Showing papers on "Reagent published in 2016"
TL;DR: It is reported that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which leads to a high local concentration of CO2 close to the active CO2 reduction reaction surface, which surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts.
Abstract: Electrochemical reduction of carbon dioxide (CO2) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concentration of CO2 surrounding typical CO2 reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species, but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO2 adsorption, but this comes at the cost of increased hydrogen (H2) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO2 close to the active CO2 reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO2 reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at -0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at -0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.
1,252 citations
TL;DR: The role of sulfur in nZVI lies essentially in its ability to poison hydrogen recombination, which drives surface reactions to favor reduction by atomic hydrogen, which implies that the reactivity of S-nZVI is contaminant-specific and is selective against the background reaction of water reduction.
Abstract: Zero-valent iron nanoparticles (nZVI) synthesized in the presence of reduced sulfur compounds have been shown to degrade trichloroethene (TCE) at significantly higher rates. However, the applicability of sulfidation as a general means to enhance nZVI reactivity under different particle preparation conditions and the underlying cause for this enhancement effect are not well understood. In this study, the effects of sulfidation reagent, time point of sulfidation, and sulfur loading on the resultant particles were assessed through TCE degradation experiments. Up to 60-fold increase in TCE reaction rates was observed upon sulfidation treatment, with products being fully dechlorinated hydrocarbons. While the reactivity of these sulfur-treated nZVI (S-nZVI) was relatively unaffected by the sulfidation reagent (viz., sodium sulfide, dithionite, or thiosulfate) or the sequence of sulfidation relative to iron reduction, TCE reaction rates were found to depend strongly on sulfur to iron ratio. At a low sulfur loadi...
270 citations
TL;DR: In this paper, the main developments on the employment of DMSO as sources of Me, SMe, SO2Me, as an oxidant etc. have been summarized and discussed.
Abstract: Dimethyl sulfoxide (DMSO) is one of the most commonly applied organic solvents in chemical transformations and is utilized widely in industrial processes as well. During the past decades, numerous procedures using DMSO as a reaction reagent have been developed and published. In this review, the main developments on the employment of DMSO as sources of Me, SMe, SO2Me, as an oxidant etc. have been summarized and discussed.
244 citations
TL;DR: A novel enantioselective copper-catalyzed intermolecular cyanotrifluoromethylation of alkenes has been developed, in which a variety of CF3-containing alkylnitriles are furnished with excellent enantiomeric excess.
Abstract: A novel enantioselective copper-catalyzed intermolecular cyanotrifluoromethylation of alkenes has been developed, in which a variety of CF3-containing alkylnitriles are furnished with excellent enantiomeric excess. Preliminary mechanistic studies revealed (1) the reaction was initiated by a SET process between activated Togni’s CF3+ reagent and a Cu(I) catalyst; (2) the released CF3 radical readily added to styrene to provide a benzylic radical, which was then trapped by a chiral Cu(II) cyanide species to deliver the desired alkylnitriles; (3) a low concentration of the CN anion was crucial to obtain high enantioselectivity.
239 citations
TL;DR: An artificial system that co-encapsulates multiple catalysts and substrates within the confined space defined by an M12L24 nanosphere that contains 24 endohedral guanidinium-binding sites is reported, demonstrated to strongly bind sulfonate-containing gold catalysts.
Abstract: Tuning reagent and catalyst concentrations is crucial in the development of efficient catalytic transformations. In enzyme-catalysed reactions the substrate is bound-often by multiple non-covalent interactions-in a well-defined pocket close to the active site of the enzyme; this pre-organization facilitates highly efficient transformations. Here we report an artificial system that co-encapsulates multiple catalysts and substrates within the confined space defined by an M12L24 nanosphere that contains 24 endohedral guanidinium-binding sites. Cooperative binding means that sulfonate guests are bound much more strongly than carboxylates. This difference has been used to fix gold-based catalysts firmly, with the remaining binding sites left to pre-organize substrates. This strategy was applied to a Au(I)-catalysed cyclization of acetylenic acid to enol lactone in which the pre-organization resulted in much higher reaction rates. We also found that the encapsulated sulfonate-containing Au(I) catalysts did not convert neutral (acid) substrates, and so could have potential in the development of substrate-selective catalysis and base-triggered on/off switching of catalysis.
217 citations
TL;DR: A two-step mechanism of Fenton oxidation and Fe(III) coagulation was proposed in sewage sludge conditioning, indicating that the coagulations by Fe(3+) species in Fenton reaction could play an important role, compared to traditional Fenton oxidisation effect on sludge Conditioning.
195 citations
TL;DR: Light is shed on the importance of Fe(III)/Fe(II) cycle for the design of high efficient Fenton system and provides an alternative pathway for the organic contaminants removal.
184 citations
TL;DR: In this article, a nucleophilic aniline tethered to an electrophilic carbonyl was designed as a bifunctional aminating reagent for both C(sp(2) )-H and C (sp(3) ) -H bonds under rhodium(III) catalysis.
Abstract: Previous direct C-H nitrogenation suffered from simple amidation/amination with limited atom-economy and is mostly limited to C(sp(2) )-H substrates. In this work, anthranil was designed as a novel bifunctional aminating reagent for both C(sp(2) )-H and C(sp(3) )-H bonds under rhodium(III) catalysis, thus affording a nucleophilic aniline tethered to an electrophilic carbonyl. A tridendate rhodium(III) complex has been isolated as the resting state of the catalyst, and DFT studies established the intermediacy of a nitrene species.
179 citations
TL;DR: The scaled-up experiments further indicated the practicality of this protocol and showed the pH value of the system plays a key role in achieving highly selective cleavage of the C-S bond instead of a S-S Bond in the transformation.
Abstract: A novel reagent, which introduces two sulfur atoms in one step, was designed and used for the construction of diverse disulfanes by copper-catalyzed oxidative cross-coupling under mild reaction conditions. By applying this stable and readily prepared reagent, late-stage modification of pharmaceuticals and natural products can be achieved straightforward. The scaled-up experiments further indicated the practicality of this protocol. The pH value of the system plays a key role in achieving highly selective cleavage of the C−S bond instead of a S−S bond in the transformation.
145 citations
TL;DR: The selective formation of partially protected nonsymmetric 2,2'-biphenols via electroorganic synthesis was accomplished with a high yield of isolated product and facilitates a large variety of new substrate combinations for oxidative cross-coupling reactions.
Abstract: The oxidative cross-coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2'-biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent-free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale-up and inherently safe. The implementation of O-silyl-protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2,2'-biphenols. The use of a bulky silyl group to block one hydroxyl moiety makes the final product less prone to oxidation. Furthermore, the partially silyl-protected 2,2'-biphenols are versatile building blocks that usually require tedious or low-yielding synthetic pathways. Additionally, this strategy facilitates a large variety of new substrate combinations for oxidative cross-coupling reactions.
144 citations
TL;DR: The super electrophilicity of a shelf-stable, easily prepared trifluoromethylthio-dibenzenesulfonimide 7 was demonstrated and exhibits reactivity remarkably higher than that of other known electrophilic trifLUorometHylthiolating reagents.
Abstract: The super electrophilicity of a shelf-stable, easily prepared trifluoromethylthiolating reagent N-trifluoromethylthio-dibenzenesulfonimide 7 was demonstrated. Consistent with the theoretical prediction, 7 exhibits reactivity remarkably higher than that of other known electrophilic trifluoromethylthiolating reagents. In the absence of any additive, 7 reacted with a wide range of electron-rich arenes and activated heteroarenes under mild conditions. Likewise, reactions of 7 with styrene derivatives can be fine-tuned by simply changing the reaction solvents to generate trifluoromethylthiolated styrenes or oxo-trifluoromethylthio or amino-trifluoromethylthio difunctionalized compounds in high yields.
TL;DR: This new zinc reagent is a free-flowing solid that can be used in combination with a nickel catalyst to difluoromethylate aryl iodides, bromides, and triflates at room temperature.
Abstract: A stable and isolable difluoromethyl zinc reagent has been prepared through the reaction of ICF2H with diethyl zinc and DMPU. This new zinc reagent is a free-flowing solid and can be used in combination with a nickel catalyst to difluoromethylate aryl iodides, bromides, and triflates at room temperature. Such mild conditions for the catalytic difluoromethylation of these substrates are unprecedented.
TL;DR: All-vacuum-deposited perovskite solar cells produced by controlling reagent partial pressure in high vacuum with newly developed multi-layer electron and hole transporting structures show outstanding power conversion efficiency and smooth, pinhole-free, micrometer-sized perovSkite crystal grains.
Abstract: All-vacuum-deposited perovskite solar cells produced by controlling reagent partial pressure in high vacuum with newly developed multi-layer electron and hole transporting structures show outstanding power conversion efficiency of 17.6% and smooth, pinhole-free, micrometer-sized perovskite crystal grains.
TL;DR: A highly tunable visible-light-promoted reaction system for the radical-mediated functionalization of tertiary aliphatic C–H bonds of complex substrates has been developed.
Abstract: A highly tunable radical-mediated reaction system for the functionalization of tertiary aliphatic C–H bonds was developed. Reactions of various substrates with the Zhdankin azidoiodane reagent 1, Ru(bpy)3Cl2, and visible light irradiation at room temperature gave C–H azidated or halogenated products in an easily controllable fashion. These reactions are efficient, selective, and compatible with complex substrates. They provide a potentially valuable tool for selectively labeling tertiary C–H bonds of organic and biomolecules with tags of varied chemical and biophysical properties for comparative functional studies.
TL;DR: In this paper, octyl hydroxamic acid (HXMA-8) was used as an associate collector with NaOl in scheelite flotation, and the flotation tests showed that a novel reagent scheme, i.e., a lower dosage of SS (300 mg/L) and mixed collectors of HXMA+NaOl (total concentration 4.5 ǫ −10 −4 Âmol/L, preferred mass ratio of 1:2).
TL;DR: A metal-free C–B bond forming reaction of aryl halides under batch and continuous-flow conditions is described.
Abstract: A rapid, chemoselective and metal-free C–B bond-forming reaction of aryl iodides and bromides in aqueous solution at low temperatures was discovered. This reaction is amenable to batch and continuous-flow conditions and shows exceptional functional group tolerance and broad substrate scope regarding both the aryl halide and the borylating reagent. Initial mechanistic experiments indicated a photolytically generated aryl radical as the key intermediate.
TL;DR: Experiments indicate that a blue LED (450-455 nm) is the most effective energy for the cleavage of the oxygen-iodine bond to initiate the reaction, which undergoes a cascade decarboxylative radical addition/cyclization process along with releasing CO2 and H2.
TL;DR: Comparing RLi reactivities in DESs with those observed in pure glycerol or THF suggests a kinetic anionic activation of the alkylating reagents occurs, favoring nucleophilic addition over competitive hydrolysis.
Abstract: Shattering the long-held dogma that organolithium chemistry needs to be performed under inert atmospheres in toxic organic solvents, chemoselective addition of organolithium reagents to non-activated imines and quinolines has been accomplished in green, biorenewable deep eutectic solvents (DESs) at room temperature and in the presence of air, establishing a novel and sustainable access to amines. Improving on existing methods, this approach proceeds in the absence of additives; occurs without competitive enolization, reduction or coupling processes; and reactions were completed in seconds. Comparing RLi reactivities in DESs with those observed in pure glycerol or THF suggests a kinetic anionic activation of the alkylating reagents occurs, favoring nucleophilic addition over competitive hydrolysis.
TL;DR: The fluorination and trifluoromethylation reactions probably proceed by a rhodium‐containing onium ylide type intermediate, which is trapped by either the F or CF3 electrophiles.
Abstract: A new reaction for the rhodium-catalyzed geminal-difunctionalization-based fluorination is presented. The substrates are aromatic and aliphatic diazocarbonyl compounds. As the fluorine source a stable and easily accessible benziodoxole reagent was used. A variety of alcohol, phenol, and carboxylic acid reagents were employed to introduce the second functionality. The reaction was extended to trifluoromethylation using a benziodoxolon reagent. The fluorination and trifluoromethylation reactions probably proceed by a rhodium-containing onium ylide type intermediate, which is trapped by either the F or CF3 electrophiles.
TL;DR: An azidation method for C-N bond formation at benzylic C-H positions is described using copper-catalyzed visible light photochemistry and the Zhdankin azidoiodinane reagent.
TL;DR: A new shelf-stable and easily scalable diffluoromethylthiolating reagent S-(difluorometHyl) benzenesulfonothioate (PhSO2 SCF2 H) was developed, which is a powerful reagent for radical diflu oromethylethiolation of aryl and alkyl boronic acids.
Abstract: A new shelf-stable and easily scalable difluoromethylthiolating reagent S-(difluoromethyl) benzenesulfonothioate (PhSO2SCF2H) was developed. PhSO2SCF2H is a powerful reagent for radical difluoromethylthiolation of aryl and alkyl boronic acids, decarboxylative difluoromethylthiolation of aliphatic acids, and a phenylsulfonyl-difluoromethylthio difunctionalization of alkenes under mild reaction conditions.
TL;DR: In this paper, an effective synthesis of surfactant-free multimetallic Pd nanosponges with tunable compositions using EDTA as the structure-directing reagent and NaBH4 as the reducing reagent was reported.
Abstract: We report an effective synthesis of surfactant-free multimetallic Pd nanosponges with tunable compositions using EDTA as the structure-directing reagent and NaBH4 as the reducing reagent. Among the mono-metallic Pd, binary PdNi and PdAu, ternary PdAuNi nanosponges and commercial Pt/C catalysts studied, Pd62Au21Ni17 nanosponges exhibit excellent activities and are the most efficient nanoparticle catalysts ever reported for both ethylene glycol and glycerol oxidation reactions.
TL;DR: In this paper, an efficient paired electrosynthesis involving C-H functionalization and subsequent C-S and C-N bond formation for the assembly of valuable 3-amino-2-thiocyanato-α,β-unsaturated carbonyl derivatives has been developed.
TL;DR: A single component Ir photoredox catalyst is reported which is capable of catalyzing the hydrotrifluoromethylation of terminal alkenes and Michael acceptors with sodium triflinate in methanol under irradiation at room temperature.
TL;DR: This protocol employs the readily prepared difluoromethyltriphenylphosphonium bromide as the diffluoromethylating reagent and alcohols/water as the nucleophiles, affording dif fluorometHyl(CF2H)-containing alcohols and ethers in moderate to excellent yields.
Abstract: A convenient, visible light induced oxidifluoromethylation of styrenes was developed. This protocol employs the readily prepared difluoromethyltriphenylphosphonium bromide as the difluoromethylating reagent and alcohols/water as the nucleophiles, affording difluoromethyl(CF2H)-containing alcohols and ethers in moderate to excellent yields.
TL;DR: In this article, a water-mediated tandem metal-coordination CO2/epoxide copolymerization and organobase catalyzed ring-opening polymerization (ROP) approach was reported for the one-pot synthesis of an ABA CO2-based triblock copolymers.
Abstract: The addition of water as a chain transfer reagent during the copolymerization reaction of epoxides and carbon dioxide has been shown as a promising method for producing CO2-based polycarbonate polyols. These polyols can serve as drop-in replacements for petroleum derived polyols for polyurethane production or designer block copolymers. Ironically, during the history of CO2/epoxide coupling development, water was generally considered primarily as an aversion reagent. That is, in its presence, low catalytic activity and high polydispersity was normally observed. Recently, we reported a water-mediated tandem metal-coordination CO2/epoxide copolymerization and organobase catalyzed ring-opening polymerization (ROP) approach for the one-pot synthesis of an ABA CO2-based triblock copolymers. As in previous studies, water was deemed as the chain transfer reagent in this tandem strategy for producing CO2-based polyols. Herein is presented a mechanistic study aimed at determining the intimate role water plays durin...
TL;DR: In this article, a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) was used to simultaneously detect atmospheric gaseous amines and amides.
Abstract: . Amines and amides are important atmospheric organic-nitrogen compounds but high time resolution, highly sensitive, and simultaneous ambient measurements of these species are rather sparse. Here, we present the development of a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) method, utilizing protonated ethanol as reagent ions to simultaneously detect atmospheric gaseous amines (C1 to C6) and amides (C1 to C6). This method possesses sensitivities of 5.6–19.4 Hz pptv−1 for amines and 3.8–38.0 Hz pptv−1 for amides under total reagent ion signals of ∼ 0.32 MHz. Meanwhile, the detection limits were 0.10–0.50 pptv for amines and 0.29–1.95 pptv for amides at 3σ of the background signal for a 1 min integration time. Controlled characterization in the laboratory indicates that relative humidity has significant influences on the detection of amines and amides, whereas the presence of organics has no obvious effects. Ambient measurements of amines and amides utilizing this method were conducted from 25 July to 25 August 2015 in urban Shanghai, China. While the concentrations of amines ranged from a few parts per trillion by volume to hundreds of parts per trillion by volume, concentrations of amides varied from tens of parts per trillion by volume to a few parts per billion by volume. Among the C1- to C6-amines, the C2-amines were the dominant species with concentrations up to 130 pptv. For amides, the C3-amides (up to 8.7 ppb) were the most abundant species. The diurnal and backward trajectory analysis profiles of amides suggest that in addition to the secondary formation of amides in the atmosphere, industrial emissions could be important sources of amides in urban Shanghai. During the campaign, photo-oxidation of amines and amides might be a main loss pathway for them in daytime, and wet deposition was also an important sink.
TL;DR: The direct methylation of ortho C-H bonds in aromatic amides with dicumyl peroxide (DCP) using a nickel complex as the catalyst is reported, showing a high functional group tolerance and is inhibited by radical scavengers.
TL;DR: A novel Rh(III)-catalyzed C-H bond amination with the simultaneous release of a formyl group at distal positions is realized employing anthranil as a new type of C- H amination reagent that possesses the advantages of high atom economy, avoids the use of external oxidants, and enables further transformation of the amination products.
TL;DR: A gold-catalyzed regioselective [3+2] cycloaddition of ynamides with 1,4,2-dioxazoles was developed and offers a novel approach to obtain highly functionalized oxazoles under mild reaction conditions.