Unexpected Side Reaction in the Intermolecular N-H Insertion of Phenyl Diazoacetates with Arylamines

Unexpected side reaction is discovered from the N-H insertion of phenyl diazoacetates with arylamines in the presence of Rh2(OAc)4 catalyst. This side reaction is not evident with copper catalysts such as Cu(acac)2 or Cu(OTf)2. Good yield of the N-H insertion was obtained by using 0.2% of copper catalyst.     

Mechanism of rhodium(Ⅲ)-catalyzed formal C(sp~3)-H activation/spiroannulation of a-arylidene pyrazolones with alkynes:A computational study

The rhodium-catalyzed formal C(sp~3)-H activation/spiroannulation of a-arylidene pyrazolones with alkynes was investigated by means of density functional theory calculations. The calculations indicate that the spiroannulation through the proposed C—C reductive elimination is kinetically unfeasible.Instead, the C—C coupling from the eight-membered rhodacycle was proposed to account for the experimental results. The overall catalytic cycle consists of six steps:(1) the keto-enol isomerization;(2)the O—H deprotonation,(3) the C(sp~2)—H bond cleavage;(4) the migratory insertion of alkyne into the Rh—C bond;(5) the C—C coupling and(6) the regeneration of the active catalyst.     

Palladium-Catalyzed Oxidation of Dihydromyrcene to Citronellal in Supercritical Carbon Dioxide

Citronellal was the major product of catalytic oxidation of dihydromyrcene with oxygen using the catalyst comprised of (MeCN)2PdC1NO2 and CuC12 in a tertiary alcohol in supercritical carbon dioxide. It was found that the chemoselectivity of the reaction and the yield of citronellal were greatly affected by the pressure of carbon dioxide, the reaction temperature and the molar ratio of Pd/Cu.     

The Real Structure of Pd(OAc)2 in Various Solvents

Pd(OAc)₂ is an extensively utilized palladium source in the palladium initiated transformations either directly or as a catalyst precursor. However, the comprehension of the real structure of Pd(OAc)₂ in solution is still vague. In this work, the structure of palladium acetate in solution was studied in detail by using X-ray absorption fine structure (XAFS) spectroscopy. The results demonstrate that monomer is the main form for Pd(OAc)₂ in the solution of 1,4-dioxane, N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), 1,2-dimethoxyethane (DME), MeCN and dimethyl sulfoxide (DMSO). In addition, Pd(II) could be reduced to Pd(0) in ethanol solution. The structural information in this research will benefit the understanding of the mechanism of Pd(OAc)₂ involved organic reactions.     

Catalytic oxidation of cyclohexene to cyclohexanone by a triple system in acidic aqueous acetonitrile medium

The catalytic oxidation of cyclohexene to cyclohexanone using Pd(OAc)2/HQ/FePc was investigated in an acidic aqueous solution of acetonitrile. The role of each component of this system in the oxidation of cyclohexene was explored by means of UV-VIS, IR, XPS spectroscopy and cyclic voltammetry, respectively. Based on the experimental results, the mechanism of the oxidation of cyelohexene catalyzed by Pd(OAc)2/HQ/FePc was elucidated.     

Influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts

Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization.This type of catalyst features six-membered chelate ring size,and can enable the copolymerizations of ethylene with a wide variety of polar monomers.In this contribution,we decide to investigate the influence of chelate ring size on the properties of phosphinesulfonate palladium catalysts.As such,a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II)complexes[κ~2-(P,O)-2-(CH_2-PR_1R_2)-4-methylphenyl-sulfonato]Pd(Me)(DMSO)(Pd1,R_1=R_2=Cy,Pd2,R_1=R_2=o-Me O-C_6H_4;Pd3,R_1=Ph,R_2=2-[2,6-(Me O)_2C_6H_3]C_6H_4;DMSO=dimethyl sulfoxide)were designed,prepared and characterized.These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether.However,their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2′.The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.     

Study of The Pd-B/ γ-Al2O3 Amorphous Alloy Catalyst

The Pd-B/γ-Al2O3 amorphous alloy catalyst and Pd/γ-Al2O3 crystalline metal catalyst were prepared by KBH4 reduction and routine impregnation,respectively.Pd-B/γ-Al2O3 and Pd/γ-Al2O3 catalysts were characterized by XRD and SEM.It was found that the catalytic activity of the Pd-B/γ-Al2O3 amorphous alloy catalyst was higher than that of the Pd/γ-Al2O3 crystalline metal catalyst in the anthraquinone hydrogenation.     

Self-regeneration of activated carbon modified with palladium catalyst for electrochemical dechlorination

Catalyst regeneration and the retention of high catalytic activity are still the critical issues in environmental application.A novel fluidized gas-liquid-solid electrochemical reactor was developed to simultaneously remove chlorinated pollutants and in situ regenerate the spent catalyst.Activated carbon modified with palladium catalyst (AC-Pd) was prepared for electrochemical dechlorination.For the 4-chloropbenol wastewater of initial concentration 200 mg L~(-1),the removal efficiency could nearly reach 100% in less than 30 min.Catalytic activity of AC-Pd catalyst was preserved effectively even in consecutive cycling run without special regeneration.OH radicals,generated by electrochemical reaction,played a critical role in self-regeneration of AC-Pd.High catalytic activity of spent AC-Pd catalyst provided an attractive alternative in wastewater treatment.     

Pd/Hβ-zeolite catalysts for catalytic combustion of toluene: Effect of SiO2/Al2O3 ratio

The effect of pure and high silica Hβ zeolites on the catalytic performance of toluene combustion over Pd/H/3 catalyst was evaluated.Pure and high silica β zeolites were prepared by direct synthesis procedures,then 0.1 wt% of palladium was impregnated on different Hβ zeolites via incipient wetness technique using palladium nitrate as the Pd source.The Pd/Hβ catalysts were characterized by XRD,N2 adsorption/desorption,H2O adsorption,NH3-TPD,H2-TPR and XPS techniques.With increasing the SIO2/Al2O3 ratio of β zeolite,the activity of the Pd/Hβ catalysts for toluene combustion increased clearly and the pure silica β zeolite supported Pd catalyst showed the best catalytic activity.The superior catalytic performance of Pd/β catalyst prepared from pure silica β zeolite was attributed to its high hydrophobicity and the preserving ability for PdO active species.     

Pd/Hβ-zeolite catalysts for catalytic combustion of toluene:Effect of SiO_2/Al_2O_3 ratio

The effect of pure and high silica Hβ zeolites on the catalytic performance of toluene combustion over Pd/Hβ catalyst was evaluated.Pure and high silica β zeolites were prepared by direct synthesis procedures,then 0.1 wt% of palladium was impregnated on different Hβ zeolites via in-cipient wetness technique using palladium nitrate as the Pd source.The Pd/Hβ catalysts were characterized by XRD,N2 adsorption/desorption,H2O adsorption,NH3-TPD,H2-TPR and XPS techniques.With increasing the SiO2/Al2O3 ratio of β zeolite,the activity of the Pd/Hβ catalysts for toluene combustion increased clearly and the pure silica β zeolite supported Pd catalyst showed the best catalytic activity.The superior catalytic performance of Pd/β catalyst prepared from pure silica β zeolite was attributed to its high hydrophobicity and the preserving ability for PdO active species.     

Comparative study on electrochemical degradation of 4-chlorophenol by different Pd/C gas diffusion electrodes

Pd/C catalyst used for the Pd/C gas diffusion cathodes was prepared by hydrogen reduction method and formaldehyde reduction method, and characterized by X-ray diffraction (XRD), transmission elec- trode microcopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) tech- niques. The electrochemical degradation of 4-chlorophenol was investigated in the diaphragm elec- trolysis system, aerating firstly with hydrogen gas then with air, using three different kinds of gas dif- fusion cathode. The results indicated that the self-made Pd/C gas diffusion cathode can not only re- ductively dechlorinate 4-chlorophenols by aerating hydrogen gas, but also accelerate the two-electron reduction of O2 to hydrogen peroxide (H2O2) by aerating air. Therefore, the removal efficiency of 4-chlorophenol by using Pd/C gas diffusion cathode is better than that of the C/PTFE gas diffusion cathode (no catalyst). The catalytic activity of Pd/C catalyst prepared by hydrogen reduction method is higher than that prepared by formaldehyde reduction method. The stability of the Pd/C gas diffusion cathodes is good. Therefore, both the removal efficiency and the dechlorination degree of 4-chlorophenol reached about 100% after 60 min, and the removal efficiency of 4-chlorophenol in terms of chemical oxygen demand (COD) in the cathodic compartment reached 87.4% after 120 min.     

Crystal Structure of Chiral Acetato-bridged Binuclear Cyclopalladated complex[Pd（μ-O2CM3）（S-C6H4CHMeNH2）]2

Reaction of (S)-α-methylbenzylamine with Pd(OAc)2 in anhydrous HOAc produced the chiral complex[Pd(μ-O2CMe)(S-C6H4CHMeNH2)]2.(1).The complex was characterized by 1H NMR spectroscopy,elemental analysis and a single-crystal Xray analysis.The X-ray crystal structure analysis revealed that complex 1 has four isomers:two outer and two inner isomers.     

An Efficient Synthesis of 2-Oxazolidinones by Palladium-catalyzed Oxidative Carbonylation of β-Aminoalcohols and 2-Aminophenol under Mild Conditions

Oxidative carbonylation of β-aminoalcohols and 2-aminophenol in Pd(OAc)2/I2 catalytic system to produce the corresponding 2-oxazolidinones was conducted with high yields and selectivities in short reaction time. Mild reaction conditions, high catalytic turnover frequency value, improved yields and selectivities are the remarkable features exhibited by this process.     

Characterization and reactivity of γ-Al_2O_3 supported Pd–Ni bimetallic nanocatalysts for selective hydrogenation of cyclopentadiene

Several g-Al2O3 supported Pd–Ni bimetallic nanocatalysts(Pd–Ni(x:y)/Al2O3; where x and y represent the mass ratio of Pd and Ni, respectively) were prepared by the impregnation method and used for selective hydrogenation of cyclopentadiene to cyclopentene. The Pd–Ni/Al2O3 samples were confirmed to generate Pd–Ni bimetallic nanoparticles by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The catalytic activity was assessed in view of the effects of different mass ratios of Pd and Ni, temperature, pressure, etc. Among all the samples, the Pd–Ni(1:1)/Al2O3(PN-1:1) catalyst showed extremely high catalytic ability. The conversion of cyclopentadiene and selectivity for cyclopentene can be simultaneously more than 90%.     

Photopromoted carbonylation of bromobenzene under ambient conditions

The photopromoted carbonylation of bromobenzene with carbon monoxide catalyzed by inexpensive commercially available cobalt salts[Co(OAc)_2,CoCl_2]was carried out under ambient conditions.The results revealed that methyl benzoate was produced in the presence of basic additives(CH_3ONa,NaOAc or(n-C_4H_9)_3N).The catalytic activity of Co(OAc)_2was higher than that of CoCl_2.Furthermore,the activity of the carbonylation was greatly improved by addition of acetophenone,e.g.both the yield and selectivity of t...     

Role of size and pretreatment of Pd particles on their behaviour in the direct synthesis of H_2O_2

Two families of catalysts, based on Pd nanoparticles supported on ceramic asymmetric tubular alumina membranes, are studies in the direct synthesis of H_2O_2. They are prepared by depositing Pd in two ways:(i) reduction with N_2H_4 in an ultrasonic bath and(ii) by impregnation-deposition. The first preparation leads to larger particles, with average size of around 11 nm, while the second preparation leads to smaller particles, with average size around 4 nm. The catalytic membranes were tested as prepared, after thermal treatment in air and after further pre-reduction with H_2 in mild(100 ℃) conditions. Samples were characterized by TEM, CO-chemisorption monitored by DRIFTS method and TPR, while catalytic tests have been performed in a semi-batch recirculation membrane reactor. Experimental catalytic results were analysed using two kinetics models to derive the reaction constants for the parallel and consecutive reactions of the kinetic network. Smaller particles of Pd show lower selectivity due to the higher rate of parallel combustion, even if the better dispersion of Pd and thus higher metal surface area in the sample lead to a productivity in H_2O_2 similar or even higher than the sample with the larger Pd particles. Independently on the presence of smaller or larger Pd nanoparticles, an oxidation treatment leads to a significant enhancement in the productivity, although the catalyst progressively reduces during the catalytic process. The inhibition of the parallel combustion reaction(to water) induced from the calcination treatment remains after the in-situ reduction of the oxidized Pd species formed during the pre-treatment.This is likely due to the elimination of defect sites which dissociatively activate oxygen, and tentatively attributed to Pd sites able to give three- and four-fold coordination of CO.     

Heck Arylation of Acrylonitrile with Aryl Iodides Catalyzed by a Silica-bound Arsine Palladium(0) Complex

The palladium-catalyzed arylation of alkenes is an important discovery in organo-palladium chemistry made by Heck et al. and has found wide application in organicsynthesis1,2. In this reaction, homogeneous palladium complexes such as Pd(OAc)2 areusually used as the catalysts and the amount of catalyst used is about 2 mol% of reactant.Although homogeneous palladium catalysts have proven to be efficient, their activity andstereoselectivity are moderate and use of homogeneous palladium catalysts…     

Effects of potassium promoter on the performance of PdCl_2–CuCl_2/AC catalysts for the synthesis of dimethyl carbonate from CO and methyl nitrite

The effect of potassium(K) promoter on the catalytic performance of activated carbon(AC) supported Wacker-type catalysts(Pd Cl2–Cu Cl2/AC) for the synthesis of dimethyl carbonate(DMC) from CO and methyl nitrite(MN) was investigated by means of N2 adsorption, H2-temperature-programmed reduction(H2-TPR), and X-ray photoelectron spectroscopy(XPS). The experimental results showed that the space time yield of DMC on Wacker-type catalysts with different K promoters ranked in the following order: KCl KOH CH3 COOK K2CO3. Especially, the addition of KCl significantly improved the catalytic activities of Pd Cl2–Cu Cl2/AC catalyst for DMC synthesis from CO and MN. N2 adsorption data indicated that the addition of K promoters did not change the textural properties of Wacker-type catalysts greatly. H2-TPR and XPS results demonstrated that the existence of KCl promoted the reducibility of Cu2+species and increased the proportion of Cu2+species on catalyst surface, which is favorable for oxidizing Pd0 to active Pd2+. Further, the addition of KCl benefited the reactivity of Pd Cl2–Cu Cl2/AC catalyst for DMC synthesis from CO and MN.     

C-H BOND ACTIVATION AND FUNCTIONALIZATION OF METHANE UNDER MILD CONDITIONS

In the presence of Rh(COD)(dppe)Cl (COD=1, 5-cyclootadiene, dppe=1,2-bis-(diphenylphosphino)ethane) and CO, we studied the H/Cl exchange reaction between CH_4 and o-dichlorobenzene, and observed that the active species of the reaction is a complex containing dppe and carbonyl ligands. We suggest that the mechanism of exchange reaction may be described by the elementary reaction of oxidative addition and reductive elimination. In the presence of trans-PtHL_2X (L=PEt_3, P(n-Pr)_3, P(n-Bu)_3, PPh_3; X=Cl~-, Br~-, I~-, CN~-) complexes, we have studied the oxidative chlorination reaction of methane. The catalytic activity was found to be related to the electron-donating properties and the cone angle of tertiary phosphine, as well as the trans-effect of X anionic ligands. In addition to the above reactions, we have also studied the insertion reaction of acetylene into C-H bond of methane catalyzed by organotransition-metal complexes containing heterocyclic chelate ligands, such as bipy, phen and TMEDA, in DMF     

HypoGel负载Pd纳米催化剂制备与表征及温和条件下催化Suzuki反应(英文)

A new heterogeneous catalyst composed of Pd nanoparticles immobilized within a HypoG el resin has been prepared in the absence of any ligands using an extensive cross-linking method.This newly developed nanocatalyst was characterized by N_2 adsorption-desorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),energy dispersive X-ray(EDX),Fourier transform infrared spectroscopy and inductively coupled plasma-mass spectrometer(ICP-MS)techniques.TEM and XRD results revealed that the Pd nanoparticles were well dispersed with diameters in the range of 4–12 nm,and an average size of about 8 nm.The cross-linked Pd catalyst demonstrated excellent catalytic activity towards the synthesis of a series of biaryl compounds by the reaction of various aryl halides(e.g.,bromides andiodides)with phenylboronic acid in the presence of tetrabutylammonium bromide.ICP-MS analysis indicated that there was only 0.25%weight loss of Pd(0.55±0.02 ppm)from the supported catalyst after the first cycle reaction.Furthermore,the catalyst showed excellent reusability(up to five uses)with consistently high levels of catalytic activity following its recovery by filtration.