Unique asymmetric catalysis of cis-beta metal complexes of salen and its related Schiff-base ligands

Complexes of chiral salen and its related tetradentate Schiff-base ligands adopt three different configurations, trans, cis-alpha and cis-beta. Of these complexes, trans-complexes have been widely used as catalysts for various asymmetric reactions. However, recent studies have disclosed that cis-beta metallosalen and its related complexes show unique asymmetric catalyses that cannot be achieved by trans-metallosalen complexes. The present article summarizes generation of cis-beta metallosalen and its related complexes, their structural features, and their application to asymmetric syntheses.