Non-Aqueous Binary and Ternary <i>n</i>HF·Base Fluoride Reagents: Characterization of Structure, Properties, and Reactivity

Binary and ternary <i>n</i>HF·base mixtures are an important class of nucleophilic fluorinating reagents used in myriad fluorination reactions. These reagents are soluble in organic media, and by varying <i>n</i>, the reactivity of fluoride can be controlled and tuned. Of particularly frequent utility are the ternary mixtures of <i>n</i>HF·amine, in which the binary 9HF·py and 3HF·NEt₃ mixtures are combined, the ratio (<i>n</i>) of which has a strong influence on the reaction yields and selectivity. The structure, properties, and reactivity of these non-aqueous ionic liquid mixtures vary considerably with <i>n</i>. Herein, we disclose a combined experimental and theoretical study aimed at characterizing binary and ternary <i>n</i>HF·base mixtures. We have measured the concentration of components, their Hammett acidity <i>H</i>₀, nucleophilicity, and basicity, while using theory to calculate the lowest energy size and structure of the clusters formed at different ratios of HF to base and analyzed the noncovalent interactions present. The quantification of properties and enhanced understanding presented should facilitate the further development and use of this important family of fluorination reagents.