Synthesis and Characterization of New, Chiral P−N Ligands and Their Use in Asymmetric Allylic Alkylation

Several new ferrocenylimines containing both planar and central chirality were prepared from (S_p)-2-(diphenylphosphino)ferrocenecarboxaldehyde and chiral primary amines. One of these compounds, (S_p,S_c)-3, induced particularly high conversions (92−99%) and enantioselectivities (91−94% ee) when applied as a P−N ligand in the asymmetric allylic alkylation (AAA). In addition, a precatalyst complex was formed from (S_p,S_c)-3 and di-μ-chlorobis[(η³-C₃H₅)palladium(II)] and isolated after anion exchange with NaBF₄ to give [Pd(η³-C₃H₅)((S_p,S_c)-3)]BF₄ (4). High conversions (99%) and enantioselectivities (90−93% ee) were also observed when the isolated precatalyst (4) was used in the AAA reaction. Crystal structures were obtained for all three ligands prepared for this study ((S_p,S_c)-1−3) and for the isolated precatalyst (4). These compounds were also investigated by CD spectroscopy.