1,720,956 research outputs found
A New N-Heterocyclic (NHC) Biscarbene Ligand: Synthesis and Catalytic Activities of Bis-gold(I) Complex and Bis-iridium(I) Complexes
No full text本論文探討新型飽和含氮雜環雙碳烯金屬錯合物的合成、結構解析以及其催化的應用。雙鎢錯合物之雜環氮上烷基化得到氮取代雙鎢錯合物，遂利用已開發的方法將含氮雜環碳烯骨架從鎢金屬轉移至金和銥金屬，分別得到雙金碳烯錯合物和雙銥碳烯錯合物。
將重氮化合物與三苯基膦反應形成膦亞胺中間體，遂與六羰鎢[W(CO)6]藉由兩次分子內環化而得到雙碳烯鎢金屬錯合物，藉由X光單晶繞射分析其晶體結構。雙鎢錯合物之雜環氮上烷基化得到氮取代雙鎢錯合物，將其和[ClAu(Me2S)]反應得到雙金錯合物，藉由質譜分析，其結構為一價金被兩個碳烯所鍵結，形成一穩定錯合物，卻降低其催化活性。另一方面，氮取代雙鎢錯合物與[Ir(COD)Cl]2反應，經由碳烯與羰基同時轉移至銥金屬，即合成出一雙銥錯合物，藉由HR-FAB證實其分子式。藉由三苯基膦置換銥中心的羰基和氯基，順利得到碳烯銥金屬錯合物之雙膦衍生物，藉由X-ray單晶繞射確定其結構。
雙銥錯合物可以應用於氫轉移反應的催化劑，特別是利用醇與胺化物反應的N-烷基化，均展現其優良的催化活性。雙銥錯合物催化對位和間位苯二胺的N-烷基化反應上，相較單核碳烯銥金屬錯合物或其他銥金屬錯合物具有較高的選擇性與活性。因此藉由雙銥錯合物的催化，可以成功從苯二胺與醇類分子製備對應的雙二級胺產物。相似條件下，於鄰位苯二胺的N-烷基化反應會直接由分子內環化得到2-苯基苯并咪唑(2-phenylbenzimidazole)；若於反應環境中使用氫氣，可以抑制分子內環化，而成功得到鄰苯二胺的雙二級胺產物。除了使用苯甲醇外，各類醇類也能用於此系統上。除此之外，雙銥錯合物也能催化含氮雜環之二級胺的N-烷基化反應得到三級胺產物。In this work, we have synthesized gold(I) and iridium(I) metal complexes containing a new bis-N-heterocyclic carbene donor. The desired complexes were obtained via a known carbene-transfer method. Thus, reaction of the bis-azido compound m-C6H4(CH2NHCH2CH2N3)2 (2) with triphenylphosphine followed by the treatment of W(CO)6 yielded the bis-carbene tungsten complex 4 and the structure was further confirmed by X-ray crystal structural determination. Alkylation of 4 with benzyl bromide provided the N-substituted NHC complex 5. Upon the reaction of the N-substituted NHC complex with [(Me2S)AuCl], the carbene fragment readily transferred from tungsten to the gold center and provided a bis-gold complex 6. A bis-Ir(I) carbene complex 7 was prepared via the reaction of 5 with [Ir(COD)Cl]2. Substitution of 7 with triphenylphosphine yielded the bis-phosphine iridium carbene complex 8. Complex 8 was confirmed by X-ray crystal structural analysis to illustrate a bis-iridium frame-work of the complex. Employment of these bis-iridium carbene complexes on the catalytic N-alkylation of phenylenediamines with various alcohols was examined. It appears that the iridium carbene complex 7 shows good catalytic activity on this N-alkylation reaction. Furthermore, N-alkylation of heterocyclic amine with benzyl alcohols could be achieved by the similar catalytic conditions
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
Electro- and Photochemical Activities of Manganese-Based Complexes for CO2 Reduction
No full textEffective CO2 reduction is a grand challenge in modern chemistry. One promising approach is via electrochemical or photochemical catalysis using molecular catalysts. Among the available options, Mn-based complexes are an emerging class of earth-abundant molecular catalysts. In this thesis, we investigated the electro- and/or photo-chemical activities of several Mn-based bipyridyl carbonyl complexes for CO2 reduction. This thesis is divided into three parts: (i) a case study of the electro- and photochemical activities of a CN-bridged binuclear Mn complex; (ii) a photophysical investigation of the CN-bridged complex; (iii) a mechanistic study of the key role played by an Mn tetracarbonyl complex in electrochemical CO2 reduction. The first part of this work was motivated by an undesirable photodimerization observed in the reaction of a benchmark [Mn(bpy)(CO)3Br] upon exposure to UV and visible light, thereby hindering the activity of this benchmark complex as a photocatalyst for CO2 reduction. To overcome this undesirable photodimerization, we proposed and characterized the cyanide-bridged complex, and investigated its activity for electrochemical CO2 reduction. The CN-bridged complex indeed inhibited the dimerization upon photolysis and carried out a photochemical CO2 reduction. In the second part of this work, we further studied the CN-bridged complex to decipher the photochemical reaction. To do so, we utilized infrared and transient spectroscopy to identify the photo-induced intermediate and the corresponding photophysics. Based on this analysis, we found that the CN-bridged complex exhibits structural robustness, which prevents the cleavage of the CN-linkage, leading to the undesirable photodegradation under photochemical conditions. Furthermore, we identified that solvent participation influences the excited state dynamic, i.e., a relatively long-lived intermediate in the coordinating solvent. In the third part of this work, we focused on understanding the mechanism behind the electrochemical CO2 reduction of the benchmark, [Mn(bpy)(CO)3Br]. In particular, we synthesized and characterized an [Mn(bpy)(CO)4]+ complex, which has been suggested theoretically in the literature as an intermediate. With the aid of infrared and in situ UV-Vis spectroelectrochemical studies, we verified the key role played by the tetracarbonyl complex—it serves as both a precatalyst and an on-cycle intermediate—in the Mn-based electrocatalytic CO2 reduction
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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