Water oxidation produces protons that can be reduced for use as a source of clean and renewable carbon-free fuel. Ruthenium complexes can be effective water oxidation catalysts but are too costly for large-scale application. Iron displays similarities to ruthenium and is much more abundant but has not been shown to be effective as a catalyst following the water oxidation mechanism suggested for ruthenium. Accordingly, we employ density functional theory (DFT) calculations of eleven mononuclear ruthenium catalysts and compare these with analogous iron catalysts to investigate the energetic bottlenecks along the water oxidation mechanism. Using insights from these results, four novel catalysts with varying electron-donating and electron-withdrawing character are proposed and characterized. The bond length of the axial ligand was monitored along the reaction mechanism to qualitatively determine the stability of the catalyst. In the final mechanistic step, where O2 is released and replaced by water, intermolecular characterization was performed to determine the most stable coordination of the O2 along with appropriate spin assignment for the catalyst complex. Our results suggest that modification of the ligands subtly influences the intramolecular features of the catalyst and catalyst stability. Additionally, the novel catalysts display kinetic and thermodynamic performance similar to ruthenium catalysts. With appropriate ligand design, our results suggest that mononuclear iron catalysts designed with a bidentate and a tridentate ligand may serve as successful water oxidation catalysts.

Effect of ligand chemistry in mononuclear metal catalysts on the intramolecular features of the water oxidation mechanism

253rd National Meeting (2017)

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