The zirconocene-ethylene complex and (Z)S 1',4-bis(trimetlzylsilyl)-1,2,3-butatriene reacted to give a mixture of 1-zirconacyclopent-3-yne and 1-zirconacyclohept-3-yne. A zirconocene-alkyne complex gave, on the other hand, 1-zirconacyclohept-2-en-5-yne, which was structurally characterized as the major product along with a lesser amount of 1-zirconacyclopent-3-yne.