Thermal C-H borylation using a CO-free iron boryl complex

Area of Science:

• Organometallic Chemistry
• Catalysis
• Synthetic Chemistry

Background:

• Iron boryl complexes are valuable synthetic intermediates.
• Developing efficient and selective borylation methods is crucial in organic synthesis.

Purpose of the Study:

• To synthesize and characterize novel carbon monoxide-free iron boryl complexes.
• To investigate the catalytic activity of these complexes in arene borylation reactions.
• To understand the mechanistic pathways and limitations of iron-catalyzed C-H borylation.

Main Methods:

• Synthesis of iron boryl complexes of the type CpFe(PR3)2(Bpin).
• Spectroscopic characterization (NMR, IR, etc.) of the synthesized complexes.
• Catalytic testing for arene borylation under various conditions, including UV-free irradiation.
• Mechanistic studies involving pKa analysis of iron hydride species.

Main Results:

• Successful synthesis of new CO-free iron boryl complexes, CpFe(PR3)2(Bpin).
• The CpFe(PEt3)2(Bpin) complex demonstrated unique UV-free arene borylation at 70 °C via a dissociative pathway.
• Catalytic C-H borylation was unsuccessful with both monometallic and heterobimetallic iron systems.
• The failure of catalytic borylation was rationalized by analyzing the relative pKa values of relevant iron hydride species.

Conclusions:

• Novel CO-free iron boryl complexes have been developed.
• A specific iron boryl complex exhibits unique reactivity for UV-free arene borylation.
• The study provides insights into the limitations of iron-catalyzed C-H borylation, linked to the stability of iron hydride intermediates.