Tipping the Balance between Concerted versus Sequential Proton-Coupled Electron Transfer

Area of Science:

• Catalysis
• Computational Chemistry
• Physical Chemistry

Background:

• Proton-coupled electron-transfer (PCET) is crucial in many chemical and biological processes.
• Understanding the interplay between concerted and sequential PCET mechanisms is key for catalyst development.

Purpose of the Study:

• To investigate the factors governing the competition between concerted and sequential PCET mechanisms in inorganic catalysts.
• To identify molecular features that control PCET reaction pathways.

Main Methods:

• Quantized molecular dynamics simulations of systems with over 1200 atoms.
• Analysis of reactive nonadiabatic PCET trajectories.
• Computation of concerted and sequential rate constants.

Main Results:

• A symmetric iron biimidazoline system strongly favors the concerted PCET mechanism due to ligand-mediated interactions and short proton-transfer distances.
• System-bath models suggest a mechanism crossover (concerted to sequential) is possible by altering solvent polarity or proton-transfer energy barriers.
• Varying ligand-mediated electron-proton interactions can also induce a crossover in PCET mechanisms.

Conclusions:

• Ligand-mediated electron-proton interactions and proton-transfer distance significantly influence PCET mechanism preference.
• Solvent polarity and intrinsic proton-transfer energy barriers are tunable parameters for controlling PCET pathways.
• Provides design principles for optimizing inorganic catalysts by controlling competing PCET mechanisms.