Many products used in everyday life and in industry, such as pharmaceuticals, plastics, and coatings, are produced with the help of chemical catalysts. These processes often rely on expensive and limited noble metals. Researchers at Karlsruhe Institute of Technology (KIT) have now presented 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 typically used in industry are noble metals, such as rhodium, iridium, or palladium. While well suited for many applications, they are 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
At the center of the work is a modular, pre-activated iron(I) source for catalysis. The Roman numeral indicates the electronic 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, thereby enabling alternative reaction paths.
Until now, a comparably stable precursor compound that makes iron(I) directly available for catalytic applications had been lacking. As a result, researchers often had to synthesize this form of iron during the reaction process itself using additional substances. While such reductants change iron to the desired form, they might also alter other components of the reaction. “This makes it difficult to precisely control which iron species forms during the reaction and how it subsequently reacts,” says Luise Kink, first 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 selectively replaced durene with other molecules to derive various iron(I) compounds. These were analyzed using X ray crystallography, spectroscopic methods, and magnetic measurements, among other techniques. In a first catalytic test, the team also demonstrated that an active iron catalyst can be generated from the new compound.
Advancing Iron Catalysts
The new iron(I) compound provides a foundation for further applications. Researchers can now more systematically investigate which variants are suitable for specific 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. https://pubs.acs.org/doi/full/10.1021/jacs.6c01660
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