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

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posted on 2014-02-10, 00:00 authored by Maritza J. Bravo, Isabelle Favier, Nathalie Saffon, Rosa M. Ceder, Guillermo Muller, Montserrat Gómez, Mercè Rocamora
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.

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