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

Lookup NU author(s): Dr Erli Lu

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Abstract

© 2019 The Royal Society of Chemistry.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.

Publication metadata

Author(s): Du J, King DM, Chatelain L, Lu E, Tuna F, McInnes EJL, Wooles AJ, Maron L, Liddle ST

Publication type: Article

Publication status: Published

Journal: Chemical Science

Year: 2019

Volume: 10

Issue: 13

Pages: 3738-3745

Online publication date: 23/02/2019

Acceptance date: 21/02/2019

Date deposited: 02/10/2019

ISSN (print): 2041-6520

ISSN (electronic): 2041-6539

Publisher: Royal Society of Chemistry

URL: https://doi.org/10.1039/C8SC05473H

DOI: 10.1039/c8sc05473h

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