Seongwan Jang

Ordered Mesoporous Carbon Supported Colloidal Pd Nanoparticle Based Model Catalysts for Suzuki Coupling Reactions: Impact of Organic Capping Agents

Recent advances in the field of nanoscience have enabled the preparation of high‐surface‐area supported catalysts with precise control over the individual structural components. As such, a range of factors that affect the catalytic reactivity, such as the size, shape, and composition of the nanoparticles (NPs), have been identified. Herein, high‐surface‐area model catalysts that were based on colloidal Pd NPs and a hexagonally ordered mesoporous carbon support were prepared and the impact of various organic capping agents for the Pd NPs on their catalytic activity towards Suzuki coupling reactions was investigated. Colloidal Pd NPs (diameter: 3 nm) were synthesized with different organic capping agents, oleylamine (OA) and trioctylphosphine (TOP), and they were subsequently incorporated into the mesopores of CMK‐3 mesoporous carbon to yield OA‐Pd/CMK‐3 and TOP‐Pd/CMK‐3 nanocatalysts, respectively. The OA‐Pd/CMK‐3 catalyst was treated with acetic acid to generate a supported catalyst with surfactant‐free Pd NPs (OA‐Pd/CMK‐3‐A). Structural characterization revealed that the Pd NPs were uniformly dispersed throughout the mesopores of the CMK‐3 support and the particle size and crystallinity of the Pd NPs were preserved following the incorporation. All of the Pd/CMK‐3 nanocatalysts exhibited higher activity than commercial activated carbon supported Pd catalysts in Suzuki coupling reactions. The catalytic activities of the three Pd/CMK‐3 nanocatalysts were in the following order: OA‐Pd/CMK‐3‐A>OA‐Pd/CMK‐3>TOP‐Pd/CMK‐3. This result suggested that the presence and type of surfactants had a significant effect on the catalytic activity. The OA‐Pd/CMK‐3‐A catalyst also showed high activity for various substrates and good recycling ability in Suzuki coupling reactions.

Azide-alkyne Huisgen [3+2] cycloaddition using CuO nanoparticles.

Recent developments in the synthesis of SpellECuO nanoparticles (NPs) and their application to the [3+2] cycloaddition of azides with terminal alkynes are reviewed. With respect to the importance of click chemistry, CuO hollow NPs, CuO hollow NPs on acetylene black, water-soluble double-hydrophilic block copolymer (DHBC) nanoreactors and ZnO–CuO hybrid NPs were synthesized. Non-conventional energy sources such as microwaves and ultrasound were also applied to these click reactions, and good catalytic activity with high regioselectivity was observed. CuO hollow NPs on acetylene black can be recycled nine times without any loss of activity, and water-soluble DHBC nanoreactors have been developed for an environmentally friendly process.

Copper Nanoparticles Catalyzed Se(Te)Se(Te) Bond Activation: A Straightforward Route Towards Unsymmetrical Organochalcogenides from Boronic Acids

A highly porous copper metal–organic framework, [Cu3(BTC)2] (BTC=benzene‐1,3,5‐tricarboxylate) was synthesized and used as a precursor for the synthesis of copper nanoparticles (NPs) and characterized by several techniques, including XRD, SEM, TEM, EDX and BET measurements. The as‐synthesized copper nanoparticles were immobilized onto activated charcoal (AC) by means of ultrasonication at room temperature without any pretreatment. The Cu NPs/AC was employed as a heterogeneous catalyst for the cross‐coupling of diphenyl diselenide and boronic acids to form diphenyl selenides through SeSe bond activation under ligand‐, base‐, and additive‐free conditions. The copper NPs/AC, which combines the architecture of MOFs and the high surface area of charcoal, could be an efficient heterogeneous catalytic system that is compatible with a variety of substituents on diphenyl selenides. Its promising catalytic activity relative to that of other homogeneous systems and low catalyst loading for the synthesis of unsymmetrical diaryl selenides is an important application in the area of nanocatalysis. The Cu NPs/AC catalyst, which exhibits excellent catalytic activity and remarkable tolerance to a wide variety of substituents, led to Se sp3‐, sp2‐, and sp‐carbon bond formation by using DMSO as a solvent and atmospheric air as oxidant. This approach can also be extended to the preparation of unsymmetrical organotelluride derivatives.

Propargylic substitution reactions with various nucleophilic compounds using efficient and recyclable mesoporous silica spheres embedded with FeCo/graphitic shell nanocrystals

Phosphomolybdic acid (PMA, H3PMo12O40) functioned as a catalyst for reactions of secondary propargylic alcohols and nucleophiles. Highly stable and magnetically recyclable mesoporous silica spheres (MMS) embedded with FeCo-graphitic carbon shell nanocrystals (FeCo/GC@MSS) were fabricated by a modified Stöber process and chemical vapor deposition (CVD) method. The FeCo/GC@MSS were loaded with phosphomolybdic acid (PMA@FeCo/GC@MSS), and their catalytic activity was investigated. Propargylic reactions of 1,3-diphenyl-2-propyn-1-ol with a wide range of nucleophiles bearing activating substituents were catalyzed under mild conditions. It was found that the MMS possess mesoporosities and have enough inner space to load FeCo and phosphomolybdic acid. The FeCo/GC@MSS were found to be chemically stable against acid etching and oxidation. This suggests that the nanocrystals can be used as a support for an acid catalyst. Moreover, the magnetic property of the nanocrystals enabled the facile separation of catalysts from the products.

Preparation of Cu@Cu2O Nanocatalysts by Reduction of HKUST-1 for Oxidation Reaction of Catechol

HKUST-1, a copper-based metal organic framework (MOF), has been investigated as a catalyst in various reactions. However, the HKUST-1 shows low catalytic activity in the oxidation of catechol. Therefore, we synthesized Fe3O4@HKUST-1 by layer-by layer assembly strategy and Cu@Cu2O by reduction of HKUST-1 for enhancement of catalytic activity. Cu@Cu2O nanoparticles exhibited highly effective catalytic activity in oxidation of 3,5-di-tert-butylcatechol. Through this method, MOF can maintain the original core-shell structure and be used in various other reactions with enhanced catalytic activity.