Exploring Structure-Activity Relationships in Molecular Catalysts for C-H Bond Oxidation and CO2 Reduction

Value-added chemicals can be generated by the functionalization of hydrocarbon substrates by C-H bond oxidation and by the reduction of carbon dioxide (CO2), where each of these processes require long-lived catalysts that are selective and efficient. Chemical feedstocks such as petroleum-derived hydrocarbons and carbon dioxide are inexpensive and readily accessible but are challenging to transform into more valuable compounds. The oxidative functionalization of unactivated C-H bonds is a difficult task because they are, in general, thermodynamically stable and kinetically inert. Bioinspired iron-oxo catalysts have shown great promise in this area, but often have limited activity, selectivity, and/or stability. In this context, two iron catalysts have been designed and developed employing preorganized polypyridyl ligands to address these limitations. Both catalysts proved themselves to maintain the beneficial characteristics seen in their mononuclear precursors while also demonstrating new reactivity with environmentally benign oxidants. Likewise, the catalytic conversion of CO2 into reduced forms of carbon is an important strategy for accessing renewable fuels and certain commodity chemicals while mitigating the environmental impact of greenhouse gas emissions. Here, a redox active pentadentate ligand featuring intramolecular hydrogen-bond donors has been developed to facilitate selective CO2 reduction into carbon monoxide and formic acid in the presence of water as a proton source. This catalyst demonstrated high selectivity, but poor stability under electrochemical conditions; however, under photochemical conditions newfound product selectivity and activity was observed. Indeed, the application of molecular catalysts for C-H bond oxidation and CO2 reduction holds great promise for processing abundant chemical feedstocks to produce more valuable or energy-rich chemicals