SYNTHESIS AND DYNAMIC STEREOCHEMISTRY OF THE COMPLEXES [PT(CH3C(CH2PPH2)3)(SR)(H)] (R = H OR PH)

The cis square-planar hydrido mercapto derivatives [Pt(triphos)(SH)(H)] and [Pt(triphos)(SPh)(H)] [triphos = CH3C(CH2PPh2)3] have been prepared by reaction of [Pt(triphos)(PPh3)] with H2S or HSPh. Analysis of the H-1 and P-31 NMR data for the two complexes over a temperature range encompassing slow- and fast-exchange limits characterizes these molecules as stereochemically nonrigid on the NMR time-scale. The fluxional behaviour can be explained on the basis of intramolecular exchange of the unco-ordinated phosphorus atom of triphos with the phosphorus atom co-ordinated in cis position to the hydride ligand. At higher temperature, a complete scrambling of the three phosphorus atoms occurs, and at the fast-exchange limit the spin correlation between the phosphorus atoms and platinum metal is retained. The related complexes [Pt(dppp)(SH)(H)] (dppp = Ph2PCH2CH2CH2PPh2), [Pt(triphos)Cl2] and [Pt(triphos)(SH)2] have been prepared in order to clarify the mechanism of the fluxionality for [Pt(triphos)(SR)(H)] (R = H or Ph).