A Theoretical Study on Divalent Heavier Group 14 Complexes as Promising Donor Ligands for Building Uranium–Metal Bonds

The study of metal–metal bonds
is one of the important challenges
in organometallic chemistry and of great significance in applied and
structural chemistry. We built a series of potential complexes (Cp­SiMe3)3­U-E­(NCH­Mes)2 (E = Si,
Ge, Sn, Pb) by constructing two neutral fragments [(Cp­SiMe3)3­U] and [E­(NCH­Mes)2] and investigated their structures with scalar-relativistic theoretical
calculations. U–E bonds possess highly polarized U–E
interactions and also strong donor–​acceptor interactions
according to the analyses of MO (molecular orbital), natural charge,
QTAIM (quantum theory of atoms in molecules), and ELF (electron localization
function). Particularly, the four U–E bonds are mainly composed
of U 6d orbitals and E ns orbital, which lead to the nature of donor–​acceptor
interaction between U and E atoms. These bonds are significantly different
from the general uranium–​transition-metal and uranium–​main-group
bonds, Moreover, the U–E bond strengths in the (Cp­SiMe3)3­U-E­(NCH­Mes)2 complexes
follow the trend of U–Si > U–Sn > U–Ge
> U–Pb
according to the results of bond orders and EDA (energy decomposed
analysis). The binding energies suggest that the four (Cp­SiMe3)3­U-E­(NCH­Mes)2 complexes
are thermodynamically accessible. This work indicates that the divalent
heavier group 14 complexes are promising donor ligands for building
unsupported uranium–​metal bonds.