Chloromethylated polystyrene cross-linked with divinylbenzene and grafted with vanadium(IV) and vanadium(V) complexes having ONO donor ligand for the catalytic activity

The ligand H(2)sal-iah (I), derived from salicylaldehyde and indole-3-acetic hydrazide, reacts with [(VO)-O-IV(acac)(2)] in methanol to give oxidovanadium(IV) complex [(VO)-O-IV(sal-iah)(H2O)] (1). In the presence of KOH, arial oxidation of 1 in methanol yields dioxidovanadium(V) complex K[(VO2)-O-V(sal-iah).H2O] (2). Complex 1 has been grafted via covalent bonding through imino nitrogen of the indole group to chloromethylated polystyrene cross-linked with 5% divinylbenzene now abbreviated as PS-[(VO)-O-V(sal-iah)(H2O)] (3)1. Its oxidomethoxido vanadium(V) analog {PS-[(VO)-O-V(OMe)(sal-iah)] (4)} can be obtained by aerial oxidation of methanolic suspension of 3. All these complexes are characterized by various spectroscopic techniques (IR, electronic,H-1 and V-51 NMR, electron paramagnetic resonance (EPR) and thermal as well as field-emission scanning electron micrographs (FE-SEM)) studies. The EPR spectrum of 3 indicates that the magnetically dilute VIv0-centers are well dispersed in the polymer matrix while EPR spectrum of 1 shows slightly different binding mode around vanadium center. H-1 and V-51 NMR spectra of 2 are compatible with the existence of expected dioxide species as the major product and oxidomethoxido species as a minor component in solution. Independent of the species presents in methanol, complexes 1 and 2 upon treatment with H2O2 both change to same oxidoperoxido species. The polymer-grafted complex 4 catalyzes the oxidation, by H2O2, of styrene and cyclohexene. Under optimized reaction conditions, the oxidation of styrene gave 95% conversion where styrene oxide, benzaldehyde, benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde are products. Oxidation of cyclohexene gave 96% conversion with cyclohexene oxide, 2-cyclohexene-l-ol, cyclohexane-1,2-diol and 2-cyclohexene-1-one as the major products. Neat complex K[(VO2)-O-V(sal-iah)].H2O (2) is equally active but the recyclability and heterogeneity tests of polymer-grafted complex make it better over neat analog. (C) 2013 Elsevier B.V. All rights reserved.