Highly active electrocatalytic CO2 reduction with manganese N-heterocyclic carbene pincer by para electronic tuning

Abstract Electronic tuning by para substitutions was explored to achieve a highly active manganese N-heterocyclic carbene pincer complex for the selective electrocatalytic reduction of CO2 to CO. [MnCNCOMe]BF4 (L2-Mn) bearing an electron-donating group (–OMe) showed high activity with 63 × catalytic current enhancement, average Faradaic efficiency of 104%, and a TOFmax value of 26,127 s−1, which is 127 times higher than that of unsubstituted [MnCNCH]Br (L1-Mn) reported previously. In contrast, the electron-withdrawing group (–COOMe) in [MnCNCCOOMe]PF6 (L3-Mn) inhibited the electrocatalytic activity. Ambient Bronstic acid, however, suppressed the activity of L2-Mn probably due to the protonation of the –OMe group. These findings indicate a potential electronic tuning strategy to improved manganese N-heterocyclic carbene catalysts for CO2 reduction.