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Tuning Uranium–Nitrogen Multiple Bond Formation with Ancillary Siloxide Ligands

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journal contribution
posted on 14.08.2013, 00:00 authored by Clément Camp, Jacques Pécaut, Marinella Mazzanti
The new homoleptic ate U­(III) siloxide [K­(18c6)]­[U­(OSi­(OtBu)3)4] 2 was prepared in 69% yield by reduction of [U­(OSi­(OtBu)3)4] 3 with KC8. The reaction of the neutral U­(III) siloxide complex [U­(OSi­(OtBu)3)2(μ-OSi­(OtBu)3)]2 1 with adamantyl azide leads to the isolation of the dinuclear U­(VI) imido complex [U2(NAd)4(OSi­(OtBu)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(OtBu)3)4] 5-TMS and [K­(18c6)]­[U­(NAd)­(OSi­(OtBu)3)4] 5-Ad pure in 48% and 66% yield, respectively. The reaction of 2 with CsN3 in THF at −40 °C yields a mixture of products from which the azido U­(IV) complex [K­(18c6)]­[U­(N3)­(OSi­(OtBu)3)4] 7 and the μ-nitrido diuranium­(V) complex [KU­(μ-N)­(OSi­(OtBu)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{(μ-N)­[U­(OSi­(OtBu)3)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 azides.