Abstract
It is generally known that small cyclic alkynes such as cyclopentyne is extremely reactive and unstable. Therefore it has been believed impossible to isolate cyclopentyne compounds.We recently reported that low-valent group 4 metallocenes reacted with 1, 2, 3-butatrienes to give 1-metallacyclopent-3-yne complexes and that resulted compounds are surprisingly stable and isolable. We succeeded in determination of their molecular structures by X-ray diffraction analyses, and showed that these are five-membered cyclic alkynes, while π, π-interaction of butatriene was also suggested. In this review, the preparation, structure and reactivity of these 1-metallacyclopent-3-yne compounds are described.The 1-zirconacyclopent-3-yne complexes reacted with another 'zirconocene' to form bimetallic complexes in which the cyclic alkyne coordinated to the other zirconocene moiety, indicating that the zirconacyclopentyne behaved as an alkyne. Seven-membered cyclic alkynes were also prepared from 1, 2, 3-butatriene and a zirconocene-alkyne compound. Protonolysis and subsequent nucleophilic attack to aldehyde gave allenyl or dienyl alcohol depending on proton source.
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