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ACS Catalysis

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
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
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
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
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
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
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
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
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
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
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
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
Molly Punk, Charlotte Merkley, Katlyn Kennedy, Jeremy B Morgan
Aziridines are important synthetic intermediates for the generation of nitrogen-containing molecules. N-Acylaziridines undergo rearrangement by ring expansion to produce oxazolines, a process known as the Heine reaction. The first catalytic, enantioselective Heine reaction is reported for meso-N-acylaziridines where a palladium(II)-diphosphine complex is employed. The highly enantioenriched oxazoline products are valuable organic synthons and potential ligands for transition-metal catalysis.
July 1, 2016: ACS Catalysis
Nina G Schmidt, Elisabeth Eger, Wolfgang Kroutil
Carbon-carbon bond formation is the key reaction for organic synthesis to construct the carbon framework of organic molecules. The review gives a selection of biocatalytic C-C-bond-forming reactions which have been investigated during the last 5 years and which have already been proven to be applicable for organic synthesis. In most cases, the reactions lead to products functionalized at the site of C-C-bond formation (e.g., α-hydroxy ketones, aminoalcohols, diols, 1,4-diketones, etc.) or allow to decorate aromatic and heteroaromatic molecules...
July 1, 2016: ACS Catalysis
Jingxiu Xie, Hirsa M Torres Galvis, Ard C J Koeken, Alexey Kirilin, A Iulian Dugulan, Matthijs Ruitenbeek, Krijn P de Jong
The Fischer-Tropsch Synthesis converts synthesis gas from alternative carbon resources, including natural gas, coal, and biomass, to hydrocarbons used as fuels or chemicals. In particular, iron-based catalysts at elevated temperatures favor the selective production of C2-C4 olefins, which are important building blocks for the chemical industry. Bulk iron catalysts (with promoters) were conventionally used, but these deactivate due to either phase transformation or carbon deposition resulting in disintegration of the catalyst particles...
June 3, 2016: ACS Catalysis
Noelia Casanova, Karina P Del Rio, Rebeca García-Fandiño, José L Mascareñas, Moisés Gulías
2-Alkenylphenols react with allenes, upon treatment with catalytic amounts of Pd(II) and Cu(II), to give benzoxepine products in high yields and with very good regio- and diastereoselectivities. This contrasts with the results obtained with Rh catalysts, which provided chromene-like products through a pathway involving a β-hydrogen elimination step. Computational studies suggest that the square planar geometry of the palladium is critical to favor the reductive elimination process required for the formation of the oxepine products...
May 6, 2016: ACS Catalysis
D A Matthijs de Winter, Florian Meirer, Bert M Weckhuysen
The overall performance of a catalyst particle strongly depends on the ability of mass transport through its pore space. Characterizing the three-dimensional structure of the macro- and mesopore space of a catalyst particle and establishing a correlation with transport efficiency is an essential step toward designing highly effective catalyst particles. In this work, a generally applicable workflow is presented to characterize the transport efficiency of individual catalyst particles. The developed workflow involves a multiscale characterization approach making use of a focused ion beam-scanning electron microscope (FIB-SEM)...
May 6, 2016: ACS Catalysis
Nikolaus Gorgas, Berthold Stöger, Luis F Veiros, Karl Kirchner
The synthesis and application of [Fe(PNP(Me)-iPr)(CO)(H)(Br)] and [Fe(PNP(Me)-iPr)(H)2(CO)] as catalysts for the homogeneous hydrogenation of aldehydes is described. These systems were found to be among the most efficient catalysts for this process reported to date and constitute rare examples of a catalytic process which allows selective reduction of aldehydes in the presence of ketones and other reducible functionalities. In some cases, TONs and TOFs of up to 80000 and 20000 h(-1), respectively, were reached...
April 1, 2016: ACS Catalysis
Hien N Pham, Jesper J H B Sattler, Bert M Weckhuysen, Abhaya K Datye
Alumina-supported Pt is one of the major industrial catalysts for light alkane dehydrogenation. This catalyst loses activity during reaction, with coke formation often considered as the reason for deactivation. As we show in this study, the amount and nature of carbon deposits do not directly correlate with the loss of activity. Rather, it is the transformation of subnanometer Pt species into larger Pt nanoparticles that appears to be responsible for the loss of catalytic activity. Surprisingly, a portion of the Sn remains atomically dispersed on the alumina surface in the spent catalyst and helps in the redispersion of the Pt...
April 1, 2016: ACS Catalysis
Anna M Wise, Johanna Nelson Weker, Sam Kalirai, Maryam Farmand, David A Shapiro, Florian Meirer, Bert M Weckhuysen
Understanding Fe deposition in fluid catalytic cracking (FCC) catalysis is critical for the mitigation of catalyst degradation. Here we employ soft X-ray ptychography to determine at the nanoscale the distribution and chemical state of Fe in an aged FCC catalyst particle. We show that both particle swelling due to colloidal Fe deposition and Fe penetration into the matrix as a result of precracking of large organic molecules occur. The application of ptychography allowed us to provide direct visual evidence for these two distinct Fe-based deactivation mechanisms, which have so far been proposed only on the basis of indirect evidence...
April 1, 2016: ACS Catalysis
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