Showing papers on "Palladium published in 1998"
807 citations
TL;DR: In this article, gold-based catalysts have been used for catalytic diol conversion to α-hydroxy carboxylates with dioxygen in an alkaline solution.
542 citations
TL;DR: In this article, a novel synthesis of palladium complexes with chelating N-heterocyclic carbene ligands is reported and direct proof is presented by X-ray diffraction.
482 citations
TL;DR: In this article, the reactions of iodobenzene with azole compounds, 1,2-disubstituted imidazoles and 2-substitized oxazoles, and thiazoles, were examined in the presence of catalytic amounts of Pd(OAc)2 and PPh3 in DMF using alkali metal carbonates as bases.
Abstract: The reactions of iodobenzene with azole compounds, 1,2-disubstituted imidazoles and 2-substituted oxazoles and thiazoles, were examined in the presence of catalytic amounts of Pd(OAc)2 and PPh3 in DMF using alkali metal carbonates as bases. It was found that the coupling products, 5-arylazoles, could be selectively produced in good yields by using Cs2CO3. In the case that their 2-position is unsubstituted, the site could also be arylated. In reactions using bromobenzene in place of iodobenzene, K2CO3 was also as effective as Cs2CO3. The addition of a stoichiometric amount of CuI appeared to specifically promote the reactions of thiazoles as well as those of thiophene derivatives. The reactions of 2-unsubstituted azole compounds with aryl iodides could be mediated by CuI to some extent without using the palladium species to give 2-arylazoles.
407 citations
TL;DR: In this article, the synthesis and characterization of palladium-grafted mesoporous MCM-41 material, designated Pd-TMS11, is investigated for carbon−carbon coupling reactions (Heck catalysis) with activated and nonactivated aryl substrates.
Abstract: The synthesis and characterization of palladium-grafted mesoporous MCM-41 material, designated Pd-TMS11, are described The material is investigated for carbon−carbon coupling reactions (Heck catalysis) with activated and nonactivated aryl substrates For the preparation of the new catalyst, a volatile organometallic precursor is reacted in the gas phase with the surface of the porous framework, generating a highly dispersed metal deposition The ultrahigh surface area, the large pore opening, and the highly dispersed catalyst species in Pd-TMS11 material create one of the most active heterogeneous catalysts for Heck reactions
378 citations
Patent•
24 Aug 1998TL;DR: A hydrogen gas extraction module includes an intermediate layer bonded between a porous metal substrate and a membrane layer that is selectively permeable to hydrogen as discussed by the authors, where the metal substrate includes a substantial concentration of a first metal at a surface of the substrate, and the intermediate layer includes an oxide of this first metal.
Abstract: A hydrogen gas-extraction module includes an intermediate layer bonded between a porous metal substrate and a membrane layer that is selectively permeable to hydrogen. The metal substrate includes a substantial concentration of a first metal at a surface of the metal substrate, and the intermediate layer includes an oxide of this first metal. In one embodiment, where the module is designed to selectively extract hydrogen at high temperatures, the porous metal substrate comprises stainless steel, and the membrane layer includes palladium or a palladium/silver alloy. A method for fabricating a hydrogen gas-extraction membrane includes reacting the porous metal substrate with an oxidizing agent to form a ceramic intermediate layer on a surface of the porous metal substrate and covering the ceramic coating with the membrane layer that is selectively permeable to hydrogen.
355 citations
324 citations
TL;DR: In this paper, the C−H bond at their 2'-position was cleaved in the presence of a catalyst system of Pd(OAc)2 and Cu(OAC)2 with a base under air.
Abstract: N-(2‘-Phenylphenyl)benzenesulfonamides react with acrylate esters accompanied via cleavage of the C−H bond at their 2‘-position in the presence of a catalyst system of Pd(OAc)2 and Cu(OAc)2 and a base under air to produce 5,6-dihydro-5-(benzenesulfonyl)phenanthridine-6-acetate derivatives in high yields. The reactions of benzoic acid with butyl acrylate and styrene can also give 3-[(butoxycarbonyl)methyl]phthalide and 3-phenylisocoumarin, respectively.
322 citations
318 citations
302 citations
TL;DR: In this paper, an efficient procedure for the oxidation of primary and secondary allylic and benzylic alcohols to aldehydes and ketones, respectively, was achieved using catalytic Pd(OAc)2 in dimethyl sulfoxide (DMSO) with oxygen gas as the sole reoxidant of the palladium.
Abstract: An efficient procedure for the oxidation of primary and secondary allylic and benzylic alcohols to aldehydes and ketones, respectively, has been achieved using catalytic Pd(OAc)2 in dimethyl sulfoxide (DMSO) with oxygen gas as the sole reoxidant of the palladium. Secondary substrates show increased reaction rates and improved yields with the addition of 2 equiv of NaHCO3. The reactions are free of acetal/ketal and ester byproducts.
TL;DR: In this paper, a triarylamines can be readily prepared in excellent yields by palladium-catalyzed cross-coupling reaction of aryl halides and diarylamines.
TL;DR: Palladium(II) compounds dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI·BF4) ionic liquid are shown to be able to catalyze the hydrodimerization of 1,3-butadiene as discussed by the authors.
TL;DR: A palladium-catalyzed α-arylation of amides was reported in this article, where the palladium catalyst was formed in situ from Pd(dba)2 (dba = trans,trans-dibenzylidene acetone).
Abstract: 2A palladium-catalyzed α-arylation of amides is reported. Intermolecular arylation of N,N-dimethylamides and lactams occurs using aryl halides, silylamide base, and a palladium catalyst. Intramolecular arylation of N-(2-halophenyl)amides occurs using alkoxide base and a palladium catalyst. The palladium catalyst was formed in situ from Pd(dba)2 (dba = trans,trans-dibenzylidene acetone) and BINAP (2,2‘-bis(diphenylphosphino)-1,1‘-binaphthalene). Although the intermolecular arylation of amides is less general than that reported previously for ketones, unfunctionalized and electron-rich aryl halides gave α-arylamides in 48−75% yield and N-methyl-α-phenylpyrrolidinone in 49% yield. These reactions provided the highest yields yet reported for regioselective amide arylations. Intramolecular amide arylation of 2-bromoanilides gave oxindoles in 52−82% yield. Mono- and disubstituted acetanilides gave 1,3-di- and 1,3,3-trisubstituted oxindoles. The use of dioxane, rather than THF, solvent was important for some of ...
TL;DR: In this paper, the binding energy of Pd 3d5/2core level spectrum of catalyst 1% Pd/ZnO prereduced at temperatures as low as 373 K and catalyst 5% pd/znO reduced at 573 K and above.
TL;DR: In this paper, the performance of ZnO-and ZrO 2 -supported Pd catalysts was investigated under feed ratios O 2 /CH 3 OH (molar) of 0.3 and 0.5 at 503-543 K, respectively.
Abstract: Hydrogen production by partial oxidation of methanol (CH 3 OH+1/2 O 2 ⇄2 H 2 +CO 2 ) was studied over ZnO- and ZrO 2 -supported Pd catalysts. Catalyst performance was investigated under feed ratios O 2 /CH 3 OH (molar) of 0.3 and 0.5 at 503–543 K. Irrespective of the large difference in BET area of Pd/ZnO and Pd/ZrO 2 catalysts, significant differences were observed when comparing H 2 selectivities. For the 1% Pd/ZnO catalyst, reaction occurs through consecutive oxidation → reforming steps. However, the behavior of catalyst 1% Pd/ZrO 2 approached that expected for Group 8 metals, that is, although the oxidation products are observed as for the catalyst 1% Pd/ZnO, the decomposition reaction seems to occur to a greater extent. Catalyst characterization by TPR, X-ray diffraction and XPS revealed that PdZn alloys can be formed upon reduction of Pd/ZnO catalysts at moderate temperatures.
TL;DR: A simple solution to the age-old problem of the Heck reaction of cheap but unreactive chloro- and bromoarenes has been found in the catalyst [Pd(CH3 CN)2 Cl2 ]⋅6 Ph4 PCl in the presence of N,N-dimethylglycine as additive.
Abstract: We sought a peptidic self-replicatingsystem that would be sensitive to environmental conditionsand reproduce only under extreme conditions. We nowdescribe a peptide that reproduces autocatalytically in anenvironmentally dependent manner.The peptide K1K2 (Figure 1) was designed based on thesequence of the KK peptide of Zhou et al.
TL;DR: In this paper, the synthesis and coordination of bidentate ligands with both imidazoline-2-ylidene and oxazoline moieties is described. But the synthesis follows straightforward routes, using N-functionalized imidisolium salts and 2-amino alcohols.
TL;DR: The catalytic transformations of 1,2-dichlorobenzene, chlorobenzenes, 4-chlorobiphenyl, γ-hexachlorocyclohexane (Lindane), naphthalene and phenanthrene were studied over palladium on alumina in hydrogen-saturated water (Pd/Al2O3/H2) at room temperature and ambient pressure as discussed by the authors.
Abstract: The catalytic transformations of 1,2-dichlorobenzene, chlorobenzene, 4-chlorobiphenyl, γ-hexachlorocyclohexane (Lindane), naphthalene and phenanthrene were studied over palladium on alumina in hydrogen-saturated water (Pd/Al2O3/H2) at room temperature and ambient pressure. The chlorinated benzenes were rapidly hydrodechlorinated and Lindane was dehydrochlorinated to benzene. Partial or complete hydrogenation was observed for biphenyl and the polycyclic aromatic hydrocarbons. The phenanthrene ring was cleaved at the 9,10-position. In general dechlorination reactions were faster than hydrogenation reactions.
TL;DR: In this article, periodic density-functional calculations have been performed for the molecular and dissociative chemisorption of NO on Pd and Rh(100) and (111) surfaces, with generalized gradient approximation exchange-correlation functionals.
Abstract: The efforts to reduce NOx pollutants have stimulated a large interest in the understanding of the elementary processes for NO transformation on transition metal surfaces. Periodic density-functional calculations have been performed for the molecular and dissociative chemisorption of NO on Pd and Rh(100) and (111) surfaces, with generalized gradient approximation exchange-correlation functionals. The periodic systems are modeled by two-dimensional palladium or rhodium slabs with frozen geometry, on which a NO, N, O, or (N+O) adlayer is set. On Pd and Rh(100) at a coverage of 0.5 monolayer (ML), the bridge site is the most stable one with respective binding energies of −1.54 and −2.18 eV. On the (111) surfaces, at a coverage of 0.33 ML, the threefold hollow sites are favored with binding energies of −2.0 eV for Pd(111) and −2.18 eV for Rh(111). For the dissociated structures, the mixed coadsorption of N and O is favored in most cases compared to separated domains. The chemisorption of NO, N, or O is stronge...
TL;DR: In this article, the steady state concentration ratio, resting state species, and overall rate of catalysis, kobs, depend on the ratio of biphenylene to PEt3.
Abstract: The complexes Pt(PEt3)3 and Pd(PEt3)3 cleave the C−C bond of biphenylene to give (PEt3)2Pt(2,2‘-biphenyl), 1, and (PEt3)2Pd(2,2‘-biphenyl), respectively. Heating (PEt3)2Pt(2,2‘-biphenyl) in the presence of biphenylene leads to C−C cleavage of a second biphenylene to give (PEt3)2Pt(2,2‘-tetraphenyl), 2, via a Pt(IV) intermediate. 2 reductively eliminates tetraphenylene at 115 °C. At 120 °C the reaction is catalytic; Pt(PEt3)3 or 1 converts biphenylene to tetraphenylene. The intermediates in the catalytic cycle have been identified, and 1 and 2 have been characterized by X-ray analysis. Under catalytic conditions 1 and 2 approach steady-state concentrations. Kinetic analysis reveals that the steady-state concentration ratio, resting state species, and overall rate of catalysis, kobs, depend on the ratio of biphenylene to PEt3. This observation is consistent with loss of PEt3 from 1, resulting in the 14-electron species (PEt3)Pt(2,2‘-biphenyl), I. At 130 °C, I coordinates to PEt3 approximately 130 times fast...
TL;DR: In this paper, a new route to α-chiral C2-symmetrical diol-substituted sandwich complexes was opened by the CBS reduction of diketones.
Abstract: A new route to α-chiral C2-symmetrical diol-substituted sandwich complexes (2) is opened by the CBS reduction of diketones 1. A variety of N-, P-, and S-chelates and the aminophosphanes 3 were synthesized from the diols 2 in a flexible and efficient manner without tedious resolution procedures. A palladium(II) chloride complex of 3 catalyzed the coupling of racemic 1-phenylethylmagnesium chloride with β-bromostyrene to afford 1,3-diphenyl-1-butene in 93% ee.
TL;DR: The Heck reaction has been computationally studied for a carbene-stabilized palladium catalyst employing a density functional method with a gradient-corrected exchange-correlation functional as mentioned in this paper.
TL;DR: A rare, structurally characterized μ1,η1 -hydrazonato complex is a probable intermediate in the Pd-catalyzed N-arylation of hydrazones and proceeds efficiently and under mild conditions with chelating phosphane ligands.
Abstract: A rare, structurally characterized μ1 ,η1 -hydrazonato complex is a probable intermediate in the Pd-catalyzed N-arylation of hydrazones. Starting from aryl halides the reaction proceeds efficiently and under mild conditions with chelating phosphane ligands (L2 ); even Cs2 CO3 can be used as the base [Eq. (a)]. R=alkyl, aryl, MeCO, MeO; X=Br, I.
TL;DR: In this paper, the complete catalytic oxidation of 1,2-dichloroethane (DCE) and trichloroenethylene (TCE) over alumina supported noble metal catalysts (Pt and Pd) was evaluated at conditions of lean hydrocarbon concentration in air, between 250°C and 550°C in a conventional fixed bed reactor.
Abstract: The complete catalytic oxidation of 1,2-dichloroethane (DCE) and trichloroethylene (TCE) over alumina supported noble metal catalysts (Pt and Pd) was evaluated. Experiments were performed at conditions of lean hydrocarbon concentration (around 1000 ppm) in air, between 250°C and 550°C in a conventional fixed bed reactor. The catalysts were prepared in a range of metal contents from 0.1 to 1 wt%. Palladium catalysts resulted to be more active than platinum catalysts in the oxidation of both chlorinated volatile organic compounds. DCE was completely destructed at 375°C, whereas TCE required 550°C. HCl was the only chlorine-containing product in the oxidation of DCE in the range of 250–400°C. Tetrachloroethylene was observed as an intermediate in the oxidation of TCE, being formed to a significant extent between 400°C and 525°C. CO was also detected in the oxidation of both DCE and TCE over Pd catalysts, though at temperatures of complete destruction, CO 2 was the only carbon-containing product. The Pt catalysts were selective to CO 2 at the studied conditions.