Synthesis, characterization and study of vanadyl tetradentate Schiff base complexes as catalyst in aerobic selective oxidation of olefins

Abstract

Novel vanadyl Schiff base complexes with the general formula VOL x ( x=7–18) were synthesized and characterized by physicochemical methods. Only an orange polymeric form was obtained for VOL 13, both brown polymeric and green monomeric forms were obtained for VOL x , x=16, 17. These observations suggest that in these complexes oxovanadium(IV) exhibit a coordination number of five. Systematic substitution on the ancillary ligand have allowed V(V)/V(IV) reduction potentials to be tuned over a range of approximately 130 mV. The complexes are catalysts for the aerobic oxidation of cyclohexene. Catalytic activity increases with increasing V(V)/V(IV) reduction potential and the catalytic selectivity varied by changes in the ligands. The catalytic system described here is an efficient and inexpensive method for oxidation of olefins, with advantages of high activity, selectivity, re-usability and short reaction times.