The efficient electrocatalytic functionalization of carbon dioxide (CO2) for use in fuels and commodity chemicals represents a continuing challenge for the storing of electrical energy from renewable sources in chemical bonds. Some of the most effective CO2 reduction catalysts are based on the Group VII bipyridine fac-tricarbonyl complexes ReI(2,2'-bipyridine)(CO)3Cl [2,2'-bipyridine = bpy] and MnI(2,2'-bipyridine)(CO)3X [X = Br and OTf], which form carbon monoxide (CO) and water (H2O) with near perfect Faradaic efficiency via a unimolecular [M(bpy)]–/2e– pathway. Interestingly, Re(bpy) compounds can also reduce CO2 via a bimolecular 2[Re(bpy)]/[1e– + 1e–] pathway, producing 0.5 equiv CO and 0.5 equiv carbonate (CO32–). We recently reported that the modification of the bipyridine ligand with methyl acetamidomethyl groups at the 4 and 4' positions enhanced the rate for this mechanism in acetonitrile (MeCN) for Re((4,4'-bis(methyl acetamidomethyl)-2,2'-bipyridine)(CO)3Cl, 1 [(4,4'-bis(methyl acetamidomethyl)-2,2'-bipyridine = dac]. Computational models, electrochemical measurements, and infrared spectroelectrochemistry (IR-SEC), revealed that the bimolecular catalytic response resulted from the supramolecular assembly of a hydrogen-bonded dimer. These results led us to the following question: could the monomer and dimer catalyst systems based on these compounds be improved in terms of current efficiency and turnover frequency (TOF) through the incorporation of additional amino acid residues? These efforts are inspired by nature, specifically metalloproteins, which place multi-metallic active sites and/or co-catalytic residues in close proximity. In these systems the inherent flexibility of the non-covalent interactions, which direct the formation of the higher-order structure, accommodate a variety of conformational changes during the course of a reaction. We reasoned that by adding amino acid residues to the previously reported monomer and dimer catalyst systems we could improve the activity by increasing the stability of the bimetallic active state and incorporating pendant proton sources

Molecular electrocatalysts for the reduction of CO2 and the effects of bioinspired, secondary-sphere interactions on mechanism

251st National Meeting (2016)

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