Photocatalytic CO₂ Reduction Using Mixed Catalytic Systems Comprising an Iron Cation with Bulky Phenanthroline...

This study reports on efficient photocatalytic CO₂ reduction reactions using mixed catalytic systems of an Fe ion source and various 1,10-phenanthroline derivatives (RRp) as ligands in the presence of triethanolamine (TEOA). As the relatively bulky substituents at positions 2 and 9 of RRp weakened the ability to coordinate to the Fe ion, the Fe ion formed TEOA complexes. The free RRp accepted an electron from the reduced photosensitizer through proton-coupled electron transfer (PCET) using protons of TEOA dissolved in a CH₃CN solution in a CO₂ 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 CO₂ reduction catalyst. The mechanism in which RRp interacts with the Fe ion after PCET was proposed for this efficient photocatalytic CO₂ 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.