Engineering Coordination Environment of Cobalt Center in Molecular Catalysts for Improved Photocatalytic CO2 Reduction

Comprehensive Summary The creation of effective and inexpensive catalysts is essential for photocatalytic CO 2 reduction. Homogeneous molecular catalysts, possessing definite crystal structures, are desirable to study the relationship between catalytic performance and coordination microenvironment around catalytic center. In this report, we elaborately developed three Co(II)‐based molecular catalysts with different coordination microenvironments for CO 2 reduction, named [CoN 3 O]ClO 4 , [CoN 4 ]ClO 4 , and [CoN 3 S]ClO 4 , respectively. The optimal [CoN 3 O]ClO 4 photocatalyst has a maximum TON of 5652 in photocatalytic reduced CO 2 reduction, which is 1.28 and 1.65 times greater than that of [CoN 4 ]ClO 4 and [CoN 3 S]ClO 4 , respectively. The high electronegativity of oxygen in L 1 ( N , N ‐bis(2‐pyridylmethyl)‐ N ‐(2‐hydroxybenzyl)amine) provides the Co(II) catalytic centers with low reduction potentials and a more stable *COOH intermediate, which facilitates the CO 2 ‐to‐CO conversion and accounts for the high photocatalytic activity of [CoN 3 O]ClO 4 . This work provides researchers new insights in development of catalysts for photocatalytic CO 2 reduction.