d0Re-Based Olefin Metathesis Catalysts, Re(⋮CR)(CHR)(X)(Y):  The Key Role of X and Y Ligands for Efficient Active Sites

2005 ◽  
Vol 127 (40) ◽  
pp. 14015-14025 ◽  
Author(s):  
Xavier Solans-Monfort ◽  
Eric Clot ◽  
Christophe Copéret ◽  
Odile Eisenstein
Keyword(s):  
Olefin Metathesis ◽  
Active Sites ◽  
Metathesis Catalysts

scholarly journals Well-defined silica supported bipodal molybdenum oxo alkyl complexes: a model of the active sites of industrial olefin metathesis catalysts

2017 ◽  
Vol 53 (82) ◽  
pp. 11338-11341 ◽  
Author(s):  
Nicolas Merle ◽  
Frédéric Le Quéméner ◽  
Samir Barman ◽  
Manoja K. Samantaray ◽  
Kai C. Szeto ◽  
...  
Keyword(s):  
Olefin Metathesis ◽  
Active Sites ◽  
Alkyl Complexes ◽  
Metathesis Catalysts

A novel well-defined supported bipodal molybdenum alkyl oxo species for “modelling MoO3/SiO2 industrial catalysts” that efficiently catalyzes olefin metathesis has been unveiled.

scholarly journals MOF Encapsulation of Ru Olefin Metathesis Catalysts to Block Catalyst Decomposition

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 687
Author(s):  
Gerard Pareras ◽  
Davide Tiana ◽  
Albert Poater
Keyword(s):  
Olefin Metathesis ◽  
Density Functional ◽  
Metal Organic Framework ◽  
Functional Theory ◽  
Ammonium N ◽  
Metathesis Catalyst ◽  
Metal Organic ◽  
Non Covalent Interactions ◽  
Metathesis Catalysts

In the present work, a catalyst variation of the second-generation Hoveyda–Grubbs catalyst, particularly the ammonium-tagged Ru-alkylidene metathesis catalyst AquaMetTM, is under study, not simply to increase the efficiency in olefin metathesis but also the solubility in polar solvents. Moreover, this ionic catalyst was combined with the metal organic framework (MOF) (Cr)MIL-101-SO3−(Na·15-crown-5)+. We started from the experimental results by Grela et al., who increased the performance when the ruthenium catalyst was confined inside the cavities of the MOF, achieving non-covalent interactions between both moieties. Here, using density functional theory (DFT) calculations, the role of the ammonium N-heterocyclic carbene (NHC) tagged and the confinement effects are checked. The kinetics are used to compare reaction profiles, whereas SambVca steric maps and NCI plots are used to characterize the role of the MOF structurally and electronically.

scholarly journals Metathesis access to monocyclic iminocyclitol-based therapeutic agents

2011 ◽  
Vol 7 ◽  
pp. 699-716 ◽  
Author(s):  
Ileana Dragutan ◽  
Valerian Dragutan ◽  
Carmen Mitan ◽  
Hermanus CM Vosloo ◽  
Lionel Delaude ◽  
...  
Keyword(s):  
Olefin Metathesis ◽  
Metabolic Disorders ◽  
Therapeutic Agents ◽  
Comparative Performance ◽  
Common Diseases ◽  
Metathesis Reactions ◽  
Recent Developments ◽  
Metathesis Catalysts ◽  
Steric Control

By focusing on recent developments on natural and non-natural azasugars (iminocyclitols), this review bolsters the case for the role of olefin metathesis reactions (RCM, CM) as key transformations in the multistep syntheses of pyrrolidine-, piperidine- and azepane-based iminocyclitols, as important therapeutic agents against a range of common diseases and as tools for studying metabolic disorders. Considerable improvements brought about by introduction of one or more metathesis steps are outlined, with emphasis on the exquisite steric control and atom-economical outcome of the overall process. The comparative performance of several established metathesis catalysts is also highlighted.

scholarly journals Olefin-surface interactions modulate the activity of silica-supported Mo-based olefin metathesis catalysts

2021 ◽  
Author(s):  
Zachariah Berkson ◽  
Moritz Bernhardt ◽  
Simon Schlapansky ◽  
Mathis Benedikter ◽  
Michael Buchmeiser ◽  
...  
Keyword(s):  
Chain Length ◽  
Olefin Metathesis ◽  
Active Sites ◽  
Reaction Rates ◽  
Catalytic Performance ◽  
Strong Activity ◽  
Oh Groups ◽  
Highly Active ◽  
Metathesis Catalysts ◽  
Internal Olefin

Molecularly defined and classical heterogenous Mo-based metathesis catalysts are shown to display distinct and unexpected reactivity patterns for the metathesis of long-chain α-olefins at low temperatures (< 100 °C). Namely, catalysts based on supported Mo oxo species, whether prepared via wet impregnation or surface organometallic chemistry (SOMC), exhibit strong activity dependencies on the α-olefin chain length, with slower reaction rates for longer substrate chain lengths. In contrast, molecular and supported Mo alkylidenes are highly active and do not display such dramatic dependence on chain length. 2D solid-state NMR analyses of post-metathesis catalysts, complemented by molecular dynamics calculations, evidence that the activity decrease observed for supported Mo oxo catalysts relates to the strong adsorption of internal olefin metathesis products due to interactions with surface Si-OH groups. Overall, this study shows that in addition to the nature and the number of active sites, the metathesis rates and overall catalytic performance depend on product desorption, even in the liquid phase with non-polar substrates. This study further highlights the need to consider adsorption when designing catalysts and the unique activity of molecularly defined supported metathesis catalysts prepared via SOMC.

Role of the Structure and Electronic Properties of Fe2O3-MoO3 Catalyst on the Dehydration of Isopropyl Alcohol

1993 ◽  
Vol 58 (7) ◽  
pp. 1591-1599 ◽  
Author(s):  
Abd El-Aziz A. Said
Keyword(s):  
Active Sites ◽  
Isopropyl Alcohol ◽  
Oxide Catalyst ◽  
Flow System ◽  
Charge Carriers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Catalyst Composition ◽  
Surface Active

Molybdenum oxide catalyst doped or mixed with (1 - 50) mole % Fe3+ ions were prepared. The structure of the original samples and the samples calcined at 400 °C were characterized using DTA, X-ray diffraction and IR spectra. Measurements of the electrical conductivity of calcined samples with and without isopropyl alcohol revealed that the conductance increases on increasing the content of Fe3+ ions up to 50 mole %. The activation energies of charge carriers were determined in presence and absence of the alcohol. The catalytic dehydration of isopropyl alcohol was carried out at 250 °C using a flow system. The results obtained showed that the doped or mixed catalysts are active and selective towards propene formation. However, the catalyst containing 40 mole % Fe3+ ions exhibited the highest activity and selectivity. Correlations were attempted to the catalyst composition with their electronic and catalytic properties. Probable mechanism for the dehydration process is proposed in terms of surface active sites.

Geometric Factor in Skeletal Reactions of 2-Methylpentane on Stepped Surfaces of Platinum Catalyst

1992 ◽  
Vol 57 (10) ◽  
pp. 2012-2020
Author(s):  
Vladimír Hejtmánek
Keyword(s):  
Active Sites ◽  
Platinum Catalyst ◽  
Point Of View ◽  
Geometric Factor ◽  
Published Data ◽  
Stepped Surfaces ◽  
Geometric Conditions ◽  
Surface Intermediates ◽  
Isomerization Mechanism

The role of geometric factor in the course of skeletal reactions (isomerization, hydrogenolysis) of 2-methylpentane on stepped (119), (557) and reconstructed R(557) surfaces of single crystals of platinum was evaluated with computer designed models. These calculations were compared with reported experimental data. It was found by analysis of geometric conditions that there are accessible active ensembles on double step of the reconstructed R(557) surface. In addition, these active sites are unsaturated in their coordination sphere and thus catalytically effective. This finding is consistent with published data, confirming higher catalytic activity of this surface. The various pathways of Bond Shift isomerization mechanism of 2-methylpentane from the point of view of steric demands of surface intermediates on differently located ensembles are discussed, too.

scholarly journals The RelA hydrolase domain acts as a molecular switch for (p)ppGpp synthesis

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Anurag Kumar Sinha ◽  
Kristoffer Skovbo Winther
Keyword(s):  
Active Sites ◽  
Molecular Switch ◽  
Cell Physiology ◽  
Synthetase Activity ◽  
Wild Type ◽  
Functional Studies ◽  
Loop Region ◽  
A Site ◽  
Trna Binding

AbstractBacteria synthesize guanosine tetra- and penta phosphate (commonly referred to as (p)ppGpp) in response to environmental stresses. (p)ppGpp reprograms cell physiology and is essential for stress survival, virulence and antibiotic tolerance. Proteins of the RSH superfamily (RelA/SpoT Homologues) are ubiquitously distributed and hydrolyze or synthesize (p)ppGpp. Structural studies have suggested that the shift between hydrolysis and synthesis is governed by conformational antagonism between the two active sites in RSHs. RelA proteins of γ-proteobacteria exclusively synthesize (p)ppGpp and encode an inactive pseudo-hydrolase domain. Escherichia coli RelA synthesizes (p)ppGpp in response to amino acid starvation with cognate uncharged tRNA at the ribosomal A-site, however, mechanistic details to the regulation of the enzymatic activity remain elusive. Here, we show a role of the enzymatically inactive hydrolase domain in modulating the activity of the synthetase domain of RelA. Using mutagenesis screening and functional studies, we identify a loop region (residues 114–130) in the hydrolase domain, which controls the synthetase activity. We show that a synthetase-inactive loop mutant of RelA is not affected for tRNA binding, but binds the ribosome less efficiently than wild type RelA. Our data support the model that the hydrolase domain acts as a molecular switch to regulate the synthetase activity.

scholarly journals Green Nanocoatings Based on the Deposition of Zirconium Oxide: The Role of the Substrate

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1043
Author(s):  
Vitor Bonamigo Moreira ◽  
Anna Puiggalí-Jou ◽  
Emilio Jiménez-Piqué ◽  
Carlos Alemán ◽  
Alvaro Meneguzzi ◽  
...  
Keyword(s):  
Zirconium Oxide ◽  
Active Sites ◽  
Modified Electrodes ◽  
Chemical Conversion ◽  
Ceramic Materials ◽  
Point Of View ◽  
Oxide Coatings ◽  
Alloying Element ◽  
Substrate Nature

Herein, the influence of the substrate in the formation of zirconium oxide monolayer, from an aqueous hexafluorozirconic acid solution, by chemical conversion and by electro-assisted deposition, has been approached. The nanoscale dimensions of the ZrO2 film is affected by the substrate nature and roughness. This study evidenced that the mechanism of Zr-EAD is dependent on the potential applied and on the substrate composition, whereas conversion coating is uniquely dependent on the adsorption reaction time. The zirconium oxide based nanofilms were more homogenous in AA2024 substrates if compared to pure Al grade (AA1100). It was justified by the high content of Cu alloying element present in the grain boundaries of the latter. Such intermetallic active sites favor the obtaining of ZrO2 films, as demonstrated by XPS and AFM results. From a mechanistic point of view, the electrochemical reactions take place simultaneously with the conventional chemical conversion process driven by ions diffusion. Such findings will bring new perspectives for the generation of controlled oxide coatings in modified electrodes used, as for example, in the construction of battery cells; in automotive and in aerospace industries, to replace micrometric layers of zinc phosphate by light-weight zirconium oxide nanometric ones. This study is particularly addressed for the reduction of industrial waste by applying green bath solutions without the need of auxiliary compounds and using lightweight ceramic materials.

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