Buchwald‐Hartwig amination reaction of aryl halides using heterogeneous catalyst based on Pd nanoparticles decorated on chitosan functionalized graphene oxide

In this work, graphene oxide was functionalized with chitosan (GO‐Chit) followed by a simple approach for immobilization of palladium nanoparticles onto a chitosan grafted graphene oxide surface. The Pd‐nanocomposite (GO‐Chit‐Pd) was characterized using Transmission Electron Microscopy (TEM), Fourier transforms infrared spectroscopy (FT‐IR), and X‐ray diffraction (XRD) measurements. The catalytic activity of the prepared heterogeneous graphene oxide functionalized chitosan‐palladium (GO‐Chit‐Pd) was investigated in term of C‐N coupling reaction (Buchwald‐Hartwig amination reaction of aryl halides) yielding products of N‐arylamines. The easy purification, convenient operation, and environmental friendliness, combined with a high yield, render this method viable for use in both laboratory research and larger industrial scales. Studying the reusability of the catalyst in this work showed that it could be reused for five times without obvious loss in catalytic activity.     

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.     

Heck and oxidative boron Heck reactions employing Pd(II) supported amphiphilized polyethyleneimine‐functionalized MCM‐41 (MCM‐41@aPEI‐Pd) as an efficient and recyclable nanocatalyst

A novel nanocatalyst was developed based on covalent surface functionalization of MCM‐41 with polyethyleneimine (PEI) using [3‐(2,3‐Epoxypropoxy)propyl] trimethoxysilane (EPO) as a cross‐linker. Amine functional groups on the surface of MCM‐41 were then conjugated with iodododecane to render an amphiphilic property to the catalyst. Palladium (II) was finally immobilized onto the MCM‐41@PEI‐dodecane and the resulted MCM‐41@aPEI‐Pd nanocatalyst was characterized by FT‐IR, TEM, ICP‐AES and XPS. Our designed nanocatalyst with a distinguished core‐shell structure and Pd²⁺ ions as catalytic centers was explored as an efficient and recyclable catalyst for Heck and oxidative boron Heck coupling reactions. In Heck coupling reaction, the catalytic activity of MCM‐41@aPEI‐Pd in the presence of triethylamine as base led to very high yields and selectivity. Meanwhile, the MCM‐41@aPEI‐Pd as the first semi‐heterogeneous palladium catalyst was examined in the C‐4 regioselective arylation of coumarin via the direct C‐H activation and the moderate to excellent yields were obtained toward different functional groups. Leaching test indicated the high stability of palladium on the surface of MCM‐41@aPEI‐Pd as it could be recycled for several runs without significant loss of its catalytic activity.     

A new strategy to design a graphene oxide supported palladium complex as a new heterogeneous nanocatalyst and application in carbon–carbon and carbon‐heteroatom cross‐coupling reactions

The palladium nanoparticles were successfully stabilized with an average diameter of 6–7 nm through the coordination of palladium and terpyridine‐based ligands grafted on graphene oxide surface. The graphene oxide supported palladium nanoparticles were thoroughly characterized and applied as an efficient heterogeneous catalyst in carbon–carbon (Suzuki‐Miyaura, Mizoroki‐Heck coupling reactions) and carbon–heteroatom (C‐N and C‐O) bond‐forming reactions. The catalyst was simply recycled from the reaction mixture and was reused consecutive four times with small drop in catalytic activity.     

Silica–acetylacetone‐supported palladium nanoparticles as an efficient and reusable catalyst in the Heck–Mizoroki C–C cross‐coupling reaction

The preparation of palladium nanoparticles supported on acetylacetone‐modified silica gel and their catalytic application for Heck olefination of aryl halides were investigated. The catalyst was characterized using X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission and scanning electron microscopies. The supported palladium nanoparticles are demonstrated to be a highly active and reusable catalyst for the Heck reaction. Several reaction parameters, including type and amount of solvent and base, were evaluated. The heterogeneity of the catalytic system was investigated with results indicating that there is a slight palladium leaching into the reaction solution under the applied reaction conditions. Despite this metal leaching, the catalyst can be reused nine times without significant loss of catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon nanospheres with well‐controlled nano‐morphologies as support for palladium‐catalyzed Suzuki coupling reaction

Uniform carbon nanospheres (UCS) with well‐controlled nano‐morphologies were fabricated by hydrothermal carbonization of sucrose in the presence of kayexalate. Highly dispersed and ultrafine palladium nanoparticles were supported on the UCS through a facile co‐reduction process with NaBH₄ as reducing agent. The obtained Pd@UCS exhibited efficient catalytic activity for the Suzuki coupling reaction. Moreover, the as‐prepared catalyst could be recycled and reused at least five times without significant loss of its catalytic activity.     

Magnetite tethered mesoionic carbene‐palladium (II): An efficient and reusable nanomagnetic catalyst for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions in aqueous medium

In this paper, a highly active, air‐ and moisture‐stable and easily recoverable magnetic nanoparticles tethered mesoionic carbene palladium (II) complex (MNPs‐MIC‐Pd) as nanomagnetic catalyst was successfully synthesized by a simplistic multistep synthesis under aerobic conditions using commercially available inexpensive chemicals for the first time. The synthesized MNPs‐MIC‐Pd nanomagnetic catalyst was in‐depth characterized by numerous physicochemical techniques such as FT‐IR, ICP‐AES, FESEM, EDS, TEM, p‐XRD, XPS, TGA and BET surface area analysis. The prepared MNPs‐MIC‐Pd nanomagnetic catalyst was used to catalyze the Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions and exhibited excellent catalytic activity for various substrates under mild reaction conditions. Moreover, MNPs‐MIC‐Pd nanomagnetic catalyst could be easily and rapidly recovered by applying an external magnet. The recovered MNPs‐MIC‐Pd nanomagnetic catalyst exhibited very good catalytic activity up to ten times in Suzuki–Miyaura and five times in Mizoroki–Heck cross‐coupling reactions without considerable loss of its catalytic activity. However, MNPs‐MIC‐Pd nanomagnetic catalyst shows notable advantages such as heterogeneous nature, efficient catalytic activity, mild reaction conditions, easy magnetic work up and recyclability.     

Palladium chloride anchored on organic functionalized MCM‐41 as a catalyst for the Heck reaction

Palladium chloride was grafted to amino‐functionalized MCM‐41 to prepare heterogeneous catalysts. XRD, N₂ adsorption–desorption isotherms, IR, ¹³C and ²⁹Si cross‐polarization magic‐angle spinning NMR spectroscopy and XPS techniques were employed to characterize the catalytic materials. The heterogeneous palladium catalyst exhibited excellent catalytic activity for the Heck vinylation of iodobenzene with methyl acrylate, giving 92% yield of methyl cinnamate in the presence of N‐methylpyrrolidone (NMP) and triethylamine (Et₃N). The stability of the heterogeneous catalyst was also studied in detail. The catalytic tests showed that the palladium leaching correlated to solvent, base and palladium loading. The heterogeneous catalyst exhibited excellent stability towards loss of activity and palladium leaching was not observed during six recycles in the presence of toluene and Na₂CO₃. Copyright © 2007 John Wiley & Sons, Ltd.     

Nano tetraimine Pd(0) complex as an efficient catalyst for phosphine‐free Suzuki reaction in water and copper‐free Sonogashira reaction under aerobic conditions

A nano tetraimine Pd(0) complex catalyst was successfully used as an efficient heterogeneous catalyst for the phosphine‐free palladium‐catalysed Suzuki coupling reaction in water at 80 °C. This nano tetraimine Pd(0) complex was also used for copper‐free Sonogashira reaction in dimethylformamide at 100 °C. The catalyst was easily recovered from the reaction mixture by centrifugation and reused for at least six cycles without any significant loss in its catalytic activity. Analysis of the reaction mixture using inductively coupled plasma analysis showed that leaching of palladium from the catalyst was negligible. The reactions can be performed efficiently for aryl iodides, bromides and also chlorides. Copyright © 2016 John Wiley & Sons, Ltd.     

Palladium nanoparticles deposited on a graphene–benzimidazole support as an efficient and recyclable catalyst for aqueous‐phase Suzuki–Miyaura coupling reaction

Graphene oxide was functionalized with benzimidazole for palladium immobilization. The resultant graphene–benzimidazole‐supported palladium composite (G‐BI‐Pd) was characterized using infrared and Raman spectroscopies, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. G‐BI‐Pd showed excellent catalytic activity and fast reaction kinetics in the aqueous‐phase Suzuki–Miyaura reaction of aryl iodides and bromides with phenylboronic acid under relatively mild conditions (5–25 min, 80 °C). The catalyst can be used several times without any significant loss of its catalytic activity.     

Copper‐ and phosphine‐free Sonogashira coupling reaction catalyzed by silica–(acac)‐supported palladium nanoparticles in water

A palladium‐based catalyst supported on acac‐functionalized silica was used as a heterogeneous catalyst for the Sonogashira cross‐coupling reaction of various aryl halides and phenylacetylene under copper‐ and phosphine‐free conditions. This catalytic system serves as an efficient and stable catalyst for this cross‐coupling reaction and allows easy separation and recycling of the catalyst. The catalyst could be recycled for five runs without appreciable loss of its catalytic activity. In addition, the reaction was carried out in water as a green solvent. Copyright © 2014 John Wiley & Sons, Ltd.     

Urea‐based amphiphilic porous organic polymer‐supported palladium as a reusable catalyst for Suzuki–Miyaura coupling and hydroxycarbonylation reactions in water

The development of environmentally friendly heterogeneous catalysts for organic reactions in water is becoming of growing importance for the development of sustainable processes. In this work, a porous organic polymer‐supported palladium catalyst (Pd@UPOP‐1) was successfully fabricated from 3,3′‐diaminobenzidine and methylenediphenyl diisocyanate through a facile urea‐forming condensation reaction. The structure and composition of the catalyst were characterized using several physicochemical methods. Pd@UPOP‐1 was found to possess good porous structure and excellent amphiphilicity. Under mild reaction conditions, the catalyst showed excellent catalytic activity and good substrate compatibility for the Suzuki–Miyaura coupling reaction of aryl bromides, as well as the hydroxycarbonylation reaction of aryl iodides. In addition, the catalyst could be used for several consecutive recycles in both cases.     

Finely dispersed palladium on silk‐fibroin as an efficient and ligand‐free catalyst for Heck cross‐coupling reaction

A palladium–fibroin complex (Pd/Fib.) was prepared by the addition of sonicated fibroin fiber in water to palladium acetate solution. Pd (OAc)₂ was absorbed by fibroin and reduced with NaBH₄ at room temperature to the Pd(0) nanoparticles. Powder‐X‐ray diffraction, scanning electron microscopy–energy‐dispersive X‐ray spectroscopy, Fourier transform‐infrared, CHN elemental analysis and inductively coupled plasma‐atomic emission spectroscopy were carried out to characterize the Pd/Fib. catalyst. Catalytic activity of this finely dispersed palladium was examined in the Heck coupling reaction. The catalytic coupling of aryl halides (‐Cl, ‐Br, ‐I) and olefins led to the formation of the corresponding coupled products in moderate to high yields under air atmosphere. A variety of substrates, including electron‐rich and electron‐poor aryl halides, were converted smoothly to the targeted products in simple procedure. Heterogeneous supported Pd catalyst can be recycled and reused several times.     

Palladium‐anchored multidentate SBA‐15/di‐urea nanoreactor: A highly active catalyst for Suzuki coupling reaction

Modification of mesoporous silica was carried out by reaction of SBA‐15 with di‐urea‐based ligand. Next, with the help of this ligand, palladium ions were anchored within the multidentate SBA‐15/di‐urea pore channels with high dispersion. The SBA‐15/di‐urea/Pd catalyst was characterized using various techniques. Theoretical calculations indicated that each palladium ion was strongly interacted with one nitrogen and two oxygen atoms from the multidentate di‐urea ligand located in SBA‐15 channels and these interactions remained during the catalytic cycle. These results are in good agreement with those of hot filtration test: the palladium ions have very high stability against leaching from the SBA‐15/di‐urea support. The catalytic performance of SBA‐15/di‐urea/Pd nanostructure was examined for the Suzuki coupling reaction of phenylboronic acid and electronically diverse aryl halides under mild conditions with a minimal amount of Pd (0.26 mol%). Compared to previous reports, this protocol afforded some advantages such as short reaction times, high yields of products, catalyst stability without leaching, easy catalyst recovery and preservation of catalytic activity for at least six successive runs.     

Novel palladium nanoparticles supported on β‐cyclodextrin@graphene oxide as magnetically recyclable catalyst for Suzuki–Miyaura cross‐coupling reaction with two different approaches in bio‐based solvents

A novel nanocatalyst was designed and prepared. Initially, the surface of magnetic graphene oxide (M‐GO) was modified using thionyl chloride, tris(hydroxymethyl)aminomethane and acryloyl chloride as linkers which provide reactive C═C bonds for the polymerization of vinylic monomers. Separately, β‐cyclodextrin (β‐CD) was treated with acryloyl chloride to provide a modified β‐CD. Then, in the presence methylenebisacrylamide as a cross‐linker, monomers of modified β‐CD and acrylamide were polymerized on the surface of the pre‐prepared M‐GO. Finally, palladium acetate and sodium borohydride were added to this composite to afford supported palladium nanoparticles. This fabricated nanocomposite was fully characterized using various techniques. The efficiency of this easily separable and reusable heterogeneous catalyst was successfully examined in Suzuki–Miyaura cross‐coupling reactions of aryl halides and boronic acid as well as in modified Suzuki–Miyaura cross‐coupling reactions of N‐acylsuccinimides and boronic acid in green media. The results showed that the nanocatalyst was efficient in coupling reactions for direct formation of the corresponding biphenyl as well as benzophenone derivatives in green media based on bio‐based solvents. In addition, the nanocatalyst was easily separable, using an external magnet, and could be reused several times without significant loss of activity under the optimum reaction conditions.     

Carboxymethylcellulose‐supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand‐ and base‐free Heck–Matsuda and Suzuki–Miyaura couplings

A novel palladium(II) carboxymethylcellulose (CMC‐Pd^II) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl₂ in aqueous solution. Its catalytic activities were explored for Heck–Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki–Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross‐coupling products in good to excellent yields under atmospheric conditions. The CMC‐Pd^II and carboxymethylcellulose‐supported palladium nanoparticles (CMC‐Pd⁰) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC‐Pd⁰ catalyst was confirmed via Hg(0) and CS₂ poisoning tests. Moreover, the CMC‐Pd⁰ catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki–Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright © 2015 John Wiley & Sons, Ltd.     

Palladium‐catalyzed carbonylation of quaternary ammonium halides to tertiary amides

Catalytic carbonylation of quaternary ammonium salts under anhydrous conditions was investigated using palladium catalyst. The carbonylation of tetramethylammonium iodide was chosen as a model reaction and studied systematically. Ligand‐free PdCl₂ showed efficient catalytic performance for this transformation. A palladium catalyst loading as low as 0.05 mol% was sufficient for high yield (96.9%) of N,N‐dimethylacetamide, corresponding to a turnover frequency of 242 h^?1. Under optimum conditions, several other quaternary ammonium halides were also carbonylated to corresponding tertiary amides in moderate to excellent yields. The catalytic activity of commercial palladium on activated carbon (Pd/C) catalyst was also evaluated. The Pd/C catalyst exhibited high activity for this carbonylation reaction and could be recycled six times with a slight decrease in activity. Furthermore, mechanistic considerations concerning Pd‐catalyzed carbonylation of quaternary ammonium halides were also discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Fabrication of Nitrogen‐Doped Mesoporous‐Carbon‐Coated Palladium Nanoparticles: An Intriguing Electrocatalyst for Methanol and Formic Acid Oxidation

Inspired by the attractive catalytic properties of palladium and the inert nature of carbon supports in catalysis, a concise and simple methodology for in situ nitrogen‐doped mesoporous‐carbon‐supported palladium nanoparticles (Pd/N‐C) has been developed by carbonizing a palladium dimethylglyoximate complex. The as‐synthesized Pd/N‐C has been exfoliated as a fuel cell catalyst by studying the electro‐oxidation of methanol and formic acid. The material synthesized at 400 °C,namely, Pd/N‐C‐400,exhibitssuperior mass activity and stability among catalysts synthesized under different carbonization temperaturesbetween300 and 500 °C. The unique 1D porous structure in Pd/N‐C‐400 helps better electron transport at the electrode surface, which eventually leads to about five times better catalytic activity and about two times higher stability than that of commercial Pd/C. Thus, our designed sacrificial metal–organic templatedirected pathway becomes a promising technique for Pd/N‐C synthesis with superior catalytic performances.     

A novel imidazolium‐supported palladium–chloroglycine complex: copper‐ and solvent‐free high‐turnover catalysts for the Sonogashira coupling reaction

A novel, effective 1‐glycyl‐3‐methyl imidazolium chloride–palladium(II) complex ([Gmim]Cl–Pd(II)) was synthesized and studied as an organocatalyst for the Sonogashira coupling reaction under solvent‐free conditions at 25 °C. The hydrophobic group on amino acid favors reagent diffusion toward the chloroglycine moiety, increasing the catalytic activity of supported palladium complex. By this protocol, different aryl halides (Cl, Br and I) were reacted with phenylacetylene in good to excellent yields with turnover number 8.0 × 10² to 9.6 × 10². The catalyst was recycled for the reaction of bromobenzene with phenylacetylene for eight runs without appreciable loss of its catalytic activity and negligible metal leaching. Copyright © 2012 John Wiley & Sons, Ltd.     

Highly dispersed palladium nanoclusters incorporated in amino‐functionalized silica spheres for the selective hydrogenation of succinic acid to γ‐butyrolactone

Highly dispersed palladium nanoclusters incorporated on amino‐functionalized silica sphere surfaces (Pd/SiO₂‐NH₂) were fabricated by a simple one‐pot synthesis utilizing 3‐(2‐aminoethylamino)propyltrimethoxysilane (AAPTS) as coordinating agent. Uniform palladium nanoclusters with an average size of 1.1 nm can be obtained during the co‐condensation of tetraethyl orthosilicate and AAPTS owing to the strong interaction between palladium species and amino groups in AAPTS. The palladium particle size can be controlled by addition of AAPTS and plays a significant role in the catalytic performance. The Pd/SiO₂‐NH₂ catalyst exhibits high catalytic activity for succinic acid hydrogenation with 100% conversion and 94% selectivity towards γ‐butyrolactone using 1,4‐dioxane as solvent at 240°C and 60 bar for 4 h. Moreover, the Pd/SiO₂‐NH₂ catalyst is robust and readily reusable without loss of its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.