The design and synthesis of new chiral ligands, which display high activity and enantioselectivity, is still a significant challenge in the development of transition-metal-catalyzed asymmetric reactions. In recent years, chelating diphosphanes supported by an atropisomeric scaffold, have proved to be among the most active, selective and versatile ligands in this area.[1] Leading diphosphanes such as binap [2] and more recently have shown excellent results, especially in the field of ruthenium-mediated asymmetric hydrogenation.[4] Many research groups have devoted their efforts toward the discovery of new efficient atropisomeric ligands [5] with unusual stereoelectronic profiles. Both the aryl phosphorus substituents and the biaryl backbone are tunable parts in this family of ligands (Figure 1). Replacing the phenyl Figure 1. General stereoelectronic tunable features of a C 2 -symmetric atropisomeric diphosphane.M = transition metal center, b = bite angle, q = dihedral angle.
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