XAFS and DFT Characterisation of Protonated Reduced Fe Hydrogenase Analogues and Their Implications for Electrocatalytic Proton Reduction

Abstract

The relationship between the structures of reduced, protonated diiron compounds relevant to the diiron subsite of the Fe-hydrogenase H cluster, [2Fe] H , and the rate of electrocatalytic proton reduction is explored by a combination of experimental and computational approaches. Analysis of the X-ray absorption fine structure (XAFS) of the two-electron, twoproton product of [Fe(CO) 3 ] 2 (μ-PPh 2 ) 2 (DP) shows distortions of the primary coordination environment of the Fe centre that result from the trans influence of the terminally bound hydrido ligand. The difference in Fe-C(O) bond lengths for the CO groups cis and trans to the hydrido ligand is similarly predicted by density functional theory, although there is relatively poor agreement between the magnitude of the difference obtained by XAFS and DFT methods. The calculated energies of the cis and trans stereoisomers of DP-H 2 with both hydrido ligands normal to the FeP2 plane (axial:axial)

Silicon–Heteroaromatic [FeFe] Hydrogenase Model Complexes: Insight into Protonation, Electrochemical Properties, and Molecular Structures

“…The acid dependence of the CV of 9 and 12 is very similar, also to that previously observed for the pdt complex and the reduction in the presence of CF 3 COOH can be described as shown in Scheme 51. 52 The first reduction observed in acidic medium comprises the electron transfers at E 1 and E 2 , and the weaker acid‐dependence of the peak than E 3 indicates a rather inefficient proton reduction process, limited by an acid‐independent, very slow reaction, probably the release of H 2 (Scheme , slow process, gray) 51–57. The release of H 2 is facilitated by the transfer of a supplementary electron at a more negative potential (potential E 3 , fast process, see also Figure 8), as reported for several electrocatalytic proton‐ reduction processes involving diiron compounds 40.…”

Electron Delocalization in Spectroelectrochemically and Computationally Characterized [Pt{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)]+ Formed by Electrochemical Oxidation of [PtII{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)]

“…Differential absorption IR-SEC measurements have been used in conjunction with the calculated ν(CO) band profile to confirm the validity of proposed structures. 66,67 This study provides a clear example of the use of DFT calculations to interpret the more complicated spectral profile characteristic of the "fingerprint" region of the IR spectrum and to confirm the assignment of the observed spectrum to the one-electron oxidized product, 1Cl + (Figure 4).…”

Lewis acid protection turns cyanide containing [FeFe]-hydrogenase mimics into proton reduction catalysts

“…The latter step potentially involves formation of a transient dihydride species, with H-H bond formation occurring via homolytic reaction. 63,64 A summary of the observed and proposed reaction steps is provided in Scheme 1. We note that a parallel catalytic cycle proceeding via 3 − can become available at more reducing potentials, however it is omitted from Scheme 1 for clarity.…”