Bridging in P 2R cations

Abstract

The cationic fragments P 2R (R = H, Li, CH 3, NH 2, F, SiH 3, PH 2, Cl, phenyl) were investigated by means of ab initio calculations at SCF and MCSCF level in a linear or cyclic structure. The two geometrical alternatives refer to a classical or nonclassical geometry of the triple bond. According to the calculations there are only small energy differences between both types of structures. The matter strongly depends on the substituents attached to phosphorus. Strong bridging is favoured for R = H, NH 2, PH 2 and R = phenyl; to a slight extent also for R = F, Cl. The consequence for the molecular design of diphosphenes with an umbrella shape is discussed. The investigations are supplemented by a vibrational analysis within the harmonic approximation at SCF level.