1,720,985 research outputs found
Chelating and 'pincer' dicarbene complexes of palladium; synthesis and structural studies
No full textA series of 'pincer' 2,6-pyridyl dicarbene complexes of the type [(C-N-C) PdX](+), 4a, 4b, 2,6-lutidinyl dicarbene complexes of the type [((CNC)-N-boolean AND-C-boolean AND) PdX](+), 4c, 4d, 1,3-xylyl dicarbene complexes of the type [((CCC)-C-boolean AND-C-boolean AND) PdX], 5a, 5b, 5c and 1,2-xylyl dicarbene complexes [(CC) PdX2], 8, where carbene is 3-arylimidazol-2-ylidene, aryl = mesityl, 2,6-Pr-2(i) C6H3, X = Br or Cl, have been prepared by (i) transmetallation from the corresponding silver complexes, i. e. [(C-N-C) Ag-2 Cl-2], [((CNC)-N-boolean AND-C-boolean AND) Ag2Cl2] and [(CC) Ag2Cl2] to palladium, (ii) substitution of cod in (cod) PdX2 by the 'pincer' (C-N-C) (iii) palladation of bis-imidazolium salts [C(H)C-boolean AND(H)C-boolean AND(H)] in the presence of base. The crystal structures show that the ligands act as chelates in 4-5, while in 8 as both chelate and bridging
Functionalised and chelate heterocyclic carbene complexes of palladium; synthesis and structural studies
No full textA series of picolyl-functionalised, [(CN) ligands act as chelates, while the methoxymethyl-and diethylcarbamoylmethyl-functions in 10, 11 and 12, respectively, are dangling. Derivatives of 5a in which the pyridine ring is substituted with electron withdrawing or bulky substituents show only minor variation of the pyridine-palladium distances
Structural diversity in pyridine-N-functionalized carbene copper(I) complexes
No full textThe use of the versatile pyridine N-functionalized carbene ligands has allowed the isolation and structural characterization of copper(I) imidazol-2-ylidene complexes of the type ([(3-R)(1-L)imidazol-2-ylidene] CuBr}, where L = 2-picolyl, R = 2,4,6-trimethylphenyl (mesityl), 2,6-(Pr2C6H3)-C-i; L = 2-pyridyl, R = 2,6-(Pr2C6H3)-C-i. They were prepared by interaction of the corresponding imidazolium bromides with Cu2O in chlorinated solvents in the presence of molecular sieves. In the solid state the 2-picolyl derivatives crystallize as dimers or polymers depending on the crystallization conditions, while the 2-pyridyl derivative crystallizes as monomer
1,2-bis-(ditertbutylphosphinomethyl)benzene in catalysis
No full textDifferent diphosphine ligands having the structure shown below have been
studied for carbonylation and hydroformylation reactions.
Depending on the substituent on the phosphorus atoms the electronic and steric properties can be tuned to direct the reaction towards the desired products.
Palladium methoxycarbonylation of a large variety of unsaturated compounds
has been attempted under very different conditions. The outcome of these
reactions was the achievement of the linear products with a selectivity higher
than 99.5 % under mild conditions of pressure and temperature.
Chloroaromatic compounds have also been employed as substrates in
methoxycarbonylation reactions. Unexpected results were observed since
carbonylation was possible only when a strong electron withdrawing group was
present. The origin of the many side products from these reactions has been
elucidated.
Rhodium hydroformylation was not as successful as palladium
Methoxycarbonylation since relatively severe conditions had to be used to get
good rates and good selectivity. In no case were there as good as those obtained
in the carbonylation reactions. However, unusual factors, such as the presence of
chlorine in the reaction media, have been found to influence either the
conversion or the selectivity
The first 1,2,3-tris(phosphinomethyl)ferrocene
No full textThe synthesis of the first 1,2,3-tris(phosphinomethyl)ferrocene is reported using an efficient lithiation and quench technique in which dimethylaminomethylferrocenes are useful intermediates
Ferrocenylmethylphosphines ligands in the palladium-catalysed synthesis of methyl propionate
No full textThe synthesis of a range of novel ferrocenylmethylphosphanes ligands is described which have direct application in the palladium catalysed reaction of carbon monoxide, methanol and ethene to obtain methyl propionate, a key intermediate in the preparation of methylmethacrylate
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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