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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
Iron(IV)-Cyanide Complexes Capable of Asynchronous Basicity-Driven PCET in C-H Activation upon Linkage Isomerization
Himangshu Kuiry1, Jishnu Sai Gopinath2, Tanishqa Chaubal1
1Department of Chemical Sciences, Indian Institute of Science Education and Research, Mohanpur, Kolkata 741246, India.
Journal of the American Chemical Society
|May 30, 2026
Summary
High-valent iron-cyanide complexes activate C-H bonds through a basicity-controlled proton-coupled electron transfer mechanism. Coordination and isomerization tune reactivity, establishing Fe-cyanide as a distinct hydrogen-atom abstractor class.
Area of Science:
- Inorganic Chemistry
- Organometallic Chemistry
- Catalysis
Background:
- High-valent iron-oxo complexes are key in C-H bond activation.
- Reactivity of non-oxo iron oxidants is less understood.
- Iron-cyanide complexes offer a new avenue for oxidation chemistry.
Purpose of the Study:
- To explore the C-H bond activation capabilities of novel Fe(IV)-cyanide complexes.
- To elucidate the mechanism of hydrogen atom abstraction by these complexes.
- To establish design principles for tuning reactivity in non-oxo iron systems.
Main Methods:
- Synthesis and structural characterization of Fe(IV)-cyanide complexes.
- Kinetic studies (KIE, Hammett analysis) of C-H and O-H bond oxidation.
- Quantum-chemical calculations to probe reaction mechanisms and energetics.
- Investigation of substrate pKa dependence.
Main Results:
- Two Fe(IV)-cyanide complexes, [Fe(IV)(CN)(bTAML)]- and [Fe(IV)(CN)2(bTAML)]2-, were synthesized.
- The six-coordinated complex activates both O-H and C-H bonds, while the five-coordinated analogue does not.
- Reactivity correlates with substrate basicity (pKa), not bond strength, indicating asynchronous proton-coupled electron transfer (PCET).
- Fe-C≡N → Fe-N≡C isomerization facilitates the PCET mechanism.
Conclusions:
- Fe-cyanide complexes represent a distinct class of hydrogen-atom abstractors.
- Coordination environment and linkage isomerization are crucial for modulating PCET asynchronicity and reactivity.
- This work provides a new paradigm for designing C-H activation catalysts beyond traditional redox control.
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