The reaction of benzyl isocyanide, tert-butyl isocyanide, and 2,6-dimethylphenyl isocyanide with tetramesityldigermene (Mes Ge=GeMes ) was examined. Whereas the addition of benzyl isocyanide gave the C-NC activation product, Mes Ge(CH Ph)Ge(CN)Mes , tert-butyl isocyanide, and 2,6-dimethylphenyl isocyanide did not give stable adducts, rather the rate of conversion of the digermene to the corresponding cyclotrigermane was accelerated. A comparison between the reactivity of the isocyanides with Mes Ge=GeMes and the Ge(100)-2×1 surface was made and some insights into the surface chemistry are offered.