Polymerization of 1,3-Butadiene Catalyzed by Half-Sandwich Titanocenes Bearing a Coordinative Ether and Ester Side Chain on the Cp Ring and MAO†

Substituted half-titanocenes bearing coordinative ether and ester moiety in their side chains, η5:η1-C5H4(CH2CH2OMe)TiCl3 (5b), η5-C5H4(CH2CH2CH2OMe)TiCl3 (5c), and η5:η1-C5H4(CH2COOMe)TiCl3 (5d), were prepared, and then their catalytic performances for the stereospecific living polymerization of 1,3-butadiene in the presence of the methylaluminoxane (MAO) were investigated. The introduction of intramolecular coordination between central titanium and the ether or ester moiety (5b,d) caused acceleration of polymer propagation rate and enhancement of cis-specificity. The catalyst 5d/MAO showed 114 times larger propagation rate constant than that of the parent nonsubstituted η5-C5H5TiCl3 (5f)/MAO catalyst. The 5b/MAO catalyzed 1,3-butadiene polymerization gave high cis-polybutadiene (99.2% cis content) with narrow molecular weight dispersity (1.14). The single-crystal X-ray crystallographic analysis of 5d and reaction pathway are also discussed.