Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Heterobimetallic alkaline earth metal–metal bonding

Nature Synthesis volume 3, pages 368–377 (2024)Cite this article

Subjects

Abstract

Low-oxidation-state complexes of type (BDI)Mg–Mg(BDI) (BDI, β-diketiminate) show broad reactivity, finding application as soluble, universal reducing agents, enriching the field of early main group metal chemistry. Attempts to isolate similar, but considerably more reactive, Ca–Ca bound complexes have so far failed. As the metal–metal bond strength descending group 2 rapidly decreases, BDI complexes of the heavier AeI (alkaline earth) ions (Ae = Ca, Sr, Ba) probably exist as (BDI)Ae· radicals of untamed reactivity. Here we describe a facile method to prepare stable but highly reactive complexes with heterobimetallic Mg–Ae bonds. Mixing [(BDI)MgˉNa+]2 and [Ae(NR2)2]2 dimers led to anion–cation exchange and exclusive formation of mixed species: (BDI)MgˉNa+/Ae(NR2)2 (Ae = Ca, Sr, Ba; R = SiMe3). Crystal structures feature examples of Mg–Ca and Mg–Sr bonding with formal oxidation states of Mg0–AeII. Best described as polarized Mgδˉ–Aeδ+ bonds, these complexes show potential as alkane-soluble reductants for bond activation, which readily react with benzene by C–H bond cleavage and are oxidized to discrete complexes with N2O.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Low-oxidation-state group 2 metal chemistry.
Fig. 2: Structures of Na–Mg–Ae complexes.
Fig. 3: AIM analysis.
Fig. 4: Formation and decomposition of 4.
Fig. 5: DFT calculations at the B3PW91-D3BJ/def2tzvp//B3PW91-D3BJ/def2svp level of theory.
Fig. 6: Reactivity of 1–3.

Similar content being viewed by others

Data availability

X-ray data are available free of charge from the Cambridge Crystallographic Data Centre under reference CCDC 2269821 (1), 2269822 (2), 2269823 (4), 2269824 (5), 2269631 (7), 2269632 (8), 2269633 (9), 2269634 (10) and 2269648 (Na(MgN″3)). Copies of the data can be obtained free of charge at https://www.ccdc.cam.ac.uk/structures/. Spectroscopic data that support the findings of this study as well as complementary crystallographic and computational details are included in Supplementary Information. Raw data are also available from corresponding author on reasonable request.

References

  1. Green, S. P., Jones, C. & Stasch, A. Stable magnesium(I) compounds with Mg–Mg bonds. Science 318, 1754–1757 (2007).

    Article  CAS  PubMed  Google Scholar 

  2. Parkin, G. Valence, oxidation number, and formal charge: three related but fundamentally different concepts. J. Chem. Educ. 83, 791–799 (2006).

    Article  CAS  Google Scholar 

  3. Jones, C. Dimeric magnesium(I) β-diketiminates: a new class of quasi-universal reducing agent. Nat. Rev. Chem. 1, 0059 (2017).

    Article  CAS  Google Scholar 

  4. Mai, J., Rösch, B., Patel, N., Langer, J. & Harder, S. On the existence of low-valent magnesium–calcium complexes. Chem. Sci. 14, 4724–4734 (2023).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  5. Platts, J. A., Overgaard, J., Jones, C., Iversen, B. B. & Stasch, A. First experimental characterisation of a non-nuclear attractor in a dimeric magnesium(I) compound. J. Phys. Chem. A 115, 194–200 (2011).

    Article  CAS  PubMed  Google Scholar 

  6. Wu, L.-C., Jones, C., Stasch, A., Platts, J. A. & Overgaard, J. Non-nuclear attractor in a molecular compound under external pressure. Eur. J. Inorg. Chem. 2014, 5536–5540 (2014).

    Article  CAS  Google Scholar 

  7. Krieck, S., Görls, H., Yu, L., Reiher, M. & Westerhausen, M. Stable ‘inverse’ sandwich complex with unprecedented organocalcium(I): crystal structures of [(thf)2 Mg(Br)-C6H2-2,4,6-Ph3] and [(thf)3Ca{μ-C6H3-1,3,5-Ph3}Ca(thf)3]. J. Am. Chem. Soc. 131, 2977–2958 (2009).

    Article  CAS  PubMed  Google Scholar 

  8. Arrowsmith, M. et al. Neutral zero- valent s-block complexes with strong multiple bonding. Nat. Chem. 8, 890–594 (2016).

    Article  CAS  Google Scholar 

  9. Wang, G. et al. A stable, crystalline beryllium radical cation. J. Am. Chem. Soc. 142, 4560–4564 (2020).

    Article  CAS  PubMed  Google Scholar 

  10. Huang, W. & Diaconescu, P. L. Rare-earth metal π-complexes of reduced arenes, alkenes, and alkynes: bonding, electronic structure, and comparison with actinides and other electropositive metals. Dalton Trans. 44, 15360–15371 (2015).

    Article  CAS  PubMed  Google Scholar 

  11. Jędrzkiewicz, D. et al. Access to a labile monomeric magnesium radical by ball-milling. Angew. Chem. Int. Ed. 61, e202200511 (2022).

    Article  Google Scholar 

  12. Breitwieser, K., Bahmann, H., Weiss, R. & Munz, D. Gauging radical stabilization with carbenes. Angew. Chem. Int. Ed. 61, e20220639 (2022).

    Article  Google Scholar 

  13. Gimferrer, M. et al. The oxidation state in low-valent beryllium and magnesium compounds. Chem. Sci. 13, 6583–6591 (2022).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  14. Pan, S. & Frenking, G. Comment on ‘The oxidation state in low-valent beryllium and magnesium compounds’ by M. Gimferrer, S. Danés, E. Vos, C. B. Yildiz, I. Corral, A. Jana, P. Salvador and D. M. Andrada, Chem. Sci. 2022, 13, 6583. Chem. Sci. 14, 379–383 (2023).

    Article  CAS  PubMed  Google Scholar 

  15. Gimferrer, M. et al. Reply to the ‘Comment on ‘The oxidation state in low-valent beryllium and magnesium compounds’ by S. Pan and G. Frenking, Chem. Sci., 2022, 13. Chem. Sci. 14, 384–392 (2023).

    Article  CAS  PubMed  Google Scholar 

  16. Kan, Y. H. Covalent or not? Energy decomposition analysis of metal–metal bonding in alkaline-earth dimetallocene complexes. J. Mol. Struct. THEOCHEM 894, 88–92 (2009).

    Article  CAS  Google Scholar 

  17. Boronski, J. T., Crumpton, A. E., Wales, L. L. & Aldridge, S. Diberyllocene, a stable compound of Be(I) with a Be–Be bond. Science 380, 1147–1149 (2023).

    Article  CAS  PubMed  Google Scholar 

  18. Rösch, B. et al. Dinitrogen complexation and reduction at low-valent calcium. Science 371, 1125–1128 (2021).

    Article  PubMed  Google Scholar 

  19. Rösch, B. et al. Strong reducing magnesium(0) complexes. Nature 592, 717–721 (2021).

    Article  PubMed  Google Scholar 

  20. Klett, J. Structural motifs of alkali metal superbases in non-coordinating solvents. Chem. Eur. J. 27, 888–904 (2021).

    Article  CAS  PubMed  Google Scholar 

  21. Kremer, T., Harder, S., Junge, M. & Schleyer, P. V. R. Mixed aggregates of alkali metal compounds: structure and stability of ‘superbase’ models. Organometallics 15, 585–595 (1996).

    Article  CAS  Google Scholar 

  22. Mullins, J. C. et al. C–H activation of inert arenes using a photochemically activated guanidinato-magnesium(I) compound. Chem. Eur. J. 28, e202202103 (2022).

    Article  CAS  PubMed  Google Scholar 

  23. Causero, A. et al. β-Diketiminate calcium hydride complexes: the importance of solvent effects. Dalton Trans. 46, 1822–1831 (2017).

    Article  CAS  PubMed  Google Scholar 

  24. Bonyhady, S. J. et al. β-Diketiminate-stabilized magnesium(I) dimers and magnesium(II)hydride complexes: synthesis, characterization, adduct formation, and reactivity studies. Chemistry 16, 938–955 (2010).

    Article  CAS  PubMed  Google Scholar 

  25. Liu, H.-Y. et al. Reductive dimerization of CO by a Na/Mg(I) diamide. J. Am. Soc. 143, 17851–17856 (2021).

    Article  CAS  Google Scholar 

  26. Friedrich, A., Eyselein, J., Langer, J., Färber, C. & Harder, S. Cationic heterobimetallic Mg(Zn)/Al(Ga) combinations for cooperative C–F bond cleavage. Angew. Chem. Int. Ed. 60, 16492–16499 (2021).

    Article  CAS  Google Scholar 

  27. Knizek, J., Krossing, I., Nöth, H., Schwenk, H. & Seifert, T. Synthesis and structures of sodium phenylhydrazides. Chem. Ber. 130, 1053–1062 (1997).

    Article  CAS  Google Scholar 

  28. Camp, C. & Arnold, J. On the non-innocence of ‘Nacnacs’: ligand-based reactivity in β-diketiminate supported coordination compounds. Dalton Trans. 45, 14462–14498 (2016).

    Article  CAS  PubMed  Google Scholar 

  29. Postils, V., Delgado-Alonso, C., Luis, J. M. & Salvador, P. An objective alternative to IUPAC’s approach to assign oxidation states. Angew. Chem. Int. Ed. 57, 10525–10529 (2018).

    Article  CAS  Google Scholar 

  30. Mackenzie, F. M. & Mulvey, R. E. The first trimetallic lithium–sodium–potassium complex: synthesis and crystal structure of a twelve-vertex Li2Na2K2N4O2 cage molecule containing an amide-alkoxide combination. J. Am. Chem. Soc. 118, 4721–4722 (1996).

    Article  CAS  Google Scholar 

  31. Wei, X. et al. Heterotrimetallic salts: synthesis, structures, and superbase reactivity of crystalline tert-butoxides [Li4Na2K2(OtBu)8(μ-L)]n. Angew. Chem. Int. Ed. 47, 3976–3978 (2008).

    Article  CAS  Google Scholar 

  32. Gentner, T. X., Kennedy, A. R., Hevia, E. & Mulvey, R. E. Alkali metal (Li, Na, K, Rb, Cs) mediation in magnesium hexamethyldisilazide [Mg(HMDS)2] catalysed transfer hydrogenation of alkenes. Chem. Cat. Chem. 13, 2371–2378 (2021).

    CAS  Google Scholar 

  33. Zhang, X.-Y., Du, H.-Z., Zhai, D.-D. & Guan, B.-T. Combined KH/alkaline-earth metal amide catalysts for hydrogenation of alkenes. Org. Chem. Front. 7, 1991–1996 (2020).

    Article  CAS  Google Scholar 

  34. Mulvey, R. E. Modern ate chemistry: applications of synergic mixed alkali-metal–magnesium or –zinc reagents in synthesis and structure building. Organometallics 25, 1060–1075 (2006).

    Article  CAS  Google Scholar 

  35. Sarazin, Y., Howard, R. H., Hughes, D. L., Humphrey, S. M. & Bochmann, M. Titanium, zinc and alkaline-earth metal complexes supported by bulky O,N,N,O-multidentate ligands: syntheses, characterisation and activity in cyclic esterpolymerisation. Dalton Trans. 14, 340–350 (2006).

    Article  Google Scholar 

  36. Westerhausen, M. Synthesis and spectroscopic properties of bis(trimethyIsily)amides of the alkaline-earth metals magnesium, calcium, strontium, and barium. Inorg. Chem. 30, 96–101 (1991).

    Article  CAS  Google Scholar 

  37. Rigaku Oxford Diffraction, CrysAlisPro Software system, version 1.171.40.84a, Rigaku Corporation, Oxford, UK (compound (BDI)MgNa/CaN″2(1)) (Rigaku, 2020).

  38. Rigaku Oxford Diffraction, CrysAlisPro Software system, version 1.171.41.113a, Rigaku Corporation, Oxford, UK (compound (BDI)MgNa/SrN″2(2); (BDI)MgNa/MgN″2(4); (BDI)MgMgN″(5)) (Rigaku, 2021).

  39. Rigaku Oxford Diffraction CrysAlisPro Software system, version 1.171.42.72a, Rigaku Corporation, Oxford, UK (other compounds) (Rigaku, 2022).

  40. Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Cryst. 42, 339–341 (2009).

    Article  CAS  Google Scholar 

  41. Sheldrick, G. M. SHELXT—integrated space-group and crystal-structure determination. Acta Cryst. A 71, 3–8 (2015).

    Article  Google Scholar 

  42. Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Cryst. C 71, 3–8 (2015).

    Article  Google Scholar 

  43. Frisch, M. J. et al. Gaussian 16 Rev. A.03 (Gaussian, 2016).

  44. Becke, A. D. Density - functional thermochemistry. III. The role of exact change. J. Chem. Phys. 98, 5648–5652 (1993).

    Article  CAS  Google Scholar 

  45. Perdew, J. P. et al. Erratum: atoms, molecules, solids, and surfaces: applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B 48, 4978–4978 (1993).

    Article  CAS  Google Scholar 

  46. Weigend, F. Accurate coulomb-fitting basis sets for H to Rn. Phys. Chem. Chem. Phys. 8, 1057–1065 (2006).

    Article  CAS  PubMed  Google Scholar 

  47. Weigend, F. & Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: design and assessment of accuracy. Phys. Chem. Chem. Phys. 7, 3297–3305 (2005).

    Article  CAS  PubMed  Google Scholar 

  48. Grimme, S., Ehrlich, S. & Goerigk, L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 32, 1456–1465 (2011).

    Article  CAS  PubMed  Google Scholar 

  49. Glendening, E. D. et al. NBO 7.0 (University of Wisconsin, 2018).

  50. Bader, R. F. W. A quantum theory of molecular structure and its applications. Chem. Rev. 91, 893–928 (1991).

    Article  CAS  Google Scholar 

  51. Keith, T. A. AIMAll (Version 17.01.25) (TK Gristmill Software, 2017).

Download references

Acknowledgements

We thank the Deutsche Forschungsgemeinschaft (DFG) for funding (HA 3218/11-1).

Author information

Author notes

  1. These authors contributed equally: Jonathan Mai, Johannes Maurer.

Authors and Affiliations

  1. Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany

    Jonathan Mai, Johannes Maurer, Jens Langer & Sjoerd Harder

Authors
  1. Jonathan Mai
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Johannes Maurer
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Jens Langer
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Sjoerd Harder
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

J. Mai: conceptualization, investigation, validation, formal analysis, writing—original draft, and visualization. J. Maurer: conceptualization, investigation, validation, formal analysis, writing—original draft, and visualization. J.L.: investigation, formal analysis and validation. S.H.: conceptualization, writing—original draft, review and editing, visualization, validation, supervision and project administration.

Corresponding author

Correspondence to Sjoerd Harder.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Synthesis thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editor: Peter Seavill, in collaboration with the Nature Synthesis team.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Experimental details and Supplementary Figs. 1–74 and Tables 1–9.

Supplementary Data 1

Crystallographic data for compound 1, CCDC 2269821.

Supplementary Data 2

Crystallographic data for compound 2, CCDC 2269822.

Supplementary Data 3

Crystallographic data for compound 4, CCDC 2269823.

Supplementary Data 4

Crystallographic data for compound 5, CCDC 2269824.

Supplementary Data 5

Crystallographic data for compound 6.

Supplementary Data 6

Crystallographic data for compound 7, CCDC 2269631.

Supplementary Data 7

Crystallographic data for compound 8, CCDC 2269632.

Supplementary Data 8

Crystallographic data for compound 9, CCDC 2269633.

Supplementary Data 9

Crystallographic data for compound 10, CCDC 2269634.

Supplementary Data 10

Crystallographic data for compound Na(MgN″3), CCDC 2269648.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Mai, J., Maurer, J., Langer, J. et al. Heterobimetallic alkaline earth metal–metal bonding. Nat. Synth 3, 368–377 (2024). https://doi.org/10.1038/s44160-023-00451-y

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s44160-023-00451-y

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing