Diphosphines Containing Stereogenic P Atoms:  Synthesis of (<i>S</i>,<i>S</i>)-<i>C</i>,<i>C</i>‘-Tetramethylsilanebis- (1-naphthylphenylphosphine) and Applications in Enantioselective Catalysis

Abstract

The diphosphine ( S, S )-Me 2 Si(CH 2 P(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 )-Me 2 Si(CH 2 P(1-Np)(Ph)(BH 3 )) 2 ( 2 ), obtained by selective methyl lithiation of the enantiomerically pure phosphine borane ( S )-P(1-Np)(Ph)(Me)(BH 3 ) ( 3 ) and coupling onto Me 2 SiCl 2 . 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 [RuCl 2 (PPh 3 )(( 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).