Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer


The desorption of dihydrogen from magnesium(II) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L = β-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(µ-H)2MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(µ-H)2MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)2Al}2] (IPr = :C[{(C6H3-i-Pr2-2,6)NCH}2]), is an N-heterocyclic carbene adduct of the elusive parent dialane(4) (Al2H4). A computational analysis of this compound is presented.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Reaction scheme showing the transfer of hydrogen between aluminium(III) and magnesium(I) complexes.
Figure 2: Molecular structure of 3.
Figure 3: Molecular structures of 4 and 13.

Change history

  • 13 October 2010

    In the HTML version of this Article originally published, the e-mail addresses for the corresponding authors were assigned incorrectly. This has now been corrected.


  1. 1

    Grochala, W. & Edwards, P. P. Thermal decomposition of the non-interstitial hydrides for the storage and production of hydrogen. Chem. Rev. 104, 1283–1316 (2004).

  2. 2

    Schüth, B., Bogdanović, B. & Felderhoff, M. Light metal hydrides and complex hydrides for hydrogen storage. Chem. Commun. 2249–2258 (2004).

  3. 3

    Aldridge, S. & Downs, A. J. Hydrides of the main-group metals: new variations on an old theme. Chem. Rev. 101, 3305–3365 (2001).

  4. 4

    Graetz, J. New approaches to hydrogen storage. Chem. Soc. Rev. 38, 73–82 (2009).

  5. 5

    Bogdanović, B., Ritter, A. & Spliethoff, B. Active MgH2–Mg systems for reversible chemical energy storage. Angew. Chem. Int. Ed. Engl. 29, 223–234 (1990).

  6. 6

    Hanada, N., Ichikawa, T. & Fuji, H. Catalytic effect of nanoparticle 3d-transition metals on hydrogen storage properties in magnesium hydride MgH2 prepared by mechanical milling. J. Phys. Chem. B 109, 7188–7194 (2005).

  7. 7

    Liang, G., Huot, J., Boily, S., Van Neste, A. & Schulz, R. Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled MgH2Tm (Tm=Ti, V, Mn, Fe and Ni) systems. J. Alloys Comp. 292, 247–252 (1999).

  8. 8

    Andreasen, A. Hydrogenation properties of Mg–Al alloys. Int. J. Hydrogen Energy 33, 7489–7497 (2008).

  9. 9

    Larsson, P., Araújo, C. M., Larsson, J. A., Jena, P. & Ahuja, R. Role of catalysts in dehydrogenation of MgH2 clusters. Proc. Natl. Acad. Sci. USA 105, 8227–8231 (2008).

  10. 10

    Green, S. P., Jones, C. & Stasch, A. Stable magnesium(I) compounds with Mg–Mg bonds. Science 318, 1754–1756 (2007).

  11. 11

    Green, S. P., Jones, C. & Stasch, A. Stable adducts of a dimeric magnesium(I) compound. Angew. Chem. Int. Ed. 48, 9079–9083 (2008).

  12. 12

    Bonyhady, S. J., Green, S. P., Jones, C., Nembenna, S. & Stasch, A. A dimeric magnesium(I) compound as a facile two-center/two-electron reductant. Angew. Chem. Int. Ed. 48, 2973–2977 (2009).

  13. 13

    Bonyhady, S. J., Jones, C., Nembenna, S., Stasch, A., Edwards, A. J. & McIntyre, G. J. β-Diketiminate stabilized magnesium(I) dimers and magnesium(II) hydride complexes: synthesis, adduct formation and reactivity studies. Chem. Eur. J. 16, 938–955 (2010).

  14. 14

    Sidiropoulos, A., Jones, C., Stasch, A., Klein, S. & Frenking, G. N-heterocyclic carbene stabilized digermanium(0). Angew. Chem. Int. Ed. 48, 9701–9704 (2009).

  15. 15

    Jones, C., McDyre, L., Murphy, D. M. & Stasch, A. Magnesium(I) reduction of benzophenone and anthracene: first structural characterisation of a magnesium ketyl. Chem. Commun. 46, 1511–1513 (2010).

  16. 16

    Datta, A. How stable are the Mg–Mg bonds in magnesium(I) compounds towards hydrogenation? J. Phys. Chem. C 112, 18727–18729 (2008).

  17. 17

    Iosub, V., Matsunaga, T., Tange, K. & Ishikiriyama, M. Direct synthesis of Mg(AlH4)2 and CaAlH5 crystalline compounds by ball milling and their potential as hydrogen storage materials. Int. J. Hydrogen Energy 34, 906–912 (2009).

  18. 18

    Baker, R. J., Davies, A. J., Jones, C. & Kloth, M. Structural and spectroscopic studies of carbene and N-donor ligand complexes of group 13 hydrides and halides. J. Organomet. Chem. 656, 203–210 (2002).

  19. 19

    Wang, Y. et al. A stable neutral diborene containing a B=B double bond. J. Am. Chem. Soc. 129, 12412–12413 (2007).

  20. 20

    Cole, M. L., Jones, C., Junk, P. C., Kloth, M. & Stasch, A. Synthesis and characterization of thermally robust amidinato group 13 hydride complexes. Chem. Eur. J. 11, 4482–4491 (2005).

  21. 21

    Ciobanu, O., Kaifer, E., Enders, M. & Himmel, H.-J. Synthesis of a stable B2H5+ analogue by protonation of a double base-stabilized diborane(4). Angew. Chem. Int. Ed. 48, 5538–5541 (2009).

  22. 22

    Uhl, W. & Vester, A. Tetraalkylhydrido- und tetraalkylmethyldialuminat(5) mit aluminium–aluminium-binding: [R2Al-AlXR2] {R=CH(SiMe3)2; X=H, Me}. Chem. Ber. 126, 941–945 (1993).

  23. 23

    Version 5.34 of the Cambridge Structural Database, Cambridge Crystallographic Data Centre; search conducted December 2009.

  24. 24

    Uhl, W. Organometallic compounds possessing Al–Al, Ga–Ga, In–In and Tl–Tl single bonds. Adv. Organomet. Chem. 51, 53–108 (2004).

  25. 25

    Weng, X., Andrews, L., Tam, S., DeRose, M. E. & Fajardo, M. E. Infrared spectra of aluminum hydrides in solid hydrogen: Al2H4 and Al2H6 . J. Am. Chem. Soc. 125, 9218–9228 (2003).

  26. 26

    Andrews, L. & Wang, X. The infrared spectrum of Al2H6 in solid argon. Science 299, 2049–2052 (2003).

  27. 27

    Lammertsma, K., Güner, O. F., Drewes, R. M., Reed, A. E. & Schleyer, P. v. R. Remarkable structures of dialane(4), Al2H4 . Inorg. Chem. 28, 313–317 (1989).

  28. 28

    Chesnut, D. B. A topological study of bonding in the Al2H2 and Al2H4 hydrides. Chem. Phys. 321, 269–276 (2006).

  29. 29

    Nogai, S. & Schmidbaur, H. Dichlorogallane (HGaCl2)2: its molecular structure and synthetic potential. Inorg. Chem. 41, 4770–4774 (2002).

  30. 30

    Wang, Y. et al. A stable silicon(0) compound with a Si=Si double bond. Science 321, 1069–1071 (2008).

  31. 31

    Szabó, A., Kovács, A. & Frenking, G. Energy decomposition analysis of E–E bonding in planar and perpendicular X2E–EX2 (E=B, Al, Ga, In, Tl; X=H, F, Cl, Br, I). Z. Anorg. Allg. Chem. 631, 1803–1809 (2005).

  32. 32

    Beste, A., Krämer, O., Fischer, A. & Frenking, G. The Lewis basicity of diaminocarbene—a theoretical study of donor–acceptor complexes of C(NH2)2, NH3 and CO with the Lewis acids EF3, ECl3 (E=B, Al, Ga, In), TiF4 and TiCl4 . Eur. J. Inorg. Chem. 2037–2045 (1999).

  33. 33

    Tonner, R. & Frenking, G. Divalent carbon(0) chemistry. Part 2: protonation and complexes with main group and transition metal derived Lewis acids. Chem. Eur. J. 14, 3273–3289 (2008).

Download references


The research was supported by the Australian Research Council (fellowships for C.J. and A.S.) and the Deutsche Forschungsgemeinschaft (grant no. FR641/25-1 to G.F.). The EPSRC is also thanked for access to the UK National Mass Spectrometry Facility.

Author information




Author listing order in the title is alphabetical. C.J. and A.S. conceived and designed the experiments. S.J.B., D.C. and A.S. performed the experiments. G.F. and N.H. carried out the computational studies. S.J.B., D.C., G.F., N.H., C.J. and A.S. analysed the data. C.J., A.S. and G.F. co-wrote the paper.

Corresponding authors

Correspondence to Gernot Frenking or Cameron Jones or Andreas Stasch.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 1015 kb)

Supplementary information

Crystallographic data for compound 3 (CIF 15 kb)

Supplementary information

Crystallographic data for compound 4 (CIF 18 kb)

Supplementary information

Crystallographic data for compound 5 (CIF 21 kb)

Supplementary information

Crystallographic data for compound 9 (CIF 21 kb)

Supplementary information

Crystallographic data for compound 10·(cyclohexane) (CIF 22 kb)

Supplementary information

Crystallographic data for compound 11·(benzene)1.5 (CIF 64 kb)

Supplementary information

Crystallographic data for compound 12·(benzene)2 (CIF 25 kb)

Supplementary information

Crystallographic data for compound 13 (CIF 20 kb)

Supplementary information

Crystallographic data for compound 16 (CIF 27 kb)

Supplementary information

Crystallographic data for compound 17 (CIF 16 kb)

Supplementary information

Crystallographic data for compound 17·(benzene) (CIF 19 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Bonyhady, S., Collis, D., Frenking, G. et al. Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer. Nature Chem 2, 865–869 (2010).

Download citation

Further reading