1,720,966 research outputs found
Estudi de la reactivitat d’un complex organometàl·lic de Co(III) amb azides
No full textMore versatile and selective synthetic methodologies are highly desired and are one of the main reasons of chemistry research. In this context, Pd-catalyzed cross-coupling reactions have become a powerful and appreciated strategies for the functionalization of different molecules. However, direct C-H functionalization reactions could become an even more efficient and cleaner option. Unfortunately, these methodologies are mostly based on the second and third transition metals. Although, they are completely functional, these metals are very environmentally dangerous and their low abundance makes them very expensive. Therefore, the development of new methodologies based on first row transition metals such as Fe, Co, Ni and Cu is needed.
Among them, Co(III) had been unknown until six years ago, and its chemistry still remains quite non-understood. Even though, it has demonstrated its capability to act as Rh substitute in many reactions. Several contributions have been done with this metal by QBIS-CAT research group. Following their work, the preparation of two different Co(III) organometallic complex have been addressed via C-H activation, aiming to functionalize the C-Co(III) bond using several organic and inorganic azides to achieve the new C-N bond, via Co(III)-nitrene intermediates formation.
The first section of this work is based on the synthesis of the macrocyclic ligand and the Co(III) complex previously reported.
Secondly, we have explored its reactivity in front of three different organic azides. Only the product derived from the benzyl azide has been isolated and characterized. Several attempts have been performed on the formation of the corresponding product using (2-azidoethyl)benzene (Az2) and (3-azidopropil)benzene (Az3), however no product formation was achieved. The relative position of the benzyl group to the new aryl-N has been identified as a critical factor on these reactions, showing reactivity for the Az2 and Az3. This factor has allowed us to identify a possible Co(IV) complex, which could be an intermediate in these kind of reactions.
Finally, the functionalization of Co(III)-C bond to form a new C-N bond using a sodium azide as inorganic azide was also investigated. Several conditions and strategies have been performed, however in all the cases only the coordination of N3 moiety on the Co(III) complex was observe
Predictive catalysis towards the transformation of C-C bonds
No full textENG- This thesis explores the use of computational chemistry in studying olefin metathesis reactions, a key process in organometallic catalysis. Computational chemistry aims to provide predictive insights into chemical processes, but reliable predictive models have only recently emerged. In organometallic catalysis, computational techniques are still underdeveloped, often limited to post-experimental interpretation. Improving these methods is crucial for achieving accurate predictions.
The thesis begins with an overview of olefin metathesis, highlighting its advantages over other carbon-carbon bond-forming methods, such as greater atom economy and functional group tolerance. A bibliographic review traces the evolution of the reaction from its industrial inception to the development of ruthenium-based catalysts. Current challenges include the need for a deeper understanding of catalyst behavior beyond the Chauvin mechanism, issues with reaction selectivity, and the relatively low activity of ruthenium catalysts. After a general introduction to the field of ruthenium olefin metathesis, we move on to the projects carried out during this thesisCAT- Aquesta tesi explora l'ús de la química computacional en l'estudi de les reaccions de metàtesi d'olefines, un procés clau en la catàlisi organometàl·lica. La química computacional té com a objectiu proporcionar coneixements predictius sobre els processos químics, però recentment han sorgit models predictius fiables. En la catàlisi organometàl·lica, les tècniques computacionals encara estan poc desenvolupades, sovint limitades a la interpretació post-experimental. Millorar aquests mètodes és crucial per aconseguir prediccions precises.
La tesi comença amb una visió general de la metàtesi d'olefines, destacant els seus avantatges respecte a altres mètodes de formació d'enllaços carboni-carboni, com ara una major economia d'àtoms i la tolerància de grups funcionals. Una revisió bibliogràfica rastreja l'evolució de la reacció des dels seus inicis industrials fins al desenvolupament de catalitzadors a base de ruteni. Els reptes actuals inclouen la necessitat d'una comprensió més profunda del comportament del catalitzador més enllà del mecanisme de Chauvin, problemes amb la selectivitat de la reacció i l'activitat relativament baixa dels catalitzadors de ruteni. Després d'una introducció general al camp de la metàtesi de l'olefina de ruteni, passem als projectes realitzats durant aquesta tesiWe acknolewdge the following funding for the PhD thesis: M1/C3N4 for CO2RR: Next step after predicting the performance of the competitive
Hydrogen evolution reaction, 1.324 58 500 500 CSUC/PIR”, RES Access Committee at MareNostrum, main researcher: Albert Poater); RES Access Committee at MareNostrum for the first period of 2023, “Single atom
metals embedded on twodimensional g-C3N4 for Hydrogen evolution reaction:
Surface or Monolayer?”, “Improving Ziegler-Natta catalysts for polyolefin production 580,60 0 600 600 BSC/MN”, RES Access Committee at MareNostrum, main researcher: Albert Poater); Agència de Gestió d'Ajuts Universitaris i de Recerca de la Generalitat de Catalunya: 2021SGR623, 60.000€, DiMoCat – Disseny i Modelatge de Reaccions Catalitzades
per Metalls de Transició (main researcher: A. Roglans); RES Access Committee at MareNostrum for the third period of 2022, "Single atom
metals embedded on two-dimensional g-C3N4 for Hydrogen evolution reaction:
Surface or Monolayer?" (QHS-2022-3-0028), RES Access Committee at
MareNostrum (Hours with priority: 691 Kh; Disk Projects: 500 GB; Disk Scratch: 500 GB; Disk AA: 500 GB; MareNostrum4; 739.37€; S. Posada-Pérez, M. Solà, A. BrotonsRufes, G. George, main researcher: Albert Poater); RES Access Committee at MareNostrum for the third period of 2022, “Selectivity of harmful gases by azole based ionic liquids” (QHS-2022-3-0029); RES Access
Committee at MareNostrum (Hours with priority: 1382 Kh; Disk Scratch: 500 GB; Disk AA: 500 GB; UV; 1478.74€ (main researcher: Albert Poater); PROYECTOS DE I+D DE GENERACIÓN DE CONOCIMIENTO (PID2021-127423NB-I00, Predictive catalysis to switch experiments and calculations sequential order (PredictiveCat), from Ministerio de Ciencia e Innovación (09/2022-08/2025) 133.100€ (main researcher: Albert Poater); ICREA Acadèmia 2019, main researcher: Albert Poater & PROYECTOS DE I+D DE GENERACIÓN DE CONOCIMIENTO (PGC2018-097722-B-I00, “In-silico rediscovery of dual assisted mechanisms from mono metalcatalysis: towards working under mild conditions (DualCatREdiscov)”), from MICINN (2019-2021); 76.230€ (main researcher: Albert Poater)Programa de Doctorat en Químic
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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