Molecular-level insight into the multiple mechanistic pathways in iron-catalysed alkene dimerisation

Area of Science:

• Organometallic chemistry
• Sustainable synthesis
• Catalysis

Background:

• Iron catalysis is crucial for sustainable synthesis due to its low cost and toxicity.
• Mechanistic understanding of iron-catalyzed reactions, especially those involving low oxidation states, remains limited.
• Reductive dimerization of alkenes is an important transformation with few reported iron-catalyzed examples and lacking in-depth mechanistic analysis.

Purpose of the Study:

• To investigate the mechanism of iron-catalyzed reductive dimerization of methyl crotonates.
• To understand the role of low oxidation-state iron intermediates in C(sp2)-H functionalization.
• To explore the complex mechanistic pathways underlying this seemingly simple dimerization.

Main Methods:

• Detailed mechanistic studies involving X-ray diffraction.
• Kinetic analysis to determine reaction rates and orders.
• In situ Nuclear Magnetic Resonance (NMR) monitoring to observe intermediates.
• Speciation studies of the iron complex [(dmpe)2FeH2].

Main Results:

• Selective dimerization of methyl crotonates to 2-ethylidene-3-methylpentanedioates with two stereogenic units was achieved.
• This represents a rare non-arene C(sp2)-H functionalization catalyzed by iron.
• The study uncovered hidden mechanistic pathways, demonstrating the complexity of the system.
• The speciation of [(dmpe)2FeH2] was elucidated through combined analytical techniques.

Conclusions:

• The reductive dimerization of methyl crotonates is a mechanistically complex iron-catalyzed C(sp2)-H functionalization.
• Understanding these complex pathways is essential for advancing iron catalysis in sustainable synthesis.
• This work provides a platform for molecular-level insights into broad-scope iron-catalyzed C-H functionalization.