Mechanism And Electronic Perspective Of Oxygen Evolution Reactions Catalyzed By [Fe(Otf)(2)(Bpbp)]

We performed first-principles molecular dynamics simulations to study the process of water oxidation by the iron-based molecular catalyst [Fe(OTf)(2)(bpbp)] (OTf = triflouromethanesulfonate, bpbp = N,N'-bis(2-pyridylmethyI)-2,2'-bipyrrolidine) in an explicit water environment at 300 K temperature. Considering [Fe-v(bpbp)(OH)-(O)](+2) as the active catalytic species, we explored each step of the catalytic process. To begin with, we set up the simulation with one active catalytic intermediate, 191 water molecules, and one manganese ion as the electron acceptor. Prior to performing the metadynamics simulation, we equilibrated the system through both classical and quantum mechanical levels. Post that, we first computed the free energy of oxygen-oxygen bond formation using the metadynamic process by [Fe-v(bpbp)(OH)(O)](+2). We observed that the release of dioxygen took place in the successive steps of the formation of the peroxide and superoxide complexes. We then studied the regeneration of the Fe-v=O complex with three subsequent proton-coupled electron transfer (PCET) reactions. We computed the Lowdin and Mulliken spin moments for each step of the mechanism. We performed Wannier center analysis to get formal charges of the atoms involved in the PCET steps; this analysis confirmed the occurrence of electron transfer during the proton migration to the water molecule. The free-energy barrier obtained from the metadynamics process was used to calculate the redox potentials of these reactions. Comparing each step of the catalytic process, the oxygen-oxygen bond formation step was found to be the rate-determining step. The proton transfer to the cis-OH was identified as the rate-determining microkinetic step.