Enhanced catalytic activity of oxovanadium complexes in oxidative polymerization of diphenyl disulfide

Oxygen-oxidative polymerization of diphenyl disulfide gives poly(1,4-phenylene sulfide) (PPS), catalyzed by a vanadyl complex and a protic acid. N,N′-Ethylenebis(salicylideneaminato)oxovanadium(iv) (VO(salen)) which has been reported to be catalytically inactive at ambient temperature because of the insufficient reactivity of its oxidized state, an oxovanadium(v) complex, for the oxidation of the monomer turned out to exhibit an excellent catalytic activity on raising the reaction temperature above 100 °C. The enhanced reactivity of VO(salen)-acid or bis(2,4-pentanedionato)oxovanadium(iv) (VO(acac)₂)-acid catalytic systems at elevated temperatures gave insight into the catalytic mechanism where oxidation of the monomer with the oxovanadium(v) complex dominated the reactivity, which was also accelerated by a second redox shuttle molecule, such as quinones with a potential near that of the [VO(salen)]^0/+ couple.