Reactivity of a Germene toward Terminal Alkynes: Competition between Cycloaddition, Ene-Addition, and CH-Insertion

A variety of terminal alkynes were added to Mes(2)Ge=CHCH(2)t-Bu, a naturally polarized germene. Three different modes of reactivity we:re observed: cycloaddition to give germacyclobutenes, ene-addition to give vinylgermanes, and addition across the acetylenic C-H bond to give germylacetylenes. Mechanisms for the formation of the products are proposed. The reactivity of the naturally polarized germene toward terminal alkynes is compared to that of the analogous silene,