Facile synthesis of palladium nanoparticles supported on silica: An efficient phosphine-free heterogeneous catalyst for Suzuki coupling in aqueous media

A convenient one-step method for synthesizing highly dispersed palladium nanoparticles supported on silica, without taking assistance from any external reductant or stabilizer, has been developed. The supported nanoparticles were characterized by N₂-adsorption desorption, XRD, HRTEM, SEM-EDX, XPS, ICP analyses and applied as catalyst for Suzuki-Miyaura reactions of aryl halides. The reactions with aryl bromides were performed in neat water at room temperature; while the reactions with aryl chlorides were conducted in aqueous-ethanol at 90 °C. The catalyst could be reused at least three times without compromising with its activity, however from the fourth cycle a progressive decrease in yield was noticed. No aggregation of NPs was observed by the TEM analysis of the six-time used catalyst.     

Palladium nanoparticles supported on Fe3O4/amino acid nanocomposite: Highly active magnetic catalyst for solvent-free aerobic oxidation of alcohols

In this paper, Fe₃O₄ nanoparticles were coated by a number of amino acids, e.g. cysteine, serine, glycine and β-alanine, via a simple method. Because of the surface modification of the magnetic nanoparticles with amino acid, the obtained magnetic nanocomposite is able to trap palladium nanoparticles through a strong interaction between the metal nanoparticles and the functional groups of amino acids. Among the synthesized nanocomposites, Fe₃O₄/cysteine-Pd exhibited the highest catalytic performance and excellent selectivity in the solvent-free aerobic oxidation of various alcohols, along with high level of reusability.     

2-Aminopyridine functionalized cellulose based Pd nanoparticles: An efficient and ecofriendly catalyst for the Suzuki cross-coupling reaction

A palladium catalyst supported on 2-aminopyridine functionalized cellulose was synthesized and fully characterized by inductively coupled plasma atomic emission spectroscopy, transmission electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectrometry. This catalyst can be applied in the Suzuki cross-coupling reaction of aryl halides with arylboronic acids in 50% ethanol to afford biaryls in good yields, and easily recycled by simple filtration after reaction without the loss of metal Pd.

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Palladium supported on amine-functionalized mesoporous silica: Highly efficient phosphine-free catalyst for alkyne–alkyne cross-coupling reaction

An amine-functionalized mesoporous silica SBA-15 supported palladium catalyst was prepared and characterized. For the first time, this supported palladium has been used as an efficient phosphine-free and reusable catalyst for the cross-coupling of haloalkynes with terminal alkynes. A variety of haloalkynes and aromatic/aliphatic terminal alkynes were selectively coupled to afford unsymmetrical 1,4-disubstituted 1,3-diynes in good yields.     

Wrinkled mesoporous carbon supported Pd nanoparticles for hydrogenation and aerobic oxidation reactions

Wrinkled mesoporous silica (WMS) was employed as a hard template to synthesize a carbon replica. The resulting carbon materials, wrinkled mesoporous carbon (WMC), retained the main structural features from the WMS, which has conical pores that radiate from the center of the spherical particle to the outer surface in all directions resulting in wrinkled shaped pore walls. This WMC material was used as a catalyst support for Pd nanoparticles. The Pd on WMC catalyst showed superior performance over commercial Pd on activated carbon for both styrene hydrogenation and the aerobic oxidation of benzyl alcohol.     

基于4,4'-联吡啶钯骨架多孔聚合物作为高效Suzuki偶联反应多相催化剂

一步法构筑了含4,4’-联吡啶钯骨架微孔聚合物材料催化剂HCP-(Bpy-Pd),通过SEM、IR和XRD等研究Pd引入方式对合成催化剂材料的形貌控制。N2吸附-脱附测试(BET)显示该催化剂具有丰富的微孔结构,比表面积达610.7 m2·g-1。HCP-(Bpy-Pd)催化剂在溴苯Suzuki偶联反应中表现出非常高的活性,80℃反应10 min,联苯产率达到99%,催化剂能够循环使用10次,通过一步法将联吡啶Pd引入催化剂骨架的方法具有重要的潜在应用价值。     

An efficient self-assembly Ru-Al material as heterogeneous catalyst for water oxidation

A self-assembly ruthenium material connected by Al^3 + ions (Ru-Al) was synthesized and used to catalyze water oxidation. This Ru-Al material displayed much better performance than its precursor and the free precursor mixed with Al^3 + ion on both efficiency and stability during the catalytic water oxidation period. Based on the catalytic metal center, a turnover number (TON) of more than 2100 was achieved.     

Pd nanoparticles supported on ZIF-8 as an efficient heterogeneous catalyst for the selective hydrogenation of cinnamaldehyde

Palladium nanoparticles supported on ZIF-8 (Pd/ZIF-8) were prepared by a facile impregnation method and characterized by XRD, TEM, ICP and N₂ adsorption. The prepared Pd/ZIF-8 catalyst exhibited excellent catalytic performance for the selective hydrogenation of cinnamaldehyde. The reaction solvents had great influences on the catalytic performance of the prepared Pd/ZIF-8 catalyst. Pd nanoparticles supported on ZIF-8 gave much higher catalytic activity and hydrocinnamaldehyde selectivity than those supported on other MOFs or the conventional inorganic supports. The prepared Pd/ZIF-8 catalyst could be reused at least four times without significant loss in activity and selectivity.     

Palladium complex embedded crosslinked polystyrene nanofibers as a green and efficient heterogeneous catalyst for coupling reactions

A simple and green chemical modification coupled with electrospinning technique has been developed to incorporate tetrakis(triphenylphosphine)palladium [Pd(PPh₃)₄] inside crosslinked polystyrene nanofibers (Pd@CPS) as an efficient and stable heterogeneous palladium catalyst. The catalytic activities and recyclabilities of the prepared Pd@CPS catalyst have been evaluated by using Suzuki and Heck reactions of various aromatic halides separately with phenylboronic acid and alkenes. The Pd@CPS exhibited high-catalytic activities for the Suzuki and Heck reactions of aromatic iodides to afford the products in excellent yields (coupling yields >88%). The catalytic activities and the nanofiber structure remained essentially unchanged even after recycling for five times. The high activities and stabilities of the prepared Pd@CPS catalyst can be attributed to the ultrafine fiber and embedment of palladium active species inside the nanofibers.     

Direct aerobic oxidation of primary alcohols to methyl esters catalyzed by a heterogeneous gold catalyst

Methyl esters can be produced in high yields by oxiding methanolic solutions of primary alcohols with dioxygen over a heterogeneous gold catalyst. The versatility of this new methodology is demonstrated by the fact that alkylic, benzylic and allylic alcohols, as well as alcohols containing an amine functionality are oxidized in good to excellent yields.     

Polymer encapsulation of metallophthalocyanines: efficient catalysts for aerobic oxidation of alcohols

Metallophthalocynines (MPcs) of iron, cobalt and copper have been successfully encapsulated for the first time on polystyrene matrix, rendering them highly dispersible in common organic solvents. These catalysts were characterised by diffuse reflectance UV–Vis as well as FT-IR spectroscopy. The encapsulated metallophthalocyanines (MCMPcs) were found to be stable and more active than their unencapsulated counterparts. These encapsulated catalysts showed enhanced activity for aerobic oxidation of alcohols mimicking cytochrome P-450 dependent mono oxygenases. These catalysts not only have high turnover frequencies but could be recovered quantitatively by simple filtration and reused without loss of activity.     

Solvent-free oxidation of alcohols catalyzed by an efficient and reusable heteropolyphosphatotungstate

With aqueous hydrogen peroxide as oxidant, secondary alcohols could be efficiently oxidized to ketones in the presence of hexadecyl trimethyl ammonium heteropolyphosphatotungstate ((n-C₁₆H₃₃N(CH₃)₃)₃[PW₄O₁₆]) under solvent-free conditions. The oxidation of alcohol over 0.5 mol% (based on molar amount of hydrogen peroxide) catalyst occurred at 90 °C to give the corresponding ketones with above 92% yield and 97% selectivity. The catalyst could be reused without loss of selectivity.     

Metal-catalyzed cross-coupling reactions with supported nanoparticles: Recent developments and future directions

The metal-catalyzed processes are ubiquitous in the modern organic synthesis toolbox. However, a continuous challenge has been related to the design of reactions from a sustainable viewpoint (e.g., easy recovery of the catalyst, ability to perform sequential steps in high yields, avoidance of high amounts of organic solvents). Supported nanocatalysts have prompted special interest because of the synergy involving eletronic and surface effects which can play key roles towards more sustainable processes. In this article, we comprehensively summarize the latest progress in cross-coupling reactions involving supported metal nanoparticles. A background to mechanisms and industrial application will also be presented.     

Co(II) coordinated metal-organic framework: An efficient catalyst for heterogeneous aerobic olefins epoxidation

An 8-connected, linear trinuclear cluster-based microporous metal organic framework (NH₄)₂[Co₃(Ina)(BDC)₃(HCOO)] (denoted as Co₃InaBDC₃, Ina = isonicotinate and BDC = 1,4-benzenedicarboxylate, CCDC is 935147) had been successfully synthesized by a facile hydrothermal synthesis method. The compound was extended through BDC linkers breadthwise and Ina linkers lengthways to the highly-connected framework. The Co₃InaBDC₃ was characterized through FT-IR, N₂ adsorption, XRD, TGA and SEM, and its characteristic structure was elucidated by single crystal X-ray diffraction. Using O₂ as oxidant, the Co₃InaBDC₃ was investigated as a good performed heterogeneous catalytic material for cyclooctene epoxidation. An extremely high turnover frequency (1370 h^− 1) for epoxycyclooctane was achieved, and Co₃InaBDC₃ exhibited excellent stabilities in 5 recycles without any loss of its catalytic performance.     

Zn-VCO3 hydrotalcite: A highly efficient and reusable heterogeneous catalyst for the Hantzsch dihydropyridine reaction

The Zn-VCO₃ hydrotalcite was found to be an excellent solid catalyst for the one-pot synthesis of triphenylpyridine-3,5-dicarboxamide via Hantzsch reaction of acetoacetanilide, ammonium hydroxide and various aromatic aldehydes. The combinatorial syntheses were achieved for the first time using hydrotalcite as a heterogeneous catalyst. The catalyst was active for the Hantzsch reaction in water at 60 °C. The products were isolated in good yields (85–93%) with short reaction times (2–3 h). The resulting substituted dihydropyridines were characterized and confirmed by ¹H and ¹³C NMR, FTIR, and HRMS spectral data and the solid catalyst was characterized by XRD, BET, SEM and TEM. The newly synthesized heterogeneous solid catalyst offers simple means for recovery and the isolated catalyst was reused for five rounds for the synthesis of compound 4a, without significant loss of catalytic activity. For all the other reactions carried out with the recycled catalyst, results were similar to with the fresh catalyst.     

Copper nanoparticles supported on CeO2 as an efficient catalyst for click reactions of azides with alkynes

Readily prepared copper nanoparticles supported on CeO₂ have been found to effectively catalyse the 1,3-dipolar cycloaddition (CuAAC) of a variety terminal alkynes and organic azides generated in situ from sodium azide and different organic halides furnishing the corresponding 1,2,3-triazoles in excellent yields. Cu nanoparticles supported on CeO₂ have been characterized by X-ray diffraction analysis, energy dispersive X-ray analysis, scanning electron microscope and transmission electron microscope. The salient features of the present protocol are shorter reaction time, mild reaction conditions, reusability of the catalyst, and applicability to a wide range of substrates.     

Palladium nanoparticles as reusable catalyst for the synthesis of N-aryl sulfonamides under mild reaction conditions

An efficient palladium nanoparticles-catalyzed N-arylation of sulfonamides and sulfonyl azides is described. This procedure serves as an active protocol for intermolecular C–N bond formation using Pd(OAc)₂ in PEG-400 under air. Aryl bromides and triflates react at 35°C, while aryl chlorides require heating to 50°C and give the desired products only in low yields. This reaction proceeds smoothly in acceptable yields using low catalyst loading.