Catalytic Hydroetherification of Unactivated Alkenes Enabled by Proton‐Coupled Electron Transfer

We report a catalytic, light‐driven method for the intramolecular hydroetherification of unactivated alkenols to furnish cyclic ether products. These reactions occur under visible‐light irradiation in the presence of an Ir^III‐based photoredox catalyst, a Brønsted base catalyst, and a hydrogen‐atom transfer (HAT) co‐catalyst. Reactive alkoxy radicals are proposed as key intermediates, generated by direct homolytic activation of alcohol O?H bonds through a proton‐coupled electron‐transfer mechanism. This method exhibits a broad substrate scope and high functional‐group tolerance, and it accommodates a diverse range of alkene substitution patterns. Results demonstrating the extension of this catalytic system to carboetherification reactions are also presented.     

Solvent-free,microwave-assisted highly efficient,rapid and simple synthesis of biphenyl compounds by using silica based Pd(II) catalyst

To maintain catalytic performance of any catalyst for a long time, the selection of support material is a very important parameter for heterogeneous catalytic systems, and this performance makes the catalyst valuable. In view of its low cost and availability, silica can be considered as a good support material for transition metal ions in the cross coupling reactions. Therefore, this study describes i) silica-gel based palladium catalyst with a long-term catalytic performance, ii) rapid, simple, economic, and green procedure which was developed for Suzuki reactions. The catalyst showed superior reusability (ten runs) and catalytic efficiency against coupling reactions under mild conditions (50°C, 5 min and air atmosphere). Moreover, the catalyst gave partially good reaction yields with aril chlorides which have poor activity in coupling reactions. In addition, an excellent turnover number (TON: 66000) and frequency (TOF: 825000) were obtained using very small catalyst loading (1.5 × 10^?3 mol %). This paper concludes that silica-gel based Pd(II) catalyst and the protocol of synthesis of biaryls were suitable for coupling reactions.     

12-Tungstophosphoric acid niched in Zr-based metal-organic framework: a stable and efficient catalyst for Friedel-Crafts acylation

Heteropoly acids(HPA) are well known for their versatile solid acid catalysis in diverse chemical reactions, however they suffer from low surface area(10 m~2/g) and leaching into the reactions media, which reduce their prospects as industrial catalyst.Herein, a novel hybrid material HPW@Zr-BTC,composed of 12-tungstophoric acid(HPW) and Zr~(Ⅳ)-benzene tri-carboxylate(Zr-BTC) metal-organic framework(MOF), was prepared via one-pot solvothermal method. Excellent HPW loading up to 32.3 wt% was achieved, and HPW@Zr-BTC composite proved to be highly stable, besides the crystalline morphology of Zr-BTC was intact. The catalytic activity of the hybrid composite was explored via Friedel-Crafts acylation of anisole with benzoyl chloride.The 28.2 wt% HPW@Zr-BTC showed excellent catalytic performance, with 99.4% anisole conversion and 97.6% yield(pmethoxybenzophenone) under solvent free conditions. Excellent retention of catalytic activity was achieved after at least five consecutive runs due to non-observable HPW leaching. The promising activity and stability of the catalyst forecasted its potential industrial applications.     

Ruthenium-Catalyzed Regioselective 1,2-Hydrosilylation of N-Heteroarenes

An efficient method for the regioselective 1,2-hydrosilylation of N-heteroarenes is reported utilizing silanes as the hydride donor. The ruthenium complex [RuCl(PPh₃)₂(η⁵-(3-phenylindenylidene))], a versatile catalyst is, for the first time, employed in this catalytic reaction. The catalyst displays high catalytic efficiency at low loading and operates under mild conditions. This catalytic approach showcases high compatibility and regioselectivity with quinolines bearing different substituents and related N- heterocyclic compounds. The mechanism of this transformation was probed by performing stoichiometric reactions and examined using DFT calculations.     

Tunable Surface Electric Field of Electrocatalysts via Constructing Schottky Heterojunctions for Selective Conversion of Trash Ions to Treasures

Surface electric field of catalyst is widely recognized as one of the key points to boost catalytic activity. However, there is still a lack of convenient ways to tune the surface electric field to selectively boost the catalytic conversions of different types of reactants in specific catalytic reactions. Here, we introduce a conceptually new method to tune the surface electric field of electrode materials by adjusting the number and density of heterojunctions inside. Both theoretical and experimental results prove that the well-designed surface electric field of an electrocatalyst plays a key role in facilitating pre-adsorption and/or activation of reactants for selective conversion of trash ions to useful products in hydrogen and oxygen evolution reactions as well as NO_x⁻ reduction reactions.     

Generation and Stabilization of a Dinickel Catalyst in a Metal-Organic Framework for Selective Hydrogenation Reactions

Although many monometallic active sites have been installed in metal–organic frameworks (MOFs) for catalytic reactions, there are no effective strategies to generate bimetallic catalysts in MOFs. Here we report the synthesis of a robust, efficient, and reusable MOF catalyst, MOF-NiH, by adaptively generating and stabilizing dinickel active sites using the bipyridine groups in MOF-253 with the formula of Al(OH)(2,2′-bipyridine-5,5′-dicarboxylate) for Z-selective semihydrogenation of alkynes and selective hydrogenation of C=C bonds in α,β-unsaturated aldehydes and ketones. Spectroscopic studies established the dinickel complex (bpy⋅⁻)Ni^II(μ₂-H)₂Ni^II(bpy⋅⁻) as the active catalyst. MOF-NiH efficiently catalyzed selective hydrogenation reactions with turnover numbers of up to 192 and could be used in five cycles of hydrogenation reactions without catalyst leaching or significant decrease of catalytic activities. The present work uncovers a synthetic strategy toward solution-inaccessible Earth-abundant bimetallic MOF catalysts for sustainable catalysis.     

Preparing Pd catalysts based on urea ligand via electrospinning for Suzuki–Miyaura cross-coupling reactions

Pd-catalyzed Suzuki–Miyaura cross-coupling (SMC) reactions are important in chemistry. In this work, using electrospinning technology, we prepared a novel type of composite catalyst with ligand structures such as urea-Pd/PAN (polyacrylonitrile) and used them to catalyze SMC reactions in nontoxic systems and “green” conditions (air atmosphere, low temperature, and short reaction time). This method of preparing hybrid materials is simple and easy to operate. The higher catalytic activity of the catalysts is attributed to active centers with rich electrons transferred from ligands with unique structures, which can decrease the activation energy of the rate-determining step (oxidative addition). In addition, urea-Pd/PAN composite catalysts exhibit higher catalytic performance than those reduced by H₂ because of the smaller size of active species and the more-efficient oxidative addition to Pd⁰–ligand complexes compared to Pd⁰.     

Ester interchange reactions catalyzed by tin compounds in reactive processing: NMR contribution via reactions with model compounds

Interchange reactions involving esters were used in reactive processing with a view to obtaining polymer blends with stabilized morphology. Dibutyltinoxide (DBTO) appeared to be an excellent catalyst for these reactions. In fact, it was shown that the true catalytic entity is a dimeric alkoxy, acyloxy distannoxane entity formed in situ, during processing, by the reaction of the DBTO with the polymer ester groups. This compound was first obtained with model esters and characterized by multinuclear NMR analysis (¹H, ¹³C, ¹¹⁹Sn). The catalytic efficiency of the in situ polymeric distannoxane was compared with other added parent distannoxanes. Later on – still with model compounds – ligand exchanges at the tin sites were investigated and it was shown that these exchanges are not essential to the catalyst activity, but when they take place it increases the catalytic efficiency. Then, this type of catalysis was successfully used for interchange reactions in reactive extrusion of different polymer blends, some applications are briefly presented. To cite this article: M.-F. Llauro and A. Michel, C. R. Chimie 9 (2006).     

Bifunctional Catalysts Based on m‐Phenylene‐Bridged Porphyrin Dimer and Trimer Platforms: Synthesis of Cyclic Carbonates from Carbon Dioxide and Epoxides

Highly active bifunctional diporphyrin and triporphyrin catalysts were synthesized through Stille coupling reactions. As compared with a porphyrin monomer, both exhibited improved catalytic activities for the reaction of CO₂ with epoxides to form cyclic carbonates, because of the multiple catalytic sites which cooperatively activate the epoxide. Catalytic activities were carefully investigated by controlling temperature, reaction time, and catalyst loading, and very high turnover number and turnover frequency were obtained: 220 000 and 46 000 h^?1, respectively, for the magnesium catalyst, and 310 000 and 40 000 h^?1, respectively, for the zinc catalyst. Results obtained with a zinc/free‐base hybrid diporphyrin catalyst demonstrated that the Br^? ions on the adjacent porphyrin moiety also function as nucleophiles.     

Carboxymethylcellulose‐supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand‐ and base‐free Heck–Matsuda and Suzuki–Miyaura couplings

A novel palladium(II) carboxymethylcellulose (CMC‐Pd^II) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl₂ in aqueous solution. Its catalytic activities were explored for Heck–Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki–Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross‐coupling products in good to excellent yields under atmospheric conditions. The CMC‐Pd^II and carboxymethylcellulose‐supported palladium nanoparticles (CMC‐Pd⁰) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC‐Pd⁰ catalyst was confirmed via Hg(0) and CS₂ poisoning tests. Moreover, the CMC‐Pd⁰ catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki–Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright © 2015 John Wiley & Sons, Ltd.     

Multi‐component reaction‐functionalized chitosan complexed with copper nanoparticles: An efficient catalyst toward A3 coupling and click reactions in water

A novel bio‐nanocomposite nanocatalyst with highly dispersed particles is synthesized through covalent functionalization of chitosan biopolymer by the multicomponent reaction (MCR) strategy. Surface functionalization of chitosan through MCR is led to the grafting of carboxamide type ligands with a high affinity toward complexation with copper nanoparticles. The catalytic activity of the synthesized catalyst was explored in various transformations such as A³ coupling and click reactions in water. Reusability and non‐hazardous nature of the catalyst, mild reaction conditions, operational simplicity, high yielding, and using water as a solvent are the main advantages of this catalytic protocol.     

Pickering Emulsion Stabilized by Catalytic Polyoxometalate Nanoparticles: A New Effective Medium for Oxidation Reactions

Decyl‐, dodecyl‐, and tetradecyltrimethylammonium cations were combined with the catalytic polyoxometalate [PW₁₂O₄₀]^3? anion to give spherical and monodisperse nanoparticles that are able to stabilize emulsions in the presence of water and an aromatic solvent. This triphasic liquid/solid/liquid system, based on a catalytic surfactant, is particularly efficient as a reaction medium for epoxidation reactions that involve hydrogen peroxide. The reactions proceed at competitive rates with straightforward separation of the phases by centrifugation. Such catalytic “Pickering” emulsions combine the advantages of heterogeneous catalysis and biphasic catalysis without the drawbacks (e.g., catalyst leaching or separation time).     

Fast Oxygen Reduction Catalyzed by a Copper(II) Tris(2‐pyridylmethyl)amine Complex through a Stepwise Mechanism

Catalytic pathways for the reduction of dioxygen can either lead to the formation of water or peroxide as the reaction product. We demonstrate that the electrocatalytic reduction of O₂ by the pyridylalkylamine copper complex [Cu(tmpa)(L)]²⁺ in a neutral aqueous solution follows a stepwise 4 e^?/4 H⁺ pathway, in which H₂O₂ is formed as a detectable intermediate and subsequently reduced to H₂O in two separate catalytic reactions. These homogeneous catalytic reactions are shown to be first order in catalyst. Coordination of O₂ to Cu^I was found to be the rate‐determining step in the formation of the peroxide intermediate. Furthermore, electrochemical studies of the reaction kinetics revealed a high turnover frequency of 1.5×10⁵ s^?1, the highest reported for any molecular copper catalyst.     

Hollow nanoshell-sphere Fe@Fe/Pd reactors: a magnetically recoverable catalyst for the C<Subscript>sp</Subscript>–S cross-coupling reactions in water

The hollow Pd–PVP–Fe nanosphere and Fe–PVP nanoparticle catalysts were synthesized by thermal method. Mixing of two metallic nanocatalysts was applied in the C_sp–S cross-coupling reactions between diphenyl disulfide and phenylacetylene under mild conditions in water. Results show that bi-catalytic system has higher catalytic efficiencies than their monocatalytic systems due to synergy between two catalysts. Order of adding two metallic catalysts were adjusted into the coupling reaction medium. Therefore, various bi-catalytic systems were obtained and characterized by XRD, SEM, EBSD, EDX, UV–Vis spectra, and particle size analyzer. Under special order of adding, the obtained hollow nanoshell-sphere Fe@Fe/Pd reactor showed higher catalytic activity in the coupling reaction compared to other bi-catalytic systems. The C_sp–S coupling products obtained of various diaryl disulfides and phenylacetylene at presence Fe@Fe/Pd (only 7.3?×?10^?5 mmol Pd) catalyst with moderate to high yields in water solvent and mild reaction conditions. After the reaction, the catalyst/product(s) separation could be easily achieved with an external magnet and more than 95% of catalyst could be recovered. The recovered catalyst was characterized by XRD, SEM, EBSD, EDX, and UV–Vis spectra. The Fe@Fe/Pd was reused at least six repeating cycles without any loss of its high catalytic activity. Tuning morphology and chemical composition of bi-catalytic system are key mainstays of high activity of Fe@Fe/Pd in repeating cycles of cross-coupling reactions.     

Unmodified Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanostructure promoted with external magnetic field: safe,magnetically recoverable,and efficient nanocatalyst for N- and C-alkylation reactions in green conditions

Transition metal compounds have emerged as suitable catalysts for organic reactions. Magnetic compounds as soft Lewis acids can be used as catalysts for organic reactions. In this report, the Fe₃O₄ nanostructures were obtained from Fe²⁺ and Fe³⁺-salts, under an external magnetic field (EMF) without any protective agent. The X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy tools were used to characterize these magnetic compounds. The two-dimensional (2-D, it showed nanometric size in the two dimensions, nanorod structure) Fe₃O₄ compound showed high catalytic activity and stability in N- and C-alkylation reactions. A diverse range of N- and C-alkylation products were obtained in moderate to high yield under green and mild conditions in air. Also the N- and C-alkylation products can be obtained with different selectivity and yield by exposure reactions with EMF. Results of alkylation reactions showed that the presence of Fe(II) and Fe(III) species on the surface of magnetic catalysts (phase structure of magnetic compounds) are essential as very cheap active sites. Also, morphology of magnetic catalysts had influence on their catalytic performances. After the reaction, the catalyst/product(s) separation could be easily achieved with an external magnet and more than 95% of catalyst could be recovered. The catalyst was reused at least four times without any loss of its high catalytic activity for N- and C-alkylation reactions.     

An efficient Yb(OTf)3 catalyzed alkylation of 1,3-dicarbonyl compounds using alcohols as substrates

A highly efficient and environmentally friendly method for catalytic benzylation/allylation of 1,3-dicarbonyl compounds with alcohols has been developed by using Yb(OTf)₃ as a catalyst. The reactions proceed smoothly to give the desired products in moderate to excellent yields, mostly at room temperature. The catalyst can be recovered and reused at least six times without visible loss of catalytic activity for such reactions.     

Effect of the functionalizing of carbon nanotubes on the electrodeposited catalysts’ structure and catalytic properties

The structure and hydrophilic-hydrophobic properties of functionalized single-wall carbon nanotubes are studied by the standard porosimetry method. It is shown that the functionalized nanotubes have highly hydrophilic surface; at that the summary surface area measured “by octane” decreased, as a result of the functionalizing, due to the blocking of the nanotubes’ inner channels by the functional groups located at the nanotubes’ ends. The nanotubes’ capacitive properties are studied; their charging-discharging curves appeared being highly reversible, unlike those of other carbonaceous materials. Catalytic properties of the functionalized nanotubes are studied, with particular tendency toward their using as a carrier of platinum catalysts for the methanol oxidation and oxygen electroreduction reactions. When minor amounts (5–10 μg cm⁻²) of platinum or platinum-ruthenium alloy are deposited onto the nanotubes’ hydrophilic surface, uniform layer of the catalyst is formed, with specific surface area up to 150–300 m² g⁻¹; high current of the methanol oxidation or oxygen electroreduction is observed at these catalysts. When the catalyst deposit mass increased, its specific surface area decreased, as well as the specific current of the reactions occurring thereon. When the current is related to the electrochemically active unit surface, the catalytic activity is nearly the same both for different catalyst mass deposited onto the nanotubes and the same catalyst mass at different carbonaceous carriers.     

Nanocatalysts Fabricated by a Dealloying Method

Two types of nanomaterials with different morphologies are described in this article: nanoporous metals and titanate nanowires. Both materials are fabricated by a dealloying method. In the former case, the catalytic properties of nanoporous gold and palladium are exemplified by many chemical transformations. The reactions proceed without any support, stabilizer, or ligands. The catalyst can be easily recovered by a simple separation process and reused many times without significant loss of catalytic activity. In the latter case, the dealloying of Ti–Al alloy is described as a new fabrication method for producing ultrafine titanate nanowires. This method does not require high‐temperature conditions, which is advantageous for the construction of fine structures. The key to this process is achieving a fine dispersion of intermetallic TiAl₃ nanocrystals in the Al matrix in the mother alloy. The resulting nanowires exhibit remarkable Sr²⁺ ion‐exchange properties.     

Facile synthesis of nanostructured Ni-Co/ZnO material: An efficient and inexpensive catalyst for Heck reactions under ligand-free conditions

A simple, efficient and economically viable method for the Heck reaction has been accomplished in the absence of phosphine ligand. The Heck reaction was performed using nanostructured Ni-Co/ZnO material as a heterogeneous catalyst in a DMF/H₂O solvent system and in the presence of K₂CO₃, at 120 °C. The Ni-Co/ZnO nanostructures were prepared by the facile reduction-impregnation method. The structural and morphological properties of Ni-Co/ZnO nanostructure were investigated using various physico-chemical characterization techniques. Structural studies displayed the formation of hexagonal (wurtzite) ZnO. Electron microscopy imaging showed the presence of agglomerated clusters of Ni-Co nanoparticles over the surfaces of elliptical, flower bud-like and irregularly shaped sub-micron sized particle bundles of ZnO. The elemental composition analysis (EDX) confirmed the loading of Ni and Co nanoparticles over the nanocrystalline ZnO. The surface chemical state analysis of Ni-Co/ZnO material validated that Ni nanostructure exists in Ni²⁺ and Ni³⁺ species, whereas, Co nanostructure exists in Co²⁺ and Co³⁺ species. UV–Vis diffuse reflectance spectroscopy displays red shift in the light absorption edge of Ni-Co/ZnO catalyst compared to pure ZnO. The as-prepared Ni-Co bimetallic supported ZnO nanostructure showed better catalytic activity and stability for the Heck reactions under phosphine ligand-free conditions. Ni-Co/ZnO catalyzed Heck reactions afforded the corresponding cross-coupled products with moderate to good yields (up to 92%). Ni-Co/ZnO catalyst could be reused for five successive runs without significant loss of catalytic activity.     

Diverse Approaches for Enantioselective C−H Functionalization Reactions Using Group 9 CpxMIII Catalysts

Transition-metal-catalyzed C−H functionalization reactions with Cp*M^III catalysts (M=Co, Rh, Ir) have found a wide variety of applications in organic synthesis. Albeit the intrinsic difficulties in achieving catalytic stereocontrol using these catalysts due to their lack of additional coordination sites for external chiral ligands and the conformational flexibility of the Cp ligand, catalytic enantioselective C−H functionalization reactions using the Group 9 metal triad with Cp-type ligands have been intensively studied since 2012. In this minireview, the progress in these reactions according to the type of the chiral catalyst used are summarized and discussed. The development of chiral Cp^x ligands the metal complexes thereof, artificial metalloenzymes, chiral carboxylate-assisted enantioselective C−H activations, enantioselective alkylations assisted by chiral carboxylic acids or chiral sulfonates, and chiral transient directing groups are discussed.