Trapping Pd(0) in nanoparticle-assembled microcapsules: an efficient and reusable catalyst

摘要

Pd nanoparticles dually encased by soft (polyamine) and hard (silica) materials in a microcapsule structure, obtained via a nanoparticle self-assembly method, exhibit excellent catalytic activity, with efficient catalyst recovery and reusability.rnPalladium is among the most widely used transition metals in modern organic synthesis and synthetic transformations. However, issues surrounding separation of the Pd from the desired product, stability to retain its activity and reusability often complicates its use. In this regard, there have been many efforts to immobilize Pd catalysts onto a support, such as charcoal, silica or alumina. However, though this may result in high catalytic activities, the stability to metal leaching is not satisfactory. Alternatively, encapsulation of the metal particles by polymers or dendrimers have been reported, but the catalysts further require mechanical stability against breakage of the host or leaching of the metallic particles. Recently, a number of reports have been published on the immobilization of Pd particles via ligand/polymer anchoring and layer-by-layer assembly onto a solid support. However, being a soft material, the ligand/polymer may not provide enough robustness against metal leaching, or for recyclability.8 Therefore, our approach has been to uniquely combine the inorganic nanoparticles and polymeric components in such way that they intersperse with each other, so as to hold the Pd nanoparticles in a well-defined structure. While the polymer stabilizes the Pd nanoparticles in the structure, the inorganic particles provide the required mechanical stability.