Ferrocenyl PNNP Ligands-Controlled Chromium Complex-Catalyzed Photocatalytic Reduction of CO to Formic Acid.

3d-transition metal complexes have been gaining much attention as promising candidates for photocatalytic carbon dioxide (CO) reduction systems. In contrast to the group 7-12 elements, Cr in group 6 has not yet been investigated as the catalyst of CO photoreduction because of its intrinsic disadvantages. Cr has a weak reducing ability due to an insufficient number of d electrons and high Lewis acidity which may deactivate the catalyst by strong coordination with a product formate.