Selective Oxidation of Anilines to Azobenzenes and Azoxybenzenes by a Molecular Mo Oxide Catalyst

Aromatic azo compounds, which play an important role in pharmaceutical and industrial applications, still face great challenges in synthesis. Herein, we report a molybdenum oxide compound, [N(C4H9)4]2[Mo6O19] (1), catalyzed selective oxidation of anilines with hydrogen peroxide as green oxidant. The oxidation of anilines can be realized in a fully selectively fashion to afford various symmetric/asymmetric azobenzene and azoxybenzene compounds, respectively, by changing additive and solvent, avoiding the use of stoichiometric metal oxidants. Preliminary mechanistic investigations suggest the intermediacy of highly active reactive and elusive Mo imido complexes. Selective synthesis of azobenzene compounds and azoxybenzene compounds with N=N bonds was performed by a molecular molybdenum oxide compound [N(C4H9)4]2[Mo6O19] (simplified as Mo6) under mild conditions. A series of symmetric and asymmetric azobenzenes and azoxybenzenes were produced in high yield and selectivity by changing additive and solvent. Moreover, the catalytic mechanism of the reaction system was also assumed appropriately.