cis-trans Isomerization of bis(Dialkylsulfide)Dihaloplatinum(II) Complexes in Solution

The equilibrium energetics and the kinetics of cis-trans isomerization of some bis(dialkylsulfide)dihaloplatinum(II) complexes have been examined by ¹H-NMR. spectroscopy. The isomers are stable in chloroform but each form isomerizes to an equilibrium mixture when free dialkylsulfide is added. The cis to trans process is endothermic and the position of the equilibrium is markedly dependent on the nature of the donor atoms and of the solvent. The rate of isomerization of Pt(Me₂S)₂Cl₂ is first order in complex and in Me₂S. The isomerization proceeds by a double displacement mechanism as it is shown that the tris(dimethylsulfide)chloroplatinum(II) cation is an isolable intermediate of the reaction. When free Me₂S is added to trans-Pd(Me₂S)₂Cl₂, isomerization does not occur and one observes instead a fast ligand exchange. Its mechanism is the usual associative one for substitutions in square planar d⁸complexes.