Probing the Oxidative Addition Transition State in Nickel Metallaphotoredox Catalysis Using Intramolecular ¹³C...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Photoredox Catalysis

Background:

• Nickel catalysis combined with photoredox methods offers mild conditions for C-C and C-X bond formation.
• Understanding the nickel species in the oxidative addition step is crucial for elucidating reaction mechanisms.
• Kinetic isotope effects (KIEs) and DFT analysis provide quantitative insights into metal oxidation states and ligand environments.

Purpose of the Study:

• To investigate the oxidative addition step in two distinct nickel metallaphotoredox-catalyzed reactions.
• To determine the active nickel species and their ligand environments during catalysis.
• To elucidate the operational catalytic cycles for C(sp²)-C(sp³) cross-coupling and amine arylation.

Main Methods:

• Application of intramolecular ¹³C kinetic isotope effects (KIEs).
• Computational analysis using Density Functional Theory (DFT).
• Evaluation of nickel-catalyzed C(sp²)-C(sp³) cross-coupling and amine arylation reactions.

Main Results:

• For NiCl₂(dtbbpy)(H₂O)₄ catalyzed N-methyl selective arylation, a Ni(I) complex is the likely species in oxidative addition, with a Ni(0) mechanism also identified.
• For Ni(THMD)₂ catalyzed deaminative arylation, an anionic Ni(I) complex is implicated in oxidative addition, explaining rate acceleration with chloride additives.
• Intramolecular ¹³C KIEs effectively probe mechanistic questions in nickel metallaphotoredox catalysis.

Conclusions:

• The study successfully identified key nickel species involved in oxidative addition for two different catalytic systems.
• The findings provide a deeper mechanistic understanding of nickel metallaphotoredox-catalyzed reactions.
• Intramolecular ¹³C KIEs are demonstrated as a powerful tool for mechanistic investigations in this field.