Catalyst For Heck Reaction Research Articles

Polyhedral Oligomeric Silsesquioxane-Encapsulating Amorphous Palladium Nanoclusters as Catalysts for Heck Reactions

Palladium nanoparticles (Pd NPs) capped with a certain protective group possessing stable reactivity of Pd-catalyzed reactions has been quickly and easily synthesized. The thiol−Pd2+ complexes of C12−Pd2+ and POSS−Pd2+ are prepared by the ligand exchange of acetate groups on Pd(OAc)2 with 1-dodecanthiol and SH-POSS (polyhedral oligomeric silsesquioxane), respectively. After thermal treatment at 120 °C for 30 min, the C12−Pd2+ and POSS−Pd2+ turn into C12−Pd(0) and POSS−Pd(0) NPs through the reduction of palladium cations with thiol groups. Unlike the well-known metallic Pd NPs with constituent Pd atoms arranged in an orderly repeating pattern, the cores of these thial−Pd(0) NPs are composed of a disordered (amorphous) aggregation of Pd atoms due to the steric hindrance caused by the affinity between in situ Pd atoms and thial groups. The relatively larger gaps between two adjacent POSS moieties, formed by solvent permeation when one isobutyl group approaches another, can be employed as transportation chann...

Identification of the Active Species Generated from Supported Pd Catalysts in Heck Reactions: An in situ Quick Scanning EXAFS Investigation

Quick scanning extended X-ray absorption fine structure (QEXAFS) studies in the subsecond time scale have been performed to gain insight into the reaction mechanism of Heck-type C-C coupling reactions in the presence of supported Pd-based catalysts. Using a specially designed in situ EXAFS cell, both the solid catalyst and the liquid reaction mixture during the reaction of phenyl bromide (PhBr) with styrene were monitored. Soluble Pd species were only, but rapidly, detected in the liquid reaction phase once the reaction temperature of 150 °C was reached. At the same time, the conversion of PhBr started, and during the following "active phase" of the catalyst hardly any changes in the corresponding EXAFS and XANES spectra were observed. The present species could be identified as colloidal Pd(0) clusters with a size of ∼2 nm estimated from the corresponding EXAFS spectra. The QEXAFS mode not only allowed monitoring rapid changes in the second time scale but also permitted minimization of effects caused by the heterogeneity of the systems. When the reaction rate started to decrease, pronounced changes in the EXAFS spectra were observed, which were attributed to an increased formation of bromo-palladates ([PdBr(4)](2-), [Pd(2)Br(6)](2-)). In addition to the liquid-phase species, significant changes were observed for the solid catalyst that was also probed in situ during the reaction. The originally oxidized Pd catalyst was efficiently reduced upon heating. Additionally, growth of the supported Pd particles was observed by both EXAFS and STEM. The above results confirm the role of the soluble molecular Pd species as the catalytically active species and clarify their conjunction with the in situ formed Pd colloids. Furthermore, the investigation demonstrates the potential of the QEXAFS not only for monitoring rapid changes during catalysis but also for gaining deeper insight into the mechanism of such complex industrially important systems under relevant reaction conditions.

Mechanism of the oxidative addition of aryl halides to bis-carbene palladium(0) complexes

Bis-N-heterocyclic carbenes Pd0 complexes, Pd0(NHC)2, are efficient catalysts in Heck reactions performed with aryl bromides or chlorides. The Pd0(NHC)2 that are not stable are generated in situ from PdII precursors PdY2(NHC)2 (Y = halides) after a chemical reduction. The latter procedure can be mimicked by an electrochemical reduction. The transient Pd0(NHCBn)2 is generated by electrochemical reduction of PdY2(NHCBn)2, and its reactivity in oxidative addition to aryl bromides and chlorides is characterized by the same electrochemical technique with the determination of the rate constants. Pd0(NHCBn)2 is found to be more reactive than the mixed complex Pd0(NHCBn)(PPh3). Both are the reactive species in an associative mechanism. Comparison with the isolated Pd0(NHCtBu)2 reveals that Pd0(NHCBn)2 is more reactive than Pd0(NHCtBu)2 even if the latter reacts via the mono-carbene Pd0(NHCtBu) in a dissociative mechanism. This suggests that the formation of mono-carbene Pd0(NHC) is not a guarantee for a fast oxidative addition because it is always generated at low concentration in its equilibrium with the related nonreactive bis-carbene Pd0(NHC)2.

Palladate salts from ionic liquids as catalysts in the Heck reaction

Palladate salts from imidazolium and pyridinium ionic liquids (ILs) were used as catalysts in Heck reaction. When compared to traditional precatalysts, they demonstrated to be more efficient catalysts. These results are attributed to the presence of nanoparticles (NPs) which served as a reservoir of palladium species. Indeed the use of palladate salts from ILs, that produce no byproducts, provide better control of the formation and surface composition of the NPs leading to a constant recyclability.

Highly Efficient, Recyclable Palladium Catalyst Immobilized on Organic-Inorganic­ Hybrid Material: Application in the Heck Reaction

Palladium immobilized on organic-inorganic (silica gel) hybrid materials behaves as a very efficient heterogeneous catalyst in Heck reactions. Iodoarenes, bromoarenes, as well as activated chloroarenes react smoothly with olefins to afford the corresponding cross-coupling products in good to excellent yields under phosphine- and amine-free reaction conditions in the presence of palladium immobilized on 3-[(2-aminoethyl)amino]propyl-functionalized silica gel (Silica-AAPTS-Pd) or palladium immobilized on 3-aminopropyl-functionalized silica gel (Silica-APTS-Pd) as catalyst. The silica-supported palladium catalyst could be recovered and recycled by simple filtration of the reaction solution, and used for more than ten consecutive trials without significant loss of catalytic activity.

New bis(fluoro-ponytailed) bipyridine ligands for Pd-catalyzed Heck reactions under fluorous biphasic catalysis condition

Three highly fluorinated bipyridine derivatives (4,4′-bis(R fCH 2OCH 2)-2,2′-bpy) {R f=HCF 2(CF 2) 7 ( 1a), n-C 8F 17 ( 1b), n-C 10F 21 ( 1c)} have been synthesized using 4,4′-bis(BrCH 2)-2,2′-bpy and the corresponding fluorinated alkoxides. The fluorine contents of ligands 1a– c are 58.3, 59.8, and 62.3%, respectively. Despite its high fluorine content, the ligand 1a with a –CF 2H polar terminal group is more soluble in organic solvents. The ligand 1b is a white solid and is still moderately soluble in CH 2Cl 2. The ligand 1c has a high fluorophilicity, the partition ratio being 42:1 for the n-C 8F 18/CH 2Cl 2 system. The reaction of ligands 1a– c with [PdCl 2(CH 3CN) 2] results in the novel Pd complexes [PdCl 2(4,4′-bis-(R fCH 2OCH 2)-2,2′-bpy)] where R f=HCF 2(CF 2) 7 ( 2a), n-C 8F 17 ( 2b), n-C 10F 21 ( 2c), respectively. The Pd complex 2b is a pale yellow solid, and has been tested unsatisfactorily for FBC. Insoluble in organic solvents, the Pd complex 2c dissolves only in fluorinated solvents, for instance FC77, which is mainly n-C 8F 18. The novel Pd complex 2c has been tested as a catalyst in Heck reactions under a fluorous biphasic catalysis condition. It was found that the Pd complex 2c, after an easy separation, keeps its catalytic activity (>90% yield), even after seven runs. The TGA studies indicate that the Pd complexes 2a– c are stable up to 330 °C.

(2,2′‐Bipyridine)palladiumdichloride Derivatives as Recyclable Catalysts in Heck Reactions

AbstractFluorous ponytailed [PdCl2(4,4′‐bis(RfCH2OCH2)‐2,2′‐bpy)], (Rf = CF3(CF2)2 2a, HCF2(CF2)3 2b, HCF2(CF2)7 2c, and non‐fluorous [PdCl2(4,4′‐bis(CH3)‐2,2′‐bpy)] 3 were prepared and successfully employed in the catalyst reusage studies running the homogeneous Heck reaction of C6H5I and H2C=CHCO2CH3, the catalysts being recycled for 8 consecutive runs without loss of activity and the recovery procedure being the direct vacuum distillation of mixtures to take advantage of the very high thermal stability of these PdCl2(2,2′‐bpy) derivatives.

1′‐Carbopalladated‐4‐ferrocenyl‐1,3‐oxazolines as Catalysts for Heck Reactions: Further Evidence in Support of the Pd(0)/Pd(II) Mechanism.

ChemInformVolume 36, Issue 40 Preparative Organic Chemistry 1′-Carbopalladated-4-ferrocenyl-1,3-oxazolines as Catalysts for Heck Reactions: Further Evidence in Support of the Pd(0)/Pd(II) Mechanism. Malgorzata Rosol, Malgorzata Rosol Dep. Quim. Org., Fac. Quim., Univ. Barcelona, E-08028 Barcelona, SpainSearch for more papers by this authorAlbert Moyano, Albert Moyano Dep. Quim. Org., Fac. Quim., Univ. Barcelona, E-08028 Barcelona, SpainSearch for more papers by this author Malgorzata Rosol, Malgorzata Rosol Dep. Quim. Org., Fac. Quim., Univ. Barcelona, E-08028 Barcelona, SpainSearch for more papers by this authorAlbert Moyano, Albert Moyano Dep. Quim. Org., Fac. Quim., Univ. Barcelona, E-08028 Barcelona, SpainSearch for more papers by this author First published: 06 September 2005 https://doi.org/10.1002/chin.200540067Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume36, Issue40October 4, 2005 RelatedInformation

1′-Carbopalladated-4-ferrocenyl-1,3-oxazolines as catalysts for Heck reactions: Further evidence in support of the Pd(0)/Pd(II) mechanism

1′-Carbopalladated complexes derived from 4-ferrocenyl-1,3-oxazolines are reported in this paper as efficient catalysts for the Heck coupling of iodo- and bromoarenes with alkenes. Experimental evidence points out strongly towards the involvement of a Pd(0)/Pd(II) catalytic cycle in the mechanism of the reaction. For the first time, the disassembly of the carbopalladated complex via coupling with the olefin in a non-catalytic Heck reaction has been demonstrated to be the origin of the release of Pd(0) from the palladacycle carrier.

Novel cyclometallated Pd(II) and Pt(II) complexes with indole derivatives and their use as catalysts in Heck reaction

Several palladacycle and platinacycle complexes have been prepared from easily available or naturally occurring indole derivatives, such as gramine and related compounds. Dimeric complexes were obtained with Pd(OAc) 2, while Pt(DMSO) 2Cl 2 mainly afforded monomeric structures. A notable feature of these reactions was the formation of new M–C bonds between Pd or Pt and C-2 and C-3 of the indole ring. With ligands like 2-(2′-pyridyl)-1 H-indoles, N–N metallacycles were generated instead: in fact new C–M bonds with the C-3 position could only form if N-substituted indoles were used. The reactivity of Pd dimeric complexes with PPh 3, sym-collidine and DMAP was explored to obtain monomeric complexes. Three such compounds were prepared, one of which was characterized by X-ray diffraction. Metathetical reactions were carried out to effect a ligand exchange replacing OAc with halide ions, with the aim to synthesize μ-Cl and μ-Br bridged structures. Turning to the synthesis of hetaryl complexes, functionalization of the C-2 position on the indole ring was achieved. These complexes were prepared by substitution reactions starting from gramine and/or its alkylammonium salts.

Heck Reaction over Pd-Loaded ETS-10 Molecular Sieve

Abstract A palladium-loaded ETS-10 molecular sieve has been used as a catalyst in Heck reaction. The catalyst exhibits high activity and selectivity towards the carbon–carbon coupling of aryl halides with olefins, even at low concentrations of Pd (0.009 to 1.4 mol% with respect to the substrate). In the case of the coupling of ethyl acrylate with iodobenzene, 96% conversion of iodobenzene with greater than 98% selectivity could be obtained within 1 h over a 0.2 wt % Pd-loaded catalyst. The catalyst activates aryl bromide and chloride substrates, and appears to be heterogeneous. The reaction has been investigated with different alkyl halides, olefins and bases.

Heck Reaction Catalyzed by Palladacycle in Neat Water

AbstractCyclopalladated ferrocenylimine has been found to be a type of excellent phosphine‐free catalyst for Heck reactions in neat water with both higher yields and turnover numbers than those reported in the literature up to now. Some commercial emulsifying agents, including the commonly used quaternary ammonium salts, have been proved to be excellent additives in the catalysis of the reactions. Not only aromatic iodide, but also aromatic bromide could be coupled with the olefins. All reactions were able to be conducted in air under refluxing condition.

Silica-supported polymeric palladium (0) complexes as catalysts for Heck reaction in organic synthesis

Silica-supported palladium (0) complexes have been prepared from γ-chloropropyl triethoxysilica and γ-aminopropyl triethoxysilica via immobilization on fumed silica, followed by reacting with ethylenediamine and salicylaldehyde, and then the reaction with palladium chloride in ethanol and reduction with KBH4 in ethanol. They are efficient catalysts for Heck reaction of aryl iodides with alkene at 90oC. These polymeric palladium (0) catalysts can be recovered and reused without loss in activity.

New Aliphatic C-Metallated Palladacycle in the Pores of 3-Hydroxypropyl Triethoxysilane Functionalized MCM-41

A new aliphatic C-metallated palladacycle has been prepared in the pores of 3-hydroxypropyl triethoxysilane functionalized MCM-41 and has been found to be a superior recyclable catalyst for Heck reaction. The thermal stability of the palladated material was found to be higher than that of the nonpalladated starting material.

Palladium(II) containing hydrotalcite as an efficient heterogeneous catalyst for Heck reaction

Palladium(II) containing hydrotalcite (Pd-HT) has been found to be an efficient and reusable catalyst in Heck reaction between aryl halides (X = Br, I) and olefins to give carbon–carbon coupled products in good to moderate yields.

Soluble polymer-supported catalysts containing azo dyes.

[structure: see text] Azo benzene derivatives were incorporated into soluble polymer-bound catalysts by two different approaches. The first was to attach the dye to the polymer-bound catalysts, using the dye as an innocent spectator to study the phase preference, concentration, and recoverability of a catalyst. The second approach used an azo dye as a ligand to form an effective soluble polymer-bound Pd(II) catalyst for Heck reactions.

MCM‐41 Supported Aminopropylsiloxane Palladium Acetate Complex: A Highly Active and Stereoselective Catalyst for Heck Reaction

AbstractA new MCM‐41 supported aminopropylsiloxane palladium acetate was prepared and characterized. This catalyst is highly active and stereoselective for Heck reaction at 70°C.

ChemInform Abstract: Propylene Carbonate Stabilized Nanostructured Palladium Clusters as Catalysts in Heck Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Propylene carbonate stabilized nanostructured palladium clusters as catalysts in Heck reactions

Nanostructured Pd clusters, prepared either electrochemically using a sacrificial Pd anode or by thermolysis of Pd(O2CMe)2, are stable in propylene carbonate even at 140–155 °C; such colloidal solutions catalyse Heck reactions in the absence of phosphine ligands.