1,720,962 research outputs found
Conversion of Dinitrogen into Acetonitrile under Ambient Conditions
No full textAbout 20% of the ammonia production is used as the chemical feedstock for nitrogen-containing chemicals. However, while synthetic nitrogen fixation at ambient conditions has had some groundbreaking contributions in recent years, progress for the direct conversion of N-2 into organic products remains limited and catalytic reactions are unknown. Herein, the rhenium-mediated synthesis of acetonitrile using dinitrogen and ethyl triflate is presented. A synthetic cycle in three reaction steps with high individual isolated yields and recovery of the rhenium pincer starting complex is shown. The cycle comprises alkylation of a nitride that arises from N-2 splitting and subsequent imido ligand centered oxidation to nitrile via a 1-azavinylidene (ketimido) intermediate. Different synthetic strategies for intra- and intermolecular imido ligand oxidation and associated metal reduction were evaluated that rely on simple proton, electron, and hydrogen-atom transfer steps.European Research Council (ERC) [646747
[IrCl{N(CHCHPtBu2)2}]−: a versatile source of the IrI(PNP) pincer platform
Full text linkThe iridium(II) complex [IrCl{N(CHCHPtBu2)2}] is reduced by KC8 to give the anionic iridium(I) pincer complex [IrCl{N(CHCHPtBu2)2}]− which was isolated and fully characterized upon stabilization of the counter cation with crown ether as [K(15-cr-5)2][IrCl{N(CHCHPtBu2)2}]. This unprecedented anionic iridium(I) pincer complex completes the unusual, structurally characterized IrI/IrII/IrIII redox series [IrCl{N(CHCHPtBu2)2}]−/0/+, all in a square-planar coordination geometry, emphasizing the versatility of this PNP pincer ligand in stabilizing a broad range of oxidation states. The anionic chloro complex is a versatile source of the Ir(PNP) platform. Its reactivity was examined towards chloride ligand substitution against CO and N2, and oxidative addition of C-electrophiles, C–H bonds and dioxygen, allowing for the isolation of iridium(I) and iridium(III) (PNP) carbonyl, hydrocarbyl and peroxo complexes which were spectroscopically and crystallographically characterized
Transient and Stable Terminal Imido Complexes of Iridium
Full text linkIn conclusion, it has been demonstrated that the proton coupled oxidation of metal-bound amines and water provide access to a wide range of imido- and oxo-complexes, respectively. The synthetic approach of using strict 1 e- / 1 H+ abstraction reagents for an overall 2 e- / 2 H+ process paves the way for possible electrochemical synthesis of a nitrene/oxo building block. Because of the possibility of using a basic aqueous solution, the oxo complex is predestined for electrochemistry. The spectroscopic, magnetic, crystallographic and computational characterization of an iridium(III/IV/V) imido redox series is in line with highly covalent Ir–NtBu bonding as expressed by the simple MO model shown in . The dicationic complex of this series is purely diamagnetic. The data supports an electronic doublet ground state for the cationic imide with cylindrical delocalization of the spin density perpendicular to the Ir–NtBu bond as a result of SOMO/LUMO mixing through SOC. The neutral imide is best described as an electronic triplet with a separated non-magnetic ground state, which results in ambiphilic nitrene transfer reactivity with both CO2 and PMe3, amongst other reactions. In comparison, the chemical inertness of this compound is surprising and somewhat contradictive to the widely accepted assumption that radical character features enhanced reactivity. Besides steric shielding, this finding can be attributed to stabilizing relativistic contributions by SOC-induced spin delocalization, which moderates the reactivity of this class of electron-rich heavy metal imido complexes
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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