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

Abstract

Reaction between [V IVO(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 [V IVO(acac)(pydx-aepy)] (1). Addition of aqueous 30% H 2O 2 to 1 yields the poor stable oxidoperoxidovanadium(V) complex [V VO(O 2)(pydx-aepy)] (2). Its formation has also been demonstrated in solution by treating 1 with H 2O 2 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 [V VO 2(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 [V VO 2(pydx-aepy)]-Y (4) catalyses the oxidation of styrene, cyclohexene, methyl phenyl sulfide and diphenyl sulfide using H 2O 2 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 [V IVO(acac)(pydx-aepy)] has been used as catalyst precursor to compare its catalytic activities with the encapsulated one.