Oral Presentation Royal Australian Chemical Institute National Congress 2026

One Complex, Two Pathways: Chemoselective Access to Al(I) and Al(II) (136912)

Fabian J Kallmeier 1 , Jamie Hicks 1
  1. The Australian National University, Acton, ACT, Australia

 

Low‑valent main‑group chemistry has recently received renewed attention in organometallic research due to the relatively non‑toxic, abundant, and inexpensive nature of these elements, as well as the distinctive reactivity they offer. In their typical +3 oxidation state, group 13 compounds, especially aluminium derivatives, are well‑established Lewis acids with broad industrial and academic utility. In contrast, low‑valent Group 13 complexes display markedly different behaviour.1 Aluminium in the oxidation states +2 and +1 has been implied and observed in the activation of small molecules, using various tailor-made ligands.2,3

In this work, we show that an aluminium iodide complex based on the TIPSNON2- ligand can be chemo-selectively reduced to either an anionic aluminium(I) species4 using potassium reductants, or to a transient, highly reactive aluminium(II) radical.5 Both compounds feature a rich follow-on chemistry that involves the activation of aromatic compounds (Figure 1). Aluminyl anions were shown to be extremely potent in CH-activation of unactivated arenes,6 while the aluminium(II) species undergoes a twofold addition to benzene to yield [(TIPSNON)2Al2CHD] complex (CHD: cyclohexa-2,5-diene-1,4-diyl).

 

Figure 1: Selected literature examples for Al(I) (top left) and Al(II) radical (middle), TIPSNON Ligand used in this work (yellow box) and the work presented herein (bottom)

 

(1)       Yamamoto, H.; Oshima, K. Main Group Metals in Organic Synthesis; Wiley-VCH: Weinheim, 2004.

(2)       Hobson, K.; Carmalt, C. J.; Bakewell, C. Recent Advances in Low Oxidation State Aluminium Chemistry. Chem. Sci. 2020, 11 (27), 6942–6956. https://doi.org/10.1039/D0SC02686G.

(3)       Coles, M. P.; Evans, M. J. The Emerging Chemistry of the Aluminyl Anion. Chem. Commun. 2023, 59 (5), 503–519. https://doi.org/10.1039/D2CC05963K.

(4)       Hicks, J.; Vasko, P.; Goicoechea, J. M.; Aldridge, S. Synthesis, Structure and Reaction Chemistry of a Nucleophilic Aluminyl Anion. Nature 2018, 557 (7703), 92–95. https://doi.org/10.1038/s41586-018-0037-y.

(5)       Mandal, D.; Demirer, T. I.; Sergeieva, T.; Morgenstern, B.; Wiedemann, H. T. A.; Kay, C. W. M.; Andrada, D. M. Evidence of Al II Radical Addition to Benzene. Angew Chem Int Ed 2023, 62 (13), e202217184. https://doi.org/10.1002/anie.202217184.

(6)       Kallmeier, F.; Nelmes, G. R.; McMullin, C. L.; Edwards, A. J.; Hicks, J. Enhancing the Nucleophilicity of Aluminyl Anions: Targeting Selective C–H Activation. Chem. Sci. 2025, 16 (16), 10750–10758. https://doi.org/10.1039/D5SC02682B.