Bimetallic carbonyl thiolates as functional models for Fe-only hydrogenases

Area of Science:

• Organometallic Chemistry
• Catalysis
• Electrochemistry

Background:

• Diiron complexes are of interest for catalytic applications, particularly in proton reduction.
• Understanding the influence of ligands on reactivity and stability is crucial for catalyst design.
• Protonation and reduction pathways dictate the catalytic cycle of metal complexes.

Purpose of the Study:

• To investigate the protonation and subsequent reduction of a specific diiron complex, [Fe(2)(S(2)C(3)H(6))(CN)(CO)(4)(PMe(3))](-).
• To explore the catalytic activity of this diiron system in proton reduction.
• To elucidate the role of coligands in determining protonation regiochemistry and catalytic efficiency.

Main Methods:

• Synthesis and characterization of protonated and modified diiron complexes.
• Nuclear Magnetic Resonance (NMR) spectroscopy (1H, 13C, 31P) for structural and stereochemical analysis.
• Electrochemical and analytical techniques to study reduction potentials and catalytic activity.
• Density Functional Theory (DFT) calculations to model protonation pathways and electronic interactions.

Main Results:

• Protonation of the diiron anion yields a hydride-bridged complex, HFe(2)(S(2)C(3)H(6))(CN)(CO)(4)(PMe(3)) (2H), which is stereochemically rigid.
• Further protonation leads to a dicationic species, [HFe(2)(S(2)C(3)H(6))(CNH)(CO)(4)(PMe(3))](+) (2H(2)(+)), capable of reducing protons to H(2).
• The diiron system exhibits catalytic proton reduction, with the 2H(2)(+)/2H(2) couple being highly efficient.
• DFT calculations indicate that protonation favors the Fe-Fe bond and is sensitive to coligand identity.

Conclusions:

• The studied diiron complex acts as an efficient catalyst for proton reduction.
• Proton reduction likely proceeds via protonation of reduced diiron hydrides.
• Coligand choice significantly impacts the regiochemistry of protonation and the overall catalytic performance.