Carbon Dioxide Reduction and Carbon Monoxide Activation Employing a Reactive Uranium(III) Complex

The highly reactive, six-coordinate tris-aryloxide U(III) species, [((^t-BuArO)₃tacn)U] (1) reacts with CO₂ in a 2e^- reduction to produce CO and a dinuclear U(IV/IV) μ-oxygen bridged complex [{((^t-BuArO)₃tacn)U}₂(μ-O)] (2). This reaction proceeds via a dinuclear CO₂-bridged intermediate 3. Also, mononuclear 1 was treated with 1 atm of CO to yield dinuclear [{((^t-BuArO)₃tacn)U}₂(μ-CO)] (4) with a CO ligand bridging two uranium ions in an unprecedented μ:η,η¹ fashion. The mixed-valent azido-bridged U(III/IV) complex 5 was synthesized from trivalent 1 and tetravalent [((^t-BuArO)₃tacn)U(N₃)] and serves as an isostructural analogue of triatomic-bridged intermediate 3 as well as an electronic model for mixed-valent 4.