A Highly Active Anilinoperinaphthenone-Based Neutral Nickel(II) Catalyst for Ethylene Polymerization

A general synthetic route for the preparation of 2-anilinoperinaphthenones is reported. 2-(2,6-Dimethylanilino)perinaphthenone ( 4a) and 2-(2,6-diisopropylanilino)perinaphthenone ( 4b) are used as ligands for the corresponding neutral nickel(II) complexes [[(2,6-Me 2 C 6 H 3 )NC 13 H 7 O]Ni(Ph)(PPh 3 )] ( 5a ) and [[(2,6- i Pr 2 C 6 H 3 )NC 13 H 7 O]Ni(Ph)(PPh 3 )] ( 5b ). The key features of these nickel complexes are a hindered N-aryl ring, a five-membered-ring nickel chelate, and an anionic N-donor moiety. Complexes 5a, b are active, but short-lived, ethylene polymerization catalysts with turnover numbers in excess of 60 000 mol ethylene/mol catalyst. Polymer branching is controlled by variation of temperature and pressure. A correlation between ethylene pressure and polymer molecular weight suggests that chain transfer occurs by a β-hydride elimination pathway. Finally, decomposition of 5b to free ligand is observed under the polymerization conditions employed.