MOLECULAR ELECTROCATALYSTS FOR THE REDUCTION OF CO2 AND THE EFFECTS OF BIOINSPIRED SECONDARY-SPHERE INTERACTIONS ON MECHANISM

摘要

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 Re~I(2,2'-bipyridine)(CO)3Cl [2,2'-bipyridine = bpy] and Mn~I(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~- + le~-] pathway, producing 0.5 equiv CO and 0.5 equiv carbonate (CO3~(2-)). 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.