Ligand dissociation as a preliminary step in methyl for halogen exchange reactions of platinum(II) complexes

Article abstract of DOI:10.1021/om50005a028

The complex cis-[PtMe₂(SMe₂)₂] exists in solution in equilibrium with [Pt₂Me₄(μ-SMe₂)₂] and free SMe₂. Methyl for halogen exchange occurs on reaction of cis-[PtMe₂(SMe₂)₂] with cis- or trans-[PtCl₂(SMe₂)₂] to give trans-[PtClMe(SMe₂)₂] as the only product, with trans-[PtI₂(SMe₂)₂] to give trans-[PtIMe(SMe₂)₂], and with trans-[PtI₂(PMePh₂)₂] to give isomers of [PtIMe(SMe₂)(PMePh₂)] as major projects, whereas cis-[PtMe₂(PMe₂Ph)₂] reacts with trans-[PtI₂(SMe₂)₂] to give trans-[PtIMe(PMe₂Ph)₂] and trans-[PtIMe(SMe₂)₂] with no scrambling of neutral ligands. Kinetic studies show that the reaction of cis-[PtMe₂(SMe₂)₂] with trans-[PtCl₂(SMe₂)₂] follows second-order kinetics (first order in each reagent) and the reaction is strongly retarded in the presence of free SMe₂. From these results, it is deduced that the methyl for halogen exchange reactions of cis-[PtMe₂(SMe₂)₂] occur after dissociation of SMe₂ to give a reactive intermediate, [PtMe₂(SMe₂)].