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 by 11B and 31P NMR spectroscopy. A theoretical study was performed to understand the tendency of 1–4 toward borane adduct formation.