[FeFe] Hydrogenase: Protonation of {2Fe3S} Systems and Formation of Super‐reduced Hydride States

Abstract

The synthesis and crystallographic characterization of a complex possessing a well-defined {2Fe3S(μ-H)} core gives access to a paramagnetic bridging hydride with retention of the core geometry. Chemistry of this 35-electron species within the confines of a thin-layer FTIR spectro-electrochemistry cell provides evidence for a unprecedented super-reduced FeI(μ-H)FeI intermediate.

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

“…In particular, the Fe2–S bond distance 2.2681(9) Å in [ 1 (μ-H)­(Me)] + is comparable to the 2.270(2) Å that was observed for [ 1 (μ-H)­H] + . In addition, the S– C H 3 distance of 1.812(3) Å is comparable to those reported for dithiolato diiron hydride complexes with bound thioethers, i.e., 1.815(3) Å for [(μ-H)­Fe 2 (MeSCH 2 C­(Me)­(CH 2 S) 2 )­(CO) 4 (PMe 3 )] + and 1.813(7) Å for [(μ-H)­Fe 2 (Me 2 pdt)­(1,2-Cy 2 PC 6 H 4 SMe)­(PPh 3 )­(CO) 3 ] + . , …”

“…In addition, the S−CH 3 distance of 1.812(3) Å is comparable to those reported for dithiolato diiron hydride complexes with bound thioethers, i.e. 75,76 H 2 Evolution. As with the synthetic diiron bridging hydride containing phosphine ligands, complex [1(μ-H)(Me)]BF 4 is stable in solution; no decomposition was found after several hours in ambient light.…”

Structural and Kinetic Studies of Intermediates of a Biomimetic Diiron Proton-Reduction Catalyst

“…In particular, examples of direct spectroscopic observation of intermediates are very scarce. Only a few examples of mechanistic investigations were reported by Pickett et al and other groups, which aimed to study the spectral characteristics of the electrocatalytic intermediates by stopped-flow spectroscopic and spectroelectrochemical techniques. − The limited time resolution intrinsic to these techniques would, however, be insufficient to capture the spectroscopic signatures and kinetics of the more reactive transients that can be anticipated to occur in the protonation of electron-rich species. , In contrast, photochemically induced reduction in flash photolysis experiments allows one to follow even diffusion-controlled reactions of the flash-generated transients on nano- to millisecond time scales. We have recently reported on the spectroscopic and kinetic characterization of intermediates in the photocatalytic proton reduction of [FeFe­(bdt)­(CO) 6 ] (bdt = benzenedithiolate) using a combination of flash-quench methods with time-resolved UV–vis and IR spectroscopies .…”

Detection of Transient Intermediates Generated from Subsite Analogues of [FeFe] Hydrogenases

“…39−41 This complex electrocatalyzes proton reduction at the that the 'additional' electron is delocalized across the di-iron system. 13,18 This interpretation was later supported by Rauchfuss and co-workers, who showed that with suitably substitution of the core a delocalized 35-electron species could be isolated and structurally characterized ( Figure 13). 43 The instability of the 35-electron systems is associated with ligand dissociation, PMe3 or intramolecularly-bound thioether, to give a 33-electron system, which is further reduced to a closedshell monoanion.…”