Towards new ferrocenyl ligands for asymmetric catalysis

Abstract

Some new approaches for asymmetric synthesis of chiral ferrocenyl ligands are described. Many types of ferrocene compounds with planar chirality were prepared through diastereoselective ortholithiation, thanks to a chiral sulfoxide or chiral acetal auxiliary. Various mono- and diphosphines may be subsequently generated. In the sulfoxide route, a key intermediate is pure monolithioferrocene. A convenient procedure was set up, involving the isolation of stable tri-n-butylstannyl-ferrocene as a precursor of monolithioferrocene. The species Fc2PH (Fc = ferrocenyl) and its borane protected derivative allowed to synthesize chiral diphosphines where the usual PPh2 groups are replaced by the PFc2 fragment.