A Bispidine Iron(IV)-Oxo Complex in the Entatic State.

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• Iron(IV)-oxo complexes are crucial intermediates in oxidation catalysis.
• Bispidine ligands offer tunable steric and electronic properties for metal complexes.
• Understanding structure-reactivity relationships is vital for catalyst design.

Purpose of the Study:

• To correlate redox potentials with catalytic reactivity for Fe(IV)=O complexes.
• To investigate the mechanisms of alkane hydroxylation (HAT), alkene epoxidation, and oxidation (OAT).
• To elucidate the impact of ligand structure on complex stability and reactivity.

Main Methods:

• Synthesis and characterization of Fe(IV)=O complexes with tetra- and pentadentate bispidine ligands.
• Electrochemical studies to determine redox potentials.
• Kinetic studies of various oxidation reactions (HAT, OAT, epoxidation).
• Density Functional Theory (DFT) calculations.

Main Results:

• Redox potentials varied by ~350 mV, correlating with reaction rates spanning 8 orders of magnitude.
• Electron transfer and reaction driving force were identified as major factors.
• DFT analysis supported the experimental findings.
• Isomeric pentadentate bispidine ligands exhibited different reactivities due to destabilization of the S=1 ferryl ground state.

Conclusions:

• Redox properties significantly influence the catalytic activity of Fe(IV)=O complexes.
• Ligand design, including isomerism, critically affects complex stability and reactivity.
• Electron transfer dynamics are paramount in these oxidation catalytic systems.