Effects of NHC-Backbone Substitution on Efficiency in Ruthenium-Based Olefin Metathesis

series of ruthenium olefin metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands with varying degrees of backbone and N-aryl substitution have been prepared. These complexes show greater resistance to decomposition through C−H activation of the N-aryl group, resulting in increased catalyst lifetimes. This work has utilized robotic technology to examine the activity and stability of each catalyst in metathesis, providing insights into the relationship between ligand architecture and enhanced efficiency. The development of this robotic methodology has also shown that, under optimized conditions, catalyst loadings as low as 25 ppm can lead to 100% conversion in the ring-closing metathesis of diethyl diallylmalonate

Etude de Diradicaux hétérocycliques

Diradicals are known to be highly unstable molecules. For example, triplet 1,3-cyclobutanediyls can only be observed in matrices at very low temperature, whilst the corresponding singlet diradicals, formally resulting from the homolytic cleavage of the bridging σ-bond, are predicted only as transition states for the inversion of the corresponding bicylo[1.0.0]butane.The first part of this manuscript is devoted to the study of diradicals based on main group elements.The first chapter is a litterature survey, which underlines the role of heteroelements in the isolation of the first localized singlet diradical. The framework of the latter is formed only of boron and phosphorus atoms.The second chapter focuses on the different isomers of this diradical, and especially its valence isomers. After an introduction to the theoretical concepts, the factors allowing the stabilization of the already known isomers are discussed, and the isolation of new isomers is described.The third chapter describes the bond-stretch isomerism. In our case, two isomers which only differ by the length of one bond are in equilibrium in solution. Variable temperature NMR experiments were performed to study the influence of the electronic factors involved in this equilibrium.This work led us to consider the preparation of an organic diradical formed of second row elements: carbon and nitrogen. This was the starting point for the development of a novel synthesis of iminium and imidazolinium salts, which will be presented in the second part.Les diradicaux sont des espèces réputées extrêmement instables. A titre d'exemple, lecyclobutanediyle qui est l'archétype de ce genre d'espèce en série carbonée n'a en effet puêtre isolé que dans des matrices à basse température.La première partie de cet exposé sera consacrée aux diradicaux formés des élémentslourds des groupes principaux.Nous montrerons dans une introduction bibliographique comment l'utilisation de ceshétéroéléments a permis l'isolation du premier diradical localisé singulet stable basé sur unsquelette formé uniquement des hétéroéléments bore et phosphore.Dans un deuxième chapitre, nous nous intéresserons aux isomères de ce diradical, enparticulier ses isomères de valence. Après un bref retour sur le concept, nous étudierons lesfacteurs qui permettent de stabiliser les différents isomères déjà connus. Nous montreronsensuite comment il a été possible d'isoler de nouveaux isomères.Dans un troisième chapitre, nous nous arrêterons sur deux isomères de valenceparticuliers et étudierons l'isomérie d'élongation (bond-stretch isomerism). Dans notre cas,deux isomères qui ne diffèrent que par la longueur d'une liaison sont en équilibre. Grâce àdes études de RMN à température variable, nous mettrons en évidence l'influence desfacteurs électroniques dans cet équilibre.Ce travail nous a amenés à nous interroger sur la possibilité de préparer un diradicalpurement organique formé uniquement d'éléments de la seconde ligne : carbone et azote.Cette réflexion nous a conduits à mettre au point une nouvelle méthode de synthèse de selsd'iminium et d'imidazolinium que nous présenterons dans une deuxième partie

Etude des diradicaux hétérocycliques

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Gründlicher Unterricht wie der Ertrag der Feld-Güter besonders durch Anlegung künstlicher Wiesen auf eine erstaunliche Weise erhöhet werden kan : aus dem Französischen übersetzt

[Jean Baptiste Miroudot]Fingerprint nach dem Ex. der ULB Sachsen-Anhalt und der FB GothaVorlageform des Erscheinungsvermerks: Frankfurt und Leipzig bey dem Commercien-Rath Fische

Mémoire sur le ray-grass ou faux-seigle <dt.>

Fingerprint nach Ex. der ULB Sachsen-Anhalt und der ThULB JenaVorlageform des Erscheinungsvermerks: Carlsruhe, druckts und verlegts Michael Macklot Markgräfl. Baden-Durl. privil. Hofbuchhändler. 1762

Abhandlung von dem Ray-Grase des Herrn Miroudot, Abts zu Jeripont Cistercienser Ordens, und Hofcapellans Ihro Majestät des Königs in Pohlen, Herzogs zu Lothringen und Bar, auch Mitgliedes der königl. Geselschaft zu Metz : Aus dem Französischen übersezt

Mit einer Vorrede Johan Jacob Reinhards Marggrävl. Baden-Durl. würkl. geheimen RathsFingerprint nach Ex. der ULB Sachsen-Anhalt und der ThULB JenaVorlageform des Erscheinungsvermerks: Carlsruhe, druckts und verlegts Michael Macklot Markgräfl. Baden-Durl. privil. Hofbuchhändler. 1762

The same but different: stable isotopes reveal two distinguishable, yet similar, neighbouring food chains in a coral reef

Stable isotope compositions were studied in particulate organic matter (POM), zooplankton and different trophic groups of teleosts to compare food chains based on plankton at two sites (lagoon and outer slope) in a New Caledonian coral reef. For each trophic compartment, d13C values were always lower in the outer slope than in the lagoon. This result may be explained by potential differences in POM composition between the two environments, suggesting that the two food chains are based on different primary sources of carbon. In contrast, d15N values did not vary between the lagoon and the outer slope, indicating that these two food chains presented similar length and trophic levels, despite being distinguishable

Linking small pelagic dietary shifts with ecosystem changes in the Gulf of Lions

Since 2008, a severe decrease in size and body condition together with a demographic truncation has been observed in the sardine (secondarily in anchovy) population of the Gulf of Lions (NW Mediterranean Sea). In parallel, sprat biomass, which was negligible before, has increased tenfold. All of these changes have strongly affected the regional fisheries. Using trophic and isotopic data from contrasting periods of low versus high growth and condition, we investigated potential changes in diet and interspecific feeding interactions through time. Evidence of resource partitioning was found between sprat and both anchovy and sardine in 2004 and 2005. Since 2010, the isotopic niches of the 3 species have tended to overlap, suggesting higher risk of competition for food resources. Moreover, the wider trophic niche of sprat indicates higher variability in individual diets. Anchovy and sardine diet varied through time, with a high proportion of large copepods or cladocerans in periods of high growth and condition (1994 and 2007, respectively) versus a dominance of small copepods in the present (2011-2012). Furthermore, an important reduction in prey diversity was also identified in the diet of both anchovy and sardine during the most recent period. Our results support the hypothesis that changes in small pelagic fish growth, size and body condition and ultimately biomass could be due to bottom-up control characterized by changes in food availability and increasing potential trophic competition