Absolute configurational assignment of self-organizing asymmetric tripodal ligand-metal complexes

Abstract

The solution configuration of labile coordination complexes may be difficult to determine, even in cases in which the solid state structure is known. We have previously synthesized a series of chiral ligands which form pseudo‐C3‐symmetric complexes with ZnII and CuII salts that possess an available electrophilic coordination site. Molecular modeling of ZnII complexes of the chiral ligand N,N‐bis[(2‐quinolyl)methyl]‐1‐(2‐pyridyl)ethanamine (α‐MeBQPA) showed that the spatial arrangement of the heterocyclic arms is controlled by a substituent on one methylene arm, resulting in the adoption of an enantiomeric conformation displaying a propeller‐like asymmetry. In this paper we report the application of the exciton chirality method to the determination of the conformation of asymmetric metal‐ligand complexes in solution. There is a good correlation between the predicted and the observed Cotton effects, demonstrating that the geometry in solution closely resembles that predicted by computational simulations and those obtained by X‐ray crystallographic studies of metal complexes with racemic and enantiomerically pure ligands. The X‐ray crystallographic structure of the first optically pure complex in this series is reported. Chirality 9:616–622, 1997. © 1997 Wiley‐Liss, Inc.

A Diastereodynamic Probe Transducing Molecular Length into Chiroptical Readout

“…Among the different molecular units reported as stereodynamic elements, tetradentate metal complexes have been extensively explored by the group of Canary, , Anslyn, ,,, and us. ,,− These systems are characterized by a propeller-like arrangement of the ligand around the metal which gives rise to the formation of two enantiomeric complexes in solution characterized by a clockwise ( P ) or counterclockwise ( M ) orientation. Tripodal ligands derived from quinoline or pyridine, in particular tris (2-pyridyl­methyl)­amine ( TPMA ), are able to form propeller-like complexes with Zn­(II) and Cu­(II) ions, which have been used as molecular sensors or as redox-triggered chiroptical molecular switches. ,, …”