Thermally Driven Tetrazine-to-Triazole Ring Contraction Mediated by Hydroxylammonium Cations

Abstract

A nitroimine-functionalized tetrazine exhibits pronounced cationdependent reactivity with ammonia, hydrazine, and hydroxylamine. While ammonia and hydrazine yield stable salts, hydroxylamine induces a thermally driven tetrazine-to-triazole transformation, revealing that the hydroxylammonium cation governs intermolecular organization and directs divergent reactivity pathways.Nitrogen-rich heterocycles, particularly 1,2,4,5-tetrazine derivatives, provide a compelling molecular platform for energetic materials design, wherein their high nitrogen density and specific reactivity at the C3 and C6 positions enable control over energy release, thermal stability, and supramolecular organization (Fig. 1A). 1-10 Functionalization of the tetrazine framework with nitroimine groups further amplifies its energetic potential by imposing strong electron-withdrawing character, while simultaneously enabling extensive hydrogenbonding interactions that favor densely packed ionic architectures. [11][12][13][14][15] While energetic salts of nitroaminesubstituted tetrazines have been widely explored for tuning physicochemical properties, the role of cation identity in directing chemical reactivity within these systems remains largely unexplored (Fig. 1B). [16][17][18][19][20] Cations in energetic salts are typically considered passive charge-balancing species that stabilize the system through intramolecular interactions. However, emerging evidence suggests that cations may play a more active role in governing reaction pathways. [21][22] Despite this possibility, studies demonstrating cation-driven divergence in chemical reactivity are rare. [23][24] Now, we demonstrate that a nitroiminefunctionalized tetrazine platform exhibits cation-controlled reactivity switching when treated with simple nitrogen bases.While ammonia and hydrazine yield conventional salts that preserve the tetrazine framework, hydroxylamine induces fundamentally different behavior, triggering a thermally driven ring transformation to generate a new nitrogen-rich triazole. This transformation reveals an unprecedented role of the hydroxylammonium cation in promoting bond reorganization, going beyond simple salt formation. These findings establish