1,721,716 research outputs found
Catalytic deuteration of silanes mediated by N-heterocyclic carbene-Ir(III) complexes
No full textThe catalytic activity of a series of coordinatively unsaturated NHC-M(III) (M = Rh, Ir; NHC = N-heterocyclic carbene) complexes was tested in the deuteration of secondary and tertiary silanes. Among these, [IrCl(I(t)Bu')(2)] provides the highest conversions to the deuterated species. Mechanistic studies highlight the reversible nature of the ortho-metalation reaction
A combined mechanistic and computational study of the gold(I)-catalyzed formation of substituted indenes
No full textSubstituted indenes can be prepared after a sequence [1,3] O-acyl shift-hydroarylation-[1,3] O-acyl shift. Each step is catalyzed by a cationic NHC-Gold(I) species generated in situ after reaction between [(IPr) AuOH] and HBF4 center dot OEt2. This interesting silver-free way is fully supported by a computational study justifying the formation of each intermediate
Gold(I)-catalyzed synthesis of furans and pyrroles via alkyne hydration
No full textFurans and pyrroles were prepared via the gold(I)-catalyzed alkyne hydration of diynes. The use of [Au(IPr)OH] as precatalyst in a silver-free protocol permits low catalyst loadings and in situ generation of the active cationic gold species. A detailed computational study confirmed the experimental results and supports the proposed mechanism
Palladium-N-heterocyclic carbene (NHC) catalyzed C?N bond formation in a continuous flow microreactor. Effect of process parameters and comparison with batch operation
No full textIn this work, the Buchwald–Hartwig aryl amination is reported in a home-made continuous plug flow
tube microreactor, using a homogeneous well-defined palladium-N-heterocyclic carbene (NHC) complex.
The microreactor enabled a 100% conversion of the reagents within 30 min, even at very low catalyst concentrations.
A direct comparison between batch and continuous flow reactions is described and shows
that the Buchwald–Hartwig reaction is faster in the microreactor than in the batch case. An investigation
of the influence of the operating parameters of the microreactor on the reaction was carried out. Increasing
temperature allowed a faster conversion of the reagents; moreover, no effect on microreactor performance
was found by changing tube diameter. The dependence of reaction kinetics on reagents and
[Pd(NHC)] pre-catalyst concentrations was investigated based on initial reaction rates. The resulting
expression for the rate of reaction showed some similarities with the one reported for palladium–phosphine
catalyst, but also some important differences
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
- …
