Visible-light-driven photocatalytic CO2 reduction using ruthenium complexes having a CNC-type pincer ligand: comparison of substituent effect on a CNC ligand†
Abstract
A series of ruthenium complexes bearing a CNC-type pincer ligand with different substituents (CF3, H, and OMe) were synthesized and characterized for visible-light-driven photocatalytic CO2 reduction. The photocatalytic reactions were conducted using [Ru(dmbpy)3]2+ as a photosensitizer and BI(OH)H as a sacrificial electron donor in a DMA–TEOA mixed solvent under LED light irradiation. The main product was formic acid, along with small amounts of CO and H2. Contrary to previous findings that Papish et al. reported, the catalyst with an electron-withdrawing CF3 substituent on the CNC ligand exhibited higher turnover number for formic acid production (TONHCOOH = 4742) compared to the electron-donating OMe substituent (TONHCOOH = 2152) after 24 hours of irradiation. Addition experiments revealed that the cessation of CO2 reduction was primarily due to the degradation of the photosensitizer rather than deactivation of the catalyst. ESI-MS analysis detected the formation of a carbonate complex prior to the photocatalytic reaction. This study provides insights into the effect of substituents on CNC pincer ligands in ruthenium complexes for photocatalytic CO2 reduction.