Absolute configurational assignment of self-organizing asymmetric tripodal ligand-metal complexes.
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.
Castagnetto
J M
JM
Department of Chemistry, New York University, New York 10003-6688, USA.
Xu
X
X
Berova
N D
ND
Canary
J W
JW
D002942:Circular Dichroism; D003300:Copper; D018360:Crystallography, X-Ray; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry*; D011804:Quinolines / Q000138:chemical synthesis / Q000737:chemistry*; D012996:Solutions; D012997:Solvents; D013053:Spectrophotometry; D013237:Stereoisomerism; D015032:Zinc
D008024:Ligands; C108745:N,N-bis((2-quinolyl)methyl)-1-(2-pyridyl)ethanamine; D011725:Pyridines; D011804:Quinolines; D012996:Solutions; D012997:Solvents; D003300:Copper; D015032:Zinc