Determination of coordination modes and estimation of the 31P-31P distances in heterogeneous catalyst by solid state double quantum filtered 31P NMR spectroscopy

To overcome the separation difficulty of the palladium-based homogeneous catalyst, the palladium complex can be anchored on various supports such as silica. However, it is difficult to determine the amounts of the two coordination modes of the Pd nucleus, that is, Pd coordinates with one phosphorus atom and Pd coordinates with two phosphorus atoms. Here a (31)P double-quantum filtered (DQ-filtered) method in solid-state NMR is introduced for the palladium-based heterogenous catalyst system. With the DQ-filtered method, we can not only determine the amounts of the two different kinds of palladium coordination modes, we can also estimate the interatomic distance of two (31)P nuclei bonded to a palladium nucleus. With the help of this method, we can quickly estimate interatomic distances in our designed system and accurately re-design the palladium system to accommodate either one (31)P or two (31)P.     

The polymer incarcerated method for the preparation of highly active heterogeneous palladium catalysts

A new method named "the polymer incarcerated (PI) method" for preparing a heterogeneous palladium catalyst has been developed. The method is operationally simple, and the Pd catalyst prepared (PI Pd) is highly active for hydrogenation, carbon-carbon, and carbon-oxygen bond-forming reactions. Remarkable points are that the activity of PI Pd is higher than that of homogeneous Pd catalysts and that PI Pd is recovered by simple filtration and reused several times without loss of activity. The catalyst is expected to replace many heterogeneous palladium catalysts, especially Pd/C, which is often used in academia and industry, but recovery of which is difficult.     

Solid-supported cross-coupling catalysts derived from homogeneous nickel and palladium coordination complexes

Solid-supported catalysts derived from homogeneous nickel(II) and palladium(II) non-symmetrical salen-type coordination complexes have been prepared and shown to be effective in the heterogeneous catalysis of carbon-carbon cross-coupling reactions. The nickel catalyst has been used in room-temperature Tamao-Kumada-Corriu reactions and the palladium catalyst in the Heck reaction at elevated temperatures. The complexes were prepared by improved methods and characterised by spectroscopic techniques. Comparisons between the solid-supported catalysts and their homogeneous analogues are reported. The single-crystal structure determination of the nickel and palladium complexes [M(salenac-OH)][M = Ni, Pd; salenac-OH = 9-(2',4'-dihydroxyphenyl)-5,8-diaza-4-methylnona-2,4,8-trienato](2-)] is reported.     

Role of polyaniline morphology in Pd particles dispersion. Hydrogenation of alkynes in the presence of Pd-polyaniline catalysts

Two polyaniline (PANI) samples of various molecular masses were used for the preparation of palladium catalysts (with 2 mass % of Pd). The physicochemical features of starting polyanilines were found to substantially affect the size and extent of palladium nanoparticles aggregation. Strongly aggregated large palladium particles appeared in the PANI sample of more compact morphology (PANI-H), higher crystallinity and lower specific surface area. Pd nanoparticles of a definitively smaller size were formed in the more amorphous PANI sample of looser morphology (PANI-L) and the extent of particles aggregation was markedly lower. The catalytic properties of Pd/PANI samples were studied in a liquid phase hydrogenation of unsaturated triple bond (C≡C) in alkynes reactants, phenylacetylene, and cyclohexylacetylene. The 2 mass % Pd/PANI-L catalyst prepared using polymer of less compact texture exhibited much higher activity in both reactions. In the presence of the 2 mass % Pd/PANI-L catalyst, alkene products were formed with a high selectivity (approximately 90 %) attained at the almost complete conversion of alkynes. This highly selective hydrogenation of the C≡C to the C=C bond was related to the presence of an electroactive polymer, PANI, in close proximity with Pd active sites. Polyaniline could have a role in a steric effect as well as in a modification of adsorptive properties of Pd centres.     

Preparation and Catalytic Performance of Carbon Nanotube Supported Palladium Catalyst

Two carbon nanotube supported palladium catalysts were prepared using a chemical reduction technique (Pd/CR‐CNT) and a conventional impregnation method (Pd/CNT) respectively, and their catalytic performances for Heck reaction were investigated. The catalysts were characterized by TEM and XPS techniques and the products were characterized by ¹H NMR. Research results showed that the (Pd/CR‐CNT) catalyst showed a better catalytic activity than the (Pd/CNT) catalyst, owing to better dispersion of palladium nanoparticles and stronger interaction between the active palladium species and carbon nanotube. Meanwhile, the product yield maintained 99.93% of its initial value at five‐times re‐use, compared with that at the first time use. The catalyst prepared with the chemical reduction method represented a better reusing performance.     

Mechanism of the solvent effect on the rate of the cyclohexene hydroxymethoxycarbonylation catalyzed by bis(triphenylphosphine)palladium

Kinetic data of the cyclohexene hydroxymethoxycarbonylation catalyzed by bis(triphenylphosphine) palladium Pd(PPh₃)₂ were processed and considered on the basis of the quantum-chemical calculations. By the method of density functional DFT PBE/3z we found that among the possible catalyst moleculs based on the tetrakis(triphenylphosphine)palladium the most stable is Pd(PPh₃)₂ with the coordination number of palladium equal 2. The interaction energy of Pd(PPh₃)₂ with acetone, acetonitrile, dichloroethane, 1,4-dioxane, nitromethane, and tetrahydrofuran calculated by PM3 method was found to correlate linearly with the reaction rate logarithm. The mechanism of the solvent effect on the reaction rate consists in a specific complexation with the catalyst depending on the molecule rigidity and the creation of energetic and steric constraints for the substrate to access the catalyst.     

钯催化CO/乙烯共聚配体和阴离子效应

由ＣＯ与乙烯共聚制备的聚酮高分子,属新型功能高分子材料,由于其具有良好的光降解性,避免了传统非降解材料对生态环境造成的白色污染,同时由价廉的ＣＯ代替５０ %的乙烯直接制备高附加值的聚酮高分子,节约了石油资源,合理精细的利用了煤资源和其它化学过程中副产的ＣＯ,符合近代化工对环保和资源的要求,因而在近二十年来得到了快速发展,目前Ｓｈｅｌｌ公司已有万吨级的工业化装置,并有少量产品上市．制备聚酮的关键技术是高效钯 (Ⅱ )催化剂,该催化剂一般以三元组合物的形式加入到聚合釜中［１］,(１)醋酸钯,(２)双膦配体 (Ｌ…     

Pd/MIL-101的制备及非均相催化吲哚C-H活化

水热合成MIL-101,过量浸渍法吸附Pd(OAc)_2,原位还原Pd~(2+)制得Pd/MIL-101催化剂.采用XRD、XPS、SEM、ICP、HRTEM和N_2吸/脱附实验对其结构进行表征,催化剂Pd纳米粒子尺寸在1.5~2.5 nm之间,含量为1.5%.催化实验表明,Pd/MIL-101能高效催化吲哚C_2位芳基化,对于活性较差的溴代芳烃,也能得到中等以上的收率,催化剂循环5次后仍能保持较高的反应活性,发展了吲哚C_2位衍生物的简单、高效的合成方法.     

纳米碳纤维负载钯催化剂在Heck反应中的应用——载体相互作用的影响

使用多元醇还原法制备了均匀分散的钯纳米颗粒.将钯纳米颗粒负载于板式、鱼骨式和管式纳米碳纤维,得到稳定、可重复使用的非均相催化剂.实验结果表明,钯纳米胶粒同载体之间的电位差对钯在载体上的负载量、粒子大小以及Heck反应中钯的溶失量有很大的影响.在制备过程中,增加钯纳米胶粒同纳米碳纤维表面的电位差能够大大降低钯在Heck反应中的流失.催化剂的反应活性随钯粒子的增大而降低.     

Preparation,structural characterization of a novel egg-shell palladium sulfide catalyst and its application in selective reductive alkylation reaction

A novel egg-shell Pd-S catalyst with palladium metal as the core and a membrane of palladium sulfide as the surface has been prepared by sulphidizing Pd/C with H₂S.This catalyst is effective for the reductive alkylation of p-amino diphenylamine（PADPA） and methylisobutyl ketone（MIBK） to afford N-（1,3-dimethylbutyl）-N′-phenyl-p-phenylenedianine（DBPPD） with conversion up to 99.42%and selectivity to 97.46%.Comparing with the other common palladium sulfide catalysts,the membrane of palladium sulfide on the surface and the core of palladium metal cause the Pd on the surface of the new catalyst in a lower sulfur coordination, which improves its activity.Our result indicates that this new egg-shell Pd-S/C is an efficient hydrogenation catalyst.     

Pyrazine Derivative as Supramolecular Host for Immobilization of Palladium Nanoparticles for Efficient Suzuki Coupling

Palladium nanoparticles (NPs) have been extensively explored as unique catalyst for carbon-carbon coupling reactions. Nonetheless, because of extreme tendency of nanoparticles to undergo agglomeration, the immobilization of these metal NPs on organic frameworks is an important area of research. The present investigation demonstrates the synthesis of pyrazine derivative PYZ - TA as a supramolecular host for holding co-released Pd NPs derived from the original catalyst (Pd(II)) under standard Suzuki coupling. Unprecedent, physical bars are not required to capture Pd NPs within the pores of supramolecular host. The as obtained catalyst PYZ - TA@Pd exhibits high potential to undergo self-assembly in solid as well as in liquid state. The PYZ - TA@Pd ensemble shows high catalytic activity and recyclability (up to seven cycles) in Suzuki-Miyaura coupling reactions using low palladium loading and provides the corresponding products in excellent yields (up to 98 %). Therefore, this study provides an efficient strategy to develop an easy to synthesize palladium centered solid catalyst through coordination between organic host and Pd NPs.     

Comparison between polyethylenglycol and imidazolium ionic liquids as solvents for developing a homogeneous and reusable palladium catalytic system for the Suzuki and Sonogashira coupling

The carbapalladacycle complex of 4-hydroxyacetophenone oxime is a highly active palladium catalyst to effect the Suzuki coupling of aryl chlorides and other C-C forming reactions in water. In an attempt to develop a reusable, homogeneous system based on this complex, its stability against prolonged heating in different ionic liquids and polyethylenglycol (PEG) has been studied. It was found that the palladium complex decomposes in water, 1-butyl-1-methylimidazolium hexafluorophosphate and 1-butyl-1-methylimidazolium chloride to form palladium nanoparticles in the first two cases and PdCl₄²⁻ in the third case. In contrast, this cyclic palladium complex was stable upon extended heating in 1-butyl-2,3-dimethylimidazolium hexafluorophosphate and in PEG. The activity of this complex for the Suzuki and Sonogashira correlates with the stability of the complex, the activity in PEG being higher than any of the ionic liquids tested. Although the carbapalladacycle complex also decomposes in PEG upon reaction, the resulting Pd nanoparticles (2-5 nm size) are stabilized by PEG acting as ligand. In this way, a reusable, homogeneous system in PEG has been developed that is able to effect the Suzuki and Sonogashira couplings without the need of copper and phosphorous ligands, working at the open air.     

Mizoroki–Heck and Suzuki–Miyaura reactions mediated by poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐stabilized magnetically separable palladium catalyst

The purpose of this work was to synthesize and characterize a new magnetic polymer nanosphere‐supported palladium(II) acetate catalyst for reactions requiring harsh conditions. In this regard, an air‐stable, moisture‐stable and highly efficient heterogenized palladium was synthesized by the coordination of palladium(II) acetate with poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐grafted modified magnetic nanoparticles with a core–shell structure. The structure of the newly developed catalyst was characterized using various techniques. The catalytic activity of the resultant nano‐organometallic catalyst was evaluated in Mizoroki–Heck and Suzuki–Miyaura reactions to afford the corresponding coupling products in good to excellent yields. High selectivity as well as outstanding turnover number (14 143, 4900) and turnover frequency (28 296, 7424) values were recorded for the catalyst in Suzuki–Miyaura and Mizoroki–Heck reactions, respectively. Magnetic separation and recycling of the catalyst for at least six runs became possible without any significant loss of efficiency or any detectable palladium leaching.     

The role of Pd nanoparticles in ionic liquid in the Heck reaction

Pd(0) nanoparticles with approximately 2 nm diameter, immobilized in 1-n-butyl-3-methylimidazolium hexafluorophosphate ionic liquid, are efficient catalyst precursors for coupling of aryl halides with n-butylacrylate. In situ TEM analysis of the ionic liquid catalytic solution after the catalytic reaction shows the formation of larger nanoparticles ( approximately 6 nm). The palladium content in the organic phase during the arylation reaction was checked by ICP-AS and shows significant metal leaching (up 34%) from the ionic phase to the organic phase at low substrate conversions and drops to 5-8% leaching at higher conversions. These results strongly suggest that the Pd(0) nanoparticles serve as a reservoir of "homogeneous" catalytic active species.     

Palladium nanoparticles stabilized by an ionic polymer and ionic liquid: a versatile system for C-C cross-coupling reactions

Highly stable palladium nanoparticles (Pd NPs), protected by an imidazolium-based ionic polymer (IP) in a functionalized ionic liquid (IL), have been prepared and characterized by transmission electron microscopy (TEM). These Pd NPs are excellent precatalysts for Suzuki, Heck, and Stille coupling reactions and can be stored without undergoing degradation for at least 2 years. The NP-IP-IL system may therefore be considered as an alternative to the traditional palladium on carbon (Pd/C) precatalyst employed in many C-C coupling reactions, also allowing reactions to be conducted under "solvent-free" conditions.     

超支化聚合物氮修饰Pd催化剂促进甲酸电催化氧化

通过原位聚合法制备了以超支化聚合物的氮修饰的PdN_x/C催化剂, 并考察了其催化甲酸电氧化反应的性能. 采用透射电子显微镜(TEM)、 X射线光电子能谱(XPS)和X射线衍射(XRD)等技术研究了氮的引入对催化活性组分Pd的形貌及表面电子形态的影响. 结果表明, 修饰氮后Pd纳米粒子粒径可稳定在2 nm, 并且保持了较高的分散度, 改善了表面Pd电子状态. 与Pd/C催化剂相比, 氮修饰的PdN₂₀/C用于甲酸电氧化的Pd单位质量比活性提高了10.9%.     

Synthesis of palladium nanoparticles by sonochemical reduction of palladium(II) nitrate in aqueous solution

The sonochemical synthesis of stable palladium nanoparticles has been achieved by ultrasonic irradiation of palladium(II) nitrate solution. The starting solutions were prepared by the addition of different concentrations of palladium(II) nitrate in ethylene glycol and poly(vinylpyrrolidone) (PVP). The resulting mixtures were irradiated with ultrasonic 50 kHz waves in a glass vessel for 180 min. The UV-visible absorption spectroscopy and pH measurements revealed that the reduction of Pd(II) to metallic Pd has been successfully achieved and that the obtained suspensions have a long shelf life. The protective effect of PVP was studied using Fourier transform infrared (FT-IR) spectroscopy. It has been found that, in the presence of ethylene glycol, the stabilization of the nanoparticles results from the adsorption of the PVP chain on the palladium particle surface via the coordination of the PVP carbonyl group to the palladium atoms. The effect of the initial Pd(II) concentration on the Pd nanoparticle morphology has been investigated by transmission electron microscopy. It has been shown that the increase of the Pd(II)/PVP molar ratio from 0.13 x 10(-3) to 0.53 x 10(-3) decreases the number of palladium nanoparticles with a slight increase in particle size. For the highest Pd(II)/PVP value, 0.53 x 10(-3), the reduction reaction leads to the unexpected smallest nanoparticles in the form of aggregates.     

Palladium Nanoparticles Supported on a Porous Organic Polymer: An Efficient Catalyst for Suzuki‐Miyaura and Sonogashira Coupling Reactions

A new porous organic polymer (POP) with high thermal stability and large surface area has been synthesized and applied in the preparation of Pd/POP catalyst. Pd/POP was characterized by XRD, TGA, SEM and TEM. The catalyst consists of highly dispersed palladium nanoparticles of 0.9–4 nm size on POP with a large surface area of 650 m²/g. It presents high catalytic activity for Suzuki‐Miyaura and Sonogashira reactions. The catalyst was reusable for three to five times without significant loss of activity.     

Preparation of N‐n‐Octyl‐D‐glucamine by the catalytic hydrogenation with palladium complex of MgO‐supported melamine‐formaldehyde polymer

The palladium complex of MgO‐supported melamine‐formaldehyde polymer catalyst was prepared and characterized by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The preparation of N‐n‐octyl‐D ‐glucamine was investigated by using this complex as the catalyst. It was found that the palladium complex of MgO‐supported melamine‐formaldehyde polymer has a good catalytic activity for the hydrogenation of n‐octylamine with D ‐glucose to produce N‐n‐octyl‐D ‐glucamine. The effects of additive, solvent, temperature, hydrogen pressure, Pd content in the catalyst and the amount of catalyst on the preparation of N‐n‐octyl‐D ‐glucamine have all been studied. Under the optimum experimental conditions—D ‐glucose, 37.2 mmol; n‐octylamine, 31 mmol; triethylamine, 1.0 ml; ethanol, 60 ml; temperature, 333 K; hydrogen pressure, 1.5 MPa; the amount of the catalyst (Pd content 3.55%, N/Pd molar ratio 12), 0.7 g—the highest yield of N‐n‐octyl‐D ‐glucamine (57.6%) was obtained. XRD results show that melamine‐formaldehyde polymer changed the structure of MgO, and XPS results suggest that coordination bonds were formed between the hexatomic ring and metal atom, and palladium particles were immobilized on the polymer. Copyright © 2004 John Wiley & Sons, Ltd.     

THE EFFECT OF MODIFICATION OF COORDINATING GROUPS ON THE CATALYTIC BEHAVIORS OF POLYMER CATALYSTS

Several polymer-supported palladium complex catalysts containing two different coordinatinggroups were prepared and the cooperative effect of the coordinating groups on the catalytic behaviorsof polymer catalysts was studied. It was found that poly(acrylic acid-co-acrylonitrile)-Pd complex(PAA-AN-Pd) is a more active and stable catalyst for hydrogenation than both poly(acrylic acid)-Pd and poly(acrylonitrile)-Pd complexes. A marked change of catalytic behaviors of poly(N-substituted maleamic acid-co-styrene)-Pd complexes was observed in comparison with poly(maleicacid-co-styrene)-Pd complex. Acetophenone was reduced to 1-phenyl ethanol by poly(N-phenylmaleamic acid-Co-styrene)-Pd complex (N-1-Pd), but ethylbenzene was obtained using poly(maleicacid-co-styrene)-Pd complex as a catalyst. The influence of solvents, additives and N/Pd gramatomic ratio on the catalytic behaviors of the polymer complexes was investigated.