Palladium nanoparticles immobilized on EDTA‐modified Fe3O4@SiO2 nanospheres as an efficient and magnetically separable catalyst for Suzuki and Sonogashira cross‐coupling reactions

In this study, a novel heterogeneous palladium catalyst was synthesized by anchoring palladium onto ethylenediaminetetraacetic acid (EDTA)‐coated Fe₃O₄@SiO₂ magnetic nanocomposite and used for the Suzuki and Sonogashira cross‐coupling reactions. The properties of the magnetic catalyst were characterized by FT‐IR, XRD, TEM, FE‐SEM, DLS EDX, XPS, N₂ adsorption‐desorption isotherm analysis, TGA, VSM, elemental analysis and the loading level of Pd in catalyst was measured to be 0.51 mmol/g by ICP. The catalyst was used in Suzuki cross‐coupling reactions of various aryl halides, including less reactive chlorobenzenes with phenylboronic acid without any additive or ligand under green conditions. Furthermore, we have reported this recyclable catalytic system for Sonogashira cross‐coupling reactions of various aryl halides (I, Br, Cl) under copper and ligand‐free conditions in the presence of DMF/H₂O (1:2/v:v) as a solvent. The magnetic catalyst could also be separated by an external magnet and reused six times without any significant loss of activity.     

Fe3O4‐SAHPG‐Pd0 nanoparticles: A ligand‐free and low Pd loading quasiheterogeneous catalyst active for mild Suzuki–Miyaura coupling and C?H activation of pyrimidine cores

This paper reports a green magnetic quasiheterogeneous efficient palladium catalyst in which Pd⁰ nanoparticles have been immobilized in self‐assembled hyperbranched polyglycidole (SAHPG)‐coated magnetic Fe₃O₄ nanoparticles (Fe₃O₄‐SAHPG‐Pd⁰). This catalyst has been used for effective ligandless Pd catalyzed Suzuki–Miyaura coupling reactions of different aryl halides with substituted boronic acids at room temperature and in aqueous media. Herein, SAHPG is used as support; it also acts as a reducing agent and stabilizer to promote the transformation of Pd^II to Pd⁰ nanoparticles. Also, this environmental friendly quasiheterogeneous catalyst is employed for the first time in the synthesis of new pyrimido[4,5‐b]indoles via oxidative addition/C? H activation reactions on the pyrimidine rings, which were obtained with higher yield and faster than when Pd(OAc)₂ was used as the catalyst. Interestingly, the above‐mentioned catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled several times with no significant decrease in the catalytic activity.     

Pd(0)‐ S‐propyl‐2‐aminobenzothioate immobilized onto functionalized magnetic nanoporous MCM‐41 as efficient and recyclable nanocatalyst for the Suzuki,Stille and Heck cross coupling reactions

The present work describes the use of Pd(0)‐ S‐propyl‐2‐aminobenzothioate Complex immobilized onto functionalized magnetic nanoporous MCM‐41(Fe₃O₄@MCM‐41@Pd‐SPATB) as efficient and recyclable nano‐organometallic catalyst for C–C bond formation between various aryl halides with phenylboronic acid (Suzuki reaction), aryl halides with triphenyltin chloride (Stille reaction), and aryl halides with n‐butyl acrylate (Heck reaction). All the reactions were carried out in PEG‐400 as green solvent with short reaction time and good to excellent yields. This catalyst was characterized by FT‐IR spectroscopy, XRD, TGA, VSM, ICP‐OES, TEM, EDX and SEM techniques. Ease of operation, high efficiency, recovery and reusability for five continuous cycles without significant loss of its catalytic activities or metal leaching are the noteworthy features of the currently employed heterogeneous catalytic system.     

Preparation and characterization of palladium immobilized on silica‐coated Fe3O4 and its catalytic performance for Suzuki reaction under microwave irradiation

Supported palladium catalyst (Pd/Fe₃O₄@SiO₂) was easily prepared by supporting PdCl₂ on silica‐coated magnetic nanoparticles Fe₃O₄ in ethylene glycol. The as‐prepared sample was characterized by infrared spectroscopy (IR), X‐ray diffraction (XRD) and X‐ray photoelectron spectrometer (XPS). The formation of active specie Pd(0) was confirmed by XRD and XPS, and the Pd loading for the fresh and recovered catalyst was determined by atomic absorption spectroscopy (AAS). Pd/Fe₃O₄@SiO₂ was employed for the synthesis of biphenyl derivatives via Suzuki reaction. In terms of the yield of biphenyl, the supported catalyst displayed nearly equal catalytic performance to that of homologous PdCl₂ under microwave irradiation for 30 min but higher than that obtained by traditional heating method for 12 h. The catalytic performance of Pd/Fe₃O₄@SiO₂ for Suzuki reactions involving various aryl halides and arylboronic acids were also examined. Impressive yield of biphenyl at 68.2% was obtained even in the presence of unreactive aryl chlorides. Pd/Fe₃O₄@SiO₂ was recovered by a permanent magnet and directly reused in the next run, and no obvious deactivation was observed for up to 6 times. Copyright © 2016 John Wiley & Sons, Ltd.     

Palladium–S‐propyl‐2‐aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)

A moisture‐ and air‐stable heterogenized palladium catalyst was synthesized by coordination of palladium with S‐propyl‐2‐aminothiobenzamide supported on Fe₃O₄ magnetic nanoparticles. The prepared nanocatalyst was characterized using Fourier transform infrared, energy‐dispersive X‐ray and inductively coupled plasma atomic emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, dynamic laser scattering and thermogravimetric analysis. This catalyst could be dispersed homogeneously in water or poly(ethylene glycol) and further applied as an excellent nano‐organometal catalyst for Suzuki and Heck reactions. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst was examined using hot filtration and inductively coupled plasma atomic emission spectroscopy. Also, the effects of various reaction parameters on the Suzuki and Heck reactions are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Hiyama cross‐coupling reaction using Pd(II) nanocatalyst immobilized on the surface of Fe3O4@SiO2

We report a simple process for the synthesis of Fe₃O₄@SiO₂/APTMS (APTMS = 3‐aminopropyltrimethoxysilane) core–shell nanocatalyst support. The new nanocatalyst was prepared by stabilization of Pd(cdha)₂ (cdha = bis(2‐chloro‐3,4‐dihydroxyacetophenone)) on the surface of the Fe₃O₄@SiO₂/APTMS support. The structure and composition of this catalyst were characterized using various techniques. An efficient method was developed for the synthesis of a wide variety of biaryl compounds via fluoride‐free Hiyama cross‐coupling reactions of aryl halides with arylsiloxane, with Fe₃O₄@SiO₂/APTMS/Pd(cdha)₂ as the catalyst under reaction conditions. This methodology can be performed at 100°C through a simple one‐pot operation using in situ generated palladium nanoparticles. High catalytic activity, quick separation of catalyst from products using an external magnetic field and use of water as green solvent are attributes of this protocol.     

Palladium nanoparticles immobilized on amphiphilic and hyperbranched polymer‐functionalized magnetic nanoparticles: An efficient semi‐heterogeneous catalyst for Heck reaction

To address the obstacles facing the use of palladium‐based homogeneous and heterogeneous catalysts in C─C cross‐coupling reactions, a novel semi‐heterogeneous support was developed based on hyperbranched poly(ethylene glycol)‐block ‐poly(citric acid)‐functionalized Fe₃O₄ magnetic nanoparticles (Fe₃O₄@PCA‐b ‐PEG). Because of the surface modification of the Fe₃O₄ nanoparticles with amphiphilic and hyperbranched polymers (PCA‐b ‐PEG), these hybrid materials are not only soluble in a wide range of solvents (e.g. water, ethanol and dimethylformamide) but also are able to trap Pd²⁺ ions via complex formation of free carboxyl groups of the PCA dendrimer with metal ions. The reduction of trapped palladium ions in the dendritic shell of Fe₃O₄@PCA‐b ‐PEG leads to immobilized palladium nanoparticles. The morphology and structural features of the catalyst were characterized using various microscopic and spectroscopic techniques. The catalyst was effectively used in the palladium‐catalysed Mizoroki–Heck coupling reaction in water as a green solvent. In addition, the catalyst can be easily recovered from the reaction mixture by applying an external magnetic field and reused for more than ten consecutive cycles without much loss in activity, exhibiting an example of a sustainable and green methodology.     

A new palladium complex supported on magnetic nanoparticles and applied as an catalyst in amination of aryl halides,Heck and Suzuki reactions

A simple, efficient and less expensive protocol for the phosphine-free C–C coupling reactions and synthesis of anilines in the presence of 2-aminobenzamide complex of palladium supported on Fe₃O₄ magnetic nanoparticles (Pd(0)-ABA-Fe₃O₄) has been reported. The Suzuki reaction was carried out in water or PEG using phenylboronic acid (PhB(OH)₂) or sodium tetraphenyl borate (NaBPh₄). Pd(0)-ABA-Fe₃O₄ has been found promising for Heck reaction of butyl acrylate, styrene or acrylonitrile with aryl halides (including Cl, Br and I). Also, Pd(0)-ABA-Fe₃O₄ has been found as efficient catalyst for the amination of aryl halides using aqueous ammonia. The products have been obtained in short reaction times and high yields. The catalyst was easily separated using an external magnet from the reaction mixture and reused for several runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst has been examined by hot filtration and ICP-OES technique. The nanomagnetical catalyst was characterized by FTIR, TGA, XRD, VSM, TEM, SEM, EDS, DLS and ICP-OES techniques.     

低温Suzuki反应合成联苯及三联苯化合物

发展了一个低温下无配体钯催化溴代芳烃与芳基硼酸的Suzuki反应体系。该体系以醋酸钯为催化剂,无水碳酸钾为碱,乙醇水溶液为溶剂,无需加入任何配体,在0oC下即可高效催化溴代芳烃与芳基硼酸的Suzuki反应;反应的底物容忍性好,产品分离收率最高达97%。以溴代芳基N-甲基亚氨基二乙酸硼酸酯为砌块分子,通过调控反应温度,实现了砌块分子选择性Suzuki反应,从而一锅合成了不对称三联苯化合物,产品收率最高为81%。     

Nanostructured Pyrophosphate Na2PdP2O7‐Catalyzed Suzuki‐Miyaura Cross‐Coupling Under Microwave Irradiation

Nanostructured palladium pyrophosphate (Na₂PdP₂O₇) catalyst was synthesized and well characterized by using different techniques (TGA, XRD, SEM, TEM....). This nanocatalyst exhibited excellent catalytic activity in the synthesis of biaryl compounds via Suzuki‐Miyaura cross‐coupling to produce their corresponding products in good to excellent yields under mild conditions. The catalyst is recyclable and was recycled for four runs for the reaction of 4‐bromoacetophenone with phenylboronic acid without appreciable loss of its catalytic activity.     

Cu(I)-anchored polyvinyl alcohol coated-magnetic nanoparticles as heterogeneous nanocatalyst in Ullmann-type C–N coupling reactions

In this paper, the preparation of a novel magnetic nanocatalyst (Fe₃O₄@PVA/CuCl) is described, which involves coating of polyvinyl alcohol (PVA) onto the surface of Fe₃O₄ nanoparticles and its subsequent coordination with CuCl catalyst. The nanocatalyst was characterized by various analytical methods, including Fourier-transform infrared, X-ray diffraction, inductively coupled plasma spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy, vibrating-sample magnetometry, and EDX elemental mapping. Moreover, the nanocatalyst was efficiently used in the N-arylation of amines via the formation of a carbon–nitrogen bond between the aryl halides and amines by Ullmann-type coupling reactions. The catalyst was sufficiently stable and can be reused for at least seven times in a model Ullmann reaction without remarkable alteration in its catalytic behavior. Heterogeneity of the catalyst was investigated by a hot filtration test.     

Fe3O4@SiO2@sulfated boric acid as superparamagnetic and recyclable nanocatalyst‐assisted,one‐pot,pseudo four‐component synthesis of 5‐amino‐2‐aryl‐3H‐chromeno[4,3,2‐de][1,6]naphthyridine‐4‐carbonitrile derivatives

The catalytic performance of the superparamagnetic nanocatalyst Fe₃O₄@SiO₂@Sulfated boric acid as a green, recyclable, and acidic solid catalyst in the synthesis of chromeno[4,3,2‐de][1,6]naphthyridine derivatives has been studied. Chromeno[4,3,2‐de][1,6]naphthyridine derivatives via a pseudo four‐component reaction from aromatic aldehydes (1 mmol), malononitrile (2 mmol), and 2′‐hydroxyacetophenone in the presence of Fe₃O₄@SiO₂@Sulfated boric acid (0.004 g) as a nanocatalyst in 3 mL of water as a green solvent at 80°C has been synthesized. The advantages of this method are higher product yields in shorter reaction times, easy recyclability and reusability of the catalyst, and easy work‐up procedures. The nanocatalyst was reused at least six times. The nanocatalyst retained its stability in the reaction, and after reusability, it was separated easily from the reaction by an external magnet.     

Synthesis and characterizations of N,N′‐bis(diphenylphosphino)‐2‐(aminomethyl)aniline derivatives: application of a palladium(II) complex as pre‐catalyst in Heck and Suzuki cross‐coupling reactions

The reaction of 2‐(aminomethyl)aniline with 2 equivalents of PPh₂Cl in the presence of Et₃N, proceeds in CH₂Cl₂ to give N,N′‐bis(diphenylphosphino)‐2‐(aminomethyl)aniline 1 in good yield. Oxidation of 1 with aqueous H₂O₂, elemental sulfur or gray selenium gave the corresponding oxide, sulfide and selenide dichalcogenides [Ph₂P(E)NHC₆H₄CH₂NHP(E)Ph₂] (E: O, 2a; S, 2b; Se, 2c), respectively. The reaction of [Ph₂PNHC₆H₄CH₂NHPPh₂] with PdCl₂(cod), PtCl₂(cod) and [Cu(MeCN)₄]PF₆ gave the corresponding chelate complexes, PdCl₂1, PtCl₂1 and [Cu(1)₂]PF₆. The new compounds were fully characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of the Pd(II) complex was tested in the Suzuki coupling and Heck reactions. The Pd(II) complex catalyzes the Suzuki coupling and Heck reaction, affording biphenyls and stilbenes respectively, in good yields. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrothermal CO2 Reduction by Glucose as Reducing Agent and Metals and Metal Oxides as Catalysts

High-temperature water reactions to reduce carbon dioxide were carried out by using an organic reductant and a series of metals and metal oxides as catalysts, as well as activated carbon (C). As CO₂ source, sodium bicarbonate and ammonium carbamate were used. Glucose was the reductant. Cu, Ni, Pd/C 5%, Ru/C 5%, C, Fe₂O₃ and Fe₃O₄ were the catalysts tested. The products of CO₂ reduction were formic acid and other subproducts from sugar hydrolysis such as acetic acid and lactic acid. Reactions with sodium bicarbonate reached higher yields of formic acid in comparison to ammonium carbamate reactions. Higher yields of formic acid (53% and 52%) were obtained by using C and Fe₃O₄ as catalysts and sodium bicarbonate as carbon source. Reactions with ammonium carbamate achieved a yield of formic acid up to 25% by using Fe₃O₄ as catalyst. The origin of the carbon that forms formic acid was investigated by using NaH¹³CO₃ as carbon source. Depending on the catalyst, the fraction of formic acid coming from the reduction of the isotope of sodium bicarbonate varied from 32 to 81%. This fraction decreased in the following order: Pd/C 5% > Ru/C 5% > Ni > Cu > C ≈ Fe₂O₃ > Fe₃O₄.     

Pd‐SBT@MCM‐41: As an efficient,stable and recyclable organometallic catalyst for C‐C coupling reactions and synthesis of 5‐substituted tetrazoles

A palladium S‐benzylisothiourea complex was anchored on functionalized MCM‐41 (Pd‐SBT@MCM‐41) and applied as efficient and reusable catalyst for the synthesis of 5‐substituted 1H –tetrazoles using [2 + 3] cycloaddition reaction of various organic nitriles with sodium azide (NaN₃) in poly(ethylene glycol) (PEG) as green solvent. Also this catalyst was applied as an versatile organometallic catalyst for Suzuki cross‐coupling reaction of aryl halides and phenylboronic acid (PhB(OH)₂) or sodium tetraphenyl borate (NaB(Ph)₄). This nanocatalyst was characterized by thermal gravimetric analysis (TGA), X‐ray Diffraction (XRD), scanning electron microscopy (SEM), inductively Coupled Plasma (ICP) and N₂ adsorption–desorption isotherms techniques. Recovery of the catalyst is easily achieved by centrifugation for several consecutive runs.     

Pd based on 2-Aminopyrimidine and 1H-benzo[d]imidazol-2-amine functionalizedFe3O4 nanoparticles as novel recyclable magnetic nanocatalysts for Ullmann coupling reaction

In this study, Pd based on 2-Aminopyrimidine and 1H-benzo[d]imidazol-2-amine functionalized Fe₃O₄ magnetic nanoparticles [(Pd-APM-PSi-Fe₃O₄) and (Pd-BIA-PSi-Fe₃O₄)] was designed and used for the synthesis of di aryl ether by Ulmann cross-coupling reactions. Ulmann reaction performed with mixing of the arylhalides and phenol derivatives in DMF solvent. The prepared catalysts were characterized with various analytical techniques such as FT-IR, XRD, TGA, SEM, TEM, EDX, ICP and VSM. Pd-APM-PSi-Fe₃O₄ and Pd-BIA-PSi-Fe₃O₄ catalysts demonstrated good to excellent yields catalytic efficiency for Ulmann reactions in comparison with to commercial palladium catalysts. The catalyst is easily recycled and reused without loss of the catalytic activity. The combined merits of reusable catalyst conditions make the condensation with safe operation, no leaching of pd into environment, low pollution, rapid access to products and simple workup. Also, these novel magnetic nanocatalysts are superior to the industry standard Pd in every relevant aspect. They feature a way higher initial activity, a much more convenient separation, better recycling, and less contamination of the products. Last but not least, they can be very easily prepared from commercially available Fe₃O₄ nanoparticles using standard laboratory equipment.     

Assembly immobilized palladium(0) on carboxymethylcellulose/Fe3O4 hybrid: An efficient tailor‐made magnetically catalyst for the Suzuki–Miyaura couplings

The Pd nanoparticles (Pd NPs) embedded on magnetically retrievable carboxymethylcellulose/Fe₃O₄ (Pd⁰@CMC/Fe₃O₄) organic/inorganic hybrid were prepared via the conventional simple process. The presence of the hydroxyl and carboxyl groups within the framework of the magnetic hybrid enables the facile preparation and stabilization of Pd NPs in this organic/inorganic hybrid. This hybrid catalyst was very effective in the Suzuki – Miyaura reaction of a variety of aryl halides with arylboronic acid to afford excellent product yields. The catalyst showed good stability and could be easily recovered with an external magnetic field and reused for several times without a significant loss in its catalytic activity. Furthermore, the Pd⁰@CMC/Fe₃O₄ hybrid catalyst was fully characterized by UV–Vis, FT–IR, XRD, SEM, EDX, TEM, XPS and TGA techniques. The hot filtration test suggests that a homogeneous mechanism is operative in Suzuki – Miyaura reaction.     

Room‐temperature Suzuki–Miyaura cross‐coupling reaction with α‐diimine Pd(II) catalysts

An α‐diimine Pd(II) complex containing chiral sec‐phenethyl groups, {bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dichloropalladium (rac‐ C1 ), was synthesized and characterized. rac‐ C1 was applied as an efficient catalyst for the Suzuki–Miyaura cross‐coupling reaction between various aniline halides and arylboronic acid in PEG‐400–H₂O at room temperature. Among a series of aniline halides, rac‐ C1 did not catalyze the cross‐coupling of aniline chlorides and fluorides but efficiently catalyzed the cross‐coupling of aniline bromides and iodides with phenylboronic acid. The catalytic activity reduced slightly with increasing steric hindrance of the aniline bromides. The complexes {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]‐2,3‐butadiene}dichloropalladium and {bis[N,N′‐(4‐fluoro‐2,6‐diphenylphenyl)imino]acenaphthene}dichloropalladium were also found to be efficient catalysts for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

Water‐Soluble and Recyclable Cyclopalladated Ferrocenylimine for Suzuki Coupling Reaction

A series of new water‐soluble cyclopalladated ferrocenylimines were designed and prepared. They were efficient catalyst for Suzuki coupling reactions of aryl bromides and phenylboronic acid in neat water under ambient atmosphere. Among of these catalysts, the catalyst ( C₂D ) could be reused for 6 times for the Suzuki coupling reaction of 4‐bromotoluene with phenylboronic acid in EtOH/H₂O under ambient atmosphere, in which no significant loss activity of C₂D was observed.     

Simple Electrodeposition of Dendritic Pd Without Supporting Electrolyte and Its Electrocatalytic Activity Toward Oxygen Reduction and H2O2 Sensing

Metallic palladium (Pd) electrocatalysts for oxygen reduction and hydrogen peroxide (H₂O₂) oxidation/reduction are prepared via electroplating on a gold metal substrate from dilute (5 to 50 mM) aqueous K₂PdCl₄ solution. The best Pd catalyst layer possessing dendritic nanostructures is formed on the Au substrate surface from 50 mM Pd precursor solution (denoted as Pd‐50) without any additional salt, acid or Pd templating chemical species. The Pd‐50 consisted of nanostructured dendrites of polycrystalline Pd metal and micropores within the dendrites which provide high catalyst surface area and further facilitate reactant mass transport to the catalyst surface. The electrocatalytic activity of Pd‐50 proved to be better than that of a commercial Pt (Pt/C) in terms of lower overpotential for the onset and half‐wave potentials and a greater number of electrons (n) transferred. Furthermore, amperometric i–t curves of Pd‐50 for H₂O₂ electrochemical reaction show high sensitivities (822.2 and ?851.9 µA mM^?1 cm^?2) and low detection limits (1.1 and 7.91 µM) based on H₂O₂ oxidation H₂O₂ reduction, respectively, along with a fast response (<1 s).