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Four-electron reduction of benzene by a samarium(ii)-alkyl without the addition of external reducing agents

Nature Chemistry volume 17, pages 20–28 (2025)Cite this article

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Abstract

Benzene reduction by molecular complexes remains an important synthetic challenge, requiring harsh reaction conditions involving group I metals. Reductions of benzene, to date, typically result in a loss of aromaticity, although the benzene tetra-anion, a 10π-electron system, has been calculated to be stable and aromatic. Due to the lack of sufficiently potent reductants, four-electron reduction of benzene usually requires the use of group I metals. Here we demonstrate the four-electron reduction of benzene and some of its derivatives using a samarium(ii) alkyl reagent, with no requirement for group I metals. Whereas organosamarium(ii) typically reacts through one-electron processes, the compounds reported here feature a rare two-electron process. Combined experimental and computational results implicate a transient samarium(i) intermediate involved in this reduction process, which ultimately provides the benzene tetra-anion. The remarkably strong reducing power of this samarium(ii) alkyl implies a rich reactivity, providing scope for its application as a reducing agent.

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Fig. 1: Reduced arene complexes of the lanthanides and actinides.
Fig. 2: Synthesis and molecular structure of Sm(ii) alkyl 3.
Fig. 3: Synthesis, molecular structure and structural data of tetra-anionic arene complexes 4–6.
Fig. 4: Reaction of Sm(ii) alkyl 3 with COT.
Fig. 5: Photolytic reduction of 3 and reduction of 2 by KC8 to provide 3-(I) before the four-electron reduction of benzene.
Fig. 6: Computed enthalpy pathway for the reaction of Sm(ii) alkyl 3 with benzene.

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Data availability

All of the data generated or analysed during this study are included in the published article and its Supplementary Information files. X-ray crystallographic data for compounds 1–7, (BDIDicyp)K and (BDIDicyp)2Sm are available in the Supplementary Information and from the Cambridge Crystallographic Data Centre (http://www.ccdc.cam.ac.uk/) under reference numbers 2244289 (1), 2244280 (2), 2244279 (3), 2244281 (4), 2244283 (5), 2244282 (6), 2244284 (7), 2244290 ((BDIDicyp)K) and 2359622 ((BDIDicyp)2Sm). Source data are provided with this paper.

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Acknowledgements

M.D.A. acknowledges government funding from the Royal Society Te Apārangi for support through a Marsden Fast-Start Grant (21-VUW-120) and Rutherford Discovery Fellowship (22-VUW-016). We are grateful for a Curtis-Gordon Research Scholarship and Victoria University of Wellington Doctoral Scholarship (to G.M.R. and F.M.B.). We also thank the MacDiarmid Institute (B.D.N.) for providing financial support. N.F.C. thanks the National Computational Infrastructure for computational resources via the Australian National University Merit Allocation Scheme.

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Authors and Affiliations

  1. School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand

    Georgia M. Richardson, Finlay M. Burke, Brooke D. Nicholls, Joanne E. Harvey, Robert A. Keyzers, Lujia Liu, Nathaniel J. L. K. Davis & Mathew D. Anker

  2. Laboratory of Physics and Chemistry of Nano-Objects (UMR 5215), Institut National des Sciences Appliquées, Université Toulouse III—Paul Sabatier, Centre National de la Recherche Scientifique and Université de Toulouse, Toulouse, France

    Thayalan Rajeshkumar & Laurent Maron

  3. Ferrier Research Institute, Victoria University of Wellington, Wellington, New Zealand

    Scott A. Cameron

  4. Robinson Research Institute, Victoria University of Wellington, Wellington, New Zealand

    Tane Butler & Simon Granville

  5. Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory, Australia

    Julien Langley, Li F. Lim, Nicholas Cox, Nicholas F. Chilton & Jamie Hicks

  6. Department of Chemistry, The University of Manchester, Manchester, UK

    Nicholas F. Chilton

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  1. Georgia M. Richardson
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Contributions

G.M.R. carried out the organometallic synthetic and reaction studies. T.R., N.F.C. and L.M. conducted the computational analysis. F.M.B., B.D.N. and J.E.H. developed the organic synthesis. R.A.K. conducted all of the GC–MS analyses. T.B., S.G. and L.L. conducted all of the superconducting quantum interference device measurements and interpreted the data. S.A.C. conducted the crystallographic studies and initiated the organic synthesis. J.L., L.F.L., J.H., M.D.A., N.F.C. and N.C. carried out the EPR studies. G.M.R. and N.J.L.K.D. conducted all of the photochemical studies. N.F.C., N.C., L.M. and M.D.A. wrote the manuscript. L.M. and M.D.A. managed the project.

Corresponding authors

Correspondence to Laurent Maron or Mathew D. Anker.

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Nature Chemistry thanks S. Chantal Stieber and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Table 1 Paramagnetic NMR shifts for 3, 4 and 7
Full size table

Supplementary information

Supplementary Information

Synthetic, solution, solid-state and computational analyses and Supplementary Figs. 1–75and Tables 1–11.

Supplementary Dataset 1

Optimized coordinates for the calculated structures.

Supplementary Dataset 2

Crystallographic data for [(BDIDicyp)K] (CCDC 2244290).

Supplementary Dataset 3

Crystallographic data for compound 1 (CCDC 2244289).

Supplementary Dataset 4

Crystallographic data for compound 2 (CCDC 2244280).

Supplementary Dataset 5

Crystallographic data for compound 3 (CCDC 2244279).

Supplementary Dataset 6

Crystallographic data for compound 4 (CCDC 2244281).

Supplementary Dataset 7

Crystallographic data for compound 5 (CCDC 2244283).

Supplementary Dataset 8

Crystallographic data for compound 6 (CCDC 2244282).

Supplementary Dataset 9

Crystallographic data for compound 7 (CCDC 2244284).

Supplementary Dataset 10

Crystallographic data for compound (BDIDicyp)2Sm (CCDC 2359622).

Source data

Source Data Fig. 4

Time dependence of the EPR intensity of the organic radical signal at 170 K.

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Richardson, G.M., Rajeshkumar, T., Burke, F.M. et al. Four-electron reduction of benzene by a samarium(ii)-alkyl without the addition of external reducing agents. Nat. Chem. 17, 20–28 (2025). https://doi.org/10.1038/s41557-024-01688-6

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