Highly Efficient Visible-Light-Driven CO-to-CO Conversion by Coordinatively Unsaturated Co-Salen Complexes in a Water-Containing System.

The development of cost-effective catalysts for CO reduction is highly desired but remains a significant challenge. The unsaturated coordination metal center in a catalyst is favorable for the process of catalytic CO reduction. In this paper, two asymmetric salen ligands were used to synthesize two coordinatively unsaturated Co-salen complexes. The two Co-salen complexes exhibit an unsaturated coordination pattern and display high activity and CO selectivity for visible-light-driven CO reduction in a water-containing system. The photocatalytic performance of is higher than that of because the reduction potential of the catalytic Co center and the energy barrier of the catalytic transition states of are lower than those of , with turnover numbers (TON), turnover frequencies (TOF), and CO selectivity values of 8640, 0.24 s, and 97% for , respectively. The photocatalytic reduction of CO to CO for is well supported by control experiments and density functional theory (DFT) calculations.