The addition of terminal alkynes to dimesitylfluorenylidenegermane

A variety of terminal alkynes were added to dimesitylfluorenylidenegermane, Mes(2)Ge=CR2 (where CR2 = fluorenylidene). The addition of phenylacetylene and 1-hexyne to Mes(2)Ge=CR2 gave a germacyclohexene via a cycloaddition where the germene acts as the 4 pi component and the alkyne as the 2 pi component. Through the use of a mechanistic probe, trans-(2-phenylcyclopropyl)-acetylene, the reaction was postulated to proceed through a concerted [2+4] cycloaddition. The addition of ethoxyacetylene to the germene produced both a [2+2] cycloadduct, a germacyclobutene, and a [2+4] cycloadduct, a germacyclohexene. The results of this study are compared to the results of the addition of alkynes to Mes(2)Ge=CHCH2-t-Bu.