Visible-light-induced photoredox catalysis with a tetracerium-containing silicotungstate.

The development of visible-light-induced photocatalysts for chemoselective functional group transformations has received considerable attention. Polyoxometalates (POMs) are potential materials for efficient photocatalysts because their properties can be precisely tuned by changing their constituent elements and structures and by the introduction of additional metal cations. Furthermore, they are thermally and oxidatively more stable than the frequently utilized organometallic complexes. The visible-light-responsive tetranuclear cerium(III)-containing silicotungstate TBA6[{Ce(H2O)}2{Ce(CH3CN)}2(μ4-O)(γ-SiW10O36)2] (CePOM; TBA=tetra-n-butylammonium) has now been synthesized; when CePOM was irradiated with visible light (λ>400 nm), a unique intramolecular Ce(III)-to-POM(W(VI)) charge transfer was observed. With CePOM, the photocatalytic oxidative dehydrogenation of primary and secondary amines as well as the α-cyanation of tertiary amines smoothly proceeded in the presence of O2 (1 atm) as the sole oxidant.