Oxygen reactivity of a nickel(II)-polyoximate complex

Area of Science:

• Coordination Chemistry
• Bioinorganic Chemistry
• Organometallic Chemistry

Background:

• Nickel complexes are crucial in catalysis and biological systems.
• Understanding nickel's redox behavior is key to designing new catalysts.
• The ligand tris(2-hydroxyiminopropyl)amine (Ox(3)H(3)) offers versatile coordination modes.

Purpose of the Study:

• To investigate the coordination chemistry of nickel(II) with tris(2-hydroxyiminopropyl)amine (Ox(3)H(3)) across different protonation states.
• To characterize the structural, electrochemical, and reactive properties of these nickel complexes.
• To explore the interaction of a deprotonated nickel complex with molecular oxygen and its catalytic potential.

Main Methods:

• X-ray crystallography to determine complex structures.
• Electrochemical studies (cyclic voltammetry) to assess oxidation potentials.
• Spectroscopic techniques (EPR) to investigate electronic properties.
• Reactivity studies with molecular oxygen and substrates like triphenylphosphine.

Main Results:

• The neutral nickel complex exhibits pseudo-octahedral geometry.
• A mono-deprotonated nickel complex forms a dimer with bridging oximate groups.
• The fully deprotonated complex shows low Ni(II) oxidation potentials and reacts with O(2) to form a Ni(III) species.
• The Ni(II)/O(2) system effectively oxidizes triphenylphosphine to its oxide.

Conclusions:

• The protonation state of Ox(3)H(3) significantly influences the structure and properties of nickel complexes.
• The fully deprotonated nickel complex displays interesting redox activity and reactivity towards O(2).
• This nickel-oxygen system demonstrates potential for catalytic oxidation reactions.