Unveiling Nonadiabatic Pathways in Small Molecule Activation: Dinuclear Uranium-Mediated H₂ and N₂ Bond Cleavage

Nonadiabatic effects have been extensively studied in photoexcited processes, but their role in thermal process so far has neither been thoroughly studied nor appreciated, despite their significance. In this work, H₂ and N₂ activation mediated by a diuranium complex was studied from a nonadiabatic perspective using multi-configurational ab initio calculations combined with density functional theory. Stepwise electron transfer during the reaction enhances degeneracy between electronic states, enabling state-to-state transitions, i.e., spin downshift. The dual functionality of transition states acting as thermodynamic gateways and channels for nonadiabatic transitions was disclosed. The π and σ cooperative activation explains the unprecedented reactivity by the diuranium cooperation. Bonding analysis reveals that U_5f/6d orbitals mixing with H_1s/N_2p orbitals afford some degree of covalency to the primarily ionic U─H/N interactions, with the 6d-orbitals contributing more pronounced than the 5f-orbitals in σ interactions, while the U─N π bonding exhibits significant U_5f contributions.