Spectroscopically Deciphering the Formation and Reactivity of a High-Valent Ni(IV)Cl₂ Species

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• Nickel complexes with redox-active ligands are valuable in catalysis and materials science.
• Ni-(salen) complexes show spin localization but limit Ni-(IV) characterization.
• A pseudopeptide ligand is needed to stabilize high-valent nickel species.

Purpose of the Study:

• To develop a biologically relevant pseudopeptide-based nickel complex.
• To enable the formation and characterization of a high-valent Ni-(IV) species.
• To investigate the reactivity of the Ni-(IV) species in electron and oxygen atom transfer reactions.

Main Methods:

• Synthesis of a pseudopeptide-based Ni-(II) complex ([LNiII]).
• Oxidation to a high-valent Ni-(IV) species ([LNiIVCl2]) using ceric ammonium nitrate and chloride ions.
• Characterization using X-ray absorption spectroscopy.
• Study of electron transfer and oxygen atom transfer reactions with thioanisoles.
• Computational analysis of reaction mechanisms.

Main Results:

• Successfully synthesized and characterized a Ni-(II) precursor complex.
• Formed and trapped a high-valent Ni-(IV) species ([LNiIVCl2]) via oxidation.
• The Ni-(IV) species demonstrated electron transfer and oxygen atom transfer (OAT) reactions.
• Computational studies elucidated a stepwise oxidation mechanism involving single electron transfer followed by OAT.
• Reaction rates were sensitive to the electronic properties of thioanisole substituents.

Conclusions:

• A novel pseudopeptide ligand facilitates the formation of a stable high-valent Ni-(IV) species.
• The Ni-(IV) complex is reactive towards thioanisoles, proceeding via a distinct electron transfer and OAT pathway.
• This work expands the scope of high-valent nickel chemistry and its potential applications in catalysis.