Design of neutral Lewis superacids of group 13 elements.

A general approach toward superstrong neutral Lewis acids, featuring both the pyramidalization of acceptor molecules and the introduction of electron-withdrawing substituents, is proposed and examined theoretically. Complexes of group 13 element derivatives with ammonia at the B3LYP and MP2 levels of theory with def2-TZVPP basis set are considered as examples. Pyramidalization of the acceptor molecule significantly increases its Lewis acidity (by 50-60 kJ mol(-1) for aluminum and gallium compounds and by 120-130 kJ mol(-1) for boron compounds). An additional increase of the complex stability of 55-75 kJ mol(-1) may be achieved by fluorination. The combined increase of the bond dissociation energy amounts to 110-190 kJ mol(-1), which is equivalent to 19-33 orders of magnitude in Lewis acidity.