Reactivity of the [η 2 ‐Bis( tert ‐butylsulfonyl)acetylene](carbonyl)(η 5 ‐cyclopentadienyl)cobalt Complex Towards Electron‐Rich and ‐Poor Acetylenes

The electron‐rich aminoacetylenes Et 2 NC 2 R ( 2a – c , R = SPh, PPh 2 , and Ph, respectively) react smoothly with [η 2 ‐bis( tert ‐butylsulfonyl)acetylene](carbonyl)(η 5 ‐cyclopentadienyl)co‐balt ( 1 ) to form the donor–acceptor stabilized (η 4 ‐cyclobutadiene)cobalt complexes 3a – c in good yields. However, treatment of the electron‐poor borylacetylenes 2d – f with the cobalt complex 1 does not lead to the expected (η 4 ‐cyclobutadiene)cobalt complexes. Analogously, the reaction of bis(1‐phenylethynyl)sulfide ( 2g ) with two equivalents of 1 gives rise to the sulfur‐bridged bis[η 4 ‐(cyclobutadiene)cobalt] complex 3g . The new cobalt complexes were characterized by NMR spectroscopy, mass spectrometry, and by X‐ray structure analysis for 3a , which reveals almost equal C–C bond lengths within the cyclobutadiene ring. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)