Energetic Effects of a Closed System Approach Including Explicit Proton and Electron Acceptors as Demonstrated by a Mononuclear Ruthenium Water Oxidation Catalyst

Abstract

When considering water oxidation catalysis theoretically, accounting for the transfer of protons and electrons from one catalytic intermediate to the next remains challenging: correction factors are usually employed to approximate the energetics of electron and proton transfer. Here these energetics were investigated using a closed system approach, which places the catalytic intermediate in a simulation box including proton and electron acceptors, as well as explicit solvent. As a proof of principle, the first two catalytic steps of the mononuclear ruthenium‐based water oxidation catalyst [Ru(cy)(bpy)(H2O)]2+ were examined using Car‐Parrinello Molecular Dynamics. This investigation shows that this approach offers added insight, not only into the free energy profile between two stable intermediates, but also into how the solvent environment impacts this dynamic evolution.

Proton Acceptor near the Active Site Lowers Dramatically the O–O Bond Formation Energy Barrier in Photocatalytic Water Splitting

“…These findings provide convincing evidence for a quite active intermediate with hydroperoxyl ligand after the O–O bond formation process as well as a considerably thermodynamically facile fourth water oxidation step (see eq , where H 5 O 2 + sol represents the hydrated excess proton complex). Interestingly, the barrier-less PT, usually considered as thermodynamically favorable after ET, proceeds spontaneously with no need for prior ET, emphasizing the possibility of rate enhancement in water oxidation catalysis by tuning solvent environment to allow prior or facilitated PT in the system. The analogy in the sequence of reaction steps predicted by the simulation after the photooxidation of the NDI (i.e., PCET followed by PT) and those observed in the oxygen-evolving complex of photosystem II after the third light flash leading to O 2 evolution is noteworthy …”

Modeling the Catalyst Activation Step in a Metal–Ligand Radical Mechanism Based Water Oxidation System

“…In this work, we use an ab-initio molecular dynamics approach (DFT-MD) with an explicit description of the aqueous solvent to model the catalyst activation step for this system. The importance of incorporating thermal fluctuations and explicit solvent in order to account for the role of the solvent environment has been shown in a number of previous studies on organometallic complexes [20][21][22][23][24] including those on water oxidation systems [25][26][27][28][29][30][31] We find that the solvent actively participates along the catalyst activation pathway via hydrogen bonding interactions resulting in a higher barrier for this pathway, when compared to a gas phase model that lacks such interactions.…”

Efficient workflow for the investigation of the catalytic cycle of water oxidation catalysts: Combining GFN‐xTB and density functional theory

“… 9 Dynamics and solvent effects should also be taken into account to simulate both water oxidation as well as the initial photooxidation of a dye‐WOC complex to obtain reliable insight in electron and hole transfer processes. 10 DFT‐based ab initio molecular dynamics coupled with enhanced sampling techniques have been employed quite successfully in determining reaction barriers for water oxidation processes with oxidized WOCs, 11 , 12 , 13 , 14 redox mediators 15 , 16 or photo‐oxidized dyes. 17 , 18 , 19 , 20 However, these simulations are computationally very demanding as they require a quantum mechanical description of the entire system, including explicit solvation, since the water solvent participates actively in the catalytic reaction.…”