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ACS Catalysis

Kingson Lin, Rebecca J Wiles, Christopher B Kelly, Geraint H M Davies, Gary A Molander
The chemoselective functionalization of polyfunctional aryl linchpins is crucial for rapid diversification. Although well-explored for Csp(2) and Csp nucleophiles, the chemoselective introduction of Csp(3) groups remains notoriously difficult and is virtually undocumented using Ni catalysts. To fill this methodological gap, a "haloselective" cross-coupling process of arenes bearing two halogens, I and Br, using ammonium alkylbis(catecholato)silicates, has been developed. Utilizing Ni/photoredox dual catalysis, Csp(3) -Csp(2) bonds can be forged selectively at the iodine-bearing carbon of bromo(iodo)arenes...
August 4, 2017: ACS Catalysis
Nicholas A Weires, Daniel D Caspi, Neil K Garg
Nickel-catalyzed coupling reactions provide exciting tools in chemical synthesis. However, most methodologies in this area require high catalyst loadings, which commonly range from 10-20 mol % nickel. Through an academic-industrial collaboration, we demonstrate that kinetic modeling can be used strategically to overcome this problem, specifically within the context of the Ni-catalyzed conversion of amides to esters. The successful application of this methodology to a multigram-scale coupling, using only 0...
July 7, 2017: ACS Catalysis
Alexey V Kubarev, Eric Breynaert, Jordi Van Loon, Arunasish Layek, Guillaume Fleury, Sambhu Radhakrishnan, Johan Martens, Maarten B J Roeffaers
Molecular-sized micropores of ZSM-5 zeolite catalysts provide spatial restrictions around catalytic sites that allow for shape-selective catalysis. However, the fact that ZSM-5 has two main pore systems with different geometries is relatively unexploited as a potential source of additional shape selectivity. Here, we use confocal laser-scanning microscopy to show that by changing the polarity of the solvent, the acid-catalyzed furfuryl alcohol oligomerization can be directed to selectively occur within either of two locations in the microporous network...
July 7, 2017: ACS Catalysis
Bryan J Jones, Zsófia Bata, Romas J Kazlauskas
Evolutionarily related hydroxynitrile lyases from rubber tree (HbHNL) and from Arabidopsis thaliana (AtHNL) follow different catalytic mechanisms with opposite enantioselectivity toward mandelonitrile. We hypothesized that the HbHNL-like mechanism evolved from an enzyme with an AtHNL-like mechanism. We created ancestor-like composite active-sites in each scaffold to elucidate how this transition may have occurred. Surprisingly, a composite active site in HbHNL maintained (S)-selectivity, while the identical set of active site residues in AtHNL maintained (R)-selectivity...
June 2, 2017: ACS Catalysis
Joris Goetze, Florian Meirer, Irina Yarulina, Jorge Gascon, Freek Kapteijn, Javier Ruiz-Martínez, Bert M Weckhuysen
The nature and evolution of the hydrocarbon pool (HP) species during the Methanol-to-Olefins (MTO) process for three small-pore zeolite catalysts, with a different framework consisting of large cages interconnected by small eight-ring windows (CHA, DDR, and LEV) was studied at reaction temperatures between 350 and 450 °C using a combination of operando UV-vis spectroscopy and online gas chromatography. It was found that small differences in cage size, shape, and pore structure of the zeolite frameworks result in the generation of different hydrocarbon pool species...
June 2, 2017: ACS Catalysis
Brandon A Vara, Niki R Patel, Gary A Molander
Alkyl xanthate esters are perhaps best known for their use in deoxygenation chemistry. However, their use in cross-coupling chemistry has not been productive, which is due, in part, to inadequate xanthate activation strategies. Herein, we report the use of O-benzyl xanthate esters, readily derived from alcohols, as radical pronucleophiles in Csp(3)-Csp(2) cross-couplings under Ni/photoredox dual catalysis. Xanthate (C-O) cleavage is found to be reliant on photogenerated (sec-butyl) radical activators to form new carbon-centered radicals primed for nickel-catalyzed cross-couplings...
June 2, 2017: ACS Catalysis
Ying Cheng, Weiyu Song, Jian Liu, Huiling Zheng, Zhen Zhao, Chunming Xu, Yuechang Wei, Emiel J M Hensen
Particulate matter and NO x emissions from diesel exhaust remains one of the most pressing environmental problems. We explore the use of hierarchically ordered mixed Fe-Ce-Zr oxides for the simultaneous capture and oxidation of soot and reduction of NO x by ammonia in a single step. The optimized material can effectively trap the model soot particles in its open macroporous structure and oxidize the soot below 400 °C while completely removing NO in the 285-420 °C range. Surface characterization and DFT calculations emphasize the defective nature of Fe-doped ceria...
June 2, 2017: ACS Catalysis
Bart Herlé, Philipp M Holstein, Antonio M Echavarren
A highly stereoselective gold(I)-catalyzed cis-vinylcyclopropanation of alkenes has been developed. Allylic gold carbenes, generated via a retro-Buchner reaction of 7-alkenyl-1,3,5-cycloheptatrienes, react with alkenes to form vinylcyclopropanes. The gold(I)-catalyzed retro-Buchner reaction of these substrates proceeds by simple heating at a temperature much lower than that required for the reaction of 7-aryl-1,3,5-cycloheptatrienes (75 °C vs 120 °C). A newly developed Julia-Kocienski reagent enables the synthesis of the required cycloheptatriene derivatives in one step from readily available aldehydes or ketones...
May 5, 2017: ACS Catalysis
Balaram Raya, Stanley Jing, T V RajanBabu
Readily accessible ( (i)(-Pr)PDI)CoCl2 [ (i)(-Pr) PDI = 2,6-bis(2,6-diisopropylphenyliminoethyl)pyridine] reacts with 2 equivalents of NaEt3BH at -78 °C in toluene to generate a catalyst that effects highly selective anti-Markovnikov hydrosilylation of the terminal double bond in 1,3- and 1,4-dienes. Primary and secondary silanes such as PhSiH3, Ph2SiH2 and PhSi(Me)H2 react with a broad spectrum of terminal dienes without affecting the configuration of the other double bond. When dienes conjugated to an aromatic ring are involved, both Markovnikov and anti-Markovnikov products are formed...
April 7, 2017: ACS Catalysis
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
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
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
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
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
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
Jacob E Dander, Neil K Garg
Amides have been widely studied for decades, but their synthetic utility has remained limited in reactions that proceed with rupture of the amide C-N bond. Using Ni catalysis, we have found that amides can now be strategically employed in several important transformations: esterification, transamidation, Suzuki-Miyaura couplings, and Negishi couplings. These methodologies provide exciting new tools to build C-heteroatom and C-C bonds using an unconventional reactant (i.e., the amide), which is ideally suited for use in multi-step synthesis...
February 3, 2017: ACS Catalysis
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
Tyler J Potter, David N Kamber, Brandon Q Mercado, Jonathan A Ellman
The transition metal catalyzed C-H bond addition to nitroalkenes has been developed. Very broad nitroalkene scope was observed for this Rh(III)-catalyzed method, including for aliphatic, aromatic and β,β-disubstituted derivatives. Additionally, various directing groups and both aromatic and alkenyl C-H bonds were effective in this transformation. Representative nitroalkane products were converted to dihydroisoquinolones and dihydropyridones in a single step and in high yield by iron mediated reduction and in situ cyclization...
January 6, 2017: 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
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