Showing papers on "Palladium published in 2002"
26 Jul 2002
TL;DR: Palladium-CATALYZED Reactions Involving Nucleophilic Attack on -Ligands of Palladium-Alkene, PalladiumAlkyne, and Related Derivatives as mentioned in this paper.
Abstract: PREFACE. CONTRIBUTORS. INTRODUCTION AND BACKGROUND. Historical Background of Organopalladium Chemistry Fundamental Properties of Palladium and Patterns of the Reactions of Palladium and Its Complexes. PALLADIUM COMPOUNDS: STOICHIOMETRIC PREPARATION, IN SITU GENERATION, AND SOME PHYSICAL AND CHEMICAL PROPERTIES. Background for Part II. Pd(0) and Pd(II) Compounds Without Carbon-Palladium Bonds. Organopalladium Compounds Containing Pd(0) and Pd(II). Palladium Complexes Containing Pd(I), Pd(III), or Pd(IV). PALLADIUM-CATALYZED REACTIONS INVOLVING REDUCTIVE ELIMINATION. Background for Part III. Palladium-Catalyzed Carbon-Carbon Cross-Coupling. Palladium-Catalyzed Carbon-Hydrogen and Carbon- Heteroatom Coupling. PALLADIUM-CATALYZED REACTIONS INVOLVING CARBOPALLADATION. Background for Part IV. The Heck Reaction (Alkene Substitution via Carbopalladation- Dehydropalladation) and Related Carbopalladation Reactions. Palladium-Catalyzed Tandem and Cascade Carbopalladation of Alkynes and 1,1-Disubstituted Alkenes. Allylpalladation and Related Reactions of Alkenes, Alkynes, Dienes, and Other -Compounds. Alkynyl Substitution via Alkynylpalladation-Reductive Elimination. Arene Substitution via Addition-Elimination. Carbopalladation of Allenes. Synthesis of Natural Products via Carbopalladation. Cyclopropanation and Other Reactions of Palladium-Carbene (and Carbyne) Complexes. Carbopalladation via Palladacyclopropanes and Palladacyclopropenes. Palladium-Catalyzed Carbozincation. PALLADIUM-CATALYZED REACTIONS INVOLVING NUCLEOPHILIC ATTACK ON LIGANDS. Background for Part V. Palladium-Catalyzed Nucleophilic Substitution Involving Allylpalladium, Propargylpalladium, and Related Derivatives. Palladium-Catalyzed Reactions Involving Nucleophilic Attack on -Ligands of Palladium-Alkene, Palladium-Alkyne, and Related Derivatives. PALLADIUM-CATALYZED CARBONYLATION AND OTHER RELATED REACTIONS INVOLVING MIGRATORY INSERTION. Background for Part VI. Migratory Insertion Reactions of Alkyl-, Aryl-, Alkenyl-, and Alkynylpalladium Derivatives Involving Carbon Monoxide and Related Derivatives. Migratory Insertion Reactions of Allyl, Propargyl, and Allenylpalladium Derivatives Involving Carbon Monoxide and Related Derivatives. Acylpalladation and Related Addition Reactions. Other Reactions of Acylpalladium Derivatives. Synthesis of Natural Products via Palladium-Catalyzed Carbonylation. Palladium-Catalyzed Carbonylative Oxidation. Synthesis of Oligomeric and Polymeric Materials via Palladium-Catalyzed Successive Migratory Insertion of Isonitriles. CATALYTIC HYDROGENATION AND OTHER PALLADIUM-CATALYZED REACTIONS VIA HYDROPALLADATION, METALLOPALLADATION, AND OTHER RELATED SYN ADDITION REACTIONS WITHOUT CARBON-CARBON BOND FORMATION OR CLEAVAGE. Background for Part VII. Palladium-Catalyzed Hydrogenation. Palladium-Catalyzed Isomerization of Alkenes, Alkynes, and Related Compounds without Skeletal Rearrangements. Palladium-Catalyzed Hydrometallation. Metallopalladation. Palladium-Catalyzed Syn-Addition Reactions of X-Pd Bonds (X = Group 15, 16, and 17 Elements). PALLADIUM-CATALYZED OXIDATION REACTIONS THAT HAVE NOT BEEN DISCUSSED IN EARLIER PARTS. Background for Part VIII. Oxidation via Reductive Elimination of Pd(II) and Pd(IV) Complexes. Palladium-Catalyzed or -Promoted Oxidation via 1,2- or 1,4-Elimination. Other Miscellaneous Palladium-Catalyzed or -Promoted Oxidation Reactions. REARRANGEMENT AND OTHER MISCELLANEOUS REACTIONS CATALYZED BY PALLADIUM. Background for Part IX. Rearrangement Reactions Catalyzed by Palladium. TECHNOLOGICAL DEVELOPMENTS IN ORGANOPALLADIUM CHEMISTRY. Aqueous Palladium Catalysis. Palladium Catalysts Immobilized on Polymeric Supports. Organopalladium Reactions in Combinatorial Chemistry. REFERENCES. General Guidelines on References Pertaining to Palladium and Organopalladium Chemistry. Books (Monographs). Reviews and Accounts (as of September 1999). SUBJECT INDEX.
2,193 citations
1,562 citations
TL;DR: Novel palladium hollow spheres were synthesized using silica spheres as a template, and they were successfully applied as recyclable heterogeneous catalysts for Suzuki cross coupling reactions.
Abstract: Novel palladium hollow spheres were synthesized using silica spheres as a template, and they were successfully applied as recyclable heterogeneous catalysts for Suzuki cross coupling reactions.
1,317 citations
TL;DR: In this article, a review examines recent developments in the complete oxidation of methane at low temperature over noble metal based catalysts in patents and open literature, focusing on low-temperature reaction conditions.
Abstract: This review examines recent developments in the complete oxidation of methane at low temperature over noble metal based catalysts in patents and open literature. The abatement of natural gas vehicle (NGV) methane emissions is taken as one example among possible applications. The review develops current ideas about the properties of palladium and platinum catalysts supported on silica and alumina supports in the complete oxidation of methane under oxidising conditions, focusing on low-temperature reaction conditions. The influence of residual chloride ions on the catalytic activity, the kinetic aspects of the oxidation of methane over these catalysts, the nature of the active sites, the influence of metal particle size and reaction products on the activity, the observed changes in catalytic activity with reaction time and the effect of sulphur containing compounds are examined. The latest studies concerned with improved palladium and platinum supported catalysts which would exhibit enhanced and stable catalytic activity at low temperature in the presence of water and sulphur containing compounds are reported. Possible routes for preparing catalysts able to meet future regulations concerning methane emissions from lean-burn NGV vehicles are discussed.
998 citations
TL;DR: Pentaphenylferrocenyl di-tert-butylphosphine has been prepared in high yield from a two-step synthetic procedure, and the scope of various cross-coupling processes catalyzed by complexes bearing this ligand has been investigated.
Abstract: Pentaphenylferrocenyl di-tert-butylphosphine has been prepared in high yield from a two-step synthetic procedure, and the scope of various cross-coupling processes catalyzed by complexes bearing this ligand has been investigated. This ligand creates a remarkably general palladium catalyst for aryl halide amination and for Suzuki coupling. Turnovers of roughly 1000 were observed for aminations with unactivated aryl bromides or chlorides. In addition, complexes of this ligand catalyzed the formation of selected aryl ethers under mild conditions. The reactions encompassed electron-rich and electron-poor aryl bromides and chlorides. In the presence of catalysts containing this ligand, these aryl halides coupled with acyclic or cyclic secondary alkyl- and arylamines, with primary alkyl- and arylamines, and with aryl- and primary alkylboronic acids. These last couplings provide the first general procedure for reaction of terminal alkylboronic acids with aryl halides without toxic or expensive bases. The ligand ...
647 citations
TL;DR: A review of palladium membrane research can be found in this article, where the authors highlight various aspects of current palladium-based membrane research and serve as a comprehensive bibliography covering palladium preparation methods and applications.
Abstract: This review highlights various aspects of current palladium membrane research and serves as a comprehensive bibliography covering palladium membrane preparation methods and applications. There are many promising uses for palladium membranes, although widespread use of the available technologies is constrained primarily by the high cost of palladium, lack of durability due to hydrogen embrittlement, and susceptibility to fouling. Various researchers in the field are tackling these problems and fabricating thinner palladium alloy composite membranes that better withstand contaminantion and thermal cycling. What has been accomplished to address these issues and the directions presently being explored are discussed.
617 citations
TL;DR: In this paper, a review of the literature on supported Pd catalysts for combustion of methane is presented, taking into consideration the oxidation/reduction mechanisms for supported palladium, poisoning, restructuring, the form of oxygen on the surface, methane activation over Pd and PdO phases, and transient behavior.
Abstract: Palladium-based catalysts are widely applied in exhaust catalytic converter and catalytic combustion systems. The mechanism for methane oxidation on a Pd-based catalyst is complex. Catalyst activity is influenced by variations in the process pressure and temperature, by the gas mixture composition, by the type of support and various additives, and by pretreatment under reducing or oxidizing atmospheres. In this paper, we review the literature on supported Pd catalysts for combustion of methane. The mechanisms involved are discussed taking into consideration the oxidation/reduction mechanisms for supported palladium, poisoning, restructuring, the form of oxygen on the surface, methane activation over Pd and PdO phases, and transient behavior. Our review helps explain the array of experimental results reported in the literature.
529 citations
TL;DR: An efficient process using a shell-and-tube reactor, in which a gaseous mixture of benzene and oxygen is fed into a porous alumina tube coated with a palladium thin layer, attained phenol formation selectivities of 80 to 97% at benzene conversions of 2 to 16% below 250°C.
Abstract: Existing phenol production processes tend to be energy-consuming and produce unwanted by-products. We report an efficient process using a shell-and-tube reactor, in which a gaseous mixture of benzene and oxygen is fed into a porous alumina tube coated with a palladium thin layer and hydrogen is fed into the shell. Hydrogen dissociated on the palladium layer surface permeates onto the back and reacts with oxygen to give active oxygen species, which attack benzene to produce phenol. This one-step process attained phenol formation selectivities of 80 to 97% at benzene conversions of 2 to 16% below 250°C (phenol yield: 1.5 kilograms per kilogram of catalyst per hour at 150°C).
478 citations
TL;DR: In this article, the selective oxidation of D-glucose to D-gluconic acid was performed at both controlled (7-9.5) and free pH values in an aqueous solution in the presence of a gold on carbon catalyst using dioxygen as the oxidant under mild conditions.
443 citations
TL;DR: A general method for the intermolecular coupling of aryl halides and amides using a Xantphos/Pd catalyst is described, and the desired C-N bond forming process proceeds in good to excellent yields with 1-4 mol % of the Pd catalyst.
Abstract: A general method for the intermolecular coupling of aryl halides and amides using a Xantphos/Pd catalyst is described. This system displays good functional group compatibility, and the desired C−N bond forming process proceeds in good to excellent yields with 1−4 mol % of the Pd catalyst. Additionally, the arylation of sulfonamides, oxazolidinones, and ureas is reported. The efficiency of these transformations was found to be highly dependent on reaction concentrations and catalyst loadings. A Pd complex resulting from oxidative addition of 4-bromobenzonitrile, (Xantphos)Pd(4-cyanophenyl)(Br) (II), was prepared in one step from Xantphos, Pd2(dba)3, and the aryl bromide. Complex II proved to be an active catalyst for the coupling between 4-bromobenzonitrile and benzamide. X-ray crystallographic analysis of II revealed a rare trans-chelating bisphosphine-Pd(II) structure with a large bite angle of 150.7°.
438 citations
TL;DR: In this paper, copolymerisation of ethene and alkylacrylates is catalysed by palladium modified with di(2-methoxyphenyl)phosphinobenzene-2-sulfonic acid (DOPPBS); a linear polymer is produced in which acrylate units are incorporated into the polyethylene backbone.
TL;DR: The Fermi level of the junction lies much closer to the HOMO than to the LUMO, and the resistance of these junctions at low bias as a function of alkane chain length is measured.
Abstract: Using conducting probe atomic force microscopy (CP-AFM), we have formed molecular tunnel junctions consisting of alkanethiols and alkane isonitrile self-assembled monolayers sandwiched between gold, platinum, silver, and palladium contacts. We have measured the resistance of these junctions at low bias (dV/dI |V=0) as a function of alkane chain length. Extrapolation to zero chain length gives the contact resistance, R0 . R0 is strongly dependent on the type of metal used for the contacts and decreases with increasing metal work function; that is, R0,Ag > R0,Au > R0,Pd > R0,Pt. R0 is ∼10% smaller for Au junctions with isonitrile versus thiol surface linkers. We conclude that the Fermi level of the junction lies much closer to the HOMO than to the LUMO.
TL;DR: The PdHAP are one of the most active heterogeneous catalysts for both alcohol oxidation under an atmospheric O(2)() pressure and the Heck reaction reported to date and are recyclable in the above organic reactions.
Abstract: Achieving precise control of active species on solid surfaces is one of the most important goals in the development of highly functionalized heterogeneous catalysts. The treatment of hydroxyapatites with PdCl(2)(PhCN)(2) gives two new types of hydroxyapatite-bound Pd complexes. Using the stoichiometric hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), we found that monomeric PdCl(2) species can be grafted on its surface, which are easily transformed into Pd(0) particles with narrow size distribution in the presence of alcohols. Such metallic Pd species can effectively promote alcohol oxidation using molecular oxygen and are shown to give a remarkably high TON of up to 236 000. Another monomeric Pd(II) phosphate complex can be generated at a Ca-deficient site of the nonstoichiometric hydroxyapatite, Ca(9)(HPO(4))(PO(4))(5)(OH), affording a catalyst with Pd(II) structure and high activity for the Heck and Suzuki reactions. To the best of our knowledge, the PdHAP are one of the most active heterogeneous catalysts for both alcohol oxidation under an atmospheric O(2)() pressure and the Heck reaction reported to date. These Pd catalysts are recyclable in the above organic reactions. Our approach to catalyst preparation based on the control of Ca/P ratios of hydroxyapatites represents a particularly attractive method for the nanoscale design of catalysts.
TL;DR: Allenes bearing a pro-nucleophile can be cyclized on treatment with a wide variety of transition metal catalysts and reagents and the metal complex can be used to introduce a variety of functional groups during cyclization.
Abstract: Allenes bearing a pro-nucleophile can be cyclized on treatment with a wide variety of transition metal catalysts and reagents: palladium, cobalt, ruthenium, silver, rhodium, lanthanides, gold. The nucleophilic groups can be nitrogen, oxygen or carbon based and can form rings of various sizes, often with good control of stereochemistry. A variety of mechanisms can be proposed for these reactions and the metal complex can be used to introduce a variety of functional groups during cyclization. Several heterocyclic natural products have been prepared using a selection of these reactions.
TL;DR: The optimization of the catalyst and reaction conditions allowed Pd/C catalysts with very high activity for Heck reactions of unactivated bromobenzene to be developed and indicate dissolution/reprecipitation of palladium during the reaction.
Abstract: A variety of palladium on activated carbon catalysts differing in Pd dispersion, Pd distribution, Pd oxi- dation state, and water content were tested in Heck reactions of aryl bro- mides with olefins. The optimization of the catalyst (structure ± activity relation- ship) and reaction conditions (temper- ature, solvent, base, and Pd loading) allowed Pd/C catalysts with very high activity for Heck reactions of unactivat- ed bromobenzene (turnover number (TON) 18 000, turnover frequency (TOF) up to 9000, Pd concentrations down to 0.005 mol %) to be developed. High Pd dispersion, low degree of re- duction, sufficient content of water, and uniform Pd impregnation are criteria for the most active system. The catalysts combine high activity and selectivity under ambient conditions (air and mois- ture), easy separation (filtration), and quantitative recovery of palladium. De- termination of Pd in solution after and during the reaction, and catalyst charac- terization before and after the reaction (transmission electron microscopy (TEM), X-ray diffraction (XRD)), indi- cate dissolution/reprecipitation of palla- dium during the reaction. The Pd con- centration in solution is highest at the beginning of the reaction and is a mini- mum ( 1 ppm) at the end of the reac- tion. Palladium leaching correlates sig- nificantly with the reaction parameters.
TL;DR: In this paper, the synthesis and X-ray crystallographic characterization of a Pd complex (3) with a rigid C,N,C-tridentate pincer carbene ligand are described.
TL;DR: The (pi-allyl)palladium complex bearing an sp2-hybridized phosphorus ligand efficiently catalyzes direct conversion of allylic alcohols in the absence of activating agents of alcohols such as Lewis acids.
Abstract: The (π-allyl)palladium complex bearing an sp2-hybridized phosphorus ligand (DPCB-OMe: 1,2-bis(4-methoxyphenyl)-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutene) efficiently catalyzes direct conversion of allylic alcohols in the absence of activating agents of alcohols such as Lewis acids. N-Allylation of aniline proceeds at room temperature to afford monoallylated anilines in 90−97% yields. C-Allylation of active methylene compounds is also successful at 50 °C using a catalytic amount of pyridine as a base, giving monoallylation products in 85−95% yields. The catalytic mechanism involving hydrido- and (π-allyl)palladium intermediates has been proposed on the basis of stoichiometric examinations using model compounds of presumed intermediates.
TL;DR: The alternating copolymerization of carbon monoxide and olefins is a reaction that transition metal complexes, generally containing palladium, catalyze in different phase variation systems as discussed by the authors.
TL;DR: Secondary 2-thiophenecarboxamides efficiently undergo unique triarylation accompanied by formal decarbamoylation under palladium catalysis.
Abstract: Secondary 2-thiophenecarboxamides efficiently undergo unique triarylation accompanied by formal decarbamoylation under palladium catalysis. 3-Substituted thiophenes, especially having an electron-withdrawing group, can also be triarylated.
TL;DR: The ligand-free palladium catalysis of the Suzuki reaction in water using microwave heating is reported, using low palladium loadings and is useful for couplings involving boronic acids and aryl iodides, bromides, and chlorides.
TL;DR: Using a novel palladium complex 2, various beta-ketoesters including cyclic and acyclic substrates were fluorinated with excellent enantioselectivity, resulting in both alpha-fluoro beta-hydroxy and beta-amino acid derivatives, which should be extremely useful in developing novel drugs.
Abstract: Reflecting the importance of fluorinated organic compounds in medicinal chemistry, development of an efficient method for catalytic enantioselective fluorination is increasingly desirable. Using a novel palladium complex 2 (1-2.5 mol %), various beta-ketoesters including cyclic and acyclic substrates were fluorinated with excellent enantioselectivity in the range of 83-94% ee. It is environmentally advantageous that this reaction proceeds well in solvents such as EtOH, rather than usual organic solvents. Furthermore, the product was successfully tranformed into both alpha-fluoro beta-hydroxy and beta-amino acid derivatives, which should be extremely useful in developing novel drugs.
TL;DR: In this article, it was shown that catalytic carbon-carbon bond formation, via transmetalation between organoboron compounds and palladium(II) halides, was found to proceed in the presence of a base.
TL;DR: It is found that copper and copper/noble metal combination nanoclusters are active catalysts for this reaction, the most active being the combined copper/palladium clusters.
Abstract: A small library of copper and noble metal nanoclusters is designed and synthesized These clusters are tested as catalysts in the Suzuki cross-coupling of various aryl halides with phenylboronic acid It is found that copper and copper/noble metal combination nanoclusters are active catalysts for this reaction, the most active being the combined copper/palladium clusters Iodo-, bromo-, and chloroarenes can be used In the case of p-nitrobromobenzene, a one-pot cross-coupling and selective hydrogenation is achieved
TL;DR: Arrays of mesoscopic palladium wires prepared by electrodepositing palladium mesowires form the basis for hydrogen sensors and hydrogen-actuated switches that exhibit a response time ranging from 20 ms to 5 s, depending on the hydrogen concentration.
Abstract: Arrays of mesoscopic palladium wires prepared by electrodeposition form the basis for hydrogen sensors and hydrogen-actuated switches that exhibit a response time ranging from 20 ms to 5 s, depending on the hydrogen concentration. These devices were constructed by electrodepositing palladium mesowires on a highly oriented pyrolytic graphite surface and then transferring these mesowires to a cyanoacrylate film supported on a glass slide. The application of silver contacts to the ends of 10−100 mesowires, arrayed electrically in parallel, produced sensors and switches that exhibited a high conductivity state in the presence of hydrogen and a low conductivity state in the absence of hydrogen. After an initial exposure to hydrogen, 15−50 nanoscopic gaps are formed in each mesowire. These nanoscopic gaps or “break junctions” close in the presence of hydrogen gas and reopen in its absence as hydrogen is reversibly occluded by the palladium grains in each wire, and the palladium lattice expands and contracts by ...
TL;DR: The Heck reaction of aryl chlorides was investigated in the presence of defined monocarbenepalladium(0) complexes to provide the corresponding cinnamic esters and stilbenes in (n)Bu(4)NBr as a ionic liquid in good to excellent yields.
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01 Jan 2002
TL;DR: In this paper, Palladium catalysts for C-N and C-O bond formation were used to generate cross-coupling reactions in C-H bonds, and direct Arylation via cleavage of activated and unactivated CH bonds.
Abstract: to Cross-Coupling Reactions.- Organoboron Compounds.- Organosilicon Compounds.- Organotin Compounds.- Practical Palladium Catalysts for C-N and C-O Bond Formation.- Direct Arylation via Cleavage of Activated and Unactivated C-H Bonds.