Synthesis and Stabilization of Highly Reactive Haloacetylium Ions.

Abstract

The reactions of selected haloacetyl fluorides with the strong Lewis acids AsF₅ and SbF₅ were investigated in the aprotic solvent SO₂ClF. Depending on the stoichiometric ratio of AsF₅ or SbF₅ and the haloacetyl fluorides, either O-coordinated adducts or the respective haloacetylium ions were isolated as solids. The compounds were characterized by low-temperature vibrational spectroscopy and single-crystal X-ray diffraction. [CClH₂CO][Sb₂F₁₁] and [CH₂FCO][Sb₂F₁₁] crystallize in the monoclinic space group P2₁ with two formula units per unit cell. The reactivity of the haloacetyl fluorides under Lewis acidic conditions is discussed based on quantum chemical calculations of fluoride ion affinities on the BP/def2SVPP level of theory. The haloacetylium ions are stabilized in the solid-state phase by intermolecular C···F contacts and electron donation of the fluorine ligands of the anions as well as intramolecular hyperconjugation.