This paper describes the synthesis of neutral nickel(II) catalysts for the polymerization of ethylene. A series of 2-(arylamino)-5-methylcyclopent-2-en-1-one (aryl = 2,6-diisopropylphenyl, 2,4,6-trimethylphenyl, 3,5-dimethylphenyl, and 4-methylphenyl) proligands, derived from the condensation of aryl amines with maple lactone, were synthesized as their keto-enamine tautomers. Deprotonation with NaH gave their respective sodium imino-enolate salts, which underwent salt metathesis with Ni(II) precursors to give square planar [Ni(Ar)(κ 2-imino-enolate)(PPh 3)] (Ar = Ph, ortho-tolyl) complexes containing 5-membered [N,O] chelates. Precatalysts with N-Dipp (Dipp = 2,6-diisopropylphenyl) substituents were found to exhibit moderate activity in the polymerization of ethylene when using B(C 6F 5) 3 or [Ni(cod) 2] (cod = 1,4-cyclooctadiene) as coactivators, producing polymers with a high molecular weight, as determined by GPC. The reaction was found to be highly dependent on temperature, with the catalysts most active at 80 °C. Differences in polymer structure were also found when using B(C 6F 5) 3 or [Ni(cod) 2] as the cocatalyst, with [Ni(cod) 2] producing a more highly branched polymer. Reducing the steric bulk at the N substituent of the ligand led to inactive species.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry
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