Title
Analytical and preparative enantioseparation and main chiroptical properties of Iridium (III)bis(4,6-difluorophenylpyridinato)picolinato
Author
Cinzia Citti, Umberto M. Battistic, Giuseppe Ciccarellaa, Vincenzo Maiorano, Giuseppe Gigli, Sergio Abbate, Giuseppe Mazzeo, Ettore Castiglioni, Giovanna Longhi, Giuseppe Cannazza
Year
2016
Journal
Journal of Chromatography A
Abstract
Almost all Iridium(III) complexes employed both as dopants in PhOLEDs and as pharmaceuticals and fluorescence bioprobes are racemic mixtures. In this study the single enantiomers of the most stable diastereomeric form fac-trans-N − N, bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) were separated and analysed. The data obtained showed that the complex can be separated into stable optically active Λ and Δ isomers employing cellulose based chiral stationary phase both in normal and polar phase mode. Their chirality was confirmed and their absolute configuration assigned employing several methods (DFT and TDDFT calculations, CD and VCD). The CPL spectroscopy of the isolated enantiomers of FIrpic was also recorded due to its possible value in the OLEDs field. The chromatographic method was applied for a semipreparative purpose demonstrating that polar organic solvent chromatography (POSC) could be used to avoid the low-solubility issues associated with these Iridium(III) complexes. Finally, the chemical and stereochemical stability of the single isomers was evaluated under thermal stress by liquid chromatography coupled to high-resolution mass spectrometry (LC-QTOF) on both chiral and achiral columns. No racemization and/or isomerization was observed; however, the dissociation of the ancillary ligand was demonstrated employing LC-QTOF.
Instrument
J-815
Keywords
Circular dichroism, Circularly polarized luminescence, Stereochemistry