Organo-Fluoro-Pnictonium Cations: Designing a New Class of Lewis Acid Catalyst

Lead Research Organisation: Nottingham Trent University
Department Name: School of Science & Technology


Commercially synthesised organic chemicals are crucial to industries as diverse as agriculture, medicine and electronics. The enormous global demand for these products is constantly rising in the face of innovations in drug design and everyday technology, such as mobile phones and solar panels. Set against this is the increasingly important need to conserve energy and raw materials, in the context of environmental concerns and diminishing natural resources. Catalysis is an extremely important tool in reconciling these competing demands. Using a catalyst lowers the energy barrier to carry out a given chemical reaction, allowing processes to function at lower temperatures and pressures, consuming less energy. Catalysts can also improve resource and time economy by promoting new reactions, reducing the number of reagents and steps required to obtain an end product. Catalysts are not consumed in these processes, but regenerated, making them a keystone of sustainable synthetic chemistry.

This project will provide the fundamental research needed for development of low cost, efficient and accessible new catalysts. Currently, many of the catalysts most widely used in commercial organic synthesis are based on costly transition metals such as platinum, palladium, rhodium and gold, which have low natural abundance. Research into new catalysts is increasingly focused on replacing these with cheaper metals in existing catalytic processes. It is also desirable to develop catalysts for new processes, leading to improved reaction pathways and new products. While simple halides of main group elements have long been used as Lewis acid catalysts, these are generally corrosive and lack any tuneability. The development of catalysts based on organometallic main group derivatives is a nascent but rapidly growing area of study. Several important advances in recent years have challenged the idea that transition metals are necessary for the catalysis of organic bond forming reactions. Main group metals such as antimony (Sb) and bismuth (Bi) are abundant and inexpensive (more than 20 times cheaper than platinum, for example).

The proposed research will develop straightforward synthetic routes to new molecules comprising organic and fluoride substituted Sb and Bi cations with weakly coordinating anions. Based on previous work, these molecules have the potential to be good catalysts for organic transformations because of their tuneable Lewis acidity and well-defined vacant binding sites. Organometallic compounds of heavy main group metals have until now received far less study than those of transition metals, and research into the organic fluorides of Sb and Bi has been particularly limited, despite these promising attributes. An important outcome of this project will be to understand the fundamental chemistry and bonding of these types of compound, and determine the most efficient ways to produce them. Investigation of their reactivity with Lewis bases and small organic molecules will help to identify potential catalysts which will be screened against a test set of key reactions. Establishing the basic chemistry governing the interaction of main group organometallic molecules with organic substrates is essential to reducing global dependence on expensive transition metal catalysts in the long term.

Planned Impact

Achievement of this project's aims by the development of tuneable main group catalysts would have a significant long term economic impact on both the bulk and fine chemical industries. Creating efficient catalysts saves both time and money in the manufacturing of products as diverse as pharmaceuticals, electronic materials, agrochemicals, plastics and fuels. In addition, there will be a positive environmental impact from reducing both the amount of energy consumed and the volume of waste produced, leading to cleaner industrial practices and a reduction in fossil fuel consumption. Tuning catalysts to improve substrate tolerance will allow economically viable reprocessing of materials which are currently considered as waste thereby transforming them into useful products. The development of easy-to-handle catalysts from abundant main group metals will also reduce reliance on costly transition metals or corrosive inorganic Lewis acids, improving economy and worker safety.
While the proposed research is at the fundamental level and these outcomes will not be immediate, we will engage with industrial chemists from day one to work towards solving real problems. Knowledge transfer with SMEs such as Key Organics Ltd will be mutually beneficial, enabling us to effectively target industrial needs. Later in the project, they will benefit from the opportunity to test novel reagents and feed back into the development process.
In the shorter term, as well as immediate impact on academic beneficiaries (see above), the project will enable the development of the PI's independent research career, forming a platform on which she will build a wider programme of research focusing on main group organometallic compounds and their applications. It will also support and train a postdoctoral researcher in cutting-edge, industrially relevant science, enabling them to pursue a career of innovative research. By engaging with politicians, journalists and members of the public we will draw attention to the importance of funding fundamental research into chemistry, and especially catalysis, for long term economic and environmental wellbeing both nationally and internationally.


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Description Several general methods were developed for the synthesis of new molecules with catalytic potential. Two families of molecules were synthesised and characterised. Both are based around a positively charged antimony (Sb) ion with both organic and halide substitutents. The reactivity of these molecules was investigated, and it was discovered that some had catalytic ability in a variety of reactions from our test set. Some also had unusual and unexpected non-catalytic reactivity with various substrates which could be exploited for chemical synthesis in the future. In order for the potential of these molecules to be realised, more work is needed in understanding the structure-function relationships which govern their reactivity, and in optimising catalyst structure and conditions.
Exploitation Route The direct outcomes of the funding have served to raise new research questions which will form the basis of further investigations by ourselves and other academic researchers into the properties and structure-function relationships of the new classes of molecule that we have produced. Hence, this funding has initiated a programme of research, the eventual aim of which is to develop catalytic molecules which are inexpensive and easy to produce, and can be used by chemical industries (e.g. pharmaceutical companies, solar panel manufacturers) to facilitate lower energy, more efficient synthesis of desirable chemical products.
Sectors Chemicals,Pharmaceuticals and Medical Biotechnology

Description Elucidating the Origins of Lewis Acidity in pentamethylcyclopentadienyl containing Antimony(III) Cations
Amount £360 (GBP)
Funding ID M19-4223 
Organisation Royal Society of Chemistry 
Sector Charity/Non Profit
Country United Kingdom
Start 06/2019 
End 08/2019
Description Old ligands, new tricks: in search of bridging pnictine coordination modes
Amount £9,870 (GBP)
Funding ID E20-3323 
Organisation Royal Society of Chemistry 
Sector Charity/Non Profit
Country United Kingdom
Start 02/2021 
End 02/2022
Description Tobias Krämer, Maynooth University 
Organisation Maynooth University
Country Ireland 
Sector Academic/University 
PI Contribution Generation of experimental data and formulation of research questions based on experimental observations.
Collaborator Contribution Computational investigation of research questions based on experimental observations, contributing to our understanding of bonding, reactivity and structure-function relationships.
Impact - Two publications: Diverse structure and reactivity of pentamethylcyclopentadienyl antimony(III) cations, O. Coughlin, T. Krämer and S. L. Benjamin, Dalton Trans., 2020, DOI: 10.1039/d0dt00024h A Five-Membered PdSbn Coordination Series. A. Jolleys, B. R. M. Lake, T. Krämer and S. L. Benjamin, Organometallics, 2018, 37, 3854, DOI: 10.1021/acs.organomet.8b00556 - Research visit funded by RSC travel grant for knowledge transfer - PhD student O. Coughlin visited University of Maynooth for 4 weeks, learning new skills in computational methods.
Start Year 2018