Study on the enantioselective oligomerization of 1-butene by chiral non-racemic Ti complexes fixed on MgCl2

A number of chiral non‐racemic titanium complexes of the type (R*O)2TiCl2 (R* being an enantiomerically pure monosaccharide derivative) was incorporated in a MgCl2 matrix by coprecipitation from a non‐solvated n/iso‐Bu2Mg solution with CCl4. The precatalysts formed were activated with different organoaluminium cocatalysts and used for the oligomerization of 1‐butene. In dependence of the cocatalyst and the temperature various reaction pathways were observed. In most cases saturated oligomers were isolated. At −20°C with i‐Bu3Al2OBuCl2 as cocatalyst 55–65% olefinic oligomers with 50–70% enantiomeric excess (ee) are formed. If the growing chain is terminated by chain transfer to the Al cocatalyst, epimerization of the last inserted monomer occurs, possibly due to a rearrangement which might be favoured by an agostic interaction. The fixation of TiCl4 to a chiral modified MgCl2 support does not lead to enantiomerically enriched oligomers under the same reaction conditions.