Hydrosilylation of ketones catalyzed by C2-symmetric proline-derived complexes

Abstract

Extracoordinate chiral hydrosilanes were generated in situ from triethoxysilane and a C2-symmetric ligand derived from bisproline 7. In the presence of a catalytic amount of ligand 7, prochiral ketones were reduced in moderate yield with moderate enantioselectivity (up to 64% ee). Alternatively, TiF4 complexes of 7 were used to provide higher enantioselectivity and with improved yields. The copper complex of ligand 7 and 29Si NMR data provide some guidance as to the key factors responsible for the observed reactivity at the silicon and at the ligand centre.Key words: extracoordinate chiral silane, C2-symmetry, enantioselectivity, Lewis acid titanium catalysis.