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Bond activation and catalysis with low-valent aluminium

Periodic Reporting for period 2 - AlCat (Bond activation and catalysis with low-valent aluminium)

Reporting period: 2018-09-01 to 2020-02-29

This project will develop the principles required to enable bond-modifying redox catalysis based on aluminium by preparing and studying new Al(I) compounds capable of reversible oxidative addition.

Catalytic processes are involved in the synthesis of 75 % of all industrially produced chemicals, but most catalysts involved are based on precious metals such as rhodium, palladium or platinum. These metals are expensive and their supply limited and unstable; there is a significant need to develop the chemistry of non-precious metals as alternatives. On toxicity and abundance alone, aluminium is an attractive candidate. Furthermore, recent work, including in our group, has demonstrated that Al(I) compounds can perform a key step in catalytic cycles - the oxidative addition of E-H bonds.

In order to realise the significant potential of Al(I) for transition-metal style catalysis we urgently need to:
- establish the principles governing oxidative addition and reductive elimination reactivity in aluminium systems.
- know how the reactivity of Al(I) compounds can be controlled by varying properties of ligand frameworks.
- understand the onward reactivity of oxidative addition products of Al(I) to enable applications in catalysis.
In this project we will:

- Study mechanisms of oxidative addition and reductive elimination of a range of synthetically relevant bonds at Al(I) centres, establishing the principles governing this fundamental reactivity.
- Develop new ligand frameworks to support of Al(I) centres and evaluate the effect of the ligand on oxidative addition/reductive elimination at Al centres.
- Investigate methods for Al-mediated functionalisation of organic compounds by exploring the reactivity of E-H oxidative addition products with unsaturated organic compounds.
Our three major objectives for the project are to:

- establish the principles governing oxidative addition and reductive elimination reactivity in aluminium systems.
- know how the reactivity of Al(I) compounds can be controlled by varying properties of ligand frameworks.
- understand the onward reactivity of oxidative addition products of Al(I) to enable applications in catalysis.

Work during the first half of the project has focused on the first two objectives.

We have prepared new ligand frameworks and used them to support reactive aluminium centres. We are systematically varying properties of the ligands and correlating changes in the ligand with changes in reactivity at the aluminium centre.

The main achievements of the project so far are:

- The synthesis of a range of new Al(III) compounds supported by tuneable ligand frameworks
- A study of the reactivity of these compounds that shows that they are active catalysts for the preparation of valuable intermediates in medicinal/synthetic chemistry
- A study of the reduction of these compounds to low-oxidation state aluminium compounds that are relevant for the development of new catalytic processes.
- An extension of the chemistry of the aluminium compounds to gallium.

The first half of the project has firmly established the foundational concepts we need to successfully pursue all of the objectives outlined above.
The major areas in which the work of the project has extended the state of the art are:

- Demonstration of new classes of supporting ligand in aluminium chemistry, in which the atoms used to bind to the aluminium centre are varied.
- The development of new synthetic routes to prepare low-oxidation state group 13 compounds.

These two hard-won advances have ideally positioned the project to be able to make rapid progress towards the project objectives over the next 30 months. By the end of the project we expect that we will have:

- established the principles behind oxidative addition and reductive elimination chemistry at low-oxidation state Al centres.
- developed varied examples of new Al(I) compounds and correlated the their reactivity to the properties of the supporting ligand frameworks.
- have discovered, and begun to develop, fundamentally new reactivity of Al(I) compounds that is of relevance to catalytic chemistry.