1,720,962 research outputs found
LIGAND EFFECTS ON THE RATES OF THE MIGRATORY INSERTION IN RHODIUM(III) METHYL CARBONYL-COMPLEXES
No full textThe complexes (eta-5-C5Me5)Rh(CO)(X)(Me) (X = I, Br, Cl, MeCO2, CF3CO2) react readily with triphenylphosphine in toluene at 25-degrees-C to yield quantitatively the corresponding acyl species (eta-5-C5Me5)Rh(COMe)(X)(PPh3). The reactions of the halide complexes are first order in both the substrate and the phosphine. The rate increases in the order I < Br < Cl, following the increasing electronegativity of the halogen atoms. The activation parameters (DELTA-H double-ended-dagger = 56 +/- 2 (I), 46 +/- 3 (Br), 36 +/- 2 (Cl) kJ mol-1; DELTA-S double-ended-dagger = -79 +/- 4 (I), -93 +/- 5 (Br), -122 +/- 3 (Cl) J K-1 mol-1) indicate that the order of reactivity is dominated by changes in DELTA-H double-ended-dagger. The carboxylate complexes exhibit saturation kinetics, typical of the formation of an intermediate and unprecedented for migratory insertion in a nonpolar solvent. It is proposed that the intermediate is (eta-5-C5Me5)Rh(eta-2-O2CR)(COMe) (R = Me, CF3), where the carboxylate moiety acts as a bidentate ligand to stabilize the otherwise unsaturated species. The rate constant for the formation of the intermediate, determined from the reactions with different nucleophiles, is somewhat larger for X = CF3CO2 (k1 = 0.16 s-1) than for X = MeCO2 (k1 = 0.105 s-1)
The migratory insertion of carbon monoxide in pentamethylcyclopentadienyliridium(III) complexes. Structural effects on reactivity and mechanism for rhodium and iridium systems
No full textThe reactions of complex (C(5)Me(5))Ir(Cl)(CO)(Me) (1a) with cyclohexylisocyanide and phosphines (L = CyNC, PHPh(2), PMePh(2), PMe(2)Ph) give the products of alkyl migratory insertion (C(5)Me(5))Ir(Cl)(COMe)(L), in toluene or tetrahydrofuran at 323 K or higher temperature. The phenyl analogue (C(5)Me(5))Ir(Cl)(CO)(Ph) or the iodide complexes (C(5)Me(5))Ir(I)(CO)(R)(R = Me, Ph) are not reactive under the same conditions. The reaction of (C(5)Me(5))Ir(Cl)(CO)(Me) with PMePh(2) and PMe(2)Ph in acetonitrile yields the chloride substitution product [(C(5)Me(5))Ir(CO)(L)(Me)]Cl-+(-). Kinetic measurements for the reactions of (C(5)Me(5))Ir(Cl)(CO)(Me) in toluene are first order in the iridium complex and exhibit a saturation dependence on the incoming donors L. Analysis of the data suggests a two-step process involving (i) rapid formation of a molecular complex [(C(5)Me(5))Ir(Cl)(CO)(Me),(L)], in which the structure of 1a is unperturbed within the limits of spectroscopic analysis, and (ii) rate determining methyl migration. The reaction parameters are K for the pre-equilibrium step (K = 1.5 (CyNC), 7.3 (PHPh(2)), 7.1 (PMePh(2)) dm(3) mol(-1) at 323 K) and k(2) for the slow carbon-carbon bond formation (k(2)(10(5)) = 6.9 (CyNC), 1.2 (PHPh(2)), 1.0 (PMePh(2)) s(-1) at 323 K). The activation parameters for the methyl migration step in the reaction with PMePh(2), obtained between 308 and 338 K, are Delta H not equal = 106 +/- 16 kJ mol(-1) and Delta S not equal = -14 +/- 5 JK(-1) mol(-1). The reaction of 1a with PMePh(2) proceeds at similar rates in tetrahydrofuran (K = 3.7 dm(3) mol(-1), k(2)(10(5)) = 1.2 s(-1), 323 K). The crystal structure of (C(5)Me(5))Ir(Cl)(COMe)(PMe(2)Ph) has been determined by X-ray diffraction. C20H29ClOPIr: M(r) = 544.1, monoclinic, P2(1)/n, a = 8.084(2), b = 9.030(2), c = 28.715(3) Angstrom, beta = 91.41(3)degrees, Z = 4, D-c = 1.71 g cm(-3), V = 2095.5 Angstrom(3), room temperature, Mo K alpha, lambda = 0.71069, mu = 65.55 cm(-1), F(000) = 1044, R = 0.037 for 2453 independent observed reflections. The complex shows a deformed tetrahedral coordination assuming the eta(5)-C(5)Me(5) molecular fragment as a single coordination site. The iridium-chlorine bond is staggered with respect to two adjacent C(ring)-methyl bonds, while the Ir-P and the Ir-COMe bonds are eclipsed with respect to C(ring)-methyl bonds
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
- …
