The chiral short-
bite ligands (Ra,Ra)-bis(dinaphthylphosphonito)methane, (Ra,Ra)-1, (Ra,Ra)-bis-dinaphthylpyrophosphite, (Ra,Ra)-2, (Sc)-bis(diphenylphosphino)-sec-butylamine, (Sc)-3, (Ra,Ra)-bis(dinaphthylphosphonito)
phenylamine, (Ra,Ra)-4a, (Ra,Ra,Sc)-bis(dinaphthylphosphonito)-sec-butylamine, (Ra,Ra,Sc)-4b, and (Ra,Sc)-(dinaphthylphosphonito)(diphenylphosphino)-sec-butylamine, (Ra,Sc)-5, have been synthesised. The cationic
palladium-allyl mononuclear chelate, [Pd(eta3-PhCHCHCHPh)(mu-L-Lshort-
bite)]PF6 [L-Lshort-
bite=(Sc)-3, (Ra,Ra)-4a, (Ra,Ra,Sc)-4b and (Ra,Sc)-5 for complexes, and, respectively] and binuclear bridged [Pd(eta3-PhCHCHCHPh)(mu-Ra,Ra-2)]2(PF6)2, 12, have been isolated. The short-
bite chiral
ligands synthesised have been tested in the
palladium-allyl catalysed substitution reaction of 1,3-diphenylallyl
acetate with
dimethyl malonate. The catalytic system was studied, in
solution, by a multinuclear NMR technique. In the catalytically active species formed with (Ra,Ra)-2
ligand, [Pd(eta3-PhCHCHCHPh)(Ra,Ra-2)]2(PF6)2, 12, the
palladium(II) centres are bridged by two
ligands which are forced to adopt a nearly cis-coordination to allow coordination of the allyl-moiety. Semiempirical calculations on a
biphenyl-model molecule, similar to the species 12, indicate that this situation induces a strain and rigid conformation in the chiral
ligands, which produce differences in the terminal allyl
carbon atoms. As consequence, the catalytic product was obtained with an enantiomeric excess of 57.1% in the S form. A low e.e. value was obtained when the (Ra,Ra)-1, (Sc)-3, (Ra,Ra)-4a, (Ra,Ra,Sc)-4b and (Ra,Sc)-5
ligands have been tested in the same
palladium-catalysed reaction.