SYNTHESIS OF A CHIRAL MESO-LIKE ANSA-ZIRCONOCENE COMPLEX AND ITS USE FOR THE CATALYTIC FORMATION OF LOW-MOLECULAR-WEIGHT POLYPROPYLENE

Reaction of lithium(neomenthylcyclopentadienid) 3 with dimethyldichlor osilane gives dimethylbis[3-(neomenthyl)cyclopentadienyl]silane 4 regi oslectivity as a mixture of double bond shift isomers (57% isolated). Deprotonation with 2 equiv. of butyllithium followed by treatment with zirconiumtetrachloride furnished a mixture of the three s[eta(5)-3-(n eomenthyl)cyclopentadienyl]}zirconium dichloride diastereomers from wh ich the pure meso-like isomer 6c [p-R(1'S,3'R,4'R),p-S(1'S,3'R,4'R)] w as isolated by fractional crystallization. Complex 6c was characterize d by an X-ray crystal structure analysis. Its D1-Zr-D2 angle of 126.8 degrees is very similar as observed in bis(eta-cyclopentadienyl)zircon ium dichloride (D1 and D2 denote the centroids of the cyclopentadienyl rings). The homogeneous 6c/methylalumoxane Ziegler-type catalyst prod uces polypropylene of low molecular weight ((M) over bar(eta) approxim ate to 670 at ambient temperature). Related catalyst systems may find interesting applications in organic synthesis.