Functionalized Cyclopentadienyl Ligands, VII[1] Cobalt‐Mediated Cyclohexadiene Formation Involving an Intramolecularly Coordinated CC Bond

Reaction of Co(η5:η2‐C5Me4CH2CH2CH = CH2)(η2‐C2H4) (1) with bis(trimethylsilyl)acetylene gives a substitution product Co(η5:η2‐C5Me4CH2CH2CHCH2)(η2‐Me3SiC≡CSiMe3) (2) which simultaneously contains both an η2‐alkene and an η2‐alkyne ligand. With 1 substituted alkynes R1C≡C2 (R1 = R2 = CO2Me, Ph; R1 = CO2Me, R2 Ph; = R1 = SiMe3, R2 = H) react to give cyclohexadiene complexes of the type Co(η5:η4‐C5Me4CH2CH2C6H3R4) (4, 5, 8, 9). This [2+2+2] cycloaddition involves two molecules of an alkyne and the intramolecularly coordinated CC bond leading to an η4‐bonded cyclohexadiene ligand which is linked to the five‐membered ring by a CH2CH2 bridge. In the case of diphenylacetylene the cyclobutadiene complex Co(η5‐C5Me4CH2CH2CHCH2(η4‐C4Ph4) (6) is formed as a byproduct.