Homogeneous Tungsten Catalysis for Controllable Selective Oxidation of Anilines via the W(O)(η²-O₂)₂ Intermediate

The controllable selective oxidation of anilines to metastable and valuable products mediated by a single catalyst represents a long-standing synthetic challenge due to the numerous active species generated in situ and their intricate interactions. This study introduces the synthesis of a μ-oxo-bridged dinuclear tungsten complex [W(O)2(Cl)4-MeObpy]2O (W-1), which demonstrates selectivity in the oxidation of anilines, enabling the precise production of various azoxybenzenes, symmetric/unsymmetric azobenzenes, nitrosobenzenes, as well as nitrobenzenes. This marks the instance of a single molecular catalyst being employed for the synthesis of four distinct products through aniline oxidation. A combination of kinetic measurements and stoichiometric experiments unveils that the original selectivity for individual products among the many that can potentially arise is governed by the precise conversion of the active intermediates N-phenylhydroxylamine and nitrosobenzene into the specific procedures. A peroxotungstate complex [W(O2)2(O)4-MeObpy] (W-2) was isolated by the reaction of W-1 with H2O2. The combined experimental results and density functional theory (DFT) investigations unraveled that W-2 was a critical species in generating both the key N-phenylhydroxylamine and the nitrosobenzene intermediates by providing the H-bonding network in catalytic systems.