152 research outputs found
Azaphosphatrane Organocatalysts in Confined Space: Cage Effect in CO2 Conversion
International audienceThe endohedral functionalization of a molecular cage by an azaphosphatrane unit has allowed for the creation of highly engineered catalytic cavities for efficient conversion of CO2 into cyclic carbonates. Strong structure/activity/stability correlations have been demonstrated by careful adjustment of the size, shape, and electronic properties of the hemicryptophane host
Azaphosphatrane Cations: Weak Acids, Robust Phase-transfer Catalysts
International audienceThe use of azaphosphatrane derivatives, which are the acidic counterparts of the well-known proazaphosphatrane superbases (also named Verkadeâs superbases), are found to function as phase-transfer catalysts. In four representative protocols of phase-transfer catalytic reactionsâtwo alkylations of enolates, one generation of carbene, and one oxidation of an electrophilic alkeneâazaphosphatranes act as catalysts in biphasic heterogeneous media
N-Heterocyclic Carbene Formation Induced Fluorescent and Colorimetric Sensing of Fluoride Using Perimidinium Derivatives
International audienceIn this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for Fâ in DMSO or more competitive media (DMSO containing 10â% water). In the presence of Fâ, the yellow and non-fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards Fâ was attributed to the formation of N-heterocyclic carbene deprotonated by Fâ, which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments
Encapsulation of Azaphosphatranes and Proazaphosphatranes in Confined Spaces
International audienceProazaphosphatranes (also named Verkade's superbases) and their azaphosphatrane conjugated acids have been recently been shown to be confined in either covalent or self-assembled molecular cages, or immobilized in nanopores of hybrid materials. The encapsulation of these phosphorus moieties turns out to strongly affect both their acid-base, catalytic, and recognition properties. The thermodynamics and kinetics of the proton transfer as well as the selectivity and catalytic activities of Verkade's superbases were strongly changed upon their confinement in a hemicryptophane cavity. Moreover, selfassembled cages, including azaphosphatrane moieties, were found to display remarkable anion recognition properties in water. In this Minireview, these new aspects of the chemistry of aza-and proaza-phosphatranes are presented, in order to highlight the great potential of such an approac
Introduction Ă la chimie supramolĂ©culaire - Concepts â Chimie hĂŽte-invitĂ©
International audienceDepuis la fin des annĂ©es soixante, la chimie supramolĂ©culaire est devenue unebranche multidisciplinaire de la chimie couvrant de vastes domaines d'investigation avecdes connexions fortes avec la biologie ou la science des matĂ©riaux. Cet article prĂ©senteles interactions intermolĂ©culaires non covalentes et leur mise en Ćuvre dans lephĂ©nomĂšne de reconnaissance molĂ©culaire. Loin d'ĂȘtre exhaustif, il cherche d'abord Ă illustrer au travers d'exemples reprĂ©sentatifs les principes et mĂ©thodes conduisant Ă descomplexes de type « hĂŽte-invitĂ© », mettant en exergue le dĂ©veloppement des rĂ©cepteursmolĂ©culaires synthĂ©tiques et leurs applications
SYNTHESE ET PROPRIETES COMPLEXANTES DE PHOSPHACAVITANDS FONCTIONNALISES
LYON-ENS Sciences (693872304) / SudocSudocFranceF
Hemicryptophaneâoxidovanadium(V) complexes: Lead of a new class of efficient supramolecular catalysts
International audienceHemicryptophaneâoxidovanadium(V) complexes 1 and 2 were tested in the oxidation of sulfide to sulfoxide. They were found to be efficient supramolecular catalysts in the oxidation of thioanisol with yields up to 95%. Furthermore, turnover up to 180 was obtained by decreasing the amount of catalyst to 0.5% molar. A direct comparison between hemicryptophane complexes 1 and 2 and the model complex 3, which lacks a cavity, was made. The cage structure in 1 and 2 strongly enhanced the catalytic activity, and higher yields were obtained with 1 or 2 than with the model compound 3. Kinetic constants for the oxidation of thioanisol were estimated up to sixfold higher with the hemicryptophane complexes than with the model complex 3
SynthÚse, complexation et auto-association de cavitands phosphorés fonctionnalisés
LYON-ENS Sciences (693872304) / SudocSudocFranceF
Les accidents par la aesoxsrcorticosthrone Gans le traiter:-ent de la r. aladie d'Ad dis on.
OPLADEN-RUG0
Les phosphonatocavitands pour la conception de récepteurs chiraux et de capsules supramoléculaires
Les phosphonatocavitands sont des molĂ©cules prĂ©sentant une cavitĂ© molĂ©culaire aromatique lipophile, avec un ensemble de sites de complexation durs Ă la pĂ©riphĂ©rie de la cavitĂ©, constituĂ© de groupements phosphonate. Il en rĂ©sulte une trĂšs forte affinitĂ© pour des cations mĂ©talliques et ammoniums, ainsi que les alcools qui forment des liaisons-H fortes avec les groupements phosphorylĂ©s. jusqu'alors synthĂ©tisĂ©s majoritairement sous forme tĂ©trafonctionnalisĂ©e par des groupements phosphoryles de stĂ©rĂ©ochimie i , nous avons mis en place une voie de synthĂšse permettant d'obtenir sĂ©lectivement les composĂ©s di et tri phosphorylĂ©s tout en conservant la stĂ©rĂ©ochimie i des ponts. Nous avons alors mis en Ă©vidence la formation en solution de capsules molĂ©culaires non covalentes sans ajout de substrat. L'Ă©tude des propriĂ©tĂ©s de complexation de ces capsules a conduit Ă la rĂ©alisation d'un systĂšme gyroscopique. Ces cavitands partiellement phosphorylĂ©s ont ensuite Ă©tĂ© utilisĂ©s afin d'y ajouter de nouvelles fonctionnalitĂ©s. L'ajout d'un groupement N-mĂ©thyltolylpyridinium Ă un triphosphonatocavitand a permis d'obtenir, par auto-association, un dimĂšre. Nous avons observĂ© que dans certaines conditions de solvant, ces dimĂšres pouvaient Ă©voluer en oligomĂšres de tailles supĂ©rieures? L'ajout Ă un diphosphonatocavitand d'un groupement quinoxaline ou d'un groupement phosphorylĂ© diffĂ©rent, a conduit Ă l'obtention, sous forme racĂ©mique, de cavitands chiraux par dissymĂ©trisation de la cavitĂ© aromatique. Les premiers rĂ©sultats obtenus lors de la complexation d'ammonium chiraux ont montrĂ© une Ă©nantiosĂ©lectivitĂ©, ces cavitands pourraient ĂȘtre utilisĂ©s pour la reconnaissance sĂ©lcetive d'Ă©nantiomĂšres d'ammoniums et d'alcools. Enfin, des cavitands phosphorĂ©s mixtes, possĂ©dant Ă la fois des fonctions phosphoryles et thiophosphoryles, ont Ă©tĂ© synthĂ©tisĂ©s. Leurs propriĂ©tĂ©s de complexation restent Ă Ă©tudier.The phosphonatocavitands are molecules which possess a lipophilic molecular cavity combined with several "hard" phosphorylated (P=O) binding sites that can be oriented towards the inside of the cavity. These particular cavitands show good binding properties towards alcohols, metal ions and more interestingly towards ammonium. They were hitherto synthetised in tretrafunctionnalized form by phosphorylated groups in stereochemistry i ; i made a synthesis path which allowed to obtain selectively di and trifunctionnalized compounds while maintaining the stereochemistry i of the bridges. I then demonstrated the formation of non covalent supramolecular capsules in solution, whithout any addition of substrates. The study of the capsules binding properties led to the building of a gyroscopic system. Subsequently these partially phosphorylated cavitands have been used so that new functionalities were added to them. I grafted a N-methylpicolium group to a triphosphonatocavitand to obtain, by self-assembling, a dimeric species. I noticed that the dinner could evolve in oligomeric species with a higher molecular weight in certain solvent conditions. The addition of a quinoxaline group or a different phosphoralyted group to a diphosphonatocavitand led to obtain chiral cavitands in racemic form by desymmetrization of the aromatic cavity. The first results obtained during chiral ammonium complexation experiment show an enantioselectivity, these cavitands could be used for selective recognition of ammonium or alcohol enantiomers. Eventually, mixed phosphoralyted cavitands, which possess both phosphoryl and thiophosphoryl groups, were prepared. Their binding properties have not been studied yet.LYON-ENS Sciences (693872304) / SudocSudocFranceF
- âŠ