Non-symmetrical tetradentate vanadyl Schiff base complexes derived from 1,2-phenylene diamine and 1,3-naphthalene diamine as catalysts for the oxidation of cyclohexene

Two series of the novel unsymmetrical diimino tetradentate Schiff bases derived from phenylenediamine and 1,3-naphthalene diamine and their vanadyl complexes were synthesized by template and non-template methods and characterized by 1H, 13C NMR, IR, UV–Vis and elemental analysis. These complexes are used as catalysts for the selective aerobic oxidation of cyclohexene. The catalytic activity increases as the number of electron-donor groups decreases, and the catalytic selectivity is varied by changing the substituents on the ligands. The catalytic system described here is an efficient and inexpensive method for the oxidation of olefins, with the advantages of high activity, selectivity, re-usability and short reaction times. Complexes containing the naphthylene bridged ligands had similiar redox potentials, however, their catalytic activities are quite varied. This difference in their activity is strongly dependent on fine structural data and ΔEp. But in the complexes containing phenylene bridged ligands, comparing the GC, redox potential and ΔEp measurements yields a good correlation between catalytic activity and redox potential and a slight corrolation to selectivity. In general, the conversion percentage decreases with the increase of ΔEp and decrease of Eredox0′.