Theoretical Study of the Structure and Bonding in Phosphatrane Molecules

Abstract

The molecular structures of a representative selection of phosphatranes were studied by means of the ab initio MP2 method. The calculated results reasonably matched the available X-ray data. The special properties of the intrabridgehead interaction were described in terms of hybridization, bond order index, force constant, and vibrational frequency. The atom-in-molecules analysis of the electronic charge density showed the presence of a CP(3,-1) betwen the bridgehead centers in the cationic species but not in all of the neutral phosphatranes. The proton affinities of bases with no apical substituent on the phosphorus were accurately calculated for both the gas phase and solution (DMSO). The unique electronic structure of phosphatranes was theoretically investigated by means of their spectroscopic properties. The NMR chemical shifts and indirect nuclear spin-spin coupling constants, computed by DFT-based methods, were fairly consistent with experimental evidence, in particular for the observables involving the central phosphorus. The photoelectron spectrum of azaphosphatrane, having NMe equatorial groups, was interpreted by means of ab initio outer valence Green's function calculations, which gave a consistent reproduction of the energies and splittings of the uppermost bands, associated with the lone pairs of the bridgehead and equatorial heteroatoms. Thus, computations provided reliable predictions of the variations of the NMR parameters and ionization energies with change of the equatorial centers and apical substitution at phosphorus.