Iron(iv) complexes with tetraazaadamantane-based ligands: synthesis, structure, applications in dioxygen activation and labeling of biomolecules

4,6,10-Trihydroxy-1,4,6,10-tetraazaadamantane (TAAD) has been shown to form a stable Fe(iv) complex having a diamantane cage structure, in which the metal center is coordinated by three oxygen atoms of the deprotonated ligand. The complex was characterized by X-ray diffraction analysis, HRMS, NMR, FT-IR, Mossbauer spectroscopy and DFT calculations, which supported the d(4) configuration of iron. The Fe(iv)-TAAD complex showed excellent performance in dioxygen activation under mild conditions serving as a mimetic of the thiol oxidase enzyme. The nucleophilicity of the bridgehead nitrogen atom in TAAD provides a straightforward way for the conjugation of Fe(iv)-TAAD complexes to various functional molecules. Using this approach, steroidal and peptide molecules having an iron(iv) label have been prepared for the first time. In addition, the Fe(iv)-TAAD complex was covalently bound to a polystyrene matrix and the resulting material was shown to serve as a heterogeneous catalyst for aerobic oxidation of thiols to disulfides.

Automated summary

TAAD can form a stable Fe(iv) complex with excellent dioxygen activation ability. It can be conjugated to various functional molecules, allowing the synthesis of steroidal and peptide molecules labeled with iron(iv). Additionally, the Fe(iv)-TAAD complex shows potential as a catalyst.