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)(CH(2)CFc)(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 (H-1, B-11, C-13), mass spectroscopy, and X-ray structural analysis.