Ammonia formation by metal–ligand cooperative hydrogenolysis of a nitrido ligand

Journal name:
Nature Chemistry
Volume:
3,
Pages:
532–537
Year published:
DOI:
doi:10.1038/nchem.1051
Received
Accepted
Published online

Abstract

Bioinspired hydrogenation of N2 to ammonia at ambient conditions by stepwise nitrogen protonation/reduction with metal complexes in solution has experienced remarkable progress. In contrast, the highly desirable direct hydrogenation with H2 remains difficult. In analogy to the heterogeneously catalysed Haber–Bosch process, such a reaction is conceivable via metal-centred N2 splitting and unprecedented hydrogenolysis of the nitrido ligands to ammonia. We report the synthesis of a ruthenium(IV) nitrido complex. The high nucleophilicity of the nitrido ligand is demonstrated by unusual N–C coupling with π-acidic CO. Furthermore, the terminal nitrido ligand undergoes facile hydrogenolysis with H2 at ambient conditions to produce ammonia in high yield. Kinetic and quantum chemical examinations of this reaction suggest cooperative behaviour of a phosphorus–nitrogen–phosphorus pincer ligand in rate-determining heterolytic hydrogen splitting.

At a glance

Figures

  1. Synthesis and reactivity of nitrido complex 5 and molecular structures of 5 and 6.
    Figure 1: Synthesis and reactivity of nitrido complex 5 and molecular structures of 5 and 6.

    a, Synthetic pathways for the formation of 1, 2, 5, 6, 7 and 8. b, Superimposition of 1H-NMR spectra (C6D6) in the NH3 region after hydrogenolysis of 14N-5 (blue) and 14N/15N-5 (red), respectively. c, Crystal molecular structure of 5. Selected bond lengths (Å) and angles (°): Ru1–N1, 2.051(1); Ru1–N2, 1.688(3) (Ru–N3, 1.628(4)); Ru1–P1, 2.3796(5); Ru1–P2, 2.3724(5); N1–Ru1–N2, 147.3(2) (N1–Ru1–N3, 165.6(3)); P1–Ru1–P2, 155.70(2) (thermal ellipsoids drawn at 50% probability; hydrogen atoms and N3 omitted for clarity). d, Crystal molecular structure of 6. Selected bond lengths (Å) and angles (°): Ru1–N1, 1.970(2); Ru1–N2, 2.124(2); Ru1–C1, 1.790(3); Ru1–P1, 2.3760(7); Ru1–P2, 2.3750(6); N1–Ru1–N2, 157.25(7); N1–Ru1–C1, 110.94(9); N2–Ru1–C1, 91.81(9); P1–Ru1–P2, 162.53(2) (thermal ellipsoids drawn at 50% probability; hydrogen atoms omitted for clarity). Quant. = quantitative yield.

  2. Computed lowest free-energy pathway for the hydrogenolysis of nitrido complex 5.
    Figure 2: Computed lowest free-energy pathway for the hydrogenolysis of nitrido complex 5.

    PBE/def2-SVP(PP) relative free energies of reaction (ΔGR) and relative free energies of activation (ΔG) for the individual steps after standard-state correction in kcal mol−1.

Compounds

4 compounds View all compounds
  1. Nitrido(2-(di-tert-butylphosphino-κP-ethyl)amidoruthenium(IV)
    Compound 5 Nitrido(2-(di-tert-butylphosphino-κP-ethyl)amidoruthenium(IV)
  2. Isocyanatocarbonyl(2-(di-tert-butylphosphino-κP-ethyl)amidoruthenium(II)
    Compound 6 Isocyanatocarbonyl(2-(di-tert-butylphosphino-κP-ethyl)amidoruthenium(II)
  3. Tetrahydrido(2-(di-tert-butylphosphino-κP-ethyl)amineruthenium(IV)
    Compound 7 Tetrahydrido(2-(di-tert-butylphosphino-κP-ethyl)amineruthenium(IV)
  4. Trihydrido(2-(di-tert-butylphosphino-κP-ethyl)amidoruthenium(IV)
    Compound 8 Trihydrido(2-(di-tert-butylphosphino-κP-ethyl)amidoruthenium(IV)

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Author information

Affiliations

  1. Department Chemie, Technische Universität München, Lichtenbergstr. 4, 85748 Garching b. München, Germany

    • Bjorn Askevold,
    • Jorge Torres Nieto &
    • Eberhardt Herdtweck
  2. Department Chemie und Pharmazie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, 91058 Erlangen, Germany

    • Bjorn Askevold &
    • Sven Schneider
  3. Insitut für Anorganische und Analytische Chemie, Goethe-Universität, Max-von-Laue-Str. 7, 60438 Frankfurt am Main, Germany

    • Samat Tussupbayev,
    • Martin Diefenbach &
    • Max C. Holthausen

Contributions

B.A. and J.T.N. performed the synthetic work and spectrosopic examination, S.T. and M.D. the quantum chemical study and E.H. the crystallographic characterization, respectively. S.S. and M.C.H. designed and supervised the experimental and computational studies, respectively. The paper was written by B.A., S.T., M.D., M.C.H. and S.S. and all the authors discussed the results and commented on the manuscript.

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The authors declare no competing financial interests.

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Crystallographic information files

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    Crystallographic data for compound 5

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    Crystallographic data for compound 6·2

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