FLP Zintl Clusters for the Electrochemical Catalytic Reduction of Small Molecules

We will harness the untapped reactivity of Zintl ions, polayanionic clusters of earth abundant main-group elements, to affect small molecule activations in stoichiometric and catalytic fashions. Coupling reactions to yield new bonds, especially C-C bonds, occupy a central position in synthetic chemistry. To this end, a rich history of Pd cross-coupling reactions exploited by both academic and industrial chemists has developed. However, the high operational costs and toxicity of metal-based catalysts has spurred an interest in main-group systems that can represent this reactivity. Perhaps the most diverse and successful examples of main-group catalysts are frustrated Lewis pairs (FLPs). Traditional FLP systems rely on a Lewis acidic and a Lewis basic site to activate small molecules, and most homoatomic and heteroatomic bond formation reactions are accessed by bond polarisation mechanisms. However, the scope of these bond formation reactions remains limited and C-C bond formation with CO2 remains unidentified in the field. In this project, a new family of FLPs consisting of clusters capable of multi-site activation will be coupled with electrochemical methods to promote bond formation chemistries.
We intend to establish Zintl clusters as the basic component in FLP chemistry. Preliminary investigations are targeted with [P7]3-, not only because of its synthetic accessibility, presence of an NMR handle, and greater stability relative to group 14 clusters, but also because of the wide-spread success of phosphines as the basic component in established FLP systems. Once functionalised with an acidic component, these polyanionic clusters are excellent targets for small molecule activation via a FLP pathway, as they feature both the necessary electron-rich and electron-poor components. With this proximity and the propensity to undergo redox reactions in mind, these systems will be assessed in the electrochemical reduction of small molecules, our most ambition target would be the selective reduction of CO2 to ethane. Recycling the C1 building-block, environmental toxin, and industrial by-product into value-added products reminiscent of the fuels from which CO2 is generated upon combustion.

This research project will be collaboratively undertaken by the Mehta and Dryfe groups, and has been divided into two work packages.

Work Package 1 (primarily based in the Mehta group):
1. Functionalise the group 15 Zintl clusters, namely [P7]3-, with a Lewis acidic component
2. Perform insertion chemistry between acidic and basic centres on these clusters akin to FLP chemistry. Small molecules of particular interest include CO2, olefins, carbonyls, carbodiimides, and isocyanates.
PhD project call 2020
3. Reductively couple activated substrates to form new bonds

Work Package 2 (primarily based in the Dryfe group):
4. Immobilise FLP Zintl material on suitable electrode surfaces, e.g. glassy carbon or edge-plane pyrolytic graphite
5. Electrochemically close catalytic cycles by reducing the expected oxidatively coupled cluster product
6. Use kinetic analysis methods to determine, and optimise, rates of catalytic processes via fitting of electrochemical data.

Zintl clusters capture the imagination of academics because they are molecular models for larger heterogenous systems. Technology we develop with [P7]3- can be expanded to larger polyphosphides, such as [P11]3-, [P16]2-, [P21]3-, and eventually inform reactivity possible with functionalised red phosphorus. The strategy of electrochemically / photochemically converting CO2 to reduced value-added products is referred to as artificial photosynthesis.

iCAT will work with industry partners to create an holistic approach to the training of students in biocatalysis, chemocatalysis, and their process integration. Traditional graduate training typically focuses on one aspect of catalysis and this approach can severely restrict innovation and impact. Advances in technology and fundamental reaction discovery are rendering this silo-approach obsolete, and a new training modality is needed to produce the next generation of chemists and engineers who can operate across a far broader chemical continuum. iCAT will meet this challenge with a state-of-the-art CDT, equipping the next generation of scientists and engineers with the skills needed to develop future catalytic processes and create the functional molecules of tomorrow.

The UK has one of the world's top-performing chemical industries, achieving outstanding levels of growth, exports, productivity and international investment. The UK's chemical industry is a significant provider of jobs and creator of wealth, with a turnover in excess of £50 billion and a contribution of over £15 Billion of value to the UK economy [2015 figures]. iCAT will deliver highly skilled people to lead this industry across its various sectors, achieving impact through the following actions:

1. Equip the next generation of science and engineering leaders with the interdisciplinary skills and knowledge needed to work across the bio and chemo catalytic remit and build the functional molecules we need to structure society.

2. Provide a highly skilled workforce and research base, skilled in the latest methodologies, strategies and techniques of catalysis and engineering that is crucial for the UK's Chemical Industry.

3. Build the critical mass necessary to support effective cohort-based training in a world-class research environment.

4. Develop and disseminate new catalytic technologies and processes that will be taken up by industrial and academic teams around the world.

5. Encourage Industry to promote research challenges within the CDT that are of core relevance to their business.

6. Provide cohesion in the integration of biocatalysis, engineering and chemocatalysis to create a more unified voice for strategic dialogue with industry, funders and policy makers, and more generally outreach and public engagement.

7. Draw-in and bring together Industrial partners to facilitate future Industrial collaborations.

8. Benefit Industrial scientists through interactions with the CDT (e.g. training and supervisory experience, exposure to cutting-edge synthesis and catalysis etc).

9. Link with other activities in the landscape: bringing unique expertise in catalysis to, for example, externally-funded University-led initiatives, EPRSC Grand Challenge Networks, and the National Catalysis Hub.