One- to Two-Electron Reduction of an [FeFe]-Hydrogenase Active Site Mimic: The Critical Role of Fluxionality of the [2Fe2S] Core

Abstract

The one- to two-electron reduction of mu-(1,2-ethanedithiolato)diironhexacarbonyl that has been observed under electrochemical conditions is dependent on scan rate and temperature, suggesting activation of a structural rearrangement. This structural rearrangement is attributed to fluxionality of the [2Fe2S] core in the initially formed anion. Computations support this assessment. Upon an initial one-electron reduction, the inherent fluxionality of the [2Fe2S] complex anion allows for a second one-electron reduction at a less negative potential to form a dianionic species. The structure of this dianion is characterized by a rotated iron center, a bridging carbonyl ligand, and, most significantly, a dissociated Fe-S bond. This fluxionality of the [2Fe2S] core upon reduction has direct implications for the chemistry of [FeFe]-hydrogenase mimics and for iron-sulfur cluster chemistry in general.

Synthesis and Characterization of [FeFe]‐Hydrogenase Models with Bridging Moieties Containing (S, Se) and (S, Te)

“…The reduction is irreversible for 2 and 3 except at larger scan rates (1-5 V/s), where some chemical reversibility is observed and where the peak current function (i p,c /v 1/2 ) decreases slightly, probably approaching the oneelectron level as recently noted for µ-(1,2-ethanedithiolato)-diironhexacarbonyl (EDT). [50] Compound 1 shows some chemical reversibility even at 0.10 V/s ( Figure 3). For all three compounds, additional cathodic processes are detected at potentials past -2 V.…”

Kinetic and thermodynamic aspects of the electrocatalysis of acid reduction in organic solvent using molecular diiron-dithiolate compounds

“…1) [39]. The two-electron process observed at v ≤ 2 V s − 1 is ascribed to a potential inversion, and suggests that 2 − undergoes a large structural rearrangements, as seen for 1 − [33].…”

A Silicon‐Heteroaromatic System as Photosensitizer for Light‐Driven Hydrogen Production by Hydrogenase Mimics

“…Similar observations were recently reported for other [2Fe2S(Si)] complexes. [32,52,[56][57][58][59][60] Typically, a potential inversion is observed when a chemical reaction (most often linked to a structural change) makes the second electron transfer thermodynamically more favorable than the first. [48] Consistent with our observations, enhanced S-C-Sn angles were observed and an interaction between a σ(Sn-C) orbital and a 3p(S) orbital was verified by photoelectron spectroscopy.…”