Crystallographic Characterization of a Fully Rotated, Basic Diiron Dithiolate: Model for the H<sub>red</sub> State?

Wang, Wenguang; Rauchfuss, Thomas B.; Moore, Curtis E.; Rheingold, Arnold L.; Gioia, Luca De; Zampella, Giuseppe

doi:10.1002/chem.201303351

Cited by 61 publications

(73 citation statements)

References 23 publications

(33 reference statements)

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“…31 Models for this rotated state have been crystallized, revealing that Fe–Fe bonding is weakened and a terminal site on one Fe center is vacant. 32 By analogy to the results in this paper, such rotated diiron complexes should perhaps be described as Fe(II)Fe(0), thus underlining the role of latent, but highly reactive intermediates.…”

Section: Discussionmentioning

confidence: 55%

Protonation of Nickel–Iron Hydrogenase Models Proceeds after Isomerization at Nickel

et al. 2014

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Theory and experiment indicate that the protonation of reduced NiFe dithiolates proceeds via a previously undetected isomer with enhanced basicity. In particular, it is proposed that protonation of (OC)3Fe(pdt)Ni(dppe) (1; pdt2– = –S(CH2)3S–; dppe = Ph2P(CH2)2PPh2) occurs at the Fe site of the two-electron mixed-valence Fe(0)Ni(II) species, not the Fe(I)-Ni(I) bond for the homovalence isomer of 1. The new pathway, which may have implications for protonation of other complexes and clusters, was uncovered through studies on the homologous series L(OC)2Fe(pdt)M(dppe), where M = Ni, Pd (2), and Pt (3) and L = CO, PCy3. Similar to 1, complexes 2 and 3 undergo both protonation and 1e– oxidation to afford well-characterized hydrides ([2H]+ and [3H]+) and mixed-valence derivatives ([2]+ and [3]+), respectively. Whereas the Pd site is tetrahedral in 2, the Pt site is square-planar in 3, indicating that this complex is best described as Fe(0)Pt(II). In view of the results on 2 and 3, the potential energy surface of 1 was reinvestigated with density functional theory. These calculations revealed the existence of an energetically accessible and more basic Fe(0)Ni(II) isomer with a square-planar Ni site.

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Section: Discussionmentioning

confidence: 55%

Protonation of Nickel–Iron Hydrogenase Models Proceeds after Isomerization at Nickel

et al. 2014

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“…Similar bimetallic hydrides have been known to adopt different isomers. 22,47 Furthermore, recent work suggests that the protonation of (dppe)Ni(pdt)-Fe(CO) 3 proceeds via an unobserved isomer. 21 …”

Section: Resultsmentioning

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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“…142 This and related sterically crowded complexes are of interest as precursors to diiron ditholates that adopt unsymmetrical, “rotated” structures (Figure 8). 140,141,143 …”

Section: Synthesis Of Diiron(i) Dithiolato Carbonyls From Iron(0) mentioning

confidence: 99%

Synthesis of Diiron(I) Dithiolato Carbonyl Complexes

2016

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Virtually all organosulfur compounds react with Fe(0) carbonyls to give the title complexes. These reactions are reviewed in light of major advances over the past few decades, spurred by interest in Fe2(μ-SR)2(CO)x centers at the active sites of the [FeFe]-hydrogenase enzymes. The most useful synthetic route to Fe2(μ-SR)2(CO)6 involves the reaction of thiols with Fe2(CO)9 and Fe3(CO)12. Such reactions can proceed via mono-, di-, and triiron intermediates. The reactivity of Fe(0) carbonyls toward thiols is highly chemoselective, and the resulting dithiolato complexes are fairly rugged. Thus, many complexes tolerate further synthetic elaboration directed at the organic substituents. A second major route involves alkylation of Fe2(μ-S2)(CO)6, Fe2(μ-SH)2(CO)6, and Li2Fe2(μ-S)2(CO)6. This approach is especially useful for azadithiolates Fe2[(μ-SCH2)2NR](CO)6. Elaborate complexes arise via addition of the FeSH group to electrophilic alkenes, alkynes, and carbonyls. Although the first example of Fe2(μ-SR)2(CO)6 was prepared from ferrous reagents, ferrous compounds are infrequently used, although the Fe(II)(SR)2 + Fe(0) condensation reaction is promising. Almost invariably low-yielding, the reaction of Fe3(CO)12, S8, and a variety of unsaturated substrates results in C–H activation, affording otherwise inaccessible derivatives. Thiones and related C═S-containing reagents are highly reactive toward Fe(0), often giving complexes derived from substituted methanedithiolates and C–H activation.

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Crystallographic Characterization of a Fully Rotated, Basic Diiron Dithiolate: Model for the H_red State?

Abstract: A lucky break: A combination of steric pressure and electron asymmetry has provided the first example of a diiron dithiolate that is both rotated and basic. The present work establishes the feasibility of a hydride free rotated structure for the Hred state of the enzyme.

Cited by 61 publications

References 23 publications

Protonation of Nickel–Iron Hydrogenase Models Proceeds after Isomerization at Nickel

Protonation of Nickel–Iron Hydrogenase Models Proceeds after Isomerization at Nickel

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

Synthesis of Diiron(I) Dithiolato Carbonyl Complexes

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Crystallographic Characterization of a Fully Rotated, Basic Diiron Dithiolate: Model for the Hred State?

Abstract: A lucky break: A combination of steric pressure and electron asymmetry has provided the first example of a diiron dithiolate that is both rotated and basic. The present work establishes the feasibility of a hydride free rotated structure for the Hred state of the enzyme.

Cited by 61 publications

References 23 publications

Protonation of Nickel–Iron Hydrogenase Models Proceeds after Isomerization at Nickel

Protonation of Nickel–Iron Hydrogenase Models Proceeds after Isomerization at Nickel

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

Synthesis of Diiron(I) Dithiolato Carbonyl Complexes

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Crystallographic Characterization of a Fully Rotated, Basic Diiron Dithiolate: Model for the H_red State?

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