Coordinatively Unsaturated Nickel Nitroxyl Complex: Structure, Physicochemical Properties, and Reactivity toward...

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Bioinorganic Chemistry

Background:

• Nitrogen monoxide (NO) is a redox-active ligand crucial in biological systems and coordination chemistry.
• Metal-NO complexes exhibit complex electronic structures requiring detailed spectroscopic and theoretical analysis.
• Sterically hindered ligands can stabilize metal-NO complexes against oxidation.

Purpose of the Study:

• To investigate the dioxygen reactivity of a new, less hindered nickel-nitrosyl complex, [Ni(NO)(I)(L1″)].
• To compare its reactivity to a previously reported sterically protected nickel-nitrosyl complex.
• To elucidate the electronic structure and reaction products of the new complex.

Main Methods:

• Synthesis and characterization of the [Ni(NO)(I)(L1″)] complex.
• X-ray crystallography for structural determination.
• Infrared (IR) and UV-Vis spectroscopy for electronic and vibrational analysis.
• Theoretical calculations to understand electronic structure.
• Reaction studies with dioxygen (O2).

Main Results:

• The new complex features a high-spin nickel(II) center coordinated to a nitrosyl (NO-) ligand, similar to the hindered analogue.
• Unlike the stable hindered complex, [Ni(NO)(I)(L1″)] reacts with O2.
• The reaction yields oxidized products, including nitrite (NO2-) and triiodide (I3-), indicating oxidation of both NO- and the iodide ligand.

Conclusions:

• The coordinatively unsaturated environment created by the less hindered ligand in [Ni(NO)(I)(L1″)] facilitates dioxygen reactivity.
• The complex undergoes oxidative degradation upon exposure to O2, leading to the formation of nitrite and triiodide.
• Ligand steric hindrance plays a critical role in the stability and reactivity of nickel-nitrosyl complexes towards dioxygen.