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

Abstract

The ligand H2sal-iah (I), derived from salicylaldehyde and indole-3-acetic hydrazide, reacts with [VIVO(acac)2] in methanol to give oxidovanadium(IV) complex [VIVO(sal-iah)(H 2O)] (1). In the presence of KOH, arial oxidation of 1 in methanol yields dioxidovanadium(V) complex K[VVO2(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-[V IVO(sal-iah)(H2O)] (3)}. Its oxidomethoxido vanadium(V) analog {PS-[VVO(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, 1H and 51V 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 VIVO-centers are well dispersed in the polymer matrix while EPR spectrum of 1 shows slightly different binding mode around vanadium center. 1H and 51V 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 H 2O2, 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-1-ol, cyclohexane-1,2-diol and 2-cyclohexene-1-one as the major products. Neat complex K[VVO2(sal-iah)]·H 2O (2) is equally active but the recyclability and heterogeneity tests of polymer-grafted complex make it better over neat analog. © 2013 Elsevier B.V.