Selectivity switch in the aerobic oxygenation of sulfides photocatalysed by visible-light-responsive decavanadate†
Nanometre-sized metal oxides are promising species for the development of visible-light-responsive photocatalysts for the selective transformation of organic functional groups. In this article, we report that decavanadate ([V10O28]6−, V10) behaved as an efficient visible-light-responsive photocatalyst in the product-selective oxygenation of sulfides achieved using O2 (1 atm) as the green oxidant. In particular, we revealed that visible-light-responsive photocatalysis of V10 showed remarkable activity for the oxygenation of structurally diverse sulfides to form the corresponding sulfones using O2 in methyl ethyl ketone (MEK). Furthermore, by simply adding water to the reaction mixture, the product selectivity of sulfide oxygenation can be significantly switched toward the production of sulfoxides, without concomitant loss of photocatalytic activity. Based on experimental evidence, we inferred the following mechanistic steps for this photocatalytic system: the aerobic oxygenation of sulfides to form the corresponding sulfoxides initiated by a visible-light-induced photoredox reaction of V10. As for the formation of sulfones, MEK-derived peroxide species as the co-catalysts are probably involved in the oxygenation of sulfoxides to sulfones. The selectivity switch of the V10-photocatalysed reaction brought about by water addition is most likely achieved by suppressing the formation of MEK-derived peroxide species.