Rate-Driving Force Relationships in the Multisite Proton-Coupled Electron Transfer Activation of Ketones

Area of Science:

• Photochemistry
• Organic Chemistry
• Physical Chemistry

Background:

• Excited-state iridium complexes are crucial electron donors.
• Aryl ketones undergo activation via proton-coupled electron transfer (PCET).
• Understanding the kinetics of multisite PCET (MS-PCET) is vital for synthetic applications.

Purpose of the Study:

• To kinetically investigate the MS-PCET activation of aryl ketones.
• To develop a method for extracting hydrogen-bonding and PCET rate constants.
• To explore the relationship between PCET rates and reaction driving forces.

Main Methods:

• Detailed kinetic studies using Ir(III)-based photocatalysts.
• Luminescence quenching experiments to probe electron transfer.
• Deconvolution of data to determine equilibrium and rate constants.

Main Results:

• MS-PCET activation of aryl ketones proceeds via a concerted mechanism.
• A linear correlation was observed between PCET rates and driving forces.
• Deviations from Marcus theory suggest non-perfect synchronization effects.

Conclusions:

• The concerted nature of MS-PCET was confirmed.
• Non-perfect synchronization provides a rationale for observed rate-driving force deviations.
• Findings have implications for designing efficient organic synthesis pathways using MS-PCET.