Tunable Masks for Triggered N-heterocyclic Carbene Organocatalysis

With the support of the Chemical Structure, Dynamics, and Mechanisms B (CSDM-B) program in the Division of Chemistry, Jessica Lamb of the University of Minnesota is studying a new way to control chemical reactivity via catalysis. Because of their wide utility, N-heterocyclic carbenes (NHCs) are a particularly important class of catalysts that has garnered a lot of attention in the past few decades. NHCs are sensitive compounds that can degrade if exposed directly to air or moisture; therefore, small molecules can be used to hide, or 'mask', the NHC reactivity until heat or light is used to release the NHC catalyst at the desired time. Despite extensive work in this area, little is known about how changing the small molecule 'mask' can tune the exact conditions under which the NHC will release. The Lamb group will explore new mask structures that will be used to systematically study how changes in the mask will alter the catalytic behavior of the NHCs. The work has broad implications for designing new releasable catalysts, catalyst recycling, and polymer synthesis in the future. The project lies at the intersection of catalysis, polymer, and physical organic chemistry and thus will provide excellent interdisciplinary training and education to the supported graduate and undergraduate students. The Lamb group is composed of a diverse group of scientists who are actively engaged in outreach activities focused on recruiting and retaining underrepresented scholars in the STEM (science, technology, engineering and mathematics) fields.

Latent/switchable catalysis uses external stimuli to control when and where chemical reactions take place. N-Heterocyclic carbenes (NHCs) are powerful, tunable organocatalysts, but their sensitivity to air and moisture often necessitates the use of latent catalysis through the use of 'masked' NHCs. Current masked NHC systems are limited because the adduct bond strength is controlled by the structure of the NHC, leading to a trade-off between latency and activity of the catalyst. This project will investigate fundamental structure-property relationships that dictate NHC adduct bond stability and release by changing the mask, not the catalyst, structure. Specifically, the Lamb group will investigate carbodiimides and triarylboranes as modular mask scaffolds that can be activated using heat or light as the external stimulus. This work will apply physical organic techniques to understand and predict structure-property relationships first between mask structure and adduct stability then further correlate that stability to catalyst activity. The work will have societal impact in terms of education of undergraduate and graduate students – including students from underrepresented groups – publication of research that increases fundamental chemical knowledge, and through supporting Dr. Lamb's outreach activities focused on recruiting and retaining underrepresented scholars in chemistry.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.