Evidence for single metal two electron oxidative addition and reductive elimination at uranium
Journal: Nature Communications
Publication Date: 01 December, 2017
Department of: Chemistry
An actinide element mimicking the chemistry of transition metals
Single-metal, two-electron oxidative addition and reductive elimination are fundamental reactions for transition metals that underpin most homogeneous catalytic cycles. These reactions are typically regarded as the preserve of the d-block, where metals typically have facile and reversible redox chemistry that makes them suitable for catalysis. In contrast, however, the f-block elements typically engage only in one-electron transfer reactions and such reactions are usually irreversible and thus stoichiometric in nature.
Utilising low-valent uranium(III) complexes, with sterically very open coordination spheres, researchers at the University of Manchester and their colleagues in Nottingham and Toulouse have now discovered that diazobenzene can react to give uranium(V) products, where a formal oxidative addition has occurred. They also found evidence for a thermally instigated reductive elimination. Computer modelling revealed a reaction intermediate where a uranium f-orbital δ-back-bonds into the π*-orbital of azobenzene. This binding mode would not normally be expected, and may contribute to the observed reactivity.
Although the system is not well balanced, it establishes evidence for reversible oxidative addition and reductive elimination at uranium, thus raising the tantalising possibility that with a better balanced system d-block reactivity could be performed by an f-element. However, the presence of f-orbitals at uranium would probably mean that any such reactivity would be different from traditional d-block catalysis, and so new types of catalysis might result.
- As a result of uranium enrichment, there are vast quantities of depleted uranium world-wide with no obvious application. Finding innovative uses for uranium could thus put a by-product from the nuclear industry to a beneficial use.
- Uranium has been used by chemical industry in catalysis before, in heterogeneous oxidation of alkanes and the original patent for the Haber Bosch process states that uranium is the best promoter for ammonia formation.