Varied Reactivity of the Germene Mes₂GeCR₂ toward Nitriles

The germene Mes₂GeCR₂ (1, CR₂ = fluorenylidene) shows varied behavior toward nitriles. It reacts as a 1,2-dipole with t-BuCN giving a four-membered ring heterocycle, 2-aza-3-germacyclobut-1-ene, as a 1,4-dipole with PhCN, leading to a six-membered ring heterocycle, 3,4-dihydro-3-germaisoquinoline, and as a base, abstracting the α-H of R‘CH₂CN to give α-cyanogermanes (R‘ = H, 2-thienyl, 2-FC₆H₄, 4-FC₆H₄).