文摘
A series of Ti(IV) post-metallocene bis(benzyl) precatalysts supported by tridentate pyridine-2-phenolate-6-(蟽-aryl) [O,N,C] ligands, featuring various substituents on the 蟽-aryl (directly adjacent to the pyridine ring: fluoro, trifluoromethyl, benzo [C4H4]) and phenolate groups (tert-butyl, trifluoromethyl, cumyl, 1,1-diphenylethyl), have been prepared. Multinuclear (including 1H, 13C, and 19F) NMR characterizations of the complexes have been performed. The principal purpose of this study was to investigate the impact of these substituents upon ethylene polymerization reactivity and polymer properties. The cumyl-phenolate 蟽-naphthyl Ti precatalyst, in conjunction with [Ph3C][B(C6F5)4], displays good activity and produces polyethylene with exceptionally high MW (Mn = 4 脳 106) and an Mw/Mn value (2.5) approaching single-site character at 50 掳C, but multisite behavior is apparent for other catalysts. DFT calculations have been performed to probe the polymerization behavior and the role of the py-adjacent substituent. These studies revealed the possibility of two distinct polymerization reactions, namely conventional and ethylene-assimilated (comprising initial ethylene insertion into the Ti鈥揅(蟽-aryl) bond) chain propagation, and found that the latter is kinetically preferred. Furthermore, the viability of another kinetically competitive pathway, namely the isomerization of the ethylene-assimilated [Ti鈭扖H2CH2鈭抋ryl] species via 尾-H elimination and 2,1-reinsertion, was also indicated.