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)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 Re^I(L)(CO)₃CH ₃CN-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 PW^VW^VI₁₁O₄₀ and a Re⁰ species with a tentative assignment of the intermediate as Re⁰(L)(CO)₃(S)-MH₃PW^VW ^VI₁₁O₄₀.