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

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posted on 2010-12-13, 00:00 authored by Kurtis E. Thiesen, Kalyani Maitra, Marilyn M. Olmstead, Saeed Attar
Several new ferrocenylimines containing both planar and central chirality were prepared from (Sp)-2-(diphenylphosphino)ferrocenecarboxaldehyde and chiral primary amines. One of these compounds, (Sp,Sc)-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 (Sp,Sc)-3 and di-μ-chlorobis[(η3-C3H5)palladium(II)] and isolated after anion exchange with NaBF4 to give [Pd(η3-C3H5)((Sp,Sc)-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 ((Sp,Sc)-13) and for the isolated precatalyst (4). These compounds were also investigated by CD spectroscopy.