The production of many products used in everyday life and in industry, such as pharmaceuticals, plastics, and coatings, requires chemical catalysts, often expensive noble metals with limited availability. Researchers at the Karlsruhe Institute of Technology (KIT) are now presenting the first air stable iron compound, which enables the direct use of iron(I) for catalysis and, unlike previous methods, does not require strong reducing agents. A first test yielded active iron catalysts. The results have been published in the Journal of the American Chemical Society. (DOI: 10.1021/jacs.6c01660)
Catalysts are required to speed up chemical reactions or even make them possible at all. The catalysts generally used in industry are noble metals, such as rhodium, iridium, or palladium. They are highly effective for many applications, but at the same time expensive and rare. “Our research focuses on sustainable and eco-friendly alternatives to noble metal catalysts,” said Dr. Oliver Townrow from KIT’s Institute of Nanotechnology. “Iron is the fourth most abundant element in the Earth’s crust, and its effectiveness in certain catalytic reactions is comparable to that of noble metals.”
Stabilizing Reactive Iron
The researchers are focusing on a modular, pre-activated iron(I) source for catalysis. The Roman numeral indicates the oxidation state of the metal. Chemical compounds usually contain iron in the form of iron(II) or iron(III). For certain catalytic reactions, however, iron(I) is the best choice because it can accept or donate electrons more easily, enabling new reaction paths.
Due to the lack of a sufficiently stable iron(I) source compound for direct use in catalytic applications, researchers had to synthesize this form of iron during the reaction process using additional substances. While such reductants change iron to the desired form, they might also alter other reaction components. “That's why you can never be sure which iron compound will be produced in the reaction and how it will react with other substances,” said Luise Kink, lead author of the study and chemistry student at KIT. “With our approach, we can use this reactive form of iron more reliably.”
Synthesizing and Testing New Iron Compounds
In preparation of the actual catalytic process, the team first synthesized a separate iron(I) compound: The iron was positioned between two ring-shaped hydrocarbons, known as durene molecules, which stabilize the reactive metal. This ensures sufficient stability of the sensitive iron(I) against atmospheric oxygen and moisture when used in subsequent reactions.
Then, the researchers systematically replaced durene with other molecules to derive various iron(I) compounds, which were subsequently analyzed using X-ray structure analysis, spectroscopic methods, and magnetic measurements. A first catalytic test revealed that the new compound was well-suited as the source for an active iron catalyst.
Refining Iron Catalysts
Based on the new iron(I) compound, the range of potential applications can be extended. Now, researchers have a more systematic approach at hand to find out which variants are suitable for which catalytic reactions. “Our results show that we can prepare iron(I) more effectively for catalysis and use it in a more controlled manner than before,” said Townrow. “The long-term goal of our approach is to help replace noble metals with iron in industrial applications.”
Original publication
Luise Kink, Robert Kruk, Oliver P. E. Townrow: A Simple, Air Stable Single-Ion Source of Iron(I). Journal of the American Chemical Society, 2026. DOI: 10.1021/jacs.6c01660.
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