1,720,995 research outputs found
Stereochemical studies on the interconversion of alkylidenecarbene, carbene, and alkyl ligands in chiral cyclopentadienyl ruthenium complexes
No full textPseudotetrahedral (S,S)-(η-C5H5)RuPh2PCH(CH 3)CH(CH3)PPh2Cl (1), (SRu,RC)-1′a, and (RRu,RC)-(η-C5H5)RuPh 2PCH(CH3)CH2PPh2Cl (1′b) have been used to investigate the stereochemistry of alkylidenecarbene and carbene formation. Depending on conditions 1′a and 1′b can react stereospecifically with terminal acetylenes, in the presence of halogen scavengers, to give the corresponding alkylidene complexes [Ru=C=CHR]PF6 (R = C6H5,2′a and 2′b; R = CH3, 6′a and 6′b). Retention of configuration at ruthenium was confirmed by an X-ray crystal structure of 6′a. 2′a and 2′b are converted with base to the corresponding phenylacetylide complexes RuC≡CC6H5 (5′a and 5′b), which, in turn, regenerated 2′a and 2′b on reaction with HPF6. Neither reaction changes the stereochemistry at the metal. 2′a and 2′b react further with CH3OH stereospecifically and with retention of the configuration at ruthenium to give the methoxycarbene complexes [Ru=C(OCH3)CH2C6H5]PF6 (3′a and 3′b). The crystal structure of 3′b has also been determined. 3′a and 3′b react with LiAlH4 in THF at low temperature to give the 2-phenylethyl complexes RuC-H2CH2C6H5 (4′a and 4′b) with retention of configuration. Labeling studies have demonstrated that the two hydrogen atoms of the new formed methylene group arise from LiAlH4. The summary of crystal data is as follows. For 6′a: a = 11.469 (4) Å, b = 14.976 (4) Å, and c = 20.696 (7) Å with Z = 4 in space group P212121 (no. 19). For 3′b: a = 12.555 (4) Å, b = 12.651 (4) Å, and c = 24.198 (8) Å with Z = 4 in space group P212121 (no. 19)
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
Synthesis and absolute configuration of a series of chiral ruthenium complexes; Crystal structure of (R)-[Ru(η5-C5H 4R*)(CO)(PPh3)I] (R* = neomenthyl)
No full textThe syntheses of [Ru(η5-C5H4R*) (CO)22] and [Ru(η5-C5H 4R*)(CO)2X] (R* = menthyl or neomenthyl; X = Cl, Br, or I) are reported. Phosphines and phosphites react with the halide complexes to give the diastereoisomers [Ru(η5-C5H 4R*)(CO)LX] [R* = menthyl, X = Cl, L = PPh2Me or PPh2(CH2OMe); X = Br, L = PBun3 or P(OPh)3; R* = neomenthyl, X = I, L = PPh3] containing a chiral ruthenium atom. These diastereoisomers have been resolved and their circular dichroism (c.d.) spectra are reported. An X-ray analysis of c.d.(-)325[Ru(η5-C5H4R*) (CO)(PPh3)I] (R* = neomenthyl) has been carried out which established the absolute configuration of the ruthenium centre to be R. The crystals are monoclinic, space group P21 (no. 4) with a = 12.833(6), b = 15.186(6), c = 7.972(5) Å, β = 101.50(4)°, and Z = 2. On the basis of 1 773 observed reflections, the structure was refined to R = 0.054. It is proposed that the c.d. spectrum in the region 300-400 nm can be used to establish the configuration of the ruthenium atom in complexes of the type [Ru(η5-C5H4R*)(CO)-LX] described
Rhenium(V) oxide complexes. Crystal and molecular structures of the compounds trans-ReI 2O(OR)(PPh 3) 2 (R = Et, Me) and of their hydrolysis derivative ReIO 2(PPh 3) 2
No full textThe structure of the complex ReI 2O(OEt)(PPh 3) 2·3/2C 6H 6 (I) has been investigated: the dark-yellow crystals are monoclinic, space group P2 1/n, with a = 17.410(8), b = 17.322(6), c = 15.039(5) Å, β = 103.49(3)°, Z = 4. Least-squares refinements based on 3636 significant counter data led to a final R value of 0.059. The compound exhibits a slightly distorted octahedral coordination, with the two PPh 3 groups trans between themselves (mean ReP 2.523 Å), as well as the two iodide ligands (mean ReI 2.789 Å). The ethoxo group (ReO 1.880(9) Å) and the oxide ligand (ReO 1.715(9) Å) occupy the other two coordination sites. Compound I in methanol transforms into ReI 2O(OMe)(PPh 3) 2 (II), which has been characterized by X-ray analysis in crystals containing CHCl 3 molecules of solvation. The crystals are triclinic, space group P1, a = 12.835(3), b = 13.067(4), c = 13.485(4) Å, α = 89.71(2)°, β = 71.61(2)°, γ = 70.19(2)°, Z = 2. The refinements gave a final R value of 0.036, on the basis of 4524 significant counter intensities. The stereochemistry and the bond parameters are similar to those found in compound I. In particular the ReO (methoxo) and ReO (oxide) bond lengths are 1.859(5) and 1.698(5) Å respectively. Hydrolysis reactions of both compounds I and II give the violet derivative ReIO 2(PPh 3) 2 (III). The crystal data are: orthorhombic, space group Aba2, a = 19.834(5), b = 16.144(3), c = 10.560(2) Å, Z = 4. 1435 significant counter reflections were used in the refinements the final R value being 0.039. The compound is an unusual example of a five coordinate Re(V) complex. It possesses a rigorous C 2 crystallographic symmetry and exhibits a distorted trigonal bipyramidal stereochemistry, with the two PPh 3 groups in an axial direction (ReP 2.488(3) Å) and the two oxide and the iodide ligands in equatorial positions. The ReI and ReO interactions have values of 2.664(2) and 1.742(11) Å respectively. © 1983
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
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