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

Reaction of Co(η 5 :η 2 ‐C 5 Me 4 CH 2 CH 2 CH = CH 2 )(η 2 ‐C 2 H 4 ) ( 1 ) with bis(trimethylsilyl)acetylene gives a substitution product Co(η 5 :η 2 ‐C 5 Me 4 CH 2 CH 2 CHCH 2 )(η 2 ‐Me 3 SiC≡CSiMe 3 ) ( 2 ) which simultaneously contains both an η 2 ‐alkene and an η 2 ‐alkyne ligand. With 1 substituted alkynes R 1 C≡C 2 (R 1 = R 2 = CO 2 Me, Ph; R 1 = CO 2 Me, R 2 Ph; = R 1 = SiMe 3 , R 2 = H) react to give cyclohexadiene complexes of the type Co(η 5 :η 4 ‐C 5 Me 4 CH 2 CH 2 C 6 H 3 R 4 ) ( 4, 5, 8, 9 ). This [2+2+2] cycloaddition involves two molecules of an alkyne and the intramolecularly coordinated CC bond leading to an η 4 ‐bonded cyclohexadiene ligand which is linked to the five‐membered ring by a CH 2 CH 2 bridge. In the case of diphenylacetylene the cyclobutadiene complex Co(η 5 ‐C 5 Me 4 CH 2 CH 2 CHCH 2 (η 4 ‐C 4 Ph 4 ) ( 6 ) is formed as a byproduct.