Asymmetric synthesis and absolute configuration of a planar chiral phosphapalladacycle with a ferrocenyl framework

A monodentate optically active tertiary α-ferrocenylethylphosphine was prepared from the corresponding tertiary α-ferrocenylethylamine; Me2N group substitution by a tert-Bu2P group occurs with complete retention of the enantiomeric composition and absolute configuration of the α-carbon stereocentre. The cyclopalladation of this phosphine ligand results in the formation of a phosphapalladacycle bearing the elements of central and planar chirality with a high diastereoselectivity. The enantiomeric composition of the CP-palladacycle was determined by 31P{1H} NMR spectroscopy using (S)-prolinate as a chiral derivatizing agent. The structure and absolute configuration of the phosphapalladacycle were established using NMR spectroscopy and an X-ray diffraction study of its (S)-prolinate derivative.

Graphical abstractThe asymmetric synthesis of a tertiary α-ferrocenylethylphosphine was performed by stereospecific substitution of the Me2N group in the tertiary α-ferrocenylethylamine by a tert-Bu2P group. The cyclopalladation of this new phosphine results in the formation of a phosphapalladacycle bearing elements of central and planar chirality with a high diastereoselectivity. The enantiomeric composition of the CP-palladacycle was determined by 31P{1H} NMR spectroscopy using (S)-prolinate as chiral derivatizing agent. The absolute configuration of the new phosphapalladacycle was established by means of an X-ray diffraction study of its (S)-prolinate derivative.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Enantiopure phosphapalladacycle of planar and C∗-central chirality. ► Double asymmetric synthesis from the (SC)-N,N-dimethyl-α-ferrocenylethylamine. ► Highly diastereoselective cyclopalladation. ► Enantio- and diastereopurity increase using (SC)-prolinate derivative.