Steven J. Peters, PhD, Illinois State University
Since receiving funding from ACS-PRF in January 2012, my research group has been active in exploring the one electron reduction of aryl substituted isocyanates. The first proposed objective was to explore the reduction of various aryl substituted isocyanates and to determine how the para substituents influence the structure of the anion radical formed. We focused on the reduction of four species: phenyl-, p-tolyl-, p-methoxyphenyl- and p-nitrophenyl isocyanate. Two undergraduate chemistry majors investigated the reduction of these systems (Mark Servos and Cody Scholtens), and both students have been working with me since funding began last year. Notably, we found that the conditions by which these isocyanates are reduced will influence the stability and reactivity of the anion radical formed. For example, we were successful at generating the anion radical of all four of these species in hexamethylphosphoramide (HMPA), a solvent which solvates cations very well. These results are significant, because these anion radicals have never been observed in solution, under room temperature conditions, prior to this work. (In previous studies, we attempted to form the anion radical of alkyl isocyanates, but we were unsuccessful due to their propensity to polymerize.) We also synthesized and reduced the carbon-13 labeled phenyl isocyanate (PhN13CO), which was invaluable towards understanding the structure of the isocyanate moiety in these anion radicals. Remarkably, the measured electron -13C coupling lead us to conclude that the unpaired electron is delocalized into the phenyl ring and not localized in the isocyanate group. With much of the electron density residing in the phenyl ring, we determined that the NCO moiety remains linear (as in the neutral species) even after reduction. Remarkably, when these same compounds are reduced in tetrahydrofuran, a much less polar solvent than HMPA, we find that the anion radical of these aryl isocyanates is not stable, but undergoes a rapid cyclotrimerization and the formation of an isocyanurate anion radical. We were able to measure all electron-nuclear coupling to the three carbons and three nitrogens within the isocyanurate ring, which was essential in proposing a structure for these heterocyclic anion radicals. Notably, we published a manuscript this year describing our results on these aryl isocyanate reduction studies.
Another interesting result of these studies is that the alkali metal used also plays a key role in the reduction of aryl isocyanates where, upon cyclotrimerization and the formation of the isocyanurate ring, the dianion can be generated instead of the anion radical. We are currently performing experiments to determine the structure of these newly discovered dianions. We hope to have a manuscript submitted later this year or early in 2015 describing some of these results. In addition, we will begin reduction experiments on annulenyl isocyanate and explore how the annulene ring, known to have a large electron affinity, will influence the isocyanate reactivity upon addition of a single electron.
Reduction of diaryl diimide compounds
A new undergraduate student (Michael Crawford) joined my group this past summer working on a project involving the reduction of diaryl diimide compounds (e.g., Ph-N=C=N-Ph). We became motivated to investigate the one electron reduction of these species largely from a reviewers comment to our recently published paper. The anion radical of these systems has not been explored before, but are a natural progression from our studies of isocyanates, which will give us further insight into the structure and reactivity of these extended p systems. Michael is a sophomore chemistry major and an honors student in our program. This past summer he was successful at synthesizing the diphenyl diimide compound, and this fall he will begin the one electron reduction studies. I am very pleased to have Michael working with me in the laboratory for the next three years before he graduates with his BS degree.
Impact on my students
At present, Mark Servos and Cody Scholtens are seniors in our program and will graduate in May 2014. Mark primarily focused on the one electron reduction of phenyl isocyanate and p-tolyl isocyanate, while Cody focused on the p-nitrophenyl- and p-methoxyphenyl isocyanate systems. The techniques used to add a single electron to these compounds require specialty glassware and must be performed under vacuum conditions. As a result, all of my students learn how to blow glass and make the special apparatuses needed for these experiments, and become proficient with vacuum line equipment. They perform all reduction experiments, collect all spectral data and work with me in analyzing and interpreting the data. Notably, Mark and Cody are co-authors on the manuscript published earlier this year. They also presented their results at a University wide Research Symposium held at Illinois State University (ISU) in April 2013, and Mark presented more recent findings on the isocyanurate dianions at the National ACS Meeting in Indianapolis, IN this past September 2013. Mark has discussed with me his intent to enroll in our MS degree program in the fall of 2014. Cody will likely go into industry for a time with plans to attend graduate school.
Impact on my career
For my part, I have truly enjoyed working side-by-side with these students and watching as they grow into talented young chemists. These interactions have enriched my career as a professor and chemist. Furthermore, the research that we have accomplished with this funding will have a direct impact on my future career here at ISU. I have recently applied for a sabbatical leave for the spring 2015 semester. If awarded, this leave will give me additional time to complete and submit manuscripts for publication on many of the projects outlined in the latter part of my ACS-PRF grant. Notably, the contributions made during this sabbatical will greatly enhance my research portfolio as I contemplate going up for full professor in the near future. Lastly, the research and scholarship that results from this funding will significantly improve my chances to obtain future external funding, which will impact both my career and the stature of ISU.