Fate of Oxidation States at Actinide Centers in Redox‐Active Ligand Systems Governed by Energy Levels of 5 f Orbitals

We report the formation of a Np IV complex from the complexation of Np VI O 2 2+ with the redox‐active ligand t Bu‐pdiop 2− =2,6‐bis[ N ‐(3,5‐di‐ tert ‐butyl‐2‐hydroxyphenyl)iminomethyl]pyridine. To the best of our knowledge, this is the first example of the direct complexation‐induced chemical reduction of Np VI O 2 2+ to Np IV . In contrast, the complexation of U VI O 2 2+ with t Bu‐pdiop 2− did not induce the reduction of U VI O 2 2+ , not even after the two‐electron electrochemical reduction of [U VI O 2 ( t Bu‐pdiop)]. This contrast between the Np and U systems may be ascribed to the decrease of the energy of the 5 f orbitals in Np compared to those in U. The present findings indicate that the redox chemistry between U VI O 2 2+ and Np VI O 2 2+ should be clearly differentiated in redox‐active ligand systems.