1,720,954 research outputs found
Preparation and Chemical Reactions of Ruthenium Cp Phosphine Complexes with 1,6-Endiyne.
No full text利用五種含有末端丙炔醇和以三甲基矽保護的末端炔相連結的1,6-雙炔化合物與氯配位釕金屬之三苯基磷化合物[Ru]-Cl ([Ru] = Cp(PPh3)2Ru)可以生成兩種不同形式的錯合物。在第一種形式,釕金屬化合物只與末端丙炔醇進行反應可以生成釕金屬亞乙烯基錯合物，釕金屬亞丙烯基錯合物，與釕金屬炔基錯合物。在第二種形式的產物中，1,6-雙炔化合物中有一碳碳鍵的生成可得到釕金屬丙烯基碳烯錯合物。化合物1與氯配位釕金之三苯基磷化合物反應會得到第一種形式的混合產物，分別為釕金屬亞丙烯基錯合物8與磷基加成之釕金屬炔基錯合物9，後者為一個三苯基磷加成雙炔配位基的三號位置碳上。加入過量的三苯基磷於反應中即可以得到單一錯合物9。然而，在1,6雙炔化合物中引入一個甲基取代於1,6-雙炔化合物三號碳位置與氯配位釕金屬之三苯基磷化合物反應會得到同樣有磷基加成在配位基上的釕金屬丙烯基碳烯錯合物11。這反應包含了兩個炔基同時配位在金屬上進行環化反應，同時伴隨著三苯基磷的遷移至1,6-雙炔配位基的一號位置碳上。在這兩種反應中，可以觀察到炔基對三苯基磷有很強的結合力，使得碳磷鍵的生成有不同的位向選擇性。利用鹽酸與五個電子配位的釕金屬丙烯基碳烯錯合物11反應可以得到高產率含有四個電子配位的1,3-丁二烯基與氯配位的金屬錯合物12。含有正丁基取代在丙烯醇的雙炔化合物3與釕金屬錯合物反應，可以同時獲得釕金屬亞丙烯基錯合物13與釕金屬丙烯基錯合物14。而利用化合物7與含氯取代的釕金屬錯合物反應則可同時獲得釕金屬亞乙烯基錯合物16與釕金屬丙烯基錯合物17。五個錯合物9，11，12，13，16的結構鑑定可以藉由X光繞射分析確定。
另外我們又研究了一系列釕金屬炔基化合物環化反應。這一系列的釕金屬炔基化合物可以由釕金屬亞丙烯基錯合物或者磷基加成在配位基上的釕金屬炔基錯合物製備而成。在鹼性條件下我們可以利用不同的醇類或者利用四丁基氟化銨在四氫呋喃溶液下將末端炔進行去保護反應得到一系列的烷氧基加成在雙炔配位基三號位置的釕金屬炔基化合物。對錯合物19進行質子化反應，可以得到釕金屬亞乙烯基錯合物混合產物20和20`，這兩個金屬錯合物可能是經由釕金屬炔基π-配位錯合物隨後發生氫和金屬的遷移。對錯合物21a - d而言，有一個碳碳鍵生成的環化反應發生在β碳和末端炔基上而形成一個六員環的釕金屬亞乙烯基錯合物。這個反應可能是經由6-endo-dig的反應途徑。這些環化的釕金屬亞乙烯基錯合物22a - d在與酸性媒介反應可以生成釕金屬烷氧基碳烯錯合物25a及25b，或者釕金屬醯基錯合物26，並且結構中都含有一個萘圓環。這樣的1,3-烷氧基的遷移可能是經由中間物金屬碳炔化合物而得到。不同於金屬炔基錯合物19，錯合物4N擁有一個缺電子的吡啶芳香環，並且能夠與鹽類六氟磷酸鉀與氯仿反應生成環化的亞乙烯基錯合物5N。這些所有的環化亞乙烯基錯合的結構是由核磁共振光譜分析鑑定，而金屬醯基錯合物則是利用X光單晶繞射鑑定結構。Reactions of five 1,6-diynes 1, 1N, 2, 3 and 7, each with one terminal propargylic alcohol and one internal triple bond containing Me3Si groups, with [Ru]-Cl ([Ru] = Cp(PPh3)2Ru) led to two types of products. In the first type, only the propargylic group involves in the reaction leading to vinylidene, allenylidene or acetylide complexes. A C-C bond formation of two triple bonds in 1,6-diynes gave allylcarbene products of the second type. The reaction of 1 with [Ru]-Cl yielded only the first type, giving a mixture of two cationic complexes; the allenylidene complex 8 and the phosphonium acetylide complex 9, the latter resulting from further addition of a phosphine molecule to Cγ of 8. The same reaction in the presence of excess phosphine gave 9 only. However, with an additional methyl group, the 1,6-diyne 2 reacted with [Ru]-Cl to give the allylcarbene complex 11 also with a phosphonium group on the ligand. The reaction proceeds by a cyclization reaction involving two triple bonds on the metal accompanied with a migration of a phosphine ligand to Cα. In both reactions strong affinity between alkyne and phosphine was observed resulting in formations of P-C bonds in different regioselectivity. Addition of HCl to 11 transforms the five-electron donor allylcarbene ligand to the four-electron donor diene ligand along with formation of a Ru-Cl bond giving complex 12 in high yield. From the reaction of [Ru]-Cl with diyne 3 containing a t-butyl group at the propargylic carbon, both the allenylidene complex 13 and the allylcarbene complex 14 were obtained. The reaction of diyne 7 with [Ru]-Cl also gave both types of complexes, namely the vinylidene complex 16 and the allylcarbene complex 17. Crystal structures of complexes 9, 11, 12, 13, and 16 are determined by single crystal X-ray diffraction analysis.
We also studied the cyclic reaction of a series of the acetylide complexes. These acetylide complexes were prepared from the allenylidene or phosphonium acetylide complexes which using the Cp(PPh3)2RuCl and 1,6-diyne-4-ene-3-ol connected with an aromatic group in presence of KPF6 in CH2Cl2. Deprotection of the terminal alkyne were carried out in different alcohol solution under basic condition or TBAF in THF solution gave a series of acetylide complexes with terminal alkyne group. For 19, protonation of acetylide complex can lead two vinylidene complexes 20 and 20’ which possibly via a π-coordinated alkynyl complex followed by hydrogen and metal migration. For 21a - d, a C-C bond-forming cyclization reaction is occurred at Cβ and the terminal alkyne to generate a six-member ring in the vinylidene complex. The reaction may undergo a 6-endo-dig reaction pathway. These cyclic vinylidene complexes 22a - d under acidic-medium condition could form the alkoxy carbene 25a - b or acyl complexe 26 which with a naphathyl ring in the structure. This 1,3-alkoxy migration might via metal carbene complex as an intermediate. For 4N, that the difference to the acetylide complex 19 is containing an electrophilic pyridinyl ring, it could form the cyclic vinylidene complex 5N in presence of KPF6 in CHCl3. All structures determinations of the cyclic vinylidene complexes are using NMR spectra analysis and the acyl complex is using the single crystal X-ray diffraction analysis
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
- …
