Thermal Formation of Metathesis-Active Tungsten Alkylidene Complexes from Cyclohexene.

A 7-tungstabicyclo[4.3.0]nonane complex forms slowly upon addition of cyclohexene to the ethylene complex, W(NAr)(OSiPh)(CH), at 22 °C.

Mononuclear Four-Coordinate Bis-Fluoride Bis-NHC Complexes of Chromium(II), Iron(II), and Cobalt(II).

The reaction between silylamido complexes of Cr(II), Fe(II), and Co(II) and IMes·2HF salt in the presence of IMes (IMes = 1,3-dimesitylimidazol-2-ylidene) led to isolation of Cr(IMes)F (), Fe(IMes)F (), and Co(IMes)F (). X-ray structural studies revealed that adopts square planar geometry, while and have distorted tetrahedral geometry. Magnetic susceptibility studies of , , and were consistent with high-spin complexes, = 2 for / and = 3/2 for .

Influence of Capping Ligands, Solvent, and Thermal Effects on CdSe Quantum Dot Optical Properties by DFT Calculations.

Cadmium selenide nanomaterials are very important materials in photonics, catalysis, and biomedical applications due to their optical properties that can be tuned through size, shape, and surface passivation. In this report, static and ab initio molecular dynamics density functional theory (DFT) simulations are used to characterize the effect of ligand adsorption on the electronic properties of the (110) surface of zinc blende and wurtzite CdSe and a (CdSe) nanoparticle. Adsorption energies depend on ligand surface coverage and result from a balance between chemical affinity and ligand-surface and ligand-ligand dispersive interactions.

Enhancing magneto-ionic effects in cobalt oxide films by electrolyte engineering.

Electric-field-driven ion motion to tailor magnetic properties of materials (magneto-ionics) offers much promise in the pursuit of voltage-controlled magnetism for highly energy-efficient spintronic devices. Electrolyte gating is a relevant means to create intense electric fields at the interface between magneto-ionic materials and electrolytes through the so-called electric double layer (EDL). Here, improved magneto-ionic performance is achieved in electrolyte-gated cobalt oxide thin films with the addition of inorganic salts (potassium iodide, potassium chloride, and calcium tetrafluoroborate) to anhydrous propylene carbonate (PC) electrolyte.

Controlling the Formation of Two Concomitant Polymorphs in Hg(II) Coordination Polymers.

Controlling the formation of the desired product in the appropriate crystalline form is the fundamental breakthrough of crystal engineering. On that basis, the preferential formation between polymorphic forms, which are referred to as different assemblies achieved by changing the disposition or arrangement of the forming units within the crystalline structure, is one of the most challenging topics still to be understood. Herein, we have observed the formation of two concomitant polymorphs with general formula {[Hg(Pip)(4,4'-bipy)]·DMF} (; Pip = piperonylic acid; 4,4'-bipy = 4,4'-bipyridine).

Influence of Aromatic Cations on the Structural Arrangement of Hg(II) Halides.

Understanding the structure and arrangement of hybrid metal halides and their contribution to the optoelectronic properties is, thus far, a challenging topic. In particular, new materials composed of d metal halides and pyridinium cations are still largely unexplored. Therefore, we report the synthesis and characterization of six Hg(II) salts built up from (HgCl) or (HgX) anions (X = Cl, Br, I) and 2,2'-bipyridium (2,2'-Hbipy), 2,2'-bipyridine-1,1'-diium (2,2'-Hbipy), or 1,10-phenantrolinium (1,10-Hphen) cations, using the same experimental conditions.

Atomically Dispersed Iridium on Indium Tin Oxide Efficiently Catalyzes Water Oxidation.

Heterogeneous catalysts in the form of atomically dispersed metals on a support provide the most efficient utilization of the active component, which is especially important for scarce and expensive late transition metals. These catalysts also enable unique opportunities to understand reaction pathways through detailed spectroscopic and computational studies. Here, we demonstrate that atomically dispersed iridium sites on indium tin oxide prepared via surface organometallic chemistry display exemplary catalytic activity in one of the most challenging electrochemical processes, the oxygen evolution reaction (OER).

Organocatalytic vs. Ru-based electrochemical hydrogenation of nitrobenzene in competition with the hydrogen evolution reaction.

The electrochemical reduction of organic contaminants allows their removal from water. In this contribution, the electrocatalytic hydrogenation of nitrobenzene is studied using both oxidized carbon fibres and ruthenium nanoparticles supported on unmodified carbon fibres as catalysts. The two systems produce azoxynitrobenzene as the main product, while aniline is only observed in minor quantities.

Water Adsorption on MO (M = Ti, Ru, and Ir) Surfaces. Importance of Octahedral Distortion and Cooperative Effects.

Understanding metal oxide MO (M = Ti, Ru, and Ir)-water interfaces is essential to assess the catalytic behavior of these materials. The present study analyzes the HO-MO interactions at the most abundant (110) and (011) surfaces, at two different water coverages: isolated water molecules and full monolayer, by means of Perdew-Burke-Ernzerhof-D2 static calculations and ab initio molecular dynamics (AIMD) simulations. Results indicate that adsorption preferably occurs in its molecular form on (110)-TiO and in its dissociative form on (110)-RuO and (110)-IrO.

Reactivity of Metal Carbenes with Olefins: Theoretical Insights on the Carbene Electronic Structure and Cyclopropanation Reaction Mechanism.

Present work addresses the reactivity of several phenyl-substituted metal-carbene complexes with 4-methylstyrene by means of density functional theory OPBE simulations. Different paths that lead to cyclopropanation were explored and compared to the olefin metathesis mechanism. For this purpose, we chose four different catalysts: (i) the Grubbs second-generation olefin metathesis catalyst, (ii) a Grubs second-generation-like complex, in which ruthenium is replaced by iron, and (iii) two iron carbene complexes (a piano stool and a porphyrin iron carbene) that experimentally catalyze alkene cyclopropanation.

Binding of Thioflavin T and Related Probes to Polymorphic Models of Amyloid-β Fibrils.

Alzheimer's disease is a challenge of the utmost importance for contemporary society. An early diagnosis is essential for the development of treatments and for establishing a network of support for the patient. In this light, the deposition in the brain of amyloid-β fibrillar aggregates, which is a distinctive feature of Alzheimer, is key for an early detection of this disease.

Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study.

Alkane metathesis transforms small alkanes into their higher and lower homologues. The reaction is catalyzed by either supported d metal hydrides (M = Ta, W) or d alkyl alkylidene complexes (M = Ta, Mo, W, Re). For the silica-supported tantalum hydrides, several reaction mechanisms have been proposed.

Visible-Light Photocatalytic Intramolecular Cyclopropane Ring Expansion.

Described herein is a new visible-light photocatalytic strategy for the synthesis of enantioenriched dihydrofurans and cyclopentenes by an intramolecular nitro cyclopropane ring expansion reaction. Mechanistic studies and DFT calculations are used to elucidate the key factors in this new ring expansion reaction, and the need for the nitro group on the cyclopropane.

Enhanced photocatalytic activity of gold nanoparticles driven by supramolecular host-guest chemistry.

Functionalization of gold nanoparticles with supramolecular hosts allows their plasmon-based photocatalytic activity to be enhanced. This is mainly ascribed to the formation of labile host-guest complexes with the reagent molecules on the metal surface, thus promoting nanoparticle-substrate approximation without interfering with the light-induced catalytic process.

Computational study on donor-acceptor optical markers for Alzheimer's disease: a game of charge transfer and electron delocalization.

According to the amyloid cascade hypothesis, amyloid-β (Aβ) deposition is a central event in the Alzheimer's disease and thus, detection of Aβ deposits is crucial to monitor the progression of the pathology. Despite its low tissue penetration, fluorescence imaging may become an alternative technique for identifying these deposits because it is less toxic and less costly than positron emission tomography. Suitable dyes, however, should emit in the near infrared (NIR) region, cross the blood-brain barrier and target Aβ aggregates.

Hydrazine N-N Bond Cleavage over Silica-Supported Tantalum-Hydrides.

Hydrazine reacts with silica-supported tantalum-hydrides [(≡SiO)2TaHx] (x = 1, 3), 1, under mild conditions (100 °C). The IR in situ monitoring of the reaction with N2H4 or (15)N2H4, and the solid-state MAS NMR spectra of the fully (15)N labeled compounds (CP (15)N, (1)H-(15)N HETCOR, (1)H-(1)H double-quantum, and (1)H-(1)H triple-quantum spectra) were used to identify stable intermediates and products. DFT calculations were used for determining the reaction pathway and calculating the (15)N and (1)H NMR chemical shifts.

Disaggregation-induced fluorescence enhancement of NIAD-4 for the optical imaging of amyloid-β fibrils.

The main hallmark of Alzheimer's disease is the deposition of amyloid-β (Aβ) aggregates in the brain. An early diagnosis of the disease requires a fast and accurate detection of such aggregates in vivo. NIAD-4 is one of the most promising in vivo markers developed due to its high emission at λ > 600 nm and its ability to rapidly cross the blood-brain barrier (BBB) and target Aβ deposits.

DFT study on the reaction mechanism of the ring closing enyne metathesis (RCEYM) catalyzed by molybdenum alkylidene complexes.

The ring closing enyne metathesis reaction (RCEYM) catalyzed by molybdenum based monoalkoxy pyrrolyl Schrock type catalysts has been studied by means of DFT (B3LYP-D) calculations. The two potential active alkylidene species as well as the three proposed reaction mechanisms (ene-then-yne, endo-yne-then-ene and exo-yne-then-ene) have been taken into account. Moreover, the influence on the exo- and endo- selectivity of the reactant substituents has also been explored.

DFT study on the recovery of Hoveyda-grubbs-type catalyst precursors in enyne and diene ring-closing metathesis.

DFT (B3LYP-D) calculations have been used to better understand the origin of the recovered Hoveyda-Grubbs derivative catalysts after ring-closing diene or enyne metathesis reactions. For that, we have considered the activation process of five different Hoveyda-Grubbs precursors in the reaction with models of usual diene and enyne reactants as well as the potential precursor regeneration through the release/return mechanism. The results show that, regardless of the nature of the initial precursor, the activation process needs to overcome relatively high energy barriers, which is in agreement with a relatively slow process.

Successive heterolytic cleavages of H2 achieve N2 splitting on silica-supported tantalum hydrides: a DFT proposed mechanism.

DFT(B3PW91) calculations have been carried out to propose a pathway for the N(2) cleavage by H(2) in the presence of silica-supported tantalum hydride complexes [(≡SiO)(2)TaH(x)] that forms [(≡SiO)(2)Ta(NH)(NH(2))] (Science 2007, 317, 1056). The calculations, performed on the cluster models {μ-O[(HO)(2)SiO](2)}TaH(1) and {μ-O[(HO)(2)SiO](2)}TaH(3), labelled as (≡SiO)(2)TaH(x) (x = 1, 3), show that the direct hydride transfers to coordinated N-based ligands in (≡SiO)(2)TaH(η(2)-N(2)) and (≡SiO)(2)TaH(η(2)-HNNH) have high energy barrier barriers. These high energy barriers are due in part to a lack of energetically accessible empty orbitals in the negatively charged N-based ligands.

O-O bond activation in H2O2 and (CH3)3C-OOH mediated by [Ni(cyclam)(CH3CN)2](ClO4)2: different mechanisms to form the same Ni(III) product?

Reaction of [Ni(II)(cyclam)(CH(3)CN)(2)](ClO(4))(2) (1) with tert-butylhydroperoxide (TBHP) or H(2)O(2), in acidic media results in a formation of [Ni(III)(cyclam)(CH(3)CN)(2)](3+) species (2), the nature of which is characterized by UV-vis, EPR and XPS. The formation rate of 2 is much higher when H(2)O(2) is used as oxidant. In absence of acid, TBHP reacts with 1 generating the same Ni(III) species but, in contrast, no reaction is observed between H(2)O(2) and 1.

Mechanistic insights into ring-closing enyne metathesis with the second-generation Grubbs-Hoveyda catalyst: a DFT study.

The full catalytic process (precatalyst activation, propagating cycle and active-species interconversion) of the ring-closing enyne metathesis (RCEYM) reaction of 1-allyloxy-2-propyne with the Grubbs-Hoveyda complex as catalyst was studied by B3LYP density functional theory. Both the ene-then-yne and yne-then-ene pathways are considered and, for the productive catalytic cycle, the feasibility of the endo-yne-then-ene route is also explored. Calculations predict that the ene-then-yne and yne-then-ene pathways proceed through equivalent steps, the only major difference being the order in which they take place.

Shutting down secondary reaction pathways: the essential role of the pyrrolyl ligand in improving silica supported d(0)-ML4 alkene metathesis catalysts from DFT calculations.

The efficiency of silica supported d(0) ML(4) alkene metathesis catalysts [([triple bond]SiO)M(NR(1))(=CHR(2))(X)] (M = Mo, W; R(1) = aryl and alkyl) is influenced by the nature of the X ancillary ligand. Replacing the alkyl ligand by a pyrrolyl ligand dramatically increases the performance of the catalyst. DFT calculations on the metathesis, the deactivation, and the byproduct formation pathways for the imido Mo and W and the alkylidyne Re complexes give a rational for the role of pyrrolyl ligand.

DFT mechanistic study on diene metathesis catalyzed by Ru-based Grubbs-Hoveyda-type carbenes: the key role of pi-electron density delocalization in the Hoveyda ligand.

The catalytic activity and catalyst recovery of two heterogenized ruthenium-based precatalysts (H and NO(2)(4)) in diene ring-closing metathesis have been studied by means of density functional calculations at the B3LYP level of theory. For comparison and rationalization of the key factors that lead to higher activities and higher catalyst recoveries, four other Grubbs-Hoveyda complexes have also been investigated. The full catalytic cycle (catalyst formation, propagation, and precatalyst regeneration) has been considered.