On the basis of the first structurally authenticated L Ar U− FeCp(CO) 2 (L Ar = deprotonated p-terphenyl bis(aniline) ligand) complex bearing an unsupported U−Fe bond, we expanded the structures of complexes L Ar U−MCp(CO) 2 (M = Fe, Ru, Os) and systematically investigated the U−M bonding nature by using scalar-relativistic quantum chemical calculations. Theoretical results reveal highly polarized U−M interactions in the three L Ar U−MCp(CO) 2 complexes. Moreover, the three U−M bonds are confirmed to show single bond feature. Topology of electron density reveals predominantly "closed shell" U−M interaction with obvious ionic interaction in the three L Ar U−MCp(CO) 2 complexes. In addition, the negative binding energy suggests that the three L Ar U− MCp(CO) 2 complexes are thermodynamically feasible. This work reveals the bonding nature of the three U−M bonds and expands our knowledge of the unsupported uranium−metal bonding in the heterobimetallic complexes.

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 (CpSiMe 3 ) 3 U-E(NCHMes) 2 (E = Si, Ge, Sn, Pb) by constructing two neutral fragments [(CpSiMe 3 ) 3 U] 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 (CpSiMe 3 ) 3 U-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 (CpSiMe 3 ) 3 U-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.