Diastereomers of the pentacoordinate chiral phosphorus compounds in solution: absolute configurations and predominant conformations

Abstract

The absolute structural information about four sets of diastereomers of pentacoordinate spirophosphoranes, derived separately from L (or D)-phenylglycine and L (or D)-phenylalanine, has been obtained by using vibrational circular dichroism (VCD) spectroscopic measurements and density functional theory (DFT) for the first time. Each compound contains a stereogenic centre at the phosphorus center and two at the amino acid ligands. Geometric searches at the B3LYP/6-311++G** level have been performed for all possible low energy conformers whose vibrational absorption (VA) and VCD spectra have also been simulated. The good agreement between the experimental VA and VCD spectra in the dimethyl sulfoxide (DMSO) solution and the simulated ones allows us to assign the absolute configurations and predominant conformations of these pentacoordinate phosphorus compounds with high confidence. Solvent effects have been examined by using both the experimental measurements and theoretical calculations. The implicit continuous polarization model and the explicit solute–solvent intermolecular hydrogen-bonding model have been considered to understand the effects of DMSO on the spectra observed. The influence of basis sets and different functionals on the VA and VCD spectra of this type of coordination compounds has also been investigated.