New C1 Symmetric Ziegler−Natta Type Zirconocenes for the Production of Isotactic Polypropylene

Abstract

As part of our continued investigation of the polymerization behavior of substituted asymmetric indenyl−fluorenyl metallocenes, three new zirconocenes bearing 2,4-disubstitution on the indenyl moiety have been synthesized and evaluated as α-olefin polymerization catalysts. For the new complex ethylene-1-(9-fluorenyl)-2-[1-(2-methyl-4-phenyl)indenyl]zirconium dichloride (11), highly isotactic polypropylene with [mmmm] = 91% and Mw 1.1 × 105 at Tp = 40 °C was produced in very high yield. The dimethylsilylene analogue (13) gave similar results in terms of stereoregularity with a 2-fold increase in Mw. In addition, dimethylsilylene(9-fluorenyl)[1-(2,4-dimethyl)indenyl]zirconium dichloride (12) was prepared and found to be an effective catalyst precursor, although the smaller methyl substituent at the 4-position resulted in polypropylenes of lower stereoregularity.