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

The bis(mu -thiolato)dicobalt complex [Co2Cp2(V-SMe)(2)] (1) reacts with alkyne-cobalt complexes [Co-2(CO)(6)(mu -F3CC_=CR)] (2) to give tri- and tetranuclear cobalt cluster compounds. When R = CF3 the main product is [Co-2(CO)(4)(mu -CF3C2CF3)(mu -Co2CF3){mu -Co2Cp2(mu- SMe)(2)}](3) but the trinuclear cluster [Co3Cp(CO)(4)(mu -SMe)(2)(mu -CF3C2CF3)] (4) is also obtained in low yield. When R = H the products are the isomeric clusters [Co3CP(CO)(4)(mu -SMe)(2)(mu -CF3C2H)] (5 and 6). [Co3Cp2(CO)(3)(mu -SMe)([mu 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) Angstrom]. 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 Angstrom] more typical of 50 electron M-3 species. In these complexes the alkyne is n-bonded to the central metal atom and cr-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 [DeltaH(double dagger) = 64 kJ mol (1) and DeltaS(double dagger) = -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) Angstrom] which is not detectable in the solution spectra. (C) 2001 Elsevier Science B.V. All rights reserved.