Chiral Metallosalen Complexes: Structures and Catalyst Tuning for Asymmetric Epoxidation and Cyclopropanation

Abstract

Optically active metallosalens are currently one of the most widely used catalysts for asymmetric synthesis. This is mainly due to the following reasons: various salen [N,N′-ethylenebis(salicyldeneaminato)] ligands form complexes with many metal ions and the resulting metallosalens adopt versatile structures, therefore, metallosalens show a variety of catalytic performances. Thus, selection of a metal ion serving the aimed reaction and regulation of ligand conformation to be suitable for the reaction are indispensable for achieving metallosalen-catalyzed asymmetric reactions. Recently, several factors controlling ligand-conformation in metallosalens have been clarified. This article provides selected examples of tuning the structures of metallosalens in compliance to the aimed reaction, by taking asymmetric oxene or carbene transfer reaction as the instance.