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Auraoxetanes as Plausible Intermediates in the Oxidation of Alkenes by Oxygen- Transfer Reaction from Gold(III) Oxo Complexes.
No full textAlkene oxidation by oxygen atom transfer reaction from late transition metal oxo complexes is, at present, an objective of particular interest. Metallaoxetanes, proposed as possible intermediates, have been recently isolated in the case of platinum(II).1 Intermediacy of metallaoxetanes in metal catalyzed alkene epoxidations has been proven in the case of silver as well.2
A series of gold(III) oxo complexes, [Au2(N,N)2(μ-O)2][PF6]2, supported by bidentate 6-substituted-2,2’- bipyridines, had been synthesized several years ago by some of us.3 Preliminary studies, indicating the feasibility of oxygen atom transfer reaction, were followed by extensive investigations on the alkene oxidation. The reaction with styrene, chosen as a model, was thoroughly studied and a gold(I) olefin complex [Au(N,N)(η2-CH2=CHPh][PF6] structurally characterised.4 Styrene oxygenated derivatives, contemporaneously formed, were identified as well. Analogous results have been successively obtained with other terminal olefins, while no reaction takes place with internal olefins. Following the hypothesis that gold(I) alkene complexes and alkene oxidation products could have been originated by a common precursor, and that the precursor was likely to be an auraoxacyclobutane, we thought to study the reaction with strained cyclic olefins, such as 2-norbornylene, nb, and 2,5-norbornadiene, nbd. These olefins, being rather reactive but lacking of active β-hydrogens, were good candidates for stabilizing a possible metallaoxetane intermediate. The reaction with both olefins proceeds slowly to give the gold(I) alkene complexes [Au2(N,N)2(μ-η4-nbd][PF6]2 and [Au(N,N)(η2-nb][PF6]2, respectively, as the main products. A second product of the reaction with nb, which depending on the substituent in 6 of the bipyridine and on the preparative conditions forms in appreciable amount, resulted to be an unprecedented auraoxetane [Au(bipyMe)(κ2-O,C-2- oxynorbornyl)][PF6].5 Plausible reaction pathways for the formation of the gold complexes and the oxygenated organic derivatives will be discussed.
References
[1] E. Szuromi, H. Shan, P.R. Sharp, J. Am. Chem. Soc. 2003, 125, 10522-10523;
[2] S. Linic, H. Piao, K. Adib, M.A. Barteau, Angew. Chem. Int. Ed. 2004, 43, 2918-2921.
[3] M.A. Cinellu, G. Minghetti, M.V. Pinna, S. Stoccoro, A. Zucca, M. Manassero, M. Sansoni, J. Chem. Soc., Dalton Trans. 1998,
1735-1741.
[4] M.A. Cinellu, G. Minghetti, S. Stoccoro, A. Zucca and M. Manassero, Chem. Commun., 2004, 1618-1619 [5] M.A. Cinellu, G. Minghetti, F. Cocco, S. Stoccoro, A. Zucca, M. Manassero, submitted
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
REACTION OF PLATINUM(II) DERIVATIVES WITH BIS(PYRAZOLYL)PROPANE - CLEAVAGE OF A C(SP3)-N BOND IN A BIS(PYRAZOLYL)ALKANE PROMOTED BY PLATINUM(II) DERIVATIVES - CRYSTAL-STRUCTURE OF CIS-PT(PYRAZOLE)2CL2
No full textThe reactions of bis(pyrazolyl)propane (CH3)2C(pz)2, (pzH = pyrazole), with PtCl2, (RCN)2PtCl2 and K2[PtCl4 have been investigated, and the results compared with those described previously for the corresponding palladium(II) derivatives. In contrast with the behaviour of the palladium analogues, the platinum derivatives promote the rupture of the ligand: simple adducts of pyrazole, cis- or trans-Pt(pzH)2Cl2, or species containing the ligand [HNC(R)pz], formally arising from the insertion of a nitrile into the NH bond of pyrazole, are obtained. For comparison, the reaction of the platinum derivatives with pyrazole itself has been investigated under various conditions. The crystal structure of cis-Pt(pzH)2Cl2 has been determined by X-ray diffraction: monoclinic, space group C2/c, a 9.180(1), b 15.084(1), c 15.1445(9) Å, β 101.536(7)°, Z - 8, R = 0.039, Rw = 0.040 for 2125 observed reflections
Synthesis of the first Pd(II), Pt(II) and Au(III) derivatives with 6,6’-dimethoxy-2,2’-bipyridine
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