Mn-Based Molecular Catalysts for the Electrocatalytic Disproportionation of CO₂ into CO and CO₃^2-

This work studies the electrocatalytic disproportionation of CO2 into CO and CO32- mediated by a [Mn-2,6-bis(1-(alkyl)imidazol-2-ylidene)pyridine]Br pincer complex. We identify three mechanistic scenarios involving one or two catalytically active metal centers in the activation of carbon dioxide and use density functional theory to map out the energy landscape for each of the mechanistic steps. Experimentally determined second-order kinetics in CO2 consumption, the formation of CO and CO32- together with an observed order in catalyst of 0.5 determined by cyclic voltammetry using the Bures normalized timescale method, suggest a turnover-limiting CO32- loss through the scission of a bimetallic species. Faradaic efficiencies for the reduction of CO2 to CO of 86 +/- 4% are observed. Given the reaction mass balance, we estimate a Faradaic efficiency from the conversion of CO2 to CO32- of 93 +/- 4%. Our combined experimental-theoretical approach suggests that two sequential CO2 insertions are followed by a rearrangement to produce carbon monoxide and carbonate from two molecules of CO2 at singly reduced catalyst molecules. The disproportionation reaction reported herein combines the power of catalytic CO2 conversion with sequestration and provides a new chemical avenue for the conversion of carbon dioxide.