Palladium Nanoparticles Captured in Microporous Polymers: A Tailor-Made Catalyst for Heterogeneous Carbon Cross-Coupling Reactions

摘要

A new strategy based on polymerization-induced phase separation (PIPS) techniques wasnproposed for fabricating palladium nanoparticles (PdNPs) captured in a microporous network polymer.nPd(OAc)2 was premixed with a monomer having a poly(amidoamine)-based dendrimer ligand, andnsubsequently this was thermally polymerized with an excess amount of ethylene glycol dimethacrylatenunder PIPS conditions. In this system, the formation of PdNPs occurred concurrently with the polymernsynthesis in a one-pot process, even with no additional reducing reagent. The resultant microporous polymernwas found to have a mesoporosity; the nitrogen sorption analysis gave a specific-surface area of 511 m2ng-1, an average pore diameter of 9.9 nm, and a total pore volume of 1.01 mL g-1. The TEM images of thenpolymer revealed that the created PdNPs were very small with a diameter of mainly ca. 2.0 nm; the highresolutionnimages were lattice-resolvable, showing the crystalline nature of the PdNPs (Pd(111) facets).nCatalytic performances of the PdNP-containing microporous polymers were investigated for a heterogeneousnSuzuki-Miyaura reaction of 4′-bromoacetophenone and phenylboronic acid in water. In the presence ofn10-2 molar equiv of the polymer, the reaction efficiently proceeded at 80 °C and gave the desired product,n4-acetylbiphenyl, in >90% yield after 2 h. On the basis of the ICP-AES analysis, the Pd content releasedninto the solution phase was estimated to be only 0.27% of the initial charge. Thereby, this polymer wasnsuccessfully recovered by simple filtration and reused with only a minimal loss of activity (yield >90%neven at the eighth run). When the catalytic reaction was examined with a low amount of the polymer catalyst,nthe turnover number (TON) reached 8.5 × 104 while maintaining a good yield. Finally, the dendrimer templateneffect of the polymer catalyst was discussed by referring to the catalytic performances of a control polymernprepared with nonintegrated ligand monomers.