Inexpensive synthesis of organic compounds
The use of precious metals such as palladium, gold, iridium and rhodium as catalysts has enabled tremendous advances in organic synthesis. However, these metals are among the scarcest and most expensive elements on Earth. Another metal used in certain reactions is tin but this is toxic and can be harmful from an environmental perspective. Synthetic chemistry can benefit from a look at how nature makes its molecules by harnessing the reactivity of more abundant metals to produce carbon-containing compounds. EU-funded research investigated iron-based catalysts for several important reaction types within the scope of the project ‘Redox ligands and iron complexes for sustainable catalysis’ (FESUSTCAT). Compounds classified as heterocyclic, cyclic and containing two or more different types of atom, are arguably the largest and most varied class of organic compounds. Scientists studied the activity of a known iron catalyst in cycloisomerisation reactions where one compound is transformed into another with the same atoms but a different arrangement. The potential of new types of iron catalysts were also studied in this reaction. Novel iron catalysts were developed and their activity characterised in radical reactions. Methods were developed for the use of these iron-based catalysts in reductive radical cyclisation reactions and atom transfer radical addition reactions. Radical cyclisation is the formation of cyclic structures via highly reactive free radical intermediates. Atom transfer radical addition is a way to form new carbon – carbon bonds with 100% atom economy using a metal catalyst. Both are industrially relevant reaction types. Environmentally benign iron was studied and viable catalysts for these reactions were developed. Scientists demonstrated the value of iron as a replacement for toxic tin in radical reactions and enhanced overall understanding of the reaction conditions supporting iron-based catalysis. Future use of iron could enhance the safety and decrease the costs of synthetic routes to heterocyclic compounds with important impact on the EU economy.
Keywords
Catalysts, iron, organic, heterocyclic, radical cyclisation, atom transfer radical addition
