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- Title
Ligand Steric and Fluoroalkyl Substituent Effects on Enchainment Cooperativity and Stability in Bimetallic Nickel(II) Polymerization Catalysts.
- Authors
Weberski, Michael P.; Chen, Changle; Delferro, Massimiliano; Marks, Tobin J.
- Abstract
The synthesis and characterization of two neutrally charged bimetallic NiII ethylene polymerization catalysts, {2,7-di-[2,6-(3,5-di-methylphenylimino)methyl]1,8-naphthalenediolato}-bis-NiII(methyl)(trimethylphosphine) [ (CH3)FI2-Ni2] and {2,7-di-[2,6-(3,5-di-trifluoromethyl-phenylimino)methyl]-1,8-naphthalenediolato}-bis-NiII(methyl)(trimethyl-phosphine) [ (CF3)FI2-Ni2)], are reported. The diffraction-derived molecular structure of (CF3)FI2-Ni2 reveals a Ni ⋅⋅⋅Ni distance of 5.8024(5) Å. In the presence of ethylene and Ni(COD)2 or B(C6F5)3 co-catalysts, these complexes along with their monometallic analogues [2- tert-butyl-6-((2,6-(3,5-dimethylphenyl)phenylimino)methyl)-phenolate]-NiII-methyl(trimethylphosphine) [ (CH3)FI-Ni] and [2- tert-butyl-6-((2,6-(3,5-ditrifluoromethyl-phenyl)phenylimino)methyl)phenolato]-NiII-methyl-(trimethylphosphine) [ (CF3)FI-Ni], produce polyethylenes ranging from highly branched Mw=1400 oligomers (91 methyl branches per 1000 C) to low branch density Mw=92 000 polyethylenes (7 methyl branches per 1000 C). In the bimetallic catalysts, Ni ⋅⋅⋅Ni cooperative effects are evidenced by increased product polyethylene branching in ethylene homopolymerizations (∼3× for (CF3)FI2-Ni2 vs. monometallic (CF3)FI-Ni), as well as by enhanced norbornene co-monomer incorporation selectivity, with bimetallic (CH3)FI2-Ni2 and (CF3)FI2-Ni2 enchaining approximately three- and six-times more norbornene, respectively, than monometallic (CH3)FI-Ni and (CF3)FI-Ni. Additionally, (CH3)FI2-Ni2 and (CF3)FI2-Ni2 exhibit significantly enhanced thermal stability versus the less sterically encumbered dinickel catalyst {2,7-di-[(2,6-diisopropylphenyl)imino]-1,8-naphthalenediolato}-bis-NiII(methyl)(trimethylphosphine). The pathway for bimetallic catalyst thermal deactivation is shown to involve an unexpected polymerization-active intermediate, {2,7-di-[2,6-(3,5-di-trifluoromethyl-phenylimino)methyl]-1-hydroxy,8-naphthalenediolato-NiII(methyl)-(trimethylphosphine).
- Publication
Chemistry - A European Journal, 2012, Vol 18, Issue 34, p10715
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201200713