ABSTRACT
Neutral arenes such as benzene have never been considered suitable ligands for electropositive actinide cations, yet we find that even simple UIII UX3 aryloxide complexes such as U(ODipp)3 bind and reduce arenes spontaneously at room temperature, forming inverse arene sandwich (IAS) complexes XnU(µ-C6D6)UXm (X = ODipp, n=2, m=3; X = OBMes2 n=m=2 or 3) (ODipp = OC6H3iPr2-2,6; Mes = 2,4,6-Me3-C6H2). In some of these cases, further arene reduction has occured as a result of X ligand redistribution. These unexpected spontaneous reactions explain the anomalous spectra and reported lack of further reactivity of strongly reducing UIII centers of U(ODipp)3. Phosphines that are not considered suitable ligands for actinides can catalyze the formation of the IAS complexes. This enables otherwise inaccessible asymmetric and less congested IAS complexes to be isolated and the bonding in this series compared.
ABSTRACT
The boroxide ligand [OBAr2]- (Ar = Mes, Trip) is shown to be able to support both UIII and UIV centres for the first time. The synthesis and structures of homoleptic and heteroleptic UIII and UIV 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].
