1,721,018 research outputs found
The formation of a metallacycloheptadienyl intermediate in the reaction of palladacyclopentadienyl derivatives with tetracyanoethylene
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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
The unexpected case of reactions of halogens and interhalogens with halide substituted Pd(ii) σ-butadienyl complexes
Full text linkWe have experimentally studied and theoretically interpreted the addition under stoichiometric conditions of halogens or interhalogens to σ-butadienyl palladium complexes bearing the heteroditopic thioquinolines as spectator ligands. The observed reactions do not involve the expected extrusion of the butadienyl fragment but rather the unpredictable substitution of the halide coordinated to palladium and in some cases also of that bound to the terminal butadienyl carbon. We have explained this peculiar reactivity with a mechanistic hypothesis based on a sequence of selective processes of oxidative addition and reductive elimination involving Pd(iv) intermediates
Transmetalation Reactions. The Surprising Role of the Stabilizing Olefin in Determining the Overall Reaction Rate
No full textSubstitution reactions between bis-chelate ligands in palladium(II) alkenyl complexes: an unusual way to form unstable trans-P complexes. A study on the isomerization mechanism
No full textThe substitution reactions between asymmetric bis-chelate ligands and alkenyl chloro derivatives of
palladium(II) of the type [Pd(L–L¢)(Rx)Cl] (L–L¢ = 2-phenylsulfanylmethyl-pyridine (HN–SPh),
2-methyl-6-phenylsulfanylmethyl-pyridine (MeN–SPh), 2,2¢-bipyridinyl (BiPy), Rx =
–CCOOMe=CMeCOOMe (Ra), –CCOOEt=CMeCOOEt (Rb), –CCOOt-Bu=CMeCOOt-Bu (Rc),
–(CCOOMe=CCOOMe)2Me (Rd)) with phosphoquinoline moieties (8-diphenylphosphanyl-quinoline
(DPPQ), 8-diphenylphosphanyl-2-methyl-quinoline (DPPQ-Me)) usually leads to the formation of the
stable geometrical isomer bearing these groups in the cis position thanks to the mutual trans influence
of the alkenyl and phosphine groups. However, when the leaving group MeN–SPh and the entering
ligand DPPQ are involved, the fast and quantitative substitution reaction leads to the formation of a
couple of geometrical isomers [Pd(DPPQ)(Rx)Cl]-trans P and [Pd(DPPQ)(Rx)Cl]-cis P (Rx = Ra, Rb,
Rc, Rd) in which the alkenyl and the phosphine groups are in mutual trans or cis position. The substrate
[Pd(DPPQ)(Rx)Cl]-trans P (Rx = Ra, Rb, Rc) slowly interconverts into its thermodynamically stable
-cis P counterpart while the bulky [Pd(DPPQ)(Rd)Cl]-trans P displays no tendency to isomerize, thereby
allowing separation of the two geometrical forms. Also, the ligand DPPQ-Me induces the formation of
the -trans P geometrical isomer which is only detectable at low temperature since it rapidly interconverts
into the -cis P derivative at RT. The kinetics of the interconversion process, a reasonable explanation of
the observed phenomenon based on theoretical calculations, and eventually an unequivocal structure
determination of the stable [Pd(DPPQ)(Rx)Cl]-cis P substrate are reported in the present pape
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
Reactivity of palladium olefin complexes with heteroditopic NHC–pyridine as spectator ligand toward olefin exchange
No full textWe have synthesized some derivatives bearing two strong sigma-donor ligands simultaneously coordinated to the palladium centre by exploiting the lability of the pyridine wing of the (1-methyl-3-((6-methylpyridine-
2-yl)methyl)-imidazole) (Me-NHC-CH2-Py) moiety as a spectator ligand in Pd(0) complexes stabilized by deactivated olefins. Unprecedented mixed complexes bearing the ligand L (L = triphenylphosphine (PPh3), 2,6-dimethylphenyl isocyanide (DIC), triethyl phosphite (P(OEt)3)) and the ligand
Me–NHC–CH2–Py with the uncoordinated dangling pyridine wing were therefore obtained by reacting an equimolar amount of the ligands L with the complex [Pd(eta2-olefin)(Me–NHC–CH2–Py)] (olefin = tetramethylethenetetracarboxylate (tmetc), fumaronitrile (fn), maleic anhydride (ma), naphthoquinone (nq)). Moreover, we have determined the equilibrium constants KE(ol) for the olefin exchange in the
complex [Pd(eta2-olefin)(Me–NHC–CH2–Py)] and the related olefin coordinative ability order
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