Periodic Reporting for period 4 - AlCat (Bond activation and catalysis with low-valent aluminium)
Reporting period: 2021-09-01 to 2022-08-31
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.
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 were 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 focused on the first two objectives. We prepared new ligand frameworks and used them to support reactive aluminium centres. We systematically varied properties of the ligands, correlating changes in the ligand with changes in reactivity at the aluminium centre. Later in the project, we reported how differing properties of the ligand modulated catalytically relevant reactivity at lower oxidation state centres. We also studied the mechanism of oxidative addition and reductive elimination/disproportionation reactions of Al(I) and Al(II) compounds.
The main achievements of the project were 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.
- An improved understanding of oxidative addition/reductive elimination chemistry at group 13 metal centres, which is directly relevant to redox-cycle catalysis.
Additional and unforeseen advances were:
- A new method for the preparation of C=P multiple bond-containing compounds (phosphaalkenes).
- The development of CH borylation catalysed by aluminium(III) compounds.
The results of the project have been and will continue to be disseminated through multiple peer-reviewed scientific publications and through conference/meeting contributions. Additionally, some results from the project received new coverage in the specialist industry/community chemical publications.
- 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 focused on the first two objectives. We prepared new ligand frameworks and used them to support reactive aluminium centres. We systematically varied properties of the ligands, correlating changes in the ligand with changes in reactivity at the aluminium centre. Later in the project, we reported how differing properties of the ligand modulated catalytically relevant reactivity at lower oxidation state centres. We also studied the mechanism of oxidative addition and reductive elimination/disproportionation reactions of Al(I) and Al(II) compounds.
The main achievements of the project were 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.
- An improved understanding of oxidative addition/reductive elimination chemistry at group 13 metal centres, which is directly relevant to redox-cycle catalysis.
Additional and unforeseen advances were:
- A new method for the preparation of C=P multiple bond-containing compounds (phosphaalkenes).
- The development of CH borylation catalysed by aluminium(III) compounds.
The results of the project have been and will continue to be disseminated through multiple peer-reviewed scientific publications and through conference/meeting contributions. Additionally, some results from the project received new coverage in the specialist industry/community chemical publications.
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 and in which their electronic/donor properties can also be easily tuned.
- The development of new synthetic routes to prepare low-oxidation state group 13 compounds including those containing Al(I) and Ga(I)
- An improved (and unforeseen) new understanding of the mechanism of oxidative addition (and by implication of reductive elimination) at Al(I) compounds. This understanding provides design rules for chemists looking to engineer this reactivity for any specific purpose.
- the project discovered, and begun to develop, fundamentally new reactivity of Al(I) compounds that is of relevance to catalytic chemistry.
- Demonstration of new classes of supporting ligand in aluminium chemistry, in which the atoms used to bind to the aluminium centre are varied and in which their electronic/donor properties can also be easily tuned.
- The development of new synthetic routes to prepare low-oxidation state group 13 compounds including those containing Al(I) and Ga(I)
- An improved (and unforeseen) new understanding of the mechanism of oxidative addition (and by implication of reductive elimination) at Al(I) compounds. This understanding provides design rules for chemists looking to engineer this reactivity for any specific purpose.
- the project discovered, and begun to develop, fundamentally new reactivity of Al(I) compounds that is of relevance to catalytic chemistry.