Protonation of CH3 N3 and CF3 N3 in Superacids: Isolation and Structural Characterization of Long-Lived Methyl- and Trifluoromethylamino Diazonium Ions

Abstract

The methylamino diazonium cations [CH₃ N(H)N₂ ]⁺ and [CF₃ N(H)N₂ ]⁺ were prepared as their low-temperature stable [AsF₆ ]^- salts by protonation of azidomethane and azidotrifluoromethane in superacidic systems. They were characterized by NMR and Raman spectroscopy. Unequivocal proof of the protonation site was obtained by the crystal structures of both salts, confirming the formation of alkylamino diazonium ions. The Lewis adducts CH₃ N₃ ⋅AsF₅ and CF₃ N₃ ⋅AsF₅ were also prepared and characterized by low-temperature NMR and Raman spectroscopy, and also by X-ray structure determination for CH₃ N₃ ⋅AsF₅ . Electronic structure calculations were performed to provide additional insights. Attempted electrophilic amination of aromatics such as benzene and toluene with methyl- and trifluoromethylamino diazonium ions were unsuccessful.

Keywords: azidomethane; azidotrifluoromethane; diazonium salts; protonation; superacids.