Six‐coordinated vanadium(IV) complexes with tridentate task‐specific ionic liquid Schiff base ligands: Synthesis,characterization and effect of ionic nature on catalytic activity

By reaction of 5‐(chloromethyl)salicylaldehyde with triphenylphosphine and N‐methylimidazole in two separate reactions, salicylaldehydetriphenylphosphonium chloride (S²) and salicylaldehydemethylimidazolinium chloride (S³) were prepared. Reaction of 2‐(aminomethyl)pyridine with these aldehydes resulted in the task‐specific ionic liquid Schiff base ligands L¹ and L², respectively. Then six‐coordinated vanadium(IV) Schiff base complexes of VO(acac)L^1–4 were synthesized by reactions of these tridentate Schiff base ligands and VO(acac)₂ in 1:1 stoichiometry. The aldehydes, ligands and VO(acac)L^1–4 complexes were characterized using infrared, ¹H NMR, ¹³C NMR, ³¹P NMR, UV–visible and mass spectroscopies, as well as elemental analysis. Paramagnetic property of the complexes was also studied using magnetic susceptibility measurements. The complexes were used as catalysts in epoxidation of cyclooctene and oxidation of methylphenyl sulfide and the reaction parameters were optimized. The effect of the ionic nature of the complexes was investigated in these oxidation reactions. The catalytic activity of the complexes could be varied by changing the ionic (cationic or anionic) character of VO(acac)L^1–4 catalysts in which counter anion variation showed a greater effect than cationic moiety variation.