Iron(IV) Complexes with Tetraazaadamantane-based Ligands: Synthesis, Structure, Application 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, HRMS, NMR, FT-IR, Mössbauer spectroscopy and DFT calculations, which supported d4 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 bridge-head nitrogen atom in TAAD provides a straightforward way for 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. Also, the Fe(IV)-TAAD complex was covalently bounded to a polystyrene matrix and the resulting material was shown to serve as a heterogeneous catalyst for aerobic oxidation of thiols to disulfides.