Polymer supported vanadium and molybdenum complexes as potential catalysts for the oxidation and oxidative bromination of organic substrates

摘要

The Schiff base (H(2)fsal-ohyba) derived from 3-formylsalicylic acid and o-hydroxybenzylamine has been covalently bonded to chloromethylated polystyrene cross-linked with 5% divinylbenzene ( abbreviated as PS-H(2)fsal-ohyba, I). Treatment of [VO(acac)(2)] with PS-H(2)fsal-ohyba in dimethylformamide (DMF) gave the oxovanadium(IV) complex PS-[VO(fsal-ohyba) center dot DMF] (1). Complex 1 can be oxidized into the dioxovanadium(V) species, PS- K[VO2(fsal-ohyba)] ( 2) on aerial oxidation in the presence of KOH or into the oxoperoxo species, PS-K[VO(O-2)(fsal-ohyba)] ( 3) in the presence of H2O2 and KOH in DMF suspension. Similarly, PS-[MoO2(fsal-ohyba) center dot DMF] ( 4) has been isolated by the reaction of [MoO2(acac)(2)] with PS-H(2)fsal-ohyba. All these complexes have been characterised by various techniques. These complexes catalyse the oxidation of styrene, ethylbenzene and phenol efficiently. Styrene gives five reaction products namely styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol, benzoic acid and phenylacetaldehyde, while ethylbenzene gives benzaldehyde, phenyl acetic acid, styrene and 1-phenylethane-1,2-diol. The oxidation products of phenol are catechol and p-hydroquinone. These catalysts are also able to catalyse the oxidative bromination of salicylaldehyde to 5-bromosalicylaldehyde with ca. 80% selectively in the presence of aqueous 30%H2O2/KBr, a reaction similar to that exhibited by vanadate-dependent haloperoxidases. Their corresponding neat complexes have also been prepared and their catalytic activities have been compared.