Nanosized Pd(0)-arabinogalactan composites as catalysts in the Sonogashira reaction

Zero-valent palladium nanoparticles stabilized by arabinogalactan polysaccharide matrix were successfully used for the first time as phosphine-free catalyst in the cross-coupling of terminal alkynes with aryl and hetaryl halides.     

Iminophosphine palladium catalysts for Suzuki carbonylative coupling reaction

Three iminophosphine ligands having soft phosphorus and hard nitrogen atoms and their Pd(II) complexes were synthesized and characterized using ¹H NMR, ¹³C NMR, ³¹P NMR and Fourier transform infrared spectroscopic techniques. Also, electrochemical properties of the iminophosphines and their Pd(II) complexes were investigated in acetonitrile–tetrabutylammonium perchlorate solution with cyclic and square wave voltammetry techniques. All Pd(II) complexes were evaluated as catalysts for carbonylative cross‐coupling reactions of aryl iodides with phenylboronic acid. The Suzuki carbonylation of aryl iodides at 80 °C under balloon pressure of carbon monoxide in the presence of K₂CO₃ as a base was examined, and good to high conversions and excellent selectivities were obtained.     

Iron pincer complex and its graphene oxide composite as catalysts for Suzuki coupling reaction

We report the synthesis of Fe-NCN pincer complex as homogenous catalyst and its composite by immobilizing the complex on amino functionalized graphene oxide as a heterogeneous catalyst for Suzuki coupling reactions. Both the complex and the composite were employed in catalyzing the Suzuki-Miyaura cross-coupling reaction between the aryl halide and phenyl boronic acid in acetonitrile solvent media with Cs₂CO₃ as a base. Effect of substitution over aryl halide was also investigated. Immobilization of the pincer complex had advantageous recovery and reuse of the catalyst as compared to its homogenous analog with no significant decrease in the catalytic efficiency.     

Phase-transfer agents as catalysts for a nucleophilic substitution reaction in microemulsions

The reaction between 4-tert-butylbenzyl bromide and potassium iodide was carried out in microemulsions based on different nonionic surfactants, and the reaction rates were compared with those obtained in two-phase systems with added phase-transfer agent, either a quaternary ammonium salt or a crown ether. The reactions were relatively fast in the microemulsions and extremely sluggish in the two-phase systems without additional phase-transfer agent. Addition of a phase-transfer agent did not accelerate the reaction when a hydrocarbon was used as organic solvent, neither in the two-phase system nor in the microemulsion. When a chlorinated hydrocarbon was used as solvent, phase-transfer catalysis became effective and the rate obtained in the two-phase system with an equimolar amount of phase-transfer agent added was higher than that obtained in the microemulsion. When a catalytic amount of phase-transfer agent was used, the rate in the two-phase system was about the same as the rate obtained in the microemulsion without the phase-transfer agent. The combined approach, that is, use of a microemulsion as the reaction medium and addition of a phase-transfer agent, gave the highest reaction rate. The quaternary ammonium salt (tetrabutylammonium hydrogen sulfate) was a more efficient catalyst in the microemulsion system than the crown ether ([18]crown-6).     

Ni-Co@C-N催化剂的制备及其催化硝基芳烃还原偶联反应

以ZIF-67为前驱体,通过高温热解和乙二醇还原的方法制备了低成本的负载镍纳米粒子催化剂Ni-Co@C-N。研究了催化剂对硝基芳烃化合物合成相应氧化偶氮苯类化合物的催化性能,并讨论了碱及分散剂种类对催化剂结构与性能的影响。结果表明,碱性增强可以加快纳米粒子的成核速率,分散剂分子量增加则会限制纳米粒子的粒径增长。其中,由弱碱与低分子量分散剂制备的Ni-Co@C-N-4对硝基芳烃还原具有良好的催化活性,原料的转化率和产率在反应30 min后分别达到92.8%和89.3%,且循环实验表明Ni-Co@C-N-4具有良好的稳定性。     

Ni-Co@C-N催化剂的制备及其催化硝基芳烃还原偶联反应

以ZIF-67为前驱体,通过高温热解和乙二醇还原的方法制备了低成本的负载镍纳米粒子催化剂Ni-Co@C-N。研究了催化剂对硝基芳烃化合物合成相应氧化偶氮苯类化合物的催化性能,并讨论了碱及分散剂种类对催化剂结构与性能的影响。结果表明,碱性增强可以加快纳米粒子的成核速率,分散剂分子量增加则会限制纳米粒子的粒径增长。其中,由弱碱与低分子量分散剂制备的Ni-Co@C-N-4 对硝基芳烃还原具有良好的催化活性,原料的转化率和产率在反应30 min 后分别达到92.8%和89.3%,且循环实验表明Ni-Co@C-N-4具有良好的稳定性。     

应用于氧还原反应的石墨烯-无定形碳核壳结构复合材料载铂催化剂(英文)

采用氯化法制备石墨烯-无定型碳复合材料(GNS@a-C),并用作质子交换膜燃料电池(PEMFC)氧还原反应Pt催化剂的载体.结果显示,所制Pt/GNS@a-C催化剂与传统商业催化剂Pt/C相比,有较好的活性和较高的稳定性:质量活性(0.121 A/mg)几乎是Pt/C(0.064 A/mg)的两倍.更重要的是,该新型催化剂加速4000圈后其电化学活性面积保留了最初的51%,与Pt/C的33%相比,前者有更好的电化学稳定性,显示它在PEMFC中将具有较好的应用潜力.     

Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction

Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation.     

Supported transition-metal catalysts for the C---C coupling reaction between ethene and diazoalkanes

The preparation of a series of immobilized transition-metal catalysts are reported. The catalysts were obtained by chemisorption of either rhodium(I) or iridium(I) complexes [MX(C₂H₄)₂]_n (M = Rh, Ir; X = Cl, OAc, acac, f₃-acac, f₆-acac) on SiO₂ or MgO supports. The oxides were also activated by SiCl₄ or TiCl₄ to give support materials in which the acidic nature of the surface is substantially increased. The activity of the immobilized catalysts was tested, particularly in the reaction of ethene with diphenyldiazomethane which yields a mixture of 1.1-diphenylpropene (8) and 1.1-diphenylcyclopropane (9). It was found that the most active and most selective (highest ratio 8:9) catalyst B1 was formed support material B (SiO₂ activated by SiCl₄) and [RhCl(C₂H₄)₂]₂ (1) and that both the activity and selectivity of B1 was comparable with that of complex 1 in solution. In contrast, the supported catalysts A2, D2 and A3, D3 obtained from [Rh(OAc)(C₂H₄)₂]₂ (2) and [Rh(acac)(C₂H₄)₂] (3) were less active than compounds 2 and 3 in solution. The immobilized catalysts A6, A7, D7 and E7, which were generated from the chloro- and acetatoiridium(I) complexes [IrCl(C₂H₄)₂]₂ (6) and [Ir(OAc)(C₂H₄)₂]₂ (7), possessed a lower activity than the rhodium counterparts. With diazoalkanes other than Ph₂CN₂, the activity of the supported catalyst B1 was partly higher and partly lower than that of complex 1 in the homogeneous phase.     

Heteropolyacids as new catalysts of the Ritter reaction

Some nitriles reacted with camphene in the presence of heteropolyacids (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₇PMo₁₂O₄₀) as catalyst to give N-(1,7,7-trimethylbicyclo[2.2.1]hept-2-yl)-substituted amides in fairly high yields.     

Imidazolinium salts as catalysts for the aza-Diels-Alder reaction

Various easily accessible imidazolinium salts have been found to be capable of catalysing an aza-Diels-Alder reaction with a range of imines and Danishefsky's diene, giving the desired products in good to excellent yields. The influence of the counter-anions on the reactivity has been explored. These salts could contribute to the field of metal-free catalysis/organocatalysis.     

S-doped carbon aerogels/GO composites as oxygen reduction catalysts

Composites of carbon aerogel and graphite oxide(GO) were synthesized using a self-assembly method based on dispersive forces. Their surface was modified by treatment in hydrogen sulfide at 650 and800 ℃. The samples obtained were characterized by adsorption of nitrogen, TA-MS, XPS, potentiometric titration, and HRTEM and tested as catalysts for oxygen reduction reactions(ORR) in an alkaline medium.The synergistic effect of the composite(electrical conductivity, porosity and surface chemistry) leads to a good ORR catalytic activity. The onset potential for the composite of carbon aerogel heated at 800 ℃ is shifted to a more positive value and the number of electron transfer was 2e-at the potential 0.68 V versus RHE and it increased to 4e-with an increase in the negative values of the potential. An excellent tolerance to methanol crossover was also recorded.     

Lowering reaction temperature: Electrochemical ammonia synthesis by coupling various electrolytes and catalysts

Ammonia is a vital emerging energy carrier and storage medium in the future hydrogen economy, even presenting relevant advantages compared with methanol due to the higher hydrogen content(17.6 wt% for ammonia versus 12.5 wt% for methanol). The rapidly growing demand for ammonia is still dependent on the conventional high-temperature and high-pressure Haber–Bosch process, which can deliver a conversion rate of about 10%–15%. However, the overall process requires a large amount of fossil fuels,resulting in serious environmental problems. Alternatively, electrochemical routes show the potential to greatly reduce the energy consumption, including sustainable energy sources and simplify the reactor design. Electrolytes perform as indispensable reaction medium during electrochemical processes, which can be further classified into solid oxide electrolytes, molten salt electrolytes, polymer electrolytes, and liquid electrolytes. In this review, recent developments and advances of the electrocatalytic ammonia synthesis catalyzed by a series of functional materials on the basis of aforementioned electrolytes have been summarized and discussed, along with the presentation and evaluation of catalyst preparation, reaction parameters and equipment.     

Systematic evaluation of a few proline derivatives as catalysts for a direct aldol reaction

A series of pyrrolidine derivatives were prepared and examined as catalysts for an aldol reaction. Structural variations in these molecules involved altering the sterics at the α-position, the position of the carbonyl group, and the acidities of the hydrogen bonding sites. The effect of these factors on catalytic activity and enantioselectivity was studied. The experimental results revealed that additional sterics at the α-position were detrimental. However, no correlation was found between the catalytic activity and N–H acidity.     

Synthetic utility of ammonium salts in a Cu-catalyzed three-component reaction as a facile coupling partner

Ammonium salts were found to be a convenient and inexpensive reagent in the Cu-catalyzed three-component reaction with terminal alkynes and sulfonyl or phosphoryl azides leading to N-unprotected amidines. Thus obtained amidines bearing 2-bromobenzenesulfonyl moiety were efficiently cyclized by the Cu-catalyzed intramolecular N-arylation to give an important pharmacophore skeleton of 2H-1,2,4-benzothiadiazine 1,1-dioxides. Conveniently, two tandem catalytic procedures could be readily operated in one pot.     

Dehydration-dehydrogenation of 2-propanol as a model reaction for acid-base characterization of catalysts

The relationship between the acid-base properties of various solids, as determined by a spectrophotometric procedure and the apparent dehydrogenation (K₁) and dehydration rate constant (K₂) of 2-propanol have been studied by using a continuous-flow reactor.     

Palladacyclic complexes bearing CNN-type ligands as catalysts in the Heck reaction

Preparations of novel unsymmetrical, tridentate nitrogen ligand precursors, PhN=C(CMe2)(NPh)C=N(CH2)2NMe2(1) and PhN=C(CMe2)(NPh)C=N(CH2)Py (2), are described. Treatment of 1 with 1 molar equiv. (COD)PdCl2 in the presence of NEt3 or with 1 molar equiv. Pd(OAc)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=N(CH2)2NMe2]PdX (X=Cl (3); X=OAc (4)), respectively. Compound can be yielded via the reaction of with an excess of LiCl in methanol. Treatment of with 1 molar equiv. of (COD)PdCl2, Pd(OAc)2 or Pd(TFA)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=NCH2Py]PdX (X=Cl (5); X=OAc (6); X=TFA (7)), respectively. The crystal and molecular structures are reported for compounds 2, 3, 5 and 6. The application of these novel palladacyclic complexes to the Heck reaction with aryl halide substrates was examined.     

Orthopalladated triarylphosphite complexes as highly efficient catalysts in the Heck reaction

An orthopalladated complex of commercially available tris(2,4-di-tert-butylphenyl)phosphite proves to be an extremely active catalyst in the Heck arylation of alkenes, with turnover numbers of up to 5,750,000 (mol product.mol Pd⁻¹) and turnover frequencies of up to nearly 300,000 (mol product.mol Pd⁻¹.h⁻¹).     

Novel sulfonylpolystyrene-supported prolinamides as catalysts for enantioselective aldol reaction in water

Five novel prolinamides derived from 1,n-diamines supported on commercially available sulfonylpolystyrene have been synthesized and successfully applied in diastereo- and enantioselective aldol reaction in water or, in one case, neat conditions. Excellent dr and er were obtained by reaction of different cyclohexanone derivatives with aromatic and heteroaromatic aldehydes in the presence of the catalysts and AcOH as co-catalyst. The supported organocatalysts work in low loading (5 mol %) exhibiting similar performances than homogeneous prolinamides, and can be reused, after activation, without loss of activity.