Olefin Polymerization Behavior of Titanium(IV) Pyridine-2-phenolate-6-(σ-aryl) Catalysts: Impact of “py-Adjacent” and Phenolate Substituents
作者:Jerry C. Y. Lo、Michael C. W. Chan、Po-Kam Lo、Kai-Chung Lau、Takashi Ochiai、Haruyuki Makio
DOI:10.1021/om300832q
日期:2013.1.28
A series of Ti(IV) post-metallocene bis(benzyl) precatalysts supported by tridentate pyridine-2-phenolate-6-(sigma-aryl) [O,N,C] ligands, featuring various substituents on the sigma-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 H-1, C-13, and F-19) 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 sigma-naphthyl Ti precatalyst, in conjunction with [Ph3C][B(C6F5)(4)], displays good activity and produces polyethylene with exceptionally high (M-n = 4 x 10(6)) and an M-w/M-n value (2.5) approaching single-site character at 50 degrees 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-C(sigma-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-CH2CH2-aryl] species via beta-H elimination and 2,1-reinsertion, was also indicated.