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An efficient synthetic method of ansa-zirconocene dimethyl complexes via Me2ZrCl2
No full textThe reaction of ZrCl4 with 2 equiv. of MeLi to form Me2ZrCl2 followed, by in situ metalation of Me2ZrCl2 with the corresponding ansa-ligands produces the respective ansa-dimethylzirconocene complexes, o-Xyl(Ind)(2)ZrMe2 [1b, Ind=eta(5)-1-indenyl, o-Xyl=C6H4(CH3)(2)-1,2], 2-Bn(Ind)(2)ZrMe2 [2b, 2-Bu=(-CH2CH=CHCH2-)], Et(Ind)(2)ZrMe2 (3b), and Me2Si(Znd)(2)ZrMe2 (4b) in high yields. Treatment of 1b-3b with HCl affords ansa-dichlorozirconocene complexes, 1a-3a, in quantitative yields. Synthesis of ansa-dimethylzirconocene via Me2ZrCl2 is more efficient than that via Cp2ZrCl2 (Cp-2=ansa-ligand) in the conventional methods. (C) 1997 Elsevier Science S.A
CONSECUTIVE C-C BOND SCISSION OF AN ALLYL LIGAND ON A WOS3 CLUSTER FRAMEWORK
No full textThe reaction, of Os-3(CO)(9)(C(2)R(2)) (R = Tol, Ph; Tol = p-C(6)H(4)Me) with Cp(CO)(2)W=CTol (Cp = eta(5)-C5H5) produces an alkylidyne-alkyne complex CpWOs(3)(CO)(10)(mu(3)-eta(2)-C(2)R(2))(mu(3)-CTol) [1a (R = Tol), 1b (R = Ph)], which is converted to two isomeric allyl complexes CpWOs(3)(CO)(10)(mu(3)-C(3)R(2)Tol) (2a,b and 3a,b) upon thermolysis. Complexes 3a,b, in which the allyl ligand is pi-coordinated to the tungsten atom, undergo consecutive allyl C-C bond cleavage to afford trialkylidyne complexes CpWOs(3)(CO)(9)(mu(3)-CR)(2)(mu 3-CTol) (5a,b) via alkylidyne-alkyne complex CpWOs(3)(CO)(10)(mu(3)-eta(2)-C(2)R(2))(mu(3)-CTol) or CpWOs(3)(Co)(10)(mu 3-eta(2)-C(2)RTol)(mu(3)-CR) (4a,b), together with formation of CpWOs(3)(CO)(8)(mu(3)-perpendicular to-C(2)R(2))(mu(3)-CTol) or CpWOs(3)(CO)(8)(mu(3)-eta(2)-perpendicular to-C(2)RTol)(mu(3)-CR) (6a,b) as a minor product
Propylene polymerization with unbridged rac- or meso-bis[1-(p-tolyl)indenyl]dichloro zirconium/methylaluminoxane catalyst
No full textA novel unbridged metallocene complex, (1-TolInd)(2)ZrCl2 (Tol = p-C6H4CH3) was prepared. Meso-like (1-TolInd)(2)ZrCl2 afforded a syndiotactic-dominant polypropylene having a short syndiotactic length at low temperatures (-30 degrees C). This stereosequence is due either to a weakly chain-end controlled or to a syndiotactic site controlled polymerization with site isomerization. Racemic isomer produced a completely atactic PP even at -30 degrees C
Synthesis, structure, and catalytic properties of ansa-zirconocenes, Me2X(Cp)(RInd)ZrCl2 (X=C, Si; R=2-p- or 3-p-tolyl)
No full textansa-Zirconocenes Me2X(Cp)(3-TolInd)ZrCl2 [X = C(7), Si(8); Cp = eta(5)-C5H5; Tol = p-C6H4CH3] and Me2Si(Cp)(2-ToIInd)ZrCl2 (9), have been prepared by the reactions of ZrCl4 with the corresponding dilithiated ligands in diethyl ether at -78 degrees C. The molecular structure of complex 9 has been determined by a single crystal X-ray diffraction study. Propylene polymerization has been studied for complexes 7, 8 and 9 in the presence of methylaluminoxane (MAO). Complex 9 reveals the highest catalytic activity of 1570 kg PP/(mol Zr h atm) and the highest molecular weight of 1.2 X 10(6) among the three catalysts. Complex 9 produces atactic polypropylene (PP), whereas 7 and 8 afford PP with a weak syndiotacticity at low temperature.We are grateful to the Korea Academy of Industrial Technology for financial support of this work
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
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