Ultrafine Pd Nanoparticles Modified on Azine-Linked Covalent Organic Polymers for Efficient Catalytic Suzuki–Miyaura Coupling Reaction

Amphiphilic Dendronized Copolymer-Encapsulated Au, Ag and Pd Nanoparticles for Catalysis in the 4-Nitrophenol Reduction and Suzuki-Miyaura Reactions

The branched structures of dendronized polymers can provide good steric stabilization for metal nanoparticle catalysts. In this work, an amphiphilic dendronized copolymer containing hydrophilic branched triethylene glycol moieties and hydrophobic branched ferrocenyl moieties is designed and prepared by one-pot ring-opening metathesis polymerization, and is used as the stabilizer for metal (Au, Ag and Pd) nanoparticles. These metal nanoparticles (Au nanoparticles: 3.5 ± 3.0 nm; Ag nanoparticles: 7.2 ± 4.0 nm; Pd nanoparticles: 2.5 ± 1.0 nm) are found to be highly active in both the 4-nitrophenol reduction and Suzuki-Miyaura reactions. In the 4-nitrophenol reduction, Pd nanoparticles have the highest catalytic ability (TOF: 2060 h-1). In addition, Pd nanoparticles are also an efficient catalyst for Suzuki-Miyaura reactions (TOF: 1980 h-1) and possess good applicability for diverse substrates. The amphiphilic dendronized copolymer will open a new door for the development of efficient metal nanoparticle catalysts.

Confinement synthesis in porous molecule-based materials: a new opportunity for ultrafine nanostructures

A balance between activity and stability is greatly challenging in designing efficient metal nanoparticles (MNPs) for heterogeneous catalysis. Generally, reducing the size of MNPs to the atomic scale can provide high atom utilization, abundant active sites, and special electronic/band structures, for vastly enhancing their catalytic activity. Nevertheless, due to the dramatically increased surface free energy, such ultrafine nanostructures often suffer from severe aggregation and/or structural degradation during synthesis and catalysis, greatly weakening their reactivities, selectivities and stabilities. Porous molecule-based materials (PMMs), mainly including metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and porous organic polymers (POPs) or cages (POCs), exhibit high specific surface areas, high porosity, and tunable molecular confined space, being promising carriers or precursors to construct ultrafine nanostructures. The confinement effects of their nano/sub-nanopores or specific binding sites can not only effectively limit the agglomeration and growth of MNPs during reduction or pyrolysis processes, but also stabilize the resultant ultrafine nanostructures and modulate their electronic structures and stereochemistry in catalysis. In this review, we highlight the latest advancements in the confinement synthesis in PMMs for constructing atomic-scale nanostructures, such as ultrafine MNPs, nanoclusters, and single atoms. Firstly, we illustrated the typical confinement methods for synthesis. Secondly, we discussed different confinement strategies, including PMM-confinement strategy and PMM-confinement pyrolysis strategy, for synthesizing ultrafine nanostructures. Finally, we put forward the challenges and new opportunities for further applications of confinement synthesis in PMMs.

Bimetallic docked covalent organic frameworks with high catalytic performance towards coupling/oxidation cascade reactions

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers that make these materials suitable for use as excellent scaffold in heterogeneous catalysis. Here we synthesize a layered two-dimensional (2D) COF (TADP–COF) through the condensation reaction between four-branched 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and linear 2,5-dihydroxyterephthalaldehyde (Dha) and 1,4-phthalaldehyde (PA) building blocks. Porphyrin units, imine and hydroxyl groups together with imines can provide wide coordination sites for metal docking. Using a programmed synthetic procedure, Cu(ii) ions first coordinated with the imine groups in conjunction with their adjacent hydroxyl groups, and porphyrin units and subsequently added Pd(ii) ions occupied the remaining imine sites in the space between adjacent COF layers. The bimetallic Pd(ii)/Cu(ii)@TADP–COF showed high catalytic activity in a one-pot coupling/oxidation cascade reaction in water. The high surface area, one-dimensional (1D) open channel structure and predesigned catalytic active sites of this material make it ideal candidate for use as heterogeneous catalyst in a wide range of catalytic reactions.

Cu(ii) and Pd(ii) ions were selectively coordinated within an imine-linked 2D COF that exhibited good catalytic performance towards a one-pot Suzuki coupling/oxidation cascade reaction.

Highly Dispersed Pd Clusters Anchored on Nanoporous Cellulose Microspheres as a Highly Efficient Catalyst for the Suzuki Coupling Reaction

With the depletion of nonrenewable resources such as oil/coal/gas, more and more research studies began to focus on the high-value utilization of residual biomass resources. Herein, for the first time, honeycomb nanoporous microspheres fabricated from renewable biomass resources of cellulose were used as a carrier to fabricate a highly dispersed palladium (Pd) nanocatalyst. Various physicochemical characterizations presented convincing pieces of evidence for the good dispersion of Pd clusters with a mean diameter of 1.6 nm. As the carrier, cellulose microspheres with an interconnected nanoporous structure contributed to the adhesion and dispersion of Pd particles, and their rich hydroxyl groups could fix the Pd particles. Importantly, the cellulose matrix could in situ induce the formation of metallic Pd(0) during calcination without a reductant. The cellulose/Pd catalyst was applied to the Suzuki coupling reaction, which exhibited promising catalytic activity compared to commercial Pd/C and unsupported homogeneous Pd(OAc)₂ catalysts, as well as good stability. The utilization of the residual biomass resource to build catalyst materials would be important for the sustainable chemistry.

Controlled Synthesis of Palladium Nanoparticles with Size-Dependent Catalytic Activities Enabled by Organic Molecular Cages

Particle size plays a key role in the performance of metal nanoparticles (MNPs). However, the size-controlled synthesis of MNPs still represents a challenging task. In this work, we revealed a strong solvent effect on the growth of palladium nanoparticles (PdNPs), which was directed by a porous [2 + 3] organic molecular cage (OMC, Phos-cage) containing triphenylphosphine moieties. PdNPs with different average diameters of 0.8, 1.2, and 3.3 nm supported by Phos-cage were obtained by simply varying the reaction media. The catalytic performance of such ultrafine PdNPs in the reduction of p-nitrophenol and a Suzuki-Miyaura coupling reaction has been studied, which clearly shows size-dependent catalytic activity and stability. The knowledge gained in this study, controlling the size of PdNPs supported by the OMC template in different solvents, will open new possibilities for size-controlled synthesis of ultrafine MNPs with high catalytic activity and stability.

Tannic Acid: A green and efficient stabilizer of Au, Ag, Cu and Pd nanoparticles for the 4-Nitrophenol Reduction, Suzuki-Miyaura coupling reactions and click reactions in aqueous solution

Due to the good electrical, optical, magnetic, catalytic properties, transition metal nanoparticles (TMNPs) have been becoming more and more interesting in the fileds of environment, material, biomedicine, catalysis, and so on. Here, tannic acid (TA) is used as a green and efficient stabilizer to fabricate all kinds of TMNPs including AuNPs, AgNPs, CuNPs and PdNPs. These TMNPs possess small sizes ranging from 1 nm to 6 nm, which is conducive to several catalytic reactions in aqueous solution, such as 4-nitrophenol (4-NP) reduction, CuAAC reactions and Suzuki-Miyaura coupling reactions. AuNPs and PdNPs are found to have distinctly higher catalytic activities than AgNPs and CuNPs in the 4-NP reduction process. Especially, PdNPs show the highest catalytic activities with TOF up to 7200 h^-1 in the 4-NP reduction. Furthermore, PdNPs also exhibit satisfying catalytic performance in the Suzuki-Miyaura coupling process, and CuNPs are catalytically active in the copper-catalyzed azide alkyne cycloaddition (CuAAC) reactions. The applicability and generality of PdNPs and CuNPs are respectively confirmed via the reaction between different substrates in the Suzuki-Miyaura coupling reactions and the CuAAC reactions. This work present a simple, fast, green and efficient strategy to synthesize TMNPs for multiple catalysis.

Synthesis of ultrafine AuPd bimetallic nanoparticles using a magnetite-cored poly(propyleneimine) dendrimer template and its sustainable catalysis of the Suzuki coupling reaction

A rational synthesis of magnetically recyclable PPI dendrimer encapsulated AuPd bimetallic nanoparticle and its catalytic examination in the Suzuki coupling reaction.