Facial triad modelling using ferrous pyridinyl prolinate complexes: synthesis and catalytic applications

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• Non-heme iron enzymes utilize a 2-His-1-carboxylate facial triad motif.
• Chiral ligands are crucial for stereoselective catalytic applications.

Purpose of the Study:

• To synthesize novel chiral pyridinyl prolinate (RPyProR) ligands and their iron(II) complexes.
• To investigate the coordination behavior of RPyProR ligands with iron.
• To evaluate the catalytic activity of these iron complexes in alkene epoxidation.

Main Methods:

• Synthesis of chiral pyridinyl prolinate ligands and iron(II) triflate/chloride complexes.
• X-ray crystallography to determine complex structures and coordination modes.
• Catalytic testing for alkene epoxidation using hydrogen peroxide.

Main Results:

• Ligand coordination to iron is influenced by counterions, solvents, and substituents.
• Formation of five- and six-coordinate iron complexes with varying ligand coordination modes (meridional vs. facial).
• Steric hindrance in substituted ligands prevents solvent coordination and rearrangement.
• Iron complexes demonstrated catalytic activity in alkene epoxidation, especially for styrene substrates.

Conclusions:

• RPyProR ligands offer tunable coordination environments for iron.
• The synthesized iron complexes are effective catalysts for epoxidation reactions.
• Catalyst performance is sensitive to ligand structure and reaction conditions.