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ACS Catalysis

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https://www.readbyqxmd.com/read/28413693/stable-fe-zsm-5-nanosheet-zeolite-catalysts-for-the-oxidation-of-benzene-to-phenol
#1
Lingqian Meng, Xiaochun Zhu, Emiel J M Hensen
Fe/ZSM-5 nanosheet zeolites of varying thickness were synthesized with di- and tetraquaternary ammonium structure directing agents and extensively characterized for their textural, structural, and catalytic properties. Introduction of Fe(3+) ions in the framework of nanosheet zeolites was slightly less effective than in bulk ZSM-5 zeolite. Steaming was necessary to activate all catalysts for N2O decomposition and benzene oxidation. The higher the Fe content, the higher the degree of Fe aggregation was after catalyst activation...
April 7, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28413692/photoredox-mediated-routes-to-radicals-the-value-of-catalytic-radical-generation-in-synthetic-methods-development
#2
REVIEW
Jennifer K Matsui, Simon B Lang, Drew R Heitz, Gary A Molander
Photoredox catalysis has experienced a revitalized interest from the synthesis community during the past decade. For example, photoredox/Ni dual catalysis protocols have been developed to overcome several inherent limitations of palladium-catalyzed cross-couplings by invoking a single-electron transmetalation pathway. This Perspective highlights advances made by our laboratory since the inception of the photoredox/Ni cross-coupling of benzyltrifluoroborates with aryl bromides. In addition to broadening the scope of trifluoroborate coupling partners, research using readily oxidized hypervalent silicates as radical precursors that demonstrate functional group compatibility is highlighted...
April 7, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28413691/proton-transfer-in-the-catalytic-cycle-of-nife-hydrogenases-insight-from-vibrational-spectroscopy
#3
REVIEW
Philip A Ash, Ricardo Hidalgo, Kylie A Vincent
Catalysis of H2 production and oxidation reactions is critical in renewable energy systems based around H2 as a clean fuel, but the present reliance on platinum-based catalysts is not sustainable. In nature, H2 is oxidized at minimal overpotential and high turnover frequencies at [NiFe] catalytic sites in hydrogenase enzymes. Although an outline mechanism has been established for the [NiFe] hydrogenases involving heterolytic cleavage of H2 followed by a first and then second transfer of a proton and electron away from the active site, details remain vague concerning how the proton transfers are facilitated by the protein environment close to the active site...
April 7, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28405491/transient-behavior-of-ni-nio-x-functionalized-srtio3-in-overall-water-splitting
#4
Kai Han, Tomas Kreuger, Bastian Mei, Guido Mul
Transients in the composition of Ni@NiO x core-shell co-catalysts deposited on SrTiO3 are discussed on the basis of state-of-the-art continuous analysis of photocatalytic water splitting, and post-XPS and TEM analyses. The formation of excessive hydrogen (H2:O2 ≫ 2) in the initial stages of illumination demonstrates oxidation of Ni(OH)2 to NiOOH (nickel oxyhydroxide), with the latter catalyzing water oxidation. A disproportionation reaction of Ni and NiOOH, yielding Ni(OH)2 with residual embedded Ni, occurs when illumination is discontinued, which explains repetitive transients in (excess) hydrogen and oxygen formation when illumination is reinitiated...
March 3, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28367354/mild-redox-neutral-alkylation-of-imines-enabled-by-an-organic-photocatalyst
#5
Niki R Patel, Christopher B Kelly, Allison P Siegenfeld, Gary A Molander
An operationally simple, mild, redox-neutral method for the photoredox alkylation of imines is reported. Utilizing an inexpensive organic photoredox catalyst, alkyl radicals are readily generated from the single-electron oxidation of ammonium alkyl bis(catecholato)silicates and are subsequently engaged in a C-C bond-forming reaction with imines. The process is highly selective, metal-free, and does not require a large excess of the alkylating reagent or the use of acidic additives.
March 3, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28286695/when-weaker-can-be-tougher-the-role-of-oxidation-state-i-in-p-vs-n-ligand-derived-ni-catalyzed-trifluoromethylthiolation-of-aryl-halides
#6
Indrek Kalvet, Qianqian Guo, Graham J Tizzard, Franziska Schoenebeck
The direct introduction of the valuable SCF3 moiety into organic molecules has received considerable attention. While it can be achieved successfully for aryl chlorides under catalysis with Ni(0)(cod)2 and dppf, this report investigates the Ni-catalyzed functionalization of the seemingly more reactive aryl halides ArI and ArBr. Counterintuitively, the observed conversion triggered by dppf/Ni(0) is ArCl > ArBr > ArI, at odds with bond strength preferences. By a combined computational and experimental approach, the origin of this was identified to be due to the formation of (dppf)Ni(I), which favors β-F elimination as a competing pathway over the productive cross-coupling, ultimately generating the inactive complex (dppf)Ni(SCF2) as a catalysis dead end...
March 3, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28367353/regioselective-carbohydrate-oxidations-a-nuclear-magnetic-resonance-nmr-study-on-selectivity-rate-and-side-product-formation
#7
Niek N H M Eisink, Martin D Witte, Adriaan J Minnaard
Palladium/neocuproine catalyzed oxidation of glucosides shows an excellent selectivity for the C3-OH, but in mannosides and galactosides, unselective oxidation was initially observed. For further application in more-complex (oligo)saccharides, a better understanding of the reaction, in terms of selectivity and reactivity, is required. Therefore, a panel of different glycosides was synthesized, subjected to palladium/neocuproine catalyzed oxidation and subsequently analyzed by qNMR. Surprisingly, all studied glucosides, mannosides, galactosides, and xylosides show selective oxidation of the C3-OH...
February 3, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28154785/palladium-catalyzed-aerobic-dehydrogenation-of-cyclic-hydrocarbons-for-the-synthesis-of-substituted-aromatics-and-other-unsaturated-products
#8
Andrei V Iosub, Shannon S Stahl
Catalytic dehydrogenation of saturated or partially saturated six-membered carbocycles into aromatic rings represents an appealing strategy for the synthesis of substituted arenes. Particularly effective methods have been developed for the dehydrogenation of cyclohexanones and cyclohexenes into substituted phenol, aniline, and benzene derivatives, respectively. In this Perspective, we present the contributions of our research group to the discovery and development of palladium-based catalysts for aerobic oxidative dehydrogenation methods, including general methods for conversion of cyclohexanones and cyclohexenones into substituted phenols and a complementary method for partial dehydrogenation cyclohexanones to cyclohexenones...
December 2, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27990319/direct-synthesis-of-symmetrical-azines-from-alcohols-and-hydrazine-catalyzed-by-a-ruthenium-pincer-complex-effect-of-hydrogen-bonding
#9
Jonathan O Bauer, Gregory Leitus, Yehoshoa Ben-David, David Milstein
Azines (2,3-diazabuta-1,3-dienes) are a widely used class of compounds with conjugated C=N double bonds. Herein, we present a direct synthesis of azines from alcohols and hydrazine hydrate. The reaction, catalyzed by a ruthenium pincer complex, evolves dihydrogen and can be run in a base-free version. The dehydrogenative coupling of benzylic and aliphatic alcohols led to good conversions and yields. Spectroscopic evidence for a hydrazine-coordinated dearomatized ruthenium pincer complex was obtained. Isolation of a supramolecular crystalline compound provided evidence for the important role of hydrogen bonding networks under the reaction conditions...
December 2, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27990318/1-4-dihydropyridines-as-alkyl-radical-precursors-introducing-the-aldehyde-feedstock-to-nickel-photoredox-dual-catalysis
#10
Álvaro Gutiérrez-Bonet, John C Tellis, Jennifer K Matsui, Brandon A Vara, Gary A Molander
A Ni/photoredox dual catalytic cross-coupling is disclosed in which a diverse range of (hetero)aryl bromides are used as electrophiles, with 1,4-dihydropyridines serving as precursors to Csp(3)-centered alkyl radical coupling partners. The reported method is characterized by its extremely mild reaction conditions, enabling access to underexplored cores.
December 2, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/28286694/highly-stereoselective-biocatalytic-synthesis-of-key-cyclopropane-intermediate-to-ticagrelor
#11
Kari E Hernandez, Hans Renata, Russell D Lewis, S B Jennifer Kan, Chen Zhang, Jared Forte, David Rozzell, John A McIntosh, Frances H Arnold
Extending the scope of biocatalysis to important non-natural reactions such as olefin cyclopropanation will open new opportunities for replacing multi-step chemical syntheses of pharmaceutical intermediates with efficient, clean, and highly selective enzyme-catalyzed processes. In this work, we engineered the truncated globin of Bacillus subtilis for the synthesis of a cyclopropane precursor to the antithrombotic agent ticagrelor. The engineered enzyme catalyzes the cyclopropanation of 3,4-difluorostyrene with ethyl diazoacetate on a preparative scale to give ethyl-(1R, 2R)-2-(3,4-difluorophenyl)-cyclopropanecarboxylate in 79% yield, with very high diastereoselectivity (>99% dr) and enantioselectivity (98% ee), enabling a single-step biocatalytic route to this pharmaceutical intermediate...
November 4, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27840771/a-synthesis-of-substituted-%C3%AE-allenols-via-iron-catalyzed-cross-coupling-of-propargyl-carboxylates-with-grignard-reagents
#12
Simon N Kessler, Fabian Hundemer, Jan-E Bäckvall
α-Allenols are attractive and versatile compounds whose preparation can be a nontrivial task. In this Letter, we provide a method for the prompt synthesis of substituted α-allenols via a catalytic cross-coupling reaction which makes use of a nontoxic and cost-effective iron catalyst. The catalyst loading is typically as low as 1-5 mol %. The mild reaction conditions (-20 °C) and the short reaction time (15 min) allow for the presence of a variety of functional groups. Moreover, the reaction was shown to be scalable up to gram-scale and the propargyl substrates are readily accessible by a one-pot synthesis...
November 4, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27990317/synergy-and-anti-synergy-between-palladium-and-gold-in-nanoparticles-dispersed-on-a-reducible-support
#13
James H Carter, Sultan Althahban, Ewa Nowicka, Simon J Freakley, David J Morgan, Parag M Shah, Stanislaw Golunski, Christopher J Kiely, Graham J Hutchings
Highly active and stable bimetallic Au-Pd catalysts have been extensively studied for several liquid-phase oxidation reactions in recent years, but there are far fewer reports on the use of these catalysts for low-temperature gas-phase reactions. Here we initially established the presence of a synergistic effect in a range of bimetallic Au-Pd/CeZrO4 catalysts, by measuring their activity for selective oxidation of benzyl alcohol. The catalysts were then evaluated for low-temperature WGS, CO oxidation, and formic acid decomposition, all of which are believed to be mechanistically related...
October 7, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27761299/improving-formate-and-methanol-fuels-catalytic-activity-of-single-pd-coated-carbon-nanotubes
#14
Xiuting Li, Hannah Hodson, Christopher Batchelor-McAuley, Lidong Shao, Richard G Compton
The oxidations of formate and methanol on nitrogen-doped carbon nanotubes decorated with palladium nanoparticles were studied at both the single-nanotube and ensemble levels. Significant voltammetric differences were seen. Pd oxide formation as a competitive reaction with formate or methanol oxidation is significantly inhibited at high overpotentials under the high mass transport conditions associated with single-particle materials in comparison with that seen with ensembles, where slower diffusion prevails...
October 7, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27761298/palladium-catalyzed-oxidative-domino-carbocyclization-arylation-of-bisallenes
#15
Chandra M R Volla, Jan-E Bäckvall
Herein we report a highly efficient and site-selective palladium-catalyzed oxidative carbocyclization-arylation reaction of bisallenes and arylboronic acids under operationally simple conditions for the selective synthesis of cyclohexadiene derivatives. The palladium source and the solvent proved to be crucial for the selectivity and the reactivity displayed. Interestingly, in the absence of the nucleophile, an oxidative carbocyclization-β-elimination pathway predominates. The reaction conditions are compatible with a wide range of functional groups, and the reaction exhibits broad substrate scope...
October 7, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27747133/metal-catalyzed-carboxylation-of-organic-pseudo-halides-with-co2
#16
Marino Börjesson, Toni Moragas, Daniel Gallego, Ruben Martin
The recent years have witnessed the development of metal-catalyzed reductive carboxylation of organic (pseudo)halides with CO2 as C1 source, representing potential powerful alternatives to existing methodologies for preparing carboxylic acids, privileged motifs in a myriad of pharmaceuticals and molecules displaying significant biological properties. While originally visualized as exotic cross-coupling reactions, a close look into the literature data indicates that these processes have become a fertile ground, allowing for the utilization of a variety of coupling partners, even with particularly challenging substrate combinations...
October 7, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/28078166/selective-cobalt-catalyzed-reduction-of-terminal-alkenes-and-alkynes-using-eto-2si-me-h-as-a-stoichiometric-reductant
#17
Balaram Raya, Souvagya Biswas, T V RajanBabu
While attempting to effect Co-catalyzed hydrosilylation of β-vinyl trimethylsilyl enol ethers we discovered that depending on the silane, solvent and the method of generation of the reduced cobalt catalyst, a highly efficient and selective reduction or hydrosilylation of an alkene can be achieved. This paper deals with this reduction reaction, which has not been reported before in spite of the huge research activity in this area. The reaction, which uses an air-stable [2,6-di(aryliminoyl)pyridine)]CoCl2 activated by 2 equivalents of NaEt3BH as a catalyst (0...
September 2, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27818842/enhancement-of-the-hydrogen-evolution-reaction-from-ni-mos2-hybrid-nanoclusters
#18
Daniel Escalera-López, Yubiao Niu, Jinlong Yin, Kevin Cooke, Neil V Rees, Richard E Palmer
This report focuses on a novel strategy for the preparation of transition metal-MoS2 hybrid nanoclusters based on a one-step, dual-target magnetron sputtering, and gas condensation process demonstrated for Ni-MoS2. Aberration-corrected STEM images coupled with EDX analysis confirms the presence of Ni and MoS2 in the hybrid nanoclusters (average diameter = 5.0 nm, Mo:S ratio = 1:1.8 ± 0.1). The Ni-MoS2 nanoclusters display a 100 mV shift in the hydrogen evolution reaction (HER) onset potential and an almost 3-fold increase in exchange current density compared with the undoped MoS2 nanoclusters, the latter effect in agreement with reported DFT calculations...
September 2, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27668125/role-of-the-three-phase-boundary-of-the-platinum-support-interface-in-catalysis-a-model-catalyst-kinetic-study
#19
Evangelos I Papaioannou, Christoph Bachmann, Jonas J Neumeier, Daniel Frankel, Herbert Over, Juergen Janek, Ian S Metcalfe
A series of microstructured, supported platinum (Pt) catalyst films (supported on single-crystal yttria-stabilized zirconia) and an appropriate Pt catalyst reference system (supported on single-crystal alumina) were fabricated using pulsed laser deposition and ion-beam etching. The thin films exhibit area-specific lengths of the three-phase boundary (length of three-phase boundary between the Pt, support, and gas phase divided by the superficial area of the sample) that vary over 4 orders of magnitude from 4...
September 2, 2016: ACS Catalysis
https://www.readbyqxmd.com/read/27563493/correlating-calmodulin-landscapes-with-chemical-catalysis-in-neuronal-nitric-oxide-synthase-using-time-resolved-fret-and-a-5-deazaflavin-thermodynamic-trap
#20
Tobias M Hedison, Nicole G H Leferink, Sam Hay, Nigel S Scrutton
A major challenge in enzymology is the need to correlate the dynamic properties of enzymes with, and understand the impact on, their catalytic cycles. This is especially the case with large, multicenter enzymes such as the nitric oxide synthases (NOSs), where the importance of dynamics has been inferred from a variety of structural, single-molecule, and ensemble spectroscopic approaches but where motions have not been correlated experimentally with mechanistic steps in the reaction cycle. Here we take such an approach...
August 5, 2016: ACS Catalysis
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