Domino C–H/N–H Allylations of Imidates by Cobalt Catalysis

Wang, Hui; Lorion, Mélanie M.; Ackermann, Lutz

doi:10.1021/acscatal.7b00756

Cited by 148 publications

(122 citation statements)

References 69 publications

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“…The catalytic properties of catalysts depend on their key parameters, such as crystallites size, structure and morphology [17]. Dispersion (and the average size) of the metallic active phase is one of the most important parameters characterizing the heterogeneous catalysts [8], which are essential for the activity, selectivity and stability of catalytic processes.…”

Section: Introductionmentioning

confidence: 99%

“…The crystallites size of metallic active phase are usually determined by hydrogen chemisorption, X-ray diffraction (XRD) or TEM (Transmission Electron Microscopy) [8,17,[20][21][22], but sometimes different results are found from various methods for the same catalyst. The differences in measurements of the crystallites size can result from methods limitation.…”

Section: Introductionmentioning

confidence: 99%

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Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

et al. 2016

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Cobalt catalysts with CeO 2 support, unpromoted and promoted with potassium were prepared by an impregnation method. Reduced catalysts were subjected to hydrogen chemisorption at different temperatures in the range of 313-453 K. Studies have shown that calculated Co crystallites size depends on the temperature of chemisorption. The average of size crystallites of the Co active phase obtained from the total and strong chemisorption data were compared with those from measurements by other techniques, TEM and XRD. The results of comparison allowed us to indicate the most suitable chemisorption temperature, different for unpromoted (383 K) and potassium-promoted (413 K) catalysts to determine the proper Co crystallites size of active phase, compatible with the crystallites size determined by the most objective method, i.e. by TEM measurements. In the case of small metal crystallites of active phase (4-5 nm) the divergence of their average size determined by hydrogen chemisorption and TEM methods and particularly by the XRD method is definitely higher than that in the case of larger crystallites (~12 nm).can significantly influence on obtained results. More than 40 years ago Bartholomew et al. [23][24][25] show that the chemisorption of hydrogen over cobalt catalysts with various supports (SiO 2 , Al 2 O 3 , C, MgO, ZSM-5, TiO 2 ) and over unsupported cobalt is activated and highly reversible. The activation was a function of the interaction of cobalt with a support or promoter. Frequently used in catalysis, potassium promoter significantly increased the adsorption activation energy for hydrogen [26]. It is also proved that some methods for determining the hydrogen uptake, i.e. flow adsorption methods such as thermal desorption and pulse methods, measure only irreversible (strong) chemisorption [23,27]. No hydrogen desorption was detected for MgOand ZSM-5-supported and low-loaded (1-3 wt.%) aluminasupported cobalt catalysts using TPD method, even though those catalysts adsorbed hydrogen when the static technique was applied [23,24]. The special case is the Co/TiO 2 system, where due to the strong metal-support interactions the stoichiometry of hydrogen chemisorption is lower than one hydrogen atom per surface cobalt atom, even in static measurements. With exception of the cobalt systems in which the strong metal-support interactions take place, the static technique was recommended for estimation of the average size of cobalt crystallites on the basis of maximal hydrogen chemisorption uptake, usually at 373 K. A good correlation with TEM measurements was found for the Co/SiO 2 , Co/γ-Al 2 O 3 and Co/C catalysts. The paper [9] also shows that the volume of chemisorbed hydrogen (including strong and weak chemisorption) on the CoRe/γ-Al 2 O 3 catalyst varies with the temperature of chemisorption, and the use of different data leads to the determination of different average size of crystallites, even though the actual crystallites size remains unchanged. They obtained the best results when the total chemisorption...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

et al. 2016

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“…Lu and coworkers reported that for the Au@Pd core shell catalysts, the catalytic activities toward solvent-free aerobic oxidation of benzyl alcohol showed a volcanolike trend as a function of Pd shell thickness. 66 Small coverage of Pd adatoms on Au@Pd had a lower activity than continuous Pd shells. The turnover frequency (TOF) and specific activity gradually increased with Pd shell thickness, and reached maximums at 27 600 and 9800 h À1 on the Au@Pd core shell catalysts with 8 cycles Pd (shell thickness $0.8 nm).…”

Section: Substrate Surface Modification With Samsmentioning

confidence: 98%

“…66 In contrast, the Pd loadings increased considerably on an Au/SiO 2 catalyst with the number of Pd ALD cycles at the same deposition condition. Evidently, the Pd grew selectively on Au nanoparticles but not on the SiO 2 support and exclusively formed Au@Pd core shell structure.…”

Section: B Ald Temperature Reduction For Selective Growthmentioning

confidence: 98%

Review Article: Catalysts design and synthesis via selective atomic layer deposition

Cao

Cai

Liu

et al. 2017

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

103

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Tailoring catalysts with atomic level control over active sites and composite structures is of great importance for advanced catalysis. This review focuses on the recent development of area selective atomic layer deposition (ALD) methods in composite catalysts design and synthesis. By adjusting and optimizing the area selective ALD processes, several catalytic structures are developed, including core shell structures, discontinuous overcoating structures, and embedded structures. The detailed synthesis strategies for these designed structures are reviewed, where the related selective approaches are highlighted and analyzed. In addition, the catalytic performance of such structures, including activity, selectivity, and stability, is discussed. Finally, a summary and outlook of area selective ALD for catalysts synthesis and applications is given.

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“…[43] Diese Art der Chemie wurde von anderen Forschern unter Verwendung verschiedener dirigierender Gruppen (DGs) zur Synthese allylischer Alkoholstrukturen weiterentwickelt (Schema 13;P rodukte 2-4). [47] Dieser Prozess beinhaltet die Bildung substituierter Dihydroisochi-noline mit lediglich CO 2 und H 2 Oa ls Nebenprodukten. Wegweisende Beiträge der Arbeitsgruppen von Ackermann und Glorius galten der Mn I -katalysierten C-H-Allylierung von Indolen mit entweder Pyridyl oder N-Pyrimidyl als dirigierende Gruppe (Schema 13;P rodukt 4).…”

Section: Allylierung Durch C-h-aktivierung Mit Vccsunclassified

Katalytische Umwandlung von funktionalisierten cyclischen organischen Carbonaten

et al. 2018

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Funktionalisierte cyclische organische Carbonate und deren heterocyclischen Derivate sind eine sehr vielseitige Gruppe heterocyclischer Substrate, deren katalytische Ringöffnung und Decarboxylierung die Entwicklung neuartiger Synthesewege zur Herstellung stereo‐ und enantioselektiver C‐N‐, C‐O‐, C‐C‐, C‐S‐ und C‐B‐Bindungen ermöglicht. Erst kürzlich wurden Übergangsmetall‐vermittelte Umwandlungen als wirksame Methode zur Synthese komplexerer Moleküle wiederentdeckt. Dieser Kurzaufsatz illustriert das Potential cyclischer Carbonate und ihrer strukturell verwandten Heterocyclen, mit einem besonderen Fokus auf dem synthetischen Nutzen und der mechanistischen Mannigfaltigkeit ihrer Umwandlungen.

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Domino C–H/N–H Allylations of Imidates by Cobalt Catalysis

Cited by 148 publications

References 69 publications

Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

Review Article: Catalysts design and synthesis via selective atomic layer deposition

Katalytische Umwandlung von funktionalisierten cyclischen organischen Carbonaten

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