Unique reactivity of B in B[Ge9Y3]3 (Y = H, CH3, BO, CN): formation of a Lewis base

Abstract

Boron compounds usually exhibit Lewis acidity at the boron center due to the presence of vacant p-orbitals. We show that this chemistry can be altered by an appropriate choice of ligands to decorate the boron center. To elucidate this effect, we studied the interactions of boron with two classes of ligands, one based on penta-substituted phenyl species (C₆X₅, X = F, BO, CN) and the other based on Zintl-ion-based groups (Ge₉Y₃, Y = H, CH₃, BO, CN). An in-depth analysis of the charges and Fukui function values at the local atomic sites of the substituted boron derivatives B(C₆X₅)₃ and B[Ge₉Y₃]₃ shows that the B-center in the former is electrophilic, while it is nucleophilic in the latter. The chemical stability of the B[Ge₉Y₃]₃ species is shown to be due to the presence of strong 2c-2e bonds between the B and Ge centers. Thus, the general notion of the Lewis acid nature of a boron center depends upon the choice of the ligand.