Alkyl Radical Coupling with Phenoxy(imine)-Nickel(II)-Aryl Complexes: Evidence for a Multistep Process in C-C Bond...

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Synthetic Organic Chemistry

Background:

• Carbon-carbon (C-C) bond formation is fundamental in organic synthesis.
• Nickel-catalyzed reactions offer versatile pathways for C-C coupling.
• Generating and controlling alkyl radicals is crucial for selective bond formation.

Purpose of the Study:

• To investigate the reaction of phenoxy(imine)-nickel(II)-aryl complexes with alkyl radicals for C-C bond formation.
• To identify selective reagents for alkyl radical generation.
• To elucidate the mechanism of radical capture and C-C bond formation by nickel complexes.

Main Methods:

• Utilized a 4-dimethylaminopyridine-titanium tris(anilide) complex for selective halogen-atom abstraction.
• Employed radical clock and competition experiments to study ligand effects.
• Performed 12C/13C kinetic isotope effect measurements and computational studies.
• Detected transient nickel(III) complexes using electron paramagnetic resonance (EPR) spectroscopy.

Main Results:

• A selective method for generating alkyl radicals from unactivated alkyl halides was developed.
• Ligand effects on phenoxy(imine) and nickel-aryl complexes in radical capture were elucidated.
• Evidence for a multistep C-C bond formation process was obtained through radical clock experiments.
• Transient nickel(III) intermediates were observed and intercepted, confirming their role in C-C bond formation.

Conclusions:

• The study established a novel route for C-C bond formation involving nickel complexes and alkyl radicals.
• A multistep mechanism, including the intermediacy of nickel(III) species, was supported by experimental and computational data.
• This work provides valuable insights into ligand design for controlling reactivity in radical-mediated coupling reactions.