Mechanistic Investigations on Group 14 Cation Radical Reactions

University Of Rochester, Rochester NY

Investigators

Abstract

With the support of the Organic and Macromolecular Chemistry Program, Professor Joseph Dinnocenzo's proposed research will provide fundamental mechanistic insight into the structures, reactivities, and reaction mechanisms of group 14 cation radical intermediates. This knowledge will establish a foundation for understanding experimental observations. The research will also provide the predictive power needed to successfully utilize ion radicals for new chemical processes in synthesis and in materials applications. The proposal has four primary research goals: (1)Generate reactive cation radicals of organo-silanes, -germanes, -stannanes, and plumbanes, and use nanosecond and picosecond transient absorption techniques to elucidate the mechanism(s) for their reactions with nucleophiles. For nucleophile assisted mechanisms they will apply additional tests, recently developed in the PI's laboratory, to distinguish between concerted and stepwise pathways. (2)Determine the stereochemical course of nucleophilic substitutions on Group 14 cation radicals using the endocyclic restriction test. (3)Perform critical mechanistic experiments to test recent molecular orbital calculations in their laboratory that predict reversible nucleophilic substitutions for some organosilane cation radical/nucleophile pairs. If confirmed, the chemistry may lead to a new experimental method for generating cation radical intermediates. (4)Investigate the fragmentation mechanisms of oligosilane cation radicals as models for polysilane cation radicals, which have been proposed as reactive intermediates produced during the photolysis of polysilane photoresists. Broader Impacts. Organic ion radical chemistry is still in its infancy in comparison with that of a variety of other reactive intermediates (e.g. carbocations, carbanions, free radicals, and carbenes). There remains a great deal to learn about ion radical chemistry and its potential applications (e.g. in synthetic and materials chemistry). History has shown that progress toward such practical goals is facilitated and accelerated by mechanistic understanding. One of the goals of this proposal is to provide such understanding. The proposed research will also provide an usually rich educational experience for students. For example, in addition to learning mechanistic methodologies, students will learn how to synthesize, purify, and spectroscopically characterize compounds. Students will also receive training in a range of less traditional techniques (transient absorption spectroscopy, time resolved single photon counting, electrochemistry, and modern computational chemistry. This proposal will also benefit undergraduate students and high school teachers through the NSF REU RET summer program at the University of Rochester. Over the past 10 years, the PI has, on average, hosted 2 summer visitors/year through this program. Nearly half of these visitors have been from groups underrepresented in science and engineering. Summer visitors learn through research and through a summer minicourse on photoinduced charge transfer co-taught by the PI.