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: [η 2 -ArNC(R 1 )C C(R 2 )C(O)CF 3 ]Ni(PPh 3 )Ph ( 3a, Ar = 3,5- i -Pr 2 C 6 H 3, R 1 = H, R 2 = COCF 3; 3b, Ar = 3,5- i -Pr 2 C 6 H 3, R 1 = Me, R 2 = COCF 3; 3c, Ar = 3,5- i -Pr 2 C 6 H 3, R 1 = Me, R 2 = H; 3d, Ar = 3,5-Me 2 C 6 H 3, R 1 = Me, R 2 = COCF 3 ). When they are activated with either Ni(COD) 2 or B(C 6 F 5 ) 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 × 10 5 at 60 °C and 200 psig of ethylene, a half-life exceeding 15 h at 35 °C, and a total turnover number exceeding 10 6 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.