Functionalized Mesostructured Silicas As Supports for Palladium Catalysts: Effect of Pore Structure and Collapse on Catalytic Activity in the Suzuki-Miyaura Reaction

Two different Pd complexes are supported on the mercaptopropyltrimethoxy silyl-functionalized mesoporous material KIT-6 and their activity in the Suzuki-Miyaura cross coupling reaction is examined. Remarkably, these materials show a much greater recyclability than the corresponding SBA-15-based materials, which lose activity quickly in the presence of hot aqueous base. The high recyclability of the KIT-6 materials is proposed to result from a greater redistribution of Pd to the external surface of the material, resulting in Pd nanoparticles that are not constrained by the size of the pores. These Pd nanoparticles are then available for catalysis after the material has collapsed, whereas in the case of SBA-15-based materials, the Pd is captured inside the pores such that catalytic activity ceases when the material collapses. Eventually, Ostwald ripening leads to larger particles and a decrease in catalytic activity.