Chiral Mixed Secondary Phosphine-Oxide-Phosphines: High-Performing and Easily Accessible Ligands for Asymmetric Hydrogenation

摘要

Chiral diphosphines are the most frequently used ligands in asymmetric catalysis.' In contrast, chiral secondary phos-phine oxides (SPOs) are little explored as ligands. While their chemical and physical properties are well known, their use in asymmetric catalysis is still in its infancy. SPOs are stable molecules which exist in equilibrium between two tautomeric forms: the preferred pentavalent phosphine oxide and the trivalent phosphinous acid. When two different substituents are attached to the phosphorus atom, a configurationally stable, P-chiral group results which can coordinate to metals either through the phosphorus atom or through the oxygen atom.