On the synthesis and structure of reactive halonium ions†

Fluorinated diethyl and dipropyl halonium salts, [Br(CH₂CF₃)₂][WCA] 1Br, [I(CH₂CHF₂)₂][WCA] 2I and [X(CH₂CH₂CF₃)₂][WCA] (X = Br 5Br, I 5I; WCA = [Sb(OTeF₅)₆]⁻), were synthesized via fluoroalkylation or oxidation of bromofluoro and iodofluoro alkanes. The molecular structures of 1Br and 2I, as well as a second different solid-state structure of the previously reported chloronium salt 1Cl, were determined by single-crystal X-ray diffraction. Additionally, the oxidation of 2-chloro-1,1,1-trifluoropropane CHCl(CH₃)(CF₃) led to the formation of a highly reactive compound that activates isobutane to form the tert-butyl cation [C₄H₉]⁺. Although the product could not be directly observed due to its thermal instability and low solubility, quantum-chemical calculations suggest the formation of an asymmetric chloronium ion with trifluoro n-propyl and isopropyl side chains.