[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH₂)₂ER₂ Linkers (E=Ge and Sn)

Abstract

Analogues of the [2Fe-2S] subcluster of hydrogenase enzymes in which the central group of the three-atom chain linker between the sulfur atoms is replaced by GeR and SnR groups are studied. The six-membered FeSCECS rings in these complexes (E=Ge or Sn) adopt an unusual conformation with nearly co-planar SCECS atoms perpendicular to the Fe-Fe core. Computational modelling traces this result to the steric interaction of the Me groups with the axial carbonyls of the Fe (CO) cluster and low torsional strain for GeMe and SnMe moieties owing to the long C-Ge and C-Sn bonds. Gas-phase photoelectron spectroscopy of these complexes shows a shift of ionization potentials to lower energies with substantial sulfur orbital character and, as supported by the computations, an increase in sulfur character in the predominantly metal-metal bonding HOMO. Cyclic voltammetry reveals that the complexes follow an ECE-type reduction mechanism (E=electron transfer and C=chemical process) in the absence of acid and catalysis of proton reduction in the presence of acid. Two cyclic tetranuclear complexes featuring the sulfur atoms of two Fe S (CO) cores bridged by CH SnR CH , R=Me, Ph, linkers were also obtained and characterized.

[FeFe]‐hydrogenase H‐cluster mimics mediated by mixed (S, Se) and (S, Te) bridging moieties: Insight into molecular structures and electrochemical characteristics

“…Generally, the higher the electron density of the iron cores, the more the negative reduction potential is observed. This fact contrasts with our results as such behavior can be explained in terms of reorganization and stabilization of the reduced species as previously reported . Furthermore, increasing the scan rates of complexes 1 and 2 up to 15 V/s enhances the reversibility of their reduction events as shown in Figure .…”

“…Based on that, the molecular structures of complexes 1 and 2 could give more than one homologue; only one of them is shown in Figure . As demonstrated in Figure , the solid‐state structures of complexes 1 and 2 espouse a pseudo‐square‐pyramidal geometry like those reported for the known diiron dithiolato complexes . The central [Fe 2 SE] (E = Se, Te) moieties of 1 and 2 are in the butterfly conformation in which each Fe atom is surrounded by three CO ligands in a facial fashion.…”

“…The active site of this system contains an organometallic Fe/S cluster, the so‐called H‐cluster (Figure A), that is, responsible for the hydrogen evolution reaction . Over the past few decades, several diiron dithiolato complexes that mimic the butterfly [Fe 2 S 2 ] sub‐unit of the H‐cluster have been synthesized and tested as electrocatalysts . Moreover, these complexes have been modified to contain heavier chalcogen donor atoms such as selenium or tellurium instead of sulfur .…”

Synthesis and Electrochemical Investigation of Mono‐ and Di‐phosphite substituted [FeFe]‐Hydrogenase H‐Cluster Mimics

“…Over the past few decades, many model complexes, which mimic the H‐cluster have been synthesized, characterized, and their catalytic applications have been studied in detail . One of the primary things to focus on these synthetic models is the enhancement of the electron density at the iron cores, which in turn leads to increase their ability to produce H 2 .…”

Carbon/Silicon Exchange at the Apex of Diphos‐ and Triphos‐Derived Ligands – More Than Just a Substitute?

“…While the stability of the Si species is indeed crucial, it will be interesting to see whether an influence of C/Si exchange can be observed for other systems. The C/Si exchange certainly has the potential to further fine‐tune existing catalytic systems, and recent reports show that it can be further extended to the higher homologous Ge and Sn …”