Photocatalytic CO 2 Reduction Using Mixed Catalytic Systems Comprising an Iron Cation with Bulky Phenanthroline Ligands.

This study reports on efficient photocatalytic CO 2 reduction reactions using mixed catalytic systems of an Fe ion source and various 1,10-phenanthroline derivatives ( R 1 R 2 p ) as ligands in the presence of triethanolamine (TEOA). As the relatively bulky substituents at positions 2 and 9 of R 1 R 2 p weakened the ability to coordinate to the Fe ion, the Fe ion formed TEOA complexes. The free R 1 R 2 p accepted an electron from the reduced photosensitizer through proton-coupled electron transfer (PCET) using protons of TEOA dissolved in a CH 3 CN solution in a CO 2 atmosphere as the initial step of the catalytic cycle. Although the mixed system of the nonsubstituted 1,10-phenanthroline generates a stable tris(phenanthroline)-Fe(II) complex in solution, this complex could not function as a CO 2 reduction catalyst. The mechanism in which R 1 R 2 p interacts with the Fe ion after PCET was proposed for this efficient photocatalytic CO 2 reduction. The proposed photocatalytic system using the 2,9-di- sec -butyl-phenanthroline ligand could produce CO with high efficiency (quantum yield of 8.2%) combined with a dinuclear Cu(I) complex as a photosensitizer.