Browsing by Author "Rojas, Rene"

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    Mono and bimetallic nickel bromide complexes bearing azolate-imine ligands: Synthesis, structural characterization and ethylene polymerization studies
    (ELSEVIER SCIENCE SA, 2009) Caris, Rodrigo; Peoples, Brian C.; Valderrama, Mauricio; Wu, Guang; Rojas, Rene
    The synthesis of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline (1) and N-(1-(indazol-2-yl)ethylidene)-2,6-diisopropylaniline (2) allowed access to new transition metal complexes. When reacted with dibromo(2,2'-dimethoxyethylether) nickel(II) the complexes [NiBr2{N-(1-(3,5-dimethylpyrazol-1-yl) ethylidene)-2,6-diisopropylaniline}] (3) and [Ni2Br2(mu-Br)2{N-(1-(indazol-1-yl)ethylidene)-2,6-diisopropylaniline} 2] (4) are yielded, respectively. The addition of MAO generates catalytically active species for the homopolymerization of ethylene. The polymer products were low molecular weight (3-6 K) and a monomodal molecular weight distribution, consistent with the presence of a single active site. In addition, the catalyst was found to efficiently oligomerize higher olefins to high molecular weights with narrow PDIs. (C) 2009 Elsevier B.V. All rights reserved.
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    New bis(azolylcarbonyl)pyridine chromium(III) complexes as initiators for ethylene polymerization
    (ELSEVIER SCIENCE SA, 2011) Hurtado, John; Ugarte, Javiera; Rojas, Rene; Valderrama, Mauricio; Mac Leod Carey, Desmond; Munoz Castro, Alvaro; Arratia Perez, Ramiro; Froehlich, Roland
    Reaction of 2,6-pyridinedicarbonyl dichloride with 3,5-dimethylpyrazole and 1H-indazole, respectively, yield the tridentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylcarbonyl)pyridine (1) and 2,6-bis(indazol-1-ylcarbonyl)pyridine (2). The molecular structure of the new compound (2) was determined by single-crystal X-ray diffraction. These ligands react with CrCl3(THF)(3) in THF to form neutral complexes of general formula [CrCl3{2,6-bis(azolylcarbonyl)pyridine-N,N,N}] (3, 4) which were isolated in high yield as air stable green solids and characterized by elemental analysis, magnetic moment, IR, and mass spectroscopies. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active for the polymerization of ethylene. (C) 2011 Elsevier B.V. All rights reserved.