Researchers from McGill University and Japan have developed a system of polymer-embedded iron nanoparticles that provide a cheaper and more sustainable way to catalyse a wide variety of hydrogenation reactions.
Current catalysts for hydrogenation — commonly used in the synthesis of many pharmaceuticals — are based on metals such as palladium and platinum, which are both expensive and potentially toxic. Iron nanoparticles are an inexpensive and non-toxic alternative; unfortunately they’re prone to rusting. “As soon as they see just a little bit of water, they’re basically dead,” says Audrey Moores, a professor of chemistry at McGill.
Moores and her team partnered with Yasuhiro Uozumi of the Japanese institute RIKEN (The Institute of Physical and Chemical Research) to protect the nanoparticles from rust. First, they used block copolymers to create microscopic beads of polystyrene (PS) coated with ‘hairs’ made of polyethylene glycol (PEG). Next, iron-containing precursors were added to the solution. By decomposing these precursors with either heat or chemical reduction, they formed pure iron nanoparticles that quickly became enveloped in the PEG matrix. “We think this is what repels water while allowing the substrates, which are less hydrophilic, to get in and be hydrogenated,” says Moores.
In a paper published in Green Chemistry, the team tested a wide variety of compounds to show that the catalysts were both active and selective, hydrogenating certain bonds with 100 per cent yield while leaving others alone. They also stayed active in solutions that were up to 90 per cent water, something no iron-based catalyst had done before. However, they did require higher hydrogen pressures than are normally used with palladium catalysts. “It’s a trade-off: if you save on catalyst price and move away from the toxicity, you can perhaps afford to use more hydrogen pressure,” says Moores. The team has patented the particles, and plans to work with the Canadian Light Source synchrotron in Saskatoon to better understand how PEG protects the iron from rusting and further improve their properties.