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

Sulfide-sulfoxide aerobic photo-oxidation is ofgreat interestin organic and medicinal chemistry; however, developing efficientand facile heterogeneous photocatalytic systems without additionaladditives remains challenging. Herein, we intentionally designed andsynthesized two polyoxometalate (POM)-based metalloviologen frameworks,formulated as [M-II(4-PBPY)(2)(H2O)][M-II(H2O)(4)][Co-III Mo-2(VI) 10H4O38]& BULL;nH(2)O (M = Cu, n = 10 for 1; M = Co, n = 11 for 2), preparedby the mild one-step synthesis strategy and characterized in detail.X-ray single-crystal diffraction analysis shows that they presenta two-dimensional layered structure formed by two parallel metalloviologenlayers pillared by dimeric Evans-Showell-type POMs. The connectionof POM to the metalloviologen framework enables easier flow of electronsto the POM port, which can theoretically further induce O-2 to generate reactive oxygen species (O-2 (& BULL;-)) to oxidize substrates to form target products. As expected, both 1 and 2 exhibit outstanding photocatalytic activityin the oxidation of sulfides. Within 6 h, methyl phenyl sulfide canbe quantitatively converted into methyl phenyl sulfoxide. The in-depthmechanism reveals that there is also a synergistic energy-transferpathway in the catalytic system in addition to the electron-transferpathway. In addition, the corresponding catalytic activity and structurecan be well maintained after at least 10 cycle experiments. The 2D Evans-Showell-type POM-basedmetalloviologenframeworks were developed as heterogeneous photocatalysts for visible-light-drivenaerobic oxidation of sulfides to sulfoxides.