Visible-Light-Responsive 2D Photocatalysts Assembled by Evans-Showell-Type POMs and Metalloviologen Frameworks for Sulfide-Sulfoxide Transformation.

Sulfide-sulfoxide aerobic photo-oxidation is of great interest in organic and medicinal chemistry; however, developing efficient and facile heterogeneous photocatalytic systems without additional additives remains challenging. Herein, we intentionally designed and synthesized two polyoxometalate (POM)-based metalloviologen frameworks, formulated as [M II (4-PBPY) 2 (H 2 O)][M II (H 2 O) 4 ][Co III 2 Mo VI 10 H 4 O 38 ]· n H 2 O (M = Cu, n = 10 for 1 ; M = Co, n = 11 for 2 ), prepared by the mild one-step synthesis strategy and characterized in detail. X-ray single-crystal diffraction analysis shows that they present a two-dimensional layered structure formed by two parallel metalloviologen layers pillared by dimeric Evans-Showell-type POMs. The connection of POM to the metalloviologen framework enables easier flow of electrons to the POM port, which can theoretically further induce O 2 to generate reactive oxygen species (O 2 •- ) to oxidize substrates to form target products. As expected, both 1 and 2 exhibit outstanding photocatalytic activity in the oxidation of sulfides. Within 6 h, methyl phenyl sulfide can be quantitatively converted into methyl phenyl sulfoxide. The in-depth mechanism reveals that there is also a synergistic energy-transfer pathway in the catalytic system in addition to the electron-transfer pathway. In addition, the corresponding catalytic activity and structure can be well maintained after at least 10 cycle experiments.