Polymerization of Propene and Butene with a Chiral Zirconocene and Methylalumoxane as Cocatalyst

Hitherto, only atactic polypropylene could be prepared with soluble bis(cyclopentadienyl)zirconium(iv)/methylalumoxane Ziegler-Natta catalysts..'' E ~ e n [ ~ ' has recently shown that mixtures of, e.g., 63% isotactic and 37% atactic polypropylene are formed with the sterically rigid ethylenebis( I-indeny1)titanium dichloride (mixture of meso form and ra~emate) . '~ ' If, however, the chiral ethylenebis(4,5,6,7-tetrahydro-lindeny1)zirconium dichloride 1 (Fig. 1) is used in combination with methylalumoxane ([AI(CH3)-O],) as cocatalyst, highly isotactic polypropylene is obtained. The racemate of 1 was used for this polymerization. The fraction of polymer soluble in toluene can be reduced to 0.2 wt.45, which is considerably lower than the 2-7% achievable with heterogeneous TiCI,/MgC12/AI(C2H5)3/ C,H,CO,C,H,-based catalysts.1h1