mmol) were added.  The suspension was stirred for 20 h, after which the solvent was removed in vacuo.  The residue was extracted with 12 ml hexanes, filtered 88  through Celite, and cooled to -35 °C. Black crystals of 4.10 were isolated in two different fractions (51.2 mg, 55.5%).  (Evans, C6D6): µeff = 3.63 µB.  Anal. Calcd for C20H21N2Cr: C, 70.37; H, 6.20; N, 8.20. Found: C, 70.56; H, 6.18; N, 8.15.  UV-vis (hexane; λmax, nm (ε, M 1 cm 1 )): 445 (11000), 502 (4100), 595 (1800), 704 (6300).      Synthesis of CpCr(PyCHNMes)(Cl) (4.11). To a suspension of CrCl2 (169. mg, 1.37 mmol) in 10 ml THF, the pyridine imine PyCHNMes (301 mg, 1.34 mmol) was added and stirred at room temperature for 20 h.  NaCp (0.70 ml, 2.0 M in THF, 1.4 mmol) was added, and the resulting black solution was stirred for 20 h.  The solvent was then removed in vacuo, the residue was extracted with 15 ml hexanes, filtered through Celite, and cooled to -35 °C. Black crystals of 4.11 were isolated in four different fractions (305 mg, 60.6%).  (Evans, C6D6): µeff = 2.60 µB. Anal. Calcd for C20H21N2CrCl: C, 63.74; H, 5.62; N, 7.43. Found: C, 63.70; H, 5.65; N, 7.24. UV-vis (THF; λmax, nm (ε, M -1 cm -1 )): 471 (7000)      Synthesis of CpCr(PyCHNMes)(I) (4.12). To a solution of CpCr(PyCHNMes) (45.8 mg, 0.134 mmol) in 7.5 ml Et2O, was added I2 (20.5 mg, 0.080 mmol) dissolved in 3 ml of Et2O. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml Et2O and 2 ml toluene filtered through Celite, and cooled to -35 °C. Black crystals of 4.12 were isolated in two fractions (25.6 mg, 40.80%).  Anal. Calcd for C20H21N2CrI: C, 51.30; H, 4.52; N, 5.98. Found: C, 53.44; H, 5.36; N, 5.45.  UV-vis (THF; λmax, nm (ε, M -1 cm -1 )): 478 (7000), 591 (2100), 692 (1100), 743 (1100).      Synthesis of CpCr(PyCHNMes)(OCMe2Ph) (4.13). To a solution of Cp2Cr (50.1 mg, 0.275 mmol) in 10 ml THF, the pyridine imine PyCHNMes (68.3 mg, 0.304 mmol) was added.  After stirring for1 h, HOCMe2Ph (43.2 mg, 0.317 mmol) and catalytic amount of NaN(SiMe3)2 (< 5 mg, < 10 mol%) dissolved of 3 ml THF were added.  The solution was stirred for 20h, after which the solvent was removed from the dark green solution in vacuo.  The residue was extracted with 6 ml hexanes, filtered through Celite, and cooled to -35 °C. Dark green crystals of 4.13 were isolated in one fraction (95.3 mg, 72.7%).  (Evans, C6D6): µeff = 2.75 µB.  Anal. Calcd for C29H32N2CrO: C, 73.09; H, 6.77; N, 5.88. Found: C, 72.96; H, 7.00; N, 5.91.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 413 (5500), 471 (6400), 612 (1800).       Synthesis of (CpCr)2(µ-NMes)(µ- 2: κ2-MesNCHPy) (4.14). To a solution of CpCr(PyCHNMes) (12.5 mg, 0.0360 mmol) in 4.5 ml THF, HOC( i Pr)2 (6.0 µL, 0.043 mmol) was added and stirred in a 90 ºC oil bath for 40 h, during which time the colour changed to red yellow. The solvent was then removed in vacuo, the residue was extracted with 1.5 ml hexanes, 89  filtered through Celite, and cooled to –35 °C. Black crystals of 4.14 were isolated one fraction (5.1 mg, 57.5%). UV-vis (THF; λmax, nm (ε, M -1 cm -1 )): 532 (3000)      Synthesis of CpCr(PyCHMeNMes)(Me) (4.15). To a solution of CpCr(PyCHNMes) (131 mg, 0.383 mmol) in 10 ml Et2O, MeI (0.10 ml, 0.20 mmol) was added and stirring for 1 h, MeMgI (0.1 ml, 0.3 mmol) was added after and left to stir at room temperature for 20 h. The 1,4- dioxide (0.2 ml, 0.2 mmol) was added at next day. After stirring for 2 h, the solvent was then removed in vacuo, the residue was extracted with 3 ml hexanes, filtered through Celite, and cooled to -35 °C. Black crystals of 4.15 were isolated in one fraction (66.6 mg, 46.8%). UV-vis (THF; λmax, nm (ε, M -1 cm -1 )): 464 (7400).      Synthesis of CpCr[(DppNCH)2](OH) (4.16). To a solution of CpCr[(DppNCH)2] (48.5 mg, 0.0980 mmol) in 20 ml THF, pyridine N-oxide (10.1 mg, 0.106 mmol) was added and stirred at room temperature for 20 h, during which time the colour changed to dark green. The solvent was removed in vacuo, the residue was extracted with 2 ml hexane filtered through Celite, and cooled to –35 °C. Black crystals of 4.16 were isolated in two fractions (25.6 mg, 51.0%). (Evans, C6D6): µeff = 2.66 µB  Anal. Calcd for C31H42N2CrO: C, 72.91; H, 8.29; N, 5.48. Found: C, 72.65; H, 7.97; N, 5.40.  UV-vis (THF; λmax, nm (ε, M -1 cm -1 )): 400 (5400).      Experimental details for reaction of CpCr[(DppNCH)2](OH), complex (4.15) with Me3SiCl.      Me3SiCl. The coumpound 4.16 with two equivalents of Me3SiCl in THF, the solution changed colour from green blue to green upon stirring for 5 minutes and was stirred overnight at room temperature to ensure the reaction had gone to completion. The UV-vis spectrum of the crude reaction mixture was identical to that of authentic Cr(III)Cl complex 4.8a.      Synthesis of CpCr[(DppNCH)2](F) (4.17). Method A. To a solution of CpCr[(DppNCH)2] (210 mg, 0.426 mmol) in 10 ml THF, AgF (69.8 mg, 0.550 mmol) was added and stirred at room temperature for 20 h, during which time the colour changed to dark green-purple. The solvent was removed in vacuo, the residue was extracted with 3 ml hexane filtered through Celite, and cooled to –35 °C. Black crystals of 4.17 were isolated in five fractions (114.9 mg, 52.6%). (Evans, C6D6): µeff = 2.68 µB  Anal. Calcd for C31H41N2CrF: C, 72.63; H, 8.06; N, 5.46. Found: C, 72.61; H, 8.09; N, 5.52.  UV-vis (THF; λmax, nm (ε, M -1 cm -1 )): 403 (6500), 559 (1100), 620 (800).      Method B. To a solution of CpCr[(DppNCH)2] (29.4 mg, 0.056 mmol) in 10 ml THF, Cp2Fe + BF4 -  (19.11 mg, 0.07 mmol) was added and stirred at room temperature for 20 h, during 90  which time the colour changed to dark green purple. The solvent was removed in vacuo, the residue was extracted with 3 ml hexane filtered through Celite, and cooled to -35 °C. Black crystals of 4.17 were isolated in five fractions (9.2 mg, 30.2%).      Cr(III) fluoride (4.17) reactions with silanes:      Me3SiCl. Compund 4.17 (10.3 mg, 0.0200 mmol) was in 1 ml C6H6, followed by addition of Me3SiCl (6.0 µL 0.047 mmol). The solution rapidly changed colour from green-purple to green upon stirring for 5 minutes and was stirred overnight at room temperature to ensure the reaction had gone to completion. The UV-vis spectrum of the crude reaction mixture was identical to that of authentic Cr(III)Cl complex 4.8a and 19 F NMR analysis showed a peak at -158.4 ppm (Me3SiF).      Cr(III) fluoride (4.17) reactions with Gomberg’s dimer: The coumpound 4.17 (5 mg, 0.009 mmol) reacts with 1.5 equivalents of Gomberg’s dimer in C6H6, the solution changed colour from green purple to blue upon stirring over six days at room temperature. The UV-vis spectrum of the crude reaction mixture was identical to that of authentic Cr(II) complex 4.1.      Ph3SiH. The coumpound 4.17 reacts with ten equivalents of Ph3SiH in THF, the solution changed colour from green purple to blue upon stirring overnight at room temperature. The UV- vis spectrum of the crude reaction mixture was identical to that of authentic Cr(II) complex 4.1.      Cr(III) fluoride (4.17) reduction with Na: The coumpound 4.17 reacts with two equivalents of Na in THF, the solution changed colour from green purple to blue upon stirring overnight at room temperature. The UV-vis spectrum of the crude reaction mixture was identical to that of authentic Cr(II) complex 4.1.      Synthesis of CpCr[(DppNCH)2](N3) (4.18). To a solution of CpCr[(DppNCH)2](F) (50.3 mg, 0.092 mmol) in 10 ml C6H6, TMSN3 (15.5 µl, 0.119 mmol) was added and stirred at 55 ºC oil bath for 40 h, during which time the colour changed to dark green. The solvent was removed in vacuo, the residue was extracted with 5 ml toluene filtered through Celite, and the filtrate was cooled to –35 °C. Black crystals of 4.18 were isolated in three fractions (47.2 mg, 89.8%). UV- vis (THF; λmax, nm): 419, 588.      Synthesis of CpCr[(DppNCH)2](N) (4.19). A solution of CpCr[(DppNCH)2](N3) (15.2 mg, 0.0266 mmol) in 3 ml C6H6 was transferred to an air-tight UV-visible cell then placed in front of a 150 W light bulb. After 80 hr the colour changed to purple. The solvent was then removed in vacuo, the residue was extracted with 1.5 ml hexane filtered through Celite, and cooled to 35 °C. Black crystals of 4.19 were isolated in two fractions (8.3 mg, 57.4%). 1H NMR (C6D6, 91  400 MHz): δ 7.1-7.2 (m, 6H, Ar-H), 6.4 (s, 2H, CHCH), 5.4 (s, 5H, Cp-H), 5.0 and 2.7 (hept, 4H, i Pr-CH) 1.1-1.3 (d, 24H, i Pr-Me). UV-vis (THF; λmax, nm): 406, 488, and 549.        X-ray Crystallography. Protocols were identical to those reported in Chapter 2. Compound 4.1 crystallizes with six independent molecules in the asymmetric unit, three of which contain a disordered Cp ligand that were subsequently modeled in two orientations. The methyl C109, C110 and C111 in the compound 4.1 were found to be disordered and were modeled in two orientations with 50% occupancy. All non-hydrogen atoms in compound 4.1 were refined anisotropically except for C1b, C2b, C3b, C4b, C7b, C8b, C9b, C10b, C11b, C12b, C13b, C14b, C15b, C17b and C18b. Compound 4.2 is highly disordered due to co-crystallization of the enantiomers of the chiral-at-Cr complex. Compound 4.8a, 4.16 and 4.19 crystallizes with one half-molecule residing on a two-fold axis of rotation. For compound 4.8b, data were corrected for absorption effects using the multiscan technique (TWINABS). 131  The material crystallizes as a two-component split crystal with the two components related by 179.9º rotation about the (1 0 0) real axis. Data were integrated for both twin components. Subsequent refinements were carried out using an HKLF 4 format data set containing complete from component 1 and all overlapped reflections form component 2. All hydrogen atoms were placed in calculated positions but were not refined. The batch scale refinement showed a roughly 54:46 ratio between the major and minor twin components. The alkoxide of compound 4.9b is disordered and was subsequently modeled in two orientations. All non-hydrogen atoms in compound 4.9b were refined anisotropically except for C33b. Compound 4.5 and 4.10 crystallize with two independent molecules in the asymmetric unit. All non-hydrogen atoms in compound 4.10 were refined anisotropically except for C1, C2, C3, C4, C6, C8, C24, C27, C28, C29, C41 and N3. For compound 4.15, data were corrected for absorption effects using the multiscan technique (TWINABS). 131  The material crystallizes as a two-component split crystal with the two components related by 42.3º rotation about the (1 0 0) real axis. Data were integrated for both twin components. Subsequent refinements were carried out using an HKLF 4 format data set containing complete from component 1 and all overlapped reflections from component 2. All hydrogen atoms were placed in calculated positions but were not refined. The batch scale refinement showed a roughly 57:43 ratio between the major and minor twin components. Compound 4.18 crystallizes with 25% of CpCr[(DppNCH)2](Cl) molecule in the asymmetric unit. All non-hydrogen atoms were refined anisotropically except for “Cl1”. Compound 4.19 92  crystallizes with 6% of CpCr[(DppNCH)2](N3) molecule in the asymmetric unit. All non- hydrogen atoms were refined anisotropically except for “N2b”. 93  Chapter 5: Synthesis and Reactivity of Chromium Complexes with Phenylenediamido Ligand-based radicals.      In Chapter 4, radical anionic diimine, pyridine imine, and bipyridine ligands were used to prepare CpCr(LX) and CpCr(LX)(X) complexes. While these ligand-based radicals successfully reproduced some of the reactivity previously observed for CpCr(nacnac) compounds, they proved to be susceptible to alkylation of the diimine ligand backbone carbon atoms. The phenylenediamido ligands employed in this chapter were expected to be more resistant to this decomposition pathway due to the aromatic backbone connecting the two NR donor groups, where R = SiMe3, CH2CMe3, or Ph.   Figure 5.1. Molecular orbital for ligand-based radicals, N-C bond lengths for phenylenediamido ligands.      Figure 5.1 suggests how (RN)2C6H4 ligands are different than the diimine ligands described in Chapter 4, where LX radicals were generated from the readily available L2 diimine precursers by single-electron reduction. While some neutral L2 (RN)2C6H4 complexes are known, 132  the most 94  common oxidation level is the dianionic X2 phenylenediamido form. Formation of ligand-based LX radicals therefore requires single-electron oxidation of the X2 ligand. Due to the aromatic C6H4 backbone, the RN-C(phenylene) bond length is the most reliable structural parameter used to distinguish beween X2 and LX oxidation levels. 133       The relatively high stability of the dianionic X2 form of the (RN)2C6H4 ligand also proved to have important reactivity consequences for the desired CpCr(LX) complexes. Unlike either CpCr(diimine) or CpCr(nacnac) compounds, CpCr[(RN)2C6H4] intermediates were found to react with neutral two-electron L ligands. This can be attributed to electron transfer from Cr(II) to the LX ligand, forming the Cr-L bond in Cr(III) X2 CpCr[(RN)2C6H4](L) complexes without the energetically unfavorable d-electron spin pairing required for the alternative low-spin Cr(II) LX electronic configuration. Similarly, CpCr[(RN)2C6H4](=O) and CpCr[(RN)2C6H4](=NR’) compounds were observed to be more stable than the related diimine and nacnac intermediates shown in Figure 4.20.      The first new Cr phenylenediamido compounds described in this chapter use the (Me3SiN)2C6H4 ligand, as the doubly protonated ligand precursor is readily prepared directly from (H2N)2C6H4. Once the synthetic routes to CpCr[(RN)2C6H4] complexes were developed with R = SiMe3, this chemistry was extended to the R = CH2CMe3 and R = Ph derivatives. Finally, the influence of the R substitutents on the stoichiometric and catalytic reactivity of CpCr complexes was investigated.  5.1 Synthesis of CpCr(II) and Cr(III) Complexes with the (Me3SiN)2C6H4 ligand.      As shown in Figure 5.2, the initial synthetic approach to CpCr[(Me3SiN)2C6H4], 5.1, involved sequential treatment of CpCr(THF)Cl2 with first the doubly protonated (Me3SiNH)2C6H4, then two equivalents of Me3SiCH2MgCl in a mixture of Et2O and THF, followed by addition of 1,4- dioxane to aid in the removal of the MgX2 byproduct. This indirect route was used instead of employing Li2[(Me3SiN)2C6H4] in order to prevent the possible reduction of the CpCr(THF)Cl2 precursor with the electron rich dianionic form of the redox active ligand. Unexpectedly, recrystallization from hexanes afforded the THF adduct CpCr[(Me3SiN)2C6H4](THF), 5.2, as confirmed by single crystal X-ray diffraction (Figure 5.3).  95   Cr ClO Cl RN NR H H + 2 R'MgCl Et2O/THF R' = CH2SiMe3 R N N Cr CrR N N R R O Cr ClO Cl RN NR Li Li + Et2O 5.1 5.2 2 R'MgCl Et2O R' = CH2SiMe3  Figure 5.2. Synthesis of CpCr[(Me3SiN)2C6H4], Cr(II) Complex 5.1 and CpCr[(Me3SiN)2C6H4]- (THF), Cr(III) Complex 5.2  Figure 5.3. Thermal ellipsoid diagram (50%) of Cr(III) complex 5.2. This Complex 5.2 crystallized on a mirror plane, with one half-molecule in the asymmetric unit. Additionally, the Cp ring and THF of compound 5.2 were disordered and subsequently modeled in two orientations.       Complex 5.2 crystallized with one half-molecule on a mirror plane in the asymmetric unit, complicating the modelling of both the Cp and THF ligands. The N-C bond length of 1.406(2) Å is consistent with a dianionic X2 phenylenediamido ligand. Similar to related CpCrX2(THF) and Cp*CrX2(THF) complexes of Cr(III), formation of the Cr-THF bond appears to be reversible. As shown in Figure 5.4. the UV-vis spectrum of 5.2 in THF displays an absorbance at 401 nm with 96  a shoulder at 480nm. Dissolving 5.2 in hexanes produces an intense red solution with a dramatically different spectrum, including a strong absorbance at 869 nm. This spectrum is qualitatively similar to the CpCr[(DppNCH)2], Cr(II) complex 4.1, and is attributed to the desired THF-free complex 5.1. The same CpCr[(Me3SiN)2C6H4] complex can be prepared by repeating the synthesis in Et2O instead of Et2O/THF, or by reacting CpCr(THF)Cl2 directly with Li2[(Me3SiN)2C6H4] in Et2O, as shown in Figure 5.2. While the elemental analysis of crystals of 5.1 was consistent with the proposed THF-free structure, attempts to obtain a sample suitable for single-crystal X-ray diffraction were unsuccessful. Isolated CpCr[(Me3SiN)2C6H4] has a magnetic moment of 3.49 µB (Evans), which is consistent with either a CpCr(X2) Cr(III) d 3  complex, or a CpCr(LX) Cr(II) d 4  center antiferromagnetically coupled to the unpaired electron of a monoanionic radical LX ligands.  Figure 5.4. UV-vis absorption spectra of complex 5.1 (red line) in hexane [1.6 x 10 -4  M] and complex 5.2 (black line) in THF [1.6*10 -4  M].      Oxidation of 5.1 with one-half equivalent of I2 in Et2O gives the Cr(III) iodo complex 5.3, while reaction with excess equivalents of PbCl2 provides corresponding Cr(III) chloro complex 5.4 (Figure 5.5). The complexes 5.3 and 5.4 have magnetic moment of 2.52 µB and 2.73 µB (Evans), respectively, consistent with the S = 1 spin state expected for Cr(III) d 3  complex with a radical anionic phenylenediamine ligand.  97   Figure 5.5. Synthesis of CpCr[(NSiMe3)2C6H4](I), Cr(III) Complex 5.3 and CpCr[(NSiMe3)2C6H4]Cl, Cr(III) Complex 5.4  5.2 Synthesis of a Cr(V) Adamantyl Imido Complex.       The reversible binding of THF to CpCr[(Me3SiN)2C6H4] is markedly different than related CpCr(nacnac) or CpCr(diimine) complexes which do not react with THF or other 2e L donors, and show relatively invariant UV-vis spectra in a range of organic solvents. This distinct reactivity for 5.1 is attributed to the relative stability of the (Me3SiN)2C6H4 ligand in the dianionic X2 oxidation level (Figure 5.1). Given that Cr(V) imido complexes, including CpCr(NR)X2 compounds, are known to be stable, 134  the reactivity of 5.1 with organic azides (N3R) to prepare CpCr[(Me3SiN)2C6H4](NR) species was investigated. Related group 6 amido complexes with the (Me3SiN)2C6H4 ancillary ligand have been reported by Boncella and co- workers for Mo and W. 135  The preparation of reactive, well-defined paramagnetic imido complexes by reaction of N3R with suitable low-valent first row transition metal precursors is a particularly active area of current research. 136       Reaction of 5.1 with commercially available adamantyl azide in Et2O generates CpCr[(Me3SiN)2C6H4](NAd), 5.5 (equation 5.1). The colour change to dark yellow-brown that accompanies this process is also observed when the reaction is conducted in THF, but at a qualitatively much slower rate. This is consistent with the presumed requirement for N3Ad to bind to Cr prior to N2 loss, which in turn requires THF to dissociate from CpCr[(Me3SiN)2C6H4](THF) in order to proceed. In contrast, CpCr[(XylNCMe)2CH] 2.1f, CpCr[(DppNCH)2] 4.1, and CpCr(PyCHNMes) 4.10 all do not react with N3Ad in Et2O, demonstrating the importance of the phenylenediamido ancillary ligand. 98  Cr N N SiSi N3Ad CrN N N Et2O Si Si (5.1) 5.1 5.5       The UV-vis spectrum of 5.5 in hexanes shows a single intense peak at 459 nm. The magnetic moment of CpCr[(Me3SiN)2C6H4](NAd) is 2.09 µB (Evans), consistent with an S = ½ spin state. Figure 5.6 shows two possible electronic structures for CpCr[(Me3SiN)2C6H4](NR’) compounds that would result in one unpaired electron, analogous to those proposed in Figure 4.20 for the potential CpCr[(Me3SiN)2C6H4](O) intermediate. If the phenylenediamido is in the dianionic X2 oxidation level, this results in a Cr(V), d 1  complex with a standard dianionic imido ligand, similar to previously reported CpCr(X)2(NR’) compounds. At the other end of the continuum would be a Cr(III) complex where the three d-electrons are antiferromagnetically coupled to two ligand-based unpaired electrons, one on the monoanionic LX phenylenediamido radical, and one on a monoanionic NR’ imidyl radical. This unusual electronic structure can perhaps best be considered as resulting from an intramolecular single-electron transfer from the HOMO of the phenylenediamido dianion to the Cr=NR’ π-system. The radical reactivity of first-row metal imido complexes for both C-H amination and NR’ group transfer reactions are expected to depend on the degree of radical character on the imido N atom. 8,9,119,136,  The CpCr[(Me3SiN)2C6H4](NR’) system potentially allows the catalytic activity of the redox-active reactive imido ligand to be controlled by altering the relative stability of the radical LX ancillary ligand by changing the phenylenediamido NR groups. Cr N N N R R R'S = 1/2CrN N N R R Cr(V), d1 Imido, NR'2- (RN)2C6H4, X2 Cr(III), d3 Imidyl, NR'1- (RN)2C6H4, LX R'  Figure 5.6. Electronic Structures of CpCr[(Me3SiN)2C6H4](NR’) complexes.      The X-ray crystal structure of 5.5 (Figure 5.7) suggests that CpCr[(Me3SiN)2C6H4](NAd) strongly favors the Cr(V), phenylediamido X2, dianionic imido electronic structure. The Cr=NAd group is almost perfectly linear (Cr-N-C = 176.0(3)º) with a short Cr=N bond (1.632(4) Å), 99  similar to related Cr(V) imido complexes. The RN-C(phenylene) bonds are 1.396(6) Å and 1.387(6) Å, consistent with the dianionic X2 oxidation level for the ancillary ligand. In the subsequent sections of this chapter, two complementary strategies will be pursued to increase the degree of radical character on the imido ligand. Replacing the NAd ligand with NAr or NSO2Ar groups should decrease the π-donor ability of the imido ligand, allowing an electron to be more easily transferred to a lower energy Cr=NR’ π* orbital. Alternatively, changing the phenylenediamido substituents from N-SiMe3 to N-CH2CMe3 should raise the energy of the ancillary ligand HOMO, facilitating electron transfer from the dianionic X2 to the monoanionic LX radical (Figure 5.1).   Figure 5.7. Thermal ellipsoid diagram (50%) of CpCr[(Me3SiN)2C6H4](NAd), Cr(V) 5.5 imido complex.  5.3 Synthesis of CpCr[(Me3SiN)2C6H4](NAr) Aryl Imido Complexes.      In reaction analogous to that shown in equation 5.1 in Et2O with ArN3 reagents led to the isolation of the corresponding chromium aryl imido complexes in moderate yields. As shown in Figure 5.8, X-ray crystal structures of CpCr[(Me3SiN)2C6H4](NAr) compounds were obtained for Ar = C6H4 (Ph, 5.6), 4-MeC6H4 (Tol, 5.7), and 2,4,6-Me3C6H4 (Mes, 5.8). The solution magnetic moments for each of these compounds was between 1.69 and 1.99 µB, consistent with an S = ½ ground state. The critical bond lengths and angles for these Cr=NAr complexes are compared with those obtained for adamantyl imido 5.5 in Table 5.1. All three CpCr[(Me3SiN)2C6H4](NAr) compounds have slightly longer Cr=NR’ bonds than the adamantyl complex, as well as slightly shorter SiN-C(phenylene) bonds. In all cases, the imido Cr-N-Ar 100  angles are not as linear as the Cr-N-Ad angle for 5.5. The relatively large Cr-N-Mes angle observed for 5.8 is presumably due to the steric demands of the ortho methyl substituents, which are absent in 5.6 and 5.7. All three CpCr[(Me3SiN)2C6H4](NAr) compounds have structures consistent with Cr(V) complexes with dianionic X2 phenylenediamido ligands. However, the parameters in Table 5.1 may indicate a slightly increased contribution from the Cr(III) LX imidyl configuration shown in Figure 5.6 for Cr=NAr complexes 5.6-5.8 compared to the Cr=NAd compound 5.5.   Figure 5.8 Thermal ellipsoid diagram (50%) of CpCr[(Me3SiN)2C6H4](NR’), Cr(V) imido complexes, R’= phenyl (5.6). R’= P-tol (5.7), and R’= mesityl (5.8). Complex 5.7 crystallizes with two independent molecules in the asymmetric unit. Table 5.1. Cr=NR’ and ligand CN Bond Lengths (Å) in CpCr[(Me3SiN)2C6H4](NR’) Complexes (R’= adamantyl (5.5), R’= phenyl (5.6). R’= tol (5.7), and R’= mesityl (5.8).). Complex # R’: Cr=NR’ (Å) C-N (Å) (Average)   Cr=N-R’ (º) (Angles) 5.5 Ad: 1.632 (4) 1.392(6) 176.0(3) 5.6 Ph: 1.669 (2) 1.386(3) 162.1(17) 5.7 Tol: 1.676 (1) 1.385(14) 155.24(9) 5.8 Mes: 1.660 (1) 1.385(2) 172.81(12) 101  5.4 Synthesis of CpCr[(Me3CCH2N)2C6H4] Complexes.      The Cr=NAr complexes 5.6-5.8 showed some structural evidence for increased radical character on both imido and phenylenediamido ligands compared to the Cr=NAd compound 5.5. In order to promote more significant single electron transfer to the Cr=NR’ group, the phenylediamido N-SiMe3 substituents were replaced with N-CH2CMe3. The CpCr[(Me3CCH2N)2C6H4] complex 5.9 was prepared similarly to 5.1, by reaction of CpCr(THF)Cl2 with Li2[(Me3CCH2N)2C6H4], or by sequential treatment with (Me3CCH2N)2C6H4 and two equivalents of Me3SiCH2MgCl as shown in Figure 5.9.  N N Cr Cr ClO Cl N N Li Li + THF 5.9 2 R'MgCl Et2O R' = CH2SiMe3 Cr ClO Cl N H N + H  Figure 5.9. Synthesis of CpCr[(Me3CCH2N)2C6H4], Cr(II) Complex 5.9       Complex 5.9 is very soluble even in concentrated, cold hexanes solutions, presumably due to more aliphatic groups of the neopentyl ligand. Dark blue solutions of CpCr[(Me3CCH2N)2C6H4] displayed a UV-vis spectrum with absorption bands at 379, 569 and 712 nm in hexanes, and unlike the NSiMe3 derivative 5.1, the distinctive long wavelength peak near 710 nm was retained in THF solution. The solution magnetic moment of 5.9 is µeff = 3.29 µB, consistent with the S = 3/2 ground state expected for both the presumed electronic structure of high-spin Cr(II) d 4  and a monoanionic LX phenylenediamido radical, or the alternative with Cr(III) d 3  and an X2 ancillary ligand. The apparent lack of THF binding to 5.9 compared to the reversible formation of 5.2 is consistent with the increased preference of the N-alkyl derivative for the radical LX phenylenediamido oxidation level compared to the (Me3SiN)2C6H4 ligand. The conformation flexibility of the N-CH2CMe3 groups should leave the Cr center of 5.9 more accessible to incoming L donor ligands compared to the more hindered Cr in Me3Si-substituted 5.1.       Although the neopentyl-substituted analogue of 5.2 was not synthetically accessible, routes to CpCr[(Me3CCH2N)2C6H4](L) derivatives were developed where L is a stronger σ-donor 102  ligand than THF. As shown in Figure 5.10, reaction of in situ generated CpCr( i Pr-NHC)Cl2 compound 3.2 with Li2[(Me3CCH2N)2C6H4] resulted in Cr(III) complex 5.10. The CpCr[(Me3CCH2N)2C6H4](CH2PPh3) complex 5.11 was prepared by addition of Ph3P=CH2 to 5.9 (Figure 5.10).  5.9 Cr N N N N Cr Cl Cl N N N N Li Li + Et2O 5.103.2 CH2=PPh3 Cr N NEt2O Cr N N 5.11 PPh3  Figure 5.10. Synthesis of CpCr( i Pr-NHC)[(Me3CCH2N)2C6H4], Cr(III) Complex 5.10, and CpCr[(Me3CCH2N)2C6H4](CH2PPh3), Cr(III) complex 5.11.      The X-ray crystal structures of NHC 5.10 and CH2PPh3 5.11 adducts are shown in Figure 5.11. The conformational flexibility of the phenylenediamido substituents are evident, with both neopentyl groups oriented away from the i Pr-NHC ligand in 5.10, while the less symmetrically distributed bulk of the Ph2PCH2 137  ligand results in a twisted (Me3CCH2N)2C6H4 ligand in 5.11. With RN-C(phenylene) bond lengths of 1.384(4) and 1.387(3) Å, respectively, compounds 5.10 and 5.11 both contain dianionic X2 (Me3CCH2N)2C6H4 ligands, although these critical bond lengths are still significantly shorter than the 1.412(2) and 1.411(2) distances observed by Heyduck and co-workers in Zr[(Me3CCH2N)2C6H4]2(THF)2. For the Zr(IV) bis(X2) compound, the different RN-C(phenylene) distances maybe the result of varying degrees of π-donation from the dianionic phenylenediamido X2 ligand to Zr(VI) d 0  and Cr(III) d 3  metal centers. 133  103   Figure 5.11. Thermal ellipsoid diagram (50%) of CpCr( i Pr-NHC)[(Me3CCH2N)2C6H4], Cr(III) complex 5.10 and CpCr[(Me3CCH2N)2C6H4](CH2PPh3), Cr(III) complex 5.11. This complex 5.10 crystallizes on a mirror plane, with one half-molecule in the asymmetric unit.       Oxidation of 5.9 with one-half equivalent of I2 gave the Cr(III) iodo complex 5.12, while the corresponding chloro compound 5.13 was obtained using excess PbCl2 (Figure 5.12). The molecular structure of CpCr[(Me3CCH2N)2C6H4](Cl) 5.13 was determined by single-crystal X- ray diffraction (Figure 5.13). The t Bu groups of the neopentyl substituents are oriented towards the relatively small chloro ligand. Compared to 5.10 and 5.11, the RN-C(phenylene) distance in 5.13 are shorter (1.357(2) Å), and the magnetic moment of 2.62 µB (Evans) is also consistent with a radical monoanionic phenylenediamido LX ligand antiferromagnetically coupled to the Cr(III) center.   Figure 5.12. Synthesis of CpCr[(Me3CCH2N)2C6H4](I), Cr(III) Complex 5.12 and CpCr[(Me3CCH2N)2C6H4](Cl), Cr(III) Complex 5.13 104   Figure 5.13. Thermal ellipsoid diagram (50%) of CpCr[(Me3CCH2N)2C6H4](Cl), Cr(III) complex 5.13.      Despite its apparent reluctance to react with 2e L donors, 5.9 reacts with adamantyl azide to give the Cr=NAd complex CpCr[(Me3CCH2N)2C6H4](NAd) 5.14 (equation 5.2). The molecular structure of 5.14 was determined by single crystal X-ray diffraction (Figure 5.14). The overall structure of 5.14 resembles the NPh and NTol derivatives with the Me3Si-substituted ligand, since like 5.6 and 5.7, both the Ad and C6H4 groups are bent towards the Cp ligand. In CpCr[(Me3CCH2N)2C6H4](NAd), the orientation of the t Bu groups directly away from the Cp may serve to reinforce the overall distortion observed for 5.14. Both the Cr-N-Ad angle (159.76(18)º) and Cr=NAd bond length (1.658(2) Å) more closely resemble those seen for NAr complexes 5.6 and 5.7 than the corresponding NAd compound 5.5, supporting the idea that electron density is more readily transferred to the Cr=NR’ group from the Me3CCH2-substituted phenylenediamido ligand than from the Me3Si derivative. Significantly, the RN-C(phenylene) bond length of 1.379(2) Å is almost exactly between the values reported by Heyduck for the X2 (1.41 Å) and LX (1.35 Å) forms of the (Me3CCH2N)2C6H4 ligands in Zr(IV) complexes. 138  105  N3Ad CrN N N Et2O Cr N N 5.14 (5.2) 5.9   Figure 5.14. Thermal ellipsoid diagram (50%) of CpCr[(Me3CCH2N)2C6H4](NAd), Cr(V) complex 5.14. This complex crystallizes on a mirror plane, with one half-molecule in the asymmetric unit.      Based on the structure of NAd complex 5.14, it was anticipated that a CpCr[(Me3CCH2N)2C6H4](NAr) complex should have still greater contributions from the Cr(III) LX imidyl electronic structure proposed in Figure 5.6. As shown in equation 5.3, the product obtained from the reaction of 5.9 and N3Mes was bis(imido) complex 5.15, The crystal structure of this unexpected product resulting from Cp loss is shown in Figure 5.15. Like related Cr(NR)2X2 complexes, it has one bent imido ligand with Cr-N-Mes =  158.88(13) º and Cr=NMes = 1.6736(16) Å, and one relatively linear imido ligand with Cr-N-Mes = 175.90(14) º and Cr=NMes = 1.6623(16) Å like Cr(NDpp)2(Cl)2 and related Cr(VI) bis(imido) derivatives, 134  Cr[(Me3CCH2N)2C6H4](NMes)2 is diamagnetic. Sharp, diamagnetic 1 H NMR signals are obtained in C6D6, showing that the two NMes ligands are equivalent in solution at room temperature. However, the RN-C(phenylene) bonds are quite short at 1.369(2) and 1.362(3) Å, indicating that the S = 0 spin state of 5.15 is due to antiferromagnetic coupling of the radical LX· 106  phenylenediamido ligand with the single d-electron of the Cr(V) center. The unexpected formation of the bis(imido) 5.15 may result from loss of C5H5 radical from a CpCr[(Me3CCH2N)2C6H4](NMes) intermediate. 139  5.9 N Cr N N N Et2O Cr N N + N3 (5.3) 5.15   Figure 5.15. Thermal ellipsoid diagram (50%) of Cr[(Me3CCH2N)2C6H4](NAd)2, Cr(V) complex 5.15.      Attempts to obtain crystals of a monomeric CpCr[(Me3CCH2N)2C6H4](O) complex by oxygen-atom transfer to 5.9 with PhI=O pyridine N-oxide, or O2 were similary unsuccessful. Reaction of CpCr[(Me3CCH2N)2C6H4] with PhI=O instead results in the purple µ-oxo complex 5.16 (equation 5.4). As shown in Figure 5.16, the molecule crystallizes with an inversion center coincident with the oxygen atom, and the ligand t Bu substituents lying on opposite sides of the phenylene ring. The Cr-O-Cr angle is perfectly linear due to symmetry constraints, and the Cr-O 107  distance of 1.8001(3) Å is significantly shorter than the 1.834(3) Å previously observed for {CpCr[(XylNCMe)2CH]}2(µ-O), 140  presumably due to the reduced steric demands of the flexible (Me3CCH2N)2C6H4 ligands. As in the case of nacnac derivative, the {CpCr[(Me3CCH2N)2C6H4]}2(µ-O) complex 5.16 is believed to result from the trapping of the initial Cr=O complex with an equivalent of the starting material 5.9. The RN-C(phenylene) distances of 1.3567(19) Å and 1.3635(19) Å are consistant with radical LX phenylenediamido ligands and Cr(III) centers. The characteristic UV-vis bands at 452 and 501 nm for µ-oxo complex 5.16 are also observed when hexanes solutions of CpCr[(Me3CCH2N)2C6H4] are exposed to air or pyridine N-oxide. Interestingly, dilute solutions of both the NHC and Ph3PCH2 adducts 5.9 and 5.10 also undergo the same charge in colour and UV-vis spectra when exposed to air. Both 5.9 and 5.10 also display bands near 710 nm when their UV-vis spectra are obtained in dilute hexanes solutions under an inert atmosphere. These spectroscopic results suggest that the NHC and Ph3PCH2 ligands of 5.9 and 5.10 maybe dissociating at UV-vis concentrations at room temperature. 5.9 Cr N N + IO Et2O Cr ON N Cr N N 0.5 5.16 (5.4)   Figure 5.16. Thermal ellipsoid diagram (50%) of {CpCr[(Me3CCH2N)2C6H4]}2(µ-O), Cr(III) complex 5.16. This complex crystallizes with an inversion center, with one half-molecule in the asymmetric unit. One of CH2CMe3 group of Compound 5.16 was disordered and subsequently modeled in two orientations. 108   5.5 Synthesis of CpCr[(PhN)2C6H4] Complexes.      The third phenylenediamido ligand to be investigated in this chapter was (PhN)2C6H4. Unlike the previous two (RN)2C6H4 precursors which could be prepared from 1,2-phenylenediamine directly (R = Me3Si) or by reduction of the bis(amide) intermediate (R = Me3CCH2), the R = Ph derivative requires the Pd-catalyzed Buchwald-Hartwig amination of 1,2-Br2C6H4 with aniline. In our hands, the more recent synthesis using NHC ligands gave a cleaner product in higher yields using lower Pd catalyst loading than the original procedure using bulky alkyl PR3 ligands. 141  Cr ClO Cl N N H H + 2 R'MgCl Et2O R' = CH2SiMe3 CrPh N N Ph Si Cr Ph N N Ph Si Mg 1/2 5.17 (5.5)       Unlike the corresponding syntheses of the Me3Si and Me3CCH2 Cr complexes, the sequential reaction of CpCr(THF)Cl2 with (RN)2C6H4 and two equivalents of Me3SiCH2MgCl gave an unexpected “ate” complex with a Cr-CH2SiMe3 ligand (equation 5.5). The crystal structure of [Mg]{CpCr[(RN)2C6H4](CH2SiMe3)}2 5.17 is shown in Figure 5.16, and consists of a Mg 2+  cation bridging two monoanionic CpCr[(RN)2C6H4](CH2SiMe3) units. The PhN-C(phenylene) bonds are between 1.425(2) Å and 1.431(2) Å, consistent with X2 ligands bound to Mg 2+  and Cr(III) centers. The Mg 2+  cation is in relatively close contact with all four N atoms (Mg-N distances between 2.17 Å and 2.20 Å) as well as the methylene carbons of both CH2SiMe3 ligands (Mg-CH2 distances of 2.5495(19) Å and 2.6383(18) Å). 109   Figure 5.17. Thermal ellipsoid diagram (50%) of [Mg]{CpCr[(RN)2C6H4](CH2SiMe3)}2, Cr(III) complex 5.17. The complex crystalizes with one half-molecule of hexane in the asymmetric unit. Additionally, one of CH2SiMe3 group was disordered and subsequently modeled in two orientations. All non-hydrogen atoms were refined anisotropically except for “C25b”.    The desired CpCr[(RN)2C6H4] complex 5.18 can be obtained by use of LiN(SiMe3)2 instead of Me3SiCH2MgCl as base, and has a strong band at 657 nm in hexanes. The magnetic moment of 3.81 µB (Evans) is consistent with a S = 3/2 spin state. Like 5.1, the longer wavelength peak of CpCr[(RN)2C6H4] near 657 nm is not observed when 5.18 is dissolved in THF, or when hexanes solutions of 5.18 are treated with PCy3 or DMAP. N N Cr Cr ClO Cl N N H H + 2 NaN(SiMe3)2 Et2O 2 PbCl2 THF CrPh N N Ph Cl 5.195.18 (5.6)       Crystals of 5.18 suitable for X-ray crystallography were not obtained. However, when CpCr[(RN)2C6H4] is prepared in situ and then oxidized with PbCl2, single crystals of the Cr(III) chloro complex 5.19 were isolated. The structure of CpCr[(RN)2C6H4](Cl) (Figure 5.18) has PhN-C(phenylene) bonds of 1.384(2) Å, consistent with a radical LX phenylenediamido ligand. The magnetic moment of 2.53 µB (Evans) indicates 5.19 is Cr(III) d 3  complex with antiferromagnetic coupling to the radical ligand, resulting in an S = 1 spin state.  110    Figure 5.18. Thermal ellipsoid diagram (50%) of CpCr[(Ph)2C6H4](Cl), Cr(III) complex 5.19. This complex 5.19, data were corrected for absorption effects using the multiscan technique (TWINABS). This complex 5.19 crystallizes with two independent molecules in the asymmetric unit. All non-hydrogen atoms in complex 5.19 were refined anisotropically except for C1, C21, C22, C42 and C44.  5.6. Radical Reactivity of CpCr[(RN)2C6H4] Complexes.      In order to encourage radical reactivity, ligands capable of stabilizing unpaired electrons were coordinated to CpCr[(RN)2C6H4] compounds. Oxidation of 2,4,6- t Bu3C6H2OH (Mes*OH) with PbO2 generates blue solutions of the stable ·OMes* aryloxy radical. Sequential reaction of Mes*OH with PbO2 and 5.1 in hexanes gave CpCr[(RN)2C6H4](OMes*), 5.20 (equation 5.7). Crystals of 5.20 suitable for X-ray diffraction were obtained in low yield, and its molecular structure is shown in Figure 5.19. The long Cr-OMes* bond (1.9304(12) Å) is attributed to both the steric demands of the two ortho tBu substituents and the stability of the ·OMes* radical. The isolated samples of 5.20 used for elemental analysis and solution magnetic moment measurements seem to have been contaminated by some unreacted, co-crystallized Mes*OH, as evident by 1 H NMR. This would account for the deviations in both the EA results (high for %C and low for %N) and the µeff of 1.67µB (lower than expected for two unpaired electrons). O + Cr N N SiSi Cr ON N Si Si (5.7) 5.20 111   Figure 5.19. Thermal ellipsoid diagram (50%) of CpCr[(NSiMe3)2C6H4](OMes*), Cr(III) alkoxide complex 5.20.       Attempts to prepare CpCr[(NSiMe3)2C6H4](NTol) 5.7 by reaction 5.1, TolNH2 and two equivalents of ·OMes* were monitored using UV-vis spectroscopy. While the spectra obtained were encouraging further work would be required to make this hydrogen-atom abstraction strategy synthetically useful (equation 5.8). 142  Cr N H N N Si Si OMes* Cr ON N Si Si Cr N N N Si Si H2NC6H4Me (5.8) 5.20 5.7      Highly reactive M=NSO2Ar intermediates are widely used in catalytic processes by synthetic organic chemists. While these reactive species are typically prepared using isolated or in situ generated PhI=NSO2Ar reagents, the corresponding N3SO2Ar reagents are also available. It was anticipated that any CpCr[(RN)2C6H4](NSO2Ar) complexes would have substantial imidyl radical character due to the much poorer π-donor ability of NSO2Ar compared to NAd or NAr imido ligands. 136       Reaction of CpCr[(RN)2C6H4] complex 5.1 (R = Me3Si) and 5.9 (R = Me3CCH2) with N3Ts (equation 5.9) resulted in new products with significantly different colours and UV-vis spectra than the other Cr=NR’ complexes described in this chapter. The molecular structure of 5.22 is shown in Figure 5.20. Based on the Cr-NTs bond length (2.013(4) Å), the Cr-N-S angle (135.2(3)º), and the magnetic moment of 2.49 µB, 5.22 appears to be the S = 1 complex CpCr[(Me3CCH2N)2C6H4](NHTs), the product resulting from addition of a hydrogen atom to the 112  expected Cr=NTs intermediate. 143  Although the crystals of 5.21 submitted for crystallographic analysis were extensively disordered, the Cr-NHTs portion of the molecule appeared similar to 5.22, indicating that the Me3Si-substitueted complex also underwent H-atom abstraction. The H- atom donor in these reactions remains to be identified. R N N Cr R Cr N H N N SR R O O N3Ts R: SiMe3  (5.21)      CH2CMe3 (5.22) (5.9) R: SiMe3, (5.1)      CH2CMe3, (5.9) Cr NN N SR R O O   Figure 5.20. Thermal ellipsoid diagram (50%) of CpCr[(Me3CCH2N)2C6H4](NHTS), Cr(III) complex 5.22.      Zhang and co-workers have used trisyl azide [NTrisyl = NSO2(2,4,6- i Pr3C6H2)] as a substrate for cobalt-catalyzed radical synthesis of benzosultams. 21,144  The desired catalytic mechanism is shown in Figure 5.21. Reaction of CpCr[(RN)2C6H4] precursor 5.1 or 5.9 with N3Trisyl forms azide adduct A, which loses N2 to generate reactive imidyl intermediate B. Intramolecular hydrogen atom abstraction of a weak and available tertiary benzylic H atom from the Trisyl ligand i Pr group forms C. Formation of the N-C bond creates the desired benzosultam adduct D, which releases product and binds substrate to complete the cycle. 113   Figure 5.21. Catalyzing cyclized organic product benzosultams by using CpCr[(R)2C6H4], Cr(II) Complexes.       When 5.1 and 5.9 were reacted with N3Trisyl, the overall colour change from dark red to dark green was similar to that observed for N3Ts but much more rapid, consistent with an enhanced rate for intramolecular H-atom abstraction. 143  However, the crystal structure of CpCr[(Me3SiN)2C6H4](NHTrisyl), 5.23 showed that the expected conversion of amido C to cyclized product D had not occurred. The Cr-NHTrisyl length (2.027(4) Å) and Cr-N-S angle (141.09(9)º) were again consistent with a Cr(III)-NHTrisyl complex with a monoanionic LX phenylenediamido ligand (Figure 5.22), with µeff = 2.30 µB and RN-C(phenylene) bond lengths of 1.361(2) Å. Despite the qualitatively faster reaction, the trisyl i Pr substituents in 5.23 remained intact. One possible explanation is that for both R = SiMe3 and CH2CMe3 complexes, intermediate C does not undergo cyclization by N-C bond formation. Instead, two molecules of C react in a H-atom transfer reaction to generate the structurally characterized product and a second organochromium complex with a H2C=C(Me)-substituted ligand that does not crystallize (equation 5.10). 114  Cr N H N N SR R O O R: SiMe3  (5.23)      CH2CMe3 (5.24) (5.10) Cr NN N SR R O O 2 Cr N H N N SR R O O +   Figure 5.22. Thermal ellipsoid diagram (50%) of CpCr[(Me3SiN)2C6H4](NHTrisyl), Cr(III) complex 5.23.      Fortunately, the reaction of CpCr[(PhN)2C6H4], 5.18 with N3Trisyl has a different outcome, as shown in Figure 5.21. Reaction of 5.18 and N3Trisyl in C6D6 overnight gives the 1 H NMR spectrum of the expected benzosultam product. The reaction also proceeds to completion with 20 mol% 5.18 after 6 days at room temperature, or 65 h at 70 ºC. The product can be obtained in 84% isolated yield after chromatography. The evident success of the NPh substituted ancillary ligand in inducing the key N-C bond formation step from C to D may be due to the relatively small NPh groups. Preliminary reactions using 20 mol% of 5.1 or 5.18 at 70 ºC with mixture of N3Tol and styrene also show distinct ancillary ligand effects on catalytic activity. 145  While the NPh complex did not generate any N-containing products derived from styrene when monitored by 1 H NMR, the NSiMe3 derivative produced the aziridine TolNCH2CHPh. Further work is clearly warranted to explore the role of phenylediamido radical ancillary ligand substituent effects on the catalytic activity of chromium imido species. 115   5.7 Experimental Section: General Considerations: All reactions were carried out under nitrogen using standard Schlenk and glove box techniques.  Solvents were dried by using the method of Grubbs. Celite (Aldrich) was dried overnight at 120 °C before being evacuated and then stored under nitrogen. Iodine was purified by sublimation. Styrene was washed with 10% NaOH and dry by MgSO4 then purified by distillation and stored at -35 ºC with 4 Å molecular sieves. 2,4,6-tri-tert- butylphenol (98%), CrCl3 (anhydrous), LiN(SiMe3)2, n-BuLi (1.6M in hexanes), NaCp (2.0M in THF), Me3SiCH2MgCl (1.0 M in Et2O), PbCl2, PbO2 (97+%), p-toluidine (99%), pyridine N- oxide (95%), NaN3, TMSN3, N3Ad and 1,4-dioxane (anhydrous) were purchased from Aldrich and used as received. (Me3SiNH)2C6H4, 146  (Me3CCH2NH)2C6H4, 142  (PhNH)2C6H4 141  and CH2PPh3 137  were prepared according to the literature procedures. Li2[R2C6H4] were prepared by reaction of the corresponding neutral, doubly protonated ligand with BuLi. The azides: PhN3, TolN3, MesN3, 147  N3Ts 148  and N3Trisyl 144  were prepared according to the literature procedures and freeze-pump-thaw degassed before use. UV-vis spectroscopic data were collected on a Varian Cary 100 Bio UV-visible or a Shimadzu UV 2550 UV-vis spectrophotometer in hexanes solution in a specially constructed cell for air-sensitive samples: a Kontes Hi-Vac Valve with PTFE plug was attached by a professional glassblower to a Hellma 10 mm path length quartz absorption cell with a quartz-to-glass graded seal. Elemental analyses were performed by Guelph Chemical Laboratories, Guelph, ON, Canada or by the UBC Department of Chemistry microanalytical services. Synthesis of CpCr[(Me3SiN)2C6H4] (5.1). Method A: To a solution of CpCr(THF)Cl2 (421 mg, 1.62 mmol) 20 ml Et2O, Li2[(Me3SiN)2C6H4] (468 mg, 1.77 mmol) was added, causing the solution to become dark red. After sitting for 20 h, the solvent was removed in vacuo, the residue was extracted with 6 ml hexanes, and then the dark red extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.1 were isolated in two different fractions (316 mg, 53.0%). (Evans, C6D6): 3.49 µB.  Anal. Calcd for C17H27N2Si2Cr: C, 55.55; H, 7.40; N, 7.62. Found: C, 54.84; H, 7.58; N, 6.07.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 359 (3100), 450 (1800), 501(1700), 869(1200). Method B: To a solution of CpCr(THF)Cl2 (313.7 mg, 1.20 mmol) 30 ml Et2O, (Me3SiNH)2C6H4 (351 mg, 1.39 mmol) was added, causing the solution to become dark green. Me3SiCH2MgCl (2.6 ml, 1.0 M in Et2O, 2.6 mmol) was added and sitting for 4 h, during which 116  time solution become dark red. 1,4-dioxane (1.3 ml, 15 mmol) was added, resulting in the immediate formation of a large quantity of white precipitate. After stirring for an additional 1 h, the solvent was removed in vacuo, the residue was extracted with 6 ml hexanes, and then the dark red extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.1 were isolated in two different fractions (298 mg, 67.5%). Synthesis of CpCr[(Me3SiN)2C6H4](THF) (5.2). To a solution of CpCr(THF)Cl2 (105 mg, 0.405 mmol) 15 ml Et2O, (Me3SiNH)2C6H4 (97.3 mg, 0.385 mmol) was added, causing the solution to become dark green. Me3SiCH2MgCl (0.85 ml, 1.0 M in Et2O, 0.85 mmol) was added and 10 ml THF was also added to dissolve the perception in the solution. After stirring for 20 h, 1,4-dioxane (1.3 ml, 15 mmol) was added, resulting in the immediate formation of a large quantity of white precipitate. After stirring for an additional 1 h, the solvent was removed in vacuo, the residue was extracted with 4 ml hexanes, and then the dark red extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.2 were isolated in two different fractions (131 mg, 77.2%).  UV-vis (THF; λmax, nm (ε, M -1 cm -1 )): 472 (1000). Synthesis of CpCr[(Me3SiN)2C6H4](I) (5.3). To a solution of CpCr[(Me3SiN)2C6H4] (82.2 mg, 0.223 mmol) in 10 ml Et2O, I2 (32.2 mg, 0.127 mmol) was added, causing the solution to become dark red yellow. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml Et2O, and then the extracts were filtered through Celite and cooled to - 35 °C.  Black crystals of 5.3 were isolated in two different fractions (56.2 mg, 50.9%).  (Evans, C6D6): 2.42 µB.  Anal. Calcd for C17H27N2Si2CrI: C, 40.46; H, 5.42; N, 5.57. Found: C,40.45; H, 5.61; N, 5.26.  UV-vis (Et2O; λmax, nm (ε, M -1 cm -1 )): 373 (1400), 397 (5700), 449 (6100), 537 (1400), 662 (1800). Synthesis of CpCr[(Me3SiN)2C6H4](Cl) (5.4). To a solution of CpCr[(Me3SiN)2C6H4] (67.2 mg, 0.183 mmol) in 10 ml Et2O, PbCl2 (30.1 mg, 0.117 mmol) was added, stirring for 20 h. During which time solution colour changed to dark green, the solvent was then removed in vacuo, the residue was extracted with 5 ml hexane, and the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.4 were isolated in one fraction (43.7 mg, 59.2%). (Evans, C6D6): 2.73 µB.  Anal. Calcd for C17H27N2Si2CrCl: C, 50.66; H, 6.75; N, 6.95. Found: C, 51.02; H, 6.70; N, 7.18.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 336 (5800), 380 (4600), 461 (1030), 530 (1700), 660 (2100) 731 (1500). Synthesis of CpCr[(Me3SiN)2C6H4](NAd) (5.5). To a solution of CpCr[(Me3SiN)2C6H4] (66.8 mg, 0.182 mmol) in 12 ml Et2O, N3Ad (35.4 mg, 0.200 mmol) was added, causing the 117  solution to become dark red yellow. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.5 were isolated in three different fractions (55.5 mg, 59.0%).  (Evans, C6D6): 2.09 µB.  Anal. Calcd for C27H42N3Si2Cr: C, 62.75; H, 8.19; N, 8.13. Found: C, 62.67; H, 8.24; N, 8.22.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 459 (3800). Synthesis of CpCr[(Me3SiN)2C6H4](NPh) (5.6). To a solution of CpCr[(Me3SiN)2C6H4] (30.2 mg, 0.0820 mmol) in 15 ml Et2O, N3Ph (11.8 mg, 0.100 mmol) was added, causing the solution to become dark brown. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 2 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.6 were isolated in one fraction (19.1 mg, 50.7%).  (Evans, C6D6): 1.99 µB.  Anal. Calcd for C23H32N3Si2Cr: C, 60.23; H, 7.03; N, 9.16. Found: C, 60.09; H, 7.07; N, 9.29.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 459 (4400). Synthesis of CpCr[(Me3SiN)2C6H4](NTol) (5.7). To a solution of CpCr[(Me3SiN)2C6H4] (30.2 mg, 0.0820 mmol) in 15 ml Et2O, N3Tol (17.8 mg, 0.134 mmol) was added, causing the solution to become dark brown. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 5 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.7 were isolated in one fraction (21.2 mg, 56.5%).  (Evans, C6D6): 1.78 µB.  Anal. Calcd for C24H34N3Si2Cr: C, 60.98; H, 7.25; N, 8.89. Found: C, 61.26; H, 7.32; N, 8.92.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 454 (4400). Synthesis of CpCr[(Me3SiN)2C6H4](NMes) (5.8). To a solution of CpCr[(Me3SiN)2C6H4] (29.1 mg, 0.0790 mmol) in 8 ml Et2O, N3Mes (15.6 mg, 0.0970 mmol) was added, causing the solution to become dark brown. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 2 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.8 were isolated in one fraction (17.0 mg, 42.9%).  (Evans, C6D6): 1.69 µB.  Anal. Calcd for C26H38N3Si2Cr: C, 62.36; H, 7.65; N, 8.39. Found: C, 57.07; H, 6.85; N, 8.69.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 377 (5900). Synthesis of CpCr[(Me3CCH2N)2C6H4] (5.9). Method A: To a solution of CpCr(THF)Cl2 (44.8 mg, 0.172 mmol) 20 ml THF, Li2[(Me3CCH2N)2C6H4]  (50.0 mg, 1.92 mmol) was added, causing the solution to become dark blue. After sitting for 20 h, the solvent was removed in vacuo, the residue was extracted with 6 ml hexanes, and then the dark blue extracts were filtered through Celite and stored under -35 °C. 118  Method B: To a solution of CpCr(THF)Cl2 (100.0 mg, 0.384 mmol) 20 ml Et2O, (Me3CCH2NH)2C6H4 (111 mg, 0.447 mmol) was added, causing the solution to become dark green. Me3SiCH2MgI (0.85 ml, 1.0 M in Et2O, 0.85 mmol) was added and sitting for 4 h, during which time solution become dark blue. 1,4-dioxane (0.9 ml, 10.2 mmol) was added, resulting in the immediate formation of a large quantity of white precipitate. After stirring for an additional 1 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexanes, and then the dark blue extracts were filtered through Celite and cooled to -35 °C.  Black powders of 5.9 were isolated in one fraction (25.5 mg, 18.2%). (Evans, C6D6): 3.29 µB.  Anal. Calcd for C21H31N2Cr: C, 69.39; H, 8.60; N, 7.70. Found: C, 71.24; H, 9.81; N, 9.77.  UV-vis (hexane; λmax, nm (ε, M - 1 cm -1 )): 373 (3900), 519 (1600), 710 (1600). Synthesis of CpCr( i Pr-NHC)[(Me3CCH2N)2C6H4] (5.10). To a solution of CpCr( i Pr- NHC)Cl (30.6 mg, 0.100 mmol) in 10 ml THF, PbCl2 (15.1 mg, 0.058 mmol) was added, causing the solution to become purple blue. After stirring for 6 h, the suspension was filtered through Celite, and the insoluble residue was washed with additional 10 ml Et2O. Li2[(Me3CCH2N)2C6H4] (29.2 mg, 0.112 mmol) was added to the Cr(III) reaction, causing the solution to become brown red. After stirring 20 hr, the solvent was removed in vacuo, the residue was extracted with 6 ml Et2O, filtered through Celite and the solution was cooled to -35 ºC. Black crystals of 5.10 were isolated in one fraction (17.6 mg, 34.1%).  (Evans, C6D6): 3.28 µB.  Anal. Calcd for C30H47N4Cr: C, 69.87; H, 9.19; N, 10.86. Found: C, 67.06; H, 8.73; N, 9.84. UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 372 (6200), 511 (1900), 708 (2200). Synthesis of CpCr[(Me3CCH2N)2C6H4](CH2PPh3) (5.11). To a solution of CpCr[(Me3CCH2N)2C6H4] (0.096 mmol) in 30 ml THF (prepared from CpCrCl2(THF) and Li2[(Me3CCH2N)2C6H4] as described in 5.9 method A, above), CH2PPh3 (31.3 mg, 0.113 mmol) was added and stirring for 20 h. The solvent was removed in vacuo, causing the solution to become dark green, the residue was extracted with 2 ml Et2O, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.11 were isolated in one fraction (33.2 mg, 54.1%). (Evans, C6D6): 3.27 µB. UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 369 (9200), 508 (3300), 707 (3900). Synthesis of CpCr[(Me3CCH2N)2C6H4](Cl) (5.13). To a solution of CpCr[(Me3CCH2N)2C6H4] (0.769 mmol) in 10 ml Et2O (prepared from CpCrCl2(THF) and Li2[(Me3CCH2N)2C6H4] as described in 5.9 method A, above), PbCl2 (109.1 mg, 0.423 mmol) was added, stirring for 20 h. During which time solution colour changed to dark green yellow, 119  the solvent was then removed in vacuo, the residue was extracted with 9 ml hexane, and the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.13 were isolated in three fractions (69.9 mg, 22.8%).  (Evans, C6D6): 2.62 µB.  Anal. Calcd for C21H31N2CrCl: C, 63.23; H, 7.83; N, 7.02. Found: C, 61.72; H, 7.58; N, 6.66.  UV-vis (hexane; λmax, nm (ε, M -1 cm - 1 )): 383 (7800), 450 (11200), 533 (1900), 632 (1500). Synthesis of CpCr[(Me3CCH2N)2C6H4](NAd) (5.14). To a solution of CpCr[(Me3CCH2N)2C6H4] (0.384 mmol) in 8 ml Et2O (prepared from CpCrCl2(THF) and Li2[(Me3CCH2N)2C6H4] as described in 5.9 method A, above), N3Ad (76.1 mg, 0.429 mmol) was added, causing the solution to become dark black. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 2 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.14 were isolated in one fraction (49.2 mg, 25.0%).  (Evans, C6D6): 1.67 µB.  Anal. Calcd for C31H46N3Cr: C, 72.62; H, 9.04; N, 8.19. Found: C, 72.95; H, 9.41; N, 8.04.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 378 (6200). Attempted synthesis of CpCr[(Me3CCH2N)2C6H4](NMes). To a solution of CpCr[(Me3CCH2N)2C6H4] (0.191 mmol) in 15 ml Et2O (prepared from CpCrCl2(THF) and Li2[(Me3CCH2N)2C6H4] as described in 5.9 method A, above), N3Mes (41.0 mg, 0.254 mmol) was added, causing the solution to become dark green. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C. Black crystals of Cr[(Me3CCH2N)2C6H4](NMes)2 5.15 (16.0 mg, 24.7%) were obtained, as characterized by X-ray crystallography. 1 H NMR (C6D6, 400 MHz): δ 7.03 (m, 2H, Ar-H), 6.92 (m, 2H, Ar-H), 6.64 (s, 4H, Mes-H), 4.3 (s, 4H, CH2), 2.35 (s, 12H, p-Mes-CH3), 2.08 (s, 6H, o-Mes-CH3), 1.04 (s, 18H, t Bu-CH3). Anal. Calcd for C34H48N4Cr: C, 72.31; H, 8.57; N, 9.92. Found: C, 72.11; H, 8.61; N, 9.83.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 343 (17000), 582 (10000). Synthesis of {CpCr[(Me3CCH2N)2C6H4]}(µ-O) (5.16). To a solution of PhI=O (31.0 mg, 0.141 mmol) in 2 ml C6H6, a solution of CpCr[(Me3CCH2N)2C6H4] (0.112 mmol) in 5 ml C6H6 (prepared from CpCrCl2(THF) and Li2[(Me3CCH2N)2C6H4] as described in 5.9 method A, above) was added slowly over 20 min, causing the solution to become dark brown. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Purple crystals of 5.16 were isolated in one fraction (6.2 mg, 14.9%). Anal. Calcd for C42H62N4Cr2O: C, 67.90; H, 8.41; N, 7.54. 120  Found: C, 62.59; H, 8.31; N, 6.55.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 452 (6300), 501 (6900). Attempted synthesis of CpCr[(PhN)2C6H4]. To a solution of CpCr(THF)Cl2 (49.0 mg, 0.188 mmol) 20 ml Et2O, (PhNH)2C6H4 (52.1 mg, 0.200 mmol) was added, causing the solution to become dark green. Me3SiCH2MgI (0.4 ml, 1.0 M in Et2O, 0.4 mmol) was added, stirring for 4 h, during which time solution become dark blue. 1,4-dioxane (0.3 ml, 4.4 mmol) was added, resulting in the immediate formation of a large quantity of white precipitate. After stirring for an additional 1 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexanes, and then the dark blue extracts were filtered through Celite and cooled to -35 °C. {CpCr[o- (PhN)2C6H4]2CH2CMe3}2 2- Mg 2+ , 5.17 (37.7 mg, 57.4%) was crystallized, as characterized by X- ray crystallography. (Evans, C6D6): 3.61 µB. Anal. Calcd for C54H60N4Cr2Si2Mg: C, 68.30; H, 6.37; N, 5.90. Found: C, 69.15; H, 6.34; N, 5.52. UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 456 (9900), 643 (5100). Synthesis of CpCr[(PhN)2C6H4] (5.18). To a solution of CpCr(THF)Cl2 (100.4 mg, 0.386 mmol) 10 ml Et2O, (PhNH)2C6H4 (123.0 mg, 0.472 mmol) was added, causing the solution to become dark green. LiN(SiMe3)2 (145 mg, 0.868 mmol) was added, stirring for 20 h, during which time solution become dark blue. The solvent was removed in vacuo, the residue was extracted with 5 ml Et2O, and then the dark blue extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.18 were isolated in two fractions (46.9 mg, 32.4%). (Evans, C6D6): 3.82 µB.  Anal. Calcd for C23H19N2Cr: C, 73.59; H, 5.10; N, 7.46. Found: C, 70.34; H, 5.25; N, 7.20. UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 373 (6400), 657 (3100). Synthesis of CpCr[(Ph)2C6H4](Cl) (5.19). To a solution of CpCr(THF)Cl2 (30.1 mg, 0.116 mmol) 10 ml Et2O, (PhNH)2C6H4 (33.2 mg, 0.128 mmol) was added, causing the solution to become dark green. LiN(SiMe3)2 (42.6 mg, 0.255 mmol) was added, stirring for 20 h, during which time solution become dark blue. The solvent was removed in vacuo, the residue was extracted with 5 ml Et2O, and then the dark blue extracts were filtered through Celite. The PbCl2 (67.4 mg, 0.242 mmol) was then added as 20 ml THF solution. After stirring for 20 h, the solution colour changed to dark green yellow, the solvent was then removed in vacuo, the residue was extracted with 4 ml hexane, and the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.19 were isolated in two fractions (22.7 mg, 48.0%).  (Evans, C6D6): 2.53 µB. Anal. Calcd for C23H19N2CrCl: C, 67.24; H, 4.66; N, 6.82. Found: C, 64.82; H, 4.80; N, 121  6.88. UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 350 (8400), 452 (8900), 504 (2900), 538 (3000), 652 (2400). Synthesis of CpCr[(Me3SiN)2C6H4](OMes*) (5.20). To a solution of CpCr[(Me3SiN)2C6H4] (80.2 mg, 0.218 mmol) in 15 ml hexane, Mes*OH (68.21 mg, 0.260 mmol) was added after passing though a 2 cm of PbO2 pipette column in 10 ml hexane, and causing the solution to become red orange. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 8 ml hexane, and then the extracts were filtered through Celite and cooled to 35 °C.  Black crystals of 5.20 were isolated in one fraction (29.5 mg, 21.5%).  (Evans, C6D6): 1.67 µB.  Anal. Calcd for C35H56N2Si2CrO: C, 66.83; H, 8.97; N, 4.45. Found: C, 69.47; H, 9.28; N, 3.16.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 399(3900), 491 (3200). Conversion of Cr-NH2Tol to Cr=NTol by stepwise H-atom abstraction with Mes*O· radical. To a solution of CpCr[(Me3SiN)2C6H4] (12.1 mg, 0.0329 mmol) in 2 ml hexane, Mes*OH (10.6 mg, 0.0404 mmol) was added after passing though a 2 cm of PbO2 pipette column as a 5 ml hexane solution, and causing the solution to become red orange. After stirring for 20 h, the solution transfer into a 10 ml volumetric flask and made up to the line by hexane. Took 1 ml out by volumetric pipette into another 10 ml volumetric flask for UV-vis (hexane; λmax, nm ) 486, 622, 825). H2NTol (3.6 mg, 0.0336 mmol) was added and caused the solution to become dark green. Same concentration UV-vis (hexane; λmax, nm ) 448, 659) was obtained after 20 h stirring. Mes*O· (11.25 mg, 0.0429 mmol) was added after passing though a 2 cm of PbO2 pipette column as a 5 ml hexane solution, and causing the solution to become dark brown. Same concentration UV-vis (hexane; λmax, nm ) 380, 399, 455) was obtained after 20 h stirring. Synthesis of CpCr[(Me3SiN)2C6H4](NHTs) (5.21). To a solution of CpCr[(Me3SiN)2C6H4] (26.7 mg, 0.0730 mmol) in 15 ml Et2O, N3Ts (27.01 mg, 0.137 mmol) was added, causing the solution to become dark green. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.21 were isolated in one fraction (17.2 mg, 43.9%).  (Evans, C6D6): 2.32 µB.  Anal. Calcd for C24H35N3Si2CrSO2: C, 53.61; H, 6.56; N, 7.81. Found: C, 53.41; H, 6.25; N, 8.57.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 450 (6400), 643 (1500). Synthesis of CpCr[(Me3CCH2N)2C6H4](NHTs) (5.22). To a solution of CpCr[(Me3CCH2N)2C6H4] (0.393 mmol) in 15 ml Et2O (prepared from CpCrCl2(THF) and Li2[(Me3CCH2N)2C6H4] as described in 5.9 method A, above), N3Ts (91.1 mg, 0.462 mmol) was added and causing the solution to become dark green. After stirring for 20 h, the solvent was 122  removed in vacuo, the residue was extracted with 3 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.22 were isolated in one fraction (23.5 mg, 11.23%). (Evans, C6D6): 2.49 µB.  Anal. Calcd for C28H39N3CrSO2: C, 63.02; H, 7.37; N, 7.87. Found: C, 62.21; H, 6.93; N, 8.06.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 378 (8300), 440 (8500), 637 (1700). Synthesis of CpCr[(Me3SiN)2C6H4](NHTrisyl) (5.23). To a solution of CpCr[(Me3SiN)2C6H4] (27.5 mg, 0.0750 mmol) in 8 ml C6H6, N3Trisyl (27.01 mg, 0.137 mmol) was added, causing the solution to become dark green yellow. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 3 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.23 were isolated in one fraction (7.6 mg, 15.6%). (Evans, C6D6): 2.37 µB. UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 451 (8000), 641 (1900). Synthesis of CpCr[(Me3CCH2N)2C6H4](NHTrisyl) (5.24). To a solution of CpCr[(Me3CCH2N)2C6H4] (0.115 mmol) in 10 ml Et2O (prepared from CpCrCl2(THF) and Li2[(Me3CCH2N)2C6H4] as described in 5.9 method A, above), N3Trisyl (43.4 mg, 0.140 mmol) was added, causing the solution to become dark green yellow. After stirring for 20 h, the solvent was removed in vacuo, the residue was extracted with 2 ml hexane, and then the extracts were filtered through Celite and cooled to -35 °C.  Black crystals of 5.24 were isolated in one fraction (10.6 mg, 14.3%). (Evans, C6D6): 2.30 µB.  Anal. Calcd for C36H55N3CrSO2: C, 66.95; H, 8.58; N, 6.50. Found: C, 59.11; H, 8.03; N, 12.11.  UV-vis (hexane; λmax, nm (ε, M -1 cm -1 )): 391 (8300), 445 (7600), 538 (1900), 641 (1900). Catalytic-in-Cr C–C bond cyclization reaction with 5.18. To a solution of CpCr[(PhN)2C6H4] (9.6 mg, 0.026 mmol, 19.2 mol%) in 1 ml of C6H6, N3Trisyl (41.1 mg, 0.133 mmol) was added and stirring for 65 hr under 70 ºC. The solvent was then removed in vacuo, the residue was extracted with 0.5 ml CDCl3 then filtered through Celite into an air-tight J. Young NMR tube. The cyclised product was characterized by 1 H NMR (CDCl3, 400 MHz): Pure product, δ7.2, 6.9 (s, 2H, Ar-H), 4.4 (s, 1H, NH), 3.5 (sept, 1H, iPr-CH), 2.9 (sept, 1H, i Pr-CH), 1.5 (s, 6 H, i Pr-Me), 1.2 (d, 6 H, i Pr-Me), 1.1 (d, 6 H, i Pr-Me). The solvent was then removed in vacuo again, the residue was purified by flash chromatography with a gradient solvent system of 100:0 (hexanes: ethyl acetate) to 50:50 (hexanes: ethyl acetate), the product is eluted at last. White powder of cyclized product was isolated (34.2 mg, 83.94%) and proved by 1 H NMR (CDCl3, 400 MHz) again. 123         Attempted hydroamination or aziridination with 5.18. To a solution of CpCr[(PhN)2C6H4] (25.0 mg, 0.0666 mmol, 19.7 mol%) in 1 ml of C6D6, N3Tol (44.9 mg, 0.337 mmol) and styrene (42 µL, 0.365 mmol) were added and was stirred for 120 hr at 70 ºC. The dark black solution was characterized by 1 H NMR, and showed no signals attributable to an azirdination product. The spectrum contains only unreacted styrene and 30% of p-toluidine. The solvent was then removed in vacuo, the residue was purified by flash chromatography with a solvent system of 70:30 (hexanes: ethyl acetate), the product is eluted at last. White powder of p-toluidine was isolated (10.1 mg, 22.0%) and characterized by 1 H NMR (CDCl3, 400 MHz), δ6.95, 6.6 (d, 2H, Tol-H), 3.5 (broad S, 1H, NH), 2.2 (S, 3H, Tol-Me).      Hydroamination or aziridination with CpCr[(Me3SiN)2C6H4], 5.1. To a solution of CpCr[(Me3SiN)2C6H4] (24.5 mg, 0.0666 mmol, 19.7 mol%) in 1 ml of C6D6, N3Tol (101.1 mg, 0.759 mmol) and styrene (43 µL, 0.374 mmol) were added and the solution was stirred for 6 days at 70 ºC. The dark black solution was characterized by 1 H NMR, which displayed signals due to the aziridination product and unreacted N3Tol. The solvent was then removed in vacuo so that the aziridination product can be separated from the stating materials by flash chromatography. While chromatography on silica with 70:30 (hexanes: ethyl acetate) did separate the organic products, the aziridine was contaminated with chromium-containing products that was eluted at the same time. 1 H NMR of final reaction solution (CDCl3, 400 MHz), δ7.3-7.5 (m, 5H, Aryl-H) 7.1, 6.8 (d, 2H, Tol-H), 4.8, 4.2, 2.9 (dd, 1H, CH), 2.2 (S, 3H, Tol-Me).  X-ray Crystallography. Protocols were identical to those reported in chapter 2. Compound 5.2, 5.10, 5.14 and 5.15 crystallize on a mirror plane, with one half-mplecule in the asymmetric unit. Additionally, the Cp ring and THF of compound 5.2 were disordered and subsequently modded in two orientations. Compound 5.7, 5.19 and 5.25 crystallizes with two independent molecules in the asymmetric unit. Compound 5.17 crystallized with one half-molecule of hexane in the asymmetric unit. Additionally, one of CH2SiMe3 group was disordered and subsequently modeled in two orientations. All non-hydrogen atoms were refined anisotropically except for “C25b”. One of CH2CMe3 group of Compound 5.15 was disordered and subsequently modeled in two orientations. This complex 5.19, data were corrected for absorption effects using the multiscan technique (TWINABS). 131  All non-hydrogen atoms in complex 5.19 were refined anisotropically except for C1, C21, C22, C42 and C44.  124  Chapter 6: Conclusion      In this thesis, the electronic structure and single electron reactivity of paramagnetic, redox- active chromium complexes have been addressed. More specifically, C-P and C-C bond formation reactions were catalyzed by newly developed organochromium complexes. The Cr catalysts mostly undergo single electron process between Cr(II) and Cr(III), except for electron rich CpCr(NHC)Ar2 complexes which undergo two electron process between Cr(I) and Cr(III) as part their catalytic cycle. The bond-forming steps in these catalytic reactions can take place away from the metal center as generating radical, can happen at the metal center, or can occur at the oxo or imido ligands.      Oxidative addition of alkyl halides with Cr(II) complexes generates alkyl radicals, which can be reversibly trapped as Cr(III) alkyl complexes. In the catalytic process, the reactions with secondary alkyl halides and Ph2PX were catalyzed by using symmetric (2.1f) or asymmetric (2.1b) CpCr(nacnac) catalysts and involving a key C-P bond formation step occurs away from the Cr metal center. The catalytic reactions require 1 mol% catalyst loading, where the complex reacts with cyclohexyl halide to generate cyclohexyl radical away from metal center, which subsequently reacts with Ph2PX to give the Ph2PCy organic product in excellent yields. Electronic and steric effects on the rate of oxidative addition reaction were observed by using symmetric and asymmetric CpCr(nacnac) Cr(II) complexes. Specifically, compared to symmetric CpCr(nacnac) complexes, the iodomethane activation was faster with the asymmetric CpCr(nacnac) complex. Furthermore, stronger aryl halide bonds can be activated by using electron rich CpCr(LX) complexes, where LX are the more electron donating ligands anilido imine and phenylienediamido.      The thermodynamics of oxidative addition and reductive elimination is critically dependent on the nature of the aryl-X bond and the electronic properties of the metal center. Particularly, the reductive elimination step can be assisted by increasing the steric bulk and decreasing the donor strength of the ligands bound to the Cr(III) metal center. Therefore, CpCr( i Pr-NHC)Ar2, Cr(III) complexes have been synthesised to perform coupling reaction of two aryl groups. Photolysis was used to induce reductive elimination of Ar-Ar from Cr(III) diaryl complexes to generate ɳ6-arene Cr(I) species as intermediates. The catalytic homo coupling reactions were also performed with 10% catalyst loading and a compatible stoichiometric oxidant to form the Ar-Ar product. The use of strong field NHC ligand stabilizes various CpCr(NHC)R complexes. With addition of ɳ5 Cp ligand, this electron rich complex actives aryl halide substrates by single 125  electron transfer. The NHC ligand can be dissociated under photolysis conditions, yet it also reduces electron density of the metal center, which leads to reductive elimination.      The redox active ligands bipyridine, diimine and pyridine imine were used to form CpCr(LX) complexes, with a radical on the ligand backbone. New paramagnetic chromium bipyridine, diimine or pyridine imine complexes have been prepared and structural characterized by single- crystal X-ray diffraction. The crystal structures and NMR Evans method together show antiferromagnetic coupling between the metal unpaired electrons and an unpaired electron on the redox active ligand. The geometry of the three-legged piano stool products appears to play a significant role in the electron transfer from Cr(II) to the ligand LUMO π*, as the four- coordinate complex Cr[N(SiMe3)2]2(bpy) remains S = 2, and displays the bond lengths expected for a neutral bipyridine ligand. Preliminary attempts to use these complexes as synthetic precursors to Cr(III) alkyl complexes have been complicated by unwanted ligand alkylation reactions.      Azide and nitrido organochromium complexes have been synthesized with a diimine ligand. Moreover, Cr(II) phenylenediamido complexes can react with various azide reagents to form Cr(V) imido complexes. We also demonstrated that the CpCr[(PhN)2C6H4] is an effective and general catalyst for catalyzing intramolecular C-H amination with arylsulfonyl azides, leading to the benzosultam organic product in excellent yields. In this radical cyclization reaction, the first critical step involves a radical that is generated on the tertiary benzylic position of the Trisyl group away from the metal center. In addition, both the unpaired electrons on the Cr(III) metal center and the radical on the redox active phenylenediamido ligand stabilize the intermediate species in the catalytic cycle. Unpaired electron density on the reactive imido ligand is believed to be critical for the hydrogen-atom abstraction process. Further work will be required to control this unpaired electron for either catalytic hydroamination or aziridination reactions.       126   References: 1  Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis. University Science Books, Sausalito, CA, 2010. 2  Johansson Seechurn, C. C. C.; Kitching, M. O.; Colacot, T. J.; Snieckus, V. Angew. Chem., Int. Ed. 2012, 51, 5062-5085. 3  Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29. 4  Schrock, R. R. Chem. Rev. 2009, 109, 3211-3226. 5  Poli, R. Chem. Rev. 1996, 96, 2135-2204. 6  Smith, K. M. Organometallics 2005, 24, 778-784. 7  (a) Rudolph, A.; Lautens, M. Angew. Chem., Int. Ed. 2009, 48, 2656-2670. (b) Glasspoole, B. W.; Crudden, C. M. Nat. Chem. 2011, 3, 912−913. 8  (a) Lyaskovskyy, V.; de Bruin, B. ACS Catal. 2012, 2, 270–279. (b) Luca, O. R.; Crabtree, R. H. Chem. Soc. Rev. 2013, 42,1440-1459. 9  Lu, H.; Zhang, X. P. Chem. Soc. Rev. 2011, 40, 1899-1909. 10  Anet, F. A. L.; Leblanc, E. J. Am. Chem. Soc. 1957, 79, 2649-2650. 11  Smith, K. M. Coord. Chem. Rev. 2006, 250, 1023-1031. 12   Fürstner, A. Chem. Rev. 1999, 99, 991-1045. 13 Guo, H.; Dong, C. G.; Kim, D. S.; Urabe, D.; Wang, J.; Kim, J. T.; Liu, X.; Sasaki, T.; Kishi, Y. J. Am. Chem. Soc. 2009, 131, 15387-15393. 14  Green, M. L. H. J. Organomet. Chem. 1995, 500, 127–148. 15  MacLeod, C. Ph.D. Thesis, University of British Columbia Okanagan, 2012. 16  Zhou, W.; Tang, L.; Patrick, B. O.; Smith, K. M. Organometallics 2011, 30, 603-610. 17  Zhou, W.; MacLeod, K. C.; Smith, K. M. Organometallics 2012, 31, 7324-7327. 18  Chirik, P. J.; Wieghardt, K. Science 2010, 327, 794-795. 19  Knijnenburg, Q.; Gambarotta, S.; Budzelaar, P. H. M. Dalton Trans. 2006, 5442-5448. 20  Danopoulos, A. A.; Wilkinson, G.; Sweet, T. K. N.; Hursthouse, M. B. Dalton Trans. 1996, 271-281. 21  Ruppel, J. V.; Kamble, R. M.; Zhang, X. P. Org. Lett., 2007, 9, 4889-4892. 22  (a) Bourget-Merle, L.; Lappert, M. F.; Severn, J. S. Chem. Rev. 2002, 102, 3031–3065. (b) Mindiola, D. J. Angew. Chem., Int. Ed. 2009, 48, 6198-6200.  127   23  Doherty, J. C.; Ballem, K. H. D.; Patrick, B. O.; Smith, K. M. Organometallics 2004, 23, 1487-1489. 24  MacLeod, K. C.; Conway, J. L.; Patrick, B. O.; Smith, K. M. J. Am. Chem. Soc. 2010, 132, 17325-17334. 25  Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165–195. 26  Zhou, W.; Therrien, J. A.; Wence, D. L. K.; Yallits, E. N.; Conway, J. L.; Patrick, B. O.; Smith, K. M. Dalton Trans. 2011, 40, 337-339. 27  Monillas, W.; Yap, G. P. A.; Theopold, K. H. J. Chem. Crystallogr. 2009, 39, 842-845. 28  MacLeod, K. C.; Conway, J. L.; Tang, L.; Smith, J. J.; Corcoran, L. D.; Ballem, K. H. D.; Patrick, B. O.; Smith, K. M. Organometallics 2009, 28, 6798-6806. 29  Champouret, Y.; MacLeod, K. C.; Baisch, U.; Patrick, B. O.; Smith, K. M.; Poli, R. P. Organometallics 2010, 29, 167-176. 30  (a) Curran, D. P.; Totleben, M. J. J. Am. Chem. Soc. 1992, 114, 6050–6058. (b) Ogoshi, S.; Stryker, J. M. J. Am. Chem. Soc. 1998, 120, 3514–3515. (c) Nicolaou, K. C.; Ellery, S. P.; Chen, J. S. Angew. Chem., Int. Ed. 2009, 48, 7140-7165. 31  Huang, Y. -B.; Jin, G.-X. Dalton Trans. 2009, 767-769. 32  Latreche, S.; Schaper, F. Organometallics 2010, 29, 2180-2185. 33  MacAdams, L. A.; Kim, W.-K.; Liable-Sands, L. M.; Guzei, I. A.; Rheingold, A. L.; Theopold, K. H. Organometallics 2002, 21, 952-960. 34  For related challenges in the selective synthesis of Cr(LX)Cl2(THF)2 complexes, see: (a) Manzer, L. E. Inorg. Chem. 1978, 17, 1552-1558. (b) Gibson, V. C.; Mastroianni, S.; Newton, C.; Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Dalton Trans. 2000, 1969-1971. (c) Jones, D. J.; Gibson, V. C.; Green, S. M.; Maddox, P. J.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 2005, 127, 11037-11046. (d) Xu, T.; An, H.; Gao, W.; Mu, Y. Eur. J. Inorg. Chem. 2010, 3360-3364. 35  Luinstra, G. A.; Teuben, J. H. J. Chem. Soc., Chem. Commun. 1990, 1470-1471. 36  Champouret, Y.; Baisch, U.; Poli, R.; Tang, L.; Conway, J. C.; Smith, K. M. Angew. Chem., Int. Ed. 2008, 47, 6069-6072. 37 Tappe, F. M. J.; Trepohl, V. T.; Oestreich, M. Synthesis 2010, 3037-3062. 38  Sato, A.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2006, 128, 4240-4241.  128   39  (a) Vaillard, S. E.; Mück-Lichtenfeld, C.; Grimme, S.; Studer, A. Angew. Chem. Int. Ed. 2007, 46, 6533–6536. (b) Lamas, M.-C.; Studer, A. Org. Lett. 2011, 13, 2236-2239. 40  (a) Surry, D. S.; Buchwald, S. L. Chem. Sci. 2011, 2, 27-50. (b) Chapman, A. M.; Haddow, M. F.; Wass, D. F. J. Am. Chem. Soc. 2011, 133, 18463-18478. (c) Lundgren, R. L.; Stradiotto, M. Chem. Eur. J. 2012, 18, 9758-69. 41  Cossairt, B. M.; Cummins, C. C. New J. Chem. 2010, 34, 1533-1536. 42  (a) Peters, J. C.; Johnson, A. R.; Odom, A. L.; Wanandi, P. W.; Davis, W. M.; Cummins, C. C. J. Am. Chem. Soc. 1996, 118, 10175-10188. (b) Agapie, T.; Diaconescu, P. L.; Mindiola, D. J.; Cummins, C. C. Organometallics 2002, 21, 1329-1340. 43  Newcomb, M.; Park, S. U. J. Am. Chem. Soc. 1986, 108, 4132-4134. 44  (a) Takai, K.; Ueda, T.; Hayashi, T.; Moriwake, T. Tetrahedron Lett. 1996, 37, 7049-7052. (b) Thom , I.; Nijs, A.; Bolm, C. Chem. Soc. Rev. 2012, 41, 979-987. 45  Without addition of bipyridine at the conclusion of the reaction, no Ph2PCy was observed by 31 P NMR after workup, presumably due to binding to high-spin d 5  MnBr2. For the interactions of manganese(II) halides with phosphines, see: (a) McAuliffe, C. A. J. Mol. Catal. 1988, 44, 35-63. (b) Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. J. Chem. Soc., Dalton Trans. 1993, 371-375. 46  For the use of MnCl2 to remove phenanthroline from molybdenum nitride and alkylidyne complexes, see: Heppekausen, J.; Stade, R.; Goddard, R.; Fürstner, A. J. Am. Chem. Soc. 2010, 132, 11045-11057. 47  For the synthesis and X-ray structures of MnX2(bipy)2, see: (a) McCann, S.; McCann, M.; Casey, M. T.; Jackman, M.; Devereaux, M.; McKee, V. Inorg. Chim. Acta 1998, 279, 24-29. (b) Hwang, I.-C.; Ha, K. Z. Kristallogr. 2007, 222, 209-210. 48  (a) Cahiez, G.; Moyeux, A. Chem. Rev. 2010, 110, 1435−1462. (b) Jana, R.; Pathak, T. P.; Sigman, M. S. Chem. Rev. 2011, 111, 1417-1492. 49  (a) Nakamura, A.; Yoshikai, N. J. Org. Chem. 2010, 75, 6061-6067. (b) Lu, Z.; Fu, G. C. Angew. Chem., Int. Ed. 2010, 49, 6676-6678. 50  MacLeod, K. C.; Patrick, B. O.; Smith, K. M. Organometallics 2010, 29, 6639-6641. 51  (a) Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.; Noack, C. L.; Piers, W. E.; Parvez, M. Organometallics 2003, 22, 1577-1579. (b) Liu, X.; Gao, W.; Mu, Y.; Li, G.; Ye, L.; Xia, H.; Ren, Y.; Feng, S.; Organometallics, 2005, 24, 1614-1619.  129   52  Ren, Y.; Liu, X.; Xia, H.; Ye, L.; Mu, Y. Eur. J. Inorg. Chem. 2007, 1808-1814. 53  Xu, T.; An, H.; Gao, W.; Mu, Y.; Eur. J. Inorg. Chem. 2010, 3360-3364. 54  Fischer, E. O.; Ulm, K.; Kuzel, P. Z. Anorg. Allg. Chem. 1963, 319, 253-265. 55  Chisholm, M. H.; Cotton, F. A.; Extine, M.W.; Rideout, D. C. Inorg. Chem. 1979, 18, 120-125. 56  Dove, A. P.; Gibson, V. C.; Marshall, E. L.; White, A. J. P.; Williams, D. J. Dalton Trans. 2004, 570-578. 57  Fürstner, A.; Shi, N. J. Am. Chem. Soc. 1996, 118, 12349-12357. 58  (a) Jensen, F. R.; Nakamaye, K. L. J. Am. Chem. Soc. 1968, 90, 3248-3250. (b) Andersen, R. A.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1977, 809-811. (c) Dryden, N. H.; Legzdins, P.; Trotter, J.; Yee, V. C. Organometallics 1991, 13, 1326-1335. 59  SADABS. Bruker Nonius area detector scaling and absorption correction, V2.10; Bruker AXS Inc.: Madison, WI, 2003. 60  SIR92. Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr. 1993, 26, 343-350. 61  SQUEEZE: Sluis, P. v. d.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, 194-201. 62  SHELXTL, Version 5.1; Bruker AXS Inc.: Madison, WI, 1997. 63  (a) Sherry, B. D.; Fürstner, A. Acc. Chem. Res. 2008, 41, 1500-1511. (b) Cahiez, G.; Moyeux, A. Chem. Rev. 2010, 110, 1435-1462. 64  (a) Fürstner, A.; Martin, R.; Krause, H.; Seidel, G.; Goddard, R.; Lehmann, C. W. J. Am. Chem. Soc. 2008, 130, 8773-8787. (b) Noda, D.; Sunada, Y.; Hatakeyama, T.; Nakamura, M.; Nagashima, H. J. Am. Chem. Soc. 2009, 131, 6078-6079. 65  Affo, W.; Ohmiya, H.; Fujioka, T.; Ikeda, Y.; Nakamura, T.; Yorimitsu, H.; Oshima, K.; Imamura, Y.; Mizuta T.; Miyoshi, K. J. Am. Chem. Soc. 2006, 128, 8068-8077. 66  (a) Jones, G. D.; Martin, J. L.; McFarland, C.; Allen, O. R.; Hall, R. E.; Haley, A. D.; Brandon, R. J.; Konovalova, T.; Desrochers, P. J.; Pulay P.; Vicic, D. A. J. Am. Chem. Soc. 2006, 128, 13175-13183. (b) Castonguay, A.; Beauchamp A. L.; Zargarian, D. Organometallics 2008, 27, 5723-5732. 67  Seyferth, D. Organometallics, 2002, 21, 1520-1530; Seyferth, D. Organometallics, 2002, 21, 2800–2820. 68  (a) Whitesides, G. M.; Ehmann, W. J. J. Am. Chem. Soc. 1970, 92, 5625-5640. (b) Jolly, P. W. Acc. Chem. Res. 1996, 29, 544-551. (c) Takahashi, T.; Liu, Y.; Iesato, A.; Chaki, S.; Nakajima,  130   K.; Kanno, K.; J. Am. Chem. Soc. 2005, 127, 11928-11929. (d) Agapie, T.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2007, 129, 14281-14295. 69  Kohler, F. H.; Metz, B.; Strauss, W. Inorg. Chem., 1995, 34, 4402-4413. 70  (a) Richeson, D. S.; Mitchell, J. F.; Theopold, K. H. Organometallics 1989, 8, 2570-2577. (b) Jonas, K. Pure Appl. Chem. 1990, 62, 1169-1174. (c) Wilke, G.; Benn, H.; Goddard, R.; Kruger, C.; Pfeil, B. Inorg. Chim. Acta 1992, 198-200, 741-748. (d) Angermund, K.; Betz, P.; Dohring, A.; Jolly, P. W.; Krugerand C.; Schonfelder, K.U. Polyhedron 1993, 12, 2663-2669. (e) Bhandari, G.; Rheingold, A. L.; Theopold, K. H. Chem. Eur. J. 1995, 1, 199-203. (f) Braunschweig, H.; Kupfer, T.; Lutz, M.; Radacki, K. J. Am. Chem. Soc. 2007, 129, 8893-8906. 71  (a) Hatakeyama, T.; Hashimoto, S.; Ishizuka, K.; Nakamura, M. J. Am. Chem. Soc. 2009, 131, 11949-11963. (b) Zhang, K.; Sheridan, M. C.; Cooke, S. R.; Louie, J. Organometallics 2011, 30, 2546-2552. (c) Zell, T.; Fischer, P.; Schmidt, D.; Radius, U. Organometallics 2012, 31, 5065-5073. (d) Mo, Z.; Zhang, Q.; Deng, L. Organometallics 2012, 31, 6518-6521. (e) Pryojski, J. A.; Arman, H. D.; Tonzetich, Z. J. Organometallics 2013, 32, 723-732. (e) Danopoulos, A. A.; Monakhov, K. Y.; Robert, V.; Braunstein, P.; Pattacini, R.; Conde- Guadano, S.; Hanton, M.; Tooze, R. P. Organometallics 2013, 32, 1842-1850. 72  Voges, M. H.; Rømming, C.; Tilset, M. Organometallics 1999, 18, 529-533. 73  Conde-Guadano, S.; Danopoulos, A. A. Pattacini, R.; Hanton, M.; Tooze, P. Organometallics 2012, 31, 1643-1652. 74  Kreisel, K. A.; Yap, G. P. A.; Theopold, K. H. Organometallics 2006, 25, 4670-4679. 75  Ballem, K. H. D.; Shetty, V.; Etkin, N.; Patrick, B. O.; Smith, K. M. Dalton Trans. 2004, 3431-3433. 76  Sneeden, R. P. A. Organochromium Compounds; Academic Press: New York, 1975. 77  (a) Scarborough, C. C.; Sproules, S.; Weyhermuller, T.; DeBeer, S.; Wieghardt, K. Inorg. Chem. 2011, 24, 12446-12462. (b) Scarborough, C. C.; Sproules, S.; Doonan, C. J.; Hagen, K. S.; Weyhermuller, T.; Wieghardt, K. Inorg. Chem. 2012, 51, 6969-6982. 78 Studer, A.; Curran, D. P. Angew. Chem. Int. Ed. 2011, 50, 5018 -5022 79  Fischer, E. O.; Ulm, K.; Kuzel, P. Z. Anorg. Allg. Chem. 1963, 319, 253-265. 80  Dohring, A.; Gohre, J.; Jolly, P. W.; Kryger, B; Rust, J.; Verhovnil, G. P. J. Organometallics 2000, 19, 388-402. 81 Kreisel, K. A.; Yap, G. P. A.; Theopold, K. H. Organometallics, 2006, 25, 4670-4679.   131   82  Rosenthal, U.; Burlakov, V. V.; Arndt, P.; Baumann, W.; Spannenberg, A. Organometallics 2003, 22, 884-900. 83  Heintz, R. A.; Ostrander, R. L.; Rheingold, A. L.; Theopold, K. H. J. Am. Chem. Soc. 1994, 116, 11387-11396. 84  MacLeod, K. C.; Patrick, B. O.; Smith, K. M. Organometallics 2012, 31, 6681-6689. 85  Liu, C.; Zhang, H.; Shi, W.; Lei, A. Chem. Rev. 2011, 111, 1780-1824. 86  Nakamura, E.; Yoshikai, N. J. Org. Chem. 2010, 75, 6061-6067. 87  Abrams, M. B.; Scott B. L.; Baker, R. T.; Organometallics 2000, 19, 4944-4956. 88  Burstein, C.; Lehmann, C. W.; Glorius, F. Tetrahedron 2005, 61, 6207–6217. 89  Schaub, T.; Backes, M.; Radius, U. Organometallics 2006, 25, 4196-4206. 90  Kim, W. K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.; Theopold, K. H. Organometallics 1998, 17, 4541. 91  Kreisel, K. A.; Yap, G. P. A.; Theopold, K. H. Inorg. Chem. 2008, 47, 5293-5303. 92  Pierpont, C . G. Inorg. Chem., 2011, 50, 9766-9772. 93  tom Dieck, H.; Kinzel, A. Angew. Chem. Int. Ed. Engl. 1979, 18, 324-325. 94  (a) Kreisel, K . A.; Yap, G. P. A.; Dmitrenko, O.; Landis, C. R.; Theopold, K. H. J. Am. Chem. Soc. 2007, 129, 14162-14163 (b) Fedushkin, I.; Makarov, V. M.; Sokolov, V. G.; Fukin, G. K. Dalton. Trans. 2009, 8047-8053 (c) Knisley,T. J.; Saly, M. J.; Heeg, M. J.; Roberts, J. L.; Winter, C. H. Organometallics, 2011, 30, 5010-5017 (e) Gao, B.; Gao, W.; Wu, Q.; Luo, X.; Zhang, J.; Su, Q.; Mu, Y.; Organometallics 2011, 30, 5480-5486. 95  Ghosh, M.; Sproules, S.; Weyhermüller, T.; Wieghardt, K. Inorg. Chem. 2008, 47, 5963-5970. 96  (a) Ahmed, M. A. K.; Fjellvag, H.; Kjeshus, A.; Birkedal, R. K.; Norby, P.; Wragg, D. S.; Gupta, N. S. Z. Anorg. Allg. Chem. 2010, 636, 2422-2432. (b) Ahmed, M. A. K.; Fjellvag, H.; Kjeshus, A.; Wragg, D. S.; Gupta, N. S. Z. Anorg. Allg. Chem. 2011, 637, 56-61. 97  Desnoyer, A. N. B.Sc. Thesis, University of British Columbia Okanagan, 2011. 98  (a) Tang Wong, K. L.; Brintzinger, H. H. J. Am. Chem. Soc. 1975, 97, 5143-5146. (b) Green, J. C.; Jardine, C. N. J. Chem. Soc., Dalton Trans. 1999, 3767-3770. (c) Schaper, F.; Wrobel, O.; Schwörer, R.; Brintzinger, H. H. Organometallics 2004, 23, 3552-3555. (d) Charbonneau, F.; Oguadinma, P. O.; Schaper, F. Inorg. Chim. Acta 2010, 363, 1779-1784. 99  (a) Piper, T. S.; Wilkinson, G. J. Inorg. Nucl. Chem. 1956, 3, 104-124. (b) Cotton, F. A.; Musco, A.; Yagupsky, G. J. Am. Chem. Soc. 1967, 89, 6136-6139. (c) Cotton, F. A.; Legzdins,  132   P. J. Am. Chem. Soc. 1968, 90, 6232–6233. (d) Hames, B. W.; Legzdins, P.; Martin, D. T. Inorg. Chem. 1978, 17, 3644-3647. Regina, F. J.; Wojcicki, A. Inorg. Chem. 1980, 19, 3803- 3807. (e) Jandciu, E. W.; Kuzelka, J.; Legzdins, P.; Rettig, S. J.; Smith, K. M. Organometallics 1999, 18, 1994-2004. (f) Cotton, F. A. Inorg. Chem. 2002, 41, 643-658. 100  Bhandari, G.; Kim, Y.; McFarland, J. M.; Rheingold, A. L.; Theopold, K. H. Organometallics 1995, 14, 738-745. 101  Horvath, B.; Strutz, J.; Horvath,, E. G. Z. Anorg. Allg. Chem. 1979, 457, 38-50. 102  Scarborough, C. C.; Wieghardt, K. Inorg. Chem. 2011, 50, 9773-9793. 103  (a) Holm, R. H.; O’Connor, M. J. Prog. Inorg. Chem. 1971, 14, 241-401. (b) Nijhuis, C. A.; Jellema, E.; Sciarone, T. J. J.; Meetsma, A.; Budzelaar, P. H. M.; Hessen, B. Eur. J. Inorg. Chem. 2005, 2089-2099. (c) Alvarez, S.; Cirera, J. Angew. Chem. Int. Ed. 2006, 45, 3012– 3020. (d) Monillas, W. H.; Yap, G. P. A.; Theopold, K. H. J. Chem. Crystallogr. 2009, 39, 73-77. (e) Latreche, S.; Schaper, F. Inorg. Chim. Acta 2011, 365, 4953. 104  (a) Stolze, G.; Hähle, J. J. Organomet. Chem. 1967, 7, 301-310. (b) Edema, J. J. H.; Gambarotta, S.; van Bolhuis, F.; Smeets, W. J. J.; Spek, A. L.; Chiang, M. Y. J. Organomet. Chem. 1990, 389, 47-59. (c) Irwin, M.; Doyle, L. R.; Krämer, T.; Herchel, R.; McGrady, J. E.; Goicoechea, J. M. Inorg. Chem. 2012. 51, 12301–12312. 105  Chisholm, M. H.; Huffman, J. C.; Rothwell, I. P.; Bradley, P. G.; Kress, N.; Woodruff, W. H. J. Am. Chem. Soc. 1981, 103, 4945-4947. 106 Wang, M.; England, J.; Weyhermϋller, T.; Kokatam, S. L.; Pollock, C. J.; DeBeer, S.; Shen, J.; Yap, G. P. A.; Theopold, K. H.; Wieghardt, K. Inorg. Chem. in press (DOI: 10.1021/ic302743s) 107  Tondreau, A. M.; Milsmann, C.; Lobkovsky, E.; Chirik, P. J. Inorg. Chem. 2011, 50, 9888- 9895. 108  Nefedov, S. E.; Pasynskii, A. A.; Eremenko, I. L.; Orasakhatov, B.; Ellert, O. G.; Novotortsev, V. M.; Katser, S. B.; Antsyshkina, A. S.; Porai-Koshits, M. A. J. Organomet. Chem. 1988, 345, 97-104. 109  Shafir, A.; Arnold, J. Inorg. Chim. Acta 2003, 345, 216-220. 110  Jonas, K. Angew. Chem. Int. Ed. Engl. 1985, 24, 295-311. 111  Ritleng, V.; Barth, C.; Brenner, E.; Milosevic, S.; Chetcuti, M. J. Organometallics 2008, 27, 4223-4228.  133   112  Kelly, R. A.; Scott, III, N. M.; Diez-Gonzalez, S.; Stevens, E. D.; Nolan, S. P. Organometallics 2005, 24, 3442-3447. 113  Gunanathan, C.; Milstein, D. Acc. Chem. Res. 2011, 44, 588-602; van der Vlugt, J. I. Eur. J. Inorg. Chem., 2012, 363-375. 114  (a) Kayal, A.; Lee, S. C. Inorg. Chem. 2002, 41, 321-330. (b) Sydora, O. L.; Wolczanski, P. T.; Lobkovsky, E. B.; Buda, C.; Cundari, T. R. Inorg. Chem. 2005, 44, 2606-2618. (c) Sydora, O. L. D.; Kuiper, S.; Wolczanski, P. T.; Lobkovsky, E. B.; Dinescu, A.; Cundari, T. R. Inorg. Chem. 2006, 45, 2008-2021. (d) Groysman, S.; Villagran, D.; Nocera, D. G. Inorg. Chem. 2010, 49, 10759–10761. (e) Sun, M.; Mu, Y.; Liu, Y.; Wu, Q.; Ye, L. Organometallics 2011, 30, 669-675. (f) Qiu, P.; Cheng, R.; Liu, B.; Tumanskii, B.; Batrice, R. J.; Botoshansky, M.; Eisen, M. S. Organometallics 2011, 30, 2144-2148. 115  McGuinness, D. S. Chem. Rev. 2011, 111, 2321-2341. 116  (a) Lu, C. C.; Bill, E.; Weyhermüller, T.; Bothe, E.; Wieghardt, K. J. Am. Chem. Soc. 2008, 130, 3181-3197. (b) Lu, C. C.; DeBeer George, S.; Weyhermüller, T.; Bill, E.; Bothe, E.; Wieghardt, K. Angew. Chem. Int. Ed. 2008, 47, 6384-6387. 117  (a) Myers, T. W.; Kazem, N.; Stoll, S.; Britt, R. D.; Shanmugam, M.; Berben, L. A. J. Am. Chem. Soc. 2011, 133, 8662-8672. (b) Myers, T. W.; Berben, L. A. J. Am. Chem. Soc. 2011, 133, 11865-11867. (c) Myers, T. W. Berben, L. A. Inorg. Chem. 2012, 51, 1480-1488. 118  Kreisel, K. A.; Yap, G. P. A.; Theopold, K. H.; Eur. J. Inorg.Chem. 2012, 520-529 119  King, E. R.; Sazama, G. T.; Betley, T. A. J. Am. Chem. Soc. 2012, 134, 17858-17861. 120  Parkin, G. Acc. Chem. Res. 1992, 25, 455-460. 121  Birk, T.; Bendix, J. Inorg. Chem. 2003, 42, 7608-7615. 122 Smythe, N. C.; Schrock, R. R.; Muller, P.; Weare, W. W. Inorg. Chem. 2006, 45, 7111-7118. 123  Gorelsky, S. I.; Solomon, E. I. Theoretical Chem. Acc. 2008, 119, 5-67. 124  Pangborn, A. B.; Giardello, M. A.; Grubbs, R. G.; Rosen, R. K.; Timmers, F.J. Organometallics 1996, 15, 1518-1520. 125  (a) Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.; Noack, C. L.; Piers, W. E.; Parvez, M. Organometallics 2003, 22, 1577-1579; (b) Liu, X.; Gao, W.; Mu, Y.; Li, G.; Ye, L.; Xia, H.; Ren, Y.; Feng, S. Organometallics 2005, 24, 1614-1619. 126  Abrams, M. B.; Scott, B. L.; Baker, R. T.; Organometallics 2000, 19, 4944-4956. 127  Burstein, C.; Lehmann, C. W.; Glorius, F. Tetrahedron 2005, 61, 6207-6217.  134   128  Eisenberg, D. C.; Lawrie, C. J. C.; Moody, A. E.; Norton, J. R. J. Am. Chem. Soc. 1991, 113, 4888-4895. 129  Chen, D. W.; Ochiai, M. J. Org. Chem. 1999, 64, 6804-6814. 130  Bradley, D. C.; Hursthouse, M. B.; Newing, C. W.; Welch, A. J. J. Chem. Soc. Chem. Commun. 1972, 567-568. 131  TWINABS. Bruker Nonius scaling and absorption for twinned crystals - V2008/2, Bruker AXS Inc., Madison, Wisconsin, USA (2008). 132  Level, A. B. P. Coord. Chem. Rev. 2010, 254, 1397-1405. 133  Brown, S. N. Inorg. Chem. 2012, 51, 1251-1260. 134  Leung, W. H. Eur. J. Inorg. Chem. 2003, 583-593. 135  Ison, E. A.; Abboud, K, A.; Boncella, J. M. Organometallics 2006, 25, 1557-1564. 136  (a) Nieto, I.; Ding, F.; Bontchev, R. P.; Wang, H.; Smith, J. M. J. Am. Chem. Soc. 2008, 130, 2716-2717. (b) King, E. R.; Hennessy, E. T.; Betley, T. A. J. Am. Chem. Soc. 2011, 133, 4917-4923. (c) Cowley, R. E.; Eckert, N. A.; Vaddadi, S.; Figg, T. M.; Cundari, T. R.; Holland, P. L.; J. Am. Chem. Soc. 2011, 133, 9796-9811. (d) Bowman, A. C.; Milsmann, C.; Bill, E.; Turner, Z. R.; Lobkovsky, E.; DeBeer, S.; Wighardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2011, 133, 17353-17369. (e) Monillas, W. H.; Yap, G. P. A.; Theopold, K. H. Inorg. Chim. Acta 2011, 369, 103-119. (f) Saouma, C. T.; Peters, J. C. Coord. Chem. Rev. 2011, 255, 920-937. (g) Gephart, R. T.; Warren, T. H. Organometallics 2012, 31, 7728-7752. (h) Wiese, S.; McAfee, J. L.; Pahls, D. R.; McMullin, C. L.; Cundari, T. R.; Warren, T. H. J. Am. Chem. Soc. 2012, 134, 10114-10121. (i) Tsai, Y. C. Coord. Chem. Rev. 2012, 256, 722-758. 137  Fortier, S.; Walensky, J. R.; Wu, G.; Hayton, T. W. J. Am. Chem. Soc. 2011, 133, 6894-6897. 138  Ketterer, N. A.; Fan, H.; Blackmore, K. J.; Yang, X.; Ziller, J. W.; Baik, M. H.; Heyduk, A. F. J. Am. Chem. Soc. 2008, 130, 4364-4374. 139  (a) Meijboom, N.; Schaverien, C. J.; Orpen, A. G. Organometallics 1990, 9, 774-782. (b) Chew, K. C.; Clegg, W.; Coles, M. P.; Elsegood, M. R. J.; Gibson, V. C.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 1999, 2633-2639. 140  MacLeod, K. C.; Patrick, B. O.; Smith, K. M. Inorg. Chem. 2012, 51, 688-700. 141  Daniele, S.; Drost, C.; Gehrhus, B.; Hawkins, M.; Hitchcock, P. B.; Lappert, M. F.; Merle, P. G.; Bott, S. G. J. Chem. Soc., Dalton Trans 2001, 3179-3188.  135   142  (a) Cowley, R. E.; Bontchev, R. P.; Sorrell, J.; Sarracino, O.; Feng, Y.; Wang, H.; Smith, J. M. J. Am. Chem. Soc. 2007, 129, 2424-2425. (b) Iluc, V. M.; Hillhouse, G. J. Am. Chem. Soc. 2010, 132, 15148-15150. 143  (a) Wicker, B. F.; Fan, H.; Hickey, A. K.; Crestani, M. G.; Scott, J.; Pink, M.; Mindiola, D. J. J. Am. Chem. Soc. 2012, 134, 20081-20096. (b) Cowley, R. E.; Holland, P. L. Inorg. Chem. 2012, 51, 8352-8361. 144  Diethelm, S.; Schindler, C. S.; Carreira, E. M. Org. Lett., 2010, 12, 3950-3953. 145  Lyaskovskyy, V.; Suarez, A. I. O.; Lu, H.; Jiang, H.; Zhang, X. P. Bruin, B. J. Am. Chem. Soc. 2011, 134, 12264-12273. 146  Birkofer, L.; Kuhlthau, H. P.; Ritter, A. Chem. Ber. 1960, 93, 2810. 147  Barral, K.; Moorhouse, A. D.; Moses, J. E. Org. Lett. 2007, 9, 1809-1811. 148  White, L. M.; Dougherty, D. A. J. Am. Chem. Soc. 1984, 106, 3466-3474. 136  Appendices Appendix A. Supplementary X-ray Data Table A. 1. Crystal data and refinement parameters for X-ray structures of 2.2a, 2.2b, 2.3a, 2.3b, 2.3c, and 2.3d.  2.2a 2.2b 2.3a 2.3b 2.3c 2.3d Formula C29H36N2IOCr C29H36N2CrI C30H39N2OCr C30H39N2Cr C29H37N2Cr C30H36N2F3Cr Formula Weight 607.5 591.50 495.63 479.63 465.61 533.61 Crystal Color, Habit black, tablet black, irregular black, prism black, prism black, plate black, prism Crystal Dimensions, mm 0.18  0.33  0.60 0.17  0.26  0.42 0.32  0.46  0.48 0.20  0.25  0.35 0.10  0.43  0.60 0.12  0.25  0.45 Crystal System monoclinic triclinic triclinic orthorhombic orthorhombic triclinic Space Group P 21/n P -1 P -1 P bca P bca P -1 a, Å 11.7438(11) 10.6796(10) 9.3251(2) 8.5493(10) 10.6610(18) 9.3223(16) b, Å 16.9018(14) 11.1452(9) 9.8141(3) 17.5673(16) 19.4810(18) 9.7973(19) c, Å 14.9717(13) 12.5877(11) 14.6976(4) 35.282(3) 24.251(3) 15.129(3) α, º 90.0 101.817(4) 80.786(1) 90.0 90.0 80.996(7) β, º 110.53(13) 109.367(4) 82.742(1) 90.0 90.0 80.608(7) γ, º 90.0 94.167(4) 86.455(1) 90.0 90.0 86.496(7) V, Å 3  2783.01(45) 1367.4(2) 1315.9(1) 5298.9(9) 5036.6(9) 1345.6(4) Z 4 2 2 8 8 2 Dcalc, g/cm 3  1.450 1.437 1.251 1.202 1.228 1.317 F000 1236.00 602.00 530.00 2056.00 1992.00 562.00 µ(Moα), cm-1 15.43 15.66 4.59 4.51 4.73 4.67 Data Images (no., t/s) 1350 1569 2047 1029 1008 1621 2θmax 56.1 56.2 56.1 56.1 56.0 55.0 Reflections measrd 37750 21588 20450 53996 53500 27365 Unique reflcn, Rint 6762, 0.030 6591, 0.024 6194, 0.023 6381, 0.041 6043, 0.033 6006, 0.061 Absorption, Tmin, Tmax 0.600, 0.757 0.620, 0.766 0.744, 0.863 0.825, 0.914 0.822, 0.954 0.734, 0.946 Obsrvd data (I>2.00σ (I)) 5818 5821 5497 5009 4835 4897 No. parameters 309 385 315 306 291 360 R1, wR2 (F 2 , all data) 0.032, 0.071 0.029, 0.057 0.039, 0.082 0.053, 0.131 0.052, 0.104 0.067, 0.162 R1, wR2 (F, I>2.00σ (I)) 0.025, 0.065 0.024, 0.054 0.032, 0.077 0.037, 0.090 0.036, 0.093 0.053, 0.143 Goodness of Fit 0.792 1.07 1.05 1.04 1.04 1.06 Max, Min peak, e - /Å 3  0.71, -0.81 0.69, -0.45 0.32, -0.36 0.29, -0.46 0.49, -0.35 1.11, -0.97 137  Table A. 2. Crystal data and refinement parameters for X-ray structures of 2.4a, 2.4b, 2,4c, 2.4d, 2.6, and 2.7.  2.4a 2.4b 2.4c 2.4d 2.6 2.7 Formula C29H36N2OCrCl C29H36N2CrCl C28H34N2CrCl C29H33N2F3ClCr C36H43N2O3CrS C35H47N2Cr Formula Weight 516.05 500.05 486.02 554.02 635.78 547.80 Crystal Color, Habit black, block black, irregular black, prism black, plate black, plate black, irregular Crystal Dimensions, mm 0.22  0.25  0.50 0.03  0.10  0.12 0.38  0.48  0.55 0.03  0.24  0.56 0.05  0.15  0.32 0.18  0.27  0.45 Crystal System trigonal monoclinic orthorhombic monoclinic Triclinic Monoclinic Space Group P -3 P 21/c P bca P 21/n P -1 P 21/c a, Å 20.603(3) 15.4866(15) 10.5875(18) 12.2431(14) 10.9124(13) 14.8508(14) b, Å 20.603 9.7132(9) 19.271(3) 9.8444(11) 11.3990(12) 10.1551(10) c, Å 11.673(19) 17.9884(18) 24.113(4) 22.431(2) 14.8482(18) 20.9587(21) α, º 90.0 90.0 90.0 90.0 83.332(5) 90.0 β, º 90.0 90.428(4) 90.0 91.349(4) 78.022(5) 99.007(5) γ, º 120.0  90.0 90.0 90.0 63.468(4) 90.0 V, Å 3  4291.2(10) 6848.2(2) 4919.9(14) 2702.7(5) 6109.8(4) 3121.8(5) Z 6 4 8 4 2 4 Dcalc, g/cm 3  1.198 1.228 1.312 1.36 1.307 1.17 F000 1638.00 1060.00 2056.00 1156.00 674.00 1179.8 µ(Moα), cm-1 5.15 5.40 5.92 5.63 4.57 3.91 Data Images (no., t/s) 1236 1174 1539 814 1647 1242 2θmax 55.9 50.0 56.0 50.28 52.9 50.75 Reflections measrd 56237 30729 80329 22251 27954 39378 Unique reflcn, Rint 6867, 0.051 4562, 0.063 5900, 0.031 4828, 0.046 6304, 0.033 5693, 0.0464 Absorption, Tmin, Tmax 0.797, 0.893 0.890, 0.984 0.730, 0.799 0.878, 0.983 0.861, 0.977 0.815, 0.932 Obsrvd data (I>2.00σ (I)) 5500 3303 5900 3456 4984 4570 No. parameters 314 305 295 329 424 343 R1, wR2 (F 2 , all data) 0.047, 0.091 0.079, 0.136 0.038, 0.083 0.073, 0.103 0.059, 0.103 0.0731, 0.1507 R1, wR2 (F, I>2.00σ (I)) 0.033, 0.086 0.049, 0.122 0.030, 0.077 0.042, 0.090 0.040, 0.094 0.0544, 0.1365 Goodness of Fit 1.07 1.09 1.07 1.013 1.05 1.081 Max, Min peak, e - /Å 3  0.34, -0.31 0.46, -0.35 0.35, -0.44 0.38, -0.30 0.59, -0.40 0.687, -0.484   138  Table A. 3. Crystal data and refinement parameters for X-ray structures of 2.8, 2.9, 3.5, 3.6, 3.7, and 3.8.  2.8 2.9 3.5 3.6 3.7 3.8 Formula C36H43N2OCr C31H34N2Cr C15H24N2Cr C20H39N3Si2Cr C20H26N2Cr C24H34N2Cr Formula Weight 571.72 486.60 284.36 429.72 346.43 402.53 Crystal Color, Habit black, irregular black, irregular brown, prism purple, prism brown, prism brown, prism Crystal Dimensions, mm 0.34  0.40  0.40 0.18  0.25  0.34 0.20  0.20  0.45 0.16  0.20  0.25 0.15  0.25  0.45 0.10  0.125  0.225 Crystal System monoclinic triclinic monoclinic orthorhombic triclinic monoclinic Space Group P 21/n P -1 P 21/n P na21 P -1 P 21/n a, Å 11.808(17) 9.2266(14) 8.6190(6) 17.0388(12) 9.8811(2) 10.5070(8) b, Å 19.00(2) 11.0286(16) 10.5220(7) 10.4627(7) 10.3481(2) 14.1701(10) c, Å 13.905(16) 13.5053(19) 17.6750(11) 27.239(2) 10.6546(3) 15.7814(12) α, º 90.0 81.930(7) 90.0 90.0 80.1010(10) 90.0 β, º 99.71(9) 82.478(7) 97.8260(10) 90.0 70.5640(10) 108.840(3) γ, º 90.0 72.311(7) 90.0 90.0 65.3050(10) 90.0 V, Å 3  3075(7) 1290.6(3) 1588.00(18) 4855.9(6) 932.71(4) 2223.7(3) Z 4 2 4 4 2 4 Dcalc, g/cm 3  1.235 1.25 1.189 1.176 1.234 1.202 F000 1220.00 515.9 608.00 1856.00 368.00 864.00 µ(Moα), cm-1 4.02 4.64 7.89 5.79 6.14 5.25 Data Images (no., t/s) 1252 1085 1008 1445 2256 992 2θmax 56.1 46.06 60.04 60.12 60.32 59.34 Reflections measrd 33167 11493 17926 51736 19704 17956 Unique reflcn, Rint 7438, 0.051 3422, 0.0392 4631, 0.0181 14116, 0.0273 5452, 0.0198 6242, 0.0582 Absorption, Tmin, Tmax 0.566, 0.872 0.723, 0.920 0.789, 0.868 0.797, 0.912 0.798, 0.912 0.851, 0.949 Obsrvd data (I>2.00σ (I)) 6029 2733 4121 12888 4999 4215 No. parameters 368 308 183 469 208 244 R1, wR2 (F 2 , all data) 0.058, 0.0129 0.0631, 0.1214 0.0317, 0.0697 0.0414, 0.0905 0.0297, 0.0739 0.0861, 0.1293 R1, wR2 (F, I>2.00σ (I)) 0.044, 0.114 0.0444, 0.1094 0.0264, 0.0670 0.0357, 0.0873 0.0264, 0.0719 0.0443, 0.1009 Goodness of Fit 1.06 1.104 1.06 1.072 1.051 1.033 Max, Min peak, e - /Å 3  0.69, -0.76 0.43, -0.487 0.435, -0.313 0.617, -0.386 0.368, -0.272 0.449, -0.470   139  Table A. 4. Crystal data and refinement parameters for X-ray structures of 3.9, 3.10, 3.12, 4.1, 4.4, and 4.5.  3.9 3.10 3.12 4.1 4.4 4.5 Formula C26H31N2Cr C28H35N2Cr C28H31N2Cr C31H41N2Cr C20H18N3Cr C22H44N4Si4Cr Formula Weight 423.53 451.58 447.55 493.66 338.36 528.97 Crystal Color, Habit red, prism red, prism black, plate black, prism black, prism black, prism Crystal Dimensions, mm 0.15  0.20  0.35 0.275  0.300  0.325 0.02  0.240  0.400 0.25  0.25  0.40 0.22  0.44  0.54 0.20  0.25  0.35 Crystal System monoclinic monoclinic monoclinic monoclinic monoclinic monoclinic Space Group P 21/c P 21/n P 21 P 21 P 21/n P 21/c a, Å 15.2220(16) 16.8643(5) 8.3298(6) 22.2076(14) 7.4323(4) 14.8670(2) b, Å 8.4120(8) 8.4154(3) 9.9848(7) 10.7791(6) 11.9141(6) 22.9622(3) c, Å 19.1190(19) 34.9049(10) 15.0057(11) 37.7205(23) 17.8562(10) 17.5517(2) α, º 90.0 90.0 90.0 90.0 90.0 90.0 β, º 110.866(2) 95.0210(10) 104.031(4) 105.701(2) 91.950(2) 99.344(1) γ, º 90.0 90.0 90.0 90.0 90.0 90.0 V, Å 3  2287.6(4) 4934.7(3) 1210.81(15) 8692.54(52) 1580.24(15) 5912.28(13) Z 4 8 2 12 4 8 Dcalc, g/cm 3  1.230 1.216 1.228 1.13 1.422 2.352 F000 900.00 1928 474.00 3180 704.00 2272 µ(Moα), cm-1 5.14 4.80 4.89 4.14 7.24 5.65 Data Images (no., t/s) 1085 1027 1653 1064 8625 103520 2θmax 60.08 60.24 60.02 55.96 56.14 59.87 Reflections measrd 25320 51850 20997 88464 21458 64040 Unique reflcn, Rint 6689, 0.0297 14427, 0.0450 6604, 0.0436 39600, 0.0453 3834, 0.031 17276, 0.0435 Absorption, Tmin, Tmax 0.873, 0.926 0.732, 0.876 0.905, 0.990 0.752, 0.902 0.755, 0.853 0.827, 0.893 Obsrvd data (I>2.00σ (I)) 5549 11637 5877 27677 3396 11815 No. parameters 262 563 280 1871 208 559 R1, wR2 (F 2 , all data) 0.0429, 0.0840 0.0666, 0.1473 0.0479, 0.0858 0.0966, 0.1118 0.0354, 0.0816 0.0803, 0.1066 R1, wR2 (F, I>2.00σ (I)) 0.0320, 0.784 0.0449, 0.1215 0.0365, 0.0858 0.0537, 0.0972 0.0300, 0.0783 0.0415, 0.0915 Goodness of Fit 1.022 1.180 1.134 1.010 1.044 1.008 Max, Min peak, e - /Å 3  0.489, -0.391 0.695, -0.991 0.485, -0.543 0.326, -0.418 0.446, -0.496 0.555, -0.348   140  Table A. 5. Crystal data and refinement parameters for X-ray structures of 4.6, 4.7, 4.8a, 4.8b, 4.9a, and 4.9b.  4.6 4.7 4.8a 4.8b 4.9a 4.9b Formula C34H46N4CrO2 C45H64N6Cr C31H41N2CrCl C25H29N2CrCl C40H52N2OCr C38H56N2OCr Formula Weight 594.74 741.00 529.11 444.95 628.84 608.85 Crystal Color, Habit black, irregular black, prism black, irregular black, plate black, tablet black, prism Crystal Dimensions, mm 0.12  0.15  0.45 0.05  0.06  0.10 0.12  0.23  0.47 0.12  0.40  0.48 0.35  0.45  0.60 0.35  0.50  0.55 Crystal System triclinic orthorhombic orthorhombic monoclinic triclinic monoclinic Space Group P -1 P ccn P bnm P 21/n P -1 P 21/c a, Å 9.3585(7) 11.2370(13) 10.5374(2) 81510(4) 12.1823(7) 11.2842(3) b, Å 12.7652(10) 25.1230(28) 13.0276(2) 13.9425(7) 12.3521(7) 27.0693(9) c, Å 13.9196(11) 15.9180(18) 20.7603(4) 19.9028(10) 13.2389(8) 12.1378(4) α, º 95.352(2) 90.0 90.0 90.0 111.688(3) 90.0 β, º 101.6460(2) 90.0 90.0 94.522(3) 106.727(3) 111.777(10) γ, º 101.640(2) 90.0 90.0 90.0 91.867(3) 90.0 V, Å 3  1593(2) 4493.77(9) 2849.91(9) 2254.82(19) 1751.06(18) 3442.97(19) Z 4 6 4 4 2 4 Dcalc, g/cm 3  1.240 1.095 1.23 1.311 1.19 1.175 F000 635.90 1600 1127.8 936 675.90 1320 µ(Moα), cm-1 3.95 2.90 5.16 6.39 3.59 3.63 Data Images (no., t/s) 2024 1100 862 1582 2992 1544 2θmax 55.78 59.28 56.12 55.88 56.1 55.78 Reflections measrd 28437 43956 25342 53834 45684 47576 Unique reflcn, Rint 7608, 0.0470 6323, 0.0557 3540, 0.0408 5394, 0.1494 8362, 0.0304 8191, 0.0454 Absorption, Tmin, Tmax 0.647, 0.954 0.714, 0.986 0.786, 0.840 0.535, 0.926 0.760, 0.882 0.798, 0.881 Obsrvd data (I>2.00σ (I)) 6104 4397 2893 3981 7338 6366 No. parameters 370 234 163 268 397 442 R1, wR2 (F 2 , all data) 0.0572, 0.1149 0.0989, 0.1620 0.0463, 0.0876 0.0964, 0.1714 0.0427, 0.0989 0.0616, 0.1148 R1, wR2 (F, I>2.00σ (I)) 0.0409, 0.1041 0.0639, 0.1415 0.0320, 0.0801 0.0697, 0.1613 0.0355, 0.0937 0.0419, 0.1032 Goodness of Fit 1.035 1.036 1.059 1.048 1.033 1.030 Max, Min peak, e - /Å 3  0.488, -0.313 0.595, -0.556 0.378, -0.393 1.025, -0.645 0.447, -0.417 0.516, -0.663   141  Table A. 6. Crystal data and refinement parameters for X-ray structures of 4.10, 4.12, 4.13, 4.14, 4.15, and 4.16.  4.10 4.12 4.13 4.14 4.15 4.16 Formula C20H21N2Cr C20H21N2CrI C29H32N2OCr C34H37N3Cr C21H25N2Cr C31H42N2OCr Formula Weight 341.39 468.29 476.57 591.67 371.46 510.66 Crystal Color, Habit black, irregular black, thin black, prism black, irregular black, needle black, plate Crystal Dimensions, mm 0.08  0.32  0.52 0.025  0.025  0.30 0.15  0.20  0.20 0.15  0.15  0.16 0.06  0.10  0.60 0.075  0.15  0.30 Crystal System orthorhombic orthorhombic triclinic triclinic orthorhombic orthorhombic Space Group P 21 P bca P -1 P -1 P 21 P bnm a, Å 13.1264(14) 10.0650(5) 8.2157(7) 12.6129(13) 7.8891(2) 10.7260(9) b, Å 7.0886(8) 17.6930(9) 8.8464(8) 15.4339(16) 13.8427(4) 12.2950(11) c, Å 18.898(2) 20.9960(11) 16.8445(15) 16.722(17) 17.3566(5) 20.8810(18) α, º 90.00 90.0 89.077(2) 65.722(2) 90.00 90.0 β, º 100.821(6) 90.0 89.842(2) 74.079(2) 90.00 90.0 γ, º 90.00 90.0 77.669(2) 83.499(2) 90.00 90.0 V, Å 3  1727.2(3) 20.9960(11) 1195.85(18) 2848.2(5) 1895.45(9) 2753.7(4) Z 4 8 2 4 4 8 Dcalc, g/cm 3  1.313 1.664 1.324 1.38 1.302 1.232 F000 716.00 1856 504.00 1240 788.00 1096 µ(Moα), cm-1 6.63 2.266 5.03 7.09 6.10 4.41 Data Images (no., t/s) 800 871 2833 2815  949 1059 2θmax 45.54 55.80 60.38 56.46 55.98 60.10 Reflections measrd 2546 26941 33519 15271 18189 31075 Unique reflcn, Rint 2546, 0.00 4465, 0.0224 7055, 0.0325 13940, 0.376 4485, 0.0581 4129, 0.0408 Absorption, Tmin, Tmax 0.626, 0.948 0.794, 0.945 0.877, 0.927 0.709, 0.888 0.878, 0.964 0.921, 0.967 Obsrvd data (I>2.00σ (I)) 2146 3991 5876 10254 3613 3253 No. parameters 362 220 301 712 230 163 R1, wR2 (F 2 , all data) 0.1022, 0.2161 0.0216, 0.0440 0.0458, 0.0867 0.1234, 0.2666 0.0568, 0.0807 0.0540, 0.1028 R1, wR2 (F, I>2.00σ (I)) 0.0816, 0.1988 0.0169, 0.0412 0.0337, 0.0811 0.0841, 0.2536 0.0376, 0.0743 0.0365, 0.0923 Goodness of Fit 1.075 1.073 1.053 1.131 1.023 1.059 Max, Min peak, e - /Å 3  2.163, -1.262 0.556, -0.371 0.485, -0.429 1.284, -0.786 0.317, -0.347 0.980, -0.441   142  Table A. 7. Crystal data and refinement parameters for X-ray structures of 4.17, 4.18, 4.19, 5.2, 5.5, and 5.6.  4.17 4.18 4.19 5.2 5.5 5.6 Formula C31H41N2CrF C31H41N5Cr C31H41N3Cr C21H35N2OSi2Cr C27H42N3Si2Cr C23H32N3Si2Cr Formula Weight 512.66 535.66 507.67 439.69 516.82 458.70 Crystal Color, Habit black, prism blue, prism black, tablet black, prism black, plate black, prism Crystal Dimensions, mm 0.30  0.30  0.40 0.040  0.085  0.21 0.08  0.16  0.28 0.10  0.15  0.25 0.10  0.40  0.40 0.10  0.15  0.25 Crystal System orthorhombic orthorhombic orthorhombic monoclinic monoclinic orthorhombic Space Group P nma P na21 P nma C 2/m P 21/n P bca a, Å 12.2435(2) 12.6761(16) 12.2312(11) 13.073(2) 10.5631(12) 18.3988(14) b, Å 20.9577(4) 20.917(3) 20.990(2) 15.574(3) 19.238(2) 18.9327(16) c, Å 10.7835(4) 10.5575(14) 10.860(10) 12.961(2) 14.5072(16) 17.386(2) α, º 90.00 90.0 90.00 90.00 90.00 90.0 β, º 90.00 90.0 90.00 118.861(9) 111.307(6) 90.0 γ, º 90.00 90.0 90.00 90.00 90.00 90.0 V, Å 3  2767.00(12) 2799.3(6) 2788.2(4) 2310.9(7) 2746.5(5) 9539.6(13) Z 4 4 4 4 4 16 Dcalc, g/cm 3  1.231 1.267 1.209 1.264 1.25 1.278 F000 1096 1140 1088 940 1108 3888 µ(Moα), cm-1 4.41 4.59 4.33 6.12 5.24 5.94 Data Images (no., t/s) 1111 975.00 1184 1239  993.00 403.00 2θmax 60.14 60.08 60.08 57.46 51.50 54.472 Reflections measrd 29157 30073 28666 11469 17253 39505 Unique reflcn, Rint 4153, 0.0260 8163, 0.0468 4176, 0.0298 3025, 0.0433 5084, 0.0767 10825, 0.0536 Absorption, Tmin, Tmax 0.798, 0.876 0.868, 0.982 0.896, 0.966 0.712, 0.869 0.811, 0.949 0.867, 0.942 Obsrvd data (I>2.00σ (I)) 12474 8175 3570 2104 3241 7188 No. parameters 3561 339 163 165 298 528 R1, wR2 (F 2 , all data) 0.451, 0.1083 0.0605, 0.0921 0.0466, 0.0993 0.0767, 0.1127 0.1148, 0.1868 0.0832, 0.1012 R1, wR2 (F, I>2.00σ (I)) 0.0371, 0.1014 0.0369, 0.0830 0.0373, 0.0993 0.0424, 0.0977 0.0653, 0.1667 0.0413, 0.0866 Goodness of Fit 1.033 1.013 1.067 1.044 1.080 1.006 Max, Min peak, e - /Å 3  1.392, -0.529 0.302, -0.564 1.271, -0.388 0.495, -0.514 0.844, -0.593 0.373, -0.379   143  Table A. 8. Crystal data and refinement parameters for X-ray structures of 5.7, 5.8, 5.10, 5.12, 5.14, and 5.15.  5.7 5.8 5.10 5.11 5.13 5.14 Formula C24H34N3Si2Cr C26H38N3Si2Cr C30H47N4Cr C40H48N2PCr C21H31N2CrCl C31H46N3Cr Formula Weight 472.72 500.77 515.72 639.77 398.93 512.71 Crystal Color, Habit black, rhombohedron black, prism red, prism black, irregular black, plate black, plate Crystal Dimensions, mm 0.20  0.25  0.35 0.15  0.20  0.25 0.10  0.13  0.25 0.03  0.10  0.11 0.05  0.25  0.30 0.10  0.15  0.25 Crystal System monoclinic monoclinic monoclinic orthorhombic orthorhombic monoclinic Space Group P 21/n P 21/c C m P na21 P bna C 2/m a, Å 9.1820(6) 9.4360(14) 9.1391(8) 11.8266(10) 13.5642(10) 15.964(3) b, Å 13.4120(9) 26.568(4) 18.9821(15) 19.1338(14) 16.8668(13) 13.0182(19) c, Å 19.9770(13) 11.3270(17) 8.4840(7) 15.6848(15) 18.2940(14) 14.345(3) α, º 90.00 90.0 90.00 90.0 90.00 90.0 β, º 101.2170(10) 108.782(3) 104.558(2) 90.0 90.00 113.436(5) γ, º 90.00 90.0 90.00 90.0 90.00 90.0 V, Å 3  2413.2(3) 2688.3(7) 1424.5(2) 3549.3(5) 4185.4(5) 2735.2(8) Z 4 4 2 4 8 4 Dcalc, g/cm 3  1.301 1.237 1.202 1.197 1.266 1.245 F000 1004 1068 558 1364 1696 1108 µ(Moα), cm-1 5.89 5.33 4.26 3.97 6.80 4.42 Data Images (no., t/s) 1191 1008 1045  910 587.00 1081 2θmax 60.06 60.14 60.18 56.56 57.42 56.00 Reflections measrd 27044 31476 8046 31939 23860 12656 Unique reflcn, Rint 7033, 0.0182 7880, 0.0376 3876, 0.0326 8617, 0.0572 5426, 0.0462 3404, 0.0359 Absorption, Tmin, Tmax 0.850, 0.889 0.877, 0.923 0.749, 0.958 0.913, 0.988 0.871, 0.967 0.860, 0.957 Obsrvd data (I>2.00σ (I)) 6277 6367 3690 7294 3888 2645 No. parameters 272 291 163 398 226 169 R1, wR2 (F 2 , all data) 0.326, 0.0821 0.0556, 0.0992 0.0617, 0.1603 0.0605, 0.1046 0.0656, 0.0952 0.0598, 0.1073 R1, wR2 (F, I>2.00σ (I)) 0.0276, 0.0784 0.0406, 0.0927 0.0527, 0.1409 0.0458, 0.0982 0.0364, 0.0814 0.0393, 0.0976 Goodness of Fit 1.047 1.067 1.167 1.025 1.010 1.053 Max, Min peak, e - /Å 3  0.517, -0.364 0.456, -0.424 0.442, -1.289 0.274, -0.405 0.363, -0.416 0.418, -0.371  144  Table A. 9. Crystal data and refinement parameters for X-ray structures of 5.16, 5.17, 5.18, 5.19, 5.21, and 5.23.  5.15 5.16 5.17 5.19 5.20 Formula C34H48N4Cr C42H62N4OCr C57H67N4Si2CrMg C23H19N2CrCl C35H56N2Si2O Cr Formula Weight 564.76 992.64 992.64 410.85 629.00 Crystal Color, Habit black, prism black, prism black, prism black, irregular black, plate Crystal Dimensions, mm 0.06  0.11  0.27 0.10  0.16  0.20 0.10  0.125  0.150 0.10  0.20  0.26 0.05  0.10  0.20 Crystal System triclinic monoclinic triclinic triclinic monoclinic Space Group P -1 P 21/c P -1 P -1 P 21/n a, Å 12.1837(4) 10.6230(13) 11.1880(7) 10.747(4) 18.319(10) b, Å 12.1849(3) 10.6710(14) 12.0030(8) 12.676(4) 10.639(8) c, Å 12.4184(4) 17.125(2) 21.5490(15) 16.141(5) 19.057(15) α, º 106.3990(10) 90.00 79.261(2) 90.420(6) 90.00 β, º 91.635(2) 90.856(2) 80.649(2) 107.496(6) 111.137(20) γ, º 113.395(2) 90.00 64.9720(10) 110.920(5) 90.00 V, Å 3  1602.36(8) 1912.6(4) 2564.8(3) 1942.6(11) 3487.1(5) Z 2 2 2 4 4 Dcalc, g/cm 3  1.171 1.290 1.285 1.405 1.20 F000 608.00 796.00 1050 848 1360 µ(Moα), cm-1 3.84 6.06 5.24 7.36 4.25 Data Images (no., t/s) 1736 1031 1560  2427 1078 2θmax 55.86 60.06 60.18 45.28 60.14 Reflections measrd 29214 21767 37008 28907 38613 Unique reflcn, Rint 7442, 0.0280 5569, 0.0374 14651, 0.0314 4962, 0.1822 10192, 0.0533 Absorption, Tmin, Tmax 0.862, 0.977 0.895, 0.941 0.897, 0.949 0.543, 0.929 0.927, 0.979 Obsrvd data (I>2.00σ (I)) 6059 4488 10663 4070 7200 No. parameters 358 246 618 462 371 R1, wR2 (F 2 , all data) 0.0558, 0.1152 0.0489, 0.0923 0.0701, 0.1061 0.1531, 0.3480 0.0769, 0.1100 R1, wR2 (F, I>2.00σ (I)) 0.0417, 0.1072 0.0346, 0.0851 0.0422, 0.0948 0.1357, 0.3382 0.0428, 0.0970 Goodness of Fit 1.049 1.020 1.008 1.099 1.012 Max, Min peak, e - /Å 3  0.508, -0.426 0.678, -0.432 0.757, -0.426 2.343, -1.140 0.544, -0.456  145  Table A. 10. Crystal data and refinement parameters for X-ray structures of 5.24.  5.22 5.23 Formula C28H38N3SO2Cr C32H51N3O2Si2SCr Formula Weight 533.68 650.00 Crystal Color, Habit black, prism black, prism Crystal Dimensions, mm 0.025  0.075  0.100 0.06  0.095  0.175 Crystal System orthorhombic monoclinic Space Group P bca P 21/n a, Å 19.539(2) 15.9850(18) b, Å 9.9443(11) 11.6860(13) c, Å 27.280(3) 19.444(2) α, º 90.0 90.00 β, º 90.0 110.836(3) γ, º 90.0 90.00 V, Å 3  5300.6(10) 3394.6(7) Z 8 4 Dcalc, g/cm 3  1.338 1.272 F000 2272 1392 µ(Moα), cm-1 5.41 5.01 Data Images (no., t/s) 930 1144 2θmax 46.04 60.14 Reflections measrd 27184 39849 Unique reflcn, Rint 3682, 0.1263 9932, 0.0576 Absorption, Tmin, Tmax 0.780, 0.987 0.917, 0.970 Obsrvd data (I>2.00σ (I)) 2370 7024 No. parameters 311 371 R1, wR2 (F 2 , all data) 0.1084, 0.1338 0.0743, 0.0969 R1, wR2 (F, I>2.00σ (I)) 0.0579, 0.1153 0.0409, 0.0855 Goodness of Fit 1.078 1.004 Max, Min peak, e - /Å 3  0.659, -0.375 0.444, -0.400   146  Appendix B. 1 H NMR and UV-vis Spectra  Figure B.1. 1H NMR (400 MHz, C6D6) spectrum 5.15. 147   Figure B.2. 1H NMR (400 MHz, CDCl3) spectrum of organic product benzosultam. S HN O O 148   Figure B.3. UV-vis absorption spectra of complex 5.18 in hexane [2.37 x 10 -4  M]. N N Cr 5.18

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