Magnetically water‐dispersible and recoverable rhodium organometallic catalyst derived from Wilkinson's catalyst for promoting organic reactions

A novel magnetic rhodium catalyst was prepared through immobilizing Wilkinson's catalyst on the surface of silica‐coated iron oxide nanoparticles. After (thio)diphenylphosphine (─S&─PPh₂) was modified on the surface of the silica‐coated iron oxide nanoparticles, tris(triphenylphosphine)rhodium(I) chloride was employed to synthesize the Rh(Cl)(PPh₃)₂(Ph₂P&─S&─) complex, affording a rhodium loading of 0.16 mmol g⁻¹. The Rh(I) organometallic magnetic nanoparticles form a novel class of heterogeneous catalyst which is particularly suitable for the practice of organic synthesis. The prepared system exhibits high catalytic efficiency in Suzuki–Miyaura and Miyaura–Michael reactions in ethanol–water solution. High yield, low reaction times, use of green solvents and non‐toxicity of the catalyst are the main merits of this protocol. Also, magnetic separation is an environmentally friendly alternative for the recovery of the catalyst, since it minimizes energy and catalyst loss by preventing mass loss and oxidation. The produced catalyst was characterized using a variety of techniques.     

Single atom catalyst for electrocatalysis

Single atom catalyst (SAC) refers to a novel catalyst with the active metal atoms individually anchored on the support. Single atom catalysts present the unique appeal due to the high atomic availability and specific activity, as well as the high pathway selectivity. Herein, we summarized the classification, preparation, characterization, and application of single atom catalysts. Finally, the current bottlenecks and the outlooks of the SAC research are discussed.     

Preparation of polystyrene-supported soluble palladacycle catalyst for Heck and Suzuki reactions

A polystyrene-supported palladium complex soluble in tetrahydrofuran and N,N-dimethylacetamide and precipitated in diethyl ether or acetonitrile was prepared from two routes as an excellent and recyclable palladacycle catalyst for carbon-carbon bond formation in Heck and Suzuki reactions to give high yields of the desired products.     

Cationic iridium complex is a new and efficient Lewis acid catalyst for aldol and Mannich reactions

A cationic iridium complex [Ir(cod)₂]SbF₆ was found to be a new and efficient Lewis acid catalyst for Mukaiyama aldol and Mannich reactions. Aldehydes react smoothly with silyl enol ethers to give β-siloxy ketones in the presence of 0.5 mol % of [Ir(cod)₂]SbF₆. The reaction of N-alkyl arylaldimines with ketene silyl acetals in the presence of 5 mol % [Ir(cod)₂]SbF₆/P(OPh)₃ gave β-amino esters. After Mannich reaction was complete, stirring of the reaction mixture for 24 h led to cyclization to give β-lactam. The reaction of N-aryl benzaldimine with silyl enol ether derived from acetophenone gave a tetrahydroquinoline derivative as a single diastereomer.     

Ring-fused aminals: catalyst and solvent-free microwave-assisted α-amination of nitrogen heterocycles

A high-yield synthesis of ring-fused aminals via microwave (MW)-assisted α-amination of nitrogen heterocycles at 130 °C under solvent- and catalyst-free conditions is described.     

Polystyrene-supported recyclable palladacycle catalyst for Heck, Suzuki and Sonogashira reactions

A new type of soluble polystyrene-supported palladium complex as an excellent and recyclable palladacycle catalyst was discovered for carboncarbon bond formation in Heck, Suzuki and Sonogashira reactions. Precipitation and filtration process for recycling the catalyst was also achieved.     

Quantum topological resolution of catalyst proficiency

The purpose of this exploratory investigation is to characterize, contrast, and explain the differences between efficient Ni(π‐allyl)₂ and inefficient Pd(π‐allyl)₂ systems in the catalyzed cross‐coupling of alkanes. Within the framework of the quantum theory of atoms in molecules, we have created quantum topology phase diagrams (QTPDs) for nonisomeric species by the creation of aggregate‐isomers; simple sum rules are introduced to ensure that the Poincaré‐Hopf relation is obeyed. We show that the catalyzed reaction cycles can be represented as a directed QTPD where each species of the main reaction cycle forms a closed loop. The topological position of the unwanted side products relative to the main reaction cycle for each catalyst is also considered. We find the more efficient Ni(π‐allyl)₂ catalyst produces a reaction cycle on the QTPD that contains no “missing” topologies, preferentially proceeding to desired product at 94% yield, while avoiding wasteful side‐product pathways, disconnected from the major pathway by “missing” topologies. The converse is true for the less efficient Pd(π‐allyl)₂ catalyst, whose reaction pathway markedly bifurcates to final yields of 56% and 44% for product and side‐product, respectively. We subsequently used our nearest neighbor ring‐critical point approach to show that the species of the main reaction cycle of the efficient Ni(π‐allyl)₂ catalyst facilitates the desired chemical transformation whilst more effectively barring the formation of unwanted side product, with respect to the inefficient Pd(π‐allyl)₂ catalyst. The findings from the QTPD analysis are in agreement with traditional energetic‐barrier interpretations of reaction pathway preference. © 2015 Wiley Periodicals, Inc.     

Use of heterogeneous catalyst KG-60-NEt2 in Michael and Henry reactions involving nitroalkanes

The N,N-diethylpropylamine supported on amorphous silica (KG-60-NEt₂) catalyses the formation of carboncarbon bonds by nitroalkanes through both the nitroaldol (Henry) and Michael reactions. The catalyst shows general utility with a variety of electrophilic acceptors. Moreover, the catalyst can be reused for two further cycles without loss of the activity.     

Efficient and ligand free palladium catalyst for Suzuki and Heck cross-coupling reactions

A simple and efficient system for Suzuki cross-coupling reactions was developed using a ligandless catalyst of Pd nanoclusters generated in situ from Pd(acac)₂. The cross-coupling reactions proceeded under mild reaction conditions with a high reaction rate (5 min) to give various biaryls in high yields. The system also exhibited catalytic potential for Heck reaction between aryl bromides and styrene.     

铜基催化剂上甲烷催化燃烧反应动力学特性研究

采用固定床微分反应器,在常压、450~500℃、甲烷体积分数10%~35%条件下,进行铜基催化剂上甲烷催化燃烧动力学特性研究。研究表明,甲烷分压对反应速率影响显著,而氧气分压的影响可以忽略。采用最小二乘法进行动力学模型参数估计,建立的反应动力学模型为-rCH4=1.61×107×e-108 000/RT×pCH40.5。检验结果表明,所建模型与实验数据良好相容,是适宜和可信的。根据实验结果推断甲烷催化燃烧分两步进行,首先氧气快速与铜基催化剂上活性空位点反应,形成吸附氧气分子;随后吸附氧气分子和甲烷分子反应,生成二氧化碳和水。     

One-step polymerization of polytrithiocarbonate using phase-transfer catalyst

A series of aliphatic and aromatic polytrithiocarbonates was prepared using a novel “one-pot” synthesis procedure employing a phase-transfer catalyst. The starting reagents were either an aliphatic or an aromatic dihalide and an excessive amount of carbon disulfide. The effects of the phase-transfer catalyst and reaction conditions on yield were studied. The structure and composition of the polymers and reaction side-products were determined from infrared, ultraviolet, ¹H-NMR spectra, and elemental analyses. The polymers were further characterized by viscosity measurement and thermal analysis. © 1993 John Wiley & Sons, Inc.     

Terephthalic acid derived ligand‐stabilized palladium nanocomposite catalyst for Heck coupling reaction: without surface‐modified heterogeneous catalyst

A new protocol is reported for the synthesis of a heterogeneous palladium nanocomposite stabilized with a terephthalic acid‐derived ligand (N ,N ‐bis(4‐hydroxy‐3‐methoxybenzylidene)terephthalohydrazide). This is a highly insoluble ligand in common organic solvents, except dimethylformamide and dimethylsulfoxide. The resulting palladium nanocomposite acts as an efficient catalyst precursor for Mizoroki–Heck coupling reactions conducted under various reaction conditions. The spectral data suggest that the rate, yield and recycling of the catalyst are more effective for C–C coupling reactions. Copyright © 2016 John Wiley & Sons, Ltd.     

Polymethyl methacrylate micro-spheres supported palladium: A new catalyst for Heck and Suzuki reactions

Polymethyl methacrylate (PMMA) micro-spheres, a kind of commercially available polymeric material was treated with PdCl₂ and formaldehyde giving a reagent with a palladium loading of 0.79 (wt.%). The Pd-PMMA catalyzed the highly efficient Heck and Suzuki reactions. The reactions can be performed under ligand-free conditions in an air atmosphere. The palladium catalyst is easily separated and can be reusable with negligible leaching of palladium.     

Heterogenized peroxopolyoxotungstate catalyst on the surface of clicked magnetite‐graphene oxide nanocomposite: Magnetically recoverable epoxidation catalyst

A new heterogeneous catalyst for the epoxidation of olefins was prepared by immobilization of peroxophosphotungstate anions on the surface of clicked magnetite‐graphene oxide as magnetically recoverable support. To prepare the heterogeneous catalyst, the clicked magnetite‐graphene oxide support was prepared by thiolene click reaction of thiol functionalized graphene oxide with vinyl modified magnetite nanoparticles. The tailored support was then modified with aminopropyl groups followed by electrostatic interaction with peroxophosphotungstate anions to achieve the desired heterogeneous catalyst. Characterization of the catalyst was performed by various physicochemical methods which confirmed the successful immobilization of peroxopolyoxotungstate species on the surface of clicked magnetite‐graphene oxide. Catalytic activity of the catalyst revealed its high catalytic activity and selectivity in the epoxidation of various olefins in the presence of H₂O₂ as green oxidant. This heterogeneous catalyst can be magnetically reused several times without significant loss of activity and selectivity.     

Palladium containing nanostructured silica functionalized with pyridine sites: a versatile heterogeneous catalyst for Heck, Sonogashira, and cyanation reactions

Nanostructured hybrid silica bearing pyridine binding sites was prepared in a template assisted hydrolysis-polycondensation of tetraethylorthosilicate (TEOS) and the ionic precursor N,N-dimethyl-pyridin-4-yl-(3-triethoxysilyl-propyl)-ammonium iodide using N-dodecyl-N′-methyl-imidazolium bromide as structure directing agent. After treatment with palladium acetate, the material appeared as a versatile heterogeneous catalyst for Heck, Sonogashira, and cyanation reactions. In Heck and Sonogashira cross-coupling reactions, unchanged catalytic activity was observed in at least five reaction cycles.     

Polymer-supported palladium (II) containing N2O2: An efficient and robust heterogeneous catalyst for C–C coupling reactions

A new polymer was prepared from 1,3,5-triformylphloroglucinol (noted as TDTB) and o-phenylenediamine through Schiff base condensation reaction, and palladium (II) was immobilized on the polymer (noted as TbPo-Pd(II)). This process was easy to work-up and cost-effective. The structure and composition of TbPo-Pd(II) were fully characterized by FTIR, TGA, XPS, AAS, SEM, and TEM analyses. Meanwhile, this catalyst showed desired thermal stability and excellent performance in water/methanol system for Suzuki and Sonogashira coupling reactions. In addition, this heterogeneous catalyst can be readily recovered by simple filtration with no appreciable Pd leaching in the reaction. This work provides a powerful protocol for rapid access to asymmetrical biphenyls and aryl alkynes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2344–2353     

Scolecite as an efficient heterogeneous catalyst for the synthesis of 2,4,5-triarylimidazoles

Natural scolecite has been found as an effective catalyst for the one-pot synthesis of 2,4,5-triarylimidazole derivatives via a three component reaction using benzil or benzoin, aldehydes and ammonium acetate. This method provides several advantages such as being environmentally benign, reusable, possessing high yields with increased variations of the substituents in the product and preparative simplicity.      

Di(2-pyridyl)methylamine-palladium dichloride complex covalently anchored to a styrene-maleic anhydride co-polymer as recoverable catalyst for C-C cross-coupling reactions in water

A new polymer-supported di(2-pyridyl)methylamine-palladium dichloride complex covalently anchored to a styrene-alt-maleic anhydride co-polymer is prepared. This complex catalyzes Heck, Suzuki and Sonogashira cross-coupling reactions in neat water with similar efficiency than the monomeric complex. The turnover number (TON) of this polymer reaches up to 10⁴ for Heck reactions, whereas for Suzuki and Sonogashira couplings TONs up to 10⁵ are achieved. There is low leaching of palladium after filtration of the polymer and the activity remains almost constant after fourth and five reaction cycles especially in Sonogashira reactions. In the case of the Suzuki reaction Pd nanoparticles are dispersed into the polymer after the first cycle according to TEM images and 2.4% of Pd are found by ICP-OES in the corresponding filtrate. Alternatively, these palladium-catalyzed reactions can also be performed under microwave heating. These couplings take place with better efficiency with polymer-supported di(2-pyridyl)methylamine-palladium dichloride complex than with the polyurea-encapsulated Pd EnCat™ 40.     

Highly efficient silica gel-supported 1,2-diaminocyclohexane-Pd catalyst for Suzuki-Miyaura and Sonogashira coupling reactions

A palladium (Pd) catalyst was prepared by immobilization of a 1,2-diaminocyclohexane based Pd-complex onto amorphous silica gel and its applications as a heterogeneous catalyst for Suzuki-Miyaura and Sonogashira coupling reactions are described. The catalyst was highly efficient, reusable and air-stable. An erratum to this article is available at .     

Highly active recyclable heterogeneous nanonickel ferrite catalyst for cyanation of aryl and heteroaryl halides

Magnetic nickel ferrite nanoparticles are found to be an efficient catalytic system for cyanation reactions of various types of aryl halides under conventional heating conditions. All the reactions result in very good to excellent yields under optimized reaction conditions. Furthermore, the catalyst is easily removed from the reaction medium and can be reused further in several subsequent runs. Copyright © 2014 John Wiley & Sons, Ltd.