Selective electrochemical CO2 reduction to CO by a series of dimeric thiosemicarbazone rhenium(I) catalysts: combined experimental and theoretical mechanistic insights.

A series of dimeric rhenium(I) fac-tricarbonyl complexes bearing thiosemicarbazone ligands were synthesized and comprehensively characterized using spectroscopic, analytical, and single-crystal X-ray diffraction techniques. These complexes were evaluated as electrocatalysts for CO2 reduction, exhibiting selective conversion to carbon monoxide (CO) in the presence of trifluoroethanol as a proton source. Systematic variation of coligands within the thiosemicarbazone framework reveals their significant influence on the electronic and steric properties of the catalysts, thereby modulating catalytic performance. Among the series, the complex incorporating the (E)-2-(benzofuran-2-ylmethylene)-N-phenylhydrazinecarbothioamide ligand displays the highest activity, achieving a faradaic efficiency of 74% for CO production. Mechanistic insights were obtained through UV-visible spectroelectrochemistry supported by time-dependent density functional theory calculations, providing evidence for the formation of the active catalytic species under reductive conditions. These findings highlight the potential of thiosemicarbazone-based rhenium(I) systems as tunable platforms for efficient and selective electrochemical CO2 reduction.