1H NMR Chiral Analysis of Charged Molecules via Ion Pairing with Aluminum Complexes

Abstract

Chiral analysis, such as determination of identity, concentration, and relative ratio of optically active (chiral) molecules, plays an indispensable role in contemporary synthetic, medicinal, and biological chemistry. Here, we describe the selective control of metal-centered chirality in an octahedral geometry to prepare negatively charged Al-III complexes, which can be used as versatile H-1 NMR chiral solvating agents for both positively and negatively charged chiral molecules in polar or nonpolar solvents. During the formation of ion pairs between the Al-III complexes and the chiral analytes such as amines and carboxylic acids, the metal-centered chirality in the Al complexes plays a crucial role in providing anisochronous chemical shifts to the H-1 NMR spectra. As a chiral solvating agent, Al-III complexes display an unprecedentedly broad substrate scope, good solvent compatibility, and operational simplicity.