Synthesis and characterization of sulfur-capped trinuclear molybdenum and tungsten clusters

Abstract

The synthesis of molybdenum and tungsten trinuclear clusters is presented. The clusters of interest contain a M3(μ3-S)(μ2-S2)3[^4+] core with nine terminal ligands, i. e. three bound to each metal center. The ligands discussed include halogens, phosphines, both monodentate and bidentate, and arsines. The M3S4 core is often viewed as an incomplete cube with metal atoms and sulfur atoms occupying alternating vertices. The synthetic route to these clusters employs M3S7X4 (M = Mo, W; X = Cl, Br) as starting materials, which form as polymeric materials with the expanded formula [(M3S(S2)3X2X4/2)[infinity]] The synthetic process involves the extraction of one sulfur atom from each of the three μ2-S2 ligands and phosphine substitution of the terminal halide atoms. The following trinuclear complexes have been synthesized and characterized by x-ray diffraction methods: Mo3S4Cl4(PPh3)3(H2O)2*3THF, Mo3S4Cl4(Pet3)3(H2O)2*OPEt3, Mo3S4Br4(Pet3)3(H2O(OPEt2H)*2THF, W3S4Br4(Pet3)3(H2O)(OPEt2H)*2THF Mo3S4Cl4(PMe3)3(CH3OH)2, [Mo2S2Br4O2]pnBu3P(CH2)4P^nBu3], Mo3S7Cl4(SAsPh3)2*2THF, [Mo3S4Br4(depe)3]OH. In addition to these, other clusters have been prepared and characterized by nuclear magnetic resonance spectroscopy and electronic adsorption spectroscopy. Among the clusters prepared, not all contain the M3S4[^4+] core, and these deviations will be discussed. All of the trinuclear clusters presented belong to the M3X13 family and contain single metal-metal bonds between adjacent metal atoms, which are in and oxidation state of four. This assignment is consistent with the structural data presented, as well as with data obtained from comparable structures reported in the literature. The work presented here explores just one area of trinuclear cluster synthesis by exhibiting the usefulness of M3Y7X4 type complexes as valuable synthons to other substituted trinuclear clusters. Full details concerning the synthetic process, structural characterization, and chemical properties of phosphine-substituted trinuclear clusters are provided.