Ordered Mesoporous Organosilica with Ionic-liquid Framework: an Efficient and Reusable Support for the Palladium-catalyzed Suzuki-Miyaura Coupling Reaction in Water

The preparation of a novel palladium-supported periodic mesoporous organosilica based on alkylimidazolium ionic liquid (Pd@PMO-IL) in which imidazolium ionic liquid is uniformly distributed in the silica mesoporous framework is described. Both Pd@PMO-IL and the parent PMO-IL were characterized by N(2)-adsorption-desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), TEM, and solid-state NMR spectroscopy. We have demonstrated that Pd@PMO-IL is an efficient and reusable catalyst for the Suzuki-Miyaura coupling reaction of various types of iodo-, bromo-, and even deactivated aryl chlorides in water. It was also found that although the PMO-IL nanostructure acts as reservoir for soluble Pd species, it can also operate as a nanoscaffold to recapture the Pd nanoparticles into the mesochannels thus preventing extensive agglomeration of Pd. This observation might be attributed to the isolated ionic liquid units that effectively control the reaction mechanism by preventing Pd agglomeration and releasing and recapturing Pd nanoparticles during the reaction process. The catalyst can be recovered and reused for at least four reaction cycles without significant loss of activity.