Planar−Chiral Ferrocenes in Asymmetric Catalysis:  The Impact of Stereochemically Inhomogeneous Ligands

The catalytic properties of stereochemically inhomogeneous mixtures of chiral ferrocenes in dimethylzinc additions to benzaldehyde have been investigated. With planar chiral ferrocene ( R p )- 4 a linear correlation between the enantiomeric excess of the ferrocene and that of the product was found. In contrast, a significant departure from linearity was revealed when mixtures of diastereomeric ferrocenes ( S, R p )- 1 and ( S, S p )- 3 were employed. Thus, even in the reaction with a catalyst obtained from a 1:1 ratio of diastereomers 1 and 3, formation of a product with an enantioselectivity of 95% ee was achieved.