SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Palladium

35

Gold recovery using environmentally benign chemistry is imperative from an environmental perspective. Here we report the spontaneous assembly of a one-dimensional supramolecular complex with an extended {[K(OH2)6][AuBr4](α-cyclodextrin)2}n chain superstructure formed during the rapid co-precipitation of α-cyclodextrin and KAuBr4 in water. This phase change is selective for this gold salt, even in the presence of other square-planar palladium and platinum complexes. From single-crystal X-ray analyses of six inclusion complexes between α-, β- and γ-cyclodextrins with KAuBr4 and KAuCl4, we hypothesize that a perfect match in molecular recognition between α-cyclodextrin and [AuBr4](-) leads to a near-axial orientation of the ion with respect to the α-cyclodextrin channel, which facilitates a highly specific second-sphere coordination involving [AuBr4](-) and [K(OH2)6](+) and drives the co-precipitation of the 1:2 adduct. This discovery heralds a green host-guest procedure for gold recovery from gold-bearing raw materials making use of α-cyclodextrin-an inexpensive and environmentally benign carbohydrate.

Concepts: Molecule, Chemistry, Atom, Gold, Materials science, Supramolecular chemistry, Platinum, Palladium

28

Gold shuttle: Bulky groups, which will not (or only very sluggishly) undergo Stille coupling with stannanes and inexpensive ligands, can be efficiently coupled using bimetallic catalysis. A gold cocatalyst serves as an efficient shuttle to convey the bulky group from tin to palladium by reducing the steric crowding in the transition-states.

Concepts: Enzyme, Hydrogen, Hydrogenation, Catalytic converter, Nitrogen, Suzuki reaction, Palladium, Stille reaction

28

Replacing noble metals in heterogeneous catalysts by low-cost substitutes has driven scientific and industrial research for more than 100 years. Cheap and ubiquitous iron is especially desirable, because it does not bear potential health risks like, for example, nickel. To purify the ethylene feed for the production of polyethylene, the semi-hydrogenation of acetylene is applied (80 × 10(6) tons per annum; refs 1-3). The presence of small and separated transition-metal atom ensembles (so-called site-isolation), and the suppression of hydride formation are beneficial for the catalytic performance. Iron catalysts necessitate at least 50 bar and 100 °C for the hydrogenation of unsaturated C-C bonds, showing only limited selectivity towards semi-hydrogenation. Recent innovation in catalytic semi-hydrogenation is based on computational screening of substitutional alloys to identify promising metal combinations using scaling functions and the experimental realization of the site-isolation concept employing structurally well-ordered and in situ stable intermetallic compounds of Ga with Pd (refs 15-19). The stability enables a knowledge-based development by assigning the observed catalytic properties to the crystal and electronic structures of the intermetallic compounds. Following this approach, we identified the low-cost and environmentally benign intermetallic compound Al(13)Fe(4) as an active and selective semi-hydrogenation catalyst. This knowledge-based development might prove applicable to a wide range of heterogeneously catalysed reactions.

Concepts: Hydrogen, Catalysis, Heterogeneous catalysis, Hydrogenation, Metallurgy, Alloy, Intermetallics, Palladium

27

In control: A highly selective carbocyclization/borylation of allenynes with bis(pinacolato)diboron (B2 pin2 ) under palladium catalysis and with p-benzoquinone (BQ) as the oxidant was developed. The use of either LiOAc⋅2 H2 O with 1,2-dichloroethane (DCE) as the solvent or BF3 ⋅Et2 O together with THF is crucial for the selective formation of borylated trienes and vinylallenes, respectively.

Concepts: Electrochemistry, Hydrogenation, Ether, Palladium

26

Biopolymers and ionic liquids are of prime importance in numerous applications. Recovery of industrially important noble metals such as palladium is of paramount significance considering their diverse applications. The main idea behind this work was to develop an effective strategy involving the impregnation of Aliquat-336 (ionic liquid) onto chitosan as a novel adsorbent for the adsorption of Pd (II). The analytical characterization was systematically done through FT-IR, XRD, SEM and EDX analysis. The interaction of the amino and hydroxyl functional groups in chitosan with the cationic nitrogen in the ionic liquid could be established through the above characterization. Several key parameters such as pH influence, amount of adsorbent, isotherms, kinetics and thermodynamic studies were also studied in detail for the adsorption of palladium. The effectiveness of adsorption was observed between pH 3.5-4.0 with 50mL of 120mgL(-1) Pd(II) solution giving a commendable monolayer adsorption capacity of 187.61mgg(-1).

Concepts: Functional group, Adsorption, Wetting, Materials science, Mercury, Ionic liquid, Aza-Baylis-Hillman reaction, Palladium

25

Late transition metal complexes that bear N-heterocyclic carbene (NHC) ligands have seen a speedy growth in their use as both, metal-based drug candidates and potentially active homogeneous catalysts in a plethora of C-C and C-N bond forming reactions. This review article focuses on the recent developments and advances in preparation and characterization of NHC-metal complexes (metal: silver, gold, copper, palladium, nickel and ruthenium) and their biomedical applications. Their design, syntheses and characterization have been reviewed and correlated to their antimicrobial and anticancer efficacies. All these initial discoveries help validate the great potential of NHC-metal derivatives as a class of effective antimicrobial and anticancer agents.

Concepts: Copper, Gold, Transition metals, Silver, Transition metal, Palladium, Nickel, Rhodium

25

Richard F. Heck, who shared the Nobel Prize in Chemistry 2010 with Akira Suzuki and Ei-ichi Negishi, passed away on October 10, 2015 at the age of 84. Heck developed the palladium-catalyzed carbon-carbon bond-forming reaction between aryl halides and olefins that is known as the Heck reaction, and also rationalized its mechanism. This reaction has become a standard procedure in modern organic synthesis.

Concepts: Chemical reaction, Organic synthesis, Alkene, Heck reaction, Palladium, Nobel Prize, Stille reaction, Richard F. Heck

25

An efficient overall two-step strategy for the synthesis of (E)-5-aminoallyl-pyrimidine-5'-triphoshate, starting from commercially available pyrimidine-5'-triphosphate is described. The method involves regioselective iodination of pyrimidine-5'-triphosphate, followed by the palladium-catalyzed Heck coupling with allylamine. The catalytic reaction is highly stereoselective and compatible with many functional groups present in the reactants.

Concepts: Chemical reaction, Alkene, Heck reaction, Suzuki reaction, Palladium, Stille reaction, Richard F. Heck

7

Many energy storage materials undergo large volume changes during charging and discharging. The resulting stresses often lead to defect formation in the bulk, but less so in nanosized systems. Here, we capture in real time the mechanism of one such transformation-the hydrogenation of single-crystalline palladium nanocubes from 15 to 80 nm-to better understand the reason for this durability. First, using environmental scanning transmission electron microscopy, we monitor the hydrogen absorption process in real time with 3 nm resolution. Then, using dark-field imaging, we structurally examine the reaction intermediates with 1 nm resolution. The reaction proceeds through nucleation and growth of the new phase in corners of the nanocubes. As the hydrogenated phase propagates across the particles, portions of the lattice misorient by 1.5%, diminishing crystal quality. Once transformed, all the particles explored return to a pristine state. The nanoparticles' ability to remove crystallographic imperfections renders them more durable than their bulk counterparts.

Concepts: Electron, Quantum mechanics, Hydrogen, Catalysis, Hydrogenation, Transmission electron microscopy, Palladium, Rhodium

6

After more than a decade, it is still unknown whether the plasmon-mediated growth of silver nanostructures can be extended to the synthesis of other noble metals, as the molecular mechanisms governing the growth process remain elusive. Herein, we demonstrate the plasmon-driven synthesis of gold nanoprisms and elucidate the details of the photochemical growth mechanism at the single-nanoparticle level. Our investigation reveals that the surfactant polyvinylpyrrolidone preferentially adsorbs along the nanoprism perimeter and serves as a photochemical relay to direct the anisotropic growth of gold nanoprisms. This discovery confers a unique function to polyvinylpyrrolidone that is fundamentally different from its widely accepted role as a crystal-face-blocking ligand. Additionally, we find that nanocrystal twinning exerts a profound influence on the kinetics of this photochemical process by controlling the transport of plasmon-generated hot electrons to polyvinylpyrrolidone. These insights establish a molecular-level description of the underlying mechanisms regulating the plasmon-driven synthesis of gold nanoprisms.

Concepts: Nanomaterials, Gold, Mercury, Silver, Palladium, Photochemistry, Photochemical reaction, Noble metals