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

Abstract

The boroxide ligand [OBAr 2 ] - (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 UX 3 complex with larger substituents, [U(OBTrip 2 ) 3 ] 2 , exhibits greater thermal stability compared to less encumbered [U(OBMes 2 ) 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(OBMes 2 ) 3 ] 2 binds and/or reductively activates a variety of small molecules such as pyridine-oxide, triphenylphosphineoxide, sulfur, and dicyclohexylcarbodiimide. While [U(OBMes 2 ) 3 ] 2 shows no reaction with CO or CO 2 , [U(OBTrip 2 ) 3 ] 2 is oxidised by both, in the former case forming [U(OBTrip 2 ) 4 ], and in the latter case forming a small quantity of the structurally characterised μ-carbonate product [(μ-CO 3 ){U(OBTrip 2 ) 3 } 2 ].