Electron transfer at a dithiolate-bridged diiron assembly: electrocatalytic hydrogen evolution

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Catalysis

Background:

• The study investigates the electrochemical behavior of the diiron complex Fe(2)(mu-pdt)(CO)(6) (1), where pdt is propane-1,3-dithiolate.
• Understanding the redox properties and reactivity of such complexes is crucial for developing new catalysts.

Purpose of the Study:

• To elucidate the electrochemical reduction pathways of complex 1.
• To explore the electrocatalytic proton reduction activity of complex 1 in acidic media.
• To investigate the influence of carbon monoxide (CO) on the electrochemistry and catalysis.

Main Methods:

• Electrochemical techniques including cyclic voltammetry.
• Spectroscopic methods such as Electron Paramagnetic Resonance (EPR), UV-vis, and Extended X-ray Absorption Fine Structure (EXAFS).
• Spectroelectrochemical analysis.

Main Results:

• Electrochemical reduction of 1 initially forms a short-lived one-electron reduced species (1-) and subsequently two-electron reduced products, including a CO-bridged diiron compound (1B).
• Complex 1B, formulated as [Fe(2)(mu-S(CH(2))(3)SH)(mu-CO)(CO)(6)](-), was characterized by spectroscopy and EXAFS, showing an Fe-Fe separation of 2.527 Å.
• Complex 1 catalyzes proton reduction in moderately strong acids via a two-electron/proton addition mechanism, producing dihydrogen (1H2) and regenerating the catalyst (1). CO inhibits this catalytic process.

Conclusions:

• The electrochemical reduction of complex 1 involves distinct intermediate species and leads to the formation of a characterized CO-bridged diiron compound.
• Complex 1 demonstrates electrocatalytic activity for proton reduction, with the catalytic cycle involving dihydrogen formation and catalyst regeneration.
• Carbon monoxide plays a dual role, improving the reversibility of complex 1's electrochemistry but inhibiting its proton reduction catalysis through side reactions.