Applications of boroxide ligands in supporting small molecule activation by U(iii) and U(iv) complexes

Abstract

The boroxide ligand [OBAr₂]⁻ (Ar = Mes, Trip) is shown to be able to support both U^III and U^IV centres for the first time. The synthesis and structures of homoleptic and heteroleptic U^III and U^IV complexes are reported. The UX₃ complex with larger substituents, [U(OBTrip₂)₃]₂, exhibits greater thermal stability compared to less encumbered [U(OBMes₂)₃]₂ but reacts with a smaller range of the small molecules tested to date. Initial studies on their capacity to participate in small molecule chemistry show that dark purple [U(OBMes₂)₃]₂ binds and/or reductively activates a variety of small molecules such as pyridine-oxide, triphenylphosphineoxide, sulfur, and dicyclohexylcarbodiimide. While [U(OBMes₂)₃]₂ shows no reaction with CO or CO₂, [U(OBTrip₂)₃]₂ is oxidised by both, in the former case forming [U(OBTrip₂)₄], and in the latter case forming a small quantity of the structurally characterised μ-carbonate product [(μ-CO₃){U(OBTrip₂)₃}₂].