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Synthesis of chromium complexes with bipyridine radican anions Moisey, Luke 2015

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  SYNTHESIS OF CHROMIUM COMPLEXES WITH BIPYRIDINE RADICAL ANIONS  by  Luke Moisey  B.Sc., The University of Alberta, 2007   A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE  in  THE COLLEGE OF GRADUATE STUDIES (Chemistry)  THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan)    June 2015 © Luke Moisey, 2015  ii  Abstract  This thesis describes the synthesis of new, well-defined paramagnetic inorganic and organometallic molecules that contain the metal chromium.  Throughout this thesis, 2,2’-bipyridines (Rbpy, R=H, CMe3) are used as an ancillary redox active ligand and explored for potential radical character.  The reaction of Cr[N(SiMe3)2]2(THF)2 with Ph-nacnacH yielded Cr(Ph-nacnac)[N(SiMe3)2].  The bound amide ligand can be removed through protonation with [tbpyH][BPh4] and tbpy to afford the octahedral [Cr(Ph-nacnac)(tbpy)2][BPh4] complex with a single unpaired electron on the tbpy ligands.  Reaction of Cr(bpy)[N(SiMe3)2]2 with two equivalents of 8-hydroxyquinoline affords the octahedral complex, Cr(bpy)(8-hydroxyquinoline)2, where the LX• radical is now centred on the single tbpy ligand.  Protonation to remove the amides in Cr[N(SiMe3)2]2(THF)2 with 2-aminodiphenylamine yielded the tetrameric [Cr(μ-NHC6H4-2-μ-NC6H5)]4 complex.  CrCl2(tBu-acac)(tbpy) reacted with AgO2CPh to yield the trans carboxylate Cr(O2CPh)2(tbpy)(tBu-acac) with a neutral tbpy ligand.  Subsequent reactions with the chromium dichloride with PhMgCl yielded a [CrPh3(tbpy)][Mg(tBu-acac)(THF)4] complex.  The complex is an unusual square-pyramidal anionic complex with a tbpy based radical. iii  Preface   Some complexes were initially prepared by previous members of the Smith group.  The initial synthesis of 2.2, 2.3, and 2.4 were performed by Wen Zhou (graduate student), 2.6 was performed by Julia L. Conway (undergraduate student) and 3.3 was performed by Thomas A. Welsh (undergraduate student).  X-ray data collection was performed by Dr. Brian O. Patrick at the University of British Columbia, Vancouver. iv  Table of Contents  Abstract ........................................................................................................................................ ii Preface ......................................................................................................................................... iii Table of Contents ......................................................................................................................... iv List of Tables ................................................................................................................................ vi List of Figures .............................................................................................................................. vii List of Abbreviations ...................................................................................................................... x Acknowledgements ..................................................................................................................... xii Dedication .................................................................................................................................. xiii Chapter 1. Chemistry of Chromium Compounds ...........................................................................1 1.1 Redox-Active Ligands ............................................................................................................... 1 1.2 Thesis Objectives ...................................................................................................................... 5 Chapter 2. Attempted Synthesis of [CrL2(LX)](X) Complexes .........................................................7 2.1 Initial pathways towards target molecule synthesis ................................................................ 7 2.2 Reactions with Cr[N(SiMe3)2]2(THF)2 to make target molecule ............................................. 10  Synthesis of Cr(Ph-nacnac)[N(SiMe3)2]............................................................................... 10 2.2.1 tBpy reactions of Cr(Ph-nacnac)[N(SiMe3)2] ....................................................................... 13 2.2.22.3 Synthesis and reactions of Cr(tbpy)[N(SiMe3)2]2 .................................................................... 18  Synthesis and structural data of Cr(tbpy)[N(SiMe3)2]2 ....................................................... 19 2.3.1 Quinoline derivatives of Cr bipyridine compounds............................................................ 24 2.3.22.4 Oxazolines and 2-aminodiphenylamine Chromium Compounds ........................................... 28  Synthesis of metallated oxazoline complexes ................................................................... 28 2.4.1 Monomeric and tetrameric aminodiphenylamine complexes .......................................... 29 2.4.22.5 Experimental Section ............................................................................................................. 35  General Considerations ...................................................................................................... 35 2.5.1 Experimental Procedures ................................................................................................... 36 2.5.2Chapter 3. Attempted Reductions of Cr(III) tBu-acac Bipyridine Complexes ................................. 40 3.1 CrCl3 Reactions With tBu-acac and Xyl-NacnacLi .................................................................... 40 v  3.2 Salt metathesis of Cr(tbpy)(tBu-acac)Cl2 with Silver Carboxylates .......................................... 43 3.3 Attempts to Reduce the Chromium Centre Directly .............................................................. 45 3.4 Synthesis of [Cr(tbpy)Ph3][Mg(tBu-acac)(THF)4] ..................................................................... 46 3.5 Experimental Section ............................................................................................................. 55  General Considerations ...................................................................................................... 55 3.5.1 Experimental Procedures ................................................................................................... 55 3.5.2Chapter 4. Conclusion ............................................................................................................... 58 References .................................................................................................................................. 60 Appendices ................................................................................................................................. 64     Supplementary X-ray Data ....................................................................................... 64 Appendix A    Supplementary UV-vis Spectra ................................................................................. 65 Appendix B vi  List of Tables  Table 2.1   Comparison of the structural details of the known three coordinate amido complexes: 2.6, Dpp-2.6 and Dpp-2.6-Me. ....................................................................... 13 Table 2.2   Selected bond lengths and dihedral angle of the two independent molecules found of both 2.10a and 2.10b. ................................................................................................... 21 Table 2.3   Bond lengths of 2.11 .......................................................................................................... 27 Table 2.4   The bond lengths of the 2-aminodiphenylamine ligand of 2.15. ...................................... 33 Table 2.5   Bond lengths and dihedral angle between the chromiums of complexes 2.15, alkyl, and silyloxide ..................................................................................................................... 35 Table 3.1   Chromium-carbon bond lengths of 3.6, a1, a2, b, c, and d ............................................... 52 Table A.1   Crystal data and refinement parameters for X-ray structures 2.7, 2.10b, 2.11, 2.15, 3.4b, and 3.5 ...................................................................................................................... 64   vii  List of Figures   Figure 1.1   The oxidation state change of the metal and ligand during a redox exchange .................. 1 Figure 1.2   The three oxidation states of diimines, bipyridine and bis-aryliminopyridines .................. 2 Figure 1.3  Oxidation states of bipyridine ............................................................................................. 3 Figure 1.4   The transfer of an electron from a high energy or a spin-paired state on chromium   to a redox-active ligand orbital, typically a π* that results in a lower energy complex ...... 5 Figure 2.1   Initial synthetic strategy for target complex from CpCr(Xyl-nacnac) (2.1). ......................... 7 Figure 2.2   Synthesis and thermal ellipsoid diagram (50%) of [(Cr(Xyl-nacnac)(μ-OH)]2  (2.2) ............. 8 Figure 2.3   Synthesis and thermal ellipsoid diagram (50%) of CpCr(Xyl-nacnac)(OTs) (2.3) and CpCr(Xyl-nacnac)(N3) (2.4) ................................................................................................... 9 Figure 2.4   Synthesis and thermal ellipsoid diagram (50%) of Cr(Ph-nacnac)[N(SiMe3)2] (2.6) .......... 10 Figure 2.5   Synthesis of the other two known three-coordinate amido type Cr(II) complexes .......... 11 Figure 2.6   The π-donation of the amido nitrogen to the chromium of 2.6 ....................................... 12 Figure 2.7   Synthesis of Cr(Ph-nacncac)2 and CrR4, where R= Me or Me3SiCH2. ................................. 13 Figure 2.8   Synthesis of [Cr(Ph-nacnac)(tbpy)2][BPh4] (2.7) and [Cr(Ph-nacnac)(THF)3][BPh4] (2.8)   and the conversion of 2.8 to 2.7 using two more tbpy ...................................................... 14 Figure 2.9   Thermal ellipsoid diagram (50%) of [Cr(Ph-nacnac)(tbpy)2][BPh4] (2.7) ............................ 15 Figure 2.10   Attempted synthesis of Cr(tbpy)2Ph2 on top with the synthesis of   Cr(bpy)2[OCH(CHMe2)2]2 .................................................................................................... 16 Figure 2.11   Synthesis and thermal ellipsoid diagram (50%) of [Cr(Xyl-nacnac)(THF)3][BPh4] (2.9) ..... 18 Figure 2.12   Synthesis of 2.10a,b, where R=H, tBu. ............................................................................... 19 Figure 2.13   Thermal ellipsoid diagram (50%) of 2.10a and 2.10b ........................................................ 20 Figure 2.14   Synthesis and thermal ellipsoid diagram (50%) of Cr[N(SiMe3)2]2(tmeda) and Cr[N(SiHMe2)2]2(tmeda) products of the Anwander group ............................................... 23 Figure 2.15   Synthesis of 2.11 ................................................................................................................ 25 Figure 2.16   Initial synthesis that determined the ligand number of Cr(C9H6ON)3 reported in   1938 ................................................................................................................................... 25 Figure 2.17   Thermal ellipsoid diagram (50%) of Cr(tbpy)(C9H6ON)2 (2.11)........................................... 26 Figure 2.18   Attempted synthesis of Cr(tbpy)(C9H7N2)2 (2.12). .............................................................. 27  viii  Figure 2.19   The coupling of a protected oxazoline to p-ClC6H4MgBr, with the presumed   metallated intermediate. ................................................................................................... 28 Figure 2.20   Synthesis attempt of Cr(C11H12NO)2 (2.13) and Cr(C11H12NO)2(tbpy) (2.14). ..................... 29 Figure 2.21   Synthesis of Cr(NMe2C6H4-2-NC6H5)2 and 2.15 .................................................................. 30 Figure 2.22   Thermal ellipsoid diagram (50%) of Cr4(μ-NHC6H4-2-μ-NC6H5)4(THF/Et2O)2·2Et2O   (2.15) .................................................................................................................................. 32 Figure 2.23   Alkyl and Silyloxide chromium tetramer compounds ....................................................... 34 Figure 2.24   Future direction for 2.15.  The dissociation by L2 type ligands. ........................................ 35 Figure 3.1   Synthesis of Cr(Rbpy)(tBu-acac)Cl2 (3.2) through the Cr(tBu-acac)Cl2(THF)2 (3.1) intermediate ...................................................................................................................... 41 Figure 3.2   Synthesis of Cr(Xyl-nacnac)(tbpy)Cl2 (3.3). ......................................................................... 41 Figure 3.3   Thermal ellipsoid diagram (50%) of 3.3 ............................................................................. 42 Figure 3.4   Synthesis of 3.4a,b from 3.2b ............................................................................................ 43 Figure 3.5   Thermal ellipsoid diagram (50%) of Cr(tbpy)(tBu-acac)(OBz)2 (3.4b)................................. 44 Figure 3.6   Synthetic routes attempted to reduce 3.2b to Cr(tBu-acac)(tbpy). ................................... 45 Figure 3.7   Potential single-electron reduction of 3.2b. ...................................................................... 46 Figure 3.8   Predicted product and formed product of the reaction of 3.2b with PhMgCl .................. 46 Figure 3.9   Thermal ellipsoid diagram (50%) of [Cr(tbpy)Ph3][Mg(tacac)(THF)4] (3.5) ......................... 47 Figure 3.10   Mechanism for the synthesis of 3.5. ................................................................................. 49 Figure 3.11   Two examples of five coordinate anionic Cr(III) with an LX ligand, [Cr(Xyl-nacnac)Ph3][Li(Bu2O)] (a1) and [Cr(Xyl-nacnac)Ph3][Li(THF)]·C5H12 (a2) ........................... 50 Figure 3.12   Two examples of five coordinate neutral Cr(III) complexes with aromatic ligands and neutral bidentate ligands.  (((iPr)2(C6H3)NHC)2CH2)CrPh3·3THF0.5C6H6 (b), Cr(C14H15N2)(C7H7)3 (c) ........................................................................................................ 51 Figure 3.13   The final coordination MeLi to [Cr(((iPr)2(C6H3)NCH)2)(CH3)2]Li to make [Cr(((iPr)2(C6H3)NCH)2)(CH3)3] [Li2(THF)3] (d) ...................................................................... 51 Figure 3.14   Mechanism for the synthesis of 3.6. ................................................................................. 53 Figure 3.15   Potential reactivity of 3.5 type molecules. ........................................................................ 54 Figure B.1  UV-vis absorption spectra of complex 2.6 ......................................................................... 65 Figure B.2  UV-vis absorption spectra of complex 2.10b..................................................................... 66 Figure B.3   UV-vis absorption spectra of complex 2.11 ....................................................................... 67 Figure B.4   UV-vis absorption spectra of complex 2.12 ....................................................................... 68 ix  Figure B.5   UV-vis absorption spectra of complex 2.15 ....................................................................... 69 Figure B.6   UV-vis absorption spectra of complex 3.2b ....................................................................... 70 Figure B.7   UV-vis absorption spectra of complex 3.4a ....................................................................... 71 Figure B.8   UV-vis absorption spectra of complex 3.4b ....................................................................... 72 Figure B.9   UV-vis absorption spectra of complex 3.5 ......................................................................... 73 Figure B.10  UV-vis absorption spectra of complex 3.6 ......................................................................... 74 x  List of Abbreviations  The following is a list of abbreviations and symbols employed in this Thesis most of which are in common use in chemical literature. °C  degrees Celsius 1H  proton Ac acetyl, CH3C(O) Acac acetylacetonate, C5H8O2 Ap N-(2,6-dimethylphenyl)-6-(2,6-di-iso-propylphenyl)-2-aminopyridinate Ar aryl bpy  2,2'-bipyridine, C10H8N2 Bu butyl Bz benzoyl, C6H5C(O) Cp  cyclopentadienyl, η5-C5H5 Cp* 1,2,3,4,5-pentamethylcyclopentadienyl, η5-C5Me5 Cy  cyclohexyl, C6H11 Dpp  2,6-di-iso-propylphenyl, C12H17 EPR electron paramagnetic resonance Et  ethyl, C2H5 Et2O diethyl ether, C4H10O g  grams h hours HOMO  highest occupied molecular orbital HOTs; OTs p-toluenesulfonic acid; tosylate iPr isopropyl, C3H7 L  neutral, 2e- donor ligand LUMO Lowest unoccupied molecular orbital LX  monoanionic, 3e- donor bidentate ligand LX• radical election on a neutral and ionic donor ligand M  generic metal; molar, mol L–1 Me  methyl, CH3 xi  Mes 2,4,6-trimethylphenyl, C9H11 mg  milligram, 10–3 g min  minutes mL millilitre, 10–3 L mmol  millimole, 10–3 mole MO  molecular orbital mol  mole, 6.022·1023 particles Nacnac β-diketiminate, (ArNCMe)2CH nBu  n-butyl, C4H9 nm  nanometers, 10–9 m NMR  nuclear magnetic resonance OAc acetate, C2H3O2 Ph  phenyl, C6H5 Ph-oxazoline 4,4-Dimethyl-2-phenyl-2-oxazoline, C11H13NO Phphen 4,7-diphenyl-1,10-phenanthroline, C24H12N2 py pyridine, C5H5N R alkyl SOMO Singly-occupied molecular orbital tbpy 4,4′-Di-tert-butyl-2,2′-bipyridine, C18H24N2 tBu tert-butyl, C4H9 tBu-acac 2,2,6,6-Tetramethyl-3,5-heptanedionate, dipivaloylmethane, C11H19O2 THF  tetrahydrofuran, C4H8O tmeda tetramethylethylenediamine, C6H16N2 Tol  4-methylphenyl, C7H7 X  halide, or other anionic 1e- donor ligand Xyl 2,6-dimethylphenyl, C8H9 η eta, hapticity, coordination of a metal to two or more contiguous atoms of a ligand μL  microlitre, 10–6 L xii  Acknowledgements  I would like to start by thanking Dr. Kevin M. Smith for supervising, encouraging, and supporting my MSc studies and research.  His patience, particularly in the first year of my research when nothing was working, was beyond the expected and truly appreciated.  The opportunities and possibilities to learn in his lab were more broad and encompassing than I expected when I started on this road.  I would also like to thank my supervisory committee, Drs. W. Stephen McNeil and Kirsten R. Wolthers for their unending encouragement, help, and ideas for my projects.  Lastly I would like to thank Dr. Paul R. Shipley for his help with NMR operation and interpretations, Dr. Frederic Menard his aid with organic ligand synthesis, and Dr. Brian O. Patrick for his assistance and patience with X-ray crystallography and interpretation.  I would also like to express my gratitude to past and present members of the Smith, McNeil, and Menard groups for the positive and fun atmosphere in the laboratory. In particular, Dr. Wen Zhou for teaching me day to day laboratory operations, upkeep, and how to actually perform a reaction in a nitrogen glove box along with his gracious support and knowledge.  I would also like to thank the staff of the department for not only the opportunities but the support of my studies and teaching.  Last, but not least, I thank my family and friends for believing in me and my studies, I would not have been able to do this without you.      xiii  Dedication Mom and Pops, Thank You for everything.  1  Chapter 1. Chemistry of Chromium Compounds  Transition metal chemistry has been studied extensively over decades by organometallic chemists.1  The second and third row transition metals have shown extensive catalytic and reactive properties, but have the disadvantage of being low in abundance. Recently the focus has been on earth-abundant first-row transition metals to better understand their reactivity, structure and electronic properties.2  First-row transition metals also possess radical reactivity.3  Adjusting and altering the ligands bound to well-defined metal complexes using both non-innocent and innocent reduction/oxidation (redox) ligands will further our understanding of their radical electronic nature.  The focus of this thesis is the preparation of chromium complexes with bipyridine, bpy, as a redox-active ligand.4 1.1  Redox-Active Ligands  Redox-active ligands have been gaining attention recently due to potential application to catalysis.  Unlike redox-innocent ligands, redox-active ligands can act as the dominant electron source or electron sink in the complex.3,5  In the past, these ligands served to force first-row metals to act as noble metals and allow them to perform two electron chemistry and eliminate any radical reactivity that the complex may have had.  A redox-active ligand is a ligand that can accept or donate an electron from a low energy LUMO orbital on the ligand to the metal (see Figure 1.1).  This change in oxidation state of both the metal and ligand is usually accompanied by a structural change in the ligand as generally an antibonding orbital on the ligand has become occupied.3  Figure 1.1  The oxidation state change of the metal and ligand during a redox exchange.  The properties of redox-active ligands, therefore, can give rise to multiple oxidation states of the bound metal.  Spectroscopic techniques can be used to determine the electronic structures of metal complexes with redox–active ligands.6  The 1,2-diimines were a convenient family of redox-active ligands initially explored specifically for redox activity by the Theopold group.  An example of these ligands are shown in Figure 1.2, where Ar=2,6-diisopropylphenyl or 2,6-dimethylphenyl.7  The 2  diimine ligand can be considered as an “electron buffer”.  The electron buffering effect would be able to supply or relieve the metal of electrons as necessary, allowing for new nodes of reactivity.  Restricting the redox chemistry to the ligands allows formally d0 or d10 metals to perform oxidative additions and reductive eliminations.  Other examples of redox-active ligands have shown this property, a notable family are the bidentate nitrogen ligands separated by two carbons, such as the diimines, bpy and bis-aryliminopyridine.3,4  Figure 1.2  The three oxidation states of diimines,7 bipyridine4 and bis-aryliminopyridines.3  Each level undergoes reduction or oxidation by a single electron.  Bpy is a convenient ligand used to explore the redox-active potential of ligands on complexes.  Past methods of identifying the oxidation state of metal bpy complexes treated the bpy as a solely neutral ligand that was able to π-accept from the metal.  Even if the metal d-orbitals 3  containing electrons are in the correct orientation, UV-vis absorption spectroscopy has shown that neutral bpy is a very weak π-acceptor or does not accept at all.  Very few structural changes have been seen from bpy complexes that do exhibit π-accepting behaviour.  The structural changes found from π-accepting are insignificant compared to the structure of free bpy.  Electronically, the LUMO of the bpy is much higher in energy than the HOMO of the metal d-orbital which limits most of the potential for π interaction.8    Bipyridine can undergo three oxidation states: a neutral L2 donor, a single electron oxidized LX• donor, and a double anionic X2 donor depending on how many electrons occupy the illustrated orbital.  This is the LUMO of neutral bipyridine, as shown in Figure 1.3.  Each of the oxidation states has discernible properties that can be used to determine which state the bpy is occupying in a complex.  The bond lengths are the most easily measured property of the oxidation state in the bpy, most notably the inter-ring length (C2-C2’) and the intra-ring carbon to the nitrogen (C2-N1).  Each single electron reduction of the bpy shows a shortening of the C2-C2’ bond and a lengthening of the C2-N1 bond.  These structural changes have been found to be independent of the metal used for the complex.7,8   Figure 1.3 Oxidation states of bipyridine.  The neutral L2 bipyridine, the monoanionic LX• bipyridine and the dianionic X2 bipyridine.  The lengths in angstroms shown are the typical average C2-C2’ bond between the two pyridine rings and the C2-N1 bond within the pyridine ring for the three oxidation states measured by X-ray diffraction.8  A pictorial top view of the p-orbitals involved in the key bipyridine MO shown.  The electron configuration of the L2 oxidation state of bpy (Figure 1.3) shows that the LUMO is an antibonding orbital.  The bond lengths in a metal bpy bound complex are very similar to those of free bpy, in which the C2-N1 length is 1.35 Å, and the inter ring C2-C2’ length is 1.49 Å.    The electron configuration of the LX• and the X2 donor (Figure 1.3) shows one or two electrons in the SOMO or HOMO level of the bpy, the first anti-bonding orbital.  The lengths of the 4  reduced bpy are C2-N1 bond, 1.39 Å for LX• and 1.44 Å for X2, and shortening of the C2-C2’ bond, 1.43 Å for LX• and 1.38 Å for X2, of the bpy that can be measured by X-ray crystallography.  The MO diagram shows no electron density on C6 or C6’ of the bpy.  The bond lengths for the L2 and LX• for the inter ring C2-C2’ of bpy have been studied across the first d-block row from chromium to nickel.9  The variance in bond lengths showed that the shortest C2-C2’ bond was from Ni(bpy)(Mes)2 at 1.465(4) Å and the longest was with Mn(bpy)(Mes)2 at 1.480(4) Å.  The shortest singly reduced bpy C2-C2’ bond length was found with [K(dibenzo-18-crown-6)·THF][Cr(bpy)(Mes)2]·2THF at 1.410(4) Å and the longest with [K(2,2,2-crypt)] [Co(bpy)(Mes)2] at 1.429(4) Å.  The bond lengths within the bpy ligand are not affected greatly by the bonded metal in both oxidation states.  The variance of the lengths show that the oxidation state of the ligand can be abstracted from the crystallography data.  Bpy metal complexes have been shown to give ambiguous oxidation states to many of the metals across the first-row transition metal block.  Notable examples include scandium and nickel complexes.  Cp*2Sc(bpy) (where Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) would initially seem like a Sc(II) d1 species, it is actually a Sc(III) d0 metal where the bpy is in the LX• reduced state.8  A nickel bpy complex has recently been shown to perform photoredox cross-coupling with an iridium bpy co-catalyst for coupling of aryl bromides to sp3 over sp2 and sp carbon centers.  Unlike traditional cross-coupling, this new method uses single-electron transmetalation to activate the sp3 carbon to a radical that bonds to the nickel center before reductive elimination of the aryl group.10,11  Cr(III) complexes with redox-active ligands have in the past has been misidentified as Cr(II) as low spin complexes with two of the electrons paired, as seen in Figure 1.4.  The oxidation state of the Cr centre was not apparent due to the electronic nature of octahedral chromium complexes with three versus four electrons.  The bpy ligand is active when adding an electron to the ligand is more beneficial for the stability of the Cr complex than spin pairing or putting the electron in a higher energy orbital on the metal.  There is strong antiferromagnetic coupling between the unpaired electron on the anionic bpy radical ligand and the three unpaired electrons on chromium.  Since the electron on the ligand has the opposite spin it can be mistaken as a low spin coupled electron since both the transfer and the low spin complexes will give the same S=1 state when viewed magnetically.    Electron paramagnetic resonance (EPR) spectroscopy is widely used to study S=1/2 systems but is typically less informative for low-symmetry molecules with S=1/2.12  Octahedral Cr(III) complexes antiferromagnetically coupled to a ligand-based bpy radical will have an S=1 ground 5  state, and are not expected to provide useful EPR spectra at room temperature in solution.  However, Wolczanski and co-workers have reported that related S=1 Cr(III) complexes with ligand-based radicals do reproducibly provide strong EPR spectra at 296 K, suggesting that this technique may be applicable to this class of compounds.13    Figure 1.4  The transfer of an electron from a high energy or a spin-paired state on chromium to a redox-active ligand orbital, typically a π* that results in a lower energy complex.  The low and high spin options for Cr(II), d4 complexes are not electronically favoured therefore the electron moves to the ligand first antibonding orbital.   There have been many bpy compounds synthesized with the first two oxidation states, though many LX• bpy compounds have been incorrectly identified as being L2 with π-accepting characteristics. There are far fewer examples of X2 bpy compounds that have unambiguously been characterised by X-ray crystallography.  The literature gives Cr(bpy)32+ as a textbook example of low spin Cr(II).  The spectral data supported Cr(bpy)32+ as Cr(II), a d4 complex with three neutral bpy ligands due to the negligible change in the obtained spectral data.4,14  Advances with structural determination and crystallography now support that the bpys are sharing the electron over all three bpy ligands and the chromium oxidation state is +3 not +2.15  A second example of a multiple bpy chromium complex in the literature was [Cr(bpy)2Ph2]+.16  The cation was synthesized through what was assumed to be a Cr(II)  Cr(bpy)2Ph2 with neutral bpy, but with recent understanding, it is more likely to be a Cr(III) species with one of the bpy reduced to LX•.  Shores and Ferreira recently reported the used of substituted Cr(III) bipyridine and phenanthroline complexes as a photoredox catalyst for Diels-Alder reactions.17   1.2 Thesis Objectives  This thesis will address the synthesis and understanding of bipyridine radicals on chromium complexes.  The use of salt metathesis, protonation and coordination were used as a synthetic 6  pathway for making unique chromium complexes.  These complexes were studied by X-ray crystallography, UV-vis spectroscopy and magnetic moment by NMR (nuclear magnetic resonance) to understand the oxidation state of the chromium centre and attached ligands.  Chapter 2 focuses on the initial attempts to prepare Cr(II) bipyridine β-diketiminate (nacnac = (ArNCMe)2CH) and its anionic counter ion complexes using CpCr(Xyl-nacnac) with protonated bpy.  The electronic structures of these complexes formed were studied.  With the failure of the synthesis using CpCr(Xyl-nacnac) to produce the desired complexes, the possibility of using Cr[N(SiMe3)2]2 (THF)2 was explored as the new Cr(II) starting material.  Along with the change in chromium source, the change in nacnac ligand was also explored to see how the bpy bonds to the chromium centre.  The nacnac ligand was also exchanged for 8-hydroxyquinoline and the reactions of these two ligands with Cr(tbpy)[N(SiMe3)2]2 was explored.  These reactions showed a change in oxidation state for chromium and geometry with the addition of multiple ligands.  The final reaction explored was with 2-aminodiphenylamine and Cr[N(SiMe3)2]2(THF)2 which showed the protonation of the amide ligands and the tetramerization of the metal complex  Chapter 3 studies the electronic structure using a much less bulky LX ligand tBu-acac counter to the bpy on the chromium.  The starting material was the robust CrCl2(tBu-acac)(tbpy), an air stable Cr(III) compound.  The ligands that were added to the chromium were chosen for potential ability to be reductively eliminated from the chromium, leaving a Cr(II) centre with a LX• radical.  The findings of stable octahedral carboxylate and square-pyramidal aryl chromium(III) compounds were unexpected outcomes. 7  Chapter 2. Attempted Synthesis of [CrL2(LX)](X) Complexes  The control and placement of ancillary ligands in a complex can increase or decrease its reactivity.  The electronic structure of the complex should be well controlled to understand the discrete oxidation state of the metal and the ligands.  An understanding of the oxidation state of the complex provides insight into reactivity and catalytic design.    An initial attempt at the protonation of a Cp ligand as a method to remove it from the metal centre and open a new coordination site was explored, and ultimately found to be unsuccessful.  The move to a more reactive bis amide chromium(II) complex was then explored and it was found that the coordination of a single L2 ligand to make a square-planar complex was unfavourable over the coordination of two to make octahedral chromium(III) complexes.  The final complex that will be discussed is the result of leaving coordination sites open in the neutral complex that resulted in the synthesis of a tetrameric chromium(II) complex. 2.1 Initial pathways towards target molecule synthesis The initial target molecule was [Cr(tbpy)(Xyl-nacnac)](OTs), where Xyl = 2,6-dimethylphenyl.  This was to be a simple protonolysis of the Cp ligand from the robust starting material CpCr(Xyl-nacnac) (2.1) leaving an open coordination site for 4,4’-di-tert-butyl-2,2’-bipyridine (tbpy) to coordinate to the chromium.  Figure 2.1  Initial synthetic strategy for target complex from CpCr(Xyl-nacnac) (2.1).  The initial target molecule was assumed to be stable as a four coordinate square-planar cationic complex due to the stability of Cr(II), d4 complexes.  The electronic structure of the target would have a three of the four electrons in the lower energy orbitals of dyz, dxz and dz2, with the last 8  electron in a more energetic orbital of dxy.  The last orbital, dx2-y2 would be empty and very high in energy.  The reaction from Figure 2.1 was attempted in THF, toluene, Et2O and hexanes.  Initially a deep purple to blue solutions formed in THF and toluene, giving promising indication that the product was forming.  The eventual final complexes found by Wen Zhou were decomposition or unwanted side products when using 2.1 as a starting material.    When 2.1 was initially reacted with p-toluenesulfonic acid mono hydrate (HOTs) the product formed was [(Cr(Xyl-nacnac)(μ-OH)]2 (2.2) an unforeseen and unwanted product (Figure 2.2).  The coordinated water of the HOTs acid was the cause of the unwanted bridging hydroxides.  The reduced form of tbpy, produced by the reaction with sodium, a deep purple solution in THF, did not add to the complex and presumably stayed dissolved in solution.  Figure 2.2  Synthesis and thermal ellipsoid diagram (50%) of [(Cr(Xyl-nacnac)(μ-OH)]2  (2.2).   All H atoms are omitted for clarity.  The protonation by HOTs of the Cp is presumably the first step in the formation of the μ-OH complex 2.2.  The water addition to the new intermediate would then be the second step, reforming the HOTs with the CpH side product, keeping the acid concentration high relative to the starting material.  The water in the solution can then form two bridging hydroxides in 2.2, which is very stable and crystallizes out of solution preferentially.  Unfortunately, when using anhydrous HOTs, the only result was a deep purple solution from which 2.2 could not be isolated.  It is unknown if this is the result of the desired protonation of the Cp or a secondary reaction.  The unreacted 2.1 of this solution will coordinate the tosylsulfate to form complex 2.3 that preferentially crystallizes over the unknown purple product.     In an effort to prevent the formation of 2.2, anhydrous HOTs was prepared and used with 2.1.  The product found from the reaction was not the predicted protonation of the Cp ring to 9  remove it, but the addition of -OTs to the complex as the crystallized product, CpCr(Xyl-nacnac)(OTs) (2.3) (Figure 2.3).  From the reaction with HOTs·H2O, the Cp can be removed through protonation.  Therefore, the assumption is that the reaction with anhydrous HOTs does not go to completion and the less soluble CpCr(Nacnac)X complexes are the preferential crystallized product.  When tbpy is added to a solution of 2.3, there is no apparent reaction.  A reaction did occur between the -OTs ligand of 2.3 with Me3SiN3.  This exchange provided N3-, which reacted to give CpCr(Xyl-nacnac)(N3) (2.4) as a crystallized product previously synthesized product by the Smith group.18  Figure 2.3  Synthesis and thermal ellipsoid diagram (50%) of CpCr(Xyl-nacnac)(OTs) (2.3) and CpCr(Xyl-nacnac)(N3) (2.4).   All H atoms are omitted for clarity.  The unwanted products 2.2, 2.3 and 2.4, which were synthesized and structurally characterized by Wen Zhou of the Smith group, led to the change in the initial approach to the target molecule.  Incomplete consumption of 2.1 by HOTs led to highly crystalline CpCr(III) byproducts that hindered isolation of the  [Cr(bpy)(Nacnac)](OTs) target molecule.  The strategy for the formation of [Cp(tbpy)(LX)]X complexes was adjusted in an attempt to reduce unwanted side reactions. 10  2.2 Reactions with Cr[N(SiMe3)2]2(THF)2 to make target molecule  The successful protonation of the Cp ligand in 2.1 to make 2.2 suggested that the coordination of the tbpy was being hindered by the LX ligand.  By decreasing the steric bulk on the LX ligand, the coordination of the tbpy could be enhanced.  Synthesis of Cr(Ph-nacnac)[N(SiMe3)2] 2.2.1 With the failures of using 2.1 to make the target molecule, the chromium source was changed to Cr[N(SiMe3)2]2(THF)2 (2.5), a square-planar complex initially synthesized in 1972.19  The initial reactivity problem of 2.1 was predicted to be avoided by the more reactive chromium amide bonds of 2.5 and give the desired product.   Initial work by the Julia Conway in the Smith group in 2007 with 2.5 as a starting material with nacnacs showed that there was no reaction with Xyl-nacnac, but was a reaction with Ph-nacnac.  The phenyl substituted nacnac formed the mono substituted, Cr(Ph-nacnac)[N(SiMe3)2] (2.6) giving a Cr(II), d4, 12e- with π-donation (Figure 2.4).  Figure 2.4  Synthesis and thermal ellipsoid diagram (50%) of Cr(Ph-nacnac)[N(SiMe3)2] (2.6).  All H atoms are omitted for clarity.  The UV-vis (ultraviolet-visible) spectrum of 2.6 (Figure B.1) showed two bands at 402 nm (ε=8274M-1cm-1) and at 502 nm (ε=357M-1cm-1) which are useful wavelengths to assess the purity of the complex.  These data, coupled with the μeff=5.19(6) μB in solution (Evans’, C6D6) confirms four unpaired electrons giving an S=2 high spin state.  The paramagnetic NMR in C6D6 also gives a very distinctive broad signal for the 18 protons of the two trimethylsilyl amide groups at 4.0 ppm.  The crystal structure showed four 2.6 independent molecules in the unit cell, with two unique conformations, both with trigonal planar geometry.  The main difference is the dihedral angle between Nnacnac-Cr-Namido-Siamido, being 72.4° and 87. 2° for the two independent molecules. 11   Two other three coordinate Cr(II) amido type structures are known, using 2,6-diisopropylphenyl-nacnac (Dpp-nacnac) with CH3SiN3 in 2010 by the Tsai group,20 and a dimethyl amine with a (DppNC(tBu))CH analogue of the nacnac ligand was synthesized by the Mindiola group in 2008,21 as shown in Figure 2.5.    Figure 2.5  Synthesis of the other two known three-coordinate amido type Cr(II) complexes.20, 21  The synthesis of these two structures did not use protonolysis to make the three coordinate complexes, but started from the corresponding [(nacnac)Cr(μ-Cl)]2 complexes.  The [(Dpp-nacnac)Cr(μ-Cl)]2 was reduced with KC8 in toluene to make an inverted sandwich with [(Dpp-nacnac)Cr] complex with a bridging η6:η6 toluene between the two chromiums to form the Cr(I) intermediate.  The Cr(I) intermediate was then oxidized back to Cr(II) with Me3SiN3 to make two products, [Cr(Dpp-nacnac)(μ-N3)]2 and Cr(Dpp-nacnac)(N(SiMe3)2) (Dpp-2.6).  The second analogue of 2.6 was made by salt metathesis directly from the [Cr((DppNC(tBu))CH)(μ-Cl)]2 with LiNMe2 directly, with no change to the oxidation state of the chromium.  The orbital overlap of the amido nitrogen p-orbital with the chromium d-orbital dictates the geometry of the three coordinate complexes, Figure 2.6.  The three coordinate geometry of 2.6 type complexes is very idealized, with the amido nitrogen at approximately equivalent angles to each of the nacnac nitrogens.21,22  Normally three coordinate structures would have the mono dentate ligand bent towards one side of the bidentate ligand on the plane to decrease the interaction of the 12  σ-donor to the filled d-orbitals.  Due to the decreased bite angle of the nacnac, the dxy* orbital is pushed much higher in energy as the nitrogens of the nacnac are positioned on the dxy* orbital lobes.  The dxy* is oriented to a π* interaction with the py orbital of the amido.    Figure 2.6  The π-donation of the amido nitrogen to the chromium of 2.6.  The amount of p-orbital overlap is measured by the angle of the py orbital to the dxy* orbital.  The angles are approximated by the angles of the ligands relative to each other, where the py orbital is perpendicular to the plane of the Si-N-Si of the amido ligand and the dxy* is on the plane of N-Cr-N of the nacnac ligand.  These approximations only work if the centres are truly trigonal planar, measured by the addition of the angles of the ligands from each other around the Cr and Namido atoms.  In all three cases, the angles around the chromium of each complex adds to over 359.8° and around the amido nitrogen the angles add to over 358.9°, which gives each centre trigonal planar status.  The angles for Dpp-2.6 and Dpp-2.6-Me were taken directly from the crystallographic information files of both journal articles.    The dihedral angles (θ) measured for the R-Namido-Cr-Nnacnac were taken to be the perpendicular angle of the py orbital (Table 2.1).  Interestingly, the Dpp-2.6 falls between the dihedral angles of the two independent structures of 2.6 despite the added steric bulk of the iso-propyl substituents on the nacnac ligand.  The dihedral angle for Dpp-2.6-Me is much smaller, decreasing the overlap of the π bond.  The amount of π-overlap does not follow a linear decline, but maps a cosine curve and can be calculated by cos2(Θ) × 100%, where Θ is the 90°-θ.23  The two extremes of 0° and 90° give the perfect overlap and non-interacting interactions of the orbitals respectively.   13  Table 2.1  Comparison of the structural details of the known three coordinate amido complexes: 2.6, Dpp-2.6 and Dpp-2.6-Me. Complex Dihedral θ/° a π-overlap/% Cr-Namido/Å Cr-Nnacnac/Å 2.6b 2.6b 72.4 87.2 90.9 99.8 1.960(2) 1.960(2) 2.008(3), 2.003(3) 2.002(2), 1.998(2) Dpp-2.6 82.4 98.2 1.963(3) 2.002(2), 2.023(2) Dpp-2.6-Me 52.1 62.3 1.9039(18) 2.0232(17), 2.0157(17) a Taken as the dihedral angle(θ) between the R-Namido-Cr-Nnacnac.  b Structure 2.6 has two independent geometries in the crystal unit cell.   This is reflected in the Cr-Namido bond length of the complexes.  The shortest bond is the Dpp-2.6-Me at 1.9039(18) Å, and 2.6 and Dpp-2.6 at almost the same length at 1.960(2) and 1.963(3) Å respectively.  The smaller dihedral angle of the NMe2 analogue shows a smaller overlap of the orbitals but still giving a shorter Cr-Namido bond distance.  The similar bond distance for the N(SiMe3)2 analogue shows that sterics are a factor in the bond length and the electronic overlaps of the π-donation interaction of the Nnacnac-Cr bonds has a smaller contribution.  Interestingly, 2.6 did not react with a second equivalent of the protonated Ph-Nacnac ligand to make the known Cr(Ph-Nacnac)2 complexes.  The bis Ph-nacnac was initially synthesized by the Theopold group from CrCl3(THF)3 with a stoichiometric amount of Ph-nacnacLi and then reacted with two portions of alkyl lithium salts (either MeLi or LiCH2SiMe3).  The result was the disproportionation of the Cr(Ph-nacnac)R2 intermediate to form a mixture of Cr(Ph-nacnac)2 and CrR4, as shown in Figure 2.7, with the two product exhibiting chromiums in differing oxidation states.24  The Cr(Ph-nacnac)2 structure gives the orientation of the two nacnacs to be near perpendicular, N1-N1-N2-N2, at 80.3°, but still is a high spin Cr(II), d4 species.  The second alkyl complex is a Cr(IV), d2 species.  Figure 2.7  Synthesis of Cr(Ph-nacncac)2 and CrR4,24 where R= Me or Me3SiCH2.  tBpy reactions of Cr(Ph-nacnac)[N(SiMe3)2] 2.2.2 With the amide instead of a Cp ligand, the hope was that 2.6 would be more susceptible to protonolysis with stronger acids.  When HOTs and tbpy were used there was either no reaction, or 14  there was decomposition of the products.  However, the reaction with protonated tbpyH+ and BPh4- gave the unexpected products, di-tbpy substituted [Cr(Ph-nacnac)(tbpy)2][BPh4] (2.7) and [Cr(Ph-nacnac)(THF)3][BPh4] (2.8), as seen in Figure 2.8.  Figure 2.8  Synthesis of [Cr(Ph-nacnac)(tbpy)2][BPh4] (2.7) and [Cr(Ph-nacnac)(THF)3][BPh4] (2.8) and the conversion of 2.8 to 2.7 using two more tbpy.  The product 2.8 was unexpected and was isolated out of the product solution before 2.7, due to being less soluble in Et2O, the recrystallization solvent.  The 2.8 byproduct was isolated as a green solid from the solution, giving a simple UV-vis spectrum in Et2O with only an absorbance shoulder at 383 nm before saturation of the detector.  After a number of months, 2.7 crystallized out of solution as a large purple crystal, which was characterized and found to have two tbpy ligands, rather than the expected one with the counter anion.   The crystal structure of 2.7 reveals that it is a Cr(III), d3, 15 e- compound, as seen in Figure 2.9.  In the structure, the counter ion and disorder have been omitted to emphasise the chromium center. 15   Figure 2.9  Thermal ellipsoid diagram (50%) of [Cr(Ph-nacnac)(tbpy)2][BPh4] (2.7).   All H atoms and tetraphenyl borate counter ion are omitted for clarity.  The solvent in the crystal lattice was eliminated by PLATON SQUEEZE25 as it could not be resolved, it is assumed to be diethyl ether.  Only the single rotamer was found in the crystal cell unit.  Selected bond lengths (Å) Cr1-N3 2.0303(18), Cr1-N4 2.0270(17), Cr1-N5 2.0495(18), Cr1-N6 2.0297(17), N3-C22 1.371(3), N4-C23 1.364(3), N5-C40 1.366(3), N6-C41 1.359(3), C22-C23 1.459(3), C40-C41 1.460(3).  Resolving the crystal structure of 2.7 was time consuming.  The disorder of the tert-butyl groups on C20 and C38 required the splitting of the groups.   The tert-butyl on C20 had to be completely split and rotated with compression of the methyl group to one side for only the one part of the methyl, the initial methyl is in optimal geometry.  The tert-butyl on C38 only required the rotation of the methyl groups about the C38-C46 bond by approximately 60°.  There was also a very disordered Et2O solvent molecule in the crystal lattice and PLATON SQUEEZE26 was used to eliminate the solvent from the crystal structure.  The representation of 2.7 with the tbpy as a L2 and a LX• is not the true depiction of the molecule.  The two tbpys share the radical between the antibonding orbitals and this gives the average shortening of the bond length from the free bpy half way between the L2 and the LX• 16  conformations for C22-C23 and C40-C41 to be 1.459(3) and 1.460(3) Å respectively.  The four C-N bonds of the molecule are lengthened, but this effect is much less obvious because there are four bonds being lengthened rather than the two which are shortened.  The new lengths for N3-C22, N4-C23, N5-C40 and N6-C41 are 1.371(3), 1.364(3), 1.366(3) and 1.359(3) Å respectively, about half way between the free bpy L2 bond length of 1.346(2) Å and the bpy LX• bond length of 1.388(2) Å.  The more accurate view of each ligand for this bpy would be L3/2(X•)1/2 to add to the full L2 and LX• over the whole molecule.  An attempt was made to synthesize Cr(tbpy)2Ph2, Figure 2.10, to expand the examples of the bpy on a single complex showing both an L2 and an LX• or show another example of a complex where the radical is shown on both ligands.  This an analogue of the previously synthesized Cr(bpy)2[OCH(CHMe2)2]2 compound by the Smith group and an intermediate to a previously synthesized [Cr(bpy)2Ph2]I.16,27,28,29  The hope was to find if the tbpy analogue of the phenyl compound would have the same L2 and LX• as the previously synthesized compound.  Unlike 2.7, the crystal structure of Cr(bpy)2[OCH(CHMe2)2]2 showed two distinct sets of bond lengths on the two bpy ligands.30,31  Figure 2.10  Attempted synthesis of Cr(tbpy)2Ph2 on top with the synthesis of Cr(bpy)2[OCH(CHMe2)2]2 on the bottom right with the thermal ellipsoid diagram (50%) of the bottom structure to the bottom left.  All H atoms are omitted for clarity.  Selected bond lengths for Cr(bpy)2[OCH(CHMe2)2]2 (Å) Cr1-N1 2.0928(15), Cr1-N2  2.1276(15), Cr1-N3 2.0040(15), Cr1-N4 2.0525(15), Cr1-O1 1.9055(12), Cr1O2 1.9088(12), N1-C5 1.358(2), N2-C6 1.356(2), N3-C15 1.383(2), N4-C16 1.381(2), C5-C6 1.474(3), C15-C16 1.425(2). 17   The two bpys are not the same electronically given one is a neutral L2 donor and one is reduced by an electron in the antibonding orbital, giving the LX• monoanionic ligand.  The nominal bond to infer the differences is the Cpy-Cpy of the two rings, C5-C6 at 1.474(3) Å and C15-C16 at 1.425(2)Å.  The longer of the two inter pyridine ring bonds is the neutral bpy, though a bit shorter than the average given in Figure 1.3, but still experimentally reasonable.  The shorter C15-C16 bond is very indicative of the LX• bond.   The four N-Cpy bonds also give indication to the changes in the bonding of the bpy rings.  The N1-C5 and N2-C6 bonds of the neutral rings are shorter than N3-C15 and N4-C16, showing more double bond character within the ring structure.30  If the synthesis for the Ph analogue was successful, it would potentially have the same electronic structure as Cr(bpy)2[OCH(CHMe2)2]2or like 2.7 with the averaged [(LX•)1/2L3/2]2.  Unfortunately, the solid sent for X-ray diffraction analysis was non crystalline and was not able to provide a structure.  Original work on the bpy form of this compound was performed in the 1960s, worked on the exact structure and reduction potentials of the compounds.   The initial hypothesis was that the bpy are neutral ligands and that the chromium was in the +2 oxidation state from dropping mercury potentiometry.32  The option of a bpy based radical was discarded based on comparisons to the reduction to free bpy measurements.  With current understanding, the more likely structure is actually the bpy based radical with a Cr(III) centre, like other octahedral Cr complexes.  The direct synthesis of the target [Cr(Xyl-nacnac)(tbpy)]X was also attempted by the direct reaction of 2.5 with Xyl-nacnac and two different counter ions [HNEt3][BPh4] and HOTs sequentially without purification before adding the tbpy to the reaction.  The stability of 2.5 to Xyl-nacnac was thought to be overcome by using an acid to protonate the amide ligand rather than relying on the proton from the Xyl-nacnac.  Unfortunately the formation of [Cr(Xyl-nacnac)(THF)3][BPh4] (2.9) was the only complex identified by X-ray crystallography, and if the reaction with tbpy did occur, it was never isolated from the reaction mixture, as shown in Figure 2.11. 18   Figure 2.11  Synthesis and thermal ellipsoid diagram (50%) of [Cr(Xyl-nacnac)(THF)3][BPh4] (2.9).   All H atoms and the counter anion are omitted for clarity.  The crystal structure of 2.9 was previously reported by the Theopold group at the University of Delaware, synthesized from Cr(Xyl-nacnac)(CH2SiMe3)2 with [HNEt3][BPh4] in THF.33  The reaction of purified 2.9 with tbpy yielded a change in colour of the solution from green to purple, but no crystals were able to be isolated.  The displacement of the THF by the tbpy should be an easy coordination/dissociation reaction on the chromium center, especially with the open axial coordination site.  The solubility of the resulting solution with the tbpy added did not allow for any solid to form, so it is unknown how the tbpy interacted with the solution and the chromium centre. 2.3 Synthesis and reactions of Cr(tbpy)[N(SiMe3)2]2  The alternative route of adding the bpy to the chromium before the desired LX ligand was explored.  The addition of the desired LX ligand to the complex to the Cr(bpy)X2 would hopefully be easier and provide isolable products that could be used for further analysis.  While the bpy complex proved to be synthetically easy, the addition of the various LX ligands were found to add twice to the Cr(II) and oxidize the metal and reduce the bpy ligand. 19   Synthesis and structural data of Cr(tbpy)[N(SiMe3)2]2 2.3.1 The synthesis of Cr(bpy)[N(SiMe3)2]2 (2.10a), previously reported in 2013,34 showed the direct coordination of bpy to 2.5 with the dissociation of the two THF ligands from the Cr centre, as shown in Figure 2.12.  The new starting material 2.10a is a Cr(II), d4, 12 e-, four coordinate distorted square-planar complex.  Figure 2.12  Synthesis of 2.10a,b, where R=H, tBu.  Using the same technique as the synthesis of Cr(bpy)[N(SiMe3)2]2 (2.10a), Cr(tbpy)[N(SiMe3)2]2 (2.10b) was made giving the same coordination and distorted geometry and electronic configuration as the analogous substituted bpy compound.34  The UV-vis spectrum of 2.10b is found in Figure B.2.  The crystal structure of 2.10b provides eight molecules in the unit cell with four each of the two different independent molecule geometries.  The compound has C2 rotation axis through the middle of the tbpy, Cr center and between the N(SiMe3)2 groups.  The angles for the two geometries differ by an amount that should have no difference on the reactivity of the two species.  As previously described for 2.10a,34 the dihedral angle between Npy-Npy-NSi-NSi on 2.10b, as shown in Figure 2.13, is 26.5° and 22.9° between the ligands for the two independent molecules.  The tbpy ligand has a much larger difference in the dihedral angle within the ligand itself about the inter ring bond.  For the first species in the unit cell, the dihedral angle between the nitrogens, N1-C5-C6-N2, is 15.7°, but along the back side of the tbpy, C7-C6-C5-C4, the dihedral angle is larger at 19.3°.  In the unit cell the second species, the tbpy has a much smaller dihedral angle for the two, N5-C35-C36-N6 at -6.0° and C34-C35-C36-C37 at 5.8°, which is less twisted from planarity of the ring system than its unit cell partner. 20                         Figure 2.13  Thermal ellipsoid diagram (50%) of 2.10a34 (left) and 2.10b (right). All H atoms are omitted for clarity.  Selected bond lengths for 2.10a (Å) Cr1-N1 2.1593(16), Cr1-N2 2.1565(16), Cr1-N3 2.0572(15), Cr1-N4 2.0524(15), N1-C5 1.356(2), N2-C6 1.350(2), C5-C6 1.481(3).  Selected bond lengths for 2.10b (Å) Cr1-N1 2.156(3), Cr1-N2 2.151(3), Cr1-N3 2.045(3), Cr1-N4 2.038(3), N1-C5 1.357(4), N2-C6 1.362(4), C5-C6 1.477(4).  The tbpy in 2.10b, like that of 2.10a, is a neutral L2 ligand given that the inter-pyridine distance of 1.477(4) Å for C5-C6 and 1.483(5) Å for C35-C36 is well within the average bond length of the free bpy ligand.  The μeff=5.30 μB in solution (Evans’, C6D6) confirms four unpaired electrons giving an S=2 spin state.  The distortions in the square-planar structure of 2.10b are likely due to steric strain between the two N(SiMe3)2 groups.  The larger distortion of half the species in the unit cell of the crystal structure is likely due to crystal packing.  The distortion results in the position of one methyl group from each of the N(SiMe3)2 ligands directly above and below the chromium centre of the molecule.  The ligand shielding the axial positions of the chromium prevents potential Cr-Cr bond formation.  If the axial positions were not protected by sterics, there existed a possibility for bimetallic complexes to form.    21  Table 2.2  Selected bond lengths and dihedral angle of the two independent molecules found of both 2.10a and 2.10b.  The N(SiMe3)2 and N(SiHMe2)2  refer to the Cr[N(SiMe3)2]2(tmeda) and Cr[N(SiHMe2)2]2(tmeda) respectfully.  The L is in reference to the bpy ligand for the 2.10 complexes and tmeda for the N(SiMe3)2 and N(SiHMe2) complexes.35 Complex Cr-Namido /Å Cr-Namido /Å Cr-NL /Å Cr-NL /Å N-C /Å N-C /Å C-C /Å dihedral/° 2.10a 2.057 2.052 2.159 2.157 1.356 1.350 1.481 20.0 2.10a 2.045 2.055 2.152 2.143 1.354 1.357 1.485 20.7 2.10b 2.039 2.045 2.151 2.156 1.364 1.357 1.477 26.5 2.10b 2.067 2.057 2.143 2.159 1.363 1.362 1.483 22.9 N(SiMe3)2 2.080 2.073 2.254 2.273 1.484 1.493 1.502 31.7 N(SiHMe2)2 2.046 2.048 2.209 2.225 1.501 1.515 1.494 17.4  The bond lengths of the Cr-Namido and the Cr-Nbpy found in  show nearly identical nature of the two independent molecules found in both 2.10a and 2.10b.  The π-donation from the amido nitrogen to the chromium centre does not increase the bond strength compared to 2.6.  The complex is high spin with four unpaired electrons, which gives the Cr-Namido π* orbitals single electron occupancy, weakening the Cr-Namido bonds.  The purely σ-donation with the π* antibonding occupancy of the Cr-Namido should have increased reactivity compared to the earlier Cr(II) starting material due to the mostly single bond character of the Cr-Namido bond.  The mesityl (Mes = 2,4,6-trimethylphenyl) analogue gives the same electronic structure in 2.10.  The Cr(Mes)2(bpy) cannot π-donate to the Cr due to the Mes, but still is square-planar, high spin with four unpaired electrons.34  The steric differences between 2.10 and N(SiMe3)2 and N(SiHMe2)2 are apparent in Table 2.2.  The change from the sp2 of the bpy to sp3 of the tmeda centres in the N(SiMe3)2 analogue gives a lengthening of all the bonds connected to the chromium centre.  The increase in bulk of the tmeda likely causes repulsion of the amide ligands and a lengthening of the Cr-Namido bond.  The shortening of the N(SiHMe2)2 Cr-Namido bond may be likely due to the reduced steric size of the amide ligand itself by changing one of the methyls to hydrogen which decreases the Namido-Cr-Namido angle from 106.76(8)° to 100.86(5)° of N(SiMe3)2 and N(SiHMe2)2 respectively.  The decrease allows for a better fit to the square-planar configuration, which gives the better fit by the dihedral angle of the ligands.   The absence of the single electron transfer to the tbpy antibonding orbital from the Cr(II) centre to make the LX• is significant and can be explained by ligand-field theory.  The electron transfer to the bpy LUMO is favourable in the octahedral complexes, as seen with the addition of bpy to 2.5 to make 2.7, so as to circumvent the high spin (S = 2, t2g3eg1) or low spin (S = 1, t2g4eg0) electronic configurations.  The electronic configuration for square-planar orbitals shows that the high-spin HOMO is lower in energy than that of the HOMO of the octahedral configuration.  The 22  LUMO of the bpy ligand likely resides between these two energies, which is why the transfer of an electron is favourable for octahedral Cr(II) complexes and not for square-planar Cr(II) complexes.  Because of the steric bulk of the N(SiMe3)2 ligands, 2.10a and 2.10b are stable as monomeric complexes with the coordination number 4.  Two similar compounds (Figure 2.14) were synthesized and characterized by the Anwander group in Germany.35  The difference is that instead of the bpy ligand, there is tetramethylethylenediamine (tmeda).  This ligand was used to stabilize the compounds from degradation.  The initial synthesis used the same starting material 2.5 with tmeda for the first analogue.  The second analogue used a transsilylamination to replace the initial amide, N(SiMe3)2, with HN(SiHMe2)2 which is able to protonate off the initial amide to form the second analogue.  Interestingly, the transsilylamination does not have to be done independently from the adduct formation with tmeda, but can be made in situ with the adduct formation as a one-pot synthesis.  When the transsilylamination was attempted without the tmeda, degradation products were observed. 23   Figure 2.14  Synthesis and thermal ellipsoid diagram (50%) of Cr[N(SiMe3)2]2(tmeda) and Cr[N(SiHMe2)2]2(tmeda) products of the Anwander group.35  C-H hydrogens and disorder about the tmeda ligand of Cr[N(SiHMe2)2]2(tmeda) removed for clarity.  The disorder of the Cr[N(SiHMe2)2]2(tmeda) was reorganized for better bond orientation, bond lengths and prevent conflicting bonding and bond lengths.  The geometry and bond lengths of the two new tmeda products are very similar to that of 2.10a and 2.10b.  The distorted square-planar geometry is conserved, but has greater and lesser dihedral angles than the bpy analogues.  The Npy-Npy-NSi-NSi dihedral angles were 31.652° and 17.46(7)° for Cr[N(SiMe3)2]2(tmeda) and Cr[N(SiHMe2)2]2(tmeda) respectively.  The Cr[N(SiMe3)2]2(tmeda) dihedral angle is greater than that of both the 2.10 compounds, potentially due to steric restraints about the molecule with the methyl groups of the tmeda and the SiMe3 clashing with each other.  There are also methyl groups almost directly above and below the chromium center of the molecule, preventing metal-metal interactions.  The bisdimethylsilyl amide analogue has a smaller dihedral angle than the rest of the compounds, due to the release of steric strain by having a Si-H bond in the place of a Si-Me.  The release of this strain allows the other methyl groups to be more perpendicular to the distorted square plane of the nitrogens.  With the 24  methyls of the tmeda on the other side of the complex, this allows for shielding of the chromium center from metal-metal interactions.    The orientations of the Si-H bonds of bisdimethylsilyl amide were not uniform.  Three of the hydrogens (H1, H2 and H3) were pointed toward the metal centre and the last (H4) was rotated 120° about the N-Si bond so that the methyl groups were pointed away from the silicons.    The bond lengths of the Cr-Namido and Cr-Ntmeda are very similar to both 2.10 compounds for the bistrimethylsilyl amide and the bisdimethylsilyl amide compounds.  The amide bond lengths found in Table 2.2 are very similar for all complexes.  The Cr-Nbpy bonds are between 0.05 and 0.10 Å shorter than that of the Cr-Ntmeda bond due to the difference between sp3 and sp2 nitrogen centres bonded to the ligand.  The same is true for the N-C and C-C bonds of the bpy and tmeda ligands with the sp3 tmeda atom centres.  The Cr-Npy bonds of the tmeda complexes being about 0.1 Å longer than bpy complexes.  When processing the crystallographic information files from the Anwander paper,35 the bistrimethylsilyl amide thermal ellipsoid diagram was solved without any structural disorder.  The bisdimethylsilyl amide structure was solved with disorder about the tmeda ligand, but the connectivity of the disorder was incorrectly placed.  Presented in Figure 2.14 is the thermal ellipsoid diagram of Cr[N(SiHMe2)2]2(tmeda) with the disorder resolved to relieve conflicting bond lengths and angles.  Quinoline derivatives of Cr bipyridine compounds. 2.3.2 The use of 8-hydroxyquinoline (oxine) as the LX ligand was performed simultaneously with 2.7.   By removing steric bulk of the nacnac to a ligand that has no portion that could point towards the metal centre would promote the desired reactivity and produce the desired cationic complex.  The reaction of oxine and a protic acid with 2.10a,b  was thought to form the square-planar cationic complex with an anionic counter ion, as shown in Figure 2.15.  The use of an acid and a protic ligand were not able to remove the amides through protonation in a one to one ratio to 2.10a.   Instead the oxine ligand undergoes a bis protonation of the amide to remove the initial ligand from the chromium center to make the neutral LX• product Cr(C9H6ON)2(bpy) (2.11) in the presence of an acid .    25   Figure 2.15  Synthesis of 2.11.  The initial product hypothesis on the top with the actual product below.  Reactions with oxine in the 1930s, showed that regardless of the oxidation state of the initial chromium center, oxine will form tris oxine chromium(III) complex (Figure 2.16).36  The tendency for chromium to coordinate three oxines in octahedral geometry has also been shown using the Cr(II) complex Cr(OAc)2 and the Cr(III) complex CrCl3·4H2O with oxine.  These reactions both form the tris oxine complex Cr(C9H6ON)3 identified by the magnetic susceptibility.37,38  The preparation of the bis oxine cannot be formed due to the very favourable oxidation of the chromium from +2 to +3 due to the octahedral complex being made by the coordination of a third oxine ligand.  Figure 2.16  Initial synthesis that determined the ligand number of Cr(C9H6ON)3 reported in 1938.36  With the formation of the tris oxine product being very favourable, it is not surprising the crystal structure of 2.11 was bis oxine rather than the mono oxine product with a counter anion, Figure 2.17.  The synthesis of 2.11 utilized Cr(II) as the starting material rather than Cr(VI) of the 1938 synthesis.  The formation of 2.11 was by oxidization of 2.10a by the oxine to give the Cr(III) complex and the 1938 complex reduced the chromium by the oxine to Cr(III), both similar 26  octahedral Cr(III) centres.  The electronic structure of the complex had changed from the initial Cr(II) source of 2.10a to a Cr(III) centre.  The extra electron of the complex was not removed; it is found in the antibonding orbital of the bpy, giving the expected C5-C6 bond length for LX• of 1.451(14) Å, only 0.02 Å from the typical bond length.  Figure 2.17  Thermal ellipsoid diagram (50%) of Cr(tbpy)(C9H6ON)2 (2.11).  All H atoms and solvents are omitted for clarity.  The image shows only the delta (Δ) enantiomer of 2.11 with the lambda (Λ) enantiomer being omitted from the image.  The crystal structure was solved as a two-component twin with TWINABS39 correction.  The structure of 2.11 was crystallized as a twin crystal that showed both enantiomers, with only minor differences in the bond lengths, Table 2.3.  The bond lengths are in the typical range found with chromium complexes.40  The geometry about chromium centre is a slightly distorted octahedral complex.  The structural distortion is due to bite angle compression of the bpy chelating nitrogens (N1-Cr1-N2) to 78.8(3)°.  This results in more available space for the oxygen atoms (O1-Cr1-O2) opposite to be 96.0(2)°.  The plane of the bpy and the oxygens is nearly planar with dihedral angles of approximately 5.2° and 7.1° for the Δ and Λ enantiomers respectively.  The axial bonds of the Cr-N of the oxine are bent by approximately 12.1° and 13.0° for the Δ and Λ enantiomers respectively due to the steric restraints of the chelating ligands.  The UV-vis spectrum (Figure B.3) shows three major absorptions at 335, 443 and 665 nm.   27  Table 2.3  Bond lengths of 2.11 using the same relative numbering scheme for both enantiomers. Bond of Δ isomer Bond length (Å) Bond of Λ isomer Bond length (Å) Cr1-O1 1.975(6) Cr2-O3 1.967(6) Cr1-O2 1.965(5) Cr2-O4 1.976(6) Cr1-N1 1.993(7) Cr2-N5 2.000(6) Cr1-N2 2.000(6) Cr2-N6 2.010(7) Cr1-N3 2.046(7) Cr2-N7 2.058(8) Cr1-N4 2.067(7) Cr2-N8 2.069(8) N1-C5 1.358(10) N5-C33 1.393(11) N2-C6 1.393(11) N6-C34 1.367(10) C5-C6 1.451(14) C33-C34 1.453(13)  When synthesizing the analogous compound with tbpy in the backbone of the compound, the residue when the solvent was removed had a similar colour and solubility properties to 2.11, but resisted recrystallization attempts.  The same reaction that produced 2.11 was attempted with 8-aminoquinoline, the amine analogue of the oxine, shown in Figure 2.18.  This produced a red solid.  The solution of 2.10b was initially dark purple, which was then reacted with 8-aminoquinoline to produce a deep red solution.  While the isolated solid 2.12 initially seemed to be crystalline, when sent for X-ray diffraction, the solid was either amorphous or decomposed en route.    Figure 2.18  Attempted synthesis of Cr(tbpy)(C9H7N2)2 (2.12).   The solid residue of 2.12 was sufficiently soluble in THF to allow a UV-visible spectrum to be recorded (Figure B.4).  The major absorbances at 524nm with a shoulder of the absorbance at 458 nm and an absorbance at 360 nm gave evidence that a new complex was made. 28  2.4 Oxazolines and 2-aminodiphenylamine Chromium Compounds  The catalytic cycles of Cr(II) complexes tend to be ambiguous for how the ligands associate and couple on the metal centre.   Trapping potential intermediates of these catalytic cycles offers insight to how and when the coupling is taking place and how they could be modified.  The potential for adding redox reactive ligands to an intermediate analogue could have beneficial or difference in future reactivity.   The protic amine ligands added to these Cr(II) centres shows that the coordination of the ligands are very favourable and can provide a complex with open coordination sites for future reactivity.  Care should be taken though to limit the amount of reactive protons in the binding sites of the ligand, the potential for multiple reactive protons can cause more than protonation from the metal centre, exposing the metal to polymeric coupling.  Synthesis of metallated oxazoline complexes 2.4.1 The coupling of aryl Grignard reagents to aromatic rings in the ortho position with catalytic CrCl2 was recently published.41  One of the successful substrates for the coupling reaction was a SiMe3 ortho protected 4,4-dimethyl-2-phenyl-2-oxazoline (oxazoline) with p-ClC6H4MgBr as the Grignard reagent, as shown in Figure 2.19.  This oxidative C-H functionalization reaction presumably proceeds via the oxazoline-directed metalation of the aryl C-H bond, as shown in square brackets.42    Figure 2.19  The coupling of a protected oxazoline to p-ClC6H4MgBr,41 with the presumed metallated intermediate. 29   The initial reaction of 2 equivalents of oxazoline with the bis amide 2.5 (Figure 2.20) gave a pale orange solution of Cr(C11H12NO)2 (2.13).  The orange solution of 2.13 produced crystals, but they did not diffract in the X-ray beam.  The elemental analysis of 2.13 matched well for both the nitrogen and the hydrogen content, but the carbon content was low with respect to the elemental formula.  The second step was the addition of tbpy to the solution after reacting with the oxazoline overnight to give Cr(C11H12NO)2(tbpy) (2.14).  The solution went green and provided good looking crystals after recrystallization, which also did not diffract due to being amorphous.  Figure 2.20  Synthesis attempt of Cr(C11H12NO)2 (2.13) and Cr(C11H12NO)2(tbpy) (2.14).  Monomeric and tetrameric aminodiphenylamine complexes 2.4.2 An interesting product was formed when attempting to make the nitrogen chelating Cr(H2NC6H4-2-NHC6H5)2 from 2.5 and the addition of two 2-aminodiphenylamine, an analogue of a previously synthesized compound from the Smith group using 2-(N,N-dimethylamino)diphenylamine (Figure 2.21).  The reaction produced tetrameric Cr4(μ-NHC6H4-2-μ-NC6H5)4(THF/Et2O)2·2Et2O (2.15).  The 2-aminodiphenylamine acted as two sources of protons rather than one to protonate the amides of 2.5.  The top product of Figure 2.21 is the previously synthesized with R=CH3 giving the monomeric species with the crystal structure and the product below is with R=H and is visualised from the perpendicular plane of the chromium atoms and beside it as the view of a single subunit of the tetrameric species.   30   Figure 2.21  Synthesis of Cr(NMe2C6H4-2-NC6H5)2 and 2.15.  The two products formed from the reaction of 2.5 with the aniline derivatives where (R=H or CH3).  Two analogous synthesis of complexes similar to 2.15.43  The crystal structure 2.15 has many interesting features.  When crystallized, the molecule partially kept the THF bound to two of the chromium centres but was sometimes replaced with Et2O when the crystal structure was resolved.  The only source of THF was from the starting material as the reaction solvent and recrystallization solvent was Et2O.  This solvent substitution seems 31  inconsequential, as there seems to be no disorder added in the rest of the molecule from the two differing solvents.  In the lattice structure, there are two Et2O solvent molecules, one of which was in the typical geometry of Et2O and refined without issue.  However, the second solvent molecule was disordered with one geometry that was well behaved and one that was twisted.  The solvent disorder did not appear to add any new disorder to the overall molecule.  There is a precedent for the bridging nitrogens in 2.15 by the formation of [Cr(μ-NPh2)(NPh2)(THF)]2 from monomeric Cr(NPh2)2(THF)2 (Figure 2.21).43  The dimer is made from the corresponding bis amide by refluxing in toluene then concentrating to a small volume before recrystallization.  The resulting dimeric Cr(II) complex can be made free of THF by repeating the reflux and concentrating to dryness three times.  The THF free [Cr(μ-NPh2)(NPh2)]2 can easily be broken back to the monomeric species by the coordination of pyridine (py) to make the square-planar Cr(NPh2)2(py)2, with trans amides like that of the Cr(NPh2)2(THF)2 starting material.  The behaviour of the nitrogen ligands in this complex was similar to that of 2.15, where the free NPh2 is on the opposite side of the Cr-Cr plane when THF is bound to the complex.    When Na[di-2-pyridylamine] was reacted with CrCl2(THF)2, the formation of the bridging amide and coordinated pyridine subunit was found across the two Cr(II) centres (Figure 2.21).43  The similarity between [Cr(N{C5H5N}2)2]2 and 2.15 was that the bridging ligands also alternate between the orientation of up and down comparatively to the two chromiums in the complex.  The possible bis amide of the pyridyl complex formed initially then coordinated to each other through the nitrogens on the pyridine rings.    The structure of 2.15 shows the four chromiums are arranged in a nearly planar diamond pattern, with a ~3° dihedral angle of the plane as shown in Figure 2.22 .   The 2-aminodiphenylamine ligands are bridging between two chromiums with both nitrogens bonding to both chromiums.  The N-phenyl rings of the ligands are situated perpendicular to the plane of the chromium, alternating above and below.  Presumably, there is not enough steric bulk on the 2-aminodiphenylamine to form the monomeric chromium complex.  The ligand also has three acidic protons that can be used to remove the amide through protonation of 2.5 rather than the single proton of the methyl derivative. 32     Figure 2.22  Thermal ellipsoid diagram (50%) of Cr4(μ-NHC6H4-2-μ-NC6H5)4(THF/Et2O)2·2Et2O (2.15). All H atoms and solvents are omitted for clarity.  Hydrogens on the nitrogens are present to show stereochemistry.  Top view is perpendicular of the plane to the chromiums with the simple pictoral box diagram of the linear and parallel phenyl rings next to it, the bottom view is pseudo-parallel to the plane of the chromiums, and the numbering scheme for the aniline ring to the right of all four ligands.  Selected bond lengths (Å) Cr1-Cr2 2.4979(5), Cr2-Cr3 2.4450(5), Cr3-Cr4 2.4997(5), Cr4-Cr1 2.4364(5), C1-C6 1.416(3), C3-C4 1.383(3), C13-C18 1.420(3), C15-C16 1.384(3), C25-C30 1.414(3), C27-C28 1.390(3), C37-C42 1.419(3), and C39-C40 1.380(3).  The bond lengths of 2.15 have shown the phenylenediamido ligand to be in its dianionic (X2) form.44  The two sets of bonds that structurally show the oxidation state are the two carbons between the chelating nitrogens and the opposite carbons.  These two bond lengths are consistent 33  with an aromatic system of the phenylenediamido ligand and therefore there is no radical on the ligand.  There is a macro structural arrangement in the crystal structure where two of the diaminophenyl ring’s planes are linear to each other across the chromium plane.  The second two ligands are not linear but nearly parallel with each other, as seen in Figure 2.22.   Unfortunately the UV-vis spectrum (Figure B.5) is almost featureless with only a gradual decrease in absorption across the spectra.  In the Cr(NMe2C6H4-2-NC6H5)2 analogue, the chromium has a square-planar geometry with a dihedral angle of 28.8° along the nitrogens.  The ligand does not have any radical character due to the tetrahedral geometry of the methylated nitrogen and can be considered as a pure LX donor to the chromium center.  The bond lengths of 1.4124 and 1.4160 Å for the carbons between the nitrogens and 1.363 and 1.3884 Å for the carbons opposite the ring can be used as a basis for the non-radical LX ligand, giving a Cr(II) oxidation state of the metal, as shown in Table 2.4.  The variation in bond lengths of the C-C bonds may be due to how they lie compared to the chromiums, where the relative angle of the plane of the phenyl ring is either linear or parallel to the ring across the chromium plane.  The methyl analogue has similar diaminophenyl bond lengths as that of 2.15.  The analogous bond lengths, between the two structures suggests the same oxidation state of the ligand and chromium centres for both compounds.44   Table 2.4  The bond lengths of the 2-aminodiphenylamine ligand of 2.15. Bridged chromium Diaminophenyl carbons Bond length (Å) Diaminophenyl carbons Bond length (Å) Ligand across chromium plane Cr2-Cr3 C1-C6 1.416(3) C3-C4 1.383(3) Linear Cr3-Cr4 C13-C18 1.420(3) C15-C16 1.384(3) Parallel Cr4-Cr1 C25-C30 1.414(3) C27-C28 1.390(3) Linear Cr1-Cr2 C37-C42 1.419(3) C39-C40 1.380(3) Parallel   Previous examples of Cr4 square configuration and Cr(II) type of compound were reported by Gambarotta with alkyl bridging ligands and Wolczanski with silyloxide bridging ligands (Figure 2.23).45,46  The alkyl and silyloxide structures helped with the understanding of the structure of 2.15. 34   Figure 2.23  Alkyl45 and Silyloxide46 chromium tetramer compounds  The alkyl structure, [Cr(μ-CH2SiMe3)2]4, has the same basic square of chromiums atoms 2.15, but all the bridging ligands are the same CH2SiMe3 ligand.  The silyloxide structure, dubbed a chromous box, [Cr(μ-Cl)(μ-OSitBu3)]4 has the same general formation as 2.15, with the bridging ligand pairs of the chloride and oxosilyl-t-butane alternating above and below the plane of the chromiums.  The bond length differences between the chromiums of the three structures (Table 2.5) show a trend that corresponds with the ligands used.  The Cr-Cr bond length trend was found to be analogous to the going across the periodic table, with the carbon bridging ligands of the alkyl structure being shortest bond lengths, followed by the nitrogen ligands of 2.15, followed by the heterogeneous chlorine and oxygen bridging ligands of the silyloxide structure.  The alkyl and silyloxide structures are also closer to a rectangle with a Cr-Cr-Cr angle closer to 90° than 2.15 which possesses a diamond shape.  The biggest difference is the two solvent molecules coordinating to opposing chromiums of 2.15.  The two chromiums bound to the solvents pulled away from the centre of the complex and the two non-solvent bound chromiums are pulled towards the centre, as seen in Cr1-Cr3 and Cr2-Cr4 bond distances of 2.15 versus the very similar distances seen for the other two structures.  The greatest dihedral angle was also found in 2.15, with the alkyl and silylyoxide structures are near planarity or planar respectively.        35  Table 2.5  Bond lengths and dihedral between the chromiums of complexes 2.15, alkyl,45 and silyloxide.46 Complex Cr1-Cr2 (Å) Cr2-Cr3 (Å) Cr3-Cr4 (Å) Cr4-Cr1 (Å) Cr1-Cr3 (Å)a Cr2-Cr4 (Å)a Dihedral (°)b 2.15 2.4979(5) 2.4450(5) 2.4975(5) 2.4364(5) 3.828 3.120 3.173 Alkyl 2.3310(10) 2.4004(10) 2.3396(10) 2.4026(10) 3.343 3.356 0.423 Silyloxidec 2.688(3) 2.670(3) 2.670(3)d 2.688(3)d 3.794 3.783 0 aDistances taken directly from the crystal structure without accounting for uncertainty.  bBased from the Cr1-Cr2-Cr3-Cr4 angle, with no uncertainty given.   cChromiums re-numbered to match numbering scheme of 2.15 and silyloxide structures, values of bond lengths and distances were tabulated independently from the structure crystallographic information file directly in Olex2 (version 1.2.6).  dCr4 with ligands placed by a [-X, +Y, 1/2-Z] projection of the literature data set.  The synthetic differences between 2.15 and alkyl and silyloxide structures was that 2.15 was prepared protonolysis, by the addition of the neutral amine to the amide 2.5, whereas the other structures were prepared by salt metathesis using either the lithium or sodium salts of the ligands with the chromium dichloride or trichloride.  Figure 2.24  Future direction for 2.15.  The dissociation by L2 type ligands.  The future direction of the tetramer complex is the dissociation of the chromium centres to monomeric complexes.  With the dissociation of 2.15 with neutral L2 ligands, it may be possible to get the desired product of monomeric chromium complexes.  The addition of L2 to 2.15 (Figure 2.24) could be possible if the ligand is able to coordinate to the metal and protect the metal centre to provide a Cr(II) square-planar structure.  2.5 Experimental Section  General Considerations 2.5.1 All reactions were carried out under nitrogen using standard Schlenk and glove box techniques.  Hexanes, diethyl ether, dichloromethane and tetrahydrofuran were purified by passage through activated alumina and deoxygenizer columns from Glass Contour Co. (Laguana Beach, CA, USA). Celite (Aldrich) was dried overnight at 120 °C before being evacuated and then stored under 36  nitrogen.  Ar-NacnacH, chromium bis(trimethylsilyl)amide bis(tetrahydrofuran), and the protonated bpy and tetraphenylborate were synthesized according to literature methods.47,19,48  p-Toluenesulfonic acid mono hydrate (98%) was either dried49 to remove the hydrate or was used as received from Aldrich.  Chromium dichloride (99.9%) was purchased from Strem Chemicals and used as received.  4,4-dimethyl-2-phenyl-2-oxazoline (96%) was freeze-pump-thaw degassed before use.  Sodium bis(trimethylsilyl)amide (95%), 1,4-dioxane (anhydrous), 4,4′-Di-tert-butyl-2,2′-dipyridine (98%), 8-hydroxyquinoline (99%), 2-aminodiphenyl amine (98%), 8-aminoquinoline (98%), and phenylmagnesium chloride (2M in THF) were purchased from Aldrich and used as received.    UV-vis spectroscopic data were collected on 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 to a Hellma 10 mm path length quartz absorption cell with a quartz-to-glass graded seal. Elemental analyses were performed by the UBC Department of Chemistry microanalytical services. 1H NMR spectra were recorded on a Varian Mercury Plus 400 spectrometer in C6D6 with chemical shifts referenced to the solvent signal.   Experimental Procedures 2.5.2 Synthesis of Cr((PhNC(Me))2CH)(N(SiMe3)2) (2.6).  To a solution of Cr[N(SiMe3)2]2(THF)2 (597 mg, 1.17 mmol) in 20 mL Et2O was added a solution of PhNHC(Me)CHC(Me)NPh (297 mg, 1.19 mmol) in 6 mL Et2O.  After stirring for 21 h, the solvent was removed in vacuo, the residue was extracted with 3 mL hexanes, filtered through Celite and the solution was cooled to -30 °C. 2.6 (388 mg, 72%) was isolated after 3 days to yield brown crystals.  Anal. Calcd. for C23H35N3CrSi2: C, 59.83; H, 7.64; N, 9.10.  Found: C, 60.66; H, 7.83; N, 9.23.  UV-vis (hexanes; λmax, nm (ε, M-1cm-1)): 402 (8300), 502 (360). μeff (294 K) = 5.19(6) μB.  Synthesis of [Cr((PhNC(Me))2CH)(tbpy)2][BPh4]•Et2O (2.7).   Method A.  To a solution of 2.6 (40 mg, 0.087 mmol) in 5 mL THF was added a solution of [tbpyH][BPh4] (53.4 mg, 0.091 mmol) in 3 mL THF.  After stirring for 3 days, yielded a purple solution and the solvent was removed in vacuo, the residue was extracted with 3 mL Et2O and 0.5 mL THF, filtered through Celite and the solution was cooled to -30°C.  Initial isolation of [Cr((PhNC(Me))2CH)(THF)3][BPh4] (2.9) was followed by isolation of 2.7 (13 mg, 25%).  Method B.  To a solution of 2.6 (60 mg, 0.13 mmol) in 10 mL THF was added a solution of [tbpyH][BPh4] (77 mg, 0.13 mmol) and tbpy (37 mg, 0.14 mmol) in 9 mL THF.  After stirring for 28 hours, yielded a purple solution and the solvent was removed in vacuo, the residue was extracted with 8 mL toluene, filtered through Celite and had three drops of THF added.   37  The solution was then cooled to -30°C.  2.7 (94 mg, 63%) was isolated as purple crystals without Et2O.  Anal. Calcd. for C77H85N6BCr·C4H10O: C, 79.00; H, 7.78; N, 9.82.  Found: C, 79.07; H, 7.35; N, 7.16.    Synthesis of [Cr((XylNC(Me))2CH)(THF)3][BPh4]·1.5THF (2.9).  To a solution of 2.5 (69 mg, 0.14 mmol) in 7 mL THF was added a solution of Xyl-nacnac (43 mg, 0.14 mmol) and [HNEt3][BPh4] (58 mg, 0.14 mmol) in 7 mL THF.  The green solution was reacted for 1 hour before a solution of tbpy (38 mg, 0.14 mmol) in 5 mL THF was added and turned the solution purple. After stirring for 22 hours, the solvent was removed in vacuo and the residue was extracted with 5 mL toluene and 6 mL THF as a clear green solution and filtered through Celite into new recrystallization vial.  The solution was layered with 2.5 mL hexanes and the solution was cooled to -30°C.  2.9 (15 mg, 11%) was isolated as a green crystal.  Synthesis of Cr(tbpy)[N(SiMe3)2]2 (2.10b).  To a solution of 2.5 (137 mg, 0.27 mmol) in 10 mL Et2O was added tbpy (79 mg, 0.29 mmol) in 5 mL Et2O, the light blue solution immediately turned dark purple.  After stirring for 22 hours, the solvent was removed in vacuo, the residue was extracted with 3 mL hexanes, filtered through Celite and the solution was cooled to -30°C.  2.10b (130 mg, 76%) was isolated as dark purple crystals.  Anal. Calcd. for C30H60N4Si4Cr: C, 56.20; H, 9.43; N, 8.74.  Found: C, 56.06; H, 9.34; N, 8.54.  UV-vis (Et2O; λmax, nm (ε, M-1cm-1)): 496 (3380), shoulder 384 (3540), 298 (30650). μeff (294 K) = 5.30 μB.  Synthesis of Cr(bpy)(8-hydroxyquinoline)2·toluene (2.11).  Method A.  To a solution of 2.10a (50 mg, 0.094 mmol) in 7 mL THF was added a solution of 8-hydroxyquinoline (14 mg, 0.094 mmol) and dried HOTs (16 mg, 0.095 mmol) in 5 mL THF, the purple solution was turning green.  After stirring for 4 days, the solvent was removed in vacuo, the residue was extracted with 3 mL toluene and 0.5 mL THF, filtered through Celite and the solution was cooled to -30°C.  2.11a was isolated as a green crystalline solid. Method B.  To a solution of 2.11 (34mg, 0.064 mmol) in 6 mL THF was added a solution of 8-hydroxyquinoline (20 mg, 0.14 mmol) in 2 mL THF, the purple solution slowly turned green.  After reacting for 17 hours, the solvent was removed in vacuo, the residue was extracted with 2 mL toluene, filtered through Celite and the solution was cooled to -30°C.  2.11 (6 mg, 11%) was isolated as a green crystalline solid.  UV-vis (toluene; λmax, nm (ε, M-1cm-1)): 665 (1600), 624 (1400), 443 (4100), 415 (3650), 356 (5750), 335 (6300).  Synthesis of Cr(bpy)(8-aminoquinoline)2 (2.12).  To a solution of 2.10b (50 mg, 0.078 mmol) in 9 mL THF was added a solution of 8-aminoquinoline (23 mg, 0.16 mmol) in 1.5 mL THF, the purple solution slowly turned bright red.  After stirring for 22 hours, the solvent was removed in vacuo, the 38  residue was extracted with 10 mL toluene, filtered through Celite and the solution was cooled to -30°C.  2.12 (5 mg, 10%) was isolated as red solid.    UV-vis (THF; λmax, nm (ε, M-1cm-1)): 524 (1160), shoulder 458 (1050), 360 (1700), 275 (8780).  Synthesis of Cr(tbpy)2Ph2.  To a solution of CrCl2 (30 mg, 0.25 mmol) in 9 mL Et2O was added a solution of tbpy (144 mg, 0.54 mmol) in 5 mL Et2O, the green solution slowly turned blue over 24 hours.  PhMgCl (0.28 mL of 2M, 0.55 mmol) was then added dropwise over 3 min.  After stirring for 2 days dioxane (47 μl, 0.55 mmol).  After stirring for 1 hour the solution was passed through a Celite frit and the solvent was removed in vacuo, the residue was extracted with 8 mL Et2O, filtered through Celite and the solution was cooled to -30°C.  Cr(tbpy)2Ph2 (112 mg, 61%) was isolated as dark blue/purple crystals.    Synthesis of Cr(oxazoline)2 (2.13).  To a solution of 2.5 (106 mg, 0.21 mmol) in 9 mL Et2O was added oxazoline (73 mg, 0.42 mmol) in 5 mL Et2O, the light blue solution turned orange.  After stirring for 18 hours, the solvent was removed in vacuo, the residue was extracted with 2 mL hexanes, filtered through Celite and the solution was cooled to -30°C. 2.13 (17mg, 20%) was isolated as brown crystals.   Anal. Calcd. for C22H24N2O2Cr: C, 65.99; H, 6.04; N, 7.00.  Found: C, 64.82; H, 6.46; N, 6.86.    Synthesis of Cr(oxazoline)2(tbpy) (2.14).  To a solution of 2.5 (101 mg, 0.20 mmol) in 9 mL Et2O was added oxazoline (68 mg, 0.39 mmol) in 5 mL Et2O, the light blue solution turned orange, stir for 18 hours and then added tbpy (58 mg, 0.21 mmol) in 9 mL Et2O.  After stirring for 2 days, the solvent was removed in vacuo, the residue was extracted with 2 mL hexanes, filtered through Celite and the solution was cooled to -30°C. 2.14 (17mg, 20%) was isolated as brown crystals.   Synthesis of Cr4(μ-NHC6H4-2-μ-NC6H5)4(THF/Et2O)2·2Et2O (2.15).  To a solution of 2.5 (108 mg, 0.21 mmol) in 5 mL Et2O was added 2-aminodiphenylamine (77 mg, 0.42 mmol) in 5 mL Et2O, the light blue solution of the amide and orange solution of the amine turned green.  After stirring for 18 hours, the solvent as removed in vacuo, the residue was extracted with 4 mL Et2O, filtered through Celite and the solution was cooled to -30°C. 2.15 (30mg, 34%) was isolated as brown/black crystals.  Anal. Calcd. for C64H76.7N8O4Cr4: C, 62.52; H, 6.28; N, 9.11.  Found: C, 61.43; H, 5.38; N, 9.99.  UV-vis (Et2O; λmax, nm (ε, M-1cm-1)): 579 shoulder (3800), 446 shoulder (8000), 336 shoulder (27000).   General procedure for X-ray crystallography.  Single crystals were mounted on a glass fiber and measurements were made by Dr. Brian O. Patrick at UBC Vancouver 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 39  integrated using the Bruker SAINT software package50 and were corrected for absorption effects using the multi-scan technique (SADABS)51 (unless otherwise mentioned).  The data was corrected for Lorentz and polarization effects and the structure was solved by direct methods.52 All non-hydrogen atoms were refined anisotropically.  All hydrogen atoms were placed in calculated positions and were not refined.  All refinements were performed using the SHELXTL52 crystallographic software package within Olex2. 53  The molecular drawings were generated by Olex2.53  Structure details.  Parameters for structures found in Table A.1.  Complexes 2.10b, 2.11, 2.15 crystallized with two independent molecules in the asymmetric unit. In complex 2.7, the tert-butyl group on C25 was disordered and modeled in in approximately 86:14 occupancy of the two orientations, the CH3 groups of the tert-butyl fragment on C50 were disordered and modeled in approximately 82:18 occupancy of the two orientations and the complex crystallizes with disordered solvent in the lattice.  No reasonable model of solvent could be obtained, therefore, the PLATON/SQUEEZE program25 was used to generate a second, solvent-free data set.  The result from this procedure removed 67 residual electron density from unit cell of 2.7 or approximately 8 electrons per asymmetric unit.  In complex 2.11, the data set was corrected for absorption effect using the multiscan technique (TWINABS)39 to generate a HKLF5 format data set.  The material crystallizes as a two-components split crystal with the components related by 180° rotation about the (0 0 1) real axis.  The data were integrated for both twin components, including both overlapping and non-overlapping reflections.  The structure was solved by using non-overlapping data from the major twin component. The batch scale refinement showed a roughly 74:36 ratio between the major and minor twin components.  The compound crystallized in both rotomer configurations as independent molecules within the asymmetric unit with a disordered toluene per independent molecule.  Complex 2.15 showed unequal occupancy of the THF and Et2O on Cr1 and Cr3.  The ratio of THF to Et2O was approximately 74:26 and 55:45 on Cr1 and Cr3 respectively.  Of the two Et2O solvent molecules in the unit cell, one refined disordered in approximately 70:30 occupancy of the two orientations.   40  Chapter 3. Attempted Reductions of Cr(III) tBu-acac Bipyridine Complexes  The approach to the synthesis of the initial target complex was changed from starting with the chromium in the desired oxidation state of Cr(II), to the higher oxidation state of Cr(III), followed by reduction to Cr(II).  The Cr(III) complexes are much more air stable and easily handled.  The potential of adding ligands to the chromium which can be reductively eliminated from the complex will give Cr(I) complexes, or Cr(II) with a bpy based radical.  The final complex could then be oxidized by one electron to the desired Cr(II) square-planar cation complex with a counter anion.  The initial chromium carboxylate proved to be easily synthesized, but initial test failed to find any further reactivity.  The attempts to add alkyl and hydrides as ligands to be immediately reductively eliminated in solution did not produce any meaningful data.  The final attempt with phenyl Grignard did not produce a product that was expected, but added three times to give an anionic chromium with a bpy based radical as a stable square pyramidal complex. 3.1 CrCl3 Reactions With tBu-acac and Xyl-NacnacLi  The initial starting material for the formation of CrCl2(tBu-acac)(Rbpy) was CrCl3(H2O)(THF)2, initially thought to be strictly CrCl3(THF)3.54  It was recently shown that dehydration of CrCl3·6H2O with Me3SiCl generates CrCl3(H2O)(THF)2 instead of the desired anhydrous CrCl3.  As CrCl3(H2O)(THF)2 is more soluble in THF than CrCl3(THF)3, the use of the incorrectly assigned starting material did not appear to affect the initial starting material preparation or future reactivity of the final product.  For reactions that are sensitive to trace water, the older Soxhlet extraction of anhydrous CrCl3 using THF should be used to make CrCl3(THF)3.  The initial synthesis of CrCl2(tBu-acac)(bpy) (3.2a), as shown in Figure 3.1, was performed through the use of intermediate CrCl2(tBu-acac) (3.1).55  The formation of 3.2 is possible without the purification of 3.1.  The removal of THF and filtering off the unreacted CrCl3(THF)2(H2O) in Et2O provides a pure enough compound for successful preparation of 3.2.  The final product for both bpys with and without the tert-butyl group only needed to have the solvent removed and the product could be used directly, providing yields over a 90% in both cases. 41   Figure 3.1  Synthesis of Cr(Rbpy)(tBu-acac)Cl2 (3.2) through the Cr(tBu-acac)Cl2(THF)2 (3.1) intermediate.55  Structural determination of 3.2 by X-ray crystallography could not be performed as the solid did not stay crystalline when the solvent was removed.  However, the carbon, nitrogen and hydrogen content of the elemental analysis did give an excellent match for Cr(tbpy)(tBu-acac)Cl2 (3.2b).  The new starting material is a Cr(III) centre that is stable to atmospheric conditions as decomposition was not detected by UV-vis spectroscopy (Figure B.6).  The new 3.2 source is advantageous due to the formation of the desired ligand set on the chromium centre in the first synthetic step.  Unfortunately, it proved difficult to reduce to Cr(II) from the more stable, octahedral Cr(III).  Similar to 3.2, Cr(Xyl-nacnac)(tbpy)Cl2 (3.3) was prepared by the reaction of anhydrous CrCl3 with Xyl-nacnacLi and then with tbpy, initially prepared by Tom Welsh of the Smith Group as shown in Figure 3.2.  The Xyl-nacnacLi was prepared by a reaction of Xyl-nacnacH with BuLi in a solution of THF.  The Xyl-nacnacLi solution was then added anhydrous CrCl3 making a dark red solution.56  The THF was then removed from the solution resulting in a red solid and the tbpy was added as a solution in toluene to obtain a brown solution.  The toluene was removed and the product was recrystallized from a hexanes/CH2Cl2 mixture.  Unfortunately, the recrystallization did not proceed in the conventional glove box solvents of hexanes, Et2O, toluene or THF (or mixtures thereof), thus the successful reaction was performed on the Schlenk line.  Figure 3.2  Synthesis of Cr(Xyl-nacnac)(tbpy)Cl2 (3.3). 42   The UV-visible spectrum of 3.3 showed that the product was stable to the atmosphere with a major band at 338 nm and shoulders at 455, 541 and 632 nm.  The magnetic moment was found to be 3.60 μB by Evans’ method, which suggests three unpaired electrons in the molecule, confirming the Cr(III) oxidation state of the complex.  The crystal structure of 3.3 (Figure 3.3) also shows that the chlorines are cis to each other in the molecule.  The tbpy is found to be a L2 donor to the chromium center with the 1.482(3) Å bond length of the Cpy-Cpy bond, further supporting the Cr(III) centre.  The N-Cpy bond length of 2.1010(17) and 2.0899(17) Å also confirms the neutrality of the tbpy.  The two differing Cr-Cl bond lengths may be due to a trans effect from the opposite ligand, the longer bond, 2.3661(6) Å, being the chloride opposite to the mono anionic Xyl-nacnac and the shorter bond, 3.320(6) Å, being the chloride opposite the neutral tbpy.  The greatest factor for the differing bond lengths of the Cr-Cl bond is the π-bonding of the trans chloride to the Nacnac would be competing for the same orbital sets, whereas the chloride trans to the bpy would have no competition, as the bpy has been shown to not act as a π-acceptor.    Figure 3.3  Thermal ellipsoid diagram (50%) of 3.3. All H atoms and solvents are omitted for clarity.  Selected bond lengths (Å) Cr1-N1 2.0516(17), Cr1-N2 2.0835(17), Cr1-N3 2.1010(17), Cr1-N4 2.0899(17), Cr1-Cl1 2.3203(6), Cr1-Cl2 2.3661(6), N3-C25 1.356(3), N4-C26 1.348(3), C25-C26 1.482(3).  The initial predicted product of 3.3 would be expected to give trans chlorides as opposed to cis chlorides, as in the crystal structure.  The initial target molecule of [Cr(Xyl-nacnac)(tbpy)]X compounds were reconsidered as being too sterically hindered to adopt  a square-planar configuration.  Having trans chlorides would mean that the square-planar cationic complex with a counter anion would be possible as the Xyl-nacnac and tbpy ligands are in the proper positions on 43  the chromium.  The fact that the orientation is not trans but cis gives an indication that the initial target structure cannot be formed due to sterics, not electronics. 3.2 Salt metathesis of Cr(tbpy)(tBu-acac)Cl2 with Silver Carboxylates  The dichloride of 3.2b gave an opportunity for ligand substitution through salt metathesis.  Silver salts are an ideal choice for this substitution because the insolubility of the AgCl product would force the reaction forward.  The reactions of 3.2b with silver acetate and silver benzoate gave pale pink products 3.4a,b (Figure 3.4).  The benzoate product, 3.4b, provided crystals of sufficient quality for X-ray crystallography.  The attempt to react 3.2b with silver tosylate or silver triflate gave no discernible products, as the solution of 3.2b stayed light green throughout the reaction time.  Figure 3.4  Synthesis of 3.4a,b from 3.2b.  The acetate and benzoate products were pink solids, Cr(tbpy)(tBu-acac)(OAc)2 (3.4a) and Cr(tbpy)(tBu-acac)(OBz)2 (3.4b).  Measurements of the magnetic moment by Evans’ method of 4.03 and 3.78 μB for the solids 3.4a and 3.4b respectively, corresponding to three unpaired electrons, showed the oxidation state as Cr(III) in both compounds.    Unfortunately the elemental analysis of 3.4a was not as close to the theoretical calculated values as hoped.  Both the nitrogen and carbon values were 0.92% and 0.54% higher than calculated 44  respectively, with the cause of this not yet been understood.  The elemental analysis of 3.4b was within the expected tolerances.    The UV-visible spectra were very similar for the two molecules (Figure B.7 and Figure B.8 in Appendix B).  The spectra for 3.4a had a small absorption at 542 nm with a molar absorption coefficient of 100 M-1cm-1, and a stronger absorption shoulder at 393 nm with a molar absorption coefficient of 556 M-1cm-1 (Figure B.7).  Correspondingly, the spectra for 3.4b had a small absorption at 540 nm with a molar absorption coefficient of 390 M-1 cm-1, and a much stronger absorption shoulder at 393 nm with a molar absorption coefficient of 6140 M-1cm-1 (Figure B.8).   The crystal structure of 3.4b, as seen in Figure 3.5, revealed that the benzoates are trans to each other rather than cis.  The benzoate position is consistent with 3.1 which has trans chlorides.    Figure 3.5  Thermal ellipsoid diagram (50%) of Cr(tbpy)(tBu-acac)(OBz)2 (3.4b).  All H atoms are omitted for clarity.  Selected bond lengths (Å)  Cr1-O1 1.9577(15), Cr1-O2 1.9677(15), Cr1-O3 1.9759(16), Cr1-O5 1.9809(16), Cr1-N1 2.0708(18), Cr1-N2 2.0575(18), N1-C5 1.372(3), N2-C6 1.358(3), C5-C6 1.494(3).  The chromium oxygen bonds of 3.4b show that the tBu-acac Cr-O bonds are shorter at an average of 1.963 Å than that of the benzoyl Cr-O bonds at an average of 1.978 Å.  This is potentially due to the π-donation of the two benzoyl oxygens into the same set of orbitals on the chromium centre.  The two benzoyls groups are turned at approximately 126° to each other, measured by O4-O3-O5-O6 dihedral angle. This angle would allow for similar π-donation to the empty orbitals of the metal centre.  The shorter tBu-acac Cr-O bonds may be due to the increased π-donation to the metal as there is no competition from the tbpy which has been shown to not π-donate.  Since there is no 45  competing interaction across the chromium from the tbpy, the tBu-acac has more affinity for the orbitals on the chromium through π-donation.  Finally, the tbpy bonds N-Cpy and Cpy-Cpy at 1.365 (average) and 1.494 Å are typical bond lengths for a neutral bpy.  The next challenge for 3.4 was the reductive elimination of benzoyl groups and then the single electron oxidation to form the desired Cr(II) square-planar complex. 3.3 Attempts to Reduce the Chromium Centre Directly  The two methods attempted to reduce the chromium centre involved using LiHBEt3 (Super Hydride) and butyl lithium, as seen in Figure 3.6.  The rationale behind these reactions were that the chloride would be able to form salts with the lithium and either the hydride or the butyl would be able to bind with the chromium through salt metathesis.  The resulting intermediates, both the chromium hydrides and the chromium alkyl, should undergo reductive elimination.  The reductive elimination would give either hydrogen gas or octane, leaving the desired Cr(tBu-acac)(tbpy) compound.  The reaction would be a two electron reductive elimination that would give a Cr(I), d5 compound.  Electron transfer from Cr to bpy would give the expected electronic structure of the square-planar product, Cr(II) d4 with a radical anionic bpy LX•.57  Figure 3.6  Synthetic routes attempted to reduce 3.2b to Cr(tBu-acac)(tbpy).  This synthetic pathway was ultimately unsuccessful and did not produce consistent UV-visible results.  The actual product from the synthesis was undetermined; it is suspected that the reaction with the Super Hydride (LiHBEt3) performed a single-electron reduction of the tbpy ligand of 3.2b, as seen in Figure 3.7.  The solid isolated did seem crystalline, but did not diffract in an X-ray beam. 46   Figure 3.7  Potential single-electron reduction of 3.2b.  The single electron reduction of 3.2b is a potential product that would be convenient to have the crystal structure to prove the reduction of tbpy.  This reduced complex with a magnesium cation instead of lithium is used in Figure 3.10 as a model for an intermediate step in the synthesis of 3.5.  The reduced tbpy does offer some possibilities for the potential further reduction of the complex, but requires a sufficiently powerful reductant to be successful. 3.4 Synthesis of [Cr(tbpy)Ph3][Mg(tBu-acac)(THF)4]  The predicted product of the reaction of 3.2b with PhMgCl was a simple Grignard reaction with the chlorides to form MgCl2 and a diphenyl complex Cr(tBu-acac)(tbpy)Ph2.  The hope was the diphenyl complex would be able to undergo reductive elimination of Ph-Ph to give Cr(tBu-acac)(tbpy), a Cr(II) complex with the predicted LX•, depicted in Figure 3.8.  Surprisingly the formation of [Cr(tbpy)Ph3][Mg(tBu-acac)(THF)4] (3.5) was observed.  Figure 3.8  Predicted product (top) and formed product (bottom) of the reaction of 3.2b with PhMgCl. 47   The formation of 3.5 from the crystal structure, as seen in Figure 3.9, showed a square-pyramidal complex that was either Cr(II) with an L2 tbpy or Cr(III) with an LX• tbpy.  The bond lengths within the structure provide the nature of the chromium centre.  For a Cr(II) complex, the Jahn-Teller effect would give a longer axial bond than the bonds of the base of the square-pyramidal complex and the bond lengths of a typical neutral tbpy.  The Cr(III) complex would give a shorter axial bond length and the single electron reduced tbpy ligand determined by the ligand bond lengths, which is what was found for 3.5.  The axial Cr1-C19 bond is 2.0370(19) Å, which is shorter than the two Cr-Ph bonds of the base of the square pyramid that are Cr1-C25 and Cr1-C32 at 2.0886(19) and 2.085(2) Å respectively.  The tbpy bonds are those typically found of an LX• ligand of N1-C6 and N2-C5 being 1.389(2) and 1.387(2) Å respectively, and the inter pyridine bond length of C5-C6 1.427(2) Å.  With the three anionic phenyl ligands and the overall -1 charge for the [Cr(tbpy)Ph3] anion, the anionic radical form of the tbpy ligand is also consistent with a Cr(III) metal centre.    Figure 3.9  Thermal ellipsoid diagram (50%) of [Cr(tbpy)Ph3][Mg(tacac)(THF)4] (3.5).  All H atoms, solvents and counter ions are omitted for clarity.  Selected bond lengths (Å) Cr1-N1 2.0779(16), Cr1-N2 2.0864(16), Cr1-C19 2.0370(19), Cr1-C25 2.0886(19), Cr1-C31 2.085(2), N1-C6 1.389(2), N2-C5 1.387(2), C5-C6 1.427(2).    The crystal structure of 3.5 showed two independent chromium centres with their respective magnesium counter ions.  Along with the independent centres, the tbutyl groups of the tBu-acac on the magnesium and on the tbpy had disorder about the central carbon of three of the 48  eight potential groups.  The rest of the anion did not show disorder in atom positions in the structure, but the magnesium cation located between the π-systems of the anion was very disordered.  The disorder required splitting of the magnesium and all the coordinated THF molecules to solve the structure.  Interestingly, the tBu-acac of this cation only showed rotational disorder about one of the tbutyl groups and was not otherwise split.  The second magnesium cation, situated across the phenyl groups of one of the chromium anions, only had rotational disorder about one of the tbutyl groups and only on one carbon atom of a coordinated THF.  The UV-vis spectrum (Figure B.9) shows only one major absorption at 338 nm with a slowly trailing decrease in absorption out to 632 nm.  The problems with the obtained crystal structure and the starting materials became apparent.  The starting material 3.2b and the product 3.5 are both Cr(III) with the tbpy in L2 and LX• respectively.  There is an extra electron that was added to the complex that is not accounted for in Figure 3.8.  The extra electron was suspected to come from the initial activation of the 3.2b by the Grignard reagent by the transfer of an electron.58  The electron can conveniently go onto the tbpy ligand in the antibonding orbital, leaving a Ph• radical and the MgCl+ cation to balance the 3.2b- anion but leaving the chromium in the +3 oxidation state (see Figure 3.10).  The next part of the reaction is the MgCl+ extracting the tBu-acac from the chromium and coordinating it giving MgCl(tBu-acac) and the Grignard reaction of PhMgCl with the two chlorides, leaving the electronically neutral CrPh2(tbpy) as a Cr(II) with no tbpy radical.  The magnesium abstraction of tBu-acac from chromium has precedent in the acac abstraction from Cr(acac)3 by CpMgBr to make CpCr(acac) and presumably Mg(acac)Br in 1956.59  The Mg(acac)Cl formation is important for the synthesis of the counter ion that is found with the crystal structure. 49   Figure 3.10  Mechanism for the synthesis of 3.5.  The last PhMgCl can add to the chromium centre, further oxidizing the metal centre rather than reducing it.  This is contrary to what was expected from a strong σ-donor molecule bonding to a metal.  With the redox-active ligand available, the complex can become anionic and can bond the new ligand in the axial position, creating the observed five coordinate square-pyramidal complex.60,61  The final steps  for the synthesis involve the MgCl(tBu-acac) that initially was released to the solution from earlier in the reaction will release its chloride to the current MgCl+ to make MgCl2 and then absorb four more THF solvent molecules to make the octahedral [Mg(tBu-acac)(THF)4]+ counter ion.  The mechanism raises the question: why does the complex not reductively eliminate Ph-Ph, but actually gets reduced by another phenyl anion to become a five-coordinate compound?  Other chromium complexes have been found to be square-pyramidal with a tris-phenyl LX ligand system.  The two very similar examples to 3.5 are [Cr(Xyl-nacnac)Ph3][Li(Bu2O)] (a1) and [Cr(Xyl-50  nacnac)Ph3][Li(THF)]·C5H12 (a2), differing from each other by the bound lithium solvent cation to the Cr(III) complex, as seen in Figure 3.11.60  The lithium bound solvent for a1 is Bu2O, and the lithium interacts with the aromatic systems of the complex at one of the ortho hydrogens of the axial phenyl ring as well to both of the two phenyl rings at the base of the square-pyramidal complex, sitting inside of the anisotropic systems.  For a2, the lithium bound solvent is THF and the lithium no longer interacts with the axial phenyl ring, which is turned so that it is no longer in line with the cation.  Both a1 and a2 are neutral chromium compounds with the ion pairs bound to each other, unlike that found in 3.5 where the two ions are discrete units.                           a1           a2  Figure 3.11  Two examples of five coordinate anionic Cr(III) with an LX ligand, [Cr(Xyl-nacnac)Ph3][Li(Bu2O)] (a1) and [Cr(Xyl-nacnac)Ph3][Li(THF)]·C5H12 (a2).60  The difference in the compounds is the solvent of cation complexation.  Hydrogens atoms have been omitted for clarity.  These two complexes a1 and a2 are both resistant to reductive elimination of Ph-Ph to make a Cr(I) complex.  Like these two (LX)CrPh3 complexes, the neutral complexes, L2CrAr3, where Ar = Ph or p-Tol, are also stable to reductive elimination, (((iPr)2(C6H3)NHC)2CH2)CrPh3· 3THF0.5C6H6 (b)62 and Cr(C14H15N2)(C7H7)3 (c) shown in Figure 3.12.61 The structures of the neutral complexes show no interacting ions, just solvents in the crystal structure in the structure of b.  The interesting note for these two structures is that the steric bulk of the neutral L2 ligand is at two extremes, where b has high steric bulk and c has very little bulk around the metal centre.  The higher steric bulk of a and b would presumably be beneficial for reductive elimination as it would push the two phenyls at the base of the square-pyramid closer together. 51                   b           c       Figure 3.12  Two examples of five coordinate neutral Cr(III) complexes with aromatic ligands and neutral bidentate ligands.  (((iPr)2(C6H3)NHC)2CH2)CrPh3·3THF0.5C6H6 (b),62 Cr(C14H15N2)(C7H7)3 (c).61  Solvent molecules and hydrogens have been omitted for clarity.  Interestingly, there is a fourth, non-aromatic five coordinate square-pyramidal complex that also does not reductively eliminate.  The formation of [Cr(((iPr)2(C6H3)NCH)2)(CH3)3][Li2(THF)3] (d)63 is very similar to the synthesis of 3.5 due to the addition of a strong σ-donor to a chromium chloride complex (Figure 3.13).  The salt metathesis does not stop after the chlorides have been used and two more methyl ligands coordinate in d, whereas only one more is added in 3.5.  The analogous complexes of complex d showed only the substitution of the chloride and the anionic formation of the imine ligand into a LX• with a coordination Li(THF)n cation.    Figure 3.13  The final coordination MeLi to [Cr(((iPr)2(C6H3)NCH)2)(CH3)2]Li to make [Cr(((iPr)2(C6H3)NCH)2)(CH3)3] [Li2(THF)3] (d).63   Solvent molecules and hydrogens have been omitted for clarity.  Thermal ellipsoid diagram shows the coordinated Li (light blue) to the structure that is not depicted in the synthesis.  In Chapter 2, the Cr(II) bpy complexes showed octahedral geometry.  The use of Cr(III) in Chapter 3 with complexation of bidentate ligands in the starting material, the addition of strong aryl donors triggered the change to square-pyramidal.  The transformation to the five coordinate square-pyramidal complex is the triggering of the electron transfer from the metal centre to the L2 52  ligand as a strong field ligand as it approaches the four coordinate square-planar complex.  The further reduction of the LX• ligand to an X2 ligand by the methyl in d is similar to the electron transfer of the previous examples of neutral L2 to the LX•.  The axial Cr-C bond length is shorter in all structures with a Cr(III) five coordinate square-pyramidal configuration compared to the two Cr-C bonds on the base of the complex.  The bond lengths shown in Table 3.1 give the difference of the various structures, and shows that the base phenyl bonds are between 1-5% longer on average than that of the axial bond.   The axial bond lengths of the complexes, especially c, show that other alkyls or aryls could be coordinated to the chromium centre.  The differences between all the aryl complexes are very small, showing that the potential for other para-substituted or potentially meta-substituted aryls could be complexed in the same manner as the phenyls. Table 3.1  Chromium-carbon bond lengths of 3.5, a1, a2, b, c, and d, with the average equatorial length and difference between the axial and square-pyramid base bond in percentage.  3.6 a160 a260 b62 c61 d63 Cr-Cax (Å) 2.037(2) 2.037(3) 2.038(4) 2.044(4) 2.034(4) 2.107(4) Cr-Cbase,1 (Å) 2.085(2) 2.114(3) 2.137(4) 2.066(4) 2.073(4) 2.150(5) Cr-Cbase,2 (Å) 2.089(2) 2.140(3) 2.125(5) 2.079(4) 2.054(4) 2.159(5) Cr-Cbase,ave (Å) 2.087(3) 2.127(4) 2.131(6) 2.073(6) 2.064(6) 2.155(7) Difference (%) 2.455(2) 4.418(2) 4.563(3) 1.419(3) 1.475(3) 2.278(4)  The substitution pattern of the starting aromatic is important for this reaction, if the ortho positions of the aromatic are occupied the reaction is terminated with the radical returned from the bpy to the chromium, as seen in Figure 3.14.  The sterics of the intermediate plays a critical role in this reaction.  Square-planar Cr(bpy)(Mes)2 has been known since 1960 as a Cr(II) compound.64,65  The crystal structure of the Cr(bpy)(Mes)2, solved by the McGrady and Goicoechea groups, shows that there is no radical on the bpy during the synthesis of the neutral complex, but could be reduced by potassium to [Cr(bpy)(Mes)2][K(dibenzo-18-crown-6)·THF]·2THF.57   The same reaction that made 3.5 was repeated with the MesMgCl, giving Cr(tbpy)(Mes)2 (3.6) as a purple crystalline solid (UV spectrum Figure B.10) , very similar to the chromium compounds made in the 1960s by the reaction CrCl2 with MesMgX and bpy. 53   Figure 3.14  Mechanism for the synthesis of 3.6.  Cr(Mes)3 complexes have been found to not reductively eliminate where Cr(Ph)3 complexes have,66,67  presumably due to steric interference of the ortho methyl groups.  The formation of 3.6 provides evidence for the initial electron transfer to 3.2b from the Grignard reagent, rather than the alternative formation of Cr(tBu-acac)(tbpy)Ar2, followed by reductive elimination of Ar-Ar (Eq. 3.1).  The formation of the Cr(I) species would very quickly abstract a chloride from 3.2b, forming a Cr(II)X complex (Eq. 3.2) before reacting with the Grignard reagent again making the tri aryl complex.  (3.1)  (3.2)  The purple solid of 3.6 did not diffract, but the reaction with two equivalents of neutral tBu-acac produced a UV-vis spectrum that was the same as that of Cr(tBu-acac)2(tbpy), previously shown by the Smith group.34  The similar UV-vis spectra of the product gives indirect evidence that intermediate on the path to 3.5 is the Cr(II) square-planar diaryl complex. 54   The structures of the five coordinate square-pyramidal complexes show that other alkyl and aryl ligands can be used as the strong donors to make five coordinate complexes.  The changes in structure with having a more or less electron donating constituent added would be interesting to investigate for structural differences of these compounds.  The aryl and alkyl functionality of p-Tol and Me derivatives are promising for future reactivity of these five coordinate compounds.  If derivatives of 3.5 can be made with other types of alkyl or aryl groups, potential substitution reactions can be performed via the route in Figure 3.15 where the group can reductively eliminate the chromium onto an electrophile.  Figure 3.15  Potential reactivity of 3.5 type molecules.  The Grignard reaction has a low functional group tolerance on the electrophile.68  Current research is looking into using alternate metals such as zinc and nickel for expanding the functional group tolerance of the substrates used in the reaction.69,70   55  3.5 Experimental Section  General Considerations 3.5.1 All reactions were carried out under nitrogen using standard Schlenk and glove box techniques.  Hexanes, diethyl ether, dichloromethane and tetrahydrofuran were purified by passage through activated alumina and deoxygenizer columns from Glass Contour Co. (Laguana Beach, CA, USA).  Celite (Aldrich) was dried overnight at 120 °C before being evacuated and then stored under nitrogen.  Ar-NacnacH, chromium trichloride tristetrahydrofuran were synthesized according to literature methods.47,71  Butyllithium (1.6M, diethylether), 1,4-dioxane (anhydrous), silver acetate (99%), silver benzoate (99%), phenylmagnesium chloride (2M in THF), and mesitylmagnesium bromide (1.0M, diethylether) were purchased from Aldrich and used as received.    UV-vis spectroscopic data were collected on 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 to a Hellma 10 mm path length quartz absorption cell with a quartz-to-glass graded seal. Elemental analyses were performed by the UBC Department of Chemistry microanalytical services. 1H NMR spectra were recorded on a Varian Mercury Plus 400 spectrometer in C6D6 with chemical shifts referenced to the solvent signal.   Experimental Procedures 3.5.2 Synthesis of Cr(tBu-acac)(tbpy)Cl2 (3.2b).  To a solution of CrCl3(THF)3 (502 mg, 1.34 mmol) in 7 mL THF was added tBu-acac (253 mg, 1.38 mmol) in 7 mL THF.  After stirring for 20 hours to produce a deep green solution, the solvent was removed in vacuo and the residue was dissolved in 20 mL Et2O and filtered through Celite and tbpy (361 mg, 1.34 mmol) in 5 mL of Et2Owas added.  After stirring for 20 hours, the solvent was removed in vacuo and the solid was collected. 3.2b (740 mg, 96%) was isolated as a green powder.  Anal. Calcd. for C29H43N2O2Cr: C, 60.62; H, 7.54; N, 4.88.  Found: C, 58.76; H, 7.26; N, 4.65.  UV-vis (THF; λmax, nm (ε, M-1cm-1)): 632 (223), 498 (181), 347 (5856).   Synthesis of Cr(Xyl-nacnac)(tbpy)Cl2·2CH2Cl2 (3.3).  To a solution of Xyl-nacnac (2.02 g, 6.59 mmol) in 25 mL THF was added BuLi (4.5 mL, 1.6 M solution in Et2O, 7.2 mmol) drop wise, the clear solution turned yellow.  After stirring for 2.5 hours, the Xyl-nacnacLi mixture was cannulated into a Schlenk with CrCl3 (1.05 g, 6.6 mmol) to make a brown solution.  After stirring for 20 hours the solvent was removed in vacuo and tbpy (1.76 g, 6.5 mmol) in 40 mL toluene was cannulated onto 56  the brown residue.  After stirring for 23 hours, the solvent was removed in vacuo, the residue was extracted with 27 mL hexanes and 25 mL CH2Cl2, filtered through Celite and the solvent was removed in vacuo until a super saturated solution was made before being cooled to -20°C.  3.3 (4.17 g, 77%) was isolated as a brown crystalline solid.  Anal. Calcd. for C39H49N4Cl2Cr·2CH2Cl2: C, 56.83; H, 6.16; N, 6.47.  Anal. Calcd. for C39H49N4Cl2Cr·CH2Cl2: C, 61.46; H, 6.58; N, 7.17.  Found: C, 61.03; H, 6.99; N, 7.11, consistent with 1 CH2Cl2 per complex.  UV-vis (Et2O; λmax, nm (ε, M-1cm-1)): 338 (6900), 455 shoulder (2700), 541 sh, (2000), 632 shoulder (1700). μeff (294 K) = 3.60 μB.  Synthesis of Cr(tBu-acac)(tbpy)(OAc)2 (3.4a).  To a solution of 3.2b (205 mg, 0.36 mmol) in 6 mL THF was added AcOAg (118 mg, 0.71 mmol) as a suspension in 5 mL THF.  After stirring for 24 hours to produce a pink solution, the solvent was removed in vacuo, the residue was extracted with 4 mL Et2O, filtered through Celite and the solution was cooled to -30°C.  3.4a (78 mg, 36%) was isolated as a pink solid.  Anal. Calcd. for C33H49N2O6Cr: C, 63.03; H, 8.10; N, 4.59.  Found: C, 63.57; H, 8.02; N, 5.51.  UV-vis (Et2O; λmax, nm (ε, M-1cm-1)): 542 (100), 393 shoulder (556). μeff (294 K) = 4.03(0) μB.  Synthesis of Cr(tBu-acac)(tbpy)(OBz)2 (3.4b).  To a solution of 3.2b (75 mg, 0.13 mmol) in 5 mL THF was added BzOAg (60 mg, 0.26 mmol) as a suspension in 5 mL THF.  After stirring for 24 hours to produce a pink solution, the solvent was removed in vacuo, the residue was extracted with 6 mL Et2O, filtered through Celite and the solution was cooled to -30°C.  3.4b (21 mg, 21%) was isolated as a pink solid.  Anal. Calcd. for C43H52N2O6Cr: C, 69.33; H, 7.04; N, 3.76.  Found: C, 69.09; H, 7.14; N, 4.08.  UV-vis (Et2O; λmax, nm (ε, M-1cm-1)): 540 (390), 336 shoulder (6140). μeff (294 K) = 3.78(4) μB.  Synthesis of [Cr(tbpy)Ph3][Mg(tBu-acac)(THF)4] (3.5).  To a solution of 3.2b (100 mg, 0.36 mmol) in 15 mL THF was added PhMgCl (0.92 mL, 2.0 M solution, 2.3 mmol) drop wise, the dark green solution immediately turned dark red.  After stirring for 3 days, dioxane (200 μl, 2.34 mmol) was added, allowed to stir for 1 hour then the solvent was removed in vacuo, the residue was extracted in 10 mL Et2O filtered through Celite and the solution was cooled to -30°C.  3.5 (51 mg, 13%) was isolated as a brown crystalline solid. Anal. Calcd. for C63H90N2O6CrMg: C, 72.22; H, 8.66; N, 2.67.  Found: C, 69.59; H, 7.69; N, not detected.  UV-vis (Et2O; λmax, nm (ε, M-1cm-1)): 338 (6900), 455 shoulder (2700), 541 shoulder, (2000), 632 shoulder (1700).  μeff (294 K) = 2.95(9) μB.  Synthesis of Cr(tbpy)(Mes)2 (3.6).  To a solution of 3.2b (67 mg, 0.24 mmol) in 15 mL THF was added MesMgBr (0.50 mL, 1.0 M solution, 0.50 mmol) drop wise, the dark green solution immediately turned purple.  After stirring for 18 hours, dioxane (45 μl, 0.53 mmol) was added, 57  allowed to stir for 1 hour then the solvent was removed in vacuo, the residue was extracted in 5 mL Et2O filtered through Celite and the solution was cooled to -30°C.  3.6 (27 mg, 20%) was isolated as a purple solid.  Anal. Calcd. for C36H46N2Cr: C, 77.38; H, 8.30; N, 5.01.  Found: C, 74.00; H, 8.68; N, 4.21.  UV-vis (THF; λmax, nm (ε, M-1cm-1)): 568 (1250).    General procedure for X-ray crystallography.  Protocols were identical to those reported in section 2.5.2.  Structure details.  Parameters for structures found in Table A.1.  Complex 3.4b showed disorder of the CH3 groups about the tert-butyl on C3 in an approximately 90:10 occupancy between the two orientations. Complex 3.5 showed disorder of the CH3 groups within each tert-butyl fragment. Each tert-butyl was modeled in two orientations with the occupancies of the disorder about C37 (81:19), C74 (85:15), and C100 (76:24).  The cation of Mg1 was completely disordered with O1 and O2 of the tBu-acac in constant position. The four THF on the Mg and the Mg were both split into two sets and were modeled separately with an approximately 66:34 occupancy of the two orientations. C124 and C130 are the same carbon in two orientations with an approximately 83:17 occupancy. 58  Chapter 4. Conclusion  In this thesis the electronic structure of paramagnetic chromium complexes were determined for two new Cr(II) and four new Cr(III) species.    The initial target of square-planar [Cr(Xyl-nacnac)(tbpy)]X complexes were found to be un-favourable under the reaction conditions attempted. The target was abandoned when the more bulky CpCr(Xyl-nacnac) did not react as desired, giving [Cr(Xyl-nacac)(μ-OH)]2 when reacted with HOTs·H2O and coordinating OTs to give CpCr(Xyl-nacnac)(OTs) when anhydrous HOTs was used.  With the failure of the initial starting material, the less bulky Cr(Ph-nacnac)[N(SiMe3)2]2 was used, but was found to coordinate two tbpy instead of the desired one, giving Cr(Ph-nacnac)(tbpy)2 with a tbpy based radical on one of the two tbpy ligands.  Cr(II) starting complexes showed the tendency to oxidize to Cr(III) and go octahedral when chelating ligands were used.  If there was a possibility of moving an electron onto a ligand, it was found to be more favourable than staying as Cr(II) square-planar.  The same tendency to go octahedral and Cr(III) was found when using the known square-planar Cr(II) precursors, bis amide, Cr[N(SiMe3)2]2(THF)2, and tbpy bis amide,  Cr(tbpy)[N(SiMe3)2]2.  The Cr(tbpy)[N(SiMe3)2]2 was made from the bis amide, and these were used as two new starting points for the formation of the complexes.  When the bpy bis amide was reacted with an alternate LX donor, 8-hydroxyquinoline, a much less bulky LX ligand than the nacnacs, the quinoline was found to coordinate twice as well, oxidizing to Cr(III) and leaving a LX• on the bpy ligand, as was found with in the previous example of Cr(Ph-nacnac)(tbpy)2.  Unlike the previous example, when the bis amide was reacted with 2-aminodiphenylamine only one equivalent of the ligand was required to deprotonate both of the amide ligands.  The expected square-planar complex that was shown with the analogous reaction of two 2-(N,N-dimethylamino)diphenylamine was not formed.  The new complex became a tetramer of these Cr(2-aminodiphenylamine) subunits where the 2-aminodiphenylamine bridged between the chromiums with both nitrogens.  This left the chromiums in a Cr(II) oxidation state and did not show any radical character on the ligand.  When starting with the Cr(III) precursor, CrCl2(tBu-acac)(tbpy),  the salt metathesis with the silver carboxylates were successful for making octahedral Cr(tBu-acac)(tbpy)(OBz)2 and Cr(tBu-acac)(tbpy)(OAc)2.  Both are pink solid products where the carboxylates are trans to each other.  The 59  product remains Cr(III) and thus far has resisted all attempts at reducing chromium and eliminating the benzoates from the molecule.  The final structure characterized by X-ray crystallography was unexpected, unusual and rare five coordinate square-pyramidal chromate with a tbpy LX•, [CrPh3(tbpy)][Mg(tBu-acac)(THF)4].  This chromate showed the Cr(III) state unchanged from the starting material, CrCl2(tBu-acac)(tbpy).  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Chem. 1990, 29, 1592–1593.  64  Appendices  Supplementary X-ray Data Appendix A Table A.1 Crystal data and refinement parameters for X-ray structures 2.7, 2.10b, 2.11, 2.15, 3.4b, and 3.5  2.7 2.10b 2.11 2.15 3.4b 3.5 Formula C77H85N6BCr C30H60N4Si4Cr C35H28N4O2Cr C67H76.7N8O4Cr4 C43H53N2O6Cr C63H90N2O6CrMg Formula Weight 1157.31 641.16 588.61 1230.04 745.87 1047.67 Crystal Colour, Habit black, prism black, plate green, irregular black, prism pink, irregular black, prism Crystal Dimensions, mm 0.26 X 0.35 X 0.42 0.08 X 0.23 X 0.33 0.07 x 0.10 x 0.32 0.20 X 0.25 X 0.29 0.02 X 0.08 X 0.18 0.33 X 0.15 X 0.12 Crystal System Orthorhombic Monoclinic Triclinic Monoclinic Monoclinic Monoclinic Space Group P b c a P 21/c P 1̅ P 21/c P 21/c P 21/c a, Å 19.6981(10) 26.842(18) 10.7073(9) 15.5936(15) 13.2567(8) 12.0157(12) b, Å 23.5287(12) 14.046(6) 12.7763(11) 15.8665(15) 13.9631(9) 19.6100(19) c, Å 32.2784(16) 21.810(14) 21.3555(14) 23.829(2) 23.1091(15) 49.596(5) α, ° 90.00 90.00 87.797(13) 90.00 90.00 90.00 β, ° 90.00 110.67(8) 89.996(3) 95.651(3) 106.484(1) 92.328(4) γ, ° 90.00 90.00 72.059(4) 90.00 90.00 90.00 V, Å3 14960.1(13) 7694(8) 2777.1(4) 5867.0(10) 4101.8(4) 11677(2) Z 8 8 4 4 4 8 Dcalc, g/cm3 1.028 1.107 1.408 1.393 1.208 1.192 F000 4944.0 2784 1224 2579 1588 4528 μ(MoKα), cm-1 1.95 4.45 4.53 7.77 3.26 3.26 Data Images (no., t/s) 878, 60 1096, 30 1383, 60 1042, 4 999, 30 3693,n= 7.5 2Ѳmax 50.82° 50.04° 45.1° 60.018° 52.06° 60.058° Reflections measrd 13742 82179 45493 67229 32912 209786 Unique reflcn, Rint 13741, 0.0000 14213, 0.1207 12426, 0.053 17167, 0.7460 5737, 0.0691 34210, 0.0662 Absorption, Tmin, Tmax 0.697, 0.745 0.848, 0.996 0.743, 0.969 0.6634, 0.7460 0.6754, 0.7453 0.683, 0.7460 Obsrvd data (I>2.00σ(I)) 9273 8763 9019 12112 5737 24162 No. parameters 809 703 824 843 469 1599 R1, wR2 (F2, all data) 0.0849, 0.1405 0.1136, 0.1274 0.114, 0.098232 0.0736, 0.1101 0.0752, 0.1049 0.0973, 0.1455 R1, wR2 (F, I>2.00σ(I)) 0.0521, 0.1300 0.0539, 0.1044 0.083, 0.212 0.0446, 0.0968 0.0439, 0.0939 0.0626, 0.1316 Goodness of Fit 1.072 1.004 1.08 1.013 1.017 1.069 Max, Min peak, e-/Å3 0.34, -0.46 0.400, -0.521 0.93, -0.43 0.82, -0.84 0.40, -0.37 0.79, -0.49 65   Supplementary UV-vis Spectra Appendix B  Figure B.1  UV-vis absorption spectra of complex 2.6 in hexanes [2.80 x 10-4 M] 0.00.51.01.52.02.53.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm)                                                                                                    66   Figure B.2  UV-vis absorption spectra of complex 2.10b in Et2O [3.90 x 10-5 M] 0.00.20.40.60.81.01.21.4250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 67   Figure B.3  UV-vis absorption spectra of complex 2.11 in toluene [2.09 x 10-4 M] 0.00.20.40.60.81.01.21.41.61.82.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 68   Figure B.4  UV-vis absorption spectra of complex 2.12 in THF [3.32 x 10-4 M]  0.00.51.01.52.02.53.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 69   Figure B.5  UV-vis absorption spectra of complex 2.15 in Et2O [5.49 x 10-5 M]  0.00.51.01.52.02.53.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 70   Figure B.6  UV-vis absorption spectra of complex 3.2b in THF [2.38 x 10-4 M] 0.00.51.01.52.02.53.03.54.04.55.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 71   Figure B.7  UV-vis absorption spectra of complex 3.4a in Et2O [3.10 x 10-3 M] 0.00.51.01.52.02.53.03.54.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 72   Figure B.8  UV-vis absorption spectra of complex 3.4b in THF [2.68 x 10-4 M] 0.00.51.01.52.02.53.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 73   Figure B.9  UV-vis absorption spectra of complex 3.5 in THF [1.66 x 10-4 M] 0.00.51.01.52.02.53.03.5250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 74   Figure B.10  UV-vis absorption spectra of complex 3.6 in THF [1.68 x 10-4 M] 0.00.20.40.60.81.01.21.41.61.82.0250 300 350 400 450 500 550 600 650 700 750 800Absorbance Wavelength (nm) 

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