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Single-Electron-Transfer Reactions of Chromium Complexes With Organic Halides and Esters Welsh, Thomas May 29, 2014

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     Single-Electron-Transfer Reactions of Chromium Complexes With Organic Halides and Esters       Thomas A. Welsh        A Thesis Submitted in Partial Fulfillment of the Requirements for CHEMISTRY 449         University of British Columbia Okanagan April 2014 © Thomas A. Welsh, 2014 Chemistry 449 Thesis: Thomas A. Welsh  ii Abstract The control of carbon-based radicals to facilitate the formation of new carbon-carbon bonds is an important application of transition metal chemistry. First row transition metals, which are relatively cheap and abundant and often have two oxidation states that differ by a single electron, offer attractive candidates for controlling carbon-based radicals. Chromium in particular, with its two oxidation states Cr(II) and Cr(III), has great potential as a catalyst for controlling carbon-based radicals through single-electron-transfer mechanisms. The purpose of this project is to study the single-electron-transfer potential of several chromium-based complexes of the form Cr(LX)2 and Cr(LX)2(bpy•). The reactivity differences between Cr(LX)2 and neutral Cr(LX)2(bpy) complexes, where LX is a bidentate, monoanionic ligand, are explored by reacting these complexes with both CpCr((ArNCMe)2CH)(X) and RX substrates, where X is a halide or carboxylate. It was found that the Cr(II) Cr(LX)2 complexes were able to reduce CpCr[(ArNCMe)2CH](X) to CpCr[(ArNCMe)2CH] much more readily than the Cr(III) Cr(LX)2(bpy•) complexes, implying an inner-sphere electron transfer mechanism is favoured. For the reactions with RX substrates, it was found that when the substrate could chelate to the four-coordinate Cr(LX)2 complexes, the R–X bond was much more readily cleaved than when the substrate could not chelate to Cr(LX)2. When the chelating RX substrate was reacted with Cr(LX)2(bpy•) complexes, the results were very unusual warranting further investigation. The results with Cr(LX)2 complexes and chelating RX substrates show great promise for ultimately developing a chromium-based complex for controlling carbon-based radicals through inner-sphere mechanisms.    Chemistry 449 Thesis: Thomas A. Welsh  iii Table of Contents Abstract............................................................................................................................... ii Table of Contents............................................................................................................... iii List of Figures.................................................................................................................... iv List of Schemes.................................................................................................................. iv List of Abbreviations.......................................................................................................... v Acknowledgments............................................................................................................ vii Quotations........................................................................................................................ viii 1.	   Introduction .................................................................................................................. 1	  1.1.	   Carbon-Carbon Bond Formation .......................................................................... 1	  1.2.	   Single-Electron Processes with Chromium .......................................................... 2	  1.3.	   Scope and Objectives ............................................................................................ 7	  2.	   Results and Discussion .............................................................................................. 11	  2.1.	   Reactions of CpCr[(ArNCMe)2CH](X) with Cr(LX)2(bpy) ............................... 11	  2.2.	   Reactions or Cr(LX)2 and Cr(LX)2(bpy•) with RX Substrates ........................... 18	  3.	   Conclusion ................................................................................................................. 28	  4.	   Experimental .............................................................................................................. 30	  4.1.	   General Methods ................................................................................................. 30	  4.2.	   Syntheses of Cr Complexes and Substrates ........................................................ 30	  4.3.	   Reactions of CpCr[(ArNCMe)2CH](X) with Cr(LX)2(bpy) ............................... 37	  4.4.	   Reactions of Cr(LX)2 and Cr(LX)2(bpy•) with RX ............................................ 40	  5.	   References .................................................................................................................. 45	    Chemistry 449 Thesis: Thomas A. Welsh  iv List of Figures Figure 1: Transition state of inner-sphere chlorine atom abstraction ................................. 3	  Figure 2: Schematic energy diagram for single-electron oxidative addition ...................... 4	  Figure 3: Crystal structures of Cr(dpm)2(bpy•) and cationic [Cr(dpm)2(bpy)]+ ................. 6	  Figure 4: MO diagram for the diimine π system of bpy ..................................................... 7	  Figure 5: The square planar Cr(II) Cr(LX)2 complexes ...................................................... 9	  Figure 6: The octahedral Cr(III) Cr(LX)2(bpy•) complexes ............................................... 9	  Figure 7: UV-vis spectra for Cr(dpm)2(bpy•) and Cr(aram)2(bpy•) ................................. 10	  Figure 8: UV-vis spectrum of CpCr[(XylNCMe)2CH] .................................................... 10	  Figure 9: UV-vis spectra for reaction 2.1.1 ...................................................................... 14	  Figure 10: RX substrate for SE oxidative addition ........................................................... 21	  Figure 11: UV-vis spectrum and crystal structure of Cr(dpm)2(PyCO2) .......................... 24	  Figure 12: Inner-sphere SET mechanism for chelating RX by Cr(dpm)2 ........................ 24	  Figure 13: UV-vis spectra for Reaction 2.2.9 ................................................................... 25	  Figure 14: Crystal structure of Cr(quin)2(bpy•) ................................................................ 27	  Figure 15: UV-vis spectra for reaction 2.2.11 .................................................................. 28	   List of Schemes Scheme 1: Two CpCr[(ArNCMe)2CH] reacting with RX .................................................. 3	  Scheme 2: CpCr[ArNC(Me)CHC(Me)NArʹ′] with CyX ..................................................... 5	  Scheme 3: Cr(dpm)2(bpy•) with Ph3CBr ............................................................................ 6	  Scheme 4: Synthesis of Cr(dpm)2 ..................................................................................... 12	  Scheme 5: Synthesis of Cr(dpm)2(bpy•) ........................................................................... 12	  Scheme 6: Synthesis of [Cr(dpm)2(bpy)][PF6] ................................................................. 12	  Scheme 7: Proposed mechanism for the photoredox reaction .......................................... 13	  Scheme 8: Synthesis of Cr(dpm)2(PyCO2) by Method 1 .................................................. 23	  Scheme 9: Synthesis of Cr(dpm)2(PyCO2) by Method 2 .................................................. 23	    Chemistry 449 Thesis: Thomas A. Welsh  v List of Abbreviations The following is a list of abbreviations and symbols employed in this Thesis, most of which are in common use in the chemical literature. Ar aryl aram aryl amine, C9H12N bpy 2,2ʹ′-bipyridine, C10H8N2 °C degree Celsius  Cp cyclopentadienyl, η5-C5H5 Cy cyclohexyl, C6H11 D deuterium, 2H DCM dichloromethane, CH2Cl2 DMAP 4-dimethylaminopyridine, C7H10N2 dpm dipivaloylmethanido, C11H19O2 Dpp 2,6-diisopropylphenyl, C12H17 Et  ethyl, C2H5 Et2O diethyl ether, C4H10O EtOAc ethyl acetate, C4H8O2 g grams 1H proton h  hours  HOMO  highest occupied molecular orbital  iPr isopropyl, C3H7 L  neutral, 2e donor ligand; or litre, 10–3 m–3 LUMO lowest unoccupied molecular orbital  LX monoanionic, 3e donor bidentate ligand M  molar, mol L–1 Me  methyl, CH3 mg milligram, 10–3 g min minutes  mmol  millimole, 10–3 mole  MO molecular orbital Chemistry 449 Thesis: Thomas A. Welsh  vi mol  mole, 6.022·10–23 particles µL microlitre, 10–6 L  mL millilitre, 10–3 L  nBu n-butyl, C4H9 nm nanometers, 10–9 m NMR nuclear magnetic resonance  OAc acetate, C2H3O2 OTs toluene-4-sulfonate, C7H7O3S Ph phenyl, C6H5 Py pyridyl, C5H4N quin 8-hydroxyquinolinonato R  alkyl SE single electron SET single electron transfer tBu tert-butyl, C4H9 THF tetrahydrofuran, C4H8O Tol 4-methylphenyl, C7H7 X halide, carboxylate, or other anionic 1e donor ligand  Xyl 2,6-dimethylphenyl, C8H9  Chemistry 449 Thesis: Thomas A. Welsh  vii Acknowledgments   I would first like to thank my supervisor Dr. Kevin Smith for his inexhaustible patience and enthusiasm. I would also like to thank Dr. Steve McNeil for his continuing encouragement and for occasionally providing much needed distractions.   Thanks to Cory MacLeod, Wen Zhou, and Addison Desnoyer who, although no longer in the Smith group, contributed to this project in spirit by developing the majority of the complexes and preparation methods in previous years.  I would especially like to thank Luke Moisey for his patience while supervising me in the lab and providing many of his compounds for my reactions, and for reacting in good humour when I called him old.  Thanks to Yann André for his help and support.  A special thanks to my fellow Chemistry 449 students and lab mates, Cate Collins, Laura Fairburn, Kristina Malekow, and Sarah Parke, who made this year the most fun I ever had at UBCO.  Finally, I would like to thank my mom and dad for their never ending support.      Chemistry 449 Thesis: Thomas A. Welsh  viii Quotations        Omnium rerum principia parua sunt.  Adde paruum paruo magnus aceruus erit.  The beginnings of all things are small.  Add a little to a little and there will be a great heap.        – Latin Proverbs  Chemistry 449 Thesis: Thomas A. Welsh  1 1. Introduction 1.1. Carbon-Carbon Bond Formation  One of the fundamental purposes of synthetic chemistry is to form new carbon-carbon bonds to synthesize new compounds. Such reactions are the basis of the chemical industry. The wide scale production of synthetic compounds for energy, plastics, and pharmaceuticals, to name a few examples, is the foundation for the modern world. At the heart of all these processes is transition metal catalysis. Many catalysts based on “noble metals” such as rhodium, palladium, and platinum are available to facilitate the formation of carbon-carbon bonds in synthesis reactions. These metals react in well-defined two-electron processes, often involving oxidative addition and reductive elimination steps in their catalytic cycles.1 While these types of catalysts are very effective, the rarity of the noble metals makes these catalysts very expensive and ultimately inefficient economically and environmentally. As a result, there is great interest in developing catalysts based on cheaper, more abundant transition metals.   First row transition metals such as chromium, iron, and cobalt offer attractive alternatives to the noble metals. First row transition metals are much more abundant, which makes extracting them from the earth much cheaper and more environmentally friendly. While the noble metals react in two electron processes, the first row metals tend to react in single-electron (SE) processes because they have oxidation states that differ by a single electron: Cr2+ and Cr3+, Fe2+ and Fe3+, and Co2+ and Co3+.2 Therefore, first row metal catalysts will have different and complimentary reactivities to noble metal Chemistry 449 Thesis: Thomas A. Welsh  2 catalysts. For example, alkyl halides are difficult substrates for palladium catalysts due to their slow rates of oxidative addition and competing β-elimination processes.3 First row metal catalysts however are well suited to reacting with alkyl halides because first row metals can activate the alkyl halide bond by a single-electron-transfer (SET) to produce a halide and alkyl radical, which can then react with another metal complex to facilitate the formation of a new carbon-carbon bond. Many organisms make use of first row metals to catalyze reactions with metalloenzymes by SE oxidations and reductions.4 Despite their abundance in nature, SE processes are much less understood than the two electron processes of the noble metals in synthetic and industrial chemistry. Exploring the reactivities of first row transition metals and their SE processes is therefore a worthwhile and important field of research for developing a new cheaper catalyst for carbon-carbon bond formation. 1.2. Single-Electron Processes with Chromium  As a first row transition metal, chromium is a promising candidate for single-electron catalysis. With its two readily available oxidation states, Cr2+ and Cr3+, chromium complexes are well suited to SE reactions. The Smith group has extensively studied well-defined high spin chromium(II) complexes of the form CpCr[ArNC(Me)CHC(Me)NArʹ′].5 Such complexes were shown to react with alkyl halides to form a chromium halide complex and an alkyl radical intermediate. The overall process is SE oxidative addition, the first step being halogen atom abstraction through an inner-sphere electron transfer. The coordination of the alkyl halide to the metal centre through the halide atom results in a SET from the Cr centre to the organic substrate. The Chemistry 449 Thesis: Thomas A. Welsh  3 calculated transition state for this step is shown in Figure 1. This results in the cleaving of the R–X bond to produce a halide coordinated to the metal centre and a carbon-based radical, which can be trapped by a second equivalent of the chromium complex to form an alkyl-chromium bond, shown in Scheme 1.6    Scheme 1: The mechanism for two equivalents of CpCr[(ArNCMe)2CH] reacting with an alkyl halide.   Figure 1: Transition state of inner-sphere chlorine atom abstraction reaction of CpCr[(XylNCMe)2CH] with Cl–R (R = CH(Me)C(=O)OMe).  CrN N ArAr CrN N ArAr X RRX CrN N ArAr X + RCrN N ArArCrN N ArAr RChemistry 449 Thesis: Thomas A. Welsh  4  Figure 2: Schematic energy diagram for single-electron oxidative addition of R–X by CpCr[(ArNCMe)2CH] (modified from reference 7).   The schematic energy diagram for this mechanism, shown in Figure 2, shows how the reaction coordinate of the SE oxidative addition depends on the relative bond strengths of R–X, Cr–X, and Cr–R.8 From Figure 2, the difference between A and B is the energy barrier for homolytically cleaving the R–X bond, and therefore indicates the rate of SE oxidative addition. The difference between A and C depends on the stability of R• and the difference between the bond strengths of R–X and Cr–X. The overall reaction is exothermic due to the strength of the Cr–R bond, indicated by the large difference between C and E.   The CpCr[ArNC(Me)CHC(Me)NArʹ′] complexes were used as catalysts to react with cyclohexyl chloride and cyclohexyl bromide to form cyclohexyl radicals, which were trapped by tetraphenylbiphosphine, shown in Scheme 2.5 Manganese was used as a stoichiometric reductant to regenerate the chromium(II) complex. The results show how such a complex can be used to facilitate the formation of new carbon-phosphorus bonds, and these results can be extended to carbon-carbon bond formation.9 BA C D ECrArN NAr CrArN NArX CrArN NArR+ R-X2 CrArN NAr+  R CrArN NArX+Chemistry 449 Thesis: Thomas A. Welsh  5  Scheme 2: The reaction mechanism for CpCr[ArNC(Me)CHC(Me)NArʹ′] with cylcohexyl halides using Mn as a stoichiometric reductant and P2Ph4 to react with the radical.   In addition to the CpCr[ArNC(Me)CHC(Me)NArʹ′] complexes, the Smith group has also studied the octahedral Cr(III) complex Cr((OCtBu)2CH)2(bpy•), which is formed by the reaction of square planar Cr(II) Cr(dpm)2 with 2,2ʹ′-bipyridine.10 The crystal structure for this complex is shown in Figure 3. This reaction involves a metal to ligand charge transfer, whereby an electron from the Cr(II) centre is delocalized onto the LUMO π* diimine orbital of the bpy, shown in Figure 4. The electron transfer reduces the diimine and changes it from a L2 ligand to a LX• ligand. Recently, the Smith group has shown that Cr(dpm)2(bpy•) reacts with Ph3CBr in a SET reaction to form a cationic [Cr(dpm)2(bpy)]+, which has an identical structure to the neutral version, also shown in Figure 3, and a trityl radical, which was confirmed by UV-vis spectrscopy.10 As is shown in Figure 3, the oxidation of Cr(dpm)2(bpy•) does not result in any major structural change in the complex. This reaction, shown in Scheme 3, is believed to occur via an outer-sphere mechanism, whereby the electron transfer occurs through space since coordination to the octahedral Cr complex is not possible. This reaction represents a Cr CrCyX Cy1/2 MnX2 1/2 MnXCy Ph2PCy+  1/2 P2Ph4 [Cr] = CpCr[ArNC(Me)CHC(Me)NArʹ′]  X = Cl or Br Chemistry 449 Thesis: Thomas A. Welsh  6 complimentary SE process to the inner-sphere reactivity of the CpCr[(ArNCMe)2CH], which may result in useful differences in alkyl halide substrate scope for the two classes of chromium complexes.   Figure 3: The crystal structures of neutral Cr(dpm)2(bpy•) (left) and cationic [Cr(dpm)2(bpy)]+ (right) with tetraphenylborate counter anion removed for clarity.    Scheme 3: The reaction of Cr(dpm)2(bpy•) with Ph3CBr to form the cationic Cr complex and trityl radical.  CrNN O OO O Ph3CBr CrNN O OO O Br CPh3+Chemistry 449 Thesis: Thomas A. Welsh  7  Figure 4: MO diagram for the diimine π system of bpy.  1.3. Scope and Objectives  The purposes of this project are to explore in more detail the Cr(II) and Cr(III) complexes outlined above. First, the catalytic mechanism with CpCr[(ArNCMe)2CH] and RX is explored. Because this mechanism requires Mn as a stoichiometric reductant, it is hoped that Mn can be substituted by a photo-excited cationic [Cr(LX)2(bpy)][X] complex, where LX is a bidentate monoanionic ligand. In the synthesis of Cr(dpm)2(bpy•) from Cr(dpm)2, an electron from the Cr(II) centre of Cr(dpm)2 is transferred to the bpy ligand at room temperature. Thus, it may be possible to ____                         ____                         ________                         ____                         ________                         ____                         ________                         ____                         ____  L2                             LX                            X2N N N N N NEChemistry 449 Thesis: Thomas A. Welsh  8 photolytically activate a cationic [Cr(dpm)2(bpy)][X] to produce a ligand-based radical and a Cr(IV) centre. This is analogous to how [Ru(bpy)3][X]2 complexes have recently been used as photoredox catalysts for organic synthesis.11 The cationic Cr(IV) bpy• complex could theoretically be used as a reductant through the ligand-based radical and as an oxidant through the Cr(IV) centre. The ligand-based radical could relax back to the Cr centre or via an alternate pathway provided by CpCr[(ArNCMe)2CH](X), thereby reducing CpCr[(ArNCMe)2CH](X) back to CpCr[(ArNCMe)2CH]. The stability of neutral Cr(LX)2(bpy•) allows the feasibility of this process to be investigated. It is hoped that by reacting photo-excited [Cr(dpm)2(bpy)][X] with CpCr[(ArNCMe)2CH](X) and CpCr[ArNC(Me)CHC(Me)NArʹ′] complexes, a chromium-based replacement for manganese in the SE oxidative R–X bond activation catalytic cycle can be identified.   In addition to these reactions, the chromium complexes of the form Cr(LX)2 and Cr(LX)2(bpy•) are explored in more detail. As outlined above, octahedral Cr(III) Cr(LX)2(bpy•) is synthesized by reacting square planar Cr(II) Cr(LX)2 with 2,2ʹ′-bipyridine. This reaction causes a metal to ligand charge transfer from the Cr(II) centre to the π* orbital of bpy. It is theorized that either the square planar Cr(LX)2 or octahedral Cr(LX)2(bpy•) can be used to activate a R–X bond, where X is a halide or carboxylate, to produce an alkyl radical through a SET mechanism. For this project, the differences in reactivities between Cr(LX)2 and Cr(LX)2(bpy•) for R–X bond activation is explored. The square planar complexes would be expected to activate the R–X bond through an inner-sphere mechanism, since the Cr centre has open coordination sites available. For X = carboxylates in particular, where the carboxylate would likely be able to chelate the Cr centre, the R–X bond activation should be very favourable. In contrast, the octahedral Chemistry 449 Thesis: Thomas A. Welsh  9 complexes would activate the R–X bond through an outer-sphere mechanism, since there are no open coordination sites on the Cr centre. Given that Cr(dpm)2(bpy•) has already been shown to activate the comparatively weak Ph3C–Br bond, applying Cr(dpm)2(bpy•) or other Cr(LX)2(bpy•) complexes to more challenging R–X substrates is of particular interest.   Differences in reactivities due to the LX ligands are also explored. There are two main types of LX ligands studied in this project: (OCtBu)2CH (dipivaloylmethanido or dpm), where the ligand coordinates through the two O atoms, and C6H4-o-CH2NMe2 (aryl amine or aram), where the ligand coordinates through the N atom and the ortho C of the phenyl group. The N and C donor atoms of C6H4-o-CH2NMe2 would donate more electron density to the Cr centre than the two O donor atoms of (OCtBu)2CH, and therefore Cr(aram)2 and Cr(aram)2(bpy•) would be expected to be stronger reductants and activate  R–X bonds faster than Cr(dpm)2 and Cr(dpm)2(bpy•), respectively.   Figure 5: The square planar Cr(II) Cr(LX)2 complexes.  Figure 6: The octahedral Cr(III) Cr(LX)2(bpy•) complexes. CrOO OO Cr NNCrNN NNCrNN O OO O N ON OCrNNChemistry 449 Thesis: Thomas A. Welsh  10  All of these complexes, especially the octahedral ligand-based radical complexes, absorb very strongly in the visible range with characteristic spectra so the primary analytical tool for all these experiments is UV-visible spectroscopy. The UV-vis spectra for the three Cr(LX)2(bpy•) complexes are shown in Figure 7. The Cr(LX)2(bpy•) complexes all appear dark green in solution and when oxidized the solutions become a light colour so these reactions can easily be monitored by eye. For the reactions of Cr(LX)2 and Cr(LX)2(bpy•) with CpCr[(ArNCMe)2CH](X), the expected CpCr[(ArNCMe)2CH] product has a strong absorption at approximately 425 nm, shown in Figure 8, so the appearance of a sharp peak around 425 nm in the spectrum would indicate the progress of the reaction.   Figure 7: The UV-vis spectra for Cr(dpm)2(bpy•) and Cr(aram)2(bpy•), respectively.  Figure 8: The UV-vis spectrum of CpCr[(XylNCMe)2CH]. Chemistry 449 Thesis: Thomas A. Welsh  11 2. Results and Discussion 2.1. Reactions of CpCr[(ArNCMe)2CH](X) with Cr(LX)2(bpy)  The initial goal of this project was to replace manganese as a stoichiometric reductant in the CpCr[(ArNCMe)2CH] catalyzed R–X bond activation5 with photo-activated cationic [Cr(dpm)2(bpy)][X]. The Smith group has previously reported on the activation of a cyclohexyl halide by CpCr[ArNC(Me)CHC(Me)NArʹ′] and CpCr[(ArNCMe)2CH]. The Cr(II) complexes cleave the Cy–X bond in a SE oxidative addition reaction that results in a [Cr]–X complex and a cyclohexyl radical, which can either be trapped by a second equivalent of Cr(II) complex or by P2Ph4.5 Manganese was needed as a stoichiometric reductant to regenerate the Cr(II) complex from the CrX product, as shown in Scheme 2.   The first proposed candidate to replace Mn was the cationic [Cr(dpm)2(bpy)][X]. The Smith group had previously reported on neutral Cr(dpm)2(bpy•), synthesized by coordinating 2,2ʹ′-bipyridine to square planar Cr(II) Cr(dpm)2.10 This reaction involved a metal to ligand charge transfer to produce a bpy-based radical and a Cr(III) centre. The Cr(dpm)2 was synthesized from CrCl2 in a straightforward reaction shown in Scheme 4 that gave high quality crystals in low yields, between 20% and 30%12. The synthesis of Cr(dpm)2(bpy•), shown in Scheme 5, gave much better yields of high quality crystals between 70% and 80%. The Cr(dpm)2(bpy•) was oxidized with ferrocenium hexafluorophosphate13 to create the cationic Cr(III) [Cr(dpm)2(bpy)][PF6] complex shown in Scheme 6. Chemistry 449 Thesis: Thomas A. Welsh  12  Scheme 4: The synthesis of Cr(dpm)2.  Scheme 5: The synthesis of Cr(dpm)2(bpy•).  Scheme 6: The synthesis of [Cr(dpm)2(bpy)][PF6].   It was hypothesized that the cationic complex could be photo-excited to induce a metal to ligand charge transfer to produce a Cr(IV) centre and a bpy-based radical. Such a complex could potentially oxidize a tetraphenylborate counter anion to produce triphenylborane and a phenyl radical.14 The neutral Cr(III) complex with the bpy-based radical could then reduce CpCr[(ArNCMe)2CH](X) to CpCr[(ArNCMe)2CH], which would trap the phenyl radical. This mechanism is shown in Scheme 7.  CrOO OOCrCl2 O O+ 2                                  + 2  n-BuLi  THF27.6% CrNN O OO OCrOO OO + NN  THF76.3%CrNN O OO O [Cp2Fe][PF6]Et2O82.6% CrNN O OO O PF6Chemistry 449 Thesis: Thomas A. Welsh  13  Scheme 7: The proposed mechanism for the photoredox reaction: (1) photo-excitation from cationic Cr(III) L2 to cationic Cr(IV) LX•, (2) photo-excited cation oxidizes BPh4– to convert to neutral Cr(III) LX• producing BPh3 and •Ph, (3) outer-sphere SET from Cr(III) LX• to CpCr[(ArNCMe)2CH](OTs), and (4) CpCr[(ArNCMe)2CH] traps •Ph.   The reaction was set up in a glass bomb under an inert atmosphere. A catalytic amount of [Cr(dpm)2(bpy)][PF6] was combined with an excess of NaBPh4 and CpCr[TolNC(Me)CHC(Me)NDpp](OTs). The solution in the bomb was exposed to high intensity light from a 42-watt compact fluorescent bulb held approximately 10 cm away from the bomb.  CrN N ArArCrN N ArAr OTsCrNN O OO O hv CrNN O OO OCrNN O OO O BPh4–BPh3Ph CrN N ArAr PhCr(III)Cr(III) Cr(III)Cr(III) Cr(IV)Cr(II)1 23 4Chemistry 449 Thesis: Thomas A. Welsh  14  2.1.1 The solution was analyzed by UV-vis spectroscopy before being exposed to light and after being exposed to light for 24 h. The UV-vis results after 24 h of light exposure did not indicate any reaction occurred. The solution was then left to react in the light for two weeks. When the UV-vis spectrum was measured after two weeks, the results indicated that the complexes had likely decomposed. The UV-vis spectra for this experiment are shown in Figure 9. From these results, it is apparent that the reaction did not occur as expected and that the conditions were not adequate for the catalytic system.  Figure 9: The UV-vis spectra for reaction 2.1.1 before exposure to light (a), after 24 h of exposure to light (b), and after two weeks of exposure to light (c).  CrN N OTs hvTHF CrN N Ph0.1 [Cr(dpm)2(bpy)][PF6]5 NaBPh4a b c Chemistry 449 Thesis: Thomas A. Welsh  15  In a similar reaction, CpCr[(XylNCMe)2CH](I) was reacted with a catalytic amount of [Ru(bpy)3][PF6]2 and an excess of NaBPh4. The CpCr[(XylNCMe)2CH](I) was synthesized by reducing CpCr[(XylNCMe)2CH] with half an equivalent of I2.15 Because [Ru(bpy)3]2+ is known to readily undergo a metal to ligand charge transfer in visible light,11 it was hoped that this would enable it to oxidize tetraphenylborate and reduce CpCr[(XylNCMe)2CH](I) as a proof of concept. After exposing the reaction mixture to light for several days the UV-vis results indicated no change. Triethylamine was added in an attempt to provide an alternate reducing agent for the system, to no avail. As a result of these failed reactions, the goal of using photo-activated [Cr(dpm)2(bpy)][PF6] to reduce CpCr[(ArNCMe)2CH](X) was abandoned.  The overall goal of replacing Mn with Cr complexes was not completely abandoned however. It was decided to attempt to reduce CpCr[(ArNCMe)2CH](X) with the neutral Cr(II) Cr(LX)2 and Cr(III) Cr(LX)2(bpy•) complexes. These reactions corresponded to step 3 in Scheme 7. For these reactions, CpCr[(XylNCMe)2CH](I) was reacted with one equivalent each of Cr(dpm)2 and Cr(dpm)2(bpy•) to see if the stoichiometric reduction of CpCr[(XylNCMe)2CH](I) to CpCr[(XylNCMe)2CH] was possible. The products for these reactions are known compounds.16   2.1.2  2.1.3 CrN NCrN N xylxyl I CrOO OO+ + Cr OIOO OOFastCrNN O OO O CrN NCrN N xylxyl I + + CrNN O OO O ISlowChemistry 449 Thesis: Thomas A. Welsh  16  As outlined above, the reduction of CpCr[(XylNCMe)2CH](X) produces CpCr[(XylNCMe)2CH] which has a strong absorption at 425 nm (Figure 8). The appearance of this peak was used to determine the extent of the reactions. Reaction 2.1.2 occurred quickly as indicated by the sharp peak at 425 nm after 1 hour. Reaction 2.1.3 on the other hand occurred much more slowly. The peak at 425 nm did appear to some extent after reacting for an hour but the characteristic peaks for Cr(dpm)2(bpy•) did not disappear in the spectrum, indicating the reaction did not go to completion. An additional CpCr[(XylNCMe)2CH](X) complex was synthesized, CpCr[(XylNCMe)2CH](O2CPh), from CpCr[(XylNCMe)2CH] and AgO2CPh,17 and reacted with the same Cr complexes. It was hypothesized that the benzoate ligand would be able to chelate to the four-coordinate square planar complex, and therefore might react more readily than the iodide.    2.1.4  2.1.5 Aside from CpCr[(XylNCMe)2CH], the products for these two reactions are not known products. The same results for reaction 2.1.4 were obtained in that the CpCr[(XylNCMe)2CH] peak was observed after 1 h. Reaction 2.1.5 did not occur at all. These results reinforced the trend observed with reactions 2.1.2 and 2.1.3, that the four-coordinate complexes are better reductants than the six-coordinate complexes. The LX ligand was also changed to the aryl amine, which would increase the reducing potential FastCrN N xylxyl O O Ph CrOO OO+ Cr OOOO OO PhCrN N +CrN N xylxyl O O Ph CrNN O OO O+ +CrN N CrNN O OO O O2CPhChemistry 449 Thesis: Thomas A. Welsh  17 of Cr(LX)2 and Cr(LX)2(bpy•). The Cr(aram)2 complex was synthesized in a similar way to Cr(dpm)2, by reacting CrCl2 with two equivalents of LiC6H4-o-CH2NMe2.18 This reaction resulted in powder quality product in yields up to 80%. The Cr(aram)2(bpy•) was synthesized the same way by reacting Cr(aram)2 with 2,2ʹ′-bipyridine. Low yields of powder for Cr(aram)2(bpy•) could only be obtained by this method, so Cr(aram)2(bpy•) was produced in situ for all of its reactions.16 The two aryl amine complexes were both reacted with CpCr[(XylNCMe)2CH](O2CPh).   2.1.6  2.1.7  Once again, the same results were observed in that the square planar complex reacted quickly while the octahedral complex did not. Reaction 2.1.6 was complete after 5 min. From the results of these reactions an obvious trend is apparent. The four-coordinate square planar complexes react readily while the six-coordinate octahedral complexes react much more slowly or not at all. This seems to apply an inner-sphere mechanism for the SET is favoured, whereby Cr(LX)2 must coordinate to the X ligand of CpCr[(XylNCMe)2CH](X) in order to facilitate the SET. Also apparent is the expected improvement in reduction by Cr(aram)2 over Cr(dpm)2 for the reactions with Cr(dpm)2 were complete after 1 h while the reaction with Cr(aram)2 was complete after 5 min. There does not appear to be any improvement observed for replacing the iodide ligand with benzoate as both reactions with Cr(dpm)2 occurred at similar rates. Nonetheless, Very fastCrN N xylxyl O O Ph Cr NN+ CrNN OO PhCrN N ++CrN NCrN N xylxyl O O Ph CrNN NN+ CrNN NN O2CPhChemistry 449 Thesis: Thomas A. Welsh  18 these results confirm that CpCr[(XylNCMe)2CH][X] can be reduced by a Cr complex, preferably a four-coordinate Cr(II) complex that provides an inner-sphere SET mechanism, and this shows promise for ultimately providing a replacement for manganese in the R–X bond activation catalytic cycle. 2.2. Reactions or Cr(LX)2 and Cr(LX)2(bpy•) with RX Substrates  The other goal of this project was to use the Cr(LX)2 and Cr(LX)2(bpy•) complexes to react with various RX substrates, where X is a halide or carboxylate, to activate the R–X bond in a SE process. As mentioned above, the square planar Cr(LX)2 complexes with open coordination sites would be expected to activate the R–X bond through an inner-sphere mechanism while the octahedral Cr(LX)2(bpy•) complexes would be expected to activate the R–X bond through an outer-sphere mechanism. The activation of the Ph3C–Br bond by Cr(dpm)2(bpy•) has already been shown to occur by the Smith group,10 so reactions with Cr(dpm)2(bpy•) and other Cr(LX)2(bpy•) complexes with other RX substrates were of particular interest.  From the reactions with CpCr[(XylNCMe)2CH](X), it was found that for LX = aram the reduction occurred faster than for LX = dpm. Thus, the first set of reactions attempted involved reacting Cr(aram)2 and Cr(aram)2(bpy•) with different types of RX substrates. Cr(aram)2 and Cr(aram)2(bpy•) were synthesized as above. Because four-coordinate Cr(aram)2 has open coordination sites, it was reacted with two potentially chelating substrates: allyl acetate and benzyl acetate. Both of these reactions were performed at known concentrations to obtain not only qualitative but also quantitative results by UV-vis spectroscopy.  Chemistry 449 Thesis: Thomas A. Welsh  19  2.2.1  2.2.2 The mixtures did not react instantly and were left to react overnight. After reacting overnight a change in the solutions was apparent by the UV-vis spectra. Because the Cr(aram)2(OAc) products are not known, it was not clear if reactions 2.2.1 and 2.2.2 had occurred as expected.   Reactions with Cr(aram)2(bpy•) with various RX substrates were then attempted. Once again, Cr(aram)2(bpy•) was synthesized in situ. Cr(aram)2(bpy•) was reacted with allyl acetate, allyl bromide, and (diacetoxyiodo)benzene. Allyl acetate was chosen to compare the Cr(aram)2(bpy•) reactivity with Cr(aram)2 from reaction 2.2.1. Allyl bromide was chosen because other allyl halides have been shown to oxidize various chromium bpy compounds with aryl to produce the Cr(III) halide complex.19 Researchers reacted a Cr(Ph)2(bpy)2 neutral complex with allyl iodide and made [Cr(Ph)2(bpy)2][I] and 1,5-hexadiene. (Diacetoxyiodo)benzene was chosen as a powerful oxidizing agent in order to fully synthesize the expected product.  2.2.3  2.2.4 SlowCr NN O O+ CrNN OO +SlowCr NN O O+ CrNN OO +O OCrNN NN + CrNN NN +OAcFastBrCrNN NN + CrNN NN +BrChemistry 449 Thesis: Thomas A. Welsh  20  2.2.5  Reaction 2.2.3 did not occur at all. Reaction 2.2.4 started to react immediately and continued to react over the next hour, as indicated by the gradual colour change of the solution from dark green to dark red. After reacting overnight this reaction was complete for the colour had changed to a light pink. And reaction 2.2.5 using the strongest oxidizing agent occurred instantly as indicated by the instantaneous change from a dark green solution to a cloudy peach-coloured mixture, which was the same as the product mixture for reaction 2.2.4. For the reactions of Cr(aram)2 and Cr(aram)2(bpy•) with RX substrates, there was once again an observed preference for substrates to react with the four-coordinate Cr(aram)2 complex over six-coordinate Cr(aram)2(bpy•). The inability for Cr(aram)2(bpy•) to react with allyl acetate was disappointing, though the reaction with allyl bromide did show some promise.  The sum of the results for this project so far seemed to indicate that four-coordinate complexes that can provide an inner-sphere mechanism for SET had promise for being able to activate R–X bonds. It was hypothesized that chelating RX substrates would be favoured, as chelation would promote the inner-sphere SET. However, the results of comparing reaction 2.1.2 with reaction 2.1.4 did not show any improvement when the iodide was replaced with a supposedly chelating benzoate for Cr(dpm)2. Reactions 2.2.1 and 2.2.2 also did not show much promise with chelating acetate or benzoate for Cr(aram)2. It was then decided to attempt to improve the reaction by changing the substrate, as shown in Figure 10. From Figure 2, the energy barrier to the SE oxidative addition is high because of the strong R–X bond and weak Cr–X bond that I OAcOAcCrNN NN + ICrNN NN +0.5 0.5OAcInstantChemistry 449 Thesis: Thomas A. Welsh  21 form in the initial step. By changing the substrate in Figure 10 to improve the Cr–X bond and weaken the R–X, the energy barrier would be reduced. The Cr–X bond strength is improved by increasing the favourability of the chelation while the R–X bond is weakened by improving the stability of R•. Chelation assistance was recently shown to be an effective method for improving substrate activation by metal catalysts.20 From Figure 10, for Y = CH the substrate would chelate to the Cr centre through the two O atoms, which would place the R group in a sterically unfavourable position. But for Y = N the substrate could chelate through the N and O atoms, which would place the bulky R group away from the metal complex and provide a strong method of chelation prior to cleaving the R–X bond.   Figure 10: RX substrate for SE oxidative addition, where Y is changed to promote chelation and A is changed to improve stability of R•.   Diphenylmethylpicolinate was synthesized as the first substrate to attempt this reaction.20 This substrate was reacted with the four-coordinate Cr(dpm)2 and the reaction progress was monitored by UV-vis spectroscopy.  2.2.6 YO OPh APh Y = CH, NA = H, PhCrOO OO + NO OPh Ph +Cr N OOOO OOFastChemistry 449 Thesis: Thomas A. Welsh  22 This reaction occurred quickly, which was a very promising result. The UV-vis spectrum of the solution gave a single peak at 553 nm. The reaction was also attempted with Cr(aram)2 and again there was an instant reaction observed. The reactions with Y = CH and changing A from H to Ph were then attempted to determine whether the chelation or the stability of R• was the primary factor affecting the reaction rate. Both diphenylmethylbenzoate20 and triphenylmethylbenzoate21 were synthesized and reacted with Cr(dpm)2.   2.2.7  2.2.8 Neither of these reactions proceeded, which provided strong evidence for the picolinate N atom being the primary factor affecting the SET. To confirm that the reaction had proceeded as expected, the suspected product, Cr(dpm)2(PyCO2), was synthesized independently following two different methods. Method 1 (Scheme 8) involved the oxidation of Cr(dpm)2 by 0.5 equivalents of I2 followed by the addition of potassium picolinate. Method 2 (Scheme 9) involved reacting Cr(NO3)3•9H2O with two equivalents of (OCtBu)2CH2 and one equivalent of picolinic acid in the presence of base.22  CrOO OO + O OPh Ph Cr OOOO OO Ph + CPh2CrOO OO + O OPh PhPh Cr OOOO OO Ph + CPh3Chemistry 449 Thesis: Thomas A. Welsh  23  Scheme 8: The synthesis of Cr(dpm)2(PyCO2) by Method 1.  Scheme 9: The synthesis of Cr(dpm)2(PyCO2) by Method 2.   The UV-vis spectra of the products of both of these reactions were measured and both spectra matched the spectrum from reaction 2.2.6. The UV-vis spectrum is shown in Figure 11. It is interesting to note that this spectrum is identical to the spectra for [Cr(dpm)2(bpy)][X] with X = BPh4, PF6, and OTs. Method 1 also provided crystals of X-ray crystallography quality. The crystal structure, also shown in Figure 11, confirms that the expected product had been synthesized. Given that the product’s UV-vis spectrum was identical to the spectrum from reaction 2.2.6, it was confirmed that the R–X bond activation for diphenylmethylpicolinate by Cr(dpm)2 had proceeded as expected. The inner-sphere SET mechanism was then deduced, shown in Figure 12.  CrOO OO THF26.5%i) 0.5 I2 ii) KO2Cpy Cr N OOOO OOCr(NO3)3•9H2O i) 2 (OCtBu)CH2ii) 2 NaOMeMeOH CrOO OO OH2OH2 i) C6H4NCO2Hii) NEt32:1:1 MeOH:iPrOH:H2O16.1% Cr N OOOO OOChemistry 449 Thesis: Thomas A. Welsh  24  Figure 11: The UV-vis spectrum and crystal structure of Cr(dpm)2(PyCO2).   Figure 12: The inner-sphere SET mechanism for chelating RX by Cr(dpm)2.   The mechanism involves the chelation of the picolinate substrate to the Cr centre first, followed by a SET onto the O coordinating atom which results in the homolytic cleavage of the C–O bond, producing the carbon-based radical. This reaction represents a clear case of a chromium-based reagent being able to produce carbon-based radicals from a normally unreactive ester substrate, and therefore offers interesting potential for being part of a catalytic mechanism to form new carbon-carbon bonds.  The diphenylmethylpicolinate substrate was also reacted with the octahedral Cr(LX)2(bpy•) complexes, starting with Cr(dpm)2(bpy•). CrOO OO NO OR+ CrOO OO NO O R Cr N OOOO OO   R+Chemistry 449 Thesis: Thomas A. Welsh  25  2.2.9 This reaction proceeded very slowly over the course of two weeks. There was a stark colour change observed during that time from the dark green Cr(dpm)2(bpy•) to a dark red mixture. Given the expected product, the UV-vis was expected to be similar to that shown in Figure 11, which as mentioned is the same UV-vis spectrum observed for several [Cr(dpm)2(bpy)][X] complexes. However, as shown in Figure 13, the final spectrum for reaction 2.2.9 looked very different.  Figure 13: The initial (a) and final (b) UV-vis spectra for Reaction 2.2.9.   Clearly, reaction 2.2.9 had not proceeded as expected. This result was difficult to rationalize. It was initially considered that the diphenylmethyl radical that formed might have been reacting with the methine group of a dpm ligand.23 However, given the bulky SlowNO OPh Ph+CrNN O OO O CrNN O OO O O O Na b Chemistry 449 Thesis: Thomas A. Welsh  26 tert-butyl groups associated with those ligands, this seemed unlikely due to steric reasons. It was then considered that if the reaction proceeded as expected to produce the diphenylmethyl radical, even if to a small extent, then this radical may react with the unpaired electron delocalized on the bpy ligand of unreacted Cr(dpm)2(bpy•). Although the radical is primarily contained in the π* orbital of the diimine of bpy, there is some delocalization around the entire aromatic system so it is possible for a radical species to react with bpy•.24 This would likely produce a large aromatic system, which would undoubtedly affect the UV-vis absorption. This is far from conclusive however and further experimentation is needed. No reaction was observed when Cr(dpm)2(bpy•) was also treated with triphenylmethylbenzoate.   Next, diphenylmethylpicolinate was reacted with Cr(aram)2(bpy•).  2.2.10 This reaction did not occur at all, even after reacting for a week. Since Cr(aram)2(bpy•) should be a stronger reductant than Cr(dpm)2(bpy•), this suggests that the observed reaction between Cr(dpm)2(bpy•) and diphenylmethylpicolinate may be the result of an inner-sphere process, preceded by dechelation of one dpm ligand. But to fully understand these results, further experimentation is needed.   A final reaction was attempted with a new Cr(LX)2(bpy•) complex, Cr(quin)2(bpy•), where quin = 8-hydroxyquinolinonato. This complex was recently prepared by Luke Moisey by the protonolysis reaction of Cr[N(SiMe3)2]2(bpy) with two equivalents of 8-hydroxyquinoline. The crystal structure is shown in Figure 14. NO OPh Ph+ OO NCrNN NN CrNN NNChemistry 449 Thesis: Thomas A. Welsh  27   Figure 14: The crystal structure of Cr(quin)2(bpy•).  For this reaction, the complex was produced following the same method and then reacted in situ with diphenylmethylpicolinate and diphenylmethylbenzoate.   2.2.11  2.2.12 Similar results were obtained as with Cr(dpm)2(bpy•), wherein reaction 2.2.11 seemed to proceed and reaction 2.2.12 did not occur at all. The UV-spectra for reaction 2.2.11 is shown in Figure 15. NO OPh Ph+N ON OCrNN N ON OCrNN OO NO OPh Ph+N ON OCrNN N ON OCrNN OOChemistry 449 Thesis: Thomas A. Welsh  28  Figure 15: The initial (a) and final (b) UV-vis spectra for reaction 2.2.11.  As shown in Figure 15, the final spectrum looks quite different from the starting spectrum and it is not clear exactly what the products might be. Thus, further experimentation is needed. Attempts to synthesize four-coordinate Cr(II) Cr(quin)2 in order to compare the reaction of Cr(quin)2 and RX with Cr(quin)2(bpy•) and RX were not successful due to the tendency of Cr(II) to form six coordinate Cr(III) Cr(quin)3.25,26 Nonetheless, the results with Cr(quin)2(bpy•) are interesting enough to warrant further investigation. Indeed, all of the unusual results with the Cr(LX)2(bpy•) and RX reactions deserve further investigation, if not for anything more than to satisfy scientific curiosity. 3. Conclusion  The overall purpose of this project was to explore the SET properties of several well-defined chromium complexes. The initial goal was to develop a chromium-based replacement for manganese as a stoichiometric reductant for CpCr[(ArNCMe)2CH](X) complexes. Several candidates were tested, including both cationic [Cr(dpm)2(bpy)][PF6] and neutral four-coordinate Cr(LX)2 complexes and six-coordinate Cr(LX)2(bpy•) a b Chemistry 449 Thesis: Thomas A. Welsh  29 complexes. The complexes were reacted with iodide and benzoate versions of CpCr[(ArNCMe)2CH](X) and the reactions were monitored by UV-vis spectroscopy. The cationic complex was photo-excited in order to promote the formation of the bpy-based radical to make the complex a possible reductant, but this was ultimately unsuccessful. For the neutral complexes, it was found that the four-coordinate complexes reacted much more readily than the six-coordinate complexes, and this indicated that an inner-sphere SET mechanism was likely being favoured.  The neutral complexes Cr(LX)2 and Cr(LX)2(bpy•) were also reacted with various RX substrates in an attempt to activate the R–X bond via a SE process. It was found that the R–X bond activation worked best for substrates that could chelate to a four-coordinate Cr centre prior to R–X bond cleavage. In particular, diphenylmethylpicolinate was found to readily react with both Cr(dpm)2 and Cr(aram)2. When this substrate was reacted with the Cr(LX)2(bpy•) complexes, very unusual results were obtained. The reactions with Cr(dpm)2(bpy•) and Cr(quin)2(bpy•) proceeded in ways not identifiable by the UV-vis spectra and the reaction with Cr(aram)2(bpy•) did not proceed at all. These results warrant further investigation.  The sum of the results from this project shows great promise for using chromium complexes to control the formation of carbon-based radicals. Now that several chromium complexes have been shown to activate a R–X bond in an inner-sphere SET mechanism, the next stage for this line of research is to develop a system that can bind with the carbon based radical in order to facilitate the formation of carbon-carbon bonds in cross coupling mechanisms and, ultimately, provide a cheaper alternative for noble metal catalysts.  Chemistry 449 Thesis: Thomas A. Welsh  30 4. Experimental 4.1. General Methods  All reactions, unless otherwise specified, were performed under anhydrous, oxygen-free conditions at room temperature using an inert-atmosphere glove box complete with active oxygen and moisture removing catalyst columns. The solvents THF, toluene, Et2O, and hexanes were made anhydrous using Grubbs/Dow columns. Unless, otherwise specified, reagents were purchased from Sigma Aldrich and used as received, including anhydrous “sure-seal” grade reagents.   UV-vis spectra were obtained using a Shimadzu UV-2550 UV-vis spectrophotometer with airtight UV-vis cells. NMR data was collected on a Varian 400 MHz Mercury Plus Spectrometer.  CpCr[(XylNCMe)2CH],27 Cr[N(SiMe3]2)2(bpy),28 and Cr[N(SiMe3)2]2(THF)229 were prepared and provided by Luke Moisey. CpCr[TolNC(Me)CHC(Me)NDpp](OTs) was prepared and provided by Wen Zhou.5 LiC6H4-o-CH2NMe2 was prepared and provided by Cory MacLeod.30 [Ru(bpy)3][PF6]2 was provided by Dr. James Bailey. 4.2. Syntheses of Cr Complexes and Substrates  TW57  CrCl2 + 2 (OCtBu)2CH2 + 2 nBuLi  Cr(dpm)2 was prepared following the synthesis developed in the literature.12 A solution of n-butyllithium (9.8 mL, 1.6 M in hexanes, 16 mmol) was added to a chilled stirring solution of 2,2,6,6-tetramethyl-3,5-heptandione in 6 pipettes of THF. The addition of nBuLi caused the mixture to increase in temperature and a white precipitate to Chemistry 449 Thesis: Thomas A. Welsh  31 form. The mixture was left to react for two hours, and then it was added to a stirred solution of CrCl2 (0.8074 g, 6.570 mmol) in THF (30 pipettes), which turned from green to red-brown after 5 min. The mixture was left to stir overnight, and then the solvent was removed in vacuo leaving a dark brown residue, which was extracted with hexanes and filtered through celite. The solution was concentrated and then left standing at -35 ºC to encourage recrystallization. Dark brown crystals were isolated in two fractions (0.7581 g, 27.6% yield).  TW59  Cr(dpm)2 + bpy  Cr(dpm)2(bpy•) was prepared according to the literature.10 Cr(dpm)2 (100.9 mg, 0.2412 mmol) was dissolved 6 pipettes of Et2O making a brown solution. To this solution was added 2,2ʹ′-bipyridine (38.4 mg, 0.2459 mmol), which resulted in an instantaneous colour change to dark blue green. The solution was left to react for 2 h and then the solvent was removed in vacuo leaving a dark green residue. This residue was extracted with hexanes and filtered through celite. Dark blue green crystals of Cr(dpm)2(bpy•) were isolated upon recrystallization at -35 ºC in two fractions (0.1057 g, 76.3% yield).  TW80  CrCl2 + LiC6H4-o-CH2NMe2  Cr(aram)2 was prepared according to the literature.18 CrCl2 (0.2006 g, 1.632 mmol) and LiC6H4-o-CH2NMe2 (0.4612 g, 3.268 mmol) were each dissolved in 10 pipettes of THF in separate 5-dram vials. Each solution was placed in the freezer for 45 min. The CrCl2 solution was transferred to a Schlenk flask, rinsing the vial with 3 pipettes of THF, and then the LiC6H4-o-CH2NMe2 solution was added dropwise over 15 Chemistry 449 Thesis: Thomas A. Welsh  32 min causing the mixture to turn brown red. The mixture was reacted for two days and the solvent was removed in vacuo leaving a brown purple residue. The residue was extracted with toluene and filtered through celite into a clean flask. After filtering the solvent was removed in vacuo leaving a brown orange residue, which was extracted with toluene and filtered through celite. Hexanes were added to the filtrate, which was stored at -35 ºC to promote recrystallization. Orange powder of Cr(aram)2 was isolated in two fractions (0.5871 g, 72% yield).  TW41  Cp2Fe + FeCl3•6H2O + NH4PF6  This reaction was performed in air following the procedure outlined in the literature.13 Ferrocene (1.00037 g, 5.38 mmol) and iron(III) chloride hexahydrate (1.95387 g, 7.23 mmol) were dissolved in 20 mL of deionized water and 8 mL of acetone making a dark brown solution. After stirring for 15 minutes the solution had turned dark blue. The dark blue solution was filtered through celite and then NH4PF6 (1.16081 g, 7.12 mmol) was added to the filtrate followed by 10 mL of EtOH. The mixture was vacuum filtered to obtain a blue powder. The powder was dissolved in a 1:2 acetone:EtOH solution and [Cp2Fe][PF6] was obtained by recrystallization (0.51822 g, 27% yield). The filtrate volume was reduced and then placed in the fridge to obtain a second crop of crystals, which were not recrystallized in acetone/EtOH (0.26486 g, 44% yield in total).   TW45  Cr(dpm)2 + bpy + [Cp2Fe][PF6]  To a solution of Cr(dpm)2 (0.2022 g, 0.4833 mmol) was added bpy (0.0764 g, 0.4892 mmol), which caused the solution to instantly turn dark green, and the mixture Chemistry 449 Thesis: Thomas A. Welsh  33 was stirred for 1 h. Then [Cp2Fe][PF6] (0.15849 g, 0.4788 mmol) was added and the mixture was stirred for 1 h, during which time the mixture turned reddish brown. After 1 h the mixture was vacuum filtered to obtain [Cr(dpm)2(bpy•)][PF6] as a pink powder, which was washed with Et2O (0.2872 g, 82.6% yield).  TW67  CpCr[(XylNCMe)2CH] + ½ I2  This procedure followed the literature.15 CpCr[(XylNCMe)2CH] (100.8 mg, 0.2386 mmol) was dissolved in 5 pipettes of Et2O to form a dark greenish brown solution. To this solution was added a solution I2 (30.3 mg, 0.119 mmol) in 3 pipettes of Et2O. After reacting overnight the solution was dark green. The solvent was removed in vacuo leaving a dark green residue, which was extracted with Et2O and filtered through celite. Dark green crystals of CpCr[(XylNCMe)2CH](I) were obtained in three fractions by recrystallization after standing at -35 ºC and concentrating the solution (37.3 mg, 33.0% yield).  TW76  CpCr[(XylNCMe)2CH] + AgO2CPh  CpCr[(XylNCMe)2CH](O2CPh) was prepared according to the literature.17 CpCr[(XylNCMe)2CH] (49.8 mg, 0.118 mmol) was dissolved in 5 pipettes of Et2O making a brown solution. Silver benzoate (28.03 mg, 0.1224 mmol) was added in 3 pipettes of Et2O causing the solution to become darker brown. After reacting for three days the mixture appeared dark green with black precipitate. The mixture was filtered through celite and the solvent was removed in vacuo leaving a dark green residue. The residue was extracted with Et2O and filtered through celite. Dark blue green crystals of Chemistry 449 Thesis: Thomas A. Welsh  34 CpCr[(XylNCMe)2CH](O2CPh) were obtained upon recrystallization in two fractions (39.7 mg, 62% yield).  TW91  PyCO2H + Ph2CHOH + CyNCNCy + ½ DMAP  Ph2CH-O2CPy was synthesized in air at room temperature following the literature procedure.20 Diphenylmethanol (1.00054 g, 5.43 mmol) was dissolved in 15 mL of DCM. Picolinic acid (0.66820 g, 5.43 mmol), dicyclohexylcarbodiimide (1.12546 g, 5.45 mmol), and DMAP (0.33100 g, 2.71 mmol) were added to the solution in sequence. After mixing overnight the solution became cloudy white. Ph2CH-O2CPy was isolated after purifying by column chromatography, eluting with 2:3 EtOAc:hexanes (1.01932 g, 64.9% yield).  TW93  PyCO2H + KOtBu  This reaction was performed in air. Picolinic acid (0.21687 g, 1.762 mmol) and potassium tert-butoxide (0.17991 g, 1.603 mmol) were mixed in Et2O, despite neither solid being soluble in Et2O. After reacting overnight the white powder was isolated by vacuum filtration and analyzed by 1H-NMR in D2O, which confirmed KO2CPy had formed (0.23028g, 89.1% yield).  TW95  Cr(dpm)2 + ½ I2 + KO2CPy  Iodine (29.0 mg, 0.119 mmol) was added to a solution of Cr(dpm)2 (99.7 mg, 0.238 mmol) in THF. After stirring for 30 min potassium picolinate (39.19 mg, 0.2431 mmol) was added as a suspension in THF. After reacting overnight the solution was Chemistry 449 Thesis: Thomas A. Welsh  35 brown with white precipitate. After reacting for two weeks the mixture was transferred to a bomb and brought out of the box. The bomb was attached to the Schlenk line and heated with a heat gun to boiling which did not result in a colour change. The mixture was left stirring in a hot water bath for two days. The bomb was brought back into the box and the mixture was filtered through celite into a clean Schlenk flask. The solvent was removed in vacuo leaving brownish purple residue which turned white when left under vacuum for 1 h. The residue was extracted with hexanes making a purple solution and filtered through celite into a vial. The residue was not fully soluble in hexanes so Et2O was used for further filtration. The purple filtrate was stored at -35 ºC to promote recrystallization. The first fraction of Cr(dpm)2(PyCO2) was isolated as a magenta powder (28.3 mg, 22.0% yield). After a week in the freezer a second fraction was isolated of purple crystals suitable for X-ray crystallography (5.8 mg, 26.5% yield in total).  TW96/TW97 Cr(NO3)3•9H2O + 2 (OCtBu)2CH2 + 2 NaOMe + PyCO2H + NEt3  This reaction was performed in air following the procedure outlined by the literature.22 To a blue solution of Cr(NO3)3•9H2O (0.78587 g, 1.9707 mmol) in MeOH (100 mL) was added 2,2,6,6-tetramethyl-3,5-heptandione (0.82 mL, 3.93 mmol). After stirring for 15 min NaOMe (0.21591 g, 3.9961 mmol) was added causing the solution to become greenish. The blue green solution was left to react for three days and then the solvent was removed in vacuo leaving dark green residue. The residue was extracted with 50 mL of a 2:1:1 MeOH:iPrOH:H2O solution making a blue green solution. Picolinic acid (0.24302 g, 1.9740 mmol) was dissolved in 10 mL of iPrOH and 10 mL of H2O. This solution was added to the blue green solution, followed by NEt3 (0.212 g, 2.10 mmol). Chemistry 449 Thesis: Thomas A. Welsh  36 After reacting for two days the solution turned purple. The volume was reduced in vacuo and then extracted several times with DCM. The combined DCM extracts were light purple and the aqueous layer was dark purple. The combined organic extracts were dried with MgSO4 and then the solvent was removed in vacuo leaving a purple powder of Cr(dpm)2(PyCO2) (0.17075 g, 16.1% yield). The UV-vis spectrum was measured: (THF; λmax, nm (ε, M–1 cm–1)) 558 (78.78).  TW99  PhCO2H + Ph2CHOH + CyNCNCy + ½ DMAP  This reaction was performed in air at room temperature following the literature procedure.20 Diphenylmethanol (1.00177g, 5.44 mmol) was dissolved in 15 mL of DCM. Benzoic acid (0.66331 g, 5.43 mmol), dicyclohexylcarbodiimide (1.12335 g, 5.44 mmol), and DMAP (0.33207 g, 2.72 mmol) were added to the solution in sequence. The addition of DMAP resulted in the formation of a white cloudy mixture. After reacting for three days Ph2CH-O2CPh was purified by column chromatography, eluting with 1:9 EtOAc: hexanes (0.60129 g, 38.4% yield).  TW104 Ph3CCl + NaO2CPh  This reaction was performed in air following the literature procedure.21 Triphenylmethylchloride (0.9999 g, 3.587 mmol) and sodium benzoate (0.5191 g, 0.3602 mmol) were dissolved in 20 mL of acetone making a cloudy mixture. The solution was refluxed overnight and then gravity filtered to isolate a clear colourless solution. The solvent was removed in vacuo to obtain a white solid, which was confirmed by NMR to be Ph3C-O2CPh (1.0859 g, 85.9% yield). Chemistry 449 Thesis: Thomas A. Welsh  37 TW108 CrCl3•6H2O + 3 quin  Cr(quin)3 was synthesized according to the literature.31 A 150 mL solution of 8-hydroxyquinoline (0.9993 g, 6.884 mmol) in EtOH was prepared by heating to aid in dissolving. To this solution was added a green solution of CrCl3•6H2O (0.6102 g, 2.290 mmol) in 10 mL of H2O. The green mixture was refluxed for 2 h and then the volume was reduced in vacuo. More water was added to encourage precipitation but no product was obtained. The mixture was then extracted several times with DCM. The combined organic extracts, which were a yellow colour, were dried with MgSO4 and the solvent was removed in vacuo, leaving an amber residue. The UV-vis spectrum of this residue was measured: (THF; λmax, nm) 422. The spectrum was identical to that of Cr(quin)3.31 4.3. Reactions of CpCr[(ArNCMe)2CH](X) with Cr(LX)2(bpy)  TW66  CpCr[TolNC(Me)CHC(Me)NDpp](OTs) + 0.1 [Cr(dpm)2(bpy)][PF6] + 5    NaBPh4  To a solution of CpCr[TolNC(Me)CHC(Me)NDpp](OTs) (10.62 mg, 0.0167 mmol) in THF was added [Cr(dpm)2(bpy)][PF6] (1.7 mg, 0.0024 mmol) and NaBPh4 (27.70 mg, 0.8094 mmol). The UV-vis spectrum was measured: (THF; λmax, nm) 416, 560. This solution was then exposed to high intensity visible light. After a day the spectrum had not changed. After two weeks the spectrum did not show any peaks between 400 nm and 800 nm.    Chemistry 449 Thesis: Thomas A. Welsh  38 TW68  CpCr[(XylNCMe)2CH](I) + 0.1 [Ru(bpy)3][PF6]2 + 5 NaBPh4  To a solution of CpCr[(XylNCMe)2CH](I) (20.5 mg, 0.0373 mmol) in THF (12 pipettes) was added NaBPh4 (64.44 mg, 0.1883 mmol) and [Ru(bpy)3][PF6]2 (4.98 mg, 0.00579 mmol). The [Ru(bpy)3][PF6]2 was only partially soluble in THF. The UV-vis spectrum was measured: (THF; λmax, nm) 579, 431. Then the mixture was placed in high intensity light overnight. After reacting for 24 h the UV-vis spectrum was measured again, which indicated little change. After reacting for another 24 h acetonitrile (1 mL) was added in an attempt to fully dissolve the [Ru(bpy)3][PF6]2. After two weeks of reacting in the high intensity light no change was observed in the UV-vis spectrum. Triethylamine (26 µL, 0.19 mmol) was added to the solution. When no change was observed after another week of reacting in the light, the experiment was ended.  TW73  CpCr[(XylNCMe)2CH](I) + Cr(dpm)2(bpy•)  Stock solutions of CpCr[(XylNCMe)2CH](I) (10.1 mg, 0.0184 mmol) and Cr(dpm)2(bpy•) (10.7 mg, 0.0186 mmol) were prepared by dissolving each complex in 10 mL of THF in separate 10 mL volumetric flasks. A reaction mixture was prepared by pipetting 1 mL of each solution into a 10 mL volumetric flask and diluting to 10 mL with THF to make a light green solution. After reacting for 15 min the UV-vis spectrum was measured: (THF; λmax, nm (ε, M-1 cm-1)) 659 (1660), 593 (1110), 548 (1520), 427 (7914). The spectrum did not change significantly after reacting for two weeks.     Chemistry 449 Thesis: Thomas A. Welsh  39 TW109 CpCr[(XylNCMe)2CH](I) + Cr(dpm)2  CpCr[(XylNCMe)2CH](I) (8.0 mg, 0.015 mmol) and Cr(dpm)2 (7.0 mg, 0.017 mmol) were dissolved in 3 pipettes of THF and stirred. The UV-vis spectrum was measured immediately: (THF; λmax, nm) 571, 427. After 1 h the UV-vis analysis indicated the reaction was complete: (THF; λmax, nm) 577, 494, 426.  TW77  CpCr[(XylNCMe)2CH](O2CPh) + Cr(dpm)2  CpCr[(XylNCMe)2CH](O2CPh) (10.3 mg, 0.019 mmol) and Cr(dpm)2 (8.3 mg, 0.020 mmol) were dissolved in 5 mL of Et2O. After stirring for one hour 1 mL of the solution was pipetted into a 25 mL volumetric flask and diluted to the mark. A UV-vis spectrum was measured of this solution indicating the reaction was complete: (THF; λmax, nm (ε, M-1 cm-1)) 570 (1090), 422 (9243).  TW78  CpCr[(XylNCMe)2CH](O2CPh) + Cr(dpm)2(bpy•)  CpCr[(XylNCMe)2CH](O2CPh) (11.1 mg, 0.020 mmol) and Cr(dpm)2(bpy•) (11.8 mg, 0.020 mmol) were dissolved in 5 mL of Et2O. After stirring for 3 h, 1 mL of the solution was pipetted into a 25 mL volumetric flask and diluted to the mark. A UV-vis spectrum was measured of this solution: (THF; λmax, nm (ε, M-1 cm-1)) 657 (3610), 596, (2860), 547 (2660), 412 (13 520). After reacting for two days the spectrum did not change.    Chemistry 449 Thesis: Thomas A. Welsh  40 TW79  CpCr[(XylNCMe)2CH](O2CPh) + Cr(aram)2  CpCr[(XylNCMe)2CH](O2CPh) (11.7 mg, 0.022 mmol) and Cr(aram)2 (7.0 mg, 0.022 mmol) were dissolved in 5 mL of Et2O. After stirring for 5 min 1 mL of the solution was pipetted into a 25 mL volumetric flask and diluted to the mark. A UV-vis spectrum was measured of this solution, indicating the reaction was complete: (THF; λmax, nm (ε, M–1 cm–1)) 560 (972), 502 (955), 425 (7909).  TW81  CpCr[(XylNCMe)2CH](O2CPh) + Cr(aram)2(tBu-bpy•) Cr(aram)2 (7.0 mg, 0.022 mmol) and 4,4ʹ′-di-tert-butyl-2,2ʹ′-bipyridine (5.72 mg, 0.0213 mmol) were dissolved in 5 mL of Et2O making a dark brown solution. After reacting overnight, the solution, now dark blue green, was mixed with CpCr[(XylNCMe)2CH](O2CPh) (10.8 mg, 0.0199 mmol). After stirring overnight 1 mL of the solution was pipetted into a 25 mL volumetric flask and diluted to the mark. A UV-vis spectrum was measured of this solution: (THF; λmax, nm (ε, M-1 cm-1)) 671 (3550), 609 (1780), 505 (4415), 469 (6003), 414 (10 440), 376 (15 380). After reacting for one week the spectrum did not change significantly. 4.4. Reactions of Cr(LX)2 and Cr(LX)2(bpy•) with RX  TW86  Cr(aram)2 + PhCH2OAc  Cr(aram)2 (8.0 mg, 0.025 mmol) was dissolved Et2O in a 10 mL volumetric flask. Benzyl acetate (4.0 µL, 0.028 mmol) was added and then the solution was diluted to the Chemistry 449 Thesis: Thomas A. Welsh  41 mark. The UV-vis spectrum showed no discernible peaks but a shoulder around 460 nm. After reacting for 24 h the UV-vis spectrum had lost this shoulder and became flat.   TW87  Cr(aram)2 + CH2CHCH2OAc   Cr(aram)2 (8.4 mg, 0.026 mmol) was dissolved Et2O in a 25 mL volumetric flask. Allyl acetate (3.5 µL, 0.032 mmol) was added and then the solution was diluted to the mark. The UV-vis spectrum showed no discernible peaks but a shoulder around 460 nm. After reacting for 24 h the UV-vis spectrum had lost this shoulder and became flat.  TW89  Cr(aram)2(tBu-bpy•) + PhI(OAc)2/CH2CHCH2OAc/CH2CHCH2Br  To a solution of Cr(aram)2 (16.3 mg, 0.0509 mmol) in Et2O (5 mL) was added 4,4ʹ′-di-tert-butyl-2,2ʹ′-bipyridine (13.64 mg, 0.05081 mmol) forming a dark brown solution. After reacting overnight the solution was dark blue green. Three 1 mL aliquots of the solution were transferred to three 10 mL volumetric flasks labelled A, B, and C. A was diluted to the mark. To B was added PhI(OAc)2 (3.54 mg, 0.0110 mmol) and then the solution was diluted to the mark. The solution in B instantly became peach coloured. To C was added allyl acetate (1 µL, 0.009 mmol) and then the solution was diluted to the mark. UV-vis spectra of A and C were measured by diluting 0.3 mL of the solution to 3 mL in the UV-vis cell. The UV-vis spectrum of B was measured without dilution. The spectrum of A was used to compare to the other solutions: (THF; λmax, nm (ε, M-1 cm-1)) 671 (4500), 609 (2220), 505 (5600), 496 (7670), 424 (5620), 375 (16 280). The spectrum of C was identical to the spectrum of A and never changed. The spectrum of B lost all the characteristic peaks shown in A. After two days allyl bromide (1 µL, 0.01 mmol) was Chemistry 449 Thesis: Thomas A. Welsh  42 added to solution A, relabelled Aʹ′. After mixing for 25 min Aʹ′ changed colour to dark red. After mixing overnight Aʹ′ was a peach colour and the spectrum had lost its peaks.  TW92  Cr(dpm)2 + Ph2CH-O2CPy  Cr(dpm)2 was dissolved in 2 pipettes of THF in a brown solution. Diphenylmethylpicolinate was added in 2 pipettes of THF, which made the solution become slightly darker. The UV-vis spectrum was measured: (THF; λmax, nm) 553. This spectrum was different from that of Cr(dpm)2, which shows no peaks in this range.  TW94  Cr(aram)2 + Ph2CH-O2CPy  Cr(aram)2 was dissolved in 4 pipettes of THF in an orange solution. Diphenylmethylpicolinate was added in 2 pipettes of THF, which made the solution become a red orange colour. The UV-vis spectrum was measured. There were no peaks in the spectrum but it was different from the spectrum of Cr(aram)2, which has a shoulder at 460 nm.  TW98  Cr(dpm)2(bpy•) + Ph2CH-O2CPy  Cr(dpm)2(bpy•) (31.6 mg, 0.055 mmol) was dissolved in 2 pipettes THF making a dark green blue solution. The UV-vis spectrum was measured: (THF; λmax, nm) 658, 598, 546, 448. Diphenylmethylpicolinate (16.11 mg, 0.055 mmol) was added in THF. After reacting for 40 min the solution had turned dark brown and the UV-vis spectrum had changed. After reacting for two weeks the solution had turned dark red and the UV-vis spectrum was very different: (THF; λmax, nm) 572, 538, 394. Chemistry 449 Thesis: Thomas A. Welsh  43 TW100 Cr(dpm)2 + Ph2CH-O2CPh  To a solution of Cr(dpm)2 (10.5 mg, 0.0251 mmol) in THF (2 pipettes) was added diphenylmethylbenzoate (6.99 mg, 0.0242 mmol) in 2 pipettes THF. After 24 h there was neither a colour change nor a change in the UV-vis spectrum.  TW101  Cr(dpm)2 + Ph2CH-O2CPh  To a solution of Cr(dpm)2(bpy•) (14.5 mg, 0.0252 mmol) in THF (2 pipettes) was added diphenylmethylbenzoate (7.64 mg, 0.0265 mmol) in 2 pipettes THF. After 24 h there was neither a colour change nor a change in the UV-vis spectrum.  TW102 Cr(aram)2(bpy•) + Ph2CH-O2CPy  To a solution of Cr(aram)2 (10.2 mg, 0.0318 mmol) in THF (2 pipettes) was added 2,2ʹ′-bipyridine (5.3 mg, 0.0339 mmol) in 3 pipettes THF. The dark green solution was left to react overnight, and then diphenylmethylpicolinate (10.04 mg, 0.0347 mol) was added. After six days there was neither a colour change nor a change in the UV-vis spectrum.  TW103 Cr[N(SiMe3)2]2(bpy) + 2 quin + Ph2CH-O2CPy/Ph2CH-O2CPh  To a purple solution of Cr[N(SiMe3)2]2(bpy) (53.0 mg, 0.100 mmol) in THF (2 pipettes) was added 8-hydroxyquinoline (29.4 mg, 0.203 mmol), which caused the solution to instantly change to dark yellow green. After reacting overnight the solution was diluted to the mark in a 10 mL volumetric flask to make a stock solution. Two 1 mL aliquots of this solution were added to 10 mL volumetric flasks labelled A and B. Also, a Chemistry 449 Thesis: Thomas A. Welsh  44 2.5 mL aliquot of the stock solution was diluted 25 mL in a 25 mL volumetric flask. The UV-vis spectrum of the stock solution was measured: (THF; λmax, nm (ε, M-1 cm-1)) 659 (3720), 436 (9180), 411 (8910), 335 (14 150). To A was added diphenylmethylpicolinate and to B was added diphenylmethylbenzoate and then both solutions were diluted to the mark. After reacting for three days solution A had changed: (THF; λmax, nm (ε, M-1 cm-1)) 585 (1580), 425 (10 600), 321 (9330). Solution B never changed after reacting for 5 days.   TW105 Cr(dpm)2 + Ph3C-O2CPh  To a solution of Cr(dpm)2 (9.5 mg, 0.0227 mmol) in THF (2 pipettes) was added triphenylmethylbenzoate (9.2 mg, 0.0261 mmol) in 2 pipettes THF. After 9 days there was neither a colour change nor a change in the UV-vis spectrum.  TW106 Cr(dpm)2(bpy•) + Ph3C-O2CPh  To a solution of Cr(dpm)2(bpy•) (14.4 mg, 0.0251 mmol) in THF (2 pipettes) was added triphenylmethylbenzoate (9.1 mg, 0.0258 mmol) in 2 pipettes THF. After 9 days there was neither a colour change nor a change in the UV-vis spectrum.  TW107 Cr[N(SiMe3)2]2(THF)2 + 2 quin + Ph2CH-O2CPy/Ph2CH-O2CPh  To a bluish purple solution of Cr[N(SiMe3)2]2(THF)2 (52.8 mg, 0.102 mmol) in THF (5 pipettes) was added 8-hydroxyquinoline (29.9 mg, 0.206 mmol). The solution instantly became amber coloured. After reacting overnight the solution was diluted to 10 mL in a 10 mL volumetric flask to make a stock solution. Two 1 mL aliquots of stock solution were added to two 10 mL volumetric flasks labelled A and B. To A was added Chemistry 449 Thesis: Thomas A. Welsh  45 diphenylmethylpicolinate (3.00 mg, 0.0104 mmol) and to B was added diphenylmethylbenzoate (3.2 mg, 0.011 mmol) and then both solutions were diluted to the mark. UV-vis samples of A and B were prepared by diluting 0.3 mL of solution to 3 mL in the UV-vis cell. After reacting for one week neither solution showed any change in colour or UV-vis spectrum. 5. References  1) Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis; University Science Books: Sausalito, CA, 2010. 2) Weighardt, K.; Chirik, P. J. Science 2010, 327, 794-795. 3) Rudolph, A.; Lautens, M. Angew. Chem., Int. Ed. 2009, 48, 2656-2670. 4) De Brun, B.; Dzik, W. I.; van der Vlugt, J. I.; Reek, J. N. H. Angew. Chem. Int. Ed. 2011, 50, 3356-3358. 5) Zhou, W.; MacLeod, K. C.; Patrick, B. O.; Smith, K. M. Organometallics 2012, 31, 7324-7327. 6) Champouret, Y.; MacLeod, K. C.; Smith, K. M.; Patrick, B. O.; Poli, R. Organometallics 2010, 29, 3125-3132. 7) Zhou, W.; Tang, L.; Patrick, B. O.; Smith, K. M. Organometallics 2011, 30, 603-610. 8) Poli, R. Angew. Chem. Int. Ed. 2006, 45, 5058-5070. 9) MacLeod, K. C.; Patrick, B. O.; Smith, K. M. Organometallics 2010, 29, 6639-6641. 10) Zhou, W.; Desnoyer, A. N.; Bailey, J. A.; Patrick, B. O.; Smith, K. M. Inorg. Chem. 2013, 52, 2271-2273.  11) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev. 2013, 113, 5322-5363. 12) Holm, R. H.; Gerlach, D. H. Inorg. Chem. 1969, 8, 2292-2297. 13) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877-910.  Chemistry 449 Thesis: Thomas A. Welsh  46  14) Pal, P. K.; Chowdhury, S.; Drew, M. G. B.; Datta, D. New J. Chem. 2002, 26, 367-371. 15) MacLeod, K. C.; Conway, J. L. Tang, L. T.; Smith, J. J. Corcoran, L. D.; Ballem, K. H. D.; Patrick, B. O.; Smith, K. M. Organometallics 2009, 28, 6798-6806. 16) Desnoyer, A. N. Honours Thesis, University of British Columbia Okanagan, 2011. 17) MacLeod, K. C.; Patrick, B. O.; Smith, K. M. Inorg. Chem. 2012, 51, 688-700. 18) Edema, J. J. H.; Gambarotta, S.; Meetsma, A.; Spek, A. L. Organometallics 1992, 11, 2452-2457. 19) Sneeden, R. P. A.; Zeiss, H. H. J. Organometal. Chem. 1973, 47, 125-131. 20) Correa, A.; León, T.; Martin, R. J. Am. Chem. Soc. 2014, 136, 1062-1069. 21) Horn, M.; Mayr, H. Chem. Eur. J. 2010, 16, 7469-7477. 22) Tsukahara, Y.; Iino, A.; Yoshida, T.; Suzuki, T.; Kaizaki, S. J. Chem. Soc. Dalton Trans. 2002, 181-187. 23) Collman, J. P.; Kittleman, E. T. Inorg. Chem. 1962, 1, 499-503. 24) Dugan, T. R.; Bill, E.; MacLeod, K. C.; Christian, G. J.; Cowley, R. E.; Brennessel, W. W.; Ye, S.; Neese, F.; Holland, P. L. J. Am. Chem. Soc. 2012, 134, 20352-20364. 25) Hume, D. N.; Stone, H. W. J. Am. Chem. Soc. 1941, 63, 1200-1203. 26) King, W. R.; Garner, C. S. J. Chem. Phys. 1950, 18, 689-691. 27) Champouret, Y.; Baisch, U. Poli, R.; Tang, L.; Conway, J. L.; Smith, K. M. Angew. Chem. Int. Ed. 2008, 47, 6069-6072. 28) Zhou, W.; Desnoyer, A. N.; Bailey, J. A. Patrick, B. O. Smith, K. M. Inorg. Chem. 2013, 52, 2271-2273. 29)  (a) Bradley, C. D.; Hursthouse, M. B.; Newing, C. W.; Welch, A. J. J. Am. Chem. Soc., Chem. Commun. 1972, 567-568.   (b) Kayal, A.; Lee, S. Inorg. Chem. 2002, 41, 321-330. 30) Manzer, L. E. J. Am. Chem. Soc. 1978, 100, 8068-8073. 31) Monzon, L. M. A.; Burke, F.; Coey, J. M. D. J. Phys. Chem. C, 2011, 115, 9182-9192. 

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