Efficient allylic oxidation of cyclohexene with oxygen catalyzed by chloromethylated polystyrene supported tridentate Schiff-base complexes

Four novel chloromethylated polystyrene supported tridentate Schiff-base metal complexes (PS–DA–M, M = Cu2+, Co2+, Ni2+ and Mn2+, respectively) were prepared by chloromethylated polystyrene and tridentate Schiff-base ligands, which were synthesized by 2,4-dihydroxyacetophotone with 2-aminopyridine. The complexes were characterized by the methods of ICP, FT-IR, XPS and TG/DTA. The catalytic activity of the complexes in the oxidation of cyclohexene with molecular oxygen was determined. The results showed that oxidation reaction was occurred in the allylic carbon atoms. The products are cyclohexene oxide, 2-cyclohexene-1-ol, 2-cyclohexene-1-one and 2-cyclohexene-1-hydroperoxide. Although all of four complexes showed good catalytic activity, PS–DA–Cu exhibited the best. The conversion of cyclohexene can be reached to 51.9% under the temperature of 343 K when using 2 mg of PS–DA–Cu to catalytic oxidation of 2 ml of cyclohexene. The influences of reaction temperature, the amount of catalyst, the reaction time were investigated, and the mechanism of cyclohexene oxidation was also discussed.