1,721,002 research outputs found
Transition metal complexes of pyridine-containing macrocycles as catalysts for selective oxidations and CO2 valorisation reactions
No full textIron, the most abundant transition metal on earth, and its complexes are knowing an increasing interest in organic synthesis. The field of iron-catalysed oxidation reactions is of great importance not only in synthetic organic chemistry, but also in biochemistry and industrial applications. In order to design catalysts capable of performing high regio- and/or stereo-selective C-OH, C-H or C=C bond oxidations, it is important the choice of critical components of iron coordination sphere, namely the donor atoms and their geometry. In this lecture, I will provide a perspective on the catalytic applications of iron(III) and zinc(II) metal complexes of tetraaza 12-membered pyridine containing macrocyclic ligands.1 I will focus on the selective iron(III) catalysed epoxidation or dihydroxylation of alkenes by using hydrogen peroxide as terminal oxidant.2 Depending on the anion of the iron(III) metal complex employed as catalyst, a completely reversed selectivity was observed (Figure). Our approach towards the selective oxidation of alcohols by using the same catalytic system will also be covered. As for iron, catalytic applications of zinc complexes fall in the scientific community’s effort to develop more eco-friendly chemical processes. CO2 is the principal greenhouse gas, largely recognized as responsible for global warming, but it is also an abundant C1 source. Limiting CO2 emissions can only stem the problem but to solve it a circular economy based on carbon dioxide should be pursued and in this respect, research in the last decade has focussed on the design of systems able to promote the functionalisation of CO2. I will outline our approach towards the synthesis of cyclic carbonates by cycloaddition of CO2 to epoxides by using zinc(II) complexes
Controlling selectivity in alkene oxidation and CO2 cycloaddition reactions: fine tuning of Pc-L transition metal complexes
Full text linkSustainable synthesis and green chemistry have become a fundamental tool when planning a new process. In catalysis this means to correctly design since the beginning the properties of the target metal complex. The cost and the availability of the metal ion, as well as its biocompatibility must be taken into account. Despite the fact that their greater reactivity makes more difficult their use, first row transition metals are to be considered as the first choice to plan a new catalytic cycle. In this lecture, I will provide a perspective on the catalytic applications of iron(III) and zinc(II) metal complexes of tetraaza 12-membered pyridine containing macrocyclic ligands.1 I will focus on the selective iron(III) catalysed epoxidation or dihydroxylation of alkenes by using hydrogen peroxide as terminal oxidant.2 Depending on the anion of the iron(III) metal complex employed as catalyst, a completely reversed selectivity was observed (Figure). Our approach towards the selective oxidation of alcohols by using the same catalytic system will also be covered. As for iron, catalytic applications of zinc complexes fall in the scientific community’s effort to develop more eco-friendly chemical processes. CO2 is the principal greenhouse gas, largely recognized as responsible for global warming, but it is also an abundant C1 source. Limiting CO2 emissions can only stem the problem but to solve it a circular economy based on carbon dioxide should be pursued and in this respect, research in the last decade has focussed on the design of systems able to promote the functionalisation of CO2. I will outline our approach towards the synthesis of cyclic carbonates by cycloaddition of CO2 to epoxides by using zinc(II) complexes
Controlling selectivity in alkene oxidation : anion driven syn-dihydroxylation or epoxidation catalysed by [Iron(III)(Pyridine-Containing Ligand)] complexes
Full text linkThe introduction of a pyridine moiety into the skeleton of a polyazamacrocyclic ligand affects both thermodynamic properties and coordination kinetics of the resulting metal complexes.1 These features have engendered a great interest of the scientific community. Much of the efforts in the use of macrocyclic pyridine containing ligands have been devoted to the study of catalytic oxidation reactions.2 We report here the synthesis and characterisation of [Fe(III)Pc-L’s)] complexes (Pc-L = Pyridine-Containing Ligand) and their catalytic applications in alkene oxidation reactions using H2O2 as the terminal oxidant under mild conditions (Figure). Depending on the anion employed for the synthesis of the iron(III) metal complex, we observed a completely reversed selectivity. When X = OTf, a selective syn-dihydroxylation reaction was observed. On the other hand, employing X = Cl, we obtained the epoxide as the major product. It should be pointed out that under otherwise identical reaction conditions, using FeCl3·6H2O as catalyst in the absence of the ligand, no reaction was observed
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
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