Date of Award
Ph.D. in Chemistry
University of Mississippi
Anthracene-bridged dinuclear rhenium complexes are reported for electrocatalytic and photocatalytic carbon dioxide (CO2) reduction to carbon monoxide (CO). Related by hindered rotation of each rhenium active site to either side of the anthracene bridge cis and trans conformers have been isolated and characterized. Electrochemical studies reveal distinct mechanisms whereby the cis conformer operates via cooperative bimetallic CO2 activation and conversion and the trans conformer reduces CO2 through well-established single-site and bimolecular pathways analogous to Re(bpy)(CO)3Cl. Higher turnover frequencies are observed for the cis conformer (35.3 s−1) relative to the trans conformer (22.9 s−1) with both outperforming Re(bpy)(CO)3Cl (11.1 s−1). Photocatalytic reactivity shows the plausible pathway for dinuclear system is one site acting as an efficient covalently-linked photosensitizer to the second site performing CO2 reduction. The excited-state kinetics and emission spectra reveal that the anthracene backbone plays a more significant role beyond a simple structural unit. The isomerizations of 3 4-diazatricyclo[4.1.0.02 7]hept-3-ene and 3 4 diazatricyclo[4.1.0.02 7]heptane to their corresponding products were studied by ab initio calculations at multiconfiguration self-consistent field level to study the stabilization effects from π bond electrons and lone pair electrons. The isomerization of 3 4-diazatricyclo[4.1.0.02 7]hept-3-ene occurs through four unique pathways. The 12.2 kcal mol-1 disparity in the disrotatory barriers is explained through π electron delocalization in the transition state. The 3 4-diazatricyclo[4.1.0.02 7]heptane structure has eight separate reaction channels for isomerization. Resonance stabilization from lone pair electron for two of the forbidden pathways results in a relative energy lowering. The isomerization of benzvalene to benzene has barriers of 20.6 kcal mol-1 for the disrotatory channel and 26.8 kcal mol-1 for the conrotatory channel. The isomerization of benzvalene back to benzvalene occurs by the transition state disTSback with barrier of 29.8 kcal mol-1. For the isomerization of benzvalyne the barriers are 22.9 kcal mol-1 for disrotatory channel and 21.7 kcal mol-1 for conrotatory channel. Intrinsic reaction coordinate shows the 122.2 kcal mol-1 relative energy could be released only by 1.4 kcal mol-1 due to the absence of normally intermediate with trans double bond.
Yang, Weiwei, "Electro- and photocatalytic carbon dioxide reduction and thermal isomerization of highly strained tricyclocompounds" (2019). Electronic Theses and Dissertations. 1797.