First row transition metal complexes have attracted attention as abundant and affordable electrocatalysts for CO2 reduction. Manganese complexes bearing bis-N-heterocyclic carbene ligands defining 6-membered ring metallacycles have proven to reduce CO2 to CO selectively at very high rates. Herein, we report the synthesis of manganese carbonyl complexes supported by a rigid ortho-phenylene bridged bis-N-heterocyclic carbene ligand (orthophenylene-bis(N-methylimidazol-2-ylidene, Ph-bis-mim), which defines a 7-membered ring metallacycle. We performed a comparative study with the analogues bearing an ethylene-bis(Nmethylimidazol-2-ylidene ligand (C2H4-bis-mim) and a methylenebis(N-methylimidazol-2-ylidene ligand (CH2-bis-mim) and found that catalysts comprising a seven-membered metallacycle retain similar selectivity and high activity as those with six-membered metallacycles, while reducing the overpotential by 120-190 mV. This study reveals general design principles for manganese bis-N-heterocyclic carbene electrocatalysts which can guide further designs of affordable, fast and low overpotential catalysts for CO2 electroreduction.

Influence of the bis‐carbene ligand on manganese catalysts for CO2 electroreduction