FRUSTRATED (LEWIS) PAIR STARTS A NEW RADICAL FAMILY
May 23, 2012 – While the Lewis pairs are frustrated, Allan Cardenas (left) and Brooks Culotta (right), student researchers in Prof. Timothy H. Warren’s laboratory, don’t have any trouble getting along. Their research alongside German collaborators demonstrates a unique way to capture nitric oxide (NO) and inject this essential small molecule with exciting reactivity. Their discovery was highlighted as News of the Week in the May 21, 2012 issue of Chemical & Engineering News.
TO GERMANY AND BACK
In August 2010, Prof. Gerhard Erker of the University of Münster in Germany delivered an invited talk at Georgetown University about frustrated Lewis pairs (FLPs). FLPs such as molecule 1 are “frustrated,” because they bear pent-up chemical reactivity; the large size of their reactive P and B components make it difficult for these atoms to directly interact. Sparked by the Warren lab’s interest with NO, a signaling molecule in biology that is produced on a massive industrial scale, both the Georgetown and German researchers were eager to examine the interaction of this small molecule with FLPs. In October 2010, Allan traveled to Münster to learn first-hand how to prepare FLPs under development in Prof. Erker’s laboratory. Immediately upon his return to Georgetown a month later, Allan captured NO!
NITRIC OXIDE RELIEVES FRUSTRATION
Allan and Brooks found that the small molecule NO serves as a conduit to complete the strong chemical attraction between the P and B atoms, greatly enhancing the reactivity of the captured NO molecule. For instance, the FLP-NO radical 2 reacts with normally unreactive C-H bonds in hydrocarbons, representing a green way to chemically modify natural petroleum resources under mild conditions. More recent work in collaboration with Prof. Amido Studer has shown that these FLP-NO species can also regulate the formation of polystyrene, one of the most widely used plastics.
FROM GENERAL CHEMISTRY LAB TO RESEARCH LAB
Allan, a fourth-year Ph.D. student, met Brooks when Allan was a General Chemistry teaching assistant. Interested in conducting research, Brooks, now a junior in Georgetown College and Chemistry major, asked Allan about research opportunities for undergraduate students. In the summer of 2010, Brooks, then a freshman, began working with Allan in Prof. Warren’s lab. Allan’s excellence in and enthusiasm for teaching contributed to Brooks’s interest. “Allan and I had a good working relationship in my lab class,” Brooks said, “and I wanted to work with him doing research.” Brooks will begin studying at Georgetown University Medical School following his graduation and was accepted early as part of the Early Assurance Program. Allan, whose teaching acumen contributed to Brooks’s interest in research, plans to take a postdoctoral position or teach once he completes his Ph.D.
FLPs ATTRACT NO & ATTENTION
This new family of molecules first brought to life by Allan and Brooks in Prof. Warren’s lab continues to receive attention from the chemical community. Editors of Angewandte Chemie highlighted their initial article as a “Hot Paper” for its importance in a rapidly evolving field of high interest. Chemical & Engineering News, the U.S. trade weekly with a wide circulation, published a news feature on the green, metal-free chemical reactivity described in the most recent scientific report by this German-American team. The Georgetown team recently received a research grant from the Petroleum Research Fund to develop these exciting molecules. Moreover, Allan will describe his groundbreaking research in June at the 2012 Graduate Research Symposium of the Inorganic Gordon Conference where he was invited to give a talk.
These new nitroxide radicals have many prospective applications. Allan describes potential uses as “an initiator for polymerization as well as a catalyst for functionalization of C-H bonds.” Prof. Warren is enthused about possible real-world applications: “These highly reactive, metal-free systems illustrate unprecedented, environmentally friendly ways to perform challenging chemical transformations with NO—an abundant, though underutilized, chemical raw material. As an inorganic chemist, I didn’t think it was possible to have this much fun without metals!”
FLPs BIND RESEARCHERS IN TRANS-ATLANTIC COLLABORATION
Four different research groups have joined forces to ensure the rapid, creative development of this new family of NO-based radicals. At Georgetown, new FLPs to reversibly bind NO are under development along with a continued examination of their chemical reactivity. These efforts take place collaboratively with Prof. Erker’s lab in Münster, Germany known worldwide for their expertise with FLP chemistry. Prof. Studer’s team in Münster focuses on new applications of the FLP-NO radicals, and Prof. Stefan Grimme performs high-level calculations to provide deep insight into their structure and reactivity. This successful trans-Atlantic collaboration receives support by the Provost's Faculty Committee for International Initiatives.
Brooks, who is currently studying at the University of Bristol in England, writes, “I plan on returning to the lab the second I get back to Georgetown for summer classes in July.” Briefly frustrated by an academic year abroad, the persistent bond first formed between teacher and freshman student in a General Chemistry laboratory will soon be revitalized.
Timothy H. Warren’s faculty profile
Chemical & Engineering News article
Journal of the American Chemical Society (Sajid, M.; Stute, A.; Cardenas, A. J. P.; Culotta, B. J.; Hepperle, J. A. A.; Warren, T. H.; Schirmer, B.; Grimme, S.; Studer, A.; Daniliuc, C. G.; Fröhlich, R.; Kehr, G.; Erker, G. J. Am. Chem. Soc. 2012. Web Publication Date: May 1, 2012. Just accepted manuscript.)
Angewandte Chemie International Edition (Cardenas, A. J. P.; Culotta, B. J.; Warren, T. H.; Grimme, S.; Stute, A.; Fröhlich, R.; Kehr, G.; Erker, G. Angew. Chem. Int. Ed. 2011, 50, 7567-7571.)