Cis-Specific Living Polymerization of 1,3-Butadiene Catalyzed by Alkyl and Alkylsilyl Substituted Cyclopentadienyltitanium Trichlorides with MAO†

Cis-specific living polymerizations of 1,3-butadiene (BD) catalyzed by the catalyst system composed of C5H4RTiCl3 (4a, R = H; 4b, R = n-butyl; 4c, R = isopropyl; 4d, R = tert-butyl; 4e, R = trimethylsilyl) with methylaluminoxane (MAO) to give polyBDs with narrow molar mass distribution and high cis content are described. Polybutadienes (polyBDs) prepared by the catalyst at −25 °C are monodispersed (Mw/Mn = 1.04−1.05) in all cases. From the comparison with propagation rate constants (kp), the order of polymerization activity was as follows:  4d > 4e > 4c > 4b = 4a. The microstructures of polyBDs were all dominated by the cis configuration. The complex 4d having bulky tert-butyl group showed higher cis specicficity. Both kps and cis specificity in the polymerization of BD were strongly affected by the substituents introduced on the cyclopentadienyl ring.