Direct Spectroscopic Detection of Key Intermediates and the Turnover Process in Catalytic H₂ Formation by a Biomimetic Diiron Catalyst

Abstract

FeFe(Cl 2 -bdt)(CO) 6 ]( 1;C l 2 -bdt = 3,6-dichlorobenzene-1,2-dithiolate), inspired by the actives ite of FeFe-hydrogenase, shows ac hemically reversible 2e À reduction at À1.20 Vv ersus the ferrocene/ferrocenium couple. The rigid and aromatic bdt bridging ligand lowers the reductionp otential and stabilizes the reduced forms,c ompared with analogous complexes with aliphatic dithiolates;t husa llowing detailso ft he catalytic process to be characterized.Herein,t ime-resolved IR spectroscopy is used to provide kinetic and structurali nformation on key catalytic intermediates. This includes the doublyr educed, protonated complex 1H À ,w hich has not been previously identifiede xperimentally.I na ddition, the first direct spectroscopic observation of the turnoverp rocess for am olecular H 2 evolving catalysti s reported, allowing for straightforward determination of the turnover frequency.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Characterizing photocatalysts for water splitting: from atoms to bulk and from slow to ultrafast processes

“…120 From in situ experiments not only intermediates can be identified, also kinetic information can be derived. [123][124][125] The challenge in these experiments is to reach concentrations of the short-lived intermediates high enough for spectroscopic detection. The single reduced species could be achieved via the laser-flash quench method, a second reduction step was not possible via this strategy.…”

“…The protonation of the hydride was identified to be the rate limiting step, enabling to calculate directly the turnover frequency (TOF) of the catalyst. 124 Also X-ray based methods have been applied in combination with pulsed irradiation to trigger photoinduced electron transfer steps and to structurally characterize the formed intermediates. Li et al applied XANES and EXAFS to investigate changes in the oxidation state and the coordination environment of a Co catalyst in a [Ru(bpy) 3 ] 2+ sensitized system in the presence of ascorbate as electron donor applying pulsed irradation.…”

Insights into Proton Coupled Electron Transfer in the Field of Artificial Photosynthesis

“…Time-resolved infrared spectroscopy has been used to obtain kinetic and structural information regarding reduced and protonated key intermediates. [18] A biomimetic diiron catalyst undergoes ET and PT steps leading to photocatalytic release of H 2 . Stopped-flow (SF) spectroscopy including rapid mixing of reagents allows the investigation of the turnover process.…”

“…Time‐resolved infrared spectroscopy has been used to obtain kinetic and structural information regarding reduced and protonated key intermediates [18] . A biomimetic diiron catalyst undergoes ET and PT steps leading to photocatalytic release of H 2 .…”

“…This technique allows the detection of CPET in the Marcus inverted region. Regarding the hydrogen evolution reaction (HER), time‐resolved infrared spectroscopy allows direct monitoring of H 2 formation [18] . This release of H 2 completes the catalytic cycle initiated by PT and ET steps.…”