Catalytic Linear Oligomerization of Ethylene to Higher α-Olefins:  Insight into the Origin of the Selective Generation of 1-Hexene Promoted by a Cationic Cyclopentadienyl-Arene Titanium Active Catalyst

2003 ◽  
Vol 22 (26) ◽  
pp. 5392-5405 ◽  
Author(s):  
Sven Tobisch ◽  
Tom Ziegler
Keyword(s):  
Active Catalyst ◽  
Linear Oligomerization ◽  
Selective Generation ◽  
Insight Into

scholarly journals Visible-Light Radical–Radical Coupling vs. Radical Addition: Disentangling a Mechanistic Knot

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 922
Author(s):  
Fernando Aguilar-Galindo ◽  
Ricardo I. Rodríguez ◽  
Leonardo Mollari ◽  
José Alemán ◽  
Sergio Díaz-Tendero
Keyword(s):  
Radical Addition ◽  
Mechanistic Study ◽  
Cascade Process ◽  
Radical Coupling ◽  
Quantum Chemistry Calculations ◽  
Heterocyclic Derivatives ◽  
Selective Generation ◽  
Imine Reduction ◽  
Process Strategy ◽  
Insight Into

A highly enantioselective protocol has been recently described as allowing the synthesis of five-membered cyclic imines harnessing the selective generation of a β-Csp3-centered radical of acyl heterocyclic derivatives and its subsequent interaction with diverse NH-ketimines. The overall transformation represents a novel cascade process strategy crafted by individual well-known steps; however, the construction of the new C-C bond highlights a crucial knot from a mechanistically perspective. We believe that the full understanding of this enigmatic step may enrich the current literature and expand latent future ideas. Therefore, a detailed mechanistic study of the protocol has been conducted. Here, we provide theoretical insight into the mechanism using quantum chemistry calculations. Two possible pathways have been investigated: (a) imine reduction followed by radical–radical coupling and (b) radical addition followed by product reduction. In addition, investigations to unveil the origin behind the enantioselectivity of the 1-pyrroline derivatives have been conducted as well.

scholarly journals Palladium(0) Nanoparticles Immobilized onto Silica/Starch Composite: Sustainable Catalyst for Hydrogenations and Suzuki Coupling

2019 ◽  
Vol 14 (3) ◽  
pp. 586
Author(s):  
Ravinderpal Kour Sodhi ◽  
Satya Paul
Keyword(s):  
Electron Microscopy ◽  
Carbonyl Compounds ◽  
Active Catalyst ◽  
Suzuki Coupling ◽  
Environmentally Benign ◽  
Reaction Conditions ◽  
Transmission Electron ◽  
Metal Acetylacetonate ◽  
Work Up ◽  
Insight Into

The present paper aims to give insight into the art in the field of the synthesis, characterization and applications of Pd(0) nanoparticles immobilized onto silica/starch composite (SS-PdNPs) for hydrogenations and Suzuki coupling. Metal(0) nanoparticles immobilized onto silica/starch composite [SS-MNPs] were prepared from different metal acetylacetonate complexes [Co(acac)2], [Cu(acac)2], [Pd(acac)2],  [Ru(acac)3], [Mn(acac)3], [Co(acac)3] by immobilizing onto silica/starch composite, followed by reduction with NaBH4. Excellent yield of the products, reusability and the facile work-up makes SS-PdNPs a unique catalyst for the reduction of nitroarenes/carbonyl compounds, a,b unsaturated carbonyl compounds and Suzuki coupling under environmentally benign reaction conditions. All the catalysts were characterized by Fourier Transform Infra Red (FTIR), Atomic Absorption Spectroscopy (AAS) analyses,  while the most active catalyst [SS-PdNPs] was further characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Copyright © 2019 BCREC Group. All rights reserved

scholarly journals Pd/TOMPP-catalyzed telomerization of 1,3-butadiene: From biomass-based substrates to new mechanistic insights

2012 ◽  
Vol 84 (8) ◽  
pp. 1713-1727 ◽  
Author(s):  
Peter J. C. Hausoul ◽  
Pieter C. A. Bruijnincx ◽  
Bert M. Weckhuysen ◽  
Robert J. M. Klein Gebbink
Keyword(s):  
Catalyst Deactivation ◽  
Active Catalyst ◽  
Synthesis Method ◽  
Catalyst System ◽  
Reaction Pathways ◽  
Mechanistic Studies ◽  
One Pot ◽  
Highly Active ◽  
System A ◽  
Insight Into

Studies aimed at synthesizing surfactants from biomass-based feedstocks using Pd-catalyzed telomerization of 1,3-butadiene resulted in the development of a highly active catalyst system. A ligand screening was performed, and Pd/tris(2-methoxyphenyl)phosphine (TOMPP) was identified as the most promising catalyst. A solvent- and base-free protocol was developed, which allows efficient and selective conversion of a wide variety of polyol substrates (e.g., glycerol, diols, carbohydrates, and sugar alcohols). In the case of hemi-acetal bearing sugars, catalyst deactivation was observed and mechanistic studies showed that extensive formation of ligand-derived phosphonium species depleted the amount of available ligand. Stoichiometric coordination reactions gave insight into the phosphine alkylation mechanism and demonstrated the reversibility of the observed reaction. A simple and efficient one-pot synthesis method was developed for the preparation of [Pd((1-3,7,8η)-(E)-octa-2,7-dien-1-yl)(PR3)]+ complexes, which are key reactive intermediates. Based on these studies, an extended telomerization mechanism is proposed, which accounts for the formation of ligand-derived phosphonium species and the reversibility of reaction pathways.

scholarly journals Comparison of carbon materials as electrodes for enzyme electrocatalysis: hydrogenase as a case study

2014 ◽  
Vol 172 ◽  
pp. 473-496 ◽  
Author(s):  
Jonathan Quinson ◽  
Ricardo Hidalgo ◽  
Philip A. Ash ◽  
Frank Dillon ◽  
Nicole Grobert ◽  
...  
Keyword(s):  
Surface Area ◽  
Carbon Materials ◽  
Active Catalyst ◽  
Redox Enzymes ◽  
E Coli ◽  
Graphitic Structure ◽  
Oxidation Current ◽  
Unified Study ◽  
Insight Into

We present a study of electrocatalysis by an enzyme adsorbed on a range of carbon materials, with different size, surface area, morphology and graphitic structure, which are either commercially available or prepared via simple, established protocols. We choose as our model enzyme the hydrogenase I from E. coli (Hyd-1), which is an active catalyst for H2 oxidation, is relatively robust and has been demonstrated in H2 fuel cells and H2-driven chemical synthesis. The carbon materials were characterised according to their surface area, surface morphology and graphitic character, and we use the electrocatalytic H2 oxidation current for Hyd-1 adsorbed on these materials to evaluate their effectiveness as enzyme electrodes. Here, we show that a variety of carbon materials are suitable for adsorbing hydrogenases in an electroactive configuration. This unified study provides insight into selection and design of carbon materials for study of redox enzymes and different applications of enzyme electrocatalysis.

Calibration problems in hydrogen luminosities

1966 ◽  
Vol 24 ◽  
pp. 322-330
Author(s):  
A. Beer
Keyword(s):  
Galactic Structure ◽  
B Stars ◽  
Insight Into

The investigations which I should like to summarize in this paper concern recent photo-electric luminosity determinations of O and B stars. Their final aim has been the derivation of new stellar distances, and some insight into certain patterns of galactic structure.

Stochasting modeling of planetary ring systems

1984 ◽  
Vol 75 ◽  
pp. 461-469 ◽  
Author(s):  
Robert W. Hart
Keyword(s):  
Maximum Entropy ◽  
Ring System ◽  
The Sun ◽  
Ultimate State ◽  
Interparticle Interactions ◽  
Ring Systems ◽  
First Order ◽  
Planetary Ring ◽  
Insight Into

ABSTRACTThis paper models maximum entropy configurations of idealized gravitational ring systems. Such configurations are of interest because systems generally evolve toward an ultimate state of maximum randomness. For simplicity, attention is confined to ultimate states for which interparticle interactions are no longer of first order importance. The planets, in their orbits about the sun, are one example of such a ring system. The extent to which the present approximation yields insight into ring systems such as Saturn's is explored briefly.

Skeletal elements of crinoid echinoderms: High-resolution structural and microanalytical results

1983 ◽  
Vol 41 ◽  
pp. 194-195
Author(s):  
D. F. Blake ◽  
L. F. Allard ◽  
D. R. Peacor
Keyword(s):  
High Resolution ◽  
Marine Invertebrates ◽  
Sea Urchins ◽  
Structural Features ◽  
Sea Stars ◽  
High Resolution Tem ◽  
Relationship Of ◽  
The Relationship ◽  
Insight Into

Echinodermata is a phylum of marine invertebrates which has been extant since Cambrian time (c.a. 500 m.y. before the present). Modern examples of echinoderms include sea urchins, sea stars, and sea lilies (crinoids). The endoskeletons of echinoderms are composed of plates or ossicles (Fig. 1) which are with few exceptions, porous, single crystals of high-magnesian calcite. Despite their single crystal nature, fracture surfaces do not exhibit the near-perfect {10.4} cleavage characteristic of inorganic calcite. This paradoxical mix of biogenic and inorganic features has prompted much recent work on echinoderm skeletal crystallography. Furthermore, fossil echinoderm hard parts comprise a volumetrically significant portion of some marine limestones sequences. The ultrastructural and microchemical characterization of modern skeletal material should lend insight into: 1). The nature of the biogenic processes involved, for example, the relationship of Mg heterogeneity to morphological and structural features in modern echinoderm material, and 2). The nature of the diagenetic changes undergone by their ancient, fossilized counterparts. In this study, high resolution TEM (HRTEM), high voltage TEM (HVTEM), and STEM microanalysis are used to characterize tha ultrastructural and microchemical composition of skeletal elements of the modern crinoid Neocrinus blakei.

Structure and function of neural networks in the retina

1988 ◽  
Vol 46 ◽  
pp. 26-27
Author(s):  
Peter Sterling
Keyword(s):  
Ganglion Cells ◽  
Three Dimensional ◽  
Structure And Function ◽  
Synaptic Connections ◽  
Visual Axis ◽  
One Dimensional ◽  
Cat Retina ◽  
Ultrathin Sections ◽  
And Function ◽  
Insight Into

The synaptic connections in cat retina that link photoreceptors to ganglion cells have been analyzed quantitatively. Our approach has been to prepare serial, ultrathin sections and photograph en montage at low magnification (˜2000X) in the electron microscope. Six series, 100-300 sections long, have been prepared over the last decade. They derive from different cats but always from the same region of retina, about one degree from the center of the visual axis. The material has been analyzed by reconstructing adjacent neurons in each array and then identifying systematically the synaptic connections between arrays. Most reconstructions were done manually by tracing the outlines of processes in successive sections onto acetate sheets aligned on a cartoonist's jig. The tracings were then digitized, stacked by computer, and printed with the hidden lines removed. The results have provided rather than the usual one-dimensional account of pathways, a three-dimensional account of circuits. From this has emerged insight into the functional architecture.

Radiation Damage Studies with the HVEM

1972 ◽  
Vol 30 ◽  
pp. 680-681
Author(s):  
J. J. Laidler ◽  
B. Mastel
Keyword(s):  
Radiation Damage ◽  
Stainless Steels ◽  
Volume Expansion ◽  
Austenitic Stainless Steels ◽  
Test Facility ◽  
Fast Breeder Reactors ◽  
Breeder Reactors ◽  
Under Construction ◽  
Development Laboratory ◽  
Insight Into

One of the major materials problems encountered in the development of fast breeder reactors for commercial power generation is the phenomenon of swelling in core structural components and fuel cladding. This volume expansion, which is due to the retention of lattice vacancies by agglomeration into large polyhedral clusters (voids), may amount to ten percent or greater at goal fluences in some austenitic stainless steels. From a design standpoint, this is an undesirable situation, and it is necessary to obtain experimental confirmation that such excessive volume expansion will not occur in materials selected for core applications in the Fast Flux Test Facility, the prototypic LMFBR now under construction at the Hanford Engineering Development Laboratory (HEDL). The HEDL JEM-1000 1 MeV electron microscope is being used to provide an insight into trends of radiation damage accumulation in stainless steels, since it is possible to produce atom displacements at an accelerated rate with 1 MeV electrons, while the specimen is under continuous observation.

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