trans-Chloromethylbis(dimethyl sulfoxide)platinum(II): X-ray Structure, Mechanism of Isomerization, and Its Use as a Precursor to Organoamine Complexes of Variable Geometrical Configurations

Article abstract of DOI:10.1021/ic960428s

An unusual 2:1 aggregate between the complex trans-[PtCl(CH₃)(DMSO)₂] (1; DMSO = dimethyl sulfoxide) and the organotin compound bis(μ ₃-oxo)bis(μ-chloro)bis(μ-dimethyltin(IV)) bis(chlorodimethyltin(IV)) [Cl(CH₃)₂-SnOSn(CH₃)₂Cl]₂ has been isolated and characterized by X-ray analysis. The crystals belong to the triclinic space group P1? with lattice constants a = 9.373(2) A?, b = 9.576(1) A?, c = 14.087(3) A?, α = 70.29(1)°, β = 72.50(1)°, γ = 72.21(2)°, and Z = 2. Least-squares refinement of the structure led to an R factor of 2.37%. ¹H, ¹³C, and ¹⁹⁵Pt NMR measurements revealed that in chloroform solution complex 1 gives a mixture of four different species, which have been unambiguously identified as the starting complex 1 in equilibrium with cis-[PtCl(CH₃)-(DMSO)₂] and the two corresponding isomeric aqua-species cis and trans-[PtCl(CH₃)(DMSO)(OH₂)]. The ¹⁹⁵Pt NMR magnetization transfer technique allowed determination of the rate of interconversion among the various complexes, showing that the direct trans-cis isomerism between the [PtCl(CH₃)(DMSO)₂] species is negligible and that the geometrical interconversion occurs through a water-catalyzed pathway. The exchange between free and coordinated DMSO in cis- and trans-[PtCl(CH₃)(DMSO)₂] has been measured by ¹H NMR magnetization transfer experiments. The molecule of DMSO in the position trans to a methyl group was found to be 10-fold more labile than that trans to another sulfur bonded dimethyl sulfoxide. The reactivity of complex 1 in chloroform with a series of monodentate nitrogen ligands having widely different electronic and steric properties has been investigated by ¹H NMR spectroscopy. The utility of this system as precursor for the synthesis of cis- and trans-[PtCl(CH₃)(DMSO)(am)] is discussed together with the evidence for the factors promoting the prevalence of a geometrical configuration.