The Chemistry of Aryl Anions with Core Substitution by Heavy Group 14 Elements

Aromatic compounds incorporating heavy Group 14 elements—such as silicon, germanium, and tin—as skeletal atoms have long attracted attention due to their unique electronic properties and potential aromatic character. However, their high intrinsic reactivity has historically hindered their isolation and practical application. This review highlights a novel class of compounds: heavy aryl anions, generated via the reductive cleavage of substituents from neutral aromatic precursors containing heavier Group 14 elements. Our research group has successfully synthesized and isolated stable germanium- and tin-based phenyl anions ("heavy phenyl anions") for the first time. Notably, these anions remain monomeric even in the absence of bulky substituents—a result that defies conventional expectations. This unexpected stability is attributed to electrostatic repulsion among anionic species, which suppresses aggregation. These heavy aryl anions exhibit aromaticity comparable to that of classical phenyl anions, but with pronounced contributions from carbene-like resonance structures, emphasizing the electronic effects of heavy atom substitution. Moreover, the extension of this chemistry to polycyclic frameworks such as 2-germanaphthalenide reveals that the electronic character of the heavy element can be significantly tuned by the surrounding aromatic system. In addition, these anions show distinct reactivity toward multiply bonded compounds, including element exchange reactions and the formation of unsaturated germanium clusters. These discoveries signal a paradigm shift in the design of reactive main-group species, paving the way for the development of new molecular architectures without relying on highly specialized ligands.