Encapsulation of oxovanadium(IV) and copper(II) complexes of monobasic bidentate NS donor ligand, 2-mercaptomethylbenzimidazole (Htmbmz) in the cavity of zeolite-Y by flexible ligand method has been described. These complexes have been characterized by various physicochemical methods. These encapsulated complexes, abbreviated as [VO(tmbmz)(2)]-Y and [Cu(tmbmz)(2)]-Y, have been used as catalysts for the oxidation of styrene, methyl phenyl sulfide and diphenyl sulfide. Under the optimized reaction conditions, [VO(tmbmz)2]-Y gave 96.4% conversion of styrene with five oxidation products, styrene oxide, benzaldehyde, benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde. Conversion of styrene with [Cu(tmbmz)(2)]-Y is considerably low (36.9%) and gave only four products, styrene oxide, benzaldehyde, benzoic acid and phenvlacetaldehyde. In both cases formation of benzaldehyde is relatively high. These catalysts are also very active for the oxidation of methyl phenyl sulfide and diphenyl sulfide. The oxidation of diphenyl sulfide required at least H2O2 to diphenyl sulfide molar ratio of 3:1 to give 91.7% conversion in 7 h of reaction time. However, 94.3% conversion of methyl phenyl sulfide has been achieved within 3 h of contact time at substrate to H2O2 molar ratio of 1:1. The catalytic activity of neat complexes using similar molar concentration as that used for the encapsulated complexes under above reaction conditions have also been tested for comparison. It has been observed that the corresponding neat complexes have shown equally good catalytic activities. But high turn over frequency and recyclability make the zeolite-Y encapsulated complexes better than their neat analogues. (c) 2007 Elsevier B.V. All rights reserved.