Optical resolutions and chelating properties of (±)-[2-(methylsulfinyl)ethyl]diphenylarsine and its phosphorus analogue

Abstract

An optical resolution of the asymmetric chelating agents (±)-[Ph2ECH2CH2S(O)Me] (E = As or P) has been achieved via fractional crystallization of a pair of diastereomeric palladium(II) complex cations containing the appropriate sulfinyl-substituted ligand and ortho-metalated (S)-(1-(dimethylamino)ethyl)naphthalene. The crystal and molecular structure of the perchlorate salt of the less soluble phosphine-palladium complex has been determined. Crystal data: monoclinic pale yellow prisms, P21, a = 10.147(2) Å, b = 10.955(2) Å, c = 26.888(5) Å, β = 97.76(2)°, Z = 4, and R = 0.0302. The optically pure compound, [α]D -16.1° (c 1.0, dichloromethane), crystallizes as a pair of interconvertible conformers arising from the adoption of different helicities by the nonplanar chelate rings. In both conformers, the sulfinyl-substituted phosphine coordinates to the palladium via phosphorus and oxygen with the uncoordinated sulfur stereocenter of S absolute configuration. Optically pure (5)-[2-(methylsulfinyl)ethyl]-diphenylphosphine, [α]D +67.5° (c 1.0, dichloromethane), was displaced from the resolving palladium complex with 1,2-bis(diphenylphosphino)ethane. The (R)-(-)589 enantiomer of the phosphine ligand was obtained in a state of 85% optical purity from the residual mixture of diastereomeric complexes and was subsequently brought to purity by fractional crystallization of the corresponding enantiomorphic complex containing (R)-(1-(dimethylamino)-ethyl)naphthalene. Enantiomerically pure forms of [2-(methylsulfinyl)ethyl]diphenylarsine are obtained similarly from the corresponding resolved palladium complexes by treatment with cyanide. The various enantiomeric forms of the sulfinyl-substituted ligands are capable of coordinating to square-planar platinum metal ions via their E, E-O, or E-S donor atoms. The mode of coordination is governed by the stereoelectronic factors of the product complexes. © 1993 American Chemical Society.