Rational Control of the Selectivity of a Ruthenium Catalyst for Hydrogenation of 4‐Nitrostyrene by Strain Regulation

Tuning the selectivity of metal catalysts is of paramount importance yet a great challenge. A new strategy to effectively control the selectivity of metal catalysts, by tuning the lattice strain, is reported. A certain amount of Co atoms is introduced into Ru catalysts to compress the Ru lattice, as confirmed by aberration‐corrected high‐resolution transmission electron microscopy (HRTEM) and X‐ray absorption fine structure (XAFS) measurements. We discover that the lattice strain of Ru catalysts can greatly affect their selectivity, and Ru with 3 % lattice compression exhibits extremely high catalytic selectivity for hydrogenation of 4‐nitrostyrene to 4‐aminostyrene compared to pristine Ru (99 % vs. 66 %). Theoretical studies confirm that the optimized lateral compressive strain facilitates hydrogenation of the nitro group but impedes the hydrogenation of the vinyl group. This study provides a new guideline for designing metal catalysts with high selectivity.     

负载型Au-Ni合金催化剂应用于芳香硝基化合物选择加氢反应

采用改进的两步还原法制备了SiO2负载的Au-Ni合金催化剂,催化剂中Au-Ni纳米颗粒高度分散于SiO2载体表面. Au-Ni合金催化剂在温和条件下芳香硝基化合物选择加氢反应中表现出比两种单金属催化剂更高的活性和选择性,体现出Au-Ni之间明显的协同作用.其中AuNi3/SiO2催化剂具有最好的性能,反应70 min,转化率和选择性分别达到90.8%和93.0%.     

The Enhanced Catalytic Performance and Stability of Ordered Mesoporous Carbon Supported Nano‐Gold with High Structural Integrity for Glycerol Oxidation

Ordered mesoporous carbon (OMC) supported gold nanoparticles of size 3–4 nm having uniform dispersion were synthesized by sol‐immobilization method. OMCs such as CMK‐3 and NCCR‐56 with high surface area and uniform pore size were obtained, respectively, using ordered mesoporous silicas such as SBA‐15 and IITM‐56 as hard templates, respectively. The resulting OMC supported monodispersed nano‐gold, i. e., Au/CMK‐3 and Au/NCCR‐56, exhibited excellent performance as mild‐oxidizing catalysts for oxidation of glycerol with high hydrothermal stability. Further, unlike activated carbon supported nano‐gold catalysts (Au/AC), the OMC supported nano‐gold catalysts, i. e., Au/CMK‐3 and Au/NCCR‐56, show no aggregation of active species even after recycling. Thus, in the case of Au/CMK‐3 and Au/NCCR‐56, both the fresh and regenerated catalysts showed excellent performane for the chosen reaction owing to an enhanced textural integrity of the catalysts and that with remarkable selectivity towards glyceric acid. The significance of the OMC supports in maintaining the dispersion of gold nanoparticles is explicit from this study, and that the activity of Au/AC catalyst is considerably decreased (～50 %) upon recycling as a result of agglomeration of the active gold nanoparticles over the disordered amorphous carbon matrix.     

Robust Synthesis of Gold‐Based Multishell Structures as Plasmonic Catalysts for Selective Hydrogenation of 4‐Nitrostyrene

A robust self‐template strategy is used for facile and large‐scale synthesis of porous multishell gold with controllable shell number, sphere size, and in situ surface modification. The process involved the rapid reduction of novel Au‐melamine colloidal templates with a great amount of NaBH₄ in presence of poly(sodium‐p‐styrenesulfonate) (PSS). After soaking the templates in other metal salt solution, the obtained bimetallic templates could also be generally converted into bimetallic multishell structures by same reduction process. In the hydrogenation of 4‐nitrostyrene using NH₃BH₃ as a reducing agent, the porous triple‐shell Au with surface modification (S‐PTSAu) exhibited excellent selectivity (97 %) for 4‐aminostyrene in contrast with unmodified triple‐shell Au. Furthermore, it also showed higher enhancement of catalytic activity under irradiation of visible light as compared to similar catalysts with fewer shells.     

Chalcogen Bonding Catalysis of a Nitro‐Michael Reaction

Chalcogen bonding is the non‐covalent interaction between Lewis acidic chalcogen substituents and Lewis bases. Herein, we present the first application of dicationic tellurium‐based chalcogen bond donors in the nitro‐Michael reaction between trans‐β‐nitrostyrene and indoles. This also constitutes the first activation of nitro derivatives by chalcogen bonding (and halogen bonding). The catalysts showed rate accelerations of more than a factor of 300 compared to strongly Lewis acidic hydrogen bond donors. Several comparison experiments, titrations, and DFT calculations support a chalcogen‐bonding‐based mode of activation of β‐nitrostyrene.     

One‐pot synthesis of 1‐ and 5‐substituted 1H‐tetrazoles using 1,4‐dihydroxyanthraquinone–copper(II) supported on superparamagnetic Fe3O4@SiO2 magnetic porous nanospheres as a recyclable catalyst

An effective one‐pot, convenient process for the synthesis of 1‐ and 5‐substituted 1H‐tetrazoles from nitriles and amines is described using1,4‐dihydroxyanthraquinone–copper(II) supported on Fe₃O₄@SiO₂ magnetic porous nanospheres as a novel recyclable catalyst. The application of this catalyst allows the synthesis of a variety of tetrazoles in good to excellent yields. The preparation of the magnetic nanocatalyst with core–shell structure is presented by using nano‐Fe₃O₄ as the core, tetraethoxysilane as the silica source and poly(vinyl alcohol) as the surfactant, and then Fe₃O₄@SiO₂ was coated with 1,4‐dihydroxyanthraquinone–copper(II) nanoparticles. The new catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, dynamic light scattering, thermogravimetric analysis, vibration sample magnetometry, X‐ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherm analysis and inductively coupled plasma analysis. This new procedure offers several advantages such as short reaction times, excellent yields, operational simplicity, practicability and applicability to various substrates and absence of any tedious workup or purification. In addition, the excellent catalytic performance, thermal stability and separation of the catalyst make it a good heterogeneous system and a useful alternative to other heterogeneous catalysts. Also, the catalyst could be magnetically separated and reused six times without significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

A Molecular mechanism for the chemoselective hydrogenation of substituted nitroaromatics with nanoparticles of gold on TiO2 catalysts: a cooperative effect between gold and the support

Nanoparticles of gold on TiO2 are highly chemoselective for the reduction of substituted nitroaromatics, such as nitrostyrene. By combining kinetics and in situ IR spectroscopy, it has been found that there is a preferential adsorption of the reactant on the catalyst through the nitro group. IR studies of nitrobenzene, styrene, and nitrostyrene adsorption, together with quantum chemical calculations, show that the nitro and the olefinic groups adsorb weakly on the Au(111) and Au(001) surfaces, and that although a stronger adsorption occurs on low-coordinated atoms in gold nanoparticles, this adsorption is not selective. On the other hand, an energetically and geometrically favored adsorption through the nitro group occurs on the TiO2 support and in the interface between the gold nanoparticle and the TiO2 support. Such preferential adsorption is not observed with nanoparticles of gold on silica which, contrary to the Au/TiO2 catalyst, is not chemoselective for the reduction of substituted nitroaromatic compounds. Therefore, the high chemoselectiviy of the Au/TiO2 catalyst can be attributed to a cooperation between the gold nanoparticle and the support that preferentially activates the nitro group.     

Thiol‐Assisted Synthesis of Carbon‐Supported Metal Nanoparticles for Efficient Electrocatalytic CO2 Reduction

The typical preparation route of carbon‐supported metallic catalyst is complex and uneconomical. Herein, we reported a thiol‐assisted one‐pot method by using 3‐mercaptopropionic acid (MPA) to synthesize carbon‐supported metal nanoparticles catalysts for efficient electrocatalytic reduction of carbon dioxide (CO₂RR). We found that the synthesized Au?MPA/C catalyst achieves a maximum CO faradaic efficiency (FE) of 96.2% with its partial current density of ?11.4 mA/cm², which is much higher than that over Au foil or MPA‐free carbon‐supported Au (Au/C). The performance improvement in CO₂RR over the catalyst is probably derived from the good dispersion of Au nanoparticles and the surface modification of the catalyst caused by the specific interaction between Au nanoparticles and MPA. This thiol‐assisted method can be also extended to synthesize Ag?MPA/C with enhanced CO₂RR performance.     

Thermodynamics of the oxygen evolution electrocatalysis in a functionalized UiO‐66 metal‐organic frameworks

A density functional theory (DFT) approach was used to predict the thermodynamic energy barriers of the oxygen evolution reaction (OER) for three functionalized Metal‐organic Frameworks (MOFs). A UiO‐66(Zr) MOF design was selected for this study that incorporates three linker designs, a 1,4‐benzenedicarboxylate (BDC), BDC functionalized with an amino group (BDC + NH₂), and BDC functionalized with nitro group (BDC + NO₂). The study found several key differences between homogeneous planar catalyst thermodynamics and MOF‐based thermodynamics, the most significant being the non‐unique or heterogeneity of reaction sites. Additionally, the functionalization of the MOF was found to significantly influence the hydroperoxyl binding energy, which proves to be the largest hurdle for both oxide and MOF‐based catalyst. Both of these findings provide evidence that many of the limitations precluding planar homogeneous catalysts can be surpassed with a MOF‐based catalyst. The BDC + NH₂ proved to be the best performing catalyst with a predicted over‐potential for spontaneous OER evolution to be 3.03eV. © 2016 Wiley Periodicals, Inc.     

Gold-Catalyzed One-Pot Synthesis of Polyfluoroalkylated Oxazoles from N-Propargylamides Under Visible-Light Irradiation

A gold-catalyzed synthesis of polyfluoroalkylated oxazoles from N-propargylamides under visible-light irradiation has been developed. These reactions display excellent compatibility of radicals and gold catalysts under visible-light irradiation. Mechanistic experiments indicate that polyfluoroalkyl iodides play a dual role in enhanced compatibility of radicals and gold catalysts through assisted protodeauration of vinyl gold and reactivated the gold catalyst. In addition, PPh₃AuNTf₂ not only activates N-propargylamide to generate vinyl gold intermediate, but also greatly promotes homolysis of polyfluoroalkyl iodides under blue light irradiation.     

Poly(ionic liquid)s based on imidazolium hydrogen carbonate monomer units as recyclable polymer‐supported N‐heterocyclic carbenes: Use in organocatalysis

Synthesis of novel poly(ionic liquid)s, namely, poly(1‐vinyl‐3‐alkylimidazolium hydrogen carbonate)s, denoted as poly([NHC(H)][HCO₃])s or PVRImHCO₃, where R is an alkyl group (R = ethyl, butyl, phenylethyl, dodecyl), is described. Two distinct synthetic routes were explored. The first method is based on the free‐radical polymerization (FRP) of 1‐vinyl‐3‐alkylimidazolium monomers featuring a hydrogen carbonate counter anion (HCO₃^?), denoted as VRImHCO₃. The latter monomers were readily synthesized by alkylation of 1‐vinylimidazole (VIm), followed by direct anion exchange of 1‐vinyl‐3‐alkylimidazolium bromide monomers (VRImBr), using potassium hydrogen carbonate (KHCO₃) in methanol at room temperature. Alternatively, the same anion exchange method could be applied onto FRP‐derived poly(1‐vinyl‐3‐alkylimidazolium bromide) precursors (PVRImBr). All PVRImHCO₃ salts proved air stable and could be manipulated without any particular precautions. They could serve as polymer‐supported precatalysts to generate polymer‐supported N‐heterocyclic carbenes, referred to as poly(NHC)s, formally by a loss of “H₂CO₃” (H₂O +CO₂) in solution. This was demonstrated through selected organocatalyzed reactions of molecular chemistry, known as being efficiently mediated by molecular NHC catalysts, including benzoin condensation, transesterification and cyanosilylation of aldehyde. Of particular interest, recycling of the polymer‐supported precatalysts was possible by re‐carboxylation of in situ generated poly(NHC)s. Organocatalyzed reactions could be performed with excellent yields, even after five catalytic cycles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4530–4540     

Synthesis of multifunctional polymer containing Ni‐Pd NPs via thiol‐ene reaction for one‐pot cascade reactions

Recently, acid–base bifunctional catalysts have been considered due to their abilities, such as the simultaneous activation of electrophilic and nucleophilic species and their high importance in organic syntheses. However, the synthesis of acid–base catalysts is problematic due to the neutralization of acidic and basic groups. This work reports a facial approach to solve this problem via the synthesis of a novel bifunctional polymer using inexpensive materials and easy methods. In this way, at the first step, heterogeneous poly (styrene sulfonic acid‐n‐vinylimidazole) containing pentaerythritol tetra‐(3‐mercaptopropionate) (PETMP) and trimethylolpropane trimethacrylate (TMPTMA) cross‐linkers were synthesized in the pores of a mesoporous silica structure using click reaction as a novel bifunctional acid–base catalyst. After that, Ni‐Pd nanoparticles supported on poly (styrenesulfonic acid‐n‐vinylimidazole)/KIT‐6 as a novel trifunctional heterogeneous acid–base‐metal catalyst was prepared. The prepared catalysts were characterized by various techniques like FT‐IR, TGA, ICP‐AES, DRS‐UV, TEM, FE‐SEM, EDS‐Mapping, and XRD. The synthesized catalysts were efficiently used as bifunctional/trifunctional catalysts for one‐pot, deacetalization‐Knoevenagel condensation and one‐pot, three‐step and a sequential reaction containing deacetalization‐Knoevenagel condensation‐reduction reaction. It is important to note that the synthesized catalyst showing high chemo‐selectivity for the reduction of nitro group, alkenyl double bond and ester group in the presence of nitrile. Moreover, it was found that the different nanoparticles including Ni, Pd, and alloyed Ni‐Pd showing different chemo‐selectivity and catalytic activity in the reaction.     

Ethylene‐Norbornene Terpolymerization with 5‐Vinyl‐2‐norbornene Using Single‐Site Catalysts

The incorporation of 5‐vinyl‐2‐norbornene (VNB) into ethylene‐norbornene copolymer was investigated with catalysts [Ph₂C(Fluo)(Cp)]ZrCl₂ ( 1 ), rac‐[Et(Ind)₂]ZrCl₂ ( 2 ), and [Me₂Si(Me₄Cp)^tBuN]TiCl₂ ( 3 ) in the presence of MAO by terpolymerizing different amounts of 5‐vinyl‐2‐norbornene with constant amounts of ethylene and norbornene at 60°C. The highest cycloolefin incorporations and highest activity in terpolymerizations were achieved with 1 . The distribution of the monomers in the terpolymer chain was determined by NMR spectroscopy. As confirmed by XRD and DSC analysis, catalysts 1 and 3 produced amorphous terpolymer, whereas 2 yielded terpolymer with crystalline fragments of long ethylene sequences. When compared with poly‐(ethylene‐co‐norbornene), VNB increased both the glass transition temperatures and molar masses of terpolymers produced with the constrained geometry catalyst whereas decreased those for the metallocenes.     

Ni3FeN‐Supported Fe3Pt Intermetallic Nanoalloy as a High‐Performance Bifunctional Catalyst for Metal–Air Batteries

Electrocatalysts for both the oxygen reduction and evolution reactions (ORR and OER) are vital for the performances of rechargeable metal–air batteries. Herein, we report an advanced bifunctional oxygen electrocatalyst consisting of porous metallic nickel‐iron nitride (Ni₃FeN) supporting ordered Fe₃Pt intermetallic nanoalloy. In this hybrid catalyst, the bimetallic nitride Ni₃FeN mainly contributes to the high activity for the OER while the ordered Fe₃Pt nanoalloy contributes to the excellent activity for the ORR. Robust Ni₃FeN‐supported Fe₃Pt catalysts show superior catalytic performance to the state‐of‐the‐art ORR catalyst (Pt/C) and OER catalyst (Ir/C). The Fe₃Pt/Ni₃FeN bifunctional catalyst enables Zn–air batteries to achieve a long‐term cycling performance of over 480 h at 10 mA cm⁻² with high efficiency. The extraordinarily high performance of the Fe₃Pt/Ni₃FeN bifunctional catalyst makes it a very promising air cathode in alkaline electrolyte.     

Gold(I)‐ and Yb(OTf)3‐Cocatalyzed Rearrangements of Epoxy Alkynes: Transfer of a Carbonyl Group in a Five‐Membered Carbocycle

We report here the intramolecular reactions between α,β‐epoxy ketones and alkynes cocatalyzed by gold(I) and Yb(OTf)₃. This new catalytic system based on a combination of gold(I) and Yb(OTf)₃ allows facile transformation of epoxy alkynes to give novel indene derivatives in moderate to good yields under mild conditions. Moreover, we describe here the first observation of a transfer of a carbonyl group in a five‐membered carbocycle during gold‐catalyzed reactions. This proposed mechanism is corroborated by isotope‐labeling experiments (D and ¹³C). Furthermore, the probable role of each catalyst in this interesting domino reaction has been examined by ³¹P NMR experiments. The utilization of gold catalysts combined with rare‐earth metal salts offers a new concept for the design of catalyst combinations for domino or cascade reactions.     

Temperature Dual Enantioselective Control in a Rhodium‐Catalyzed Michael‐Type Friedel–Crafts Reaction: A Mechanistic Explanation

By changing the temperature from 283 to 233 K, the S (99 % ee) or R (96 % ee) enantiomer of the Friedel–Crafts (FC) adduct of the reaction between N‐methyl‐2‐methylindole and trans‐β‐nitrostyrene can be obtained by using (S_Rh,R_C)‐[(η⁵‐C₅Me₅)Rh{(R)‐Prophos}(H₂O)][SbF₆]₂ as the catalyst precursor. This catalytic system presents two other uncommon features: 1) The ee changes with reaction time showing trends that depend on the reaction temperature and 2) an increase in the catalyst loading results in a decrease in the ee of the S enantiomer. Detection and characterization of the intermediate metal–nitroalkene and metal–aci‐nitro complexes, the free aci‐nitro compound, and the FC adduct‐complex, together with solution NMR measurements, theoretical calculations, and kinetic studies have allowed us to propose two plausible alternative catalytic cycles. On the basis of these cycles, all the above‐mentioned observations can be rationalized. In particular, the reversibility of one of the cycles together with the kinetic resolution of the intermediate aci‐nitro complexes account for the high ee values achieved in both antipodes. On the other hand, the results of kinetic measurements explain the unusual effect of the increment in catalyst loading.     

Novel Flower‐Like Ag‐SiO2‐MgO‐Al2O3 Material: Preparation,Characterization and Catalytic Application in Methanol Dehydrogenation

Catalytic direct dehydrogenation of methanol to formaldehyde was carried out over Ag‐SiO₂‐MgO‐Al₂O₃ catalysts prepared by sol‐gel method. The optimal preparation mass fractions were determined as 8.3% MgO, 16.5% Al₂O₃ and 20% silver loading. Using this optimum catalyst, excellent activity and selectivity were obtained. The conversion of methanol and the selectivity to formaldehyde both reached 100%, which were much higher than other previously reported silver supported catalysts. Based on combined characterizations, such as X‐ray diffraction (XRD), scanning electronic microscopy (SEM), diffuse reflectance ultraviolet‐visible spectroscopy (UV‐Vis, DRS), nitrogen adsorption at low temperature, temperature programmed desorption of ammonia (NH₃‐TPD), desorption of CO₂ (CO₂‐TPD), etc., the correlation of the catalytic performance to the structural properties of the Ag‐SiO₂‐ MgO‐Al₂O₃ catalyst was discussed in detail. This perfect catalytic performance in the direct dehydrogenation of methanol to formaldehyde without any side‐products is attributed to its unique flower‐like structure with a surface area less than 1 m²/g, and the strong interactions between neutralized support and the nano‐sized Ag particles as active centers.     

Enantioselective Alkynylation of Trifluoromethyl Ketones Catalyzed by Cation‐Binding Salen Nickel Complexes

Cation‐binding salen nickel catalysts were developed for the enantioselective alkynylation of trifluoromethyl ketones in high yield (up to 99 %) and high enantioselectivity (up to 97 % ee). The reaction proceeds with substoichiometric quantities of base (10–20 mol % KOt‐Bu) and open to air. In the case of trifluoromethyl vinyl ketones, excellent chemo‐selectivity was observed, generating 1,2‐addition products exclusively over 1,4‐addition products. UV‐vis analysis revealed the pendant oligo‐ether group of the catalyst strongly binds to the potassium cation (K⁺) with 1:1 binding stoichiometry (K_a=6.6×10⁵ m ^?1).     

Polystyrene‐Supported (Catecholato)oxorhenium Complexes: Catalysts for Alcohol Oxidation with DMSO and for Deoxygenation of Epoxides to Alkenes with Triphenylphosphine

Polymer‐supported catalysts offer practical advantages for organic synthesis, such as improved product isolation, ease of catalyst recycling, and compatibility with parallel solution‐phase techniques. We have developed the (carboxypolystyrene‐catecholato)rhenium catalyst 2 derived from tyramine (=4‐(2‐aminoethyl)phenol), which is effective for alcohol oxidation with dimethylsulfoxide (DMSO) and for epoxide deoxygenation with triphenylphosphine. The supported [Re(catecholato)]catalyst 2 is air‐ and moisture‐stable and can be recovered and used repeatedly without decreasing activity. The procedures work with non‐halogenated solvents (toluene). DMSO for Re‐catalyzed alcohol oxidation is inexpensive and safer for transport and storage than commonly used peroxide reagents. The oxidation procedure was best suited for aliphatic alcohols, and the mild conditions were compatible with unprotected functional groups, such as those of alkenes, phenols, nitro compounds, and ketones (see Tables 1 and 2). Selective oxidation of secondary alcohols in the presence of primary alcohols was possible, and with longer reaction time, primary alcohols were converted to aldehydes without overoxidation. Epoxides (oxirans) were catalytically deoxygenated to alkenes with this catalyst and Ph₃P (see Table 3). Alkyloxiranes were converted to the alkenes with retention of configuration, while partial isomerization was observed in the deoxygenation of cis‐stilbene oxide ( cis‐1,2‐diphenyloxirane). These studies indicate that supported [Re(catecholato)] complexes are effective catalysts for O‐atom‐transfer reactions, and are well suited for applications in organic synthesis.     

Dehydrogenation of Isobutane to Isobutene with Carbon Dioxide over SBA‐15‐Supported Chromia‐Ceria Catalysts

A series of SBA‐15‐supported chromia‐ceria catalysts with 3% Cr and 1%–5% Ce (3Cr‐Ce/SBA) were prepared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N₂ adsorption, SEM, TEM‐EDX, Raman spectroscopy, UV–vis spectroscopy, XPS and H₂‐TPR, and their catalytic performance for isobutane dehydrogenation with CO₂ was tested. The addition of ceria to SBA‐15‐supported chromia improves the dispersion of chromium species. 3Cr‐Ce/SBA catalysts are more active than SBA‐15‐supported chromia (3Cr/SBA), which is due to a higher concentration of Cr⁶⁺ species present on the former catalysts. The 3Cr‐3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570 °C after 10 min of the reaction.