Thorium- and Uranium-Nitrogen Multiple Bonding Chemistry Supported by Triamidoamine Ligands

Abstract

Although the chemistry of uranium-nitrogen multiple bonding is burgeoning, analogous thorium complexes are rare and there were no reports of any thorium nitides under ambient conditions at the start of this project. Herein, we report that reduction of [{U(TrenDMBS)(-N3)}4] (99) with 4.0 equivalents of KC8 gives [{U(TrenDMBS)}2(-N)][K(THF)6] (100) and [{U(TrenDMBS)}2(-N)] (101) and it was found that these UNU cores are stable and do not engage in C-H bond activation. However, reductions of [{Th(TrenDMBS)(-N3)}4] (97) in arene (benzene or toluene) or ethereal solvents (THF or DME) afford [{Th(TrenDMBS)}2(-NH)] (102) or [{Th(TrenDMBS)}{Th(N[CH2CH2NSiMe2But]2CH2CH2NSi[-CH2]MeBut)}(-NH)][K(DME)4] (103), respectively. The isolation of 102 and 103 provides evidence for an unprecedented transient dithorium-nitride species with a Th=N=Th linkage outside of matrix isolation conditions. In contrast, reduction of [Th(TrenTIPS)N3] (105) supported by a more sterically demanding TrenTIPS ligand with MC8 (M = K, Rb, Cs) produces a transient Th≡N triple bond, again, this species activates C-H bonds to give isolable parent imido derivatives [{Th(TrenTIPS)(µ-NHM)}2] (107M) or it can be trapped in an N-heterocycle amine HN(SiMe2CH2)2. Furthermore, the whole series of 107M (M = Li, Na, K, Rb, Cs) can also be prepared from a thoiurm parent amide complex [Th(TrenTIPS)NH2] (108). Computational studies on these thorium-nitrogen multiple bonds consistently evidence a  >  energy ordering (a phenomenon called ‘pushing from below’). Previously this was dismissed for thorium, being the preserve of uranium-nitrides or the uranyl dication. Lastly, a series of monomeric thoiurm parent imido complexes [Th(TrenTIPS)(μ-NH){M(Me6-TREN)}] (116M), uranium congeners [U(TrenTIPS)(μ-NH){M(Me6-TREN)}] (117M), and analogous uranium nitrides [U(TrenTIPS)(μ-N){M(Me6-TREN)}] (118M) (M = Li, Na, K, Rb, Cs) have been synthesised and charactersied. These complexes have been inverstigaed spectroscopically and crystallographically with respect to how these alkali metal ions affect the stability and the extent of covalency within these actinide-nitrogen multiple bonds, in comparison with related terminal uranium parent imido and nitride species reported by the Liddle group.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stephen Liddle (Supervisor) & David Mills (Supervisor)