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 ReI(L)(CO)3CH3CN−MHPW12O40 (L = 15-crown-5-phenanthroline, M = Na+, H3O+). X-ray diffraction, 1H and 13C NMR, ESI-MS, IR, and elemental analysis were used to characterize this complex. In the presence of Pt/C, the polyoxometalate moiety in ReI(L)(CO)3CH3CN−MHPW12O40 can oxidize H2 to two protons and two electrons which in the presence of visible light can catalyze the photoreduction of CO2 to CO with H2 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 PWVWVI11O40 and a Re0 species with a tentative assignment of the intermediate as Re0(L)(CO)3(S)−MH3PWVWVI11O40.