ABSOLUTE CONFIGURATIONAL ASSIGNMENT OF SELF-ORGANIZING ASYMMETRIC TRIPODAL LIGAND-METAL COMPLEXES

The solution configuration of labile coordination complexes may be dif ficult to determine, even in cases in which the solid state structure is known. We have previously synthesized a series of chiral ligands wh ich form pseudo-C-3-symmetric ic complexes with Zn-II and Cu-II salts that possess an available electrophilic coordination site. Molecular m odeling of Zn-II complexes of the chiral ligand ,N-bis[(2-quinolyl)met hyl]-1-(2-pyridyl)ethanamine (alpha-MeBQPA) showed that the spatial ar rangement of the heterocyclic arms is controlled by a substituent on o ne methylene arm, resulting in the adoption of an enantiomeric conform ation displaying a propeller-like asymmetry. In this paper we report t he application of the exciton chirality method to the determination of the conformation of asymmetric metal-ligand complexes in solution. Th ere is a good correlation between the predicted and the observed Cotto n effects, demonstrating that the geometry in solution closely resembl es that predicted by computational simulations and those obtained by X -ray crystallographic studies of metal complexes with racemic and enan tiomerically pure ligands. The X-ray crystallographic structure of the first optically pure complex in this series is reported. (C) 1997 Wil ey-Liss, Inc.