Reactivity of Ar‘GeGeAr‘ (Ar‘ = C₆H₃-2,6-Dipp₂, Dipp = C₆H₃-2,6-iPr₂) toward Alkynes:  Isolation of a Stable Digermacyclobutadiene

The first reactions of the “digermyne” Ar‘GeGeAr‘ (1, Ar‘ = C₆H₃-2,6-Dipp₂, Dipp = C₆H₃-2,6-iPr₂) with alkynes are reported. 1 reacts with 1 equiv of H₅C₆CCC₆H₅ to afford the 1,2-digermacyclobutadiene 2 in high yield, while it reacts with 2 equiv of the less hindered alkyne Me₃SiCCH to yield an unexpected bicyclic compound 3. Molecular structures of 2 and 3 were determined by X-ray crystallography. A possible mechanism for the formation of 3 is discussed. The high reactivity of 1, even at room temperature, emphasizes the fundamental differences between the GeGe and CC multiple bonds.