Synthesis, characterization and catalytic activities of vanadium complexes containing ONN donor ligand derived from 2-aminoethylpyridine

Reaction between [(VO)-O-IV(acac)(2)] and the ONN donor Schiff base Hpydx-aepy (I) (Hpydx-aepy = Schiff base obtained by the condensation of pyridoxal and 2-aminoethylpyridine) resulted in the formation of a complex [(VO)-O-IV(acac)(pydx-aepy)] (1). Addition of aqueous 30% H2O2 to 1 yields the poor stable oxidoperoxidovanadium(V) complex [(VO)-O-V(O-2)(pydx-aepy)] (2). Its formation has also been demonstrated in solution by treating 1 with H2O2 in methanol. Reaction of vanadium exchanged zeolite-Y with I in methanol followed by aerial oxidation gave zeolite-Y encapsulated dioxidovanadium(V) complex, abbreviated as [(VO2)-O-V(pydx-aepy)]-Y (4). The crystal and molecular structure of 1 has been determined, confirming the ONN binding mode of the ligand. The encapsulated complex [(VO2)-O-V(pydx-aepy)]-Y (4) catalyses the oxidation of styrene, cyclohexene, methyl phenyl sulfide and diphenyl sulfide using H2O2 as oxidant in good yield. Styrene under optimised reaction conditions gave four reaction products namely, styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol and benzoic acid while organic sulfides gave the corresponding sulfoxide as the major product. Cyclohexene gave cyclohexene epoxide, 2-cyclohexene-1-one, 2-cyclohexene-1-ol and cyclohexane-1,2-diol. Neat complex [(VO)-O-IV(acac)(pydx-aepy)] has been used as catalyst precursor to compare its catalytic activities with the encapsulated one. (C) 2011 Elsevier B.V. All rights reserved.