Determination of Molecular Structure of Bisphenylene Homologues of BINOL-Based Phosphoramidites by Chiroptical Methods

Abstract

Vibrational (VCD), electronic circular dichroism (ECD), and IR absorption spectra together with transparent spectral region optical rotation (OR) of two derivatives of bisphenylene 1,1'-binaphthyl-based phosphoramidites containing three stereogenic axes were measured and the results were compared with simulated data obtained by ab initio calculations with density functional theory. An excellent agreement between experimental and predicted B3LYP/6-31G** and BPW91/6-31G** VCD spectra enabled the assignment of all VCD bands in the experimental spectra, while the Gibbs free energy of all the conformers allowed the determination of their relative populations. The calculation of ECD spectra showed that CAM-B3LYP/6-311G** provided results superior to those of B3LYP/6-311G**. The theoretical results for the OR at the B3LYP/6-311G** and CAM-B3LYP/6-311G** levels were in good agreement with experimental optical rotations, but exhibited lower sensitivity in determining particular conformers than VCD and ECD. By a careful comparison of experimental VCD, IR, and ECD spectra and OR with calculated data, it was possible to assign the absolute configuration of all three stereogenic axes and to determine the molecular structure of the studied bisphenylene 1,1'-binaphthyl-based phosphoramidites in solution with a high degree of confidence.