Nonclassical Oxidation Reactions

University Of Notre Dame, Notre Dame IN

Investigators

Abstract

In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor Seth Brown of the University of Notre Dame is developing new types of catalysts to utilize oxygen to make new compounds and to remove hydrogen from existing compounds. Catalysts are compounds that accelerate and direct reactions toward desirable products without themselves being consumed. Many catalysts contain a metal atom and surrounding organic compounds bound to it, called ligands, and in most catalysts the reaction chemistry occurs on the metal atom. Professor Brown is studying ways in which to make the ligand participate in the catalysis along with the metal atom or to perform all of the catalysis itself. The structural features of the catalysts and the mechanisms through which the chemical bonds are made or broken are being studied, and this information is being used to design new ligands that should perform better catalysis. Because catalysis accounts for processes that total one third of the global gross domestic product and a majority of the commercial chemical products and chemical processes, the discovery of new or improved catalysts for organic reactions can have a great impact on economic development and growth. The research team investigating these issues includes high school students, undergraduate students, and graduate students, with the aim of developing their technical and intellectual skills to prepare them appropriately for further training and careers in science or engineering. Professor Brown is preparing new multidentate redox-active ligands to create environments where "nonclassical" redox reactions can take place. One target is oxygen atom transfer or dioxygen activation in which bonds to oxygen will be formed at the metal center, but redox events will take place at the ligands. A key design element is the use of high coordination numbers, which may stabilize small bite angle intermediates such as peroxo complexes and allow the assembly of enough ligands around the metal to marshal up to four electrons at a single site. A second class of reactions being explored is based on concerted, purely ligand-centered 1,2-dehydrogenations of substrates. These can be carried out even by coordinatively saturated metal complexes, which may lead to greater catalyst lifetimes. The scope of such reactions, and the possibility that orbital symmetry constraints will steer the selectivity of such reactions, are being explored. Novel catalysis mechanisms often open up new selectivity pathways, and understanding what electronic and structural features make the reactions more efficient may lead to improved catalysts with impact in the use or production of chemicals and chemical fuels. A series of educational materials are being developed to help bring introductory students up to speed on practical approaches to chemical kinetics, allowing students to be intellectually engaged with the work at an early stage in their studies.