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Gold catalysis

Courtney A Smith, Stephen E Motika, Lukasz Wojtas, Xiaodong Shi
An intermolecular condensation of alkynols and terminal alkynes is reported. Using IPrAuNTf2, an efficient Au-catalyzed cyclization-alkynylation strategy furnishes (2-arylalkynyl) cyclic ethers in moderate to excellent yields (up to 94%). This strategy is extended to the synthesis of functionalized 2,3-dihydrooxepines via the sequential Au-catalyzed ring expansion of the cyclic ether substrates.
January 11, 2017: Chemical Communications: Chem Comm
Kang Liu, Yanru Bu, Yuanhui Zheng, Xuchuan Jiang, Aibing Yu, Huanting Wang
Gold nanorods (AuNRs) are versatile materials due to their broadly tuneable optical properties associated with the anisotropic feature. However, conventional seed-mediated synthesis is not only limited by the operational complexity and over-sensitivity towards subtle changes of experimental conditions, but also suffers from low yield (~15%). Herein, a facile seedless method is reported to overcome the above challenge. Monodispersed AuNRs with high yield (~100%) and highly adjustable longitudinal surface plasmon resonance (LSPR) are reproducibly synthesized...
January 10, 2017: Chemistry: a European Journal
Lucia Mora-Tamez, Vicente Esquivel-Peña, Ana Lilia Ocampo, Eduardo Rodríguez de San Miguel, Daniel Grande, Josefina de Gyves
A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in-situ reduction of gold(III) salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen® 364 or Alamine® 336) were the most efficient supports for Au(III) extraction...
January 7, 2017: ChemSusChem
Jun-Gang Wang, Xin Hua, Meng Li, Yi-Tao Long
Polydopamine functionalized plasmonic nanocomposites with well distributed catalytically active small gold nanoislands around large gold core were fabricated without using any chemical reductant or surfactant. The optical properties, surface molecular structures and ensemble catalytic activity of the gold nanocomposites were investigated by time-of-flight secondary ion mass spectrometry and UV-Vis spectroscopy, respectively. Moreover, the considerable catalytic activity of the nanocomposites toward 4-nitrophenol reduction was real time monitored by dark-field spectroscopy techniques at single-nanoparticle level avoiding averaging effects in bulk systems...
December 27, 2016: ACS Applied Materials & Interfaces
Jungjoon Kim, Wook Jeong, Young Ho Rhee
A flexible synthetic method toward highly substituted tetrahydropyran is reported. The key transformation involves atom-efficient sequential metal catalysis consisting of Pd-catalyzed addition of homopropargylic alcohols to alkoxyallene and the subsequent gold(I)-catalyzed cycloisomerization. Notably, this method gives access to both 2,6-cis- and 2,6-trans-tetrahydropyrans possessing diverse substitution patterns.
December 22, 2016: Organic Letters
Felix W W Hartrampf, Takayuki Furukawa, Dirk Trauner
An enantioselective total synthesis of the Lycopodium alkaloid lycoposerramine R is presented. It relies on a base-mediated cyclization that resembles the Conia-ene reaction of ynones and gold-catalyzed variants thereof. Thus, hydrindanones and other functionalized ring systems bearing an exocyclic alkene can be rapidly accessed at room temperature without noble metal catalysis or substrate preactivation.
December 21, 2016: Angewandte Chemie
Aslam C Shaikh, Dnyanesh S Ranade, Pattuparambil R Rajamohanan, Prasad P Kulkarni, Nitin T Patil
Oxidative intramolecular 1,2-amino-oxygenation reactions, combining gold(I)/gold(III) catalysis, is reported. The reaction provides efficient access to a structurally unique ionic pyridinium-oxazole dyad with tunable emission wavelengths. The application of these fluorophores as potential biomarkers has been investigated.
December 21, 2016: Angewandte Chemie
Jun Li, Lili Lin, Bowen Hu, Pengfei Zhou, Tianyu Huang, Xiaohua Liu, Xiaoming Feng
A highly efficient asymmetric cascade reaction between alkynyl esters and allylic alcohols has been realized. Key to success was the combination of a hydroalkoxylation reaction catalyzed by a π-acidic gold(I) complex with a Claisen rearrangement catalyzed by a chiral Lewis acidic N,N'-dioxide-nickel(II) complex. A range of acyclic α-allyl β-keto esters were synthesized in high yields (up to 99 %) with good diastereoselectivities (up to 97:3) and excellent enantioselectivities (up to 99 % ee) under mild reaction conditions...
December 20, 2016: Angewandte Chemie
Geoffroy Hervé Lonca, Ciputra Tejo, Hui Ling Chan, Shunsuke Chiba, Fabien Gagosz
Denitrogenative 6-endo-dig azide-yne cyclization of α-propargyloxy-β-haloalkylazides was enabled by gold catalysis, thus providing 2H-1,3-oxazines. This rare cyclization mode in gold-catalyzed reactions of azide-yne substrates was demonstrated to be facilitated and controlled by electronic and resonance effects of the alkyne substituents. Molecular transformations of the as-prepared 2H-1,3-oxazines were also investigated.
December 19, 2016: Chemical Communications: Chem Comm
Yan Zhao, Yucheng Huang, Hui Zhu, Qingqing Zhu, Yunsheng Xia
We herein present a three-in-one nanoplatform for sensing, self-assembly, and cascade catalysis, enabled by cyclodextrin modified gold nanoparticles (CD@AuNPs). Monodisperse AuNPs 15-20 nm in diameter are fabricated in an eco-friendly way by the proposed one-step colloidal synthesis method using CD as both reducing agents and stabilizers. First, the as-prepared AuNPs are employed as not only scaffolds but energy acceptors for turn-on fluorescent sensing based on guest replacement reaction. Then, the macrocyclic supramolecule functionalized AuNPs can be controllably assembled and form well-defined one- and two-dimensional architectures using tetrakis(4-carboxyphenyl)porphyrin as mediator...
December 28, 2016: Journal of the American Chemical Society
Wangcheng Zhan, Qian He, Xiaofei Liu, Yanglong Guo, Yanqin Wang, Li Wang, Yun Guo, Albina Y Borisevich, Jinshui Zhang, Guanzhong Lu, Sheng Dai
Supported gold (Au) nanocatalysts hold great promise for heterogeneous catalysis; however, their practical application is greatly hampered by poor thermodynamic stability. Herein, a general synthetic strategy is reported where discrete metal nanoparticles are made resistant to sintering, preserving their catalytic activities in high-temperature oxidation processes. Taking advantage of the unique coating chemistry of dopamine, sacrificial carbon layers are constructed on the material surface, stabilizing the supported catalyst...
December 14, 2016: Journal of the American Chemical Society
Demian Marchione, Maria Izquierdo, Giovanni Bistoni, Remco W A Havenith, Alceo Macchioni, Daniele Zuccaccia, Francesco Tarantelli, Leonardo Belpassi
The Dewar-Chatt-Duncanson (DCD) model provides a successful theoretical framework to describe the nature of the chemical bond in transition metal compounds and is especially useful in structural chemistry and catalysis. However, how to actually measure its constituents (substrate to metal donation and metal to substrate back-donation) is yet uncertain. Recently, we demonstrated that the DCD components can be neatly disentangled and the π back-donation component put in strict correlation with some experimental observables...
December 10, 2016: Chemistry: a European Journal
Min-Chul Kim, Dukhee Lee, Seong Hoon Jeong, Sang-Yup Lee, Eunah Kang
Novel nanodiamond-gold nanocomposites (NDAus) are prepared, and their oxidative catalytic activity is examined. Gold nanoparticles are deposited on carboxylated nanodiamonds (NDs) by in situ chemical reduction of gold precursor ions to produce NDAus, which exhibit catalytic activity for the oxidation of o-phenylenediamine in the presence of hydrogen peroxide similarly to a peroxidase. This remarkable catalytic activity is exhibited only by the gold nanoparticle-decorated NDs and is not observed for either Au nanoparticles or NDs separately...
December 21, 2016: ACS Applied Materials & Interfaces
Qu Chen, Kuang He, Alex W Robertson, Angus I Kirkland, Jamie H Warner
The atomic level dynamics of gold on graphene is studied at temperatures up to 800 °C using an in situ heating holder within an aberration-corrected transmission electron microscope. At this high temperature, individual gold atoms and nanoclusters are mobile across the surface of graphene and attach to defect sites and migrate along the edges of holes in graphene. Gold nanoclusters on clean graphene show crystallinity at temperatures above their predicted melting point for equivalent sized clusters due to strong epitaxial interactions with the underlying graphene lattice...
November 22, 2016: ACS Nano
Weiwei Qin, Tianhuan Peng, Yanjing Gao, Fei Wang, Xiaocai Hu, Kun Wang, Jiye Shi, Di Li, Jicun Ren, Chunhai Fan
It is highly demanding to design active nanomotors that can move in response to specific signals with controllable rate and direction. A catalysis-driven nanomotor was constructed by designing catalytically and plasmonically active Janus gold nanoparticles (Au NPs), which generate an asymmetric temperature gradient of local solvent surrounding NPs in catalytic reactions. The self-thermophoresis behavior of the Janus nanomotor is monitored from its inherent plasmonic response. The diffusion coefficient of the self-thermophoresis motion is linearly dependent on chemical reaction rate, as described by a stochastic model...
January 9, 2017: Angewandte Chemie
Judith Schöbel, Matthias Burgard, Christian Hils, Roland Dersch, Martin Dulle, Kirsten Volk, Matthias Karg, Andreas Greiner, Holger Schmalz
Heterogeneous catalysis with supported nanoparticles (NPs) is a highly active field of research. However, the efficient stabilization of NPs without deteriorating their catalytic activity is challenging. By combining top-down (coaxial electrospinning) and bottom-up (crystallization-driven self-assembly) approaches, we prepared patchy nonwovens with functional, nanometer-sized patches on the surface. These patches can selectively bind and efficiently stabilize gold nanoparticles (AuNPs). The use of these AuNP-loaded patchy nonwovens in the alcoholysis of dimethylphenylsilane led to full conversion under comparably mild conditions and in short reaction times...
January 2, 2017: Angewandte Chemie
Pradip N Bagle, Manoj V Mane, K Vanka, Dinesh R Shinde, Samir R Shaikh, Rajesh G Gonnade, Nitin T Patil
A co-operative Au(i)/Ag(i) catalyst system has been developed to utilize N-allenamides as nucleophilic enal equivalents for the interceptive capturing of incipient carbocations generated through π-acid-triggered imino-alkyne cyclization. The salient features include the in situ generation of silver-bound carbocations (from iminoalkynes), α-gold(i) enals (from N-allenamides) and union of these two species to form indolizines with the regeneration of Au and Ag catalysts.
December 13, 2016: Chemical Communications: Chem Comm
Massimo Rigo, Lara Hettmanczyk, Frank J L Heutz, Stephan Hohloch, Martin Lutz, Biprajit Sarkar, Christian Müller
Gold(i) complexes based on a 2,4,6-triarylphosphinine and a mesoionic carbene derivative have been prepared and characterized crystallographically. Although structurally related, both heterocycles differ significantly in their donor/acceptor properties. These opposed electronic characteristics have been exploited in Au(i)-catalyzed cycloisomerization reactions. For the conversion of the standard substrate dimethyl 2-(3-methylbut-2-enyl)-2-(prop-2-ynyl)malonate the results obtained for both Au-catalysts were found to be very similar and comparable to the ones reported in the literature for other carbene- or phosphorus(iii)-based Au(i)-complexes...
December 20, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
Chuanhua Qu, Songlin Zhang, Hongbin Du, Chengjian Zhu
A new method for the synthesis of 3-arylindoles has been developed by visible light mediated dual gold/photoredox catalysis. This transformation has many features such as cascade catalysis, high efficiency, redox-neutral reaction conditions and good functional group tolerance. The reaction proceeds through the photoredox-promoted formation of an electrophilic arylgold(iii) intermediate that undergoes coupling with the arylamine nucleophile.
December 13, 2016: Chemical Communications: Chem Comm
Samir A Belhout, Ji Yoon Kim, David T Hinds, Natalie J Owen, Jonathan A Coulter, Susan J Quinn
The preparation of a family of composite particles comprising gold nanoparticles (AuNP) assembled at a polystyrene (PS) surface is reported. Tunable loading is demonstrated for AuNP sizes (4.5-26 nm). The robust composites are stable to multiple centrifugation and dispersion cycles and to conditions of high ionic strength, physiological buffer and cell culture media. These properties provide potential for a variety of applications from cellular studies to catalysis.
December 13, 2016: Chemical Communications: Chem Comm
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