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 δ_P value for the tricyclic derivative. The δ_P–structural parameters relationship is discussed in terms of the changes in hybridization of phosphorus and the variation in the P–N bond order.