Synthesis and Structure of Seven-Membered Metallacycloalkynes



Seven-membered metallacycloalkyne compounds were synthesized. The reaction of the zirconocene–ethylene complex and (Z)-1,4-bis(trimethylsilyl)buta-1,2,3-triene gave a mixture of 1-zirconacyclopent-3-yne and 1-zirconacyclohept-3-yne. In contrast, zirconocene–alkyne complexes, such as those of 1-(trimethylsilyl)prop-1-yne and diphenylacetylene, gave 1-zirconacyclohept-2-en-5-yne in good yields. Consideration of structural parameters suggests that both a seven-membered cyclic alkyne and a five-membered structure contribute to generation of this complex. Coupling of benzyne and [3]cumulenes on a metal was also found to afford the corresponding metallacycles.