Heck Cross-coupling Reactions Research Articles

Ultrafine palladium nanoparticles immobilized into poly(4-vinylpyridine)-based porous monolith for continuous-flow Mizoroki–Heck reaction

Ultrafine Pd nanoparticles (dm=2.3nm), obtained by metal vapor synthesis technique, were immobilized into a poly(4-vinylpyridine)-based porous monolith by means of a new synthetic approach. The synthesis involves stabilization of Pd nanoparticles with 4-vinylpyridine ligand and their subsequent immobilization into the monolith by radical co-polymerization of the resulting metal-embedding monomer with ethylene glycol dimethacrylate in presence of porogenic agents (i.e. DMF and PEG-400) inside stainless-steel columns (HPLC type). The hybrid monolithic reactors containing highly dispersed Pd nanoparticles were effectively used as catalyst for Mizoroki–Heck cross-coupling reactions carried out under continuous-flow conditions. The devices showed long life-time (>65h) and very low Pd leaching (<2ppm).

NIR bacteriochlorin chromophores accessed by Heck and Sonogashira cross-coupling reactions on a tetrabromobacteriochlorin derivative.

The synthesis of a new tetrabromobacteriochlorin BCBr4 is reported having the 3,4-dibromo-1H-pyrrole-2-carbaldehyde (10) as the major precursor. The BCBr4 was successfully employed in Pd cross-coupling reactions with methyl acrylate, phenyl acetylene and 4-ethynylanisole. In all three cases, the desired tetra-coupled products were obtained in good to excellent yields, and present a significant red shift in the UV-Vis bands above 800 nm. DFT and TD-DFT theoretical analyses of the NIR bacteriochlorin chromophores were performed in order to evaluate the effect of β substitution on their electronic structures.

C2-Symmetric ferrocenyl bisthiazoles: synthesis, photophysical, electrochemical and DFT studies.

A series of donor-acceptor ferrocenyl substituted bisthiazoles 3-8 were designed and synthesized by the Pd-catalyzed Suzuki, Heck, and Sonogashira cross-coupling reactions. Their photophysical, electrochemical and computational studies reveal strong donor-acceptor interactions. The photonic and electrochemical studies show that the ferrocenyl bisthiazoles with vinyl linkage ferrocenyl-bisthiazole 4, show better electronic communication compared to rest of the ferrocenyl bisthiazoles. The time dependent density functional theory (TD-DFT) calculation at B3LYP on the ferrocenyl substituted bisthiazoles 3-5 was performed, in which the ferrocenyl-bisthiazole 4 shows strong donor-acceptor interactions compared to the Fc-bisthiazoles 3 and 5. The thermal stability of the ferrocenyl substituted bisthiazoles 3-8 is reported, in which Fc-bisthiazole 8 shows high thermal stability. The single crystal structures of ferrocenyl-bisthiazoles 3 and 5 are reported.

Suzuki, Stille and Heck cross-coupling reactions catalyzed by Fe3O4@PTA–Pd as a recyclable and efficient nanocatalyst in green solvents

A novel heterogeneous Pd-catalyst was designed and successfully employed in C–C coupling reactions under green conditions.

Synthesis and Characterization of Pd{II) and Ni(II) Complexes of Schiff Bases and Catalytic Activity of Pd(II) Complexes

Six new Pd(Il) and Ni(Il) metal complexes of N, O-bidentate (LI, L2) and ONNO-tetradentate (L3) Schiff base ligands have been synthesized. The compounds were characterized via various physicochemical and spectroscopic techniques namely elemental analysis (CHN), FT-IR, 1H and 13C NMR. as well as magnetic susceptibility measurement. All complexes showed diamagnetism indicating that they are square planar complexes. Catalytic performance of Pd(Ll)2 and Pd(L2)2 were investigated/or Heck cross-coupling reaction under optimum operating parameters, monitored using GC-FID for 6 h of reaction time in inert conditions. High catalytic activities of up to 90% were observed in the presence of triethylamine as base and DMA as solvent at J0()"C with I mmol% catalyst loading. The mechanism of catalyzed Heck reaction is proposed to go through a series of conversion of Pd(0)/Pd(Il).

Synthesis and Characterization of Pd(II) and Ni(II) Complexes of Schiff Bases and Catalytic Activity of Pd(II) Complexes

Six new Pd(Il) and Ni(Il) metal complexes of N, O-bidentate (LI, L2) and ONNO-tetradentate (L3) Schiff base ligands have been synthesized. The compounds were characterized via various physicochemical and spectroscopic techniques namely elemental analysis (CHN), FT-IR, 1H and 13C NMR. as well as magnetic susceptibility measurement. All complexes showed diamagnetism indicating that they are square planar complexes. Catalytic performance of Pd(L1)2 and Pd(L2)2 were investigated for Heck cross-coupling reaction under optimum operating parameters, monitored using GC-FID for 6 h of reaction time in inert conditions. High catalytic activities of up to 90% were observed in the presence of triethylamine as base and DMA as solvent at 100C with 1 mmol% catalyst loading. The mechanism of catalyzed Heck reaction is proposed to go through a series of conversion of Pd(0)/Pd(II).

ChemInform Abstract: An Expedient Approach to Enhance Mizoroki—Heck Coupling Reaction by Infrared Irradiation Using Palladacycle Compounds.

An alternative and environmentally friendly strategy to promote the Mizoroki–Heck cross-coupling reaction by the use of infrared irradiation using palladacycles as precatalysts is reported. Coupling products are obtained in high yield and short reaction time. A comparison with the classical use of reflux conditions, and commercial sources of palladium complexes, shows the advantages of this new alternative for promoting coupling reactions. Copyright © 2015 John Wiley & Sons, Ltd.

C(sp2)–C(sp2) cross coupling reaction catalyzed by a palladacycle phosphine complex: A simple and sustainable protocol in aqueous media

The Heck reactions of various aryl halides with olefins using {[Ph2PCH2PPh2CH = C(O)(C10H7)] PdCl2} as efficient catalyst has been investigated. The mononuclear palladacycle complex showed excellent activity in aqueous phase including the C(sp 2)–C(sp 2) cross coupling reactions. The advantages of the protocol are high yields, short reaction time, a cleaner reaction profile and notable simplicity. Application of the palladacycle complex in the Heck cross coupling reaction of various aryl halides with styrene and ethyl acrylate is reported.

High catalytic active palladium nanoparticles gradually discharged from multilayer films to promote Suzuki, Heck and Sonogashira cross coupling reactions

To improve the catalytic activity and reduce the dosage of noble metal catalysts has attracted much more attention for organic synthetic chemists. We facilely fabricated multilayer films of PEI-(PdCl2/1)n through layer-by-layer (LBL) self-assembly method (PEI=polyethylenmine, 1=2,2′,7,7′-tetra(4-pyridyl)-9,9′-spirobifluorene, psf). UV–vis spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to monitor the growth of multilayer films. X-ray photoelectron spectroscopy (XPS) proved the palladium and ligand 1 were deposited on the film. The PEI-(PdCl2/1)n multilayer films were used as the cisterns of catalysts to gradually discharge high active catalytic moieties in the Suzuki–Miyaura, Heck and Sonogashira cross-coupling reactions. The Pd-loading was as low as 12.1×10−6mol% measured by inductively coupled plasma OES spectrometer (ICP), and gave high yields in the typical reactions of bromobenzenes with phenylboronic acids. The LbL catalyst featured the simplicity of fabrication, high efficiency, reusability, convenient control and no sensitive to air in the reactions.

Palladium-Schiff Base Complex Immobilized Covalently on Magnetic Nanoparticles as an Efficient and Recyclable Catalyst for Heck and Suzuki Cross-Coupling Reactions

A new palladium-Schiff base complex immobilized covalently on magnetic nanoparticles (Pd-imino-Py-γ-Fe2O3) was synthesized via the reaction of chloro-functionalized γ-Fe2O3 with iminopyridine followed by the reaction with palladium acetate. Characterization of Pd-imino-Py-γ-Fe2O3 was carried out by various techniques such as XRD, SEM, TEM, FT-IR, TGA, ICP, XPS, VSM and elemental analysis. Pd-imino-Py-γ-Fe2O3 was successfully applied as a magnetically recyclable heterogeneous catalyst in Heck and Suzuki cross-coupling reactions of various aryl halides (iodide, bromides and chlorides as challenging substrates) with olefins and phenylboronic acid, respectively. The synthesized catalyst was separated easily by using an external magnet and recycled eight runs without appreciable loss of its catalytic activity and leaching of the significant quantity of Pd.

ChemInform Abstract: New Developments in the Synthesis of (E)‐8‐Styrylflavones.

A novel route for the synthesis of new (E)-8-styrylflavones is reported. This methodology involves the regio- and stereoselective Heck cross-coupling reaction of 8-iodoflavones and styrene derivatives. The Heck precursors, 8-iodoflavones, were obtained through an efficient regioselective one-pot oxidative cyclization–iodination reaction of (E)-2′-hydroxychalcones by applying the iodine/dimethyl sulfoxide system.

Synthesis of π-Bridged Dually-Dopable Conjugated Polymers from Benzimidazole and Fluorene: Separating Sterics from Electronics

We describe the synthesis and characterization of three new alternating copolymers containing fluorene and a dually dopable benzimidazole moiety. Poly(2-n-heptyl-benzimidazole-alt-9,9-di-n-octylfluorene) (PBIF), poly(2-n-heptyl-benzimidazole-vinylene-9,9-di-n-octylfluorene) (PBIF-VL), and poly(2-n-heptyl-benzimidazole-ethynylene-9,9-di-n-octylfluorene) (PBIF-EL) were synthesized from Suzuki, Heck, and Sonogashira cross-coupling reactions in reasonable yield. The materials were characterized through ultraviolet–visible spectroscopy, photoluminescence, and cyclic voltammetry. The vinyl and ethynyl bridges in PBIF-VL and PBIF-EL were incorporated to separate benzimidazole and fluorene units while retaining conjugation. This allowed us to differentiate between steric and electronic contributions to the band gap (Eg) changes that occur upon acid/base doping of these materials. We demonstrate that the blue shift arising from acid doping PBIF is due to steric torsion, while the red shift found upon base doping P...

Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki–Miyaura and Mizoroki–Heck Cross Coupling Reactions

A pyridyl fluorene ligand, 2,7-bis(4-pyridyl)-9,9-diethylfluorene (1), has been synthesized by a simple route. The ability of the two linearly terminal pyridyl nitrogen atoms of 1 to coordinate with the Pd(II) or Ni(II) ions has enabled the use of 1 as a linking ligand in the preparation of (PdCl2/1) n , (Ni(NO3)2/1) n films, PdCl2/1 and Ni(NO3)2/1 complex. The resulting films and complexes were characterized by UV–vis spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectrometer. The application of films and complexes as catalysts for Suzuki–Miyaura and Mizoroki–Heck reactions was carried out. (PdCl2/1) n films show high catalytic activity in the reactions with the Pd loading of ppm. (Ni(NO3)2/1) n multilayers as the active catalytic moieties for these reactions were investigated with very low Ni(II)-loading. The (Pd or Ni/1) n multilayer films were used as high active catalysts for the C-C formation with extremely low M(II)-loading in ppm level.

Palladium Nanoparticles Supported on MIL-101 as a Recyclable Catalyst in Water-Mediated Heck Reaction.

Pd nanoparticles supported on the chromium terephthalate metal organic framework, Pd0.9/MIL-101, was prepared by simple Pd-acetate adsorption on MIL-101 followed by reduction in acetone. The material was characterized by XRD, N2 adsorption-desorption isotherm, TEM and ICP analysis. Pd0.9/MIL-101 was found to be an effective heterogeneous catalyst for the water-mediated Heck cross-coupling reaction of various aryl iodides and alkenes under mild reaction conditions with product yields of 81 to 97%. The electron-withdrawing group attached to aryl iodide reacted faster than the electron-donating one, and the activity increased in the sequence of 4-methoxy-1- iodobenzene << iodobenzene < 1-iodo-4-nitrobenzene. The catalyst could be reused several times without losing its initial catalytic activity, and XRD and TEM confirmed that the crystallinity of Pd0.9/MIL-101 had been retained during the reaction with no metal leaching or agglomeration observed.

Palladium immobilized on Fe3O4/ZnO nanoparticles: a novel magnetically recyclable catalyst for Suzuki–Miyaura and heck reactions under ligand-free conditions

Magnetically separable Pd(0)/Fe3O4/ZnO catalyst was easily synthesized by immobilizing Pd on the surface of magnetic Fe3O4–ZnO nanoparticles. The nano-Pd/Fe3O4/ZnO was found as a magnetically separable and highly active catalyst for Suzuki–Miyaura as well as Heck cross-coupling reactions under ligand-free conditions. Under appropriate conditions, all reactions afforded the desired products in moderate to excellent yields. Moreover, this catalyst can be easily recovered using simple magnet and directly reused without significant loss of its activity.

Developing chitosan-based composite nanofibers for supporting metal catalysts

Using electrospinning technique to prepare chitosan (CS) nanofibers from an inexpensive solvent such as acetic acid has been a challenge, due to the lack of sufficient entanglements in these semi-rigid polyelectrolytes. Incorporating polymers such as poly(methacrylic acid) (PMAA) into the solution lowers the entanglement concentration of the polymers, and make all three morphology regimes (polymer droplets, beaded nanofibers and nanofibers with uniform thickness) accessible to electrospinning method. Uniform composite nanofibers are found at concentrations well above the entanglement concentration. The thickness and morphology of nanofibers can be regulated by addition of small amount of organic solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The composite nanofibers are subsequently crosslinked at an elevated temperature to improve their thermal and solvent stability. The mechanical properties of the crosslinked CS/PMAA fibers can be modulated by varying the amount and molecular weight of PMAA incorporated in the blend. The composite fiber materials provide a useful platform to support a variety of catalysts. As a demonstration, palladium catalyst has been immobilized on the crosslinked CS/PMAA nanofibers to carry out Mizoroki–Heck cross-coupling reactions of aromatic halides and acrylates. We found remarkable catalytic efficiency and stability in these materials. We also demonstrate that, by the “post-modification” of the nanofibers with ligands that chelate metal catalysts, a variety of metal catalysts can be incorporated into the fiber platform, with further improved stability and activity.

NiCl2·6H2O: an efficient catalyst precursor for phosphine-free Heck and Sonogashira cross-coupling reactions

An efficient and simple protocol for the Heck reaction of aryl iodides and bromides using NiCl2·6H2O as the pre-catalyst is presented. The reactions proceed well in ethylene glycol in the absence of phosphine ligands and reducing agent. Compared to the frequently used expensive palladium catalysts, the use of nickel catalyst has an economic advantage and hence, remains attractive for large or industrial scale preparations. The efficient copper- and phosphine-free Sonogashira coupling reaction of aryl iodides is also demonstrated using this catalytic system.

Synthesis of globular precursors.

o-Carborane (C2 B10 H12 ) was adapted to perform as the core of globular macromolecules, dendrons or dendrimers. To meet this objective, precisely defined substitution patterns of terminal olefin groups on the carborane framework were subjected to Heck cross-coupling reactions or hydroboration leading to hydroxyl terminated arms. These led to new terminal groups (chloro, bromo, and tosyl leaving groups, organic acid, and azide) that permitted ester production, click chemistry, and oxonium ring opening to be performed as examples of reactions that demonstrate the wide possibilities of the globular icosahedral carboranes to produce new dendritic or dendrimer-like structures. Polyanionic species were obtained in high yield through the ring-opening reaction of cyclic oxonium compound [3,3'-Co(8-C4 H8 O2 -1,2-C2 B9 H10 )(1',2'-C2 B9 H11 )] by using terminal hydroxyl groups as nucleophiles. These new polyanionic compounds that contain multiple metallacarborane clusters at their periphery may prove useful as new classes of compounds for boron neutron capture therapy with enhanced water solubility and as cores to make a new class of high-boron globular macromolecules.

Reactions of nitroxides 15. Cinnamates bearing a nitroxyl moiety synthesized using a Mizoroki-Heck cross-coupling reaction.

Cinnamic acid derivatives bearing a nitroxyl moiety (2,2,6,6-tetramethyl-1-oxyl-4-piperidyl 3-E-aryl acrylates) were synthesized in 30–100% yield using a Mizoroki–Heck cross-coupling reaction between 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl and iodobenzene derivatives in the presence of palladium(II) acetate coordinated with a tri(o-tolyl)phosphine ligand immobilized in a polyurea matrix.

New Developments in the Synthesis of (E)-8-Styrylflavones

A novel route for the synthesis of new (E)-8-styrylflavones is reported. This methodology involves the regio- and stereoselective Heck cross-coupling reaction of 8-iodoflavones and styrene derivatives. The Heck precursors, 8-iodoflavones, were obtained through an efficient regioselective one-pot oxidative cyclization–iodination reaction of (E)-2′-hydroxychalcones by applying the iodine/dimethyl sulfoxide system.