Phosphoric triamides. 31Phosphorus NMR chemical shift as a function of the P–N bond characteristics
Abstract
Six phosphoric triamides in which amide nitrogens are incorporated into an increasing number (from 0 to 3) of the 1,3,2-diazaphospholidin-2-one rings have been prepared and their crystal structures have been determined. The structural changes from the non-cyclic to the mono-, di- and tri-cyclic systems result in the decrease of the N–P–N bond angles and the increase of the P–N bond distance. These changes are paralleled by a strong deshielding of the 31P nucleus, leading to an exceptionally high δP value for the tricyclic derivative. The δP–structural parameters relationship is discussed in terms of the changes in hybridization of phosphorus and the variation in the P–N bond order.