Four-Electron Reduction of O2 at a Single Metal Center: Redox Chemistry of a Uranium(II) Synthon

Abstract

One-electron reduction of the N,N′-tethered U(III) complex κ2:η6-LArUI(THF) (A), featuring a ligand imposed η6-arene-metal interaction, generates the reduced species [K(2.2.2-cryptand)][(κ2:η6-LAr)UI] (1) in good yield. Complex 1 exhibits severe distortion of the anchored arene, indicating ligand-based rather than metal-centered reduction. In line with this, close inspection of the structural parameters of 1 reveals bond localization consistent with two-electron reduction of the arene concomitant with reduction-induced oxidation of the metal center, giving a formally U(IV) complex. Nonetheless, 1 is a potent U(II) synthon capable of four-electron transfer chemistry, activating the small molecules PhN3, PhNO, and O2 to yield the multiply bonded, hexavalent products trans-(κ2:η6-LAr)U(NPh)2 (3) and trans-(κ2-LAr)U(E)(E’)(THF) (E = NPh, E′ = O (4); and E = E′ = O (5)). Formation of mononuclear uranyl complex 5 is especially significant, as it constitutes the first reported example of O2 activation via four-electron transfer from a single actinide center.