Cobalt-mediated oligomerization reactions of amino-substituted acetylene derivatives

Abstract Reactions of the aminoacetylenes Et 2 N–C C–R (R = SiMe 3 , SPh, PPh 2 ; 1a – c ) with (η 5 -pentamethylcyclopentadienyl)bis(ethene)cobalt yield the corresponding (η 5 -pentamethylcyclopentadienyl)(η 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 (η 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 A) lying between a single and a double bond, whereas the former CC triple bond is completely ruptured (2.13 A). The Co–C(carbene) distances in 7 and 8 are 1.93 and 1.95 A, respectively.