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Synthesis of Aqueous Polyethylene Dispersions with Electron-Deficient Neutral Nickel(II) Catalysts with Enolatoimine Ligands

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posted on 06.02.2007, 00:00 by Sze-Man Yu, Andreas Berkefeld, Inigo Göttker-Schnetmann, Gerhard Müller, Stefan Mecking
A series of new, electron-poor neutral κ2-N,O chelated Ni(II) complexes were studied for ethylene polymerization in aqueous emulsion. Complexes based on enolatoimine ligands bearing electron-withdrawing trifluoromethyl and trifluoroacetyl groups [κ2-N,O-{2,6-R2C6H3NC(H)C(COCF3)C(O)CF3}]Ni(L)Me (4a, R = iPr, L = pyridine; 4b, R = 3,5-(CF3)2C6H3, L = pyridine; 5b, R = 3,5-(CF3)2C6H3, L = PPh3) were prepared. The complexes are very active in aqueous emulsions, with 1.4 × 104 TO h-1 for 4a (50 °C) and 1.9 × 104 TO h-1 for 4b (70 °C), affording stable polyethylene dispersions. The phosphine complex 5b is active in the absence of a phosphine scavenger, with similar activities as 4b. Polyethylenes of typically Mw 3 × 104 g mol-1 (Mw/Mn 2.0−2.5) with 25−50 branches per 1000 carbon atoms and Tm 94−112 °C are obtained.