Continuous-flow synthesis of carboxylic acids from alcohols platinum and silicon dioxide-catalyzed hydrogen peroxide oxidation.

A continuous-flow method for the direct oxidation of alcohols to carboxylic acids is reported, employing hydrogen peroxide (HO) and a platinum (Pt) catalyst within a flow reactor system. This approach allows for precise control over the contact time between the reactants and the catalyst, enabling optimization of reaction conditions. By analyzing the yields of both aldehydes and carboxylic acids as a function of weight hourly space velocity (WHSV), selective synthesis of carboxylic acids was achieved without the formation of corresponding aldehydes.

Selective Detection of Toxic C1 Chemicals Using a Hydroxylamine-Based Chemiresistive Sensor Array.

Formaldehyde (FA) is a deleterious C1 pollutant commonly found in the interiors of modern buildings. C1 chemicals are generally more toxic than the corresponding C2 chemicals, but the selective discrimination of C1 and C2 chemicals using simple sensory systems is usually challenging. Here, we report the selective detection of FA vapor using a chemiresistive sensor array composed of modified hydroxylamine salts (MHAs, ArCHONH·HCl) and single-walled carbon nanotubes (SWCNT).

Hydrogen Generation from Organic Hydrides under Continuous-Flow Conditions Using Polymethylphenylsilane-Aluminum Immobilized Platinum Catalyst.

Hydrogen is an important resource for realizing the goal of a hydrogen-based society as well as for synthetic organic chemistry. Catalytic dehydrogenation of organic hydrides such as methyl cyclohexane is attractive for hydrogen storage and transportation in terms of reversibility and selectivity of catalytic reactions and hydrogen storage density. We developed a highly active polymethylphenylsilane-aluminum immobilized platinum catalyst (Pt/MPPSi-Al O ) for dehydrogenation of organic hydrides.

Reaction Rate Acceleration of Cooperative Catalytic Systems: Metal Nanoparticles and Lewis Acids in Arene Hydrogenation.

Employing two distinct catalysts in one reaction medium synergistically is a powerful strategy for activating less reactive substrates. Although the approach has been well-developed in homogeneous conditions, it remains challenging and rare in heterogeneous catalysis, especially under gas-liquid-solid multiphase reaction conditions. Here, we describe the development of cooperative and synergistic catalyst systems of heterogeneous Rh-Pt bimetallic nanoparticle catalysts, Rh-Pt/DMPSi-Al O , and Sc(OTf) in the liquid phase for the hydrogenation of arenes under very mild conditions.

Chiral Rhodium Nanoparticle-Catalyzed Asymmetric Arylation Reactions.

The development of heterogeneous catalyst systems for enantioselective reactions is an important subject in modern chemistry as they can be easily separated from products and potentially reused; this is particularly favorable in achieving a more sustainable society. Whereas numerous homogeneous chiral small molecule catalysts have been developed to date, there are only limited examples of heterogeneous ones that maintain high activity and have a long lifetime. On the other hand, metal nanoparticle catalysts have attracted much attention in organic chemistry due to their robustness and ease of deposition on solid supports.

Heterogeneous Supramolecular Catalysis through Immobilization of Anionic ML Assemblies on Cationic Polymers.

Although most of the currently developed supramolecular catalysts that emulate enzymatic reactivity with unique selectivity and activity through specific host-guest interactions work under homogeneous conditions, enzymes in nature can operate under heterogeneous conditions as membrane-bound enzymes. In order to develop such a heterogeneous system, an immobilized chiral supramolecular cluster Ga () was introduced into cross-linked polymers with cationic functionalities. These heterogeneous supramolecular catalysts were used in aza-Prins and aza-Cope reactions and successfully applied to continuous-flow reactions.

Heterogeneous Rh and Rh/Ag bimetallic nanoparticle catalysts immobilized on chiral polymers.

The development of heterogeneous chiral catalysts has lagged far behind that of homogeneous chiral catalysts in spite of their advantages, such as environmental friendliness for a sustainable society. We describe herein novel heterogeneous chiral Rh and Rh/Ag bimetallic nanoparticle catalysts consisting of polystyrene-based polymers with chiral diene moieties. The catalysts enable high-to-excellent yields and enantioselectivities to be obtained in asymmetric 1,4-addition reactions of arylboronic acids with α,β-unsaturated carbonyl compounds such as ketones, esters, and amides, and in other asymmetric reactions.

Direct Synthesis of Hydroquinones from Quinones through Sequential and Continuous-Flow Hydrogenation-Derivatization Using Heterogeneous Au-Pt Nanoparticles as Catalysts.

Pt-Au bimetallic nanoparticle catalysts immobilized on dimethyl polysilane (Pt-Au/(DMPSi-Al O )) have been developed for selective hydrogenation of quinones to hydroquinones. High reactivity, selectivity, and robustness of the catalysts were confirmed under continuous-flow conditions. Various direct derivatizations of quinones, such as methylation, acetylation, trifluoromethanesulfonylation, methacrylation, and benzoylation were successfully performed under sequential and continuous-flow conditions to afford the desired products in good to excellent yields.

Polysilane-Immobilized Rh-Pt Bimetallic Nanoparticles as Powerful Arene Hydrogenation Catalysts: Synthesis, Reactions under Batch and Flow Conditions and Reaction Mechanism.

Hydrogenation of arenes is an important reaction not only for hydrogen storage and transport but also for the synthesis of functional molecules such as pharmaceuticals and biologically active compounds. Here, we describe the development of heterogeneous Rh-Pt bimetallic nanoparticle catalysts for the hydrogenation of arenes with inexpensive polysilane as support. The catalysts could be used in both batch and continuous-flow systems with high performance under mild conditions and showed wide substrate generality.

Rhodium-catalyzed asymmetric 1,4-addition reactions of aryl boronic acids with nitroalkenes: reaction mechanism and development of homogeneous and heterogeneous catalysts.

Asymmetric 1,4-addition reactions with nitroalkenes are valuable because the resulting chiral nitro compounds can be converted into various useful species often used as chiral building blocks in drug and natural product synthesis. In the present work, asymmetric 1,4-addition reactions of arylboronic acids with nitroalkenes catalyzed by a rhodium complex with a chiral diene bearing a tertiary butyl amide moiety were developed. Just 0.

Integration of aerobic oxidation and intramolecular asymmetric aza-Friedel-Crafts reactions with a chiral bifunctional heterogeneous catalyst.

A new class of chiral bifunctional heterogeneous materials composed of Au/Pd nanoparticles and chiral phosphoric acids as active orthogonal catalysts was prepared by utilizing a facile pseudo-suspension co-polymerization method. It was found that this heterogeneous catalyst was capable of facilitating the sequential aerobic oxidation-asymmetric intramolecular aza-Friedel-Crafts reaction between benzyl alcohols and -aminoethylpyrroles. Moreover, the designed chiral heterogeneous catalyst could be recovered and reused several times without significant loss of activity or enantioselectivity.

Asymmetric Arylation of Imines Catalyzed by Heterogeneous Chiral Rhodium Nanoparticles.

Asymmetric arylation of aldimines catalyzed by heterogeneous chiral rhodium nanoparticles has been developed. The reaction proceeded in aqueous media without significant decomposition of the imines by hydrolysis to afford chiral (diarylmethyl)amines in high yields with outstanding enantioselectivities. This catalyst system exhibited the highest turnover number (700) in heterogeneous catalysts reported to date for these reactions.

Chiral Nanoparticles/Lewis Acids as Cooperative Catalysts for Asymmetric 1,4-Addition of Arylboronic Acids to α,β-Unsaturated Amides.

Cooperative catalysts consisting of chiral Rh/Ag nanoparticles and Sc(OTf)3 have been developed that catalyze asymmetric 1,4-addition reactions of arylboronic acids with α,β-unsaturated amides efficiently. The reaction has been considered one of the most challenging reactions because of the low reactivity of the amide substrates. The new catalysts provide the desired products with outstanding enantioselectivities (>98 % ee) in the presence of low loadings (<0.

Cellulose-supported chiral rhodium nanoparticles as sustainable heterogeneous catalysts for asymmetric carbon-carbon bond-forming reactions.

Cellulose-supported chiral Rh nanoparticle (NP) catalysts have been developed. The Rh NPs, which were well dispersed on cellulose, catalyzed the asymmetric 1,4-addition of arylboronic acids to enones and enoates, one of the representative asymmetric carbon-carbon bond-forming reactions, in the presence of chiral diene ligands, providing the corresponding adducts in high yields with outstanding enantioselectivities without metal leaching. The solid-state NMR analysis of the chiral NP system directly suggested interactions between the Rh NPs and the chiral ligand on cellulose.

Self-Assembled Nanocomposite Organic Polymers with Aluminum and Scandium as Heterogeneous Water-Compatible Lewis Acid Catalysts.

While water-compatible Lewis acids have great potential as accessible and environmentally benign catalysts for various organic transformations, efficient immobilization of such Lewis acids while keeping high activity and without leaching of metals even under aqueous conditions is a challenging task. Self-assembled nanocomposite catalysts of organic polymers, carbon black, aluminum reductants, and scandium salts as heterogeneous water-compatible Lewis acid catalysts are described. These catalysts could be successfully applied to various C-C bond-forming reactions without leaching of metals.

Size of gold nanoparticles driving selective amide synthesis through aerobic condensation of aldehydes and amines.

Metal nanoparticles (NPs) have attracted much attention in many fields due to their intrinsic characteristics. It is generally accepted that smaller NPs (1.5-3 nm) are more active than larger NPs, and reverse cases are very rare.

Chiral Metal Nanoparticle Systems as Heterogeneous Catalysts beyond Homogeneous Metal Complex Catalysts for Asymmetric Addition of Arylboronic Acids to α,β-Unsaturated Carbonyl Compounds.

We describe the use of chiral metal nanoparticle systems, as novel heterogeneous chiral catalysts for the asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds, as representative C-C bond-forming reactions. The reactions proceeded smoothly to afford the corresponding β-arylated products in high to excellent yields and outstanding enantioselectivities with wide substrate scope. Remarkably, the nanoparticle catalysts showed performance in terms of yield, enantioselectivity, and catalytic turnover that was superior to that of the corresponding homogeneous metal complexes.

Synergistic cascade catalysis by metal nanoparticles and Lewis acids in hydrogen autotransfer.

Of the many types of catalysis involving two or more catalysts, synergistic catalysis is of great interest because novel reactions or reaction pathways may be discovered when there is synergy between the catalysts. Herein, we describe a synergistic cascade catalysis, in which immobilized Au/Pd bimetallic nanoparticles and Lewis acids work in tandem to achieve the -alkylation of primary amides to secondary amides with alcohols hydrogen autotransfer. When Au/Pd nanoparticles were used with metal triflates, a significant rate acceleration was observed, and the desired secondary amides were obtained in excellent yields.

Tandem oxidative processes catalyzed by polymer-incarcerated multimetallic nanoclusters with molecular oxygen.

Heterogeneous catalysis and one-pot tandem reactions are key for efficient and practical organic syntheses and for green and sustainable chemistry. Heterogeneous catalysts can be recovered and reused. These catalysts can be applied to efficient systems, such as continuous-flow systems.

Chiral metal nanoparticle-catalyzed asymmetric C-C bond formation reactions.

Chiral ligand-modified metal nanoparticles possess an attractive potential for application in asymmetric synthesis. This article focuses on chiral-nanoparticle-catalyzed asymmetric C-C bond formation reactions and discusses the nature of the active species.

Direct amidation from alcohols and amines through a tandem oxidation process catalyzed by heterogeneous-polymer-incarcerated gold nanoparticles under aerobic conditions.

We describe herein a highly elegant and suitable synthesis of amide products from alcohols and amines through a tandem oxidation process that uses molecular oxygen as a terminal oxidant. Carbon-black-stabilized polymer-incarcerated gold (PICB-Au) or gold/cobalt (PICB-Au/Co) nanoparticles were employed as an efficient heterogeneous catalyst depending on alcohol reactivity and generated only water as the major co-product of the reaction. A wide scope of substrate applicability was shown with 42 examples.

A heterogeneous layered bifunctional catalyst for the integration of aerobic oxidation and asymmetric C-C bond formation.

The design and synthesis of a heterogeneous bifunctional chiral catalyst for the sequential aerobic oxidation-asymmetric Michael reactions between primary allylic alcohols and dibenzyl malonate are described. Interestingly, we found that layering bimetallic nanoparticles over the organocatalyst, within the chiral composite material, is crucial for catalytic activity.

Copolymer-incarcerated nickel nanoparticles with N-heterocyclic carbene precursors as active cross-linking agents for Corriu-Kumada-Tamao reaction.

We have developed heterogeneous polymer-incarcerated nickel nanoparticles (NPs), which catalyze cross-coupling reactions. The matrix structure of these catalysts incorporates both N-heterocyclic carbenes (NHCs) as ligands and Ni-NPs, thanks to a new design of cross-linking agents in polymer supports. These embedded NHCs were detected by field gradient swollen-resin magic angle spinning NMR analysis.

Selective imine formation from alcohols and amines catalyzed by polymer incarcerated gold/palladium alloy nanoparticles with molecular oxygen as an oxidant.

Carbon black stabilized, polymer incarcerated gold/palladium alloy nanoparticles (PICB-Au/Pd) act as an efficient, reusable heterogeneous catalyst for imine synthesis from alcohols and amines through a tandem oxidative process using molecular oxygen as the terminal oxidant.

Polymer-incarcerated chiral Rh/Ag nanoparticles for asymmetric 1,4-addition reactions of arylboronic acids to enones: remarkable effects of bimetallic structure on activity and metal leaching.

Robust and highly active bimetallic Rh nanoparticle (NP) catalysts, PI/CB Rh/Ag, have been developed and applied to the asymmetric 1,4-addition of arylboronic acids to enones without leaching of the metals. We found that the structures of the bimetallic Rh/Ag catalysts and chiral ligands strongly affect their catalytic activity and the amount of metal leaching. PI/CB Rh/Ag could be recycled several times by simple operations while keeping high yields and excellent enantioselectivities.