The Activation of Dioxygen with Biomimetic Iron Complexes: Structures, Spectroscopy, Intermediates, and Mechanis
Small molecule activation by transition metal centers is at the heart of chemistry and biology. Some of the most important and difficult challenges facing humanity include disease, energy transduction and storage, and environmental sustainability, and in all of these areas small molecules (e.g. O2, N2, CO2, NO, H2S, CH4) and their redox transformations, mediated by transition metal centers, play an essential role. Nature has devised a remarkable tool box containing metalloenzymes to carry out these transformations, and our laboratory is interested in extracting the principles by which these enzymes operate, and then employing these principles to build functioning, synthetic systems for small molecule activation. This talk will focus on our recent efforts to construct heme and nonheme metal complexes for the activation of O2, and the examination of downstream intermediates following that activation. In one example, a heme-related, sterically bulky iron(II) corrole complex is shown to bind and activate O2 to give an iron(III)-superoxo complex, which reacts with H-atom transfer and indole substrates. In other efforts, we have shown that a well-defined, nonheme iron(II) complex can activate a single molecule of O2 to give iron-peroxo, -oxo, and -hydroxo intermediates. In a different, sulfur-ligated Fe complex, we have found that 2nd-coordination sphere hydrogen bonds are critical to capturing a “side-on” bound superoxide derived from iron(II)/O2, and which converts to sulfur-oxygenated products. These studies have led to structure/function information relevant to nonheme iron oxygenases, including the thiol dioxygenases. With time remaining, a series of nonheme, cis-ligated (FeIII(OH)(X) (e.g. X = halide, thiolate) complexes will be described that exhibit preferential reactivity in radical transfer (or “rebound”) reactions with carbon radicals. Radical transfer reactions are fundamental to the functioning of nonheme iron halogenases as well as related transition metal catalysts.
Hosted by Professor Marke Lipke