1,721,162 research outputs found
Radical-initiated alkene hydroauration as a route to gold(III) alkyls: an experimental and computational study
No full textThe hydroauration of functionalised 1-alkenes by the gold(III) hydride (C^NOMe^C)AuH is initiated by organic radicals and proceeds via (C^N^C)Au(II) radical intermediates following a bimolecular outer-sphere mechanism. The outcome of these reactions is determined by the stability of the gold-substituted radicals. The reaction is sensitive to steric as well as electronic factors; disubstituted alkenes and alkenes that form unstable radicals give product mixtures or are unreactive. As DFT calculations show, the reactions agree well with the calculated reaction enthalpies and the standard free energy change for the reaction of the gold(II) radical with the respective alkene
Group 4 salicyloxazolines are potent polymerization catalysts
No full textOctahedral titanium and zirconium complexes based on salicyloxazoline ligands with sterically demanding ortho-substituents provide a new family of extremely active ethene polymerization catalysts [up to 10(8) g PE (mol bar h)–1] which are in some cases "single site"
Hybrid catalysts: the synthesis, structure and ethene polymerisation activity of (salicylaldiminato)(pyrrolylaldiminato) titanium complexes
No full textThe mono(salicylaldiminato) complexes Ti{3-Bu-t-2-(O)C6H3CH=N(R)}Cl-3(THF) (where R = C6H5, C6F5) react with the metallated pyrrolylaldiminato ligand, K[2-(C6H5NCH)C4H3N], to afford the first examples of hybrid salicylaldiminato-ligated octahedral titanium complexes; the pre-catalysts give from very high to extremely high ethene polymerisation productivities when activated with MAO
The synthesis of new weakly coordinating diborate anions: anion stability as a function of linker structure and steric bulk
No full textThe successive addition of KCN and Ph3CCl to B(C6F4-C6F5-2)(3) (PBB) affords triphenylmethyl salts of the [NC-PBB](-) anion. By contrast, the analogous reaction with sodium dicyanamide followed by treatment with Ph3CCl leads to the zwitterionic aminoborane H2NB(C12F9)(2)C12F8, via nucleophilic attack on an o-F atom, together with CPh3[F-PBB]. Whereas treatment of [NC-PBB](-) with either PBB or B(C6F5)(3) fails to give isolable cyano-bridged diborates, the reaction of Me3SiNC-B(C6F5)(3) with PBB in the presence of Ph3CCl affords [Ph3C][PBB-NC-B(C6F5)(3)]. Due to steric hindrance this anion is prone to borane dissociation. The longer linking group N(CN)(2)(-) gives the very voluminous anions [N{CNB(C6F5)(3)}(2)](-) and [N(CN-PBB)(2)](-). A comparison of propylene polymerisations with rac-Me2Si(Ind)(2)ZrMe2 activated with the various boranes or trityl borates gives an anion-dependent activity sequence, in the order [NC-PBB](-) < [MeB(C6F5)(3)](-) < [MePBB](-) approximate to [PBB-NCB(C6F5)(3)](-) approximate to [N{CNB(C6F5)(3)}(2)](-) < [F-PBB](-) << [B(C6F5)(4)](-) < [N(CN-PBB)(2)](-). The anion [N(CN-PBB)(2)](-) gives a catalyst productivity about 2500 times higher than that of [NC-PBB](-) and exceeds that of [B(C6F5)(4)](-) based catalysts. The van der Waals volumes and surface areas of the anions have been calculated and provide a rationale for the observed reactivity trends in polymerisation reactions
Synthesis and catalytic activity of dinuclear imido titanium complexes: the molecular structure of [Ti(NPh)Cl( mu-Cl)(THF)(2)](2)
No full textReaction of TiCl4 with the reagents RN(SiMe3)(2) in dichloromethane precipitates red to black powders (R = 1-adamantyl, phenyl. pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl), which on treatment with tetrahydrofuran gives the new THF adducts [Ti(NR)Cl(mu-Cl)(THF)(2)](2). The complexes are dimeric in the solid state with bridging chloride and terminal imido ligands. Activation with MAO (methylaluminoxane) gives ethene polymerisation catalysts with productivities of up to 31 kg PE [(mol complex) h bar](-1)
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
Hydride transfer to gold: Yes or no? Exploring the unexpected versatility of Au···H-M bonding in heterobimetallic dihydrides
Full text linkThe potential for coordination and H-transfer from Cp2MH2 (M = Zr, W) to gold(I) and gold(III) complexes was explored in a combined experimental and computational study. [(L)Au]+ cations react with Cp2WH2 giving [(L)Au(κ2-H2WCp2)]+ (L = IPr ( 1 ), cyclic (alkyl)(amino)carbene ( 2) , or phosphines PPh3 (3) and Dalphos-Me (4) [IPr = 1,3-bis(diisopropylphenyl)imidazolylidene; Dalphos-Me = di(1-adamantyl)-2-(dimethylamino)phenyl-phosphine], while [Au(DMAP)2]+ (DMAP = p-dimethylaminopyridine) affords the C2-symmetric [Au(κ-H2WCp2)2]+ (5) . The Dalphos complex 4 can be protonated to give the bicationic adduct 4H , showing Au(I)…H+-N hydrogen bonding. The gold(III) Lewis acid [(C^N-CH)Au(C6F5)(OEt2)]+ binds Cp2WH2 to give an Au-H-W σ-complex. By contrast, the pincer species [(C^N^C)Au]+ adds Cp2WH2 by a purely dative W→Au bond, without Au···H interaction. The biphenyl-based chelate [(C^C)Au]+ forms [(C^C)Au(µH)2WCp2]+, with two 2-electron-3-centre W-H…Au interactions and practically no Au-W donor acceptor contribution. In all these complexes strong but polarised W-H bonds are maintained, without H-transfer to gold. On the other hand, the reactions of Cp2ZrH2 with gold complexes led in all cases to rapid H-transfer and formation of gold hydrides. Relativistic DFT calculations were used to rationalize the striking reactivity and bonding differences in these heterobimetallic hydride complexes along with an analysis of their characteristic NMR parameters and UV-Vis absorption properties
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