Highly Reduced Alkali-Metal Nickelates: Synthesis, Structure, Catalytic Applications, and Alkali-Metal Effects

Area of Science:

• Organometallic Chemistry
• Nickel Catalysis
• Main Group Chemistry

Background:

• Low-valent nickel complexes (Ni(I) and Ni(0)) are crucial in cross-coupling and bond-forming reactions.
• Nickel's ability to access multiple oxidation states drives its catalytic versatility.
• Complexes with formally negative nickel oxidation states are rare and poorly understood.

Purpose of the Study:

• To synthesize and characterize a novel family of highly reduced alkali-metal nickelate complexes.
• To investigate the structure, electronic properties, and bonding of these electron-rich nickel systems.
• To explore the reactivity of these complexes in various transformations, including C-F activation and catalysis.

Main Methods:

• Synthesis of alkali-metal nickelate complexes using (E)-4,4-dimethylstilbene ligands.
• Characterization in solid-state (X-ray diffraction) and solution.
• Experimental charge density analysis for the lithium congener.
• Evaluation of reactivity in stoichiometric and catalytic reactions (C-F activation, coupling, hydrosilylation, isomerization).

Main Results:

• A novel family of alkali-metal nickelate complexes, [{(THF)xAM}2Ni(4-Mestb)y], was successfully synthesized across the alkali-metal series (Li to Cs).
• These complexes are highly electron-rich, with the lithium congener characterized by experimental charge density to reveal detailed bonding and electronic structure.
• The nickelate complexes demonstrated reactivity in C-F activation, reductive norbornene coupling, hydrosilylation, and alkene isomerization, outperforming some Ni(0) systems.

Conclusions:

• The study introduces a new class of highly reduced nickel complexes with significant alkali-metal influence.
• These nickelates offer unique bonding and electronic properties, expanding the known chemistry of low-valent nickel.
• The demonstrated reactivity highlights their potential as novel catalysts and reagents in organic synthesis.