Photocatalytic Reduction of CO2 to CO in Aqueous Solution under Red-Light Irradiation by a Zn-Porphyrin-Sensitized Mn (I) Catalyst

This work demonstrates photocatalytic CO2 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'-(Et2O3PCH2}(2)-2,2'-bipyridyl)(CO)(3)] (1), has been fully characterized, including single-crystal X-ray crystallography, and shown to reduce CO2 to CO following photosensitization by tetra(N-methyl-4-pyridyl)-porphyrin Zn(II) tetrachloride [Zn(TMPyP)]Cl-4 (2) under 625 nm irradiation. This is the first example of 2 employed as a photosensitizer for CO2 reduction. The incorporation of -P(O)-(OEt)(2) groups, decoupled from the core of the catalyst by a -CH2- 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-1 and C-13{H-1} 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.

Automated summary

This work demonstrates the photocatalytic reduction of CO2 by a noble-metal-free photosensitizer-catalyst system in aqueous solution under red-light irradiation. The water-soluble Mn(I) tricarbonyl diimine complex acts as the catalyst, while tetra(N-methyl-4-pyridyl)-porphyrin Zn(II) tetrachloride functions as the photosensitizer. This research opens up new possibilities for the use of intrinsically photounstable Mn(I) complexes as solar-driven catalysts in an aqueous environment.