Photochemical Synthesis of Transition Metal-Capped Uranium(VI) Nitride Complexes

Abstract

Uranium nitrides play important roles in dinitrogen activation and functionalization and in nuclear power chemistry, but the synthesis and isolation of mono-uranium molecular nitrides remains a challenge due to their high reactivity. Here, we report the first example of transition metal (TM)-capped mono-U(VI) nitride complexes, which was generated by the photolysis of azide-bridged U(IV)-TM (TM = Rh, Ir) precursors. The U(V) nitride intermediates with bridged azide ligands were isolated successfully by careful control of the irradiation time, suggesting that the photolysis of azide-bridged U(IV)-TM precursors is a stepwise process. The presence of two U(VI) nitrides capped by three TMs was clearly demonstrated by an X-ray crystallographic study. These TM-capped mono-U(V) nitride intermediates and mono-U(VI) nitride products exhibit excellent stability both in the solid-state and in THF solution under ambient light. Density functional theory calculations show that the photolysis was necessary to break the N-N bond of the azide ligands, as suggested by the antibonding N-N interaction in their lowest unoccupied molecular orbitals.