Showing papers on "Palladium published in 2013"
TL;DR: Rate measurements are reported on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals, and it is found that carbon monoxide oxidation inceria-based catalysts is greatly enhanced at the cia- metal interface sites for a range of group VIII metal catalysts.
Abstract: Interactions between ceria (CeO2) and supported metals greatly enhance rates for a number of important reactions However, direct relationships between structure and function in these catalysts have been difficult to extract because the samples studied either were heterogeneous or were model systems dissimilar to working catalysts We report rate measurements on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals We found that carbon monoxide oxidation in ceria-based catalysts is greatly enhanced at the ceria-metal interface sites for a range of group VIII metal catalysts, clarifying the pivotal role played by the support
1,053 citations
996 citations
TL;DR: A broad range of aryl electrophiles, which are conventionally challenging, by applying palladium catalysts can now be coupled efficiently with boron reagents in the presence of nickel catalysts.
Abstract: In the transition-metal-catalyzed cross-coupling reactions, the use of the first row transition metals as catalysts is much more appealing than the precious metals owing to the apparent advantages such as cheapness and earth abundance. Within the last two decades, particularly the last five years, explosive interests have been focused on the nickel-catalyzed Suzuki–Miyaura reactions. This has greatly advanced the chemistry of transition-metal-catalyzed cross-coupling reactions. Most notably, a broad range of aryl electrophiles such as phenols, aryl ethers, esters, carbonates, carbamates, sulfamates, phosphates, phosphoramides, phosphonium salts, and fluorides, as well as various alkyl electrophiles, which are conventionally challenging, by applying palladium catalysts can now be coupled efficiently with boron reagents in the presence of nickel catalysts. In this review, we would like to summarize the progress in this reaction.
854 citations
TL;DR: It was found that replacing the chloride in the previous version of the precatalyst with a mesylate leads to a new class of precatalysts with improved solution stability and that are readily prepared from a wider range of phosphine ligands.
Abstract: A series of easily prepared, phosphine-ligated palladium precatalysts based on the 2-aminobiphenyl scaffold have been prepared. The role of the precatalyst-associated labile halide (or pseudohalide) in the formation and stability of the palladacycle has been examined. It was found that replacing the chloride in the previous version of the precatalyst with a mesylate leads to a new class of precatalysts with improved solution stability and that are readily prepared from a wider range of phosphine ligands. The differences between the previous version of precatalyst and that reported here are explored. In addition, the reactivity of the latter is examined in a range of C-C and C-N bond forming reactions.
521 citations
TL;DR: In this article, a multi-layer molybdenum disulfphide channel can be hole-doped by palladium contacts, yielding MoS2 p-type transistors.
Abstract: Semiconducting molybdenum disulfphide has emerged as an attractive material for novel nanoscale optoelectronic devices due to its reduced dimensionality and large direct bandgap. Since optoelectronic devices require electron-hole generation/recombination, it is important to be able to fabricate ambipolar transistors to investigate charge transport both in the conduction band and in the valence band. Although n-type transistor operation for single-layer and few-layer MoS2 with gold source and drain contacts was recently demonstrated, transport in the valence band has been elusive for solid-state devices. Here we show that a multi-layer MoS2 channel can be hole-doped by palladium contacts, yielding MoS2 p-type transistors. When two different materials are used for the source and drain contacts, for example hole-doping Pd and electron-doping Au, the Schottky junctions formed at the MoS2 contacts produce a clear photovoltaic effect.
486 citations
TL;DR: This Perspective offers an account of research employing three ligand scaffolds, mono-N-protected amino acids, 2,6-disubstituted pyridines, and 2,2'-bipyridine, to address challenges posed by several synthetically versatile substrate classes.
Abstract: Homogeneous transition-metal-catalyzed reactions are indispensable to all facets of modern chemical synthesis. It is thus difficult to imagine that for much of the early 20th century, the reactivity and selectivity of all known homogeneous metal catalysts paled in comparison to their heterogeneous and biological counterparts. In the intervening decades, advances in ligand design bridged this divide, such that today some of the most demanding bond-forming events are mediated by ligand-supported homogeneous metal species. While ligand design has propelled many areas of homogeneous catalysis, in the field of Pd(II)-catalyzed C–H functionalization, suitable ligand scaffolds are lacking, which has hampered the development of broadly practical transformations based on C–H functionalization logic. In this Perspective, we offer an account of our research employing three ligand scaffolds, mono-N-protected amino acids, 2,6-disubstituted pyridines, and 2,2′-bipyridines, to address challenges posed by several synthet...
414 citations
TL;DR: A prior mechanistic hypothesis that partially saturated amine(imine)diphosphine ligands (P-NH-N-P) activate iron to catalyze the asymmetric reduction of the polar bonds of ketones and imines to valuable enantiopure alcohols and amines is validated.
Abstract: A rational approach is needed to design hydrogenation catalysts that make use of Earth-abundant elements to replace the rare elements such as ruthenium, rhodium, and palladium that are traditionally used. Here, we validate a prior mechanistic hypothesis that partially saturated amine(imine)diphosphine ligands (P-NH-N-P) activate iron to catalyze the asymmetric reduction of the polar bonds of ketones and imines to valuable enantiopure alcohols and amines, with isopropanol as the hydrogen donor, at turnover frequencies as high as 200 per second at 28°C. We present a direct synthetic approach to enantiopure ligands of this type that takes advantage of the iron(lI) ion as a template. The catalytic mechanism is elucidated by the spectroscopic detection of iron hydride and amide intermediates.
413 citations
TL;DR: New reactions enabled by a single class of ligands, phosphine-sulfonate (ortho-phosphinobenzenesulfonates), using their palladium complexes, are summarized, which have developed four unusual reactions, and three of these have produced novel types of polymers.
Abstract: Ligands, Lewis bases that coordinate to the metal center in a complex, can completely change the catalytic behavior of the metal center. In this Account, we summarize new reactions enabled by a single class of ligands, phosphine–sulfonates (ortho-phosphinobenzenesulfonates). Using their palladium complexes, we have developed four unusual reactions, and three of these have produced novel types of polymers.In one case, we have produced linear high-molecular weight polyethylene, a type of polymer that group 10 metal catalysts do not typically produce. Secondly, complexes using these ligands catalyzed the formation of linear poly(ethylene-co-polar vinyl monomers). Before the use of phosphine–sulfonate catalysts, researchers could only produce ethylene/polar monomer copolymers that have different branched structures rather than linear ones, depending on whether the polymers were produced by a radical polymerization or a group 10 metal catalyzed coordination polymerization. Thirdly, these phosphine–sulfonate ca...
406 citations
TL;DR: It is believed that the conduction electrons of the NPs gain the light absorbed energy producing energetic electrons at the surface Pd sites, which enhances the sites' intrinsic catalytic ability.
Abstract: The intrinsic catalytic activity of palladium (Pd) is significantly enhanced in gold (Au)-Pd alloy nanoparticles (NPs) under visible light irradiation at ambient temperatures. The alloy NPs strongly absorb light and efficiently enhance the conversion of several reactions, including Suzuki-Miyaura cross coupling, oxidative addition of benzylamine, selective oxidation of aromatic alcohols to corresponding aldehydes and ketones, and phenol oxidation. The Au/Pd molar ratio of the alloy NPs has an important impact on performance of the catalysts since it determines both the electronic heterogeneity and the distribution of Pd sites at the NP surface, with these two factors playing key roles in the catalytic activity. Irradiating with light produces an even more profound enhancement in the catalytic performance of the NPs. For example, the best conversion rate achieved thermally at 30 °C for Suzuki-Miyaura cross coupling was 37% at a Au/Pd ratio of 1:1.86, while under light illumination the yield increased to 96...
393 citations
TL;DR: In this paper, four groups of catalysts have been tested for hydrodeoxygenation (HDO) of phenol as a model compound of bio-oil, including oxide catalysts, methanol synthesis catalysts and reduced noble metal catalysts.
Abstract: Four groups of catalysts have been tested for hydrodeoxygenation (HDO) of phenol as a model compound of bio-oil, including oxide catalysts, methanol synthesis catalysts, reduced noble metal catalysts, and reduced non-noble metal catalysts. In total, 23 different catalysts were tested at 100 bar H2 and 275 °C in a batch reactor. The experiments showed that none of the tested oxides or methanol synthesis catalysts had any significant activity for phenol HDO under the given conditions, which were linked to their inability to hydrogenate the aromatic ring of phenol. HDO of phenol over reduced metal catalysts could effectively be described by a kinetic model involving a two-step reaction in which phenol initially was hydrogenated to cyclohexanol and then subsequently deoxygenated to cyclohexane. Among reduced noble metal catalysts, ruthenium, palladium, and platinum were all found to be active, with activity decreasing in that order. Nickel was the only active non-noble metal catalyst. For nickel, the effect o...
353 citations
TL;DR: The authors show that palladium nanoparticles loaded on porous nitrogen-doped carbon are highly active catalysts under laboratory and industrially relevant conditions and provide great potential for the application of ambient air and recyclable palladium catalysts in fine-chemical production with high activity.
Abstract: The development of efficient systems for selective aerobic oxidation of hydrocarbons and alcohols to produce more functional compounds (aldehydes, ketones, acids or esters) with atmospheric air or molecular oxygen is a grand challenge for the chemical industry. Here we report the synthesis of palladium nanoparticles supported on novel nanoporous nitrogen-doped carbon, and their impressive performance in the controlled oxidation of hydrocarbons and alcohols with air. In terms of catalytic activity, these catalysts afford much higher turnover frequencies (up to 863 turnovers per hour for hydrocarbon oxidation and up to ~210,000 turnovers per hour for alcohol oxidation) than most reported palladium catalysts under the same reaction conditions. This work provides great potential for the application of ambient air and recyclable palladium catalysts in fine-chemical production with high activity.
TL;DR: These reactions provide a convenient and straightforward method for the preparation of high-value N-containing products from readily available amine and alkyl iodide precursors.
Abstract: We report an efficient method for the alkylation of γ-C(sp3)–H bonds of picolinamide-protected aliphatic amine substrates with primary alkyl iodides via palladium catalysis. Ag2CO3 and dibenzyl phosphate, (BnO)2PO2H, are critical promoters of this reaction. These reactions provide a convenient and straightforward method for the preparation of high-value N-containing products from readily available amine and alkyl iodide precursors.
TL;DR: Palladium modified mesoporous graphitic carbon nitride polymer (Pd/mpg-C 3 N 4 ) was fabricated and used for the degradation of bisphenol A (BPA) in water as discussed by the authors.
Abstract: Palladium modified mesoporous graphitic carbon nitride polymer (Pd/mpg-C 3 N 4 ) was fabricated and used for the degradation of bisphenol A (BPA) in water. Doping Pd on the surface of mpg-C 3 N 4 enhanced the light absorbance in the range of UV–vis region. Most of the embedded Pd was present as Pd 0 and could act as electron traps and facilitate the separation of photogenerated holes and electron pairs. As a result, the photocatalytic performance was improved significantly. The reaction rate constant ( k obs ) increased with the Pd loading on the surface of mpg-C 3 N 4 and the maximum was achieved with 1.50% Pd. Almost 100% of BPA (20 mg L −1 ) was photodegraded by the solids of 0.5 g L −1 Pd/mpg-C 3 N 4 after irradiation with simulated solar light for 360 min. The Pd/mpg-C 3 N 4 exhibited very stable and high efficient photocatalytic activity to BPA in a wide range of pH 3.08–11.00. It also displayed high photocatalytic activity without photocorrosion after reuse for many times. Hydroxyl radicals, photogenerated holes, and superoxide radical species were responsible for the photodegradation while the superoxide radical species were more predominant in the Pd/mpg-C 3 N 4 reaction system.
TL;DR: This tutorial review intends to offer an overview of recent progress in homogeneous palladium catalyzed asymmetric hydrogenation and should serve as an inspiration for further advances in this area.
Abstract: The transition metal catalyzed asymmetric hydrogenation of unsaturated compounds arguably presents one of the most attractive methods for the synthesis of chiral compounds. Over the last few decades, Pd has gradually grown up as a new and popular metal catalyst in homogeneous asymmetric hydrogenation the same as traditional Ru, Rh and Ir catalysts. Much progress has been successfully achieved in the asymmetric reduction of imines, enamines, olefins, ketones and heteroarenes. It was also found that palladium catalyzed asymmetric hydrogenation could be used as a key step in tandem reactions to quickly synthesize chiral compounds. This tutorial review intends to offer an overview of recent progress in homogeneous palladium catalyzed asymmetric hydrogenation and should serve as an inspiration for further advances in this area.
TL;DR: The methyl group in a simple derivative of readily available alanine under palladium catalysis was followed by intramolecular amidation to give chiral α-amino-β-lactams with a wide range of aryl substituents.
Abstract: Give Me an Ar, give Me an N! Arylation of the methyl group in a simple derivative of readily available alanine under palladium catalysis was followed by intramolecular amidation at the same position to give chiral α-amino-β-lactams with a wide range of aryl substituents (see scheme; Phth=phthaloyl). The α-amino-β-lactams were obtained in moderate to high yields with good functional-group tolerance and high diastereoselectivity.
TL;DR: A review of cyclometalated C N complexes and C N C, C N N and C n S pincer complexes of platinum, palladium, gold, ruthenium, rhodium, and iridium can be found in this article.
TL;DR: In this article, a fabrication of PdAg nanorings supported by graphene nanosheets is demonstrated; the fabrication is based on the galvanic displacement reaction between pre-synthesized Ag nanoparticles and palladium ions.
Abstract: Due to the high costs, slow reaction kinetics, and methanol poisoning of platinum-based cathode catalysts, designing and exploring non-Pt or low-Pt cathode electrocatalysts with a low cost, high catalytic performance, and high methanol-tolerance are crucial for the commercialization of fuel cells. Here, a facile method to fabricate a system of PdAg nanorings supported by graphene nanosheets is demonstrated; the fabrication is based on the galvanic displacement reaction between pre-synthesized Ag nanoparticles and palladium ions. X-ray diffraction and high-resolution transmission electron microscopy show that the synthesized PdAg nanocrystals exhibit a ring-shaped hollow structure with an average size of 27.49 nm and a wall thickness of 5.5 nm. Compared to the commercial PdC catalyst, the PdAg nanorings exhibit superior properties as a cathode electrocatalyst for oxygen reduction. Based on structural and electrochemical studies, these advantageous properties include efficient usage of noble metals and a high surface area because of the effective utilization of both the exterior and interior surfaces, high electrocatalytic performance for oxygen reduction from the synergistic effect of the alloyed PdAg crystalline phase, and most importantly, excellent tolerance of methanol crossover at high concentrations. It is anticipated that this synthesis of graphene-based PdAg nanorings will open up a new avenue for designing advanced electrocatalysts that are low in cost and that exhibit high catalytic performance for alkaline fuel cells.
TL;DR: The synthesised nanomaterials were remarkably stable for a long period and synthesis of stable metal NPs will need to be explored using biobased materials as reducing agents.
TL;DR: In this article, the potential of metallic nanoparticles for use in ultraviolet plasmonics (3-6 eV) applications was assessed by an exhaustive numerical analysis, and the potential for applications such as surface-enhanced Raman spectroscopy, accelerated photodegradation and photocatalysis was addressed.
Abstract: The practical efficacy of technologically promising metals for use in ultraviolet plasmonics (3–6 eV) is assessed by an exhaustive numerical analysis. This begins with estimates of the near- and far-field electromagnetic enhancement factors of isolated hemispherical and spherical metallic nanoparticles deposited on typical dielectric substrates like sapphire, from which the potential of each metal for plasmonic applications may be ascertained. The ultraviolet plasmonic behavior of aluminum, chromium, copper, gallium, indium, magnesium, palladium, platinum, rhodium, ruthenium, titanium, and tungsten was compared with the well-known behavior of gold and silver in the visible. After exploring this behavior for each metal as a function of nanoparticle shape and size, the deleterious effect caused by the metal’s native oxide is considered, and the potential for applications such as surface-enhanced Raman spectroscopy, accelerated photodegradation and photocatalysis is addressed.
TL;DR: A Pd(II)-catalyzed C-H phosphorylation reaction has been developed using heterocycle-directed ortho-palladation using H-phosphonates and diaryl phosphine oxides as suitable coupling partners for this reaction.
Abstract: A Pd(II)-catalyzed C–H phosphorylation reaction has been developed using heterocycle-directed ortho-palladation. Both H-phosphonates and diaryl phosphine oxides are suitable coupling partners for this reaction.
TL;DR: A rapid, efficient, and green approach to the fabrication of highly active catalysts by coating Pd nanoparticles (NPs) on reduced graphene oxide (rGO)-carbon nanotube (CNT) nanocomposite is reported.
Abstract: Facile and Green Synthesis of Palladium Nanoparticles-Graphene-Carbon Nanotube Material with High Catalytic Activity
TL;DR: C–H arylation and methylation of 3-phenylpropanoic acid and phenolic derivatives were developed using an easily removable nitrile template and mono-protected amino acid ligand for the cross-coupling of C–H bonds with organoborons.
Abstract: meta-C–H arylation and methylation of 3-phenylpropanoic acid and phenolic derivatives were developed using an easily removable nitrile template. The combination of a weakly coordinating U-shaped template and mono-protected amino acid ligand was crucial for the cross-coupling of C–H bonds with organoborons.
TL;DR: Supported gold–palladium nanoparticles are active for the oxidation of methane, giving a high selectivity for the formation of methyl hydroperoxide and methanol, using hydrogen peroxide as the oxidant.
Abstract: Supported gold–palladium nanoparticles are active for the oxidation of methane, giving a high selectivity for the formation of methyl hydroperoxide and methanol, using hydrogen peroxide as the oxidant (see picture). The optimal methanol selectivity is achieved by performing the reaction in the presence of hydrogen peroxide that has been generated in situ from hydrogen and oxygen.
TL;DR: Pd-catalyzed direct carboxylation ofAlkenyl C-H bonds with carbon dioxide was realized for the first time and isolation of the key alkenylpalladium intermediate via C- H bond cleavage was achieved.
Abstract: Pd-catalyzed direct carboxylation of alkenyl C–H bonds with carbon dioxide was realized for the first time. Treatment of 2-hydroxystyrenes and a catalytic amount of Pd(OAc)2 with Cs2CO3 under atmospheric pressure of CO2 afforded corresponding coumarins in good yield. Furthermore, isolation of the key alkenylpalladium intermediate via C–H bond cleavage was achieved. The reaction was proposed to undergo reversible nucleophilic addition of the alkenylpalladium intermediate to CO2.
TL;DR: This review provides a brief introduction to the new methods used to determine trace amounts of Pd(2+), which mainly focuses on the different reporting systems and unique mechanisms of the colourimetric and fluorescent probes used to detect Pd (2+) complex formation or Pd-catalysed reactions.
Abstract: In recent years, the development of optical probes to analyse trace palladium ions (Pd2+) has attracted great attention because of the residual palladium released by catalytic converters or from various Pd-catalysed reactions. These residual palladium ions may cause potential health hazards. This review provides a brief introduction to the new methods used to determine trace amounts of Pd2+, which then mainly focuses on the different reporting systems and unique mechanisms of the colourimetric and fluorescent probes used to detect Pd2+, including Pd2+ complex formation or Pd-catalysed reactions.
TL;DR: The scope of palladium-catalyzed, auxiliary-assisted direct arylation and alkylation of sp(2) and sp(3) C-H bonds of amine and carboxylic acid derivatives has been investigated and some optimization of base, additives, and solvent is required for achieving best results.
Abstract: The scope of palladium-catalyzed, auxiliary-assisted direct arylation and alkylation of sp2 and sp3 C–H bonds of amine and carboxylic acid derivatives has been investigated. The method employs a palladium acetate catalyst, substrate, aryl, alkyl, benzyl, or allyl halide, and inorganic base in tert-amyl alcohol or water solvent at 100–140 °C. Aryl and alkyl iodides as well as benzyl and allyl bromides are competent reagents in this transformation. The picolinic acid auxiliary is used for amine γ-functionalization, and the 8-aminoquinoline auxiliary is used for carboxylic acid β-functionalization. Some optimization of base, additives, and solvent is required for achieving best results.
TL;DR: In this article, an ultrasonic-assisted method was used to prepare palladium catalysts (Pd@C3N4) for hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline under mild temperature (30-50°C) and H2 pressure (1bar).
TL;DR: This work shows that the modification of a gold/carbon catalyst with platinum or palladium produces stable and recyclable catalysts for the selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid (FDCA), a significant advance over current conversion technology.
Abstract: Mixed noblility: We show that the modification of a gold/carbon catalyst with platinum or palladium produces stable and recyclable catalysts for the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA): the support and nanoparticle chemistry directly mediate the selective oxidation of terminal hydroxyl groups in bio-derived HMF. This finding is a significant advance over current conversion technology because of the technological importance of FDCA.