Density Functional Theory Study of Ultrashort Metal−Metal Distances in Diberyllium Complexes Bearing Carbene Ligands.

Diberyllium complexes with ultrashort metal−metal distances (USMMDs, defined as dM−M<1.900 Å) are fascinating for the nature of the valence electronic structure of Be atoms. In this paper a family of diberyllium complexes [L−BeH3Be−L]+ (1–7), in which L was an N‐heterocyclic carbene (NHC) or a mesoionic carbene (MIC), were studied by Density Functional Theory (DFT) at the B3LYP/cc‐pVTZ level. It was found that complexes 1–7 possessed ultrashort Be−Be distances of 1.754 Å–1.779 Å and strong covalent bonds between a Be atom and its adjacent carbene center (Ccarb) at once. Electronic structures and chemical bonding analyses ascribed USMMDs between the Be atoms to the Be−H−Be three‐center two‐electron (3c‐2e) bonds. The strong Be−Ccarb bonds were determined by combining effects of covalent interaction and electrostatic interaction between the Be and the Ccarb atoms. These complexes exhibited a great stability with large highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) gaps, high vertical detachment energies (VDEs) and low vertical electron affinities (VEAs) and are potential targets in future experiments. [ABSTRACT FROM AUTHOR]