Influence of the Conformation of Salen Complexes on the Stereochemistry of the Asymmetric Epoxidation of Olefins

Abstract

Abstract Compared with Katsuki’s or Jacobsen’s catalysts ( R , R , R , R )‐ 1 or ( R , R )‐ 2 , the phenomenon of reversed asymmetric induction in the course of the epoxidation of unfunctionalised olefins in the presence of (salen) manganese complex ( S , S )‐ 3 is indirectly explained by means of quantumchemical calculations, as well as by 1 H NMR spectra of salen ligand ( S , S )‐ 10 and diamagnetic low‐spin nickel complex ( S , S )‐ 7 and by its X‐ray structure analysis. Whereas in ( R , R , R , R )‐ 1 and ( R , R )‐ 2 the phenyl and cyclohexyl substituents occupy equatorial positions, the origin for the reversed enantioselection caused by manganese catalyst ( S , S )‐ 3 , is based on an axial position of the acyclic heteroalkyl substituents in the diimine backbone of ( S , S )‐ 3 as exemplarily confirmed by model nickel complex ( S , S )‐ 7 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)