Electrocatalytic CO2 reduction using rhenium(I) complexes with modified 2-(2′-pyridyl)imidazole ligands

Abstract The reduction of CO 2 to CO is an ongoing chemical challenge of great interest for the development of renewable and sustainable technologies. Coordination complexes of rhenium(I) are widely known as CO 2 reduction electrocatalysts, with emphasis on complexes bearing 2,2′-bipyridine (bpy) ligands. Recent research efforts have focused on incorporation of these catalysts into solid, electroactive supports, which can be challenging due to the requirement for synthetic modification to bpy ligands. Development of related ligand sets with modular syntheses is therefore an attractive goal. We investigated electrocatalytic CO 2 reduction using ReCl(CO) 3 (N-N) complexes, where N-N is 2-(2′-pyridyl)imidazole (PyIm), 2-(2′-pyridyl)benzimidazole (PyBIm), 2-(2′-quinolyl)imidazole (QuIm), or 2-(2′-quinolyl)benzimidazole (QuBIm) ligands. In CO 2 -saturated MeCN solutions, cyclic voltammograms of the Re-QuBIm complex showed current enhancement at a peak potential of −2.01 V vs. Cp 2 Fe +/0 . The catalytic current was stable upon repeated cycling. Re-QuBIm has an overpotential ∼200 mV lower than related Re-bpy catalysts, but also is kinetically slower. The redox reactivity of each complex can be correlated to electronic parameters of the N-N chelating ligands. These results suggest that modular reduction potential tuning of CO 2 reduction catalysts is possible, but associated penalties to activity are important considerations.