Enantioselective catalysis: Part 114. Chirostructural analysis of bis(diphenylphosphanyl)ethane transition metal chelates

Abstract

Transition metal complexes of bis(diphenylphosphanyl)ethane type ligands play an important role in asymmetric catalysis. The four phenyl substituents form a chiral array responsible for the high optical yields achieved with these ligands. In this paper we present an analysis of the phenyl ring orientations based on a search in the Cambridge Structural Database (CSD). The phenyl arrangements are not only subdivided into the well known face and edge exposed types, but they are additionally distinguished by the sign of the torsion angle M–P–C ipso –C ortho according to their chirality into face-P, face-M, edge-P, and edge-M. This approach allows a more differentiated examination. We found, that the phenyl rings prefer certain orientations within a small range depending on their axial or equatorial position and the ligand chirality. A comparison of these results with those of an analysis of achiral bis(diphenylphosphanyl)ethane complexes shows, that the substituents at the ligand backbone of the chiral phosphines reinforce the typical phenyl ring orientation in optically active phosphine complexes.