A new generation of iron-based asymmetric hydrogenation catalysts outperforms conventional precious-metal catalysts while cutting costs and toxicity concerns, claim researchers at the University of Toronto, Toronto, Ont. The catalysts' conversion rates exceed those of precious metal catalysts while providing similar yields, notes lead researcher Robert Morris of the university's chemistry department. Moreover, unlike precious metals, iron is abundant and inexpensive; its low toxicity profile means that residual catalyst in product is less of an issue, too.
The current catalysts represent a significant improvement over the researchers' earlier iron-based hydrogenation catalysts (see: "Iron Replaces Ruthenium as Catalyst"), says Morris. "After studying the catalyst kinetics of previous versions, we discovered that they were being slowly converted into a more-active form, even though they were already quite active and selective. What we discovered is that the optimal activation process involved reducing only one of its two imine groups that were attached to the iron core to its amine form. If both were reduced, the system is barely active. That was a big surprise. Also, base is required to remove a proton next to the remaining imine group. Taking these into consideration, we created new precatalysts that quickly activate into this amine-imine form around the iron atom. These are exceedingly active transfer hydrogenation catalysts for the asymmetric reduction of carbon-oxygen and carbon-nitrogen double bonds." (A recent article in Science describes the synthesis and use of the catalysts.)
"Also, the new synthesis allows a much wider range of active catalyst structures to be made conveniently, with different groups on each side of the molecule. This is important when substrates of different structures need to be reduced selectively," adds Morris.
GreenCentre Canada (GCC), Kingston, Ont., a not-for-profit organization that focuses on commercializing technologies developed at academic institutions, has exclusive rights to the catalyst technology. It is pursuing two distinct strategies, notes GCC's Andrew Pasternak. "The first is to make the catalyst commercially available to the global research community through small-volume distributors… Individual researchers in the pharmaceutical and fine chemical industry will be able to purchase small samples of the catalysts to quickly test in their own internal synthetic chemistry processes. This will allow them to develop proprietary uses of the catalysts that will support their product development efforts… Concurrent to the efforts, GreenCentre will also market the catalysts directly to companies who are currently using ruthenium or other metal-based hydrogenation catalysts for similar chemical transformations. By offering them an alternative… that is at least as fast and probably faster, it is hoped that these companies will quickly try to adopt the catalyst for use in their current fine chemical and drug production efforts."