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Mono- and binuclear orthopalladated complexes of phosphorus ylides containing nitrogen, phosphorus or bridging diphosphine ligands: Self-assembly, theoretical calculations and comparative catalytic activity
No full textBinuclear orthopalladated complexes of phosphorus ylides containing electron-withdrawing fluoro (Y1),
bromo (Y2) or phenyl (Y3) substituent, [Pd{ k 2 (C,C)-[(C 6 H 4 -2)PPh 2 ]CH(CO)C 6 H 4 X-4}( m -Cl)] 2 (X 1⁄4 F (1), Br
(2), Ph (3)) were obtained by two different methods from the reaction of corresponding ylides and PdCl 2
or Pd(OAc) 2 . The synthesized orthopalladated complexes 1 and 2 reacted with the monodentate ligands
with various donor abilities affording the mononuclear complexes [PdCl{C,C-{CH[P(C 6 H 4 -2)Ph 2 ]C(O)
C 6 H 4 X-4]}}L] [L 1⁄4 triphenylphosphine (X 1⁄4 Cl (1a), X 1⁄4 Br (2a)); 3-methylpyridine (X 1⁄4 Cl (1b), X 1⁄4 Br
(2b)); 4-methylpyridine (X 1⁄4 Br (2c)); 2,4,6-trimethylpyridine (X 1⁄4 Cl (1c)); pyridine (X 1⁄4 Cl (1d));
piperidine (X 1⁄4 Cl (1e)). The reaction of chloro-bridged complex 3 with bis(diphenylphosphino)ethane,
dppe, and bis(diphenylphosphino)propane, dppp, in the 1:1 ratio occurred to give the symmetrical
bridged complexes of general formula [Pd 2 Cl 2 {C,C-{CH[P(C 6 H 4 -2)Ph 2 ]C(O)C 6 H 4 X-4]} 2 }}( m -P^P)]
(P^P 1⁄4 dppe (3a) and dppp (3b)). New complexes were fully characterized by elemental analysis, IR and
NMR spectroscopies. The crystal structures of 1, 1a, 2a, 3 and 3a were determined by single-crystal X-ray
diffraction analysis that revealed the self-assembly of complexes via the short contacts between donor
and acceptor groups to form polymer, sheet or network supramolecular structures. Density functional
theory (DFT) calculations for complexes 1, 1a and 2a indicated the good agreement with the experi-
mental value reported in this work. The catalytic activity of 1, 1a and 2a were comparatively studied in
the Suzuki cross-coupling reactions which showed the more efficiency of mononuclear complex 1a with
fluoro substituent
NC Palladacycles and C,C-chelating phosphorus ylide complexes: synthesis, X-ray characterization, and comparison of the catalytic activity in the Suzuki-Miyaura reaction
No full textSix secondary amine palladacycles bearing monodentate ligands (1a, 2a), 1,2-bis(diphenylphosphino)ethane (dppe) and 1,3-bis(diphenylphosphino)propane (dppp) containing bridging and bidentate ligands (1b, 2b–d), and four C,C-type phosphorus ylide complexes containing thiourea (tu) (3a), phenyl isothiocyanate (4a), and bridging and terminal azide groups (5 and 5a) have been synthesized. Resulting complexes have been characterized by elemental analyses, IR, 1H-, 13C{1H}-, and 31P{1H}-NMR spectroscopy with single crystal X-ray structure determination of 1a and 2a. The Pd in 1a and 2a occupies the center of a slightly distorted square planar environment formed by Caryl, Namine, Npyridine, and Cl. The catalytic efficiency of complexes showed that in most cases, amine palladacycles display better catalytic activities than the phosphorus ylide Pd(II) complexes. Comparison between bidentate and bridging dppe complexes showed that dppe-bridged dimer 2d has higher catalytic activity than dppe bidentate complex.</p
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
Synthetic Receptors: A Modular Approach to Large Structures
Get PDFCombination of medium-sized building blocks comprises a new strategy for the synthesis of artificial receptor molecules. These building blocks should have relatively rigid structures to which functional groups can be attached, such as calix[4]- and -[6]arenes, resorcin[4]arenes, porphyrins, and cyclodextrins. Combination of a (3- cyclodextrin with a calix[4]arene moiety resulted in water soluble receptor molecules. Large multifunctional receptors have been prepared by the covalent combination of two calix[4]arenes and one Zn-tetraarylporphyrin. The controlled conformation of p-tert-butylcalix[6]arenes which are alternately substituted with methoxy groups, was used to synthesize a cryptocalix[6]arene consisting of a calix[6]arene and a cyclotriveratrylene unit. A new type of diastereoisomerism (carceroisomerism) was found during the synthesis of carceplexes constructed from one calix[4]arene and one resorcin[4]arene. In a (2+2)-mode of coupling, the combination of calix[4]arenes and resorcin[4]arenes gave a large rigid receptor molecule of nanosize dimensions (ho/and). The combination of two calix[4]arenes with one resorcin[4)arene resulted in three different compounds (endo-endo, endo-exo, and exo-exo) with large hydrophobic surfaces to which steroids can be complexed
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
Memories of my activities in the field of science
No full textCelem artykułu jest przedstawienie ważniejszych zagadnień związanych z przebiegiem działalności w sferze nauki profesora Janusza Lipkowskiego, fizykochemika, członka rzeczywistego Polskiej Akademii Nauk, prezesa Towarzystwa Naukowego Warszawskiego 2007–2020, a w latach 2003–2006 wiceprezesa PAN. Opracowanie ma charakter autobiograficzny i stanowi fragment pracy, która opublikowana zostanie w 2022 r. w serii Fontes rerum ad historiam scientiae spectantium Instytutu Historii Nauki Polskiej Akademii Nauk.The aim of the article is to present more important issues related to the course of activities in the field of science of Professor Janusz Lipkowski, physicochemist, real member of the Polish Academy of Sciences, president of the Warsaw Scientific Society 2007–2020, and vice-president of the Polish Academy of Sciences in the years 2003–2006. The study is autobiographical in nature and is part of a work that will be published in 2022 in the series Fontes rerum ad historiam scientiae spectantium of the Institute of the History of Science of the Polish Academy of Sciences
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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