Executive Summary : | Sustainable catalytic oxygenation of organic substrates using environmentally benign oxidants require appropriately designed catalysts. Taking inspiration from versatile oxidation reactions catalyzed by dioxygen-utilizing iron enzymes where such reactions take place with unparallel selectivity and efficiency, extensive attempts have been made to develop iron-based synthetic catalysts employing reduced oxygen species. Some of the synthetic systems display moderate to good selectivity, but most of these systems are not efficient enough for practical applications. Free radical autooxidation, undesired side products, unproductive decay, quenching of active oxidants and catalyst degradation limit the efficiency and selectivity in oxidation/oxygenation reactions. Improvements in these iron catalysts require systematic evaluation of stereoelectronic, thermodynamic and kinetic parameters influencing their efficiencies in oxidation catalysts. The specific objective of this project is to have precise synthetic control of the catalyst properties for designing robust systems to perform dioxygen/peroxide-dependent selective oxidations. Toward these objectives, the steric and electronic properties in the primary and secondary coordination sphere of synthetic complexes will be coupled in a highly regulated manner. Such regulations in combination with appropriate catalytic additives would help in selective and controlled electron transfer in redox reactions during the catalytic cycle. For that purpose, rationally designed ligands involving built-in functional groups for providing electrons in dioxygen reduction on iron center will be utilized. In peroxide-dependent oxidations, the generation of high-valent iron-oxo oxidants without involving free radicals would be an efficient strategy for selective catalytic oxidation. In this strategy, iron complexes of ligands bearing functional groups for suitable steric, electronic and secondary interactions will be exploited. Furthermore, mechanistic investigations of the decay pathways of iron-oxo complexes will be performed to gain insights into the systems for further improvement through stereoelectronic tuning and catalytic additives. An in-depth understanding of these properties and subsequent tuning of iron-oxygen intermediates would no doubt explore their highly oxidizing power and selectivity to address synthetic challenges. |