1,720,957 research outputs found
The intriguing methoxycarbonylation of trimethylsilylacetylene in the presence of Drent's catalytic system
Get PDFThe alkoxycarbonylation of trimethylsilylacetylene has been studied in order to develop an atom economic sustainable synthesis of 2-(trimethylsilyl)acrylates, a family of valuable intermediates. Pd(OAc)2 in combination with CH3SO3H and diphenyl-(pyridin-2-yl)phosphine or diphenyl-(6-methyl-pyridin-2-yl)phosphine is an active catalyst for the reaction affording mixtures of the sought 2-(trimethylsilyl)acrylate and the isomeric 3-(trimethylsilyl)acrylate. The phosphine ligand has a dramatic effect on the reaction. When employing diphenyl-(pyridin-2-yl)phosphine, it is necessary to carry out the reaction at 80°C in order to observe a modest catalytic activity, and the product is an almost equimolecular mixture of the two isomeric esters. On the contrary, when employing diphenyl-(6-methyl-pyridin-2-yl)phosphine, the reaction proceeds under much milder conditions affording with high rate (turnover frequency [TOF] up to 1200 h−1) and selectivity (>95%) of the sought 2-(trimethylsilyl)acrylate. The reaction conditions have been optimized, and the effects of phosphine/palladium, acid/palladium, reaction time, temperature, and CO pressure have been investigated. © 2021 The Authors. Applied Organometallic Chemistry published by John Wiley & Sons Ltd
Synthesis of a water‐soluble thio‐triazole ligand for biphase rhodium catalyzed hydroformylation of styrene
No full textAn environmentally safe water-soluble new ligand (2-(1-(2-(methylthio)ethyl)-1H-1,2,3-triazol-4-yl)ethanol) (ligand 1) has
been synthesized by the click reaction between (2-azidoethyl)(methyl)sulfane and 3-butyn-1-ol. The structure of the novel
ligand was confirmed by NMR spectroscopy. In situ combination of ligand 1 with [Rh(COD)Cl]2 and [Rh (CO)2(acac)] (Rh:
ligand = 1: 4) successfully employed for the biphasic catalytic hydroformylation of styrene. The formation of branched
2-phenylpropanol was confirmed by gas chromatogphic analysis. The recycled catalytic aqueous phase can be used
three runs with remarkable catalytic efficiency
The alkoxycarbonylation of protected propargyl alcohols
No full textPalladium-catalyzed alkoxycarbonylation of the C≡C triple bond of propargyl alcohol is a sustainable synthetic
approach to 2-(hydroxymethyl)acrylates, a family of valuable intermediates. The developed synthetic protocol
includes protection of the alcoholic function of the alkyne before its carbonylation in the presence of Drent’s
catalytic system. Protection step effectively extends the catalyst life hence enhancing the practical applicability
of the reaction. The effectiveness of some different protecting groups (benzyl, acetyl and trimethylsilyl) has been
assessed and the influence of the reaction parameters investigated.Palladium-catalyzed alkoxycarbonylation of the C≡C triple bond of propargyl alcohol is a sustainable synthetic approach to 2-(hydroxymethyl)acrylates, a family of valuable intermediates. The developed synthetic protocol includes protection of the alcoholic function of the alkyne before its carbonylation in the presence of Drent's catalytic system. Protection step effectively extends the catalyst life hence enhancing the practical applicability of the reaction. The effectiveness of some different protecting groups (benzyl, acetyl and trimethylsilyl) has been assessed and the influence of the reaction parameters investigated
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
Preparation and Characterization of a Molecular Cobalt Complex Containing a Water Soluble Triazole Ligand
No full textCobalt(II) perchlorate hexahydrate, (Co(ClO4)2.6H2O) was reacted with a water soluble sulphonated pyridyl-triazole N,N-bidentate ligand (2-(1-((pyridine-2-yl)methyl)-1H-1,2,3-triazol-4-yl)ethyl sodium sulfate, `ligand 1.Na) in methanol to form [Co(ligand 1)2(H2O)2].4H2O as a microcrystalline solid. In this context, ligand 1.Na was first synthesized by the cycloaddition reaction of 2-(azidomethyl)pyridine and sodium 3-butyn-1-sulfate in 4:1 tert-BuOH/water solvents in presence of Cu(AcO)2H2O (10-15 mol %) as catalyst. The ligand 1.Na was white solid, absorbed moisture at open air, soluble in methanol and DMSO and characterized by elemental analysis, ESI-MS spectrum in the negative mode, 1H NMR and 13C NMR spectroscopy. In the 1H NMR spectrum of ligand 1.Na in CD3OD, a characteristic triazole strong singlet peak appeared at 7.97 ppm, a remarkable shift of δ value for CH2 proton of 2-(azidomethyl)pyridine was observed. In the 13C NMR spectrum, the triazole carbon resonates at 137.90 ppm. The prepared complex was characterized by physical data, FT-IR, ESI-MS and elemental analysis. The light pink crystals are fairly stable at open atmosphere even if they slowly loose the lattice solvent. The ESI-MS spectrum of [Co(ligand 1)2(H2O)2].4H2O indicates the species [Co(ligand 1.Na)(ligand 1)]+ and [Co(ligand 1.Na)]+ which corresponds to the m/z value at 648.6 and 402.6 respectively. Based on the observed data, octahedral geometry of the synthesized complex was suggested
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
- …
