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(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(κ7-{(tBu2ArO)(tBu2ArO-κ2-N,C)Me2-cyclam})] (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) -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.