1,721,031 research outputs found
Sulfimidation: a new and versatile strategy for the post ring-closure derivatisation of mixed thia/oxa crowns
No full textReaction of [18]aneO5S with the aminating agent MSH results in the {[18]aneO5SNH2}+ cation which may be converted through to the linked crown system [({[18]aneO5S}2N)]+via deprotonation, bromination and reaction with the parent crown; significantly, despite their positive charge, both systems can coordinate sodium cations to the ether linkages
Sulfimidation of thioether groups—a versatile method for modifying and linking thia/oxa crowns
Get PDFReaction of the mixed thioether/ether crowns [9]aneO2S 1, [12]aneO3S 2 and [18]aneO4S2 3 with one mol. equivalent of the aminating agent MSH (o-mesitylsulfonylhydroxylamine) in Et2O results in the formation of the mono-sulfimidated systems {[9]aneO2(SNH2)}+ 1a, {[12]aneO3(SNH2)}+ 2a and {[18]aneO4S(SNH2)}+ 3a, while using two mol. equivalents of MSH with 3 gives the disulfimidium cation {[18]aneO4(SNH2)2}2+ 3b. All of these species have been isolated in good yields as the [mesSO3]- (mes = 2,4,6-Me3C6H2) salts and can be readily converted to the [BPh4]- salts by metathesis with Na[BPh4]. Treatment of 1a or 2a with lithium diisopropylamide (LDA) and N-bromosuccinimide (NBS) at -78 °C, followed by addition of a further equivalent of the parent thia/oxa crown, gives monocationic N-bridged sulfimide bicyclic compounds ( 4 and 5 respectively), in which the crowns are linked by the sulfimidic nitrogen. Reaction of 3a with LDA and NBS leads to formation of the {([18]aneO4S2)N}+ cation 6 which exhibits an intramolecular S–N–S bridge. Crystallographic studies on representative examples of each compound type are described, together with their spectroscopic properties
The first use of the free selenimide Ph2SeNH as a synthon; the synthesis and X-ray crystal structure of [Ph2SeNSePh2][BPh4]
Get PDFReaction of o-mesitylsulfonylhydroxylamine (MSH) with Ph2Se results in the [Ph2SeNH2]+ cation; low temperature deprotonation (LDA), bromination (NBS) and then treatment with Ph2Se–Na[BPh4] generates [Ph2SeNSePh2][BPh4], via the selenimides Ph2SeNH and Ph2SeNBr
Synthesis and Characterisation of Transition Metal Complexes of a Novel 1,5‐benzodiazepine‐Functionalised Tertiary Phosphine
No full textThe one-step synthesis (44 % isolated yield) of the 1,5-benzodiazapine functionalised phosphine 1, C
31H
31N
2OP, is reported. Bridge cleavage of {MCl(μ-Cl)(η
5-Cp*)}
2 (M=Ir, Rh) with 2 equiv. of 1 in CH
2Cl
2 gave the mononuclear compounds [MCl
2(η
5-Cp*)(P-1)] (M=Ir, 2 a; M=Rh, 2 b) in which 1 functions as a P-monodentate ligand. Rapid C(sp
3)−H bond activation, at room temperature, is observed for 2 a leading to the unusual cyclometallated complex [Ir(η
5-Cp*)(P,N,C-1)]Cl
2 3 (or 3‘) bearing an anionic P/N
amine/C-terdentate ligand. Reaction of [Pt(CH
3)Cl(η
4-cod)] with one equiv. of 1 led to [Pt(CH
3)Cl(P,N-1)] 4, suggesting that 3 may form via an intermediate Ir
III cationic species in which the ligand is P,N-bound. The Ir
I complex [IrCl(η
4-cod)(P-1)] 5 does not, under similar conditions, show any evidence for C−H activation. Single crystal X-ray studies on 1, 2 a, 2 b, 3, 3‘, 4, and 5 reveal intramolecular N ⋅⋅⋅ H−O H-bonding in all cases.
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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
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