1,720,959 research outputs found
Synthesis of Chiral Binaphthyl Metalloporphyrins and their use as catalysts for Olefin Epoxidationand Cyclopropanation
No full textThe key intermediate in the amination of C–H bonds : synthesis, X-ray characterization and catalytic activity of Ru(TPP)(NAr)2
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Synthesis, reactivity and structural characterization of ruthenium complexes of tetraphenylporphyrin
No full textAmination of C-H Bonds by Metal Porphyrins Catalysed Nitrene Transfer Reaction
No full textThe biological and pharmaceutical activities of organonitrogen compounds prompted the scientific community to develop new methods for the direct and selective C-N bond formation, working within restricted financial parameters and environmentally friendly requirements.In the last few years we have reported on the catalytic activity of metal porphyrin complexes in a wide range of reactions, such as olefin epoxidation,1 hydrocarbon amination and olefin aziridination. For these last reactions arylazides, a versatile class of starting material, was employed as atom-efficient aminating agents.2 ArN3 generate a nitrene functionality “ArN” and the eco-friendly molecular nitrogen is the only side product.
The selective insertion of “ArN” into C–H bonds of benzylic substrates or olefins yields benzylic amines, benzylic imines or allylic amines. To clarify the mechanism of the C-H amination reactions, the ruthenium bis-imido porphyrin complex (1) was isolated and characterised by X-ray analysis.
The role of 1 in catalytic nitrene insertions into C H bonds was studied in the reaction of ArN3 with several hydrocarbons proving that 1 is an active reaction intermediate. It also appears to have equilibrium between stability and reactivity.3 To the best of our knowledge, complex 1 is the first structurally characterized bis-imido porphyrin complex that shows a good catalytic activity in this class of reactions.
References: [1] S. Fantauzzi, E. Gallo, E. Rose, N. Raoul, A. Caselli, S. Issa, F. Ragaini, S. Cenini, Organometallics , 2008, 27, 6143; [2] For a review see: S. Fantauzzi, A. Caselli and E. Gallo, Dalton Trans., 2009, 5434; [3] S. Fantauzzi, E. Gallo, A. Caselli, F. Ragaini, N. Casati, P. Macchi and S. Cenini Chem. Commun., 2009, 3952–395
Allylic amination and aziridination of olefins by aryl azides catalyzed by Co(II)(tpp) : a synthetic and mechanistic study
No full textCoII(TPP) catalyzes the reaction of aromatic azides (ArN3) with non-activated olefins to yield allylic amines or aziridines in moderate to good yields. The chemoselectivity of the catalytic reaction is particularly high. Depending on the substrate employed allylic amines or aziridines can be obtained. The reaction mechanism has been investigated. The reaction proceeds through a reversible coordination of the aryl azide to the CoII-porphyrin complex. The often postulated “nitrene” complex is not an intermediate in this reaction. The kinetics for the allylic amination is first order in azide, Co(TPP) and olefin. For the aziridination the kinetics is again first order in azide and catalyst, but we observed a first order dependence of the rate on alpha-methylstyrene only up to a 6.9 M concentration of the olefin. An inhibiting role of the competitively formed 1-(4-nitrophenyl)-5-methyl-5-phenyl-1,2,3-triazoline was identified. The triazoline was shown to reversibly coordinate to Co(TPP) blocking the free coordination site necessary for the catalytic reaction to proceed and is responsible for the catalyst deactivation in the aziridination reaction of alpha-methylstyrene by 4-nitrophenyl azide
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
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