Theoretical Insights Into Structures and U-C Bonding in the Uranium Benzyl Derivatives

The uranium benzyl derivatives are a class of uranium carbon complex with saturated carbon atom coordination. We investigated the electronic structures of the tetravalent uranium benzyl (Bn) complex U(CH₂Ph)₄ and its derivatives U(2-CH₂(NC₅H₄))₄, U(o-OMeBn)₄, U(m-OMeBn)₄, and the bonding nature between the uranium atom and methylene carbon atom (U-C_me) using scalar-relativistic quantum chemical calculations. The structures of the four uranium benzyl derivatives identify that the electronic structures are not sensitive to meta-OMe substitution, while they are significantly sensitive to the ortho-OMe and pyridine due to the coordination of O and N to the uranium atom. The U-C_me bonds have highly polarized σ-bonding with partial covalency, which are predominantly composed of U 6d and 5f orbitals. Moreover, U 6d orbitals are favored for the U-C_me bonds compared with U 5f orbitals. Furthermore, there are no additional π interactions in the U(o-OMeBn)₄ and the corresponding U-C_me bonds appear the strongest covalent character among the four U(IV) system. The energy decomposition analysis suggests that the electrostatic interaction plays a dominant role between uranium and ligands. Finally, the complexes U(2-CH₂(NC₅H₄))₄ and U(o-OMeBn)₄ are the most thermodynamically accessible among the four complexes based on the binding energies. This study improves our understanding of tetravalent uranium benzyl derivatives bearing uranium-saturated carbon bondings.