On the structure of the P-iodo-, bromo- and chloro-bis(imino)phosphoranes: A DFT study

Abstract

Abstract As demonstrated by DFT calculations, the bonding situation of P-iodo, bromo and chloro-bis(imino)phosphoranes XP(NR)2, X=Cl, Br, I, differs from that of conventional amino-bis(imino)phosphoranes (X=NR2). The monomers are highly reactive compounds with relatively small adiabatic singlet-triplet energy differences. They can dimerize by a mutual polarization mechanism between the electropositive iodine center of one monomeric unit and the more electronegative nitrogen centers of the other unit. It causes a slight depletion of p-electron density at iodine and an accumulation at the nitrogen atoms. The polarization induces electrostatic attraction, attenuated by stack formation into a one-dimensional array of monomers. The weak electrostatic binding is strongly superimposed by steric attraction among the bulky substituents of the stack array, which can end up essentially stronger than the electrostatic interaction forces. The factors which govern the dispersion forces are evaluated. The substituent effects for stack formation are studied in detail for the association of two monomers.