Inspiration, Frustration, and Fascination: An Excursion into Low-Oxidation State Main Group Chemistry

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A catalyst is a substance that speeds or otherwise facilitates a chemical reaction. Catalysts are critical to the chemical and pharmaceutical industries, where they are used to reduce energy requirements of chemical processes and to guide the details of precise chemical transformations. Many of the most active catalysts are based on expensive, rare metals. An important area of current research is to find cheap, abundant replacements for the current metal catalysts. Dr. Gregory H. Robinson, Chemistry Department, the University of Georgia, is supported by the Chemical Synthesis Program of the Chemistry Division to make and study highly reactive chemical compounds containing abundant elements including silicon and aluminum. The approach uses radical chemistry. Most chemical compounds contain an even number of electrons, while radicals contain an odd number. This gives the radical compounds the ability to stabilize metals with unusual electrical charges; Specifically, it permits silicon, aluminum, or other abundant elements to mimic the behavior of the rare, expensive metals that are currently used in catalysts. Chemistry students engaged in this work acquire valuable skills to permit them to enter the technologically sophisticated workforce. Professor Robinson is committed to presenting chemistry (and science in general) to a broad range of students. His presentations include visits to troubled high schools to talk to the students about careers in chemistry/science. He is a unique role model for individuals from underrepresented groups and has mentored a number of students who have gone on to positions in academia and industry. This project utilizes N-heterocyclic carbenes (NHCs) and anionic dithiolene radical ligands to form and stabilize unusual main group species. Group 13 element containing dithiolene radicals are obtained from the reactions of lithium dithiolene radicals with XER2 (X=halide, E = group 13 element, R). These combined with NHCs give radicals where the unpaired electron is primarily associated with the main group atom. NHCs together with the dithiolene radical ligands are used to form species containing E-O or E=O bonds (E = main group element, O = oxygen). Reactions of NHC stabilized chlorosilanes and phosphines give S-heterocyclic silylenes and phospheniums, which is then extended to species containing E-E bonds. These compounds are characterized by the usual chemical and physical methods. This project allows the study of the largely unexplored synthetic and structural chemistry of low-oxidation state, earth-abundant chemical elements at the carbene-dithiolene radical interface. The project also contains an outreach/mentoring component that targets a range of students from underrepresented groups.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.