Asymmetric catalytic epoxidation of styrene by dissymmetric Mn(III) and Ru(III) chiral Schiff base complexes synthesis and physicochemical studies

Some dissymmetric Mn(III) and Ru(III) chiral Schiff base complexes derived from 1R,2R(-)1,2-diaminocyclohexane with 3-acetyl-4-hydroxy-6-methyl-2-pyrone and salicylaldehyde, 5-chloro-5-methoxy-and 5-nitrosalicylaldehyde have been synthesized. The characterization of the complexes was accomplished by microanalysis, IR, UV-Vis, CD spectroscopy, conductance measurements, magnetic susceptibility, optical rotation and electrochemical studies. The asymmetric epoxidations catalyzed by the complexes were examined with styrene using the terminal oxidant, iodosylbenzene to assess the stereoselectivity in the epoxidation of styrene by changing substituents on the catalyst. In all cases the R form of the catalyst resulted in S(-) form of the product as a dominant enantiomer. Optical yield of the resulting epoxide was determined by GLC using chiral capillary column/H-1 NMR using Eu(hfc)(3) as a chiral shift reagent.