N‐heterocyclic carbene–palladium(II) complex supported on magnetic mesoporous silica for Heck cross‐coupling reaction

Magnetic mesoporous silica was prepared via embedding magnetite nanoparticles between channels of mesoporous silica (SBA‐15). The prepared composite (Fe₃O₄@SiO₂‐SBA) was then reacted with 3‐chloropropyltriethoxysilane, sodium imidazolide and 2‐bromopyridine to give 3‐(pyridin‐2‐yl)‐1H‐imidazol‐3‐iumpropyl‐functionalized Fe₃O₄@SiO₂‐SBA as a supported pincer ligand for Pd(II). The functionalized magnetic mesoporous silica was further reacted with [PdCl₂(SMe₂)₂] to produce a supported N‐heterocyclic carbene–Pd(II) complex. The obtained catalyst was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, vibrating sample magnetometry, Brunauer–Emmett–Teller surface area measurement and X‐ray diffraction. The amount of the loaded complex was 80.3 mg g^?1, as calculated through thermogravimetric analysis. The formation of the ordered mesoporous structure of SBA‐15 was confirmed using low‐angle X‐ray diffraction and transmission electron microscopy. Also, X‐ray photoelectron spectroscopy confirmed the presence of the Pd(II) complex on the magnetic support. The prepared magnetic catalyst was then effectively used in the coupling reaction of olefins with aryl halides, i.e. the Heck reaction, in the presence of a base. The reaction parameters, such as solvent, base, temperature, amount of catalyst and reactant ratio, were optimized by choosing the coupling reaction of 1‐bromonaphthalene and styrene as a model Heck reaction. N‐Methylpyrrolidone as solvent, 0.25 mol% catalyst, K₂CO₃ as base, reaction temperature of 120°C and ultrasonication of the catalyst for 10 min before use provided the best conditions for the Heck cross‐coupling reaction. The best results were observed for aryl bromides and iodides while aryl chlorides were found to be less reactive. The catalyst exhibited noticeable stability and reusability.     

New bis(N‐heterocyclic carbene) palladium complex immobilized on magnetic nanoparticles: as a magnetic reusable catalyst in Suzuki‐Miyaura cross coupling reaction

A new bis(N ‐heterocyclic carbene) (NHC) palladium complex supported on silica coated magnetic nanoparticles (MNPs) was prepared using the reaction of synthesized Pd‐NHC complex with MNPs. The Pd‐NHC complex was prepared using the reaction of a hydroxyl‐functionalized bis‐imidazolium ionic liquid. The Pd‐NHC organometallic complex was used as a heterogeneous recyclable and active catalyst in the Suzuki‐Miyaura reaction and various aryl halides were coupled with arylboronic acids in order to synthesize diverse biaryls in good to excellent yields. The prepared catalyst was characterized by use of some different microscopic and spectroscopic techniques including elemental analysis, FT‐IR spectroscopy, diffuse reflectance UV–Vis spectrophotometery, scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and X‐ray diffraction (XRD). The Pd‐NHC catalyst system is a magnetic reusable catalyst and it can be separated from the reaction mixture using an external magnetic field. The catalyst was reusable in the Suzuki‐Miyaura coupling reaction at least for 6 times without significant decreasing in its catalytic activity.     

Highly Efficient Palladacycle/Dihydroimidazolium Chloride System for the Suzuki‐Miyaura Cross‐Coupling of Aryl Halides (I,Br, Cl) with Arylboronic Acids

A combination of a tertiary amine‐based palladacycle and an N‐heterocyclic carbene ligand precursor ( 1 , N,N‐bis‐mesityl‐4,5‐dihydroimidazolium chloride) has been applied to catalyze the Suzuki‐Miyaura cross‐coupling of aryl halides with arylboronic acids. The substrate scope is general: a variety of electron rich and deficient aryl halides (I, Br, Cl) and arylboronic acids were found to undergo the cross‐coupling reaction in good to excellent yields at low catalyst loading of 0.01–1 mol%.     

Biochar as heterogeneous support for immobilization of Pd as efficient and reusable biocatalyst in C–C coupling reactions

Biochar is a stable and carbon‐rich solid which has a high density of carbonyl, hydroxyl and carboxylic acid functional groups on its surface. In this work, the surface of biochar nanoparticles (BNPs) was modified with 3‐choloropropyltrimtoxysilane and further 2‐(thiophen‐2‐yl)‐1H‐benzo[d]imidazole was anchored on its surface. Then, palladium nanoparticles were fabricated on the surface of the modified BNPs and further the catalytic application was studied as recyclable biocatalyst in carbon–carbon coupling reactions such as Suzuki–Miyaura and Heck–Mizoroki cross‐coupling reactions. The structure of the catalyst was characterized using scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, X‐ray diffraction and atomic absorption spectroscopy. The catalyst can be reused several times without a decrease in its catalytic efficiency. In addition to the several advantages reported, application of biochar as catalyst support for the first time is a major novelty of the present work.     

Preparation,characterization and application of silica‐supported palladium complex as a new and heterogeneous catalyst for Suzuki and Sonogashira reactions

An efficient heterogeneous Pd catalytic system has been developed, based on immobilization of Pd nanoparticles (PNPs) on a silica‐bonded propylamine–cyanuric–cysteine (SiO₂–pA–Cyan–Cys) substrate. The synthesized catalyst was characterized by transmission electron microscopy, scanning electron microscopy, FT‐IR, N₂ adsorption analysis (BET), TGA and inductively coupled plasma/atomic emission spectroscopy, and catalytic activity of this catalyst was investigated in the Suzuki and Sonogashira cross‐coupling reactions. The catalysts showed excellent performance in these two reactions, including various aryl halide derivatives (except aryl chloride derivatives) with phenylboronic acid and phenylacetylene under green conditions. Moreover, the catalyst was recycled for several runs without any significant loss of catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Sulfonated palladium(II) N‐heterocyclic carbene complex immobilized on nano–micro size poly(4‐vinylpyridinium chloride) for Suzuki‐Miyaura cross‐coupling reaction

The sulfonated palladium(II) N‐heterocyclic carbene complex Pd^II(NHC)SO₃^?, supported on poly(4‐vinylpyridinium chloride), was used as a heterogeneous, recyclable and active catalyst for the Suzuki–Miyaura reaction. This catalyst was applied for coupling of various aryl halides with phenylboronic acid and the corresponding products were obtained in excellent yields and short reaction times. The catalyst was characterized using Fourier transform infrared and diffuse reflectance UV–visible spectroscopies, scanning electron microscopy and elemental analysis. After each reaction, the catalyst was recovered easily by simple filtration and reused several times without significant loss of its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon‐Supported Copper Nanomaterials: Recyclable Catalysts for Huisgen [3+2] Cycloaddition Reactions

Highly disperse copper nanoparticles immobilized on carbon nanomaterials (CNMs; graphene/carbon nanotubes) were prepared and used as a recyclable and reusable catalyst to achieve Cu^I‐catalyzed [3+2] cycloaddition click chemistry. Carbon nanomaterials with immobilized N‐heterocyclic carbene (NHC)‐Cu complexes prepared from an imidazolium‐based carbene and Cu^I show excellent stability including high efficiency at low catalyst loading. The catalytic performance evaluated in solution and in bulk shows that both types of Cu‐CNMs can function as an effective recyclable catalysts (more than 10 cycles) for click reactions without decomposition and the use of external additives.     

N‐Heterocyclic carbene/phosphite synergistically assisted Pd/C‐catalyzed Suzuki coupling of aryl chlorides

An N‐heterocyclic carbene and phosphite synergistically enhanced Pd/C catalyst system has been developed for Suzuki coupling of aryl chlorides and aryl boronic acids from commercially available Pd/C with sterically demanding N,N′‐bis(2,6‐diisopropylphenyl)imidazolylidene and trimethylphosphite. A remarkable increase in catalytic activity of Pd/C was observed when used along with 1 equiv. N,N′‐bis(2,6‐diisopropylphenyl)imidazolium chloride and 2 equiv. phosphite with respect to palladium in appropriate solvents that were found to play a crucial role in Pd/C‐NHC‐P(OR)₃‐catalyzed Suzuki coupling. A dramatic ortho‐substitution effect of carbonyl and nitrile groups in aryl chlorides was observed and explained by a modified quasi‐heterogeneous catalysis mechanism. The Pd/C catalyst could be easily recovered from reaction mixtures by simple filtration and only low palladium contamination was detected in the biparyl products. A practical process for the synthesis of 4‐biphenylcarbonitrile has therefore been developed using the N‐heterocyclic carbene/phosphite‐assisted Pd/C‐catalyzed Suzuki coupling. Copyright © 2013 John Wiley & Sons, Ltd.     

Well‐dispersed N‐heterocyclic carbene–palladium complex anchored onto poly(acrylic acid)/poly(vinyl alcohol) nanofibers: Novel,superior and ecofriendly nanocatalyst for the Suzuki–Miyaura cross‐coupling reaction

Polymeric nanocomposite@Pd is one of the crown jewels for the catalysis of cross‐coupling reactions. This Pd nanocomposite on various polymeric supports has been well established to catalyze cross‐coupling reactions, but its preparation supported on the surface of nanofibers has been largely overlooked. Herein, we report the preparation of a poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) nanofiber‐supported N‐heterocyclic carbene–Pd complex. The first step involves the preparation of PAA/PVA nanofibers using the electrospinning process. The second step comprises the reaction of water‐soluble poly(ethylene glycol)‐imidazole with modified PAA/PVA nanofibers followed by introduction of PdCl₂ to achieve successfully the desired nanocomposite. The catalytic activity of this nanocomposite was examined in the expeditious synthesis of biaryl compounds using the Suzuki–Miyaura cross‐coupling reaction under mild reaction conditions. The composite offers multiple features such as good hydrophilic properties, high surface area, admirable potential in repeatability tests and being recyclable for several runs without significant loss in its activity under the optimum reaction conditions. Our results showed the superior applicability of this novel nanocatalyst in terms of conversion reaction, yields and turnover frequencies. The structure of the catalyst was characterized using a variety of techniques.     

New palladium(II)–N‐heterocyclic carbene complexes containing benzimidazole‐2‐ylidene ligand derived from menthol: synthesis,characterization and catalytic activities

A new series of sterically hindered ligands containing (1R,2S,4R)‐(+)‐menthoxymethyl group attached to benzimidazole‐based N‐heterocyclic carbene (NHC), palladium–bis‐NHC complexes and (κ²‐C,N)‐palladacyclic NHC complexes have been synthesized and characterized using appropriate spectroscopic techniques. Catalytic performance of the palladium complexes has been investigated for allylic alkylation, Suzuki and Heck carbon–carbon coupling reactions. These complexes smoothly catalyse the carbon–carbon bond formation reactions. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of dendrimers terminated by DABCO ligands and applications of its palladium nanoparticles for catalyzing Suzuki–Miyaura and Mizoroki–Heck couplings

A new kind of silica‐supported third‐generation dendrimers capped by 1,4‐diaza‐bicyclo[2.2.2]octane (DABCO) group‐stabilized palladium(0) nanoparticles, and their enhanced catalytic activity in Suzuki–Miyaura and Mizoroki–Heck reactions in excellent yield under mild conditions, was reported. The resulting silica‐supported dendrimer‐stabilized palladium(0) nanoparticles with a particle size of 10–20 nm were prepared in situ by treatment with PdCl₂ and hydrazine in ethanol at 60 °C for 24 h. The catalyst as prepared was characterized by FT‐IR, X‐ray diffraction, thermal analysis, elementary analysis (EA), scanning electron microscopy and transmission electron microscopy. Recycling experiments showed that the catalyst could be easily recovered by simple filtration and reused for up to five cycles without losing its activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Nickel‐Catalyzed Cross‐Coupling of Organolithium Reagents with (Hetero)Aryl Electrophiles

Nickel‐catalyzed selective cross‐coupling of aromatic electrophiles (bromides, chlorides, fluorides and methyl ethers) with organolithium reagents is presented. The use of a commercially available nickel N‐heterocyclic carbene (NHC) complex allows the reaction with a variety of (hetero)aryllithium compounds, including those prepared via metal‐halogen exchange or direct metallation, whereas a commercially available electron‐rich nickel‐bisphosphine complex smoothly converts alkyllithium species into the corresponding coupled product. These reactions proceed rapidly (1 h) under mild conditions (room temperature) while avoiding the undesired formation of reduced or homocoupled products.     

Facile Chan‐Lam coupling using ferrocene tethered N‐heterocyclic carbene‐copper complex anchored on graphene

Ferrocene tethered N‐heterocyclic carbene‐copper complex anchored on graphene ([GrFemImi]NHC@Cu complex) has been synthesized by covalent grafting of ferrocenyl ionic liquid in the matrix of graphene followed by metallation with copper (I) iodide. The [GrFemImi]NHC@Cu complex has been characterized by fourier transform infrared (FT‐IR), fourier transform Raman (FT‐Raman), CP‐MAS ¹³C NMR spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), energy dispersive X‐ray (EDX) analysis, X‐ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area analysis and X‐ray diffractometer (XRD) analysis. This novel complex served as a robust heterogeneous catalyst for the synthesis of bioactive N‐aryl sulfonamides from variety of aryl boronic acids and sulfonyl azides in ethanol by Chan‐Lam coupling. Recyclability experiments were executed successfully for six consecutive runs.     

Magnetic iron oxide nanoparticles–N‐heterocyclic carbene–palladium(II): a new,efficient and robust recyclable catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling reactions

A new and efficient nanoparticle–N‐heterocyclic carbene–palladium complex was synthesized and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy‐dispersive X‐ray analysis, X‐ray diffraction, transmission electron microscopy, elemental analysis, inductively coupled plasma analysis and vibrating sample magnetometry. This catalytic system was found to be a highly active catalyst in the Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions. These reactions were best performed in dimethylformamide and water, respectively, in the presence of only 0.054 mol% of palladium under mild conditions. Moreover, the catalyst could be recovered easily and reused at least ten times without any considerable loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Platinum Nanoparticles Modified with Perfluorinated Alkylamines as a Model Cathode Catalyst for Fuel Cells

Platinum nanoparticles (NPs) modified with undecafluorohexylamine (UFHA) and octylamine were synthesized as a novel model cathode catalyst for fuel cells. The modified Pt NPs were well characterized by FTIR, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and transmission electron microscopy. These NPs supported on carbon black were applied as electrocatalysts for the oxygen reduction reaction. The UFHA‐modified Pt NP catalyst showed high electrocatalytic activity and durability compared to a commercial catalyst. Besides suppression of undesired oxide formation on the Pt surface, the affinity between the perfluorinated alkyl chains of UFHA and Nafion^® improved the catalyst activity by creating a desirable proton conduction path. Additionally, UFHA modification improved durability by suppressing Pt dissolution and carbon corrosion because of restricted water accessibility. The β ‐oxide formation, which is responsible for Pt dissolution, was significantly attenuated by surface modification.     

Ultra‐small and highly dispersed Pd nanoparticles inside the pores of ZIF‐8: Sustainable approach to waste‐minimized Mizoroki–Heck cross‐coupling reaction based on reusable heterogeneous catalyst

The rapid development of nanomaterials, particularly advanced hybrid nanoparticles, has made new opportunities for the design and fabrication of high‐performance metal‐based catalysts. However, generating metal nanoparticles of desired size without aggregation is an important challenge for enhancing the catalytic activity of metal nanoparticles supported in the host matrix. In this work, a hybrid nanoporous material, namely Pd nanoparticles@N‐heterocyclic carbene@ZIF‐8, with a high internal surface area was successfully prepared using a dispersed anionic sulfonated N‐heterocyclic carbene–Pd(II) precursor inside the cavities of zeolitic imidazolate framework (ZIF‐8) using an impregnation approach followed by reduction with NaBH₄. The anionic sulfonated N‐heterocyclic carbene was found to be a superb ligand for the stabilization of Pd nanoparticles in the pores of ZIF‐8. The resulting system was applied to the Mizoroki–Heck cross‐coupling reaction, in which the catalyst showed high catalytic activity under mild 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.     

NHC copper complexes functionalized with sulfoxide and sulfone moieties

A series of N‐heterocyclic copper carbene complexes bearing sulfoxide and sulfone moieties have been prepared. In case of new copper compounds with sulfone ligand, the solid‐state structures were determined using X‐Ray crystallography. Obtained complexes were investigated as catalysts in such transformations as: 1,3‐dipolar cycloaddition of alkynes and azides (CuAAC), A³ coupling reaction and β‐hydroboration and compared with standard copper catalytic systems.     

Spinel copper ferrite nanoparticles: Preparation,characterization and catalytic activity

The magnetic CuFe₂O₄ nanoparticles have been synthesized and characterized by various spectroscopic methods, including X‐ray diffraction (XRD), O K, Cu and Fe K ‐edge X‐ray absorption near edge structure (XANES), energy dispersive X‐ray analysis (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The azide‐alkyne cycloaddition by the reaction of various phenylacetylenes with a mixture of benzyl halides and NaN₃ and also three component (A³) coupling reaction of aldehyde, alkyne and amine catalyzed by CuFe₂O₄ nanoparticles under aerobic conditions led to the formation of the 1,4‐disubstituted‐1,2,3‐triazoles and propargylamines in excellent yields. The catalyst can be recovered by applying an external magnetic field for the subsequent cycloaddition reactions and reused without any tangible loss in catalytic efficiency.     

Mo (CO)6‐assisted Pd‐supported magnetic graphene oxide‐catalyzed carbonylation‐cyclization as an efficient way for the synthesis of 4(3H)‐quinazolinones

In this paper, a novel catalyst is introduced based on the immobilization of palladium on modified magnetic graphene oxide nanoparticles. The catalyst is characterized by several methods, including transmission electron microscopy, scanning electron microscopy, X‐ray fluorescence, vibrating‐sample magnetometer, Fourier transform‐infrared and dynamic light scattering (DLS) analysis. The activity of the catalyst was investigated in the synthesis of 4(3H)‐quinazolinones via Pd‐catalyzed carbonylation‐cyclization of N‐(2‐bromoaryl) benzimidamides by Mo (CO)₆. The Mo (CO)₆ is used as a carbon monoxide source for performing the reaction under mild conditions. The catalyst showed good reusability, and no change in activity was observed after 10 cycles of recovery.