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Innovative Syntheses of Cyano(fluoro)borates: Catalytic Cyanation, Electrochemical and Electrophilic Fluorination

Different types of high-yield, easily scalable syntheses for cyano(fluoro)borates Kt[BFn (CN)4-n ] (n=0-2) (Kt=cation), which are versatile building blocks for materials applications and chemical synthesis, have been developed. Tetrafluoroborates react with trimethylsilyl cyanide in the presence of metal-free Brønsted or Lewis acid catalysts under unprecedentedly mild conditions to give tricyanofluoroborates or tetracyanoborates. Analogously, pentafluoroethyltrifluoroborates are converted into pentafluoroethyltricyanoborates. Boron trifluoride etherate, alkali metal salts, and trimethylsilyl cyanide selectively yield dicyanodifluoroborates or tricyanofluoroborates. Fluorination of cyanohydridoborates is the third reaction type that includes direct fluorination with, for example, elemental fluorine, stepwise halogenation/fluorination reactions, and electrochemical fluorination (ECF) according to the Simons process. In addition, fluorination of [BH(CN)2 {OC(O)Et}]- to result in [BF(CN)2 {OC(O)Et}]- is described.

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

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.

Azidoperfluoroalkanes: Synthesis and Application in Copper(I)-Catalyzed Azide-Alkyne Cycloaddition

We report an efficient and scalable synthesis of azidotrifluoromethane (CF₃ N₃ ) and longer perfluorocarbon-chain analogues (R_F N₃ ; R_F =C₂ F₅ , ⁿ C₃ F₇ , ⁿ C₈ F₁₇ ), which enables the direct insertion of CF₃ and perfluoroalkyl groups into triazole ring systems. The azidoperfluoroalkanes show good reactivity with terminal alkynes in copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), giving access to rare and stable N-perfluoroalkyl triazoles. Azidoperfluoroalkanes are thermally stable and the efficiency of their preparation should be attractive for discovery programs.