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An alkyl-substituted aluminium anion with strong basicity and nucleophilicity

Abstract

Aluminium anions with an unoccupied orbital are generally considered as highly difficult synthetic targets, as aluminium is the most electropositive element in the p block. Stabilizing effects from two nitrogen substituents and/or the coordination of a Lewis base were recently used to synthesize the first examples of anionic nucleophilic aluminium species. Here we show the synthesis and properties of a potassium salt of a non-stabilized dialkylaluminium anion that exhibits very strong basicity, which reflects the electropositive character of aluminium. An X-ray diffraction analysis revealed a monomeric structure and the shortest Al–K distance hitherto reported. The ultraviolet visible spectrum in combination with density functional theory calculations suggests an electronic structure characterized by a lone pair of electrons and an unoccupied p orbital on the aluminium centre. This species readily deprotonates benzene to form the corresponding (hydrido)(phenyl)aluminate. Reactions with other electrophiles corroborate the nucleophilicity of the aluminium centre.

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Fig. 1: Group-13-element anions and related compounds.
Fig. 2: Synthesis and characterization of alumanylpotassium 5.
Fig. 3: Characteristic molecular orbitals of alumanylpotassium 5.
Fig. 4: Reactivity of alumanylpotassium 5.

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Data availability

Crystallographic data for the structures in this paper have been deposited at the Cambridge Crystallographic Data Centre under reference numbers 1869762 (2), 1869763 (3), 1869764 (4·hexane), 1869765 (5), 1869766 (6), 1869767 (7·DMAP), 1869768 (8), 1869769 (9·pyridine) and 1869770 (12). Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/structures/. All other data supporting the findings of this study are available within the article and its Supplementary Information, or from the corresponding author upon reasonable request.

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Acknowledgements

We are grateful to T. Iwamoto and S. Ishida for helpful discussions regarding the preparation of 2 from 1. This research was supported by a Grant-in-Aid for Scientific Research (A) (JSPS KAKENHI grant 17H01191) and by JST CREST (14529307). Theoretical calculations were carried out using resources at the Research Center for Computational Science (Okazaki).

Author information

Authors and Affiliations

Authors

Contributions

S.K. and S.T. carried out all the experimental work. S.K. and M.Y. carried out the spectroscopic, crystallographic and computational analyses and wrote the manuscript. M.Y. managed the project.

Corresponding author

Correspondence to Makoto Yamashita.

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Competing interests

The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary methods, Figs. 1–42, Tables 1–4 and references 1–27.

Crystallographic data

CIF for 2; CCDC reference: 1869762.

Crystallographic data

CIF for 3; CCDC reference: 1869763.

Crystallographic data

CIF for 4·hexane; CCDC reference: 1869764.

Crystallographic data

CIF for 5; CCDC reference: 1869765.

Crystallographic data

CIF for 6; CCDC reference: 1869766.

Crystallographic data

CIF for 7·DMAP; CCDC reference: 1869767.

Crystallographic data

CIF for 8; CCDC reference: 1869768.

Crystallographic data

CIF for 9·pyridine; CCDC reference: 1869769.

Crystallographic data

CIF for 12; CCDC reference: 1869770.

Optimized structures

Cartesian coordinate for the optimized structures.

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Kurumada, S., Takamori, S. & Yamashita, M. An alkyl-substituted aluminium anion with strong basicity and nucleophilicity. Nat. Chem. 12, 36–39 (2020). https://doi.org/10.1038/s41557-019-0365-z

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