Precise Design of Polyoxometalates and their Application to Photocatalyst

Polyoxometalates, which are anionic metal oxide clusters, have recently attracted considerable attention as photocatalysts because of their unique photoinduced charge-transfer properties, multielectron redox properties, acid-base properties, and reactivities of the photoexcited species. In particular, polyoxometalate photocatalysis has been utilized for liquid-phase organic reactions. However, typical polyoxometalate photocatalysts, including decatungstate, require irradiation with UV light because of the large energy gaps between the O2−-based highest occupied molecular orbitals(HOMOs)and the W6+-based lowest unoccupied molecular orbitals(LUMOs)therein. We have developed a new precise synthesis method of polyoxometalates by controlled reaction of lacunary polyoxometalates and metal species in organic solvents. Based on the design of the structures and electronic states of polyoxometalates, we have developed visible-light responsive polyoxometalate photocatalysts. This article describes the precise synthesis of polyoxometalates and their applications to visible-light-responsive photocatalysis for organic synthesis.