Letter | Published:

Synthesis, structure and reaction chemistry of a nucleophilic aluminyl anion

Naturevolume 557pages9295 (2018) | Download Citation

Abstract

The reactivity of aluminium compounds is dominated by their electron deficiency and consequent electrophilicity; these compounds are archetypal Lewis acids (electron-pair acceptors). The main industrial roles of aluminium, and classical methods of synthesizing aluminium–element bonds (for example, hydroalumination and metathesis), draw on the electron deficiency of species of the type AlR3 and AlCl31,2. Whereas aluminates, [AlR4], are well known, the idea of reversing polarity and using an aluminium reagent as the nucleophilic partner in bond-forming substitution reactions is unprecedented, owing to the fact that low-valent aluminium anions analogous to nitrogen-, carbon- and boron-centred reagents of the types [NX2], [CX3] and [BX2] are unknown3,4,5. Aluminium compounds in the +1 oxidation state are known, but are thermodynamically unstable with respect to disproportionation. Compounds of this type are typically oligomeric6,7,8, although monomeric systems that possess a metal-centred lone pair, such as Al(Nacnac)Dipp (where (Nacnac)Dipp = (NDippCR)2CH and R = tBu, Me; Dipp = 2,6-iPr2C6H3), have also been reported9,10. Coordination of these species, and also of (η5-C5Me5)Al, to a range of Lewis acids has been observed11,12,13, but their primary mode of reactivity involves facile oxidative addition to generate Al(iii) species6,7,8,14,15,16. Here we report the synthesis, structure and reaction chemistry of an anionic aluminium(i) nucleophile, the dimethylxanthene-stabilized potassium aluminyl [K{Al(NON)}]2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene). This species displays unprecedented reactivity in the formation of aluminium–element covalent bonds and in the C–H oxidative addition of benzene, suggesting that it could find further use in both metal–carbon and metal–metal bond-forming reactions.

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Change history

  • 04 June 2018

    In Fig. 1 of this Letter, the hydrogen (H) atoms attached to each of the two nitrogen (N) atoms in the chemical structure of (NON)H2 were inadvertently missing. The original figure has been corrected online.

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Acknowledgements

This work was supported by the SCG-Oxford Centre of Excellence. P.V. thanks the Magnus Ehrnrooth and Emil Aaltonen Foundations for postdoctoral funding. We thank the University of Oxford Advanced Research Computing facility, and N. Rees and H. Tuononen for assistance with NMR and quantum chemical studies, respectively.

Author contributions J.H. carried out the synthetic and reaction studies, P.V. carried out the computational analyses, J.H. and J.M.G. conducted the crystallographic studies, and J.M.G. and S.A. wrote the manuscript and managed the project.

Competing interests: The authors declare no competing interests.

Author information

Affiliations

  1. Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, UK

    • Jamie Hicks
    • , Petra Vasko
    • , Jose M. Goicoechea
    •  & Simon Aldridge
  2. Department of Chemistry, NanoScience Center, University of Jyväskylä, Jyväskylä, Finland

    • Petra Vasko

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Extended data figures and tables

  1. Extended Data Fig. 1 Molecular structure of (NON)AlI as determined by X-ray crystallography.

    Hydrogen atoms have been omitted and selected carbon atoms shown in wireframe format for clarity; thermal ellipsoids have been drawn at the 35% probability level. Key bond lengths (Å) and angles (°): Al(1)–I(1) 2.497(1), Al(1)–N(1) 1.846(2), Al(1)–N(2) 1.846(2), Al(1)–O(1) 1.967(2), N(1)–Al(1)–N(2) 143.0(1).

  2. Extended Data Fig. 2 Molecular structure of [Al(NON)]2 as determined by X-ray crystallography.

    Hydrogen atoms have been omitted and selected carbon atoms shown in wireframe format for clarity; thermal ellipsoids have been drawn at the 35% probability level. Key bond lengths (Å) and angles (°): Al(1)–Al(2) 2.646(1), Al(1)–N(1) 1.902(2), Al(1)–N(2) 1.895(2), Al(2)–N(3) 1.901(2), Al(2)–N(4) 1.900(2), Al(1)–O(1) 1.976(2), Al(2)–O(2) 1.981(2), N(1)–Al(1)–N(2) 119.0(1), N(3)–Al(2)–N(4) 118.6(1).

  3. Extended Data Fig. 3 Molecular structure of one of the molecules in the asymmetric unit of [K{H2Al(NON)}]2 as determined by X-ray crystallography.

    Second (essentially identical) component, benzene solvate molecules and carbon-bound hydrogen atoms have been omitted and selected carbon atoms shown in wireframe format for clarity; thermal ellipsoids have been drawn at the 35% probability level. Key distances (Å) and angles (°): Al(1)–N(1/2) 1.933(2)/1.921(2), Al(2)–N(3/4) 1.934(2)/1.917(2), Al(1)–O(1) 2.131(1), Al(2)–O(2) 2.124(2), Al(1)…Al(2) 6.356(1), Al(1)…K(1/2) 3.648(1)/4.065(1), Al(2)…K(1/2) 3.580(1)/4.039(1), Al(1)–H(1 A/1B) 1.69(4)/1.55(4), Al(2)–H(2 A/2B) 1.71(4)/1.58(4), N(1)–Al(1)–N(2) 130.3(1), N(3)–Al(2)–N(4) 131.1(1).

  4. Extended Data Fig. 4 Infrared spectra of [K{Al(NON)}]2 and [K{H2Al(NON)}]2.

    a, [K{Al(NON)}]2. b, [K{H2Al(NON)}]2. Both spectra have been measured on samples as Nujol mulls; the blue asterisk highlights the Al–H stretching band of [K{H2Al(NON)}]2.

  5. Extended Data Fig. 5 Molecular structure of [K{Ga(NON)}]2 as determined by X-ray crystallography.

    Hydrogen atoms have been omitted and selected carbon atoms shown in wireframe format for clarity; thermal ellipsoids have been drawn at the 35% probability level. Key bond lengths and distances (Å) and angles (°): Ga(1)…Ga(1′) 6.134(1), Ga(1)…K(1) 3.970(1), Ga(1)…K(1′) 3.784(1), Ga(1)–N(1) 2.093(2), Ga(1)–N(2) 2.106(2), Ga(1)–O(1) 2.542(2), N(1)–Ga(1)–N(2) 126.0(1).

  6. Extended Data Fig. 6 Molecular structure of (NON)AlH·toluene as determined by X-ray crystallography.

    Most hydrogen atoms have been omitted and selected carbon atoms shown in wireframe format for clarity; thermal ellipsoids have been drawn at the 35% probability level. Key bond lengths (Å) and angles (°): Al(1)–N(1) 1.873(1), Al(1)–N(2) 1.872(1), Al(1)–O(1) 1.944(1), Al(1)–H(1) 1.49(2), N(1)–Al(1)–N(2) 134.1(1).

  7. Extended Data Fig. 7 Molecular structure of [K{Ph(H)Al(NON)}]2 as determined by X-ray crystallography.

    Most hydrogen atoms and benzene solvate molecules have been omitted, and selected carbon atoms shown in wireframe format for clarity; thermal ellipsoids have been drawn at the 35% probability level. Key bond lengths (Å) and angles (°): Al(1)–N(1) 1.945(2), Al(1)–N(2) 1.944(2), Al(1)–O(1) 2.122(1), Al(1)–C(48) 2.007(1), Al(1)–H(1) 1.82(3), N(1)–Al(1)–N(2) 132.2(1).

  8. Extended Data Table 1 Selected X-ray data collection and refinement parameters for complexes prepared in this study

Supplementary information

  1. Supplementary Tables

    This file contains Supplementary Tables 1-4

  2. Supplementary Data

    This file contains Supplementary Data files 1-10 and a guide.

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https://doi.org/10.1038/s41586-018-0037-y

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