Synthesis of methylthiosubstituted heterocycles using the complex of trifluoromethanesulfonic anhydride with dimethyl sulfide

A new method was developed for the electrophilic introduction of methylthio group into a series of aromatic heterocyclic compounds through the hetaryl(dimethyl)sulfonium salts formed in the course of the reaction of the respective heterocycles with the complex of dimethyl sulfide and trifluoromethanesulfonic anhydride. By demethylation with triethylamine it was possible to obtain the methylthio-substituted heterocycles.M. V. Lomonosov Moscow State University. Moscow; e-mail: nen@acylium.chem.msu.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 171–177, February, 2000.     

Multiarm Star-Shaped Polydimethylsiloxanes with a Dendritic Branching Center

New multiarm stars have been synthesized based on polylithium derivatives of high-generation carbosilane dendrimers. In the synthesis of multiarm stars based on the eighth-generation dendrimer, steric hindrances were observed even during the synthesis of a polylithium initiator. Subsequently, this led to chain transfer reactions between growing arms, as well as other side effects. As a result, dense nanogel formations with a higher tendency of ordering than in classical objects of this type were isolated from the reaction mixture. The study of the rheology of multiarm stars based on sixth-generation dendrimers made it possible to determine the activation energies of viscous flow in these objects, which makes it possible to consider them as objects with a macromolecular nature and a reptation flow mechanism.     

Porphyrin-functionalized dendrimers: synthesis and application as recyclable photocatalysts in a nanofiltration membrane reactor

The convergent synthesis of a series of porphyrin-functionalized pyrimidine dendrimers has been accomplished by a procedure involving the nucleophilic aromatic substitution (NAS) as a key reaction step. The resulting dendritic porphyrin catalysts show high activity in the light-induced generation of singlet oxygen ((1)O2) from ground-state oxygen. These materials are synthetically useful photosensitizers for the oxidation of various olefinic compounds to the corresponding allylic hydroperoxides. Catalytic activities and regio- and stereoselectivities of the dendritic photosensitizers are comparable to those observed for mononuclear porphyrin catalysts. Recycling of the dendrimer-enlarged homogeneous photocatalysts was possible by solvent-resistant nanofiltration (SRNF) by using an oxidatively stable membrane consisting of a polysiloxane polymer and ultrastable Y zeolite as inorganic filler. Moreover, this membrane technology provides a safe way to isolate the hydroperoxide products under very mild conditions. The membrane showed high retention for the macromolecular catalysts, even in chlorinated solvents, but some oxidative degradation of the porphyrin units of the dendrimer was observed over multiple catalytic runs.     

Water Oxidation Catalysis Beginning with CuCo2S4: Investigation of the True Electrochemically Driven Catalyst

The exploitation of efficient and stable water oxidation catalysts is a pressing challenge to solve the energy crisis. Herein, flower‐like CuCo₂S₄ microspheres were successfully synthesized and used as an effective water oxidation catalyst. CuCo₂S₄/NF (NF=nickel foam) affords electrocatalytic water oxidation activity, with a current density of 20 mA cm^?2 at a low overpotential of 260 mV. The overpotential value is lower than that of benchmark RuO₂/NF (overpotential of 340 mV at a current density of 20 mA cm^?2). The water oxidation activity increases linearly before nonlinearly improving with increasing pH; this indicates that the substrate changes from water to hydroxyl. The CuCo₂S₄/NF catalyst is demonstrated to be a real water oxidation catalyst based on diverse experiments.     

Encapsulating Sulfur into Hierarchically Ordered Porous Carbon as a High‐Performance Cathode for Lithium–Sulfur Batteries

A three‐dimensional (3D) hierarchical carbon–sulfur nanocomposite that is useful as a high‐performance cathode for rechargeable lithium–sulfur batteries is reported. The 3D hierarchically ordered porous carbon (HOPC) with mesoporous walls and interconnected macropores was prepared by in situ self‐assembly of colloidal polymer and silica spheres with sucrose as the carbon source. The obtained porous carbon possesses a large specific surface area and pore volume with narrow mesopore size distribution, and acts as a host and conducting framework to contain highly dispersed elemental sulfur. Electrochemical tests reveal that the HOPC/S nanocomposite with well‐defined nanostructure delivers a high initial specific capacity up to 1193 mAh g^?1 and a stable capacity of 884 mAh g^?1 after 50 cycles at 0.1 C. In addition, the HOPC/S nanocomposite exhibits high reversible capacity at high rates. The excellent electrochemical performance is attributed exclusively to the beneficial integration of the mesopores for the electrochemical reaction and macropores for ion transport. The mesoporous walls of the HOPC act as solvent‐restricted reactors for the redox reaction of sulfur and aid in suppressing the diffusion of polysulfide species into the electrolyte. The “open” ordered interconnected macropores and windows facilitate transportation of electrolyte and solvated lithium ions during the charge/discharge process. These results show that nanostructured carbon with hierarchical pore distribution could be a promising scaffold for encapsulating sulfur to approach high specific capacity and energy density with long cycling performance.     

Optically active dendrimers based on the planar chiral ferrocene core

The new planar chiral racemic and enantiomerically enriched Frechet-type dendrimers of the first and second generations bearing one and two branches and 1,2-disubstituted ferrocene as the core moiety were synthesized. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1220–1222, June, 2008.     

Synthesis of a β-strand mimetic based on a pyridine scaffold

A synthetic route to a 2,4-disubstituted pyridine as a potential β-strand mimetic has been developed and applied in the synthesis of a tripeptidomimetic of Leu-Gly-Gly. The pyridine scaffold replaces the central glycine, and is substituted with analogues of leucine and glycine in positions 4 and 2, respectively. 2-Fluoro-4-iodopyridine was chosen as the functionalized scaffold and was substituted with protected leucinal in position 4 via a Grignard exchange reaction using iso-propyl magnesium chloride. The glycine moiety was introduced in position 2 via a nucleophilic aromatic substitution reaction (S_NAr) facilitated by microwave irradiation. The synthetic sequence involved 12 steps with an overall yield of 7%.     

Sulfur-containing polymers by the reaction of diphenyl sulfide with sulfur chlorides

The electrophilic reaction of sulfur dichloride with diphenyl sulfide proceeds efficiently at room temperature to yield oligo(phenylene sulfide) in the presence of a catalytic amount of Fe powder. Sulfur dichloride shows higher reactivity than sulfur monochloride. The reaction is promoted through the activation of sulfur dichloride by Fe powder. The polymeric product contains a linear structure linked by disulfide and sulfide bonds.     

Routes to metallodendrimers: synthesis of isomeric neutral metallomacromolecules based on bis(2,2':6',2"-terpyridine)ruthenium(II) connectivity

Routes for the syntheses of isomeric, zwitterionic, bisterpyridine-Ru(II)-based macromolecules are described. Access to these novel architectures is facilitated by the construction of terpyridine-modified, 1-->3 C-branched, ester-terminated building blocks. Constitutional isomers result from the interchangable placement of methyl and tert-butyl ester groups on both the branched framework near the Ru(II) centers and the termini of the branched construct. Water solubility is imparted to each isomer through selective transformation of the tert-butyl esters to their corresponding carboxylates. Along with the standard characterization techniques, electrochemical and spectroscopic data also support the structural formation.     

Conjugated dendrimers with triazine peripheries and a distyrylanthracene core

We describe the synthesis and luminescence characterization of conjugated dendrimers with triazine peripheries and a distyrylanthracene core that are suitable for electroluminescence applications. The dendrimers consist of dendritic triazine wedges with high electron affinity, stilbene branches, and a distyrylanthracene core as an emitting moiety. The dendrimers have lowest unoccupied molecular orbital values of about ?2.7 eV. Photoluminescence studies have indicated that a cascade energy transfer occurs from the triazine wedges to the stilbene bridges and finally to the distyrylanthracene core. Thus, the emission wavelength is determined by the distyrylanthracene core unit. The energy‐transfer efficiency of the distyrylanthracene‐cored dendrimers is about 47 and 20% for the first and second generations, respectively. A preliminary electroluminescence property investigation has also been conducted. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5855–5862, 2006     

Reinvestigation of the noncatalyzed coupling of aryllithium with haloarene: a novel aromatic nucleophilic substitution pathway

Noncatalyzed coupling reactions of aryllithiums and haloarenes proceed not only through the well-known aryne route but also, in some cases, through a novel addition-elimination pathway. Indeed, ortho-chloro- and ortho-bromomethoxyarenes lead selectively to the corresponding ortho-biaryls through a chelation-driven aromatic nucleophilic substitution pathway. Contrary to common belief, such noncatalyzed coupling reactions often proceed with high regioselectivity and high yield. These results underline the potency of such simple reactions and open up a straightforward access to a wide range of biaryl structures; this also appears particularly useful for large-scale and biaryl building-block syntheses, as only cheap and readily available substrates are involved.     

Dendrimers with a cyclam core. Absorption spectra, multiple luminescence, and effect of protonation

We have synthesized two dendrimers (4 and 5) consisting of a 1,4,8,11-tetraazacyclotetradecane (cyclam) core appended with four dimethoxybenzene and eight naphthyl units (4) and 12 dimethoxybenzene and 16 naphthyl units (5). The absorption and luminescence spectra of these compounds and the changes taking place upon protonation of their cyclam core have been investigated. In acetonitrile-dichloromethane 1:1 v/v solution they exhibit three types of emission bands, assigned to naphthyl localized excited states (λ_max=337 nm), naphthyl excimers (λ_max ca 390 nm), and naphthyl-amine exciplexes (λ_max=480 nm). The tetraamine cyclam core undergoes only two protonation reactions, whose constants have been obtained by fitting the spectral changes. Protonation not only prevents exciplex formation for electronic reasons, but also causes strong nuclear rearrangements in the cyclam structure which affect excimer formation between the peripheral naphthyl units of the dendrimers.     

Solution‐Liquid‐Solid Synthesis of Hexagonal Nickel Selenide Nanowire Arrays with a Nonmetal Catalyst

Inorganic nanowire arrays hold great promise for next‐generation energy storage and conversion devices. Understanding the growth mechanism of nanowire arrays is of considerable interest for expanding the range of applications. Herein, we report the solution‐liquid‐solid (SLS) synthesis of hexagonal nickel selenide nanowires by using a nonmetal molecular crystal (selenium) as catalyst, which successfully brings SLS into the realm of conventional low‐temperature solution synthesis. As a proof‐of‐concept application, the NiSe nanowire array was used as a catalyst for electrochemical water oxidation. This approach offers a new possibility to design arrays of inorganic nanowires.     

Supermolecular liquid crystals with a six-armed cyclotriphosphazene core: from columnar to cubic phases

New liquid crystals having a non‐conventional structure have been synthesised from a six‐armed cyclotriphosphazene core, [N₃P₃(OC₆H₄OH‐4)₆], which was condensed with polycatenar acids. Reactions were monitored by ³¹P{¹H} and ¹H NMR spectroscopy and the chemical structure of the resulting materials was confirmed by different spectroscopic techniques and mass spectrometry (MALDI‐TOF). Results were in accordance with monodisperse, fully functionalised cyclotriphosphazenes. Thermal and mesomorphic properties were studied by optical microscopy, differential scanning calorimetry and X‐ray diffraction. All of the synthesised phosphazenes, substituted with benzyl ether chains, show a high thermal stability and exhibit mesomorphic properties, which depend on the number and type of alkyl terminal chains located at the periphery of the mesogens. Mesomorphic properties range from Col_h for cph‐A1 and cph‐A2 to a cubic phase detected for cph‐A3 , which has the larger number of alkyl chains. Furthermore, helical order was detected on X‐ray data of cph‐A2 , which has chiral branched chains. Circular dichroism spectra of annealed films at mesophase temperature show a signal attributed to the chiral helical arrangement of the mesogenic chromophores.     

Programmable Engineering of a Biosensing Interface with Tetrahedral DNA Nanostructures for Ultrasensitive DNA Detection

Self‐assembled DNA nanostructures with precise sizes allow a programmable “soft lithography” approach to engineer the interface of electrochemical DNA sensors. By using millimeter‐sized gold electrodes modified with several types of tetrahedral DNA nanostructures (TDNs) of different sizes, both the kinetics and thermodynamics of DNA hybridization were profoundly affected. Because each DNA probe is anchored on an individual TDN, its lateral spacing and interactions are finely tuned by the TDN size. By simply varying the size of the TDNs, the hybridization time was decreased and the hybridization efficiency was increased. More significantly, the detection limit for DNA detection was tuned over four orders of magnitude with differentially nanostructured electrodes, and achieved attomolar sensitivity with polymeric enzyme amplification.     

Fabrication of a Hierarchical Ni(OH)2@Ni3S2/Ni Foam Electrode from a Prussian Blue Analogue-Based Composite with Enhanced Electrochemical Capacitive and Electrocatalytic Properties

Developing high-efficiency, cost-effective, and durable electrodes is significant for electrochemical capacitors and electrocatalysis. Herein, a 3D bifunctional electrode consisting of nickel hydroxide nanosheets@nickel sulfide nanocubes arrays on Ni foam (Ni(OH)₂@Ni₃S₂/NF) obtained from a Prussian blue analogue-based precursor is reported. The 3D higher-order porous structure and synergistic effect of different compositions endow the electrode with large specific surface area, facile ion/electron transport path, and improved conductivity. As a result, the Ni(OH)₂@Ni₃S₂/NF electrode exhibits a high specific capacity of 211 mA h g⁻¹ at a current density of 1 A g⁻¹ and 73 % capacity retention after 5000 cycles at 5 A g⁻¹. Moreover, the Ni(OH)₂@Ni₃S₂/NF electrode has superior electrocatalytic activity for the hydrogen evolution reaction with low overpotentials of 140 and 210 mV at current densities of 10 and 100 mA cm⁻², respectively. The synthetic strategy for the unique higher-order porous structure can be extended to fabricate other composite materials for energy storage and conversion.