Two modes of C–H bond activation of tris(2-thienyl)phosphine in trinuclear osmium carbonyl clusters

Tris(2-thienyl)phosphine, P(C4H3S)3, reacts with [Os3(CO)12] at 110 °C to give the phosphine-substituted derivatives [Os3(CO)11{P(C4H3S)3}] (1), [Os3(CO)10{P(C4H3S)3}2] (2) and [Os3(CO)9{P(C4H3S)3}3] (4), as well as the C–H activated product [Os3(μ-H)(CO)9{μ-P(C4H2S)(C4H3S)2}{P(C4H3S)3}] (3), in which the bridging ligand is equatorially coordinated to two osmium atoms. Thermolysis of 2 in refluxing toluene results in the formation of 3. Compound 1 can also be prepared in high yield from [Os3(CO)11(NCMe)]. The reaction of [Os3(μ-H)2(CO)10] with tris(2-thienyl)phosphine at room temperature afforded [Os3(μ-H)2(CO)9{P(C4H3S)3}] (5) and [Os3H(μ-H)(CO)10{P(C4H3S)3}] (6), with the ligand coordinated through the phosphorus atom whereas at elevated temperature the cyclometallated compounds [Os3(μ-H)(CO)9{μ3-P(C4H2S)(C4H3S)2}] (7) and [Os3(μ-H)(CO)8{μ3-P(C4H2S)(C4H3S)2{P(C4H3S)3}] (8) were obtained in addition to 5. Heating 6 in refluxing heptane furnished 5 via loss of one carbonyl ligand. Thermolysis of 1 and 3 in refluxing toluene gives 7 and 8, respectively, in good yields. In 3, the μ-P(C4H2S)(C4H3S)2 ligand is coordinated through the phosphorus to one Os atom and through a σ–Os–C bond to the second osmium atom. Compound 7 contains the μ3-P(C4H2S)(C4H3S)2 ligand bound through phosphorus to one Os atom, through a σ–Os–C bond to another and by an η2 (π)-interaction to the third osmium atom. Compounds 1, 2 and 4 contain the ligand coordinated exclusively through the phosphorus atom. The crystal and molecular structures of 2, 3, 5, 6 and 7 are reported.