Highly Reactive Low-valent Aluminium Complexes and their Application in Synthesis and Catalysis

Project Information

ALLOWE

Grant agreement ID: 101001591

DOI

10.3030/101001591

Project closed

EC signature date 18 December 2020

Start date 1 June 2021

End date 31 May 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 997 750,00

EU contribution

€ 1 997 750,00

Coordinated by

TECHNISCHE UNIVERSITAET MUENCHEN
Germany

Periodic Reporting for period 3 - ALLOWE (Highly Reactive Low-valent Aluminium Complexes and their Application in Synthesis and Catalysis)

Reporting period: 2024-06-01 to 2025-11-30

Summary of the context and overall objectives of the project

Aluminium is the most abundant metal in the earth’s crust and already has a wide range of uses, particularly in the materials industry, owing to its low density, ductility and resistance to corrosion. It also has a very low environmental impact and toxicity. Aluminium is in group 13 and period 3 of the periodic table. Possessing only 3 valence electrons, it is classically considered to be “electron-deficient”. In the context of its molecular-level chemistry, aluminium shows a high degree of Lewis acidity, and Lewis adduct formation with a suitable donor is often used to stabilize Al(III) species and facilitate their easy use in the synthetic laboratory. Al(III) is the most stable oxidation state, with most aluminium-mediated organic reactions of aluminium (for example Zieglar-Natta catalysis or Friedel-Crafts reactions) employing Al(III) compounds. Low-oxidation state aluminium compounds have presented a particular challenge for synthetic chemists, with a noticeable dearth of such compounds in the literature compared to those based on neighbouring elements.
The overall aim of this project is the design and exploration of neutral low-valent aluminium compounds stabilized by N-heterocyclic carbenes. With novel alumylenes and dialumenes in hand, investigation into their structural and electronic nature will be undertaken through a combined experimental and computational approach. Finally, investigation into their reactivity towards small molecule activation and catalysis as well as their coordination chemistry will also be explored.

Establishment of low-valent aluminium compounds (alumylenes and dialumenes) and their applications in bond activations, catalysis and coordination chemistry is the desired outcome of this proposal. The success of this research plan would be a significant milestone in the field of organometallic and main group chemistry. In a practical sense, chemical transformations with the most abundant metal, namely, aluminium as catalyst would potentially reduce the cost of chemical production, generate little waste and even allow access to novel small organic molecules and materials. Investigations into the highly reactive ambiphilic aluminium complexes will afford a wealth of brand-new stoichiometric and catalytic reactions. The utilization of low-valent aluminium complexes enables the direct preparation of divergent novel organoaluminium compounds through the small molecule activations or coordination to transition metals. Therefore, development of the chemistry of low-valent aluminium compounds can be the key concept for making of the next generation of sustainable aluminium-based applications.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first period (18 months), we were able to synthesize several N-heterocyclic carbene (NHC) stabilized aluminium dihalides with various substituents (m-terphenyl, 2,4,6-triisopropylphenyl, 2,4,6-trimethylphenyl, tBu3Si, tBu2MeSi, (Me3Si)3Si, (Me3Si)2N, etc.). Corresponding aluminium dihydrides have also been prepared and fully characterised including X-ray diffraction analysis.
As described in the Annex I, Part B, we have conducted the reactivity studies of these complexes and found that isolation of diverse molecular aluminium sulfides demonstrate is achievable by the reaction of corresponding aluminium dihydrides with various sulfer reagents.
In addition, reactions towards elemental chalcogens (sulfur, selenium and tellurium) afforded the expected compounds, so-called, aluminium chacogenides. In fact, compound with the terminal aluminium telluride double bond has successfully isolated. Interestingly this aluminium telluride complex does react with carbon monoxide and afforded intriguing complex with carbon tellurium double bond.
Meanwhile, we have also developed the reactivity of dialumenes towards various small molecules. Intriguing activation products from the reaction of NHC-coordinate dialumenes with white phosphorus or pyridine have been isolated.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have developed the neutral dialane(4) with aluminium-aluminium single bond and their reduction aiming at the generation of dianionic dialumenes.
Introduction of four bulky silly groups (tBu2MeSi) into the aluminium centre allowed us to isolate dialane(4) (tBu2MeSi)2Al-Al(SiMetBu2)2.
Reactivity of this tetrasilyldialane(4) is currently undergoing. In fact, two-electron reduction of this dialane(4) produced dianionic species which is presumably desired dianionic dialumenes with double bond.

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