Synthesis, Characterization, and Ethylene Polymerization Activities of Neutral Nickel(II) Complexes Derived from Anilino-Substituted Enone Ligands Bearing Trifluoromethyl and Trifluoroacetyl Substituents

A series of neutral Ni(II) complexes derived from anilino-substituted enone ligands bearing electron-withdrawing trifluoromethyl and trifluoroacetyl groups have been synthesized and characterized:  [η2-ArNC(R1)CC(R2)C(O)CF3]Ni(PPh3)Ph (3a, Ar = 3,5-i-Pr2C6H3, R1 = H, R2 = COCF3; 3b, Ar = 3,5-i-Pr2C6H3, R1 = Me, R2 = COCF3; 3c, Ar = 3,5-i-Pr2C6H3, R1 = Me, R2 = H; 3d, Ar = 3,5-Me2C6H3,
R1 = Me, R2 = COCF3). When they are activated with either Ni(COD)2 or B(C6F5)3, these complexes
are active for the polymerization of ethylene to branched polyethylenes. Complex 3a is especially active
and long-lived, with a turnover frequency of 5 × 105 at 60 °C and 200 psig of ethylene, a half-life
exceeding 15 h at 35 °C, and a total turnover number exceeding 106 at 35 °C and 200 psig. Molecular
weights and degrees of branching of polyethylenes obtained from 3a are reported as a function of reaction
temperature and ethylene pressure.