The synthesis and characterization of two neutrally charged Ni(II) ethylene polymerization catalysts, [2-tert-butyl-6-((2,6-(3,5-dimethylphenyl) phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CH 3)FI-Ni) and [2-tert-butyl-6-((2,6-(3,5-bis(trifluoromethyl)phenyl) phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CF 3)FI-Ni) are reported. In the presence of a Ni(COD) 2 cocatalyst, these catalysts produce markedly different polyethylenes: densely branched oligomers with M w = 1.4 × 10 3 g mol -1 for (CH 3)FI-Ni vs lightly branched polyethylenes with M w = 92 × 10 3 g mol -1 for (CF 3)FI-Ni and with ∼6.5× the polymerization activity and with much greater performance thermal stability. HOESY 2D 19F, 1H NMR spectra of a model Ni-ethyl compound, [2-tert-butyl-6-((2,6- (3,5-bis(trifluoromethyl)phenyl)phenylimino)methyl)phenolato]nickel(II) ethyl 2,4-lutidine ((CF 3)FI-Ni-Et), indicate non-negligible C β-H β•••F 3C through-space dipolar interactions, and molecular modeling reveals that C β-H β•••F(C) distances can be as small as ∼2.61 Å during the polymerization process. Furthermore, there is no structural or spectroscopic evidence for fluorocarbon inductive effects on the structure, bonding, and reactivity of these complexes, and a catalyst with CF 3 introduced β to the imino N produces only low-M w oligomers with low activity. These results argue that weak (ligand)C-F•••H-C(polymer) interactions can significantly influence the chain transfer characteristics of these catalysts.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry