SubVAR - Sub-Valent Alkaline Earth Reagents

Our society relies on the chemical industry for the production of materials that assist and sustain our modern way of life. Manufacturing processes based on relatively simple chemical transformations are responsible for the production of drugs, pesticides, fuels and fertilisers, and it is quite common for these processes to be constructed around fundamental building blocks such as hydrogen, carbon monoxide and nitrogen. A typical example is the Fischer-Tropsch (FT) process, which is one of the most popular gas-to-liquid processes and is used for the production of long chain hydrocarbons from carbon monoxide and hydrogen. Its national strategic importance is demonstrated by the significant investments made by British companies (e.g. Johnson Matthey, BP, Velocys) in the development of new catalysts and FT reactors for the conversion of urban waste and biomass into renewable fuels, which is in line with the UK Government strategy to increase the number of FT plants and synthetic fuel supply by 2030. However, costs associated with these types of chemical manufacturing processes are usually very high, as they often rely on expensive and toxic transition metal reagents, and require very high temperatures and pressures.

Earth abundant and non-toxic metals promise cheaper and more sustainable alternatives for chemical manufacturing processes. However, reagents based on these metals cannot break apart many of the small molecules used by these processes because of their lack of redox reactivity. Nonetheless, in recent years there have been many developments towards the generation of redox active Group 2 reagents, leading to the report of the first monovalent beryllium, magnesium and calcium species. This field is still in its infancy and these new species are yet to deliver transformations comparable to those of the traditional transition metal systems used by the chemical industry. New approaches must be devised to discover more sustainable alternatives and cheaper reagents that can mimic the performance of transition metal catalysts. This project will investigate the fundamental properties of the Alkaline Earth family (with the exception of beryllium and radium); these are Earth abundant and non-toxic metals, which could one day provide more sustainable alternatives for current materials employed by the chemical industry.

In preliminary work we have demonstrated monovalent Alkaline Earth complexes can be stabilised with judicious and tailored molecular design. Our previous experimental and theoretical studies provide a blueprint that is transferrable to all the elements of the Group and will afford a new class of species in which the heavy Alkaline Earth metals possess transition metal-like electronic configuration, unlike previous examples of sub-valent Group 2 complexes. This is a first crucial step towards the preparation of Alkaline Earth reagents that will perform in redox reactivity in the same vein as classic transition metals employed in synthesis and catalysis. The repercussions of this are significant, both from the fundamental and applicative point of view. Group 2 elements are generally considered unable to behave like transition metals, and this project will provide the first experimental proof of viable molecular species where the electronic and chemical properties of the Alkaline Earth metals will parallel those of transition metals. The resulting compounds will be capable of transforming common gases used by the chemical industry (hydrogen, nitrogen, carbon monoxide), thus opening up new synthetic possibilities for improving the sustainability of chemical manufacturing processes.