Bioinspired Di-Fe Complexes: Correlating Structure and Proton Transfer over Four Oxidation States

Area of Science:

• Bioinorganic Chemistry
• Coordination Chemistry
• Enzyme Mechanisms

Background:

• Di-Fe cores in metalloproteins are vital for diverse chemical reactivity.
• Proton and electron transfer are critical but structurally challenging to study.
• Spectroscopic methods often confirm redox changes, but proton movement remains difficult to assess.

Purpose of the Study:

• To develop di-Fe complexes for pinpointing proton and electron movements during stepwise oxidation.
• To investigate the role of dynamic coordination spheres in regulating electron and proton transfer.
• To gain mechanistic insights into di-Fe enzyme stability and reactivity.

Main Methods:

• Synthesis of novel di-Fe complexes using a phosphinic amido tripodal ligand ([poat]3-).
• Stepwise electrochemical oxidation of di-Fe complexes.
• Spectroscopic analysis to monitor structural and electronic changes.
• Reactions with phenols to probe reaction mechanisms.

Main Results:

• Developed di-Fe complexes capable of stepwise oxidation from di-Fe(II) to Fe(III)Fe(IV) cores.
• Observed dynamic coordination spheres that facilitate electron and proton transfer.
• Identified the conversion of a hydroxido bridge to an oxido bridging ligand with protonation of the ligand.
• Demonstrated homolytic O-H bond cleavage in reactions with phenols, with electron transfer to Fe(IV) and proton transfer to the oxido ligand.

Conclusions:

• The developed di-Fe complexes provide a platform for studying coupled electron-proton transfer.
• Mechanistic insights into the stability and reactivity of di-Fe active sites were obtained.
• Findings contribute to understanding the function of di-Fe enzymes.