Ligand steric and fluoroalkyl substituent effects on enchainment cooperativity and stability in bimetallic nickel(II) polymerization catalysts

Michael P. Weberski, Changle Chen, Massimiliano Delferro*, Tobin J. Marks

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

98 Scopus citations

Abstract

The synthesis and characterization of two neutrally charged bimetallic Ni II ethylene polymerization catalysts, {2,7-di-[2,6-(3,5-di- methylphenylimino)methyl]1,8-naphthalenediolato}-bis-Ni II(methyl) (trimethylphosphine) [(CH 3)FI 2-Ni 2] and {2,7-di-[2,6-(3,5-di-trifluoromethyl-phenylimino)methyl]-1,8-naphthalenediolato} -bis-Ni II(methyl)(trimethyl-phosphine) [(CF 3)FI 2-Ni 2)], are reported. The diffraction-derived molecular structure of (CF 3)FI 2-Ni 2 reveals a Ni⋯Ni distance of 5.8024(5) Å. In the presence of ethylene and Ni(COD) 2 or B(C 6F 5) 3 co-catalysts, these complexes along with their monometallic analogues [2-tert-butyl-6-((2,6- (3,5-dimethylphenyl)phenylimino)methyl)-phenolate]-Ni II- methyl(trimethylphosphine) [(CH 3)FI-Ni] and [2-tert-butyl-6-((2,6-(3, 5-ditrifluoromethyl-phenyl)phenylimino)methyl)phenolato]-Ni II-methyl- (trimethylphosphine) [(CF 3)FI-Ni], produce polyethylenes ranging from highly branched M w=1400 oligomers (91 methyl branches per 1000 C) to low branch density M w=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 (CF 3)FI 2-Ni 2 vs. monometallic (CF 3)FI-Ni), as well as by enhanced norbornene co-monomer incorporation selectivity, with bimetallic (CH 3)FI 2-Ni 2 and (CF 3)FI 2-Ni 2 enchaining approximately three- and six-times more norbornene, respectively, than monometallic (CH 3)FI-Ni and (CF 3)FI-Ni. Additionally, (CH 3)FI 2-Ni 2 and (CF 3)FI 2-Ni 2 exhibit significantly enhanced thermal stability versus the less sterically encumbered dinickel catalyst {2,7-di-[(2,6-diisopropylphenyl)imino]-1,8-naphthalenediolato}-bis-Ni II(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-Ni II(methyl)-(trimethylphosphine). Ni-ce cats: Two neutrally charged bimetallic phenoxyiminato Ni II ethylene polymerization catalysts are reported. Significant Ni⋯Ni cooperative effects are shown by increased product polyethylene branching in ethylene homopolymerizations and by enhanced norbornene co-monomer incorporation selectivity in ethylene-norbornene copolymerization compared with monometallic controls.

Original languageEnglish (US)
Pages (from-to)10715-10732
Number of pages18
JournalChemistry - A European Journal
Volume18
Issue number34
DOIs
StatePublished - Aug 20 2012

Keywords

  • bimetallic catalysts
  • cooperative effects
  • homogeneous catalysis
  • nickel
  • polymerization

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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