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.