1,720,969 research outputs found
The Photochemistry of the (cycloalkene)(hydro)(trispyrazolylborato)iridium complexes [Ir(eta4-cod)(TpMe2)] and [Ir(eta2-coe)H2(TpMe2)]: the Formation of [IrH4(TpMe2)] and [Ir(CO)H2(TpMe2)]
No full textPhotolysis of [Ir(eta(2)-coe)H-2(Tp(Me2))] (1; Tp(Me2)=hydrotris(3,5-dimethylpyrazolyl)borato, coe = (Z)-cyclooctene) in CH3OH gives a mixture of [IrH4(Tp(Me2))] (4) and [Ir(CO)H-2(Tp(Me2))] (5) in a ca. 1 : 1 ratio. Mass-spectral analysis of the distillate of the reaction mixture at the end of the photolysis shows the presence of coe. When pure CD3OD is used as solvent, the deuteride complexes [IrD4(Tp(Me2))] ((D-4)-4) and [Ir(CO)D-2(Tp(Me2))] ((D-2)-5) are obtained. Also the photolysis of [Ir(eta(4)-cod)(Tp(Me2))] (3) (cod = cycloocta-1,5-diene) gives 4 and 5. A key feature of this photoreaction is the intramolecular dehydrogenation of cod with formation of cycloocta-1,3,5-triene, detected by mass spectroscopy at the end of the photolysis. Labeling experiments using CD3OD show that the hydrides in 4 originate from MeOH. When (CH3OH)-C-13 is used as solvent, [Ir((CO)-C-13)H-2(Tp(Me2))] is formed demonstrating that CH3OH is the source of the CO ligand. The observation that the photolysis of both 1 and 3 give the same product mixture is attributed to the formation of a common intermediate, i.e., the coordinatively unsaturated 16e(-) species {IrH2(Tp(Me2))}
The photochemistry of (diene)(hydro)[tris(3,5- dimethylpyrazolyl)borato]rhodium complexes: Preliminary communication
No full textThe photochemical rearrangement of [Rh(eta(4)-1,5-cod)Tp(Me2)](Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)-borato, 1,5-cod = cycloocta-1,5-diene) to the new compound [Rh(eta(4)-1,3-cod)Tp(Me2)] (2) is described. The characterization of 2 was carried out using H-1-, C-13-, and Rh-103-HMQ - NMRspectroscopy. Photolysis of 2 is a versatile entry point into the organometallic chemistry of the {RhTp(Me2)} fragment as it can be used to produce a) hydrido-carbonyl ([Rh(CO)H(2)Tp(Me2)]), b) hydrido-phenyl-phosphite ([RhH(Ph)(P(OMe)(3))Tp(Me2)]), and c) ethoxide-hydrido-phosphite ([RhH(OEt)(P(OMe)(3))Tp(Me2)]) complexes
Photochemistry of Dihydrido(hydrotris(3,5- dimethylpyrazolyl)borato)(Z-cyclooctene)iridium. Synthetic Intermediates and Mechanism of the Photochemical Formation of Hydridophenyl(hydrotris(3,5-dimethylpyrazolyl)borato)(trimethyl phosphite)iridium
No full textThe photolysis of a benzene solution of [Tp(Me2)IrH(2)(COE)], 1 (Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate, COE = Z-cyclooctene), in the presence of P(OMe)(3), gives the stable novel complex [Tp(Me2)IrH(C6H5)(P(OMe)(3))], 3a. The photochemical syntheses of [Tp(Me2)IrH(2)(P(OMe)(3))], from 1 and P(OMe)(3) in diethyl ether, and [Tp(Me2)-IrH2(CH2=CHCOO(t)Bu)], from 1 in tert-butyl acrylate, are also reported. The above reactions and several experiments using C6D6 and P(OCD3)(3) show that, in all cases, the primary photoproduct is the 16-electron, five-coordinate iridium(III) intermediate {Tp(Me2)IrH(2)}, 6a, produced by loss of COE from 1. The above experiments also allow the postulation of a mechanistic pathway for the formation of 3a which involves the oxidative addition of an aromatic C-H bond by 6a. Furthermore, the photochemical reaction of 1 in the presence of P(OCD3)(3) shows that, under the reaction conditions used, oxidative addition of C-H bonds of P(OMe)(3) and of coordinated Tp(Me2)-ligands, presumably, to the intermediates 6a and {Tp(Me2)IrH(C6H5)}, also occurs. Thus, coordinatively unsaturated iridium(III) species readily activate C-H bonds
Reaction of Phosphide-Bridged Palladium(I) Dimers Containing Secondary Phosphines with Ethylene and Isoprene. Coordination vs Insertion
No full textThe Pd(I)-Pd(I) dimer [Pd2(mu-PBu2t)(mu-PHBu2t)(PHBu2t)2](CF3SO3) (1(CF3SO3)) reacts with excess isoprene, giving [Pd2(mu-PBu2t)(mueta4-CH2=CHC(CH3)=CH2)(PHBu2t)2](CF3SO3) (2(CF3SO3)). Ethylene reacts with complex 1, giving [Pd2(mu-PBu2t){mueta2-O2S(O)CF3}(PEtBu2t)2 (3), which arises from insertion of the olefin into the two secondary phosphine P-H bonds. Complexes 2 and 3 were characterized via X-ray diffraction and multinuclear, multidimensional NMR spectroscopy. Relevant crystallographic parameters are as follows: for 2, space group Pbca, a = 17.321(4) angstrom, b = 22.115(3) angstrom, c = 21.531(9) angstrom, V = 8205(4) angstrom3, Z = 8; for 3, space group Cmc2(1), a = 15.435(3) angstrom, b = 18.142(9) angstrom, c = 14.833(4) angstrom, V = 4154(2) angstrom3, Z = 4
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
- …
