Strain factors in quinquecovalent phosphoranes. Sulphur-containing rings and six-membered rings

Abstract

Variable-temperature n.m.r. spectroscopy on a range of spirophosphoranes has given data on the increase in energy when five-membered rings containing sulphur attached to phosphorus move from a diequatorial to an apicalequatorial position in a trigonal-bipyramidal phosphorane. The results have been compared with those from the corresponding oxygen-containing systems and the remarkable similarity has been explained in terms of compensating lone-pair orientation and strain terms. Lone-pair orientation effects are also important in determining the preference of six-membered rings containing heteroatoms attached to phosphorus for an apical-equatorial as oppose to a diequatorial disposition in trigonal bipyramidal phosphoranes.