Efficient Palladium Catalysts Containing Original Imidazolium-Tagged Chiral Diamidophosphite Ligands for Asymmetric Allylic Substitutions in Neat Ionic Liquid

New
imidazolium-tagged chiral diamidophosphite ligands, (S,S)-a and (R)-b, derived from (S,S)-N,N′-dibenzyl-1,2-cyclohexanediamine
and (R)-N,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine,
respectively, and the corresponding palladium allylic complexes of
general formula [PdCl­(η3-2-Me-C3H4)­(κ1P-L)]­BF4 (1a,b) and [Pd­(η3-2-Me-C3H4)­(κ1P-L)2]­(BF4)3 (2a,b) were synthesized and fully characterized, including the X-ray crystal
structure for 1b. These original Pd/L catalytic systems
were applied in asymmetric allylic alkylation, amination, and sulfonylation
using rac-3-acetoxy-1,3-diphenyl-1-propene as a substrate
in neat ionic liquids, [bmim]­[PF6] and [Pyr]­[NTf2]. The best results in terms of enantioselectivity were obtained
with the catalytic precursor 1b in [Pyr]­[NTf2]. The catalytic phase containing 1b for the allylic
amination could be recycled up to six times without significant loss
of asymmetric induction.