Photocatalytic Reduction of CO to CO in Aqueous Solution under Red-Light Irradiation by a Zn-Porphyrin-Sensitized Mn(I) Catalyst.

This work demonstrates photocatalytic CO reduction by a noble-metal-free photosensitizer-catalyst system in aqueous solution under red-light irradiation. A water-soluble Mn(I) tricarbonyl diimine complex, [MnBr(4,4'-{EtOPCH}-2,2'-bipyridyl)(CO)] (), has been fully characterized, including single-crystal X-ray crystallography, and shown to reduce CO to CO following photosensitization by tetra(-methyl-4-pyridyl)porphyrin Zn(II) tetrachloride [Zn(TMPyP)]Cl () under 625 nm irradiation. This is the first example of employed as a photosensitizer for CO reduction. The incorporation of -P(O)(OEt) groups, decoupled from the core of the catalyst by a -CH- spacer, afforded water solubility without compromising the electronic properties of the catalyst. The photostability of the active Mn(I) catalyst over prolonged periods of irradiation with red light was confirmed by H and C{H} NMR spectroscopy. This first report on Mn(I) species as a homogeneous photocatalyst, working in water and under red light, illustrates further future prospects of intrinsically photounstable Mn(I) complexes as solar-driven catalysts in an aqueous environment.