Reactions of the μ-alkyne-dicobalt complexes [Co2(CO)6(μ-CF3–CC–R)] (R=CF3, H) with [Co2Cp2(μ-SMe)2]: substitution and insertion leading to novel thiolato-alkyne tetra- and tricobalt clusters

The bis(μ-thiolato)dicobalt complex [Co2Cp2(μ-SMe)2] (1) reacts with alkyne-cobalt complexes [Co2(CO)6(μ-F3CCCR)] (2) to give tri- and tetranuclear cobalt cluster compounds. When R=CF3 the main product is [Co2(CO)4(μ-CF3C2CF3){μ-Co2Cp2(μ-SMe)2}] (3) but the trinuclear cluster [Co3Cp(CO)4(μ-SMe)2(μ-CF3C2CF3)] (4) is also obtained in low yield. When R=H the products are the isomeric clusters [Co3Cp(CO)4(μ-SMe)2(μ-CF3C2H)] (5 and 6), [Co3Cp2(CO)3(μ-SMe)(μ-CF3C2CH)] (7) and [CpCo(CO)2]. The solid state structures of 3,4, 5 and 7 have been established by X-ray analysis. The 50 electron triangular cluster 4 has weak Co–Co bonds [2.573(1), 2.800(1), 2.838(1) Å]. The alkyne ligand bridges the shortest of these bonds in perpendicular fashion. 5 and 7 contain open chain tricobalt units [Co–Co 2.39–2.57 Å] more typical of 50 electron M3 species. In these complexes the alkyne is π-bonded to the central metal atom and σ-bonded to both terminal cobalt atoms. Variable temperature NMR indicates that 5, 6 and 7 each exist in solution as interconverting isomers which differ in the configuration at one sulphur atom. For 5 the activation parameters [ΔH‡=64 kJ mol−1 and ΔS‡=−85 J K−1 mol−1] were obtained spectroscopically. In the solid, molecules of 7 contain an asymmetrically bridging carbonyl [Co–C 1.833(4) and 2.050(3) Å] which is not detectable in the solution spectra.