Crystal and molecular structure of cis-[dichlorobis(methyl phenyl sulphoxide)]platinum(II) and cis-[dichlorobis(benzyl methyl sulphoxide)]platinum(II). An X-ray and NMR spectroscopic study

Abstract

Reactions of (R,S)-methyl phenyl sulphoxide and (R,S)-benzyl methyl sulphoxide with K₂PtCl₄ give diastereomeric mixtures of cis- L₂PtCl₂ complexes. The mixtures isolated from the reactions, change their composition when allowed to stand in solution, to give, at equilibrium, ratios of ± and meso forms which differ as a function of the sulphoxide employed. The crystal structure of one of the diastereoisomers isolated in the case of the complex obtained from (R,S)-methyl phenyl sulphoxide is built up from racemic pairs of discrete molecules with R,R and S,S configurations at chiral sulphur atoms. The crystals of the complex prepared from (S)-benzyl methyl sulphoxide contain two crystallographically independent but chemically equivalent molecules with S,S absolute configuration at sulphur atoms, and one methanol solvate molecule. In both complexes the metal atom shows cis square-planar co-ordination geometry of the two chlorine and two sulphur atoms from the organic ligands. The complexes show differences in the orientation of the sulphoxide ligands with respect to the co-ordination plane. The NMR parameters obtained at ¹H, ¹³C and ¹⁹⁵Pt frequencies provide useful indications for recognizing ± and meso forms of platinum(II) complexes of sulphoxides and also contain information on the relative conformational patterns of the free and complexed ligands.