Low-coordinated phosphorus-phosphorus compounds. An ab initio study of the H 2P 2 and H 2P +2 species

Abstract

The unimolecular rearrangement of diphosphene, HPPH, and phosphinophosphinidene, H 2PP, is studied in the lowest singlet, triplet and ionized (H 2P + 2) states employing ab initio methods. Geometries of stationary points were optimized using the 3–21G* basis set. Energy differences were estimated at the fourth-order Møller-Plesset perturbation theory (MP4SDQ/6-31 + +G*). Vibrational frequencies and some thermochemical parameters of species considered are reported. H 2P-P has a triplet ground state but the singlet—triplet separation is small. Both the triplet and ionized structures present a reversed stability ordering (the non-classical species being the more stable). The intrinsic free energy barrier (Δ G + 0) derived from a Marcus-type equation suggests that the 1,2-hydrogen shifts occurring in three different electronic states do not belong to the same homogeneous series of reactions. Phosphinophosphinidenes bearing appropriate substituents constitute realistic targets for a laboratory preparation and characterization (in both triplet and single states). Finally, the ▪ and their cations can also be regarded as possible candidates for a neutralization—reionization mass spectroscopy (NRMS) experiment.