By Wendy Plump
Department of Chemistry
Tuesday, Jun. 30, 2026
The Princeton Department of Chemistry publishes nearly 300 journal papers each year. Some of them make quite a stir. Others glide along under the radar with citations that ebb and flow based on whether a particular field is in play. Still others lodge themselves in their authors’ minds as representative of a lab’s greater mission.
This summer, we’re highlighting papers in this third group; the ones that were magical, even formative in a faculty member’s research program.
Like this one from Edwards S. Sanford Professor of Chemistry and Department Chair Paul Chirik: Ligand Field Sensitive Spin Acceleration in the Iron-Catalyzed [2+2] Cycloaddition of Unactivated Alkenes and Dienes, which appeared in the Journal of the American Chemical Society (JACS) in March 2024 under authors Hanna Cramer, Coralie Duchemin, Carli Kovel, Junho Kim, Matthew Pecoraro, and Paul Chirik.
Enjoy our brief Q&A below.
Why is this paper important to you?
This paper revealed why the iron catalysts we have studied for nearly 20 years are so special. One reaction they promote is the 2+2 cycloaddition of alkenes with alkenes or alkenes with dienes to form cyclobutanes (’squares’). These reactions are forbidden under thermal conditions, and we had shown some time ago that iron catalysts with redox-active pyridine(diimine) ligands on them were unique in promoting cyclobutane formation. These reactions are important because they are a straightforward route to unique fuels and chemically recyclable plastics that can’t be made any other way. This is even more remarkable when you think about the petrochemical industry and scores of academic labs that had been studying the reactions of alkenes and dienes with metal catalysts for decades!
In this paper, my postdoc at the time, Hanna Cramer, made several variants of the iron catalyst to see how changes to the structure made cyclobutane formation go faster or slower. By doing this along with isotopic labeling experiments and DFT calculations, she figured out why the iron catalysts are special. …
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