The Actual Active Species of Sulfur-Modified Gold-Supported Palladium as a Highly Effective Palladium Reservoir in the Suzuki-Miyaura Coupling

Preparation of a platinum nanoparticle catalyst located near photocatalyst titanium oxide and its catalytic activity to convert benzyl alcohols to the corresponding ethers

A novel platinum nanoparticle catalyst closely located near the surface of titanium oxide, PtNP/TiO₂, has been prepared. This catalyst has both the properties of a photocatalyst and a metal nanoparticle catalyst, and acquired environmentally friendly catalytic activity, which cannot be achieved by just one of these catalysts, to afford ethers from benzyl alcohols under the wavelength of 420 nm.

A novel platinum nanoparticle catalyst closely located near the surface of titanium oxide, PtNP/TiO₂, has been prepared. It has catalytic activity to afford ethers from benzyl alcohols under the wavelength of 420 nm.

Self-Assembled Multilayer Iron(0) Nanoparticle Catalyst for Ligand-Free Carbon-Carbon/Carbon-Nitrogen Bond-Forming Reactions

Self-assembled multilayer iron(0) nanoparticles (NPs, 6-10 nm), namely, sulfur-modified Au-supported Fe(0) [SAFe(0)], were developed for ligand-free one-pot carbon-carbon/carbon-nitrogen bond-forming reactions. SAFe(0) was successfully prepared using a well-established metal-nanoparticle catalyst preparative protocol by simultaneous in situ metal NP and nanospace organization (PSSO) with 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (Si-DHP) as a strong reducing agent. SAFe(0) was easy to handle in air and could be recycled with a low iron-leaching rate in reaction cycles.

A magnetically retrievable air and moisture stable gold and palladium nanocatalyst for efficient C-C coupling reactions

In this study, we report the synthesis of a highly stable, magnetically retrievable gold and palladium nanocatalyst (AuPd@AMNPs), highly active in Suzuki cross-coupling and related homocoupling reactions. The active catalytic component in this system is palladium, which can only be stabilized in the presence of gold nanoparticles. There is no significant loss of activity even after prolonged storage exposed air and moisture. The versatile nature AuPd@AMNPs is demonstrated through the selective catalysis of the homocoupling of phenylboronic acid under low concentrations of O₂ and the oxidation of phenylboronic acid to phenol under high O₂ concentrations. AuPd@AMNPs also demonstrated Ullmann-type homocoupling of 4-iodotolene with excellent yields. The magnetically retrieved catalyst could be re-used up to six times in Suzuki-Miyaura cross-coupling with consistently high activity and with a minimal loss of the noble metal species. Through these reactions we show that the gold-stabilized AuPd@AMNPs can be used as stable and recyclable palladium reservoir for multiple palladium-catalysed reactions.

Development of Metal Nanoparticle Catalysis toward Drug Discovery

Transition-metal nanoparticles (NPs) catalysts supported on solid material represent one of the most important subjects in organic synthesis due to their reliable carbon-carbon or carbon-heteroatom bond-forming cross-coupling reactions. Therefore methodologically and conceptually novel immobilization methods for nonprecious transition-metal NPs are currently required for the development of organic, inorganic, green, materials, and medicinal chemistry. We discovered a self-assembled Au-supported Pd NPs catalyst (SAPd(0)) and applied it as a catalyst to Suzuki-Miyaura coupling, Buchwald-Hartwig reaction, Carbon(sp² and sp³)-Hydrogen bond functionalization, double carbonylation, removal of the allyl protecting groups of allyl esters, and redox switching. SAPd(0) comprises approximately 10 layers of self-assembled Pd(0) NPs, whose size is less than 5 nm on the surface of a sulfur-modified Au. The Pd NPs are wrapped in a sulfated p-xylene polymer matrix. We thought that the self-assembled Au-supported Pd NPs could be made by in situ metal NP and nanospace simultaneous organization (PSSO). This methodology involves 4 kinds of simultaneous procedures: i) reduction of a higher valence metal salt, ii) growth of metal NPs with appropriate size, iii) growth of a matrix with appropriate pores, and iv) wrapping of the metal NPs by matrix nanopores. This methodology is different from previously reported metal NPs-immobilizing methods, which use solid supports with preformed pores or coordination sites. We also applied the in situ PSSO method to prepare various immobilized transition-metal NPs, including base metals. For example, the in situ PSSO method can be applicable to easily prepare Ni, Ru, and Fe NPs with good recyclability and low metal leaching for use in organic synthesis.

Development of a Sulfur-Modified Glass-Supported Pd Nanoparticle Catalyst for Suzuki-Miyaura Coupling

A safe, facile and low-leaching (up to 0.17 ppm) sulfur-modified glass-supported palladium nanoparticle catalyst has been developed for the Suzuki-Miyaura coupling of aryl halides with aryl boronic acids. Most notably, this catalyst was highly recyclable and could be used up to 10 times without any discernible decrease in its activity.

Redox Switching of Orthoquinone-Containing Aromatic Compounds with Hydrogen and Oxygen Gas

Unique redox switching of orthoquinone-containing pentacyclic aromatic compounds with molecular hydrogen and oxygen in the presence of a palladium nanoparticle catalyst (SAPd) is disclosed. These molecules were predicted by in silico screening before synthesis. Efficient protocols for the synthesis of orthoquinone-containing aromatic compounds by palladium-mediated homocoupling and the benzoin condensation reaction were developed. Clear switching between orthoquinone and aromatic hydroquinone compounds was observed on the basis of their photoluminescence properties. Furthermore, the twist strain of the orthoquinone moiety could induce dramatic changes in color and emission.

Formation of self-assembled multi-layer stable palladium nanoparticles for ligand-free coupling reactions

SAPD works for ligand-free Buchwald–Hartwig reaction and Suzuki–Miyaura coupling with low-leaching (<1 ppm) and high recyclability (>10 times).

Direct Arylation of Benzo[b]furan and Other Benzo-Fused Heterocycles

The direct arylation of benzo[b]furan, benzo[b]thiophene, and indole has been studied by using aromatic bromides as the aryl source. The protocol employing common reagents and a Pd catalyst has led to the regioselective arylation of these heterocycles at the 2-position. A range of functional groups were tolerated, providing quick access to a variety of arylated benzo-fused heterocycles that would be accessible more elaborately using classical synthetic strategies. This is the first systematic study of the direct arylation of benzo[b]furan.

Palladium-nanoparticle-catalyzed 1,7-palladium migration involving C-H activation, followed by intramolecular amination: regioselective synthesis of N1-arylbenzotriazoles and an evaluation of their inhibitory activity toward indoleamine 2,3-dioxygenase

A sulfur-modified gold-supported palladium material (SAPd) has been developed bearing palladium nanoparticles on its surface. Herein, we report for the first time the use of SAPd to affect a Pd-nanoparticle-catalyzed 1,7-Pd migration reaction for the synthesis of benzotriazoles via C-H bond activation. The resulting benzotriazoles were evaluated in terms of their inhibitory activity toward indoleamine 2,3-dioxygenase.

Ligand-free Suzuki-Miyaura coupling with sulfur-modified gold-supported palladium in the synthesis of a conformationally-restricted cyclopropane compound library with three-dimensional diversity

A conformationally restricted privileged structure library with stereochemical diversity for a "fragment growth" methodology comprising 90 compounds was designed and systematically and efficiently synthesized using sulfur-modified Au-supported Pd (SAPd)-catalyzed ligand-free Suzuki-Miyaura coupling of vinyl iodide promoted by microwave and subsequent amidation in liquid-phase combinatorial chemistry as key reactions. Evaluation of the compounds with a 20-kinase panel indicated the usefulness of this "fragment growth" methodology for finding hit library compounds for fragment-based drug discovery.