Facile N-C bond cleavage and arene reduction by a transient uranium(ii) complex

Complexes of uranium(ii) remain extremely rare and their reactivity is practically unexplored. Here we report that the reduction of the heteroleptic bis-aryloxide U(iii) complex [U(κ ⁶-{( ^tBu2ArO)₂Me₂-cyclam})I], A, yields a rare and highly reactive U(ii) intermediate that enables a rare example of intramolecular uranium mediated N-C cleavage and effects arene reduction resulting in the isolation of the U(iv) complex [U{κ ⁵-(( ^t Bu₂ArO)Me₂-cyclam)}{κ ²-( ^t Bu₂ArOCH₂)}] (2) and of the inverse-sandwich complex [{U(κ ⁵-{( ^tBu2ArO)₂Me₂-cyclam})}₂(μ-η ⁶:η ⁶-benzene)] (3) respectively. Moreover, the U(ii) solvent-dependent reactivity results in the formation of a putative U-N₂ complex in diethyl ether. Computational, EPR and magnetic studies indicate the electronic structure of 3 to be an equilibrium between two possible electronic structures very close in energy: (U(iv)-arene^4--U(iv) and U(iii)-arene^2--U(iii)). These results indicate that polydentate amine-phenolate ligands can be used to access highly reactive U(ii) intermediates and that provides evidence that U(ii) species are involved in the formation of inverse sandwich complexes.