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Issue 13, 2019
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Thorium- and uranium-azide reductions: a transient dithorium-nitride versus isolable diuranium-nitrides

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Abstract

Molecular uranium-nitrides are now well known, but there are no isolable molecular thorium-nitrides outside of cryogenic matrix isolation experiments. We report that treatment of [M(TrenDMBS)(I)] (M = U, 1; Th, 2; TrenDMBS = {N(CH2CH2NSiMe2But)3}3−) with NaN3 or KN3, respectively, affords very rare examples of actinide molecular square and triangle complexes [{M(TrenDMBS)(μ-N3)}n] (M = U, n = 4, 3; Th, n = 3, 4). Chemical reduction of 3 produces [{U(TrenDMBS)}2(μ-N)][K(THF)6] (5) and [{U(TrenDMBS)}2(μ-N)] (6), whereas photolysis produces exclusively 6. Complexes 5 and 6 can be reversibly inter-converted by oxidation and reduction, respectively, showing that these UNU cores are robust with no evidence for any C–H bond activations being observed. In contrast, reductions of 4 in arene or ethereal solvents gives [{Th(TrenDMBS)}2(μ-NH)] (7) or [{Th(TrenDMBS)}{Th(N[CH2CH2NSiMe2But]2CH2CH2NSi[μ-CH2]MeBut)}(μ-NH)][K(DME)4] (8), respectively, providing evidence unprecedented outside of matrix isolation for a transient dithorium-nitride. This suggests that thorium-nitrides are intrinsically much more reactive than uranium-nitrides, since they consistently activate C–H bonds to form rare examples of Th–N(H)–Th linkages with alkyl by-products. The conversion here of a bridging thorium(IV)-nitride to imido-alkyl combination by 1,2-addition parallels the reactivity of transient terminal uranium(IV)-nitrides, but contrasts to terminal uranium(VI)-nitrides that produce alkyl-amides by 1,1-insertion, suggesting a systematic general pattern of C–H activation chemistry for metal(IV)- vs. metal(VI)-nitrides. Surprisingly, computational studies reveal a σ > π energy ordering for all these bridging nitride bonds, a phenomenon for actinides only observed before in terminal uranium nitrides and uranyl with very short U–N or U–O distances.

Graphical abstract: Thorium- and uranium-azide reductions: a transient dithorium-nitride versus isolable diuranium-nitrides

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Publication details

The article was received on 07 Dec 2018, accepted on 21 Feb 2019 and first published on 23 Feb 2019


Article type: Edge Article
DOI: 10.1039/C8SC05473H
Chem. Sci., 2019,10, 3738-3745
  • Open access: Creative Commons BY license
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    Thorium- and uranium-azide reductions: a transient dithorium-nitride versus isolable diuranium-nitrides

    J. Du, D. M. King, L. Chatelain, E. Lu, F. Tuna, E. J. L. McInnes, A. J. Wooles, L. Maron and S. T. Liddle, Chem. Sci., 2019, 10, 3738
    DOI: 10.1039/C8SC05473H

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