Electronic Effect Promoted Visible-Light-Driven CO-to-CO Conversion in a Water-Containing System.

The design of unsaturated nonprecious metal complexes with high catalytic performance for photochemical CO reduction is still an important challenge. In this paper, four coordinatively unsaturated Co-salen complexes - were explored in situ using -phenylenediamine derivatives and 5-methylsalicylaldehyde as precursors of the ligands in -. It was found that complex , bearing a nitro substituent (-NO) on the aromatic ring of the salen ligand, exhibits the highest photochemical performance for visible-light-driven CO-to-CO conversion in a water-containing system, with TON and CO selectivity values of 5300 and 96%, respectively. DFT calculations and experimental results revealed that the promoted photocatalytic activity of is ascribed to the electron-withdrawing effect of the nitro group in compared to - (with -CH, -F, and -H groups, respectively), resulting in a lower reduction potential of active metal centers Co and lower barriers for CO coordination and C-O cleavage steps for than those for catalysts -.