Ab initio calculations employing a large basis set have been carried out for a model molecule (PH5) to investigate the reaction profiles corresponding to the Berry pseudorotation (BPR) and the turnstile rotation (TR), these being the mechanistic possibilities proposed for the intramolecular ligand exchange in phosphoranes. Results suggest that the BPR should be a concerted process involving a very low (1.95 kcal/mol) energy of activation. In contrast, the TR process, which could be the active reaction coordinate for structurally restricted systems, may be better described as a sequential type process with a considerably larger (10.05 kcal/mol) overall activation energy. Examination of the reaction hypersurface in the vicinity of the Cs and C4υ, points revealed that only the C4υ geometry represents a genuine saddle point. This implies that, at least in the case of structurally flexible phosphoranes as modeled by PHH5, the TR should be regarded as a vibrationally excited mode of the BPR.
ASJC Scopus subject areas
- Colloid and Surface Chemistry