Electronic Effect Promoted Visible-Light-Driven CO₂-to-CO Conversion in a Water-Containing System.

Area of Science:

• Coordination Chemistry
• Photocatalysis
• Green Chemistry

Background:

• Developing efficient nonprecious metal catalysts for CO2 reduction is crucial for sustainable energy solutions.
• Unsaturated metal complexes offer unique catalytic properties but designing highly active ones remains challenging.

Purpose of the Study:

• To synthesize and investigate novel coordinatively unsaturated cobalt-salen complexes for photochemical CO2 reduction.
• To understand the structure-activity relationship influencing catalytic performance.

Main Methods:

• In situ synthesis of four cobalt-salen complexes (1-4) using o-phenylenediamine derivatives and 5-methylsalicylaldehyde.
• Photocatalytic CO2-to-CO conversion using visible light in a water-containing system.
• Density Functional Theory (DFT) calculations to elucidate reaction mechanisms.

Main Results:

• Complex 4, featuring a nitro substituent, demonstrated the highest photocatalytic activity.
• Complex 4 achieved a turnover number (TON) of 5300 for CO production with 96% selectivity.
• DFT calculations and experimental data indicated the nitro group's electron-withdrawing effect lowers the cobalt center's reduction potential and activation barriers for CO2 conversion.

Conclusions:

• The electron-withdrawing nitro group significantly enhances the photocatalytic performance of cobalt-salen complexes for CO2 reduction.
• This study provides insights into designing efficient nonprecious metal catalysts for CO2 utilization.