A PROTON NMR STUDY OF THE STEREOCHEMISTRY AND KINETICS OF THE REACTIONS OF DIMETHYL SULFOXIDE WITH POTASSIUM DICLOROGLYCINATOPLATINATE(II) AND ITS METHYL DERIVATIVES

Abstract

Amino acid complexes of general formula K[Pt(NO)Cl₂], where NO denotes the metal bonded atoms of the amino acid, react completely with solvent DMSO to yield two products, cis- and trans-Pt(NO) (DMSO)Cl, where cis and trans refer to positions of DMSO relative to coordinated nitrogen. The products were identified and kinetic data were obtained from changes in the proton nmr spectra of the amino acid, when DMSO-d₆ was the solvent, or of both amino acid and coordinated DMSO, when ordinary DMSO was the solvent. For glycine and π-aminoisobutyric acid complexes, the rate of displacement of trans chloride exceeds that of cis chloride by a factor of 3. However, subsequent equilibration favors the cis isomer over the trans isomer by a factor of 10. By contrast, for the corresponding N, N-dimethyl derivatives, the rates of formation of the two isomers are more nearly the same and the equilibrium ratio does not differ from the kinetic ratio. In addition to providing a sensitive technique for evaluating small differences in kinetic trans-effects, these observations strongly suggest that the stereochemistry of Pt(NO) (DMSO)Cl for the corresponding alanine complex described by Kukushkin and Guryamava should be denoted cis, rather than the trans reported.