Coordination Chemistry and Asymmetric Catalysis with a Chiral Diphosphonite

Abstract

AbstractThe 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)