ZIF-8-based vs. ZIF-8-derived Au and Pd nanoparticles as efficient catalysts for the Ullmann homocoupling reaction

The Ullmann coupling reaction of aromatic halides is the most challenging C–C coupling reaction. Both MOF-based and MOF-derived types of catalysts have recently provided useful nanocatalysts for a variety of reactions, but they have rarely been compared. Herein, the Ullmann-type aryl iodide homocoupling is efficiently catalyzed by gold and palladium nanoparticles (NPs) loaded on ZIF-8 before (ZIF-8-based nanocatalyst: M@ZIF-8) and after calcination (ZIF-8-derived catalyst: M@CN). The nanocatalysts M@ZIF-8 (M = Pd, Au) are found to be more efficient than the catalysts M@CN. Pd@ZIF-8 exhibits better performances than those of Au@ZIF-8 for a series of aryl iodides, but in the case of 4-nitro-iodobenzene, deshydroiodination was observed besides the coupling product. Mechanisms are proposed and discussed for both Au(0) and Pd(0) nanocatalysts.