Photoreduction of Carbon Dioxide to Carbon Monoxide with Hydrogen Catalyzed by a Rhenium(I) Phenanthroline-Polyoxometalate Hybrid Complex

A phenanthroline ligand decorated at the 5,6-position with a 15-crown-5 ether was used to prepare a metalorganic-polyoxometalate hybrid complex Re-I(L)(CO)(3)CH3CN-MHPW12O40 (L = 15-crown-5-phenanthroline, M = Na+, H3O+). X-ray diffraction, H-1 and C-13 NMR, ESI-MS, IR, and elemental analysis were used to characterize this complex. In the presence of Pt/C, the polyoxometalate moiety in Re-I(L)(CO)(3)CH3CN-MHPW12O40 can oxidize H-2 to two protons and two electrons which in the presence of visible light can catalyze the photoreduction of CO2 to CO with H-2 as the reducing agent instead of the universally used amines as sacrificial reducing agents. An EPR spectrum of a stable intermediate species under reaction conditions shows characteristics of a (PWW11O40)-W-V-O-VI and a Re-0 species with a tentative assignment of the intermediate as Re-0(L)(CO)(3)(S)-(MH3PWW11O40)-W-V-O-VI.