Active Site Of Fe-only Hydrogenases Research Articles

A new reactivity pattern of heterodinuclear complexes [MnRe(CO)6(μ-S2CPR3)] with nBuLi/protonation and its electrochemistry properties investigation as structure and function models for the Fe-only hydrogenase active site

A novel reaction pattern of heterodinuclear complexes was reported. Namely, nucleophilic attack of nBuLi/protonation of complexes [MnRe(CO)6(μ-S2CPR3)] occurs with the cleavage of the Mn–Re, (P)C–S bond and formation of new (Bu)C–S bond, to afford the novel complexes [MnRe(CO)6(μ-SnBu)(μ-S-C(H)PR3)] (L) (L = PR3, C5H5N) 3 and 4 which are different from previous complexes (1 and 2 or other complexes) obtained by the reduction with Na[Hg] or superhydride reagent. Additionally, in order to develop these complexes application, several similar structure Mn–Re binuclear complexes, MnRe(CO)6(μ-H)[μ-S(SnBu)CC(PiPr3)S] (1), MnRe(CO)6(μ-H)[μ-S(SCH3)CC(PiPr3)S] (2), MnRe(CO)6(μ-SnBu)[μ-SC(H)PCy3PPh3] (3), MnRe(CO)6(μ-SnBu)[μ-SC(H)PCy3Py] (4), which serve as structural models for the active site of Fe-hydrogenase, were chosen to investigate their possible electrochemical properties. Consequently, they are indeed shown to be electrocatalysts for H2 production in the presence of acetic acid in acetonitrile. The electrocatalysis is initiated by electrochemical reduction of these Mn–Re complexes, which subsequently, under weak acid conditions, undergo protonation of the reduced rhenium center to produce H2. And two probable electrochemical mechanisms (EECC and ECCE) are also proposed.

A new cumulene diiron complex related to the active site of Fe-only hydrogenases and its phosphine substituted derivatives: Synthesis, electrochemistry and structural characterization

A new cumulene diiron complex related to the Fe-only hydrogenase active site [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 6] ( 1) was obtained by treatment of (μ-LiS) 2Fe 2(CO) 6 with excess 1,4-dichloro-2-butyne. By controllable CO displacement of 1 with PPh 3 and bis(diphenylphosphino)methane (dppm), mono- and di-substituted complexes, namely [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 5L] ( 2: L = PPh 3; 3: L = dppm) and [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 4L 2] ( 4: L = PPh 3; 5: L = dppm) could be prepared in moderate yields. Treatment of 1 with bis(diphenylphosphino)ethane (dppe) afforded a double butterfly complex [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 5] 2(μ-dppe) ( 7). With dppm in refluxing toluene, a dppm-bridged complex [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 4(μ-dppm)] ( 6) was obtained. These model complexes were characterized by IR, 1H, 31P NMR spectra and the molecular structures of 1, 2 and 5– 7 were determined by single crystal X-ray analyses. The electrochemistry of 1– 3 was studied and the electrocatalytic property of 1 was investigated for proton reduction in the presence of HOAc.

Fe-only hydrogenase active site mimics: Fe2(CO)6(μ-ADT) (ADT=azadithiolate) clusters bearing pendant 2,2′:6′,2″-terpyridine domains and containing alkynylthienylene or alkynylphenylene spacers

We report the syntheses and single crystal structures of two Fe2(CO)6(μ-ADT) (ADT = azadithiolate) clusters bearing pendant tpy (tpy = 2,2′:6′,2″-terpyridine) domains and containing alkynylthienylene or alkynylphenylene spacers between the Fe-only hydrogenase active site mimic and tpy metal-binding unit.

Carboxy-functionalized dithiolate di-iron complexes related to the active site of Fe-only hydrogenase

Reactions of the di-iron complex [Fe 2(μ-S) 2(CO) 6] 2− with carboxy-functionalized dihalide derivatives (XCH 2) 2R (X = Cl, R = NC 6H 4CH 2CO 2CH 3; X = Br, R = C 6H 3COOH, C 6H 3COON(COCH 2) 2) gave new functionalized dithiolate di-iron complexes [Fe 2(μ-SRS)(CO) 6] (R = (CH 2) 2NC 6H 4CH 2CO 2CH 3 ( 1), (CH 2) 2C 6H 3COOH ( 2), (CH 2) 2C 6H 3COON(COCH 2) 2 ( 3)) in low yields. The azadithiolate complex 1 has been characterized by a single crystal X-ray diffraction analysis and studied by electrochemical methods.

Diiron models for the active site of Fe-only hydrogenase with terminal organosulfur ligation: Synthesis, structures and electrochemistry

Diiron model complexes (μ-SCH 2CH 2CH 2S)Fe 2(CO) 5L with thioether-substitution, L = S(CH 2CH 3) 2 ( 2), S(CH 2CH 3)(CH 2CH 2Cl) ( 3), S(CH 2CH 3)(C 6H 5) ( 4), or sulfoxide-substitution, L = SO(CH 2CH 2CH 3) 2 ( 5), SO(CH 3) 2 ( 6), were synthesized as active site analogues of Fe-only hydrogenase. The organosulfur ligands were introduced into the diiron centers via moderately stable intermediates following two routes. The X-ray crystallographic structures of complexes 2– 6 show the apical positions of terminal organosulfur ligands. The electrochemical behaviors of the model complexes were investigated, especially for the interesting properties of the derivative of 6 which is proposed to be the first model with weak donor ligand similar to CO.

Synthesis, structure and electrochemical property of diphenylacetypene-substituted diiron azadithiolates as active site of Fe-only hydrogenases

The model complexes 1– 3 of functionalized azadithiolate (ADT)-bridged Fe-only hydrogenases, [Fe 2(Co) 6(μ-ADT)C 6H 4C CR] [R = C 6H 4NO 2-4 ( 1), C 6H 5 ( 2), C 6H 4OCH 3-4 ( 3)] have been synthesized in high yields under mild conditions by using Sonogashira reaction. Spectroscopic study and X-ray crystal structural analysis of 1 demonstrate that the model complexes retain the butterfly structure of 2Fe2S model analogues. The intermolecular C–H⋯O, C–H⋯π hydrogen bonding and π–π interactions play important roles in molecular packing of 1. In the presence of HOAc, complex 1 features the catalytic electrochemical proton reduction.

Fe–S complexes containing five-membered heterocycles: novel models for the active site of hydrogenases with unusual low reduction potential

Three biomimetic 2Fe2S complexes [{(micro-SCH2)2NCH2(2-C4H3O)}](Fe2(CO)6), [{(micro-SCH2)2 NCH2(2-C4H3S)}](Fe2(CO)6) and [{(micro-SCH2)2NCH2(5-Br-2-C4H2S)}Fe2(CO)6] were prepared as models for the active site of Fe-only hydrogenase by the convergent process from [(micro-S2)Fe2(CO)6] and N,N-bis(hydromethyl)-2-furan and thiophene. The structures of these complexes were identified spectroscopically and crystallographically. The electrochemical behavior of the complexes and was unique as they showed catalytic proton reduction with a low reduction potential at -1.13 and -1.09 V vs Fc/Fc+, respectively, in the presence of HClO4.

Carbene–pyridine chelating 2Fe2S hydrogenase model complexes as highly active catalysts for the electrochemical reduction of protons from weak acid (HOAc)

Two asymmetrically disubstituted diiron complexes (micro-pdt)[Fe(CO)(3)][Fe(CO)(eta(2)-L)] (L = 1-methyl-3-(2-pyridyl)imidazol-2-ylidene (NHC(MePy)), 2; 1,3-bis(2-picolyl)imidazol-2-ylidene (NHC(diPic)), 4) and a mono-substituted diiron complex (mu-pdt)[Fe(CO)(3)][Fe(CO)(2)(NHC(diPic))] (3) were prepared as biomimetic models of the Fe-only hydrogenase active site. X-Ray studies show that the NHC(MePy) and NHC(diPic) ligands in 2 and 4 each coordinate to the single iron atom as NHC-Py chelating ligands in two basal positions and the NHC(diPic) ligand of complex 3 lies in an apical position as a monodentate ligand. The large ranges of the highest and the lowest nu(CO) frequencies of 2 and 4 reflect that the relatively uneven electron density on the two iron atoms of the 2Fe2S model complexes 2 and 4 is as that observed for mono-substituted diiron complexes of good donor ligands. The cyclic voltammograms and the electrochemical proton reduction by 2 and 3 were studied in the presence of HOAc to evaluate the effect of asymmetrical substitution of strong donor ligands on the redox properties of the iron atoms and on the electrocatalytic activity for proton reduction.

Preparation, structures and electrochemical property of phosphine substituted diiron azadithiolates relevant to the active site of Fe-only hydrogenases

Mono- and di-phosphine diiron azadithiolate complexes [{(μ-SCH 2) 2N(4-NO 2C 6H 4)}Fe 2(CO) 5(PMe 3)] ( 2), [{(μ-SCH 2) 2N(4-NO 2C 6H 4)}{Fe(CO) 2L} 2] ( 3, L = PMe 3; 4, PMe 2Ph) and the μ-hydride diiron complex [ 3(FeHFe)] +[PF 6] − were prepared as biomimetic models of the active site of Fe-only hydrogenases. The complexes 2– 4 and [3(FeHFe)] +[PF 6] − were characterized by IR, 31P, 1H and 13C NMR spectra and their molecular structures were determined by single crystal X-ray analyses. The PMe 3 ligand in complex 2 lies on the basal position. The PMe 3-disubstituted complex 3 exists as two configuration isomers, transoid basal/basal and apical/basal, in the crystalline state, while two PMe 2Ph ligands of 4 are in an apical/basal orientation. The variable temperature 31P NMR spectra of 2 and 3 were made to have an insight into the existence of the possible conformation isomers of 2 and 3 in solution. The [ 3(FeHFe)] + cation possesses the sole transoid ba/ba geometry as other reported μ-hydride diiron analogues. The electrocatalytic property of {(μ-SCH 2) 2NC 6H 5}[Fe(CO) 2PMe 3] 2 ( 5) was studied for proton reduction in the presence of HOAc.

Density functional theory approach for improving the catalytic activity of a biomimetic model based on the Fe-only hydrogenase active site

Abstract A complete catalytic cycle for H2 oxidation on a model emulating the active site of Fe-only hydrogenases, [Fe2(μ-DTMA)(CO)4(CN)2]2− (DTMA = SCH2NHCH2S), has been investigated using density functional theory (DFT). Our calculations show that the bridged CO group in the fully reduced species does not play a significant role on the H2 activation. According to the studied mechanism, the rate-determining step is neither kinetically nor thermodynamically favorable for the second proton transfer. A modified model aiming to improve the catalytic efficiency has been designed and a plausible catalytic mechanism is suggested. In the new model, [Fe2(μ-PDTN)(CO)4(CN)2]2− (PDTN = SCH2CH(NH2)CH2S), a shorter proton transfer path has been obtained by changing the base position and the process is significantly facilitated. In the modified catalytic cycle, the highest barrier for H2 oxidation is only 7.90 kcal mol−1.

Synthesis, structures and electrochemical properties of hydroxyl- and pyridyl-functionalized diiron azadithiolate complexes

The hydroxyl- and pyridyl-functionalized diiron azadithiolate complexes [{(μ-SCH 2) 2N(CH 2CH 2OH)}Fe 2(CO) 6] ( 1) and [{(μ-SCH 2) 2N(CH 2CH 2OOCPy)}Fe 2(CO) 6] (Py = pyridyl) ( 2) were prepared as biomimetic models of the active site of Fe-only hydrogenases. Both complexes were characterized by MS, IR, 1H NMR spectra and elemental analysis. The molecular structures of 1 and 2 were determined by single crystal X-ray analysis. A network is constructed by intermolecular H-bonds in the crystals of 1. An S⋯O intermolecular contact was found in the crystals of 2, which is scarcely found for organometallic complexes. Cyclic voltammograms of 1 and 2 were studied to evaluate their redox properties.

A furan-containing diiron azadithiolate hexacarbonyl complex with unusual lower catalytic proton reduction potential

A new biomimetic model of the active site of Fe-only hydrogenase [{(μ-SCH 2) 2N(2-C 4H 3O)}Fe 2(CO) 6] ( 6) was synthesized and characterized by IR, 1H, 13C NMR spectroscopy. The butterfly based core structure was also confirmed by X-ray diffraction. The electrochemistry data indicated that the reductive potential at −1.13 V versus Fc/Fc + by HClO 4 is the lowest of that reported.

An insight into the protonation property of a diiron azadithiolate complex pertinent to the active site of Fe-only hydrogenases

Protonation of [{(mu-SCH2)2N(C6H4-p-NO2)}{Fe(CO)2(PMe3)}2] in the presence of 4 equiv. of HOTf afforded two species, a micro-hydride diiron complex, the molecular structure of which was crystallographically characterized, and a micro-S-protonated species, which was readily deprotonated in the presence of pyridine.

Electron‐Rich Diferrous–Phosphane–Thiolates Relevant to Fe‐only Hydrogenase: Is Cyanide “Nature's Trimethylphosphane”?

The two-step one-pot oxidative decarbonylation of [Fe2(S2C2H4)(CO)4(PMe3)2] (1) with [FeCp2]PF6, followed by addition of phosphane ligands, led to a series of diferrous dithiolato carbonyls 2-6, containing three or four phosphane ligands. In situ measurements indicate efficient formation of 1(2+) as the initial intermediate of the oxidation of 1, even when a deficiency of the oxidant was employed. Subsequent addition of PR3 gave rise to [Fe2(S2C2H4)(mu-CO)(CO)3(PMe3)3]2+ (2) and [Fe2(S2C2H4)(mu-CO)(CO)2(PMe3)2(PR3)2]2+ (R = Me 3, OMe 4) as principal products. One terminal CO ligand in these complexes was readily substituted by MeCN, and [Fe2(S2C2H4)(mu-CO)(CO)2(PMe3)3(MeCN)]2+ (5) and [Fe2(S2C2H4)(mu-CO)(CO)(PMe3)4(MeCN)]2+ (6) were fully characterized. Relevant to the H(red) state of the active site of Fe-only hydrogenases, the unsymmetrical derivatives 5 and 6 feature a semibridging CO ligand trans to a labile coordination site.

Diiron Oxadithiolate Type Models for the Active Site of Iron-Only Hydrogenases and Biomimetic Hydrogen Evolution Catalyzed by Fe2(μ-SCH2OCH2S-μ)(CO)6

The biomimetic chemistry of single and double oxadithiolatodiiron-containing model compounds for the active site of Fe-only hydrogenases (FeHases) has been systematically studied. The simplest such model, Fe2(μ-SCH2OCH2S-μ)(CO)6 (1), was prepared by reaction of (μ-S2)Fe2(CO)6 with 2 equiv of Et3BHLi followed by direct treatment with excess (ClCH2)2O or by successive treatment with 2 equiv of CF3CO2H and excess (ClCH2)2O in the presence of Et3N. Further reaction of 1 with 1 equiv of Me3NO in MeCN at room temperature followed by treatment of the intermediate Fe2(μ-SCH2OCH2S-μ)(CO)5L (L = MeCN or Me3N) with 1 equiv of Et4NCN, PPh3, or Cp(CO)2FeSPh gave the single models Fe2(μ-SCH2OCH2S-μ)(CO)5La (2, La = (CN)(Et4N); 3, PPh3; 4, Cp(CO)2FeSPh) in 62−93% yields, whereas the in situ treatment of the intermediate Fe2(μ-SCH2OCH2S-μ)(CO)5L with 0.5 equiv of 1,4-(CN)2C6H4, (η5-Ph2PC5H4)2Fe (dppf), or (η5-Ph2PC5H4)2Ru (dppr) afforded the double models [Fe2(μ-SCH2OCH2S-μ)(CO)5]2Lb (5, Lb = 1,4-(CN)2C6H4; 6, dppf; 7, d...

An Unusual Cyclization in a Bis(cysteinyl-S) Diiron Complex Related to the Active Site of Fe-Only Hydrogenases

Die Autoren dieser Zuschrift bitten, in der Danksagung folgende Zeile zu ergänzen: B. Å. and L. S. thank the Swedish Energy Agency and the Swedish Research Council for financial support.

Spectroscopic and crystallographic evidence for the N-protonated FeIFeI azadithiolate complex related to the active site of Fe-only hydrogenases

The complex [{(mu-SCH2)2N(CH2C6H4-2-Br)}Fe2(CO)6] and its N-protonated species, as structural models of the Fe-only hydrogenase active site, were identified spectroscopically and crystallographically, and their molecular structures show the 0.04-0.1 A lengthening of the three N-C bonds and an intramolecular HBr contact (2.82 Angstroms) in the crystalline state of the N-protonated species.

Di-Iron Aza Diphosphido Complexes: Mimics for the Active Site of Fe-Only Hydrogenase, and Effects of Changing the Coordinating Atoms of the Bridging Ligand in [Fe2{μ-(ECH2)2NR}(CO)6

The bis(phosphido)-bridged complex [Fe(2)(mu-PPhH)(2)(CO)(6)] (1) undergoes double deprotonation to give the phosphorus-centered dianionic derivative [Fe(2)(mu-PPh)(2)(CO)(6)](2)(-) (2) which in turn reacts with the tertiary base RN(CH(2)Cl)(2) to give [Fe(2)[(PPhCH(2))(2)NR](CO)(6)] (3) in moderate yield. Treatment of 3 with HBF(4).Et(2)O affords the N-protonated species [Fe(2)[(PPhCH(2))(2)NHR](CO)(6)] BF(4) (4). The structural changes to the heavy atom skeleton of 3 arising from protonation are slight, the most obvious being a ca. 0.03 Alengthening of the N-C bonds.

Dihydrogen activation by a diruthenium analogue of the Fe-only hydrogenase active site.

The photochemical reaction of Ru2(S2C3H6)(CO)4(PCy3)2 (1) and H2 gives the dihydride Ru2(S2C3H6)(mu-H)(H)(CO)3(PCy3)2 (2). NMR and crystallographic studies reveal mutually trans basal phosphine ligands and both bridging and terminal hydrides. Ru2(S2C2H4)(CO)4(PCy3)2 behaves similarly. Other HX substrates undergo photoaddition to 1, affording Ru2(S2C3H6)(mu-H)(X)(CO)3(PCy3)2 for X = OTs (3a), Cl (3b), and SPh (3c). Treatment of Ru2(S2C3H6)(mu-H)(H)(CO)3(PCy3)2 with [H(OEt2)]BArF4 (ArF = B(C6H3-3,5-(CF3)2) in CD2Cl2 gives [Ru2(S2C3H6)(mu-H)(CO)3(PCy3)2(H2)]+ (4), which catalyzes H2-D2 exchange. The reaction of 2 with [D(OEt2)]BArF4 gave [Ru2(S2C3H6)(mu-H)(CO)3(PCy3)2(HD)]+ (JH-D = 31 Hz). These studies provide the first models for the Fe-only hydrogenases that bear dihydrogen and terminal hydrido ligands.

Synthesis, structures and electrochemical properties of nitro- and amino-functionalized diiron azadithiolates as active site models of Fe-only hydrogenases.

Complex [[(mu-SCH2)2N(4-NO2C6H4)]Fe2(CO)6] (4) was prepared by the reaction of the dianionic intermediate [(mu-S)2Fe2(CO)6](2-) and N,N-bis(chloromethyl)-4-nitroaniline as a biomimetic model of the active site of Fe-only hydrogenase. The reduction of 4 by Pd-C/H2 under a neutral condition afforded complex [[(mu-SCH2)2N(4-NH2C6H4)]Fe2(CO)6] (5) in 67 % yield. Both complexes were characterized by IR, 1H and 13C NMR spectroscopy and MS spectrometry. The molecular structure of 4, as determined by X-ray analysis, has a butterfly 2Fe2S core and the aryl group on the bridged-N atom slants to the Fe(2) site. Cyclic voltammograms of 4 and 5 were studied to evaluate their redox properties. It was found that complex 4 catalyzed electrochemical proton reduction in the presence of acetic acid. A plausible mechanism of the electrocatalytic proton reduction is discussed.