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. The reversible σ-dimerization of radicals is a fundamental process in bond formation and cleavage, yet is challenging to achieve with an isolable heavy carbyne analog. Herein, the authors report the synthesis and characterization of an isolable germylyne radical that demonstrates ambient stability while undergoing reversible σ-dimerization via a Ge–Ge single bond.