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Functionalised and cyclometallated N-Heterocyclic Carbene complexes of Pd, Ni, Rh and Ir : synthesis and applications
No full textNew imidazolinium salts have been synthesised with the following substitution: (i) 2-(3-methylpyridyl), 2-pyridyl; (ii) alkoxyphenyl (o-OMe-phenyl, p-OMe-phenyl, o,p-(OMe)2-phenyl, o,p,o-(OMe)3-phenyl, o-OiPr-phenyl, p-OiPr-phenyl); (iii) substituted aryl (o-Et-phenyl, o-iPr-phenyl); (iv) fluoraryl (m, m-(CF3)2-phenyl, o-F-phenyl, o,p-F2-phenyl). In addition, novel pyridyl functionalised imidazolium salts have been synthesised. The targeted imidazol(in)ium salts were hoped to give rise to metal complexes with hemilabile coordination sites (pyridine functionalised species) or to cyclometallated complexes which on heating may generate active catalysts. Deprotonation of two of the imidazolium salts led to the isolation of the corresponding free carbenes. Five novel pyridyl functionalised imidazoline-2-ylidene complexes of palladium, three novel imidazolin-2-ylidene palladacycle complexes, four novel aryl substituted imidazoline-2-ylidene palladium complexes and two novel alkoxyphenyl imidazolin-2-ylidene palladacycle complexes have been synthesised by reacting the in situ deprotonated salt with various palladium precursors or by transmetallation reactions from silver carbine complexes. The complexes were characterised by analytical, spectroscopic and diffraction techniques. Interestingly, the first palladium ‘C-C-C pincer’ type complex (3.14) has been isolated after facile double cyclometallation succeeding the ligand complexation. Selected palladium imidazoline-2-ylidene complexes have been tested as catalysts for Heck coupling reactions. [1,3-Bis(4-methoxyphenyl)imidazolin-2-ylidene] {2-[3-(4-methoxyphenyl) imidazolin-2-ylidene] -5- methoxy phenyl-κ2C,C’} methyl palladium(II) (3.16) and [1,3-bis(2,4-dimethoxyphenyl)imidazolin-2-ylidene] { 2-[3-(2,4-dimethoxy phenyl) imidazolin-2-ylidene] -3,5- dimethoxy phenyl- κ2C,C’} methyl palladium(II) (3.15) have been found to be excellent catalysts for the Heck couplings of aryl bromides, deactivated aryl bromides and activated aryl chlorides, while moderate results for the Heck coupling of chlorobenzene have been achieved. These complexes surpass the activity of standard palladium phosphine complexes and are amongst the most active palladium NHC complexes reported to date. Five novel picolyl-functionalised imidazol-2-ylidene complexes of Rh(I) and Ir(I) have been prepared and characterised by the reaction of [M(COD)C1]2 (M = Rh, Ir) with 1-[2-(3-methyl)pyridyl]3-[2,6-diisopropyl)phenyl]imidazol-2-ylidene (2.1b). When M = Rh the nature of the products was found to be dependent on the reactant ratio. Furthermore, one novel Ir(III) picolyl functionalised imidazolin-2-ylidene complex featuring a 1-κ-4,5,6-η-C8H12 moiety (5,6) has been synthesised by reacting [Ir(COD)C1]2 with, in situ formed, 1-[2-(3-picolyl)]-3- (2,6-diisopropylphenyl) imidazolin-2-ylidene.</p
(1)Pyridine and phosphine functionalised N-heterocyclic carbene complexes of rhodium and iridium
No full textThe pyridine functionalised N-heterocyclic carbene complexes [M(kappa(2)-NCDIPP)(COD)](+)A(-), NCDIPP = 3-(2, 6-(Pr2C6H3)-C-i)-1-[2-(3-picolyl)]-imidazol-2-ylideni, A(-) = [(Ar4B)-B-F](-), [{3,5-(CF3)(2)C6H2}(4)B](-), M = Rh, 1b, Ir, 4, have been prepared in two steps by reaction of the [M(COD)Cl](2) with the isolated NCDIPP to [Rh(kappa(1)-NCDIPP)(COD)Cl], 2, and [Ir(kappa(2)-NCDIPP)(COD)Cl], 3, followed by anion exchange with Na(+)A(-). The phosphine functionalised N-heterocyclic carbene complex [Rh(PCH2Cmes)(2)]Br, 6, PCH2Cmes = 1-(diphenylphosphino-methyl)-3-(2,4,6-Me3C6H2)-imidazol-2-ylidene, was prepared by the reaction of the [Rh(COD)Cl](2) with the corresponding N-heterocyclic carbene generated in situ. Monomeric [Rh(PCH2CH2CDIPP)(acac)], 7 was prepared by an analogous reactions from [Rh(COE)(2)(acac)]. In contrast, phosphine functionalised N-heterocyclic carbene complexes of iridium (I) were not easily accessible. However, the reaction of [Ir(COD)(mu-Cl)2(mu-H)]2 with PCH2CH2Cmes gave complex [Ir(COD)(PCH2CH2Cmes.)Br], 8, in which the carbene is coordinated to the metal in an 'abnormal' mode
Picoline and pyridine functionalised chelate N-heterocyclic carbene complexes of nickel: synthesis and structural studies
No full textThe first pyridine and picoline functionalised N-heterocyclic carbene complexes of nickel are described in this paper. The nature of the isolated complexes is critically dependent on the bite angle and the substituents of the ligand used and the synthetic method for the introduction of the ligand on the metal. From NiBr2 (DME), DME=1,2-dimethoxyethane, by transmetallation with one equivalent of Ag(CN)2]Br2 (3). Transmetallation with Ag(C-N)Cl, (C-N) = [3-(2,6-Pr-2(i) C6H3)1[1-(2-pyridyl)imidazol-2-ylidene] afforded the bimetallic species [(C-N)(2)Ni(mu-Br)(2) NiBr2] (4), containing one octahedral and one tetrahedral nickel centre. Finally, from the reaction of NiBr2 (DME) with free (C-N*), (C-N*) = 3-(2,6-(Pr2C6H3)-C-i)-1-[2-(3-picolyl)]-imidazol-2-ylidene, good yields of Ni(C-N*)Br-2, (6) were obtained. Attempts to alkylate (1) were not successful
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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