Optically active asymmetric di(tertiary phosphines). Crystal and molecular structure of [SP-4-3-(SP,S)]-{1-[(2-chlorophenyl)methylphosphino]-2-(dimethylphosphino)benzene-P,P′}{1-[1-(dimethylamino)ethyl]naphthyl-C2,N}palladium(II) hexafluorophosphate

Abstract

Mono-deprotonation of the bis(secondary phosphine) (R_P*,R_P*)- and (R_P*,S_P*)-1,2-phenylenebis(methylphosphine) has been achieved using potassium in liquid ammonia to give a ca. 4 ∶ 1 mixture of (±)-1-(dimethylphosphino)-2-(methylphosphino)benzene and 1,2-phenylenebis(dimethylphosphine) upon addition of a solution of methyl iodide in the same solvent. This mixture has been further treated with sodium in THF followed by the addition of 1,2-dichlorobenzene to give (±)-(2-chlorophenyl)(2-dimethylphosphinophenyl)methylphosphine and unchanged 1,2-phenylenebis(dimethylphosphine). The two di(tertiary phosphines) are readily separated by fractional distillation. Asymmetric di(tertiary phosphine) (±)-(2-chlorophenyl)(2-dimethylphosphinophenyl)methylphosphine has been resolved by separation via fractional crystallisation of internally diastereomeric palladium(II) complexes containing the racemic ligand and orthometallated (S)-dimethyl[1-(1-naphthyl)ethyl]amine. The absolute configuration of the R enantiomer of the ligand has been assigned by a crystal structure determination of the least soluble diastereomeric palladium(II) complex [SP-4-3-(S_P,S)]{1-[(2-chlorophenyl)methylphosphino]-2-(dimethylphosphino)benzene-P,P′}{1-[1-(dimethylamino)ethyl]naphthyl-C²,N}palladium(II) hexafluorophosphate.