Ligand Cooperative Iridium PCP Complexes for Small Molecule Activation

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Simple small molecules are perhaps the most fundamental components to synthetic chemistry, acting as the building blocks from which larger, more complex compounds are made. These simple molecules are also important in of themselves, sometimes as fuels, greenhouse gases, the water we drink, or the air we breathe. Studying the way in which these molecules behave and react is therefore of great importance. Organometallic chemistry has had considerable success in using transition metal complexes to manipulate small molecules and perform otherwise difficult transformations such as the splitting of water into H2 and O2 or the decomposition of harmful emissions such as CO2 or N2O. This thesis presents the synthesis of a new PCP pincer ligand framework bearing benzo[b]thiophene linking groups as an alternative to the parent ortho-phenylene linkers. This ligand was installed onto an iridium center via double C-H activation at the central carbon atom, resulting in a carbene donor which can be used in favorable metal-ligand cooperative processes. This design feature was used for the activation of N2O, where a series of “iridaepoxide” complexes were made through oxygen atom transfer to the iridium-carbon bond with the release of N2 gas. The formal hydrogenation of N2O to H2O was accomplished by reaction of the iridaepoxide species with H2. The mechanistic details of these processes were studied extensively and reveal a unique ligand cooperative system. Halide abstraction from several neutral iridium complexes was then performed to explore the reactivity of their cationic counterparts. This allowed for the use of milder conditions in previous reactions and for the formation of highly reactive species capable of numerous bond activations including the strong O-H bonds of water and alcohols.
Doyle, L. E. (2017). Ligand Cooperative Iridium PCP Complexes for Small Molecule Activation (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/26761