1,720,958 research outputs found
Synthesis of the new RU(II) complexes containing DMSO and N-dondor ligands as catalysts for nitrile hydration
No full textThanks to the experience of the research group in the synthesis of ruthenium complexes with dmso and N-donor ligands and their application in catalysis, in this work we have developed new ruthenium complexes using N-donor ligands that have been subsequently evaluated as catalysts for the nitrile hydrolysis reaction.
First, two new ruthenium complexes ([2] and [3]) with one or two pzph-OH ligand have been synthesized, together with a ruthenium complex ([4]) with the terpyridine ligand, in all cases with dmso and Cl ligands. The complexes have been characterized using different spectroscopic and electrochemical techniques.
With respect to structural characterization, the formation of a single isomer for [2] and [3] complexes has been shown. It should be noted that in the case of complex [2] the crystal structure has been obtained that has been solved by X-ray diffraction analysis. The characterization of complex [4] has also been carried out for one of the isomers that has been obtained in pure form. It should be mentioned that in this case, it is observed the formation of a second isomer for longer reaction times.
UV-Vis spectra have been performed in methanol for complexes [2] and [3] and dichlormetane for the [4] complex, where the presence of MLCT and intraligand π-π * bands it evidenced in the three cases, and the corresponding extinction coefficients could be calculated. For complexes [2] and [3] a wavelength shift along the time is observed, possibly due to exchange of one ligand by methanol.
Subsequently, the electrochemical properties of the three complexes have been studied by cyclic voltammetry (CV). For complex [2], a reversible wave corresponding to the Ru(III/II) redox pair has been observed. On the contrary, complex [3] exhibits an irreversible wave due to a Ru-dmso bond isomerization process. To demonstrate this fact, an electrochemical study of the two mentioned complexes has been carried out, which has cofirmed that the isomerization process is shown only by complex [3]. Moreover, we also registered the CVs for complex [4], which exhibits a reversible wave; a second wave was observed for longer reaction times evidencing once again the formation of a second isomer.
Finally, the catalytic activity in the hydrolysis of nitriles of the complex [3] and [4] has been evaluated using two different substrates, obtaining moderate to high conversions and excellent selectivity for the amide produc
Chelation-assisted metal-catalyzed functionalization of strong Csp2-H/Heteroatom bonds: trapping intermediate species and unveiling mechanistic details
Full text linkThe development of new methodologies for the construction of complex molecules is one of the principal objectives in synthetic organic chemistry. Although huge advances have been made on cross-coupling reactions, there is continuous research on direct C-H functionalization of non-prefunctionalized substrates or more challenging substrates bearing strong C-F or C-OR groups. The first part of this PhD dissertation describes the advances reported in the literature in cobalt cross-coupling catalysis demonstrating the capability of cobalt to catalyze these transformations. Then, C–H amination reactions using a high valent cobalt system and azides are studied in order to elucidate the involvement of a Co-nitrene intermediate species. To do so, the reactivity of well-defined aryl–Co(III) organometallic complex towards inorganic and organic azides is tested. On the other hand, this thesis deals with the use of non-cyclic model platforms bearing direct groups to study Ni-catalyzed C–F and C–OMe functionalization. The synthesis of isoquinolones and aromatic homologation products using alkynes as coupling partner is explored. Thanks to coordination properties of 8-aminoquinoline bidentate directing group, a key double alkyne inserted intermediate species is isolated. Finally, the ability of 8-aminoquinoline directing group was also explored in the study of Ag-catalyzed aryl-halide cross-coupling transformations using several nucleophiles, where the two-electron redox Ag(I)/Ag(III) reactivity is operatingEl desenvolupament de noves metodologies per la construcció de compostos complexes és un dels principals objectius de la química orgànica sintètica. Tot i que importants avenços s’han fet en aquest àmbit, hi ha una investigació contínua utilitzant substrats no prefuncionalitzats o més desafiants que presenten grups C–F o C–OR. En la primera part d’aquesta tesi doctoral, es descriu el progrés fet en el camp de reaccions d’acoblament creuat catalitzades per cobalt, demostrant la capacitat del cobalt per catalitzar aquestes transformacions. Posteriorment, aquesta tesi es focalitza en esbrinar el mecanisme que opera en els processos d’aminació a través de l’activació d’enllaços C–H emprant espècies de cobalt en alt estat d’oxidació. Per tal elucidar el mecanisme, s’estudia la reactivitat d’espècies organometàl·liques de aril–Co(III) amb azides inorgàniques i orgàniques. Per altra banda, s’explora la funcionalització selectiva d’enllaços C–F i C–OMe catalitzada per níquel utilitzant plataformes no cícliques que contenen grups directors. S’estudia la síntesi de isoquinolones i productes d’homologació aromàtica utilitzant alquins. Les propietats coordinatives de la 8-aminoquinolina permeten l’estabilització d’espècies claus per la síntesi de productes d’homologació aromàtics. Finalment, s’explora l’habilitat de la 8-aminoquinolina com a grup director per tal d’estudiar reaccions d’acoblament creuat catalitzades per salts de plata utilitzant diferents nucleòfils, on s’evidencia la implicació de cicles redox Ag(I)/Ag(III)Programa de Doctorat en Químic
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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