Synthesis and Characterization of a Chiral, Aza-15-Crown-5-Functionalized Ferrocenyldiphosphine Ligand for Asymmetric Catalysis
journal contributionposted on 19.02.2000, 00:00 by Clark R. Landis, Rachel A. Sawyer, Ekasith Somsook
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 PtMe2(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.