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Gold catalysis

Anthony M Pembere, Mengzhou Yang, Zhixun Luo
The conversion of glycerol to epichlorohydrin (GTE) is of great interest because the product is widely used in plastics, rubbers and adhesives, and also contributes to the disposal of the reactant glycerol, a major by-product in biodiesel production. Here we find effective catalysis by small gold clusters for the GTE reaction in water with an enhanced selectivity towards the desired product. Along with natural bond orbital (NBO) analysis rationalizing the donor-acceptor charge-transfer interactions, we illustrate the mechanism for bond activation in the reactants and intermediates over gold cluster catalysts, and present thermodynamically and kinetically favoured reaction pathways for dehydrochlorination in GTE processes...
September 20, 2017: Physical Chemistry Chemical Physics: PCCP
Md Abu Bakar, Mizuho Sugiuchi, Mitsuhiro Iwasaki, Yukatsu Shichibu, Katsuaki Konishi
It is well known that various transition elements can form M···H hydrogen bonds. However, for gold, there has been limited decisive experimental evidence of such attractive interactions. Herein we demonstrate an example of spectroscopically identified hydrogen bonding interaction of C-H units to Au atoms in divalent hexagold clusters ([Au6](2+)) decorated by diphosphine ligands. X-ray crystallography reveals substantially short Au-H/Au-C distances to indicate the presence of attractive interactions involving unfunctionalized C-H moieties...
September 18, 2017: Nature Communications
Abdallah Zeineddine, Laura Estévez, Sonia Mallet-Ladeira, Karinne Miqueu, Abderrahmane Amgoune, Didier Bourissou
The reluctance of gold to achieve oxidative addition reaction is considered as an intrinsic limitation for the development of gold-catalyzed cross-coupling reactions with simple and ubiquitous aryl halide electrophiles. Here, we report the rational construction of a Au(I)/Au(III) catalytic cycle involving a sequence of Csp(2)-X oxidative addition, Csp(2)-H auration and reductive elimination, allowing a gold-catalyzed direct arylation of arenes with aryl halides. Key to this discovery is the use of Me-Dalphos, a simple ancillary (P,N) ligand, that allows the bottleneck oxidative addition of aryl iodides and bromides to readily proceed under mild conditions...
September 18, 2017: Nature Communications
Katja Heinze
The chemistry of gold strongly focuses on the ubiquitous oxidation states +I and +III. The intermediate oxidation state +II is generally avoided in mononuclear gold species. In recent years, gold(II) has been increasingly suggested as key intermediate in artificial photosynthesis systems with gold(III) moieties as electron acceptors or in gold-catalyzed photoredox catalysis and radical chemistry. This Minireview provides a concise summary on confirmed and characterized mononuclear open-shell gold(II) complexes...
September 18, 2017: Angewandte Chemie
Zhenglong Zhang, Marie Richard-Lacroix, Volker Deckert
Plasmon-induced chemical reactions have recently attracted great attention as a promising method for high efficiency light-energy conversion and proved to be useful in a wealth of different domains of chemistry and physics. One of the interesting and, so far, less explored avenues of such reactions is their potential for efficient, highly localized and controlled polymer production. Here, we present the first example of a localized, directed plasmon catalyzed polymerization process of a self-assembled monolayer on both silver and gold surfaces monitored by surface- and tip-enhanced Raman spectroscopy (SERS and TERS)...
September 15, 2017: Faraday Discussions
Yong Li, Mufeng Wei, Mingji Dai
A concise approach to synthesize the 5-7-6 tricyclic carbon skeleton of the daphnane/tigliane diterpene natural products has been accomplished via a sequential gold-catalyzed furan formation and furan-allene [4+3] cycloaddition. This work provides new avenues for rapid and diverted synthesis of the medicinally important daphnane/tigliane diterpenes and their unnatural analogues.
July 20, 2017: Tetrahedron
Youlin Zhang, Xiaokun Li, Kai Li, Bin Xue, Chunmei Zhang, Cheng Du, Zhijian Wu, Wei Chen
Design of catalytically active Pt-based catalysts with minimizing the usage of Pt is a major issue in fuel cells. Herein, for the first time, we have developed a Au catalytic reduction strategy to synthesize a Au@Pt core-shell electrocatalyst with a quasi-monolayer Pt skin spontaneously formed from the gold surface catalysis. In the presence of presynthesized gold nanocrystals (used as the catalyst and Au seeds) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (used as reductant), under the Au surface catalysis, platinum ions can be reduced and deposited on the gold nanocrystals to form a Pt skin surface with a quasi-monatomic thickness...
September 15, 2017: ACS Applied Materials & Interfaces
Nishtha Agarwal, Simon J Freakley, Rebecca U McVicker, Sultan M Althahban, Nikolaos Dimitratos, Qian He, David J Morgan, Robert L Jenkins, David J Willock, Stuart H Taylor, Christopher J Kiely, Graham J Hutchings
The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. Using colloidal gold-palladium nanoparticles rather than the same nanoparticles supported on titanium oxide, we oxidized methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Using isotopically labeled O2 as an oxidant in the presence of H2O2, we demonstrate that the methanol produced incorporated a substantial fraction (70%) of gas-phase O2 More oxygenated products were formed than H2O2 consumed, suggesting that the controlled breakdown of H2O2 activates methane which subsequently incorporates molecular oxygen through a radical process...
September 7, 2017: Science
Sandra Marianne Lang, Thorsten M Bernhardt, Valeriy Chernyy, Joost M Bakker, Robert N Barnett, Uzi Landman
Methane represents the major constituent of natural gas. It is primarily used only as a source of energy by means of combustion, but could also serve as an abundant hydrocarbon feedstock for high quality chemicals. One of the major challenges in catalysis research nowadays is therefore the development of materials that selectively cleave one of the four C-H-bonds of methane and make it thus amenable for further chemical conversion to more valuable compounds. Employing infrared spectroscopy and first-principles calculations it is uncovered herein that the interaction of methane with small gold cluster cations leads to selective C-H bond dissociation and the formation of hydrido-methyl complexes H-Aux+-CH3...
September 4, 2017: Angewandte Chemie
Alois Fürstner
2-Pyrones and 4-pyrones are common structural motif in bioactive natural products. Traditional methods for their synthesis, which try to emulate the biosynthetic pathway of cyclization of a 1,3,5-tricarbonyl precursor, are often harsh and therefore not particularly suitable for applications to polyfunctionalized and/or sensitive target compounds. -Acid catalysis, in contrast, proved much more adequate for a systematic exploration of the pyrone estate. To this end, alkynes are used as stable ketone surrogates, which can be activated under exceedingly mild conditions due to the pronounced carbophilicity of LAu+ (L = two electron donor ligand); intramolecular attack of a tethered ester carbonyl group onto the transient alkyne-gold complex then forges the pyrone ring in a fully regiocontrolled manner...
September 1, 2017: Angewandte Chemie
Matthew J Harper, Edward J Emmett, John F Bower, Christopher A Russell
Under the conditions of oxidative gold catalysis, exposure of ethylene to aryl silanes and alcohols generates products of 1,2-oxyarylation. This provides a rare example of a process that allows catalytic differential 1,2-difunctionalization of this feedstock chemical.
September 5, 2017: Journal of the American Chemical Society
Gaoxing Su, Huaqiao Jiang, Hongyan Zhu, Jing-Jing Lv, Guohai Yang, Bing Yan, Jun-Jie Zhu
Plasmonic Au-Pd nanostructures have drawn significant attention for use in heterogeneous catalysis. In this study, palladium nanodendrite-tipped gold nanorods (PdND-T-AuNRs) were subjected to a facile fabrication under mild reaction conditions. The palladium amounts on the two tips were tunable. In the preparation of PdND-T-AuNRs, dense capped AuNRs, a low reaction temperature, and suitable stabilizing agents were identified as critical reaction parameters for controlling palladium nanodendrites deposited on both ends of AuNRs...
August 31, 2017: Nanoscale
Zhuangqiang Gao, Haihang Ye, Dianyong Tang, Jing Tao, Sanaz Habibi, Adrienne Minerick, Dianping Tang, Xiaohu Xia
Au nanoparticles (AuNPs) as signal reporters have been utilized in colorimetric in vitro diagnostics (IVDs) for decades. Nevertheless, it remains a grand challenge to substantially enhance the detection sensitivity of AuNP-based IVDs as confined by the inherent plasmonics of AuNPs. In this work, we circumvent this confinement by developing unique dual-functional AuNPs that were engineered by coating conventional AuNPs with ultrathin Pt skins of sub-10 atomic layers (i.e., Au@Pt NPs). The Au@Pt NPs retain the plasmonic activity of initial AuNPs while possessing ultrahigh catalytic activity enabled by Pt skins...
September 13, 2017: Nano Letters
Mathéo Berthet, Olivier Songis, Catherine Taillier, Vincent Dalla
A completely regioselective and challenging gold(I)-catalyzed ring-opening of cyclic 1,3-dioxolanes and dioxanes by trimethylsilyl alkynes to set diol-derived propargyl trimethylsilyl bis-ethers is reported. This unprecedented and not trivial transformation does not operate with the catalytic methodologies recently reported for catalytic alkynylation of acyclic acetals/ketals, and is uniquely enabled by the application of a recently introduced synergistic gold(I)-silicon catalysis concept capable of producing simultaneously catalytic amounts of two key players, a silicon-based Lewis superacid and a nucleophilic gold acetylide...
August 30, 2017: Journal of Organic Chemistry
Shengzong Liang, Rene Ebule, Gerald B Hammond, Bo Xu
A novel chlorinating reagent with a high concentration of HCl has enabled the highly regioselective hydrochlorination of unactivated alkynes using a commercial nanogold catalyst. No overchlorination or hydration products were formed, and various functional groups were tolerated. This hydrochlorination method could be conducted under open air.
September 1, 2017: Organic Letters
Rajkumar Lalji Sahani, Rai-Shung Liu
This work describes gold-catalyzed annulations of electron-deficient alkynes with benzisoxazoles to yield quinoline oxides chemoselectively. Chemical functionalizations of these resulting azacyclic compounds afforded various oxygenated tetrahydroquinolines that are present as the cores of many bioactive molecules. With the same reactants, a new relay catalysis using gold and Zn(II) catalysts affords highly oxygenated tetrahydroquinoline derivatives stereoselectively.
August 13, 2017: Angewandte Chemie
Shuai Chen, Pin Liu, Kewen Su, Xuan Li, Zhen Qin, Wei Xu, Jun Chen, Chaorui Li, Jingfu Qiu
In this work, novel octahedral Cu2O-Au nanocomposites were synthesized and first applied in an electrochemical aptasensor to detect thrombin (TB) with the aid of a DNAzyme for signal amplification. The octahedral Cu2O-Au nanocomposites have not only simultaneously served as signal amplifying molecules but have also been utilized as an ideal loading platform to immobilize a large number of electroactive substances and recognition probes. Gold nanoparticles (AuNPs) were grown directly on the surface of the octahedral Cu2O nanocrystals, and the Cu2O-Au nanocomposites obtained had the advantages of large surface areas and excellent biocompatibilities...
August 5, 2017: Biosensors & Bioelectronics
Vishal J Mayani, Suranjana V Mayani, Sang Wook Kim
Up to now, a very few catalysts have been developed approaching the heterogeneous catalytic degradation of Eosin Y and Chromotrope 2R dyes (Acid Red 29). The present study provides a complete perspective of recyclable nanocomposite Au(Salen)@CC for catalytic degradation of hazardous water pollutant dyes viz., Eosin Y & Chromotrope 2R using mild reaction conditions. New gold Salen complex doped carbon nanocomposite Au(Salen)@CC was developed by easy methodology using nano carbon cage (CC) prepared from low-priced Pyrolysis fuel oil (PFO) residue based Pitch...
August 3, 2017: Scientific Reports
Ana Maria Craciun, Monica Focsan, Klara Magyari, Adriana Vulpoi, Zsolt Pap
Metal and in particular noble metal nanoparticles represent a very special class of materials which can be applied as prepared or as composite materials. In most of the cases, two main properties are exploited in a vast number of publications: biocompatibility and surface plasmon resonance (SPR). For instance, these two important properties are exploitable in plasmonic diagnostics, bioactive glasses/glass ceramics and catalysis. The most frequently applied noble metal nanoparticle that is universally applicable in all the previously mentioned research areas is gold, although in the case of bioactive glasses/glass ceramics, silver and copper nanoparticles are more frequently applied...
July 21, 2017: Materials
Patrick T Bohan, F Dean Toste
The development of a gold(III) catalyzed direct enantioconvergent 1,5-enyne cycloisomerization and kinetic resolution reaction is described. The transformation results in highly enantioenriched bicyclo[3.1.0]hexenes at all levels of conversion, with no racemization or symmetrization taking place during the course of the reaction, and simultaneously affords optically enriched 1,5-enynes. This report marks the first highly enantioselective transformation catalyzed by a well-defined cationic gold(III) catalyst and demonstrates the unique potential of gold(III) complexes in enantioselective catalysis...
August 16, 2017: Journal of the American Chemical Society
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