Werner Complexes Can Still Surprise: The Chelated O₂BOH^2- Ligand

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Inorganic Chemistry

Background:

• Mononuclear transition metal complexes are crucial in catalysis and materials science.
• Oxoanion ligands play diverse roles in coordination chemistry, but borate ligands are less common.
• Understanding the reactivity of novel ligand systems is key to developing new chemical transformations.

Purpose of the Study:

• To synthesize and characterize a novel cobalt(III) complex incorporating a hydrogen borate ligand.
• To investigate the structural and electronic properties of this unprecedented mononuclear complex.
• To explore the reactivity of the complex with alcohols and assess oxygen exchange dynamics.

Main Methods:

• Synthesis via air oxidation of cobalt(II) precursors in the presence of the pmap ligand and borax.
• Purification using cation exchange chromatography.
• Characterization through X-ray crystallography (implied by bond length analysis), mass spectrometry, and computational studies.

Main Results:

• Successful synthesis and characterization of the mononuclear cobalt(III) complex [Co(pmap)(O2BOH)]ClO4·4H2O.
• Structural analysis confirmed the presence of a chelated hydrogen borate (O2BOH2-) ligand, distinct from carbonate.
• The complex readily reacts with methanol and ethanol to form borate monoesters and undergoes rapid 18O exchange, suggesting an electron-deficient boron atom.

Conclusions:

• This study reports the first mononuclear transition metal complex with a deprotonated boric acid ligand.
• The hydrogen borate ligand's structure and the complex's reactivity highlight the unique electronic properties of the boron center.
• The findings open avenues for exploring borate-containing metal complexes in catalysis and synthetic chemistry.