Acid-catalyzed chemodivergent reactions of 2,2-dimethoxyacetaldehyde and anilines

Chemodivergent reactions of 2,2-dimethoxyacetaldehyde and anilines were described, which were established on the basis of either a CC bond cleavage or a rearrangement process of a reaction intermediate. These reactions proceeded in a condition-determined manner with good functional group tolerance. In the first model, 2,2-dimethoxyacetaldehyde reacted with aniline to form a new CN bond, in the presence of O₂, via a CC bond cleavage reaction. However, in the second model, by performing the reaction in the absence of O₂, Heyns rearrangement occurred and generated a new CO bond to form methyl phenylglycinate. Such condition-determined reactions not only offered the new way for value-added conversion of biomass-derived platform molecule, 2, 2-dimethoxyacetaldehyde, but also provided efficient methods for the synthesis of N-arylformamides and methyl phenylglycinates.     

InP quantum dots on g-C3N4 nanosheets to promote molecular oxygen activation under visible light

Largely limited by the high dissociation energy of the OO bond, the photocatalytic molecular oxygen activation is highly challenged, which restrains the application of photocatalytic oxidation technology for atmospheric pollutants removal. Herein, we design and fabricate the InP QDs/g-C₃N₄ compounds. The introduction of InP QDs promotes the charge transfer within the interface resulting in the effective separation of photo-generated carriers. Furthermore, InP QDs greatly facilitates the activation of molecular oxygen and promote the formation of O₂⁻ under visible-light illumination. These conclusions are identified by experimental and calculation results. Hence, NO can be combined with the O₂⁻ to form OONO intermediate to direct conversion into NO₃⁻. As a result, the NO removal ratio of g-C₃N₄ has a onefold increase after InP QDs loaded and the generation of NO₂ is effectively inhibited. This work may provide a strategy to design highly efficient materials for molecular oxygen activation.     

Effect of oxygen-containing functional groups on the wettability of coal through DFT and MD simulation

To investigate the wettability of different oxygen-containing functional group (OFG) surfaces, graphite substrates were used as a model for coal adsorbents. The substrates were modified with COOH, OH, CO, and OCH₃. The adsorption-diffusion behavior of H₂O molecules/water droplets on different OFG surfaces was investigated using molecular dynamics (MD) simulations with frontier orbital energy difference as a metric for different surface wettability degrees in quantum chemical analysis. The results indicated that the frontier orbital energy difference of the H₂O molecule was 3.480, 3.491, 3.631, and 3.680 eV for PhCOOH, PhOH, PhCO, and PhOCH₃, respectively. In addition, the equilibrium contact angle, interaction energy, and number of hydrogen bonds after the adsorption equilibrium of water droplets for COOH, OH, CO, and OCH₃ surfaces were 22.34°, ?5.03 kcal/mol, and 652; –23.72°, ?4.19 kcal/mol, and 450; 68.01°, ?0.79 kcal/ mol, and 61; 90.51°, ?0.50 kcal/mol, and 28, respectively. The smaller the energy difference between the frontier orbitals of the H₂O molecule and the OFG, the smaller the equilibrium contact angle between the water droplet and the OFG surface, the more hydrogen bonds were formed, and the larger the absolute value of the interaction energy, the better the wettability of the surface of the OFG. The order of wettability of the different OFG surfaces was COOH > OH > CO > OCH₃, which is consistent with the radial distribution function and the analysis results for the extended area, etc. The results of density functional theory (DFT) calculations and MD simulations exhibited identical patterns, indicating the reasonableness of the simulations. This study may serve as a reference for the suppression of hydrophilicity in low-order coal and the enhancement of the flotation effect.     

Copper-catalyzed oxidative CH bond functionalization of N-allylbenzamide for CN and CC bond formation

CH bond functionalization for CN and CC bond formations via cross-dehydrogenative coupling (CDC) of N-allylbenzamides with indole as amine source has been developed under a copper-catalyzed condition. To the best of our knowledge, these are the first examples in which different classes of N-containing compounds were directly prepared from the readily available N-allylbenzamides using an inexpensive catalyst-oxidant (CuSO₄/TBHP) system. Further, it was applied for the synthesis of α-substituted N-allylbenzamides by using Grignard reagent as nucleophiles.     

Non-directed highly para-selective CH functionalization of TIPS-protected phenols promoted by a carboxylic acid ligand

Palladium-catalyzed non-directed CH functionalization provides an efficient approach for direct functionalization of arenes, but it usually suffers from poor site selectivity, limiting its wide application. Herein, it is reported for the first time that the carboxylic acid ligand of 3,5-dimethyladamantane-1-carboxylic acid (1-DMAdCO₂H) can affect the site selectivity during the CH activation step in palladium-catalyzed non-directed CH functionalization, leading to highly para-selective CH olefination of TIPS-protected phenols. This transformation displayed good generality in realizing various other para-selective CH functionalization reactions such as halogenation, and allylation reactions. A wide variety of phenol derivatives including bioactive molecules of triclosan, thymol, and propofol, were compatible substrates, leading to the corresponding para-selective products in moderate to good yields. A preliminary mechanism study revealed that the spatial repulsion factor between carboxylic acid ligand and bulky protecting group resulted in the selective CH activation at the less sterically hindered para-position. This new model non-directed para-selective CH functionalization can provide a straightforward route for remote site-selective CH activations.     

Reaction pathway change on plasmonic Au nanoparticles studied by surface-enhanced Raman spectroscopy

Gold nanoparticles (Au NPs) are nanoscale sources of light and electrons, which are highly relevant for their extensive applications in the field of photocatalysis. Although a number of research works have been carried out on chemical reactions accelerated by the energetic hot electrons/holes, the possibility of reaction pathway change on the plasmonic Au surfaces has not been reported so far. In this proof-of-concept study, we find that Au NPs change the reaction pathway in photooxidation of alkyne under visible light irradiation. This reaction produces benzil (COCO) without the presence of Au NPs. In contrast, as indicated by surface-enhanced Raman spectroscopic (SERS) results, the CC triple bonds (CC) adsorbed on Au NPs are converted into carboxyl (COOH) and acyl chloride (COCl) groups. The plasmonic Au NPs not only provide energetic charge carriers but also activate the reactant molecules as conventional heterogeneous catalysts. This study discloses the second role of plasmonic NPs in photocatalysis and bridges the gap between plasmon-driven and conventional heterogeneous catalysis.     

I2/TBHP mediated multiple CH bonds functionalization of azaarenes with methylarenes to synthesize iodoisoquinolinones via iodination/N-benzylation/amidation sequence

An oxidative multi-functionalization of azaarenes with benzylic CH bonds of methylarenes via iodination/N-benzylation/amidation cascade, to produce N-benzyl-4-iodoisoquinolin-1(2H)-ones and N-benzyl-3-iodoquinolin-2(1H)-ones is developed. The molecular iodine plays a triple role in activating benzylic sp³ CH bond of methylbenzenes, accelerating the oxidation process and serving as iodination reagent. This reaction utilizes cheap and readily available azaarenes and methylarenes as starting materials and proceeds under metal-free conditions to construct C-I, CN and CO bonds consecutively and afford iodo(iso)quinolinones efficiently.     

Metal-free C(sp2)-H perfluoroalkylsulfonylation and configuration inversion: Stereoselective synthesis of α-perfluoroalkylsulfonyl E-enaminones

The perfluoroalkylsulfonylation (CF₃SO₂, C₂F₅SO₂ and CHF₂SO₂) in the enaminone CH bonds has been developed simply via the promotion of molecular iodine by using stable and cheap sodium perfluoroalkyl sulfinates as coupling partners. The stereoselective synthesis of E-configurated α-perfluoroalkylsulfonyl enaminones has been realized via unprecedented CH bond elaboration and CC double bond configuration inversion by free radical process.     

Palladium-catalyzed meta-CH bond iodination of arenes with I2

Palladium-catalyzed highly meta-selective CH iodination of phenylacetic acid, benzylphosphonate and benzylsulfonate scaffolds with molecular I₂ is developed using a pyridine-type template. The practical ester linkages enable the directing template easily installed and readily removed. The substrate scope is broad, and alkyl, methoxyl, trifluomethyl, and halo substituents are compatible with this reaction. Further transformations of ibuprofen iodide intermediates by Pd-catalyzed CC and C–heteroatom bond formation illustrate the broad utility of this method.     

Hydrogen generation of ammonia borane hydrolysis catalyzed by Fe22@Co58 core-shell structure

In this paper, the process of ammonia borane (AB) hydrolysis generate H₂ on the transition metal Fe@Co core-shell structure has been obtained. According to the different roles played by H₂O molecules and the number of H₂O molecules involved, there are three schemes of reaction paths. Route I does not involve the dissociation of H₂O molecules and all H atoms come from AB. Moreover, the H₂O molecule has no effect on the breaking of the BH bond or the NH bond. The reaction absorbs more heat during the formation of the second and third H₂ molecules. Route II includes the dissociation of H₂O molecules and the cleavage of BH or NH bonds, respectively, and the reaction shows a slight exotherm. Route III started from the break of the BN bond and obtained 3H₂ molecules through the participation of different numbers of H₂O molecules. After multiple comparative analyses, the optimal hydrolysis reaction path has been obtained, and the reaction process can proceed spontaneously at room temperature.     

Spectral characterization,electrochemical, antimicrobial and cytotoxic studies on new metal(II) complexes containing N2O4 donor hexadentate Schiff base ligand

We report the biological activity of the new Schiff base ligand H₂L (H₂L = 6,6′-((1E,11E)-5,8-dioxa-2,11-diazadodeca-1,11-diene-1,12-diyl)bis(2,4-dichlorophenol)), its derived metal(II) complexes [Cu(L)] (1), [Co(L)] (2), [Ni(L)] (3) and [Zn(L)] (4), along with their structural characterizations by using various analytical and spectroscopic techniques. Electrochemical investigations showed that all of these Cu(II), Co(II) and Ni(II) complexes were reversibly reducible. Although the change of the number of unpaired electrons are different of the metal cations, they have an effect on the redox potentials of the Co(II)/(I), Ni(II)/(I) and Cu(II)/(I) couples. The ¹H NMR and FTIR data concluded that the Schiff base ligand H₂L acts as a hexadentate ligand coordinating with metal(II) ions through the oxygen atoms of the (COC), phenolic (COH) groups and nitrogen atom of the azomethine (CHN) group. UV-Visible absorption spectra studies clearly revealed the octahedral geometry of the prepared metal(II) complexes. Complexes 1 and 4 were found to be efficient in bringing about antimicrobial activities. The proposed mechanism of their antimicrobial activities has been discussed. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed the remarkable cytotoxicity of complex 1 (IC50 = 17 ± 1.3 μg/mL) on human breast cancer MCF-7 cells than Schiff base ligand H₂L and complexes 2–4. Moreover, AO/EB staining assay revealed cell death due to apoptosis in MCF-7 cells and the generation of ROS by the Schiff base ligand H₂L and its derived metal(II) complexes 1–4 may be a possible cause for their cytotoxic activity.     

Glycidyl ether of naturally occurring sesamol in the synthesis of mussel-inspired polymers

The objective of this work is to synthesize the mussel-mimicking ionic polymers bearing electron-rich 1,3,4-triphenoxy motifs of naturally occurring sesamol [3,4-(methylenedioxy)phenol] I. To our knowledge, the work would represent, for the first time, the ring-opening reaction of epoxide built upon the triphenoxy motifs of hydroxyhydroquinone. Sesamol I upon O-alkylation using epibromohydrin has been converted to its epoxy monomer II in 77% yield. Monomer II under ring-opening polymerization using basic Bu₄NOH and Bu₄NF as well as by Lewis acid initiator/catalyst MePh₃PBr/ⁱBu₃Al led to polyether III in 80–99% yields. Monomer II and allyl glycidyl ether (i.e. allyl 2,3-epoxypropyl ether) IV upon polymerization gave random copolymer V of number average molar mass of 9570 g mol⁻¹, which upon thiol-ene reaction with HSCH₂CH₂NH₃⁺Cl⁻ and HSCH₂CO₂H afforded cationic (^^^NH₃⁺) VI and anionic (^^^CO₂⁻) VII copolymers, respectively. For facile deprotection, the methylenedioxy (OCH₂O) motifs in VI was activated by its conversion to labile acetoxymethylenedioxy [OCH(OAc)O] unit to obtain VIII in 80% yields. The pendant allyl groups in VIII upon elaboration via thiol-ene reaction using cysteamine hydrochloride and subsequent hydrolysis of [OCH(OAc)O] under a mild condition led to a mussel-inspired cationic copolymer IX (78%) having catechol motifs-embedded pendants of 3,4-dihydroxyphenoxy groups.     

Mapping the reactivity of the quinoline ring-system – Synthesis of the tetracyclic ring-system of isocryptolepine and regioisomers

Bromoquinolines (2-bromoquinoline – 8-bromoquinoline and 5-bromo-3-methoxyquinoline) and 2-aminophenylboronic acid hydrochloride were subjected to Suzuki-Miyaura cross-coupling conditions resulting in formation of the desired biaryl systems in good yields. The resulting biaryls were then subjected to palladium catalyzed CH activation/CN bond formation utilizing PdCl₂(dppf). The reactions revealed large differences in reactivity depending on the attachment point for the 2-aminophenyl group on the quinoline. The variation in the reactivity was rationalized based on the electron distribution around the quinoline ring-system.     

Spectroscopic identification of water splitting by neutral group 3 metals

Spectroscopic study of water splitting by neutral metal clusters is crucial to understanding the microscopic mechanism of catalytic processes but has been proven to be a challenging experimental target due to the difficulty in size selection. Here, we report a size-specific infrared spectroscopic study of the reactions between neutral group 3 metals and water molecules based on threshold photoionization using a vacuum ultraviolet laser. Quantum chemical calculations were carried out to identify the structures and to assign the experimental spectra. All the M₂O₄H₄ (M = Sc, Y, La) products are found to have the intriguing M₂(μ₂-O)(μ₂-H)(μ₂-OH)(η¹-OH)₂ structures, indicating that the HOH bond breaking, the MO/MH/MOH bond formation, and hydrogen production proceed efficiently in the reactions between laser-vaporized metals and water molecules. The joint experimental and theoretical results on the atomic scale demonstrate that the water splitting by neutral group 3 metals is both thermodynamically exothermic and kinetically facile in the gas phase. These findings have important implications for unravelling the structure-reactivity relationship of catalysts with isolated metal atoms/clusters dispersed on supports.     

Base-catalyzed synthesis of quinazolines in aqueous medium

An alternative green protocol and step economy for the synthesis of quinazoline has been developed. The reaction of readily available 2-aminobenzonitriles with various organometallic reagents led to ortho-aminoaryl NH ketimine species. The subsequent base catalysed NC bond formation with various isothiocyanates afforded quinazoline scaffolds in aqueous medium. The salient features of this protocol are use of readily available inexpensive precursors, water as a green environmentally benign solvent, short reaction time, operational simplicity, easy workup procedure and good functional group tolerance.     

Recyclable Cu/g-C3N4 nanometric semiconductor catalyzed N-formylation of amines via photocatalytic aerobic oxidative CC bond cleavage of aldehydes under visible-light irradiation

Due to its difficulty and complexity, the cleavage and subsequent functionalization of the C(sp³)-C(sp³) single bond has received less attention than the CC bond formation reactions that have been extensively studied. Herein, by utilizing Cu/g-C₃N₄ nanometric semiconductor as a recyclable photocatalyst, an aerobic oxidative CC bond cleavage of aldehydes was developed with the promotion of amines under visible light irradiation. Based on the reaction, phenylacetaldehyde was selected as a highly efficient formylation reagent for amines. Under blue light irradiation, good to excellent yields of formamides were achieved for various amines in 1 atm oxygen atmosphere at room temperature. This methodology offers a practical, neutral and gentle alternative to the preparation of formamides.     

Photogenerated electrophilic radicals for the umpolung of enolate chemistry

The use of enolate chemistry is the election choice when a CC bond formation is required exploiting the acidity of carbonyl derivatives in the α position. However, a reversed-polarity equivalent of enolate chemistry is emerging making use of electrophilic radicals having a radical site in place of a negative charge in the same α position. Visible light photoredox catalysis is becoming the ideal tool for the generation of these radicals thus allowing their wide application in several synthetic routes. Aim of this review is to collect recent examples of the chemistry of photogenerated electrophilic radicals for the forging of new CC or other CY bonds.     

Photoredox-neutral ring-opening pyridylation of cyclic oximes via phosphoranyl radical-mediated NO/CC bond cleavages and sequential radical-radical coupling

A novel photoredox-neutral ring-opening pyridylation of non-prefunctionalized cyclic oximes has been accomplished through phosphoranyl radical-mediated NO/CC bond cleavages followed by radical-radical coupling. This mild acid-, base-, and oxidant-free protocol provides highly site-selective and efficient access to distally pyridylated alkylnitriles, which could be scale-up synthesized and readily converted into skeletally diverse compounds. Notably, the oxidized ground-state photocatalyst generated via the SET oxidation of the highly reducing excited-state photocatalyst by cyanopyridines might initiate the following phosphoranyl radical-mediated deoxygenative process.     

Synthesis,physico-chemical characterization,antimicrobial activity and toxicological features of AgZnO nanoparticles

Silver-zinc oxide nanoparticles (AgZnO NPs) were chemically synthesized by the deposition of Ag NPs on the surface of ZnO NPs using silver nitrate, three types of anionic polyelectrolytes and citric acid as reagents. The Wavelength Dispersive X-ray Fluorescence (WDXRF) spectrometry of AgZnO NPs revealed 0.41–0.69 wt% Ag, and balance ZnO. The existence of Ag NPs on the surface of ZnO NPs with hexagonal wurtzite structure was highlighted by X-ray Diffraction (XRD) analysis, scanning electron microscopy (SEM), and Ultraviolet–Visible (UV–Vis) spectroscopy. The diffuse reflectance absorption of AgZnO NPs in the visible light region increased with the increase of Ag NPs content. The Fourier Transform Infrared (FTIR) spectrometry revealed no chemical bonding between Ag NPs and ZnO NPs and confirmed the presence of functional groups characteristic to ZnO and carboxylic acid salts. The newly synthesized AgZnO NPs displayed antimicrobial activity against all the tested medically relevant pathogens, with minimal (biofilm) inhibitory concentrations ranging from 1.875 mg/mL to 7.5 mg/mL. Although the in vitro genotoxicity assay revealed a relatively high micronuclei index, the in vivo micronucleus (MN) test revealed a low MN frequency in animals treated with AgZnO NPs. The histopathological analysis revealed non-significant structural changes of the hepatic parenchyma, renal cortex and intestinal mucosa and minimal inflammatory reactions. The AgZnO NPs administration induced TUNEL positive nuclei of Kupffer cells in the liver parenchyma. The present study shows that the newly synthesized AgZnO NPs are active against planktonic and adherent microorganisms and could be exploited to develop novel antimicrobial strategies for the biotechnology and biomedical fields. Easy scalability of the developed chemical synthesis is a major advantage in producing large batches of AgZnO NPs with reproducible properties.     

How long a C–C bond can be? An example of extraordinary long C–C single bond in 1,2-diarylamino-o-carborane

The longest C-C single bond of 1.990(4) Å known thus far is observed in the single crystal X-ray structure of 1,2-(NHMes)₂-o-carborane (Mes = 2,4,6-trimethylphenyl), which is readily synthesized via a one-pot process.