Intermolecular Electrophilic Germylation Using GeCl 4 and Al 2 Cl 6

Electrophilic aromatic substitution is a textbook transformation for the lighter Group 14 elements. In contrast to acylation, alkylation, and silylation, electrophilic germylation is extremely underdeveloped. Herein we report the first effective intermolecular Germa-Friedel-Crafts reaction. Specifically, combining the key industrial precursor GeCl4, with Al2Cl6 and an inexpensive hindered pyridine base enables electrophilic C-H germylation of a range of arenes. The process can be applied for selective synthesis of either the mono- or the di-aryl germanes, ArGeCl3 and Ar2GeCl2, respectively. ArGeCl3 are versatile intermediates that can be transformed in situ into the synthetically desirable ArGe(alkyl)3 derivatives. Mechanistic and computational analysis support an SEAr-type process where Al2Cl6 is the key halophilic activator that generates a germanium electrophile able to effect C-H germylation in combination with the base. Overall, this work demonstrates that a high-yielding intermolecular Germa-Friedel-Crafts reaction is possible provided an appropriate Brønsted base is used.