Synthesis, physicochemical studies and aerobic enantioselective epoxidation of non functionalized olefins catalyzed by new Co(II) chiral salen complexes

Abstract

Co(II) chiral salen complexes 1– 3 derived from α-naphthyl salicylaldehyde with 1 S,2 S (+) diaminocyclohexane, 1 R,2 R (−) diaminodiphenylethane and S(+) 1,2-diaminopropane have been prepared. The characterization of the complexes was done by microanalysis, magnetic moment, IR-, UV/Vis-, CD spectral studies, optical rotation, conductance measurements and cyclic voltammetry. Epoxidation of non-functionalized prochiral olefins viz. styrene, trans 3-nonene and trans 4-octene was achieved by the combined use of an atmospheric pressure of molecular oxygen and sacrificial reductant isobutyraldehyde catalyzed by the above synthesized Co(II) chiral salen complexes with and without pyridine N-oxide as cooxidant. Good yields of the desired epoxide were obtained with the substrate trans 3-nonene and trans 4-octene by GLC. Enantiomeric excess of the epoxide were evaluated by 1 H NMR using chiral shift reagent Eu(hfc) 3 and by chiral capillary column.