σ‐Bond Activation in Aluminium‐Functionalized Alkynylchlorogermanes: Facile Insertion of Isocyanate and Azide into Al–C and Ge–Cl Bonds

Hydroalumination of Cl‐functionalized alkynylgermanes yielded mixed Al/Ge compounds (1). The Cl atoms adopted bridging positions between the Ge and Al atoms to form four‐membered GeCAlCl heterocycles with relatively long endocyclic Ge–Cl and Al–C bonds. Reactions with isocyanates resulted in the insertion of the heterocumulenes into both activated bonds and the formation of four‐membered GeC2N heterocycles, which featured exocyclic C–C and C–O double bonds with C–O oxygen atoms coordinated to ClAltBu2 molcules (2). An intermediate (3) was isolated with Ad‐NCO (Ad = 1‐adamantyl) from the insertion of isocyanate into the endocyclic Al–C bond. These products are characterized by intact Ge–Cl bonds and a chelating coordination of the Al atoms by the OCN groups. They rearranged at elevated temperature to yield compounds of type 2. Quantum‐chemical calculations were applied to evaluate the thermodynamics of these isocyanate insertion reactions. An azide reacted similarly by insertion into the Al–C and Ge–Cl bonds and afforded a GeCN3 heterocycle with an intact N3 group.