New P-chirogenic diphosphines and their use in catalytic asymmetric reactions

Abstract

Enantiomerically pure (S,S)-l,2-bis[(o-alkylphenyl)phenylphosphino]ethanes (o-alkylphenyl = o-methylphenyl, o-ethylphenyl, o-isopropylphenyl, 5′,6′,7′,8′-tetrahydronaphthyl), (S,S)-1,2-bis(alkyl-methylphosphino)ethanes (alkyl = t-butyl, 1-adamantyl, 1-methylcyclo-hexyl, 1,1-diethylpropyl, cyclopentyl, cyclohexyl) (abbreviated as BisP*), and (R,R)-1,1-bis(alkylmethylphosphino)methanes (alkyl = isopropyl, t-butyl, cyclohexyl, phenyl) (abbreviated as MiniPHOS) were prepared from phosphorus trichloride via short routes using, phosphine-boranes as intermediates. The crystal structures of cationic rhodium complexes, [Rh((S,S)-1,2-bis((phenyl)(5′,6′,7′,8′ -tetrahydronaphthyl)phosphino)ethane)(cod)]BF4, and [Rh((S,S)-t-Bu-BisP*(nbd))]BF4, and [Rh((R,R)-t-Bu-MiniPHOS)2]PF6, clearly indicate the ideal asymmetric environments. These ligands exhibited an excellent to almost perfect level of enantioselectivity in asymmetric hydrogenations of α-dehydroamino acid derivatives and other catalytic asymmetric reactions.