Reinvestigation of the aromaticity of mono- and polyphosphacyclopentadienide ions at the DFT level

Abstract

Aromaticity of mono- and polyphospha-analogues of cyclopentadienide ion has been investigated at the DFT (B3LYP/6-31+G∗∗) level using bond-equalization, hypohomodesmotic reactions, NBO analysis, NICS and 1H NMR chemical shifts criteria. The bond distances are averaged between the corresponding single and double bonds, while hypohomodesmotic reactions give high stabilization energies on CH/P exchange in the cyclopentadienide ring. NBO analysis reveals strong LP→π∗ interactions comparable with those in the parent ion. NICS and 1H NMR chemical shift values support the presence of strong diatropic currents thereby confirming their aromatic character. There is found to be nearly linear correlation between the NICS values and the electron density at the ring critical points.