New capacity of (salen)manganese complexes:: Asymmetric oxidation of C-H σ-bond and dynamic control of ligand conformation

Chiral (salen)manganese(III) complexes (Mn-salen complexes) bearing chiral centers at their ethylenediamine moiety and chiral binaphthyl units in the salicylaldehyde moiety are excellent catalysts for asymmetric oxidation and the relative configuration between the two chiral units (at the ethylenediamine and salicylaldehyde moieties) has been found to strongly relate to the substrate-specificity of the Mn-salen complexes. In this paper, we describe asymmetric C-H bond oxidation using new Mn-salen complexes prepared by tuning the relative configuration and substituents on the salen ligand. The relationship between relative configuration and the conformation of the ligand which affects asymmetric; induction by Mn-salen complexes, is also discussed. Ligand conformation has also been found to be dynamically controlled by external chiral donor ligand; Thus, achiral Mn-salen complex can be used as a chiral catalyst by simply controlling the ligand conformation. New features of Mn-salen chemistry brought by the control of ligand conformation are also discussed in this paper.