Frozen aryldiazonium chlorides in radical reactions with alkenes and arenes

Frozen aryldiazonium chlorides have been investigated in radical alkene and arene functionalizations. Through freezing at – 84?°C, aryldiazonium chlorides, which otherwise show significant decomposition in aqueous solution after several hours at room temperature, can be stored for at least 20 days. In addition, the slow melting of aryldiazonium-containing ice cubes can serve as an alternative to syringe pumps that are commonly used if a controlled addition of the diazonium salt to the reaction mixture is required.     

Role of triplet states of aryldiazonium cations in the Meerwein reaction

The mechanism of the Meerwein reaction was interpreted on the basis of quantum-chemical calculations of the optimal geometry, electronic spectra, and ground state of a large number of diazonium cations. The relationship of this process with the triplet excited state of aryldiazonium cations and the role of spin catalysis in thermal excitation of these states via ligand-to-metal and metal-to-ligand electron transfer involving organic ligands and complex copper chlorides as catalysts were examined.     

Reaction of 3-oxodihydrothionaphthenes with aryl diazonium chlorides and aryl isothiocyanates

The reaction of 3-oxodihydrothionaphthenes with aryl diazonium chlorides gives 2-arylhydrazono-3-oxodihydrothionaphthenes. By oxidation of the latter with hydrogen peroxide in glacial acetic add, new 2-arylhydrazonodihydrothionaphthene-(3)-one-1, 1-dioxides are synthesized. Condensation of aryl isothiocyanates with 3-oxodihydrothionaphthenes in tetrahydrofuran gives 2-(arylthiocarbamyl)-3-oxodihydrothionaphthenes; cyclization of the latter with -bromoacetophene leads to the synthesis of 4-phenyl-3-aryl-2-(3 -oxodihydrothionaphthylidene-2)-⁴-thiazolines.     

Surface modification of gold electrodes with anthraquinone diazonium cations

Electrochemical grafting of anthraquinone (AQ) groups to gold electrodes was carried out in acetonitrile (ACN) and in aqueous acidic media (0.05 M H₂SO₄). For the first time, the covalent attachment of AQ to gold is demonstrated. Electrochemical quartz crystal microbalance (EQCM), atomic force microscopy (AFM) and cyclic voltammetry (CV) were used to characterise the AQ-modified Au electrodes. Electrografting from both solutions containing the corresponding diazonium salt yielded a strongly attached AQ layer. AFM examination showed that a multilayer AQ film was formed. The CV behaviour of the modified electrodes was tested in 0.1 M KOH and a quasi-reversible response was observed.     

Isotope effects, dynamics, and the mechanism of solvolysis of aryldiazonium cations in water

The mechanism of the heterolytic solvolysis of p-tolyldiazonium cation in water was studied by a combination of kinetic isotope effects, theoretical calculations, and dynamics trajectories. Significant (13)C kinetic isotope effects were observed at the ipso (k(12)C/k(13)C = 1.024), ortho (1.017), and meta (1.013) carbons, indicative of substantial weakening of the C(2)-C(3) and C(5)-C(6) bonds at the transition state. This is qualitatively consistent with a transition state forming an aryl cation, but on a quantitative basis, simple S(N)1 heterolysis does not account best for the isotope effects. Theoretical S(N)2Ar transition structures for concerted displacement of N(2) by a single water molecule lead to poor predictions of the experimental isotope effects. The best predictions of the (13)C isotope effects arose from transition structures for the heterolytic process solvated by clusters of water molecules. These structures, formally saddle points for concerted displacements on the potential energy surface, may be described as transition structures for solvent reorganization around the aryl cation. Quasiclassical dynamics trajectories starting from these transition structures afforded products very slowly, compared to a similar S(N)2 displacement, and the trajectories often afforded long-lived aryl cation intermediates. Critical prior evidence for aryl cation intermediates is reconsidered with the aid of DFT calculations. Overall, the nucleophilic displacement process for aryldiazonium ions in water is at the boundary between S(N)2Ar and S(N)1 mechanisms, and an accurate view of the reaction mechanism requires consideration of dynamic effects.     

Surface modification of indium tin oxide via electrochemical reduction of aryldiazonium cations

The facile deposition of para-substituted aryl films onto indium-tin oxide (ITO) electrodes by the electrochemical reduction of aryl diazonium salts in acetonitrile is reported. For the deposition conditions used in this report, the aryl film thicknesses are on the order of 1-6 nm, suggesting a multilayer structure. Regardless of the functional group on the aryl diazonium cation, (NO(2), CO(2)H, or fluorene) the electrodeposition behavior onto ITO electrodes is similar to that seen on other electrode materials. XPS and UV-vis data support the introduction of organic functional surface groups to ITO. The blocking behavior of the aryl films on ITO toward the Ru(NH(3))(6)(3+/2+) redox couple is in agreement with electron transfer through conjugated organic layers. The facile preparation of patterned aryl films with regular-spaced 700 nm voids on ITO is also described. Atomic force microscopy and scanning surface potential microscopy on patterned NO(2) aryl films are used to assess the molecular structure and orientation. A 100 mV decrease in the contact potential over NO(2) aryl films relative to bare ITO suggests that the aryl films are loosely structured as deposited with the NO(2) groups oriented at a small angle away from the ITO surface.     

Studies on the polarographic reduction of the azomethine bond in the products of beta-keto-esters coupled with aryldiazonium chlorides

The products of coupling beta-keto-esters with aryldiazonium chlorides have been studied polarographically and give a single well-defined 4-electron diffusion-controlled irreversible wave in the pH range 2.0-11.0. The effect of electron-donating and electron-withdrawing substituents and the correlation between the half-wave potential and Hammett substituent constant have been studied.     

Synthesis and structure of N-ethyl-N-propargylphosphonamidic chlorides

Conclusions N-Ethyl-N-propargylethyl(phenyl)phosphonamidic, -phosphonamidothioic, and -phosphonamidoselenoic chlorides were obtained.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1869–1872, August, 1985.     

Electrochemical derivatization of carbon surface by reduction of in situ generated diazonium cations

The derivatization of a glassy carbon electrode surface was achieved by electrochemical reduction of several in situ generated diazonium cations. The diazonium cations were synthesized in the electrochemical cell by reaction of the corresponding amines with NaNO2 in aqueous HCl. The versatility of the method was demonstrated by using six diazonium cations. This deposition method, which involves simple reagents and does not require the isolation and purification of the diazonium salt, enabled the grafting of covalently bounded layers which exhibited properties very similar to those of layers obtained by the classical derivatization method involving isolated diazonium salt dissolved in acetonitrile or aqueous acid solution. Cyclic voltammetry and electrochemical impedance spectroscopy carried out in aqueous solutions containing electroactive redox probe molecules such as Fe(CN)6(3-/4-) and Ru(NH3)6(3+) confirmed the barrier properties of the deposited layers. The chemical composition of the grafted layers was determined by X-ray photoelectron spectroscopy and surface coverage in the range 3 x 10(-10) to 6 x 10(-10) mol cm(-2) was estimated for films grown in our experimental conditions.     

Characterization of the deposition of organic molecules at the surface of gold by the electrochemical reduction of aryldiazonium cations

The deposition of 4-X phenyl groups (X = NO2, COOH, N-(C2H5)2) on polycrystalline gold electrode was achieved by the electrochemical reduction of the corresponding 4-substituted phenyldiazonium tetrafluoroborate salts in anhydrous acetonitrile media. The electrochemical quartz crystal microbalance measurements evidenced a two-step deposition process: the first one is the deposition of close to a monolayer and the second one is the relatively slower growth of multilayers. In this second region, the deposition is less efficient than for the first one. The electrochemical behavior of the resulting modified gold electrode was investigated in the presence of an electroactive redox probe and these results, together with the electrochemical quartz crystal microbalance data, demonstrated significant differences in reactivity and in deposition efficiency between the diazonium salts. The characterization of the modified electrodes by cyclic voltammetry and electrochemical impedance spectroscopy, as well as X-ray photoelectron spectroscopy measurements, showed that the formation of multilayers is possible and that a significant fraction of the deposited material remained at the electrode surface, even following ultrasonic treatment. The X-ray photoelectron spectroscopy data indicate that the existence of Au-C and Au-N=N-C linkages (where C represents a carbon atom of the phenyl group) is uncertain. Nonetheless, the deposition of the aryl groups by electrochemical reduction of diazonium cations yielded a film that adheres well to the gold surface and the deposited organic film hindered gold oxides formation in acidic medium.     

Synthesis and structure of some diazonium salts of the 1,2,4-triazole series

Diazotriazolecarboxylic acid, its methyl ester, and 3-diazonium-5-nitrophenyltriazoles have an internal salt structure. 3-Diazonium-5-methyl- and -5-phenyl-1,2,4-triazoles have been isolated as nitrates, perchlorates, and fluoroborates. All the compounds mentioned exist in strongly acid media as salts of the corresponding acid with diazo cations, but in weakly acid and neutral solutions they exist as zwitterions, formed by elimination of a proton from the imino nitrogen of the heterocycle.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 705–709, May, 1970.     

Quantitative structure-property relationships in the series of diazonium cations, intermediate products in the synthesis of analytical forms and dyes

It was demonstrated that the reduction potentials, dimerization potentials, and half-equivalence point potentials in the titration of aryldiazonium cations XC₆H₄N⁺N are linearly related to the quantum-chemically calculated values of electron affinities (A) and stabilization energies of radicals formed in the reduction of diazonium cations. Linear correlations between the frequencies (v) characterizing the set of stretching vibrations in the C—N⁺N fragment of XC₆H₄N⁺N cations and NN and C—N bond orders, charges on carbon atoms in the para positions of aromatic rings of C₆H₅X molecules, and mesomeric dipole moments (µ_m) of substituents X were found. Quantitative relationships relating µ_m and v to A were revealed. These relationships have clear physical meaning, are characterized by relatively large correlation coefficients, and possess predictive power for redox properties, electron affinity, and vibrational spectra of aryldiazonium cations and mesomeric dipole moments of atomic groups in organic molecules.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 149–156. Original Russian Text Copyright © 2005 by Pankratov.     

(Sensitized) photolysis of diazonium salts as a mild general method for the generation of aryl cations. Chemoselectivity of the singlet and triplet 4-substituted phenyl cations

The photolysis of a series of 4-X-benzenediazonium tetrafluoroborates is studied in MeCN. Loss of nitrogen occurs from the singlet excited state with X=H, t-Bu, and NMe2 and leads to the singlet aryl cation. This adds to the solvent yielding the corresponding acetanilides. With other substituents, ISC competes with (X=Br, CN) or overcomes (X=COMe, NO2) fragmentation and the aryl cation is formed in part or completely in the triplet state. In neat MeCN, this either abstracts hydrogen from the solvent (in most cases inefficiently) or undergoes intersystem crossing to the more stable singlet that reacts as above. In the presence of pi nucleophiles (allyltrimethylsilane or benzene), the triplet aryl cation is efficiently trapped giving substituted allylbenzenes and biphenyls, respectively. By triplet sensitization by xanthone, the triplet cation and the products from it are obtained from the whole series considered. The direct or sensitized photodecomposition of diazonium fluoroborates, substituted with both electron-donating and -withdrawing substituents, in the presence of alkenes and arenes offers an access to an alternative arylation procedure.     

On the electronic structure of dihalogenophosphenium cations

The bonding properties of the dihalogenophosphenium cations, PX₂⁽⁺⁾, X = F, Cl, Br, I, are evaluated by relativistic effective core potential calculations with a DZP basis set. Our investigations include an analysis of the singlet-triplet energy separation in the cations and the determination of the relative cation and anion stabilities in the gas phase, via corresponding group transfer reactions. A comparison is made with other stabilized, previously reported low-coordinated π-bonded phosphorus cations.     

Synthesis of O-substituted acetohydroximoyl chlorides and the structure of O-carbamoylacetohydroximoyl chloride

A method was proposed for the synthesis of the Z isomer of O- carbamoylacetohydroximoyl chloride from 1,1-dichloro-1-nitrosoethane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2849–2851, December, 1989.