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ACS Catalysis

Cheng-Liang Zhu, Cheng Wang, Qi-Xue Qin, Sam Yruegas, Caleb D Martin, Hao Xu
We report herein an iron-catalyzed azidotrifluoromethylation method for expedient vicinal trifluoromethyl primary-amine synthesis. This method is effective for a broad range of olefins and N-heterocycles, and it facilitates efficient synthesis of a wide variety of vicinal trifluoromethyl primary amines, including those that prove difficult to synthesize with existing approaches. Our preliminary mechanistic studies revealed that the catalyst-promoted azido-group transfer proceeds through a carbo-radical instead of a carbocation species...
June 1, 2018: ACS Catalysis
Mohamed Habib, Milos Trajkovic, Marco W Fraaije
Syringaresinol was synthesized in a one-pot conversion containing eugenol oxidase (EUGO) and horseradish peroxidase (HRP) using the relatively cheap 2,6-dimethoxy-4-allylphenol as a substrate. This conversion is fully coupled as the hydrogen peroxide generated from the reaction of EUGO with the substrate is utilized by the HRP to convert the formed sinapyl alcohol into syringaresinol. To improve the performance of EUGO on 2,6-dimethoxy-4-allylphenol, structure-inspired enzyme engineering was performed. This yielded the I427A EUGO mutant that is significantly more efficient with 2,6-dimethoxy-4-allylphenol...
June 1, 2018: ACS Catalysis
Shou-Jie Shen, Cheng-Liang Zhu, Deng-Fu Lu, Hao Xu
We herein report an iron-catalyzed direct diazidation method via activation of bench-stable peroxyesters promoted by nitrogen-based ligands. This method is effective for a broad range of olefins and N -heterocycles, including those that are difficult substrates for the existing olefin diamination and diazidation methods. Notably, nearly a stoichiometric amount of oxidant and TMSN3 are sufficient for high-yielding diazidation for most substrates. Preliminary mechanistic studies elucidated the similarities and differences between this method and the benziodoxole-based olefin diazidation method previously developed by us...
May 4, 2018: ACS Catalysis
Yuvraj Y Birdja, Rafaël E Vos, Tim A Wezendonk, Lin Jiang, Freek Kapteijn, Marc T M Koper
Heterogenization of molecular catalysts for CO2 electroreduction has attracted significant research activity, due to the combined advantages of homogeneous and heterogeneous catalysts. In this work, we demonstrate the strong influence of the nature of the substrate on the selectivity and reactivity of electrocatalytic CO2 reduction, as well as on the stability of the studied immobilized indium(III) protoporphyrin IX, for electrosynthesis of formic acid. Additionally, we investigate strategies to improve the CO2 reduction by tuning the chemical functionality of the substrate surface by means of electrochemical and plasma treatment and by catalyst encapsulation in polymer membranes...
May 4, 2018: ACS Catalysis
Yang Yang, Li Cheng Kao, Yuanyue Liu, Ke Sun, Hongtao Yu, Jinghua Guo, Sofia Ya Hsuan Liou, Michael R Hoffmann
TiO2 has long been recognized as a stable and reusable photocatalyst for water splitting and pollution control. However, it is an inefficient anode material in the absence of photoactivation due to its low electron conductivity. To overcome this limitation, a series of conductive TiO2 nanotube array electrodes have been developed. Even though nanotube arrays are effective for electrochemical oxidation initially, deactivation is often observed within a few hours. To overcome the problem of deactivation, we have synthesized cobalt-doped Black-TiO2 nanotube array (Co-Black NTA) electrodes that are stable for more than 200 h of continuous operation in a NaClO4 electrolyte at 10 mA cm-2 ...
May 4, 2018: ACS Catalysis
Mathias Glatz, Berthold Stöger, Daniel Himmelbauer, Luis F Veiros, Karl Kirchner
Several hydride Mn(I) and Re(I) PNP pincer complexes were applied as catalysts for the homogeneous chemoselective hydrogenation of aldehydes. Among these, [Mn(PNP- i Pr)(CO)2 (H)] was found to be one of the most efficient base metal catalysts for this process and represents a rare example which permits the selective hydrogenation of aldehydes in the presence of ketones and other reducible functionalities, such as C=C double bonds, esters, or nitriles. The reaction proceeds at room temperature under base-free conditions with catalyst loadings between 0...
May 4, 2018: ACS Catalysis
Meirong Jia, Terrence E O'Brien, Yue Zhang, Justin B Siegel, Dean J Tantillo, Reuben J Peters
Sclareol synthase from Salvia sclarea (SsSS) naturally acts on 8α-hydroxy-copalyl diphosphate ( 1 ), stereoselectively adding water to produce (13 R )-sclareol ( 2a ), and similarly yields hydroxylated products with manifold other such bicyclic diterpene precursors. Here a key residue for this addition of water was identified. Strikingly, substitution with glutamine switches stereochemical outcome with 1 , leading to selective production of (13 S )-sclareol ( 2b ). Moreover, changes to the stereospecificity of water addition with the structurally closely-related substrate copalyl diphosphate ( 4 ) could be accomplished with alternative substitutions...
April 6, 2018: ACS Catalysis
Sandra S Nurttila, Pim R Linnebank, Tetiana Krachko, Joost N H Reek
The hydroformylation reaction is one of the most intensively explored reactions in the field of homogeneous transition metal catalysis, and many industrial applications are known. However, this atom economical reaction has not been used to its full potential, as many selectivity issues have not been solved. Traditionally, the selectivity is controlled by the ligand that is coordinated to the active metal center. Recently, supramolecular strategies have been demonstrated to provide powerful complementary tools to control activity and selectivity in hydroformylation reactions...
April 6, 2018: ACS Catalysis
Marta C Figueiredo, Vinh Trieu, Stefanie Eiden, Jan Heijl, Marc T M Koper
In this work, we study the synthesis of diphenyl carbonate (DPC) from phenol and CO on gold electrodes studied by means of in situ Fourier transform infrared spectroscopy (FTIR). The results show that, on gold electrodes, the formation of DPC is observed at potentials as low as 0.4 V vs Ag/AgCl, together with the formation of dimethyl carbonate (DMC) from the carbonylation of methanol that was used as a solvent. The spectroelectrochemical results also suggest that the formation of DPC occurs via the replacement of the methoxy groups from DMC with phenoxy groups from phenol and not directly by the carbonylation of phenol...
April 6, 2018: ACS Catalysis
Andrew Currin, Mark S Dunstan, Linus O Johannissen, Katherine A Hollywood, Maria Vinaixa, Adrian J Jervis, Neil Swainston, Nicholas J W Rattray, John M Gardiner, Douglas B Kell, Eriko Takano, Helen S Toogood, Nigel S Scrutton
The realization of a synthetic biology approach to microbial (1 R ,2 S ,5 R )-( - )-menthol ( 1 ) production relies on the identification of a gene encoding an isopulegone isomerase (IPGI), the only enzyme in the Mentha piperita biosynthetic pathway as yet unidentified. We demonstrate that Δ5-3-ketosteroid isomerase (KSI) from Pseudomonas putida can act as an IPGI, producing ( R )-(+)-pulegone (( R )- 2 ) from (+)- cis -isopulegone ( 3 ). Using a robotics-driven semirational design strategy, we identified a key KSI variant encoding four active site mutations, which confer a 4...
March 2, 2018: 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
Wei Chen, Tobias F Kimpel, Yuanjun Song, Fu-Kuo Chiang, Bart Zijlstra, Robert Pestman, Peng Wang, Emiel J M Hensen
One of the well-known observations in the Fischer-Tropsch (FT) reaction is that the CH4 selectivity for cobalt catalysts is always higher than the value expected on the basis of the Anderson-Schulz-Flory (ASF) distribution. Depositing graphitic carbon on a cobalt catalyst strongly suppresses this non-ASF CH4 , while the formation of higher hydrocarbons is much less affected. Carbon was laid down on the cobalt catalyst via the Boudouard reaction. We provide evidence that the amorphous carbon does not influence the FT reaction, as it can be easily hydrogenated under reaction conditions...
February 2, 2018: ACS Catalysis
Zixi Zhu, Xinghan Li, Sicong Chen, Peng-Hao Chen, Brent A Billett, Zhongxing Huang, Guangbin Dong
A Co(0)-catalyzed intramolecular alkyne/benzocyclobutenone coupling through C-C cleavage of benzocyclobutenones is described. Co2 (CO)8 /P[3, 5-(CF3 )2 C6 H3 ]3 was discovered to be an effective metal/ligand combination, which exhibits complementary catalytic activity to the previously established rhodium catalyst. In particular, the C8-substituted substrates failed in the Rh system, but succeeded with the Co catalysis. Experimental and computational studies show that the initially formed tetrahedral dicobalt-alkyne complex undergoes C1-C2 activation via oxidative addition with Co(0), followed by migratory insertion and reductive elimination to give the β -naphthol products...
February 2, 2018: ACS Catalysis
Timothy B Boit, Nicholas A Weires, Junyong Kim, Neil K Garg
We report the Ni-catalyzed Suzuki-Miyaura coupling of aliphatic amide derivatives. Prior studies have shown that aliphatic amide derivatives can undergo Ni-catalyzed carbon-heteroatom bond formation but that Ni-mediated C-C bond formation using aliphatic amide derivatives has remained difficult. The coupling disclosed herein is tolerant of considerable variation with respect to both the amide-based substrate and the boronate coupling partner and proceeds in the presence of heterocycles and epimerizable stereocenters...
February 2, 2018: ACS Catalysis
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