Solvent and Ligand Substitution Effects on the Electrocatalytic Reduction of CO2 with [Mo(CO)4(x,x′‐dimethyl‐2,2′‐bipyridine)] (x=4–6) Enhanced at a Gold Cathodic Surface

Abstract

AbstractA series of molybdenum tetracarbonyl complexes with dimethyl‐substituted 2,2′‐bipyridine (dmbipy) ligands were investigated by cyclic voltammetry (CV) combined with infrared spectroelectrochemistry (IR‐SEC) in tetrahydrofuran (THF) and N‐methyl‐2‐pyrrolidone (NMP) to explore their potential in a reduced state to trigger electrocatalytic CO2 reduction to CO. Addressed is their ability to take advantage of a low‐energy, CO‐dissociation two‐electron ECE pathway available only at an Au cathode. A comparison is made with the reference complex bearing unsubstituted 2,2′‐bipyridine (bipy). The methyl substitution in the 6,6′ position has a large positive impact on the catalytic efficiency. This behavior is ascribed to the advantageous positioning of the steric bulk of the methyl groups, which further facilitate CO dissociation from the one‐electron‐reduced parent radical anion. On the contrary, the substitution in the 4,4′ position appears to have a negative impact on the catalytic performance, exerting a strong stabilizing effect on the π‐accepting CO ligands and, in THF, preventing exploitation of the low‐energy dissociative pathway.