Selective alcohol oxidation to aldehydes and ketones over base-promoted gold–palladium clusters as recyclable quasihomogeneous and heterogeneous metal catalysts

Bimetallic gold–palladium clusters, with an average size of 1.9 nm and composed of 80 mol% gold, proved to be highly active and selective metal catalysts for the organic phase oxidation with O₂ of aliphatic, allylic and benzylic alcohols to the corresponding carbonyl products. Polyvinylpyrrolidone stabilized gold–palladium clusters dispersed in N,N-dimethylformamide emerged as promising quasihomogeneous metal catalysts for the oxidation of benzyl alcohol to benzaldehyde with full selectivity; they could be efficiently recycled with unaffected catalytic performance by solvent-resistant nanofiltration. Highly active and durable heterogeneous catalysts for the amide phase or solvent-free alcohol oxidation were prepared by the quantitative immobilization of the optimized gold–palladium clusters on the high surface area basic BaAl₂O₄ spinel support with preservation of the bimetallic clusters’ nanodispersion.     

Ionic liquid-containing polyethylene supported palladium: a green,highly efficient and stable catalyst for Suzuki reaction

The Suzuki coupling was carried out using a new, efficient and reusable polymer-supported Pd/IL catalyst (PEt@IL/Pd) under aqueous conditions. This catalyst was prepared through coacervation approach followed by treatment with Pd(OAc)₂. The FT-IR, SEM, TGA, TEM, XPS, ICP and EDX techniques were employed to characterize the PEt@IL/Pd. This catalyst exhibited high activity in the Suzuki coupling reaction under green conditions. Moreover, the catalyst could be recycled and reapplied for six times with no appreciable loss in its activity. The leaching test also showed high stability of catalytic Pd species under applied conditions.     

Hierarchical TiO2 microspheres supported ultrasmall palladium Nanocrystals: A highly efficient catalyst for Suzuki reaction

A hierarchical titanium dioxide microspheres-supported palladium catalyst (Pd/TiO₂-350) was prepared and characterized using BET, XRD, XPS, SEM, EDX, and TEM analyses. An ICP-OES analysis of Pd/TiO₂-350 further confirmed the successful Pd immobilization on TiO₂ with a palladium loading of 0.1 mmol g^?1. Pd/TiO₂-350 efficiently catalyzed the Suzuki-Miyaura reaction of aryl iodides with arylboronic acids to give the corresponding biaryl derivatives in good to excellent yields. After the reaction, the catalyst was recovered by centrifugation and reused three times without significant loss of its catalytic activity. Moreover, the loading of palladium species further decreased to 0.001 mol%, and the total turnover number and turnover frequency of the catalyst reached as high as 99 000 and 0.57 s^?1, respectively.     

Anchored palladium bipyridyl complex in nanosized MCM-41: a recyclable and efficient catalyst for the Kumada-Corriu reaction

A palladium bipyridyl complex anchored onto nanosized mesoporous silica MCM-41 catalyzed the cross-coupling of aryl iodides or bromides with Grignard reagents to provide the corresponding biaryls in high yields. The reaction proceeded smoothly with an equal molar amount of substrate and Grignard reagent in the presence of 0.2-0.02 mol % of catalyst in THF at 50 °C or under refluxing conditions. The catalyst prepared may be used in a very low percentage, recovered after reaction, and re-used.     

Macroporous magnetic poly(GMA-EGDMA-DVB) microspheres supported palladium complex as an efficient catalyst for Heck reaction

<正>Macroporous magnetic poly(GMA-EGDMA-DVB) microspheres synthesized by suspension polymerization were used as supports for palladium catalyst.The results showed the novel magnetic catalyst can promote Heck reaction of aryl halides with acrylic acid efficiently without an inert atmosphere.In addition,the novel catalyst can be conveniently recovered by applying an external magnet and reused at least five times without significant loss of its activity.     

高效可循环离子型钯配合物催化羰化Sonogashira反应

炔酮类化合物作为一类具有生物活性的分子,是天然产物全合成中构建杂环类化合物的重要中间体.炔酮类化合物的传统合成方法是通过过渡金属催化金属有机炔烃和酰氯的交叉偶联,但存在酰氯本身稳定性和底物官能团耐受力较差的缺点.近年来,钯催化的羰化Sonogashira反应(末端炔烃和芳基卤化物与CO的偶联反应)成为合成炔酮类化合物更为直接和有效的方法,其中与钯中心原子配位的配体的电子效应和空间效应可显著调控钯配合物的催化性能.但均相钯催化的羰化Sonogashira反应体系存在催化剂流失、分离困难和难以循环使用的问题.我们以2-(1-咪唑基)噻唑为母体分子,合成了具有P,S,N杂合配体特征的配体L1,同时将配体L1通过与MeOTf的季铵化反应得到相应的离子型膦配体L2.在此基础上,利用L1和L2与过渡金属中心的配位作用合成相应的钯配合物1A和2A.由于L1和L2中含有多种不同配位能力的配体(P-配体,S-配体和/或N-配体),故通过N/S杂原子对Pd-中心原子的协同弱配位作用,可以调变相应钯配合物对羰化Sonogashira反应的催化性能.另外,2A中具有强吸电子效应的正电荷的存在,使其结构和催化性能也必然不同于中性配合物1A.实验结果表明,在温和的反应条件(90℃,lh,CO压强1.0 MPa)下,对于碘苯和苯乙炔的羰化Sonogashira偶联反应,1A体现出优于2A的催化性能,TOF值达到840 h-1;但反应温度提高到120℃时,1A的TOF高达3560 h-1,2A的TOF为2960 h-1.与L1的2JP-Se=744 Hz相比,L2的2JP-Se=768 Hz,说明L2中具有吸电子效应的正电荷的存在降低了相应P原子的σ给电子能力(2JP-Se数值越大,相应膦配体的6给电子能力越弱);同时,1A中具有弱配位能力的N配体的缺失削弱了配体对Pd活性中心的稳定作用.在底物普适性研究中发现,4-硝基溴苯在相同反应条件下几乎得不到羰化Sonogashira偶联产物.而将反应体系中的CO换为同样压强下的N2,却可以顺利实现Sonogashira偶联反应.我们推测,在CO氛围下形成的pd0-CO活性物种(与N2氛围下形成的Pd0活性物种相比)具有相对较低的对底物的氧化加成能力.离子型钯配合物2A的优势在于,当将其与室温离子液体[Bmim]PF6(溶剂)结合使用,在2A催化碘苯与苯乙炔的羰化Sonogashira偶联反应过程中,循环使用8次催化性能没有明显下降.     

聚多巴胺功能化硅胶沉积单分散Pd纳米粒子的简易原位合成及用作醇需氧氧化反应的多相可循环使用的纳米催化剂（英文）

本文报道了一种不使用任何稳定剂或还原剂,原位合成硅胶/聚多巴胺复合物(SiO_2/PDA)负载的Pd纳米颗粒(Pd NPs)的简易方法.该方法先将PDA涂覆的SiO_2颗粒浸在Pd镀液中,然后利用PDA中含N基团的还原能力将Pd物种原位还原为纳米簇合物.并采用高分辨透射电镜、前场扫描电镜、能量散射谱、X射线衍射、X射线光电子能谱、诱导耦合等离子体和红外光谱等手段对所得纳米复合物的结构、形貌和物化性质进行了表征.被PDA基团锚合的Pd NPs具有显著的小颗粒(30–40 nm)特性.作为一个可循环使用的纳米催化剂,SiO_2/PDA/Pd NPs在醇的需氧氧化反应中表现出高活性.另外,催化剂经回收和多次重复使用时未出现明显的失活.     

N-Doped porous carbon supported palladium nanoparticles as a highly efficient and recyclable catalyst for the Suzuki coupling reaction

A new catalyst, Pd particles supported on the N-doped porous carbon(PC) derived from Zn-based metal–organic frameworks(zeolitic imidazolate framework: ZIF-8), was successfully prepared for the first time.The as-prepared catalyst was designated as N-doped PC-Pd, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscope, N_2 adsorption and inductively coupled plasma atomic emission spectroscopy. The N-doped PC-Pd composite exhibited high catalytic activity toward the Suzuki–Miyaura cross-coupling reactions. The yields of the products were in the range of 90%–99%. The catalyst could be readily recycled and reused at least 6 consecutive cycles without a significant loss of its catalytic activity.     

Eumelanin as a support for efficient palladium nanoparticle catalyst for Suzuki coupling reaction of aryl chlorides in water

Eumelanin-supported palladium (Pd) nanoparticle (NP) catalysts was found to exhibit excellent catalytic activities with high turnover number (TON, 2000) and turnover frequency (TOF, 1000 h^?1) for Suzuki cross coupling reaction of aryl chlorides in water. We propose that the amphiphilic property of the eumelanin support helps Pd NPs to catalyse the C–C coupling reaction in water through hydrophobic effect.     

Studies of the oxidation of palladium complexes by the advanced oxidation process Pretreatment of model catalysts for precious metal analysis

The advanced oxidation process (AOP) for the pretreatment of model palladium catalysts has been studied. Most standard metal analysis techniques are for metal ions free of organic ligands. Spent palladium catalysts contain organic ligands that need to be removed prior to analysis. AOP uses a combination of hydrogen peroxide and UV light to generate radicals that decompose such ligands, freeing up metals for further analysis. Palladium acetate Pd(OAc)₂, palladium acetylacetonate Pd(acac)₂, and tris(dibenzylideneacetone)dipalladium (Pd₂(dba)₃) were chosen as model precious metal catalysts for investigation. AOP was found to decompose ligands in Pd(OAc)₂, Pd(acac)₂ and give accurate Pd(II) quantification, while ligand decomposition and oxidation of Pd(0) to Pd(II) were demonstrated in treatments involving Pd₂(dba)₃. The effects of solubility of the palladium complexes, continuous addition of H₂O₂ during AOP treatments, sample pH, concentration of H₂O₂, and length of UV irradiation are reported.     

A novel palladium catalyst for the synthesis of hydrogen peroxide from carbon monoxide, water and oxygen

The synthesis of hydrogen peroxide from carbon monoxide, water and oxygen in a biphasic system using palladium complexes with bidentate nitrogen ligands as catalysts was investigated. After testing a series of phenanthroline derivatives, 2,9-dimethyl-4,7-diphenylphenanthroline (8) was selected as the most efficient ligand. The palladium complex with ligand 8 showed high stability and catalytic activity (turnover number up to 600 moles of hydrogen peroxide per mole of palladium per hour) and, on the basis of a preliminary study, carried out in continuous operation mode, it appears a promising catalyst for the development of an industrial process.     

A novel fumed silica-supported nitrogenous platinum complex as a highly efficient catalyst for the hydrosilylation of olefins with triethoxysilane

A novel fumed silica-supported nitrogenous platinum complex was conveniently prepared from cheap γ-aminopropyltriethoxysilane via immobilization on fumed silica in toluene, followed by a reaction with hexachloroplatinic acid. The title complex was characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the complex is an efficient and stable catalyst for the hydrosilylation of olefins with triethoxysilane. The title platinum complex could be separated by simple filtration and reused several times without any appreciable loss in the catalytic activity.     

Highly efficient Wacker oxidation catalyzed by heterogeneous Pd montmorillonite under acid-free conditions

Palladium-montmorillonite was proven to be highly efficient for the Wacker oxidation of terminal olefins to the corresponding methyl ketones. The catalyst was reusable while maintaining high activity and selectivity.     

Bis-chelate tetracarbene palladium(II) complex as an efficient and recyclable catalyst precursor for Heck reaction

A homoleptic Pd(II) complex with two chelating di-N-heterocyclic carbene (NHC) ligands has been synthesized and its square planar molecular geometry has been determined by X-ray diffraction analysis. The complex proved to be an efficient catalyst having exceedingly high turnover number and good reusability in Heck reaction.     

Allylation of 1-phenyl-1-propyne with N- and O-pronucleophiles using polymer supported triphenylphosphine palladium complex as a heterogeneous and recyclable catalyst

Simple methodology for the allylation of various N- and O-pronucleophiles with 1-phenyl-1-propyne as an allylating agent, using PS-TPP-Pd (polymer supported triphenylphosphine palladium) as a highly active heterogeneous recyclable catalyst has been developed. The protocol is applicable for a wide variety of hindered and functionalized aromatic amines, alcohols, and carboxylic acids. The catalyst exhibited remarkable catalytic activity for five consecutive recycles.     

A highly efficient and recyclable fluorous palladium catalyst for Heck reactions in water

Abstract  

A fluorous nano-palladium catalyst has been synthesized and characterized. The catalyst is highly active for the Heck reaction of aryl halides with substituted styrenes in water under air. The corresponding Heck products were obtained in high yields with good stereoselectivity (E/Z up to 98:2). In addition, the catalyst could be recovered by fluorous liquid–liquid separation and reused four times without significant loss of activity or stereoselectivity.     

MCM-41-supported bidentate phosphine palladium(0) complex: a highly active and recyclable catalyst for the Sonogashira reaction of aryl iodides

The first MCM-41-supported bidentate phosphine palladium(0) complex has been prepared. This complex is a highly efficient catalyst for Sonogashira reaction and can be reused at least 10 times without any decrease in activity.     

An ionic liquid-coordinated palladium complex: a highly efficient and recyclable catalyst for the Heck reaction

[structure: see text] The monoquaternary product of 2,2'-biimidazole with iodobutane is an ionic liquid that acts as both the solvent and ligand for catalytic reactions. A new palladium complex was prepared by adding PdCl(2) to this ionic liquid to form a catalytic solution that is effective for Heck reactions with good recyclability.     

A highly efficient catalyst for Suzuki coupling of aryl halides and bromoarylphosphine oxides

The biphenyl-based phosphine, P(o-C₆H₄C₆H₄Me)Ph₂, is a moderately bulky and electron-rich phosphine, which has been successfully applied to the palladium catalyzed Suzuki coupling of activated and deactivated aryl halides as well as bromoarylphosphines and bromoarylphosphine oxides, with low catalyst loading and good to excellent conversions and turnovers.     

Nitrite-containing resin as an efficient and recyclable catalyst for aerobic oxidation of oximes to carbonyl compounds

Using novel nitrite-containing resin as an NO source and Amberlyst-15 as cocatalyst, we developed aerobic oxidation of oximes to corresponding carbonyl compounds with molecular oxygen as a clean oxidant reagent. It was distinguished from the previous related reports, and the experimental results indicated that additional water obviously decreased the yield. This process provides a better choice for oxidative deoximation with many advantages, such as high yield, simple procedure, high catalytic performance, and recyclable catalyst.