Synthesis and Characterization of a Chiral, Aza-15-Crown-5-Functionalized Ferrocenyldiphosphine Ligand for Asymmetric Catalysis

A chiral ferrocenyldiphosphine ligand that is functionalized with an aza crown ether, ( S )-1-[( R )-1‘,2-bis(diphenylphosphino)ferrocenyl]ethyl-1-aza-2,3-benzo-15-crown-5 ( 1 ), has been synthesized. Both the resolved and racemic ligands react rapidly with Pt(II) precursors to form stable metal−ligand adducts; the complexes PtMeI( rac - 1 ) and PtMe 2 ( rac - 1 ) have been characterized crystallographically. Reaction of rac - 1 with [Rh(NBD) 2 ]OTf yields [Rh(NBD)( rac - 1 )]OTf. The three-dimensional solution structure of [Rh(NBD)( rac - 1 )]OTf has been determined by NOESY experiments and analysis using the two-dimensional conformer population analysis algorithm (2DCPA). The NOESY data reveal a rapid, pairwise chemical exchange between vinyl protons. The complex [Rh(NBD)( rac - 1 )]OTf is a catalyst precursor for hydrogenation reactions. However, we demonstrate that the lability of the aza crown ether may limit the ability of these catalysts to control selectivity via secondary interactions.