Quaternary Ammonium Salts and Brønsted Superacids based on Weakly Coordinating [Al(OTeF5)4]− Anion

Abstract

A series of tetraalkylammonium tetrakis(pentafluoroorthotellurato)aluminate salts [NAlk4][Al(OTeF5)4], Alk4 = –(CH3)4, –(C2H5)4, –(C2H5)3CH3, –(C3H7)4, –(C4H9)4 were described, characterized and some identified as ionic liquids. The Brønsted superacid [o-C6H4F2-H][Al(OTeF5)4] was applied for the protonation of very weak bases – halogenated pyridines C5F5N, C5F4ClN, C5Cl5N and C5H2F2N and C5H4BrN – to yield the corresponding [C5F5N-H][Al(OTeF5)4], [(C5F5N)2H][Al(OTeF5)4], [C5F4ClN-H][Al(OTeF5)4], [(C5Cl5N)2H][Al(OTeF5)4], [C5H4BrN-H][Al(OTeF5)4] and [C5F3H2N-H][Al(OTeF5)4] salts. The obtained crystal structures in the solid state of these salts show rare non-covalent interactions like anion-π and σ-hole interactions between pyridinium cations and the [Al(OTeF5)4]– weakly coordinating anion. The reaction of commercial refrigerant HFO-1234yf with arene-based Brønsted superacids lead to selective C(sp3)-F bond activation and resulted in the typical trifluoroallyl-substituted arenes, which are Friedel-Crafts like products.