Greener Catalysis

By Jessica Sonnenberg, Media Coordinator for the GCI

Some of the main objectives of the GCI are to get researchers thinking about and practicing green and sustainable chemistry in their own labs. Through educational programs, seminar series and workshops we have gotten our department thinking about green chemistry, but introducing green practices and research in the lab setting is not always straightforward. This month we would like to highlight several important inorganic chemistry discoveries that are beginning to change how the academic community looks at research and what industry is now starting to target.

Catalysis is ubiquitous in academia and industry; it yields most of the pharmaceutical products people take every day, generates the plastics and materials that go in to most commercial products, and is at the forefront of the energy sector. The problem with this ubiquity is the compounds with which this catalysis is run. The majority of catalytic reactions are done using precious metal catalysts, specifically rhodium, iridium, ruthenium, platinum and palladium. Not only are these metals very expensive, but their natural abundances are rapidly diminishing and cannot sustain our growing needs. Research groups all over the world have begun to redirect their focus towards the development of more sustainable base metal catalysts to address this issue. Complexes based on iron, cobalt, copper and nickel have begun to emerge in the literature as potential green alternatives. Not only are these metals significantly cheaper and more earth abundant, but they are also much less toxic, which is important when evaluating allowable trace metal impurities in final products for consumer use.

In order to make a real impact on industry, new catalysts need to be equally efficient, selective and stable compared to the well-established precious metal catalysts already in use, and this has proven to be quite problematic. Base metals are much smaller and have different reactivities than larger precious metals, and hence interact differently with the organic ligands typically used to induce specific reactions. What this means is that new organic ligand scaffolds need to be developed from scratch to specifically optimize the reactivity of these smaller metal centres to induce comparable activity. Progress has been slow, but some revolutionary systems have begun to pop up in the literature, including the most recent issue of Science, which highlights three new discoveries using base metals in catalysis. First is work out of the Morris group at the University of Toronto who used iron catalysts to convert ketones (C-O double bonds) into chiral alcohols, using catalyst systems that have been thoroughly studied mechanistically, which allowed for optimization. Next is the Beller group at the University of Rostock in Germany who used iron nanoparticles to convert nitro (NO2) groups into amines (NH2) using much milder conditions than conventional methods. Lastly, the Chirik group at Princeton who used high-throughput techniques to develop cobalt catalysts that selectively convert alkenes (C-C double bonds) to chiral alkanes (C-C single bonds). All three discoveries are jointly highlighted in a Perspective article in Science by Bullock at Pacific Northwest National Labs that is definitely worth checking out (doi: 10.1126/science.1247240).

There has been tremendous progress in the area of green catalysis, but much work is still needed towards the development of new systems, and improving known systems to make them yield comparable activity to precious metal systems. To truly make a difference, more groups need to turn their attention to this important issue, the government needs to step up and improve funding for green and sustainable research in all areas, not just catalysis, and the industry needs to start investing in the infrastructure to make changing to these new systems more feasible. The GCI will be elaborating on the importance of green catalysis in their inorganic session of our annual workshop in the spring of 2014.