O2 activation by bis(imino)pyridine iron(II)-thiolate complexes

Area of Science:

• Bioinorganic Chemistry
• Organometallic Chemistry
• Enzyme Mimicry

Background:

• Cysteine dioxygenase (CDO) is a crucial enzyme that catalyzes the oxidation of cysteine to cysteinesulfinic acid.
• CDO utilizes a conserved (His)(3)Fe(II) active site for its catalytic function.
• Understanding CDO's mechanism requires biomimetic models that replicate its active site environment.

Purpose of the Study:

• To synthesize and characterize novel iron(II)-thiolate complexes as models for cysteine dioxygenase.
• To investigate the reactivity of these models with molecular oxygen (O(2)).
• To elucidate the role of the thiolate ligand in O(2) activation and product formation.

Main Methods:

• Synthesis of iron(II)-thiolate complexes with a bis(imino)pyridine (BIP) ligand.
• Reaction of the synthesized complexes with O(2) under controlled conditions.
• Spectroscopic analysis (e.g., NMR, UV-Vis) and (18)O isotope labeling studies to characterize reaction products.
• Electrochemical studies to determine Fe(III)/Fe(II) redox potentials.

Main Results:

• Two iron(II)-thiolate complexes, [((iPr)BIP)Fe(II)(SPh)(Cl)] (1) and [((iPr)BIP)Fe(II)(SPh)(OTf)] (2), were successfully prepared.
• Reaction of complex 1 with O(2) yielded an iron(IV)-oxo species, indicating Fe-oxygenation.
• Reaction of complex 2 with O(2) resulted in direct S-oxygenation to a sulfonato product.
• (18)O isotope studies confirmed the oxygenation pathways.

Conclusions:

• The positioning of the thiolate ligand is critical in determining the outcome of O(2) activation by these Fe(II) complexes.
• These models demonstrate distinct Fe-oxygenation and S-oxygenation pathways relevant to CDO mechanism.
• Thiolate ligands are essential for O(2) reactivity and influence the redox potential of the iron center.