Cobalt-mediated oligomerization reactions of amino-substituted acetylene derivatives

Reactions of the aminoacetylenes Et2N-C equivalent to C-R (R = SiMe3, SPh, PPh2; 1a-c) with (eta(5)-pentamethylcyclopentadienyl)bis(ethene)cobalt yield the corresponding (eta(5)-pentamethylcyclopentadienyl)(eta(4)-cyclobutadiene)cobalt complexes 2a-c. Treatment of 1-phenylthio-2-diethylaminoacetylene 1b with three equivalents of CpCo(CO)(2) leads to the 1,3-dicobalta-bicyclobutane derivative 3'b. The analogous compound 3'd and the trinuclear cobalt complex 4'd are obtained from the reaction of bis(diethylamino)acetylene (1d) with (eta(5)-cyclopentadienyl)bis(ethene)cobalt. Treatment of 1d with excess Co-2(CO)(8) yielded unexpectedly a mixture of di- and tetranuclear cobalt-carbene complexes 7 and 8, most likely formed through interaction of oxygen. A designed route to 7 and 8 is found by reacting the tetraethyloxamide 6 with Co-2(CO)(8) and Co-4(CO)(12), respectively. The catalytic cyclotrimerization reaction of the aminothioacetylene derivative 1b with [CpCO(CO)(2)] or [Co-2(CO)(8)] leads to tris(phenylthio)-tris(diethylamino)benzene derivative 9. The new compounds have been characterized by NMR spectroscopy, mass spectrometry as well as by X-ray structure analyses for 3'd, 7 and 8. The molecular structure of 3'd in the crystal reveals the presence of a bicyclobutane framework with a Co-Co distance (2.36 angstrom) lying between a single and a double bond, whereas the former CC triple bond is completely ruptured (2.13 angstrom). The Co-C(carbene) distances in 7 and 8 are 1.93 and 1.95 angstrom, respectively. (c) 2005 Elsevier B.V. All rights reserved.