Tuning of Ionic Second Coordination Sphere in Evolved Rhenium Catalyst for Efficient Visible-Light-Driven CO2 Reduction

Developing an efficient and easy-to-handle strategy in designing catalysts for CO2 reduction into CO by harnessing sunlight is a promising project. Here, a facile strategy was developed to design a Re catalyst modified with an ionic secondary coordination sphere for photoreduction of CO2 to CO by visible light. By adding ionic liquids or tuning a different ionic secondary coordination sphere, it was discovered that an outstanding optical property, other than CO2 absorption ability or the ability to dissociation of chloride anion, is the prerequisite for catalyst design. Accordingly, a novel Re catalyst, {Re[BpyMe(tris(2-hydroxyethyl)amine)](CO)(3)Cl}Br (Re-THEA), was designed, screened, and resulted in a relative high quantum yield (up to 34 %) for visible-light-induced CO2 reduction with a single-molecule system. DFT calculations, combined with experimental outcomes, suggested the pendant ionic tris(2-hydroxyethyl)amino (THEA) group on Re-THEA can enhance visible-light absorption, stabilize reaction intermediates, and suppress the Re-Re dimer formation.