Planar-Chiral Secondary Ferrocenylphosphanes

Abstract

An efficient way to obtain pure diastereomeric mixtures of C-chiral, P-chiral, planar-chiral ferrocenylphosphanes is demonstrated by ortho-lithiation of enantiomerically pure (SC)-N,N-dimethyl-1-ferrocenylethylamine (Ugi's amine) and reaction with RPX2[X = Cl, Br; R = tBu, 2,4,6-Me3C6H2(Mes)]. Four secondary ferrocenylphosphanes [Fe(C5H5)(1-PHR-2-CHR′NMe2-C5H3)] [R′ = H, R = tBu (1); R′ = H, R = Mes (2); R′ = CH3, R = tBu (3); R′ = CH3, R = Mes (4)] were synthesised and characterised. Pure diastereomeric mixtures of 1 and 2, a mixture of the pure major diastereomers of 4, as well as diastereomerically pure 3 were obtained by column chromatography under a nitrogen atmosphere. The formation of amine–borane or phosphane–borane adducts was studied by11B and31P NMR spectroscopy. A theoretical study was performed to understand the tendency of 1–4 toward borane adduct formation.