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Magnesium Diimidosulfinates – Conformational Studies in the Solid State and in Solution
No full textThe magnesium diimidosulfinates [(thf)(2)MgX{(NR)(2)SR'}] (X = Cl, Br; R = tBu, SiMe(3); R' = Ph, Bz, Me, nBu; 1-5) have been synthesised by treating sulfur diimides with different Grignard reagents and characterized by X-ray crystallography and NMR spectroscopy. The structural analyses of compounds 1-5 show that they contain either monomeric or dimeric structural motifs, depending on the steric requirements of the sulfur-bound organic substituent. NMR experiments suggest a temperature-dependent dynamic equilibrium between different conformers for all compounds
[(thf)Li-21{H2CS((NBu)-Bu-t)(2)}](2): Synthesis, polymorphism, and experimental charge density to elucidate the bonding properties of a lithium sulfur ylide
No full textSulfur ylides (R2S+--CR2) are widely used in organic synthesis for stereoselective epoxidations, cyclopropane formations, and ring expansion reactions. Nevertheless, their electronic properties are still under debate, because their ylenic textbook formulation (R2S=CR2) contradicts the reactivity. In order to elucidate the electronic situation in a sulfur ylide, we present an experimental charge density study via multipole refinement and subsequent topological analysis based on high-resolution X-ray data of [(thf)Li-2{H2CS((NBu)-Bu-t)(2)}](2) (1). The title compound is of special interest, since additionally the formal hypervalency can be investigated along with the controversial interaction between a carbanion with a Li-3 triangle. As a prerequisite for these studies, the polymorphism and synthesis of I were investigated. The findings clearly support the ylidic, non-hypervalent description of the molecule. The ylidic carbanion was determined to be 6-fold coordinated with three single bonds to the sulfur atom and both hydrogen atoms and three closed-shell interactions to the lithium atoms of the Li-3 triangle
1-Phenyl-1,2-cyclohexadiene: Generation, Interception by Activated Olefins, Dimerisation and Trimerisation
No full textFour possible precursors of 1-phenyl-1,2-cyclohexadiene (2) were examined, namely, 6,6-dibromo-1-phenylbicyclo[3.1.0]hexane, (1 alpha,5 alpha,6 alpha)-6-bromo-6-fluoro-1-phenylbicyclo-[3.1.0]hexane, 1-bromo-2-phenylcyclohexene and 1-bromo-6-phenylcyclohexene. All four compounds could be converted into 2, as demonstrated by the products of the interception of 2 with activated olefins. Styrene, 1,1-diphenyl-ethene, indene, furan and 2,5-dimethylfuran were employed as such. Whereas the first three gave [2+2] cycloadducts of 2, the last two provided one [4+2] cycloadduct each. To create the [2+2] cycloadducts, the it bond of 2 that is more remote from the phenyl group reacted, whereas the pi bond of 2 conjugated with the phenyl group exclusively produced the [4+2] cycloadducts. The generation of 2 in the absence of a trapping reagent brought about relatively good yields of a dimer or a trimer of 2 depending on the mode of the liberation of 2. Being derivatives of triphenylene, the dimer as well as the trimer have unusual structures, thereby indicating that a phenyl group is participating in the formation of these compounds. The most surprising structure of the trimer was elucidated by X-ray crystal diffraction. As to the mechanisms, diradical intermediates are proposed both for the cycloadditions and for the dimerisation. The initial steps of the latter seem to proceed also in the trimerisation.Deutsche Forschungsgemeinschaft; Fonds der Chemischen Industri
Access to new Janus head ligands: linking sulfur diimides and phosphanes for hemilabile tripodal scorpionates
No full textReactions of lithium dialkyl/phenyl phosphanylmethylides, RR'PCH(X)Li (R, R' = Me, Et, Ph and R = Me, R; = Ph; X = H or Me), with sulfur diimides S(NR '')(2) (R '' = (t)Bu or SiMe(3)) in an equimolar ratio yielded Janus head complexes with the structural motif [Li{RR'PCH(X)S(NR '')(2)}](2) (R '' = (t)Bu, SiMe(3)). The basic core of these dimeric complexes is composed of a (LiN)(2) four-membered ring containing two four-coordinated lithium atoms. A lithium complex of the new Janus head ligand with another structural motif [TMEDA center dot Li{Ph(2)PCH(2)S(NSiMe(3))(2)}] (6) could be isolated from the reaction of [Ph(2)PCH(2)Li center dot TMEDA] with S(NSiMe(3))(2). Two monomeric complexes [Mg{Me(2)PCH(2)S(NR '')(2)}(2)] (7, 8) were synthesised by a straightforward reaction of [Li{Me(2)PCH(2)S(NR '')(2)}(2)] with MgCl(2) in pentane. The magnesium atom is chelated by one phosphorus atom and two nitrogen atoms of each unit of the hemilabile ligand in a tripodal manner, leading to octahedral geometry around the magnesium cation. A complete analysis of [Ph(2)PCH(2)(SNSiMe(3))(HNSiMe(3))] (9) is also described in which one nitrogen atom of the imido moiety is protonated.DFG [1178]; Center of Materials Crystallography; INS
‐Bis(1,3‐disila‐2‐lithiumamido)‐ethylensilylaminen – Synthesen, Kristallstrukturen, Reaktionen
No full textEthylenediamine reacts with the chloro-functional tris(silyl)amines ClSiMe2N(SiMe3)SiMe2R in a molar ratio of 1:2 to give the N,N'-bis(1,1,3-trisila-2-aza)-ethylenediamines, [CH2-NH-SiMe2-N(SiMe3)SiMe2R](2), R = Me (1) and CMe3 (2). A structural isomer of 2 (CH2-NSiMe2CMe3-SiMe2-NHSiMe3 = 3) is formed thermally, via 1,3-silyl group migration from the ME3CSiMe2-N-SiMe3 group, at 200 degrees C. 1 reacts with butyllithium at 0 degrees C in a molar ratio of 1:2, forming the diamide 4, which was characterized as the monomer [CH2-NiSMe3-SiMe2-N(SiMe3)Li](2). Again two silyl groups migrate from the N(SiMe3)(2) groups to the ethyleneamine nitrogen atoms. The lithium ions are coordinated by both amido groups forming a planar four-membered ring. With THF as a solvent, each lithium ion of 4 coordinates one THF molecule. [CH2-NSiMe3-SiMe2-N-(SiMe3)Li-THF](2) (5) is obtained. With TMEDA as the donor base the cage structures of 4 and 5 are broken up to give an open-chain dilithium salt [CH2-NiSMe3-SiMe2-N(SiMe3)Li-TMEDA](2) (6) with each lithium ion coordinated by one TMEDA molecule. Halosilanes and haloboranes react with 4, 5, and 6 to give an N,N'-bis(1,1,3-trisila-2-aza)-ethylenesilylamine [CH2-NiSMe3-SiMe2-N(SiMe3)R](2), R= SiF2CMe3 (7), and N,N'-bis(1-bora-1,3-disila-2-aza)-ethylene-silylamines, R = B(F)N(SiMe3)(2) (8). B(F)[N(CMe2CH2)(2)CH2] (9). Thermally, 9 forms (FSiMe2-NSiMe3-CH2)(2) and via transient iminoborene. Me3SiN=BR, the four-membered ring (Me3SiN-BR)(2), (10). R = [N(CMe2CH2)(2)CH2]. Ring closure occurs and cyclononanes are obtained in the reaction of 4 with BF3 (11) and SiF4 (12). The crystal structures 4-10 are discussed
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
Competing reactions of hypercoordinate silicon dichelates
No full textNeutral hexacoordinate silicon complexes derived from hydrazide chelating ligands with imino-donor groups, and their pentacoordinate ionic dissociation products, undergo facile intramolecular aldol-type condensation catalyzed by their chloride counterion leading to formation of a third chelate ring. In analogous silacyclobutane dichelates, in the absence of halide counterion, a similar uncatalyzed rearrangement takes place, accompanied by opening of the four-membered ring. In the absence of et-protons necessary for the condensation, the four-membered ring residue adds directly to one of the imino-carbon atoms forming a new C-C bond and closing a different chelate ring. This latter addition to the imino carbon is the preferred reaction pathway, even in the presence of 12 alpha-protons, when cyanide ion replaces the chloride counterion and acts as nucleophile. The cyanide reactivity is rationalized in terms of the HSAB concept. An unusual intramolecular rearrangement involving the migration of a t-butyl group from silicon to carbon, while enabling the unprecedented attachment of a third hydrazide chelating agent, leading to a hexacoordinate trichelate complex, is presented. Copyright (C) 2008 John Wiley & Sons, Ltd.Israel Science Foundation [ISF-139/05]; INTAS [03-51-4164
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
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