Reactivity of the [η2‐Bis(tert‐butylsulfonyl)acetylene](carbonyl)(η5‐cyclopentadienyl)cobalt Complex Towards Electron‐Rich and ‐Poor Acetylenes

The electron-rich aminoacetylenes Et2NC2R (2a–c, R = SPh, PPh2, and Ph, respectively) react smoothly with [η2-bis(tert-butylsulfonyl)acetylene](carbonyl)(η5-cyclopentadienyl)co-balt (1) to form the donor–acceptor stabilized (η4-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 (η4-cyclobutadiene)cobalt complexes. Analogously, the reaction of bis(1-phenylethynyl)sulfide (2g) with two equivalents of 1 gives rise to the sulfur-bridged bis[η4-(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)