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Efficient electrosynthesis of ultrasmall spherical mono- and bimetallic nanoparticles (NPs) of Rh and Pd stabilized in the shell of cetyltrimethylammonium chloride (CTAC) in the solution bulk was carried out by methylviologen (MV) mediated reduction of equimolar amounts of Pd(II) and Rh(III) (1.5 mM) in the presence of CTAC (10 mM) at controlled potentials of the MV2+/MV˙+ redox couple in a water/0.1 M NaCl medium at room temperature. Similar electrosynthesis of RhNPs also effectively proceeds when poly(N-vinylpyrrolidone) (10 mM) is used as a stabilizer. Metal ions are quantitatively converted to NPs upon consumption of the theoretical amount of electricity. Sizes of isolated PdNPs and RhNPs are 4.6 ± 0.9 nm and 1.7 ± 0.3 nm, respectively. Bimetallic (Pd,Rh)NPs were obtained by three procedures: (i) preliminary synthesis of RhNPs followed by reduction of Pd(II) ((Rh/Pd)NPs, 2.2 ± 0.7 nm); (ii) preliminary synthesis of PdNPs followed by reduction of Rh(III) ((Pd/Rh)NPs, 4.9 ± 1.0 nm); (iii) joint reduction of Pd(II) and Rh(III) ((Pd–Rh)NPs, 3.1 ± 0.5 nm). In all cases, solid-solution alloy (Pd,Rh)NPs are obtained. In an aqueous medium, all the NPs obtained are catalytically active in the hydrogenation of p-nitrophenol with sodium borohydride to p-aminophenol, but their use in the Suzuki coupling reaction of iodobenzene with phenylboronic acid does not lead to the target product. An increase in the CTAC concentration by 7.5 times leads to an increase in the catalytic activity of PdNPs in both types of reactions.

Metal complexes [Cr(bipy)3]3+, [Co(bipy)3]3+, and [Co(sep)]3+ in aqueous media at the potentials of M(III)/M(II) redox couple are shown playing a role of mediators in the electrosynthesis of silver nanoparticles, stabilized in a polyvinylpyrrolidone shell, by means of Ag(I) reduction. [Cr(bipy)3]3+ is consumed under the conditions of long-term preparative electrolysis, the reduction process is accompanied by cathode passivation, therefore, the Ag+ ions complete conversion to the Ag-nanoparticles is unattainable. The two other metal complexes are fully remained unimpaired; the mediated electrosynthesis of the Ag-nanoparticles is carried out well effectively: the Ag-nanoparticles are produced in the solution bulk with a nearly quantitative yield, a theoretical charge being consumed. the [Co(bipy)3]3+-mediated reduction of the Ag+ ions, generated by a silver anode in situ dissolution in the course of single compartment cell electrolysis, is accompanied by the anode metal dispersion and results in the formation of polydisperse Ag-nanoparticles. The summary Ag-nanoparticle current efficiency in the solution bulk comes to 128%. Thus formed Ag-nanoparticles are characterized by using dynamic light scattering, scanning and transmission electron microscopy, and X-ray powder diffraction. The Ag-nanoparticles are spherical, with a mean size of 83 ± 53 nm, or have a form of nanowires, with a length of l = 1216 ± 664 nm and diameter of d = 94 ± 17 nm. The [Co(sep)]3+-mediated AgCl reduction gives ellipsoidal Ag-nanoparticles sized l = 46 ± 19 nm, d = 27 ± 7 nm; the silver crystallite mean size is 20(1)–34.4(9) nm.

Ultra-fine gold (

Efficient mediated electrosynthesis of nanocomposite Au@р(MVCA8+-co-St) (~6 nm), in which ultrasmall Au nanoparticles (Au-NP) were bound in nanocapsules of water-soluble nanoparticles of соpolymer р(MVCA8+-co-St) of tetraviologen calix[4]resorcinol (MVCA8+) with styrene (St), was accomplished by the reduction of AuI in aqueous medium. The quanti- tative reduction of AuI was carried out using the theoretically necessary amount of electricity and was not accompanied by the deposition of metal on the electrode. Radical cations of viologen units MV•+ of the molecule р(MVCA4•+-co-St) adsorbed on the electrode and π-dimers MV•+···MV•+ of π-polymers [р(MVCA4•+-co-St)] n deposited on the electrode act- ed as the reducing agents with respect to AuI. During electrolysis, the nanoparticles agglo- merated to 37—50 nm. The nanocomposite particles dispersed in ethanol had sizes of 72±16 nm and also contained Au-NP with sizes of 51±8 and 19±3 nm. The catalytic activity of the nanocomposite in the reduction of p-nitrophenol with sodium borohydride was demon- strated. A similar reduction of AgCl nanoparticles (~250 nm) led to the formation of silver nanoparticles with crystallite sizes in the range of 7—11 nm, the process was inefficient, however, even when using 250% of electricity, an incomplete reduction of AgCl was still observed.

Methylviologen mediated reduction of Au i ions generated in situ by dissolution of a gold anode in single compartment cell has been used for the electrosynthesis of spherical gold nanoparticles (Au-NPs) stabilized by poly(N-vinylpyrrolidone). The size of Au-NPs was from 15±6 to 27±9 nm, depending on the electrosynthesis conditions. Au-NPs were characterized by cyclic voltammetry, UV-VIS spectroscopy, dynamic light scattering, scanning and transmission electron microscopy.

Platinum nanoparticles (PtNPs) are synthesized by methylviologen-mediated reduction of PtCl2 at the potentials of the MV2+/MV•+ redox couple in 40% aqueous DMF solution. In the absence of stabilizing agents and in the presence of a stabilizer in the form of spherical silica NPs or alkylamine-modified silica NPs (SiO2-NHR), a part of PtNPs (14–18%) are deposited on the electrode while the rest of particles remain in solution to form coarse aggregates which precipitate. In the latter case, PtNPs are also partly bound to form individual ultrafine NPs (3 ± 2 nm) on the SiO2-NHR surface. In the presence of polyvinylpyrrolidone (PVP), the generated PtNPs (18 ± 9 nm) neither aggregate nor deposit on the cathode but are completely stabilized in solution being encapsulated within the PVP matrix. The obtained PtNPs are characterized by the methods of dynamic light-scattering and electron microscopy.

In this article, we report the synthesis of mono- and bimetallic Pd–Ni nanocomposites supported on a multicharged polymeric matrix for catalytic applications. The morphology and catalytic properties of the composites depend on the Pd–Ni ratio. In the Suzuki–Miyaura coupling reaction, the composite with an equal amount of palladium and nickel is the most active and the reaction occurs within six hours in water at room temperature.

C 60 fullerene mediated electroreduction of Au(I) at potentials of the C 60 /C 60 •− redox couple was used to perform the electrosynthesis of an AuNP/C 60 nanocomposite in DCB-DMF (2:1)/0.1 M Bu 4 NCl medium. The nanocomposite consists of separate gold nanoparticles with var...

The possibility of using of molecular oxygen as a mediator in electrosynthesis of metal nanoparticles by reduction of their ions and complexes in aprotic media was demonstrated by the example of electrosynthesis of gold nanoparticles by reduction of Au(I) in DMF. Keywords: Electrochemical synthesis, Molecular oxygen, Mediator, Au nanoparticle

By example of fullerene-mediated electrosynthesis of Ag–C60 nanocomposite in water–o-dichlorobenzene, the possibility of using a liquid–liquid two-phase system for the electro- synthesis of metal nanoparticles has been demonstrated for the first time.

An efficient mediated electrosynthesis of the spherical (85 nm) nanocomposite material Pd@p(MVCA8+-co-St) was carried out in an aqueous medium. Ultrasmall palladium nanoparticles (3—8 nm) are stabilized in nanocapsules of water-soluble nanoparticles of the copolymer p(MVCA8+-co-St) consisting of tetraviologen calix[4]resorcinol (MVCA8+) with styrene (St). The role of the mediator is played by viologen units of a polymer nanoparticle at potentials of the MV2+/MV∙+ redox couple. The high catalytic activity of the nanocomposite material in the reduction of nitrophenol with sodium borohydride is shown.

Electrosynthesis of gold nanoparticles (AuNp) was carried out by methylviologen mediated reduction of Au(I) at potentials of the MV2+/MV˙+ redox couple in water/0.1 M NaCl medium, in the absence and in the presence of stabilizers. In all the cases, AuNp are formed in the solution bulk and are not deposited on the cathode. In the absence of stabilizers, AuNp (14–100 nm) coalesce to give aggregates of various shapes that eventually form a deposit. Sonication reversibly destructs the deposit into nanoparticles. In the presence of alkylamino-modified silicate nanoparticles (SiO2–NHR, 120–160 nm), spherical AuNp (≤20 nm) are bound as inclusions in the SiO2–NHR surface layer. Polyvinylpyrrolidone (40 000 D) stabilizes spherical AuNp with a mean diameter of 5–14 nm. All the particles were characterized by electron microscopy methods (SEM, STEM) and X-ray powder diffraction (XRPD).

The work introduces chemical and electrochemical synthetic routes to obtain Pd(0) nanoparticles (PdNPs) deposited onto silica supports in aqueous media. The former route is performed through reduction of Na 2 [PdCl 4 ] by ascorbic acid in the presence of amino-modified silica nanoparticles (SiO 2 –NH 2 ). The time-dependent variation of pH and the reductant concentration is the simple synthetic route to get uniform deposition of 215 nm sized silica supports by Pd(0) nanoparticles (3–10 nm). The methylviologen-mediated electrochemical synthetic route results in small PdNPs (3–9 nm) located both onto and beyond the silica supports. Thus, the chemical synthetic route provides more homogeneous Pd(0)–SiO 2 –NH 2 aqueous colloids. The results reveal that attractive interactions of amino/ammonium groups of SiO 2 –NH 2 with both [PdCl 4 ] 2− and ascorbate-stabilized Pd(0) seeds are the key reasons for the better Pd(0)-deposition onto silica supports. The chemically deposited Pd(0)–SiO 2 –NH 2 nanoparticles catalyze the chemiluminescence of luminol resulted from the H 2 O 2 -facilitated oxidation in alkaline aqueous solutions.

Efficient electrosynthesis of palladium(0) nanoparticles is carried out in solution by mediated electrochemical reduction of a complex dianion [PdCl4]2– in the DMSO/0.1 M Bu4NCl medium. The mediator function was performed by methylviologen and tetraviologen calix[4]resorcines MVCA-C 8+ with methyl (n = 1), n-pentyl (n = 5), and n-decyl (n = 10) substituents in resorcinol rings at the potentials of redox pairs MV2+/MV•+, MVCA-C 8+ /MVCA-C 4•+ . The resulting metal nanoparticles gradually aggregate to yield coarser particles. The smallest size (255 nm) have metal particles obtained in the presence of MVCA-C 5 8+ for the rest mediators, metal particles of the micron size are formed. Sonication results in disintegration of aggregates to nanoparticles.

Methylviologen mediated electrochemical reduction of AgCl precipitate to Ag0 in the presence of alkylamino-modified silica nanoparticles (SiO2-NHR) in an aqueous medium was performed. The main products of reduction at potentials of the MV2+/MV•+ redox couple are spherical SiO2-NHR/Ag core/shell nanoparticles (size range 120–160 nm) in solution. Keywords: Electrochemical synthesis, Mediator, Methylviologen, Silica/Ag, Core/shell nanoparticles

Based on ferrocene-1,1'-diyl-bisphosphinic acids Fc[P(R)(O)OH]2 (R = H, Me, Et, Ph) in methanol, two types of electrochemically driven molecular rotors are developed. Monoanions of acids are fixed in the cis-conformation due to the presence of an intramolecular hydrogen bond, whereas dianions are fixed in the trans-conformation due to electrostatic repulsion forces. Upon the transformation of monoanions to dianions, the controlled rotation of cyclopentadienyl rings from cis to trans-conformation occurs; the reverse switching leads to the reverse rotation. In one type of rotors, the rotation is controlled by the reversible variation of the solution pH and composition in the electrochemical oxidation-re-reduction cycle of N-phe-nyl-N'-isopropyl-1,4-phenylenediamine; in the other type, the rotation is determined by the one electron oxidation-re-reduction of the ferrocene nucleus in monoanions. The latter rotor type at room temperature can operate stably only for a short time (τ< 1 s) and at longer times is irreversibly destructed during the oxidation stage.

The binding of the amphiphilic 1,5-bis(para-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane dianion (APCO2−) with the octacation of the amphiphilic tetramethylviologen calix[4]resorcin having a methyl radical in the resorcinol ring (MVCA-C 1 8+ ) in 30% aqueous DMSO in a 0.1M NaCl supporting solution was studied by various methods. The dianion was bound at the upper rim of calixresorcin due to the donor-acceptor interactions between the viologen acceptor units and the nitrogen- and phosphorus-centered electron-donor fragments of APCO2− and at the lower rim due to hydrophobic interactions. The composition of the complex depended on the MVCA-C 1 8+ : APCO2− ratio. The complexes aggregated, forming insoluble precipitates. MVCA-C 1 8+ -APCO2− is a system with reversibly electro-switchable aggregation. The starting MVCA- 1 8+ octacation partially bound APCO2−, a certain quantity of both substrates remaining in a free state in solution. The MVCA-C 1 4+· tetraradical tetracation formed as a result of the reduction of MVCA-C 1 8+ completely bound APCO2− due to hydrophobic interactions when the MVCA-C 1 8+ : APCO2− ratio was 1: 3. The reversible oxidation of MVCA-C 1 4+· to the starting MVCA-C 1 8+ octacation brought the system back to its starting state

Binding of an amphiphilic dianion 1,5-bis(p-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane (APCO2−) with an amphiphilic octacation tetra(methyl viologen) calix[4]resorcinol (MVCA8+) in media containing different amounts of water and DMSO using NaClO4 or NaCl as supporting electrolytes was shown for the first time by cyclic voltammetry and spectrophotometry. The stoichiometry of the complex depends on the MVCA8+: APCO2− ratio, medium, and supporting electrolyte. A 1: 1 charge-transfer complex is mainly formed (λmax = 480 nm) in 30% DMSO at a ratio of the compounds of 1: 1. A similar 1: 1 complex of APCO2− with a model compound methyl viologen MV2+ (λmax = 482 nm) is formed under these conditions. A donor-acceptor interaction occurs between the acceptor viologen units and nitrogen-centered electron-donating fragments of the APCO2− dianion. An increase in the content of APCO2− in the solution leads to an additional binding of one (30 vol.% DMSO, water, NaClO4) or two (30 vol.% DMSO, water, NaCl) particles of APCO2− with the hydrophobic fragments of MVCA8+. The complexes aggregate to form insoluble precipitates in aqueous and water-DMSO media. A selective reversible electroswitching from the bound to free state of one of the three bound APCO2− particles was performed when reducing MVCA8+ to MVCA4·+ in a 30 vol.% DMSO/NaCl medium.

Electrooxidation of spatially hindered amines of the series of 2,2,6,6-tetramethylpiperidine in the medium of acetonitrile results in formation of radical cations, aminyl radicals, nitroxyl radicals, and oxoammonium salts identified using the methods of cyclic voltammetry and ESR spectroscopy.

Electrochemical oxidation of 1-haloamines of the 2,2,6,6-tetramethylpiperidine series results in the formation of relatively stable radical-cations, detected by the methods of cyclic voltammetry and ESR spectroscopy. The final products of electrochemical oxidation of these haloamines are stable nitroxyl radicals.

The results of authors on designing electroswitchable supramolecular systems based on calix[4]arenes, calix[4]resorcinols, and transition metal ions and complexes are summarized. We consider systems in which the switching is performed owing to electrochemical reactions both of groups grafted to the macrocycle and bound substrates. Examples of electrochemically switchable luminescence are given.

In the review, we generalize the results of studies on electrochemical oxidation of indolysines, biindolysines, bisindolysines, and bisindolysine podands, which contain two quinoxaline and various numbers of oxaethylene and methylene groups in spacer, with the formation of various products of dehydrocoupling of generating radical cations, namely: redox-active conducting polyindolysine surface films or heterocyclophanes, according to electrochemical oxidation of heterocyclophanes, and a voltage-amperometric study of binding of single-, double, and triple-charged metal ions by them and their precursors.

The methods of cyclic voltammetry, electrolysis, and spectrophotometry were used to study electrochemical properties of (TCAS + Fe3+ + dipy), (CCAS + Fe3+ + dipy), and (CCAS + Fe3+ + [Co(dipy)3]3+) triple systems (where TCAS is n-sulfonatothiacalix[4]arene, CCAS is tetracarboxylate n-sulfonatocalix[4]arene, and dipy = α,α′-dipyridyl) in an aqueous solution. One-electron reduction of Fe(III) in the (TCAS + Fe3+ + dipy) system at pH 2.5 results in electroswitching of iron ions from the lower TCAS ring to the upper ([Fe(dipy)3]2+). Reverse electrochemical switching of the system is impossible due to mediator ([Fe(dipy)3]2+/3+) oxidation of TCAS. Reverse electroswitching of Fe(III) ions from unbound to bound state as ([Fe(dipy)3]2+) with CCAS has been revealed in the system (CCAS + Fe3+ + dipy) (pH 1.7) upon single-electron transfer, whereas reversible electroswitching by the upper rim of CCAS from one complex ion ([Co(dipy)3]3+) to another ([Fe(dipy)3]2+) has been demonstrated in the system ([Co(dipy)3]3+ + CCAS + Fe3+ upon double-electron transfer. In all systems, electric switching was accompanied by synchronous color switching.

The binding of ions Li+, Na+, K+, (group I), Mg2+, Al3+, Ga3+ (group II), Ca2+, Pb2+ (group III) ions, Ba2+ and paraquat by heterocyclophanes containing biindolizine and quinoxaline fragments connected by 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosane spacers, and also their acyclic analogues, in the acetonitrile-0.1 M Bu4NBF4 is studied by cyclic voltammetry. A conclusion is drawn that the ions of the group I are not bound by these compounds; the paraquat is not bound by heterocyclophane with the 5,8,11,14,17-pentaoxageneicosan spacers. For ions of the group II, reversible redox-switchable binding by the macrocycles with the 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosan spacers is observed: the initial compounds show the binding; their radical cations and dications do not. The binding of the ions of the group III and Ba2+ is determined by the macrocycles’ size. In particular, these ions are bound not only by the heterocyclophane with 3,6,9-trioxaundecane spacers but also by its radical cation or dication. The binding results in the corresponding dication stabilization. The heterocyclophane with the 5,8,11,14,17-pentaoxageneicosan spacers demonstrates the redox-switchable binding of Ca2+ and Pb2+ ions; no effect of Ba2+ ions on the cyclic voltammograms of this heterocyclophane was observed. In the ternary system “heterocyclophane with 3,6,9-trioxaundecane spacers + ions of the group II (Al3+, Ga3+) + ions of the group III (Ca2+, Pb2+)” either primary binding of the group III ion Pb2+ or concurrent binding of the ions of the group II and the group III, with the system’s reversible redox-switching from one metal complex to another, was observed.

Phenylindolizinylquinoxalinomonopodands, obtained by the reaction of 1-(phenylindolizin-2-yl)quinoxalin-2(1H)-one with corresponding dibromotrioxa- and dibromopentaoxaalkanes, undergo oxidative dehydrocyclization assisted by molecular iodine to yield new redox-active diindolizinadiquinoxalinacyclooxaalkaphanes. Using CVA, the indolizine fragments of the heterocyclophanes in acetonitrile are found to undergo three-step oxidation with transfer of one electron in each step. The first and the third steps are reversible, whereas the second is irreversible. The oxidation at potentials of the first peak leads to the stable radical cations registered by ESR (g = 2.0024, a2N = 0.26 mT).

The electrochemical properties of n-sulfonatothiacalyx[4]arene (H4XNa4) complexes with [Co(dipy)3]3+ and Fe3+ ions were studied by means of cyclic voltammetry in aqueous solution at pH 2.5. The observed single-electron reduction of [Co(dipy)3]3+ bound extraspherically to the upper rim and Fe3+ ion bound intraspherically to the lower rim of n-sulfonatothiacalyx[4]arene in binary [Co(dipy)3]3+ · H3X5−, H3X5− · Fe3+, and ternary [Co(dipy)3]3+ · H3X5− · Fe3+ heterometal complexes was more difficult than in the free state. The reversible single-electron transfer to the metal ion results in lower binding energy ([Co(dipy)3]3+, ΔΔG 0 = 3.9 kJ/mol) or in full fast dissociation of the complex (Fe3+). The ternary complex in the solution forms the aggregates, in which inner encapsulated Fe(III) and Co(III) ions are not reduced on the electrode. Their quantitative reduction takes place by the relay mechanism of intra- and intermolecular electron transfer through electrochemically generated [Co(dipy)3]2+ outer ions.

The binding of cations Li+, Na+, K+, Cs+, Ag+, Zn2+, Ni2+, Co2+, NH4 + (group I), H+, Mg2+, Al3+, Ga3+ (group II), and Ca2+, Pb2+ (group III) by 21,31-diphenyl-l 2,42-dioxo- 7,10,13-trioxa-l,4(3,1)-diquinoxalina-2(2,3),3(3,2)-diindolizinacyclopentadecaphane (1), which contains two indolizine and two quinoxaline fragments and 3,6,9-trioxaundecanes spacer, and by its acyclic analog (2) was studied using cyclic voltammetry in MeCN/0.1 M Bu4NBF4. It was concluded that the ions of group I are not bound by these compounds, the ions of group II exhibit the reversible redox-switched binding by the carbamoyl groups of the quinoxaline fragments, whereas the ions of group III are bound not only by the initial compounds and radical cations 1 and 2, but also by dication 1. This binding of the Ca2+ and Pb2+ ions stabilizes dication 1.

1H NMR titration and X-ray diffraction analysis revealed that [Ru(bipy)3]2+ forms an outer-sphere inclusion complex with p-sulfonatothiacalix[4]arene in a ratio of 1: 1 in both aqueous solutions and the solid state. According to cyclic voltammograms and fluorimetric data, the outer-sphere association of [Ru(bipy)3]2+ with p-sulfonatothiacalix[4]arene changes the reversible character of the electrochemical oxidation of [Ru(bipy)3]2+ and lowers its emission intensity.

Electrochemical oxidation of 1,11-bis(3-indolizinin-2-ylquinoxalin-2-on-1-yl)-3,6,9-trioxyundecane in 0.1 M Et4NClO4 in MeCN on a glassy-carbon electrode leads to surface films of two types depending on the film formation mode. Oxidation at controlled first-peak potentials (Ep1 = 0.30 V relative to Fc/Fc+) or in the range of potentials −0.60 → +0.40 → −0.60 V, −0.60 → +0.40 → −1.60 → −0.60 V in the polycycling mode forms a redox-active film that covers the entire surface of the electrode. The quinoxaline fragments of the film are reduced irreversibly in the supporting solution, while the indolizine fragments are reduced reversibly, forming stable radical cation states; the latter are recorded by ESR in the form of a singlet with a variable width (g = 2.0025, ΔH = 0.15−0.5 mT). The oxidized (radical cation) form of the film is conductive, while the neutral film is not. An insulating film is obtained when oxidation is performed under rigid conditions (−0.60 → +1.70 → −1.70 → −0.60 V). Both types of film are colored and have nanosized pores (channels), which can play a discriminant role. It is demonstrated (using the discriminant role of pores) that small molecules may be selectively reduced on film-coated electrodes in the presence of bulkier and more reactive substrates.

The oxidative dehydrocyclization of the 3-(indolizin-2′-yl)-2-oxoquinoxaline monopodand performed either electrochemically or under the action of molecular iodine affords new redox-active heterocyclophane consisting of the redox-switchable biindolizine fragment combined with the polyether-bridged π-deficient quinoxaline systems. The single-crystal X-ray diffraction study showed that the trioxaundecane chain of heterocyclophane adopts an extended conformation, and one of the phenyl substituents of the molecule closes the pseudocavity formed by the spacer from one of the sides. The cyclic voltammetric study of heterocyclophane in MeCN and DMF showed the three-step oxidation of the indolizine fragments accompanied by the single-electron transfer in each step. The first and third steps are reversible, and the second step is irreversible. The oxidation at potentials of the first peak gives rise to stable radical cations detected by the ESR method (g = 2.0024, a 2N = 0.26 mT).

The binding of the Li+, Na+, K+, Mg2+, and Co2+ ions by 21,31-diphenyl-12,42-dioxo-7,10,13-trioxa-1,4(3,1)-diquinoxaline-2(2,3),3(3,2)-diindolysine-cyclopentadecaphane containing two indolysine fragments, two quinoxaline fragments, and 3,6,9-trioxyundecane spacer in the acetonitrile/0.1 M Bu4NBF4 environment is studied by the method of cyclic voltammetry. It is demonstrated that the Li+, Na+, K+, and Co2+ ions are not bound by this macrocycle, whereas selective redox-switchable binding is observed for the Mg2+ ions. The macrocycle binds the Mg2+ ions way more efficiently as compared with its radical cation and dication. The indolysinequinoxaline fragments play the determining role in the binding.

The electrochemical reduction of carbonyl-containing methanofullerenes is studied by methods of cyclic voltammetry and ESR with in situ electrolysis in the environment of 0.1 M Bu4NBF4 in o-dichlorobenzene-dimethylformamide (3:1 by volume). It is shown that the one-electron transfer onto the fullerene sphere of these compounds induces opening of the three-membered cycle, which leads to processes of retrocyclopropanation, transfer of the adduct onto the fullerene sphere of another molecule with the formation of bismethanofullerenes, and transformation into fullerodihydrofuran. The totality of competitive processes and the balance between these is defined by the nature of substituents at the exocarbon atom and the experimental conditions. The opening process is interpreted as the intramolecular electron transfer from the fullerene sphere onto the three-membered cycle.

The reactions of fullerene C60 with thiophosphorylated mono-or dialdehydes and N-methylglycine in toluene afforded new thiophosphorylated fullerenopyrrolidines, including those containing the free aldehyde group. The purity and compositions of the reaction products were confirmed by MALDI-TOF mass spectrometry and HPLC. The structures of the reaction products were established by two-dimensional homo-and heterocorrelation NMR experi-ments. The properties of the products were studied by cyclic voltammetry and quantum chemical methods. The Pishchimuka rearrangement in thiophosphorylated derivatives of fullerenopyrrolidines was performed for the first time, and thiol esters of phosphonic acids of fullerenopyrrolidines were prepared.

The electrochemical oxidation of substituted mono-and 3,3′-biindolysines is studied by methods of cyclic voltammetry and electron spin resonance (ESR) combined with in situ electrolysis. In acetonitrile, there occurs easy irreversible electrochemical oxidation and proceed processes of association of generated radical cations via unsubstituted positions of five-membered cycles. Polymeric products of oxidation of 2-arylindolysines, 3-indolysine-2-yl-quinoxalines, and 2,2′-diaryl-3,3′-biindolysines are obtained when cycling potential in the interval −0.3 V → +0.8 V → −1.3 V → −0.3 V (Fc/Fc+). The products deposit on the electrode with the formation of redox-active films that are capable of undergoing reversible oxidation with the formation of stable paramagnetic states registered by the ESR method.

The reactions of 3-acetylquinoxalin-2-one with methyl-and benzylpyridines in the presence of iodine produce the corresponding 3-(2-alkylpyridinioacetyl)quinoxalin-2(1H)-one iodides. Treatment of the latter with triethylamine affords the corresponding 3-indolizin-2-ylquinoxalin-2-ones. Due to the presence of the endocyclic carbamoyl group, the reactions of these compounds with bisalkylating reagents give quinoxaline-containing monopodands and monoalkylation products containing spacers with different lengths and of different nature.

61‐(Dimethoxyphosphoryl)‐61‐(methoxycarbonyl)methano[60]fullerene was produced by using the joint electrochemical reduction of fullerene C60 and (dimethoxyphosphoryl)methoxycarbonyldibromomethane. A few steps of reduction were detected for phosphorylated methano[60]fullerenes. When two electrons per molecule are transferred, the methano fragment is rapidly eliminated (retro‐Bingel reaction). This process involves the step‐by‐step cleavage of two C–C bonds of exo‐carbon with the fullerene shell in combination with the stepwise transfer of other two electrons and a proton to form finally the carbanion of the methano fragment and fullerene dianion.

A new dynamic electroswitchable supramolecular system consisting of tetraferrocene-resorcinarene and viologen has been developed.

The electrochemical reduction of methano[60]fullerenes (61-acetyl-61-(diethoxyphosphoryl)methano-60-fullerene 1, 61-acetyl-61(diisopropoxyphosphoryl)methano-60-fullerene 2, 61-(2,2-diethoxyacetyl)-61-(diethoxy-phosphoryl)methano-60-fullerene 3, 61-phenyl-61(1,2-dioxo-3,3-dimethyl-buthyl)methano-60-fullerene 4 )i no-dichlorobenzene-DMF (3:1 v/v)/0.1 M Bu4NBF4 on a glass–carbon electrode proceeds in a few steps. The reversible transfer of the first electron results in the formation of radical anions registered by ESR method. The subsequent reduction proceeds differently because of the various stability of anionic intermediates. The radical anions of the methanofullerenes 3 and 4 are less stable than the radical anions of compounds 1 and 2 and less stable than the radical anions of methanofullerenes, which contain an ester and/or a phosphonate group. The opening of a cyclopropane ring occurs during the stage of the formation of radical trianions of methanofullerenes 1, 2. The same process for compounds 3, 4 proceeds slowly in radical anions and fast in dianions. The opening of cyclopropane ring for all compounds is not accompanied by the elimination of methanogroup and results in the formation of dihydrofullerenofurane derivatives. The transformation of methanofullerene 3 induced by single electron transfer proceeds via a chain reaction mechanism. © 2004 Elsevier Ltd. All rights reserved.

Applications of voltammetry and electrosynthesis in the chemistry of fullerenes and their derivatives are considered. Effect of structural factors and environment on the reduction potentials of fullerenes and stability of their anion intermediates are analyzed. Emphasis is laid on the reduction of phosphorylated methanofullerenes.

Electrochemical reduction of phthalazines and 1,2,5-thiadiazoles containing nucleofugaceous groups at the carbon α-atoms are studied in aprotic and proton-donating media. Heteroatoms, substituents, and media are found to affect potentials and reaction path for the electroreduction. The factors determining the reductive opening of heterocycles are revealed. In diazines the heterocycle opening in annelated systems is induced by the electron transfer, provided there exist (a) a heteroatom–heteroatom bond and (b) an easily splitting-off group at the carbon α-atom, whose nucleofugacity is comparable with or exceeds that of the chloride ion. Stability of the 1,2,5-thiadiazole cycle toward its reduction is determined by the substituent and the medium nature. On adding a nucleofugaceous group to the molecule, the transfer of two electrons in an aprotic medium results in the heterocycle opening with the formation of iminonitrile; when two easily splitting-off groups are present, the electron transfer makes the cycle decompose into inorganic anions.

The electrochemical oxidation of a number of aminomethylated calix[4]resorcinarenes (AMC) with different substituents at the nitrogen atom and the kinetics of nucleophilic substitution reactions of these compounds with p-nitrophenyl bis(chloromethyl)phosphinate were studied. The reactivity of the ionic associates of AMC in the nucleophilic substitution and the behavior of AMC in electrooxidation are determined by the same factors, namely, the amino-group basicity and the nature of the substituents at the nitrogen atom. These factors influence the ratio of the zwitter-ionic and anionic forms of AMC.

Catalytic electroreduction of several substituted gem-dihalocyclopropanes was studied in the presence of metal salen-complexes by polarography, cyclic voltammetry, and preparative electrolysis. Monohalocyclopropanes (54—59%) and the corresponding allene (5—9%) were the main reduction products. The reaction rate constants were determined. The inner-sphere electron transfer was shown to occur under these conditions.

The electron-acceptor nitrogen and sulfur atoms in 3,4-disubstituted 1,2,5-thiadiazoles are responsible for much decreased reduction potentials and much increased oxidation potentials of these compounds compared with the corresponding carbocyclic derivatives. The thiadiazole ring is resistant to oxidation, and the reversible electron transfer gives rise to fairly stable radical cations. Reductive stability of the heterocycle depends on the nature of its substituents and on the medium: When nucleofuge substituents are present, two-electron transfer in aprotic media results in heteroring opening with iminonitrile formation, whereas in the presence of two readily leaving groups, the electron transfer induces cleavage of the complete heteroring into inorganic anions.

The character of the first stage of reduction of 5-X-5-nitro-1,3-dioxanes 1—10 and 2-X-2-nitro-1,3-propanediols 11 and 12 is independent of the nature of halogen (X = Br, Cl) and substituents in position 2 of the dioxane cycle. The transfer of two electrons to a molecule of compound 1—12 is accompanied by the anionoid elimination of halogen and formation of the anion of nitronic acid. The high mobility of halogen is mainly due to the acceptor nitro group capable of further transformations in the α-position to halogen. The direction of further reduction involving the electron transfer to electrochemically active groups in the aromatic fragment of the molecule is determined by the nature of these groups. Chloro-, bromo-, and iodophenyl-substituted derivatives 4, 5, and 8—10 are reduced as typical halobenzenes. In the case of nitrophenyl-substituted compounds 3 and 7, the dioxane cycle opens to form dianions of p- and m-nitrobenzaldehydes along with the reduction of the nitroso group through the stages of formation of the radical anion and radical anion of the nitroso group. The radical anions of the nitro and nitroso derivatives were identified by ESR.

Four steps of reduction were detected for bis(diethoxyphosphoryl)- and bis(diisopropoxyphosphoryl)methano[60]fullerenes (1, 2) and bis(diethoxyphosphoryl)methano[70]fullerene (3) by cyclic voltammetry in the o-dichlorobenzene—DMF (3 : 1, v/v)/Bu4NBF4 (0.1 mol L–1) system on a glass-carbon electrode. At the first step the reversible transfer of one electron affords stable radical anions 1 and 2 (g = 1.9999, ΔH = 1.9 G). When two electrons per molecule are transferred, the methano fragment is rapidly eliminated (retro-Bingel reaction). This process involves the step-by-step cleavage of two C—C bonds of exo-carbon with the fullerene shell in combination with the stepwise transfer of other two electrons and a proton to form finally the carbanion of the methano fragment and fullerene dianion. For all studied compounds, the elimination rate is much higher than that for bis(alkoxycarbonyl)- and dialkoxyphosphoryl(alkoxycarbonyl)methano[60]fullerenes, which makes it possible to propose bisphosphorylmethane groups as protective in synthesis of new fullerene derivatives.

Electroreduction and electrooxidation of monosubstituted N-methyl[60]fullerenopyrrolidines were studied by cyclic voltammetry and potentiostatic microelectrolysis in the cavity of an ESR spectrometer. Stepwise reversible transfer of three electrons to the fullerenopyrrolidine molecule results in the formation of stable radical anions (according to ESR, g = 2.0000, ΔH = 0.8 G), dianions, and radical trianions (according to ESR, g = 2.0015, ΔH = 1.5 G). The reduction potentials vary over narrow limits depending on the nature of the substituents in the pyrrolidine fragment of the compounds. Electrooxidation is irreversible and occurs in either one or two steps. For compounds containing the aniline, indole, or phenol fragment, the first step is associated with oxidation of these fragments and only after that, is the fullerenopyrrolidine core oxidized. Oxidation of the pyrrolidine fragment is substantially more difficult than that of tertiary amines.

Electrochemical reduction in dimethylformamide of unsymmetrical 1-Cl-4-X-phthalazines and symmetrical 1,4-X2-phthalazines (X = Cl, PhO, MeO, EtO, i-PrO) was studied by voltammetry and electrolysis-ESR. The electron trasfer on 1,4-dichlorophthalazine and unsymmetrical 1-Cl-4-X-phthalazines induces anionoid elimination of Cl and X, pyridazine ring cleavage, and phthalonitrile formation. In this previously unknown process the transfer of two electrons induces cleavage of three σ bonds and formation of two new π bonds. The reduction of 1,4-dialkoxy(diaryloxy)phthalazines involves formation of stable radical anions which undergo no heteroring cleavage. Possible mechanisms of the processes studied were discussed. It was assumed that the same mechanism with pyridazine ring cleavage may be realized with other phthalazine derivatives and heteroannelated pyridazines containing readily leaving nucleofuge groups α to nitrogens.

Fulleropyrrolidine containing a sterically hindered phenolic fragment was synthesized by the reaction of fullerene C60 with N-methylglycine and 3,5-di-tert-butyl-4-hydroxybenzaldehyde. Electrochemical reduction of fulleropyrrolidine-containing phenol 1 and the corresponding phenoxide ion proceeded stepwise to form stable radical anions, dianions, and trianions. The radical anion (g = 2.0000) and the phenoxyl radical (g = 2.0045) obtained by chemical oxidation with lead dioxide were identified by ESR spectroscopy. The electron affinity of fulleropyrrolidine was estimated at 2.58 eV. For the phenoxide ion, the electrochemical gap was determined (ΔE = EIox – EIred = 0.47 V). The heats of formation and the energies of the frontier orbitals of fulleropyrrolidine and its transformation products were evaluated by the PM3 method.