Unraveling the Role of the Nitrate Ion and Solvent Water on the O―O Bond Formation Step in Fe―TAML Catalyzed Water Oxidation

Density functional theory-based molecular dynamics (DFT-MD) combined with an explicit solvation model were employed to further elucidate the O─O bond formation step in Fe─TAML catalyzed water oxidation reaction. The water nucleophilic attack (WNA) and nitrate nucleophilic attack (NNA) on the oxo group of the high-valent [TAML^+•─Fe⁵⁺═O] species were calculated to have comparable active barriers (24 kcal/mol versus 22 kcal/mol). This suggests nitrate ion can behave as a cocatalyst to promote the O─O bond formation. More importantly, a crucial role of the presence and thermal motion of solvent water in the NNA process was observed. This was quantified by an increase of the activation energy barrier by 4 kcal/mol, determined by comparing the explicit solvent DFT-MD simulation with implicit solvent static DFT calculation.