Coupling Self-Sensitized CO2 Photoreduction of Silicon(IV)-Terpyridine Complexes with Organic Synthesis

The development of new molecular photocatalysts for CO2 reduction has considerable interest. Furthermore, the direct utilization of CO2 reduction products in organic synthesis is a promising strategy for the valorization of CO2. Herein, we report the first use of main-group silicon(IV) coordination complexes as self-sensitized molecular photocatalysts for the near-unity-selective reduction of CO2 to CO without requiring an external photosensitizer. Under visible-light irradiation, these Si(IV) complexes are photoexcited and can be reductively quenched by 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH). Mechanistic studies reveal five ligand-based reduction processes for Si(IV) complexes, with CO2 reduction occurring at a five-electron-reduced state of the ligand. The self-sensitized process was further elucidated by theoretical calculations, spectroelectrochemical analysis, emission quenching experiments, controlled-potential electrolysis, and in situ DRIFTS measurements. Notably, a sunlight-driven tandem catalytic system has been established by integrating this Si(IV)-based CO2 photoreduction with organic carbonylation to produce valuable carbonyl compounds.