Synthesis, Coordination Properties and Application of New N,N-Ligands Based on Bornyl and Binaphthylazepine Chiral Backbones in Palladium-Catalyzed Allylic Substitution Reactions

The synthesis of new imine-amine and diamine ligands, based on both the atropisomeric (S(a))- or (R(a))-1,1'-binaphthyl and (R)-bornyl backbones, and incorporating an ethylenediamino spacer, are reported. In addition, analogue ligands in which one chiral arm is replaced by the achiral NMe(2) group were synthesized. These N,N-ligands when coordinated to a palladium metal centre form highly enantioselective catalysts for the asymmetric allylic alkylation of rac-2-acetoxy-1,3-diphenylpropene by dimethyl malonate. In one case, the synergic effect of the chirality elements in the palladium catalyst afforded the (S) substitution product with an enantiomeric excess (ee) of >99%. Based on NMR studies of the active species in solution, a reliable explanation for the origin of the enantioselectivity of these palladium catalysts is also provided.