Showing papers on "Heck reaction published in 2001"
TL;DR: In the presence of Cy2NMe, Pd/P(t-Bu)3 serves as an exceptionally mild and versatile catalyst for Heck reactions of aryl chlorides and bromides, representing an advance over previously reported catalysts for these Heck coupling processes.
Abstract: In the presence of Cy2NMe, Pd/P(t-Bu)3 serves as an exceptionally mild and versatile catalyst for Heck reactions of aryl chlorides and bromides. A sterically and electronically diverse array of aryl bromides, as well as activated aryl chlorides, couple with a range of mono- and disubstituted olefins at room temperature, furnishing the arylated product with high E/Z stereoselection. The corresponding reactions of a broad spectrum of electron-neutral and electron-rich aryl chlorides proceed at elevated temperature, also with high selectivity. In terms of scope and mildness, Pd/P(t-Bu)3/Cy2NMe represents an advance over previously reported catalysts for these Heck coupling processes.
604 citations
TL;DR: The bis-carbene precursor, 1, gives a thermally very robust γPd(II) catalyst for Heck coupling that maintains activity even in boiling diethylacetamide (bp 184 °C) in air.
377 citations
TL;DR: A review of the application of palladium metal catalysts to the Heck reaction can be found in this paper, where a brief outline of the historical development of heterogeneous catalysis as applied to catalysis is given.
Abstract: This review is devoted to the application of palladium metal catalysts to the Heck reaction (arylation or vinylation of alkenes with aryl or vinyl halides and pseudohalides). The number of relevant articles published in recent years shows steadily increasing interest in this field. A brief outline of the historical development of heterogeneous catalysis as applied to the Heck reaction is given (Section 2). Both supported metal catalysts (Section 3) and stabilized colloidal palladium catalysts (Section 4) are included. Heterogeneous catalysts supported over different kinds of supports (carbon, inorganic oxides, molecular sieves, polymeric materials, etc.) are reviewed under separate headings. Particular attention is paid to the metal leaching and the nature of catalysis, two tightly connected problems which appear to be still controversial (Section 5). Some perspectives are shortly discussed in the final section (Section 6).
377 citations
TL;DR: Heterogeneous catalysts prepared, characterized, and applied for the first time for catalytic carbon-carbon coupling reactions exhibit a high activity and selectivity toward the Heck reaction of aryl bromides with olefins for small palladium concentrations.
Abstract: [Pd]-exchanged NaY zeolites have been prepared, characterized, and applied for the first time for catalytic carbon-carbon coupling reactions. The catalysts exhibit a high activity and selectivity toward the Heck reaction of aryl bromides with olefins for small palladium concentrations (< or =0.1 mol % of Pd). The catalysts can easily be separated from the reaction mixture and reused after washing without loss in activity. No limitation to the diffusion of adducts in the zeolite cages was observed (for linear alkenes). The electronic nature of the aryl bromides and the olefins has a dominating effect on the reaction yield and selectivity. The heterogeneous catalysts quantitatively convert all types of all aryl bromide (complete conversion of bromobenzene within 30 min) and activated aryl chlorides under standard reaction conditions. Product form selectivity is observed in the Heck reaction with cyclic olefins.
331 citations
TL;DR: Mechanistically, palladium-to-ligand ratio studies strongly support an active species bearing one nucleophilic carbene ligand in the synthesis of an important new antibiotic.
Abstract: Nucleophilic N-heterocyclic carbenes have been conveniently used as catalyst modifiers in amination reactions involving aryl chlorides, aryl bromides, and aryl iodides with various nitrogen-containing substrates. The scope of a coupling process using a Pd(0) or Pd(II) source and an imidazolium salt in the presence of a base, KO(t)Bu or NaOH, was tested using various substrates. The Pd(2)(dba)(3)/IPr.HCl (1, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) system presents the highest activity with respect to electron-neutral and electron-rich aryl chlorides. The ligand is also effective for the synthesis of benzophenone imines, which can be easily converted to the corresponding primary amines by acid hydrolysis. Less reactive indoles were converted to N-aryl-substituted indoles using as supporting ligand the more donating SIPr.HCl (5, SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene). The Pd(OAc)(2)/SIPr.HCl/NaOH system is efficient for the N-arylation of diverse indoles with aryl bromides. The general protocol developed has been applied successfully to the synthesis of a key intermediate in the synthesis of an important new antibiotic. Mechanistically, palladium-to-ligand ratio studies strongly support an active species bearing one nucleophilic carbene ligand.
317 citations
TL;DR: An overview of the use of the Heck reaction for the production of fine chemicals is given in this paper, where five commercial products have been identified that are produced on a scale in excess of 1 ton/year.
Abstract: An overview is given of the use of the Heck reaction for the production of fine chemicals. Five commercial products have been identified that are produced on a scale in excess of 1 ton/year. The he...
298 citations
TL;DR: Palladium nanoparticles (2−3 nm in diameter) have been prepared within covalently functionalized poly(propylene imine) dendrimers, and the resulting composite materials are shown to be effective for Heck coupling reactions as discussed by the authors.
Abstract: Palladium nanoparticles (2−3 nm in diameter) have been prepared within covalently functionalized poly(propylene imine) (PPI) dendrimers, and the resulting composite materials are shown to be effective for Heck coupling reactions. Two novel concepts are demonstrated in this report. The first concept involves the incorporation of Pd0 nanoparticles into PPI dendrimers covalently functionalized with perfluorinated polyether chains on their periphery. The second concept involves the first example of a carbon−carbon coupling reaction catalyzed by a dendrimer-templated nanomaterial, specifically, the catalytic heterocoupling between nonactivated aryl halides and n-butylacrylate mediated by the dendrimer-encapsulated catalysts. These reactions were carried out in a homogeneous fluorous/organic reaction phase at elevated temperature, and the catalyst was recovered by cooling to room temperature and concomitant phase separation. The catalyst was found to be catalytically active at a reaction temperature of only 90 ...
285 citations
TL;DR: Heck reaction proceeds at ambient temperature with considerably enhanced reaction rate through the formation of Pd-biscarbene complexes and stabilized clusters of zero-valent Pd nanoparticles in ionic liquids under ultrasonic irradiation.
269 citations
TL;DR: A new phosphine-imidazolium salt that has proven to be highly efficient in the Heck coupling reactions of aryl bromides with n-butyl acrylate in the presence of Cs(2)CO(3) as base.
226 citations
TL;DR: The behavior of PAMAM-dendrimer encapsulated palladium nanoparticles as catalysts for the Heck reaction has been examined, and it has been demonstrated that this simple system is a very efficient catalyst giving good yields under phosphine-free conditions and with 200−400 times less Pd than usual as discussed by the authors.
Abstract: The behavior of PAMAM-dendrimer encapsulated palladium nanoparticles as catalysts for the Heck reaction has been examined, and it has been demonstrated that this simple system is a very efficient catalyst giving good yields under phosphine-free conditions and with 200−400 times less Pd than usual.
179 citations
TL;DR: Comparison between phosphine- and nonphosphine-based palladacycles suggests that they follow the same reaction mechanism, and the role of water in accelerating the initial formation of the active catalyst species is noted.
Abstract: Experimental kinetic studies of the coupling of p-bromobenzaldehyde (1) with butyl acrylate (2) using the dimeric palladacycles complex (4) with chelating nitrogen ligands were carried out together with kinetic modeling using a reaction rate expression based on the mechanism shown in Scheme 2. The oxidative addition product of 1 was found to be the resting state within the catalytic cycle. The formation of dimeric Pd species external to the catalytic cycle helped to rationalize a non-first-order rate dependence on catalyst concentration. Theoretical modeling showed how the relative concentrations of the different intermediate species within the catalystic cycle can influence the observed rate dependence on Pd concentration. It was shown how conventional kinetic studies may give reaction orders in substrates which differ from those which would be observed under practical synthetic conditions. Comparison between phosphine- and nonphosphine-based palladacycles suggests that they follow the same reaction mechanism. The role of water in accelerating the initial formation of the active catalyst species is noted.
TL;DR: In this article, three conjugated polymers comprised of 9,9-dioctylfluorene and 2,2-bipyridine, which are alternatively linked by the C−C single bond (P1), vinylene and ethynylene bonds (P3), have been synthesized via the Suzuki reaction, the Wittig−Horner reaction, and the Heck reaction, respectively.
Abstract: Three conjugated polymers comprised of 9,9-dioctylfluorene and 2,2‘-bipyridine, which are alternatively linked by the C−C single bond (P1), vinylene bond (P2), or ethynylene bond (P3), have been synthesized via the Suzuki reaction, the Wittig−Horner reaction, and the Heck reaction, respectively The optical, electrochemical, and other physical properties of the polymers are dependent on the linkers The polymer linked by the C−C single bond exhibits a much larger Stokes shift compared with the other two polymers, indicative of higher extended and rigid backbone conformations in the polymers linked by the vinylene and ethynylene bonds All the three polymers are sensitive to the existence of a variety of transition metal ions due to the chelation between the 2,2‘-bipyridyl moieties and the metal ions For the metal ions which have moderate and weak coordination ability with the 2,2‘-bipyridyl moieties, an obvious difference in response sensitivity is observed among the three polymers: P1 has the highest s
TL;DR: In this article, it was shown that heterogeneous palladium metal catalysts employed in Heck-type reactions mainly act as sources of soluble palladium(II) complexes, which are the true catalytically active species.
Abstract: Novel experimental evidence is presented pointing out that “heterogeneous” palladium metal catalysts employed in Heck-type reactions mainly act as sources of soluble palladium(II) complexes, which are the true catalytically active species.
TL;DR: The Heck reaction finds several applications in industry because it is one of the effective tools for the formation of a new C-C bond as mentioned in this paper. In addition to the catalytic activity and selectivity, catalyst-product separation strategies are very important for the industrial application.
Abstract: The Heck reaction finds several applications in industry because it is one of the effective tools for the formation of a new C─C bond. In addition to the catalytic activity and selectivity, catalyst–product separation strategies are very important for the industrial application. There are various methods of interest ranging from conventional heterogeneous catalysts to heterogenization of homogeneous catalysts. The heterogeneous catalysts are classified into supported metal catalysts, zeolite-encapsulated catalysts, colloids–nanoparticles, and intercalated metal compounds. The homogeneous metal complexes catalysts are heterogenized using modified silica catalysts, polymer-supported catalysts, biphasic catalysts, supported liquid-phase catalysts, nonionic liquids solvents, perfluorinated solvents, and reusable homogeneous complexes. In general, heterogeneous catalysts are effective and stable at higher temperatures, which may be important for the activation of less reactive but less expensive chloroaryls su...
TL;DR: Chiral complexes of palladium, 1, with the tridentate ligand 2,6-lutidinyl-biscarbene (C⁁N⁁C), have been prepared and in the solid state they exhibit helical symmetrical structures which are persistent in solution at least up to 80 °C as discussed by the authors.
TL;DR: These assemblies show increased catalytic activity in the palladium-catalyzed Heck reaction and rhodium-Catalyzed hydroformylation and M=transition metal catalyst.
Abstract: Enforced ligand dissociation as a result of steric interactions between ZnII porphyrin units and the N atoms of pyridylphosphane ligands determines the catalytic properties of the encapsulated transition metal complexes. These assemblies show increased catalytic activity in the palladium-catalyzed Heck reaction and rhodium-catalyzed hydroformylation. M=transition metal catalyst.
TL;DR: The sequential integration of Heck-type (or double Heck) coupling and Hiyama-type coupling produced the multisubstituted olefins in regioselective, stereoselectives, and diversity-oriented fashions.
Abstract: A novel strategy for the diversity-oriented synthesis of multisubstituted olefins, where 2-pyridyldimethyl(vinyl)silane functions as a versatile platform for olefin synthesis, is described. The palladium-catalyzed Heck-type coupling of 2-pyridyldimethyl(vinyl)silanes with organic iodides took place in the presence of Pd2(dba)3/tri-2-furylphosphine catalyst to give β-substituted vinylsilanes in excellent yields. The Heck-type coupling occurred even with α- and β-substituted 2-pyridyldimethyl(vinyl)silanes. The one-pot double Heck coupling of 2-pyridyldimethyl(vinyl)silane took place with two different aryl iodides to afford β,β-diarylated vinylsilanes in good yields. The palladium-catalyzed Hiyama-type coupling of 2-pyridyldimethyl(vinyl)silane with organic halides took place in the presence of tetrabutylammonium fluoride to give di- and trisubstituted olefins in high yields. The sequential integration of Heck-type (or double Heck) coupling and Hiyama-type coupling produced the multisubstituted olefins in ...
TL;DR: The calculations show that intermediate ligand detachment and reattachment is necessary in the course of the oxidative addition to Pd II, and the PdII/PdIV mechanism is expected to be only feasible if a weakly coordinating ligand is present.
Abstract: In this theoretical study on the Heck reaction we explore the feasi- bility of an alternative pathway that involves a Pd II /Pd IV redox system. Usu- ally, the catalytic cycle is formulated based on a Pd 0 /Pd II mechanism. We performed quantum chemical calcula- tions using density functional theory on a model system that consisted of diphos- phinoethane (DPE) as a bidentate li- gand and the substrates ethylene and phenyl iodide to compare both mecha- nisms. Accordingly, the Pd II /Pd IV mech- anism is most likely to occur in the equatorial plane of an octahedral Pd IV complex. The energy profiles of both reaction pathways under consideration are largely parallel. A major difference is found for the oxidative addition of the CI bond to the palladium centre. This is a rate-determining step of the Pd II /Pd IV mechanism, while it is facile for a Pd 0 catalyst. The calculations show that intermediate ligand detachment and re- attachment is necessary in the course of the oxidative addition to Pd II . Therefore, we expect the Pd II /Pd IV mechanism to be only feasible if a weakly coordinating ligand is present.
TL;DR: Simple tricyclohexylphosphine adducts of palladium complexes with orthometallated N-donor ligands show by far the highest activity yet reported in the Suzuki coupling of aryl chlorides, even under aerobic conditions.
TL;DR: Small, yet measurable deviations of the phosphapalladacycle 1 from the other catalysts 2 and 3 in the product distribution of Styrene, in competition experiments of styrene and n-butyl acrylate, in the isotope effect on styrene, and the Hammett correlation on aryl bromides led to the conclusion that a different catalytic cycle is operative.
Abstract: The mechanism of the (Mizoroki-)Heck vinylation of aryl bromides catalyzed by the phosphapalladacycle [[PdCH2C6H4P(o-Tol)2(OAc)]2] (1) was investigated in order to determine whether palladium(IV) intermediates play a significant role in the catalytic cycle. The phosphapalladacycle 1 was compared to the related palladium(0) catalyst [Pd[P(o-Tol)3]2] (2) and an intermediate of the classical catalytic cycle [[PdAr[P(o-Tol)3]Br]2] (3) obtained by oxidative addition of an aryl bromide to 2. Small, yet measurable deviations of the phosphapalladacycle 1 from the other catalysts 2 and 3 in the product distribution of styrene, in competition experiments of styrene and n-butyl acrylate, in the isotope effect on styrene, and the Hammett correlation on aryl bromides led to the conclusion that a different catalytic cycle is operative. Nevertheless, due to only small differences in these competition experiments a modified classical catalytic cycle with a novel, cyclometallated, anionic palladium(0) species 6 is proposed rather than palladium(IV) intermediates. Species 6 accounts for the observed high activity and stability of palladacycle catalysts in the Heck reaction. Palladium(IV) intermediates can be ruled out by taking into account the experiments performed here and recently published by others.
TL;DR: In this paper, 1,5-Bis(4,4‘-bis(perfluorooctyl)phenyl)-1,4-pentadien-3-one stabilizes palladium(0) nanoparticles (transmission electron microscopy) formed in the reduction of palladium dichloride with methanol.
TL;DR: Pd/C-catalyzed Heck reactions of aryl halides with olefins with moderate to satisfactory yields in ionic liquid was reported in this paper, where a catalyst was easily recycled.
TL;DR: The catalytic activity and selectivity of palladium supported on various metal oxides and zeolites in carbon-carbon coupling reactions of aryl bromides with olefins (Heck reaction) are reported and reviewed in this article.
TL;DR: In this article, the reaction of imidazolium-linked ortho-cyclophanes with nickel and palladium(II) salts in the presence of acetate base led to the formation of complexes where a metal centre is bound by a pair of heterocyclic carbenes which themselves are part of a cyclophane skeleton.
Abstract: Reaction of imidazolium-linked ortho-cyclophanes with nickel(II) and palladium(II) salts in the presence of acetate base led to the formation of complexes where a metal centre is bound by a pair of heterocyclic carbenes which themselves are part of a cyclophane skeleton These cyclophane–metal complexes have been characterised by NMR spectroscopy and (for five complexes) X-ray diffraction studies The complexes are highly active as promoters of Heck and Suzuki couplings, with preliminary studies showing Heck reactions with turnover numbers approaching 107
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TL;DR: The catalyst-directing alkyl dimethylamino functionality was rapidly and efficiently released by microwave hydrolysis after Heck multiarylation reactions, and the liberated aromatic carbonyl compounds were thereafter isolated and fully characterized.
Abstract: This article describes the development of new auxiliary-accelerated Heck multiarylations by intramolecular presentation of the oxidative addition complex. The introduction of a specific, palladium-coordinating dimethylamino group allows for the desired chelation-accelerated and chelation-controlled tri- and diarylation reactions. We report (a) the first example of a Heck triarylation process, (b) highly selective palladium-catalyzed diarylations of alkyl vinyl ethers, and (c) a very rapid two-phase protocol for the microwave-assisted hydrolysis of amino-substituted, arylated vinyl ethers constituting an entry to diarylated ethanals and substituted desoxybenzoins. X-ray structures and product patterns support the suggested substrate-controlled Heck reaction pathway. The catalyst-directing alkyl dimethylamino functionality was rapidly (1−2 min) and efficiently released by microwave hydrolysis after Heck multiarylation reactions. The liberated aromatic carbonyl compounds were thereafter isolated and fully ch...
TL;DR: It is shown that a number of catalyst systems exist for efficient cross coupling of electron-deficient aryl chlorides with various olefins for Heck coupling reaction of 4-trifluoromethyl-1-chlorobenzene.
Abstract: A detailed investigation into the influence of phosphines, additives, bases and solvents on the Heck coupling reaction of 4-trifluoromethyl-1-chlorobenzene (2) is presented. It is shown that a number of catalyst systems exist for efficient cross coupling of electron-deficient aryl chlorides with various olefins. Basicity and steric demand of the ligand are two factors which determine the success of the reaction. In addition the phosphine/palladium ratio, the correct type and amount of additive, and finally the use of an appropriate base and solvent are also important. The optimised reaction conditions are applied for the arylation of styrene, 2-ethylhexyl acrylate and N,N-dimethyl acrylic amide with various aryl chlorides.
TL;DR: In this paper, a cyclopalladated Pd2(μ-L)2(NC)2] palladacycle with OC coordination was proposed for the Heck reaction.
TL;DR: In this article, the crystal structure of complex 9, the triphenylphosphine adduct of the pre-supported precursor complex 8, has been determined and the solid-supported catalysts show considerably lower activity in the Suzuki reaction than their homogeneous counterparts.
TL;DR: A Pd-catalyst with benzothiazole carbene as ligands allows, in tetrabutylammonium bromide melt as solvent, very fast and efficient reactions of bromoaromatics with 3-hydroxy-2-methylenealkanoates to give β-arylketones as mentioned in this paper.
TL;DR: In this paper, the use of nanofiltration membranes enabled catalyst separation and allowed subsequent catalyst recycle and reuse, which demonstrated potential for general applicability to homogeneously catalysed organic syntheses.