Di/mono-nuclear iron(i)/(ii) complexes as functional models for the 2Fe2S subunit and distal Fe moiety of the active site of [FeFe] hydrogenases: protonations, molecular structures and electrochemical properties

Abstract

Di/mono-nuclear iron(I)/(II) complexes containing conjugated and electron-withdrawing S-to-S linkers, [{(μ-S)(2)(C(4)N(2)H(2))}Fe(2)(CO)(6)] (1), [{(μ-S)(2)(C(4)N(2)H(2))}Fe(2)(CO)(5)(PMe(3))] (1P), and [{(μ-S)(2)(C(4)N(2)H(2))}Fe(CO)(2)(PMe(3))(2)] (2) were prepared as biomimetic models for the 2Fe2S subunit and distal Fe moiety of the active site of [FeFe] hydrogenases. The N atoms in the heterocyclic pyrazines of 1 and 2 were protonated in the presence of proton acid to generate one and two hydrides, [1(NH)](+) CF(3)SO(3)(-), [2(NH)](+) CF(3)SO(3)(-), and [2(NH)(2)](2+) (CF(3)SO(3)(-))(2), respectively. The protonation processes were evidenced by in situ IR and NMR spectroscopy. The molecular structures of the protonated species [1(NH)](+) CF(3)SO(3)(-) and [2(NH)(2)](2+) (CF(3)SO(3)(-))(2) together with their originating complexes and , and the mono-PMe(3) substituted diiron complex were identified by X-ray crystallography. The IR and single-crystal analysis data all suggested that the electron-withdrawing bridge, pyrazine, led to decreased electron density at the Fe centers of the model complexes, which was consistent with the electrochemical studies. The cyclic voltammograms indicated that complex exhibited a low primary reduction potential at -1.17 V vs. Fc-Fc(+) with a 270 mV positive shift compared with that of the benzene-1,2-dithiolate (bdt) bridged analogue [(μ-bdt)Fe(2)(CO)(6)]. Under the weak acid conditions, complexes 1 and 2 could electrochemically catalyze the proton reduction. More interestingly, the mononuclear ferrous complex 2 showed two catalytic peaks during the formation of hydrogen, confirming its potential as a catalyst for hydrogen production.

Role of Metals Content in Spinach in Enhancing the Conductivity and Optical Band Gap of Chitosan Films

“…Theoretically, chitosan has a free amine group in its molecular structure. On the other hand, ferredoxin which is linked with sulfur consists of Fe 3+ where it can reduce to Fe 2+ by interacting with the free amine group in chitosan [23]. The complex formation induces the increment of conductivity since it creates an extra pathway for the electrons to flow, which is consistent with data of conductivity and band gap as depicted in Table 1.…”

A mononuclear iron carbonyl complex [Fe(μ-bdt)(CO)2(PTA)2] with bulky phosphine ligands: a model for the [FeFe] hydrogenase enzyme active site with an inverted redox potential

“…5 Complex d reported by Gao and co-workers can also catalyze the production of hydrogen from acetic acid via two different pathways (ECCE and EECC) depending on the sequence of one-electron reduction events (−2.02 and −2.28 V vs. Fc/Fc + ). 7 The results for complex d were consistent with those obtained by Ott et al on analogous complexes (a and c). 5 Ott and co-workers have also reported penta-coordinated Fe-complexes (e-j) as minimal models for the Fe d -centre.…”

“…2). [5][6][7] The mononuclear complexes have gained significant interest as minimal functional models of the coordination of Fe d (d = distal) where H 2 is formed.…”

A DFT study of structure and electrochemical properties of diiron-hydrogenase models with benzenedithiolato and benzenediselenato ligands

“…Viable alternatives to the currently used noble metal catalysts for large-scale electrochemical production of H 2 are complexes based on the first d-block transition metals. 2 Particularly promising are biomimetic catalysts [3][4][5][6][7][8][9][10][11][12] inspired by the Fe 2 S 2 active site of iron-iron hydrogenases, a class of enzymes responsible for dihydrogen production in microbes. 13,14 For example, a diiron complex containing a benzenedithiolato (bdt) ligand and six carbonyl groups (i.e.…”