Electrochemical proton reduction by thiolate-bridged hexacarbonyldiiron clusters

Capon, Jean‐François; Gloaguen, Frédéric; Schollhammer, Philippe; Talarmin, Jean

doi:10.1016/j.jelechem.2003.11.032

Cited by 135 publications

(113 citation statements)

References 44 publications

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“…[14,15] Functional studies of synthetic models of the active site have thus far been restricted to complexes containing either of these structural elements, that is, either electron-donating ligands with an all-carbon propyldithiolate (pdt = S-CH 2 -CH 2 -CH 2 -S) bridge or all-carbonyl structures with a nitrogen-containing adt bridge. For the cyano-and/or phosphinesubstituted pdt complexes, [16][17][18] reduction of the m-hydrido complex results in electrocatalytic hydrogen production at less negative potentials than for their hexacarbonyl analogues, [18][19][20] where reduction has to precede the oxidative protonation. For the adt all-carbonyl motif, [21] on the other hand, protonation of the bridge nitrogen results in a major shift of the potential required for reduction of the complex that allows for hydrogen formation at potentials even less negative than for the cyanide/phosphine-substituted pdt complexes.…”

Section: + To a C H T U N G T R E N N U N G [1 Hy]mentioning

confidence: 99%

Ligand versus Metal Protonation of an Iron Hydrogenase Active Site Mimic

Eilers

Schwartz

Stein

et al. 2007

Chemistry A European J

133

139

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The protonation behavior of the iron hydrogenase active-site mimic [Fe2(mu-adt)(CO)4(PMe3)2] (1; adt=N-benzyl-azadithiolate) has been investigated by spectroscopic, electrochemical, and computational methods. The combination of an adt bridge and electron-donating phosphine ligands allows protonation of either the adt nitrogen to give [Fe2(mu-Hadt)(CO)4(PMe3)2]+ ([1 H]+), the Fe-Fe bond to give [Fe2(mu-adt)(mu-H)(CO)4(PMe3)2]+ ([1 Hy]+), or both sites simultaneously to give [Fe2(mu-Hadt)(mu-H)(CO)4(PMe3)2]2+ ([1 HHy]2 +). Complex 1 and its protonation products have been characterized in acetonitrile solution by IR, (1)H, and (31)P NMR spectroscopy. The solution structures of all protonation states feature a basal/basal orientation of the phosphine ligands, which contrasts with the basal/apical structure of 1 in the solid state. Density functional calculations have been performed on all protonation states and a comparison between calculated and experimental spectra confirms the structural assignments. The ligand protonated complex [1 H]+ (pKa=12) is the initial, metastable protonation product while the hydride [1 Hy]+ (pKa=15) is the thermodynamically stable singly protonated form. Tautomerization of cation [1 H]+ to [1 Hy]+ does not occur spontaneously. However, it can be catalyzed by HCl (k=2.2 m(-1) s(-1)), which results in the selective formation of cation [1 Hy]+. The protonations of the two basic sites have strong mutual effects on their basicities such that the hydride (pK(a)=8) and the ammonium proton (pK(a)=5) of the doubly protonated cationic complex [1 HHy]2+ are considerably more acidic than in the singly protonated analogues. The formation of dication [1 HHy]2+ from cation [1 H]+ is exceptionally slow with perchloric or trifluoromethanesulfonic acid (k=0.15 m(-1) s(-1)), while the dication is formed substantially faster (k>10(2) m(-1) s(-1)) with hydrobromic acid. Electrochemically, 1 undergoes irreversible reduction at -2.2 V versus ferrocene, and this potential shifts to -1.6, -1.1, and -1.0 V for the cationic complexes [1 H]+, [1 Hy]+, and [1 HHy]2+, respectively, upon protonation. The doubly protonated form [1 HHy]2+ is reduced at less negative potential than all previously reported hydrogenase models, although catalytic proton reduction at this potential is characterized by slow turnover.

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Section: + To a C H T U N G T R E N N U N G [1 Hy]mentioning

confidence: 99%

Ligand versus Metal Protonation of an Iron Hydrogenase Active Site Mimic

Eilers

Schwartz

Stein

et al. 2007

Chemistry A European J

133

139

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“…[37][38][39] This approach has been well illustrated by [Fe 2 (m-bdt)(CO) 6 ] (1; bdt = benzenedithiolate; Scheme 1), which is an easily synthesized proton-reduction catalyst combining reversible reductive electrochemistry and good activity at mild potentials in organic solvents: E 1/2 = À1.30 V versus ferrocenium/ferrocene (Fc + /0 ) in MeCN. [40][41][42] Recently, we have demonstrated that complex 1 was still reduced at mild potentials in aqueous solutions [E 1/ Encouraged by these results, we reasoned that complex 1 included in SDS micelles could potentially be an efficient protonreduction catalyst for photocatalytic H 2 production in water. Herein we report the performance of a PGM-free system consisting of complex 1, EY 2À as a sensitizer, and triethylamine (Et 3 N) as a sacrificial electron donor in an aqueous SDS solution.…”

Section: Introductionmentioning

confidence: 99%

Photocatalytic Hydrogen Production Using Models of the Iron–Iron Hydrogenase Active Site Dispersed in Micellar Solution

2013

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International audienceIron–thiolate complexes of the type [Fe2(μ-bdt)(CO)6−xP(OMe3)x] (bdt=S2C6H4=benzenedithiolate, x≤2) are simplified models of iron–iron hydrogenase enzymes. Recently, we have shown that these water-insoluble organometallic complexes, when included into micelles formed by sodium dodecyl sulfate (SDS), are good catalysts for the electrochemical production of hydrogen in aqueous solutions at pH<6. We herein report that the all-CO derivative [Fe2(μ-bdt)(CO)6] (1), owing to its comparatively low reduction potential, is also a robust molecular catalyst for visible-light-driven production of H2 in aqueous SDS solutions at pH 10.5. Irradiation at λ=455 nm of a system consisting of complex 1, Eosin Y as a sensitizer, and triethylamine as an electron donor produced up to 0.86 mL of H2 in 4.5 h, corresponding to a turnover number of 117 mol of H2 per mol of catalyst. In the presence of a large excess of sensitizer, the production of H2 lasted for more than 30 h, stressing the relative stability of complex 1 under the photocatalytic conditions used herein. Thermodynamic considerations and UV/Vis spectroscopy experiments suggest that the catalytic cycle begins with the photo-driven reduction of complex 1. The reduced intermediate reacts with a proton source to yield iron hydride. Subsequent reduction and protonation steps produce H2, regenerating the starting complex. As a result, the iron–thiolate complex 1 is a versatile proton reduction catalyst that can utilize either solar or electrical energy inputs, providing a starting point for the construction of noble metal-free molecular systems for renewable H2 production

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“…Diiron-dithiolate compounds of the type [Fe 2 (µ-SRS)(CO) 6-x L x ] (R = organic group, L = electron-donor ligand, x ≤ 4) have been shown to electrocatalyze the reduction of acid in organic solvents [19][20][21] and, very recently, in aqueous micellar solutions [22,23](for examples of photo-driven H 2 -production by diiron-dithiolate compounds see [24,25]). The electrocatalytic pathway entails successive electron and proton transfers in a sequence that depends on the nature of the terminal ligand L and the strength of the acid used as proton source [16,26] We [27][28][29][30][31][32], and others [33][34][35][36][37] [27,28].…”

Section: Introductionmentioning

confidence: 99%

Kinetic and thermodynamic aspects of the electrocatalysis of acid reduction in organic solvent using molecular diiron-dithiolate compounds

Quentel

Gloaguen

2013

Electrochimica Acta

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To cite this version:Francois Quentel, Frederic Gloaguen. Kinetic and thermodynamic aspects of the electrocatalysis of acid reduction in organic solvent using molecular diiron-dithiolate compounds. 2015. AbstractIn an attempt to obtain molecular H 2 production electrocatalysts achieving balanced basicity and reduction potential, we focused on the mono-substituted diiron-dithiolate derivative [Fe 2 (µ-bdt)(CO) 5 (P(OMe) 3 )] (bdt = benzenedithiolate). The electrocatalytic efficiency of this iron-iron hydrogenase model was determined by cyclic voltammetry in acetonitrile using ptoluenesulfonic acid as a proton source. Detailed analysis of the current -potential responses and comparison with the all-CO diiron-dithiolate parent compound clearly show that the effect of the chemical properties on the electrocatalytic efficiency is not fully determined by the turnover frequency under pseudo-first-order approximation and the overpotential defined as the difference between the reduction potential of the electrocatalysts in the absence of acid and the reversible potential of the couple H 2 /acid.

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Electrochemical proton reduction by thiolate-bridged hexacarbonyldiiron clusters

Cited by 135 publications

References 44 publications

Ligand versus Metal Protonation of an Iron Hydrogenase Active Site Mimic

Ligand versus Metal Protonation of an Iron Hydrogenase Active Site Mimic

Photocatalytic Hydrogen Production Using Models of the Iron–Iron Hydrogenase Active Site Dispersed in Micellar Solution

Kinetic and thermodynamic aspects of the electrocatalysis of acid reduction in organic solvent using molecular diiron-dithiolate compounds

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