Light-Driven Hydrodefluorination of Electron-Rich Aryl Fluorides by an Anionic Rhodium-Gallium Photoredox Catalyst

Area of Science:

• Organometallic Chemistry
• Photocatalysis
• Fluorine Chemistry

Background:

• Carbon-fluorine (C-F) bonds are strong and challenging to activate, limiting synthetic transformations.
• Developing efficient catalytic methods for C-F bond hydrodefluorination is crucial for organic synthesis.
• Photoinduced single-electron transfer (SET) offers a promising pathway for activating stable bonds.

Purpose of the Study:

• To develop a novel catalytic system for the hydrodefluorination of challenging C-F bonds.
• To elucidate the mechanism of photocatalytic C-F bond activation mediated by an anionic Rh-Ga complex.
• To investigate the role of bimetallic excitation and SET in the catalytic cycle.

Main Methods:

• Photocatalysis using an anionic Rh-Ga complex under violet light irradiation.
• Stoichiometric reactions, control experiments, and deuterium-labeling studies.
• Theoretical calculations (DFT) to understand the electronic structure and excitation.
• Electron paramagnetic resonance (EPR) spectroscopy to detect reaction intermediates.

Main Results:

• Successful hydrodefluorination of electron-rich aryl fluorides and trifluoromethylarenes.
• Demonstrated photoinduced single-electron transfer (SET) mediated by the excited anionic Rh-Ga complex.
• Detection of a neutral Rh(0) intermediate via EPR spectroscopy, consistent with theoretical predictions.
• Evidence for aryl radical generation and subsequent hydrogen-atom abstraction from the solvent.

Conclusions:

• An unconventional bimetallic excitation mechanism enables the activation of strong C-F bonds.
• The Rh-Ga complex acts as a photocatalyst, utilizing H2 and base as terminal reductants.
• This work provides a new strategy for C-F bond functionalization via photoredox catalysis.