Graduate student Jeremy John holds up two vials, one containing his new ruthenium-based catalyst and the other its dichloride analogue. The complexes allow for the rapid hydrogenation of amines, a reaction that was previously possible only under extreme conditions.
By Tyler Irving
Posted January 2012
The hydrogenation of amides to form amines and alcohols is a notoriously difficult chemical transformation. So the recent discovery at the University of Alberta of a new, highly active catalyst for this kind of reaction could mean big changes for hundreds of synthetic chemical processes.
The new catalyst is a variation of a system developed by Ryoji Noyori, who shared the 2001 Nobel Prize in Chemistry for his work on catalyzing hydrogenations. Noyori catalysts consist of ruthenium metal atoms complexed with various organic ligands. The active catalysts in these reactions are unstable and are usually made from stable precursors during the hydrogenation reaction they are catalyzing. As such, they are very difficult to directly study on their own. Steve Bergens and his group decided to do just that. “We found that the Noyori catalysts are much more active than anyone ever expected, but despite this high activity, they didn’t give us any significant product for amide hydrogenations,” says Bergens. Bergens and his graduate student Jeremy John hypothesized that the complex was falling apart at the higher temperatures that are required to get amide hydrogenations to work. To solve this, they used a system where the organic ligands were chemically bonded to each other, in addition to the metal itself. “Out of the 20 ideas we had that week, that one worked,” says Bergens. “Like most discoveries, we got lucky.”
In 24 hours, each molecule of the new catalyst system can achieve up to 7,600 amide hydrogenations under relatively mild conditions; the previous record was only about a hundred hydrogenations in 48 hours. Since amines and alcohols - the products of amide hydrogenation - are used in everything from polymers to perfume, the catalyst could open up new synthetic pathways and lead to processes that are more efficient and environmentally friendly. “Right now we’re overrun with ideas,” says Bergens. “For example, breaking down nylon might be something to look at. We are thinking about hydrogenating peptides and it might be possible to do that selectively.” Best of all, the system hasn’t yet been optimized, meaning that even better results may lie just around the corner. The work is published in Angewandte Chemie.
Photo Credit: Michael Holly, University of Alberta
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