Redox Reactivity of a Mononuclear Manganese-Oxo Complex Binding Calcium Ion and Other Redox-Inactive Metal Ions.

Mononuclear nonheme manganese(IV)-oxo complexes binding calcium ion and other redox-inactive metal ions, [(dpaq)Mn(O)]-M (1-M, M = Ca, Mg, Zn, Lu, Y, Al, and Sc) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino- N-quinolin-8-yl-acetamidate), were synthesized by reacting a hydroxomanganese(III) complex, [(dpaq)Mn(OH)], with iodosylbenzene (PhIO) in the presence of redox-inactive metal ions (M ). The Mn(IV)-oxo complexes were characterized using various spectroscopic techniques. In reactivity studies, we observed contrasting effects of M on the reactivity of 1-M in redox reactions such as electron-transfer (ET), oxygen atom transfer (OAT), and hydrogen atom transfer (HAT) reactions.

How Does the Oxidation State of Palladium Surfaces Affect the Reactivity and Selectivity of Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen Gases? A Density Functional Study.

Direct synthesis of HO from H and O is an environmentally benign and atom economic process and as such is the ideal pathway in catalysis. However, currently no low-cost pathway of this kind of catalysis exists, although it would be an attractive alternative strategy to the common industrial anthraquinone method for HO production. Metal-based catalysts are widely employed in such a direct synthesis process but often need to be oxidized, alloyed, or supplied with additives to make them selective.

A Mononuclear Nonheme Iron(IV)-Amido Complex Relevant for the Compound II Chemistry of Cytochrome P450.

A mononuclear nonheme iron(IV)-amido complex bearing a tetraamido macrocyclic ligand, [(TAML)Fe(NHTs)] (1), was synthesized via a hydrogen atom (H atom) abstraction reaction of an iron(V)-imido complex, [(TAML)Fe(NTs)] (2), and fully characterized using various spectroscopies. We then investigated (1) the p K of 1, (2) the reaction of 1 with a carbon-centered radical, and (3) the H atom abstraction reaction of 1. To the best of our knowledge, the present study reports for the first time the synthesis and chemical properties/reactions of a high-valent iron(IV)-amido complex.

Construction of core-shell mesoporous carbon nanofiber@nickel cobaltite nanostructures as highly efficient catalysts towards 4-nitrophenol reduction.

We herein report small sized nickel cobaltite (NiCoO) nanosheets (103-144 nm × 71-97 nm) firmly coated on mesoporous carbon nanofibers (MCNFs), as active and stable catalysts for degradation of 4-nitrophenol in sewage with NaBH as the reductant. MCNFs with surface O-functionalities were first constructed by morphology-conserved transformation of zinc-trimesic acid fibers, which provide scaffolds to anchor trisodium citrate-induced Ni-Co hydroxide nanosheets. Upon calcination, the resultant core-shell MCNF@NiCoO nanostructures were fabricated and characterized by SEM, TEM, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and N adsorption/desorption techniques.

Quantum chemical simulations revealed the toxicokinetic mechanisms of organic phosphorus flame retardants catalyzed by P450 enzymes.

The metabolic fate and toxicokinetics of organic phosphorus flame retardants catalyzed by cytochrome P450 enzymes (CYPs) are here investigated by in silico simulations, leveraging an active center model to mimic the CYPs, triphenyl phosphate (TPHP), tris(2-butoxyethyl) phosphate and tris(1,3-dichloro-2-propyl) phosphate as substrates. Our calculations elucidated key main pathways and predicted products, which were corroborated by current in vitro data. Results showed that alkyl OPFRs are eliminated faster than aryl and halogenated alkyl-substituted OPFRs.

Recent advances of polyoxometalate-catalyzed selective oxidation based on structural classification.

The structural diversity and tenability observed in POMs has encouraged extensive investigations into their catalytic activity. Based on the structural classification of POMs, this review summarizes recent advances relating to POM-catalyzed selective oxidation and places most emphasis on dynamic developments from 2015 onwards. Work which contributes to comparing the catalytic performance of POMs with delicate structural differences (e.

Design, Synthesis of -phenethyl Cinnamide Derivatives and Their Biological Activities for the Treatment of Alzheimer's Disease: Antioxidant, Beta-amyloid Disaggregating and Rescue Effects on Memory Loss.

Gx-50 is a bioactive compound for the treatment of Alzheimer's disease (AD) found in Sichuan pepper (). In order to find a stronger anti-AD lead compound, 20 gx-50 (⁻) analogs have been designed and synthesized, and their molecular structures were determined based on nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis, as well as comparison with literature data. Compounds ⁻ were evaluated for their anti-AD potential by using DPPH radical scavenging assay for considering their anti-oxidant activity, thioflavin T (ThT) fluorescence assay for considering the inhibitory or disaggregate potency of A, and transgenic model assay for evaluating their rescue effect on memory loss.

Hypoglycemic triterpenes from Gynostemma pentaphyllum.

To search for bioactive gypenosides and their analogues, a saponin enriched fraction and its hydrolyzate from Gynostemma pentaphyllum were phytochemically investigated. Fractionation by diverse chromatographic methods, including HPLC, Sephadex LH-20, silica gel, and C18 reverse phase silica gel, led to the isolation and purification of twelve triterpenes, including five undescribed and seven known. The chemical structures of all compounds were determined as analyzed by nuclear magnetic resonance (NMR), high resolution mass spectrometry (HR-MS), infrared spectrum (IR), optical rotation, and chemical transformations.

Brønsted Acid-Promoted Friedel-Crafts Alkylation/Cyclization of (7-Hydroxynaphthalenyl)pyrrole or (2-Hydroxyphenyl)pyrroles with Isatins for the Construction of Pyrrolospirooxindole Derivatives.

An efficient trifluoroacetic acid-catalyzed cascade Friedel-Crafts alkylation/cyclization of 1-(7-hydroxynaphthalenyl)pyrrole or 1-(2-hydroxyphenyl)pyrroles with isatins has been developed, providing practical access to a variety of biologically important pyrrole-containing spirooxindoles.

Quantum Mechanics/Molecular Mechanics Studies on the Relative Reactivities of Compound I and II in Cytochrome P450 Enzymes.

The cytochromes P450 are drug metabolizing enzymes in the body that typically react with substrates through a monoxygenation reaction. During the catalytic cycle two reduction and protonation steps generate a high-valent iron (IV)-oxo heme cation radical species called Compound I. However, with sufficient reduction equivalents present, the catalytic cycle should be able to continue to the reduced species of Compound I, called Compound II, rather than a reaction of Compound I with substrate.

Non-Bonding Interactions Enable the Selective Formation of Branched Products in Palladium-Catalyzed Allylic Substitution Reactions.

Palladium-catalyzed allylic substitution reactions have become established as an important tool for the construction of carbon-carbon and carbon-heteroatom bonds in modern organic synthesis. However, controlling the regioselectivity of this type of transformation to afford chiral branched products, in addition to controlling the enantioselectivity, is a significant challenge. Excitingly, controlling nonbonding interactions between the substituents on the π-allyl-palladium intermediate and the nucleophile or palladium catalyst has been shown to be effective in achieving this goal.

Synthesis of Secondary and Tertiary Alkyl Boronic Esters by gem-Carboborylation: Carbonyl Compounds as Bis(electrophile) Equivalents.

An unprecedent gem-carboborylation of aldehydes and ketones provides access to various secondary and tertiary alkyl boronic esters. The addition of B pin to a carbonyl compound generates α-oxyl-substituted alkyl boron species. Organolithium and Grignard reagents are then applied as C nucleophiles for the 1,2-metalate rearrangement process.

Transition-Metal-Free Reductive Deoxygenative Olefination with CO.

A new transition-metal-free reductive deoxygenative olefination of phosphorus ylides with CO, an abundant and sustainable C1 chemical feedstock, is described. This catalytic CO fixation afforded β-unsubstituted acrylates and vinyl ketones in good yields with broad scope and good functional group tolerance under mild reaction conditions. Cost-effective and easily handled polymethylhydrosiloxane was used as a reductant.

Towards Hydrogen Storage through an Efficient Ruthenium-Catalyzed Dehydrogenation of Formic Acid.

Hydrogen is of fundamental importance for the construction of modern clean-energy supply systems. In this context, the catalytic dehydrogenation of formic acid (FA) is a convenient method to generate H gas from an easily available liquid. One of the issues associated with current catalytic dehydrogenation systems is insufficient stability.

Regioselectivity inversion tuned by iron(iii) salts in palladium-catalyzed carbonylations.

Impactful regioselectivity control is crucial for cost-effective chemical synthesis. By using cheap and abundant iron(iii) salts, the hydroxycarbonylations of both aromatic and aliphatic alkenes were significantly enhanced in both reactivity and selectivity (iso/n or n/iso up to >99 : 1). Moreover, Pd-catalyzed carbonylation selectivity can be switched from branched to linear by using different Fe(iii) salts.

Dual Functionalization of α-Monoboryl Carbanions through Deoxygenative Enolization with Carboxylic Acids.

A dual functionalization of 1,1-diborylalkanes through deoxygenative enolization with carboxylic acids was developed. 1,1-Diborylalkanes were activated by MeLi to generate α-monoboryl carbanions. In situ IR spectroscopy indicated an interaction between carboxylic acid and 1,1-diborylalkane before addition of the activation reagent.

Copper-catalyzed decarboxylative cyclization via tandem C-P and C-N bond formation: access to 2-phosphorylmethyl indoles.

A novel copper-catalyzed decarboxylative cyclization of ethynyl benzoxazinanones with P(O)H compounds has been developed. This protocol leads to a series of 2-phosphorylmethyl indoles with high efficiency and selectivity (up to 99% yield) through tandem C-P/C-N bond formation under mild conditions.

A Pd-catalyzed optional approach for the synthesis of dibenzothiophenes.

A direct and practical approach for the construction of DBTs was developed via a Pd-catalyzed tandem reaction, in which commercially available o-bromo-iodobenzenes combined with benzene thiols or iodobenzenes combined with o-bromo-benzene thiols were applied. These two approaches will provide an alternative for the synthesis of DBT derivatives.

Efficient and reusable SBA-15-immobilized Brønsted acidic ionic liquid for the ketalization of cyclohexanone with glycol.

Ketalization of cyclohexanone with glycol has been carried out using molecular sieve SBA-15 immobilized Brønsted acidic ionic liquid catalyst. The properties of the heterogeneous catalysts were characterized by elemental analysis, Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), thermogravimetry/differential scanning calorimetry (TG/DSC), and N adsorption-desorption (BET). The results suggested that Brønsted acidic ionic liquid [BSmim][HSO] had been successfully immobilized on the surface of SBA-15 and the catalytic performance evaluation demonstrated that the catalyst BAIL@SBA-15 exhibited excellent catalytic activities in the ketalization of cyclohexanone with glycol.

Efficient Aliphatic C-H Bond Oxidation Catalyzed by Manganese Complexes with Hydrogen Peroxide.

A tetradentate nitrogen ligand containing a benzimidazole ring and an electron-rich pyridine ring was developed, the resulting manganese complex exhibited good activity in the C-H oxidation of simple alkanes. In particular, cyclic aliphatic alkanes were transformed into ketones in very good yields (up to 89 %) by using environmentally benign H O as the terminal oxidant. This protocol was also applied successfully in benzylic C-H oxidation, giving the corresponding ketones with very good selectivities.

Palladium-catalyzed synthesis of fluoreones from bis(2-bromophenyl)methanols.

A palladium-catalyzed synthesis method of fluorenones has been developed. A variety of bis(2-bromophenyl)methanols could undergo the reaction smoothly in the presence of Pd(OAc), affording a series of fluorenones in moderate to good yields (two steps). Mechanistic studies reveal that the reaction might be triggered by oxidation of alcohol followed by intramolecular reductive coupling.

Chiral Bifunctional Phosphine-Carboxylate Ligands for Palladium(0)-Catalyzed Enantioselective C-H Arylation.

Previous enantioselective Pd -catalyzed C-H activation reactions proceeding via the concerted metalation-deprotonation mechanism employed either a chiral ancillary ligand, a chiral base, or a bimolecular mixture thereof. This study describes the development of new chiral bifunctional ligands based on a binaphthyl scaffold which incorporates both a phosphine and a carboxylic acid moiety. The optimal ligand provided high yields and enantioselectivities for a desymmetrizing C(sp )-H arylation leading to 5,6-dihydrophenanthridines, whereas the corresponding monofunctional ligands showed low enantioselectivities.

Manganese complex-catalyzed oxidation and oxidative kinetic resolution of secondary alcohols by hydrogen peroxide.

The highly efficient catalytic oxidation and oxidative kinetic resolution (OKR) of secondary alcohols has been achieved using a synthetic manganese catalyst with low loading and hydrogen peroxide as an environmentally benign oxidant in the presence of a small amount of sulfuric acid as an additive. The product yields were high (up to 93%) for alcohol oxidation and the enantioselectivity was excellent (>90% ee) for the OKR of secondary alcohols. Mechanistic studies revealed that alcohol oxidation occurs hydrogen atom (H-atom) abstraction from an α-CH bond of the alcohol substrate and a two-electron process by an electrophilic Mn-oxo species.

In Situ Coupling Strategy for the Preparation of FeCo Alloys and Co N Hybrid for Highly Efficient Oxygen Evolution.

An in situ coupling approach is developed to create a new highly efficient and durable cobalt-based electrocatalyst for the oxygen evolution reaction (OER). Using a novel cyclotetramerization, a task-specific bimetallic phthalocyanine-based nanoporous organic framework is successfully built as a precursor for the carbonization synthesis of a nonprecious OER electrocatalyst. The resultant material exhibits an excellent OER activity with a low overpotential of 280 mV at a current density of 10 mA cm and high durability in an alkaline medium.

Sequential Visible-Light Photoactivation and Palladium Catalysis Enabling Enantioselective [4+2] Cycloadditions.

Catalytic asymmetric cycloadditions of reactive ketene intermediates provide new opportunities for the production of chiral heterocyclic molecules. Though known for over 100 years, ketenes still remain underexplored in the field of transition-metal (TM)-catalyzed asymmetric cycloadditions because (1) ketenes, as highly electron-deficient species, are possibly unstable to low-valence TMs (i.e.