Alternating Metal-Ligand Coordination Improves Electrocatalytic CO₂ Reduction by a Mononuclear Ru Catalyst

Molecular electrocatalysts for CO₂ -to-CO conversion often operate at large overpotentials, due to the large barrier for C-O bond cleavage. Illustrated with ruthenium polypyridyl catalysts, we herein propose a mechanistic route that involves one metal center that acts as both Lewis base and Lewis acid at different stages of the catalytic cycle, by density functional theory in corroboration with experimental FTIR. The nucleophilic character of the Ru center manifests itself in the initial attack on CO₂ to form [Ru-CO₂ ]⁰ , while its electrophilic character allows for the formation of a 5-membered metallacyclic intermediate, [Ru-CO₂ CO₂ ]^0,c , by addition of a second CO₂ molecule and intramolecular cyclization. The calculated activation barrier for C-O bond cleavage via the metallacycle is decreased by 34.9 kcal mol^-1 as compared to the non-cyclic adduct in the two electron reduced state of complex 1. Such metallacyclic intermediates in electrocatalytic CO₂ reduction offer a new design feature that can be implemented consciously in future catalyst designs.