Photocatalytic Oxidative Coupling of Arylamines for the Synthesis of Azoaromatics and the Role of O₂ in the Mechanism

Abstract

The photocatalytic oxidative coupling of aryl amines to selectively synthesize azoaromatic compounds has been realized. Multiple different photocatalysts can be used to perform the general reaction; however, Ir(dF-CF 3 -ppy) 2 (dtbpy) + , where dF-CF 3 -ppy is 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine and dtpby is 4,4′-tert-butyl-2,2′-bipyridine, showed the greatest range of reactivity with various amine substrates. Both electron-rich and -deficient amines can be coupled with yields up to 95% under an ambient air atmosphere. Oxygen was deemed to be essential for the reaction and is utilized in the regeneration of the photocatalyst. Fluorescence quenching and radical trap experiments indicate an amine radical coupling mechanism that proceeds through a hydrazoaromatic intermediate before further oxidation occurs to form the desired azoaromatic products.

Hollow mesoporous atomically dispersed metal-nitrogen-carbon catalysts with enhanced diffusion for catalysis involving larger molecules

“…As a proof-of-concept application, oxidative coupling of anilines to azo aromatic compounds was used as the probe reaction (Fig. 4a ) 39 – 41 . Hollow mesoporous h-CoNC was tested compared with the counterparts of hollow NC (h-NC), hollow NC with Co nanoparticles (h-Co NP NC), and solid CoNC (s-CoNC), which were derived from hollow ZIF-8, hollow ZnCo-BZIF with Zn/Co ratio of 20:1, and solid ZnCo-BZIF with Zn/Co ratio of 60:1, respectively (see SI Methods and Supplementary Figs.…”

Selective Electrosynthetic Hydrocarboxylation of α,β‐Unsaturated Esters with Carbon Dioxide**

“…Further examination with a blank reaction in the absence of 1 q but with aniline present resulted in the isolation of azobenzene 4 in 22 % unoptimized yield (Scheme 4 ), possibly opening up a new route to these important molecules and a complementary process to the photochemical route recently reported by Vannucci. [18] …”

Selective Electrosynthetic Hydrocarboxylation of α,β‐Unsaturated Esters with Carbon Dioxide**

“…For example, aniline 3 was completely consumed under the reaction conditions although 2 q was produced in 62 %. Further examination with a blank reaction in the absence of 1 q but with aniline present resulted in the isolation of azobenzene 4 in 22 % unoptimized yield (Scheme 4), possibly opening up a new route to these important molecules and a complementary process to the photochemical route recently reported by Vannucci [18] …”

“…Further examination with ab lank reaction in the absence of 1qbut with aniline present resulted in the isolation of azobenzene 4 in 22 %u noptimized yield (Scheme 4), possibly opening up an ew route to these important molecules and ac omplementary process to the photochemical route recently reported by Va nnucci. [18] We recently investigated the mechanism of hydrocarboxylation of both styrenes and dienes. [7a,b] Ther eduction potentials of CO 2 and styrenes have been reported to be very similar, CCO 2 À E 1/2 = À2.21 V, styrene E 1/2 = À2.58 Vv s. SCE in DMF, [19] and those of the acrylates studied in this work are also in asimilar range,for example,methyl acrylate 1a E 1/ 2 = À2.10 Vand methyl crotonate 1eE 1/2 = À2.41 Vvs.…”