Enhanced Electrocatalytic and Selective CO ₂ -to-CO Reduction by a Rhenium(I) Complex Bearing 6,6′-Substituted 2,2′-Bipyridines

The electrochemical reduction of CO2 (CO2RR) into value-added chemicals offers a promising route toward a circular carbon economy and a reduced reliance on fossil fuels. A detailed understanding of the structural and electronic factors that govern the performance of molecular CO2RR electrocatalysts is essential for designing efficient and tunable systems. Here, we report a series of rhenium(I) complexes, fac-[ReI(6,6′-(R)2-bpy)(CO)3Cl] (bpy = 2,2′-bipyridine; R = mesityl (mes), 2,4,6-triisopropylphenyl (trip), or isophthalic acid (phth)) and evaluate their electrocatalytic activity. Among these, fac-[ReI(6,6′-(mes)2-bpy)(CO)3Cl] exhibited the highest performance, enabling selective CO2-to-CO conversion for 1 h with Faradaic efficiency (FE) >97%, representing an enhanced activity level for Rebpy catalysts. Single-crystal X-ray diffraction and density functional theory (DFT) calculations indicated that favorable CO2 binding can be promoted by tilting the 6,6′-(mes)2-bpy ligand (from the Re–CO coordination plane), providing mechanistic insight into the observed enhancement. The study consequently demonstrates a rational correlation between the CO2 electrocatalytic performance of Rebpy catalysts and their structural variations, as derived from X-ray data and corroborated by computational modeling.