Catalysis with chemically modified mesoporous silicas: Stability of the mesostructure under Suzuki-Miyaura reaction conditions

摘要

The use of functionalized mesoporous silicas such as SBA-15 and MCM-41 as supports for Pd catalysis has become increasingly common, notably in important reactions such as the Suzuki-Miyaura reaction. However the analysis of the structural consequences of exposure to these harsh reaction conditions is not nearly as common. We report herein a study of the effect of the Suzuki-Miyaura reaction conditions on the mesoporous material, and on the catalytic activity of the resulting material. Although it has been determined that aqueous base is highly detrimental to the structure of the material, the boric acid produced during the actual coupling reaction has a significant protective effect on the material. This protective effect can be mimicked by the addition of exogenous boric acid to the reaction medium. The use of aluminum-doped material provides an additional protective effect that is not dependent on the presence of boric acid. Finally, we demonstrate conclusively that access to the pores is essential for catalysis, since loss of mesoporosity is coincident with loss of catalytic activity.