| Metal-organic frameworks （MOFs） are a new class of hybrid organic-inorganic materialsthat are comprised of organic bridging ligands and inorganic metal cations. MOFs have showngreat potential in gas storage and separation, heterogeneous catalysis, drug delivery, due totheir high surface area, well-defined porosity, and chemical tenability. The application can belargely broadened by designing functional MOFs with specific functionalikty or byintroducing active sites to the MOFs sturcuture.C-C coupling reactions are the most practical and powerful methods for the constructionof C-C bonds, which have been used in modern organic synthesis, such as natural products,pharmaceuticals, agrochemicals, functionalized materials,etc. Therefore, C-C couplingreactions plays an important role in academic research and practical application. Ullmannreaction is a powerful tool for the assembly of biaryl structures in organic synthesis, however,the high temperature （over200℃） and the consumption of a stoichiometric amount of copperrequired in the reaction present serious problems regarding energy and purification.Compared to the traditional copper-mediated Ullmann reactions, the palladium catalyzedhomocoupling of aromatic halides has been demonstrated as a more convenient and effectivemethod for biaryl synthesis.In this work, palladium supported on a typical MOF named MOF-253, which wasprepared and used as a catalyst for the Ullmann reaction. The microstructure andphysicochemical properties of the synthesized catalyst were characterized by PXRD and N2adsorption, respectively. The reaction conditions in this catalyst system, such as solvent, base,reaction time and temperature, have been optimized. And accordingly, the catalyst system isapplied to various different substrates, and the reuse of the catalyst was investigated as well.Under the optimized reaction conditions, the electronic and steric effects toward the reactivityof different substrates have been studied and the recyclability of the catalyst has beeninvestigated as well. The results show that the Ullmann cross-coupling reaction could behighly efficiently catalyzed by MOF-2530.05PdCl2in the presence of KOAc. The catalysthas been shown to be highly active, selective and recyclable for the reductive homocoupling of aromatic halides. |
