Frustration of Orbital Interactions in Lewis Base/Lewis Acid Adducts: A Computational Study of H2 Uptake by Phosphanylboranes R2P=BR′2

The reaction of molecular hydrogen with phosphanylboranes R2P=BR'(2) (1) is systematically studied by means of density functional theory calculations and second order Moller-Plesset perturbation theory. The potential energy barriers and the exothermicity of H-2 uptake are reported for a series of phosphanylboranes with different electron-donating and -withdrawing groups bound to phosphorus and boron. Systematic molecular orbital analysis reveals that the frustration between boron and phosphorus can be increased by modifying the substituents, and thus, atomic orbital interactions could be exploited in order to increase the reactivity of 1. Additionally, we found a correlation between the potential energy barrier for H-2 uptake and the energy of the HOMO of the P=B complex, which could be relevant for the prediction of the proper-ties of candidate compounds for H-2 activation and therefore useful for the development of such systems. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)