Coordination Chemistry and Asymmetric Catalysis with a Chiral Diphosphonite

The improved synthesis of the chiral diphosphonite, XantBino (1), based on a xanthene backbone and bearing chiral binaphthyl groups on both P-atoms is described together with its PdII and RhI complexes. The 31P NMR spectra of both complexes point out that the two phosphorus atoms are chemically inequivalent. The complex cis-[PdCl2(1)] (2) is structurally characterized by NMR spectroscopy and X-ray crystallography. The molecular structure reveals an unusually small bite angle for this member of the xantphos family of only 100°. The rhodium-catalyzed asymmetric hydroformylation of styrene and vinyl acetate as well as the asymmetric hydrogenation of methyl (Z)-2-acetamidocinnamate, applying this chiral diphosphonite 1, are described. Low enantiomeric excesses are obtained in the asymmetric hydroformylation, while use of the catalyst precursor [Rh(cod)(1)]BF4 (3) results in a promising enantiomeric excess in the Rh-catalyzed asymmetric hydrogenation.