Showing papers on "Palladium published in 2007"
TL;DR: Pd on Modified Silica 159 4.5.1.
Abstract: 4.4. Pd on Modified Silica 159 4.5. Pd on Clay and Other Inorganic Materials 159 5. Stille, Fukuyama, and Negishi Reactions 159 5.1. Stille Reactions 159 5.1.1. Pd on Carbon (Pd/C) 159 5.1.2. Palladium on KF/Al2O3 159 5.1.3. Pd on Modified Silica (SiO2/TEG/Pd) 159 5.2. Fukuyama Reactions 159 5.2.1. Pd on Carbon (Pd/C) 159 5.2.2. Pd(OH)2 on Carbon (Perlman’s Catalyst) 160 5.3. Pd/C-Catalyzed Negishi Reactions 160 6. Ullmann-Type Coupling Reactions 161 6.1. Pd/C-Catalyzed Aryl−Aryl Coupling 161 6.2. Pd/C-Catalyzed Homocoupling of Vinyl Halides 162
1,900 citations
TL;DR: The basics of Pd-NHC chemistry are discussed to understand the peculiarities of these catalysts and a critical discussion on their application in C-C and C-N cross-coupling as well as carbopalladation reactions is given.
Abstract: Palladium-catalyzed C-C and C-N bond-forming reactions are among the most versatile and powerful synthetic methods. For the last 15 years, N-heterocyclic carbenes (NHCs) have enjoyed increasing popularity as ligands in Pd-mediated cross-coupling and related transformations because of their superior performance compared to the more traditional tertiary phosphanes. The strong sigma-electron-donating ability of NHCs renders oxidative insertion even in challenging substrates facile, while their steric bulk and particular topology is responsible for fast reductive elimination. The strong Pd-NHC bonds contribute to the high stability of the active species, even at low ligand/Pd ratios and high temperatures. With a number of commercially available, stable, user-friendly, and powerful NHC-Pd precatalysts, the goal of a universal cross-coupling catalyst is within reach. This Review discusses the basics of Pd-NHC chemistry to understand the peculiarities of these catalysts and then gives a critical discussion on their application in C-C and C-N cross-coupling as well as carbopalladation reactions.
1,471 citations
1,017 citations
TL;DR: In this paper, a quantitative comparison of the catalytic activity of palladium nanoparticles immobilized in different colloidal carrier systems, namely, in spherical polyelectrolyte brushes (SPB) and core−shell microgels, is presented.
Abstract: We present a quantitative comparison of the catalytic activity of palladium nanoparticles immobilized in different colloidal carrier systems, namely, in (i) spherical polyelectrolyte brushes (SPB) and (ii) core−shell microgels. The first system given by the SPB carrier particles consist of a solid core of polystyrene onto which long chains of poly((2-methylpropenoyloxyethyl) trimethylammonium chloride) (PMPTAC) are grafted. These positively charged polyelectrolyte chains form a dense layer on the surface of the core particles which binds the divalent PdCl42- ions. Reduction leads to metallic Pd particles. System 2 is given by core−shell microgels which consists of a solid core of polystyrene and a shell of cross-linked poly(N-isopropylacrylamide) (PNIPA). The metal ions were strongly localized within the network because of complexation of the PdCl42- ions and the nitrogen atoms of PNIPA. Reduction of these ions leads to nearly monodisperse nanoparticles of metallic palladium that are only formed within th...
661 citations
TL;DR: The direct intermolecular arylation reactions of heteroaromatic compounds such as pyrroles, furans, thiophenes, azoles, and pyridines with aryl halides using palladium or rhodium catalysts have been studied as discussed by the authors.
Abstract: The direct intermolecular arylation reactions of heteroaromatic compounds such as pyrroles, furans, thiophenes, azoles, and pyridines with aryl halides using palladium or rhodium catalysts have sig...
602 citations
TL;DR: Evidence is presented suggesting that the treated cells underwent programmed cell death through a p53-dependent pathway, and while the palladium complexes 1a and 1b displayed potent anticancer activity, the gold and silver complexes exhibited significant antimicrobial properties.
Abstract: Complete synthetic, structural, and biomedical studies of two Pd complexes as well as Au and Ag complexes of 1-benzyl-3-tert-butylimidazol-2-ylidene are reported. Specifically, trans-[1-benzyl-3-tert-butylimidazol-2-ylidene]Pd(pyridine)Cl2 (1a) was synthesized from the reaction of 1-benzyl-3-tert-butylimidazolium chloride (1) with PdCl2 in the presence of K2CO3 as a base. The other palladium complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]2PdCl2 (1b), and a gold complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AuCl (1c), were synthesized by following a transmetallation route from the silver complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AgCl (1d), by treatment with (COD)PdCl2 and (SMe2)AuCl, respectively. The silver complex 1d in turn was synthesized by the reaction of 1 with Ag2O. The molecular structures of 1a−d have been determined by X-ray diffraction studies. Biomedical studies revealed that, while the palladium complexes 1a and 1b displayed potent anticancer activity, the gold (1c) and silver ...
563 citations
TL;DR: In this article, the Pd supported on carbon microspheres has excellent electrocatalytic properties and may be of great potential in direct ethanol fuel cells, but it is well known that palladium is not a good electrocatalyst for methanol oxidation.
468 citations
TL;DR: Palladium was infiltrated into the highly porous metal-organic framework MOF-5 using [Pd(acac)2] (acac = acetylacetonate) as the precursor in chloroform solution viaipient wetness impregnation.
Abstract: Palladium was infiltrated into the highly porous metal–organic framework MOF-5 {[Zn4O(bdc)3], bdc = benzene-1,4-dicarboxylate} using [Pd(acac)2] (acac = acetylacetonate) as the precursor in chloroform solution via
‘incipient wetness’ impregnation. The specific surface area decreases from 2885 m2 g−1 to 958 m2 g−1 after infiltration. After reduction in hydrogen or under vacuum, the hydrogen adsorption capacity is increased from 1.15 wt% to 1.86 wt% at 1 atm and 77 K. The palladium loaded MOF-5 has a high catalytic activity in styrene hydrogenation comparable to that of palladium on activated carbon, but cis-cyclooctene hydrogenation is considerably slower. Even at room temperature, the catalyst is not stable in air due to the low hydrothermal stability of the MOF-5 support.
438 citations
403 citations
TL;DR: In this article, a review of the literature on conjugate addition of carbon nucleophiles to acceptor activated olefins is presented, starting from solely Lewis acidic M(II) and M(III) compounds, such as magnesium, zinc, boron, aluminum and the lanthanoids.
Abstract: The conjugate addition of carbon nucleophiles to acceptor activated olefins is one of the most important reactions for carbon-carbon bond formation. With optically active metal complexes this transformation can be catalyzed enantioselectively. This review is a collection of the newer literature (since 2001) on this topic. The metal salts and complexes applied are in a broad range, starting from solely Lewis acidic M(II) and M(III) compounds, such as magnesium, zinc, boron, aluminum and the lanthanoids. Transition-metal catalysts suitable for asymmetric conjugate additions are compounds of ruthenium, iridium, nickel, and palladium. The most flourishing fields are, however, the catalysis with rhodium and copper complexes. Rhodium catalysts often have a chiral diphosphane like BINAP, or an optically active olefin as the ligand, the latter being a newer development. The privileged ligand structures for copper catalysts are monodentate phosphoramidites with axially chiral BINOL or other biphenol units.
397 citations
TL;DR: In this paper, a review article lists known hydration catalysts and discusses applications of catalytic hydration to different classes of substrates, with an emphasis on functional group tolerance and regioselectivity.
Abstract: The catalytic addition of water to alkynes (hydration) generates valuable carbonyl compounds from unsaturated hydrocarbon precursors. Traditional mercury(II) catalysts hydrate terminal alkynes with Markovnikov selectivity to methyl ketones. Much research has been devoted to finding catalysts based on less toxic metals, the most promising being gold(I), gold(III), platinum(II), and palladium(II). Catalytic anti-Markovnikov hydration of terminal alkynes to aldehydes has been realized in an efficient manner with ruthenium(II) complex catalysts. The present review article lists known hydration catalysts and discusses applications of catalytic hydration to different classes of substrates, with an emphasis on functional group tolerance and regioselectivity.
TL;DR: A mechanism of formation of the metal nanowire networks is proposed based on confined metal growth within a soft template consisting of a network of swollen inverse wormlike micelles.
Abstract: Platinum nanowire networks have been synthesized by chemical reduction of a platinum complex using sodium borohydride in the presence of a soft template formed by cetyltrimethylammonium bromide in a two-phase water-chloroform system. The interconnected polycrystalline nanowires possess the highest surface area (53 ± 1 m2/g) and electroactive surface area (32.4 ± 3.6 m2/g) reported for unsupported platinum nanomaterials; the high surface area results from the small average diameter of the nanowires (2.2 nm) and the 2−10 nm pores determined by nitrogen adsorption measurements. Synthetic control over the network was achieved simply by varying the stirring rate and reagent concentrations, in some cases leading to other types of nanostructures including wormlike platinum nanoparticles. Similarly, substitution of a palladium complex for platinum gives palladium nanowire networks. A mechanism of formation of the metal nanowire networks is proposed based on confined metal growth within a soft template consisting ...
TL;DR: This tutorial review focuses on several practical synthetic transformations utilising palladium catalysis that facilitate the synthesis of functionalized unsaturated heterocycles in a regioselective (site-selective) manner.
Abstract: This tutorial review focuses on several practical synthetic transformations utilising palladium catalysis that facilitate the synthesis of functionalised unsaturated heterocycles in a regioselective (site-selective) manner. Cross-couplings of electron-deficient, electron-neutral and electron-rich unsaturated halogenated heterocycles with various organometallic reagents, and other types of nucleophiles, are detailed. Direct arylation of electron-rich unsaturated heterocyclic compounds by C–H functionalisation is also presented.
TL;DR: In this article, a study on the catalytic properties of palladium for hydrodechlorination using nanoscale zero-valent iron particles is presented. But the results of the study were limited to the case of chlorinated ethylenes.
Abstract: Reported herein is a study on the catalytic properties of palladium for hydrodechlorination using nanoscale zero-valent iron particles. Temperature-dependent experiments and X-ray diffraction (XRD) are conducted to characterize reactions of chlorinated ethylenes with nanoscale Fe and Pd/Fe particles. XRD results suggest bimetallic structures are created as a result of Pd(II) reduction by zero-valent iron and the degree of surface palladium loading is proportional to the initial amount of palladium applied. The optimal content of palladium in the bimetallic particles for dechlorination is in the range of 1–5% by weight. XRD analyses further suggest that oxidation of iron produces mainly iron oxides. No oxidized species of palladium (e.g., PdO) is found before or after the reactions. Activation energies of the dechlorination reactions with the nanoscale Pd/Fe and Fe particles are estimated to be 31.1 and 44.9 kJ/mol, respectively. A conceptual model for the catalytic hydrodechlorination by the nanoscale Pd/Fe particles is presented.
TL;DR: It is shown that by selection of an appropriate palladium/ligand system, temperature, concentration, and stoichiometry of reagents, ammonia may be selectively arylated to give either anilines, symmetrical di-, or triarylamines.
Abstract: It is shown that by selection of an appropriate palladium/ligand system, temperature, concentration, and stoichiometry of reagents, ammonia may be selectively arylated to give either anilines, symmetrical di-, or triarylamines. Furthermore different aryl halides may be added sequentially to the reaction mixture, allowing the synthesis of unsymmetrical di- and triarylamines from aryl halides and ammonia in a one-pot protocol
TL;DR: The sequential transfer of two sulfonamides to internal alkenes affords the construction of vicinal diamines and generates a convenient access to heterocyclic structures such as bisindoline, annelated indolines, and bispyrrolidines.
Abstract: The sequential transfer of two sulfonamides to internal alkenes affords the construction of vicinal diamines. In the presence of a palladium catalyst, the reaction proceeds through two mechanistically different C−N bond formation reactions. It is initiated by aminopalladation, followed by a reductive amination of a palladated secondary carbon. The overall process proceeds with complete selectivity for both steps and thereby generates a convenient access to heterocyclic structures such as bisindolines, annelated indolines, and bispyrrolidines.
TL;DR: A highly sensitive fluorescent sensor is developed that is capable of detecting 1 ng of palladium quantitatively with the naked eye and was able to selectively detect palladium contamination in aspirin tablets, on the surface of flasks previously exposed to palladium, and in rocks containing palladium.
Abstract: Although palladium catalysts are powerful reagents in organic synthesis, hazardous palladium is often found in reaction products even after purifications. Thus, the detection of palladium is an important process in the production of fine chemicals and active pharmaceutical ingredients. We have developed a highly sensitive fluorescent sensor that is capable of detecting 1 ng of palladium quantitatively with the naked eye. Using this method, we were able to selectively detect palladium contamination in aspirin tablets (10 ppm Pd in 1 mg aspirin; mixed in the laboratory for this study), on the surface of flasks previously exposed to palladium, and in rocks containing palladium.
TL;DR: Linear copolymers of ethylene and acrylonitrile were prepared using palladium complexes bearing phosphine-sulfonate bidentate ligands and located in the linear polyethylene backbones were detected for the first time by 13C NMR spectroscopy.
Abstract: Linear copolymers of ethylene and acrylonitrile were prepared using palladium complexes bearing phosphine-sulfonate bidentate ligands. Acrylonitrile units located in the linear polyethylene backbones were detected for the first time by 13C NMR spectroscopy. Catalyst systems employing isolated palladium complexes such as 3 showed much higher activity for the copolymerization than the in situ generation procedures, and molecular weight of the copolymers and acrylonitrile incorporation were dependent on the palladium complexes. Obtained linear copolymers of ethylene and acrylonitrile melt at higher temperature than branched copolymers.
TL;DR: This Review concerns platinum-catalyzed electrophilic alkene activation reactions, with a special emphasis on the mechanistic properties of known systems, on the differences between platinum and palladium catalysts, and on the prospects for the development of new systems.
Abstract: The electrophilic activation of alkenes by transition-metal catalysts is a fundamental step in a rapidly growing number of catalytic processes. Although palladium is the best known metal for this purpose, the special properties of its third-row cousin platinum (strong metal-ligand bonds and slow substitution kinetics) have enabled the development of transformations that are initiated by addition to the C=C bonds by protic carbon, nitrogen, oxygen, and phosphorus nucleophiles, as well as alkene or arene nucleophiles. Additionally, reactivity profiles, which are often unique to platinum, provide wholly new reaction products. This Review concerns platinum-catalyzed electrophilic alkene activation reactions, with a special emphasis on the mechanistic properties of known systems, on the differences between platinum and palladium catalysts, and on the prospects for the development of new systems.
TL;DR: Results show that the composites exhibit high thermal stability and are more crystalline compared with pristine POT, and it was found that the electrical conductivity of the POT-DBSA/Au or Pd composites is 2 orders of magnitude higher than that of pristine polymer.
Abstract: Poly(ortho-toluidine) (POT)-gold (Au) and palladium (Pd) composite nanospheres were successfully synthesized by the reaction of o-toluidine with the corresponding metal (Au or Pd) colloidal solution through self-assembly process in the presence of dodecylbenzenesulfonic acid (DBSA), which acts as both a dopant and surfactant, and ammonium peroxydisulfate as an oxidizing agent. The composites (POT-DBSA/Au or Pd) were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, UV-Visible (UV-Vis) spectroscopy, and electrical conductivity measurements. TEM images of the nanocomposites reveal that metal (Au or Pd) nanoparticles were well dispersed on POT spheres. TGA and XRD results show that the composites exhibit high thermal stability and are more crystalline compared with pristine POT. It was found that the electrical conductivity of the POT-DBSA/Au or Pd composites is 2 orders of magnitude higher than that of pristine polymer. Also, the POT-DBSA/Pd composite exhibits magnetic property. The formation mechanism of the POT-DBSA/Au or Pd composite nanosphere is discussed.
TL;DR: Inductively coupled plasma (ICP) mass-spectrometric analysis of the filtrate from the reaction mixture of 4-bromonitrobenzene with phenylboronic acid demonstrated that the palladium metal hardly leached into the solution within the limits of the detector, thus suggesting that the present Suzuki-Miyaura reaction proceeded by heterogeneous catalysis.
Abstract: A mild and efficient ligand-free Suzuki-Miyaura coupling reaction catalyzed by heterogeneous Pd/C was developed. Aryl bromides and triflates undergo the cross-coupling with aryl boronic acids in excellent yields without the presence of any additives in aqueous media at room temperature. Aryl vinyl boronic acids are also applicable to this coupling reaction and provide the trans-stilbene derivatives in high yields. The application of wet-type Pd/C to the coupling reaction was achieved without any loss of activity under aerobic conditions, and the reuse of Pd/C is feasible for a fifth run without significant loss of activity. Inductively coupled plasma (ICP) mass-spectrometric analysis of the filtrate from the reaction mixture of 4-bromonitrobenzene with phenylboronic acid demonstrated that the palladium metal hardly leached into the solution within the limits of the detector (<1 ppm), thus suggesting that the present Suzuki-Miyaura reaction proceeded by heterogeneous catalysis.
TL;DR: An efficient synthesis of functionalized 3-alkyl-3-cyanomethyl-2-oxindole 1 by a palladium-catalyzed domino Heck-Cyanation reaction has been developed and an enantioselectivity of up to 79 % ee in the enantiomerically enriched oxindole was obtained under optimized conditions.
Abstract: An efficient synthesis of functionalized 3-alkyl-3-cyanomethyl-2-oxindole by a palladium-catalyzed domino Heck-cyanation reaction has been developed. Reaction of ortho-iodoanilide with potassium ferro(II)cyanide in the presence of palladium acetate and sodium carbonate afforded oxindole derivs., e.g., I, in good to excellent yields. An enantioselective domino Heck-cyanation process has been developed for the first time using (S)-DIFLUORPHOS as a chiral supporting ligand, and an enantioselectivity of up to 79% ee in the enantiomerically enriched oxindole was obtained under optimized conditions. A concise total synthesis of (+-)-esermethole (II, R = Me) and (+-)-physostigmine (II, R = CONHMe), powerful inhibitors of acetyl- and butyryl-cholinesterase, is also described. [on SciFinder (R)]
TL;DR: It is maintained that palladium nanoparticles are not the true catalysts in C--C coupling reactions, instead, catalysis is carried out by either palladium(0) atoms or Palladium(II) ions that leach into solution.
Abstract: Leaching of palladium species from Pd nanoparticles under C - C coupling conditions was observed for both Heck and Suzuki reactions by using a special membrane reactor. The membrane allows the passage of palladium atoms and ions, but not of species larger than 5 nm. Three possible mechanistic scenarios for palladium leaching were investigated with the aim of identifying the true catalytic species. Firstly, we examined whether or not palladium(0) atoms could leach from clusters under non-oxidising conditions. By using our membrane reactor, we proved that this indeed happens. We then investigated whether or not small palladium(0) clusters could in fact be the active catalytic species by analysing the reaction composition and the palladium species that diffused through the membrane. Neither TEM nor ICP analysis supported this scenario. Finally, we tested whether or not palladium(II) ions could be leached in the presence of PhI by oxidative addition and the formation of [PdIIArI] complexes. Using mass spectrometry, UV-visible spectroscopy and 13C NMR spectroscopy, we observed and monitored the formation and diffusion of these complexes, which showed that the first and the third mechanistic scenarios were both possible, and were likely to occur simultaneously. Based on these findings, we maintain that palladium nanoparticles are not the true catalysts in C - C coupling reactions. Instead, catalysis is carried out by either palladium(0) atoms or palladium(II) ions that leach into solution.
TL;DR: A 3-mercaptopropyl-functionalized silica, SH-SBA-15, is used both as a support for palladium acetate, Pd-SH, and as a selective poison of soluble palladium complexes.
Patent•
20 Aug 2007
TL;DR: A layered, three-way conversion catalyst with the capability of simultaneously catalyzing the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides is described in this article.
Abstract: A layered, three-way conversion catalyst having the capability of simultaneously catalyzing the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides is disclosed In one or more embodiments, the catalyst comprises three layers in conjunction with a carrier: a first layer deposited on the carrier and comprising palladium deposited on a refractory metal oxide and an oxygen storage component; a second layer deposited on the first layer and comprising rhodium deposited on a refractory metal oxide and an oxygen storage component; and a third layer deposited on the second layer and comprising palladium deposited on a refractory metal oxide
TL;DR: Palladium(II) acetate-catalyzed Heck-type reactions have been performed from the arene 1 and alkenes (n-butyl acrylate, styrene) in acetic acid at room temperature, in the presence of a catalytic amount of benzoquinone or hydroquinone as discussed by the authors.
Abstract: Palladium(II) acetate-catalyzed Heck-type reactions have been performed from the arene 1 and alkenes (n-butyl acrylate, styrene) in acetic acid at room temperature, in the presence of a catalytic amount of benzoquinone or hydroquinone. The reactions have been made catalytic in benzoquinone [which is used to continuously oxidize the Pd(0) into to the active Pd(II) species able to activate the Ar-H bond] by the electrochemical oxidation of hydroquinone, formed in the reaction, back to benzoquinone.
TL;DR: This study establishes that, in comparison to porphyrins and other tetrapyrrolic macrocyclic systems, porphycenes exhibit many desirable attributes for use as sensitizers in two-photon initiated photodynamic therapy.
Abstract: Porphycenes are structural isomers of porphyrins that have many unique properties and features. In the present work, the resonant two-photon absorption of 2,7,12,17-tetraphenylporphycene (TPPo) and its palladium(II) complex (PdTPPo) has been investigated. The data obtained are compared to those from the isomeric compound, meso-tetraphenylporphyrin (TPP). Detection of phosphorescence from singlet molecular oxygen, O2(a1Δg), produced upon irradiation of these compounds, was used to obtain two-photon excitation spectra and to quantify two-photon absorption cross sections, δ. In the spectral region of 750−850 nm, the two-photon absorption cross sections at the band maxima for both TPPo and PdTPPo, δ = 2280 and 1750 GM, respectively, are significantly larger than that for TPP. This difference is attributed to the phenomenon of so-called resonance enhancement; for the porphycenes, the two-photon transition is nearly resonant with a comparatively intense one-photon Q-band transition. The results of quantum mecha...