Asymmetric epoxidation of styrene by novel chiral ruthenium(II) Schiff base complexes, synthesis and characterization.

Abstract

Synthesis of some novel Chiral Ru(II) Schiff base complexes of the type [RuL(PPh 3)(H 2O) 2] 1–6 where L = Chiral Schiff bases derived from salicylaldehyde and L-amino acids namely, L-alanine, L-valine, L-Serine, L-Arginine, L-Cystein and L-aspartic acid are reported. The characterisation of the complexes has been accomplished by microanalysis. IR-,UV/visible,[ 1H], 13C[ 1H] and 31P[ 1H] NMR spectroscopy, conductance measurements, electrochemical studies, optical rotation and circular dichroism soectroscopy. The conformational aspects regarding the asymmetric arrangement of substituents R at aminoacid moiety of the Schiff bases around Ru(II) metal ion has been discussed. The complexes show quasireversible behaviour and the redox potential of Ru(II)/Ru(I) couple lie in the range −0.34 to −0.18 volts. In the asymmetric epoxidation of styrene by the complexes 1 – 6 and idosylbenzene, we observed that on employment of the R form of the catalyst resulted in the formation of (S) styrene oxide as dominant enantiomer by GLC and NMR. Enantiomeric excess for the resulting epoxides were determined by [ 1H] NMR spectroscopy using Chiral shift reagent, tris[3-(heptafluoropropyl hydroxymethylene − (+) camphoratoleuropium(III), Eu(hfc) 3.