RESOLUTIONS INVOLVING METAL COMPLEXATION - OPTICAL RESOLUTION AND PHOTOCHEMICAL-REARRANGEMENT OF (+/-)-(2-MERCAPTOETHYL)METHYLPHENYLPHOSPHINE

The asymmetric bidentate (+/-)-(2-mercaptoethyl)methylphenylphosphine has been resolved by the fractionial crystallization of a pair of diastereomeric thiolato-S-bridged dipalladium(II) complexes containing the deprotonated form of the ligand and ortho-metalated (R)-(1-(dimethylamino)naphthalene. In order to recover the resolved ligand from the less soluble diastereomer of the dipalladium complex, the terminal palladium resolving unit was displaced with ethane-1,2-diamine, and the residual (thiolato)palladium(II) complex was treated with benzyl bromide; this gave a bromopalladium(II) complex containing (S)-(2-(benzylthio)ethyl)methylphenylphosphine bound through phosphorus only. The crystal and molecular structure of the bromo-palladium complex has been determined. Crystal data: orthorhombic, P2(1)2(1)2(1), a = 8.774 (1) angstrom, b = 17.908 (3) angstrom, c = 18.412 (4) angstrom, Z = 4, and R = 0.042. The geometry around the palladium is distorted square-planar with the tertiary phosphine-P stereocenter of S absolute configuration trans to the tertiary amine-N of the resolving ligand of R absolute configuration. Optically pure (R)-(2-(benzylthio)ethyl)methylphenylphosphine, [alpha]D -27.8-degrees (c 1.6, dichloromethane), was displaced from the bromo-palladium complex with (R*,R*)-(+/-)-1,2-phenylenebis(methylphenylphosphine) and was, in turn, converted by sodium in ammonia into a separable mixture of optically pure (R)-(2-mercaptoethyl)methylphenylphosphine, [alpha]D -17.0-degrees (c 3.0, dichloromethane), and optically pure (R)-ethylmethylphenylphosphine, [alpha]D -7.3-degrees (c 2.4, toluene). The (R)-(mercaptoethyl)phosphine rearranges in light with retention of configuration at phosphorus into optically pure (S)-ethylmethylphenylphosphine sulfide, [alpha]D -21.6-degrees (c 2.0, methanol), by an intermolecular radical chain mechanism.