Synthesis and small molecule reactivity of uranium(IV) alkoxide complexes with both bound and pendant N-heterocyclic carbene ligands

The syntheses of two tetravalent uranium alkoxide-carbene complexes are reported, UIL3], and UL4] where L = OCMe2CH21-C(NCHCHNiPr)]. The latter shows dynamic behaviour of the alkoxycarbene ligands in solution at room temperature, and the crystal structure of UL4] shows that one carbene group remains uncoordinated. The unbound N-heterocyclic carbene group is trapped by a range of reagents such as 16-valence-electron metal carbonyl fragments and BH3 moieties, forming, for example, UL3(mu-L)W(CO)5], UL2(mu-L)2Mo(CO)4], and UL(n)(L-BH3)(4-n)] (n = 1-4), demonstrating the potential for these hemilabile electropositive metal-carbene complexes to participate in the bifunctional activation of small molecules.