DFT mechanistic study of reactions of С6H6 and 1,3,5-Ad3C6H3 with CBr3. The first example of hydride transfer from aromatic C[sbnd]H 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 55kcalmol−1 in the case of C6H6 and Ad3C6H3, respectively.