Dual Role of a Novel heteroleptic Cu(I) Complex in Visible‐Light‐Driven CO2 Reduction

A novel mononuclear Cu(I) complex was synthesized via coordination with a benzoquinoxalin‐2’‐one‐1,2,3‐triazole chelating diimine and the bis[(2‐diphenylphosphino)phenyl] ether (DPEPhos), to target a new and efficient photosensitizer for photocatalytic CO2 reduction. The Cu(I) complex absorbs in the blue‐green region of the visible spectrum, with a broad band having a maximum at 475 nm 
(ε = 4500 M‐1cm‐1), which is assigned to the metal‐to‐ligand charge transfer (MLCT) transition from the Cu(I) to the benzoquinoxalin‐2’‐one moiety of the diimine. Surprisingly, photo‐driven experiments for the CO2 reduction showed that this complex can undergo a photoinduced electron transfer with a sacrificial electron donor and accumulate electrons on the diimine backbone. Photo‐driven experiments in a CO2 atmosphere revealed that this complex can not only act as a photosensitizer, when combined with an Fe(III)‐porphyrin, but can also selectively produce CO from CO2. Thus, owing to its charge‐accumulation properties, the non‐innocent benzoquinoxalin‐2‐one based ligand enabled the development of the first copper(I)‐based photocatalyst for CO2 reduction.