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-CO2CO2](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.

Automated summary

This study proposes a mechanistic route for CO2-to-CO conversion using ruthenium polypyridyl catalysts. The study reveals that the ruthenium center acts as both Lewis base and Lewis acid at different stages of the catalytic cycle. By forming a 5-membered metallacyclic intermediate, the activation barrier for C-O bond cleavage is significantly decreased, leading to lower overpotentials in electrocatalytic CO2 reduction. These metallacyclic intermediates offer a new design feature for future catalyst designs.