Conformational Mobility and Pendent Base Effects on Electrochemistry of Synthetic Analogues of the [FeFe]-Hydrogenase Active Site

Crouthers, Danielle J.; Denny, Jason A.; Bethel, Ryan D.; Muñoz, David G.; Darensbourg, Marcetta Y.

doi:10.1021/om500023j

Cited by 47 publications

(43 citation statements)

References 62 publications

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“…All of the previously reported [FeFe]‐hydrogenase models adopt a chair/boat conformation (Figure ) of the two fused six‐membered FeSCECS rings in the solid state as well as in solution and many complexes such as 1 , R=H or Me, undergo FeSCECS ring inversion with the E atom exchanging places on either side of the molecule. The flap angle ( α ) formed from the intersection between the C 2 E and S 2 C 2 planes, as shown in Figure , lies within the range 118°> α >160° in various [FeFe]‐hydrogenase models.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, their solution NMR spectra show equivalent Me groups for E=Ge and Sn. This may result from a planar structure or rapid equilibration (ring inversion) of nonplanar isomers (as observed in the room‐temperature 1 H NMR spectrum of 1 , R=Me) . However, the Me groups in 4 a remain equivalent even at −90 °C.…”

Section: Resultsmentioning

confidence: 99%

“…We report in the present paper the synthesis of models with μ‐(SCH 2 ) 2 ER 2 linkers, where the central atom E is Ge or Sn. Here, the steric hindrance can be varied by judicious choice of R. We now study in a systematic manner the molecular structures and electronic structures of the series of complexes depicted in Scheme , where complexes 1 (R=H or Me) and 2 (R=Me) have been reported previously.…”

Section: Introductionmentioning

confidence: 99%

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[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH₂)₂ER₂ Linkers (E=Ge and Sn)

Abul‐Futouh

Almazahreh

Sakamoto

et al. 2016

Chemistry A European J

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Analogues of the [2Fe-2S] subcluster of hydrogenase enzymes in which the central group of the three-atom chain linker between the sulfur atoms is replaced by GeR and SnR groups are studied. The six-membered FeSCECS rings in these complexes (E=Ge or Sn) adopt an unusual conformation with nearly co-planar SCECS atoms perpendicular to the Fe-Fe core. Computational modelling traces this result to the steric interaction of the Me groups with the axial carbonyls of the Fe (CO) cluster and low torsional strain for GeMe and SnMe moieties owing to the long C-Ge and C-Sn bonds. Gas-phase photoelectron spectroscopy of these complexes shows a shift of ionization potentials to lower energies with substantial sulfur orbital character and, as supported by the computations, an increase in sulfur character in the predominantly metal-metal bonding HOMO. Cyclic voltammetry reveals that the complexes follow an ECE-type reduction mechanism (E=electron transfer and C=chemical process) in the absence of acid and catalysis of proton reduction in the presence of acid. Two cyclic tetranuclear complexes featuring the sulfur atoms of two Fe S (CO) cores bridged by CH SnR CH , R=Me, Ph, linkers were also obtained and characterized.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH₂)₂ER₂ Linkers (E=Ge and Sn)

Abul‐Futouh

Almazahreh

Sakamoto

et al. 2016

Chemistry A European J

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“…This implies that the proton reduction to hydrogen catalyzed by 4 occurred around its original first and second reduction potentials. 38,39 To confirm the H 2 production catalyzed by 1, 4, and 8, we carried out the bulk electrolysis of a MeCN solution of 1, 4, or 8 (0.5 mM) with excess HOAc (15 mM) at −2.17, −2.18, and −1.93 V, respectively. The initial rates for the electrolysis of HOAc in the presence of catalysts 1, 4, and 8 are ca.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Synthesis, Structure, and Electrocatalysis of Butterfly [Fe₂SP] Cluster Complexes Relevant to [FeFe]-Hydrogenases

Song

Zhang

et al. 2015

Organometallics

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The first [Fe 2 SP] model complexes for the active site of [FeFe]-hydrogenases have been prepared. Thus, the μ-CO-containing complex salt [Et 3 NH][(μ-CO)(μ-SCH 2 CH 2 OH)Fe 2 (CO) 6 ] (m 1 ) formed from Fe 3 (CO) 12 , HSCH 2 CH 2 OH, and Et 3 N was treated in situ with PCl 3 and PPhCl 2 followed by treatment with Et 3 N/DBU to give the all-carbonyl complexes (μ-SCH 2 CH 2 OPR-μ)Fe 2 (CO) 6 (1, R = Cl; 3, Ph), whereas the functional transformation of 1 with PhOH/NaH and CO substitution of 3 with PPh 3 or PPh 2 H in the presence of Me 3 NO afforded the corresponding complexes (μ-SCH 2 CH 2 OPOPh-μ)Fe 2 (CO) 6 (2) and (μ-SCH 2 CH 2 OPPh-μ)Fe 2 (CO) 5 L (4, L = PPh 3 ; 5, PPh 2 H), respectively. Similarly, when complex salt [Et 3 NH][(μ-CO)(μ-SC 6 H 4 OH)Fe 2 (CO) 6 ] (m 4 ) generated from Fe 3 (CO) 12 , 2-HOC 6 H 4 SH, and Et 3 N was treated in situ with PCl 3 and PPhCl 2 followed by treatment with Et 3 N/DBU, the expected all-carbonyl complexes (μ-SC 6 H 4 OPR-μ)Fe 2 (CO) 6 (6, R = Cl; 8, Ph) were produced. In addition, further functional transformation of 6 with MeOH/Et 3 N and CO substitution of 8 with t-BuNC in the presence of Me 3 NO yielded the corresponding complexes (μ-SC 6 H 4 OPOMe-μ)Fe 2 (CO) 6 (7) and (μ-SC 6 H 4 OPPh-μ)Fe 2 (CO) 5 (t-BuNC) (9), respectively. However, it should be noted that when complex salt m 4 was treated with PBr 3 under similar conditions, [(μ-SC 6 H 4 OPO(CH 2 ) 4 Br-μ]Fe 2 (CO) 6 (10) was unexpectedly obtained. While the possible pathways for formation of the unexpected 10 were suggested, all complexes 1−10 were characterized by elemental analysis and spectroscopy and for some of them by X-ray crystallography. Interestingly, model complexes 1, 4, and 8 have been found to be catalysts for HOAc proton reduction to H 2 under CV conditions. ■ INTRODUCTION[FeFe]-Hydrogenases (hereafter denoted as [FeFe]Hases) are a class of natural enzymes that catalyze H 2 production at rapid rates in a broad range of prokaryotic and eukaryotic microorganisms. 1−5 The X-ray crystallographic 6−8 and FTIR spectroscopic 9−11 studies revealed that the active site of [FeFe]Hases consists of a butterfly [Fe 2 S 2 ] cluster core and a cubic [Fe 4 S 4 ] cluster core, which are connected together via a cysteine S atom. In addition, the two Fe atoms in the butterfly [Fe 2 S 2 ] core are bridged by a dithiolate ligand and coordinated by three CO and two CN − ligands. Recently, the dithiolate ligand has been identified as an azadithiolate μ-SCH 2 NHCH 2 S-μ ligand, evidenced by 14 N HYSCORE 12 and controlled metalloenzyme activation 13 (Figure 1a). Encouraged by the well-established active site structure, synthetic chemists have prepared a great number of models for the active site of [FeFe]Hases, such as the butterfly [Fe 2 E 2 ] (E = S, Se, Te) and [Fe 2 P 2 ]-type model complexes. 14−17 However, it is worth noting that up to now no butterfly [Fe 2 SP]-type model complex has been prepared, albeit some ordinary butterfly [Fe 2 SP] complexes are known. 18−21 Therefore, to further understand the active site struc...

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“…Such modelling has usually delivered active systems for the generation of H 2 from H ? [28][29][30][31][32][33][34][35][36][37][38]. Even though some of these systems might actually be amenable to studies with EPR spectroscopy, very little information is available in that direction [35][36][37].…”

Section: Activation Of Dihydrogenmentioning

confidence: 99%

Use of EPR Spectroscopy to Unravel Reaction Mechanisms in (Catalytic) Bond Activation Reactions: Some Selected Examples

Manck

Sarkar

2015

Top Catal

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Paramagnetic species are ubiquitous intermediates in many different reactions involving chemical bond activation and catalysis. Despite this fact, the use of electron paramagnetic resonance (EPR) spectroscopy for unraveling reaction mechanisms for homogeneous catalytic reactions has been rather limited. This overview article details several areas dealing with small molecule activation in the homogeneous medium where EPR spectroscopy is potentially useful and has sometimes been used. We will present various examples from the literature to show the usefulness of this method in studying the activation and possible fixation of small molecules such as H 2 , O 2 , and N 2 . Additionally, some examples related to nitridyl radicals and their relation with carbene radicals will also be discussed with a focus on their detection through EPR spectroscopy. We will present the usefulness and the limitations of this method by discussing selected examples from the literature. This is not meant to be a comprehensive review.

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Conformational Mobility and Pendent Base Effects on Electrochemistry of Synthetic Analogues of the [FeFe]-Hydrogenase Active Site

Cited by 47 publications

References 62 publications

[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH₂)₂ER₂ Linkers (E=Ge and Sn)

[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH₂)₂ER₂ Linkers (E=Ge and Sn)

Synthesis, Structure, and Electrocatalysis of Butterfly [Fe₂SP] Cluster Complexes Relevant to [FeFe]-Hydrogenases

Use of EPR Spectroscopy to Unravel Reaction Mechanisms in (Catalytic) Bond Activation Reactions: Some Selected Examples

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Conformational Mobility and Pendent Base Effects on Electrochemistry of Synthetic Analogues of the [FeFe]-Hydrogenase Active Site

Cited by 47 publications

References 62 publications

[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH2)2ER2 Linkers (E=Ge and Sn)

[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH2)2ER2 Linkers (E=Ge and Sn)

Synthesis, Structure, and Electrocatalysis of Butterfly [Fe2SP] Cluster Complexes Relevant to [FeFe]-Hydrogenases

Use of EPR Spectroscopy to Unravel Reaction Mechanisms in (Catalytic) Bond Activation Reactions: Some Selected Examples

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Product

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[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH₂)₂ER₂ Linkers (E=Ge and Sn)

[FeFe]‐Hydrogenase H‐Cluster Mimics with Unique Planar μ‐(SCH₂)₂ER₂ Linkers (E=Ge and Sn)

Synthesis, Structure, and Electrocatalysis of Butterfly [Fe₂SP] Cluster Complexes Relevant to [FeFe]-Hydrogenases