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: [eta(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 x 10(5) at 60 degrees C and 200 psig of ethylene, a half-life exceeding 15 h at 35 degrees C, and a total turnover number exceeding 10(6) at 35 degrees 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.