The simple molecule carbon monoxide (CO) can be used as the starting point for synthesizing a specific organic compound called anionic ketenes, according to research from Germany’s Ruhr University Bochum. These could previously not be used as defined reagents because they were only recognized as reactive intermediates.
The compounds are handled in a glove box to shield them from air and humidity. Image Credit: RUB, Marquard
The Bochum-based scientists created isolable anionic ketenes that were remarkably stable. This method does not require costly or hazardous metals, in contrast to earlier ones that could synthesize more valuable compounds from basic molecules.
The Ruhr Explores Solvation (RESOLV) Cluster of Excellence’s Mike Jörges, Felix Krischer, and Professor Viktoria Däschlein-Gessner published their research on December 22nd, 2022, in the journal Science.
Small molecules such as hydrogen, carbon dioxide or carbon monoxide often occur as by-products of large-scale technical processes or are easily accessible from renewable raw materials. Since they are readily available, they are of interest as synthesis building blocks to obtain essential feedstock or fine chemicals such as agrochemicals or pharmaceuticals. It’s a promising avenue for the development of sustainable synthesis processes.
Viktoria Däschlein-Gessner, Professor, Ruhr University Bochum
Conversion Without Transition Metals
In most cases, it is necessary to use specific metals that are known as transition metals because of their location in the subgroups of the periodic table to activate small molecules and transform them into more complex compounds. These are frequently rare and occasionally toxic precious metals.
Only a few of the widely accessible main group element compounds have been found to be capable of activating small molecules thus far; the same holds for carbon monoxide. Furthermore, reactions using CO as a building block have been less selective; frequently, undesirable byproducts form along with the desired high-value compounds.
To address this issue, the researchers from the Chair of Inorganic Chemistry II at Ruhr University Bochum have now combined simple phosphorus compounds, also known as ylides, with sodium or potassium bases.
These carbon compounds exhibit a previously unrecognized transition metal-like reaction mode, which they were able to realize. This allowed them to effectively and selectively incorporate CO into larger molecules.
Just Like a Molecular Model Kit
“The selectivity of these transformations are impressive, especially compared to other synthesis methods. This is due to the stability of the anions, resulting from their unique electronic structure. They can be specifically converted with other molecules just like in a molecular model kit, which means that different, complex structures can be rapidly built up,” Däschlein-Gessner added.
The Bochum group will next investigate the reaction theory and the potential of the anionic ketenes for additional research directions.
The research was supported by the European Research Council (grant no. 677749) and the German Research Foundation as part of the RESOLV Cluster of Excellence (EXC-2033).
Journal Reference:
Jörges, M., et al. (2022) Transition metal–free ketene formation from carbon monoxide through isolable ketenyl anions. Science. doi:10.1126/science.ade4563.