Formally Ferric Heme Carbon Monoxide Adduct

Area of Science:

• Inorganic Chemistry
• Bioinorganic Chemistry
• Computational Chemistry

Background:

• Thiolate-bound iron porphyrins are crucial in biological systems.
• Understanding the electronic structure of iron-sulfur-carbon monoxide complexes is challenging.
• Thiyl radicals are often short-lived reactive intermediates.

Purpose of the Study:

• To synthesize and characterize stable ferric carbonyl adducts of thiolate-bound iron porphyrins.
• To elucidate the electronic ground state of these novel iron complexes.
• To investigate the role of backbonding in stabilizing the Fe(II)-thiyl radical species.

Main Methods:

• Synthesis of thiolate-bound iron porphyrin carbonyl adducts.
• Spectroscopic characterization using Resonance Raman, EPR, and FTIR.
• Density Functional Theory (DFT) calculations.

Main Results:

• Ferric carbonyl adducts with Fe-S and Fe-CO bonds were successfully synthesized.
• EPR spectroscopy identified an S=1/2 species with a ligand-based electron hole, indicating an Fe(II)-thiyl radical ground state.
• FTIR data showed higher C-O vibrations compared to ferrous adducts, and DFT calculations supported the stabilization of the Fe(II)-thiyl radical state via backbonding.

Conclusions:

• Stable Fe(II)-thiyl radical species have been accessed and characterized.
• The findings provide insights into the electronic structure and stabilization mechanisms of iron-sulfur-carbon monoxide complexes.
• This work contributes to understanding elusive thiyl radicals, important in various chemical reactions.