Synthesis and Ethylene Polymerization Activity of a Series of 2-Anilinotropone-Based Neutral Nickel(II) Catalysts

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Abstract

A method for the synthesis of bulky 2-anilinotropones has been developed, utilizing palladium-catalyzed cross-coupling techniques. Deprotonation of these anilinotropones followed by reaction with (PPh3)2Ni(Ph)Cl produces ethylene polymerization catalysts of the general formula [[(2-R-6-R‘C6H3)NC7H5O]Ni(Ph)(PPh3)] (3a−j: R, R‘ = Me, Me (a), iPr, iPr (b), tBu, H (c), tBu, Me (d), Ph, Ph (e), Cl, Cl (f), Br, Br (g), 2,3,4,5,6-F5 (h), Me, H (j), Me, CF3 (k)). Ethylene polymerizations with 3a−j have been explored under a variety of reaction conditions. The complex [[(2,6-iPr2C6H3)NC7H4O(7-aryl)]Ni(Ph)(PPh3)] (14: aryl = phenyl (a), 1-naphthyl (b)), possessing steric bulk at the 7-position, have been prepared and are both long-lived and active ethylene polymerization catalysts. At low temperatures 14a,b produce polyethylene with narrow molecular weight distributions (MWD ca. 1.2). The polymerization results suggest that chain transfer occurs via a β-hydride elimination pathway and that catalyst decomposition proceeds through reductive elimination of the free ligand from a nickel−hydride intermediate.

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