1374460-55-5Relevant articles and documents
Suppression of β-hydride chain transfer in nickel(II)-catalyzed ethylene polymerization via weak fluorocarbon ligand-product interactions
Weberski, Michael P.,Chen, Changle,Delferro, Massimiliano,Zuccaccia, Cristiano,MacChioni, Alceo,Marks, Tobin J.
, p. 3773 - 3789 (2012/07/02)
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 Mw = 1.4 × 103 g mol -1 for (CH3)FI-Ni vs lightly branched polyethylenes with Mw = 92 × 103 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 ((CF3)FI-Ni-Et), indicate non-negligible C β-Hβ???F3C through-space dipolar interactions, and molecular modeling reveals that C β-Hβ???F(C) distances can be as small as ～2.61 A 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 CF3 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.
