Syndiospecific polymerization of styrene. 3. Catalyst structure

The active oxidation state of Ti in the cyclopentadienyl-tributoxyltitanium methylaluminoxane (CpTi(OBu) sub(3)/MAO) catalyst has been determined by electron paramagnetic resonance (EPR) and redox titration. The results, together with previously reported active species concentrations measured by radio-labeling techniques, showed that all the catalytic species are trivalent Ti. The syndiospecific species (78% Ti) is characterized by a sharp EPR resonance at g = 1.989 ( super(H) alpha = 7 G) which corresponds to a titanium(III) hydride. The nonspecific species (13% Ti) has a g value at 1.995.