Modulating the Catalytic Properties of Polyoxovanadates with Transition-Metal-Complex Units for Selective Oxidation...

Selective oxidation of sulfides to sulfoxides is of great significance in the synthesis of pharmaceuticals, desulfurization of fuels, and detoxification of sulfur mustard chemical warfare agents. Designing selective catalysts to achieve the efficient transformation of sulfides to sulfoxides is thus highly desired. Herein, we report three transition metal-complex-functionalized polyoxovanadates, [Zn₂(BPB)₂][V₄O₁₂]·0.5BPB·H₂O (1), [Ni(BPB)(H₂O)][V₂O₆]·2H₂O (2), and [Co(HBPB)₂][V₄O₁₂] (3) (BPB = 1,4-bis(pyrid-4-yl)benzene)), and explore their applications for selective oxidation of sulfides using H₂O₂ as an oxidant. All three compounds were catalytically effective for the oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide, with 1 being best-performing with complete conversion and a selectivity of 96.7%. In the selective oxidation of a series of aromatic and aliphatic sulfides to corresponding sulfoxides, 1 also showed satisfactory performance; in particular, the chemical warfare agent stimulant 2-chloroethyl ethyl sulfide can be completely and selectively oxidized to the nontoxic 2-chloroethyl ethyl sulfoxide within 20 min at room temperature. Catalyst 1 can be recycled and reused at least six times with uncompromised performance. The perfect performance of 1 is attributed to the synergistic effect of coordinatively unsaturated V and Zn sites in bimetallic oxide, as revealed by comparative structural and catalytic studies.