Incorporation of CuO NPs into modified UiO-66-NH2 metal–organic frameworks (MOFs) with melamine for catalytic C–O coupling in the Ullmann condensation

Abstract

Herein, the UiO-66-NH₂ metal–organic framework (MOF) is initially modified with melamine via a post-synthetic approach. CuO nanoparticles (NPs) are then anchored via the available functional groups (amine groups and π–electron interactions of melamine and ligand) on the surface of the modified MOF. The as-synthesized UiO-66-NH₂-Mlm/CuO NPs are characterized using different techniques including XRD, TGA, TEM, EDX, and XPS. The CuO-supported MOF is successfully used as a heterogeneous catalyst for C–O coupling in Ullmann condensation. A catalytic amount of the supported catalyst (5% CuO) promotes the condensation reaction for various aryl chlorides, bromides, and iodides under mild reaction conditions (100 °C with KOH serving as a base) in good yield (30–95%) within 18–24 h. Even in the absence of KOH, the reaction is enabled with 55% yield in 24 h by grafting melamine with amine groups to create base active sites on the MOF, which indicates the additional role of the support as a base active site. The supported catalyst is easily recycled and reused several times with negligible loss in its activity. Furthermore, the copper leaching from the catalyst is as low as 1.2 wt% after being reused four times.