Nickel-catalyzed intermolecular oxidative Heck arylation driven by transfer hydrogenation

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Conventional palladium-catalyzed oxidative Heck reactions often lead to C=C bond isomerization.
• These reactions typically require external oxidants and involve a Pd^II/Pd⁰/Pd^II catalytic cycle.
• Controlling regioselectivity and pathway selectivity in alkene arylation remains a challenge.

Purpose of the Study:

• To develop a directed nickel-catalyzed alkene arylation with tunable regioselectivity and pathway selectivity.
• To establish a Ni(0)-catalyzed oxidative Heck reaction that overcomes limitations of traditional methods.
• To investigate the mechanistic aspects governing selectivity and catalytic turnover.

Main Methods:

• Optimization of phosphine ligands and directing groups to tune the nickel catalyst's coordination environment.
• Development of a Ni(0)-catalyzed oxidative Heck arylation utilizing transfer hydrogenation of an acceptor olefin.
• Mechanistic investigations including computational studies to elucidate reaction pathways.

Main Results:

• Achieved controlled regioselectivity (γ-selectivity vs. δ-selectivity) and pathway selectivity (hydroarylation vs. oxidative Heck coupling).
• Developed a Ni(0)-catalyzed oxidative Heck arylation with excellent E/Z selectivity and regioselectivity.
• Demonstrated that acceptor olefin addition is crucial for carbometalation and catalytic turnover.

Conclusions:

• Judicious tuning of the nickel catalyst's coordination sphere enables precise control over directed alkene arylation.
• The developed Ni(0)-catalyzed oxidative Heck reaction offers a selective and efficient alternative to conventional methods.
• Understanding the role of acceptor olefins provides insights for designing future catalytic systems.