1,720,981 research outputs found
Inside Back Cover: A Simple Synthesis of Triangular All-Metal Aromatics Allowing Access to Isolobal All-Metal Heteroaromatics (Chem. Eur. J. 35/2015)
No full textThe famous dream of the ouroboros, the symbol of the circle, which inspired Kekulè’s structure of benzene leading to the concept of aromatic chemistry, can also be applied to metals. Noble metals can be assembled in molecules with an equilateral metal core. This regular geometry remains untouched even if mixing different atoms, as a result of cyclic electron delocalization, leading to all-metal aromatics and all-metal heteroaromatics. More details can be found in the Communication by G. Maestri et al. on page 12271 f
Voie d'accès aux benzophenanthridines naturelles et la chimie des composés métallo-aromatiques stables
No full textRecent developments on dual palladium/norbornene catalytic reactions led to one-pot synthesis of complexes polyheterocyclic molecules. By extension of this reaction, the coupling of aryl triflates and bromobenzylamines permitted us to synthesize natural benzophenanthridine. In parallel, a new family of triangular palladium complexes has been isolated in our research group. These 44 valence electrons complexes possessing a positive charge delocalized on the trimetallic core were the first stable compounds which presented δ-type aromaticity. After optimization of a new synthetic route, we could be able to isolate platinum analogues and also heterometallic clusters which interestingly had the same asymmetric unit than their homonuclear peers. Despite the unavoidable charge repulsion, the Lewis basic character revealed to be strong enough to bind other cationic species. Indeed, we reached to synthesize tetrahedral [M”(M₃)(Ln)]²⁺ complexes. In another side, we wondered if the stability and special properties of [Pd₃]⁺ clusters could confer to it some catalytic activities. Our studies were focused on semi-reduction reactions of alkynes. After optimization process, the catalyst [Pd₃(SMe)₃{P(C₇H)₃)₃}]⁺ showed results beyond our greatest expectations. Indeed, this cluster selectively produced thermodynamically less stable Z-alkene without traces of over-reduced compound. Total chemioselectivity towards alkynes was proved by the reaction on several molecules bearing functional groups which are sensitive to hydrogenation conditions.Depuis plusieurs décennies, la chimie du palladium a connu un véritable essor. Afin de de continuer dans cette optique, plusieurs axes de recherche ont été investigués dans le cadre de cette thèse. Grâce aux récents développements de la catalyse duale palladium/norbornène, la réaction de couplage entre des triflates aryliques et des partenaires bromobenzylamines nous a permis d’accéder à des motifs benzophénanthridines naturels. En parallèle, une nouvelle famille de complexes triangulaires de palladium a été isolée dans notre groupe. Cette espèce arborant 44 électrons de valence et une charge positive délocalisée sur son cœur tri-métallique, est la première molécule stable qui présente un caractère métallo-aromatique de type δ. Après l’optimisation d’une nouvelle voie de synthèse, nous avons pu accéder à des analogues de platine mais aussi à des composés hétéro-métalliques possédant des unités asymétriques similaires. Le caractère base de Lewis de ces complexes ont permis l’isolation de composés tétraédriques de type [M”(M₃)(Ln)]²⁺ malgré la répulsion des charges positives. Ces espèces triangulaires aromatiques ont aussi prouvé leur habileté en tant que catalyseur pour la réaction de semi-hydrogénation d’alcynes. En effet, ce complexe transforme chimiosélectivement les alcynes en alcènes de configuration Z sans présence de produit doublement réduit
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Boosting catalyst activity in cis-selective semi-reduction of internal alkynes by tailoring the assembly of all-metal aromatic tri-palladium complexes
Get PDFInternational audienceHighly symmetric [Pd3]+ clusters that present delocalized metal–metal bonds can catalyse the selective semi-reduction of internal alkynes to cis-alkenes. Studies on factors governing the formation of all-metal aromatics enabled the design of an optimised catalytic system that delivers cis-alkenes with almost complete selectivity on a gram scale with very low catalyst loadings (0.03 mol%)
Catalytic Semireduction of Internal Alkynes with All-Metal Aromatic Complexes
No full textA simple catalytic method involving all-metal aromatic frameworks as precatalysts ensures an efficient route to (Z)-alkenes. Aromatic triangular palladium clusters were used to reduce internal alkynes without any trace of the formation of alkane side products. These trinuclear complexes provide a catalytic system that parallels the activity and selectivity of their best mononuclear peers, and the catalyst likely operates through complementary mechanism
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
