Catalytic Asymmetric Synthesis of Planar-Chiral Transition-Metal Complexes

Although "central chirality" based on stereogenic carbon atoms is arguably the most common chiral element in organic chemistry, chiral molecules devoid of stereogenic centers play important roles in stereoselective organic transformations. Among these chiral compounds with "non-centrochirality", planar-chiral transition-metal complexes have been utilized as chiral ligands, chiral catalysts, or chiral building blocks in asymmetric synthesis. However, enantiomerically enriched forms of these compounds are primarily obtained by rather classical methods. Examples of catalytic enantioselective induction of planar-chirality in transition-metal species have been extremely rare and still a developing area in this field. In this review article, catalytic asymmetric synthesis of various "planar-chiral transition-metal complexes" are surveyed in a comprehensive manner.