x Steric Effects and Photolysis in Chromium-Catalyzed Carbon-Carbon Bond Forming Reactions Laura Fairburn A Thesis Submitted in Partial Fulfillment of the Requirements for CHEMISTRY 449 THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan) April 2014 © Laura Fairburn, 2014 Chemistry 449 Thesis – Laura K. Fairburn ii Abstract Previously, well-defined chromium complexes with small NHC ligands were determined to need intense light to induce activity for catalytic carbon-carbon bond-forming reactions, because of their relatively strong Cr-NHC bonds. Due to this requirement, the use of chromium catalysts with larger aromatic substituted NHC ligands and weaker Cr-NHC bonds was tested, and demonstrated catalysis without photolysis. Now, it has been determined that not only do these catalytic carbon-carbon bond-forming reactions proceed in the absence of intense light, improved yields were also observed when the reactions are protected from the ambient light in the lab. Since the alkyl substituted NHC ligands require photolysis and the aromatic substituted NHC ligands are light sensitive, the focus then shifted to the possible synthesis of a NHC ligand that sterically was in between the two previously tested ligands. A new unsymmetric NHC ligand was designed and coordinated to a chromium centre, which was found to have catalytic properties that fall between the two previously studied NHC substituted complexes. Using previously and newly designed ligands, in situ generation of the catalyst, using Cr(II) and Cr(III) sources, and the use of isolated catalysts were tested for catalytic homocoupling ability. The best catalyst was found to be the isolated CpCr(NHC)Cl complex with the 2,6-diisopropylphenyl substituted NHC ligand at 10 mol% catalyst loading. This complex provided a 81% yield of 4,4'-dimethylbiphenyl from the homocoupling of p-tolyl magnesium bromide using 1,2-dichlorobutane as the stoichiometric oxidant. Chemistry 449 Thesis – Laura K. Fairburn iii Table of Contents Abstract ........................................................................................................................................... ii  Table of Contents ........................................................................................................................... iii  List of Tables ................................................................................................................................. iv  List of Figures ................................................................................................................................. v  List of Symbols and Abbreviations ................................................................................................ vi  Acknowledgements ....................................................................................................................... vii  Introduction ..................................................................................................................................... 8  Results and Discussion ................................................................................................................. 16  Experimental ................................................................................................................................. 27  Conclusion .................................................................................................................................... 35  References ..................................................................................................................................... 36 Appendix ....................................................................................................................................... 37 Chemistry 449 Thesis – Laura K. Fairburn iv List of Tables Table 1. Results of the reactions involving isolated CpCr(NHC)Cl complexes ........................... 22  Table 2. Results the in situ reactions involving CpCrCl2(THF) and NHC ligands ...................... 23  Table 3. Result of the control reactions involving different Cr(II) and Cr(III) sources. .............. 25  Table 4. Isolated CpCr(NHC)Cl homocoupling reactions completed in darkness ....................... 30  Table 5. Isolated CpCr(NHC)Cl homocoupling reactions completed in ambient light ................ 30  Table 6. CpCrCl2(THF) + NHC homocoupling reactions completed in darkness ....................... 31  Table 7. CpCrCl2(THF) + NHC homocoupling reactions completed in ambient light ................ 32  Table 8. Cp2Cr + NHC homocoupling reactions in situ reactions ................................................ 32  Table 9. In situ reactions to determine cyclopentadiene effects ................................................... 33  Table 10. Cr-catalyzed homocoupling control reactions .............................................................. 34   Chemistry 449 Thesis – Laura K. Fairburn v List of Figures Figure 1. The chromium-catalyzed homocoupling achieved by CrCl3 ........................................... 8  Figure 2. Chromium(I) cationic arene complex isolated from 1914 chromium-catalyzed homocoupling reaction .................................................................................................................... 9  Figure 3. The production of (C6H6)(C6H5C6H5)Cr from Cr(Ph)3(THF)3 ........................................ 9  Figure 4. The ligand-free chromium-catalyzed cross coupling achieved by CrCl2 ........................ 9  Figure 5. Synthesis of CpCr(1,3,4,5-tetramethylimidazol-2-ylidene)Me2 ................................... 10  Figure 6. Synthesis of CpCr(Mes-NHC)Cl ................................................................................... 11  Figure 7. Iron with a N-heterocyclic carbene (NHC) ligand catalyzed cross coupling reaction. . 11  Figure 8. Synthesis of CpCr(iPr-NHC)Ph2 from CpCr(iPr-NHC)Cl ............................................. 12  Figure 9. Synthesis of biphenyl through photolysis of CpCr(iPr-NHC)Ph2 ................................. 13  Figure 10. Reaction to confirm photolysis of NHC ligand ........................................................... 13  Figure 11. The homocoupling reaction of toluene by CpCr(iPr-NHC)Cl ..................................... 14  Figure 12. Hypothesized catalytic cycle of homocoupling by CpCr(iPr-NHC)Cl ........................ 14  Figure 13. The NHC imidazolium salts used ................................................................................ 15  Figure 14. Experiment completed to counteract dilution effects. ................................................. 16  Figure 15. The catalytic reaction using the isolated CpCr(NHC)Cl complexes. .......................... 18  Figure 16. The control reaction to observe effects of light in the absence of the NHC ligand. .... 18  Figure 17. [CpCr(µ-Tol)]n multimetallic complex ........................................................................ 19  Figure 18. The synthetic reaction for Mes/Cy-NHC•HCl ............................................................ 20  Figure 19. Crystal Structure of CpCr(Mes/Cy-NHC)Cl ............................................................... 21  Figure 20. The in situ catalytic reaction using the CpCrCl2(THF) with imidazolium salts .......... 22  Figure 21. The in situ catalytic reaction using the Cp2Cr and different NHC ligands ................. 24  Chemistry 449 Thesis – Laura K. Fairburn vi List  of  Symbols  and  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. Å Ångstrom, 10–10 m br broad 13C carbon-13 °C degree Celsius Cp cyclopentadienyl, η5-C5H5 Cy cyclohexyl, C5H9 d days, or doublet (in a spectrum) DCM dichloromethane Dpp 2,6-diisopropylphenyl, C12H17 equiv equivalents Et ethyl, CH3CH2 Et2O diethyl ether g grams 1H proton h hours iPr isopropyl, (CH3)2CH- L neutral, 2-electron-donor ligand; or litre, 10–3 m–3 M metal; or molar, molL–1 Me methyl, CH3- Mes mesityl, 1,3,5-trimethylphenyl min minutes mmol millimole, 10–3 mole mol mole, 6.022·10–23 particles NHC N-heterocyclic carbene NMR nuclear magnetic resonance Ph phenyl, C6H5- ppm parts per million R alkyl s singlet (in a spectrum) t triplet (in a spectrum) THF tetrahydrofuran, C4H8O Tol tolyl, C7H7 X halide or other anionic 1-electron-donor ligand Chemistry 449 Thesis – Laura K. Fairburn vii Acknowledgements Thank you to my supervisor, Kevin Smith, for your support and guidance throughout this project. To all the chemistry professors, thank you for making my education so memorable and fostering my love of chemistry. To Cate, Kristina, Sarah, Tom, Luke and Yann, the lab wouldn’t have been the same without you. Thank you for being a continual source of knowledge and entertainment! To my Mum, Dad, Sarah and Jack, thank you for all your love, support, and your never wavering enthusiasm in everything I do. Chemistry 449 Thesis – Laura K. Fairburn 8 Introduction Although palladium and nickel are the most frequently catalysts associated with cross coupling reactions, similar reactions involving first-row Earth-abundant transition metals are being investigated. Cross coupling reactions involve the formation of a carbon-carbon bond between an organic halide and a main group organometallic species through the use of a transition metal catalyst. The mechanism usually begins with the oxidative addition of the organic halide to the catalyst. Subsequently, the coupling partner, such as a Grignard reagent, undergoes transmetallation onto the same metal centre. The final step is a reductive elimination of the two coupling fragments, resulting in the regeneration of the reactive metal complex to give the organic product.1 As early as 1914, the use of stoichiometric quantities of chromium(III) chloride for the dimerization of phenylmagnesium bromide, seen in Figure 1, had been reported by Bennet and Turner.2 Figure 1. The chromium-catalyzed homocoupling achieved by CrCl3 in 1914. While the underlying organometallic chemistry of this reaction remained a mystery for several decades, an ongoing attempt by Hein to isolate the organochromium complexes resulted in the isolation of chromium(I) cationic arene complexes after aqueous workup, such as the example shown in Figure 2. The bonding interactions between the arenes and the metal centre were not fully understood until after the discovery of ferrocene in the 1950s.3 CrCl3 MgBr+ CrCl2 + 0.5Et2OChemistry 449 Thesis – Laura K. Fairburn 9 Figure 2. Chromium(I) cationic arene complex isolated from 1914 chromium-catalyzed homocoupling reaction The synthesis of a Cr(Ph)3(THF)3 complex, which had been Hein’s expected product, was completed at -40°C by Zeiss.3 The chromium(I) cationic arene complex was the product of the mechanism involving shown Cr(Ph)3(THF)3 in Figure 3, after the work up. In order for Cr(Ph)3(THF)3 to undergo reductive elimination to form the (η6-arene)chromium(I) phenyl, one of the neutral stabilizing THF ligands must be removed from the complex followed by the other residual THF dissociating.3 Figure 3. The production of (C6H6)(C6H5C6H5)Cr from Cr(Ph)3(THF)3 Recently, a ligand-free chromium-catalyzed cross coupling reaction has been reported using CrCl2, shown in Figure 4.4 This has been found to be effective between sp2 carbon centres with little presence of homocoupling side products, compared to similar studies completed with iron and cobalt. Figure 4. The ligand-free chromium-catalyzed cross coupling achieved by CrCl24 Since the first reported synthesis of a stable N-heterocyclic carbene (NHC), these molecules have become increasingly used as ligands in organometallic chemistry. The CrN Br+ 3 mol% CrCl2THF, 25 oC NMgClLiClChemistry 449 Thesis – Laura K. Fairburn 10 benchmark report about the first stable, free NHC 1,3-di(adamantyl)imidazol-2-ylidene, through the deprotonation of its imidazolium precursor was by Arduengo and co-workers.5 Free NHC ligands are stable in an inert atmosphere because of the nitrogen atoms adjacent to the carbene, which interact with the empty p orbital, resulting in a very effective π donation of electron density onto the carbon centre. NHC ligands act as strong nucleophiles, making them an effective L-type neutral ligand. When they are reacted with a metal centre, they engage in pronounced σ-donation with very limited π-acceptor characteristics. NHC metal complexes are resistant to decomposition due to the strong metal-NHC bond.6 NHC ligands can also be altered both electronically and sterically through the changing of substituents present on the nitrogen or carbon atoms and by the saturation of the heterocyclic ring. Due to these features, NHC substituted metal complexes have been studied for a variety of applications and have proven to be an effective ligand for first-row metals for cross coupling reactions. The coordination of an NHC ligand to a metal centre can be accomplished by two common procedures: ligand substitution with neutral NHC ligands or protonolysis with NHC•HCl imidazolium precursors. Jolly et al. reported the synthesis of CpCr(NHC)Cl2, through ligand substitution of a neutral THF ligand for a neutral 1,3,4,5-tetramethylimidazol-2-ylidene carbene, seen in Figure 5.7 Figure 5. Synthesis of CpCr(1,3,4,5-tetramethylimidazol-2-ylidene)Me2 The synthesis of CpCr(NHC)Cl through the protonolysis of the NHC•HCl imidazolium precursors was reported by Tilset, and is the way by which CpCr(NHC)Cl complexes in this Chemistry 449 Thesis – Laura K. Fairburn 11 project were synthesized, seen in Figure 6.8 The imidazolium salts are air stable and easier to store than the free NHC ligands, which makes them the ideal precursor reagents. Figure 6. Synthesis of CpCr(Mes-NHC)Cl as reported by Tilset.8 In situ formed iron NHC complexes are often employed in many different catalytic applications, including cross coupling and C−X bond formation.6 Nakamura’s group has reported that for cross coupling reactions catalyzed by iron, bulky N-heterocyclic carbene (NHC) ligands have been proven to be selective and effective, seen in Figure 7.6, 9, 10 Figure 7. The cross coupling reaction catalyzed by iron and a bulky N-heterocyclic carbene (NHC) ligand.9 Previous Smith group students have prepared well-defined CpCr(NHC) complexes in an attempt to develop new chromium-based carbon-carbon bond-forming catalysts.11 Their work focused on the CpCr(iPr-NHC)Cl complex, from which group members attempted the synthesis of the CpCr(iPr-NHC)Ph2 through an interesting route. The CpCr(iPr-NHC)Ph complex was synthesized through a salt metathesis of CpCr(iPr-NHC)Cl using one equivalent of MgPhX, while the CpCr(iPr-NHC)Ph2 was much harder to isolate. The synthesis of CpCr(iPr-NHC)Cl2 was achieved through the oxidation of CpCr(iPr-NHC)Cl with PbCl2.11 Initially, the synthesis of Cr(iPr-NHC)Ph2 was attempted through reacting the previously synthesized CpCr(iPr-NHC)Cl2 NN H ClCr + CrN N Cl CrN NMes MesPhMgBrFeF3 3 H2O+EtMgBr + NNCl(3 mol%)(18 mol%) (9 mol%) ClMgBrChemistry 449 Thesis – Laura K. Fairburn 12 with MgPh2, but this was unsuccessful, so an oxidative pathway was used by reacting CpCr(iPr-NHC)Cl with MgPh2 and ½ an equivalent of I2, shown in Figure 8. Figure 8. Synthesis of CpCr(iPr-NHC)Ph2 from CpCr(iPr-NHC)Cl When the CpCr(iPr-NHC)Ph2 complex was exposed to intense light, the production of the biphenyl was achieved. This reaction does not appear to proceed via Cr-Ph bond homolysis, but instead involved the photolytic dissociation of the NHC ligand and the reductive elimination of biphenyl. This results in the production of the CpCr(iPr-NHC)Ph Cr(II) complex from the comproportionation of CpCr(iPr-NHC)Ph2, a Cr(III) complex, and the CpCr(iPr-NHC) intermediate, a Cr(I) complex, seen in Figure 9. CrN N ClCrN NPhMgX1) MgPh22) 1/2 I2 Cr PhN N PhCr NN MgXPhMgX 1/2 I2 -MgX2Chemistry 449 Thesis – Laura K. Fairburn 13 Figure 9. Synthesis of biphenyl through photolysis of CpCr(iPr-NHC)Ph2 Photolysis is believed to trigger the NHC dissociation required for the key carbon-carbon bond-forming step, as illustrated in the proposed catalytic cycle. The dissociation of the NHC ligand through photolysis was confirmed through an experiment, which involved trapping of a NHC-free complex. This was done through the photolysis of CpCr(iPr-NHC)Cl2 in the presence of [HNEt3]Cl to react with both the free NHC ligand and CpCr(THF)Cl2 shown in Figure 10. Figure 10. Reaction to confirm photolysis of NHC ligand The confirmation of the light-induced NHC dissociation was crucial, as its loss is critical for the cross coupling mechanism, but also makes the isolation and UV/Vis characterization of these complexes very difficult. CrN N Cl light NN CrO ClClCl [HNEt3]Cl Cr ClClClNN HChemistry 449 Thesis – Laura K. Fairburn 14 Previously in the Smith group, Wen Zhou had achieved homocoupling of ArMgX catalyzed by CpCr(NHC)Cl, Cr(II) complexes, through a redox pathway shown in Figure 11. Figure 11. The homocoupling reaction of toluene by CpCr(iPr-NHC)Cl Once all of these steps were confirmed with isolated experiments, a mechanism for the homocoupling of p-tolylMgBr by CpCr(iPr-NHC)Cl, in the presence of an oxidant, was proposed in Figure 12. Figure 12. Hypothesized catalytic cycle of homocoupling by CpCr(iPr-NHC)Cl Starting with CpCr(iPr-NHC)Cl, a Cr(II) complex, it undergoes a salt metathesis reaction, in which the chlorine atom is replaced with a p-tolyl. This is followed by a second equivalent of CrN N ClMgBr 10 mol%+ Cl Cl 150 W 86%+TolrMgXMgX2 TolMgXClCl CrN N Cl CrN NCrN N Cr TolN N Tol Cr NN MgXNCN Cr light Cl ClCrChemistry 449 Thesis – Laura K. Fairburn 15 p-tolylMgBr reacting with the CpCr(iPr-NHC)Tol to produce a [CpCr(Tol)2]-[NHC-MgX]+ Cr(II) ‘ate’ complex. After this step, an oxidant is required to reach the CpCr(iPr-NHC)Tol2, as was seen previously in the synthesis of the CpCr(iPr-NHC)Ph2 complex. Intense light then causes the dissociation of the NHC ligand, leaving a CpCrTol2 Cr(III) complex. The two toluene ligands then reductively eliminate to produce a 4,4'-dimethylbiphenyl η6-coordinated ligand, which allows for the free NHC ligand to recoordinate to the metal centre, resulting in a Cr(I) complex. This complex is then oxidized to free the 4,4'-dimethylbiphenyl which returns the complex to its original CpCr(iPr-NHC)Cl Cr(II) form. Consistent with this mechanism, replacing the iPr substituents on the NHC ligand with bulkier 2,6-diisopropyl phenyl groups should allow for catalysis without photolysis. Figure 13. The NHC imidazolium salts used to synthesize the CpCr(NHC)Cl complexes used. The first was the focus of Wen Zhou’s PhD thesis, while the other two NHCs were the focus of this project. By altering the substituents on the NHCs to be larger, or even unsymmetrical as seen in Figure 13, the goal of this project was to develop a sterically protected chromium centre, while allowing the complex to remain reactive enough to allow homo- or cross-coupling. The initial goal for these newly designed chromium complexes was for Negishi cross coupling reactions, though due to the difficulty of characterizing the alkylated CpCr(NHC)Ph complex, focus shifted to optimization of the NHC ligands and Cr(II) and Cr(III) sources for homocoupling. NN ClNN ClNN ClChemistry 449 Thesis – Laura K. Fairburn 16 Results and Discussion The goal of this research project initially was to synthesize and characterize different CpCr(NHC)R complexes for the goal of catalyzed cross coupling reactions. This was going to be achieved by the oxidative addition of an organic ligand, using organic halides, followed by reductive elimination of the two different organic compounds resulting in a cross-coupled product. The product would then undergo ligand substitution with the NHC, leaving the free homocoupled product and the catalyst to be regenerated by an oxidizing agent. Although the crystal structure was obtained of the CpCr(Dpp-NHC)Ph, this complex was unable to be characterized through UV/Vis, unlike the previously reported CpCr(iPr-NHC)Ph and CpCr(iPr-NHC)Mes.11 This is thought to be due to the dissociation of the NHC ligand caused by dilution, as the Cr-NHC bond is weak in the CpCr(Dpp-NHC)X complexes. This is supported through the observed lightening of the solution from a brown to a bright green colour when the concentration decreases. This NHC dissociation is necessary for cross coupling reactions, as it opens up the metal centre to reductively eliminate the R ligands, but it makes isolation and UV/Vis characterization of these complexes incredibly difficult. An experiment was conducted in hopes of shifting the equilibrium back to the bound NHC form. Through the deprotonation of the Dpp-NHC•HBF4 with NaH and a catalytic amount of KOtBu, a free form of the Dpp-NHC was synthesized.12 This free form was then used for the following experiment, seen in Figure 14. To a stock solution of CpCr(Dpp-NHC)Ph in THF, an excess of free Dpp-NHC ligand was added. Figure 14. Experiment completed to counteract dilution effects. CrN N CrO + NN20THFChemistry 449 Thesis – Laura K. Fairburn 17 However, even in the presence of 20 equiv. of free NHC, the dilution effects were unable to be counteracted and the equilibrium was unable to be shifted. The solution resulting from this experiment was still analyzed by UV/Vis spectroscopy, even though the colour of the solution did not become darker. A CpCr(NHC)R Cr(II) complex is expected to have two strong absorbance peaks around the ranges 356 nm and 462 nm, as previously reported by the Smith group and Tilset.8,11 Even in the presence of 20 equiv. of free NHC, the solution was a bright green and displayed only one band around 422 nm in the UV/Vis. The inability to completely characterize any of the alkyl Cr complexes prevented each individual step of the catalytic cycle to be investigated separately, therefore, the project’s focus shifted to observing homocoupling catalysis. This involved the observation of three different types of experiments; the use of isolated CpCr(NHC)Cl complexes, the in situ generation of Cp2Cr catalysts with varied NHC ligands, and the in situ generation of CpCrCl2(THF) catalysts with varied NHC ligands. These different variables were studied as to optimize the catalytic reaction. For all of these experiments, the reactivity of each catalyst was measured by the final yield of the homocoupled product, 4,4'-dimethylbiphenyl. The production of the homocoupled product was confirmed through both 1H and 13C NMR spectroscopy. Wen Zhou had started a similar project, though the reactions were not explicitly studied with a variety of different NHC-substituted complexes. Previously the CpCr(iPr-NHC)Cl complex was proven to require photolysis to induce catalysis, while the CpCr(Dpp-NHC)Cl could be completed in darkness, not requiring photolysis for the dissociation of the NHC ligand. Chemistry 449 Thesis – Laura K. Fairburn 18 Figure 15. The catalytic reaction, and its yields, using the isolated CpCr(NHC)Cl complexes. When I attempted to reproduce this experiment, seen in Figure 15, on several occasions, I consistently obtained lower yields of the product than previously reported. After the replications of this experiment continued to have lower yields of 4,4'-dimethylbiphenyl, the reaction was carried out with aluminum foil used to prevent exposure to ambient light, which resulted in similar yields as previously reported. This result was surprising, since when Wen Zhou completed the reaction initially, the use of darkness was only used to prove the hypothesis that the Dpp-NHC did not require photolysis for NHC dissociation. The effect of light on product’s yield is reversed by the steric bulk of the NHC ligand. While ambient light is detrimental for the reaction of the large Dpp-NHC ligand, no product is obtained when the smaller iPr-NHC ligand is used unless irradiated with a 150W incandescent light bulb. A control reaction, in both ambient light and darkness, was completed using the CpCrCl2(THF) complex in the absence of an NHC ligand, shown in Figure 16. As seen in the initial reaction, higher yields were observed when the reaction was completed in darkness. Figure 16. The control reaction, and its yields, used to observe effects of light in the absence of the NHC ligand. Light: 38 %Dark: 81%MgBr10 mol% + Cl Cl 20 h+CrN N ClCrO ClCl BrMg + Cl Cl 20 h+10 mol% Light: 29%Dark: 43%Chemistry 449 Thesis – Laura K. Fairburn 19 The lower yield under ambient light (29% compared to 43%) suggests that under the reaction conditions, an NHC-free intermediate is generated that decomposes photolytically, which could potentially be the CpCr(η6-arene) intermediate, as seen in Figure 12. Similar η6-arene complexes have been previously reported, but the stability of these complexes only increases with a higher number of methyl substituents on the arene and Cp ligands.13 As this intermediate has no substituents on the cyclopentadienyl ring and only two methyl substituents on the arene, it is likely that this complex is unstable and prone to decomposition. The ambient light could be causing the arene to dissociate too soon, resulting in a very unstable CpCr intermediate that undergoes comproportionation with CpCrTol2 to produce a [CpCr(µ-Tol)]n multimetallic complex, similar to what is shown in Figure 17. This resulting complex could leave the catalyst unreactive, stopping the reaction and lowering the yield of the homocoupled product, 4,4'-dimethylbiphenyl. A similar complex [CpCr(µ-Mes)]2 was reported by the Smith group and [Cp*Cr(µ-R)]2 complexes are surprisingly resistant to dissociation with strong σ-donor ligands,.11,14 Figure 17. [CpCr(µ-Tol)]n multimetallic complex synthesized through a comproportionation reaction. Due to the bulkiness of the diisopropylphenyl substituted NHC and the very strong Cr-NHC bond of the isopropyl substituted NHC, as observed in previously obtained crystal structures, the possible synthesis of a NHC ligand that sterically was in between the two previously tested ligands was completed in hopes of preventing the previously mentioned dilution effect and decreasing its light sensitivity. Baslé and Mauduit recently reported an Chemistry 449 Thesis – Laura K. Fairburn 20 unsymmetrical NHC ligand substituted with intermediate sized alkyl and aromatic groups.15 Following the reported procedure, the ligand that was substituted with a cyclohexane and a mesityl was synthesized, seen in Figure 18. Figure 18. The synthetic reaction for Mes/Cy-NHC•HCl.15 This is a very different procedure to what is normally used to synthesize unsymmetrical imidazolium salts, as previously the one-pot synthesis always resulted in the symmetrical salts. Normally to synthesize an unsymmetrical imidazolium salt, a singly substituted salt would have to be synthesized before adding a different substituent to the other nitrogen atom. Through the reduction of the reaction temperature and shortening the reaction time, Baslé and Mauduit achieved a one-pot synthesis of the unsymmetrical imidazolium salts. The CpCr(Mes/Cy-NHC)Cl complex was synthesized by protonolysis of chromocene with the 1-cyclohexyl-3-mesitylimidazolium chloride in THF, similar to the related synthesis of the symmetric bis(mesityl) NHC complex.8 Its solid-state molecular structure was then determined by single-crystal X-ray diffraction, shown in Figure 19. NH2 H2NHO HO OH H AcOH, 40 oC10 min, then NaCl NN ClChemistry 449 Thesis – Laura K. Fairburn 21 Figure 19. Crystal Structure of CpCr(Mes/Cy-NHC)Cl Through the comparison of the X-ray crystal structure of CpCr(Dpp-NHC)Cl to the newly synthesized CpCr(Mes/Cy-NHC)Cl complex, the bond lengths between the Cr and NHC ligand were found to differ. The Cr-Mes/Cy-NHC bond is 2.059(14) Å, while the Cr-Dpp-NHC bond is 2.1160(15) Å. The Cr-Dpp-NHC bond is longer than the Cr-Mes/Cy-NHC bond, due to the steric pressure of the substituents on the Cr-NHC bond. As the Cr-Dpp-NHC bond is longer, this supports the previous assumption that the Cr-Dpp-NHC bond is weak enough to dissociate through dilution. Alternatively, the Cr-Mes/Cy-NHC bond is shorter, and therefore is expected to dissociate less readily. Through the synthesis of CpCr(Mes/Cy-NHC)Cl, the hope was that the NHC would not as readily dissociate and allow for the proper characterization of an alkylated complex. Unfortunately, the CpCr(Mes/Cy-NHC)Ph was unable to be isolated. Chemistry 449 Thesis – Laura K. Fairburn 22 As the larger NHC ligands appeared to be more susceptible to the effects of ambient light, CpCr(Mes/Cy-NHC)Cl was tested for its reactivity in the presence of ambient light as well as darkness. As the NHC was sterically smaller than the Dpp-NHC, the CpCr(Mes/Cy-NHC)Cl should be less susceptible to dissociation and catalytic decomposition of a NHC-free intermediate. The reaction was completed in the similar manner to the initial reaction involving the CpCr(Dpp-NHC)Cl complex. The hypothesis was proven to be correct, as it appears to be less susceptible to the catalytic decomposition caused by ambient light, as seen by a decreased difference in yields between the light (42%) and dark reactions (47%), as seen in Table 1. Although this reaction didn’t have a yield comparable to the CpCr(Dpp-NHC)Cl complex, the decreased difference between the light and dark reactions indicates it is closer to a complex that doesn’t require photolysis, but isn’t prone to decomposition by ambient light either. Catalyst Percent Yield Ambient Light Darkness CpCr(Dpp-NHC)Cl 38% 81% CpCr(Mes/Cy-NHC)Cl 42% 47% Table 1. The percent yield of 4,4'-dimethylbiphenyl produced by the reactions involving isolated CpCr(NHC)Cl complexes Though the isolated compounds were tested and showed good reactivity, experiments were completed using in situ generation of catalysts, as seen in Figure 20, in the hopes that one would work on a comparable level to the isolated CpCr(Dpp-NHC)C, as they would be much easier to use in organic reactions. Figure 20. The in situ catalytic reaction using the CpCrCl2(THF) and different imidazolium salts. CrO ClCl10 mol% NN R'H Cl+ BrMg + Cl Cl 20 h+10 mol%R 2 R,R'= Mes, 3 R= Mes, R'=Cy4 R,R'= DppChemistry 449 Thesis – Laura K. Fairburn 23 The suggested catalytic cycle should proceed regardless of whether it is started with Cr(II) or Cr(III), so Cp2Cr or CpCrCl2(THF) were considered to be a suitable precursors for the in situ generation of catalyst.8 Due to the air sensitivity of the isolate complexes, experiments were also conducted using CpCrCl2(THF), as it is a much less air sensitive complex. With the goal of homocoupling, these two precursors were used with a variety of different sized NHC ligands to observe the effects of sterics on the catalytic process. The results of these experiments can be seen in Table 2. Entry Reaction Percent Yield Ambient Light Darkness 1 CpCrCl2(THF) 29% 43% 2 CpCrCl2(THF) + Mes-NHC•HCl 37% - 3 CpCrCl2(THF) + Mes/Cy-NHC•HCl 25% - 4 CpCrCl2(THF) + Dpp-NHC•HCl 27% 38% 5 CpCrCl2(THF) + Free Dpp-NHC 23% 20% 6 CpCrCl2(THF) + Dpp-NHC•HBF4 33% - Table 2. Results of the in situ reactions involving CpCrCl2(THF) and NHC ligands As mentioned before, different sized NHC ligands have been synthesized, bound to chromium centres, and compared for relative bond lengths and strengths. The length of their Cr-NHC bond is directly correlated to whether they require photolysis to dissociate or if they dissociate unassisted. The Dpp-NHC ligand (entry 4), which previously had shown the highest reactivity and the highest yield in the CpCr(NHC)Cl complexes, had an average result and performed worse than when only the CpCrCl2(THF) complex was used in the absence of an NHC ligand. A similar trend was observed of most of the ligands tested, seen in entries 3, 4, 5. The use of a Dpp-NHC•HBF4 (entry 6) was also tested and showed a better yield in the presence of ambient light, though it wasn’t further investigated, as the isolated CpCr(Dpp-NHC)Cl complex still produced the homocoupled product in the highest yield . Chemistry 449 Thesis – Laura K. Fairburn 24 The free NHC ligand synthesized for the experiment conducted in an attempt to properly characterize the CpCr(NHC)Ph complex, was also used in these experiments. The free-form NHC would be expected to be the most reactive, as replacing a neutral coordinated THF with a free NHC ligand should be a quick reaction allow it to immediately undergo catalysis. Unfortunately, the yields were not very high, though it was the only reaction not affected by the presence of ambient light. This is possibly due to the speed of the NHC coordination, preventing an intermediate that would be susceptible to photolytic decomposition from forming. Figure 21. The in situ catalytic reaction using the Cp2Cr and different NHC ligands. As the isolated CpCr(NHC)Cl complexes showed the most reactivity, in situ generation of these catalysts from Cp2Cr were tested, shown in Figure 21. The Dpp-NHC ligand (entry 4), which previously had shown the highest reactivity and the highest yield in the CpCr(NHC)Cl complexes, produced an average yield of 23%. This reaction did perform higher than when just chromocene was used as a catalyst. All of the in situ experiments involving Cp2Cr and NHC ligands didn’t produce any similar yields to the isolated CpCr(NHC)Cl complexes, as seen in Table 3. Entry Reaction Percent Yield 1 Cp2Cr + Dpp-NHC•HCl 23% 2 Cp2Cr + Mes-NHC•HCl 29% 3 Cp2Cr + Mes/Cy-NHC•HCl 22% Table 3. Results of the in situ reactions involving Cp2Cr and NHC ligands There was a worry that the free cyclopentadiene resulting from the synthesis of CpCr(Dpp-NHC)Cl from the chromocene was interfering with the reaction. Therefore, two in situ reactions Cr NN R'H Cl+ BrMg + Cl Cl 20 h+10 mol% 10 mol%R 1 R,R'= Dpp2 R,R'= Mes, 3 R= Mes, R'=CyChemistry 449 Thesis – Laura K. Fairburn 25 were completed to observe the effect of the free CpH on the reaction. In the first reaction, the Dpp-NHC•HCl ligand and Cp2Cr were left to react overnight, followed by an immediate addition to the tolyl Grignard, resulting in a yield of 36%. For the second reaction, the Dpp-NHC ligand and Cp2Cr were left to react overnight then the reaction solution was evaporated in vacuo. The crude product was then s and added to tolyl Grignard, which resulted in a yield of 49%. Through these experiments, it was determined that the removal of the cyclopentadiene was required for a better yield. Unfortunately, none of the resulting yields in any of the in situ experiments compared to the yields isolated from the CpCr(Dpp-NHC)Cl catalyst, as seen in Tables 2 and 3. Control experiments, using different Cr(II) and Cr(III) sources, were completed to determine the effects of all the ligands, including the Cp and NHC, on the chromium’s reactivity. The results of these control experiments can be seen in Table 4. Cr Source Percent Yield Ambient Light Darkness Cp2Cr 20% 17% CrCl2 72% 69% CrCl3 86% 79% CrCl3(THF)3 65% 36% Table 4. The percent yield of 4,4'-dimethylbiphenyl produced by the control reactions involving different Cr(II) and Cr(III) sources. The observations from the controls were completely opposite to what was observed with the isolated CpCr(NHC)Cl complexes, as well as the in situ CpCrCl2(THF) and Cp2Cr in the presence of NHC ligands experiments. Yields of the homocoupled product increased with light, though they were much harder to isolate due to the excess present of salts. This possibly is due to absence of the cyclopentadiene ligand, as previously it had been hypothesized that the ambient light may be causing the decomposition of the NHC free CpCr(η6-arene) complex. After comparing the results from isolated catalysts to that of the in situ generation of the catalyst, the conclusion was that isolated CpCr(Dpp-NHC)Cl complex still works the most Chemistry 449 Thesis – Laura K. Fairburn 26 efficiently, especially in the dark. The yield was higher than all the controls, except for CrCl3 in the light. Chemistry 449 Thesis – Laura K. Fairburn 27 Experimental General Methods All reactions, with the exception of the synthesis of 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, 1,3-bis(2,6-diisopropylphenyl)imidazolium boron tetrafluoride and 3-cyclohexyl-1-mesitylimidazolium chloride, were performed under anhydrous, oxygen-free conditions using an inert-atmosphere glove box complete with active oxygen and moisture removing catalyst columns or using standard Schlenk techniques. The THF, Et2O, and hexanes solvents were made anhydrous using Grubbs/Dow columns. Anhydrous “sure-seal” grade reagents, such as 1,4-dioxane, NaCp in THF, PhMgBr in Et2O, MeMgI in Et2O, and PhMgCl in Et2O were purchased from Aldrich and used as received. Other liquid reagents were purchased from Aldrich and free-pump-thaw degassed before being brought into the glove box. UV-Vis spectra were collected using a Shimadzu UV-2550 UV-Vis spectrophotometer with airtight UV cells. 1H NMR spectra were collected by a Varian Mercury Plus 400MHz spectrometer in CDCl3 or C6D6 with chemical shifts referenced to the solvent peak. General Synthesis Cp2Cr was synthesized from CrCl2 (anhydrous powder, Strem) and 2.2 equivalents of NaCp (1.0 M in THF, Aldrich). CpCr(THF)Cl2 was prepared by the reaction of HCl/Et2O with Cp2Cr in THF.16 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride was synthesized from N,N'-bis(2,6-diisopropylphenyl)diimine, paraformaldehyde and TMSCl using a previously described procedure.17 The free 1,3-bis(2,6-diisopropylphenyl)NHC ligand was synthesized using a procedure described by Nolan.12 Chemistry 449 Thesis – Laura K. Fairburn 28 LF36 CpCr(Dpp-NHC)Cl This was completed using a procedure previously reported by Tilset.8 To a solution of chromocene (0.3551 g, 1.949 mmol) in anhydrous THF (20 mL), a suspension of Dpp-NHC•HCl (0.8336 g, 1.960 mmol) in THF (27 mL) was added. The solution went from dark red to bright purple and was left to stir overnight. The solvent was removed in vacuo and the bright purple solid was redissolved in 1:1 ether:hexanes (15 mL) solution and filtered through Celite in a pipette. This resulting solution was a dark purple and was placed in the freezer (-35°C) overnight. The next day, bright purple crystals were isolated (655.9 mg, 56%). LF38 CpCr(Dpp-NHC)Me To a purple solution of CpCr(Dpp-NHC)Cl (0.2076 g, 0.3836 mmol) in anhydrous THF (10 mL), 3.0 M MeMgI (0.13 mL) was added. The solution went from bright purple to dark brown and was left to stir overnight. The solvent was removed in vacuo and the dark brown solid was redissolved in hexanes (10 mL) solution and filtered through Celite in a pipette. This resulting solution was a dark brown and was placed in the freezer (-35°C) overnight. The next day, dark brown crystals were isolated (45.2 mg, 23%). LF24 CpCr(Dpp-NHC)Ph To a purple solution of CpCr(Dpp-NHC)Cl (0.2076 g, 0.3836 mmol) in anhydrous THF (10 mL), 2.0 M PhMgI (0.11 mL) was added. The solution went from bright purple to dark brown and was left to stir overnight. The solvent was removed in vacuo and the dark brown solid was redissolved in hexanes (10 mL) solution and filtered through Celite in a pipette. This resulting solution was a dark brown and was placed in the freezer (-35°C) overnight. The next day, dark brown crystals were isolated (74.5 mg, 65%). Chemistry 449 Thesis – Laura K. Fairburn 29 LF30 Mes/Cy-NHC•HCl A solution of 2,4,6-trimethylaniline (1.20 mL, 10 mmol), cyclohexylamine (1.40 mL, 10 mmol), and acetic acid (5.1 mL) was heated to 40°C for 5 minutes. A second solution of glyoxal (40% wt, 1.20 mL, 10 mmol), formaldehyde (0.74 mL, 10 mmol) and acetic acid (5.1 mL) was heated for 40°C for 5 minutes. The second mixture was added to the first mixture, then stirred at 40°C for 10 more minutes. The solution was then cooled down to room temperature, extracted with DCM (100 mL), washed with water (200 mL) then brine (2 x 100 mL). The extract was dried over MgSO4 and volatiles were evaporated in vacuo resulting in a white solid. Ethyl acetate (20 mL) was added and suspension was heated for 5 min. The solution was cooled to 0°C. A white solid was isolated using vacuum filtration then washed with ethyl acetate (10 mL) (0.94986 g, 31% yield). LF27 CpCr(Mes/Cy-NHC)Cl This was completed using a procedure previously reported by Tilset.8 To a solution of chromocene (77.6 mg, 0.4259 mmol) in anhydrous THF (5 mL), a suspension of Mes/Cy-NHC•HCl (0.1307 g, 0.4287 mmol) in THF (15 mL) was added. The solution went from dark red to bright purple and was left to stir overnight. The solvent was removed in vacuo and the bright purple solid was redissolved in THF (8 mL) solution and filtered through Celite in a pipette. This resulting solution was a dark purple and was placed in the freezer (-35°C) overnight. The next day, bright purple crystals were isolated (54.7 g, 16%). Typical procedure for the CpCr(NHC)Cl homocoupling reactions (dark) A solution of p-tolylmagnesium bromide (0.5M in Et2O, 0.9 mL, 0.45 mmol) was measured out into a 20 mL vial and its solvent was evaporated in vacuo. A suspension of the Chemistry 449 Thesis – Laura K. Fairburn 30 CpCr(NHC)Cl (10% mol, 0.045 mmol) in THF (1.5 mL) was added. (See Table 5 for specific compounds and masses). 1,2-dichlorobutane (56.4 mg, 0.45 mmol) was then added to the solution. The vial was wrapped in tin foil, and the solution was left to stir for 20 h. The solution was concentrated in vacuo and removed from the glove box. The organic product was extracted using hexanes and filtered through silica in a pipette. The solution was then evaporated in vacuo, resulting in fine white crystals. Cr source Amount Percent Yield CpCr(Dpp-NHC)Cl 12.7 mg 38% CpCr(Mes/Cy-NHC)Cl 21.3 mg 42% Table 5. Amounts of CpCr(NHC)Cl added for each experiment Typical procedure for the CpCr(NHC)Cl homocoupling reactions (light) A solution of p-tolylmagnesium bromide (0.5 M in Et2O, 0.9 mL, 0.45 mmol) was measured out into a 20 mL vial and its solvent was evaporated in vacuo. A suspension of the CpCr(NHC)Cl (10% mol, 0.045 mmol) in THF (1.5 mL) was added. (See Table 6 for specific compounds and masses). 1,2-dichlorobutane (56.4 mg, 0.45 mmol) was then added to the solution. The solution was left to stir for 20 h. The solution was concentrated in vacuo and removed from the glove box. The organic product was extracted using hexanes and filtered through silica in a pipette. The solution was then evaporated in vacuo, resulting in fine white crystals. Cr source Amount Percent Yield CpCr(Dpp-NHC)Cl 26.0 mg 81% CpCr(Mes/Cy-NHC)Cl 19.1 mg 47% Table 6. Amounts of CpCr(NHC)Cl added for each experiment Typical procedure for the CpCrCl2(THF) + NHC homocoupling reactions (dark) A solution of p-tolylmagnesium bromide (0.5 M in Et2O, 0.9 mL, 0.45 mmol) was measured out into a 20 mL vial and its solvent was evaporated in vacuo. A suspension of the NHC (10% mol, 0.045 mmol) in THF (1.5 mL) was added to the CpCrCl2(THF), then added to Chemistry 449 Thesis – Laura K. Fairburn 31 the vial containing the p-tolylmagnesium bromide. (See Table 7 for specific compounds and masses). 1,2-dichlorobutane (varied between experiment) was then added to the solution. The vial was wrapped in tin foil, and the solution was left to stir for 20 h. The solution was concentrated in vacuo and removed from the glove box. The organic product was extracted using hexanes and filtered through silica in a pipette. The solution was then evaporated in vacuo, resulting in fine white crystals. Cr source Amount Amount of 1,2-dichlorobutane Percent Yield CpCrCl2(THF) + - 11.8 mg 55.3 mg 43% CpCrCl2(THF) + Dpp-NHC•HCl 12.3 mg 23.0 mg 58.4 mg 38% CpCrCl2(THF) + Free Dpp-NHC 11.4 mg 18.7 mg 57.4 mg 20% Table 7. Amount of CpCrCl2(THF), NHC ligand and 1,2-dichlorobutane added for each experiment Typical procedure for the CpCrCl2(THF) + NHC homocoupling reactions (light) A solution of p-tolylmagnesium bromide (0.5 M in Et2O, 0.9 mL, 0.45 mmol) was measured out into a 20 mL vial and its solvent was evaporated in vacuo. A suspension of the NHC (10% mol, 0.045 mmol) in THF (1.5 mL) was added to the CpCrCl2(THF), then added to the vial containing the p-tolylmagnesium bromide. (See Table 8 for specific compounds and masses). 1,2-dichlorobutane (varied between experiment) was then added to the solution. The solution was left to stir for 20 h. The solution was concentrated in vacuo and removed from the glove box. The organic product was extracted using hexanes and filtered through silica in a pipette. The solution was then evaporated in vacuo, resulting in fine white crystals. Chemistry 449 Thesis – Laura K. Fairburn 32 Cr source Amount Amount of 1,2-dichlorobutane Percent Yield CpCrCl2(THF) + - 12.5 mg 56.0 mg 29% CpCrCl2(THF) + Dpp-NHC•HCl 11.8 mg 17.6 mg 54.4 mg 27% CpCrCl2(THF) + Mes/Cy-NHC•HCl 11.8 mg 15.2 mg 65.0 mg 25% CpCrCl2(THF) + Free Dpp-NHC 12.4 mg 17.4 mg 58.3 mg 23% CpCrCl2(THF) + Mes-NHC•HCl 11.1 mg 16.8 mg 61.7 mg 37% CpCrCl2(THF) + Dpp-NHC.HBF4 11.8 mg 21.0 mg 54.2 mg 33% Table 8. Amount of CpCrCl2(THF), NHC ligand (in bold) and 1,2-dichlorobutane added for each experiment Typical procedure for the Cp2Cr + NHC homocoupling reactions A solution of p-tolylmagnesium bromide (0.5 M in Et2O, 0.9 mL, 0.45 mmol) was measured out into a 20 mL vial and its solvent was evaporated in vacuo. A suspension of the NHC (10% mol, 0.045 mmol) in THF (1.5 mL) was added to the Cp2Cr, and then left to stir for 22 h. The solution was either pumped dry or directly added to the 20 mL vial containing the p-tolylmagnesium bromide. (See Table 9 for specific compounds and masses). 1,2-dichlorobutane (varied between experiment) was then added to the solution. The vial was wrapped in tin foil, and the solution was left to stir for 20 h. The solution was concentrated in vacuo and removed from the glove box. The organic product was extracted using hexanes and filtered through silica in a pipette. The solution was then evaporated in vacuo, resulting in fine white crystals. Cr source Amount Amount of 1,2-dichlorobutane Percent Yield Cp2Cr + Dpp-NHC•HCl 8.2 mg 20.7 mg 56.4 mg 23% Cp2Cr + Mes-NHC•HCl 9.3 mg 15.7 mg 58.9 mg 29% Cp2Cr + Mes/Cy-NHC•HCl 8.2 mg 13.7 mg 52.6 mg 22% Table 9. Amount of Cp2Cr, NHC ligand (in bold) and 1,2-dichlorobutane added for each experiment Chemistry 449 Thesis – Laura K. Fairburn 33 Typical procedure for the Cp2Cr + NHC homocoupling in situ reactions A solution of p-tolylmagnesium bromide (0.5 M in Et2O, 0.9 mL, 0.45 mmol) was measured out into a 20 mL vial and its solvent was evaporated in vacuo. A suspension of the Dpp-NHC•HCl (10% mol, 0.045 mmol) in THF (1.5 mL) was added to the Cp2Cr, and then left to stir for 22 h. The solution was then pumped dry then added using 1.5 mL or immediately added to the vial containing the p-tolylmagnesium bromide. (See Table 10 for specific masses and method). 1,2-dichlorobutane (50 µL, 0.45 mmol) was then added to the solution. The vial was wrapped in tin foil, and the solution was left to stir for 20 h. The solution was concentrated in vacuo and removed from the glove box. The organic product was extracted using hexanes and filtered through silica in a pipette. The solution was then evaporated in vacuo, resulting in fine white crystals. Cr source Amount Percent Yield Pumped Dry? Cp2Cr + Dpp-NHC•HCl 8.3 mg 21.7 mg 49% Yes Cp2Cr + Dpp-NHC•HCl 10.0 mg 23.8 mg 36% No Table 10. Amount of Cp2Cr, NHC ligand (in bold) and 1,2-dichlorobutane added for each experiment Typical procedure for the Cr-catalyzed homocoupling control reactions A solution of p-tolylmagnesium bromide (0.5 M in Et2O, 0.9 mL, 0.45 mmol) was measured out into a 20 mL vial and its solvent was evaporated in vacuo. A suspension of a chromium source (10% mol, 0.045 mmol) in THF (1.5 mL) was added. (See Table 11 for specific compounds and masses). 1,2-dichlorobutane (varied between experiment) was then added to the solution. The solution was either wrapped in tin foil or completed in the presence of ambient light, then left to stir for 20 h. The solution was concentrated in vacuo and removed from the glove box. The organic product was extracted using hexanes and filtered through silica in a pipette. The solution was then evaporated in vacuo, resulting in fine white crystals. Chemistry 449 Thesis – Laura K. Fairburn 34 Cr source Amount Amount of 1,2-dichlorobutane Dark/ Ambient Light Percent Yield Cp2Cr 9.0 mg 57.4 mg Dark 17% 8.8 mg 50 µL Ambient light 20% CrCl2 7.3 mg 54.6 mg Dark 69% 7.2 mg 50 µL Ambient light 72% CrCl3 8.9 mg 51.7 mg Dark 79% 8.1 mg 50 µL Ambient light 86% CrCl3(THF)3 19.1 mg 60.3 mg Dark 36% 18.0 mg 50 µL Ambient light 65% Table 11. Amount of Cr source and 1,2-dichlorobutane added for each experiment Chemistry 449 Thesis – Laura K. Fairburn 35 Conclusion The intention of this project was to produce CpCr(NHC)R complexes for the step-by-step study of a proposed cross coupling reaction, similar to that of Negishi’s. Unfortunately, due to the difficulty of characterizing the alkylated CpCr(NHC)Ph complex, focus shifted to optimization of the NHC ligands, and Cr(II) and Cr(III) sources for homocoupling. Through the development of different NHC ligands, the study of their effects on the reactivity of the catalyst was completed. With more sterically bulky substituted NHC ligands, dissociation through dilution and susceptibility to photolytic decomposition was observed. Through a variety of different experiments, it was determined that isolated catalysts resulted in greater yields than in situ generated catalysts. As a response to the ligand dissociation observed by the Dpp-NHC substituted complex, a new unsymmetrical CpCr(Mes/Cy-NHC)Cl complex was synthesized and shown to have less susceptibility to catalytic decomposition from ambient light. Chemistry 449 Thesis – Laura K. Fairburn 36 References   1 Lei, A.; Chao, L.; Zhang, H.; Shi, W. Chem. Rev. 2011, 111, 1780-1824. 2 Bennet, G. M.; Turner, E. E. J. Chem. Soc. Trans., 1914, 105, 1057-1062 3 (a) Uhlig, E. Organometallics, 1993, 12, 4751-4756 (b) Seyferth, D. Organometallics, 2002, 21, 2800-2820 4 Knochel, P.; Steib, A. S.; Kuzmina, O. M.; Fernandez, S.; Flubacher, D. J. Am. Chem. Soc. 2013, 135, 15346-15349 5Benhamou, L.; Chardon, E.; Lavigne, G.; Bellemin-Laponnaz, S.; Cesar, V. Chem. Rev. 2011, 111, 2705–2733 6 Kühn, F.E.; Herrmann, W.A.; Riener, K.; Haslinger, S.; Raba, A.; Högerl, M.P.; Cokoja, M. Chem. Rev. 2014, DOI: 10.1021/cr4006439. 7 Jolly, P.W.; Göhre, J.; Döhring, A.; Rust, J.; Verhovnik, G.P.J. Organometallics, 2000, 19, 388-402 8 Voges, M.H.; Rømming, C.; Tilset, M. Organometallics 1999, 18, 529-533 9 Nakamura, M.; Hatakeyama, T. J. Am. Chem. Soc. 2007, 129, 9844-9845 10 Hayashi, T.; Nagano, T. Org. Lett. 2005, 7, 491-493 11 Zhou, W; Therrien, J.A.; Wence, D.L.K.; Yallits, E.N.; Conway, J.L.; Patrick, B.O.; Smith, K.M. Dalton Trans., 2011, 40, 337-339 12 Nolan, S.P.; Bantreil, X. Nat. Protoc. 2011, 6, 69-77 13 Köhler, F.H.; Metz, B; Strauss, W. Inorg. Chem. 1995, 34, 4402-4413 14 Theopold, K.H.; Heintz, R.A.; Ostrander, R.L.; Rheingold, A.L., J. Am. Chem. Soc. 1994, 116, 11387-11396 15 Baslé, O.; Mauduit, M.; Queval, P.; Jahier, C.; Rouen, M.; Artur, I.; Legeay, J.C.; Falivene, L.; Toupet, L.; Crévisy, C.; Cavallo, L. Angew. Chem. Int. Ed. 2013, 52, 14103-14107 16 Fürstner, A.; Shi, N. J. Am. Chem. Soc. 1996, 118, 12349-12357 17 Arduengo, AJ; Krafczyk, R; Schmutzler, R. Tetrahedron. 1999, 55, 14523-14524 Chemistry 449 Thesis – Laura K. Fairburn 37 Appendix    –  Crystallographic  Data  for  CpCr(Mes/Cy-­‐NHC)Cl  Experimental Data Collection A purple, block crystal of C23H29N2CrCl, having approximate dimensions of 0.04 x 0.06 x 0.075 mm was mounted on a glass fiber. All measurements were made on a Bruker APEX DUO diffractometer with cross-coupled multilayer optics Cu-Kα radiation.. The data were collected at a temperature of -183 + 2oC to a maximum 2q value of 100.8o. Data were collected in a series of φ and w scans in 3o oscillations using 90.0- and 180.0-second exposures. The crystal-to-detector distance was 49.88 mm. Data Reduction Of the 7963 reflections that were collected, 2522 were unique (Rint = 0.220); equivalent reflections were merged. Data were collected and integrated using the Bruker SAINT1 software package. The linear absorption coefficient, m, for Cu-Ka radiation is 55.61 cm-1. Data were corrected for absorption effects using the multi-scan technique (SADABS2), with minimum and maximum transmission coefficients of 0.393 and 0.800, respectively. The data were corrected for Lorentz and polarization effects. Structure Solution and Refinement The structure was solved by direct methods3. Only relatively low resolution data was collected due to the exceedingly small crystals available to us. Additionally, the material crystallizes with disorder in the orientation of the cyclohexyl substituent. The disorder was modelled in two orientations with roughly equal populations. Restraints were employed to maintain reasonable bond lengths in both disordered fragments. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in calculated positions. The final cycle of full-matrix least-squares refinement4 on F2 was based on 2522 reflections and 296 variable parameters and converged (largest parameter shift was 0.00 times its esd) with unweighted and weighted agreement factors of: R1 = S ||Fo| - |Fc|| / S |Fo| = 0.200 wR2 = [ S ( w (Fo2 - Fc2)2 )/ S w(Fo2)2]1/2 = 0.297 The standard deviation of an observation of unit weight5 was 0.98. The weighting scheme was based on counting statistics. The maximum and minimum peaks on the final difference Fourier map corresponded to 0.59 and -0.68 e-/Å3, respectively. Neutral atom scattering factors were taken from Cromer and Waber6. Anomalous dispersion effects were included in Fcalc7; the values for Df' and Df" were those of Creagh and McAuley8. The values for the mass attenuation coefficients are those of Creagh and Hubbell9. All refinements were performed using the SHELXL-201310 via the Olex211 interface. References (1) SAINT. Version 8.34A. Bruker AXS Inc., Madison, Wisconsin, USA. (1997-2013). (2) SADABS. Sheldrick, G. M.; Acta Cryst., A64, 112-122 (2008). (3) SIR97 - Altomare A., Burla M.C., Camalli M., Cascarano G.L., Giacovazzo C. , Guagliardi A., Moliterni Chemistry 449 Thesis – Laura K. Fairburn 38 A.G.G., Polidori G.,Spagna R. J. Appl. Cryst. 1999, 32, 115-119. (4) Least Squares function minimized: Sw(Fo2-Fc2)2 (5) Standard deviation of an observation of unit weight: [Sw(Fo2-Fc2)2/(No-Nv)]1/2 where: No = number of observations Nv = number of variables (6) Cromer, D. T. & Waber, J. T.; "International Tables for X-ray Crystallography", Vol. IV, The Kynoch Press, Birmingham, England, Table 2.2 A 1974. (7) Ibers, J. A. & Hamilton, W. C.; Acta Crystallogr., 1964, 17, 781. (8) Creagh, D. C. & McAuley, W.J .; "International Tables for Crystallography", Vol C, (A.J.C. Wilson, ed.), Kluwer Academic Publishers, Boston, Table 4.2.6.8, pages 219-222 (1992). (9) Creagh, D. C. & Hubbell, J.H..; "International Tables for Crystallography", Vol C, (A.J.C. Wilson, ed.), Kluwer Academic Publishers, Boston, Table 4.2.4.3, pages 200-206 (1992). (10) SHELXL-2013, Sheldrick, G.M, Acta Crystallogr., Sect. A64, 112-122 (2008)). (11) Olex2 – V1.2.5 – Dolomanov, O.V.; Bourhis, L.J.;Gildea, R.J.;Howard, J.A.K.;Puschmann, H., J. Appl. Cryst., 42, 339-341 (2009). EXPERIMENTAL DETAILS A. Crystal Data Empirical Formula C23H29N2CrCl Formula Weight 420.93 Crystal Colour, Habit purple, block Crystal Dimensions 0.04 x 0.06 x 0.075 mm Crystal System monoclinic Lattice Type Primitive Lattice Parameters a = 8.537(3) Å b = 21.374(7) Å c = 12.182(4) Å a = 90o b = 104.09(3)o g = 90o V = 2155.8(13) Å3 Space Group P21/c (#14) Z value 4 Dcalc 1.297 g/cm3 F000 888.00 m(Cu-Ka) 55.61 cm-1 Chemistry 449 Thesis – Laura K. Fairburn 39 B. Intensity Measurements Diffractometer Bruker APEX DUO Radiation Cu-Ka (l = 1.54178 Å) Data Images 892 exposures @ 90.0 and 180.0 seconds Detector Position 49.88 mm 2qmax 100.8o No. of Reflections Measured Total: 7963 Unique: 2522 (Rint = 0.220) Corrections Absorption (Tmin = 0.393, Tmax= 0.800) Lorentz-polarization C. Structure Solution and Refinement Structure Solution Direct Methods (SIR97) Refinement Full-matrix least-squares on F2 Function Minimized S w (Fo2 - Fc2)2 Least Squares Weights w=1/(s2(Fo2)+(0.1323P) 2+ 0.0000P) Anomalous Dispersion All non-hydrogen atoms No. Observations (I>0.00s(I)) 2522 No. Variables 296 Reflection/Parameter Ratio 8.52 Residuals (refined on F2, all data): R1; wR2 0.200; 0.297 Goodness of Fit Indicator 0.98 No. Observations (I>2.00s(I)) 1028 Residuals (refined on F2): R1; wR2 0.093; 0.219 Max Shift/Error in Final Cycle 0.00 Maximum peak in Final Diff. Map 0.59 e-/Å3 Minimum peak in Final Diff. Map -0.68 e-/Å3 Chemistry 449 Thesis – Laura K. Fairburn 40 Table A1. Atomic coordinates (x 10^4) and equivalent isotropic displacement parameters (Å^2 x 10^3) for CpCr(Mes/Cy-NHC)Cl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. ________________________________________________________________ x y z U(eq) occ ________________________________________________________________ Cr(1) -71(3) 6373(1) 2512(2) 46(1) Cl(1) -585(4) 6908(2) 4037(3) 47(1) N(1) 3385(13) 5827(5) 3314(9) 47(3) N(2) 3522(13) 6818(5) 3291(9) 42(3) C(1) 2408(16) 6337(6) 3043(11) 43(3) C(2) 4980(18) 5975(6) 3674(13) 61(5) C(3) 5047(17) 6604(6) 3655(13) 52(4) C(4) 2802(16) 5175(6) 3217(12) 43(3) C(5) 2250(16) 4940(7) 4106(12) 48(4) C(6) 1784(16) 4296(6) 4034(11) 45(4) C(7) 1966(18) 3919(7) 3153(12) 51(4) C(8) 2451(16) 4185(6) 2267(12) 44(3) C(9) 2930(16) 4832(6) 2304(12) 45(3) C(10) 2158(18) 5341(7) 5140(11) 59(4) C(11) 1581(19) 3225(6) 3135(13) 65(5) C(12) 3492(18) 5097(6) 1320(11) 54(4) C(13) 3010(50) 7512(15) 3300(20) 40(4) 0.55(3) C(13B) 3050(60) 7461(19) 3000(30) 40(4) 0.45(3) C(14) 3920(40) 7924(11) 2610(30) 45(7) 0.55(3) C(14B) 4130(50) 7744(13) 2270(30) 39(8) 0.45(3) C(15) 3300(40) 8605(11) 2650(20) 55(8) 0.55(3) C(15B) 3550(50) 8423(12) 1980(30) 69(10) 0.45(3) C(16) 3470(40) 8817(12) 3890(20) 62(8) 0.55(3) C(16B) 3640(60) 8825(16) 3050(30) 75(12) 0.45(3) C(17) 2610(30) 8375(10) 4570(30) 58(8) 0.55(3) C(17B) 2710(50) 8513(13) 3840(30) 56(9) 0.45(3) C(18) 3160(50) 7684(11) 4560(20) 57(8) 0.55(3) C(18B) 3220(50) 7824(13) 4120(30) 46(8) 0.45(3) C(19) -469(19) 5994(8) 720(13) 70(4) C(20) -1467(18) 6509(8) 677(14) 68(4) C(21) -2588(19) 6368(7) 1312(13) 62(4) C(22) -2282(18) 5734(7) 1705(13) 66(4) C(23) -960(20) 5520(9) 1333(14) 80(4) ________________________________________________________________ Chemistry 449 Thesis – Laura K. Fairburn 41 Table A2. Bond lengths [Å] and angles [deg] for CpCr(Mes/Cy-NHC)Cl. _____________________________________________________________ Cr(1)-C(1) 2.059(14) Cr(1)-C(19) 2.274(14) Cr(1)-C(20) 2.281(16) Cr(1)-C(21) 2.285(15) Cr(1)-Cl(1) 2.313(4) Cr(1)-C(23) 2.331(16) Cr(1)-C(22) 2.342(14) N(1)-C(2) 1.362(16) N(1)-C(1) 1.363(16) N(1)-C(4) 1.474(16) N(2)-C(3) 1.349(15) N(2)-C(1) 1.384(15) N(2)-C(13B) 1.45(5) N(2)-C(13) 1.55(4) C(2)-C(3) 1.345(17) C(2)-H(2) 0.9500 C(3)-H(3) 0.9500 C(4)-C(9) 1.360(17) C(4)-C(5) 1.377(18) C(5)-C(6) 1.429(17) C(5)-C(10) 1.540(17) C(6)-C(7) 1.382(17) C(6)-H(6) 0.9500 C(7)-C(8) 1.370(17) C(7)-C(11) 1.519(18) C(8)-C(9) 1.440(17) C(8)-H(8) 0.9500 C(9)-C(12) 1.506(16) C(10)-H(10A) 0.9800 C(10)-H(10B) 0.9800 C(10)-H(10C) 0.9800 C(11)-H(11A) 0.9800 C(11)-H(11B) 0.9800 C(11)-H(11C) 0.9800 C(12)-H(12A) 0.9800 C(12)-H(12B) 0.9800 C(12)-H(12C) 0.9800 C(13)-C(14) 1.547(9) C(13)-C(18) 1.551(12) C(13)-H(13) 1.0000 C(13B)-C(18B) 1.547(18) C(13B)-C(14B) 1.548(18) C(13B)-H(13B) 1.0000 C(14)-C(15) 1.553(12) C(14)-H(14A) 0.9900 C(14)-H(14B) 0.9900 C(14B)-C(15B) 1.549(18) C(14B)-H(14C) 0.9900 C(14B)-H(14D) 0.9900 C(15)-C(16) 1.551(12) C(15)-H(15A) 0.9900 C(15)-H(15B) 0.9900 C(15B)-C(16B) 1.548(18) C(15B)-H(15C) 0.9900 C(15B)-H(15D) 0.9900 C(16)-C(17) 1.551(12) C(16)-H(16A) 0.9900 C(16)-H(16B) 0.9900 Chemistry 449 Thesis – Laura K. Fairburn 42 C(16B)-C(17B) 1.546(18) C(16B)-H(16C) 0.9900 C(16B)-H(16D) 0.9900 C(17)-C(18) 1.554(12) C(17)-H(17C) 0.9900 C(17)-H(17D) 0.9900 C(17B)-C(18B) 1.551(18) C(17B)-H(17A) 0.9900 C(17B)-H(17B) 0.9900 C(18)-H(18A) 0.9900 C(18)-H(18B) 0.9900 C(18B)-H(18C) 0.9900 C(18B)-H(18D) 0.9900 C(19)-C(20) 1.38(2) C(19)-C(23) 1.39(2) C(19)-H(19) 0.9500 C(20)-C(21) 1.401(19) C(20)-H(20) 0.9500 C(21)-C(22) 1.44(2) C(21)-H(21) 0.9500 C(22)-C(23) 1.390(19) C(22)-H(22) 0.9500 C(23)-H(23) 0.9500 C(1)-Cr(1)-C(19) 101.0(6) C(1)-Cr(1)-C(20) 124.4(6) C(19)-Cr(1)-C(20) 35.4(5) C(1)-Cr(1)-C(21) 159.3(6) C(19)-Cr(1)-C(21) 59.2(6) C(20)-Cr(1)-C(21) 35.7(5) C(1)-Cr(1)-Cl(1) 98.5(4) C(19)-Cr(1)-Cl(1) 159.0(4) C(20)-Cr(1)-Cl(1) 124.6(4) C(21)-Cr(1)-Cl(1) 100.6(4) C(1)-Cr(1)-C(23) 108.7(6) C(19)-Cr(1)-C(23) 35.0(5) C(20)-Cr(1)-C(23) 58.8(6) C(21)-Cr(1)-C(23) 59.2(6) Cl(1)-Cr(1)-C(23) 141.7(5) C(1)-Cr(1)-C(22) 140.5(5) C(19)-Cr(1)-C(22) 58.2(6) C(20)-Cr(1)-C(22) 59.2(6) C(21)-Cr(1)-C(22) 36.2(5) Cl(1)-Cr(1)-C(22) 109.5(4) C(23)-Cr(1)-C(22) 34.6(5) C(2)-N(1)-C(1) 113.3(12) C(2)-N(1)-C(4) 122.5(11) C(1)-N(1)-C(4) 124.2(11) C(3)-N(2)-C(1) 112.0(11) C(3)-N(2)-C(13B) 126(2) C(1)-N(2)-C(13B) 121(2) C(3)-N(2)-C(13) 125.0(18) C(1)-N(2)-C(13) 122.4(18) N(1)-C(1)-N(2) 101.2(11) N(1)-C(1)-Cr(1) 128.9(10) N(2)-C(1)-Cr(1) 129.8(10) C(3)-C(2)-N(1) 105.7(13) C(3)-C(2)-H(2) 127.2 N(1)-C(2)-H(2) 127.2 C(2)-C(3)-N(2) 107.7(13) C(2)-C(3)-H(3) 126.2 N(2)-C(3)-H(3) 126.2 C(9)-C(4)-C(5) 124.0(13) Chemistry 449 Thesis – Laura K. Fairburn 43 C(9)-C(4)-N(1) 118.8(13) C(5)-C(4)-N(1) 117.1(12) C(4)-C(5)-C(6) 116.5(13) C(4)-C(5)-C(10) 122.4(13) C(6)-C(5)-C(10) 121.1(13) C(7)-C(6)-C(5) 121.9(14) C(7)-C(6)-H(6) 119.1 C(5)-C(6)-H(6) 119.1 C(8)-C(7)-C(6) 118.9(14) C(8)-C(7)-C(11) 120.0(13) C(6)-C(7)-C(11) 121.1(13) C(7)-C(8)-C(9) 120.8(13) C(7)-C(8)-H(8) 119.6 C(9)-C(8)-H(8) 119.6 C(4)-C(9)-C(8) 117.7(13) C(4)-C(9)-C(12) 123.6(13) C(8)-C(9)-C(12) 118.7(12) C(5)-C(10)-H(10A) 109.5 C(5)-C(10)-H(10B) 109.5 H(10A)-C(10)-H(10B) 109.5 C(5)-C(10)-H(10C) 109.5 H(10A)-C(10)-H(10C) 109.5 H(10B)-C(10)-H(10C) 109.5 C(7)-C(11)-H(11A) 109.5 C(7)-C(11)-H(11B) 109.5 H(11A)-C(11)-H(11B) 109.5 C(7)-C(11)-H(11C) 109.5 H(11A)-C(11)-H(11C) 109.5 H(11B)-C(11)-H(11C) 109.5 C(9)-C(12)-H(12A) 109.5 C(9)-C(12)-H(12B) 109.5 H(12A)-C(12)-H(12B) 109.5 C(9)-C(12)-H(12C) 109.5 H(12A)-C(12)-H(12C) 109.5 H(12B)-C(12)-H(12C) 109.5 N(2)-C(13)-C(14) 111(2) N(2)-C(13)-C(18) 106(2) C(14)-C(13)-C(18) 118(2) N(2)-C(13)-H(13) 106.9 C(14)-C(13)-H(13) 106.9 C(18)-C(13)-H(13) 106.9 N(2)-C(13B)-C(18B) 107(3) N(2)-C(13B)-C(14B) 110(3) C(18B)-C(13B)-C(14B) 112(3) N(2)-C(13B)-H(13B) 109.2 C(18B)-C(13B)-H(13B) 109.2 C(14B)-C(13B)-H(13B) 109.2 C(13)-C(14)-C(15) 107(2) C(13)-C(14)-H(14A) 110.2 C(15)-C(14)-H(14A) 110.2 C(13)-C(14)-H(14B) 110.2 C(15)-C(14)-H(14B) 110.2 H(14A)-C(14)-H(14B) 108.5 C(13B)-C(14B)-C(15B) 107(3) C(13B)-C(14B)-H(14C) 110.2 C(15B)-C(14B)-H(14C) 110.2 C(13B)-C(14B)-H(14D) 110.2 C(15B)-C(14B)-H(14D) 110.2 H(14C)-C(14B)-H(14D) 108.5 C(16)-C(15)-C(14) 111(2) C(16)-C(15)-H(15A) 109.5 C(14)-C(15)-H(15A) 109.5 Chemistry 449 Thesis – Laura K. Fairburn 44 C(16)-C(15)-H(15B) 109.5 C(14)-C(15)-H(15B) 109.5 H(15A)-C(15)-H(15B) 108.1 C(16B)-C(15B)-C(14B) 112(3) C(16B)-C(15B)-H(15C) 109.2 C(14B)-C(15B)-H(15C) 109.2 C(16B)-C(15B)-H(15D) 109.2 C(14B)-C(15B)-H(15D) 109.2 H(15C)-C(15B)-H(15D) 107.9 C(15)-C(16)-C(17) 113(2) C(15)-C(16)-H(16A) 108.9 C(17)-C(16)-H(16A) 108.9 C(15)-C(16)-H(16B) 108.9 C(17)-C(16)-H(16B) 108.9 H(16A)-C(16)-H(16B) 107.7 C(17B)-C(16B)-C(15B) 111(3) C(17B)-C(16B)-H(16C) 109.4 C(15B)-C(16B)-H(16C) 109.4 C(17B)-C(16B)-H(16D) 109.4 C(15B)-C(16B)-H(16D) 109.4 H(16C)-C(16B)-H(16D) 108.0 C(16)-C(17)-C(18) 113(2) C(16)-C(17)-H(17C) 109.0 C(18)-C(17)-H(17C) 109.0 C(16)-C(17)-H(17D) 109.0 C(18)-C(17)-H(17D) 109.0 H(17C)-C(17)-H(17D) 107.8 C(16B)-C(17B)-C(18B) 113(3) C(16B)-C(17B)-H(17A) 109.0 C(18B)-C(17B)-H(17A) 109.0 C(16B)-C(17B)-H(17B) 109.0 C(18B)-C(17B)-H(17B) 109.0 H(17A)-C(17B)-H(17B) 107.8 C(13)-C(18)-C(17) 106(2) C(13)-C(18)-H(18A) 110.5 C(17)-C(18)-H(18A) 110.5 C(13)-C(18)-H(18B) 110.5 C(17)-C(18)-H(18B) 110.5 H(18A)-C(18)-H(18B) 108.7 C(13B)-C(18B)-C(17B) 109(3) C(13B)-C(18B)-H(18C) 109.9 C(17B)-C(18B)-H(18C) 109.9 C(13B)-C(18B)-H(18D) 109.9 C(17B)-C(18B)-H(18D) 109.9 H(18C)-C(18B)-H(18D) 108.3 C(20)-C(19)-C(23) 109.7(17) C(20)-C(19)-Cr(1) 72.6(9) C(23)-C(19)-Cr(1) 74.7(10) C(20)-C(19)-H(19) 125.2 C(23)-C(19)-H(19) 125.2 Cr(1)-C(19)-H(19) 119.2 C(19)-C(20)-C(21) 107.8(17) C(19)-C(20)-Cr(1) 72.0(9) C(21)-C(20)-Cr(1) 72.3(9) C(19)-C(20)-H(20) 126.1 C(21)-C(20)-H(20) 126.1 Cr(1)-C(20)-H(20) 121.3 C(20)-C(21)-C(22) 107.0(15) C(20)-C(21)-Cr(1) 72.0(9) C(22)-C(21)-Cr(1) 74.1(9) C(20)-C(21)-H(21) 126.5 C(22)-C(21)-H(21) 126.5 Chemistry 449 Thesis – Laura K. Fairburn 45 Cr(1)-C(21)-H(21) 119.4 C(23)-C(22)-C(21) 107.4(16) C(23)-C(22)-Cr(1) 72.2(9) C(21)-C(22)-Cr(1) 69.7(8) C(23)-C(22)-H(22) 126.3 C(21)-C(22)-H(22) 126.3 Cr(1)-C(22)-H(22) 123.4 C(19)-C(23)-C(22) 108.1(17) C(19)-C(23)-Cr(1) 70.3(9) C(22)-C(23)-Cr(1) 73.1(9) C(19)-C(23)-H(23) 125.9 C(22)-C(23)-H(23) 125.9 Cr(1)-C(23)-H(23) 122.3 _____________________________________________________________ Symmetry transformations used to generate equivalent atoms: Table A3. Anisotropic displacement parameters (Å^2 x 10^3) for CpCr(Mes/Cy-NHC)Cl. The anisotropic displacement factor exponent takes the form: -2 pi^2 [ h^2 a*^2 U11 + ... + 2 h k a* b* U12] _______________________________________________________________________ U11 U22 U33 U23 U13 U12 _______________________________________________________________________ Cr(1) 46(2) 45(2) 51(2) -3(1) 20(1) -2(1) Cl(1) 49(2) 49(2) 50(2) -1(2) 22(2) -4(2) N(1) 44(5) 42(4) 56(7) -7(4) 18(5) 0(4) N(2) 35(5) 41(4) 51(7) -5(4) 13(5) 2(4) C(1) 42(5) 42(5) 47(8) -3(5) 17(4) -3(4) C(2) 45(6) 34(6) 101(12) -4(6) 14(6) 5(5) C(3) 33(6) 31(5) 91(12) -10(6) 10(6) 0(4) C(4) 45(8) 37(5) 48(6) -5(4) 14(5) 1(5) C(5) 51(9) 43(6) 53(7) -2(5) 17(6) 3(6) C(6) 45(9) 45(6) 46(7) 1(5) 14(6) 3(5) C(7) 62(10) 49(6) 44(7) 0(5) 15(7) -1(6) C(8) 55(9) 35(5) 42(7) -3(5) 15(6) 4(5) C(9) 48(9) 41(6) 46(6) -4(4) 13(6) 2(5) C(10) 68(11) 55(8) 58(8) -5(6) 21(7) 16(8) C(11) 83(12) 49(7) 68(10) -3(6) 27(9) -5(7) C(12) 72(11) 43(8) 52(8) -1(6) 22(7) 2(7) C(13) 29(7) 40(5) 51(10) -4(5) 11(7) 1(4) C(13B) 29(7) 40(5) 51(10) -4(5) 11(7) 1(4) C(14) 35(15) 50(9) 47(13) -2(8) 6(11) -5(8) C(14B) 33(16) 32(10) 53(15) -8(9) 12(13) 4(9) C(15) 57(18) 46(10) 64(14) -1(8) 19(12) -2(10) C(15B) 100(20) 39(10) 87(19) 9(10) 62(16) 26(11) C(16) 80(20) 46(11) 63(15) 0(9) 22(13) -2(11) C(16B) 110(30) 40(12) 100(20) -3(11) 80(20) 5(11) C(17) 69(17) 46(10) 59(15) -6(8) 18(13) 1(10) C(17B) 60(20) 44(10) 68(19) 0(9) 36(16) 3(10) C(18) 80(20) 43(10) 52(11) -4(7) 22(10) 2(9) C(18B) 40(20) 41(9) 56(13) -9(8) 20(11) -4(9) C(19) 49(8) 97(9) 58(7) -36(6) 1(6) -11(6) C(20) 56(8) 76(8) 71(7) -18(6) 16(6) -14(6) C(21) 55(7) 63(7) 68(8) -13(6) 14(6) 0(6) C(22) 50(7) 61(7) 81(9) -15(6) 7(6) -12(6) C(23) 60(8) 78(8) 98(10) -28(6) 13(7) -4(6) Chemistry 449 Thesis – Laura K. Fairburn 46 _______________________________________________________________________ Table A4. Hydrogen coordinates ( x 10^4) and isotropic displacement parameters (Å^2 x 10^3) for CpCr(Mes/Cy-NHC)Cl. _______________________________________________________________ x y z U(eq) ________________________________________________________________ H(2) 5862 5693 3892 73 H(3) 5997 6852 3862 63 H(6) 1337 4123 4609 54 H(8) 2472 3939 1621 52 H(10A) 1657 5096 5644 89 H(10B) 1509 5715 4886 89 H(10C) 3250 5465 5548 89 H(11A) 2585 2986 3388 98 H(11B) 1036 3098 2363 98 H(11C) 874 3141 3642 98 H(12A) 3332 5551 1290 82 H(12B) 2868 4909 614 82 H(12C) 4641 5003 1414 82 H(13) 1840 7533 2910 48 H(13B) 1900 7471 2558 48 H(14A) 3694 7775 1816 54 H(14B) 5095 7905 2939 54 H(14C) 4034 7496 1572 47 H(14D) 5278 7742 2701 47 H(15A) 3928 8889 2278 66 H(15B) 2151 8630 2228 66 H(15C) 4229 8618 1514 82 H(15D) 2424 8416 1516 82 H(16A) 3013 9243 3889 75 H(16B) 4629 8838 4278 75 H(16C) 4789 8880 3458 89 H(16D) 3185 9244 2821 89 H(17C) 1426 8398 4242 69 H(17D) 2823 8523 5361 69 H(17A) 1536 8526 3471 67 H(17B) 2889 8755 4550 67 H(18A) 4295 7638 5001 68 H(18B) 2469 7408 4890 68 H(18C) 4350 7808 4572 55 H(18D) 2520 7632 4567 55 H(19) 420 5971 380 84 H(20) -1404 6889 287 81 H(21) -3396 6640 1457 74 H(22) -2872 5505 2138 79 H(23) -482 5117 1475 96 ________________________________________________________________ Chemistry 449 Thesis – Laura K. Fairburn 47 Table A5. Torsion angles [deg] for CpCr(Mes/Cy-NHC)Cl. ________________________________________________________________ C(2)-N(1)-C(1)-N(2) -1.5(15) C(4)-N(1)-C(1)-N(2) 179.4(11) C(2)-N(1)-C(1)-Cr(1) -177.8(10) C(4)-N(1)-C(1)-Cr(1) 3.1(19) C(3)-N(2)-C(1)-N(1) 1.4(14) C(13B)-N(2)-C(1)-N(1) 172.2(17) C(13)-N(2)-C(1)-N(1) -170.7(14) C(3)-N(2)-C(1)-Cr(1) 177.7(11) C(13B)-N(2)-C(1)-Cr(1) -12(2) C(13)-N(2)-C(1)-Cr(1) 6(2) C(1)-N(1)-C(2)-C(3) 1.0(18) C(4)-N(1)-C(2)-C(3) -179.9(12) N(1)-C(2)-C(3)-N(2) -0.1(18) C(1)-N(2)-C(3)-C(2) -0.9(17) C(13B)-N(2)-C(3)-C(2) -171.1(19) C(13)-N(2)-C(3)-C(2) 171.0(15) C(2)-N(1)-C(4)-C(9) -78.8(18) C(1)-N(1)-C(4)-C(9) 100.2(16) C(2)-N(1)-C(4)-C(5) 97.2(16) C(1)-N(1)-C(4)-C(5) -83.8(16) C(9)-C(4)-C(5)-C(6) 0(2) N(1)-C(4)-C(5)-C(6) -176.2(12) C(9)-C(4)-C(5)-C(10) 178.6(13) N(1)-C(4)-C(5)-C(10) 2.8(19) C(4)-C(5)-C(6)-C(7) 4(2) C(10)-C(5)-C(6)-C(7) -175.3(12) C(5)-C(6)-C(7)-C(8) -7(2) C(5)-C(6)-C(7)-C(11) 175.4(13) C(6)-C(7)-C(8)-C(9) 7(2) C(11)-C(7)-C(8)-C(9) -175.6(13) C(5)-C(4)-C(9)-C(8) 0(2) N(1)-C(4)-C(9)-C(8) 176.0(11) C(5)-C(4)-C(9)-C(12) 178.2(13) N(1)-C(4)-C(9)-C(12) -6(2) C(7)-C(8)-C(9)-C(4) -3(2) C(7)-C(8)-C(9)-C(12) 178.5(13) C(3)-N(2)-C(13)-C(14) 58(3) C(1)-N(2)-C(13)-C(14) -131(2) C(13B)-N(2)-C(13)-C(14) -42(11) C(3)-N(2)-C(13)-C(18) -72(3) C(1)-N(2)-C(13)-C(18) 99(3) C(13B)-N(2)-C(13)-C(18) -171(14) C(3)-N(2)-C(13B)-C(18B) -77(3) C(1)-N(2)-C(13B)-C(18B) 113(3) C(13)-N(2)-C(13B)-C(18B) 14(11) C(3)-N(2)-C(13B)-C(14B) 44(3) C(1)-N(2)-C(13B)-C(14B) -125(3) C(13)-N(2)-C(13B)-C(14B) 135(15) N(2)-C(13)-C(14)-C(15) 179(2) C(18)-C(13)-C(14)-C(15) -58(4) N(2)-C(13B)-C(14B)-C(15B) 179(3) C(18B)-C(13B)-C(14B)-C(15B) -62(4) C(13)-C(14)-C(15)-C(16) 54(3) C(13B)-C(14B)-C(15B)-C(16B) 58(4) C(14)-C(15)-C(16)-C(17) -56(3) C(14B)-C(15B)-C(16B)-C(17B) -55(4) C(15)-C(16)-C(17)-C(18) 55(3) C(15B)-C(16B)-C(17B)-C(18B) 52(5) Chemistry 449 Thesis – Laura K. Fairburn 48 N(2)-C(13)-C(18)-C(17) -178(2) C(14)-C(13)-C(18)-C(17) 56(4) C(16)-C(17)-C(18)-C(13) -51(3) N(2)-C(13B)-C(18B)-C(17B) -179(3) C(14B)-C(13B)-C(18B)-C(17B) 60(4) C(16B)-C(17B)-C(18B)-C(13B) -54(4) C(23)-C(19)-C(20)-C(21) 2.2(17) Cr(1)-C(19)-C(20)-C(21) -63.9(10) C(23)-C(19)-C(20)-Cr(1) 66.1(11) C(19)-C(20)-C(21)-C(22) -2.6(16) Cr(1)-C(20)-C(21)-C(22) -66.3(10) C(19)-C(20)-C(21)-Cr(1) 63.7(10) C(20)-C(21)-C(22)-C(23) 2.1(16) Cr(1)-C(21)-C(22)-C(23) -62.9(10) C(20)-C(21)-C(22)-Cr(1) 64.9(10) C(20)-C(19)-C(23)-C(22) -0.9(18) Cr(1)-C(19)-C(23)-C(22) 63.8(11) C(20)-C(19)-C(23)-Cr(1) -64.7(11) C(21)-C(22)-C(23)-C(19) -0.7(17) Cr(1)-C(22)-C(23)-C(19) -62.0(11) C(21)-C(22)-C(23)-Cr(1) 61.2(10) ________________________________________________________________