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 synthes ised 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 configura tion. 1D and 2D variable temperature H-1,C-13, P-31 and Pt-195 NMR dat a show that the complex has several different fluxional modes and are consistent with the presence in solution of the four possible anti-iso mers, and the two conformers with both thiolate ligands and the iodine atom in a cisoid disposition. Theoretical ab initio studies on the mo del complex [(H2PCH2CH2PH2)Pt(mu-SCH3)(2)PtIMe3] have led to an estima tion of the relative energies of the different isomers, confirming the interpretation of the NMR data. The transition states for the interco nversion between the most stable isomers have been located. NMR data a nd theoretical results strongly support a mechanism for the pyramidal sulfur inversion, which involves splitting of one of the two Pt-IV-S b onds, followed by rotation about its neighbouring Pt-II-S bond. (C) 19 97 Elsevier Science S.A.