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We have designed and synthesized three novel twistacene-modified enlarged pentagon-containing π-systems (6 and 9) with mismatched structures. The introduction of electron-withdrawing cyclopenta rings in the parent skeleton effectively stabilizes the electron-rich arenes. Their optoelectronic properties were studied via ultraviolet-visible (UV-vis) absorption spectra, fluorescence spectra, cyclic voltammetry, and density functional theory (DFT) calculation. In addition, chemical oxidation of the as-prepared compounds with nitrosonium hexafluoroantimonate could form the corresponding cationic radicals.

A one-pot method for the synthesis of azo compounds by the reaction of β-naphthol with aryl amines using t-BuONO as the nitrosonium source in DCM at room temperature was developed. This method features mild reaction conditions, a simple experimental procedure, and is free of acidic or alkaline additives.

The reactions of diaryl-, aryl-, and alkyl–arylcyclopropanes with ethyl nitrite in the presence of sulfur trioxide and sulfur trioxide dioxane complex, as well as the reactions of 1-alkyl-2-arylcyclopropanes with NOBF4 were studied. It was found that the attack of the nitrosonium cation, accompanied by the formation of a benzyl carbocation, leads to the formation of isoxazolines. The introduction of bulky alkyl substituents into the cyclopropane ring changes the regioselectivity of nitrosation, favoring the attack of the electrophilic particle on the benzyl position and leading to the competitive formation of an alkyl carbocation. Depending on the structure of the alkyl substituent, both products of intramolecular heterocyclization accompanied by skeletal rearrangements and products formed with the participation of an external nucleophile are formed.

In this article we minutely discuss the so-called “oxidative” mechanism of mononuclear form of dinitrosyl iron complexes (M-DNICs) formations proposed by the author. M-DNICs are proposed to be formed from their building material—neutral NO molecules, Fe2+ ions and anionic non-thiol (L−) and thiol (RS−) ligands based on the disproportionation reaction of NO molecules binding with divalent ion irons in pairs. Then a protonated form of nitroxyl anion (NO−) appearing in the reaction is released from this group and a neutral NO molecule is included instead. As a result, M-DNICs are produced. Their resonance structure is described as [(L−)2Fe2+(NO)(NO+)], in which nitrosyl ligands are represented by NO molecules and nitrosonium cations in equal proportions. Binding of hydroxyl ions with the latter causes conversion of these cations into nitrite anions at neutral pH values and therefore transformation of DNICs into the corresponding high-spin mononitrosyl iron complexes (MNICs) with the resonance structure described as [(L−)2Fe2+(NO)]. In case of replacing L− by thiol-containing ligands, which are characterized by high π-donor activity, electron density transferred from sulfur atoms to iron-dinitrosyl groups neutralizes the positive charge on nitrosonium cations, which prevents their hydrolysis, ensuring relatively a high stability of the corresponding M-DNICs with the resonance structure [(RS−)2Fe2+ (NO, NO+)]. Therefore, M-DNICs with thiol-containing ligands, as well as their binuclear analogs (B-DNICs, respective resonance structure [(RS−)2Fe2+2 (NO, NO+)2]), can serve donors of both NO and NO+. Experiments with solutions of B-DNICs with glutathione or N-acetyl-L-cysteine (B-DNIC-GSH or B-DNIC-NAC) showed that these complexes release both NO and NO+ in case of decomposition in the presence of acid or after oxidation of thiol-containing ligands in them. The level of released NO was measured via optical absorption intensity of NO in the gaseous phase, while the number of released nitrosonium cations was determined based on their inclusion in S-nitrosothiols or their conversion into nitrite anions. Biomedical research showed the ability of DNICs with thiol-containing ligands to be donors of NO and NO+ and produce various biological effects on living organisms. At the same time, NO molecules released from DNICs usually have a positive and regulatory effect on organisms, while nitrosonium cations have a negative and cytotoxic effect.

We report the synthesis of aryldiazonium tetrachloroaurate(III) salts [X-4-C6H4N≡N]AuCl4 (X = F, Cl, Br, I, CN, NO2) and their mild reduction to covalently functionalized nanoparticles. The synthesis of the salts was carried out by the oxidation of anilines, dissolved in HCl, using sodium nitrite followed by the exchange of the counter anion with [AuCl4]- in water. In another procedure, the anilines were protonated with H[AuCl4] in acetonitrile followed by one-electron oxidation using nitrosonium salt [NO]X (X = BF4−, PF6−). Raman and ATR-FTIR spectroscopy displayed the diazonium νN≡N and Raman showed the tetrachloroaurate νAu-Cl stretching frequencies. X-ray crystal structure of [NO2-4-C6H4N≡N]AuCl4 salt showed N≡N bond distance typical of a triple bond. Gold-aryl nanoparticles were constructed by the mild chemical reduction of the diazonium gold(III) salts using 9-borabicyclo[3.3.1]nonane (9-BBN). Nanoparticles hydrodynamic diameter, elemental composition, dynamics information, and stability data were determined. Transmission electron microscopy (TEM) measurements showed limited aggregation due to the small suppressing organic shell. However, dynamic light scattering (DLS) measurements showed considerable aggregation in acetonitrile. X-ray photoelectron spectrometry (XPS) showed the gold core in zero oxidation state and manifested the gold-organic shell connectivity. The –N=N-aryl interfacial formation on the gold surface can be ruled out since the N1s peak assigned to the diazonium moiety showed no sign in the XPS nitrogen area in addition to its absence in the ATR-FTIR spectra. Raman spectroscopy measurements showed a peak assigned to gold-carbon bonding supported by density functional calculations (DFT) on Au20-C6H4-CN model.

Selective oxidative homo- and cross-coupling of electron-rich phenols and anilides was developed using nitrosonium tetrafluoroborate as a catalyst. Oxidative coupling of phenols revealed unusual selectivities, which translated into the unprecedented synthesis of inverse Pummerer-type ketones. Mechanistic studies suggest that oxidative coupling of phenols and anilides shares a common pathway via homolytical heteroatom-hydrogen bond cleavage. Nitrosonium salt catalysis was applied for cross-dehydrogenative coupling initiated by generation of heteroatom-centered radicals.

A catalytic, metal-free intramolecular rearrangement of benzyl phenyl ethers using nitrosonium salt as a catalyst is described. The optimized reaction conditions enabled a catalytic and metal-free Friedel–Crafts alkylation reaction with benzylic alcohols, producing water as the stoichiometric byproduct. A comprehensive scope (>50 examples) for both approaches and application in drug synthesis were demonstrated. Mechanistic studies suggest a Lewis acid-based mechanism for the metal-free Friedel–Crafts reaction.

The aim of this work is to introduce, model, and optimize a new non-acid-catalyzed system for a direct N $$=$$ N–C bond formation. By reacting naphthols or phenol with anilines in the presence of the sodium nitrite as nitrosonium ( $$\hbox {NO}^{+})$$ source and triethylammonium acetate (TEAA), a N $$=$$ N–C group can be formed in non-acid media. Modeling and optimization of the reaction conditions were investigated by response surface method. Sodium nitrite, TEAA, and water were chosen as variables, and reaction yield was also monitored. Analysis of variance indicates that a second-order polynomial model with F value of 35.7, a P value of 0.0001, and regression coefficient of 0.93 is able to predict the response. Based on the model, the optimum process conditions were introduced as 2.2 mmol sodium nitrite, 2.2 mL of TEAA, and 0.5 mL $$\hbox {H}_{2}\hbox {O}$$ at room temperature. A quadratic (second-order) polynomial model, by analysis of variance, was able to predict the response for a direct N=N–C group formation. Predicted response values were in good agreement with the experimental values. Electrochemistry studies were done to introduce new Michael acceptor moieties. Broad scope, high yields, short reaction time, and mild conditions are some advantages of the presented method.

A simple yet robust flow set-up for the efficient desulfurization of a series of thioimidazoles is presented, which generates the corresponding imidazole derivatives in high yields. The strategic choice of peristaltic over piston pumps allowed reliable delivery of the heterogeneous stream of the thioimidazole substrate into a T-piece where it reacted with NaNO2 in the presence of acetic acid. This approach enabled the controlled and safe formation of the reactive nitrosonium species without uncontrolled exposure to hazardous nitrous oxide by-products as observed in related batch protocols. The value of the resulting imidazole products was further demonstrated by their conversion into various esters representing new derivatives of the known analgesic etomidate through an efficient one-pot Corey–Gilman–Ganem oxidation procedure.

Nitrosonium ions are versatile and mild oxidants, which were successfully employed in organic transformations. The applications cover different fields, such as the functionalization of carbon-carbon and carbon-heteroatom bonds, functionalization of unsaturated bonds and the oxidative coupling of arenes, catalyzed by nitrosonium ions. Due to the ability of nitrosonium ions to modify various types of bonds with different modes of action, a variety of applications has been established, which addresses current challenges in organic chemistry research. By considering additional points, such as safety of reagents, by-product formation, employed solvents and energy consumption, several aspects of green and sustainable chemistry can be addressed. Within this review, synthetic applications of nitrosonium ions under transition metal-free reaction conditions are summarized.

The formation of electron donor-acceptor complexes is studied with global and local charge transfer partitionings. The 1-parabola model is applied to the bromination reaction of alkenes and the correlations found between the global and local charge transferred with the transition energy of the charge transfer bands and the kinetic rate constants indicate that the nucleophilic attack of alkenes to bromine is the electronic process controlling the reactivity in the formation of the electron donor-acceptor complexes in this reaction. The 2-parabolas model is used in studying the nitrosation of aromatic compounds where colorful electron donor-acceptor complexes are formed. In this case, and like previous applications of the 2-parabolas model, the consistent usage of the model mandates the explicit consideration of reaction conditions in preparing the reactants to have a direction of electron transfer that is consistent with the chemical potential differences. For the nitrosation reaction this implies considering the nitrosonium cation as the charge acceptor. Both applications support that the charge transferred predicted from chemical reactivity models can be used as a scale to measure the nucleophilicity in reactivity trends. Graphical Abstract ᅟ.

The nitrosonium ion-catalyzed dehydrogenative coupling of heteroarenes under mild reaction conditions is reported. The developed method utilizes ambient molecular oxygen as a terminal oxidant, and only water is produced as byproduct. Dehydrogenative coupling of heteroarenes translated into the rapid discovery of novel hedgehog signaling pathway inhibitors, emphasizing the importance of the developed methodology.

A number of nitrosonium and nitronium salts were probed as reagents for the heterocyclization of 1-bromo-1-fluorocyclopropanes in the presence of organic nitriles to give pyrimidine N -oxides. Nitronium triflate, either preformed or generated in situ from nitric and triflic acids, was shown to be the most efficient reagent for this reaction, affording a mild and convenient procedure for the synthesis of 4-halogenopyrimidine derivatives. X-ray crystallography was used to confirm the ionic structure of nitronium triflate (NO 2 + )(CF 3 SO 3 − ).

Nitrosonium complexes of 1-methylthymine and 9-methyladenine, as well as of their complementary pair, have been studied at the RI-MP2/L1 level of theory. The addition of nitrosonium ion to molecules of these compounds or their H-bonded pair gives a set of nitrosonium complexes of different types (1η–3η). The complex with the NO+ ion coordinated to N3 of the adenine moiety corresponds to the global minimum on the potential energy surface. The gain in energy in the interaction of nitrosonium complexes of 1-methylthymine and 9-methyladenine with 9-methyladenine and 1-methylthymine, respectively, is larger than in the formation of a neutral 9-methyladenine–1-methylthymine couple. Specific structural features and dynamics of the nitrosonium complexes are discussed.

By the method RI-MP2/L1 nitrosonium complexes were explored of 1-methylcytosine and 9-methylguanine, structural analogs of nucleotide bases cytosine and guanine, as well as of their complementary pair. The addition of a nitrosonium cation to the molecules of these compounds and to their pair leads to the formation of various types of nitrosonium complexes (1η–3η). n-Complexes with the coordination of NO+ cation to nitrogen and oxygen atoms are commonly more feasible in energy as compared with π-complexes. The complex with cation NO+ coordinated at the oxygen atom of the carbonyl group and N7 atom of the guanine fragment of the pair corresponds to the global minimum on the potential energy surface. The energy gain at the interaction of nitrosonium complexes of 1-methylcytosine and 9-methylguanine with 9-methylguanine and 1-methylcytosine respectively is usually larger than at the formation of a neutral pair 1-methylcytosine-9-methylguanine.

The synthesis and structural characterization of trans-[IrCl(NO)(PtBu2H)(2)]BF4 (1) is reported. The title compound was prepared in good yield in the reaction of in situ-prepared trans-[IrCl(coe)(PtBu2H)(2)] (coe = cis-cyclooctene) with an appropriate amount of nitrosonium tetrafluoridoborate in dichloromethane at room temperature. Single crystals of 1 were grown from dichloromethane/diethyl ether and were analyzed by X-ray crystallography.

The synthesis and structural characterization of trans-[RhCl(NO)(PtBu2H)(2)]BF4 (2) is reported. The title compound could easily be prepared in good yields by a kind of bridge-splitting reaction of [{Rh(-Cl)(PtBu2H)(2)}(2)] (1) with an appropriate amount of nitrosonium tetrafluoridoborate in dichloromethane at room temperature. Single crystals of 2 were grown from dichloromethane/diethyl ether and were analyzed by X-ray crystallography.

1H and 13C NMR studies and quantum chemical calculations show the interaction between 2,11-dithia-5,6,8,9-tetramethyl[32](1,4)cyclophane and nitrosonium cation to result in the formation of π- and n-complexes. According to DFT/B3LYP/6-31G(2d,p) calculations, formation of nitrosonium complexes is a strongly exothermic process both in gas phase and in SO2. Affinity of single-charged complexes to NO+ is usually larger than that of double-charged and triple-charged complexes, affinity of all the charged complexes to nitrosonium cation in SO2 being larger than that in gas phase. The π-complex with nitrosonium cation coordinated to the methylated aromatic ring is the most stable with structural characteristics being close to those obtained by X-ray diffraction for nitrosonium π-complexes of hexamethylbenzene and other arenes. The N―O bond lengths in all the complexes are quite close to each other and larger than that in NO+ cation. The S―N bond length increases upon transition from single-charged to double-charged and polycharged complexes. Copyright © 2014 John Wiley & Sons, Ltd.

A new ionic liquid, 1-methyl-3-(2-[2-(1-methyl-1H-imidazol-3-ium-3-yl)ethyloxy] ethyl)-1H-imidazol-3-ium dinitrite, was synthesized. This ionic liquid was used as a convenient nitrosonium source in diazotization of aryl amines into their corresponding diazonium salts, which were converted into aryl iodides and aryl azides using potassium iodide or sodium azide, respectively. Various aryl amines possessing electron-withdrawing groups or electron-donating groups were converted into the corresponding aryl iodides and aryl azides in excellent yields. Advantages of this methodology are the use of mild reaction conditions, short reaction times, and avoiding the use of toxic solvents.

Nanoparticles of organosilane-based nitrite ionic liquid immobilized on silica, 1-butyl-3-methylimidazolium nitrite, and 1-(3-trimethoxysilylpropyl)-3-methylimidazolium nitrite were used as effective reagents for the preparation of benzotriazole derivatives from 1,2-diaminobenzenes at room temperature under mild solvent-free conditions. These ionic liquids play as nitrosonium sources in this procedure.1,2-Diaminobenzene derivatives have been treated with ionic liquids to give the related diaminobenzenes in very good to excellent yields in short reaction times. Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the full experimental and spectral details.

Cytosine complexes with nitrosonium ion were studied by the RI-MP2/L1 method. Addition of nitrosonium ion to cytosine tautomers leads to formation of a set of nitrosonium complexes with different structures (1η–3η). n-Complexes formed via NO+ coordination to the nitrogen and oxygen atoms are energetically more favorable than π-complexes. The complex of cytosine as 4-aminopyrimidin-2(1H)-one tautomer with nitrosonium ion coordinated to the carbonyl oxygen atom occupies the global minimum on the potential energy surface. Structural features of the complexes are discussed.

Adenine complexes with nitrosonium ion have been studied by the RI-MP2/L1 quantum-chemical method. Addition of nitrosonium ion to adenine tautomers produces a set of nitrosonium complexes of different types (1η–3η). n-Complexes involving NO+ coordination to nitrogen atoms are more energetically favorable than π-complexes. The global minimum on the potential energy surface is occupied by the complex of 7H-adenine tautomer with nitrosonium ion coordinated at the N3 atom.

Quantum-chemical calculations at the RI-MP2/L1 level of theory showed that the most energetically favorable complexes of uracil and thymine with nitrosonium cation are those of n-type with NO+ coordination at the nitrogen or oxygen atom. A correlation was found between the experimental and calculated affinities of the dioxo tautomer of thymine for nitrosonium ion ( $$ A_{NO^ + } $$ ). A linear relation was revealed between $$ A_{NO^ + } $$ values for structurally similar tautomers of uracil and thymine.

Imidazolium based nitrite ionic liquid containing trimethoxysilyl group was prepared from the reaction of N-methylimidazole and (3-chloropropyl) trimethoxysilane. This ionic liquid was immobilized on silica covalently to give nanoparticles with the imidazolium nitrite moiety remaining intact. The diazotization reaction was performed as a model reaction to examine the activity of these nanoparticles as a nitrosonium source. Excellent performance was exhibited in the diazotization reaction of various aniline derivatives in the presence of HCl under mild heterogeneous conditions (room temperature and short reaction time). In-situ coupling of diazonium salts to a range of tertiary anilines, phenols and naphthols afforded the requisite azo dyes in good yield, using standard experimental procedures.

A new task-specific nitrite containing ionic liquid derived from the O-nitrosation of N-methyl-N-hydroxybutylimidazolinium chloride was synthesized and used as a source of nitrosonium ion to affect the efficient diazotization of arylamines. The diazonium salts thus obtained were coupled, using standard experimental procedures, to a range of tertiary anilines, phenols and naphthols to afford the requisite azo dyes in good yield. The diazotization and subsequent azo-coupling generated the related azo dyes at 0–5 °C in short reaction times with a simple experimental procedure.

The affinities of bi- and polycyclic aromatic compounds for nitrosonium ion (\(A_{NO^ + } \)) were calculated at the RI-MP2/L1 and DFT/PBE/3z levels of theory. Both methods gave generally similar geometric parameters of nitrosonium complexes. The formation of pincer complexes in which the NO+ ion is linked to two aromatic rings is more energetically favorable than the formation of analogous complexes through external binding of NO+ to one aromatic ring. Linear correlations were found between the calculated \(A_{NO^ + } \) values of aromatic compounds and experimental equilibrium constants for the reactions of these compounds with nitrosonium ion in solution. Structural peculiarities of the examined nitrosonium complexes are discussed.

With the use of Hartree-Fock and DFT methods we demonstrated that for the benzene derivatives with the substituents Me, Et, Pr, i-Pr, t-Bu, CF3, F, and Cl π-complexes are more favorable by energy, whereas with the substituents CHO, MeCO, PhCO, CN, NO, and NO2 n-complexes are more feasible. The affi nity of aromatic compounds to the nitrosonium-cation (ANO+) at the formation of the π-complexes grows with the growing donor character of the substituents in the ring and with their number. The best agreement between the calculated and experimental ANO+ values for benzene was obtained with the use of RI-MP2/L1 method.

Many studies have noted that mixtures of nitrogen oxides (or oxyanions; NOx = NO3–, NO2–, NO–, etc.) and halide (particularly bromine) with or without a transition metal salt (most frequently, copper and iron complexes) are fast and highly selective catalysts for aerobic sulfoxidation and decontamination of many oxidizable toxic compounds. However, the lack of extensive and rigorous kinetic information has kept unequivocal mechanistic inferences on these important catalyst systems to a minimum. Through a series of spectroscopic and kinetics studies on NOx/bromine systems in acetonitrile, the following clarifying technical points have been established: (1) bromine is the reactive species in these oxidations; (2) nitrosonium and hypobromite are not kinetically important, (3) tribromide (Br3–) functions as a stable reservoir for Br2; (4) salts of Br3– and nitrate are stable, storable decontamination catalyst precursors; and (5) most importantly, the multiple complex roles of water (required for catalysts yet...

Several pure α-esters of N-benzyloxycarbonyl-l-aspartic acid have been obtained in high yields by esterification of N-benzyloxycarbonyl-L-aspargine, followed by deamidation with nitrosonium hydrogen sulfate (NO · HSO4) in glacial acetic acid.

The halogen–lithium exchange reaction is of one of the most powerful method for the preparation of organolithium compounds, but its mechanism is still controversial. To afford some new elements, we synthesized a new suitable fast radical clock, bearing a phenyl group at the alkene C-terminal. The examination of some mechanistic clues, as well as the identification of the unexpected by-products allowed the conclusion that the reaction proceeds by a polar mechanism and no evidence for radicals were found. The second reaction discussed is the insertion of NO in the NLi bond of lithium amides. Evidence for the involving of paramagnetic and nitrosonium intermediates, as well as equilibria between different reactive species were essential for the proposal of a whole complex mechanism, which was confirmed by theoretical calculations. Finally, results on the addition of heteroaromatic organocuprates to α,β-unsaturated substrates are presented. Several reaction conditions were looked for to lead the reaction toward the more interesting 1,4-conjugated addition. Thus, addition of up to 6 equivalents of TMSCl to the reaction with arylcuprates leads to a clean addition yielding more than 95% of the 1,4-addition product. A further objective of the paper is to show how the search of unexpected routes of reaction allowed developing original pathways to lead them toward the formation of appealing functionalized compounds. Copyright © 2010 John Wiley & Sons, Ltd.

According to the 1H and 13C NMR data, triptycene reacts with nitrosonium tetrachloroaluminate to form positively charged π-complexes with one and two nitrosonium ions, which are rapidly (on the NMR time scale) converted into each other. DFT quantum-chemical calculations with Λ02 basis set indicated higher stability of singly charged complexes relative to doubly charged. Addition of three nitrosonium ions to triptycene molecule is unfavorable from the energy viewpoint.

The O-2(+) ion is sufficiently similar in size to NO+ and so the difference in lattice energy in salts with a common anion can be expected to be negligible. Comparative analysis of O2F vs. NOF and of O-2(+) vs. NO+-salts is given in this paper and some surprising and unexpected differences between corresponding species are discussed. (C) 2009 Elsevier B.V. All rights reserved.

The reaction of fluorene and 9,9-dimethylfluorene with nitrosonium tetrachloroaluminate was investigated using 1H and 13C NMR spectroscopy with deuterium perturbation. The arising positively charged complexes with one and two nitrosonium cations are involved into an interconversion fast in the NMR time scale. The data of quantum-chemical calculations performed by DFT method (basic Λ02) indicate the higher stability of single-charged π-complexes of 2η type compared with the π-complexes corresponding to the addition of two NO+ cations. In the dication π-complexes the transoid position of the NO groups is more favorable than the cisoid position.

This work reviews the use of pyrrole, chloroform, methanol, as well as methoxy and nitrosonium groups generated ‘in situ’, as infrared and NMR probe molecules to characterize zeolites basicity. The main results reported in the bibliography about the correlation of the spectroscopic properties of the adsorbed molecule with the framework basicity, the host–guest interactions, and the limitations in the use of these molecules as probes for zeolite basicity are discussed. Special attention is paid to the results reported for the adsorption of pyrrole and halocarbons, most specially CHCl3 and CHClF2 over alkali-exchanged FAU-type zeolites using IR and NMR spectroscopies.

It has been shown for the first time that nitrosation of phenylcyclopropanes with bulky alkyl substituents in the small ring proceeds predominantly with attack of the nitrosonium cation on the benzyl carbon atom of the cyclopropane ring with intermediate formation of an alkyl carbocation. In addition to isoxazolines, 1,2-oxazines and Δ 1 -pyrroline N-oxide are formed, formation of the latter is preceded by skeletal rearrangement.

We report the synthesis and encapsulation properties of long (up to 5 nm) molecular nanotubes 1-4, which are based on calix[4]arenes and can be filled with multiple nitrosonium (NO + ) ions upon reaction with NO 2 /N 2 O 4 gases. These are among the largest nanoscale molecular containers prepared to date and can entrap up to five guests. The structure and properties of tubular complexes 1·(NO + ) 2 -4·(NO + ) 5 were studied by UV/Vis, FTIR, and 1 H NMR spectroscopy in solution, and also by molecular modeling. Entrapment of NO + in 1·(NO + ) 2 -4·(NO + ) 5 is reversible, and addition of [18]crown-6 quickly recovers starting tubes 1-4. The FTIR and titration data revealed enhanced binding of NO+ in longer tubes, which may be due to cooperativity. The described nanotubes may serve as materials for storing and converting NO x and also offer a promise to further develop supramolecular chemistry of molecular containers. These findings also open wider perspectives towards applications of synthetic nanotubes as alternatives to carbon nanotubes.

Arylcyclopropanes react with nitrosyl chloride activated by sulfur(VI) oxide to give the corresponding 5-aryl-4,5-dihydro-1,2-oxazoles in quantitative yields. The complex NOC1·2SO3 is a highly efficient nitrosating agent which makes it possible to involve in the process arylcyclopropanes having both donor and acceptor substituents in the aromatic ring.

The affinities of a series of azines for nitrosonium ion (A NO +) were calculated by quantum-chemical methods, AM1 and ab initio. The A NO + values were found to increase as the number of nitrogen atoms in the ring decreases and the donor power of substituents increases; ring fusion also increases A NO +. The best agreement between the calculated and experimental A NO + values was attained with the use of AM1 calculations and ab initio methods with split polarization or diffuse functions. Substituted pyridines showed linear correlations between the calculated A NO + values and substituent constants σ or σ+ or overall charges on the NO group in the complex. Linear correlations were also found between the calculated A NO + values of azines and their experimental proton affinities.

The reaction of [2.2]paracyclophane with nitrosonium tetrachloroaluminate was studied by NMR (1H, 13C) spectroscopy using deuterium isotopic perturbation technique. The resulting cationic complexes containing one and two nitrosonium ions are involved in fast (on the NMR time scale) interconversion. Quantum-chemical calculations performed on the DFT level (using triple zeta basis set) indicate the higher stability of 2η single-charged π-complexes relative to σ complexes corresponding to the addition of NO+ ion at the ipso and ortho positions. The formation of the single-charged π-complex is energetically more favorable, compared to the double-charged π-complex. The affinity of NO+ for [2.2]paracyclophane is much greater than for p-xylene, presumably due to stacking interaction between the aromatic rings in the π-complex.

Hydroperoxide decomposition by hindered amine light stabilizers (HALSs) is an important process producing active HALS derivatives and has been studied energetically. The decisive active species of the decomposition, however, has not been proposed yet. In this article, HALS nitrosonium that forms in the decomposition of a hydroperoxide by HALSs and a ring-opening product of the nitrosonium, a nitroso compound, are proposed as active species for hydroperoxide decomposition. Furthermore, the reactivity of the nitrosonium with phenols is discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1310–1317, 2006

The effect of acidic compound on the formation of active species in homolytic hydroperoxide decomposition by hindered amine light stabilizers (HALS) was studied. The hydroperoxide decomposition activity of HALS is an important to characteristics of HALS. HALS Ammonium salt, which is a fundamental compound involved in the antagonism between HALS and acidic compounds including phenolic antioxidants, was found to be a key compound for the formation of HALS nitrosonium salt, which was identified as the active species of hydroperoxide decomposition. HALS Nitrosonium salt was not formed from active species for polymer stabilization, such as nitroxide, alkoxide, or hydroxylamine of HALS, but from HALS salt. A formation mechanism of HALS nitrosonium salt is proposed. Furthermore, molecular aggregates formed between HALS and acid compounds are discussed to be important for HALS properties.

[reaction: see text] Alpha-tocopherol (alpha-TOH), the main oil component making up vitamin E, and its nonnatural solid 6-hydroxy-2,2,5,7,8-pentamethylchroman and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid structurally related analogues were oxidized quantitatively with 2 mol equiv of NO+ SbF6(-) in CH3CN at 233 K to form phenoxonium cations (alpha-TO+ SbF6(-)) in a chemically reversible two-electron/one-proton process. Solution-phase infrared spectroscopy, 1H and 13C NMR spectroscopy, and corresponding theoretical calculations of the spectroscopic data using density-based and wave-function-based models support the identity of the remarkably stable phenoxonium cations. The presence of an oxygen atom in the para position to the hydroxyl group and the chromanol ring structure appear to be important factors in stabilization of the phenoxonium ions, which raises the interesting possibility that the cations play a crucial role in the mode of action of vitamin E in biological systems. Although the phenoxonium cations are reactive toward nucleophiles such as water, they may be moderately stable in the hydrophobic (lipophilic) environment where vitamin E is known to occur naturally.

The reactivity of a nitrosating agent (N2O3) on oxidations of alcohols and the methyl group of acetophenone were tested. Active electrophylic surface nitrosonium ions (NO+) was detected on H2SO4/SiO2 catalysts by Raman spectroscopy, suggesting a surface ionic mechanism of oxidation in agreement with the one proposed in acid aqueous solutions. Alcohols are selectively oxidized to ketones and aldehydes in high yield, useful for synthetic applications, at 25 °C in 1,2-dichlorethane and using commercial sulfonated styrene divinyl benzene resins (Amberlyst 15®) as catalysts. In addition, nitrous acid ester has been observed as intermediates according to an ionic mechanism by surface NO+. Under the same reaction conditions, acetophenone is selectively oxidized to benzoyl cyanide in high yield and selectivity. The comparison with oxidation carried out in aqueous solution of HNO2, where benzoyl formic acid was obtained, suggests that the differences in the final products are likely due to the specific stabilizing effect of each solvent. Moreover, the reactivity of the intermediates isolated in aqueous systems implies that α-nitroso-acetophenone is a probable reaction intermediate also in aprotic heterogeneous systems.

The use of simple calix[4]arenes for chemical conversion of NO2/N2O4 gases is demonstrated in solution and in the solid state. Upon reacting with these gases, calixarenes 1 encapsulate nitrosonium (NO+) cations within their cavities with the formation of stable calixarene-NO+ complexes 2. These complexes act as encapsulated nitrosating reagents; cavity effects control their reactivity and selectivity. Complexes 2 were effectively used for nitrosation of secondary amides 5, including chiral derivatives. Unique size-shape selectivity was observed, allowing for exclusive nitrosation of less crowded N-Me amides 5 a-e (up to 95 % yields). Bulkier N-Alk (Alk>Me) substrates 5 did not react due to the hindered approach to the encapsulated NO+ reagents. Robust, silica gel based calixarene material 3 was prepared, which reversibly traps NO2/N2O4 with the formation of NO+-storing silica gel 4. With material 4, similar size-shape selectivity was observed for nitrosation. The N-Me-N-nitroso derivatives 6 d,e were obtained with approximately 30 % yields, while bulkier amides were nitrosated with much lower yields (

Supramolecular approaches to visual detection, storage, conversion and use of NO X gases are described that deploy calixarenes and their derivatives, such as hemicarcerands and synthetic nanotubes. Polymer-supported calixarene materials for NO X are also introduced. Chemical fixation of NO2/N2O4 is demonstrated through the transformation into calixarene–NO+ complexes and their use as nitrosonium storing and releasing reagents for organic synthesis. These findings highlight perspectives of supramolecular chemistry and molecular recognition in sensing and fixation of environmentally important gases.

The use of simple calix[4]arenes 1a,b for NO2/N2O4 sensing and conversion is demonstrated, both in solution and in the solid state. Upon reacting with these gases, compounds 1a,b encapsulate reactive NO+ cations within their cavities with the formation of deeply colored (λmax∼570 nm) charge-transfer complexes 2a,b . Further functionalization of the calix[4]arene platform is reported for attachment to solid supports. Polymer-supported calixarene material 3 was prepared, which reversibly traps NO2/N2O4 with the formation of nitrosonium storing polymer 4 . Material 4 was effectively used for nitrosation of amides.

2-(4-Azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (14), 2-(4-azidophenyl)benzimidazole-1-oxide-3-oxyl (16), 2-(4-azidophenyl)-1,2,6-triphenylverdazyl (19), 2-(3-azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (21), and (3-azidophenyl)-N-tert-butyl-N-aminoxyl (25) were photolyzed in frozen solution to give S = 3/2 state ESR spectra of the corresponding nitrenophenyl radicals with the following zero-field splitting parameters: |D/hc| = 0.277 cm(-1), |E/hc| < or = 0.002 cm(-1) (7 from 14); |D/hc| = 0.256 cm(-1), |E/hc| < or = 0.002 cm(-1) (8 from 16); |D/hc| = 0.288 cm(-1), |E/hc| < or = 0.002 cm(-1) (9 from 19); |D/hc| = 0.352 cm(-1), |E/hc| = 0.006 cm(-1) (10 from 21); |D/hc| = 0.336 cm(-1), |E/hc| = 0.004 cm(-1) (11 from 25). UB3LYP/6-31G computations and ESR spectroscopic analyses suggest that these are nitreno radicals, even para-linked systems with possible quinonoidal resonance forms. Neat samples of azidophenyl radicals 14 and 21 showed bulk paramagnetic behavior, consistent with the lack of close contacts in their crystal structures. Efforts to make photolabile coordination complexes of 14 and 21 with paramagnetic transition metal ions were unsuccessful: Cu(ClO4)2 x 6H2O instead oxidized them to the corresponding diamagnetic nitrosonium perchlorate salts.

It was established by means of multinuclear magnetic resonance method (1H, 1 3C, 1 9F and 1 4N) that reaction of 2,2,6,6-tetramethyl-4-R-piperidin-1-oxyl radicals (R = H, OH, OMe, OCOPh, NHCOMe) with nitrosonium tetrafluoroborate gave rise to the corresponding 2,2,6,6-tetramethyl-1-oxo-4-R-piperidinium tetrafluoroborates. Linear correlations were found between the chemical shifts of atoms H4, C4 of cations and respectively σ1-constants of substituents R and chemical shifts of C4 atom calculated from increments of substitution. The conformational features of the generated nitrosonium cations are considered on the grounds of vicinal coupling constants J H H and quantum-chemical calculations by AM1 method.