Facile Functionalization of Multilayer Fullerenes (Carbon Nano‐Onions) by Nitrene Chemistry and “Grafting from” Strategy

Facile functionalization of multilayer fullerenes (carbon nano‐onions, CNOs) was carried out by [2+1] cycloaddition of nitrenes. The products were further derivatized by using the “grafting from” strategy of in situ ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Using one‐step nitrene chemistry with high‐energy reagents, such as azidoethanol and azidoethyl 2‐bromo‐2‐methyl propanoate, in N‐methyl‐2‐pyrrolidone at 160°C for 16 h, hydroxyl and bromide functionalities were introduced onto the surfaces of CNOs. These hydroxyl CNOs (CNO‐OH) and bromic CNOs (CNO‐Br) were extensively characterized by various techniques such as thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), Raman spectroscopy and X‐ray photo electron spectroscopy (XPS). TGA measurements indicated that the surface hydroxyl and bromide group density reached 1.49 and 0.49 mmol g^?1, respectively. The as‐functionalized CNOs showed much better solubility in solvents than pristine CNOs. The CNO‐OH were also observed to fluoresce at λ=453 nm in water. The CNO‐OH and CNO‐Br can be conveniently utilized as macroinitiators to conduct surface‐initiated in‐situ polymerizations. Poly(ε‐caprolactone) (PCL, 45wt %) and polystyrene (PS, 60 wt%) were then grafted from surfaces of CNOs through the ROP of ε‐caprolactone with the macroinitiator CNO‐OH and the ATRP of styrene with the macroinitiator CNO‐Br, respectively. The structures and morphology of the resulting products were characterized by ¹H NMR, scanning electron microscopy (SEM), TEM, and atomic force microscopy (AFM). The polymer functionalized CNOs have good solubility/dispersibility in common organic solvents. The facile and scalable functionalization approaches can pave the way for the comprehensive investigation of chemistry of CNOs and fabrication of novel CNO‐based nanomaterials and nanodevices.     

Lewis Acid or Brønsted Acid Catalyzed Reactions of Vinylidene Cyclopropanes with Activated Carbon–Nitrogen,Nitrogen–Nitrogen,and Iodine–Nitrogen Double‐Bond‐Containing Compounds

Lewis acid or Brønsted acid catalyzed reactions of vinylidene cyclopropanes (VDCPs), 1 , with activated carbon–nitrogen, nitrogen–nitrogen, and iodine–nitrogen double‐bond‐containing compounds have been thoroughly investigated. We found that pyrrolidine and 1,2,3,4‐tetrahydroquinoline derivatives can be formed in good yields in the reactions of VDCPs 1 with ethyl (arylimino)acetates 2 by a [3+2] cycloaddition or intramolecular Friedel–Crafts reaction pathway. Based on these results, we found that activated carbon–nitrogen and nitrogen–nitrogen double‐bond‐containing compounds, such as N‐toluene‐4‐sulfonyl (N‐Ts) imines 5 and diisopropylazodicarboxylate ( 7 ), can also react with VDCPs 1 to give [3+2] cycloaddition products in moderate to good yields in the presence of a Lewis acid. When N‐tert‐butoxycarbonyl aldimine 9 was used as the substrate, six‐membered cycloaddition products 10 and 11 were formed in moderate yields in the presence of a Brønsted acid, trifluoromethanesulfonic acid (TfOH). The reactions of VDCPs 1 with N‐Ts‐iminophenyliodinane ( 12 ) were also carried out in the presence of (CuOTf)₂ ? C₆H₆ and it was found that nitrogen‐containing indene derivatives 13 were obtained, rather than the aziridination products. Plausible mechanisms for all of these transformations are discussed, based on the obtained results.     

Influence of the Synthetic Conditions on the Structural and Electrochemical Properties of Carbon Nano‐Onions

Thermal annealing of nanodiamonds with diameters of a few nanometers (in an inert atmosphere and at temperatures in the range: 1500–1800 °C) leads to the formation of carbon nano‐onions (CNOs) with diameters between 5 and 6 nm, which correspond to nanostructures with six to eight graphitic layers. The resulting spherical CNO structures were thermally modified under different atmospheres and characterized by SEM, TEM, thermogravimetric analysis and spectroscopic (Raman and diffuse reflectance infrared Fourier transform/FTIR) spectroscopy. The electrochemical properties of the CNOs prepared under different conditions were determined and compared. The results reveal that the CNOs show different structures with predominant spherical “small” carbon nano‐onions. The aim of this article is to investigate the impact of the CNO′s synthesis conditions on the resulting structures and study the effect of further thermal modifications on the sizes, shapes and homogeneity of these carbon nanostructures.     

Enantioselective Reactions of N‐Acyliminium Ions Using Chiral Organocatalysts

N‐acyliminium ions are reactive intermediates that can act as electron‐deficient electrophiles toward weak or soft nucleophiles, thereby providing useful methods for both intermolecular‐ and intramolecular carbon–carbon and carbon–heteroatom bond formation. Nucleophilic additions to N‐acyliminium ions constitute an important method for providing α‐functionalized amino compounds and many other biologically active nitrogen‐containing heterocycles. The development of efficient catalytic asymmetric reactions is a key objective in modern organic chemistry and is very important for the synthesis of natural products, pharmaceuticals, and agrochemicals. Various methods are available for this purpose and mostly rely on the use of chiral catalysts for enantioselective synthesis. This review deals with one aspect of such catalysis, which has emerged only in the past few years, and its applications in enantioselective reactions of N‐acyliminium ions to provide various nitrogen‐containing heterocycles.     

Electrochemical Properties of Oxidized Carbon Nano‐Onions: DRIFTS‐FTIR and Raman Spectroscopic Analyses

The electrochemical reactions of carboxylic and lactone groups on carbon nano‐onions (CNOs) in aqueous solutions result in non‐Kolbe products: alcohols, ketones, ethers and epoxides. The anodic/cathodic conversion of ox‐CNOs was assessed by Boehm titrations and by Raman and DRIFTS‐FTIR (diffuse reflectance infrared Fourier transform spectroscopy). The electrochemical properties of oxidized carbon nano‐onions were investigated by cyclic voltammetry in aqueous solutions. The ox‐CNOs are electrochemically active as a result of the reduction of the oxygen‐containing groups.     

Chemical versus Electrochemical Synthesis of Carbon Nano‐onion/Polypyrrole Composites for Supercapacitor Electrodes

The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g^?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g^?1 for the CNOs/Ppy bilayer (electrochemical deposition).     

Small Noncytotoxic Carbon Nano‐Onions: First Covalent Functionalization with Biomolecules

Small carbon nano‐onions (CNOs, 6–8 shells) were prepared in high yield and functionalized with carboxylic groups by chemical oxidation. After functionalization these nanostructures were soluble in aqueous solutions. 3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2 tetrazolium (MTS) tests showed excellent cytocompatibility of all CNOs analyzed at 30 and 300 μg mL^?1, so these carbon nanostructures can be safely used for biological applications. The first covalent functionalization of oxidized CNOs (ox‐CNOs) with biomolecules, by using biotin–avidin interactions is reported here. Multilayers were prepared on a gold surface by layer‐by‐layer assembly and the process was monitored by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM). Covalent binding of molecules to the short amine‐terminated organosulfur monolayers was assessed by Fourier transform infrared spectroscopy using total attenuated reflactance mode (FT‐IR/HATR).     

Electron ionization and electrospray ionization mass spectrometric study of a series of isomeric N‐chloro(or bromo)benzyl‐substituted (E)‐2′(3′‐ or 4′)‐hydroxy‐4‐stilbazole halides

The electron ionization (EI) mass spectra and electrospray ionization (ESI) mass spectra of a series of isomeric N‐chlorobenzyl‐ and N‐bromobenzyl‐substituted (E)‐2′(3′ or 4′)‐hydroxy‐4‐stilbazole chlorides and bromides (1–12) were recorded. The fragmentation pathways of all of the compounds and the characteristic fragment ions formed by EI‐MS were studied by means of B/E and B²/E constant linked‐scanning techniques. The formation of ions originating from preionization reactions, characteristic of quaternary halides under EI‐MS conditions, such as the elimination of chloro‐ or bromobenzyl halides, dehydrohalogenation or substitution reactions, is explained. As soft ionization methods cause no such degradation reactions, the ESI‐MS spectra of the studied compounds were also obtained for comparison. We thus demonstrated the applicability of EI‐MS even in cases when preionization takes place, as long as such secondary processes are properly accounted for. Copyright © 2010 John Wiley & Sons, Ltd.     

Functionalization of Reduced Graphite Oxide Sheets with a Zwitterionic Surfactant

Films of a few layers in thickness of reduced graphite oxide (RGO) sheets functionalized by the zwitterionic surfactant N‐dodecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate (DDPS) are obtained by using the Langmuir–Blodgett method. The quality of the RGO sheets is checked by analyzing the degrees of reduction and defect repair by means of X‐ray photoelectron spectroscopy, atomic force microscopy (AFM), field‐emission scanning electron microscopy (SEM), micro‐Raman spectroscopy, and electrical conductivity measurements. A modified Hummers method is used to obtain highly oxidized graphite oxide (GO) together with a centrifugation‐based method to improve the quality of GO. The GO samples are reduced by hydrazine or vitamin C. Functionalization of RGO with the zwitterionic surfactant improves the degrees of reduction and defect repair of the two reducing agents and significantly increases the electrical conductivity of paperlike films compared with those prepared from unfunctionalized RGO.     

Synthesis and some aspects of the formation mechanism of carbon structures under hydrothermal conditions

The formation of carbon structures upon the reactions of organic compounds with strong mineral acids under hydrothermal conditions was studied. The reactions were found to give amorphous carbon, microcrystalline graphite, nanodiamonds, diamond-like carbon, diamonds, C₆₀ and C₇₀ fullerenes, and carbolite. Hydrocarbons of various compositions including aromatics and naphthenes were detected among the reaction products. A possible mechanism of the formation of carbon structures with sp ² bond hybridization under hydrothermal conditions was proposed.     

New Electroactive Hybridization Indicators 2‐Phthalimido‐N‐Substitutedphenylethanesulfonamide Derivatives for Biosensor Applications: Ring Substituent Effect on Interaction between Compound and DNA

In this work, an electrochemical DNA‐based sensor was developed for the detection of the interaction between the anticonvulsant compounds 2‐phthalimido‐N‐substituted phenylethanesulfonamides (PMPES‐derivatives) and 24‐mer short DNA sequences by using differential pulse voltammetry (DPV) based on both compound and guanine oxidation signals at the renewable carbon graphite electrode (CGE) surface. The influence of compounds on DNA showed differences depending on the nature and position of the substituent on the N‐phenyl ring. Compounds bearing 3‐methoxy, 4‐chloro and 2,6‐dimethyl substituents bind to single stranded probe DNA more strongly than the other derivatives of PMPES. Thus, these compounds were evaluated for use as an electrochemical hybridization label (indicator).     

Microwave‐assisted synthesis of optically active poly(amide imide)s derived from diacid chloride containing epiclon and L‐leucine with aromatic diamines

Epiclon [3a,4,5,7a‐tetrahydro‐7‐methyl‐5‐(tetrahydro‐2,5‐dioxo‐3‐furanyl)‐1,3‐isobenzofurandione or 5‐(2,5‐dioxotetrahydrofurfuryl)‐3‐methyl‐3‐cyclohexyl‐1,2‐dicarboxylic acid anhydride] was reacted with L ‐leucine in acetic acid, and the resulting imide acid ( 3 ) was obtained in a high yield. The diacid chloride ( 4 ) was obtained from its diacid derivative 3 by a reaction with oxalyl chloride in dry carbon tetrachloride. The polycondensation reaction of 4 with several aromatic diamines, such as 4,4′‐sulfonyldianiline, 4,4′‐diaminodiphenylmethane, 4,4′‐diaminodiphenylether, p‐phenylenediamine, m‐phenylenediamine, 2,4‐diaminotoluene, and 1,5‐diaminonaphthalene, was developed with a domestic microwave oven in the presence of a small amount of a polar organic medium such as N‐methylpyrrolidone. The polymerization reactions were also performed with two other methods: low‐temperature solution polycondensation in the presence of trimethylsilyl chloride and reflux conditions. A series of optically active poly(amide imide)s with moderate yields and inherent viscosities of 0.12–0.19 dL/g were obtained. All of these polymers were fully characterized by IR, elemental analysis, and specific rotation techniques. Some structural characterizations and physical properties of these optically active poly(amide imide)s are reported. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1077–1090, 2003     

Preparation and Characterization of Carbon Nano‐Onion/PEDOT:PSS Composites

Composites of unmodified or oxidized carbon nano‐onions (CNOs/ox‐CNOs) with poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are prepared with different compositions. By varying the ratio of PEDOT:PSS relative to CNOs, CNO/PEDOT:PSS composites with various PEDOT:PSS loadings are obtained and the corresponding film properties are studied as a function of the polymer. X‐ray photoelectron spectroscopy characterization is performed for pristine and ox‐CNO samples. The composites are characterized by scanning and transmission electron microscopy and differential scanning calorimetry studies. The electrochemical properties of the nanocomposites are determined and compared. Doping the composites with carbon nanostructures significantly increases their mechanical and electrochemical stabilities. A comparison of the results shows that CNOs dispersed in the polymer matrices increase the capacitance of the CNO/PEDOT:PSS and ox‐CNO/PEDOT:PSS composites.     

Direct sp3 C?H Amination of Nitrogen‐Containing Benzoheterocycles Mediated by Visible‐Light‐Photoredox Catalysts

Visible‐light‐mediated direct sp³ C? H amination of benzocyclic amines via α‐aminoalkyl radicals by using photoredox catalysts is described here. The obtained N,N‐acetals were also successfully applied for carbon–carbon bond forming reactions with carbon nucleophiles. The procedure is suitable for a late‐stage modification of C? H bonds to C? C bonds.     

Diastereo‐ and Regioselective Addition of Thioamide Dianions to Imines and Aziridines: Synthesis of N‐Thioacyl‐1,2‐diamines and N‐Thioacyl‐1,3‐diamines

Addition reactions of thioamide dianions that were derived from N‐arylmethyl thioamides to imines and aziridines were carried out. The reactions of imines gave the addition products of N‐thioacyl‐1,2‐diamines in a highly diastereoselective manner in good‐to‐excellent yields. The diastereomeric purity of these N‐thioacyl‐1,2‐diamines could be enriched by simple recrystallization. The reduction of N‐thioacyl‐1,2‐diamines with LiAlH₄ gave their corresponding 1,2‐diamines in moderate‐to‐good yields with retention of their stereochemistry. The oxidative‐desulfurization/cyclization of an N‐thioacyl‐1,2‐diamine in CuCl₂/O₂ and I₂/pyridine systems gave the cyclized product in moderate yield and the trans isomer was obtained as the sole product. On the other hand, a similar cyclization reaction with antiformin (aq. NaClO) as an oxidant gave the cis isomer as the major product. The reactions of N‐tosylaziridines gave the addition products of N‐thioacyl‐1,3‐diamines with low diastereoselectivity but high regioselectivity and in good‐to‐excellent yields. The use of AlMe₃ as an additive improved the efficiency and regioselectivity of the reaction. The stereochemistry of the obtained products was determined by X‐ray diffraction.     

Advancements in the Synthesis and Applications of Cationic N‐Heterocycles through Transition Metal‐Catalyzed C−H Activation

Cationic N‐heterocycles are an important class of organic compounds largely present in natural and bioactive molecules. They are widely used as fluorescent dyes for biological studies, as well as in spectroscopic and microscopic methods. These compounds are key intermediates in many natural and pharmaceutical syntheses. They are also a potential candidate for organic light‐emitting diodes (OLEDs). Because of these useful applications, the development of new methods for the synthesis of cationic N‐heterocycles has received a lot of attention. In particular, many C?H activation methodologies that realize high step‐ and atom‐economies toward these compounds have been developed. In this review, recent advancements in the synthesis and applications of cationic N‐heterocycles through C?H activation reactions are summarized. The new C?H activation reactions described in this review are preferred over their classical analogs.     

Nucleophilicities and carbon basicities of pyridines

Rate and equilibrium constants for the reactions of pyridines with donor‐substituted benzhydrylium ions have been determined spectrophotometrically. The correlation equation log k(20 °C)=s(N+E), in which s and N are nucleophile‐specific parameters and E is an electrophile‐specific parameter, has been used to determine the nucleophilicity parameters of various pyridines in CH₂Cl₂ and aqueous solution and to compare them with N of other nucleophiles. It is found that the nucleophilic organocatalyst 4‐(dimethylamino)pyridine (DMAP) and tertiary phosphanes have comparable nucleophilicities and carbon basicities despite widely differing Brønsted basicities. For that reason, these reactivity parameters are suggested as guidelines for the development of novel organocatalysts. The Marcus equation is employed for the determination of the intrinsic barriers of these reactions.     

Synthesis and X‐ray Crystal Structures of Zinc Complexes Supported by Chelating Ligands: Various Reactions of α‐Iminopyridines with ZnEt2

α‐Iminopyridine (α‐IP) is an important redox‐noninnocent ligand. The substituents on the imino function of α‐IPs have important impact on the reaction selectivity with diethylzinc. For the α‐IPs with a hydrogen substituent on the imino carbon, reduction occurred for the non‐bulky N‐substituents phenyl and 2‐methylphenyl groups, whereas alkyl addition and coupling reactions can be selectively achieved for the sterically bulky N‐substituents 2,6‐dimethylphenyl or 2,4,6‐trimethylphenyl group. However, for the α‐IPs with a CH₃ substituent on the imino carbon, the deprotonation reaction happened regardless of the N‐substituents of 2‐methylphenyl or 2,6‐dimethylphenyl group. All the products were isolated and characterized by single‐crystal X‐ray diffraction. The possible mechanisms of these reactions were also discussed.     

Synthesis of the Naphthalenone,Dihydroquinoline, and Dihydrofuran Derivatives

The reactions of enaminones with dimethyl diazomalonate were investigated in the presence of copper(II) acetylacetonate. From the reaction of (E)‐3‐[methyl(phenyl)amino]‐1‐phenylprop‐2‐en‐1‐one ( 6c ), dimethyl 2‐[methyl(phenyl)amino]‐4‐oxonaphthalene‐1,1‐(4H)‐dicarboxylate, was unexpectedly obtained as the major product. Quinoline derivatives were formed as the major products in the case of N‐methyl‐p‐anisidino and N‐methyl‐p‐toluidino enaminones. The reactions of acetyl enaminones were also realized, and quinoline derivatives were isolated as the major products. 3H‐ and 5H‐dihydrofurans were also formed as side products in these reactions. These results differ from those reported earlier on the reactions of tertiary enaminones with carbenes/metal carbenes.     

Practical Aerobic Oxidations of Alcohols and Amines with Homogeneous Copper/TEMPO and Related Catalyst Systems

Oxidations of alcohols and amines are common reactions in the synthesis of organic molecules in the laboratory and industry. Aerobic oxidation methods have long been sought for these transformations, but few practical methods exist that offer advantages over traditional oxidation methods. Recently developed homogeneous Cu/TEMPO (TEMPO=2,2,6,6‐tetramethylpiperidinyl‐N‐oxyl) and related catalyst systems appear to fill this void. The reactions exhibit high levels of chemoselectivity and broad functional‐group tolerance, and they often operate efficiently at room temperature with ambient air as the oxidant. These advances, together with their historical context and recent applications, are highlighted in this Minireview.