Mn‑NHC Electrocatalysts: Increasing π Acidity Lowers the Reduction Potential and Increases the Turnover Frequency for CO2 Reduction

A new manganese­(I) N-heterocyclic carbene electrocatalyst containing a benzimidazole–pyrimidine-based ligand is reported for the two-electron conversion of CO2. The increased π acidity of pyrimidine shifts the two-electron reduction to −1.77 V vs Fc/Fc+, 70 mV more positive than that for MnBr­(2,2′-bipyridine)­(CO)3; increased catalytic current enhancement is also observed (5.2× vs 2.1×). Theoretical analyses suggest that this heightened activity may follow from the preference for a reduction-first dehydroxylation mechanism.