1,720,993 research outputs found
Recommended from our members
Synthesis and Structure of Two New (Guanidinate) Boron Dichlorides and their Attempted Conversion to Boron(I) Derivatives
Get PDFTo test the feasibility of the guanidinate architecture for the support of boron( I) carbene analogues the energy gap between the singlet and triplet states of the model compound, [Me(2)NC{N(Ph)}(2)B:] (7), has been probed by both DFT and second order Moller - Plesset (MP2) methods. The singlet state is calculated to be more stable than the triplet state by between 6.0 and 10.1 kcal mol(-1). The new (guanidinate)boron dichlorides [Ph(2)NC{N(Mes)(2)]BCl(2) (14) and [Ph(2)NC{N(Dipp)(2)]BCl(2) (15) have been prepared and characterized by single- crystal X-ray diffraction. Attempts to reduce 14 and 15 to the corresponding boron(I) species were not successful.National Science Foundation CHE-0240008Robert A. Welch Foundation F-0003Chemistr
Recommended from our members
Synthesis and Structures of Boron Dihalides Supported by the C6F5-Substituted Beta-Diketiminate Ligand Hc(Cme)(2)(Nc6F5)(2) (-)
Get PDFThe new boron dihalides of the type [HC(CMe)(2)(NC6F5)(2)]BX2 (X = Cl, Br, I) have been prepared and characterized by single-crystal X-ray diffraction. Of the various synthetic approaches explored, the best method in terms of yield and product purity involves the silylhalide elimination reaction of the silylated iminoamine [HC(CMe)(2)(NC6F5)(N{SiMe3}C6F5)] with BX3. Chloroborenium salt [HC(CMe)(2)(NC6F5)(2)BCl][AlCl4] was prepared by treatment of [HC(CMe)(2)(NC6F5)(2)]BCl2 with AlCl3 in CH2Cl2 solution. This salt was also structurally authenticated and represents the first such data for a beta-diketiminate-supported haloborenium cation.Chemistr
Recommended from our members
Boron Di- and Tri-Cations
Get PDFPrevious work on boron di- and tri-cations is reviewed. The structural chemistry of representative examples of these classes of compound has been probed by determination of the single-crystal X-ray structures of [(4-Mepy)(4)B]Br-3 and [py(3)BH]Br-2. The electronic structures of the polycations [(py)(3)BH](2+), [(py)(3)BBr](2+), [(4-Mepy)(3)BH](2+), [(4-Mepy)(4)B](3+), [(Me3P)(3)BH](2+) and [(Me3P)(4)B](3+) have been examined by DFT methods. The atomic charges on these cations were evaluated by Mulliken, natural population analysis (NPA), Hirschfeld and Voronoi deformation density (VDD) methods.Robert A. Welch Foundation F-0003McMaster UniversityNatural Sciences and Engineering Research Council of CanadaChemistr
Recommended from our members
Synthesis Of Heteroaromatic 3,3 '-Bridged Biscarbenes Of The 1,2,4-Triazole Series And Their Properties
Get PDFThe stable 3,3'-bridged biscarbenes, 1,4- and 1,3-bis[1-alkyl-4-phenyl-1,2,4-triazol-5-yliden-3yl] benzenes (5a,b,d) and 1,3-bis[1-(1-adamantyl)-4-phenyl-1,2,4-triazol-5-yliden-3-yl] butane (5c) have been prepared. Treatment of 5b with copper (I) chloride in tetrahydrofuran/acetonitrile solution and cobalt (II) chloride in acetonitrile or acetonitrile/toluene solution afforded the biscarbene copper (I) complex 8. The reactions of 5d with diphenyldiazomethane and sulfur resulted in the novel bisthione 6 and bisazine (7) derivatives, respectively. The X-ray crystal structures of 5d, 8 were determined.Ukrainian State Fund F25.3/049Robert A. Welch Foundation F0003Biochemistr
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
The Preparation, Characterization and, Reactivity of Transition Metal Complexes: 1) The Chemistry of Low Oxidation State Iridium Pincer Complexes and, 2) Organic Transformations Catalyzed by (BIAN)-Iron Complexes
No full textIn recent decades pincer ligands have gained much more attention in the field of organometallic chemistry. The thermal stability and highly tunable steric and electronic properties of pincer ligands make them desirable in catalysis. Iridium based pincer complexes found to be efficient catalysts in variety of organic transformations, such as hydrofunctionalization, C–H bond activation, and dehydrogenation reactions. The ability of pincer ligands to stabilize transition metals in their reactive, low-coordination mode has received extensive attention in recent years. The first section of this dissertation focuses on the using of the pincer-ligated iridium fragment [(RPOCOP)Ir] (RPOCOP = 2,6-bis(di-tert-butyl-phosphonito) benzene or 2,6-bis(di-iso-propyl-phosphonito)benzene) to synthesize a range of complexes with widely varying steric and electronic properties. The complexes include the novel Ir species (tBuPOCOP)Ir(L) (L= MeCN, pyridine, 2,4,6-triphenylphosphinine), (iPrPOCOP)Ir(H)(Cl)(L) (L = PPh3, PCy3, 2,4,6-triphenylphosphinine) and (iPrPOCOP)Ir(L) (L = PPh3, PCy3), 2,4,6-triphenylphosphinine). (tBuPOCOP)Ir(PPh3), has served as a convenient source of the latent Ir(I), 14-electron species [(tBuPOCOP)Ir], and applied in ligand exchange chemistry with CO, C2H4, H2, BH3, HBPin, acetylene, MeCN and pyridine. In the case of MeCN and pyridine the reaction generated an equilibrium among species. Varying concentrations of both pyridine and acetonitrile, the thermodynamic parameters of this ligand exchange process between (tBuPOCOP)Ir(PPh3) and L (L = MeCN or pyridine) were determined employing NMR spectroscopy. Discussion of these results allows us to address whether phosphine displacement occurs via an associative or dissociative pathway. The second part of this dissertation involves the catalytic applications of BIAN (bis-(arylimino) acenaphthene) based iron complexes for the hydroboration and cyclotrimerization of alkynes. Hydroboration of alkynes is regarded as one of the most common methods to prepare alkenyl boronates, which can be used as intermediates in a number of important transformations including Suzuki-Miyaura coupling, Diels-Alder reaction, preparation of three-membered rings, and enantioselective hydrofunctionalization. Our (BIAN)-iron complexes were found to be viable catalysts for the regioselective hydroboration of terminal and internal alkynes. The hydroboration of alkynes in the presence of HBpin and an activator afforded vinyl boronic esters with the exclusive formation of trans product. The metal-catalyzed [2+2+2] cyclotrimerization of alkynes is one of the most powerful methods to form benzene derivatives due to the high atom-efficiency and wide substrate scope that can be employed. There are only a handful of reports on iron catalyzed cyclotrimerization of alkynes. Simple iron salts or iron-carbene complexes mainly dimerize or homo-coupled terminal alkynes. Therefore, we have recently started studying the efficacy of our dppBIANFe(C7H8) complex in the cyclotrimerization of both terminal and internal alkynes. Our preliminary results showed the versatility of our system in regioselective cyclotrimerization of alkynes.Embargo status: Restricted to TTU community only. To view, login with your eRaider (top right). Others may request the author grant access exception by clicking on the PDF link to the left
- …
