Reactivity of the 16-Electron CpCo versus Cp*Co Half-Sandwich Complex Containing an o-Carborane-1,2-dithiolate Ligand toward Ethynylferrocene

The reaction of the 16-electron (16e) half-sandwich complex CpCo(S2C2B10H10) (1; Cp = cyclopentadienyl) with ethynylferrocene (Fc–CCH) in CH2Cl2 at ambient temperature leads to (CHCFc)(S2C2B10H10) (2), where the alkyne is added to the o-carborane-1,2-dithiolate ligand at the two sulfur sites with the loss of the CpCo unit. However, in MeOH the reaction gives rise to an additional product, CpCo(S2C2B9H9)(CH2CFc)(CH2CFc) (3), in which one alkyne has been reduced to an alkane containing a B–CH2 unit and the second alkyne is present as a terminal alkene at the second sulfur site. If silica and moisture are present, CpCo(S2C2B9H10)(CHCFc)(CH2C(O)Fc) (4) could be generated, in which one alkyne is stereoselectively inserted into one Co–S bond and the second alkyne is present as an acetyl ferrocenyl group at the second sulfur site. Both 3 and 4 contain a nido-C2B9 unit. Moreover, in boiling toluene the reaction leads to CpCo(S2C2B10H10)(CHCFc) (5), where the cleavage of the weaker Co–C and C–S bonds and the formation of a stronger C–C bond has occurred. In comparison, the reaction of Cp*Co(S2C2B10H10) (1*; Cp* = pentamethylcyclopentadienyl) at ambient temperature gives rise to the alkyne 2-fold inserted product Cp*Co(S2C2B10H10)(FcCCHCHCFc) (6). If 6 is heated in boiling toluene, the unusual product (FcCSCHCHCFc)(SC2B10H10) (7) is obtained, where two alkynes are dimerized with the formation of two five-membered S-heterocycles and the loss of a Cp*Co unit. The five new compounds 3–7 were characterized by NMR (1H, 11B, 13C), mass spectroscopy, and X-ray structural analysis.