Dative bonds versus electron solvation in tri-coordinated beryllium complexes: Be(CX)3 [X = O, S, Se, Te, Po] and Be(PH3)3 versus Be(NH3)3

The formation mechanism and bonding scheme for the titled molecules is proposed based on high-level theoretical calculations. All species are formed via three dative bonds from the ligands to Be. For Be(CX)(3) [X = O, S, Se, Te, Po] species and Be(PH3)(3) the two electrons of beryllium are promoted from 2s to 2p facilitating these bonds. At the same time, electronic density is donated toward the ligands via the pi-frame. In contrast, ammonia partly solvates the valence 2s electrons of Be, which are delocalized in the periphery of the molecule. Based on the proton affinity of all of these complexes and their derivatives, we found that they are strong Lewis bases. For example, Be(PMe3)(3) is stronger than ammonia and its ethyl substituted analogue and could serve as the basis of more efficient frustrated Lewis pairs.