Metallocene catalysts for olefin polymerizations. XXIV. Stereoblock propylene polymerization catalyzed by rac-[anti-ethylidene(1-η5-tetramethylcyclopentadienyl)(1-η5-indenyl)dimethyltitanium: A two-state propagation

Racemic-anti-ethylidene(1-η⁵-tetramethylcyclopentadienyl) (1-η⁵-indenyl)dimethyltitanium ( 6 ) has been synthesized and its molecular structure determined by x-ray diffraction methods. The two Ti?Me(1) and Ti?Me(2) units have bond distances differing by 0.08 Å and their proton NMR resonances are separated by over 1 ppm. Using this compound and methylaluminoxane (MAO) as the activator, at 25°C the 6 /MAO catalyst produced polypropylene having crystalline domain with physical crosslinks. The polymers obtained at lower polymerization temperatures are rheologically liquids. The behaviors of this catalyst system resembles closely the previously reported rac-anti-ethylidene(1-η⁵-tetramethylcyclopentadienyl) (1-η⁵-indenyl)dichlorotitanium ( 4 )/MAO system. The structure of 6 determined here furnishes tangible support for the proposed two-state (isomeric)-switching propagation mechanism. Addition of MAO to 6 causes broadening of the Me(1) resonance in the ¹H-NMR spectra, and 6 is decomposed by Ph₃C⁺B(C₆F₅)^-₄. © 1992 John Wiley & Sons, Inc.