Methoxyphenyl‐Functionalized Diiron Azadithiolates as Models for the Active Site of Fe‐Only Hydrogenases: Synthesis, Structures, and Biomimetic H₂ Evolution

Abstract

A series of methoxyphenyl-functionalized diiron azadithiolate (ADT) complexes,

[FeFe]‐Hydrogenase Models: Overpotential Control for Electrocatalytic H2 Production by Tuning of the Ligand π‐Acceptor Ability

“…On the other hand, the reduction shifts are smaller than those observed for complex 6 and other reported phosphane-substituted diiron complexes. [19,20,30,42] Within the series of 2, 4, and 6, we can see that the reduction potentials gradually shift to more positive potentials with displacement of the phenyl ring by the pyrrol-1-yl group, consistent with the change trends of the IR ν CO bands.…”

“…It has been demonstrated that complexes 2 and 3 display two irreversible oxidation peaks, whereas 4 and 5 show one irreversible oxidation peak. In publications, those reported for ADT-, PDT-, and ODT-bridged (ODT = oxadithiolato) analogs, [19][20][21]30,41,42] In all cases discussed in this paper, it is noticeable that the 1st oxidation for complexes 2-5 exhibits a current intensity ca. twice that of the corresponding 1st reduction event, which was confirmed as a one-electron process by bulk electrolysis (vide infra).…”

“…In contrast, the PPyr 3 ligand (or PPyr 2 Ph and PPyrPh 2 ) with a smaller π-acceptor ability modulates the nucleophilicity of the diiron core of the reduced species (Fe I Fe 0 level) of 4 at a functional level for H 2 production. On the basis of the electrochemical observations described above and similar cases of phosphane-substituted 2Fe2S complexes previously reported, [19][20][21]30,[41][42][43] …”

“…All of these features are clearly indicative of a catalytic proton reduction process. [19][20][21]30,[41][42][43]46] The CVs of complexes 2-5 indicate they are electrocatalytically active at the first reduction potentials for proton reduction from HOAc. The electrocatalytic properties of complexes 2-5 are very similar to that of [(µ-pdt)Fe 2 (CO) 5 PTA] reported by Darensbourg and coworkers, [20] which also shows the first reduction peak is catalytically active in the presence of a weak acid (HOAc).…”

“…However, for the electron counting of the 1st reduction process of the parent complex 1, whether it is a one-electron process or a two-electron process, is disputable. [19][20][21]30,[41][42][43][44] For most model complexes including ADT, PDT, and ODT derivatives, the concerned reduction event was considered to be a one-electron process.…”