Enantioselective Preparation of Planar-Chiral Transition Metal Complexes by Asymmetric Olefin-Metathesis Reactions in Metal Coordination Spheres

Planar-chiral transition metal complexes are useful chiral auxiliaries in organic and organometallic chemistry, and they have been utilized as chiral ligands, chiral catalysts, or chiral building blocks, etc. Despite the importance of such planar-chiral species in asymmetric synthesis, their preparation in optically active forms is still a challenging problem. Indeed, reported examples of catalytic enantioselective synthesis of planar-chiral complexes have been rare, and this has been a developing area in this field. In this personal account, recent results from our research group on the catalytic asymmetric synthesis of various planar-chiral transition metal complexes are summarized. The asymmetric ring-closing metathesis reactions catalyzed by the well-defined molybdenum-alkylidene species are powerful methods to control the planar chirality in ferrocenes, ruthenocenes, (eta(6)-arene)chromium complexes, and (eta(5)-cyclopentadienyl)manganese(I) complexes. Application of the enantiomerically enriched complexes obtained by our methods is described as well.