Persistent N-chirality as the only Source of asymmetry in nonracemic N 2PdCl2 complexes

Article abstract of DOI:10.1021/om0498495

The combination of prochiral 1,2-diamines, Pd(OAc)₂, and (R)-K₂-3,3′-Me₂BINOL leads to enantio- and diastereopure N₂Pd(3,3′-Me₂BINOL) complexes. HCl removes the Me₂BINOL resolving ligand and provides a family of enantiopure N₂PdCl₂ complexes whose only stereochemistry resides on the stereogenic nitrogen centers. In effect, nitrogen inversion (>10⁵ s^-1) is halted by metal coordination and utilized to generate enantiopure complexes. When the diamine substituents are relatively small, the N-chirality is stable; however, large substituents accelerate N-dissociation processes and concomitant racemization. Enantiopure N ₂Pd²⁺-Lewis acid catalysts can be generated for the Diels-Alder reaction, and although enantioselectivities are low (<25% ee), this is due to inefficient stereochemical transfer and not a degradation of the catalyst's chirality.