Researchers from the Ruhr University Bochum in Germany have discovered a new synthetic route by which they can produce a specific organic compound from a simple carbon monoxide (CO) molecule, namely the anionic ketene. They were previously known only as reactive intermediates and therefore could not be used as defined reagents. Researchers from Bochum produced anionic ketenes that were so stable that they could be isolated. Unlike previous methods, which can produce compounds of higher value from simple molecules, this approach does not require expensive or toxic metals.
Mike Jörges, Felix Krischer and Professor Viktoria Däschlein-Gessner from the Ruhr Explores Solvation Cluster of Excellence (RESOLV) published their findings in the journal Science from December 22, 2022.
“Small molecules such as hydrogen, carbon dioxide or carbon monoxide often appear as by-products of large-scale technical processes or are readily available from renewable raw materials,” explains Däschlein-Gessner. “Because they are readily available, they are interesting as synthesis building blocks to obtain basic raw materials or fine chemicals such as agrochemicals or pharmaceuticals. This is a promising route for the development of sustainable synthesis processes.”
Conversion without transition metals
In order to activate small molecules and turn them into more complex compounds, it is usually necessary to use certain metals, which are known as transition metals due to their position in subgroups of the periodic table. These are often precious metals, which are scarce and sometimes toxic. To date, only a few compounds from widely available main group elements have succeeded in activating small molecules. This also applies to carbon monoxide. Moreover, the reactions with CO as a building block were less selective: in addition to the desired high-value compounds, unwanted by-products were often formed.
Researchers from the Department of Inorganic Chemistry II at Ruhr University Bochum have now used simple phosphorus compounds, i.e. so-called ylides, in combination with sodium or potassium bases to tackle this challenge. By realizing a previously unknown way of reaction of these carbon compounds similar to a transition metal, they enabled the efficient incorporation of CO into larger molecules with a high degree of selectivity.
Just like a molecular model kit
“The selectivity of these transformations is impressive, especially compared to other synthesis methods,” Viktoria Däschlein-Gessner points out. “This is due to the stability of the anions, which derives from their unique electronic structure. They can be specifically morphed with other molecules just like in a molecular model kit, meaning that different, complex structures can be built quickly.”
In the next step, the group from Bochum intends to investigate the principle of the reaction and the potential of anionic ketenes in further research directions. “The way phosphorus compounds react is revolutionary for the development of further processes for the use of sustainable building blocks such as CO,” emphasizes Däschlein-Gessner. “We are also confident that anionic ketenes have even greater potential for synthetic chemistry than we have shown so far.”
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Materials provided by Ruhr University Bochum. Original written by Julia Weiler. Note: Content may be edited for style and length.