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ACS Catalysis

Vivek Sinha, Nitish Govindarajan, Bas de Bruin, Evert Jan Meijer
Insights into the mechanism of the catalytic cycle for methanol dehydrogenation catalyzed by a highly active PNP pincer ruthenium complex in methanol solvent are presented, using DFT-based molecular dynamics with an explicit description of the solvent, as well as static DFT calculations using microsolvation models. In contrast to previous results, we find the amido moiety of the catalyst to be permanently protonated under catalytic conditions. Solvent molecules actively participate in crucial reaction steps and significantly affect the reaction barriers when compared to pure gas-phase models, which is a direct result of the enhanced solvent stabilization of methoxide anion intermediates...
August 3, 2018: ACS Catalysis
Milton R Smith, Ranjana Bisht, Chabush Haldar, Gajanan Pandey, Jonathan E Dannatt, Behnaz Ghaffari, Robert E Maleczka, Buddhadeb Chattopadhyay
High ortho selectivity for Ir-catalyzed C-H borylations (CHBs) of anilines results when B2 eg2 (eg = ethylene glycolate) is used as the borylating reagent in lieu of B2 pin2 , which is known to give isomeric mixtures with anilines lacking a blocking group at the 4-position. With this modification, high selectivities and good yields are now possible for various anilines, including those with groups at the 2- and 3-positions. Experiments indicate that ArylN(H)Beg species are generated prior to CHB and support the improved ortho selectivity relative to B2 pin2 reactions arising from smaller Beg ligands on the Ir catalyst...
July 6, 2018: ACS Catalysis
Ya-Qiong Su, Jin-Xun Liu, Ivo A W Filot, Long Zhang, Emiel J M Hensen
Methane (CH4 ) combustion is an increasingly important reaction for environmental protection, for which Pd/CeO2 has emerged as the preferred catalyst. There is a lack of understanding of the nature of the active site in these catalysts. Here, we use density functional theory to understand the role of doping of Pd in the ceria surface for generating sites highly active toward the C-H bonds in CH4 . Specifically, we demonstrate that two Pd2+ ions can substitute one Ce4+ ion, resulting in a very stable structure containing a highly coordinated unsaturated Pd cation that can strongly adsorb CH4 and dissociate the first C-H bond with a low energy barrier...
July 6, 2018: ACS Catalysis
Miguel Martínez-Calvo, José R Couceiro, Paolo Destito, Jéssica Rodríguez, Jesús Mosquera, José L Mascareñas
Discrete palladium(II) complexes featuring purposely designed phosphine ligands can promote depropargylation and deallylation reactions in cell lysates. These complexes perform better than other palladium sources, which apparently are rapidly deactivated in such hostile complex media. This good balance between reactivity and stability allows the use of these discrete phosphine palladium complexes in living mammalian cells, whereby they can mediate similar transformations. The presence of a phosphine ligand in the coordination sphere of palladium also provides for the introduction of targeting groups, such as hydrophobic phosphonium moieties, which facilitate the accumulation of the complexes in mitochondria...
July 6, 2018: ACS Catalysis
Alex J Nett, Santiago Cañellas, Yuki Higuchi, Michael T Robo, Jeanne M Kochkodan, M Taylor Haynes, Jeff W Kampf, John Montgomery
The synthesis and catalytic activity of several classes of NHC-Ni(0) pre-catalysts stabilized by electron-withdrawing alkenes are described. Variations in the structure of fumarate and acrylate ligands modulate the reactivity and stability of the NHC-Ni(0) pre-catalysts and lead to practical and versatile catalysts for a variety of transformations. The catalytic activity and efficiency of representative members of this class of catalysts have been evaluated in reductive couplings of aldehydes and alkynes and in N -arylations of aryl chlorides...
June 6, 2018: 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
Marianne Schulte, Dušan Petrović, Philipp Neudecker, Rudolf Hartmann, Jörg Pietruszka, Sabine Willbold, Dieter Willbold, Vineet Panwalkar
2-Deoxyribose-5-phosphate aldolase (DERA) catalyzes the reversible conversion of acetaldehyde and glyceraldehyde-3-phosphate into deoxyribose-5-phosphate. DERA is used as a biocatalyst for the synthesis of drugs such as statins and is a promising pharmaceutical target due to its involvement in nucleotide catabolism. Despite previous biochemical studies suggesting the catalytic importance of the C-terminal tyrosine residue found in several bacterial DERAs, the structural and functional basis of its participation in catalysis remains elusive because the electron density for the last eight to nine residues (i...
May 4, 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
Terrence E O'Brien, Steven J Bertolani, Yue Zhang, Justin B Siegel, Dean J Tantillo
Terpene synthases comprise a family of enzymes that convert acyclic oligo-isoprenyl diphosphates to terpene natural products with complex, polycyclic carbon backbones via the generation and protection of carbocation intermediates. To accommodate this chemistry, terpene synthase active sites generally are lined with alkyl and aromatic, i.e., nonpolar, sidechains. Predicting the correct, mechanistically relevant binding modes for entire terpene synthase reaction pathways remains an unsolved challenge. Here we describe a method for identifying such modes: TerDockin , a series of protocols to predict the orientation of carbon skeletons of substrates and derived carbocations relative to the bound diphosphate group in terpene synthase active sites...
April 6, 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
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