Theoretical predictions of aromatic Be-O rings

We have carried out a theoretical investigation of benzene substituted with BeO to assess stability and aromatic properties (with 1-3 BeO units in a six-membered ring); C4H4BeO, C2H2Be2O2, and Be3O3. All species retain a planar geometry. We considered both bare complexes and Be coordinated with L = CO, pyridine, PMe3, and NHC. Coordination of a ligand to Be atoms causes increased Be-O bond distances. Aromatic character has been investigated with NICS and NICS-scan calculations, EDA analysis, as well as considering the energetics of hydrogenation. The complexes with the greatest aromatic character are C4H4BeO (3), and C4H4Be(CO), which have negative NICS(1)zz values and minima in the NICS-scan. Coordination of two ligands to make the Be four-coordinate disrupts ring planarity and reduces aromatic character.