Keener M, Scopelliti R, Mazzanti M. Nitride protonation and NH
3 binding
versus N-H bond cleavage in uranium nitrides.
Chem Sci 2021;
12:12610-12618. [PMID:
34703546 PMCID:
PMC8494049 DOI:
10.1039/d1sc03957a]
[Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Accepted: 08/13/2021] [Indexed: 11/24/2022] Open
Abstract
The conversion of metal nitrides to NH3 is an essential step in dinitrogen fixation, but there is limited knowledge of the reactivity of nitrides with protons (H+). Herein, we report comparative studies for the reactions of H+ and NH3 with uranium nitrides, containing different types of ancillary ligands. We show that the differences in ancillary ligands, leads to dramatically different reactivity. The nitride group, in nitride-bridged cationic and anionic diuranium(iv) complexes supported by –N(SiMe3)2 ligands, is resistant toward protonation by weak acids, while stronger acids result in ligand loss by protonolysis. Moreover, the basic –N(SiMe3)2 ligands promote the N–H heterolytic bond cleavage of NH3, yielding a “naked” diuranium complex containing three bridging ligands, a nitride (N3−) and two NH2 ligands. Conversely, in the nitride-bridged diuranium(iv) complex supported by –OSi(OtBu)3 ligands, the nitride group is easily protonated to afford NH3, which binds the U(iv) ion strongly, resulting in a mononuclear U–NH3 complex, where NH3 can be displaced by addition of strong acids. Furthermore, the U–OSi(OtBu)3 bonds were found to be stable, even in the presence of stronger acids, such as NH4BPh4, therefore indicating that –OSi(OtBu)3 supporting ligands are well suited to be used when acidic conditions are required, such as in the H+/e− mediated catalytic conversion of N2 to NH3.
Ancillary ligands alter the reactivity of U-nitrides with H+, relevant to N2 conversion to NH3. The amides lead to complete ligand loss and NH3 activation, while for siloxides, the nitride is protonated to NH3 leaving the ancillary ligands intact.![]()
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