Pd-Nanoparticles Confined Within Hollow Polymeric Framework as Effective Catalysts for the Synthesis of Fine Chemicals

Encapsulation of metal nanoclusters in porous solid polymer materials is a promising approach to combine the outstanding properties of both, heterogeneous and homogeneous catalysts. We report heterogeneous nano-engineered catalysts containing Pd-nanoparticles (NPs) confined within highly-porous hollow polymeric framework of hyper cross-linked polystyrene (HPS). HPS with different surface functionalities (amine vs. sulfonate) were used for impregnation by Pd precursors of different nature and followed by a variety of catalyst post-treatments. The catalysts have been tested in two model key reactions for the synthesis of fine chemicals: selective hydrogenation of 2-methyl-3-butyne-2-ol to 2-methyl-3-butene-2-ol (MBE) and Suzuki cross-coupling of 4-bromoanisole with phenylboronic acid. Optimization of the Pd/HPS preparation and reaction conditions allowed attaining high selectivity (similar to 99 %) to target MBE at close to full conversion. For Suzuki cross-coupling more than 90 % yield of coupling product was obtained under mild reaction conditions and the absence of phase transfer agent. Our results demonstrate the potential of HPS as a suitable support for tailoring metal NPs properties and circumvent undesirable metal leaching

Pd Nanoparticles Stabilized by Hypercrosslinked Polystyrene Catalyze Selective Triple C-C Bond Hydrogenation and Suzuki Cross-Coupling

This paper describes the synthesis of Pd-containing catalysts based on nonfunctionalized hypercrosslinked polystyrene via impregnation with Pd acetate. Developed Pd nanoparticulate catalyst allowed achieving conversion of aryl halide up to 90% in Suzuki cross-coupling reaction under mild conditions and at the absence of phase-transfer agents. During the selective hydrogenation of triple C-C bond of 2-methyl-3-butyn-2-ol, up to 96% selectivity with respect to corresponding olefinic alcohol was found at 95% conversion. The influences of the procedure of catalyst synthesis like precursor decomposition and reductive activation method on Pd nanoparticle formation are discussed

Au Core-Pd Shell Bimetallic Nanoparticles Immobilized within Hyper-Cross-Linked Polystyrene for Mechanistic Study of Suzuki Cross-Coupling: Homogeneous or Heterogeneous Catalysis?

The synthesis of catalytically active bimetallic Au-Pd nanoparticles stabilized in hyper-cross-linked polystyrene (HPS) for Suzuki cross-coupling of 4-bromoanisole (4-BrAn) and phenylboronic acid is presented. The core-shell structure with a thin (less than 1 nm) Pd shell and a Au core was proven by X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy. More than a 2-fold increase in 4-BrAn conversion was found in comparison with monometallic Pd/HPS. Moreover, when the Suzuki reaction was carried out under visible-light irradiation, the product yield further increased by about 1.3 times (from 56.1% up to 73.7%). This effect was assigned to a local surface plasmon resonance arising in the Au core that allowed electron transfer to the extremely thin Pd layer due to intimate contact with gold. The results suggest that the rate-limiting step of the catalytic cycle takes place on the surface of the Pd shell, serving as evidence of the heterogeneous catalysis nature

Catalysts of Suzuki Cross-Coupling Based on Functionalized Hyper-cross-linked Polystyrene: Influence of Precursor Nature

This paper describes synthesis of Pd-containing catalysts of Suzuki cross-coupling based on amino-functionalized hyper-cross-linked polystyrene at variation of Pd precursor nature (PdCl2, PdCl2(CH3CN)(2), or PdCl2(PhCN)(2)). The investigation of the influence of palladium, oxidation state (Pd(II) or Pd(0)) and form (Pd-n dusters or Pd nanoparticles) on the rate of Suzuki cross-coupling of 4-bromoanisole and phenylboronic acid is discussed. Developed catalysts are shown to allow achieving, conversion of 4-bromoanisole higher than 98% under mild reaction conditions. Independently of the precursor nature, Pd(II) is mainly responsible for observed catalytic activity. However, preliminary reduction of catalysts with H-2 results in formation of a large number of Pd-n. clusters, the contribution of which in the Suzuki reaction becomes predominant