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Showing papers on "Palladium published in 2003"


Journal ArticleDOI

1,076 citations


Journal ArticleDOI
TL;DR: In this article, the palladium-catalyzed α-arylation of ketones has become a useful and general synthetic method, and the reduction of the carbon−carbon bond of the product is formed by reductive elimination from an arylpalladium enolate intermediate.
Abstract: The palladium-catalyzed α-arylation of ketones has become a useful and general synthetic method. In this process, an enolate is generated from a ketone and base in the presence of an aryl halide, and a palladium catalyst couples this enolate with the aryl halide. With the advent of new catalysts composed of sterically hindered, electron-rich alkylphosphine and N-heterocyclic carbene ligands, this process now encompasses a broad range of enolates and related anions, including those derived from amides, esters, aldehydes, nitriles, malonates, cyanoesters, nitroalkanes, sulfones, and lactones. In the proposed mechanism for this reaction, the carbon−carbon bond of the product is formed by reductive elimination from an arylpalladium enolate intermediate. The structures and reactions of arylpalladium complexes of enolate, cyanoalkyl, and malonate ions have been studied to determine how the binding mode and electronic and steric parameters influence the rate and mechanism of reductive elimination.

773 citations


PatentDOI
TL;DR: In this article, a reusable heterogeneous nanopalladium (0) catalysts were used for coupling products by C-C bond formation reaction of haloarenes that include unreactive chloroarenes in the presence of base.
Abstract: The present invention relates to a novel process for the preparation of a reusable heterogeneous nanopalladium (0) catalysts, which is a eco-friendly and economical process employing re-usable heterogeneous catalyst in place of soluble palladium catalysts for preparing coupling products by C—C bond formation reaction of haloarenes that include unreactive chloroarenes in the presence of base. The use of heterogeneous nanopalladium catalyst precludes the presence of palladium in traces with the product.

666 citations


Journal ArticleDOI
TL;DR: Ligand-free Pd(OAc)(2) can be used as a catalyst in the Heck reaction of aryl bromides as long as the amount of catalyst is kept between 0.01 and 0.1 mol %.

495 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of the anode catalyst composition on fuel cell performance is investigated and the performance of Pt, Pt/Pd and Pt/Ru catalysts for direct formic acid fuel cells is compared.

476 citations


Journal ArticleDOI
TL;DR: In this article, a comparative study was performed to determine the reactivity of nitrate ions at 0.1 M on eight polycrystalline electrodes (platinum, palladium, rhodium, ruthenium, iridium, copper, silver and gold) in acidic solution using cyclic voltammetry (CV), chronoamperometry and differential electrochemical mass spectroscopy (DEMS).

435 citations






Journal ArticleDOI
TL;DR: This Account covers the work by the group and by others toward the development of new metal-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes.
Abstract: Over the past five years, several metal-catalyzed asymmetric ring-cleaving reactions have been developed that generate ring-opened products in high yield and enantiomeric excess. These reactions can be carried out with a range of nucleophiles including hydride, stabilized and nonstabilized carbanions, alcohols, amines, and carboxylates. To achieve these results, three different transition metals have been employed, namely nickel, palladium, and rhodium, leading not only to synthetically useful transformations but also to a greater understanding of the reaction manifolds possible with these metals. This Account covers the work by our group and by others toward the development of new metal-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes.

Journal ArticleDOI
TL;DR: A summary of catalytic applications of palladium complexes with phosphorus ligands containing a metallated sp3-carbon centre (palladacycles) or with N-heterocyclic carbene ligands in C-C and C-N coupling reactions of aryl halides including recent results of mechanistic discussions about their role in the catalytic cycle is presented in this article.

Journal ArticleDOI
TL;DR: A novel method for the synthesis of oxindoles using triethylamine as a stoichiometric base and the cyclization is highly regioselective, obviating the need for prefunctionalized arenes.
Abstract: A novel method for the synthesis of oxindoles is described. In the presence of catalytic palladium acetate and 2-(di-tert-butylphosphino)biphenyl, α-chloroacetanilides are converted to oxindoles in good to excellent yields with high functional group compatibility using triethylamine as a stoichiometric base. The cyclization is highly regioselective, obviating the need for prefunctionalized arenes. Plausible mechanistic pathways for the reaction are discussed.

Journal ArticleDOI
TL;DR: A palladium-nanoparticle-cored G-3 dendrimer with TEM, TGA, absorption, and IR spectroscopies is described in this article.
Abstract: A palladium-nanoparticle-cored G-3 dendrimer, characterized by TEM, TGA, absorption, and IR spectroscopies, has approximately 300 Pd atoms in the metallic core and an average diameter of 2.0 nm, to which are attached fourteen G-3 dendrons. Nearly 90% of the metal nanoparticle surface is unpassivated and available for catalysis. The dendrons inhibit metal agglomeration without adversely affecting chemical reactivity. Thus, preliminary investigations have shown that Pd-G-3 can efficiently catalyze Heck and Suzuki reactions.

Journal ArticleDOI
TL;DR: The adsorption of n-alkanethiols onto polycrystalline thin films of palladium containing a strong (111) texture produces well-organized, self-assembled monolayer of alkanethiolates, which are stable in air, although the sulfur present at the surface oxidizes in air over a period of 2-5 days at room temperature.
Abstract: The adsorption of n-alkanethiols onto polycrystalline thin films of palladium containing a strong (111) texture produces well-organized, self-assembled monolayers. The organization of the alkane chains in the monolayer and the nature of the bonding between the palladium and the thiol were studied by contact angle measurements, optical ellipsometry, reflection absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). The XPS data reveals that a compound palladium-sulfide interphase is present at the surface of the palladium film. The RAIR spectra, ellipsometry data, and wetting properties show that the palladium-sulfide phase is terminated with an organized, methyl-terminated monolayer of alkanethiolates. The local molecular environment of the alkane chains transitions from a conformationally disordered, liquidlike state to a mostly all-trans, crystalline-like structure with increasing chain length (n = 8-26). The intensities and dichroism of the methylene and methyl stretching modes support a model for the average orientation of an ensemble of all-trans-conformer chains with a tilt angle of approximately 14-18 degrees with respect to the surface normal and a twist angle of the CCC plane relative to the tilt plane of approximately 45 degrees. The SAMs are stable in air, although the sulfur present at the surface oxidizes in air over a period of 2-5 days at room temperature. The differences in chain organization between SAMs formed by microcontact printing and by solution deposition are also examined by RAIRS and XPS.

Journal ArticleDOI
TL;DR: The fastest aminations of thiazoles, benzimidazoles, and benzoxazoles occurred with the combination of palladium trifluoroacetate and P(t)Bu(3) as catalyst.
Abstract: Detailed studies have been conducted to determine the activity of palladium catalysts for the amination of five-membered heterocyclic halides and to determine the factors that control the scope of this reaction. Palladium-catalyzed aminations of the electron-rich furanyl, thiophenyl, and indolyl halides and of the related 2-halogenated thiazoles, benzimidazole, and benzoxazole have been shown to occur with a subset of amines. Various combinations of palladium precursors and P(t)Bu(3) were tested as catalysts for reaction of 3-bromothiophene with N-methylaniline, and the fastest reactions occurred with the Pd(I) dimer, [PdBr(P(t)Bu(3))](2). The fastest aminations of thiazoles, benzimidazoles, and benzoxazoles occurred with the combination of palladium trifluoroacetate and P(t)Bu(3) as catalyst.

Journal ArticleDOI
TL;DR: Under low-pressure conditions, hydrogenation of alkenes, such as 2-pentene and ethene, is shown to occur on supported palladium nanoparticles, whereas single-crystal palladium surfaces are inactive.
Abstract: Under low-pressure conditions, hydrogenation of alkenes, such as 2-pentene and ethene, is shown to occur on supported palladium nanoparticles, whereas single-crystal palladium surfaces are inactive. This finding is rationalized on the basis of the accessibility of weakly bound subsurface hydrogen (see picture), which is enhanced on particles of nanometer dimensions.

Journal ArticleDOI
TL;DR: Asymmetric hydrosilylation of styrene with trichlorosilane in the presence of chiral BINAP-Pd nanoparticles afforded an optically active 1-phenyl-1-trichlorol (95% enantiomeric excess) by oxidative cleavage of the carbon-silicon bond.
Abstract: The reduction of tetrachloroaurate or potassium tetrachloropalladate with sodium borohydride in the presence of optically active 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl [BINAP] gave the chiral (S)- or (R)-BINAP-stabilized gold or palladium nanoparticles which showed the small core (1.7 nm for BINAP−Au and 2.0 nm for BINAP−Pd) with narrow size distribution and remarkably high stability. Asymmetric hydrosilylation of styrene with trichlorosilane in the presence of chiral BINAP−Pd nanoparticles afforded an optically active 1-phenyl-1-trichlorosilylethane which was converted into an optically active 1-phenylethanol (95% enantiomeric excess) by oxidative cleavage of the carbon−silicon bond.


Journal ArticleDOI
TL;DR: Results of single-particle X-ray energy dispersive spectroscopy (EDS) and catalysis experiments indicate that the hydrogenation rate of allyl alcohol is enhanced in the presence of the bimetallic nanoparticles compared to DECs containing only platinum or only palladium nanoparticles.
Abstract: We report the synthesis, characterization, and catalytic activity of bimetallic palladium−platinum dendrimer-encapsulated catalysts (DECs). These materials are prepared by co-complexation of different ratios of palladium and platinum salts to the interior tertiary amines of fourth-generation, hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers. Chemical reduction of these composites yields stable, fairly monodisperse, water-soluble bimetallic DECs having sizes on the order of 1.9 ± 0.4 nm. Evidence that these nanoparticles are bimetallic comes from single-particle X-ray energy dispersive spectroscopy (EDS) and catalysis experiments. The latter indicate that the hydrogenation rate of allyl alcohol is enhanced in the presence of the bimetallic nanoparticles compared to DECs containing only platinum or only palladium nanoparticles. EDS results indicate that the percentage composition of the bimetallics is reflected by the percentage of metal salts initially complexed with the dendrimer.

Journal ArticleDOI
TL;DR: A new palladium-dipyridylmethylamine complex is an excellent catalyst for C-C bond-forming processes such as the Heck, Suzuki, and Sonogashira reactions in organic and aqueous solvents under homogeneous conditions.


Journal ArticleDOI
TL;DR: Differently substituted 2,5-diarylthiazoles are found to exhibit a stable liquid crystal phase in a wide temperature range and the color of light emission is tunable by the introduction of the substituent.
Abstract: A mild and regioselective C−H substitution reaction of thiazole by the catalysis of the palladium/copper system is found to proceed in the presence of tetrabutylammonium fluoride under mild conditions. Applying the new reaction, we synthesized various 2,5-diarylthiazoles that exhibit light-emitting and liquid crystalline characteristics in good yields. The color of light emission is tunable by the introduction of the substituent. Differently substituted 2,5-diarylthiazoles are found to exhibit a stable liquid crystal phase in a wide temperature range.


Journal ArticleDOI
TL;DR: Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides, with K(3)PO(4) and N,N-dimethylacetamide being the optimal base and solvent, respectively.
Abstract: Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides. Both the base and the solvent were found to have a fundamental influence on the efficiency of the reaction, with K3PO4 and N,N-dimethylacetamide being the optimal base and solvent, respectively.

Journal ArticleDOI
TL;DR: Cyclic voltammetry established that the complete electron-transfer series consisting of a dianion, monoanion, neutral complex, a mono- and a dication exists.
Abstract: Two series of square planar, diamagnetic, neutral complexes of nickel(II), palladium(II), and platinum(II) containing two N,N-coordinated o-diiminobenzosemiquinonate(1-) π radical ligands have been synthesized and characterized by UV−vis and 1H NMR spectroscopy: [MII(2LISQ)2], M = Ni (1), Pd (2), Pt (3), and [MII(3LISQ)2] M = Ni (4), Pd (5), Pt (6). H2[2LPDI] represents 3,5-di-tert-butyl-o-phenylenediamine and H2[3LPDI] is N-phenyl-o-phenylenediamine; (LISQ)1- is the o-diiminobenzosemiquinonate π radical anion, and (LIBQ)0 is the o-diiminobenzoquinone form of these ligands. The structures of complexes 1, 4, 5, and 6 have been (re)determined by X-ray crystallography at 100 K. Cyclic voltammetry established that the complete electron-transfer series consisting of a dianion, monoanion, neutral complex, a mono- and a dication exists: [M(L)2]z z = −2, −1, 0, 1+, 2+. Each species has been electrochemically generated in solution and their X-band EPR and UV−vis spectra have been recorded. The oxidations and red...

Journal ArticleDOI
TL;DR: In this paper, the various applications of indium in organic synthesis are highlighted, especially Barbier-type reactions, especially allyl additions to carbonyl compounds, and Reformatsky reactions.
Abstract: The various applications of indium in organic synthesis are highlighted in this review. Major fields are Barbier-type reactions, especially allyl additions to carbonyl compounds, and Reformatsky reactions. Special emphasis is placed on reactions, which have been examined only recently, i.e. reductions of various functionalities, indium-catalyzed reactions and palladium/indium-mediated reactions.

Journal ArticleDOI
TL;DR: It is possible to prepare biaryls in good yield very rapidy on small and larger scales from aryl halides and phenylboronic acid using water as a solvent and palladium acetate as catalyst.
Abstract: It is possible to prepare biaryls in good yield very rapidy (5-10 min) on small (1 mmol) and larger (10-20 mmol) scales from aryl halides and phenylboronic acid using water as a solvent and palladium acetate as catalyst. The reaction can be performed equally well using microwave and conventional heating, showing that using these conditions probably no nonthermal microwave effects are associated with the impressive speed of the reaction.

Journal ArticleDOI
TL;DR: In this article, living polymerization of ethylene with palladium(II) diimine complexes coupled with use of a functionalized initiator and/or cleavage of the palladium−polymer bond with various reagents provides a protocol for synthesis of mono-and di-end functionalized, branched, amorphous polyethylenes.
Abstract: Living polymerizations of ethylene with palladium(II) diimine complexes coupled with use of a functionalized initiator and/or cleavage of the palladium−polymer bond with various reagents provides a protocol for synthesis of mono- and di-end-functionalized, branched, amorphous polyethylenes. The functional initiator used is the chelate complex (Ar = 2,6-(iPr)2C6H3) (3). The alkyl chain is cleaved by insertion of alkyl acrylates or methyl vinyl ketone, followed by cleavage with Et3SiH to generate alkyl ester or methyl ketone end groups, respectively. Insertion of 5-hexen-1-ol, followed by chain running and β-elimination, results in formation of aldehyde end groups. Conditions for living polymerization of propylene, 1-hexene, and 1-octadecene have also been established. Rates of first monomer insertion and subsequent chain growth are shown to be a sensitive function of the palladium complex used for initiation and the nature and concentration of auxiliary nitrile ligands. Block copolymers of ethylene and 1-o...

Journal ArticleDOI
TL;DR: In this paper, the effect of the concentration of the protective agents on the particle size and morphology were investigated in detail, and the average diameter of Au or Pt nanoparticles tends to decrease with an increase in the concentration ratios of the protection agents to AuCl4− or PtCl62−.
Abstract: Gold and platinum nanoparticles were synthesized by the reduction of their salts with potassium bitartrate as the reductant and poly(N-vinyl-2-pyrrolidone) (PVP), polyethylene glycol (PEG) (for Pt nanoparticles) or 3,3′-thiodipropionic acid (TDPC) as the protective agent. In the presence of PVP or TDPC, the preparation of palladium and silver nanoparticles were also realized by the reduction of their salts with potassium bitartrate under alkaline conditions. The effect of the concentration of the protective agents on the particle size and morphology were investigated in detail. At a constant concentration of Au and Pt ions, the average diameter of Au or Pt nanoparticles tends to decrease with an increase in the concentration ratios of the protective agents to AuCl4− or PtCl62−. Except for PVP passivated Au nanoparticles, smaller Au and Pt particles with a sharp size distribution could be obtained at higher concentration ratios of the protective agents to the metal ions, as determined by TEM measurements. All the noble metal colloidal particles have very high stability.