Tuning of Redox Potentials by Introducing a Cyclometalated Bond to Bis-tridentate Ruthenium(II) Complexes Bearing Bis(N-methylbenzimidazolyl)benzene or -pyridine Ligands

Tuning of Redox Potentials
by Introducing a Cyclometalated
Bond to Bis-tridentate Ruthenium(II) Complexes Bearing Bis(N-methylbenzimidazolyl)benzene or -pyridine Ligands:

Inorganic Chemistry

DOI: 10.1021/ic2016885

Crowded Diphosphinomethane Ligands in Catalysis: [(R2PCH2PR′2-κ2P)NiR″]+ Cations for Ethylene Polymerization without Activators

Crowded Diphosphinomethane
Ligands in Catalysis: [(R2PCH2PR′2-κ2P)NiR″]+ Cations for Ethylene
Polymerization without Activators:

Organometallics

DOI: 10.1021/om200715w

The structures of P2NiCl2 and P2Ni(R)2 are beautifully square-planar, whereas the dppm which is familiar to our group is not able to make square-planar complexes. This ligand might be useful for our modelling chemistry.

Incorporation of an n-Butylsulfonate Functionality To Induce Aqueous Solubility on Ruthenium(II) η6-Arene Complexes

Incorporation of an n-Butylsulfonate
Functionality To Induce Aqueous Solubility on Ruthenium(II) η6-Arene Complexes:

Organometallics DOI: 10.1021/om2005595

Preorganized Frustrated Lewis Pairs

Preorganized Frustrated Lewis Pairs:

Journal of the American Chemical Society DOI: 10.1021/ja210214r

Crystallographic Snapshots of the Bond-Breaking Isomerization Reactions Involving Nickel(II) Complexes with Hemilabile Ligands

Crystallographic Snapshots of the Bond-Breaking Isomerization Reactions Involving Nickel(II) Complexes with Hemilabile Ligands:

Freeze-frame: Octahedral and square-planar structural isomers, representing the two “end states” in a hemilabile ligand bond-breaking isomerization reaction, have been characterized in solution by spectroscopic methods and in the solid state by X-ray crystallography (see picture: Ni green, C gray, P orange, N blue, S yellow).

Well-Defined Heterometallic and Unsymmetric M2O2 Complexes Arising from Binding and Activation of O2

Well-Defined Heterometallic and Unsymmetric M2O2 Complexes Arising from Binding and Activation of O2:

AbstractOxygen binding and activation reactions at dimetal sites constitute chemical processes of fundamental interest, because of the implication of these reactions in biology, chemical synthesis, and catalysis. This account collects and discusses studies of O₂ binding and/or activation by inequivalent dimetal sites, and it specially focuses on systems in which O₂-bound reaction intermediates have been experimentally characterized. Homometallic unsymmetric systems and heterometallic complexes are reviewed, and their chemistry in oxidative transformations is described. Introduction of asymmetry into M₂O₂ cores poses important challenges to their preparation, and strategies developed to address this problem are discussed. Distinct spectroscopic and chemical properties emerge from these unsymmetric systems.

Oxygen binding and activation at unsymmetric and heterometallic complexes by well-defined MO₂M′ species is reviewed. Studies described so far have provided evidence for a rich chemistry. Novel spectroscopic properties, electronic structures and reactivities are emerging, and they suggest a myriad of fresh avenues still to be explored.

Ruthenium Hydride Complexes with Zwitterionic Quinonoid Ligands – Isomer Separation, Structural Properties, Electrochemistry, and Catalysis

Ruthenium Hydride Complexes with Zwitterionic Quinonoid Ligands – Isomer Separation, Structural Properties, Electrochemistry, and Catalysis:

Reactions of [Ru(PPh₃)₃(CO)(H)Cl] with the zwitterionic p-benzoquinonemonoimine-type ligands 4-(n-butylamino)-6-(n-butylimino)-3-oxocyclohexa-1,4-dien-1-olate (Q¹), 4-(isopropylamino)-6-(isopropylimino)-3-oxocyclohexa-1,4-dien-1-olate (Q²), and 4-(benzylamino)-6-(benzylimino)-3-oxocyclohexa-1,4-dien-1-olate (Q³) in the presence of a base led to the formation of mononuclear complexes [Ru(PPh₃)₂(CO)(H)(Q¹_–H)] (1a and 1b), [Ru(PPh₃)₂(CO)(H)(Q²_–H)] (2a and 2b), and [Ru(PPh₃)₂(CO)(H)(Q³_–H)] (3a and 3b), respectively. The positional isomers (a and b) that were formed in each case were separated by preparative TLC. The structural characterization of 2a and 3a·MeCN helped to identify the isomers, and established the distorted octahedral coordination geometry around the ruthenium center. The bond lengths in the complexes are consistent with localization of the double bonds in Q²_–H and Q³_–H in both their monodeprotonated and metal-coordinated forms. The Ru–C–O(carbonyl) bond angle is almost linear. Cyclic voltammetry of the complexes showed one oxidation and one reduction process. These are predominantly centered on the quinonoid ligands, which shows their redox-noninnocent character. Studies of transfer hydrogenation with 2a as a precatalyst showed that, in the presence of KOH, acetophenone could be converted to 1-phenylethanol within 10 h in over 90 % yield.

Ruthenium hydride complexes derived from zwitterionic quinonoid ligands have been synthesized, and their isomers have been separated and structurally characterized. Cyclic voltammetry of the complexes showed the redox noninnocent nature of the quinonoid ligands. One of the complexes showed good activity as a catalyst for the transfer hydrogenation of acetophenone.

EJIC

Thiolato-Bridged Arene–Ruthenium Complexes: Synthesis, Molecular Structure, Reactivity, and Anticancer Activity of the Dinuclear Complexes [(arene)2Ru2(SR)2Cl2]

Thiolato-Bridged Arene–Ruthenium Complexes: Synthesis, Molecular Structure, Reactivity, and Anticancer Activity of the Dinuclear Complexes [(arene)2Ru2(SR)2Cl2]:

Treatment of an arene–ruthenium dichloride dimer with thiols RSH to lead to cationic trithiolato complexes of the type [(arene)₂Ru₂(SR)₃]⁺ was shown to proceed through the neutral thiolato complexes [(arene)₂Ru₂(SR)₂Cl₂], which have been isolated and characterized for arene = p-MeC₆H₄iPr and R = CH₂Ph (1), CH₂CH₂Ph (2), CH₂C₆H₄-p-tBu (3), and C₆H₁₁ (4). The single-crystal X-ray structure analysis of the p-tert-butylbenzyl derivative 3 reveals that the two ruthenium atoms are bridged by the two thiolato ligands without a metal–metal bond. The neutral dithiolato complexes[(arene)₂Ru₂(SR)₂Cl₂] (1–3) are intermediates in the formation of the cationic trithiolato complexes [(arene)₂Ru₂(SR)₃]⁺ (5–7). Of the new [(arene)₂Ru₂(SR)₂Cl₂] complexes, derivative 2 is highly cytotoxic against human ovarian cancer cells, with IC₅₀ values of 0.20 μM for the A2780 cell line and 0.31 for the cisplatin-resistant cell line A2780cisR.

Treatment of p-cymene–ruthenium dichloride dimer with aliphatic thiols to give cationic trithiolato–diruthenium complexes was shown to proceed through the intermediacy of the corresponding neutral dithiolato complexes.

Raja!

Acid-Induced Degradation of Phosphorescent Dopants for OLEDs and Its Application to the Synthesis of Tris-heteroleptic Iridium(III) Bis-cyclometalated Complexes

Acid-Induced Degradation of Phosphorescent Dopants for OLEDs and Its Application to the Synthesis of Tris-heteroleptic
Iridium(III) Bis-cyclometalated Complexes:

Inorganic Chemistry DOI: 10.1021/ic202162q

Easy way to introduce luminescence into our systems, cleave mu-Cl dimer with pdt monomer.

Manganese Carbonyls Bearing Tripodal Polypyridine Ligands as Photoactive Carbon Monoxide-Releasing Molecules

Manganese Carbonyls Bearing Tripodal Polypyridine Ligands as Photoactive Carbon Monoxide-Releasing Molecules:

Inorganic Chemistry DOI: 10.1021/ic2021287

Related to Chris Letko's ligands

Synthesis, Cu(II) complexation, 64Cu-labeling and biological evaluation of cross-bridged cyclam chelators with phosphonate pendant arms

Synthesis, Cu(II) complexation, 64Cu-labeling and biological evaluation of cross-bridged cyclam chelators with phosphonate pendant arms:

Dalton Trans., 2012, Advance Article DOI: 10.1039/C1DT11743B

Riccardo Ferdani, Dannon J. Stigers, Ashley L. Fiamengo, Lihui Wei, Barbara T. Y. Li, James A. Golen, Arnold L. Rheingold, Gary R. Weisman, Edward H. Wong, Carolyn J. Anderson
New phosphonate-pendant-armed cross-bridged cyclams have been synthesized and conveniently radiolabeled with ⁶⁴Cu at room temperature.

an unusual and versatile ligand framework for controlling two adjacent sites

Merging the old with the new

Biomimetic chemistry: Merging the old with the new

• Marcetta Y. Darensbourg
• & Ryan D. Bethel

• The classic organometallic compound ferrocene has been combined with a unique diiron unit in the latest synthetic analogue of an enzyme active site, achieving the three functionalities needed for a working model of diiron hydrogenase, itself of ancient origin.

Highlight of Camara's Nature Chemistry written by MYD in Nature Chemistry

Response to Comment on “A Nickel(II)-Based Radical-Ligand Complex as a Functional Model of Hydrogenase”

Response to Comment on “A Nickel(II)-Based Radical-Ligand Complex as a Functional Model of Hydrogenase”:

Paramagnetic, monoanionic and square-planar nickel bisdithiolene complexes are best described as having delocalized class-III mixed-valent radical anionic ligands coordinated to a closed shell low-spin d⁸ central metal, based on combined structural and spectroscopic studies given in several publications. They can be described by the resonance structures [Ni^II(L²⁻)(L^−.)]⁻ ↔ [Ni^II(L^−.)(L²⁻)]⁻. In our formulation we have not differentiated the ligand “L”, which can carry the charges 2− or 1−^..and vice versa.

Comment on “A Nickel(II)-Based Radical-Ligand Complex as a Functional Model of Hydrogenase”

Comment on “A Nickel(II)-Based Radical-Ligand Complex as a Functional Model of Hydrogenase”:

Where is the spin? Nickel bisthiolenes form paramagnetic monoanionic species. The non-innocence of the sulfur ligands makes a definite assignment of the oxidation state of the central metal atom difficult. EPR spectroscopy and DFT calculations reveal that there is an even distribution of unpaired spin between the nickel and each of the ligands (ca. 1/3 each). There is no evidence for a Ni^II-based radical ligand complex as indicated in the original publication.

Photochemistry of CpMn(CO)3 and Related Derivatives: Spectroscopic Observation of Singlet and Triplet CpMn(CO)2

Photochemistry of CpMn(CO)3 and Related
Derivatives: Spectroscopic Observation of Singlet and Triplet CpMn(CO)2:

Organometallics

DOI: 10.1021/om200555e

New Approach to [FeFe]-Hydrogenase Models Using Aromatic Thioketones

New Approach to [FeFe]-Hydrogenase Models Using Aromatic Thioketones: Wolfgang Weigand et al.

Abstract The reactions of triiron dodecacarbonyl with thiobenzophenone (2a) and 9H-thioxanthene-9-thione (2b) were investigated under different conditions. In the case of a 1:1 molar ratio of triiron dodecacarbonyl and 2a or 2b, the ortho-metallated complexes [Fe₂(CO)₆{μ,κ,S,SCH(C₆H₅)C₆H₄-η²}] (3a) and [Fe₂(CO)₆{μ,κ,S,SCH(C₆H₄)–S–C₆H₃-η²}] (4a) were obtained as the major products, respectively. In contrast, the treatment of triiron dodecacarbonyl with an excess of 2a or 2b afforded [Fe₂(CO)₆{μ-SCH(C₆H₅)C₆H₄S-μ}] (3b) and [Fe₂(CO)₆{μ-SCH(C₆H₄)–S–C₆H₃S-μ}] (4b), respectively, which are both bioinspired models for the active site of [FeFe]-hydrogenase. In addition to these complexes, the two reactions afforded [Fe₂(CO)₆{μ-SC(C₆H₅)₂S-μ}] (3c) and [Fe₂(CO)₆{μ-SC(C₆H₄–S–C₆H₄)S-μ}] (4c). Furthermore, [{Fe₂(CO)₆{μ-SCH(C₆H₅)₂}}₂(μ⁴-S)] (3d) was isolated from the reaction of Fe₃(CO)₁₂ with 2a. The molecular structures of all of the new complexes were determined from the spectroscopic and analytical data and the crystal structures for 3c, 3d, 4b, and 4c were obtained. A plausible mechanism for the formation of the isolated complexes that involves dithiirane derivatives as the key intermediates is proposed. Herein, thioketones 2a and 2b act as sulfur transfer reagents. The electrochemical experiments showed that complex 3b behaves as a catalyst for the electrochemical reduction of protons from acetic acid.

The generation of the [FeFe]-hydrogenase model complexes [Fe₂(CO)₆{μ-SCH(C₆H₅)C₆H₄S-μ}] (3b) and [Fe₂(CO)₆{μ-SCH(C₆H₄)–S–C₆H₃S-μ}] (4b) is reported. A plausible mechanism for the formation of 3b is described, in which thiobenzophenone (2a) acts as a sulfur transferreagent, while the ortho-metallated complex [Fe₂(CO)₆{μ,κ,S,SCH(C₆H₅)C₆H₄-η²}] (3a) is the reaction pathway intermediate.

Nickel–Thiolate Complex Catalyst Assembled in One Step in Water for Solar H2 Production

Nickel–Thiolate Complex Catalyst Assembled in One Step in Water for Solar H2 Production:

Journal of the American Chemical Society DOI: 10.1021/ja208555h

Metal–Alane Adductswith Zero-Valent Nickel,Cobalt, and Iron

Metal–Alane Adducts
with Zero-Valent Nickel,
Cobalt, and Iron:

Journal of the American Chemical Society

DOI: 10.1021/ja2099744

Spectroscopic characterization of the key catalytic intermediate Ni-C in the O2-tolerant [NiFe] hydrogenase I from Aquifex aeolicus: evidence of a weakly bound hydride

Spectroscopic characterization of the key catalytic intermediate Ni-C in the O2-tolerant [NiFe] hydrogenase I from Aquifex aeolicus: evidence of a weakly bound hydride:

Chem. Commun., 2012, DOI: 10.1039/C1CC16109A

Maria-Eirini Pandelia, Pascale Infossi, Matthias Stein, Marie-Therese Giudici-Orticoni, Wolfgang Lubitz
Ni-C in the O₂-tolerant [NiFe] hydrogenase from A. aeolicus is shown by pulse EPR to carry a photo-labile hydride ligand, which is weaker bound compared to O₂-sensitive hydrogenases.

Synthesis and Structural Characterization of Half-Sandwich Nickel Complexes Bearing Two Different N-Heterocyclic Carbene Ligands

Synthesis and Structural Characterization of Half-Sandwich
Nickel Complexes Bearing Two Different N-Heterocyclic Carbene Ligands:

OrganometallicsDOI: 10.1021/om200864z

relevant to Chem 317 exp

Aminolysis of Bis[bis(trimethylsilyl)amido]iron and -cobalt as a Versatile Route to N-Heterocyclic Carbene Complexes

Aminolysis of Bis[bis(trimethylsilyl)amido]iron
and-cobalt as a Versatile Route to N-Heterocyclic Carbene Complexes:

OrganometallicsDOI: 10.1021/om200951m

precursor for FeL2CO site?

An Iron(III) Dithiolene Complex as a Functional Model of Iron Hydrogenase

An Iron(III) Dithiolene Complex as a Functional Model of Iron Hydrogenase:

The iron(III) dithiolene complex [PPh₄]₂[Fe(mnt)₂(SPh)] (1, mnt = maleonitrile dithiolate) has a highly distorted square-pyramidal geometry and an intermediate spin ferric ion (S_Fe = 3/2), and catalyzes electrochemical H₂ evolution at the lowest achievable reduction potential known for iron-containing electrocatalytic systems to date: E_p = –0.309 V in CH₃CN and E_p = –0.53 V in water vs. Ag/AgCl using a modified glassy carbon working electrode. Control experiments suggest that the electrochemical H₂ evolution at low potential is promoted by metal-assisted protonation at the S donors of the thiophenolato and mnt ligands, which liberate H₂ gas upon electrochemical reduction.

The iron(III) dithiolene complex [PPh₄]₂[Fe(mnt)₂(SPh)] (1) has a highly distorted square-pyramidal geometry and an intermediate spin ferric ion, which catalyzes electrochemical H₂ evolution at the lowest achievable reduction potential known to date: E_p = –0.309 V in CH₃CN and E_p = –0.53 V in H₂O.

Sarkar, EJIC. Maria to check overpotential and rate please

Molecular approaches to the electrochemical reduction of carbon dioxide

Molecular approaches to the electrochemical reduction of carbon dioxide:

Chem. Commun., 2012, Advance Article DOI: 10.1039/C1CC15393E, Feature Article

Colin Finn, Sorcha Schnittger, Lesley J. Yellowlees, Jason B. Love

Oxidatively Induced Reactivity of [Fe2(CO)4(κ2-dppe)(μ-pdt)]: an Electrochemical and Theoretical Study of the Structure Change and Ligand Binding Processes

Oxidatively Induced Reactivity of [Fe2(CO)4(κ2-dppe)(μ-pdt)]:
an Electrochemical and Theoretical Study of the Structure Change and Ligand Binding Processes

by Dounia Chouffai, Giuseppe Zampella, Jean-François Capon, Luca De Gioia, Frédéric Gloaguen, François Y. Pétillon, Philippe Schollhammer and Jean Talarmin

Inorganic Chemistry DOI: 10.1021/ic201601q

Regioselectivity of H Cluster Oxidation

Regioselectivity of H Cluster Oxidation: by Marta K. Bruska, Martin T. Stiebritz and Markus Reiher

Journal of the American Chemical Society DOI: 10.1021/ja209165r

A Valence Bond Description of Dizwitterionic Dithiolene Character in an Oxomolybdenum–Bis(dithione) Complex

A Valence Bond Description of Dizwitterionic Dithiolene Character in an Oxomolybdenum–Bis(dithione) Complex:

Abstract

Metallodithiolene non-innocence is explored in an oxomolybdenum–bis(dithione) complex, [Mo⁴⁺O(iPr₂Pipdt)₂Cl][PF₆] (where Pipdt is N,N′-piperazine-2,3-dithione), which has a piperazine ring as an integral part of the dithiolene ligand. The title complex displays spectroscopic features that are unusual for a formally reduced Mo^IV–dithiolene complex, namely a low-energy metal-to-ligand charge-transfer band with appreciable intensity and C–C and C–S stretching frequencies that are markedly different from those of oxomolybdenum complexes coordinated to dianionic dithiolene ligands. The electronic structure of the ligand has been described in valence bond terms as a resonance hybrid of dithione and dizwitterionic dithiolene structures.

Metallodithiolene non-innocence is explored in [Mo⁴⁺O(iPr₂Pipdt)₂Cl][PF₆] (Pipdt: N,N′-piperazine-2,3-dithione), which possesses a piperazine ring as an integral part of the dithiolene ligand and displays unusual spectroscopic features for a formally reduced Mo^IV–dithiolene complex. The electronic structure of the ligand can be described in valence bond terms as a resonance hybrid of dithione and dizwitterionic dithiolene.

Cooperative Aliphatic PNP Amido Pincer Ligands – Versatile Building Blocks for Coordination Chemistry and Catalysis

Cooperative Aliphatic PNP Amido Pincer Ligands – Versatile Building Blocks for Coordination Chemistry and Catalysis:

Abstract

In this review, the coordination chemistry of electron-rich metal complexes with the simple aliphatic, anionic diphosphanylamido ligand {N(CH₂CH₂PR₂)₂}^– is covered and compared with other commonly used, anionic PEP (E = C, N) pincer ligands. The strong π-basicity of this ligand enables both the stabilization of electronically and coordinatively highly unsaturated complexes and their use as cooperating ligands in bifunctional stoichiometric bond activation reactions and catalysis. Versatile ligand backbone dehydrogenation gives access to related enamido and dienamido ligands {(R₂PCHCH)N(CH₂CH₂PR₂)}^– and {N(CHCHPR₂)₂}^–, respectively. This oxidative functionalization enables fine-tuning of the ligand donor properties and thereby of the structural features, electronic structure, and reactivity of the respective complexes, which is discussed for several examples.

Aliphatic PNP pincer ligands, HN(CH₂CH₂PR₂)₂, and ligands derived from them by backbone functionalization, are versatile chelating ligands for metal–ligand cooperative small molecule activation and catalysis. This microreview covers the recent work with these ligands and provides a comprehensive comparison with related pincer systems.

Vanadium nitrogenase: A two-hit wonder?

Vanadium nitrogenase: A two-hit wonder?:

Dalton Trans., 2012, Advance Article
DOI: 10.1039/C1DT11535A, Perspective

Yilin Hu, Chi Chung Lee, Markus W. Ribbe
V-nitrogenase is not only capable of reducing N₂ to NH₃, but also capable of reducing CO to hydrocarbons.
To cite this article before page numbers are assigned, use the DOI form of citation above.
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Unexpected Direct Reduction Mechanism for Hydrogenation of Ketones Catalyzed by Iron PNP Pincer Complexes

Unexpected Direct Reduction
Mechanism for Hydrogenation
of Ketones Catalyzed by Iron PNP Pincer Complexes:

Inorganic Chemistry

DOI: 10.1021/ic2020176

Double Metalation of Acetone by a Nickel–NHC Complex: Trapping of an Oxyallyl Ligand at a Dinickel Center

Double Metalation of Acetone
by a Nickel–NHC
Complex: Trapping of an Oxyallyl Ligand at a Dinickel Center:

Organometallics DOI: 10.1021/om200819c

We are making CpNi(NHC)Cl in our course

[Brevia] Evidence for Interstitial Carbon in Nitrogenase FeMo Cofactor

Evidence for Interstitial Carbon in Nitrogenase FeMo Cofactor: Structural data show that the light atom at the center of the nitrogenase active site cofactor is a carbon.

Authors: Thomas Spatzal, Müge Aksoyoglu, Limei Zhang, Susana L. A. Andrade, Erik Schleicher, Stefan Weber, Douglas C. Rees, Oliver Einsle

Hydrogen Production Coupled to Hydrocarbon Oxygenation from Photocatalytic Water Splitting

Hydrogen Production Coupled to Hydrocarbon Oxygenation from Photocatalytic Water Splitting:

On the sunny side: A homogeneous system for H₂ production and hydrocarbon oxidation was developed in the absence of any sacrificial reagent. This system consists of [Ru(TPA)(H₂O)₂]²⁺ and [Fe₃(CO)₁₂] as catalysts and [Ru(bpy)₃]²⁺ and [Ir(bpy)(ppy)₂]⁺ as photosensitizers (PS). Water is the oxygen source as well as the source for H₂ formation (see picture; Sub=organic substrate).

Structural basis for a [4Fe-3S] cluster in the oxygen-tolerant membrane-bound [NiFe]-hydrogenase

Structural basis for a [4Fe-3S] cluster in the oxygen-tolerant membrane-bound [NiFe]-hydrogenase:

Structural basis for a [4Fe-3S] cluster in the oxygen-tolerant membrane-bound [NiFe]-hydrogenase

Nature 479, 7372 (2011). doi:10.1038/nature10504

Authors: Yasuhito Shomura, Ki-Seok Yoon, Hirofumi Nishihara & Yoshiki Higuchi

Membrane-bound respiratory [NiFe]-hydrogenase (MBH), a H2-uptake enzyme found in the periplasmic space of bacteria, catalyses the oxidation of dihydrogen: H2 → 2H+ + 2e− (ref. 1). In contrast to the well-studied O2-sensitive [NiFe]-hydrogenases (referred to as the standard enzymes), MBH has an O2-tolerant H2 oxidation activity; however, the mechanism of O2 tolerance is unclear. Here we report the crystal structures of Hydrogenovibrio marinus MBH in three different redox conditions at resolutions between 1.18 and 1.32 Å. We find that the proximal iron-sulphur (Fe-S) cluster of MBH has a [4Fe-3S] structure coordinated by six cysteine residues—in contrast to the [4Fe-4S] cubane structure coordinated by four cysteine residues found in the proximal Fe-S cluster of the standard enzymes—and that an amide nitrogen of the polypeptide backbone is deprotonated and additionally coordinates the cluster when chemically oxidized, thus stabilizing the superoxidized state of the cluster. The structure of MBH is very similar to that of the O2-sensitive standard enzymes except for the proximal Fe-S cluster. Our results give a reasonable explanation why the O2 tolerance of MBH is attributable to the unique proximal Fe-S cluster; we propose that the cluster is not only a component of the electron transfer for the catalytic cycle, but that it also donates two electrons and one proton crucial for the appropriate reduction of O2 in preventing the formation of an unready, inactive state of the enzyme.

The crystal structure of an oxygen-tolerant hydrogenase uncovers a novel iron-sulphur centre

The crystal structure of an oxygen-tolerant hydrogenase uncovers a novel iron-sulphur centre:

The crystal structure of an oxygen-tolerant hydrogenase uncovers a novel iron-sulphur centre

Nature 479, 7372 (2011). doi:10.1038/nature10505

Authors: Johannes Fritsch, Patrick Scheerer, Stefan Frielingsdorf, Sebastian Kroschinsky, Bärbel Friedrich, Oliver Lenz & Christian M. T. Spahn

Hydrogenases are abundant enzymes that catalyse the reversible interconversion of H2 into protons and electrons at high rates. Those hydrogenases maintaining their activity in the presence of O2 are considered to be central to H2-based technologies, such as enzymatic fuel cells and for light-driven H2 production. Despite comprehensive genetic, biochemical, electrochemical and spectroscopic investigations, the molecular background allowing a structural interpretation of how the catalytic centre is protected from irreversible inactivation by O2 has remained unclear. Here we present the crystal structure of an O2-tolerant [NiFe]-hydrogenase from the aerobic H2 oxidizer Ralstonia eutropha H16 at 1.5 Å resolution. The heterodimeric enzyme consists of a large subunit harbouring the catalytic centre in the H2-reduced state and a small subunit containing an electron relay consisting of three different iron-sulphur clusters. The cluster proximal to the active site displays an unprecedented [4Fe-3S] structure and is coordinated by six cysteines. According to the current model, this cofactor operates as an electronic switch depending on the nature of the gas molecule approaching the active site. It serves as an electron acceptor in the course of H2 oxidation and as an electron-delivering device upon O2 attack at the active site. This dual function is supported by the capability of the novel iron-sulphur cluster to adopt three redox states at physiological redox potentials. The second structural feature is a network of extended water cavities that may act as a channel facilitating the removal of water produced at the [NiFe] active site. These discoveries will have an impact on the design of biological and chemical H2-converting catalysts that are capable of cycling H2 in air.

Visible light-driven CO2 reduction by enzyme coupled CdS nanocrystals

Visible light-driven CO2 reduction by enzyme coupled CdS nanocrystals:

Chem. Commun., 2012, Advance Article DOI: 10.1039/C1CC16107E, Communication

Yatendra S. Chaudhary, Thomas W. Woolerton, Christopher S. Allen, Jamie H. Warner, Elizabeth Pierce, Stephen W. Ragsdale, Fraser A. Armstrong

Carbon monoxide dehydrogenase (CODH) co-attached with CdS nanocrystals (quantum dots or nanorods) exhibits fast CO₂ reduction under visible light.

(Metallocenylphosphane)palladium Dichlorides – Synthesis, Electrochemistry and Their Application in C–C Coupling Reactions

(Metallocenylphosphane)palladium Dichlorides – Synthesis, Electrochemistry and Their Application in C–C Coupling Reactions:

AbstractThe synthesis and characterization of a series of metallocenylphosphanes of the type PR₂Mc/Se=PR₂Mc [Mc = Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅), R = C₆H₅ (3a/4a), 2-MeC₆H₄ (3b/4b), c-C₄H₃O (3c/4c), tBu (3d/4d), c-C₆H₁₁ (3e/4e); Mc = Rc = Ru(η⁵-C₅H₄)(η⁵-C₅H₅), R = C₆H₅ (6a/7a), 2-MeC₆H₄ (6b/7b), c-C₄H₃O (6c/7c), c-C₆H₁₁ (6d/7d)] and their palladium complexes [PdCl₂(PR₂Mc)₂] [Mc = Fc, R = C₆H₅ (9a), 2-MeC₆H₄ (9b), c-C₄H₃O (9c), tBu (9d), c-C₆H₁₁ (9e); Mc = Rc, R = C₆H₅ (10a), 2-MeC₆H₄ (10b), c-C₄H₃O (10c), c-C₆H₁₁ (10d)] is reported. The solid-state structure of 4b confirms the tetrahedrally distorted geometry at phosphorus with the o-tolyl groups indicating steric congestion, which is confirmed by ¹H and ¹³C{¹H} NMR spectroscopy. Phosphanes 3, 4, and 9 were characterized by cyclic voltammetry with [N(nBu)₄][B(C₆F₅)₄] as the supporting electrolyte. In general, the first oxidation occurs at the phosphane metallocenyl unit(s), although the appropriate Pd complexes are oxidized at more positive potentials. Depending on the phosphane or selenophosphane, follow-up reactions occur, which are discussed. In contrast, the palladium complexes show reversible redox behavior. UV/Vis/NIR spectroelectrochemical studies carried out on 9b indicate an electrostatic interaction between the two terminal ferrocenyl groups. All of the palladium complexes were examined as catalysts in Heck and Suzuki C–C cross-coupling and showed high catalytic activities. These results can be correlated to the electronic (¹J) parameters of the selenophosphanes.

Evidence for acyl-iron ligation in the active site of [Fe]-hydrogenase provided by mass spectrometry and infrared spectroscopy

Evidence for acyl-iron ligation in the active site of [Fe]-hydrogenase provided by mass spectrometry and infrared spectroscopy:

Dalton Trans., 2012, Advance ArticleDOI: 10.1039/C1DT11093D, Paper

Seigo Shima, Michael Schick, Jorg Kahnt, Kenichi Ataka, Klaus Steinbach, Uwe Linne
MS and IR analyses provided strong evidence for the acyl-iron ligation in the iron guanylylpyridinol cofactor of [Fe]-hydrogenase.