Reactions of benzothiazolide triosmium clusters with tetramethylthiourea

The valence saturated benzothiazolide triosmium cluster [Os3(CO)10(μ-η2-C7H4NS)(μ-H)] (1) reacts with tetramethylthiourea in refluxing toluene to give [Os3(CO)8(μ-η2-C7H4NS)(η2-SCNMe2NMeCH2)(μ-H)2] (5), which exists as a mixture of two isomers in solution, whereas the electron-deficient cluster [Os3(CO)9(μ3-η2-C7H4NS)(μ-H)] (2) reacts with tetramethylthiourea in refluxing cyclohexane to give two new compounds [Os3(CO)8(μ-η2-C7H4NS)(η2-SCNMe2NMeCH2)(μ-H)2] (6) and [Os3(CO)9(μ-η2-C7H4NS)(η1-SC(NMe2)2)(μ-H)] (7). In contrast, the reaction of [Os3(CO)9(μ3-η2-C7H3(2-CH3)NS)(μ-H)](3) with tetramethylthiourea in refluxing cyclohexane at 81 °C, gives only [Os3(CO)9(μ-η2-C7H3(2-CH3)NS)(η1-SC(NMe2)2)(μ-H)] (8) in 15% yield. Compound 7 converts into 6 in refluxing toluene whereas a similar thermolysis of 8 results non-specific decomposition. All the compounds have been characterized by elemental analysis, IR, 1H NMR and mass spectroscopic data together with single crystal X-ray diffraction analysis for 5 and 7. Both compounds 5 and 6 contain a cyclometallated tetramethylthiourea ligand which is chelating at the rear osmium atom and are structurally very similar. In 5, the benzothiazolide ligand is coordinated to Os3 triangle via the nitrogen lone pair and C(2) carbon atom of the heterocyclic ring whereas in 6 the ligand is coordinated to the Os3 triangle via the nitrogen lone pair and the C(7) carbon atom of carbocyclic ring. In 7 and 8, the tetramethylthiourea ligand is coordinated at an equatorial site of the osmium atom which is also bound to the nitrogen atom of the benzothiazolide ligand.