Showing papers on "Palladium published in 2000"
TL;DR: s, or keywords if they used Heck-type chemistry in their syntheses, because it became one of basic tools of organic preparations, a natural way to make organic preparations.
Abstract: s, or keywords if they used Heck-type chemistry in their syntheses, because it became one of basic tools of organic preparations, a natural way to
3,373 citations
TL;DR: A water-soluble palladium(II) bathophenanthroline complex is a stable recyclable catalyst for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic water-alcohol system.
Abstract: Alcohol oxidations are typically performed with stoichiometric reagents that generate heavy-metal waste and are usually run in chlorinated solvents. A water-soluble palladium(II) bathophenanthroline complex is a stable recyclable catalyst for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic water-alcohol system. The use of water as a solvent and air as the oxidant makes the reaction interesting from both an economic and environmental point of view.
1,024 citations
TL;DR: The anion ligated to the palladium(0) affects the kinetics of the oxidative addition to ArI as well as the structure and reactivity of the arylpalladium(II) complexes produced in this reaction.
Abstract: The anions of PdCl(2)L(2) and Pd(OAc)(2), precursors of palladium(0) used in cross-coupling and Heck reactions, play a crucial role in these reactions. Tricoordinated anionic complexes Pd(0)L(2)Cl(-) and Pd(0)L(2)(OAc)(-) are the effective catalysts instead of the usually postulated Pd(0)L(2) complex. The anion ligated to the palladium(0) affects the kinetics of the oxidative addition to ArI as well as the structure and reactivity of the arylpalladium(II) complexes produced in this reaction. Thus, pentacoordinated anionic complexes are formed, ArPdI(Cl)L(2)(-) or ArPdI(OAc)L(2)(-), the precursor of neutral trans-ArPd(OAc)L(2), instead of the usually postulated trans-ArPdIL(2) complex (L = PPh(3)).
923 citations
TL;DR: Nanosized palladium colloids are involved in the catalysis of phosphane-free Heck and Suzuki reactions with simple palladium salts such as PdCl(2) or Pd(OAc)(2), as demonstrated by transmission electron microscopic investigations.
Abstract: Nanosized palladium colloids, generated in situ by reduction of PdII to Pd0 [Eq. (a)], are involved in the catalysis of phosphane-free Heck and Suzuki reactions with simple palladium salts such as PdCl2 or Pd(OAc)2, as demonstrated by transmission electron microscopic investigations.
738 citations
TL;DR: Efficient electrophilic metalation of aromatic C-H bonds leading to new C-C bond formation through regio- and stereoselective addition to alkynes and alkenes has been realized by a catalytic amount of palladium( II) or platinum(II) compounds in a mixed solvent containing trifluoroacetic acid at room temperature.
Abstract: Efficient electrophilic metalation of aromatic C-H bonds leading to new C-C bond formation through regio- and stereoselective addition to alkynes and alkenes has been realized by a catalytic amount (0.02 to 5 mole percent) of palladium(II) or platinum(II) compounds in a mixed solvent containing trifluoroacetic acid at room temperature. Various arenes undergo unexpected selective trans hydroarylation to terminal or internal CcC bonds inter- and intramolecularly with high efficiency (up to a turnover number of 4500 for palladium), especially for electron-rich arenes, giving thermodynamically unfavorable cis-alkenes, and the oxygen- and nitrogen-containing heterocycles. The simplicity, generality, and efficiency of this process should be very attractive to the possible industrial application for the functionalization of arenes.
731 citations
712 citations
TL;DR: These ligands are effective for almost all substrate combinations that have been previously reported with various other ligands, and they represent the most generally effective catalyst system reported to date.
Abstract: Palladium complexes supported by (o-biphenyl)P(t-Bu)2 (3) or (o-biphenyl)PCy2 (4) are efficient catalysts for the catalytic amination of a wide variety of aryl halides and triflates. Use of ligand 3 allows for the room-temperature catalytic amination of many aryl chloride, bromide, and triflate substrates, while ligand 4 is effective for the amination of functionalized substrates or reactions of acyclic secondary amines. The catalysts perform well for a large number of different substrate combinations at 80−110 °C, including chloropyridines and functionalized aryl halides and triflates using 0.5−1.0 mol % Pd; some reactions proceed efficiently at low catalyst levels (0.05 mol % Pd). These ligands are effective for almost all substrate combinations that have been previously reported with various other ligands, and they represent the most generally effective catalyst system reported to date. Ligands 3 and 4 are air-stable, crystalline solids that are commercially available. Their effectiveness is believed t...
708 citations
TL;DR: In this paper, the deactivation of catalysts has been investigated in the presence of palladium and platinum catalysts under mild conditions (293 −353 K and atmospheric pressure) and several causes of deactivation have been put forward: oxidation of metal, blocking of active sites by strong adsorption of sideproducts, metal leaching and growth of platinum crystallites.
593 citations
TL;DR: In this paper, a magnetite colloid was prepared in alkaline solution according to the procedure published by Massart [11], an aqueous solution containing 2.3 g (8.5 mmol), FeCl 3 ×6H 2 O in 4 mL H 2 O and 1.69 g (4.3 mmol) Fe(NH 4 ) 2 (SO 4) 2 in 1 mL of 2 M HCl, was added to 50 mL of 1 M (CH 3) 4 NOH×5H 2.
Abstract: A magnetite colloid was prepared in alkaline solution according to the procedure published by Massart [11]. An aqueous solution containing 2.3 g (8.5 mmol) FeCl 3 ×6H 2 O in 4 mL H 2 O and 1.69 g (4.3 mmol) Fe(NH 4) 2 (SO 4) 2 in 1 mL of 2 M HCl, was added to 50 mL of 1 M (CH 3) 4 NOH×5H 2 O. The resulting black suspension was stirred for 1 h at room temperature and then sonicated in an ultrasonic bath for 1 h. The colloid was then centrifuged at 20 000 g for 1 h. The supernatant was decanted and the slurry resuspended in 20 mL water by sonication before being passed through a 0.2 mm pore cellulose nitrate membrane. A titanium dioxide sol was prepared by hydrolysis of titanium tetraiso-propoxide under a nitrogen atmosphere following the procedure described by O'Regan et al. [12]. 25 mL of titanium tetraisopropoxide was mixed with 4 mL of isopropanol in a dropping-funnel under a nitrogen atmosphere. This mixture was added slowly over a period of 5 min to 150 mL of vigorously stirred double-distilled, deionized water in a 250 mL three-neck flask equipped with heater, thermometer and stirrer. Ten minutes after the final alkoxide addition, 1 mL of 69 % HNO 3 was added. The white hydrolysis mixture was then stirred for 8 h at 80 C to remove the isopropanol, filtered through a 0.2 mm pore cellulose nitrate membrane, and sonicated for 1 h to produce a stable colloidal solution with a bluish-white coloration. Preparation of the Composites and Method of Calcination: Typically, a sample of the sliced copolymer gel (ca. 5 mm thick) was added to the colloidal sol and left for the desired period of time. The colloid-loaded gels were removed, washed with water and allowed to dry in air. Thermogravi-metric analysis (TGA) measurements were made using a NETZSCH STA 409EP machine. Samples were heated under air in an alumina crucible to a final temperature of 800 C at a rate of 5 K/min. Large samples of the miner-alized gels were calcined by heating to a temperature of 450 or 500 C in a Carbolite furnace (type ELF11/6) at a heating rate of 1 C min ±1. Analytical Methods: The morphology of the copolymer gel in the water-swollen state was examined using a Jeol 6310 SEM equipped with a cryo-stage and energy-dispersive X-ray (EDX). …
431 citations
426 citations
TL;DR: Mixtures of Pd(2)(dba)(3) or PD(OAc)(2) and BINAP catalyze the cross-coupling of amines with a variety of aryl bromides, and certain classes of secondary amines are also effectively transformed.
Abstract: Mixtures of Pd2(dba)3 or Pd(OAc)2 and BINAP catalyze the cross-coupling of amines with a variety of aryl bromides. Primary amines are arylated in high yield, and certain classes of secondary amines are also effectively transformed. The process tolerates the presence of several functional groups including methyl and ethyl esters, enolizable ketones, and nitro groups provided that cesium carbonate is employed as the base. Most reactions proceed to completion with 0.5−1.0 mol % of the palladium catalyst; in some cases, catalyst levels as low as 0.05 mol % Pd may be employed. Reactions are considerably faster if Pd(OAc)2 is employed as the precatalyst, and the order in which reagents are added to the reaction has a substantial effect on reaction rate. It is likely that the catalytic process proceeds via bis(phosphine)palladium complexes as intermediates. These complexes are less prone to undergo undesirable side reactions which lead to diminished yields or catalyst deactivation than complexes of the correspon...
TL;DR: The first general intermolecular C-N bond-forming reactions between aryl halides and amides were realized using a palladium catalyst with Xantphos as the ligand.
TL;DR: In this article, the authors studied the cyclotrimerization of acetylene on size-selected Pdn clusters (1 ≤ n ≤ 30) supported on thin MgO(100) films by thermal desorption and Fourier transform infrared spectroscopy.
Abstract: We studied the cyclotrimerization of acetylene on size-selected Pdn clusters (1 ≤ n ≤ 30) supported on thin MgO(100) films by thermal desorption and Fourier transform infrared spectroscopy. Surprisingly, the production of benzene is already observed on a single palladium atom at low temperature (300 K). Using density functional theory (DFT) calculations we show that free inert Pd atoms are activated by charge transfer from defect sites of the MgO substrate upon deposition. For larger clusters (7 ≤ n ≤ 30) benzene is additionally produced at a temperature of 430 K and our results suggest the existence of a critical ensemble of seven palladium atoms for this high-temperature reaction mechanism.
TL;DR: In this article, the preparation of nanosized gold/palladium bimetallic particles utilizing a cavitation phenomenon induced by irradiation of high-intensity ultrasound in an aqueous solution of gold(III) and palladium(II) ions is described.
Abstract: This is a report regarding the preparation of nanosized gold/palladium bimetallic particles utilizing a cavitation phenomenon induced by irradiation of high-intensity ultrasound in an aqueous solution of gold(III) and palladium(II) ions. The particles are found to be composed of gold-core and palladium-shell by a transmission electron microscopic and nanoarea energy-dispersive X-ray spectroscopic analyses. Sodium dodecyl sulfate added to the sample solution is found to be a stabilizer for the nanoparticles generated as well as an important source of reducing species for noble metal ions. The thickness of a palladium shell and the size of a gold core seem to depend on the ratio of the concentrations of noble metal ions. The morphological differences in the sonochemical and radiochemical products suggest that the formation of a core−shell structure can be affected by the physical effects of ultrasound, such as effective stirring, microjet stream, or shock wave during the collapse of a cavitation bubble. Bim...
TL;DR: In this article, the authors investigated the dissociative adsorption of oxygen on the (111) surfaces of platinum, palladium, and nickel using ab initio local spin-density calculations.
Abstract: The dissociative adsorption of oxygen on the (111) surfaces of platinum, palladium, and nickel has been investigated using ab initio local-spin-density calculations. For all three surfaces, adsorption is shown to be precursor-mediated and the structural, energetic, vibrational and electronic properties of the precursors are in very good agreement with the available experimental information. The investigation of the transition states shows that on Pt and Pd the barriers for dissociation are comparable to (or at sufficiently high coverage even higher than) the desorption barriers. In combination with large energies for atomic adsorption, this also leads to a high barrier for associative desorption---in agreement with observation. In contrast, the dissociation barrier for ${\mathrm{O}}_{2}$ on Ni(111) is low and occurs already for a less stretched molecule. The trends in molecular and atomic adsorption and in the dissociation barriers are discussed in relation to the geometric and electronic properties of the substrate and to the sticking probabilities observed in molecular-beam experiments.
TL;DR: In this article, the preparation of catalysts for cationic nickel and palladium complexes with multidentate ligands has been studied and a review of the recent advances is presented.
TL;DR: N-Heterocyclic dicarbene chelate complexes efficiently catalyze the Heck reaction of activated and non-activated arylbromides, are recyclable under aerobic conditions and exhibit hardly any leaching, which is in line with theoretical investigations on ligand dissociation energies related to Pd0 and PdII centres.
Abstract: N-Heterocyclic dicarbene chelate complexes of formula [cis-CH2{N(H)CC(H)N(R)C}2PdX2] (X=Br, I; R=(CH2)nOH; n=2, 3) have been prepared and structurally characterized (for X=I, n=2). The complexes were immobilized on a functionalized polystyrene support (Wang resin) through one of the oxygen centres. The complexes efficiently catalyze the Heck reaction of activated and non-activated arylbromides, are recyclable under aerobic conditions and exhibit hardly any leaching, which is in line with our theoretical investigations on ligand dissociation energies related to Pd0 and PdII centres.
TL;DR: The metal-catalyzed borylation of alkenes, alkynes, and organic electrophiles with BB compounds was developed for the synthesis of organoboronic esters from simple organic substrates as discussed by the authors.
TL;DR: The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate and it was found that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed.
Abstract: The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate. The reaction can be performed in air without any solubilizing or activating ligands. It was found that significant amounts of palladium leach out into the solvent and these dissolved Pd species essentially catalyze the reaction. It is interesting, however, that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed (at 100% conversion of iodobenzene). Thus, the catalysts were recyclable without loss of activity. The use of both inorganic and organic bases is very effective in the promotion of the palladium redeposition as well as in the enhancement of the reaction rate. For Heck reactions with bromobenzene and chlorobenzene it was found that the use of triethylamine and sodium carbonate increases the selectivity of the Heck coupling product (benzene is also produced for these two substrates), but the mixed bases do not affect the overall rate of reaction as much.
TL;DR: Palladium(0) complexes of N-heterocyclic carbenes (NHC) are easily obtained starting from the free carbene and bis(tri-orthotolylphosphine)palladium by ligand exchange as discussed by the authors.
TL;DR: In this article, an alloy of palladium and silver dispersed on Al2O3 has been used for the selective hydrogenation of acetylene, but the selectivity of Pd-Ag catalyst is higher and less impaired by temperature increase than that of pure metal Pd catalyst.
Abstract: An alloy of palladium and silver dispersed on Al2O3 has been used for the selective hydrogenation of acetylene. The activity of Pd–Ag catalyst is lower than that of pure metal Pd catalyst. But the selectivity of Pd–Ag catalyst is higher and less impaired by temperature increase than that of Pd catalyst. X-ray diffraction (XRD) indicates that metal Pd and Ag can form an alloy on the surface of alumina. X-ray photoelectron spectroscopy (XPS) shows that the Pd–Ag alloy is formed with enrichment of Ag on the surface. Results of hydrogen adsorption isotherm, temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) reveal that the bulk of palladium of Pd–Ag catalyst adsorbed a small amount of hydrogen, which is desorbed at a higher temperature than that in the case of Pd catalyst.
TL;DR: In this article, a modified biosorbent was used for palladium recovery in an acidic medium (around pH 2), and the influence of several parameters such as pH and competitor anions were studied with respect to sorption equilibrium.
Abstract: The high nitrogen content of chitosan is the main reason for its ability to sorb metal ions through several mechanisms including ion-exchange or chelation, depending on the metal and the pH of the solution. Glutaraldehyde is used to crosslink chitosan through imine linkage between amine groups of chitosan and aldehyde groups of the crosslinking agent. This modified biosorbent was studied for palladium recovery in acidic medium (around pH 2). The influence of several parameters such as pH and competitor anions were studied with respect to sorption equilibrium. Sorption isotherms were obtained and modeled using the Langmuir and the Freundlich model. This study also examines the effect of palladium concentration, particle size, sorbent dosage, and the extent of crosslinking on sorption kinetics. Kinetic curves are modeled using single diffusion model equations to evaluate the predominance of either external or intraparticle mass transfer resistance. The influence of the acid used to control the pH of the solution was examined in conjunction with the influence of competitor anions. Sulfuric acid proves to be unfavorable to palladium sorption, in comparison with hydrochloric acid. However, the addition of chloride anions in a palladium solution, whose pH is controlled with sulfuric acid, enhances metal anion sorption: results are interpreted with reference to chloropalladate speciation.
TL;DR: The scope of the new reaction medium is outlined for the first time for the vinylation of various aryl halides using different mono- and disubstituted olefins as well as a variety of known palladium(0) and palladium (II) catalyst systems.
Abstract: Nonaqueous ionic liquids, that is molten salts, constitute an activating and stabilizing noninnocent solvent for the palladium-catalyzed Heck-vinylation of all types of aryl halides. Especially with chloroarenes an improved activity and stability of almost any known catalyst system is observed as compared to conventional, molecular solvents (e.g. dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), or dioxane). Thus, even catalytic amounts of ligand-free PdCl2 yield stilbene from technically interesting chlorobenzene and styrene in high yield (turnover number (TON) = 18) without the need for further promoting salt additives such as tetraphenylphosphonium chloride. The scope of the new reaction medium is outlined for the first time for the vinylation of various aryl halides using different mono- and disubstituted olefins as well as a variety of known palladium(0) and palladium(II) catalyst systems. Furthermore, a novel means of catalyst recycling is presented and its scope is evaluated.
TL;DR: In this paper, the use of thermomorphic catalysts for palladium-catalyzed carbon−carbon bond forming reactions is described, where the authors show that these SCS catalysts are efficient in Heck, Suzuki, and sp−sp2 cross-coupling reactions.
Abstract: Liquid−liquid biphasic systems that exhibit an increase in phase miscibility at elevated temperature together with soluble polymer-bound catalysts that have a strong phase preference at ambient temperature are described. In such systems, product isolation and catalyst recovery are effected by a liquid/liquid separation. This report describes the use of such thermomorphic catalyst recovery systems for palladium-catalyzed carbon−carbon bond forming reactions. Poly(N-isopropylacrylamide) (PNIPAM)-bound phosphine ligands with a Pd(0) catalyst used previously in allylic substitution chemistry are efficient catalysts in Heck, Suzuki, and sp−sp2 cross-coupling reactions. Air-stable tridentate SCS-Pd(II) catalysts bound to PNIPAM or poly(ethylene glycol) (PEG) are also described. A particular advantage of these SCS catalysts is that no precautions against adventitious catalyst oxidation need be taken with the polymer-bound SCS-PdCl catalysts, thus avoiding time-consuming solvent purification and degassing protocols.
TL;DR: In this article, the reduction of NO3− on palladium/copper electrodes has been studied using differential electrochemical mass spectroscopy (DEMS), rotating ring-disk electrodes (RRDE) and quartz microbalance electrodes (ECQM).
Abstract: The reduction of NO3− on palladium/copper electrodes has been studied using differential electrochemical mass spectroscopy (DEMS), rotating ring-disk electrodes (RRDE) and quartz microbalance electrodes (ECQM). In acidic electrolytes, the activity increases linearly with Cu coverage, in alkaline electrolytes, a different dependence on coverage is observed. One monolayer of Cu gives a different selectivity from bulk copper. The adsorption of NO3− is competitive with SO42−, whereas Cl− adsorption blocks the reduction. Competitive adsorption lowers both the activity and the selectivity to N2. Copper activates the first electron transfer, the role of palladium is to steer the selectivity towards N2. The trends in activity and selectivity are explained in terms of coverage of N-species.
TL;DR: In this paper, a template is formed by polystyrene latex spheres self-assembled on gold electrodes and after deposition of platinum, palladium or cobalt, the spheres are fully removed by washing in toluene to leave a highly periodic, hexagonal close packed, interconnected network of spherical pores within the metal film.
TL;DR: Palladium catalysed Suzuki cross-coupling reactions have been conducted in the ambient temperature ionic liquid, 1-butyl-3methylimidazolium tetrafluoroborate.