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

A series of ansa-cyclopentadienyl-phenoxy titanium complexes (PHENICS: phenoxy-induced complex of Sumitomo) (1a-e), [{Me2CCp(OC6H2-3-R-5-R')}TiCl2] (1a, R = R' = H; 1b, R = Bu-t, R' = Me) and [{Me2Si(C5Me4)(OC6H2-3-R ''-5-Me)}TiCl2] (1c, R '' = Pr-i; 1d, R '' = Bu-t; 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 Id. revealed by X-ray crystal structure analysis, are 63.0 degrees (1b) and 68.2 degrees (1d), indicating a distortion from a Mutual perpendicular arrangement, whereas the symmetrical patterns of the H-1 NMR spectra indicate a dynamic behavior in solution. The PHENICS-type complexes exhibit good to excel lent catalytic activities for copolymerization of ethylene and 1-hexeric upon activation with (AlBu3)-Bu-t/[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 degrees C, 6000 kg mol(-1) h(-1) at 180 degrees 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 degrees C. Whereas the PHENICS catalyst system acts as a single-site catalyst at 180 degrees 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.