1,4‐Digermacyclopenta‐1,3‐diene: Continuous Cyclic σ*–π Delocalization Enables Aromatic Stabilization in a Heavy‐Element 4π System

Abstract

ABSTRACT Aromaticity in heavy‐element systems can arise from unconventional modes of cyclic electron delocalization that are not accessible in lighter‐element frameworks. Herein, we report 1,4‐digermacyclopenta‐1,3‐diene as an unusual aromatic system in which a formally 4π electron framework is stabilized through cooperative σ*–π interactions. X‐ray crystallography reveals a nearly planar [Ge 2 C 3 ] ring, while magnetic and electronic analyses (NICS, GIMIC, ACID, and EDDB) consistently indicate significant aromatic stabilization. In particular, GIMIC calculations show a pronounced diatropic ring current with an average strength of +8.38 nA T −1 . Natural bond orbital analysis reveals that this stabilization originates from σ*–π delocalization involving the Ge–Ge bond and adjacent π orbitals. Despite a low‐lying open‐shell contribution (y ≈ 0.11), the system remains predominantly closed‐shell. Notably, this system represents a rare case in which σ*–π interactions form a continuous cyclic delocalization pathway, resulting in a distinct form of aromatic stabilization.