Iron Catalyzed Double Bond Isomerization: Evidence for an Fe^I /Fe^III Catalytic Cycle

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Alkene isomerization is a fundamental organic transformation.
• Developing efficient and selective catalysts for alkene isomerization remains an active area of research.
• Iron catalysis offers a cost-effective and sustainable alternative to precious metal catalysts.

Purpose of the Study:

• To report a novel iron-catalyzed system for alkene isomerization.
• To investigate the catalytic mechanism of the iron pre-catalyst.
• To explore the scope of the reaction with various alkene substrates.

Main Methods:

• Utilized an iron(II) β-diketiminate pre-catalyst.
• Employed catalytic amounts of hydride sources, including pinacol borane (HBpin) and ammonia borane (H3N⋅BH3).
• Investigated the mechanism using deuteration studies, Density Functional Theory (DFT), and Electron Paramagnetic Resonance (EPR) spectroscopy.

Main Results:

• Demonstrated iron-catalyzed isomerization of both allyl arenes and aliphatic alkenes.
• Identified key intermediates in the catalytic cycle, including an Fe(I)-alkene complex and an Fe(III) intermediate.
• Proposed a mechanism involving pre-catalyst activation, oxidative addition, and reductive elimination.

Conclusions:

• The developed iron catalyst system is effective for alkene isomerization.
• The mechanistic studies provide insights into the iron-catalyzed isomerization pathway.
• This work expands the utility of iron complexes in catalytic organic transformations.