Controlled Redox Chemistry at Cerium within a Tripodal Nitroxide Ligand Framework

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Cerium Redox Chemistry

Background:

• Ligand structure significantly influences metal redox behavior.
• Tetravalent cerium complexes are often highly reactive and difficult to isolate.
• Developing controlled synthetic routes for cerium compounds is crucial for catalysis and materials science.

Purpose of the Study:

• To synthesize and characterize novel tetravalent cerium complexes using a tripodal nitroxide ligand.
• To investigate the impact of ligand design on cerium redox chemistry.
• To explore the solution behavior and electronic properties of these unique cerium complexes.

Main Methods:

• Synthesis of tethered, tripodal, trianionic nitroxide ligand (TriNOx).
• Isolation and characterization of cationic and halide complexes of tetravalent cerium.
• Solution-phase electrochemistry and 1H NMR spectroscopy.
• Density Functional Theory (DFT) calculations.

Main Results:

• Successful synthesis of rare cationic tetravalent cerium complexes, including [Ce(TriNOx)thf][BAr(F)4] and [Ce(TriNOx)py][OTf].
• Formation of a complete Ce-halide series: Ce(TriNOx)X (X=F-, Cl-, Br-, I-).
• Electrochemical and NMR studies revealed anion-dependent speciation in solution.
• DFT calculations supported experimental observations regarding electronic structure and reactivity.

Conclusions:

• The TriNOx ligand provides exceptional control over cerium redox states, enabling isolation of normally elusive species.
• Ligand architecture plays a critical role in stabilizing high oxidation states of cerium.
• The synthesized cerium complexes offer new platforms for exploring fundamental redox processes and potential applications.