Unprecedented Bonding Situation in Viable E 2 (NHB Me ) 2 (E=Be, Mg; NHB Me =(HCN Me ) 2 B) Complexes: Neutral E 2 Forms a Single E−E Covalent Bond

Is it possible to facilitate the formation of a genuine Be−Be or Mg−Mg single bond for the E 2 species while it is in its neutral state? So far, (NHC R )Be−Be(NHC R ) (R=H, Me, Ph) have been reported where Be 2 is in 1 Δ g excited state imposing a formal Be−Be bond order of two. Herein, we present the formation of a single E−E (E=Be, Mg) covalent bond in E 2 (NHB Me ) 2 (E=Be, Mg; NHB Me =(HCN Me ) 2 B) complexes where E 2 is in 3 ∑ u + excited state having (nσ g + ) 2 (nσ u + ) 1 ((n+1)σ g + ) 1 ( n =2 for Be and n =4 for Mg) valence electron configuration and it forms electron‐shared bonding with two NHB Me radicals. The effects of bonding with nσ u + and (n+1)σ g + orbitals will cancel each other, providing the former E−E bond order as one. Be 2 (NHB Me ) 2 complex is thermochemically stable with respect to possible dissociation channels at room temperature, whereas the two exergonic channels, Mg 2 (NHB Me ) 2 → Mg + Mg(NHB Me ) 2 and Mg 2 (NHB Me ) 2 → Mg 2 + (NHB Me ) 2 , are kinetically inhibited by a free energy barrier of 15.7 and 18.7 kcal mol −1 , respectively, which would likely to be further enhanced in cases of bulkier substituents attached to the NHB ligands. Therefore, the title complexes are first viable systems which feature a neutral E 2 moiety with a single E−E covalent bond.