A persistent germylyne radical enabling reversible σ-dimerization and diverse bond activation

The reversible σ-dimerization of radicals is a fundamental process in bond formation and cleavage, yet achieving this with an isolable heavy carbyne analogue has remained a paramount challenge. Herein, we report the synthesis and characterization of an isolable germylyne radical that demonstrates remarkable ambient stability while undergoing clean, reversible σ-dimerization via a Ge-Ge single bond. This reversible process, which exhibits a pronounced thermochromic response, is thoroughly elucidated through variable-temperature NMR/EPR spectroscopy and X-ray crystallography, revealing a moderate bond dissociation enthalpy. Beyond dimerization, this germylyne radical acts as a versatile synthon for main-group bond activation, readily cleaving chalcogen-chalcogen (S-S, Se-Se), phosphorus-phosphorus (in P₄), and even challenging aromatic carbon-chlorine (C-Cl) bonds. This work provides the direct structural evidence of a heavy carbyne's dimerization pathway and establishes a new platform for dynamic covalent bonding in main-group chemistry, with implications for stimuli-responsive materials and radical-mediated activation.