Diphosphines containing stereogenic P atoms:: Synthesis of (S,S)-C,C′-tetramethylsilanebis-(1-naphthylphenylphosphine) and applications in enantioselective catalysis

The diphosphine (S,S)-Me2Si(CH2P(1-Np)(Ph))(2) (1-Np = 1-naphthyl) (1), containing stereogenic P atoms, is prepared with high diastereo-and enantiomeric purity by a multistep asymmetric synthesis via its borane adduct (S,S)-Me2Si(CH2P(1-Np)(Ph)(BH3))(2) (2), obtained by selective methyl lithiation of the enantiomerically pure phosphine borane (S)-P(1-Np)(Ph)(Me)(BH3) (3) and coupling onto Me2SiCl2. The absolute configuration of 3 is established by X-ray studies. Reacting 2 with morpholine gives free diphosphine (S,S)-1 with a (S,S): (R,R) enantiomeric ratio better than 99:1. The Rh(I) and Ru(II) derivatives [Rh(diene)((S,S)-1)] (diene norbornadiene, 4a; 1,5-cyclooctadiene, 4b) and [RuCl2(PPh3)((S,S)-1)] (5) are prepared and tested as catalyst precursors in enantioselective reactions with standard substrates. In the presence of 4b as catalyst precursor, a series of dehydroamino acid derivatives are hydrogenated with up to 97.7% ee. Complex 5 catalyzes the hydrogenation of pentane-2,4-dione to (S,S)-pentane-2,4-diol with up to 56% ee. Ligand 1 gives enantioselection also in the Pd-catalyzed allylic alkylation of 1,3-diphenyl-3-acetoxypropene with dimethyl malonate (27% ee).