Ferrocenyl Diphosphines Containing Stereogenic Phosphorus Atoms. Synthesis and Application in the Rhodium-Catalyzed Asymmetric Hydrogenation

Enantiomerically pure ( R )-2-methoxyphenyl(phenyl)- O -methylphosphinite borane ( 1a ) and ( R )-1-naphthyl(phenyl)- O -methylphosphinite borane ( 1b ) react with 1,1‘-dilithioferrocene to give ( S,S )-1,1‘-bis(2-methoxyphenyl(phenyl)phosphino)ferrocene borane ( 2a ) and ( S,S )-1,1‘-bis(1-naphthyl(phenyl)phosphino)ferrocene borane ( 2b ). Deboranation with morpholine yields the diphosphines ( S,S )-1,1‘-bis(2-methoxyphenyl(phenyl)phosphino)ferrocene ( 3a ) and ( S,S )-1,1‘-bis(1-naphthyl(phenyl)phosphino)ferrocene ( 3b ) in high yields and high diastereo- and enantiomeric purity, as determined on the corresponding phosphine oxides 4 a, b . X-ray investigations support the ( S,S ) configuration of 2a and disclose the coordination properties of 3a in the platinum derivative [PtCl 2 ( 3a )] ( 5a ). The rhodium(I) derivatives [Rh(COD)( 3 a, b )]BF 4 ( 6 a, b ) have been prepared and tested in the enantioselective catalytic hydrogenation of various olefins and ketones. Excellent enantioselectivity is achieved in the asymmetric hydrogenation of methyl ( Z )-α- N -methyl-acetamidocinnamate to ( R )- N -methyl- N -acetylphenylalanine methyl ester with 6a (97% ee). Methyl ( Z )-α-acetamidocinnamate is hydrogenated to ( R )- N -acetylphenylalanine methyl ester with up to 96% ee with 6b as the catalyst.