Dimeric σ-complexes : intermediates in the oxidative dimerization of aromatics (Aminobenzenes ; 19)

Abstract

Dimeric σ-complexes 2, postulated intermediates in the oxidative dimerization of aromatics, were obtained by oxidation of tripprolidin-1-ylbenzenes 1a-f with silver nitrate. Treatment of 2 with strong base gave biphenyls 4. In solution, especially under the influence of light, compounds 2 dissociate to radical cations 1o+,which react irreversibly with solvent under H abstraction to give σ-complexes 3. Crystal structures were determined by X-ray diffraction methods for compounds 2a and 2c. Reactions of triaminobenzenes 8 and 9 with bromine and halocyanogens gave mixtures of substitution (10/ 11) and dimerization products (12/ 13). This product formation can be plausibly explained in terms of known steric and electronic factors of both reaction partners.