Activation of thiosaccharin at a polynuclear osmium cluster

Abstract

The reaction of thiosaccharin (tsacH) with the triosmium cluster [Os3(CO)10(NCMe)2] furnishes the decacarbonyl isomers [HOs3(CO)10(μ-S-tsac)] (1) and [HOs3(CO)10(μ-N,S-1,3-tsac)] (2) in a 3:1 ratio at room temperature. These isomers differ by the coordination mode displayed by tsac ligand. The tsac moiety functions as an edge-bridging ligand via the sulfur atom in 1 while in 2 the bridging of adjacent osmium centers is achieved through the sulfur and nitrogen groups. The ancillary hydride in both products shares the OsOs edge that is bridged by the heterocyclic ligand. Heating 1 at 80 °C affords 2 and demonstrates that the former cluster is the product of kinetic control. The conversion of 1 → 2 has been investigated by DFT and the isomerization pathway elucidated. The DFT calculations confirm cluster 2 as the thermodynamically preferred isomer in this pair of products. Thermolysis of 2 in refluxing toluene affords the hexanuclear cluster [H2Os6(CO)17(μ-C,N-1,2-C6H4CNSO2)2(μ3-S)(μ4-S)] (3) via carbon-sulfur bond scission and subsequent capture of the extruded sulfur by the cluster core. The molecular structures for the three new clusters have been determined by single-crystal X-ray diffraction analyses.