Highly effective activation of aryl chlorides for Suzuki coupling in aqueous media using a ferrocene-based Pd(II)–diimine catalyst

The Suzuki coupling of aryl chlorides with boronic acids using a ferrocene-containing Pd(II)–diimine complex as catalyst, in aqueous media, under microwave heating is reported. A small amount of the catalyst (0.1%) was found to be highly effective for coupling unactivated aryl chlorides with boronic acids to form sterically hindered ortho-substituted biaryls. The same catalyst also enabled the coupling of aryl bromides and iodides with various boronic acids in very high yields. The catalyst is air stable and the catalytic reaction can be completed in 15 min.     

Efficient construction of C–C bonds from aryl halides/aryl esters with arylboronic acids catalysed by palladium(II) thiourea complexes

A new set of palladium(II) complexes comprising phenyl(thiazolyl)thiourea ligands have been successfully synthesized and characterized with the aid of analytical as well as spectral (IR, UV–visible and NMR) methods. A distorted square‐planar geometry with N^S coordination mode of thiourea ligands in the new palladium complexes was corroborated by single‐crystal X‐ray diffraction methods. Interestingly, the palladium(II) thiourea complexes showed the highest catalytic activity with 0.1 mol% catalyst loading in Suzuki–Miyaura cross‐coupling reactions utilizing a range of aryl bromides/unactivated aryl chlorides with arylboronic acids as coupling partners in aqueous–organic media. Syntheses of diaryl ketones using aryl esters and arylboronic acids as coupling partners were also achieved with low catalyst loading within 20 h. The potential of our catalyst was demonstrated by its wide substrate scope, low catalyst loadings and high isolated yield. Moreover, the influences of key parameters like solvent, base, temperature and catalyst loading were also investigated.     

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.     

Efficient N-heterocyclic carbene nickel pincer complexes catalyzed cross coupling of benzylic ammonium salts with boronic acids

Pyridine-bridged bis-benzimidazolylidene nickel complexes exhibited very high catalytic activity toward cross coupling of inactive (hetero)aryl benzylic ammonium salts with (hetero)aryl and alkenyl boronic acids under mild reaction conditions. Even at 2 mol% catalyst loading, a wide range of substrates for both coupling partners with different steric and electronic properties were well tolerated.     

Heterogeneous Heck reaction catalysed by silica gel-supported 1,2-diaminocyclohexane–Pd complex

A 1,2-diaminocyclohexane–Pd complex was immobilized onto the surface of silica gel and investigated as a catalyst for Heck coupling reactions. The immobilized catalyst exhibited high catalytic activity in the coupling of activated and nonactivated aryl substrates with various acrylates. Moreover, the catalyst was air-stable that could be recycled and reused without significant loss of catalytic activity.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

Synthesis of Enaminone‐Pd(II) Complexes and Their Application in Catalysing Aqueous Suzuki‐Miyaura Cross Coupling Reaction

A series of Pd(II)‐enaminone complexes, termed Pd(eao)₂, have been synthesized and characterized. The investigation on the catalytic activities of these new Pd(II)‐reagents has proved that the Pd(eao)₂‐ 1 possesses excellent catalytic activity for the Suzuki‐ Miyaura cross coupling reactions of aryl bromides/chlorides with aryl/vinyl boronic acids in the environmentally benign media of aqueous PEG400 at low loading (5 mol‰). The superiority of this Pd(II)‐reagent to those commercial Pd(II) and Pd(0) catalysts in catalyzing the reactions has been confirmed by parallel experiments. What's more, Pd(eao)₂‐ 2 has been found as a practical catalyst for the homo‐coupling reactions of aryl boronic acids.     

Simple amine/Pd(OAc)(2)-catalyzed suzuki coupling reactions of aryl bromides under mild aerobic conditions

A new palladium catalyst (DAPCy) made from Pd(OAc)(2) and commercially available, inexpensive dicyclohexylamine has been developed for the Suzuki coupling reaction of aryl bromides with boronic acids to give the coupling products in good to high yields. The air-stable catalyst was characterized and well-defined by X-ray crystallography. A catalytic system involving DAPCy in dioxane demonstrates a temperature-dependent reactivity toward aryl bromides with different electronic substituents, and selectively couples electron-deficient aryl bromides with boronic acids over electron-rich ones at room temperature. Another catalytic system employing DAPCy in EtOH provides a general and convenient method to prepare biaryls from aryl bromides and boronic acids with a broad range of functional groups at room temperature and under aerobic conditions.     

Solvent-free,microwave-assisted highly efficient,rapid and simple synthesis of biphenyl compounds by using silica based Pd(II) catalyst

To maintain catalytic performance of any catalyst for a long time, the selection of support material is a very important parameter for heterogeneous catalytic systems, and this performance makes the catalyst valuable. In view of its low cost and availability, silica can be considered as a good support material for transition metal ions in the cross coupling reactions. Therefore, this study describes i) silica-gel based palladium catalyst with a long-term catalytic performance, ii) rapid, simple, economic, and green procedure which was developed for Suzuki reactions. The catalyst showed superior reusability (ten runs) and catalytic efficiency against coupling reactions under mild conditions (50°C, 5 min and air atmosphere). Moreover, the catalyst gave partially good reaction yields with aril chlorides which have poor activity in coupling reactions. In addition, an excellent turnover number (TON: 66000) and frequency (TOF: 825000) were obtained using very small catalyst loading (1.5 × 10^?3 mol %). This paper concludes that silica-gel based Pd(II) catalyst and the protocol of synthesis of biaryls were suitable for coupling reactions.     

Triazine‐Based Mesoporous Covalent Imine Polymers as Solid Supports for Copper‐Mediated Chan–Lam Cross‐Coupling N‐Arylation Reactions

The synthesis of a novel mesoporous covalent imine polymeric (MCIPs) material, involving simple Schiff‐base chemistry, is reported. This highly functionalised nitrogen‐rich material acts as a good support for immobilising Cu^II ions, exhibiting excellent catalytic activity in promoting the Chan–Lam cross‐coupling reaction between biologically active amines and arylboronic acids. The performance of this catalyst is also evident from its broad substrate scope, high stability, real heterogeneity, mild reaction conditions and reusability without loss of activity. The observed results will provide additional scope on the design and catalytic applications of this emerging class of materials.     

Nitrogen-rich porous covalent imine network (CIN) material as an efficient catalytic support for C-C coupling reactions

In an effort to expand the realm of possibilities of nitrogen-rich porous materials that could be used in catalysis, herein we report the synthesis of a new highly nitrogen rich (ca. 45%) porous covalent imine network (CIN-1) material employing simple Schiff base chemistry and further grafting its surface with palladium. Pd-loaded CIN-1 support acts as a truly heterogeneous catalyst towards Suzuki C-C coupling reaction between aryl halides with arylboronic acids. High surface area and excellent accessibility of the catalytic sites make it very efficient for heterogeneous catalysis. The stability of the catalyst due to intimate contact between nitrogen-rich organic support and metal allows several reuses with only a minor loss in catalytic activity.     

Nickel‐Catalyzed Direct Coupling of Allylic Alcohols with Organoboron Reagents

The direct coupling of allylic alcohols with arylboronic acids or their derivatives catalyzed by Ni(cod)₂ in the presence of a catalytic amount of base has been developed. A wide variety of allylic substrates or arylboronic acids turned out to be applicable to this catalytic system. The present method does not require the use of ligands for stabilizing the nickel catalyst in most cases or additional activators for activation of allylic alcohols.     

Novel monoligated imine–Pd–NHC complexes: extremely active pre-catalysts for Suzuki–Miyaura coupling of aryl chlorides

Novel monoligated imine–Pd–NHC pre-catalysts with extremely high activity for the coupling of aryl chlorides and aryl boronic acids have been well explored. Three diffident catalysts could be obtained through one reaction. Changes in imine ligands would lead to remarkable variation on catalytic activity. Under mild reaction conditions, high reaction yields were achieved. A wide range of biphenyls could be efficiently obtained at ultra low catalyst loadings of 0.005 mol %.     

Heterogeneous Suzuki and copper-free Sonogashira cross-coupling reactions catalyzed by a reusable palladium(II) complex in water medium

A new polystyrene anchored Pd(II) azo complex has been synthesized and characterized. The present Pd(II) azo complex behaves as a very efficient heterogeneous catalyst in the Suzuki coupling and Sonogashira coupling reaction in water medium. Aryl halides, coupled with phenylboronic acids (Suzuki-Miyaura reaction) or terminal alkyne (Sonogashira reaction), smoothly afford the corresponding cross-coupling products in excellent yields (83-100% yield for Suzuki reaction and 68-96% yield for Sonogashira reaction of aryl halides) under phosphine-free reaction conditions in the presence of polystyrene anchored Pd(II) azo complex catalyst in water medium. Furthermore, the catalyst has shown good thermal stability and recyclability. This polymer-supported Pd(II) catalyst could be easily recovered by simple filtration of the reaction mixture and reused for more than six consecutive trials without a significant loss of its catalytic activity.     

Highly efficient Suzuki-Miyaura coupling reactions catalyzed by bis(oxazolinyl)phenyl-Pd(II) complex

Bis(oxazolinyl)phenyl-palladium(II)(Phebox-Pd) complexes were found to be efficient catalysts for Suzuki-Miyaura coupling reactions of aryl boronic acids and their derivatives with aryl halides to give the corresponding biaryl products in high yield along with moderate enantioslectivities in the case of axially chiral induction. The catalytic activity was attained more than 900,000 of TON and 45,000 of TOF. The catalyst can be recovered quantitatively and could be reused for Suzuki-Miyaura reactions.     

Rapid Suzuki‐Miyaura cross‐coupling reaction catalyzed by zirconium carboxyphosphonate supported mixed valent Pd(0)/Pd(II) catalyst

Mixed valent Pd(0)/Pd(II) nano‐sized aggregates supported onto a chemically robust layered zirconium carboxyphosphonate framework is prepared and its catalytic activity in Suzuki‐Miyaura cross coupling reaction is explored. The exceptionally high catalytic efficacy of the heterogeneous catalyst in Suzuki‐Miyaura cross coupling reaction is signified by remarkably short reaction time 2 minutes and high turnover frequency of 1.3 x 10⁴ hr^?1. The catalyst can be recycled several times without significant loss of catalytic efficacy, while spectroscopic, structural and microscopic investigations suggest the integrity of the catalyst even after fifth catalytic cycle. The unique ability of the zirconium carboxyphosphonate framework to interact strongly with palladium in dual Pd(0)/Pd(II) oxidation states has been attributed to this remarkable augmentation of catalytic efficacy.     

Facile synthesis of Fe@Pd nanowires and their catalytic activity in ligand-free CN bond formation in water

This work reports a facile synthesis of Fe@Pd nanowires. Ligand-free cross coupling reactions of arylboronic acids with various amines in aqueous medium proceed in very good to excellent yield with the use of Fe@Pd nanowires. Furthermore, the catalyst could be easily separated from the reaction mixture using a magnet and could be recycled several times without loss of 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.     

Highly active and reusable hydrotalcite-supported Pd(0) catalyst for Suzuki coupling reactions of aryl bromides and chlorides

A palladium(0) nanocluster supported on hydrotalcite has been prepared and tested for the Suzuki coupling reaction. The prepared catalyst showed very efficient catalytic activity for cross coupling of iodo- and bromoarenes under very mild reaction conditions, affording >90% yield. Under the optimized reaction conditions, chloroarenenes also showed very good reactivity. Transmission electron microscopic imaging data showed the formation of very small Pd(0)-nanoclusters (d = 2.2 ± 0.5 nm) well dispersed on the support, which enhanced the activity and stability of the catalyst for the Suzuki cross-coupling reaction. This catalytic system offers an easy method of preparation with good activity and reusability up to five cycles.