Bonding in M(NHBMe)2 and M[Mn(CO)5]2 complexes (M=Zn, Cd, Hg; NHBMe=(HCNMe)2B): divalent group 12 metals with zero oxidation state

Quantum chemical studies using density functional theory were carried out on M(NHBMe)(2) and M[Mn(CO)(5)](2) (M=Zn, Cd, Hg) complexes. The calculations suggest that M(NHBMe)(2) and M[Mn(CO)(5)](2) have D-2d and D-4d symmetry, respectively, with a (1)A(1) electronic ground state. The bond dissociation energies of the ligands have the order of Zn > Cd > Hg. A thorough bonding analysis using charge and energy decomposition methods suggests that the title complexes are best represented as NHBMe⇆M-0 reversible arrow NHBMe and Mn(CO)(5)⇆M-0 reversible arrow Mn(CO)(5) where the metal atom M in the electronic ground state with an ns(2) electron configuration is bonded to the (NHBMe)(2) and [Mn(CO)(5)](2) ligands through donor-acceptor interaction. These experimentally known complexes are the first examples of mononuclear complexes with divalent group 12 metals with zero oxidation state that are stable at ambient condition. These complexes represent the rare situation where the ligands act as a strong acceptor and the metal center acts as strong donor. The relativistic effect of Hg leads to a weaker electron donating strength of the 6s orbital, which explains the trend of the bond dissociation energy.