Synthesis and characterization of a uranyl() complex with 2,6-pyridine-bis(methylaminophenolato) and its ligand-centred aerobic oxidation mechanism to a diimino derivative

A uranyl( vi ) complex with 2,6-bis(3,5-di- tert -butyl- o -phenolateaminomethyl)pyridine (UO 2 ( t Bu-pdaop), 1 ) was synthesized and thoroughly characterized by 1 H NMR, IR, elemental analysis, and single-crystal XRD. Right after the dissolution of complex 1 in pyridine or DMSO, the solution was pale red, whereas it gradually turned to dark purple under an ambient atmosphere. 1 H NMR spectra at the initial and final states suggested that both of the two aminomethyl groups in 1 were converted to azomethine ones through aerobic oxidation. Indeed, a uranyl( vi ) complex with 2,6-bis(3,5-di- tert -butyl- o -phenolateiminomethyl)pyridine (UO 2 ( t Bu-pdiop), 2 ) was obtained from the concentrated solution once the reaction was completed, and was characterized by IR, and single-crystal XRD. Kinetic analyses as well as mechanistic studies based on quantum chemical calculations suggested that hydrogen atom transfer from one of the amino groups in complex 1 to nearby O 2 initiates the stepwise oxidation processes to finally afford 2 . The present findings demonstrate the novel reactivity of a uranyl( vi ) complex, and provide new insights to construct thermally-driven molecular conversion systems by a UO 2 2+ complex catalyst. Both aminomethylene groups of a uranyl( vi ) complex bearing a 2,6-pyridine-bis(methylaminophenolato) ligand are oxidized to azomethine ones by an O 2 molecule under an ambient atmosphere to provide a diimino derivative of the parent uranyl( vi ) complex.