Chiral sensor for enantiomeric purity of amines, amino alcohols and amino esters based on bis-cyclometalated Ir(III) complex using 1H NMR spectroscopy

Abstract

A new chiral sensor assembly with enantiomeric Ir(III) complex Δ-[Ir(ppy)2(MeCN)2](PF6) (ppy is 2-phenylpyridine) and 3-hydroxypyridine-2-carboxaldehyde as anxiliaries for chiral amines and amino derivatives, including α-amines, α-amino alcohols, α-amino esters, β-amines and β-amino alcohols as well as amino ether, was developed on the basis of 1H NMR spectroscopy. The assembly reaction is rapid and quantitative in equivalent under mild conditions, generating the corresponding diastereomers that are applied to discriminate the absolute configuration and quantitatively determine the enantiomeric excess (ee) directly without physical separation. The chelating coordination to Ir(III) ion much enhances the stability of the formed Schiff base ligand. Furthermore, more than one pair of diastereotopic resonances in wide detection regions ensures a convenient and high degree of accuracy in quantifying the ee value of chiral amines and amino derivatives. The absolute errors of the ee determinations by 1H NMR spectroscopy in different detection windows are within 1.9%. The linear relationship between the experimentally measured ee values and the gravimetrically prepared samples is found to be excellent.