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Herein, this work presents the preparation and characterization of a di-iron toluene-3,4-dithiolate complex with monosubstituted 1,1′-bis(diphenylphosphino)ferrocene (dppf). The reaction of complex [Fe2(CO)6{μ-SC6H3(CH3)S}] (1) with dppf in refluxing toluene gave the monosubstituted analog [Fe2(CO)5(κ1-dppf){μ-SC6H3(CH3)S}] (2) in 50% yield. Complex 2 was identified by elemental analysis, spectroscopies including FT-IR, 1H, 31P{1H}, 13C{1H} NMR and single crystal X-ray diffraction analysis. Moreover, cyclic voltammetry revealed that complex 2 can reduce the protons to dihydrogen in the presence of an acetic acid as a proton source under the electrochemical conditions. [ABSTRACT FROM AUTHOR]

Several species of microalgae can convert light energy into molecular hydrogen (H2) by employing enzymes of early phylogenetic origin, [FeFe]-hydrogenases, coupled to the photosynthetic electron transport chain. Bacterial [FeFe]-hydrogenases consist of a conserved domain that harbors the active site cofactor, the H-domain, and an additional domain that binds electron-conducting FeS clusters, the F-domain. In contrast, most algal hydrogenases characterized so far have a structurally reduced, so-termed M1-type architecture, which consists only of the H-domain that interacts directly with photosynthetic ferredoxin PetF as an electron donor. To date, only a few algal species are known to contain bacterial-type [FeFe]-hydrogenases, and no M1-type enzymes have been identified in these species. Here, we show that the chlorophycean alga Uronema belkae possesses both bacterial-type and algal-type [FeFe]-hydrogenases. Both hydrogenase genes are transcribed, and the cells produce H2 under hypoxic conditions. The biochemical analyses show that the two enzymes show features typical for each of the two [FeFe]-hydrogenase types. Most notable in the physiological context is that the bacterial-type hydrogenase does not interact with PetF proteins, suggesting that the two enzymes are integrated differently into the alga's metabolism. [ABSTRACT FROM AUTHOR]

A series of Fe2(μ‐SR)2(CO)6 complexes {R=Me (1Me), Et (1Et), Pr (1Pr), iPr (1iPr), tBu (1tBu), PhCH2 (1Bn) and Ph (1Ph)} have been synthesised. Complexes 1Me, 1tBu, 1Bn and 1Ph were produced by addition of S2R2 to Fe3(CO)12, with all but 1tBu giving excellent yields. Two isomers of 1Me and 1Ph were isolated: the anti‐ and 'open' syn‐products. Complexes 1Et, 1Pr and 1iPr were synthesised by treatment of RSH with Fe3(CO)12; two isomers of each complex were isolated. Addition of one equivalent of PR'3 (R'=Me, Cy, Ph) yields the corresponding mono(phosphine) adducts, whilst use of two equivalents of the phosphine (under mild condition, reflux, or irradiation using a deep blue LED depending on SR group) affords the corresponding bis(phosphine) adducts in good to excellent yield. Treatment of 1Ph or 1Me with two equivalents of PMe3 gives the corresponding bis‐substituted phosphines when carried out in the absence of light but leads to oxidative cleavage to Fe(μ‐SPh)2(PMe3)2(CO)2 and Fe(μ‐SMe)2(PMe3)2(CO)2, respectively, under blue light irradiation. Treatment of 1Pr with two equivalents of PCy3 under blue light irradiation leads to reductive breakdown of the Fe−Fe bond to yield Fe(CO)3(PCy3)2, but in the dark at room temperature the desired product Fe2(μ‐SPr)2(PCy3)2(CO)4 may be isolated. Single crystal X‐ray structures were obtained for most family members of 'butterfly' {Fe2S2} cores. Cyclic voltammetry shows PMe3‐containing complexes undergo irreversible oxidation, whereas both PCy3 and PPh3 complexes show one (quasi)reversible oxidation, IR of in situ protonation showed COv blue shifting around 80–100 cm−1, while 31P{1H} NMR spectroscopy showed shifting to low field. [ABSTRACT FROM AUTHOR]

To further develop the active site models of [FeFe]‐hydrogenases, a new series of diiron model complexes [{(μ‐SCH2)2CHCH2OC(O)C6H4I)}Fe2(CO)6] (I is located at ‐para for 1, ‐meta for 2, and ‐ortho for 3) bearing dithiolato‐bridgehead functionality were successfully prepared by treatments of bridghead‐hydroxyl‐containing parent complex [{(μ‐SCH2)2CHCH2OH)}Fe2(CO)6] (A) and three different iodobenzoic acids (IC6H4CO2H) in the presence of 4‐dimethylaminopyridine (DMAP) as catalyst and dicyclohexylcarbodiimide (DCC) as dehydrating reagent. All these new complexes 1–3 have been fully characterized through elemental analysis, FT‐IR and NMR (1H, 13C) spectroscopies, and X‐ray crystallography. Further electrochemical and electrocatalytic properties of complexes 1–3 are studied and compared in the absence and presence of acetic acid (HOAc) as a proton source by cyclic voltammetry (CV), indicating that they may be considered as the active biomimetic electrocatalysts for proton reduction to hydrogen (H2). [ABSTRACT FROM AUTHOR]

In this work, a new series of azadithiolato‐bridged diiron complexes [Fe2(μ‐adtNOH)(CO)5{P(C6H4R)3}] (adtNOH = (SCH2)2N(C6H4CH2CH2OH‐p) and R = Cl‐p, 1; Me‐m, 2; OMe‐p, 3 supported by tertiary phosphines, which may be considered as the active site models of [FeFe]‐hydrogenases, has been prepared in 73–81% yields by the Me3NO‐assisted decarbonylating reactions of all‐CO precursor [Fe2(μ‐adtNOH)(CO)6] (A) with several tertiary phosphines [(P(C6H4R)3] in MeCN at room temperature. All the new complexes 1–3 are fully characterized by elemental analysis, spectroscopic techniques (Fourier transform‐infrared spectroscopy [FT‐IR] and nuclear magnetic resonance [NMR]), and especially for 1 and 3 by X‐ray crystallography. The IR and 31P{1H} NMR spectroscopic analyses have shown that the electron density of diiron center in 1–3 may be adjusted by the introduction of the different substituents (R) of the P(C6H4R)3 ligands into the [2Fe2S] cluster. The X‐ray crystallographic investigation has displayed that the typical Fe‐Fe, Fe‐P, and Fe‐C distances of 1–3 are significantly influenced by the electronic effects of the P(C6H4R)3 phosphines coordinated apically to one Fe atom, whereas their Papical‐Fe‐Fe and Capical‐Fe‐Fe angles are mainly controlled by the steric interaction between the phosphine ligands and the dithiolate bridges. Further, the electrochemical performances of 1–3 are studied and compared in the absence or presence of acetic acid (HOAc) as proton source by using cyclic voltammetry, suggesting that they are active for the electrocatalytic proton reduction to hydrogen (H2). [ABSTRACT FROM AUTHOR]

In this report, two diiron ethane-1,2-dithiolate carbonyl complexes with bridging 1,3-bis(diphenylphosphino)propane (dppp) or tris(3-fluorophenyl)phosphine have been synthesized and characterized. Treatment of complex [Fe2(CO)6(µ-SCH2CH2S)] (1) with a diphosphine ligand dppp or a monophosphine ligand tris(3-fluorophenyl)phosphine using Me3NO·2H2O as the decarbonylating reagent afforded the corresponding derivatives [{Fe2(CO)5(µ-SCH2CH2S)}2(Ph2PCH2CH2CH2PPh2)] (2) and [Fe2(CO)5(µ-SCH2CH2S){P(3-C6H4F)3}] (3) in 82% and 92% yields, respectively. Complexes 2 and 3 have been characterized by elemental analysis, IR, NMR spectroscopy, as well as confirmed by single crystal X-ray diffraction analysis. Moreover, the electrochemistry of these complexes were studied by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

Two diiron ethane-1,2-dithiolate complexes were prepared and structurally characterized. Reactions of the parent complex [Fe2(CO)6(μ-SCH2CH2S)] (1) with tris(4-trifluoromethylphenyl)phosphine or triethyl phosphite and Me3NO·2H2O as the oxidative reagent resulted in the formation of the phosphine-substituted analog [Fe2(CO)5{P(4-C6H4CF3)3}(μ-SCH2CH2S)] (2) and phosphite-substituted analogue [Fe2(CO)5{P(OCH2CH3)3}(μ-SCH2CH2S)] (3) in 84% and 78% yields, respectively. The new complexes 2 and 3 were characterized by elemental analysis, IR, NMR spectroscopy, and single crystal X-ray diffraction analysis. Moreover, the electrochemical properties of both complexes were studied by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

Two diiron toluene-3,4-dithiolate complexes with a phosphine ligand or a phosphite ligand were prepared and characterized. Treatment of complex [Fe2(CO)6{µ-SC6H3(CH3)S}] (1) with one equivalent of ethyldiphenylphosphine or methyldiphenylphosphinite and the decarbonylation agent Me3NO·2H2O gave analogues [Fe2(CO)5(Ph2PCH2CH3){µ-SC6H3(CH3)S}] (2) [Fe2(CO)5(Ph2POCH3){µ-SC6H3(CH3)S}] (3) and in 84% and 61% yields, respectively. Both analogues have been characterized by spectroscopy, elemental analysis, and X-ray crystallography. The electrochemical properties were probed by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

We report a novel diiron propane-1,3-dithiolate complex [Fe2(CO)5PH(C10H15)2(μ-SCH2CH2CH2S)] containing a di-1-adamantylphosphine ligand. Trimethylamine N-oxide-induced decarbonylation of complex [Fe2(CO)6(μ-SCH2CH2CH2S)] followed by reaction with di-1-adamantylphosphine yielded the target product in 86% yield. The title compound was identified by spectroscopy, elemental analysis, as well as further determined by single crystal X-ray diffraction analysis. Electrochemical properties were studied by cyclic voltammetry without or with HOAc. Interestingly, the fungicidal activity of the title compound showed moderate activity against Phytophthora infestans, Pyricularia oryae, Botrytis cinerea, and Physalospora piricola. [ABSTRACT FROM AUTHOR]

Insight into wide aqueous pH influence on the electrocatalytic HER activity and stability of carbon nanotube-supported diiron dithiolato compound labeling as hybrid 2Fe2S-f-CNT are studied in this work. [Display omitted] • New diiron dithiolato compounds 1–3 were prepared as a library of [FeFe]-hydrogenase models. • A new CNT-covalently-supported diiron compound labeling as 2Fe2S-f-CNT was constructed. • Electrocatalytic HER activity and stability of 2Fe2S-f-CNT is studied in wide pH aqueous media. • Electrochemical reconstruction of 2Fe2S-f-CNT leads to high HER activity in alkaline medium. • Electrochemical degradation of 2Fe2S-f-CNT results in low HER activity in neutral and acidic media. Biomimetic chemistry on structure, function and external environment of [FeFe]-hydrogenases for hydrogen evolution reaction (HER) has shown a promising way to develop non-precious metal electrocatalysts for H 2 production in the current Pt-dominated HER system. Herein, three new diiron dithiolato compounds [{(μ -SCH 2) 2 N(C 6 H 4 CH 2 CO 2 R)}Fe 2 (CO) 6 ] (R = H (1), C 6 H 4 CHO- p (2), and C 6 H 4 Me- m (3)) were first prepared and identified as a library of [FeFe]-hydrogenase models in this work. Subsequently, the as-prepared diiron molecule 2 can be covalently attached onto carbon nanotubes (CNTs), resulting in the obtainment of target CNT-supported [FeFe]-hydrogenase model labeling as covalent hybrid 2Fe2S-f-CNT. Notably, the electrocatalytic HER performance and stability of the resulted hybrid 2Fe2S-f-CNT immobilized respectively on a gassy carbon (GC) electrode are systematically studied and compared in 0.1 M KOH (pH = 13), 0.1 M phosphate buffer (pH = 7), and 0.05 M H 2 SO 4 (pH = 1) aqueous solutions by various spectroscopic and electrochemical techniques. The result has shown that the higher electrocatalytic HER activity is observed in alkaline solution (pH = 13) relative to neutral and acidic solutions (pH = 7, 1), being attributed to the different electrochemical HER processes of diiron cluster in wide pH aqueous media as revealed by post operando analysis. [ABSTRACT FROM AUTHOR]

In this report, we describe the preparation of two diiron butane-1,2-dithiolate pentacarbonyl complexes with tris(3-fluorophenyl)phosphine or tris(3-chlorophenyl)phosphine as mimics for the active site of [FeFe]-hydrogenases. The two complexes were synthesized by the reactions of hexacarbonyl complex [Fe2(CO)6{µ-SCH2CH(CH2CH3)S}] (1) with the corresponding tertiary phosphine ligands by using Me3NO·2H2O as the decarbonylation reagent in 70% and 66% yields, respectively. The new complexes were characterized by means of elemental analysis, spectroscopy, and X-ray crystallography. Furthermore, the electrochemistry was studied by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

Biomimics for the active site of [FeFe]-hydrogenases, have been synthesized and characterized. Treatment of [Fe2(CO)6{μ-SCH2CH(CH3)S}] (1) and phosphine ligands tris(2-furyl)phosphine, tri(m-tolyl)phosphine, bis(diphenylphosphino)methane (dppm), or 1,2-bis(diphenylphosphino)benzene (dppbz) with Me3NO·2H2O as the decarbonylation agent afforded the corresponding phosphine-containing derivatives [Fe2(CO)5(L){μ-SCH2CH(CH3)S}] (L = P(2-C4H3O)3, 2; P(3-C6H4CH3)3, 3; Ph2PCH2PPh2, 4) and [Fe2(CO)4{κ2-(Ph2P)2(1,2-C6H4)}{μ-SCH2CH(CH3)S}] (5) in moderate to good yields. The new complexes 2‒5 have been structurally characterized by elemental analysis, IR, NMR spectroscopy, and further confirmed by X-ray diffraction analysis. The electrochemistry of complexes 2‒5 have been investigated by cyclic voltammetry, showing that they can catalyze the reduction of protons to H2 in the presence of HOAc. [ABSTRACT FROM AUTHOR]

Herein, we report the preparation and characterization of two diiron carbonyl complexes with ethyldiphenylphosphine or dicyclohexylphenylphosphine. Me3NO-driven decarbonylation of complex [Fe2(CO)6(µ-SCH2CH2CH2S)] (1) with the corresponding phosphine ligands afforded the products [Fe2(CO)5(Ph2PCH2CH3)(µ-SCH2CH2CH2S)] (2) and [Fe2(CO)5PhP(C6H11)2(µ-SCH2CH2CH2S)] (3) in 91% and 84% yields, respectively. The structures of complexes 2 and 3 have been identified by spectroscopy, elemental analysis, and X-ray diffraction analysis. Moreover, the electrochemistry was investigated by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

In this contribution, two diiron propane-1,3-dithiolate complexes with monosubstituted phosphine ligands have been synthesized and structurally characterized. Reactions of complex [Fe2(CO)6(µ-SCH2CH2CH2S)] (1) with a monophosphine ligand tri(m-tolyl)phosphine or tris(3-fluorophenyl)phosphine in the presence of Me3NO·2H2O as the CO-removing agent gave complexes 2 and 3 in 79% and 92% yields, respectively. Complexes 2 and 3 have been characterized by elemental analysis, IR, NMR spectroscopy, and X-ray diffraction analysis. Furthermore, the electrochemical properties of complexes 2 and 3 were studied by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

In this paper, three diiron butane-1,2-dithiolate complexes have been prepared and characterized. Treatment of the starting complex [Fe2(CO)6{µ-SCH2CH(CH2CH3)S}] (1) with a monophosphine ligand tris(2-thienyl)phosphine, tris(4-trifluoromethylphenyl)phosphine, or 4-(dimethylamino)phenyldiphenylphosphine and Me3NO·2H2O as the decarbonylating agent gave the target products 2‒4 in 75‒91% yields. These complexes have been characterized by elemental analysis, IR, NMR spectroscopy, as well as by X-ray crystallography. Moreover, the electrochemical properties of complexes 3 and 4 were investigated by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

In this article, five diiron 1,2-dithiolate complexes containing phosphine ligands are reported. Treatment of complex [Fe2(CO)6(μ-SCH2CH2S)] (1) with the phosphine ligands tris(4-methylphenyl)phosphine, tris(4-methoxyphenyl)phosphine, tris(3-chlorophenyl)phosphine, tris(3-methylphenyl)phosphine, or 2-(diphenylphosphino)biphenyl in the presence of Me3NO·2H2O as the decarbonylating agent afforded the target products [Fe2(CO)5(L)(μ-SCH2CH2S)] [L = P(4-C6H4CH3)3, 2; P(4-C6H4OCH3)3, 3; P(3-C6H4Cl)3, 4; P(3-C6H4CH3)3, 5; Ph2P(2-C6H4Ph), 6] in 80–93% yields. Complexes 2–6 have been characterized by elemental analysis, spectroscopy, and X-ray crystallography. Additionally, the electrochemical properties were studied by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

FeIFeI Fe2(S2C3H6)(CO)6(µ-CO) (1a–CO) and its FeIFeII cationic species (2a+–CO) are the simplest model of the CO-inhibited [FeFe] hydrogenase active site, which is known to undergo CO photolysis within a temperature-dependent process whose products and mechanism are still a matter of debate. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations, the ground state and low-lying excited-state potential energy surfaces (PESs) of 1a–CO and 2a+–CO have been explored aimed at elucidating the dynamics of the CO photolysis yielding Fe2(S2C3H6)(CO)6 (1a) and [Fe2(S2C3H6)(CO)6]+ (2a+), two simple models of the catalytic site of the enzyme. Two main results came out from these investigations. First, a–CO and 2a+–CO are both bound with respect to any CO dissociation with the lowest free energy barriers around 10 kcal mol−1, suggesting that at least 2a+–CO may be synthesized. Second, focusing on the cationic form, we found at least two clear excited-state channels along the PESs of 2a+–CO that are unbound with respect to equatorial CO dissociation.

In this paper, two diiron complexes have been prepared by CO exchange and structurally characterized. Treatment of complex [Fe2(CO)6{μ-SCH2CH(CH2O2CCH3)S}] (1) with diphenyl-2-pyridylphosphine in the presence of Me3NO·2H2O as the decarbonylating agent gave the corresponding monophosphine-substituted complex [Fe2(CO)5{Ph2P(2-C5H4N)}{μ-SCH2CH(CH2O2CCH3)S}] (2) in 85% yield. Similarly, complex [Fe2(CO)5{P(3-C6H4F)3}{μ-SCH2CH(CH2O2CPh)S}] (4) was obtained in 78% yield by the reaction of complex [Fe2(CO)6{μ-SCH2CH(CH2O2CPh)S}] (3) with tris(3-fluorophenyl)phosphine. The new complexes 2 and 4 have been characterized by elemental analysis, IR spectroscopy, NMR spectroscopy, as well as by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

[FeFe]-hydrogenases catalyse H production at exceptionally high turnover numbers (up to 10 s). They are found in a variety of strict or facultative anaerobic microorganisms, such as bacteria of the genus Clostridium, Desulfovibrio, Thermotoga, and eukaryotes ranging from unicellular and coenobial green algae to anaerobic fungi, ciliates and trichomonads. Key to their activity is an organometallic centre, the H-cluster that cooperates tightly with the protein framework to reduce two protons into molecular hydrogen. The assembly of the catalytic site requires a specialised cellular mechanism based on the action of three other enzymes, called maturases: HydE, HydF and HydG. Recent advancements in the recombinant production of [FeFe]-hydrogenases have provided leaps forward in their exploitation in H production for clean energy storage. [FeFe]-hydrogenases have been used in several fermentative approaches where microorganisms are engineered to overexpress specific [FeFe]-hydrogenases to convert low-cost materials (e.g. wastes) into H. [FeFe]-hydrogenases have also been proven to be excellent catalysts in different in vitro devices that can produce hydrogen directly from water, either via water electrolysis or via light-driven mechanisms, thus allowing the direct storage of solar energy into H. [ABSTRACT FROM AUTHOR]

To probe the influence of redox non-innocent ligands on a well-known class of [FeFe]-hydrogenase models, three new asymmetrically disubstituted diiron complexes of the general formula (µ-SRS)[Fe(CO)3][Fe(CO)(N-N)] {SRS = propane- 1,3-dithiolate (pdt) or benzene-1,2-dithiolate (bdt), and N-N = 2,2'-bipyridine (bipy) or 2,2'-bipyrimidine (bpym)} have been synthesized from their parent hexacarbonyls and characterized. The new complexes, (µ-pdt)Fr(CO)4(κ²-bpym) (2), (µ-bdt)-Fe2(CO)4(κ²-bipy) (3), and (µ-bdt)Fe2(CO)4(κ²-bpym) (4), were fully characterized by spectroscopic and electrochemical techniques, and the results are compared to those of a related complex, (µ-pdt)Fe2(CO)4(κ²-bipy) (1). The crystal structures of 2-4 show that, in each complex, the two iron units are in an eclipsed orientation, and the N-N ligand lies in the basal plane. IR spectra and electrochemical analyses indicate that electron density at the iron centers decreases in the order 1 > 2 > 3 > 4. Furthermore, compound 2 undergoes a ligand-centered reduction at the same potential that the hexacarbonyl precursor undergoes its first reduction. However, unlike the 2,2'-bipy derivatives 1 and 3, the 2,2'-bpym complexes 2 and 4 are not effective catalysts for electrochemical proton reduction from acetic acid. [ABSTRACT FROM AUTHOR]

This paper reports the first characterization of an [FeFe]-hydrogenase from a Clostridium perfringens strain previously isolated in our laboratory from a pilot-scale bio-hydrogen plant that efficiently produces H2 from waste biomasses. On the basis of sequence analysis, the enzyme is a monomer formed by four domains hosting various iron-sulfur centres involved in electron transfer and the catalytic center H-cluster. After recombinant expression in Escherichia coli, the purified protein catalyzes H2 evolution at high rate of 1645 ± 16 s−1. The optimal conditions for catalysis are in the pH range 6.5-8.0 and at the temperature of 50 °C. EPR spectroscopy showed that the H-cluster of the oxidized enzyme displays a spectrum coherent with the Hox state, whereas the CO-inhibited enzyme has a spectrum coherent with the Hox-CO state. FTIR spectroscopy showed that the purified enzyme is composed of a mixture of redox states, with a prevalence of the Hox; upon reduction with H2, vibrational modes assigned to the Hred state were more abundant, whereas binding of exogenous CO resulted in a spectrum assigned to the Hox-CO state. The spectroscopic features observed are similar to those of the [FeFe]-hydrogenases class, but relevant differences were observed given the different protein environment hosting the H-cluster. [ABSTRACT FROM AUTHOR]

• New diiron monophosphine precursors FePR (R = F , H, and Me) were prepared and characterized. • A new family of CNT-supported diiron monophosphine hybrids CNT- f -FePR was fabricated and characterized. • Substituent effects of FePR on electrocatalytic HER behaviros of CNT- f -FePR were investigated systematically. • Electrochemical studies indicate hybrid CNT- f -FePF exhibits a better HER activity in 0.1 M H 2 SO 4. • DFT calculation reveals hybrid CNT- f -FePF has a lower Δ G H* value relative to homologues CNT- f -FePR (R = H , Me). In order to explore substituent effects of PR 3 -phosphine ligands of diiron dithiolato complexes on the catalytic performances of [FeFe]-hydrogenase mimics for hydrogen evolution reaction (HER) in an aqueous medium, three new diiron monophosphine complexes [{(μ -SCH 2) 2 N(C 6 H 4 CH 2 CH 2 OH)}Fe 2 (CO) 5 {P(C 6 H 4 R- 4) 3 }] (labeled as FePR ; R = F , H, and Me) were prepared and can be further linked covalently into carbon nanotube (CNT) to construct the target CNT-supported hybrids denoting as CNT- f -FePR. The molecular structures of diiron complexes FePR are well characterized through element analysis, fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and X-ray crystallography, whereas the formations of target hybrids CNT- f -FePR have been confirmed by using X-ray photoelectron spectroscopy (XPS), Raman and FT-IR. Notably, the electrochemical HER performances of target hybrids CNT- f -FePR (R = F , H, and Me) are studied and compared in 0.1 M H 2 SO 4 aqueous solution by means of linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and density functional theory (DFT) calculation. Among these hybrids, the CNT- f -FePF hybrid exhibits a more efficient HER activity in an aqueous media based on their electrochemical observations that the CNT- f -FePF hybrid with F-substituted phosphine has lower applied overpotential, smaller Tafel slope, larger electrochemical active surface area, smaller charge transfer resistance, and lower hydrogen chemisorption free energy relative to its analogues CNT- f -FePH and CNT- f -FePMe with H- or Me-substituted phosphines. A new family of CNT-supported diiron monophosphine complexes denoting as CNT- f -FePR (R = F vs. H vs. Me) was constructed in order to investigate the substituent effects of diiron phosphine clusters FePR on the electrochemical HER performances of hydrogenase-inspired catalysts CNT- f -FePR in aqueous medium. [Display omitted] [ABSTRACT FROM AUTHOR]

The expression of recombinant [FeFe]-hydrogenases is an important step for the production of large amount of these enzymes for their exploitation in biotechnology and for the characterization of the protein-metal cofactor interactions. The correct assembly of the organometallic catalytic site, named H-cluster, requires a dedicated set of maturases that must be coexpressed in the microbial hosts or used for in vitro assembly of the active enzymes. In this work, the effect of the post-induction temperature on the recombinant expression of CaHydA [FeFe]-hydrogenase in E. coli is investigated. The results show a peculiar behavior: the enzyme expression is maximum at lower temperatures (20°C), while the specific activity of the purified CaHydA is higher at higher temperature (30°C), as a consequence of improved protein folding and active site incorporation. [ABSTRACT FROM AUTHOR]

Reaction of 2-phenyl-1,3-dibromopropane with in situ generated NaSe gave 4-phenyl-1,2-diselenolancyclopentane, which subsequently underwent the oxidative addition with Fe(CO) yielding the diiron diselenolato complex [( μ-SeCH)CHCH]Fe(CO) ( 1). Substitution of one or two carbonyls of complex 1 for triphenylphosphine (PPh) or cis-1,2-bis(diphenylphosphine)ethylene ( cis-dppv) in the presence of decarbonylating agent MeNO·2HO afforded the PPh-monosubstituted complex [( μ-SeCH)CHCH]Fe(CO)(PPh) ( 2) or the dppv-disubstituted complex [( μ-SeCH)CHCH]Fe(CO)( κ-dppv) ( 3). The structures of the four compounds were fully characterized by elemental analysis and various spectroscopic methods and for complexes 2 and 3 by X-ray crystallography. The cycle voltammetry under different conditions, such as CFCOOH, MeCN or CHCl, potential scan rate and temperature, was investigated. [ABSTRACT FROM AUTHOR]

Reaction of the diiron propanedithiolate complex [ μ-(SCH)CHOCCH]Fe(CO) ( A) with bis-(diphenylphosphino)methane (dppm) in the presence of MeNO·2HO in MeCN yielded a mono-substituted complex [ μ-(SCH)CHOCCH]Fe(CO)( κ-dppm) ( 1), whereas in refluxing xylene gave a bridged complex [ μ-(SCH)CHOCCH]Fe(CO)( μ-dppm) ( 2). The structures of both complexes were fully characterized by spectroscopic methods and X-ray crystallography. In solid state, one phosphine atom of dppm in complex 1 occupies an apical position of the square pyramidal geometries of the Fe center or two phosphine atoms of dppm in complex 2 bridge two Fe centers in a cisoid dibasal conformation. The cyclic voltammograms of both complexes in the presence of HBF were investigated. [ABSTRACT FROM AUTHOR]

[FeFe]-hydrogenases are the best natural hydrogen-producing enzymes but their biotechnological exploitation is hampered by their extreme oxygen sensitivity. The free energy profile for the chemical attachment of O2 to the enzyme active site was investigated by using a range-separated density functional re-parametrized to reproduce high-level ab initio data. An activation free-energy barrier of 13 kcal mol−1 was obtained for chemical bond formation between the di-iron active site and O2, a value in good agreement with experimental inactivation rates. The oxygen binding can be viewed as an inner-sphere electron-transfer process that is strongly influenced by Coulombic interactions with the proximal cubane cluster and the protein environment. The implications of these results for future mutation studies with the aim of increasing the oxygen tolerance of this enzyme are discussed. [ABSTRACT FROM AUTHOR]

[FeFe]-hydrogenases are the best natural hydrogen-producing enzymes but their biotechnological exploitation is hampered by their extreme oxygen sensitivity. The free energy profile for the chemical attachment of O2 to the enzyme active site was investigated by using a range-separated density functional re-parametrized to reproduce high-level ab initio data. An activation free-energy barrier of 13 kcal mol−1 was obtained for chemical bond formation between the di-iron active site and O2, a value in good agreement with experimental inactivation rates. The oxygen binding can be viewed as an inner-sphere electron-transfer process that is strongly influenced by Coulombic interactions with the proximal cubane cluster and the protein environment. The implications of these results for future mutation studies with the aim of increasing the oxygen tolerance of this enzyme are discussed. [ABSTRACT FROM AUTHOR]

Biological hydrogen production through the anaerobic digestion is an environmental friendly alternative for satisfying future hydrogen demands. Microorganisms residing into waste water treatment plants are far from being exhaustively characterized and surveys on hydrogen production through FeFe-hydrogenase in such ecosystems are scarce. This study combined the analysis of 16S rRNA and [FeFe]-hydrogenase ( hydA) genes with statistical tools to estimate richness and diversity of the microbial community of a domestic sewage treatment plant at the phylogenetic and functional levels. Archaeal groups were represented by 69 % of sequences assigned to Methanosarcinales and the remaining belonged to Methanomicrobiales. Within the bacterial library, 136 operational taxonomic units (OTUs) were distributed into 9 phyla, being 86 OTUs related to uncultivated bacteria. From these, 25 OTUs represented potential novel taxa within Synergistetes. Proteobacteria was the most predominant (36 % of the OTUs) and diversified phylogenetic group in the bacterial library, most of them assigned to the class Betaproteobacteria. Twenty-two putative hydA sequences were recovered into four distinct clusters and most of them were more closely related to each other than with sequences retrieved from databases, indicating they are hitherto undetected [Fe-Fe]-hydrogenase gene sequences. The richness estimates revealed that the number of sampled sequences was enough for full coverage of the archaeal diversity but not sufficient to cover both bacterial and hydA gene diversities. The results confirmed a great richness and diversity of bacterial and hydA sequences retrieved from the sewage sludge sample, suggesting such environment as a potential reservoir of new hydrogenase genes for biotechnological exploration. [ABSTRACT FROM AUTHOR]

Abstract: [FeFe]-Hydrogenases, encoded by hydA are thought to require the products of three accessory genes, hydE, F and G, for the biosynthesis of a functional H-cluster and maturation into a functional protein capable of reducing protons to hydrogen. Genome sequencing has shown that some organisms, including several strains of purple non-sulfur photosynthetic bacteria, possess orphan hydAs. It is unknown if these orphan HydAs can be matured into functional proteins. A construct where transcription of the apparent orphan hydA of Rhodospirillum rubrum was driven by the nifH2 promoter failed to restore hydrogen production to a Nif− strain of R. rubrum under nitrogen-limited photoheterotrophic conditions. However, RrhydA could be overexpressed and matured in Escherichia coli BL21(DE3) containing the hydE, F and G maturation genes from Desulfovibrio vulgaris Hildenborough or Clostridium acetobutylicum ATCC 824. Co-expression of R. rubrum hydA with the maturation genes of C. acetobutylicum gave the highest hydrogenase activity, 107 nmol/min/mg, whereas it was 6.6 nmol/min/mg with the maturation genes from D. vulgaris. Interestingly, R. rubrum HydA was twice as active as the HydA of C. acetobutylicum when both were matured with the maturases from the latter organism. [Copyright &y& Elsevier]

Light, polymer, action: A set of water‐soluble poly(acrylic acid) catalysts PAA‐g‐Fe2S2 containing {Fe2S2}, an [FeFe]‐hydrogenase active‐site mimic, is synthesized. This system, combined with CdSe quantum dots and ascorbic acid, has an exceptional turnover number and initial turnover frequency (27 135 and 3.6 s−1) for the photocatalytic production of H2 in water, which is the highest efficiency to date for [FeFe]‐hydrogenase mimics. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of [(μ-SCH2)2NCH2CO2Me]Fe2(CO)6 with 4-PyN(PPh2)2 (Py=C5H4N) in the presence of the decarbonylating agent Me3NO·2H2O afforded unexpected complexes [(μ-SCH2)2NCH2CO2Me]Fe2(CO)5(Ph2PNHPy-4) (1) and [(μ-SCH2)2NCH2CO2Me]Fe2(CO)5[Ph2PP(O)Ph2] (2) in 40% and 14% yields, respectively. The new complexes 1 and 2 have been characterized by elemental analysis, IR and 1H (31P, 13C) NMR spectroscopic techniques. In addition, their structures were determined by single-crystal X-ray diffraction analysis, indicating that the monophosphine ligands in complexes 1 and 2 both reside in an axial position of the square-pyramidal coordination sphere of the Fe atoms. [Copyright &y& Elsevier]

Abstract: Treatment of parent compounds [(μ-SCH2)2X]Fe2(CO)6 (A, X=O; B, X=NBu-t; C, X=NC6H4OMe-p) with N-heterocyclic carbene IMes (IMes =1,3-bis(mesityl)imidazol-2-ylidene) generated in situ through reaction of imidazolium salt IMes ·HCl with n-BuLi or t-BuOK afforded the monocarbene-substituted complexes [(μ-SCH2)2X]Fe2(CO)5(IMes) (1, X=O; 2, X=NBu-t; 3, X=NC6H4OMe-p). Similarly, the monocarbene and dicarbene-substituted complexes [(μ-SCH2)2NBu-t]Fe2(CO)5[I∗ Mes(CH2)3I∗ Mes]·HBr (4) and [(μ-SCH2)2CH2Fe2(CO)5]2[μ-I∗ Mes(CH2)3I∗ Mes] (5, I∗ Mes =1-(mesityl)imidazol-2-ylidene) could be prepared by reactions of parent compound B with the mono-NHC ligand-containing imidazolium salt [I∗ Mes(CH2)3I∗ Mes]·HBr and parent compound [(μ-SCH2)2CH2]Fe2(CO)6 (D) with di-NHC ligand I∗ Mes(CH2)3I∗ Mes (both NHC ligands were generated in situ from reaction of n-BuLi with imidazolium salt [I∗ MesI∗ Mes(CH2)3I∗ Mes]·2HBr), respectively. The imidazolium salt [I∗ Mes(CH2)3I∗ Mes]·2HBr was prepared by reaction of 1-(mesityl)imidazole with Br(CH2)3Br. All the new model compounds 1–5 and imidazolium salt [I∗ Mes(CH2)3I∗ Mes]·2HBr were fully characterized by elemental analysis, spectroscopy, and X-ray crystallography. On the basis of electrochemical studies of 1 and 2, compound 2 was found to be a catalyst for proton reduction to hydrogen. In addition, an EECC mechanism for this electrocatalytic reaction is preliminarily suggested. [Copyright &y& Elsevier]

The potential influence of pendant amine of phosphine ligands on the structural, protophilic, and electrocatalytic properties of diiron model complexes for proton reduction to H 2 are described. [Display omitted] • Diiron monophosphine complexes 1 and 2 were prepared and characterized. • Complexes 1 and 2 are partially protonated with CF 3 CO 2 H but are unreactive with CH 3 CO 2 H. • Complex 1 shows a faster catalysis of proton reduction to H 2 in contrast to reference 2. To explore the influence of pendant amine of phosphine ligands on the structural, protophilic, and electrochemical properties of diiron model complexes related to [FeFe]-hydrogenases, one new aminophosphine-substituted diiron oxadithiolate (odt) complex Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 NMe 2)} (1) and its new reference analogue Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 Ph)} (2) were synthesized and characterized through elemental analysis, FT-IR as well as NMR spectroscopies, and X-ray crystallography. Notably, a comparative study on the protonation and electrochemistry of 1 and 2 is performed in the absence or presence of strong acid CF 3 CO 2 H and weak acid CH 3 CO 2 H by using in situ spectroscopic techniques (IR and NMR) and cyclic voltammetry (CV). The protonation study reveals that complexes 1 and 2 are treated with excess CF 3 CO 2 H to form a small amount of their respective Fe-protonated products [(μ -H)Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 NMe 2)}](CF 3 CO 2) ([1(μ H)]+) and [(μ -H)Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 Ph)}](CF 3 CO 2) ([2(μ H)]+), but they are unreactive with excess CH 3 CO 2 H. The CV investigation suggests that complexes 1 and 2 are found to be active biomimetic electrocatalysts for proton reduction to hydrogen (H 2) with CF 3 CO 2 H and CH 3 CO 2 H, in which complex 1 shows a slightly greater turnover frequency (TOF) value for H 2 evolution in contrast to its reference 2. [ABSTRACT FROM AUTHOR]

FeIFeI Fe2(S2C3H6)(CO)6(µ-CO) (1a–CO) and its FeIFeII cationic species (2a+–CO) are the simplest model of the CO-inhibited [FeFe] hydrogenase active site, which is known to undergo CO photolysis within a temperature-dependent process whose products and mechanism are still a matter of debate. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations, the ground state and low-lying excited-state potential energy surfaces (PESs) of 1a–CO and 2a+–CO have been explored aimed at elucidating the dynamics of the CO photolysis yielding Fe2(S2C3H6)(CO)6 (1a) and [Fe2(S2C3H6)(CO)6]+ (2a+), two simple models of the catalytic site of the enzyme. Two main results came out from these investigations. First, a–CO and 2a+–CO are both bound with respect to any CO dissociation with the lowest free energy barriers around 10 kcal mol−1, suggesting that at least 2a+–CO may be synthesized. Second, focusing on the cationic form, we found at least two clear excited-state channels along the PESs of 2a+–CO that are unbound with respect to equatorial CO dissociation. [ABSTRACT FROM AUTHOR]

A new series of the asymmetrically PNP-chelate diiron edt complexes 1 – 3 were prepared and especially an electrocatalytic comparison with all-CO precursor A is investigated, aiming to better explore the role of the asymmetrically PNP-chelate ligands in diiron subsite models of [FeFe]-hydrogenases. • A new series of the PNP-chelate diiron edt complexes 1‒3 were prepared. • The molecular structures of 1‒3 have been fully characterized. • Electrochemical and electrocatalytic properties of 1‒3 and A are investigated. • Complexes 1‒3 all display a higher TOF and a lower overpotential in contrast to A. As a further exploration of the desirable diiron subsite models of [FeFe]-hydrogenases for hydrogen (H 2) evolution, the asymmetrically PNP-chelate diiron ethanedithiolate complexes Fe 2 (μ -edt)(CO) 4 { κ2 -(Ph 2 P) 2 NR} (1 – 3) can be synthesized in good yields through the substitution reactions of diiron all-carbonyl complexes Fe 2 (μ -edt)(CO) 6 (A , edt = SCH 2 CH 2 S) with different PNP ligands (PNP = (Ph 2 P) 2 NR, R = (CH 2) 2 CHMe 2 , (CH 2) 3 OMe, (CH 2) 3 SMe) in the presence of Me 3 NO·2H 2 O as decarbonylating agent. These new complexes 1 – 3 have been fully characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1 by X-ray crystallography. Further, the electrochemical and electrocatalytic properties of complexes 1 – 3 and their precursor A as a reference compound are studied and compared through cyclic voltammetry (CV) in the absence and presence of HOAc as a proton source, suggesting that they are all found to be electrochemically active but show the distinct electrocatalytic abilities for proton reduction to H 2. [ABSTRACT FROM AUTHOR]

Small molecule biomimetics inspired by the active site of the [FeFe]‐hydrogenase enzymes have shown promising electrocatalytic activity for hydrogen (H2) generation. However, most of the active‐site mimics based on [2Fe‐2S] clusters are not water‐soluble which limits the use of these electrocatalysts to organic media. Polymer‐supported [2Fe‐2S] systems, in particular, single‐site metallopolymer catalysts, have shown drastic improvements for electrocatalytic H2 generation in aqueous milieu. [2Fe‐2S] complexes functionalized within well‐defined macromolecular supports via covalent bonding have demonstrated water solubility, enhanced site‐isolation, and improved chemical stability during catalysis. In this report, the synthesis of a new propanedithiolate (pdt)‐[2Fe‐2S] complex bearing a single α‐bromoester moiety for use in atom transfer radical polymerization (ATRP) is demonstrated as a novel metalloinitiator to prepare water‐soluble poly(2‐dimethylaminoethyl methacrylate) grafted (PDMAEMA‐g‐[2Fe‐2S]) metallopolymers. Using this approach, metallopolymers with controllable molecular weights (Mn = 5–40 kg mol−1) and low dispersity (Đ, Mw/Mn = 1.09–1.36) are prepared, which allows for the first time observation of the effect of the metallopolymers' chain length on the electrocatalytic activity. The ability to control the composition and molecular weight of these metallopolymers enables macromolecular engineering via ATRP of these materials to determine optimal structural features of metallopolymer catalysts for H2 production. [ABSTRACT FROM AUTHOR]

• Constructing a photosensitizable UiO-MOF from mixed functional dicarboxylate ligands. • Integrating a covalently bonded hydrogen evolving catalyst (Complex A) into a highly stable photosensitizable UiO-MOF. • Improving the electron transfer efficiency between the photosensitizer and the Fe 2 S 2 catalytic site. • The photocatalytical mechanism was investigated and well supported by fluorescent spectra and cyclic voltammetry data. We have successfully integrated a covalently bonded hydrogen evolving catalyst (Complex A) into a highly stable photosensitizable UiO-MOF by a facile click reaction synthesis. The UiO-MOF was constructed from mixed functional dicarboxylate ligands, in which a [Ru(bpy) 3 ]2+-derived dicarboxylate ligand (H 2 L1) acts as a photosensitizer and an azide-modified dicarboxylate ligand (H 2 L2) allows the catalyst Complex A to be firmly bound to the framework by covalent bonds. The integration of the photosensitizer and catalyst molecules together into the same UiO-MOF decreases the distance between them, and leads to improvement of the electron transfer efficiency between the photosensitizer and the Fe 2 S 2 catalytic site. Reference experiments show that the resultant UiO-MOF-Fe 2 S 2 exhibits exponentially enhanced photocatalytic activity and stability in a visible-light driven hydrogen process. The excellent performance of the UiO-MOF-Fe 2 S 2 indicates that incorporation of the Fe 2 S 2 catalytic center into UiO-MOF is a promising strategy with which to stabilize Fe 2 S 2 catalyst in water and improve the photocatalytic efficiency of hydrogen evolution. [ABSTRACT FROM AUTHOR]