Synthesis, dynamics and redox properties of eight-coordinate zirconium catecholate complexes

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Zirconium complexes are vital in catalysis and materials science.
• Exploring novel ligand architectures is key to developing new functional materials.
• Understanding the structural dynamics and redox properties of metal complexes is crucial.

Purpose of the Study:

• To synthesize and characterize novel zirconium complexes using the 9,9-dimethylxanthene-bis(imine)-bis(catechol) ligand (XbicH4).
• To investigate the structural, dynamic, and redox properties of these new zirconium complexes.
• To elucidate the mechanisms behind the observed fluxionality in these coordination compounds.

Main Methods:

• Synthesis of tetracatecholate and heteroleptic complexes via reactions with Zr(acac)4 and (TPP)Zr(OAc)2.
• Structural characterization using Nuclear Magnetic Resonance (NMR) spectroscopy.
• Investigation of dynamic behavior through NMR and kinetic isotope effect measurements.
• Computational studies to understand reaction mechanisms.

Main Results:

• Formation of neutral tetracatecholate ((XbicH2)2Zr) and heteroleptic ((TPP)Zr(XbicH2)) zirconium complexes.
• Both complexes exhibit an eight-coordinate square antiprismatic geometry around the zirconium center.
• Observed fluxionality in both complexes, with mechanisms involving catecholate oxygen dissociation.
• Demonstrated reversible one-electron oxidation of catecholates to semiquinones.

Conclusions:

• The synthesized zirconium complexes possess unique structural and dynamic properties.
• The fluxional behavior is attributed to a dissociative mechanism involving the catecholate ligands.
• The reversible redox activity suggests potential applications in electrochemistry and redox-switchable systems.