Iron, Cobalt and Nickel complexes with N4-donor ligands catalysts for the CO2 photoreduction

Iron(II), cobalt(II) and nickel (II) complexes bearing phenanthroline- and bipyridine-bis(imino) ligands have been prepared and tested as catalysts for the photoreduction of CO2 at atmospheric pressure and room temperature in the presence of a photosensitizer (PS) and sacrificial electron donor (SD) producing mixtures of CO and H2. The best results were obtained with a Fe(II) catalyst using triethanolamine/1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimida-zole (BIH) in acetonitrile using a blue LED irradiation with [Ru(bpy)3]PF6]2 (bpy = 2,2′-bipyridine) as PS. With this system, a mixture of CO/H2 (68/32) was obtained with a turnover number (TONCO 166, 24 h). Analogous Co(II) and Ni(II) complexes produced H2 as a major product. Cyclic voltammetry demonstrates that the electrons uptake is centered on the ligand. Computational calculations allow to propose the most stable location of the electrons.