DFT mechanistic study of reactions of С6H6 and 1,3,5-Ad3C6H3 with CBr3. The first example of hydride transfer from aromatic CH bond to electrophile

Abstract

The DFT B3LYP/6-31G* calculations were carried out for the reactions of C₆H₆ and Ad₃C₆H₃ (Ad = 1,3,5-adamantyl) with superelectrophile CBr₃⁺ as a model of superelectrophilic catalyst CBr₃⁺ Al₂Br₇⁻. The reaction of C₆H₆ with CBr₃⁺ proceeds via the classical scheme of electrophilic reactions of aromatic C − H bond to form initially the barrier-free σ-complex C₆H₆CBr₃⁺. This mechanism was confirmed by the aug-cc-pVDZ basis set calculations. The reaction of Ad₃C₆H₃ with CBr₃⁺ occurs via a quite novel mechanism involving aryl cation formation followed by hydride abstraction of the Ar⁺ from the 2-Ad group and the rearrangement of the 2-Ad⁺ cation into the 4-phenyl-4-protoadamantyl cation. The hydride transfer from both arenes was shown to be more favorable than H radical transfer by more than 40 and 55 kcal mol⁻¹ in the case of C₆H₆ and Ad₃C₆H₃, respectively.