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.