Doctor of Philosophy (PhD)
The “old” bimetallic nickel complexes, meso- and rac-Ni2Cl4(et,ph-P4) were investigated as possible “catalysts” for the oxidative cleavage of alkenes using an unsaturated fatty acid, oleic acid, as the substrate. The “new” bimetallic nickel complexes with a stronger chelating tetraphosphine ligand, meso- and rac-Ni2Cl4(et,ph-P4-Ph), were also synthesized and tested for the oxidative cleavage of oleic acid. All four dinickel complexes were found to be active for the oxidative cleavage of oleic acid, producing extremely small amounts of aldehyde product. The Stanley research group also discovered the oxidative cleavage of alkenes using only the “old” et,ph-P4 tetraphosphine ligands with no metal centers. As a result of this discovery, the oxidative cleavage of oleic acid was attempted with both “old” and “new” tetraphosphine ligands (without metal centers) and found to be active, producing extremely small amounts of aldehyde as well. In attempt to make the system catalytic, some simple phosphine ligands (PPh3, P(C6H11)3, and dppm) and some mono- and bimetallic cobalt complexes were tested for the oxidative cleavage of oleic acid. The phosphine ligands and monometallic cobalt complex, [Co(H2O)6][BF4]4, found to be active, but still only producing an extremely small amount of aldehyde. The reactivity of the bimetallic nickel complexes with H2O was investigated through 31P NMR studies and the bridged-hydroxide complexes, rac-[Ni2(ì-OH)Cl2(et,ph-P4)]+ and meso- and rac-[Ni2(ì-OH)Cl2(et,ph-P4-Ph)]+ was proposed to be the most stable intermediate during the reaction. Further studies, such as COSY-NMR, are needed to prove this proposal, however. Numerous synthetic methods were explored to synthesize a bimetallic cobalt carbonyl complex for hydroformylation and aldehyde-water shift catalysis. The first method was the reduction of the dicobalt tetrachloride complexes, meso- and rac-Co2Cl4(et,ph-P4)/(et,ph-P4-Ph), in the presence of CO using 1:1 H2/CO, NaBH4, LAH, LiEt3BH, Mg, and Zn. Of these reducing agents, Zn resulted in the cleanest reduction by FT-IR analyses, yielding a proposed mixture of the dicationic penta- and hexacarbonyl dicobalt complexes, meso- and rac-[Co2(CO)5-6(et,ph-P4)/(et,ph-P4-Ph)]2+. The H2/CO reduction results indicated that perhaps, a 1:6 H2/CO, not the 1:1 mixture originally used, would be a more suitable autoclave gas mixture. Future experiments will be performed to test this hypothesis. Experiments using Co2(CO)8 resulted in a mixture of cobalt carbonyl complexes, including the formation of [Co(CO)4]-. Preliminary experiments to reduce the non-halide containing dicobalt complexes, [Co2(H2O)x(et,ph-P4)/(et,ph-P4-Ph)][BF4]2, using 1:1 H2/CO and Zn resulted in incomplete reductions. Future experiments using a stronger one-electron reducing agent in the presence of CO with an easily isolable by product should be a better synthetic route for the formation of a bimetallic cobalt carbonyl complex.
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Duronslet, Ciera Vonn, "Exploration of Bimetallic Nickel and Cobalt Complexes for Catalytic Oxidative Cleavage of Alkenes and Hydroformylation" (2016). LSU Doctoral Dissertations. 4283.