| Abstract: | Is it possible to facilitate the formation of a genuine Be?Be or Mg?Mg single bond for the E2 species while it is in its neutral state? So far, (NHCR)Be?Be(NHCR) (R=H, Me, Ph) have been reported where Be2 is in 1Δg 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 E2(NHBMe)2 (E=Be, Mg; NHBMe=(HCNMe)2B) complexes where E2 is in 3∑u+ excited state having (nσg+)2(nσu+)1((n+1)σg+)1 (n=2 for Be and n=4 for Mg) valence electron configuration and it forms electron‐shared bonding with two NHBMe radicals. The effects of bonding with nσu+ and (n+1)σg+ orbitals will cancel each other, providing the former E?E bond order as one. Be2(NHBMe)2 complex is thermochemically stable with respect to possible dissociation channels at room temperature, whereas the two exergonic channels, Mg2(NHBMe)2 → Mg + Mg(NHBMe)2 and Mg2(NHBMe)2 → Mg2 + (NHBMe)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 E2 moiety with a single E?E covalent bond. |
