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

Using 13C- and 1H-NMR spectroscopy, titanium(IV) species formed in the catalytic systems Cp*TiMe3/MAO and Cp*TiCl3/MAO (Cp*=C5(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−Al(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=35, and is about 10% at Al/Ti=700.