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

✍ Scribed by Jesus M. Castagnetto; Xiaodong Xu; Nina D. Berova; James W. Canary

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 152 KB
• Volume: 9
• Category: Article
• ISSN: 0899-0042
• DOI: 10.1002/(sici)1520-636x(1997)9:5/6<616::aid-chir32>3.0.co;2-p

✦ Synopsis

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 (alpha-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.