Pairs of Zirconium Site and Hydroxyl in MOFs Enable Generating Peroxo Species for Efficiently Tandem Oxidative Condensation of Aromatic Amines.

Abstract

Selective oxidation of aromatic amines to azoxyarenes is important but challenging owing to complex reaction pathways. Here, we report that constructing pairs of Lewis acidic Zr sites and terminal hydroxyl in zirconium trimesate MOF-808 enables activation of H₂O₂ for the formation of non-radical Zr-OOH species via hydrogen-bonding interaction, achieving tandem oxidation of aniline to intermediates and their condensation into azoxybenzene via a non-radical pathway. This catalyst displays 97.1% selectivity for azoxybenzene at nearly complete conversion under 25°C, along with good stability over fifteen successive runs, which is far superior to contrast ZrO₂ and Zr(OH)₄. Moreover, the gram-scale synthesis of azoxybenzene is achieved through Zr-OOH species. Its universality is validated by the tandem oxidative condensation of 22 aniline derivatives to corresponding homo-coupled azoxyarenes as well as the successful synthesis of 6 hetero-condensation azoxyarenes. Substantially, the general applicability is confirmed by constructing other MOFs-based pairs of Lewis acidic metal sites and terminal hydroxyl for achieving excellent performances to produce azoxybenzene. This work establishes a new avenue for H₂O₂ activation via major-auxiliary cooperation to drive selective oxidation reactions.