Unraveling the Role of Particle Size and Nanostructuring on the Oxygen Evolution Activity of Fe-Doped NiO.

Nickel-based oxides and oxyhydroxide catalysts exhibit state-of-the-art activity for the sluggish oxygen evolution reaction (OER) under alkaline conditions. A widely employed strategy to increase the gravimetric activity of the catalyst is to increase the active surface area via nanostructuring or decrease the particle size. However, the fundamental understanding about how tuning these parameters influences the density of oxidized species and their reaction kinetics remains unclear.

Dichloromethane as C Synthon for the Photoredox Catalytic Cyclopropanation of Aromatic Olefins.

Dichloromethane, as a readily available and inexpensive C synthon is proposed as a powerful building block for cyclopropanation of alkenes under mild conditions. Herein, we report a highly efficient and versatile dual photoredox system, involving a nickel aminopyridine coordination complex and a photocatalyst, for the cyclopropanation of aromatic olefins using dichloromethane, under visible-light irradiation. The cyclopropanation protocol has been successfully applied at gram scale.

An Electrocatalytic Cascade Reaction for the Synthesis of Ketones Using CO as a CO Surrogate.

The construction of carbonyl compounds via carbonylation reactions using safe CO sources remains a long-standing challenge to synthetic chemists. Herein, we propose a catalyst cascade Scheme in which CO is used as a CO surrogate in the carbonylation of benzyl chlorides. Our approach is based on the cooperation between two coexisting catalytic cycles: the CO-to-CO electroreduction cycle promoted by [Fe(TPP)Cl] (TPP=meso-tetraphenylporphyrin) and an electrochemical carbonylation cycle catalyzed by [Ni(bpy)Br] (2,2'-bipyridine).

Synthesis and characterization of highly diluted polyanionic iron(II) spin crossover systems.

Spin crossover (SCO) complexes, through their reversible spin transition under external stimuli, can work as switchable memory materials. Here, we present a protocol for the synthesis and characterization of a specific polyanionic iron SCO complex and its diluted systems. We describe steps for its synthesis and the determination of crystallographic structure of the SCO complex in diluted systems.

An investigation of steric influence on the reactivity of Fe(O)(OH) tautomers in stereospecific C-H hydroxylation.

Two new tetradentate N4 ligands (LN4), LN4 = Me2,Me2PyzTACN (1-(2-(3,5-dimethyl-1-pyrazol-1-yl)ethyl)-4,7-dimethyl-1,4,7-triazacyclononane) and Me2,MeImTACN (1-((1-methyl-1-imidazol-1-yl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane) have been synthesized and their corresponding Fe(II) complexes [Fe(Me2,Me2PyzTACN)(CFSO)], 1Pz, and [Fe(Me2,MeImTACN)(CFSO)], 1Im, have been prepared and characterized. Complexes 1Pz and 1Im catalyse the hydroxylation of C-H bonds of alkanes with excellent efficiencies, using hydrogen peroxide as oxidant. The high H/D kinetic isotope effect values for C-H hydroxylation, large normalized tertiary/secondary C-H (C3/C2) bond selectivities in adamantane oxidation, and high degrees of stereoretention in the oxidation of -1,2-dimethylcyclohexane are indicative of metal-based oxidation processes.

XAS and EPR in Situ Observation of Ru(V) Oxo Intermediate in a Ru Water Oxidation Complex.

In this study, we combine in situ spectroelectrochemistry coupled with electron paramagnetic resonance (EPR) and X-ray absorption spectroscopies (XAS) to investigate a molecular Ru-based water oxidation catalyst bearing a polypyridinic backbone . Although high valent key intermediate species arising in catalytic cycles of this family of compounds have remain elusive due to the lack of additional anionic ligands that could potentially stabilize them, mechanistic studies performed on this system proposed a water nucleophilic attack (WNA) mechanism for the O-O bond formation. Employing experimental conditions and complementary spectroscopic techniques allowed to observe intermediates that provide support for a WNA mechanism, including for the first time a Ru(V) oxo intermediate based on the ligand, in agreement with the previously proposed mechanism.

Light-driven reduction of aromatic olefins in aqueous media catalysed by aminopyridine cobalt complexes.

A catalytic system based on earth-abundant elements that efficiently hydrogenates aryl olefins using visible light as the driving-force and HO as the sole hydrogen atom source is reported. The catalytic system involves a robust and well-defined aminopyridine cobalt complex and a heteroleptic Cu photoredox catalyst. The system shows the reduction of styrene in aqueous media with a remarkable selectivity (>20 000) water reduction (WR).

Spectroelectrochemical Analysis of the Water Oxidation Mechanism on Doped Nickel Oxides.

Metal oxides and oxyhydroxides exhibit state-of-the-art activity for the oxygen evolution reaction (OER); however, their reaction mechanism, particularly the relationship between charging of the oxide and OER kinetics, remains elusive. Here, we investigate a series of Mn-, Co-, Fe-, and Zn-doped nickel oxides using UV-vis spectroscopy coupled with time-resolved stepped potential spectroelectrochemistry. The Ni/Ni redox peak potential is found to shift anodically from Mn- < Co- < Fe- < Zn-doped samples, suggesting a decrease in oxygen binding energetics from Mn- to Zn-doped samples.

Photoredox Activation of Inert Alkyl Chlorides for the Reductive Cross-Coupling with Aromatic Alkenes.

The inertness of chloroalkanes has precluded them as coupling partners for cross-coupling reactions. Herein we disclose a general strategy for the activation of inert alkyl chlorides through photoredox catalysis and their use as coupling partners with alkenes. The catalytic system is formed by [Ni(OTf)(Py tacn)](OTf) (1 ), which is responsible for the Csp -Cl bond activation, and [Ir( bpy)(ppy) ]PF (PC ), which is the photoredox catalyst.

Isolation of a Ru(IV) side-on peroxo intermediate in the water oxidation reaction.

The electrons that nature uses to reduce CO during photosynthesis come from water oxidation at the oxygen-evolving complex of photosystem II. Molecular catalysts have served as models to understand its mechanism, in particular the O-O bond-forming reaction, which is still not fully understood. Here we report a Ru(IV) side-on peroxo complex that serves as a 'missing link' for the species that form after the rate-determining O-O bond-forming step.

Electrocatalytic Water Oxidation with α-[Fe(mcp)(OTf)] and Analogues.

The complex α-[Fe(mcp)(OTf)] (mcp = ,'-dimethyl-,'-bis(pyridin-2-ylmethyl)-cyclohexane-1,2-diamine and OTf = trifluoromethanesulfonate anion) was reported in 2011 by some of us as an active water oxidation (WO) catalyst in the presence of sacrificial oxidants. However, because chemical oxidants are likely to take part in the reaction mechanism, mechanistic electrochemical studies are critical in establishing to what extent previous studies with sacrificial reagents have actually been meaningful. In this study, the complex α-[Fe(mcp)(OTf)] and its analogues were investigated electrochemically under both acidic and neutral conditions.

Luminescent Rhenium(I)tricarbonyl Complexes Containing Different Pyrazoles and Their Successive Deprotonation Products: CO Reduction Electrocatalysts.

Cationic -[Re(CO)(pz*H)(pypzH)]OTf (pz*H = pyrazole, pzH; 3,5-dimethylpyrazole, dmpzH; indazole, indzH; 3-(2-pyridyl)pyrazole, pypzH) were obtained from -[ReBr(CO)(pypzH)] by halide abstraction with AgOTf and subsequent addition of the corresponding pyrazole. Successive deprotonation with NaCO and NaOH gave neutral -[Re(CO)(pz*H)(pypz)] and anionic Na{-[Re(CO)(pz*)(pypz)]} complexes, respectively. Cationic -[Re(CO)(pz*H)(pypzH)]OTf, neutral complexes -[Re(CO)(pz*H)(pypz)], and -[Re(CO)(pypz)Na] were subjected to photophysical and electrochemical studies.

Crystal-to-Crystal Synthesis of Photocatalytic Metal-Organic Frameworks for Visible-Light Reductive Coupling and Mechanistic Investigations.

Postmodification of reticular materials with well-defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal-organic frameworks (MOFs) to exploit the potential of crystal-to-crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF-520-PC1 and MOF-520-PC2, are straightforwardly obtained by the postfunctionalization of MOF-520 with perylene-3-carboxylic acid (PC1) and perylene-3-butyric acid (PC2).

The synergy between the CsPbBr nanoparticle surface and the organic ligand becomes manifest in a demanding carbon-carbon coupling reaction.

We demonstrate here the suitability of CsPbBr nanoparticles as photosensitizers for a demanding photoredox catalytic homo- and cross-coupling of alkyl bromides at room temperature by merely using visible light and an electron donor, thanks to the cooperative action between the nanoparticle surface and organic capping.

Octahedral iron(iv)-tosylimido complexes exhibiting single electron-oxidation reactivity.

High valent iron species are very reactive molecules involved in oxidation reactions of relevance to biology and chemical synthesis. Herein we describe iron(iv)-tosylimido complexes [Fe(NTs)(MePytacn)](OTf) () and [Fe(NTs)(Me(CHPy)tacn)](OTf) (), (MePytacn = -methyl-,-bis(2-picolyl)-1,4,7-triazacyclononane, and Me(CHPy)tacn = 1-(di(2-pyridyl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane, Ts = Tosyl). and are rare examples of octahedral iron(iv)-imido complexes and are isoelectronic analogues of the recently described iron(iv)-oxo complexes [Fe(O)(L)] (L = MePytacn and Me(CHPy)tacn, respectively).

Cobalt Amide Imidate Imidazolate Frameworks as Highly Active Oxygen Evolution Model Materials.

Two imidazolate-based Co-MOFs, IFP-5 and IFP-8 (imidazolate framework Potsdam), with a different peripheral group -R (-Me and -OMe, respectively) have been synthesized by a solvothermal method and tested toward the oxygen evolution reaction (OER). Remarkably, IFP-8 presents much lower overpotentials (319 mV at 10 mA/cm and 490 mV at 500 mA/cm) than IFP-5 toward OER, as confirmed by online gas chromatography measurements (Faradaic yield of O > 99%). Moreover, the system is extraordinarily stable during 120 h, even when used as a catalyst toward the overall water splitting reaction without any sign of fatigue.

A Unified Electro- and Photocatalytic CO to CO Reduction Mechanism with Aminopyridine Cobalt Complexes.

A mechanistic understanding of electro- and photocatalytic CO reduction is crucial to develop strategies to overcome catalytic bottlenecks. In this regard, for a new CO-to-CO reduction cobalt aminopyridine catalyst, a detailed experimental and theoretical mechanistic study is herein presented toward the identification of bottlenecks and potential strategies to alleviate them. The combination of electrochemistry and spectroelectrochemistry together with spectroscopic techniques led us to identify elusive key electrocatalytic intermediates derived from complex [LCo(OTf)] () (L = 1-[2-pyridylmethyl]-4,7-dimethyl-1,4,7-triazacyclononane) such as a highly reactive cobalt(I) () and a cobalt(I) carbonyl () species.

Reductive Cyclization of Unactivated Alkyl Chlorides with Tethered Alkenes under Visible-Light Photoredox Catalysis.

The chemical inertness of abundant and commercially available alkyl chlorides precludes their widespread use as reactants in chemical transformations. Presented in this work is a metallaphotoredox methodology to achieve the catalytic intramolecular reductive cyclization of unactivated alkyl chlorides with tethered alkenes. The cleavage of strong C(sp )-Cl bonds is mediated by a highly nucleophilic low-valent cobalt or nickel intermediate generated by visible-light photoredox reduction employing a copper photosensitizer.

Design of Iron Coordination Complexes as Highly Active Homogenous Water Oxidation Catalysts by Deuteration of Oxidation-Sensitive Sites.

The nature of the oxidizing species in water oxidation reactions with chemical oxidants catalyzed by α-[Fe(OTf)(mcp)] (1α; mcp = N, N'-dimethyl- N, N'-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine, OTf = trifluoromethanesulfonate anion) and β-[Fe(OTf)(mcp)] (1β) has been investigated. Mössbauer spectroscopy provides definitive evidence that 1α and 1β generate oxoiron(IV) species as the resting state. Decomposition paths of the catalysts have been investigated by identifying and quantifying ligand fragments that form upon degradation.

Dual cobalt-copper light-driven catalytic reduction of aldehydes and aromatic ketones in aqueous media.

We present an efficient, general, fast, and robust light-driven methodology based on earth-abundant elements to reduce aryl ketones, and both aryl and aliphatic aldehydes (up to 1400 TON). The catalytic system consists of a robust and well-defined aminopyridyl cobalt complex active for photocatalytic water reduction and the [Cu(bathocuproine)(Xantphos)](PF) photoredox catalyst. The dual cobalt-copper system uses visible light as the driving-force and HO and an electron donor (EtN or PrEtN) as the hydride source.

Enhancement and control of the selectivity in light-driven ketone versus water reduction using aminopyridine cobalt complexes.

Cobalt(ii) complexes with the general structure [CoII(OTf)(Y,XPy2Tstacn)](OTf) (1R, where Y,XPy2Tstacn is 1,4-di(p-Y,m-X-picolyl)-7-R-1,4,7-triazacyclononane; 1H, 1CO2Et, 1DMM) and [CoII(OTf)2(Y,XPyMetacn)] (2R, where Y,XPyMetacn is 1-(p-Y,m-X-picolyl)-7,4-di-methyl-1,4,7-triazacyclononane; 2CO2Et, 2Cl, 2H, 2DMM, 2NMe2) were active in both light-driven acetophenone (3a) and water reduction. Competition studies show that aromatic ketone/water reduction selectivity ranks from 0.2 to 8.

Understanding light-driven H evolution through the electronic tuning of aminopyridine cobalt complexes.

A new family of cobalt complexes with the general formula [Co(OTf)(Pytacn)] ( , Pytacn = 1-[(4-X-3,5-Y-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, (X = CN ( ), COEt ( ), Cl ( ), H ( ), NMe ( )) where (Y = H, and X = OMe when Y = Me ( )) is reported. We found that the electronic tuning of the Pytacn ligand not only has an impact on the electronic and structural properties of the metal center, but also allows for a systematic water-reduction-catalytic control. In particular, the increase of the electron-withdrawing character of the pyridine moiety promotes a 20-fold enhancement of the catalytic outcome.

A Highly Active N-Heterocyclic Carbene Manganese(I) Complex for Selective Electrocatalytic CO Reduction to CO.

We report here the first purely organometallic fac-[Mn (CO) (bis- NHC)Br] complex with unprecedented activity for the selective electrocatalytic reduction of CO to CO, exceeding 100 turnovers with excellent faradaic yields (η ≈95 %) in anhydrous CH CN. Under the same conditions, a maximum turnover frequency (TOF ) of 2100 s was measured by cyclic voltammetry, which clearly exceeds the values reported for other manganese-based catalysts. Moreover, the addition of water leads to the highest TOF value (ca.

Spectroscopic and DFT Characterization of a Highly Reactive Nonheme Fe-Oxo Intermediate.

The reaction of [(PyNMe)Fe(CFSO)], 1, with excess peracetic acid at -40 °C generates a highly reactive intermediate, 2b(PAA), that has the fastest rate to date for oxidizing cyclohexane by a nonheme iron species. It exhibits an intense 490 nm chromophore associated with an S = 1/2 EPR signal having g-values at 2.07, 2.

Bioinspired Electro-Organocatalytic Material Efficient for Hydrogen Production.

Commercial carbon fibers can be used as electrodes with high conductive surfaces in reduced devices. Oxidative treatment of such electrodes results in a chemically robust material with high catalytic activity for electrochemical proton reduction, enabling the measurement of quantitative faradaic yields (>95 %) and high current densities. Combination of experiments and DFT calculations reveals that the presence of carboxylic groups triggers such electrocatalytic activity in a bioinspired manner.