Five-membered zircona- and titanacycloallenes; their diverse reactivity depending upon the position of substituents

The 2,5-bis(trialkylsilyl)-1-zirconacyclopenta-2,3-diene complexes 3, stable five-membered zirconacycloallenes, were prepared from 1,4-disilylbut-1-en-3-ynes. Complexes 3 reacted with ketones or nitrile to afford allenyl alcohols and the corresponding pyrolle, respectively.99