Incorporating Amino AcidEsters into Catalysts forHydrogen Oxidation: Steric and Electronic Effects and the Role ofWater as a Base

Incorporating Amino Acid
Esters into Catalysts for
Hydrogen Oxidation: Steric and Electronic Effects and the Role of
Water as a Base:

Organometallics

DOI: 10.1021/om300409y

Multielectron-Transfer Templates via Consecutive Two-Electron Transformations: Iron–Sulfur Complexes Relevant to Biological Enzymes

Multielectron-Transfer Templates via Consecutive Two-Electron Transformations: Iron–Sulfur Complexes Relevant to Biological Enzymes:

[FeFe] hydrogenase mimics: Two polynuclear iron–sulfur complexes (2 and 3; see figure) were prepared and structurally characterized. They are potentially effective and stable multielectron-transfer relays for mediating four- and six-electron transformations via a cascade of reversible two-electron redox steps with relatively narrow potential spans.

Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production [Chemistry]

Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production [Chemistry]: The design of molecular electrocatalysts for H2 oxidation and production is important for the development of alternative renewable energy sources that are abundant, inexpensive, and environmentally benign. Recently, nickel-based molecular electrocatalysts with pendant amines that act as proton relays for the nickel center were shown to effectively catalyze H2 oxidation...

Artificial photosynthesis of CO [Chemistry]

Artificial photosynthesis of CO [Chemistry]: The effective design of an artificial photosynthetic system entails the optimization of several important interactions. Herein we report stopped-flow UV-visible (UV-vis) spectroscopy, X-ray crystallographic, density functional theory (DFT), and electrochemical kinetic studies of the Re(bipy-tBu)(CO)3(L) catalyst for the reduction of CO2 to CO. A remarkable selectivity for CO2 over H+...

H2 evolution: [Ni(P2N2)2]2+ in acidic ionic liq./H2O [Chemistry]

H2 evolution: [Ni(P2N2)2]2+ in acidic ionic liq./H2O [Chemistry]: The electrocatalytic reduction of protons to H2 by (where in the highly acidic ionic liquid dibutylformamidium bis(trifluoromethanesulfonyl)amide shows a strong dependence on added water. A turnover frequency of 43,000–53,000 s-1 has been measured for hydrogen production at 25 °C when the mole fraction of water (χH2O) is 0.72. The same catalyst in...

Cobalt-dithiolene complexes for proton reduction. [Chemistry]

Cobalt-dithiolene complexes for proton reduction. [Chemistry]: Artificial photosynthesis (AP) is a promising method of converting solar energy into fuel (H2). Harnessing solar energy to generate H2 from H+ is a crucial process in systems for artificial photosynthesis. Widespread application of a device for AP would rely on the use of platinum-free catalysts due to the scarcity...

Catalytic hydrogen evolution [Chemistry]

Catalytic hydrogen evolution [Chemistry]: A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p-toluenesulfonic acid as evidenced by electrocatalytic waves at -0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions. Rates of hydrogen evolution were determined from catalytic current peak heights (kapp = 1100 ± 70 M-1 s-1). Electrochemical...

Redox-Active Ligands in Catalysis

Redox-Active Ligands in Catalysis:

Abstract

Nature’s use of redox-active moieties combined with 3d transition-metal ions is a powerful strategy to promote multi-electron catalytic reactions. The ability of these moieties to store redox equivalents aids metalloenzymes in promoting multi-electron reactions, avoiding high-energy intermediates. In a biomimetic spirit, chemists have recently developed approaches relying on redox-active moieties in the vicinity of metal centers to catalyze challenging transformations. This approach enables chemists to impart noble-metal character to less toxic, and cost effective 3d transitional metals, such as Fe or Cu, in multi-electron catalytic reactions.

Juggling with both hands: For sustainable energy, mastering multi-electron catalytic processes is the key feature. To address this challenge, nature combines redox-active metals with redox-active mediators or ligands. The resulting catalytic transformations (e.g. water splitting, CO₂ reduction, CH activation) proceed with low kinetic barriers. This Minireview highlights recent examples of homogeneous catalysis involving redox-active ligands.

Redox-Active Ligands in Catalysis

Redox-Active Ligands in Catalysis:

Abstract

Nature’s use of redox-active moieties combined with 3d transition-metal ions is a powerful strategy to promote multi-electron catalytic reactions. The ability of these moieties to store redox equivalents aids metalloenzymes in promoting multi-electron reactions, avoiding high-energy intermediates. In a biomimetic spirit, chemists have recently developed approaches relying on redox-active moieties in the vicinity of metal centers to catalyze challenging transformations. This approach enables chemists to impart noble-metal character to less toxic, and cost effective 3d transitional metals, such as Fe or Cu, in multi-electron catalytic reactions.

Juggling with both hands: For sustainable energy, mastering multi-electron catalytic processes is the key feature. To address this challenge, nature combines redox-active metals with redox-active mediators or ligands. The resulting catalytic transformations (e.g. water splitting, CO₂ reduction, CH activation) proceed with low kinetic barriers. This Minireview highlights recent examples of homogeneous catalysis involving redox-active ligands.

Mechanisms of cobalt catalyzed hydrogen evolution [Chemistry]

Mechanisms of cobalt catalyzed hydrogen evolution [Chemistry]: Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change....

Effective Fixation of CO2 by Iridium-Catalyzed Hydrosilylation

Effective Fixation of CO2 by Iridium-Catalyzed Hydrosilylation:

CO₂ as feedstock: An air- and moisture-stable iridium(III) catalyst effectively promotes the hydrosilylation of CO₂. This reaction leads to silyl formate in a highly selective manner and proceeds efficiently under mild conditions, most likely by an outer-sphere mechanism, as suggested by theoretical calculations.

Oxygen Reduction ElectrocatalystBased on StronglyCoupled Cobalt Oxide Nanocrystals and Carbon Nanotubes

Oxygen Reduction Electrocatalyst
Based on Strongly
Coupled Cobalt Oxide Nanocrystals and Carbon Nanotubes:

Journal of the American Chemical Society

DOI: 10.1021/ja305623m

Thermodynamic and KineticHydricity of Ruthenium(II)Hydride Complexes

Thermodynamic and Kinetic
Hydricity of Ruthenium(II)
Hydride Complexes:

Journal of the American Chemical Society

DOI: 10.1021/ja302937q

Thermodynamic and KineticHydricity of Ruthenium(II)Hydride Complexes

Thermodynamic and Kinetic
Hydricity of Ruthenium(II)
Hydride Complexes:

Journal of the American Chemical Society

DOI: 10.1021/ja302937q

A Binuclear Iron–Thiolate Catalyst for Electrochemical Hydrogen Production in Aqueous Micellar Solution

A Binuclear Iron–Thiolate Catalyst for Electrochemical Hydrogen Production in Aqueous Micellar Solution:

Abstract

The substituted iron–thiolate complex [Fe₂(μ-bdt)(CO)₄{P(OMe)₃}₂] (bdt=benzenedithiolate) is an active catalyst for electrochemical hydrogen production in aqueous sodium dodecyl sulfate solution, with a high apparent rate constant of 4×10⁶ M⁻¹ s⁻¹. The half-peak potential for catalysis of proton reduction is less negative than −0.6 V versus the standard hydrogen electrode at pH 3. Voltammetric data are consistent with the rate of electrode reaction controlled by diffusion. A mechanism that begins with the rapid protonation of the iron–thiolate catalyst is proposed. The Faradaic efficiency in diluted HCl solutions is close to 100 %, but the catalytic activity decayed after about twelve turnovers when electrolysis was carried out in the presence of acetic acid.

Iron brew: [Fe₂(μ-bdt)(CO)₄{P(OMe)₃}₂] (bdt=benzenedithiolate) catalyzes electrochemical hydrogen production in an aqueous micellar solution (see scheme). It achieves a turnover frequency of 4400 s⁻¹ at a potential less negative than −0.6 V (versus a standard hydrogen electrode) at pH 3.

Silver Complex with an N,S,S-Macrocyclic Ligand Bearing an Anthracene Pendant Arm for Optical Ethylene Monitoring

Silver Complex with an N,S,S-Macrocyclic Ligand Bearing an Anthracene Pendant Arm for Optical Ethylene Monitoring:

Chem. Commun., 2012, Accepted Manuscript
DOI: 10.1039/C2CC35277J, Communication

Yutaka Hitomi, Toshiyuki Nagai, Masahito Kodera
We have designed and synthesized a silver complex with a metal-arene interaction, in which the anthracene ring of the ligand sidearm is positioned above the silver(I) ion. The metal-arene interaction...
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A Functional-Group-Tolerant Catalytic trans Hydrogenation of Alkynes

A Functional-Group-Tolerant Catalytic trans Hydrogenation of Alkynes:

Against the rules: During the hundred years following Sabatier’s groundbreaking work on catalytic hydrogenation, syn delivery of the H atoms to the π system of a substrate remained the governing stereochemical rule. An exception has now be found with the use of cationic [Cp*Ru] templates, which accounts for the first practical, functional-group-tolerant, broadly applicable and highly E-selective semihydrogenation method for alkynes.

Synthesis of a FeIISH Complex Stabilizedby an Intramolecular N–H···S Hydrogen Bond,Which Acts as a H2S Donor

Synthesis of a FeIISH Complex Stabilized
by an Intramolecular N–H···S Hydrogen Bond,
Which Acts as a H2S Donor:

Inorganic Chemistry

DOI: 10.1021/ic300952d

Efficient [FeFe] Hydrogenase Mimic Dyads Covalently Linking to Iridium Photosensitizer for Photocatalytic Hydrogen Evolution

Efficient [FeFe] Hydrogenase Mimic Dyads Covalently Linking to Iridium Photosensitizer for Photocatalytic Hydrogen Evolution:

Dalton Trans., 2012, Accepted Manuscript
DOI: 10.1039/C2DT31618H, Paper

Hong-hua Cui
Two [FeFe] hydrogenase mimics, [Fe2([small mu ]-pdt)(CO)5L1] (L1 = PPh2SPhNH2) (Ph = phenyl)) (2), [Fe2([small mu ]-pdt)(CO)5L2] (L2 = PPh2PhNH2) (3) and two molecular photocatalysts, [(CO)5([small mu ]-pdt)Fe2PPh2SPhNHCO(bpy)(ppy)2Ir]PF6 (bpy = bipyridine, ppy = 2-phenylpyridine) (2a) and...
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Alkene Hydrogenation Catalyzed by Nickel Hydride Complexes of an Aliphatic PNP Pincer Ligand

Alkene Hydrogenation Catalyzed by Nickel Hydride Complexes of an Aliphatic PNP Pincer Ligand:

Abstract

To investigate metal–ligand cooperativity as a strategy for promoting nickel-catalyzed alkene hydrogenation, cationic and neutral nickel(II) hydride complexes of the aliphatic pincer ligand PNHP^Cy {PNHP^Cy = HN[CH₂CH₂P(Cy)₂]₂} have been synthesized and characterized. Cationic hydride complex [(PNHP^Cy)Ni(H)]BPh₄ (2) catalyzed the hydrogenation of styrene and 1-octene under mild conditions. Only low conversion was observed in the hydrogenation of 3,5-dimethoxybenzaldehyde using 2. The neutral hydride complex (PNP^Cy)Ni(H) (3) was also found to be an alkene hydrogenation catalyst. Mechanistic experiments suggest that for catalyst 2, the hydrogenation reaction proceeds through a pathway involving initial insertion of the alkene into the Ni–H bond. Contrary to the initial hypothesis, reactivity comparisons with the methyl-substituted hydride complex [(PNMeP^Cy)Ni(H)]BPh₄ {PNMeP^Cy = (CH₃)N[CH₂CH₂P(Cy)₂]₂} suggest that metal–ligand cooperativity is not involved in these rare examples of mild and homogeneous nickel hydrogenation catalysis.

Cationic and neutral nickel(II) hydride complexes of the aliphatic pincer ligand PNHP^Cy {PNHP^Cy = HN[CH₂CH₂P(Cy)₂]₂} have been prepared and were found to be active alkene hydrogenation catalysts. Mechanistic experiments suggest that for cationic catalyst 2, hydrogenation may proceed through a pathway involving initial insertion of the alkene into the Ni–H bond.

Reactions coupled to palladium

Reactions coupled to palladium:
Reactions coupled to palladium

Nature Chemistry 4, 764 (2012).
doi:10.1038/nchem.1437

Author: Matthew Hartings
You would be forgiven if you thought the most important element in an organic transformation was carbon. Matthew Hartings argues that, for just over half a century in many of chemistry's most renowned organic reactions, it has actually been palladium.

Mononuclear Five- andSix-Coordinate Iron Hydrazidoand Hydrazine Species

Mononuclear Five- and
Six-Coordinate Iron Hydrazido
and Hydrazine Species:

Inorganic Chemistry

DOI: 10.1021/ic301704f

Ferrocenyl(trihydro)borates: Building Blocks for the Synthesis of Heterooligonuclear Metallocene Complexes

Ferrocenyl(trihydro)borates: Building Blocks for the Synthesis of Heterooligonuclear Metallocene Complexes:

Dalton Trans., 2012, Accepted Manuscript
DOI: 10.1039/C2DT31732J, Paper

Adelina Reichert, Michael Bolte, Hans-Wolfram Lerner, Matthias Wagner
This is an Accepted Manuscript, which has been through the RSC Publishing peer review process and has been accepted for publication. Accepted manuscripts are published online shortly after acceptance. This version of the article will be replaced by the fully edited, formatted and proof read Advance Article as soon as this is available.

An Organic Hydride Transfer Reaction of a Ruthenium NAD Model Complex Leading to Carbon Dioxide Reduction

An Organic Hydride Transfer Reaction of a Ruthenium NAD Model Complex Leading to Carbon Dioxide Reduction:

Ruthenium will fix it: CO₂ undergoes reduction to HCO₂⁻ when placed over a solution of a ruthenium complex bearing an NADH model ligand 1 (black in right structural formula). The organic hydride transfer is triggered by the addition of benzoate anion, which rapidly forms a complex with 1, a complex that is a stronger reductant than 1. A photocatalytic variant of the reaction using triethanolamine as a sacrificial reagent has also been developed.

Towards Alternatives to Anodic Water Oxidation: Basket-Handle Thiolate FeIII Porphyrins for Electrocatalytic Hydrocarbon Oxidation

Towards Alternatives to Anodic Water Oxidation: Basket-Handle Thiolate FeIII Porphyrins for Electrocatalytic Hydrocarbon Oxidation:

Abstract

Selective electrocatalytic oxidation of hydrocarbons to alcohols, epoxides or other (higher value) oxygenates should in principal present a useful complementary anodic half-cell reaction to cathodic generation of fuels from water or CO₂ viz. an alternative to oxygen evolution. A series of new basket-handle thiolate Fe^III porphyrins have been synthesised and shown to mediate anodic oxidation of hydrocarbons, specifically adamantane hydroxylation and cyclooctene epoxidation. We compare yields obtained by electrochemical and chemical oxidation of the thiolate porphyrins and benchmark their behaviour against that of Fe^III tetraphenyl porphyrin chloride and its tetrapentafluorophenyl analogue.

A preference for alcohol over oxygen: We show that iron porphyrins can mediate the anodic oxidation of hydrocarbons, thus providing a potential complementary reaction to cathodic generation of fuels or feedstocks as an alternative to oxygen evolution.

A Three-Stage MechanisticModel for Ammonia–BoraneDehydrogenation by Shvo’s Catalyst

A Three-Stage Mechanistic
Model for Ammonia–Borane
Dehydrogenation by Shvo’s Catalyst:

Organometallics

DOI: 10.1021/om300562d

Stepwise construction of grid-type Cu(II)/Cd(II) heterometallic MOFs based on an imidazole-appended dipyrrin ligand

Stepwise construction of grid-type Cu(II)/Cd(II) heterometallic MOFs based on an imidazole-appended dipyrrin ligand:

Chem. Commun., 2012, Accepted Manuscript
DOI: 10.1039/C2CC35543D, Communication

Antoine Beziau, Stephane Baudron, Dmitry Pogozhev, Audrey Fluck, Mir Wais Hosseini
An imidazole-appended dipyrrin ligand yields, upon coordination to Cu(II) cations, a linear metallatecton that self-assembles with Cd(II) salts to afford 2D grid-type MOFs which, upon parallel stacking, leads to porous...

Mononuclear Water Oxidation Catalysts

Mononuclear Water Oxidation Catalysts:

Abstract

Recently, several mononuclear water oxidation catalysts have been reported, a breakthrough considering the dogma that at least two metal sites were required to oxidize water efficiently. In this Review various mononuclear catalysts which have been reported in the last five years are reviewed, as well as their implementation in prototype devices that allow dioxygen formation to be coupled to dihydrogen production will be discussed.

One is enough: Mononuclear water oxidation catalysts are noteworthy as they can achieve turnover frequencies similar to those of the oxygen-evolving center of Photosystem II. Several of these mononuclear catalysts are highlighted, as well as studies on their incorporation into a device that splits water upon irradiation with visible light (see scheme)—an important first step towards efficient solar energy to fuel conversion.