Recyclable Catalyst System Research Articles

A Simple Nickel Metal-Organic Framework-Catalyzed Borylation of Aryl Chlorides and Bromides.

We report a recyclable and efficient catalyst system based on a nickel-benzene tricarboxylic acid metal-organic framework (Ni-BTC MOF) for the borylation of aryl halides, including aryl chlorides, with bis(pinacolato)diboron, affording aryl boronate esters in high yields (up to >99% yield) with high selectivity. This protocol demonstrates broad functional group tolerance. Catalyst can be recyclable up to four times, and gram-scale reactions further highlights the usefulness of this method. In situ EPR experiments confirmed the formation of catalytically active Ni(I) species.

Green Chemistry Approach toward the Regioselective Synthesis of α,α-Disubstituted Allylic Amines.

Molybdenum-catalyzed allylic substitution reactions are known to provide direct and practical ways to construct new carbon-carbon bonds and privileged compounds. However, due to the lack of reports on carbon-heteroatom bond formation as a common deficiency, these reactions still face a great challenge. Described herein is a robust and convenient molybdenum-catalyzed regioselective allylic amination of tertiary allylic carbonates with an amine as the heteroatom nucleophile. Both aromatic and aliphatic amines react with various tertiary allylic alcohol derivatives to deliver the desired α,α-disubstituted allylic amines in high yield with complete regioselectivity. In addition, ethanol as the green solvent, a recyclable catalyst system through simple centrifugation techniques, and simple handling procedures make the current approach green, economic, and sustainable.

Novel Spinel Nanomaterials for Photocatalytic Hydrogen Evolution Reactions: An Overview

The energy demand generated by fossil fuels is increasing day by day, and it has drastically increased after the COVID-19 pandemic as industries and household utilities rejuvenate. Renewable sources are thus becoming more essential as easily available, alternative methods of low-cost energy generation. Among these renewables, solar energy, i.e., solar power, is a promising energy source and can be used for solar-based H2 evolution because H2 technology is a leading source of eco-friendly electricity generation, and most of the worldwide efforts to develop this method involve heterogeneous catalysis for H2 evolution via water splitting and its storage, i.e., using a fuel cell. In the current scenario, there is a need to develop a stable, recyclable, and reusable heterogeneous catalyst system, which is a great challenge. In the current study, we have focused on novel ferrite magnetic nanomaterials for recyclable and reusable robust photocatalysis. Moreover, discussions of the factors contributing to the photocatalytic hydrogen evolution, low-cost synthesis techniques, and prospects for making them ideal photocatalysts are uncommon in the literature. The study will impart possible approaches for the design and development of novel ferrite nanomaterials and their nanocomposites for H2 generation in the forthcoming years.

Aza‐Michael Mono‐ and Bis‐Addition of Primary and Secondary Amines Promoted by Silica‐Supported Polyphosphoric Acid, PPA/SiO2

AbstractThe development of new protocols using non‐toxic, low cost, eco‐friendly, recyclable catalyst systems which give high productivity under mild reaction conditions has received much attention in organic synthesis in the last couple of years. A collection of structurally diverse β‐amino carbonyl compounds was successfully synthesized by aza‐Michael mono‐ and double‐additions using silica‐supported polyphosphoric acid as catalyst under solventless conditions. Highlighted advantages of this particular catalyst include ease of preparation and long‐term stability under storage.

Controlling the aggregation and assembly of boron‐containing molecular and polymeric materials

AbstractBoron‐containing molecules and polymers are attractive as powerful tunable Lewis acids for small molecule activation and catalysis, as luminescent materials for organic electronic device and (bio)imaging applications, and as smart chemical sensors. While the characteristics of the boron‐containing building blocks are attractive in and of themselves, their assembly into higher order supramolecular materials offers access to unique properties and emerging functions. Herein, we highlight recent achievements in the field of aggregated organoboron materials. We discuss how supramolecular interactions can be exploited to precisely control the structure of the assemblies and impact their functions as luminescent materials, recyclable and smart catalyst systems, chemical sensors, stimuli‐responsive and self‐healing materials.

Recent advances in the asymmetric reduction of imines by recycled catalyst systems

Recent advances relating to the asymmetric reduction of imines to afford optically active amines via recyclable catalyst systems are reviewed.

Nickel foam supported porous copper oxide catalysts with noble metal-like activity for aqueous phase reactions.

Contiguous metal foams offer a multitude of advantages over conventional powders as supports for nanostructured heterogeneous catalysts; most critically a preformed 3-D porous framework ensuring full directional coverage of supported catalyst, and intrinsic ease of handling and recyclability. Nonetheless, metal foams remain comparatively underused in thermal catalysis compared to more conventional supports such as amorphous carbon, metal oxides, zeolites and more recently MOFs. Herein, we demonstrate a facile preparation of highly-reactive, robust, and easy to handle Ni foam-supported Cu-based metal catalysts. The highly sustainable synthesis requires no specialized equipment, no surfactants or additive redox reagents, uses water as solvent, and CuCl2(H2O)2 as precursor. The resulting material seeds as well-separated micro-crystalline Cu2(OH)3Cl evenly covering the Ni foam. Calcination above 400 °C transforms the Cu2(OH)3Cl to highly porous CuO. All materials display promising activity towards the reduction of 4-nitrophenol and methyl orange. Notably, our leading CuO-based material displays 4-nitrophenol reduction activity comparable with very reactive precious-metal based systems. Recyclability studies highlight the intrinsic ease of handling for the Ni foam support, and our results point to a very robust, highly recyclable catalyst system.

Reduction of Aldehydes with Formic acid in Ethanol using Immobilized Iridium Nanoparticles on a Triazine‐phosphanimine Polymeric Organic Support

A novel triazine‐phosphanimine polymeric organic support (TPA) was synthesized successfully by a controllable one‐pot method using melamine (1,3,5‐triazine‐2,4,6‐triamine) and trichlorophosphane (PCl3). The TPA substrate is a material incorporating P and N atoms which can coordinate with metals as a pincer ligand to stabilize them, providing an efficient heterogeneous support to prepare recyclable transition metal catalyst systems. In this study, TPA was used as support to immobilize iridium nanoparticles in the range of ~8 nm on its surface, resulting in the generation of a novel iridium nanocatalyst system (INP‐TPA‐POP). This catalyst system was characterized using different microscopic and spectroscopic techniques such as FT‐IR, TEM, XPS, XRD, SEM, EDX, elemental analysis, ICP and BET analysis. The INP‐TPA‐POP nanocatalyst exhibited remarkable activity in reduction of aldehydes to alcohols using formic acids as reducing agent in ethanol as solvent.

Tailoring Graphene Oxide Framework with N- and S- Containing Organic Ligands for the Confinement of Pd Nanoparticles Towards Recyclable Catalyst Systems

Graphene oxide frameworks (GOFs) tailored with heteroatom-containing organic ligands were utilized for the efficient confinement of Pd nanoparticles (NPs) to achieve highly recyclable Pd catalysts for Suzuki-Miyaura cross-coupling reaction (SMC). The tailored GOFs were constructed using benzene-1,4-diboronic acid as a pillaring unit and N- and S- containing additional organic ligands to anchor Pd NPs. Highly dispersed Pd NPs with narrow size distribution were generated inside the gallery space of the GOFs. The presence of the anchoring ligands significantly enhanced the stability of Pd NPs via strong Pd−N and Pd−S bonds, leading to high activity and recyclability in the SMC reaction.

Synthesis and characterization of Pd(II)–vitamin B6 complex supported on magnetic nanoparticle as an efficient and recyclable catalyst system for C–N cross coupling of amides in deep eutectic solvents

Vitamin B6–Pd(II) immobilized onto magnetic nanoparticles have been successfully prepared and applied for C–Xcross‐coupling reactions with aryl halides in green deep eutectic solvents. The results prove that the Fe3O4@vitamin B6–Pd(II) magnetic nanoparticles show high catalyst activity and good stability. It was also revealed that this complex can be recycled up to five times without any significant loss in catalytic activity.

Aerobic Oxidation of Alcohols Catalyzed by in Situ Generated Gold Nanoparticles inside the Channels of Periodic Mesoporous Organosilica with Ionic Liquid Framework.

In situ generated gold nanoparticles inside the nanospaces of periodic mesoporous organosilica with an imidazolium framework (Au@PMO-IL) were found to be highly active, selective, and reusable catalysts for the aerobic oxidation of activated and nonactivated alcohols under mild reaction conditions. The catalyst was characterized by nitrogen adsorption-desorption measurement, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), elemental analysis (EA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The catalyst exhibited excellent catalytic activity in the presence of either Cs2CO3 (35 °C) or K2CO3 (60 °C) as reaction bases in toluene as a reaction solvent. Under both reaction conditions, various types of alcohols (up to 35 examples) including activated benzylic, primary and secondary aliphatic, heterocyclic, and challenging cyclic aliphatic alcohols converted to the expected carbonyl compounds in good to excellent yields and selectivity. The catalyst was also recovered and reused for at least seven reaction cycles. Data from three independent leaching tests indicated that amounts of leached gold particles were negligible (<0.2 ppm). It is believed that the combination of bridged imidazolium groups and confined nanospaces of PMO-IL might be a major reason explaining the remarkable stabilization and homogeneous distribution of in situ generated gold nanoparticles, thus resulting in the highly active and recyclable catalyst system.

Performance enhancing additives for reusable ruthenium-triphos catalysts in the reduction of CO2to dimethoxymethane

Additives enhance the performance of a recyclable ruthenium-triphos catalyst system in the hydrogenation of carbon dioxide to dimethoxymethane.

Ortho[sbnd]C[sbnd]H amidations enabled by a recyclable manganese-ionic liquid catalytic system

We described an environmentally benign, recyclable base metal catalyst system (MnBr(CO)5/[Hmim]OAc) for orthoCH amidation. The readily available dioxazolones was used as the amidation agents. A broad substrate scope and high functional group tolerance were observed. The catalyst system (MnBr(CO)5/[Hmim]OAc) could be easily reused by simple phase separations.

Synthesis and Characterization of Copper(I)‐Cysteine Complex Supported on Magnetic Layered Double Hydroxide as an Efficient and Recyclable Catalyst System for Click Chemistry Using Choline Azide as Reagent and Reaction Medium

In this study, Fe3O4@LDH@cysteine–Cu(I) nanoparticles as a novel and recyclable catalytic system was designed and successfully synthesized. These nanoparticles show high catalytic activity for preparation of the triazole family through reaction of the organic halides with alkynes in the presence of choline azide as reagent and reaction medium. In addition, Fe3O4@LDH@cysteine–Cu(I) could be easily recovered and reused for five times without any significant loss in catalytic activity.

Continuous synthesis of 5-hydroxymethylfurfural from glucose using a combination of AlCl3 and HCl as catalyst in a biphasic slug flow capillary microreactor

5-Hydroxymethylfurfural (HMF) was synthesized from glucose in a slug flow capillary microreactor, using a combination of AlCl3 and HCl as the homogeneous catalyst in the aqueous phase and methyl isobutyl ketone as the organic phase for in-situ HMF extraction. After optimization, an HMF yield of 53% was obtained at a pH of 1.5, 160 °C and a residence time of 16 min, and it could be further increased to 66.2% by adding 20 wt% NaCl in the aqueous phase. Slug flow operation in the microreactor greatly promoted mixing/reaction in the aqueous droplet and facilitated HMF extraction to the organic slug, enabling the reaction to run (largely) under kinetic control and an enhanced HMF yield by suppressing its further rehydration, degradation and/or polymerization. Confining reaction in the aqueous droplet prevented humin deposition on the microreactor wall. In line with the literature, [Al(OH)2]+ was confirmed by ESI-MS as the catalytically active species, and is responsible for the glucose isomerization to fructose under various pH values. The ratio between AlCl3 and HCl was optimized for the highest HMF yield and the best results were obtained with 40 mM AlCl3 and 40 mM HCl. Compared with batch results, a higher HMF yield was obtained in the microreactor at the same reaction time mainly due to a higher heating rate therein. The aqueous catalyst was recycled and reused three times without a noticeable performance loss. Thus, the present recyclable and stable homogenous catalyst system, combined with biphasic microreactor operation, is an attractive concept for the glucose conversion to HMF.

Formate-Catalyzed Selective Reduction of Carbon Dioxide to Formate Products Using Hydrosilanes

Formate salts were found to be active and selective homogeneous catalysts for the hydrosilylation of CO2. Counter cations and solvents strongly affected their catalytic activity. The use of toluene as a solvent rendered the recyclable catalyst system. Lewis basic polar solvents such as N-methylpyrrolidone and dimethyl sulfoxide significantly accelerated the reaction. The turnover number approached up to 1800. Analyses of the Fourier-transform infrared spectroscopy and in situ 1H nuclear magnetic resonance spectra suggested that the catalysis proceeds via electron donation from the solvent to hydrosilane, thereby accelerating the hydride transfer step.

Regioselective Hydrogenation of Itaconic Acid to γ-Isovalerolactone by Transition-Metal Nanoparticle Catalysts.

Current methods for hydrogenation of bio-derived itaconic acid (IA) lead to a mixture of isomeric lactone products. Transition-metal nanoparticles (TM-NPs), in situ-generated through thermolysis of TM(0) (Ru, Fe, W, Cr) carbonyls, in particular Ru-NPs, were found to catalyze regioselective hydrogenation of IA by syngas (2 H2 /CO) into γ-isovalerolactone (GiVL) in approximately 70 % isolated yield. Key sustainability features of this new route include: a one-pot direct transformation of bio-renewable IA into value-added GiVL selectively, use of inexpensive and renewable syngas in aqueous solution, and development of a supported recyclable NP catalyst system, Al2 O3 -Ru-NPs.

Application of a zwitterionic palladium complex as a metal precursor of recyclable palladium nanoparticles for catalyzing Suzuki-Miyaura coupling reactions

An efficient recyclable catalyst system for Suzuki-Miyaura coupling reactions in water was developed based on a zwitterionic palladium complex bearing an imidazolium-based carbon donor and tricyclohexylphopshine. The complex served as an effective metal precursor for the formation of catalytically active palladium nanoparticles. The addition of excess n-tetrabutylammonium bromide (TBAB) was essential for stabilizing the nanoparticles in water. After several catalytic runs, a phase separation was observed and TBAB became an ionic liquid phase, supporting the palladium nanoparticles. The nanoparticles was recyclable, which allowed up to nine consecutive catalytic runs to be completed without significant loss of activity. The recyclable catalyst system allowed the use of unreactive aryl chlorides as substrates, changes of substrates between catalytic runs, manipulation of the reactions in air, and upscaling of the catalytic reaction.

Solid Acid-Catalyzed Dehydration of Pinacol Derivatives in Ionic Liquid: Simple and Efficient Access to Branched 1,3-Dienes

The selective dehydration of pinacol derivatives to branched 1,3-dienes is extremely challenging because of the predominance of pinacol rearrangement. Herein, we successfully achieve this goal by employing a recyclable solid acid/ionic liquid catalyst system. The dehydration of alkyl- and cycloalkyl-derived diols in an Amberlyst-15/[Emim]Cl system afforded the corresponding 1,3-dienes in good yields, while a Nafion/[Emim]Cl system was demonstrated to be a better catalyst system for the dehydration of aryl-substituted substrates. Our protocol features straightforward and simple access to branched 1,3-dienes, high chemoselectivity, a recyclable catalyst system, a facile separation of dienes just by decantation, and a broad substrate scope.

Pd-PEPPSI-IPentCl: a new highly efficient ligand-free and recyclable catalyst system for the synthesis of 2-substituted indoles via domino copper-free Sonogashira coupling/cyclization

One pot synthesis of 2-substituted indolesviaSonogashira coupling (without a copper catalyst) followed by intermolecular cyclization using Pd-PEPPSI-IPentCl.