88 research outputs found
Substrate-Selective C-H Functionalization for the Preparation of Organosulfur Compounds from Crude Oil-Derived Components
The
direct utilization of a natural feedstock in organic synthesis
is an utmost challenge because the selective production of one product
from a mixture of starting materials requires unprecedented substrate
selectivity. In the present study, a simple and convenient procedure
is evaluated for the substrate-selective alkenylation of a single
component in a mixture of organosulfur compounds. Pd-catalyzed alkenylation
of two-, three-, four-, and five-component mixtures of crude oil-derived
sulfur species led to the exclusive CâH functionalization of
only one compound. The observed remarkable substrate selectivity opens
new opportunities for sustainable organic synthesis
Intermolecular Photocatalytic Chemoâ, Stereoâ and Regioselective ThiolâYneâEne Coupling Reaction
The first example of an intermolecular thiolâyneâene coupling reaction is reported for the one-pot construction of CâS and CâC bonds. Thiolâyneâene coupling opens a new dimension in building molecular complexity to access densely functionalized products. The employment of Eosinâ
Y/DBU/MeOH photocatalytic system suppresses hydrogen atom transfer (HAT) and associative reductant upconversion (via CâS three-electron Ï-bond formation). Investigation of the reaction mechanism by combining online ESI-UHRMS, EPR spectroscopy, isotope labeling, determination of quantum yield, cyclic voltammetry, SternâVolmer measurements and computational modeling revealed a unique photoredox cycle with four radical-involving stages. As a result, previously unavailable products of the thiolâyneâene reaction were obtained in good yields with high selectivity. They can serve as stable precursors for synthesizing synthetically demanding activated 1,3-dienes
Plausible role of nanoparticle contamination in the synthesis and properties of organic electronic materials
Traceless transition metal catalysis (Pd, Ni, Cu,
etc.) is very difficult to achieve. Metal contamination in
the synthesized products is unavoidable and the most important
questions are: How to control metal impurities?
What amount of metal impurities can be tolerated? What is
the influence of metal impurities? In this brief review, the
plausible origins of nanoparticle contamination are discussed
in the framework of catalytic synthesis of organic
electronic materials. Key factors responsible for increasing
the probability of contamination are considered from the
point of view of catalytic reaction mechanisms. The purity
of the catalyst may greatly affect the molecular weight of
a polymer, reaction yield, selectivity and several other parameters.
Metal contamination in the final polymeric products
may induce some changes in the electric conductivity,
charge transport properties, photovoltaic performance
and other important parameters
OrganicâInorganic Hybrid Nanomaterials
The paramount progress in the field of organic–inorganic hybrid nanomaterials was stimulated by numerous applications in chemistry, physics, life sciences, medicine, and technology. Currently, in the field of hybrid materials, researchers may choose either to mimic complex natural materials or to compete with nature by constructing new artificial materials. The deep mechanistic understanding and structural insight achieved in recent years will guide a new wave in the design of hybrid materials at the atomic and molecular levels
Modeling Key Pathways Proposed for the Formation and Evolution of âCocktailâ-Type Systems in Pd-Catalyzed Reactions Involving ArX Reagents
Reversible leaching of palladium nanoparticles occurs in a variety of catalytic reactions including cross-couplings, amination, the Heck reaction, etc. It is complemented by capturing of soluble palladium species on the surface of nanoparticles and de novo formation of nanoparticles from Pd precatalysts. We report here a detailed computational study of leaching/capture pathways and analysis of related stabilization energies. We demonstrate the validity of the "cocktail-of-species" model for the description of Pd catalysts in ArX oxidative addition-dependent reactions. Three pools of Pd species were evaluated, including (1) the pool of catalytically active Pd nanoparticles with a high concentration of surface defects, (2) the pool of monomeric and oligomeric L[ArPdX]<sub>n</sub>L species, and (3) the pool of irreversibly deactivated Pd. Stabilization by ArX oxidative addition, coordination of base species, and binding of X<sup>â</sup> anions (derived from salt additives) were found to be crucial for "cocktail"-type systems, and the corresponding reaction energies were estimated. An inherent process of ArX homocoupling, leading to the formation of Pd halides that require re-activation, was considered as well. The pool of irreversibly deactivated Pd comprises nanoparticles with (1 1 1) and (1 0 0) facets and Pd in the bulk form. The study is based on DFT modeling and specifies the role of Pd nanoparticles in (quasi )homogeneous coupling reactions involving ArX reagents.ChemE/Inorganic Systems Engineerin
Recent advances in applications of vinyl ether monomers for precise synthesis of custom-tailored polymers
International audienceThis review highlights recent progress in the synthesis and application of vinyl ethers (VEs) as monomers for modern homo- and co-polymerization processes. VEs can be easily prepared using a number of traditional synthetic protocols including a more sustainable and straightforward manner by reacting gaseous acetylene or calcium carbide with alcohols. The remarkably tunable chemistry of VEs allows designing and obtaining polymers with well-defined structures and controllable properties. Both VE homopolymerization and copolymerization systems are considered, and specific emphasis is given to the novel initiating systems and to the methods of stereocontrol
Computational Study of a Model System of Enzyme-Mediated [4+2] Cycloaddition Reaction
<div><p>A possible mechanistic pathway related to an enzyme-catalyzed [4+2] cycloaddition reac-tion was studied by theoretical calculations at density functional (B3LYP, O3LYP, M062X) and semiempirical levels (PM6-DH2, PM6) performed on a model system. The calculations were carried out for the key [4+2] cycloaddition step considering enzyme-catalyzed biosynthesis of Spinosyn A in a model reaction, where a reliable example of a biological Diels-Alder reaction was reported experimentally. In the present study it was demonstrated that the [4+2] cycloaddition reaction may benefit from moving along the energetically balanced reaction coordinate, which enabled the catalytic rate enhancement of the [4+2] cycloaddition pathway involving a single transition state. Modeling of such a system with coordination of three amino acids indicated a reliable decrease of activation energy by ~18.0 kcal/mol as compared to a non-catalytic transformation.</p></div
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