Inhibition of the [2 + 2 + 2] Cyclization by the Formation of Chelates: Alkyne and Vinylidene Complexes with Cyclopentadienylcobalt( I )

The trimerization of alkynes to arenes usually observed in the reaction of cyclopentadienyl‐cobalt(I) complexes with alkynes could be prevented by chelation of the metal center with a “phosphane arm” on the cyclopentadienyl ligand. Instead alkyne complexes were obtained in very good yields. The reaction with ethyne leads to the vinylidene complex 1 (88 % yield), a possible precursor to the carbene–cobalt complex.