Synthesis of Dicarbonyl(η4-tricarbonylcobaltacyclopentadiene)cobalt Complexes from Co2(CO)8. A General Route to Intermediates in Cobalt Carbonyl Mediated Alkyne Trimerization

We have shown that cobaltacyclopentadiene complexes, derived from cobalt carbonyl and two alkyne molecules and long believed to be intermediates in cyclotrimerization as well as in the formation of the (three-alkyne-derived) “flyover” complexes, can be isolated in selected cases if the mono(alkyne)−Co 2 (CO) 6 complexes are treated at room temperature with just 1 equiv of alkyne in the presence of trimethylamine N -oxide. The complex (PhC CHCMe CMe)Co 2 (CO) 5 has been characterized by X-ray crystallography.