Phosphorylated PEG (PPEG) as a new support for generation of nano‐Pd(0): application to the Heck–Mizoroki and Suzuki–Miyaura coupling reactions

Polyethylene glycols (PEGs) with different molecular weights (M_w = 200, 400, 1000) were phosphorylated to their bis‐diphenyl phosphinite derivatives as stable solids which are melted in the range 140–160°C. These phosphorylated PEGs were used as ligands and reducing agents to generate nano‐Pd(0) catalysts in 2.5–8.3 nm. The nano‐Pd(0) particles supported on phosphorylated PEG₂₀₀ were applied for the efficient Heck–Mizoroki carbon–carbon coupling reactions of ArX (X = Cl, Br, I) at 80–100°C under solvent‐free conditions and for the Suzuki–Miyaura coupling reaction in ethanol at 70°C. The catalyst was recycled easily and reused for several runs. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

A highly selective synthesis of 1‐substituted (E)‐buta‐1,3‐dienes with 4,4,5,5‐tetramethyl‐2‐vinyl‐1,3,2‐dioxaborolane as building block

Highly selective synthesis of 1‐substituted (E)‐buta‐1,3‐dienes via palladium‐catalyzed Suzuki–Miyaura cross‐coupling of (E)‐alkenyl iodides with 4,4,5,5‐tetramethyl‐2‐vinyl‐1,3,2‐dioxaborolane ( 1 ) is reported. The vinylboronate pinacol ester ( 1 ) acts as a vinyl building block to show high chemoselectivity for the Suzuki–Miyaura pathway versus Heck coupling in the presence of biphasic conditions (Pd(PPh₃)₄, aqueous K₂CO₃, toluene and ethanol). Copyright © 2014 John Wiley & Sons, Ltd.     

Mono‐, bis‐ and tris‐piperidine fused imidazolinium salts: their in situ catalytic applications for C?C bond formation in aqueous solutions

The 1,5,6,7,8,8a‐hexahydroimidazo[1,5‐a]pyridine, 3, was quaternized with 2‐(bromomethyl‐1,3,5‐trimethylbenzene, 1,4‐bis(bromomethyl)‐2,3,5,6‐tetramethylbenzene, 2,4‐bis(bromomethyl)‐1,3,5‐trimethylbenzene, 1,3,5‐tris(bromomethyl)‐2,4,6‐trimethylbenzene and 1,3,5‐tris(bromomethyl)‐2,4,6‐triethylbenzene to obtain mono‐, bis‐ and tris‐imidazolinium salts (4–7) which were characterized by elemental analysis and NMR spectroscopy. In order to understand the effects of these changes on the N‐substituent and how they translate to catalytic activity, these new salts (4–7) with Pd(OAc)₂ were applied as in situ catalysts for Suzuki‐Miyaura and Heck‐Mirozoki cross‐coupling reactions of aryl chlorides and aryl bromides, respectively. The tris‐imidazolinium salts (7) were found to be more efficient than the related analogs 4–6. Copyright © 2009 John Wiley & Sons, Ltd.     

Highly ordered amphiphilic cyclopalladated arylimine self‐assembly films for catalyzing Heck and Suzuki coupling reactions

A series of new cyclopalladated arylimine compounds ( 3a , 3b , 3c , 4a , 4b , 4c ) were synthesized and characterized. Their catalytic properties for Heck and Suzuki coupling reactions in a homogeneous system were preliminarily investigated using water as solvent, in which no ligands, air isolation or assistant solvents were needed in cross‐coupling reactions. The optimization of the homogeneous system provided a basis for research on the heterogeneous catalytic reaction catalyzed by ordered self‐assembly films. Organized monolayers of 3a , 3b , 3c were prepared and utilized as C? C coupling catalysts. Monolayers of 3a , 3b , 3c were deposited using Langmuir–Blodgett techniques and analyzed using π–A isotherms, UV–visible and X‐ray photoelectron spectroscopies and atomic force microscopy, which showed near orientation on the surface and stability under the optimized experimental conditions suitable for exploring Heck and Suzuki coupling reactions. The activity of immobilized 3c monolayer is enhanced relative to homogeneous reaction, in which the ordered monolayers are efficient with a catalyst loading as low as 10^?5 mol%, turnover number as high as 79 200 and turnover frequency as high as 2640 h^?1. The catalytic efficiency is 100 times higher than that in the homogeneous case using the same amount and ratio of reagent. The increased activity of immobilized 3c monolayer is due to a combination of its structure and changes in conformation when deposited onto the substrate. The topographic changes of catalyst films, stability of films and catalytic activity were investigated with atomic force microscopy, cyclic voltammetry, X‐ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectrometry, from which a heterogeneous catalytic mechanism for Suzuki coupling reaction is proposed. The study demonstrates that careful monolayer studies can provide useful models for the design and study of supported molecular catalyst systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and microwave‐assisted catalytic activity of novel bis‐benzimidazole salts bearing furfuryl and thenyl moieties in Heck and Suzuki cross‐coupling reactions

A mixture of bis‐benzimidazole salts ( 1–7 ), Pd(OAc)₂ and K₂CO₃ in DMF ? H₂O catalyzes, in high yield, the Suzuki and Heck cross‐coupling reactions assisted by microwave irradiation in a short time. In particular, the yields of the Heck and Suzuki reactions with aryl bromides were found to be nearly quantative. The synthesized bis‐benzimidazole salts ( 1 – 7 ) were identified by ¹H? ¹³C NMR, IR spectroscopic methods and micro analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

Catalytic activities of NHC‐PdCl2 species based on functionalized tetradentate imidazolium salt in three types of C‐C coupling reactions

A functionalized tetradentate imidazolium salt 9,10‐bis{di[2′‐(N‐ethylimidazolium‐1‐yl)ethyl]aminomethyl}anthracene tetrakis(hexafluorophosphate) ( 1 ) has been synthesized and characterized. The catalytic activity of the NHC‐PdCl₂ species formed by compound 1 and PdCl₂ was tested in Suzuki‐Miyaura, Heck‐Mizoroki and Sonogashira reactions. The results showed that this catalytic system was effective for above three types of C‐C coupling reactions.     

New route to synthesis of PVP‐stabilized palladium(0) nanoclusters and their enhanced catalytic activity in Heck and Suzuki cross‐coupling reactions

Herein we report a new method for the synthesis and characterization of PVP‐stabilized palladium(0) nanoclusters and their enhanced catalytic activity in Suzuki coupling and Heck reactions of aryl bromides with phenylboronic acid and styrene, respectively, under mild conditions. The PVP‐stabilized palladium(0) nanoclusters with a particle size of 4.5 ± 1.1 nm were prepared using a new method: refluxing a mixture of potassium tetrachloropalladate(II) and PVP in methanol at 80 °C for 1 h followed by reduction with sodium borohydride. Palladium(0) nanoclusters prepared in this way were stable in solution for weeks, could be isolated as solid materials and were characterized by TEM, XPS, UV–vis, and XRD techniques. The PVP‐stabilized palladium(0) nanoclusters were active catalysts in Heck and Suzuki coupling reactions of arylbromides with styrene and phenylboronic acid affording stilbenes and biphenyls, respectively, in high yield. Recycling experiments showed that PVP‐stabilized palladium(0) nanoclusters could be used five times with essentially no loss in activity in the Heck and Suzuki coupling reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

Dendron‐Functionalized Core–Shell Superparamagnetic Nanoparticles: Magnetically Recoverable and Reusable Catalysts for Suzuki C?C Cross‐Coupling Reactions

A metallodendron functionalized with dicyclohexyldiphosphino palladium complex was synthesized. The metallodendron was grafted onto core–shell superparamagnetic nanoparticles (γ‐Fe₂O₃/polymer, 200–500 nm) to give optimal catalytic reactivity in cross‐coupling reactions. The grafted nanoparticles were used as recoverable and reusable catalysts for Suzuki C? C cross‐coupling reactions. They showed remarkable reactivity towards iodo‐ and bromoarenes under mild conditions, and unprecedented reactivity towards chloroarenes. On completion of the catalytic reaction, the catalysts were readily recovered by using a simple magnet to attract the superparamagnetic grafted nanoparticles. Catalysts were recovered more than 25 times with almost no discernable loss of reactivity.     

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.     

Benzimidazolin‐2‐ylidene–palladium‐catalysed coupling reactions of aryl halides

The in situ prepared three‐component system Pd(OAc)₂–1,3‐dialkylbenzimidazolium chlorides ( 2a – f ) and Cs₂CO₃ catalyses, quantitatively, the Suzuki cross‐coupling of deactivated aryl chlorides and Heck coupling reactions of aryl bromide and iodide substrates. The 1,3‐dialkylbenzimidazolium salts ( 2a – f ) were characterized by conventional spectroscopic methods and elemental analysis. Copyright © 2005 John Wiley & Sons, Ltd.     

Recyclable Polymer‐Supported Nanometal Catalysts in Water

Two types of polymer‐supported nanometal catalysts with high catalytic activity and recyclability in water have been developed. One catalyst was composed of linear polystyrene‐stabilized metal nanoparticles (PS‐MtNPs). A palladium catalyst (PS‐PdONPs) was prepared in water by the thermal decomposition of Pd(OAc)₂ in the presence of polystyrene. The degree of immobilization of Pd, but not the size of the Pd nanoparticles, was dependent on the molecular weight and cross‐linking of the polystyrene. The PS‐PdONPs exhibited high catalytic activity for Suzuki, Heck, and Sonogashira coupling reactions in water and they could be recycled without loss of activity. Linear polystyrene was also suitable as a stabilizer for in situ generated PdNPs and PtNPs. The second catalyst was a polyion complex that was composed of poly[4‐chloromethylstyrene‐co‐(4‐vinylbenzyl)tributylammonium chloride] and poly(acrylic acid)‐stabilized PdNPs (PIC‐PdNPs). Aggregation and redispersion of PIC‐PdNPs were easily controlled by adjusting the pH value of the solution.     

σ‐Alkylpalladium Intermediates in Intramolecular Heck Reactions:Isolation and Catalytic Activity

The isolation of σ‐alkylpalladium Heck intermediates, possible when β‐hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N‐allyl‐2‐halobenzylamines in the presence of [Pd(PPh₃)₄], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X‐ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five‐membered palladacycle with the metal center bearing a PPh₃ ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ‐alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β‐hydride elimination. Subsequently, the thus obtained bridged five‐membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross‐coupling processes such as Suzuki and Stille reactions.     

Palladium(II)‐N‐heterocyclic carbene complexes: synthesis,characterization and catalytic application

N‐Heterocyclic carbenes (NHCs) are of great importance and are powerful ligands for transition metals. A new series of sterically hindered benzimidazole‐based NHC ligands (LHX) ( 2a , 2b , 2c , 2d , 2e , 2f ), silver–NHC complexes ( 3a , 3b , 3c , 3d , 3e , 3f ) and palladium–NHC complexes ( 4a , 4b , 4c , 4d , 4e , 4f ) have been synthesized and characterized using appropriate spectroscopic techniques. Studies have focused on the development of a more efficient catalytic system for the Suzuki coupling reaction of aryl chlorides. Catalytic performance of Pd–NHC complexes and in situ prepared Pd(OAc)₂/LHX catalysts has been investigated for the Suzuki cross‐coupling reaction under mild reaction conditions in aqueous N,N‐dimethylformamide (DMF). These complexes smoothly catalyzed the Suzuki–Miyaura reactions of electron‐rich and electron‐poor aryl chlorides. Copyright © 2014 John Wiley & Sons, Ltd.     

Pd(II) complexes of Schiff bases and their application as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions

Schiff bases of 2‐(phenylthio)aniline, (C₆H₅)SC₆H₄N?CR (R = (o‐CH₃)(C₆H₅), (o‐OCH₃)(C₆H₅) or (o‐CF₃)(C₆H₅)), and their palladium complexes (PdLCl₂) were synthesized. The compounds were characterized using ¹H NMR and ¹³C NMR spectroscopy and micro analysis. Also, electrochemical properties of the ligands and Pd(II) complexes were investigated in dimethylformamide–LiClO₄ solution with cyclic and square wave voltammetry techniques. The Pd(II) complexes showed both reversible and quasi‐reversible processes in the ?1.5 to 0.3 V potential range. The synthesized Pd(II) complexes were evaluated as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions. Copyright © 2015 John Wiley & Sons, Ltd.     

Magnetically‐recoverable Schiff Base Complex of Pd (II) Immobilized on Fe3O4@SiO2 Nanoparticles: An Efficient Catalyst for Mizoroki‐Heck and Suzuki‐Miyaura Coupling Reactions

The activity of Pd(II)‐Schiff base complex molecules grafted on the surface of Fe₃O₄@SiO₂ particles were investigated in the palladium‐catalyzed coupling reactions of aryl halides with alkenes (Mizoroki‐Heck reaction) and phenylboronic acids (Suzuki‐Miyaura reaction) in the absence of phosphorous ligands. This method shows notable advantages such as heterogeneous nature of the catalyst, excellent yields, short reaction times, easy preparation, simplicity of operation, and cleaner reaction profiles. The catalyst can be separated from the reaction mixture by applying a permanent magnet externally and can be reused for several times without significant loss of activity. Also, the amount of palladium leaching has been determined by ICP analysis.     

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.     

氯化钯在氟化四丁基铵中当场生成纳米钯：一种高效、可回收的催化体系，在无配体和无溶剂条件下催化Suzuki-Miyaura反应

氯化钯在氟化四丁基铵中当场生成纳米钯,该钯催化剂在Suzuki-Miyaura交叉偶联反应中显示很高的催化效率。在氯化钯和氟化四丁基铵存在下,许多芳基卤代烃可以顺利与芳基硼酸发生偶联反应,得到中等到高的产率。此外,在Suzuki-Miyaura偶联反应中该氯化钯/氟化四丁基铵催化体系可以回收重复使用多次,并且芳基溴代烃可以在15-60分钟内反应完全。值得指出的是,该反应是在无溶剂、无配体和催化体系可回收重复使用的条件下进行的。这和无配体条件下TBAB中钯催化卤代芳烃与芳基硼酸的Suzuki-Miyaura交叉偶联反应方法。该氯化钯/氟化四丁基铵催化反应的反应机理也进行了讨论。     

Highly efficient orthopalladated complexes of second and third benzyl amine for catalyzing the Suzuki cross‐coupling reaction

In this work, ortho‐palladated complexes [Pd(µ‐Cl)(C₆H₄CH₂ NRR′‐κ²‐C,N)]₂ and [Pd(C₆H₄CH₂NH₂‐2‐C,N)Cl(Y)] were tested in the Suzuki–Miyaura cross‐coupling reaction. Cyclopalladated Pd(II) complexes as thermally stable catalysts can activate aryl bromides and chlorides. These complexes were active and efficient catalysts for the Suzuki–Miyaura reaction of aryl bromides and even less reactive aryl chlorides. The cross‐coupled products of a variety of aryl bromides and aryl chloride with phenylboronic acid in methanol as solvent at 60 °C were produced in excellent yields. Copyright © 2010 John Wiley & Sons, Ltd.     

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.