Chiral N-Heterocyclic Carbenes with Restricted Flexibility in Asymmetric Catalysis^†

A chiral C₂-symmetric diamine was prepared from (S)-3-phenyl-3,4-dihydroisoquinoline by the virtue of asymmetric transformation. Rhodium and iridium complexes of chiral N-heterocyclic carbenes with restricted flexibility derived from 3,3‘-substituted partially reduced biisoquinoline were obtained by transmetalation from the corresponding silver(I) complexes. Unexpected double-bond formation in the carbene ligand has occurred during a transmetalation step. The structures of these complexes were verified by X-ray diffraction. Metal complexes of these N-heterocyclic carbenes were applied to the asymmetric hydrogenation of methyl 2-acetamidoacrylate. Good enantioselectivities of up to 67% ee were achieved.