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ACS Catalysis

Qing-Feng Wu, Xiao-Bing Wang, Peng-Xiang Shen, Jin-Quan Yu
Chiral mono- N -protected aminomethyl oxazoline (MPAO) ligands are found to promote enantioselective C-H arylation and vinylation of the cyclobutyl carboxylic acid derivatives via Pd(II)/Pd(IV) redox catalysis. This ligand scaffold overcame two important limitations of the previous MPAHA (mono- N -protected α-amino- O -methylhydroxamic acid) ligands-enabled asymmetric C-H activation/C-C coupling reactions of cyclic carboxylic amides through Pd(II)/Pd(0) catalysis: substrates containing α-hydrogen atoms are not compatible; vinylation has not been developed...
March 2, 2018: ACS Catalysis
Stefan E Payer, Hannah Pollak, Silvia M Glueck, Kurt Faber
The promiscuous regio- and stereoselective hydration of 4-hydroxystyrenes catalyzed by ferulic acid decarboxylase from Enterobacter sp. (FDC_ Es ) depends on bicarbonate bound in the active site, which serves as a proton relay activating a water molecule for nucleophilic attack on a quinone methide electrophile. This "cofactor" is crucial for achieving improved conversions and high stereoselectivities for ( S )-configured benzylic alcohol products. Similar effects were observed with simple aliphatic carboxylic acids as additives...
March 2, 2018: ACS Catalysis
Robin G Geitenbeek, Anne-Eva Nieuwelink, Thimo S Jacobs, Bastiaan B V Salzmann, Joris Goetze, Andries Meijerink, Bert M Weckhuysen
Bandshape luminescence thermometry during in situ temperature measurements has been reported by preparing three catalytically relevant systems, which show temperature-dependent luminescence. One of these systems was further investigated as a showcase for application. Microcrystalline NaYF4 doped with Er3+ and Yb3+ was mixed with a commercial zeolite H-ZSM-5 to investigate the Methanol-to-Hydrocarbons (MTH) reaction, while monitoring the reaction products with online gas chromatography. Due to the exothermic nature of the MTH reaction, a front of increased temperature migrating down the fixed reactor bed was visualized, showing the potential for various applications of luminescence thermometry for in situ measurements in catalytic systems...
March 2, 2018: ACS Catalysis
Wei Zhang, Giada Innocenti, Paula Oulego, Vitaly Gitis, Haihong Wu, Bernd Ensing, Fabrizio Cavani, Gadi Rothenberg, N Raveendran Shiju
The direct oxidative dehydrogenation of lactates with molecular oxygen is a "greener" alternative for producing pyruvates. Here we report a one-pot synthesis of mesoporous vanadia-titania (VTN), acting as highly efficient and recyclable catalysts for the conversion of ethyl lactate to ethyl pyruvate. These VTN materials feature high surface areas, large pore volumes, and high densities of isolated vanadium species, which can expose the active sites and facilitate the mass transport. In comparison to homogeneous vanadium complexes and VO x /TiO2 prepared by impregnation, the meso-VTN catalysts showed superior activity, selectivity, and stability in the aerobic oxidation of ethyl lactate to ethyl pyruvate...
March 2, 2018: ACS Catalysis
Eric Tan, Ophélie Quinonero, M Elena de Orbe, Antonio M Echavarren
We report the alkynylation of C(sp2 )-H bonds with bromoalkynes (inverse-Sonogashira reaction) directed by synthetically useful ester, ketone, and ether groups under rhodium catalysis. Other less common directing groups such as amine, thioether, sulfoxide, sulfone, phenol ester, and carbamate are also suitable directing groups. Mechanistic studies indicate that the reaction proceeds by a turnover-limiting C-H activation step via an electrophilic-type substitution.
March 2, 2018: ACS Catalysis
Joris Goetze, Irina Yarulina, Jorge Gascon, Freek Kapteijn, Bert M Weckhuysen
In small-pore zeolite catalysts, where the size of the pores is limited by eight-ring windows, aromatic hydrocarbon pool molecules that are formed inside the zeolite during the Methanol-to-Olefins (MTO) process cannot exit the pores and are retained inside the catalyst. Hydrocarbon species whose size is comparable to the size of the zeolite cage can cause the zeolite lattice to expand during the MTO process. In this work, the formation of retained hydrocarbon pool species during MTO at a reaction temperature of 400 °C was followed using operando UV-vis spectroscopy...
March 2, 2018: ACS Catalysis
Francisco Esteban, Wioleta Cieślik, Enrique M Arpa, Andrea Guerrero-Corella, Sergio Díaz-Tendero, Josefina Perles, José A Fernández-Salas, Alberto Fraile, José Alemán
An organocatalytic strategy for the synthesis of tetrasubstituted pyrrolidines with monoactivated azomethine ylides in high enantiomeric excess and excellent exo/endo selectivity is presented. The key to success is the intramolecular activation via hydrogen bonding through an o -hydroxy group, which allows the dipolar cycloaddition to take place in the presence of azomethine ylides bearing only one activating group. The intramolecular hydrogen bond in the azomethine ylide and the intermolecular hydrogen bond with the catalyst have been demonstrated by DFT calculations and mechanistic proofs to be crucial for the reaction to proceed...
March 2, 2018: ACS Catalysis
Konstantin G Kottrup, Silvia D'Agostini, Phebe H van Langevelde, Maxime A Siegler, Dennis G H Hetterscheid
The synthesis, characterization, and electrochemical studies of the dinuclear complex [(MeOH)Fe(Hbbpya)-μ-O-(Hbbpya)Fe(MeOH)](OTf)4 (1) (with Hbbpya = N,N-bis(2,2'-bipyrid-6-yl)amine) are described. With the help of online electrochemical mass spectrometry, the complex is demonstrated to be active as a water oxidation catalyst. Comparing the results obtained for different electrode materials shows a clear substrate influence of the electrode, as the complex shows a significantly lower catalytic overpotential on graphitic working electrodes in comparison to other electrode materials...
February 2, 2018: ACS Catalysis
Roderigh Y Rohling, Evgeny Uslamin, Bart Zijlstra, Ionut C Tranca, Ivo A W Filot, Emiel J M Hensen, Evgeny A Pidko
The one-pot Diels-Alder cycloaddition (DAC)/dehydration (D) tandem reaction between 2,5-dimethylfuran and ethylene is a potent pathway toward biomass-derived p-xylene. In this work, we present a cheap and active low-silica potassium-exchanged faujasite (KY, Si/Al = 2.6) catalyst. Catalyst optimization was guided by a computational study of the DAC/D reaction mechanism over different alkali-exchanged faujasites using periodic density functional theory calculations complemented by microkinetic modeling. Two types of faujasite models were compared, i...
February 2, 2018: ACS Catalysis
Laurent Liardet, Xile Hu
The water-splitting reaction provides a promising mechanism to store renewable energies in the form of hydrogen fuel. The oxidation half-reaction, the oxygen evolution reaction (OER), is a complex four-electron process that constitutes an efficiency bottleneck in water splitting. Here we report a highly active OER catalyst, cobalt vanadium oxide. The catalyst is designed on the basis of a volcano plot of metal-OH bond strength and activity. The catalyst can be synthesized by a facile hydrothermal route. The most active pure-phase material (a-CoVO x ) is X-ray amorphous and provides a 10 mA cm-2 current density at an overpotential of 347 mV in 1 M KOH electrolyte when immobilized on a flat substrate...
January 5, 2018: ACS Catalysis
Ya-Qiong Su, Ivo A W Filot, Jin-Xun Liu, Emiel J M Hensen
Doping CeO2 with Pd atoms has been associated with catalytic CO oxidation, but current surface models do not allow CO adsorption. Here, we report a new structure of Pd-doped CeO2(111), in which Pd adopts a square planar configuration instead of the previously assumed octahedral configuration. Oxygen removal from this doped structure is favorable. The resulting defective Pd-doped CeO2 surface is active for CO oxidation and is also able to cleave the first C-H bond in methane. We show how the moderate CO adsorption energy and dynamic features of the Pd atom upon CO adsorption and CO oxidation contribute to a low-barrier catalytic cycle for CO oxidation...
January 5, 2018: ACS Catalysis
Chong Liu, Rutger A van Santen, Ali Poursaeidesfahani, Thijs J H Vlugt, Evgeny A Pidko, Emiel J M Hensen
The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane-propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate of hydride transfer in comparison to the competitive oligomerization and deprotonation reactions resulting in catalyst deactivation...
December 1, 2017: ACS Catalysis
Adrian Romero-Rivera, Marc Garcia-Borràs, Sílvia Osuna
Enzymes exist as ensembles of conformations that are important for function. Tuning these populations of conformational states through mutation enables evolution toward additional activities. Here we computationally evaluate the population shifts induced by distal and active site mutations in a family of computationally designed and experimentally optimized retro-aldolases. The conformational landscape of these enzymes was significantly altered during evolution, as pre-existing catalytically active conformational substates became major states in the most evolved variants...
December 1, 2017: ACS Catalysis
Wei Chen, Ivo A W Filot, Robert Pestman, Emiel J M Hensen
Fischer-Tropsch (FT) synthesis is one of the most complex catalyzed chemical reactions in which the chain-growth mechanism that leads to formation of long-chain hydrocarbons is not well understood yet. The present work provides deeper insight into the relation between the kinetics of the FT reaction on a silica-supported cobalt catalyst and the composition of the surface adsorbed layer. Cofeeding experiments of12 C3 H6 with13 CO/H2 evidence that CH x surface intermediates are involved in chain growth and that chain growth is highly reversible...
December 1, 2017: ACS Catalysis
Wei Chen, Robert Pestman, Bart Zijlstra, Ivo A W Filot, Emiel J M Hensen
The mechanism of CO hydrogenation to CH4 at 260 °C on a cobalt catalyst is investigated using steady-state isotopic transient kinetic analysis (SSITKA) and backward and forward chemical transient kinetic analysis (CTKA). The dependence of CH x residence time is determined by12 CO/H2 →13 CO/H2 SSITKA as a function of the CO and H2 partial pressure and shows that the CH4 formation rate is mainly controlled by CH x hydrogenation rather than CO dissociation. Backward CO/H2 → H2 CTKA emphasizes the importance of H coverage on the slow CH x hydrogenation step...
December 1, 2017: ACS Catalysis
Shuai Zheng, David N Primer, Gary A Molander
A nickel/photoredox, dual-catalyzed amidation reaction between alkylsilicate reagents and alkyl/aryl isocyanates is reported. In contrast to the previously reported reductive coupling process, this protocol is characterized by mild reaction conditions and the absence of a stoichiometric reductant. A mechanistic hypothesis involving a nickel-isocyanate adduct is proposed based on literature precedent and further validation by experimental results.
November 3, 2017: ACS Catalysis
Irene Schaffner, Georg Mlynek, Nicola Flego, Dominic Pühringer, Julian Libiseller-Egger, Leighton Coates, Stefan Hofbauer, Marzia Bellei, Paul G Furtmüller, Gianantonio Battistuzzi, Giulietta Smulevich, Kristina Djinović-Carugo, Christian Obinger
The heme enzyme chlorite dismutase (Cld) catalyzes the degradation of chlorite to chloride and dioxygen. Although structure and steady-state kinetics of Clds have been elucidated, many questions remain (e.g., the mechanism of chlorite cleavage and the pH dependence of the reaction). Here, we present high-resolution X-ray crystal structures of a dimeric Cld at pH 6.5 and 8.5, its fluoride and isothiocyanate complexes and the neutron structure at pH 9.0 together with the pH dependence of the Fe(III)/Fe(II) couple, and the UV-vis and resonance Raman spectral features...
November 3, 2017: ACS Catalysis
Xiao-Jing Wei, Wout Boon, Volker Hessel, Timothy Noël
The development of synthetic methodologies which provide access to both stereoisomers of α,β-disubstituted olefins is a challenging undertaking. Herein, we describe the development of an operationally simple and stereoselective synthesis of difluoromethylated styrenes via a visible-light photocatalytic decarboxylation strategy using fac-Ir(ppy)3 as the photocatalyst. Meta- and para-substituted cinnamic acids provide the expected E-isomer. In contrast, ortho-substituted cinnamic acids yield selectively the less stable Z-product, whereas the E-isomer can be obtained via continuous-flow processing through accurate control of the reaction time...
October 6, 2017: ACS Catalysis
Spencer P Pitre, Juan C Scaiano, Tehshik P Yoon
Indole alkaloids represent an important class of molecules, with many naturally occurring derivatives possessing significant biological activity. One area that requires further development in the synthesis of indole derivatives is the Diels-Alder reaction. In this work, we expand on our previously developed heterogeneous protocol for the [4+2] cycloaddition of indoles and electron-rich dienes mediated by platinum nanoparticles supported on titanium dioxide semiconductor particles (Pt(0.2%)@TiO2) with visible-light irradiation...
October 6, 2017: ACS Catalysis
Kai Hong, Hojoon Park, Jin-Quan Yu
Palladium-catalyzed methylene β-C(sp(3))-H arylation of aliphatic ketones using a transient directing group is developed. The use of α-benzyl β-alanine directing group that forms a six-membered chelation with palladium is crucial for promoting the methylene C(sp(3))-H bond activation.
October 6, 2017: ACS Catalysis
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