2‐Pyridylquinoxaline derivatives as N,N‐ligands for palladium‐catalyzed Suzuki–Miyaura reaction

The Suzuki–Miyaura reaction of aryl bromides with benzeneboronic acid catalyzed by bis(chloro)(2‐pyridylquinoxaline)palladium(II) was investigated. The scope of the bis(chloro)(2‐pyridylquinoxaline)palladium(II) was determined in toluene at 80 °C using KOH as base. Using a 0.1% molar ratio of bis(chloro)(2‐pyridylquinoxaline)palladium(II) C1 as a catalyst, aryl bromides reacted with benzeneboronic acid to afford diaryl derivatives in excellent yield. Copyright © 2009 John Wiley & Sons, Ltd.     

Palladium–cadmium sulfide nanopowder at oil–water interface as an effective catalyst for Suzuki–Miyaura reactions

A simple and effective strategy is described for the synthesis of Pd–CdS nanopowder by the reduction of an organopalladium(II) complex, [PdCl₂(cod)] (cod = cis ,cis ‐1,5‐cyclooctadiene), in the presence of CdS quantum dots (QDs) at a toluene–water interface. We investigated the impact of addition of CdS QDs on catalytic activity of Pd nanoparticles (NPs). The Pd–CdS nanopowder functions as an efficient catalyst for Suzuki–Miyaura reactions for the formation of carbon–carbon bonds. There is a high electron density on Pd NPs and due to their high electron affinity they behave as an electron scavenger from CdS increasing the rate of oxidative addition, which is the rate‐determining step of the catalytic cycle, and, just as we expect, the C─C coupling reaction with the Pd–CdS nanopowder is faster and occurs in less time than that with Pd nanocatalysts. Compared to classical reactions, this method consistently has the advantages of short reaction times, high yields in a green solvent, reusability of the catalyst without considerable loss of catalytic activity and low cost, and is a facile method for the preparation of the catalyst.     

A soluble polyethyleneglycol-anchored phosphine as a highly active, reusable ligand for Pd-catalyzed couplings of aryl chlorides: comparison with cross and non-cross-linked polystyrene and silica supports

The so-called SPhos phosphine, an extremely active ligand in the amination and Suzuki coupling of sterically-hindered aryl chlorides, has been anchored on different supports such as non-soluble (cross-linked polystyrene) and soluble (non-cross-linked polystyrene and polyethyleneglycol) polymers, as well as high surface silica. SPhos anchored on polyethyleneglycol (PEG-SPhos) showed the best activity for both amination and Suzuki couplings. The PEG-SPhos ligand can be quantitatively recovered from the reaction mixture through precipitation with diethyl ether and recycled in four consecutive runs without loosing activity. ³¹P NMR spectra of the reused anchored ligand showed that deactivation of the PEG-SPhos ligand comes from the progressive oxidation of the phosphine-to-phosphine oxide.     

Pd(l‐proline)2 complex: an efficient catalyst for Suzuki–Miyaura coupling reaction in neat water

An efficient catalytic system for Suzuki–Miyaura coupling reactions in neat water has been developed by using a water‐soluble Pd(l ‐proline)₂ catalyst. Under the optimized conditions, various biaryl compounds were obtained in good to excellent yields and a wide range of functional groups on the tested substrates were well tolerated. The catalytic system could be reused at least six times with no significant loss in its activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Pd nanoparticles immobilized on PNIPAM–halloysite: highly active and reusable catalyst for Suzuki–Miyaura coupling reactions in water

Poly(N‐isopropylacrylamide)–halloysite (PNIPAM‐HNT) nanocomposites exhibited inverse temperature solubility with a lower critical solution temperature (LCST) in water. Palladium (Pd) nanoparticles were anchored on PNIPAM‐HNT nanocomposites with various amounts of HNT from 5 to 30 wt%. These Pd catalysts exhibited excellent reactivities for Suzuki–Miyaura coupling reactions at 50–70 °C in water. In particular, Pd anchored PNIPAM/HNT (95:5 w/w ratio) nanocomposites showed excellent recyclability up to 10 times in 96% average yield by simple filtration. Copyright © 2014 John Wiley & Sons, Ltd.     

A highly water‐dispersible and magnetically separable palladium catalyst based on functionalized poly(ethylene glycol)‐supported iminophosphine for Suzuki–Miyaura coupling in water

A magnetically separable Fe₃O₄@poly(ethylene glycol) (PEG)–iminophosphine palladium complex was successfully prepared by reacting a palladium complex containing the ligand 2‐(diphenylphosphino)benzaldehyde with amino‐functionalized PEG‐coated iron oxide nanoparticles. The novel catalyst was characterized using inductively coupled plasma atomic emission and Fourier transform infrared spectroscopies, transmission electron microscopy, vibrating sample magnetometry, X‐ray diffraction and thermogravimetric analysis. It showed high activity for the Suzuki–Miyaura coupling reaction in pure water. Furthermore, it was found that the highly water‐dispersible catalyst can be recovered by applying an external magnetic field and used in five consecutive runs without significant decrease in activity. Copyright © 2015 John Wiley & Sons, Ltd.     

A highly efficient heterogeneous montmorillonite K‐10‐supported palladium catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous medium

A heterogeneous montmorillonite K‐10‐supported palladium triphenylphosphine catalyst is reported for the Suzuki–Miyaura cross‐coupling reaction at room temperature. A library of electronically diverse aryl bromides and arylboronic acids underwent the cross‐coupling reaction at very good rates in aqueous solvent. The reusability of the catalyst was also examined and it was found to be effective up to three catalytic cycles. Copyright © 2014 John Wiley & Sons, Ltd.     

Porphyrin‐based polymer‐supported palladium as an excellent and recyclable catalyst for Suzuki–Miyaura coupling reaction in water

A porphyrin‐based polymer with high surface area was synthesized using 5,10,15,20‐tetraphenylporphyrin through a one‐pot Friedel–Crafts alkylation reaction. Pd(II) was successfully supported on this polymer. This strategy provides an easy approach to produce highly stable Pd–porphyrin‐based polymer. The resulting Pd catalyst was characterized using Fourier transform infrared and X‐ray photoelectron spectroscopies, thermogravimetric analysis, scanning and transmission electron microscopies and N₂ adsorption–desorption measurements. This porphyrin‐based polymer‐supported Pd was used as a heterogeneous catalyst for Suzuki–Miyaura coupling reaction in water. The results demonstrated that this Pd catalyst indeed exhibited excellent catalytic activity and recycling performance in water, even for inactive aryl chloride substrate. A new heterogeneous strategy for catalyzing the Suzuki–Miyaura reaction in water is provided.     

A highly active palladium(II)–bis(oxazoline) catalyst for Suzuki–Miyaura,Mizoroki–Heck and sonogashira coupling reactions in aqueous dimethylformamide

An efficient catalytic system based on a new palladium–bis(oxazoline) ( Pd-BOX-1 ) complex has been developed. The complex Pd-BOX-1 adopts a legless chair‐type structure where the distorted square planar [PdN₂Cl₂] moiety and the benzene ring spacer represent the seat and the chair back, respectively. The catalytic activity of Pd-BOX-1 has been investigated in dimethylformamide–water under aerobic and mild conditions in Suzuki–Miyaura coupling reactions of arylboronic acids with aryl iodides, aryl bromides and aryl chlorides, Mizoroki–Heck coupling reactions of aryl halides with styrene derivatives, and Sonogashira coupling reactions of aryl halides with terminal alkynes. A wide range of functional groups as substituents on the arylboronic acids and aryl halides were considered. Pd-BOX-1 demonstrates exceptional air and moisture stability. Of note, the catalyst system based on Pd-BOX-1 shows high recycling ability in Suzuki–Miyaura coupling reactions in dimethylformamide–water without any loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Salicylaldoxime‐functionalized poly(ethylene glycol)‐bridged dicationic ionic liquid ([salox‐PEG1000‐DIL][BF4]) as a novel ligand for palladium‐catalyzed Suzuki–Miyaura reaction in water

Two novel salicylaldoxime‐functionalized poly(ethylene glycol)‐bridged dicationic ionic liquids ([salox‐PEG₁₀₀₀‐DIL][BF₄] and [salox‐PEG₁₀₀₀‐DIL][PF₆]) were prepared and characterized. [salox‐PEG₁₀₀₀‐DIL][BF₄] was found to be an efficient and recyclable ligand for palladium‐catalyzed Suzuki–Miyaura reaction in water. The catalytic system could be easily recovered and reused for at least five runs only with slight decrease in its activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Efficient and Magnetically Recoverable “Click” PEGylated γ‐Fe2O3–Pd Nanoparticle Catalysts for Suzuki–Miyaura,Sonogashira, and Heck Reactions with Positive Dendritic Effects

The engineering of novel catalytic nanomaterials that are highly active for crucial carbon–carbon bond formations, easily recoverable many times, and biocompatible is highly desirable in terms of sustainable and green chemistry. To this end, catalysts comprising dendritic “click” ligands that are immobilized on a magnetic nanoparticle (MNP) core, terminated by triethylene glycol (TEG) groups, and incorporate Pd nanoparticles (PdNPs) have been prepared. These nanomaterials are characterized by transmission electron microscopy (TEM), high‐resolution TEM, inductively coupled plasma analysis, Fourier transform infrared spectroscopy, X‐ray photoelectron spectra and energy‐dispersive X‐ray spectroscopy. They are shown to be highly active, dispersible, and magnetically recoverable many times in Suzuki, Sonogashira, and Heck reactions. In addition, a series of pharmacologically relevant or natural products were successfully synthesized using these magnetic PdNPs as catalyst. For comparison, related PdNP catalysts deposited on MNPs bearing linear “click” PEGylated ligands are also prepared. Strong positive dendritic effects concerning ligand loading, catalyst loading, catalytic activity, and recyclability are observed, that is, the dendritic catalysts are much more efficient than non‐dendritic analogues.     

Synthesis,characterization and catalytic activity of Pd(II) complexes with N‐allyl functionalized imidazol‐2‐ylidenes in Suzuki–Miyaura reaction

A series of Pd–N‐heterocyclic carbene (Pd–NHC) complexes were synthesized and characterized by elemental analysis and spectroscopic methods. In addition, the molecular structures of 3c and 4c were determined by X‐ray diffraction studies. Finally, the performance of complexes 3 and 5 were studied on Suzuki–Miyaura reactions of phenylboronic acid with aryl bromides. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

2-Aminophenyl diphenylphosphinite as an easily accessible ligand for heterogeneous palladium-catalyzed Suzuki-Miyaura reaction in water in the absence of any organic co-solvent

In this article, we have introduced application of 2-aminophenyl diphenylphosphinite as an easily accessible ligand for heterogeneous palladium-catalyzed Suzuki-Miyaura reaction in water in the absence of any organic co-solvent. By using 2-aminophenyl diphenylphosphinite as a ligand and Pd(OAc)₂ as the pre-catalyst, structurally different aryl halides (I, Br, Cl) were reacted efficiently with phenylboronic acid in water to produce their corresponding biphenyl products in good to excellent yields under heterogeneous conditions. The catalyst is recyclable and was recycled for seven runs for the reaction of bromobenzene with phenylboronic acid without appreciable loss of its catalytic activity.     

Pentacoordination versus tetracoordination in silicon derivatives of an O,N,O′‐tridentate ligand

Bis[2‐(2‐hydroxy‐3‐methoxybenzylideneamino)phenolato‐κO]dimethylsilicon, C₃₀H₃₀N₂O₆Si, (II), was isolated from the reaction of 2‐(2‐hydroxy‐3‐methoxybenzylideneamino)phenol, (I), with dichlorodimethylsilane at 339 K. It consists of two ligand molecules and the Me₂Si unit forming a dialkoxydimethylsilane with a tetracoordinate Si atom. [2‐(3‐Methoxy‐2‐oxidobenzylideneamino)phenolato‐κ³O,N,O′]dimethylsilicon, C₁₆H₁₇NO₃Si, (III), was isolated from the same reaction conducted at 263 K. In this complex, the dianion of (I) is coordinated via two O atoms and an azomethine N atom to the pentacoordinate Si atom. According to quantum chemical calculations, (II) is the thermodynamically stable product and (III) is the kinetically favoured product.     

Pd(OAc)2@SBA‐15/PrEn nanoreactor: a highly active,reusable and selective phosphine‐free catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous media

A series of ordered mesoporous organic–inorganic hybrid material was designed by using the amine‐functionalized SBA‐15 (PdX₂@SBA‐15/N_Y, Y = 1, 2) as solid support for palladium complexes. Among them, the Pd(OAc)₂/ethylenediamine complex encapsulated into SBA‐15 (Pd(OAc)₂@SBA‐15/PrEn or Pd(OAc)₂@SBA‐15/PrNHEtNH₂) exhibits higher activity and selectivity toward Suzuki cross‐coupling reaction under aerobic conditions and water solvent mixture. The SBA‐15/PrEn supported palladium pre‐catalyst could be separated easily from reaction products and used repetitively several times, showing its superiority over homogeneous catalysts for industrial and chemical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Nanosilica‐anchored Pd(II)‐Schiff base complex as efficient heterogeneous catalyst for activation of aryl halides in Suzuki–Miyaura cross‐coupling reaction in water

A nanosilica (derived from rice husk)‐anchored Pd(II)–Schiff base complex has been synthesized and characterized. This immobilized complex has been found to be a very effective and recyclable heterogeneous catalyst for the Suzuki–Miyaura cross‐coupling reaction of various aryl halides with arylboronic acid in aqueous medium under mild conditions. The products were identified using ¹H NMR and mass spectral studies. This complex can be easily filtered out from the reaction medium and reused up to six times without significant loss of catalytic activity. Since the reaction proceeds under mild conditions in aqueous medium as well as the catalyst being recyclable, it provides an environmentally benign alternative route to the existing protocols for the Suzuki–Miyaura reaction.     

Synthesis and characterization of 4‐AMTT‐Pd(II) complex over Fe3O4@SiO2 as supported nanocatalyst for Suzuki‐Miyaura and Mizoroki‐heck cross‐coupling reactions in water

Immobilization of Pd(II) nanoparticles on silica‐coated modified magnetite particles has been readily achieved via a surface modification of Fe₃O₄ particles with 4‐amino‐5‐methyl‐4‐H‐1,2,4‐triazole‐3‐thiol (4‐AMTT) as a ligand. This magnetite nanocatalyst was characterized by various analyses such as FT‐IR, SEM/EDX, ICP‐AES, VSM, TEM, XRD, XPS and TGA. This nanocatalyst showed admirable catalytic activity for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions under mild conditions in water, and could be simply separated by an outer magnet and reused for several times.     

Concomitant polymorphism in an organometallic ruthenium(II) complex with an N,N′‐donor ligand

The simultaneous crystallization of different polymorphs, i.e. concomitant polymorphism, is a phenomenon which, when properly recognized and studied, can provide useful information for a variety of disciplines. It is rare for ruthenium complexes, although it has been observed. In the synthesis of the ruthenium(II) complex chlorido(η⁶‐p‐cymene)(dimethyl 2,2′‐bypyridine‐4,5‐dicarboxylate‐κ²N,N′)ruthenium(II) hexafluoridophosphate, [RuCl(C₁₀H₁₄)(C₁₄H₁₂N₂O₄)]PF₆, concomitant polymorphs were crystallized under the same conditions. The colour of both crystals was orange, but the shapes, as well as the orientation of the p‐cymene and methoxycarbonyl groups, were different. The crystal structures of both isomers show approximately the same bond lengths. In the asymmetric unit, there is one cation and one anion. Due to the absence of strong hydrogen bonds, only weak intermolecular interactions were observed. The Hirshfeld surface and two‐dimensional fingerprint plots of both isomers satisfactorily explain the difference in the melting points.     

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.