Hydrogen Isotope Exchange in Pyridine Catalyzed by an Iron(II) Imido Complex: Counterion-Directed Regioselectivity

Area of Science:

• Organometallic Chemistry
• Catalysis
• Isotope Exchange Reactions

Background:

• Hydrogen isotope exchange (HIE) is crucial for synthesizing isotopically labeled compounds.
• Iron imido complexes show potential as catalysts but their selectivity is often challenging to control.
• The role of counter-cations in transition metal catalysis is an active area of research.

Purpose of the Study:

• To investigate the catalytic activity of high-spin iron(II) imido complexes in HIE reactions.
• To explore the influence of different counter-cations (Li+, K+) on the regioselectivity of pyridine deuteration.
• To elucidate the mechanism of HIE catalyzed by these iron complexes.

Main Methods:

• Synthesis and characterization of iron(II) imido complexes with varying counter-cations.
• Hydrogen isotope exchange experiments using pyridine as a substrate and deuterated reagents.
• Experimental and computational mechanistic studies, including stoichiometric reactions and structural analysis.

Main Results:

• Iron imido complexes with Li+ and K+ counter-cations catalyze site-selective deuteration of pyridine.
• Li+ facilitates regioselective α-deuteration by stabilizing the substrate during the catalytic cycle.
• K+ promotes α,β,γ- and β,γ-deuteration by stabilizing different pyridyl regioisomers.

Conclusions:

• The counter-cation plays a critical role in activating the substrate, facilitating deuteration, and dictating HIE regioselectivity.
• This study demonstrates a novel method for controlling HIE regioselectivity in pyridine using iron catalysts.
• The findings offer insights into the design of selective catalysts based on counter-cation effects.