Issue 26, 2019

Use of 15N NMR spectroscopy to probe covalency in a thorium nitride

Abstract

Reaction of the thorium metallacycle, [Th{N(R)(SiMe2)CH2}(NR2)2] (R = SiMe3) with 1 equiv. of NaNH2 in THF, in the presence of 18-crown-6, results in formation of the bridged thorium nitride complex, [Na(18-crown-6)(Et2O)][(R2N)3Th(μ-N)(Th(NR2)3] ([Na][1]), which can be isolated in 66% yield after work-up. Complex [Na][1] is the first isolable molecular thorium nitride complex. Mechanistic studies suggest that the first step of the reaction is deprotonation of [Th{N(R)(SiMe2)CH2}(NR2)2] by NaNH2, which results in formation of the thorium bis(metallacycle) complex, [Na(THF)x][Th{N(R)(SiMe2CH2)}2(NR2)], and NH3. NH3 then reacts with unreacted [Th{N(R)(SiMe2)CH2}(NR2)2], forming [Th(NR2)3(NH2)] (2), which protonates [Na(THF)x][Th{N(R)(SiMe2CH2)}2(NR2)] to give [Na][1]. Consistent with hypothesis, addition of excess NH3 to a THF solution of [Th{N(R)(SiMe2)CH2}(NR2)2] results in formation of [Th(NR2)3(NH2)] (2), which can be isolated in 51% yield after work-up. Furthermore, reaction of [K(DME)][Th{N(R)(SiMe2CH2)}2(NR2)] with 2, in THF-d8, results in clean formation of [K][1], according to 1H NMR spectroscopy. The electronic structures of [1] and 2 were investigated by 15N NMR spectroscopy and DFT calculations. This analysis reveals that the Th–Nnitride bond in [1] features more covalency and a greater degree of bond multiplicity than the Th–NH2 bond in 2. Similarly, our analysis indicates a greater degree of covalency in [1]vs. comparable thorium imido and oxo complexes.

Graphical abstract: Use of 15N NMR spectroscopy to probe covalency in a thorium nitride

Supplementary files

Article information

Article type
Edge Article
Submitted
19 Apr 2019
Accepted
02 Jun 2019
First published
04 Jun 2019
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2019,10, 6431-6436

Use of 15N NMR spectroscopy to probe covalency in a thorium nitride

S. L. Staun, D. Sergentu, G. Wu, J. Autschbach and T. W. Hayton, Chem. Sci., 2019, 10, 6431 DOI: 10.1039/C9SC01960J

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