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ansa-Cyclopentadienyl-Phenoxy Titanium(IV) Complexes (PHENICS): Synthesis, Characterization, and Catalytic Behavior in Olefin Polymerization

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journal contribution
posted on 13.07.2009 by Masaaki Nabika, Hiroaki Katayama, Tsuyoshi Watanabe, Hiroshi Kawamura-Kuribayashi, Kazunori Yanagi, Akio Imai
A series of ansa-cyclopentadienyl-phenoxy titanium complexes (PHENICS: phenoxy-induced complex of Sumitomo) (1ae), [{Me2CCp(OC6H2-3-R-5-R′)}TiCl2] (1a, R = R′ = H; 1b, R = tBu, R′ = Me) and [{Me2Si(C5Me4)(OC6H2-3-R′′-5-Me)}TiCl2] (1c, R′′ = iPr; 1d, R′′ = tBu; 1e, R′′ = Adm), have been synthesized and characterized. It is noteworthy that the dihedral angles of the cyclopentadienyl and phenoxy moieties of the complexes 1b and 1d, revealed by X-ray crystal structure analysis, are 63.0° (1b) and 68.2° (1d), indicating a distortion from a mutual perpendicular arrangement, whereas the symmetrical patterns of the 1H NMR spectra indicate a dynamic behavior in solution. The PHENICS-type complexes exhibit good to excellent catalytic activities for copolymerization of ethylene and 1-hexene upon activation with AliBu3/[Ph3C][B(C6F5)4] cocatalyst. Particularly, the complexes with a bulky substituent at the ortho position of the phenoxy moiety showed excellent catalytic features (1d, 27 200 kg mol−1 h−1 at 80 °C, 6000 kg mol−1 h−1 at 180 °C). These data show that the catalytic activity of the PHENICS-type catalysts is higher than that reported for the so-called constrained geometry catalyst (CGC) precursors. This becomes even more evident in light of the results for polymerization at 180 °C. Whereas the PHENICS catalyst system acts as a single-site catalyst at 180 °C, the CGC-type catalysts proved to be inactive under analogous conditions. Moreover, the copolymers obtained with PHENICS incorporate much higher content of 1-hexene than those obtained with CGC.