Cobalt-mediated oligomerization reactions of amino-substituted acetylene derivatives

Reactions of the aminoacetylenes Et2N–Ctriple bond; length of mdashC–R (R = SiMe3, SPh, PPh2; 1a–c) with (η5-pentamethylcyclopentadienyl)bis(ethene)cobalt yield the corresponding (η5-pentamethylcyclopentadienyl)(η4-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 (η5-cyclopentadienyl)bis(ethene)cobalt. Treatment of 1d with excess Co2(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 Co2(CO)8 and Co4(CO)12, respectively. The catalytic cyclotrimerization reaction of the aminothioacetylene derivative 1b with [CpCo(CO)2] or [Co2(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 Å) lying between a single and a double bond, whereas the former CC triple bond is completely ruptured (2.13 Å). The Co–C(carbene) distances in 7 and 8 are 1.93 and 1.95 Å, respectively.