Hexa- and triosmium carbonyl clusters bearing bridging dppm and capping sulfido ligands

Treatment of [Os3(CO)7(μ3-S)2(μ-dppm)] (1) with Me3NO in toluene at 80 °C affords the trinuclear cluster [Os3(CO)6(μ3-S)2(NMe3)(μ-dppm)] (2) and the hexanuclear cluster [Os6(CO)12(μ3-S)4(μ-dppm)2] (3) in 30% and 51% yields, respectively. The reaction of 1 with [Os3(CO)10(MeCN)2] in refluxing benzene at 80 °C gives the hexanuclear cluster [Os6(CO)14(μ3-S)2(μ-dppm)] (4) in 15% yield. Compound 2 reacts with CO, PPh3 and P(OMe)3 at room temperature to give 1, [Os3(CO)6(μ3-S)2(μ-dppm)(PPh3)] (5) and [Os3(CO)6(μ3-S)2(μ-dppm){P(OMe)3}] (6), respectively; in high yields indicating that the NMe3 ligand is weakly bound. Compound 1 reacts with PPh3 in presence of Me3NO to afford 5, 2 and 3 in 53%, 6% and 18% yields, respectively, whereas with P(OMe)31 gives only 6 in 84% yield. Compound 3 reacts with CO at 98 °C to regenerate 1 by the cleavage of the three unsupported osmium–osmium bonds. The molecular structures of 4 and 6 have been unambiguously determined by single crystal X-ray diffraction studies. The hexanuclear compound 3 appears to be a64-electron butterfly core with four triply bridging sulfido ligands and two bridging dppm ligands based on the spectroscopic and analytical data. The metal core of 4 can be described as a central tetrahedral array capped on two faces with two additional osmium atoms. The triply bridging sulfido ligands face cap the two tetrahedral arrays formed by metal capping of the two faces of the central tetrahedron. The dppm ligand bridges one edge of one of the external tetrahedral arrays. Compounds 5 and 6 are formed by the displacement of equatorial carbonyl group of 1 by a PPh3 and P(OMe)3 ligand respectively and their structures are comparable to that of 1.