Synthesis of Platinum group metal cluster complexes with redox active ligands.

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The commercial hydrodesulfurization (HDS) catalysts generally comprise metal sulfides supported on gamma-alumina. Molybdenum or tungsten are essential components but the catalytic activity increases remarkably by addition of other transition metals such as Ni, Co, Ru, Ir, Rh, Pt, Pd, Os, Re as promoters. The role playd by these promoters is still unknown. Although the isolation and characterization of the intermediate species that is formed prior to the desulfurization step are attracting much attention, such model complexes are still far from the structure of the surface of the catalysts. It is very important to study and understand the reaction of thiometallate anions with metal complexes which can be promoters.In the course of our study of the reaction of dinuclear Pt (III) complexes of pyridinethiol, [Pt_2Cl_2(5-mpyt)_4] , With tetrathiotungstate, WS_4^<2->, we unexpectedly found the formation of tetrasulfido bridged dimer of the "Pt_2" unit, [{ ClPt_2(5-mpyt)_4}_2S_4]. The formation of tetrasulfide anion (S_4^<2->) from tetrathiotungstate is very unusual, since we know only one example in which tetrathiometallate anions act as a source of disulfide anion (S_2^<2->). [{ClPt_2(5-mpyt)_4}_2S_4] Can be converted to the starting compound, [Pt_2Cl_2(5-mpyt)_4] , by exposing the CHCl_3 solution toward room light. The isolation of this compound enabled us to know whole the reaction in which WS_4^<2-> was converted to elemental sulfur via S_4^<2-> ion. The isolation of [(ClPt_2(5-mpyt)_4)_2S_4] corresponds to the identification of the intermediate compound of this reaction.