Unlocking CO₂ Activation With a Novel Ni-Hg-Ni Trinuclear Complex

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Catalysis

Background:

• Compounds containing bonds between mercury and transition metals exhibit unique bonding and reactivity profiles.
• The exploration of mercury-transition metal complexes is crucial for understanding fundamental chemical principles and developing new catalytic systems.

Purpose of the Study:

• To synthesize and characterize a novel trinuclear nickel-mercury compound, [(POCOP)Ni]2Hg ([Ni2Hg]).
• To investigate the reactivity of [Ni2Hg] with carbon dioxide (CO2) and related species.
• To elucidate the mechanism of CO2 transformation and explore its potential for catalytic applications.

Main Methods:

• Synthesis of the trinuclear nickel-mercury complex [Ni2Hg] using a POCOP ligand.
• Reaction of [Ni2Hg] with CO2 to form a carbonate-bridged complex [Ni2CO3].
• Investigation of the interconversion between [Ni2CO3] and its CO2 analogue [Ni2CO2] using CO gas.
• Mechanistic studies involving CO2 insertion and decarbonylation steps.
• Reductive regeneration of [Ni2Hg] using sodium amalgam (Na/Hg) to assess catalytic potential.

Main Results:

• Successful synthesis of the novel trinuclear compound [Ni2Hg] with a Ni-Hg-Ni core.
• Observation of [Ni2Hg] reacting with CO2 to yield the carbonate complex [Ni2CO3].
• Demonstration of reversible interconversion between [Ni2CO3] and a μ-CO2 analogue [Ni2CO2], indicating CO2 disproportionation.
• Elucidation of a three-step mechanism for CO2 transformation, involving CO2 insertion and decarbonylation.
• Regeneration of the starting material [Ni2Hg] from [Ni2CO3] using a reductant, suggesting catalytic CO2 deoxygenation.

Conclusions:

• The synthesized [Ni2Hg] complex facilitates the reductive disproportionation of CO2 into carbonate and carbon monoxide.
• The observed reversible interconversion and catalytic regeneration highlight the potential of this system for CO2 utilization.
• This study provides valuable insights into the reactivity of mercury-transition metal complexes and their role in CO2 transformation.