A COMPUTATIONAL STUDY OF THE MOLECULAR-STRUCTURES, CONFORMATIONAL PREFERENCES AND ANOMERIC EFFECTS IN MONOAMINOPHOSPHANES AND BISAMINOPHOSPHANES

The molecular structures of a number of mono- and bisaminophosphanes, A(2)PNB(2) or AP(NB2)(2), have been optimised by ab initio calculation s at the MP2/6-31G level. The equilibrium structures of the aminophos phanes H2PNH2, H2PNMe2, Me=CH3, Cl2PNMe2 and HFPNH2 are characterised by nonplanar N and P atoms and equilibrium conformations where the ele ctron lone pair on the N atom is trans to the most electronegative of the remaining substituents on the P atom (X). It is suggested that the se conformations are stabilised by anomeric effects, i.e. through delo calisation of the N electron lone pair into the antibonding sigma(P-X ) orbital. The IV atom in F2PNMe2 is found to be planar or near-planar , and the equilibrium conformation is such as to allow interaction bet ween the N lone pair and both P-F antibonding orbitals. The equilibriu m conformations of HP(NH2)(2) and HP(NMe2)(2) are such that the electr on lone pair on each N atom is trans to the other P-N bond. (C) 1998 E lsevier Science B.V.