Novel vanadyl Schiff base complexes with the general formula VOLx (x = 7-18) were synthesized and characterized by physicochemical methods. Only an orange polymeric form was obtained for VOL13, both brown polymeric and green monomeric forms were obtained for VOLx, 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 130mV. 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. (9 2002 Elsevier Science B.V. All rights reserved.