Unbridged bicyclic cyclopentadienyl zirconocene complexes: Their possible application as Fluxional catalysts in propene polymerization

Three series of novel unbridged bicyclic cyclopentadienyl zirconium complexes, containing six-, seven- and eight-membered saturated rings fused to the cyclopentadienyl unit and bearing different substituents (-H, -CH3, -Ph) in position 2, were used in combination with methylaluminoxane (MAO) for the polymerization of propene at different temperatures. All the catalysts have been shown to be active, the lowest activity being observed with the eight-membered ring systems. With most catalysts the polymers obtained are fully atactic when the polymerizations are conducted at 30°C, and become partially isotactic at lower temperatures. The 13C NMR analysis shows that in one case, that is, when the seven-membered ring is associated with the phenyl substituent in position 2, a preponderance of the isotactic heptad in the methyl region of 13C NMR spectrum is observed, which allows us to hypothesize the formation of stereoblocks