13C-NMR study of Ti(IV) species formed by Cp*TiMe3 and Cp*TiCl3 activation with methylaluminoxane (MAO)

Using C-13- and H-1-NMR spectroscopy, titanium(IV) species formed in the catalytic systems Cp*TiMe3/MAO and Cp*TiCl3/MAO (Cp* = C-5(CH3)(5)) in toluene and chlorobenzene were studied within the temperature range 253-293 K and at Al/Ti ratios 30-300. It was shown that upon activation of Cp*TiMe3 with methylaluminoxane (MAO) mainly the 'cation-like' intermediate Cp*Me2Ti+ <-- Me- -Alequivalent to(MAO) (2) is formed. Three types of titanium(IV) complexes were identified in Cp*TiCl3/MAO catalytic system. They are methylated complexes Cp*TiMeCl2 and Cp*TiMe2Cl, and the 'cation-like' intermediate 2. Complex 2 dominates in Cp*TiCl3/MAO system in conditions approaching to those of practical polymerization (Al/Ti ratios more than 200). According to the EPR measurements, the portion of EPR active Ti(III) species in the Cp*TiCl3/MAO system is smaller than 1% at Al/Ti = 3 5, and is about 10% at Al/Ti = 700. (C) 2003 Elsevier Science B.V. All rights reserved.