Nature of the species responsible for the high activity of RCOX·2A1X3 complexes in reactions with alkanes and cycloalkanes

The reasons for the high reactivity of aprotic organic superacids (AOS) containing an acyl halide and a double molar excess of Lewis acid in reactions with saturated hydrocarbons are studied. The synthesis and spectral properties of two pairs of acyl salts are studied: MstCO⁺AlBr₄ ^– and MstCO⁺Al₂Br₇ ^– (Mst=2,4,6-Me₃C₆H₂) and Ac⁺SbF₆ ^– and Ac⁺Sb₂F₁₁ ^–. Comparison of the reactivities of these salts in cracking of alkanes and isomerization of trimethyl-enenorbornane demonstrated that the AOS activity is due to generation of acyl salts with a dimeric anion in the slightly polar solutions. Analysis of the¹³C NMR spectra suggests that the superacid properties of these salts are due to formation of species containing acyl cations coordinated to the Lewis acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2490–2496, November, 1990.