Synthesis and Reactivity of Small Metallacyclic Alkynes

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Small cyclic alkyne are, in general, believed to be unstable due to their high strain around the triple bond. Indeed, cycloheptyne compounds, seven-membered cyclic alkynes are the smallest examples ever isolated in a pure form. Heteroatoms allowed a smaller ring stable and tetrasilacylohexane was isolated and structurally determined. I recently found that five-membered cyclic alkyne that contain a transition metal in the ring are readily prepared and remarkably stable, and reported their molecular structures. In this project I pursued the molecular structure and reactivity of these unique compounds and found the followings.1.A versatile synthetic method of non-substituted zirconacyclopentyne was found, and its molecular structure was determined. It has fundamentally similar structure to the substituted one, although it was more stable than the substituted complexes probably because the absence of steric repulsion.2.The non-substituted zirconacyclopentyne compound reacted with other low-valent zirconocne to give bimetallic complexes. This result revealed that the zirconacyclopentyne reacted as an alkyne compound. In the absence of neutral ligands such as photphines, symmetric dinuclear complex was obtained.3.Metallacyclopentyne complexes of other group 4 metals, titanium and hafnium, were also synthesized and structurally characterized.4.A seven-membered alkyne complex was prepared by the reaction of a zirconium-alkyne compound and a butatriene and its molecular structure was determined by X-ray diffraction analysis. This is a rare example of seven-membered alkyne that contains a transition metal in the ring system. The compound has a strained seven-membered ring due to interaction of the triple bond to the metal.