Determination of the absolute stereochemistry of chiral biphenanthryls in solution phase using chiroptical spectroscopic methods: 2,2'-Diphenyl-[3,3'-biphenanthrene]-4,4'-diol

Abstract

Although the exciton coupling model has been widely used in the literature to suggest the absolute configuration using electronic circular dichroism (ECD) spectra, chiral biphenanthryl systems are one group of molecules where the application of the exciton model yields ambiguous conclusions. The use of 2,2'-diphenyl-[3,3'-biphenanthrene]-4,4'-diol, known as VAPOL, as a chiral ligand for enantioselective catalysis necessitates the reliable determination of its absolute configuration. Based on the X-ray diffraction data of its phosphoric amide derivative, the configuration of VAPOL has been determined in the literature to be (+)-(aS). The experimental vibrational circular dichroism, ECD and optical rotatory dispersion spectra, and corresponding quantum mechanical predictions of VAPOL are used in this manuscript to independently determine its absolute configuration.