| Abstract
| - The synthesis, characterization, and ethylene polymerization behavior of a series of iron and cobalthalide complexes, LMXn (M = Fe, X = Cl, n = 2, 3, X = Br, n = 2; M = Co, X = Cl, n = 2), bearingchelating 2,6-bis(imino)pyridyl ligands L [L = 2,6-(ArNCR1)2C5H3N] is reported. X-ray diffraction studiesshow the geometry at the metal centers to be either distorted square pyramidal or distorted trigonal bipyramidal.Treatment of the complexes LMXn with methylaluminoxane (MAO) leads to highly active ethylenepolymerization catalysts converting ethylene to highly linear polyethylene (PE). LFeX2 precatalysts with ketimineligands (R1 = Me) are approximately an order of magnitude more active than precatalysts with aldimine ligands(R1 = H). Catalyst productivities in the range 3750−20600 g/mmol·h·bar are observed for Fe-based ketiminecatalysts, while Co ketimine systems display activities of 450−1740 g/mmol·h·bar. Molecular weights (Mw)of the polymers produced are in the range 14000−611000. Changing reaction conditions also affects productivityand molecular weight; in some systems, a bimodal molecular weight distribution is observed. On the basis ofevidence gathered to date, the lower molecular weight fraction is a result of chain transfer to aluminum whilethe higher molecular weight fraction is produced by a combination of mainly β-H transfer and some chaintransfer to aluminum.
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