Terminal Thiolate-Dominated H/D Exchanges and H₂ Release: Diiron Thiol-Hydride

Area of Science:

• Bioinorganic Chemistry
• Organometallic Chemistry
• Enzyme Mechanism Elucidation

Background:

• Understanding reaction pathways at enzyme active sites is crucial for bioinorganic chemistry.
• Diiron complexes are relevant models for studying metalloenzyme mechanisms, particularly those involving H₂ activation.

Purpose of the Study:

• To investigate reaction pathways at a metal-ligand site by incorporating a terminal thiolate into a diiron bridging hydride.
• To synthesize and characterize a novel trithiolato diiron hydride complex.
• To explore the catalytic activity of the complex in H₂ formation and H/D exchange reactions.

Main Methods:

• Synthesis of the trithiolato diiron hydride complex, (μ-H)Fe₂(pdt)(dppbz)(CO)₂(SR), via photoassisted oxidative addition.
• Protonation of the terminal thiolate to form a thiol-hydride complex.
• H/D exchange reactions with D₂, D₂O, and CD₃OD to study reaction intermediates and isotopic effects.

Main Results:

• The synthesized complex undergoes protonation, leading to intramolecular thiol-hydride coupling and H₂ release.
• A diiron η²-H₂ intermediate was proposed and evidenced through H/D exchange studies.
• The complex catalyzes H/D scrambling between H₂ and deuterated solvents, producing HD.

Conclusions:

• The study demonstrates a novel "proton-hydride" model for H₂ activation and release.
• The findings provide significant insights into the reversible heterolytic cleavage of H₂ by hydrogenase enzymes.
• The observed isotopic effects highlight the role of equilibrium in H/D exchange processes.