Site-Isolated Azobenzene-Containing Metal-Organic Framework for Cyclopalladated Catalyzed Suzuki-Miyuara Coupling in Flow.

Sites isolation of active metals centers, systematically studied in homogeneous systems, has been an alternative to develop low metal consuming, highly active next generation catalysts in heterogeneous condition. Because of the high porosity and facile synthetic procedures, MOF-based catalysts are excellent candidates for heterogenization of well-defined homogeneous catalysts. Herein, we report the direct Pd coordination on the azobenzene linker within a MOF catalyst through a postsynthetic modification method for a Suzuki-Miyaura coupling reaction. The immobilized cyclopalladated complexes in MOFs were analyzed by a series of characterization techniques including XPS, PXRD, and deuterium NMR (2H NMR) spectroscopy. The heterogeneous nature of the catalyst as well as its stability were demonstrated though "hot filtration" and recycling experiments. Furthermore, we demonstrate that the MOF packed column promoted the reaction between phenyl boronic acid and bromobenzene under microflow conditions with a 85% yield continuously for 12 h. This work sheds light on the potential of site-isolated MOF catalysts in efficient, recyclable and continuous flow systems for industrial application.