Hydrophobic Hydrolytic-Stable N-Alkylimidazole-Cyanoborane Complexes as Ultrafast-Igniting Hypergolic Fuels

Introduction of cyano group into the molecules of borane-based hypergolic fuels can greatly reinforce the hydrolytic stability. By the formation of complex between BH₂CN and imidazole, six complexes were readily prepared from N-alkyl substituted imidazole hydrochloride salts and NaBH₃CN in THF and fully characterized by ¹H and ¹³C NMR, IR spectroscopy, high-resolution mass spectrum, and differential scanning calorimetry (DSC). Among them, 1-allylimidazole-cyanoborane complex (5) displayed some attractive properties such as water immiscibility and good hydrolytic stability, high density (>1.0 g cm⁻³), good thermal stability (T_d, 193 °C, onset), high calculated density impulse (ρI_sp, 358 s g cm⁻³), ultra-short ignition delay time (WFNA, 3 ms), and super low viscosity (8.4 mPa s), showing the real application potential as a fuel and an efficient fuel additive in bipropellants.