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

Abstract

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(κ⁶-{(^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{κ⁵-((^tBu₂ArO)Me₂-cyclam)}{κ²-(^tBu₂ArOCH₂)}] (2) and of the inverse–sandwich complex [{U(κ⁵-{(^tBu2ArO)₂Me₂-cyclam})}₂(μ-η⁶:η⁶-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)–arene⁴⁻–U(IV) and U(III)–arene²⁻–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.