Chiral Bis(imidazolidine)-Derived NCN Pincer Rh Complex for Catalytic Asymmetric Mannich Reaction of Malononitrile with N-Boc Imines.

Chiral bis(imidazolidine)-derived NCN-rhodium complexes ([PhBidine-RhX2 ] and [tBu-PhBidine-RhX2 ]) were prepared by a CH insertion method, and the structures were unequivocally determined by X-ray crystallographic analysis. The [tBu-PhBidine-Rh(OAc)2 ] complex smoothly catalyzed an asymmetric Mannich reaction of malononitrile with N-Boc imines to give products in up to 94 % ee, which are useful for the synthesis of chiral α-amino acids.