Metal-Free Oxidative C–C Coupling of Arylamines Using a Quinone-Based Organic Oxidant

Abstract

A variety of arylamines are shown to undergo oxidative C-C bond formation using quinone-based chloranil/H reagent as the recyclable organic (metal-free) oxidant system to afford benzidines/naphthidines. Arylamines (3°/2°) designed with various substituents were employed to understand the steric as well as electronic preferences of oxidative dimerization, and a mechanism involving amine radical cation has been proposed. The tetraphenylbenzidine derivative obtained via oxidative C-C coupling has been further converted to blue-emissive hole-transporting material via a simple chemical transformation. This study highlights the preparation of novel HTMs in a simple, economic, and efficient manner.

Competitive Routes for Electrochemical Oxidation of Substituted Diarylamines: the Guidelines

“…Analysis of the experimental data obtained in the present work shows that in all cases oxidative C−C coupling leading to 4,4’‐N,N’‐diarylbenzidine occurs via electron‐ rich phenyl rings and at the para ‐position only. This result is also in line with the recently published report on chemical oxidation of a large series of arylamines using quinone‐based organic oxidant . The observed regioselectivity (the preferential attack at the electron‐rich phenyl ring) is attributed to the electrophilic nature of the radical cations.…”

“…Chemical oxidation of diarylamines can lead to a variety of products, and is dependent upon the type of the oxidant, amines nature and the reaction medium . Electrochemical oxidation (potential values and the products obtained) is mainly determined by the structure of the amine itself.…”

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…Anilines, as a consequence of their electron‐rich character and thus lower oxidation potentials, should undergo oxidative aromatic coupling more easily than phenolic derivatives. Indeed, treatment of some secondary and tertiary anilines with p ‐chloranil as an oxidizing agent produces dimerization products 15 – 19 (Scheme ). From a structural point of view, the method tolerates a variety of functional groups (even those with electron‐withdrawing character) as well as substrates with sterically hindered reactive sites.…”

Redox‐Active Guanidines in Proton‐Coupled Electron‐Transfer Reactions: Real Alternatives to Benzoquinones?

“…The results demonstrate the superior functional‐group tolerance of such coupling reactions. UV/Vis experiments showed the presence of reaction intermediates, arising from substrate oxidation (see the Supporting Information) . In principle, the triphenylamine derivatives could be protonated by the strong acid.…”

“…Obviously, ( 1 +2 H)(BF 4 ) 4 forms from 1 (BF 4 ) 2 upon acid addition, but the oxidation potential of these organic substrates is still higher than the reduction potential of ( 1 +2 H)(BF 4 ) 4 . Hence the addition of excess acid boosts the oxidation power, as also found for benzoquinones in aqueous and aprotic solutions …”