Optically active asymmetric bidentate ligands. Crystal and molecular structure of {(R), (S)-(–)589-2-[1-(dimethylamino)ethyl]phenyl-C2,N}[1-(diphenylphosphino)-2-(methylphenylphosphino) benzene-P,P′]palladium(II) hexafluorophosphate

Abstract

Asymmetric bidentate (±)-1-(diphenylphosphino)-2-(methylphenylphosphino)benzene has been prepared by the reaction of sodium methylphenylphosphide with 1-chloro-2-(diphenylphosphino)-benzene in tetrahydrofuran. The chiral di(tertiary phosphine) has been resolved by fractional crystallisation of a pair of internally diastereomeric palladium(II) complexes containing the racemic ligand and an orthometallated (S)-dimethyl(1-phenylethyl)amine. The optically pure antipodes have α± 51°(589 nm) in acetone. This is the first resolution of an asymmetric di(tertiary phosphine) containing a chirotopic phosphorus stereocentre. The absolute configuration of the S enantiomer of the ligand has been assigned by a crystal structure determination of the least-soluble diastereomeric complex {(R),(S)-(–)₅₈₉-2-[1-(dimethylamino)ethyl]phenyl-C²,N}[1-(diphenylphosphino)-2-(methylphenylphosphino)-benzene-P,P′]palladium(II) hexafluorophosphate. Chemoselective cleavage of the diphenylphosphino moiety of the free ligand occurs in the presence of alkali metals.