RESUMEN
A series of new titanium complexes with two asymmetric bidentate ß-enaminoketonato [N,O] ligands (2b-t), [PhN=C(CF(3))CHC(Ar)O](2)TiCl(2) (2b, Ar = -C(6)H(4)F(o); 2c, Ar = -C(6)H(4)F(m); 2d, Ar = -C(6)H(4)F(p); 2e, Ar = -C(6)H(4)Cl(p); 2f, Ar = -C(6)H(4)OMe(p); 2g, Ar = -C(6)H(4)CF(3)(p); 2h, Ar = -C(6)H(4)CF(3)(m); 2i, Ar = -C(6)H(4)CF(3)(o); 2j, Ar = -C(6)H(4)Cl(o); 2k, Ar = -C(6)H(4)Br(o); 2l, Ar = -C(6)H(4)I(o); 2m, Ar = -C(6)H(3)F(2)(2,4); 2n, Ar = -C(6)H(3)F(2)(2,6); 2o, Ar = -C(6)H(3)F(2)(3,4); 2p, Ar = -C(6)H(3)F(2)(3,5); 2q, Ar = -C(6)F(5); 2r, Ar = C(6)F(4)OMe; 2s, Ar = -C(6)H(3)Cl(2)(2,6); 2t, Ar = -C(6)H(3)Cl(2)(2,5)), have been synthesized based on substituted acetophenones. X-Ray analyses reveal that complexes 2h, 2k, 2m, and 2n adopt distorted octahedral geometry around the titanium center, in which the two chloride ligands are situated in the cis-orientation. 2s also adopts distorted octahedral geometry, but the two chloride ligands in it are situated in the trans-orientation due to the increase of the steric effect of the phenyl derived from the acetophenone. The influence of the substituent effects on catalyst performance, including catalytic activities and the molecular weight distribution of the polymers obtained, was investigated in detail. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 2b-r and 2t are active catalysts for ethylene polymerization at room temperature, and produce high molecular weight polymers. It is observed that the catalytic activities are significantly enhanced by introducing some electron-withdrawing groups, such as -F, -Cl and -CF(3), into the suitable positions of the phenyl ring close to the oxygen donor. It should be noted that complexes 2c-i, 2p, 2n and 2t are also capable of promoting the living copolymerization of ethylene with norbornene at room temperature, yielding high molecular weight copolymers with narrow molecular weight distributions (PDI = 1.05-1.30).
RESUMEN
A series of new titanium complexes bearing two regioisomeric trifluoromethyl-containing enaminoketonato ligands (3a-h and 6a-h), [PhN=CRCHC(CF3)O]2TiCl2 (3a, R = Me; 3b, R = n-C5H11; 3c, R = i-Pr; 3d, R = Cy; 3e, R = t-Bu; 3f, R = CH=CHPh; 3g, R = Et; 3h, R = n-C11H23) and [PhN=C(CF3)CHC(R)O]2TiCl2 (6a, R = Ph; 6b, R = n-C5H11; 6c, R = i-Pr; 6d, R = Cy; 6e, R = t-Bu; 6f, R = CH=CHPh; 6g, R = CHPh2; 6h, R = CF3) have been synthesized and characterized. X-ray crystal structures analyses suggest that complexes 3c-e and 6c-d all adopt a distorted octahedral geometry around the titanium center. Complexes 3c, 3d and 6c display a cis-configuration of the two chlorine atoms around the titanium center, while complex 6d shows a trans-configuration of the two chlorine atoms. Especially, the configurational isomers (cis and trans) of complex 3e were identified both in solution and in the solid state by NMR and X-ray analyses. With modified methylaluminoxane as a cocatalyst, all the complexes are active towards ethylene polymerization, and produce high molecular weight polymers. With the variation of the relative position of the imino group and the trifluoromethyl group of the beta-enaminoketonato ligands, the polymerization behavior of the catalysts changed remarkably. It is observed that the substituent directly joined to the carbonyl in the ligands plays an important role for both the catalytic activities and the properties of the polymers produced.