Showing papers on "Palladium published in 1997"
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TL;DR: In this article, the α-diimine ligand ArNC(me)C(Me)NAr (Ar = 2,6-C6H3-iPr2) reacts with Pd(OAc)2 in the presence of HBF4·Et2O, or [Pd(MeCN)4]-BF4] in the absence of acid, to give ethylene polymerization catalysts.
339 citations
TL;DR: In this article, a block copolymer stabilized palladium colloid was used for the Heck reaction, which was successfully applied for the Pd-catalyzed carbon−carbon coupling of aryl halides with alkenes.
Abstract: Colloidal dispersions of nanometer sized palladium colloids with very high stability were prepared in block copolymer micelles of polystyrene-b-poly-4-vinylpyridine and analyzed by electron microscopy and X-ray analysis. The resulting polymer/metal hybrids can easily be dissolved and handled in standard organic solvents such as toluene, tetrahydrofuran, and cyclohexane. They were successfully used for the Pd-catalyzed carbon−carbon coupling of aryl halides with alkenes (Heck reaction). Such block copolymer stabilized palladium colloids exhibit about the same reactivity as low molecular weight Pd complexes classically used for the Heck reaction, but show a much higher stability: in most reactions, the hybrids remain catalytically active even after 50000 turn-over cycles. Reaction rates were significantly controlled by the reactivity of the educts, but also respond to micelle architecture and dispersity of the palladium. Other advantages of the block copolymer stabilizer are that they are more simple and r...
330 citations
TL;DR: In this article, the crosscoupling reaction of (RO)2BB(OR)2 (RO =methoxo and pinacolato) with aryl triflates to give arylsboronates was carried out at 80 °C in the presence of PdCl2(dppf) (3 mol%), dppf(3 mol%) and KOAc (3 equivs) in dioxane.
323 citations
TL;DR: In this paper, a sonochemical method was used to extract bimetallic nanoparticles composed of gold and palladium, which were then reduced by ultrasound irradiation in the presence of sodium dodecyl sulfate.
Abstract: Colloidal dispersions of bimetallic nanoparticles composed of gold and palladium were prepared by a sonochemical method, in which Au(III) and Pd(II) ions in an aqueous solution of sodium tetrachloroaurate(III)dihydrate and sodium tetrachloropalladate(II) were reduced by ultrasound irradiation in the presence of sodium dodecyl sulfate (SDS). In addition to the stabilizing effect, SDS remarkably enhanced the reduction rate, probably due to the thermal decomposition that occurs at the interfacial region between cavitation bubbles and bulk solution and provides reducing radicals. Transmission electron microscopy (TEM) photographs showed spherical particles whose size had a fairly narrow distribution with a geometric mean diameter about 8 nm and a geometric standard deviation of 1.1. Analyses with UV−vis spectra indicated that Au(III) ions were first reduced and after their consumption reduction of Pd(II) ions set in. A core−shell structure of the particles, a core of gold and a shell of palladium, was confirm...
288 citations
276 citations
TL;DR: In this paper, it was shown that hydrogen gas intercalated in a palladium lattice is the powerful reducing agent that reductively dechlorinates chlorinated organic compounds that are adsorbed on the surface of palladized electrodes.
Abstract: We have hypothesized that hydrogen gas intercalated in a palladium lattice is the powerful reducing agent that reductively dechlorinates chlorinated organic compounds that are adsorbed on the surface of palladized electrodes. We have shown that dechlorination of 4-chlorophenol to phenol occurs rapidly on palladized carbon cloth or pal ladized graphite electrodes. The reactions on the palladized carbon cloth and graphite depend on the adsorption of the chlorinated organic compound on the carbon surface and the reaction with hydrogen at the palladium/carbon interface. Palladium was much more effective in promoting the dechlorination reaction than platinum, probably because of its ability to intercalate hydrogen in its lattice.
TL;DR: In this paper, high-dispersed palladium catalysts on carbon supports have been evaluated for the oxidation of hydrogen, methanol, formaldehyde and ethylene glycol and reduction of oxygen.
Abstract: Highly dispersed palladium catalysts on carbon were prepared by reduction of their salts with various reducing agents. The crystallite parameters and metal surface area were evaluated by XRD and electrochemical techniques. The electrochemical activity for the oxidation of hydrogen, methanol, formaldehyde and ethylene glycol and reduction of oxygen was evaluated in alkaline solutions by making PTFE bonded carbon electrodes. The electrochemical activity was correlated with the catalyst properties. Pd dispersed catalysts on carbon supports exhibit high activity for the oxidation of hydrogen and ethylene glycol in alkaline medium. Their electrochemical activity is dependant upon the crystallite properties like surface area, dispersion and crystallite size. For oxygen reduction reaction, the activity can be increased by alloying with other elements.
TL;DR: These methods provide a practical approach to the rational design of multichelating ligands for coo-tritopic and hetero-ditopic ligands in fair to excellent yields.
Abstract: Rigid preorganized multitopic ligands have been designed and synthesized. The Pd(0)-catalyzed cross-coupling reactions between ethynylated derivatives of bipyridine or terpyridine and the corresponding bipyridine or terpyridine halides or triflates provide access to various homo-ditopic, hetero-ditopic, homo-tritopic, and hetero-tritopic ligands bearing acetylene or diphenylacetylene central units in fair to excellent yields. Optimal conditions were found with [Pd(PPh3)2Cl2], CuI in THF and diisopropylamine at rt, or with [Pd(PPh3)4] in benzene and diisopropylamine at 80 °C. When a phenylethynyl group is present in the molecule, the relevant conditions involve [Pd(PPh3)4] in n-propylamine at 60 °C. Oxidative dimerization of the ethynylated derivatives in the presence of cupric salts and oxygen gives the corresponding homo-ditopic ligands bearing diacetylene or diphenyldiacetylene as a spacer in good yields. These methods provide a practical approach to the rational design of multichelating ligands for coo...
TL;DR: In this paper, the authors describe several oxidation reactions conducted either at high temperatures in the gas phase or at moderate temperatures in liquid phase; in both cases they proceed via a mechanism of oxidative dehydrogenation on the metal surface.
TL;DR: In this article, a mechanistic and synthetic study of the catalytic behavior of aryl halides and tin amides or amines in the presence of base base is described.
Abstract: Palladium complexes of trio-o-tolyl phosphine and bis(diphenylphospino)ferrocene catalyze the reaction between aryl halides and either tin amides or amines in the presence of base to form aryl amines by halide substitution. This account describes our mechanistic and synthetic studies related to the amination reactions. These studies include kinetic behavior of the catalytic systems as well as direct observation of the primary stoichiometric reactions comprising the catalysis - including the rare C-N bond-forming reductive eliminations - and the mechanisms of these individual reactions. This paper also describes the development of tin-free amide sources and second generation amination catalysts that have resulted from our mechanistic understanding of the amination chemistry.
TL;DR: In this article, a series of monomeric palladium amido complexes of the form trans-(PPh3)2Pd(Ar)(NAr‘2) and (DPPF)Pd[1,1,bis(diphenylphosphino)ferrocene) were obtained by the reaction of lithium and potassium amides with palladium aryl halide complexes.
Abstract: A series of monomeric palladium amido complexes of the form trans-(PPh3)2Pd(Ar)(NAr‘2) and (DPPF)Pd(Ar)(NAr‘2) (DPPF = 1,1‘-bis(diphenylphosphino)ferrocene) and dimeric palladium amido complexes of the form {(PPh3)Pd(Ar)(μ-NHR)}2 (R = Ph, t-Bu) have been prepared by the reaction of lithium and potassium amides with palladium aryl halide complexes. An X-ray crystal structure of (DPPF)Pd(p-NMe2C6H4)[N(p-CH3C6H4)2] was obtained. Upon thermolysis in the presence of PPh3, serving as a trapping agent, both the monomeric and dimeric palladium amido complexes underwent C−N-bond-forming reductive elimination to form arylamines in high yields along with a Pd(0) species. Reductive elimination was also observed from azametallacycle (PPh3)Pd(η2-C6H4C6H4NH), to form carbazole and Pd(PPh3)4 at room temperature. Mechanistic studies on the reductive elimination reactions of the monomeric PPh3-ligated amido complexes indicated the presence of two competing pathways for the formation of amine. At low [PPh3], reductive elimi...
TL;DR: The "ligandless" palladium acetate-catalyzed Suzuki cross-coupling reaction of ArX with aryl- and vinylboronic acids in water without organic cosolvent in the presence of tetrabutylammonium bromide is reported.
Abstract: The “ligandless” palladium acetate-catalyzed Suzuki cross-coupling reaction of ArX with aryl- and vinylboronic acids in water without organic cosolvent in the presence of tetrabutylammonium bromide is reported. Aryl bromides give high yields and considerably accelerate the coupling. A wide variety of functional groups can be tolerated. Aryl iodides, however, give incomplete conversion and aryl triflate coupling shows no improvement over reported conditions.
TL;DR: An intriguing relationship between substitution on the oxazoline ring, particularly the commonly-derivatized 4-position, and catalyst efficiency was discovered and the results are rationalized by either partial or complete bis(oxazoline) decomplexation during the course of the reaction.
Abstract: Studies toward the development of an enantioselective diazomethane-based cyclopropanation reagent derived from bis(oxazoline)palladium(II) complexes are reported. Several simple palladium chelates, 2 and 7, in addition to the novel carbon-bound complexes 15 were synthesized and evaluated in the cyclopropanation of various electron-deficient olefins. The X-ray crystal structure of aryl−bis(oxazoline)palladium complex 15c is described. Although all catalysts efficiently affected cyclopropanation, all products were racemic. An intriguing relationship between substitution on the oxazoline ring, particularly the commonly-derivatized 4-position, and catalyst efficiency was discovered. The results are rationalized by either partial or complete bis(oxazoline) decomplexation during the course of the reaction.
TL;DR: In this article, the choice of ligand in the palladium-catalyzed coupling is critical to the format of the N-aryl derivatives of enantiomerically enriched amines with aryl bromides.
Abstract: The coupling of enantiomerically enriched amines with aryl bromides produces the corresponding N-aryl derivatives. The choice of ligand in the palladium-catalyzed coupling is critical to the format...
TL;DR: A series of bis-chelated palladium(II) complexes [Pd(N-N)2][X]2 (n-N = 2,2-bipyridine (bipy), 1,10-phenanthroline (phen), and their substituted derivatives; X = PF6-, BF4-, OTf-, OTs-) has been synthesized and completely characterized both in the solid state and in solution as discussed by the authors.
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23 Dec 1997
TL;DR: In this article, the preparation of Halogen Compounds Cross Coupling between 1-Alkynes and 1-Bromoalkynes Copper Catalyzed Aminoalkylation of Acetylenes.
Abstract: Catalysts, Ligands and Reagents Procedures for the Preparation of Halogen Compounds Cross Coupling between 1-Alkynes and 1-Bromoalkynes Copper Catalyzed Aminoalkylation of Acetylenes Copper(I)halide Catalyzed Oxidative Coupling of Acetylenes Copper(I)halide Catalyzed Substitution of sp2-Halogen by Alkoxide Copper Catalyzed Carbon-Carbon Bond Formation by 1,1- and 1,3-Substitution Reactions Nickel Catalyzed Iodo-Dechlorination and Iodo-Debromination of sp2-Halides Nickel and Palladium Catalyzed Cyanation of sp2-Halides and sp2-Triflates Couplings of Acetylenes with sp2-Halides Nickel and Palladium Catalyzed Cross Coupling Reactions with Organometallic Intermediates.
TL;DR: In this article, a modified Suzuki cross-coupling reaction between arylboronic acids or sodium tetraphenylborate and aryls was performed in aqueous solvents or water using a phosphine-free palladium catalyst.
TL;DR: Under mild conditions, an interesting selectivity was observed with functional groups that are known to react either in palladium-catalyzed reactions or reactions catalyzed by other transition-metals, and aryl halides, terminal alkynes, 1,6-enynes, and alpha-allenic alcohols were tolerated.
Abstract: The scope of the palladium-catalyzed cyclization/dimerization of terminal allenyl ketones 1 to the 2,4-disubstituted furans 3 has been investigated. Simplified and improved conditions almost exclusively provided the dimer 3, accompanied by only traces of the easily separable monomer 2. The formation of an isomer of 3, the unconjugated ketone 4, was completeley suppressed. Under these mild conditions, besides the normal functional group tolerance known for palladium-catalyzed reactions, an interesting selectivity was observed with functional groups that are known to react either in palladium-catalyzed reactions or reactions catalyzed by other transition-metals. Thus aryl halides, terminal alkynes, 1,6-enynes, and α-allenic alcohols were tolerated. In the latter example the selective reaction of only one out of two different allenes was achieved. Mechanistic investigation indicated a Pd(II)/Pd(IV)-cycle involving palladium(II)-γ-alkoxyvinylcarbene and furylpalladium(IV) hydride intermediates, although a sec...
TL;DR: Aryl iodides are coupled with amines to give the corresponding arylamines in high yield in the presence of palladium, a suitable ligand, and NaOt-Bu as mentioned in this paper.
TL;DR: In this paper, the synthesis of functionalized imidazoline-2-ylidene complexes suitable for reactions with functionalized polymers is reported, as well as a water-soluble metal complex.