Bioorganometallic tagging of N-acetylhistamine with an Fe(CO)₃ unit: synthesis, X-ray structure, and protonation behavior

This study highlights the potential of organometallic carbonyl complexes as selective markers for biomolecules, enabling sensitive infrared (IR) detection. The regio- and stereoselective coupling of N-acetylhistamine, a histidine analogue, with the precursor complex 1 [Fe(CO)₃(1,4-η⁵-N-pyridiniocyclohexa-1,3-diene)] BF₄ affords the labeled complex 3 [Fe(CO)₃(1,4-η⁵-N-acetylhistaminocyclohexa-1,3-diene)]. X-ray diffraction (XRD) confirms the exo stereochemistry and reveals a rigid, well-defined architecture. IR and ¹H nuclear magnetic resonance spectroscopic studies combined with IR-monitored acid-base titration demonstrate the complex's stability in aqueous media between pH 5 and 8, alongside a modest increase in basicity relative to the free ligand. These findings establish the Fe(CO)₃ moiety as a robust platform for selective labeling of peptides and proteins, paving the way for targeted applications in bioorganometallic chemistry and spectroscopic imaging.