Fostering the Basic Instinct of Boron in Boron-Beryllium Interactions.

A set of complexes LHB···BeX (L = CNH, CO, CS, N, NH, NCCH, PH, PF, PMe, OH; X = H, F) containing a boron-beryllium bond is described at the M06-2X/6-311+G(3df,2pd)//M062-2X/6-31+G(d) level of theory. In this quite unusual bond, boron acts as a Lewis base and beryllium as a Lewis acid, reaching binding energies up to -283.3 kJ/mol ((HO)HB···BeF). The stabilization of these complexes is possible thanks to the σ-donor role of the L ligands in the LHB···BeX structures and the powerful acceptor nature of beryllium. According to the topology of the density, these B-Be interactions present positive laplacian values and negative energy densities, covering different degrees of electron sharing. ELF calculations allowed measuring the population in the interboundary B-Be region, which varies between 0.20 and 2.05 electrons upon switching from the weakest ((CS)HB···BeH) to the strongest complex ((HO)HB···BeF). These B-Be interactions can be considered as beryllium bonds in most cases.