Mechanism and Electronic Perspective of Oxygen Evolution Reactions Catalyzed by [Fe(OTf)₂(bpbp)]

Abstract

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-pyridylmethyl)-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 ratedetermining step. The proton transfer to the cis-OH was identified as the rate-determining microkinetic step.

Mechanistic Insights into Cobalt-Based Water Oxidation Catalysis by DFT-Based Molecular Dynamics Simulations

“…We reported the effect of water molecules on the water oxidation process in our earlier studies. 40,41 Luber and co-workers 73 also explained the difference between the static and explicit models on the reaction process. The main differences in the free energies are the solvation free energies.…”

“…These dynamic simulations were carried out at the PBE level of DFT with the Grimme-D2 dispersion correction . At the PBE-D2 level, , we find the water density of 1.00 gm cm –3 . These calculations were performed with a double-valence polarizable basis set, and Goedecker–Teter–Hutter pseudopotentials were employed for the core electrons.…”

“…After forming the oxygen–oxygen bond, further oxidation and deprotonation through PCET occur before the release of the oxygen molecule. Computational studies based on the density functional theory (DFT) − and molecular dynamics − provided the relevant mechanistic details of the reactions at the atomic level and the catalyst’s structural and electronic nature.…”

Non-heme oxoiron complexes as active intermediates in the water oxidation process with hydrogen/oxygen atom transfer reactions

“…Density functional theory (DFT) is one of the efficient tools of the computational method [36][37][38] for mechanistic studies. DFT [39][40][41][42][43] and DFT-based molecular dynamics methods [44][45][46] were widely applied to understand the water oxidation process's mechanism and thermodynamics. In the water oxidation process catalyzed by iron complexes, the iron (V)-oxo entities 47,48 are the critical intermediates that are involved in the O-O bond formation.…”

Catalytic Mechanism of Competing Proton Transfer Events from Water and Acetic Acid by [CoII(bpbH2)Cl2] for Water Splitting Processes

“…In the water reduction process, the successive addition of the proton and electron to the metal center happens by forming the hydrogen–hydrogen bond before the liberation of the hydrogen molecule. Computational studies based on first principles calculations − and molecular dynamics − can help in understanding the appropriate mechanistic insights and atomistic details of the catalytic process. The proton reduction process catalyzed by the metal complexes primarily happens by forming the metal hydride intermediate.…”