Elucidating electron-transfer events in polypyridine nickel complexes for reductive coupling reactions

Area of Science:

• Organometallic Chemistry
• Catalysis
• Nickel Complexes

Background:

• Polypyridine-ligated nickel complexes are vital catalysts in cross-coupling reactions.
• Their catalytic activity is linked to oxidation state changes and electron transfer, but mechanisms remain unclear.

Purpose of the Study:

• Investigate the electron-transfer reactivity of pseudohalide- and halide-ligated Ni(II) complexes.
• Understand the mechanistic basis for differences in catalytic activity.

Main Methods:

• Studied Ni(II) complexes with polypyridine ligands and either halide or pseudohalide ligands.
• Employed electrochemical techniques and quantum mechanical calculations.
• Examined the effect of exogenous salts on catalyst activity.

Main Results:

• Ni(II) halide complexes readily undergo comproportionation with Ni(0) to form Ni(I) species.
• Ni(II) pseudohalide complexes resist electron transfer, and their Ni(I) forms are prone to disproportionation.
• Catalytically inactive Ni(II) pseudohalide complexes can be reactivated with exogenous salts.

Conclusions:

• Provides mechanistic rationalizations for fundamental steps in nickel-catalyzed cross-coupling.
• Highlights the distinct roles of halide and pseudohalide ligands in nickel catalyst electron transfer.
• Offers guidance for designing improved nickel catalysts for cross-coupling reactions.