Tuning Uranium-Nitrogen Multiple Bond Formation with Ancillary Siloxide Ligands

The new homoleptic ate U(III) siloxide [K-(18c6)][U(OSi((OBu)-Bu-t)(3))(4)] 2 was prepared in 69% yield by reduction of [U(OSi((OBu)-Bu-t)(3))(4)] 3 with KC8. The reaction of the neutral U(III) siloxide complex [U(OSi((OBu)-Bu-t)(3))(2)(mu-OSi((OBu)-Bu-t)(3))](2) 1 with adamantyl azide leads to the isolation of the dinudear U(VI) imido complex [U-2(NAd)(4)(OSi((OBu)-Bu-t)(3))(4)] 4. The X-ray crystal structure shows the presence of a cation-cation interaction between the two [U(NAd)(2)](2+) groups. In contrast the reactions of 2 with the trimethylsilyl and adamantyl azides afford the U(V) imido complexes [K(18c6)][U(NSiMe3)(OSi((OBu)-Bu-t)(3))(4)] 5-TMS and [K(18c6)][U(NAd)(OSi((OBu)-Bu-t)(3))(4)] 5-Ad pure in 48% and 66% yield, respectively. The reaction of 2 with CsN3 in THF at -40 degrees C yields a mixture of products from which the azido U(IV) complex [K(18c6)][U(N-3)((OSiOBu)-Bu-t)(3))(4)] 7 and the mu-nitrido diuranium(V) complex [KU(mu-N)(OSi((OBu)-Bu-t)(3))](2) 8 were isolated. The crystal structure of 8 shows the presence of a rare U2N2 core with two nitrido atoms bridging two uranium centers in a diamond-shaped geometry. In contrast, the reaction of 1 with CsN3 affords the diuranium(IV) complex Cs{(mu-N)[U(OSi((OBu)-Bu-t)(3)](2)} 9 presenting a nitrido ligand bridging two uranium and one cesium cations. These results show the importance of the coordination environment in the outcome of the reaction of U(III) with asides.