Theoretical, structural and NMR studies of fluxionality in thiolato-bridged platinum(II)-platinum(IV) dinuclear complexes

The complex [(dppe)Pt{mu-SCH(CH2CH2)(2)NMe}(2)PtIMe3] has been synthesised and structurally characterised by X-ray diffraction. It consists of dinuclear sulfur-bridged enantiomeric pairs containing a folded Pt-II(mu-S)(2)Pt-IV ring with the thiolate substituents in anti configuration. 1D and 2D variable temperature H-1,C-13, P-31 and Pt-195 NMR data show that the complex has several different fluxional modes and are consistent with the presence in solution of the four possible anti-isomers, and the two conformers with both thiolate ligands and the iodine atom in a cisoid disposition. Theoretical ab initio studies on the model complex [(H2PCH2CH2PH2)Pt(mu-SCH3)(2)PtIMe3] have led to an estimation of the relative energies of the different isomers, confirming the interpretation of the NMR data. The transition states for the interconversion between the most stable isomers have been located. NMR data and theoretical results strongly support a mechanism for the pyramidal sulfur inversion, which involves splitting of one of the two Pt-IV-S bonds, followed by rotation about its neighbouring Pt-II-S bond. (C) 1997 Elsevier Science S.A.