Tunable and Practical Homogeneous Organic Reductants for Cross-Electrophile Coupling

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Catalysis

Background:

• Homogeneous reductants are crucial for metal-mediated reductive transformations like cross-electrophile coupling (XEC).
• Existing reductants often suffer from poor air stability and limited tunability, hindering their widespread application.
• There is a need for robust and versatile reductants that enable milder reaction conditions and broader substrate scope.

Purpose of the Study:

• To synthesize and characterize novel, air-stable, homogeneous organic reductants based on a tetraaminoethylene scaffold.
• To evaluate the efficacy of these new reductants in facilitating challenging Ni-catalyzed C(sp2)-C(sp3) cross-electrophile coupling reactions.
• To develop a new strategy for controlled alkyl radical generation by tuning reductant redox potentials.

Main Methods:

• Synthesis of four new tetraaminoethylene-based organic reductants with tunable redox potentials.
• Assessment of air stability and reduction potentials (vs. ferrocene) of the synthesized reductants.
• Application of the reductants in Ni-catalyzed C(sp2)-C(sp3) cross-electrophile coupling reactions involving Katritzky salts and aryl halides.

Main Results:

• The new reductants exhibit enhanced air stability, with one being indefinitely stable in air (-0.85 V vs. Fc).
• All synthesized reductants effectively promote Ni-catalyzed C(sp2)-C(sp3) XEC reactions, even with complex substrates.
• A novel method for controlled alkyl radical generation was demonstrated by tuning reductant and Katritzky salt redox potentials, enabling challenging XEC transformations.

Conclusions:

• The developed tetraaminoethylene-based reductants offer a stable and tunable alternative to conventional homogeneous reductants.
• These reductants facilitate milder and more controlled Ni-catalyzed reductive transformations, including C(sp2)-C(sp3) XEC.
• The tunability of these reductants opens avenues for developing new synthetic methodologies and expanding the scope of reductive coupling reactions.