Covalent Immobilization of Imidazolium Cations Inside a Silica Support: Palladium-Catalyzed Olefin Hydrogenation

Mesoporous organosilica materials with different contents of bistrialkoxysilyl imidazolium salts in the framework were synthesized by a one-step synthesis. Textural characterization of the materials confirmed that the morphology and surface properties of the imidazolium-bridged organosilicas depended critically on the amount of organic groups in the framework, whereas solid-state NMR characterization showed that the imidazolium fragments were integrated covalently into the framework. Further reaction of these materials with Pd(OAc)(2), followed by reduction with NaBH4 yielded palladium nanoparticles stabilized in the mesoporous organosilicas. The stabilizing effect of the imidazolium cations and the mesostructure contributed to the high activity, selectivity, and stability of the palladium nanoparticles and allowed olefin hydrogenation under mild reaction conditions.