Thiolate‐Bridged Iron–Nickel Models for the Active Site of [NiFe] Hydrogenase

Ohki, Yasuhiro; Tatsumi, Kazuyuki

doi:10.1002/ejic.201001087

Cited by 79 publications

(59 citation statements)

References 127 publications

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“…3,4,11 In contrast, models of the oxygentolerant [NiFe]-hydrogenases are less mature, and comparisons to the enzymatic system are sometimes less applicative. 3,4,12,13 …”

Section: Introductionmentioning

confidence: 99%

Models of the Ni-L and Ni-SI_a States of the [NiFe]-Hydrogenase Active Site

Chambers

Huynh

et al. 2015

Inorg. Chem.

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A new class of synthetic models for the active site of [NiFe]-hydrogenases are described. The NiI/II(SCys)2 and FeII(CN)2CO sites are represented with (RC5H4)NiI/II and FeII(diphos)(CO) modules, where diphos = 1,2-C2H4(PPh2)2(dppe) or cis-1,2-C2H2(PPh2)2(dppv). The two bridging thiolate ligands are represented by CH2(CH2S)22− (pdt2−), Me2C(CH2S)22− (Me2pdt2−), and (C6H5S)22−. The reaction of Fe(pdt)(CO)2(dppe) and [(C5H5)3Ni2]BF4 affords [(C5H5)Ni(pdt)Fe(dppe)-(CO)]BF4 ([1a]BF4). Monocarbonyl [1a]BF4 features an S = 0 NiIIFeII center with five-coordinated iron, as proposed for the Ni-SIa state of the enzyme. One-electron reduction of [1a]+ affords the S = 1/2 derivative [1a]0, which, according to density functional theory (DFT) calculations and electron paramagnetic resonance and Mössbauer spectroscopies, is best described as a NiIFeII compound. The NiIFeII assignment matches that for the Ni-L state in [NiFe]-hydrogenase, unlike recently reported NiIIFeI-based models. Compound [1a]0 reacts with strong acids to liberate 0.5 equiv of H2 and regenerate [1a]+, indicating that H2 evolution is catalyzed by [1a]0. DFT calculations were used to investigate the pathway for H2 evolution and revealed that the mechanism can proceed through two isomers of [1a]0 that differ in the stereochemistry of the Fe(dppe)CO center. Calculations suggest that protonation of [1a]0 (both isomers) affords NiIII–H–FeII intermediates, which represent mimics of the Ni-C state of the enzyme.

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“…3,4,11 In contrast, models of the oxygentolerant [NiFe]-hydrogenases are less mature, and comparisons to the enzymatic system are sometimes less applicative. 3,4,12,13 …”

Section: Introductionmentioning

confidence: 99%

Models of the Ni-L and Ni-SI_a States of the [NiFe]-Hydrogenase Active Site

Chambers

Huynh

et al. 2015

Inorg. Chem.

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“…1,8 Since 2009, several nickel-iron hydrides have been reported, but all of these models feature Fe(CO) 3-x (PR 3 ) x centers (x = 0, 1, 2). 9-12 In contrast to these cationic models, the active site is expected to be anionic since six cofactors - two cyanide and four thiolate groups - are anionic.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Activation by Biomimetic [NiFe]-Hydrogenase Model Containing Protected Cyanide Cofactors

Manor

Rauchfuss

2013

J. Am. Chem. Soc.

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Described are experiments that allow incorporation of cyanide cofactors and hydride substrate into active site models [NiFe]-hydrogenases (H2ases). Complexes of the type (CO)2(CN)2Fe(pdt)Ni(dxpe), (dxpe = dppe, 1; dxpe = dcpe, 2) bind the Lewis acid B(C6F5)3 (BArF3) to give the adducts (CO)2(CNBArF3)2Fe(pdt)Ni(dxpe), (1(BArF3)2, 2(BArF3)2). Upon decarbonylation using amine oxides, these adducts react with H2 to give hydrido derivatives Et4N[(CO)(CNBArF3)2Fe(H)(pdt)Ni(dxpe)], (dxpe = dppe, Et4N[H3(BArF3)2]; dxpe = dcpe, Et4N[H4(BArF3)2]). Crystallographic analysis shows that Et4N[H3(BArF3)2] generally resembles the active site of the enzyme in the reduced, hydride-containing states (Ni-C/R). The Fe-H…Ni center is unsymmetrical with rFe-H = 1.51(3) and rNi-H = 1.71(3) Å. Both crystallographic and 19F NMR analysis show that the CNBArF3− ligands occupy basal and apical sites. Unlike cationic Ni-Fe hydrides, [H3(BArF3)2]− and [H4(BArF3)2]− oxidize at mild potentials, near the Fc+/0 couple. Electrochemical measurements indicate that in the presence of base, [H3(BArF3)2]− catalyzes the oxidation of H2. NMR evidence indicates dihydrogen bonding between these anionic hydrides and ammonium salts, which is relevant to the mechanism of hydrogenogenesis. In the case of Et4N[H3(BArF3)2], strong acids such as HCl induce H2 release to give the chloride Et4N[(CO)(CNBArF3)2Fe(pdt)(Cl)Ni(dppe)].

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“…However, these criteria are not easy to meet in model systems [150]. The work on biomimetic models for [NiFe] and [FeFe] hydrogenase has been described in several review articles [150][151][152][153][154][155][156][157][158]. In this work, many of the structural features important for proper function found in the native systems have been successfully incorporated -for example, the bimetallic Ni-Fe or Fe-Fe core with rather short metalmetal distances and an open coordination site at one metal, the sulfur-rich environment (terminal and bridging thiolate ligands), CO/CN ligation of the iron(s), and the incorporation of a base for acceptance of the proton and, more recently, of hydride bridges.…”

Section: Molecular Catalysts For H 2 Conversion and Productionmentioning

confidence: 99%