Enantioselective Oligomerization of α-Olefins with Chiral Zirconocene/Aluminoxane Catalysts

Summary

Chiral metallocenes can be used with methylaluminoxane to oligomerize olefins. The use of (S)-(1,1′-ethylenebis (4, 5, 6, 7-tetra-hydro-1-indenyl)) zirconiumbis-(0-acetyl-(R)-mandelate) allowed the preparation of optically active branched olefins. The oligomerization can be controlled in such a way that mainly tri-, tetra-, and pentamers are produced. The optical rotation depends extremely on the oligomerization temperature and is nearly zero at 70 °C. At a reaction temperature of 20 °C trimeric propene (2, 4-dimethyl-1-heptene) is obtained in the (S)-configuration with an optical purity of 97,5 %. The trimers could be separated analytically into ’* pure enantiomers by gas-chromatography over a modified cyclodextrine phase. The tetramers are diastereomers and show higher optically rotation than the trimers.