Showing papers on "Palladium published in 2011"
1,637 citations
TL;DR: The facile synthesis of freestanding hexagonal palladium nanosheets that are less than 10 atomic layers thick are reported, using carbon monoxide as a surface confining agent and exhibit a well-defined but tunable surface plasmon resonance peak in the near-infrared region.
Abstract: Ultrathin sheets of palladium exhibit a tunable surface plasmon resonance in the near infrared and useful catalytic properties.
1,337 citations
TL;DR: C-C Couplings in Continuous Systems 2308 12.1.
Abstract: 5.4. Miscellaneous Examples 2295 5.4.1. Couplings with Other Catalysts 2295 5.4.2. The Use of Other Boron Reagents 2295 5.4.3. Related Coupling Reactions 2296 5.5. Summary 2297 6. Sonogashira Coupling 2297 6.1. Couplings with Pd Particles 2297 6.2. Studies with Immobilized Palladium Complexes 2299 6.3. Miscellaneous Examples 2301 6.4. Carbonylative Sonogashira Couplings 2302 6.5. Summary 2302 7. Stille Couplings 2302 7.1. Stille Coupling 2302 7.2. Carbonylative Stille Coupling 2304 7.3. Summary 2304 8. Miscellaneous Cross-Coupling Reactions 2304 9. Allylations 2305 9.1. Tsuji-Trost Allylation 2305 9.2. Allylation of Boron Reagents 2306 10. Homocouplings 2307 10.1. Summary 2308 11. C-C Couplings in Continuous Systems 2308 12. Conclusions and Outlook 2311 Author Information 2314 Biography 2314 References 2314
934 citations
711 citations
569 citations
TL;DR: In this article, a review describes palladium and palladium alloy membranes for hydrogen separation prepared by different fabrication methods and using different membrane supports, and several correlations of structure and function for those membranes are provided based on mechanistic considerations of permeance along with structural properties and membrane morphologies.
539 citations
TL;DR: The activity trend found on the polycrystalline surfaces was in good agreement with the trend in the discharge voltage of Li-O(2) cells catalyzed by nanoparticle catalysts, providing insights into Li(+)-ORR mechanisms in nonaqueous media and design of efficient air electrodes for Li-air battery applications.
Abstract: We report the intrinsic oxygen reduction reaction (ORR) activity of polycrystalline palladium, platinum, ruthenium, gold, and glassy carbon surfaces in 0.1 M LiClO4 1,2-dimethoxyethane via rotating disk electrode measurements. The nonaqueous Li+-ORR activity of these surfaces primarily correlates to oxygen adsorption energy, forming a “volcano-type” trend. The activity trend found on the polycrystalline surfaces was in good agreement with the trend in the discharge voltage of Li-O2 cells catalyzed by nanoparticle catalysts. Our findings provide insights into Li+-ORR mechanisms in nonaqueous media and design of efficient air electrodes for Li-air battery applications.
513 citations
TL;DR: Palladium has the potential to play a major role in virtually every aspect of the envisioned hydrogen economy, including hydrogen purification, storage, detection, and fuel cells as discussed by the authors.
398 citations
TL;DR: This research aims to demonstrate the efforts towards in-situ applicability of EMMARM, which aims to provide real-time information about the physical and emotional impacts of EMT on young people in China.
Abstract: NSF[DMR-0804088, ECS-0335765]; Washington University in St. Louis; China Scholarship Council (CSC)
375 citations
TL;DR: In this paper, the authors developed an efficient method to generate highly active Pd nanoparticles supported on graphene (Pd/G) by microwave-assisted chemical reduction of corresponding aqueous mixture of a palladium salt and dispersed graphite oxide (GO) sheets.
365 citations
TL;DR: A palladium(II) catalyst system, incorporating an unconventional ortho-dimethylaminopyridine ligand, is reported, for the conversion of substituted cyclohexanones to the corresponding phenols, demonstrating a versatile and efficient strategy for the synthesis of substituted aromatic molecules with fundamentally different selectivity constraints from the numerous known synthetic methods.
Abstract: Aromatic molecules are key constituents of many pharmaceuticals, electronic materials, and commodity plastics. The utility of these molecules directly reflects the identity and pattern of substituents on the aromatic ring. Here, we report a palladium(II) catalyst system, incorporating an unconventional ortho-dimethylaminopyridine ligand, for the conversion of substituted cyclohexanones to the corresponding phenols. The reaction proceeds via successive dehydrogenation of two saturated carbon-carbon bonds of the six-membered ring and uses molecular oxygen as the hydrogen acceptor. This reactivity demonstrates a versatile and efficient strategy for the synthesis of substituted aromatic molecules with fundamentally different selectivity constraints from the numerous known synthetic methods that rely on substitution of a preexisting aromatic ring.
TL;DR: In this article, the recent progress of electrocatalysis of palladium-based materials including both extended surfaces and nanostructured ones for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) is summarized.
TL;DR: A new technique for the ex situ generation of carbon monoxide (CO) and its efficient incorporation in palladium catalyzed carbonylation reactions was achieved using a simple sealed two-chamber system, eliminating the need for specialized equipment such as CO-detectors and equipment for running high pressure reactions.
Abstract: A new technique for the ex situ generation of carbon monoxide (CO) and its efficient incorporation in palladium catalyzed carbonylation reactions was achieved using a simple sealed two-chamber system. The ex situ generation of CO was derived by a palladium catalyzed decarbonylation of tertiary acid chlorides using a catalyst originating from Pd(dba)2 and P(tBu)3. Preliminary studies using pivaloyl chloride as the CO-precursor provided an alternative approach for the aminocarbonylation of 2-pyridyl tosylate derivatives using only 1.5 equiv of CO. Further design of the acid chloride CO-precursor led to the development of a new solid, stable, and easy to handle source of CO for chemical transformations. The synthesis of this CO-precursor also provided an entry point for the late installment of an isotopically carbon-labeled acid chloride for the subsequent release of gaseous [13C]CO. In combination with studies aimed toward application of CO as the limiting reagent, this method provided highly efficient pall...
TL;DR: It is concluded that the reaction of a palladium hydroxo complex with boronic acid, not the Reaction of a Palladium halide complex with trihydroxyborate, accounts for transmetalation in catalytic Suzuki-Miyaura reactions conducted with weak base and aqueous solvent mixtures.
Abstract: We report a systematic study of the stoichiometric reactions of isolated arylpalladium hydroxo and halide complexes with arylboronic acids and aryltrihydroxyborates to evaluate the relative rates of the two reaction pathways commonly proposed to account for transmetalation in the Suzuki−Miyaura reaction. On the basis of the relative populations of the palladium and organoboron species generated under conditions common for the catalytic process and the observed rate constants for the stoichiometric reactions between the two classes of reaction components, we conclude that the reaction of a palladium hydroxo complex with boronic acid, not the reaction of a palladium halide complex with trihydroxyborate, accounts for transmetalation in catalytic Suzuki−Miyaura reactions conducted with weak base and aqueous solvent mixtures.
TL;DR: This tutorial review summarizes the advances on palladium-catalysed C-O bond formation, means hydroxylation and alkoxylation reactions.
Abstract: The formation of oxygen–carbon bonds is one of the fundamental transformations in organic synthesis. In this regard the application of palladium-based catalysts has been extensively studied during recent years. Nowadays it is an established methodology and the success has been proven in manifold synthetic procedures. This tutorial review summarizes the advances on palladium-catalysed C–O bond formation, means hydroxylation and alkoxylation reactions.
TL;DR: The first catalytic alkynylation of unactivated C(sp(3))-H bonds has been accomplished and can be applied to the rapid elaboration of complex aliphatic acids, for example, via azide/alkyne cycloaddition.
Abstract: The first catalytic alkynylation of unactivated C(sp3)–H bonds has been accomplished. The method allows for the straightforward introduction of an ethynyl group into aliphatic acid derivatives under palladium catalysis. This new reaction can be applied to the rapid elaboration of complex aliphatic acids, for example, via azide/alkyne cycloaddition.
TL;DR: A practical synthetic strategy based on the picolinamide-directed palladium-catalyzed arylation and alkenylation of the remote C(sp) H bonds of a variety of aliphatic substrates under mild conditions and the application of this transformation to the formal synthesis of (+)-obafluorin is reported.
Abstract: Powerful synthetic methods based on the regioselective functionalization of C(sp) H bonds of arenes and heteroarenes are becoming readily available. In keeping with this trend, the selective functionalization of C(sp) H bonds to construct stereogenic centers and create complex structures would be an important and useful advance. As well as providing straightforward and operationally economical solutions for target-oriented synthesis, C(sp) H functionalization could also significantly expand current strategies for diversity-oriented synthesis in medicinal-chemistry research. Readily accessible aliphatic substrates could be tailored by the selective replacement of C(sp) H bonds with other structural motifs. Such a method would offer advantages over conventional de novo synthesis. Catalytic processes for the functionalization of nonactivated C(sp) H bonds are less developed than reactions which involve aryl or vinyl C H bonds. In comparison with radical-, carbene-, and nitrene-mediated processes, 6] the palladium-catalyzed functionalization of C(sp) H bonds through an innersphere mechanism offers the advantage of more versatile bond transformations via palladacycle intermediates. Although a number of ligand directing strategies have been successfully developed for such transformations, truly practical methods are still lacking. Interestingly, the research groups of Daugulis and Yu have demonstrated that amide groups possess a superior ability to direct palladium-catalyzed regioselective functionalizations of C(sp) H bonds. If generally applicable, we envisioned that this amide directing strategy might find great utility in the synthesis of many nitrogen-containing pharmaceutical agents and natural products. Herein, we report a practical synthetic strategy based on the picolinamide-directed palladium-catalyzed arylation and alkenylation of the remote C(sp) H bonds of a variety of aliphatic substrates under mild conditions and the application of this transformation to the formal synthesis of (+)-obafluorin. We envisioned a general three-step sequence to introduce different R groups at remote C H bonds through the direction of an amide-linked auxiliary (Scheme 1A). For this strategy to be synthetically useful, the auxiliary should be easy to introduce and should promote the highly regioand even stereoselective functionalization of a specific C(sp) H bond. Furthermore, the C H functionalization must be sufficiently mild to be compatible with sensitive functional groups and stereogenic centers in complex substrates. Finally, the removal of the auxiliary to reveal the amine should be facile. The discovery of a picolinamide-directed C H arylation by Daugulis and co-workers provided a key blueprint for our initial study. The original study demonstrated that a picolinamide (PA) moiety facilitates the palladium-catalyzed arylation of the g C(sp) H bonds of aliphatic substrates with aryl iodides as the arene source. However, rather forcing
TL;DR: The first amide-directed, palladium-catalyzed, intermolecular, highly selective C-H aminations with the non-nitrene-based nitrogen source N-fluorobenzenesulfonimide have been developed.
Abstract: The first amide-directed, palladium-catalyzed, intermolecular, highly selective C-H aminations with the non-nitrene-based nitrogen source N-fluorobenzenesulfonimide have been developed. This methodology might provide a new pathway for directed metal-catalyzed aromatic C-H amination.
TL;DR: The Pd-catalyzed reaction of Weinreb amides with aryl iodides gives biologically important phenanthridines directly as discussed by the authors. But the Weinreb reaction does not work well with other amides.
Abstract: The Pd-catalyzed reaction of Weinreb amides with aryl iodides gives biologically important phenanthridines directly.
TL;DR: Mechanistic studies demonstrate that this reaction involves a fast arylation of the olefin and a rate-determining C-H activation of the acetonitrile.
Abstract: Not one but two: The title reaction proceeds through the dual C-H bond cleavage of both aniline and acetonitrile. The reaction affords a variety of cyano-bearing indolinones in excellent yield. Mechanistic studies demonstrate that this reaction involves a fast arylation of the olefin and a rate-determining C-H activation of the acetonitrile.
TL;DR: In this article, the authors synthesized sub-10 nm Pd cubic and octahedral nanocrystals and then evaluated their activities towards oxygen reduction reaction (ORR) and showed that their ORR activity was one order of magnitude higher than that of Pd octahedra, and comparable to that of the state-of-theart Pt catalysts.
TL;DR: The experiment results showed that the sensor exhibits good reproducibility and long-term stability, as well as high selectivity with no interference from other potential competing species.
TL;DR: Among the 8 nm CoPd catalysts tested for the hydrolysis of AB, the Co(35)Pd(65) NP catalyst exhibited the highest catalytic activity and durability, and is an exciting alternative in pursuit of practical implementation of AB as a hydrogen storage material for fuel cell applications.
Abstract: Monodisperse 8 nm CoPd nanoparticles (NPs) with controlled compositions were synthesized by the reduction of cobalt acetylacetonate and palladium bromide in the presence of oleylamine and trioctylphosphine. These NPs were active catalysts for hydrogen generation from the hydrolysis of ammonia borane (AB), and their activities were composition dependent. Among the 8 nm CoPd catalysts tested for the hydrolysis of AB, the Co35Pd65 NPs exhibited the highest catalytic activity and durability. Their hydrolysis completion time and activation energy were 5.5 min and 27.5 kJ mol–1, respectively, which were comparable to the best Pt-based catalyst reported. The catalytic performance of the CoPd/C could be further enhanced by a preannealing treatment at 300 °C under air for 15 h with the hydrolysis completion time reduced to 3.5 min. This high catalytic performance of Co35Pd65 NP catalyst makes it an exciting alternative in pursuit of practical implementation of AB as a hydrogen storage material for fuel cell applic...
TL;DR: The release of CO from crystalline MePh( 2)SiCO(2)H proved to be highly efficient, and it was successfully applied in a selection of palladium-catalyzed carbonylative couplings using near-stoichiometric quantities of carbon monoxide precursor.
Abstract: Silacarboxylic acids have been demonstrated to be easy to handle, air-stable carbon monoxide precursors. Different silacarboxylic acids were synthesized from the corresponding chlorosilanes and carbon dioxide, and their decarbonylation, upon treatment with an array of activators, was evaluated. The release of CO from crystalline MePh2SiCO2H proved to be highly efficient, and it was successfully applied in a selection of palladium-catalyzed carbonylative couplings using near-stoichiometric quantities of carbon monoxide precursor. Finally, the synthesis of MePh2Si13CO2H and its application in carbonyl labeling of two bioactive compounds was demonstrated.
TL;DR: Bulky, thermally stable, chiral palladium complexes generated from N-heterocyclic carbenes (NHCs) were successfully applied to the synthesis of highly enantioenriched trans-fused indolines.
Abstract: Selectivity at high temperatures: Bulky, thermally stable, chiral palladium complexes generated from N-heterocyclic carbenes (NHCs; see picture) were successfully applied to the synthesis of highly enantioenriched trans-fused indolines. Remarkably, this reaction occurs at elevated temperatures with excellent asymmetric recognition of an enantiotopic C-H bond in an unactivated methylene unit.
01 Aug 2011
TL;DR: The ORR activity of Pd nanocubes was one order of magnitude higher than that of PD octahedra, and comparable to that of the state-of-the-art Pt catalysts.
Abstract: We have synthesized sub-10 nm Pd cubic and octahedral nanocrystals and then evaluated their activities towards oxygen reduction reaction (ORR). The ORR activity of Pd nanocubes was one order of magnitude higher than that of Pd octahedra, and comparable to that of the state-of-the-art Pt catalysts.
TL;DR: In this article, the oxygen reduction reaction (ORR) was investigated on graphene-supported electrocatalysts in alkaline media, and the kinetic parameters were determined by the rotating disk electrode (RDE) technique.
TL;DR: The superior performance of the ultrasmall Pd nanowire network based sensors demonstrates the novelty of the fabrication approach, which can be directly applied to palladium alloy and other hydrogen sensing materials.
Abstract: Hydrogen sensors based on single Pd nanowires show promising results in speed, sensitivity, and ultralow power consumption. The utilization of single Pd nanowires, however, face challenges in nanofabrication, manipulation, and achieving ultrasmall transverse dimensions. We report on hydrogen sensors that take advantage of single palladium nanowires in high speed and sensitivity and that can be fabricated conveniently. The sensors are based on networks of ultrasmall (<10 nm) palladium nanowires deposited onto commercially available filtration membranes. We investigated the sensitivities and response times of these sensors as a function of the thickness of the nanowires and also compared them with a continuous reference film. The superior performance of the ultrasmall Pd nanowire network based sensors demonstrates the novelty of our fabrication approach, which can be directly applied to palladium alloy and other hydrogen sensing materials.
TL;DR: In this paper, a new hybrid material, PdNPs@CNCs, consisting of monodisperse Pd nanoparticles (PdNs) evenly deposited onto colloidal cellulose nanocrystallites, was presented.
TL;DR: A palladium-catalyzed cyanation of the 3-position of indole sp(2) C-H bonds by the combination of NH(4)HCO(3) and DMSO as the "CN" source was achieved to provide aromatic nitriles in moderate to good yields with excellent regioselectivity.