Stable Meisenheimer Complexes as Powerful Photoreductants Readily Obtained from Aza-Hetero Aromatic Compounds

Area of Science:

• Organic Photochemistry
• Photoredox Catalysis
• Radical Chemistry

Background:

• Excited states of radical anions are potent reductants but often too short-lived for bimolecular reactions.
• Long-lived excited states of Meisenheimer complexes have emerged as effective species for reducing challenging organic substrates.

Purpose of the Study:

• To develop stable and accessible Meisenheimer complexes as powerful photoreductants.
• To investigate the photoreactivity of generated Meisenheimer complexes for synthetic applications.

Main Methods:

• Addition of n-butyllithium (nBuLi) to aromatic heterocycles to generate Meisenheimer complexes.
• Photophysical analyses and computational studies (DFT, TD-DFT) to determine redox potentials and excited-state properties.
• Experimental mechanistic investigations of photoreactions.

Main Results:

• Straightforward preparation of a family of powerful photoreductants with excited-state oxidation potentials below -3 V vs. SCE.
• Demonstrated ability to induce dehalogenation of electron-rich aryl chlorides.
• Facilitated C-C bond formation through radical cyclization reactions.
• Confirmed strong electron-donating ability under visible light irradiation.

Conclusions:

• The synthesized Meisenheimer complexes are potent, long-lived photoreductants suitable for visible-light-mediated organic transformations.
• These novel photoreductants offer a versatile platform for challenging dehalogenation and C-C bond-forming reactions.