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 CO 2 (CO 2 RR) 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 CO 2 RR electrocatalysts is essential for designing efficient and tunable systems. Here, we report a series of rhenium(I) complexes, fac-[Re I (6,6′-(R) 2 -bpy)(CO) 3 Cl] (bpy = 2,2′-bipyridine; R = mesityl (mes), 2,4,6-triisopropylphenyl (trip), or isophthalic acid (phth)) and evaluate their electrocatalytic activity. Among these, fac-[Re I (6,6′-(mes) 2 -bpy)(CO) 3 Cl] exhibited the highest performance, enabling selective CO 2 -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 CO 2 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 CO 2 electrocatalytic performance of Rebpy catalysts and their structural variations, as derived from X-ray data and corroborated by computational modeling.