Viatcheslav Jouikov

Novel method for grafting alkyl chains onto glassy carbon. Application to the easy immobilization of ferrocene used as redox probe.

Primary alkyl iodides (RI) have been found to react with a cathodically charged glassy carbon surface at potentials more negative than -1.7 V vs Ag/AgCl. In aprotic solvents, this reaction results in grafting of the alkyl chains onto carbon. It is proposed that the process corresponds to the cathodic charge of graphitized and fullerenized zones present in carbon followed by a displacement reaction (analogous to a nucleophilic attack) toward alkyl iodides. This new mode of grafting is applied to the immobilization of ferrocene used as an electrochemical probe. The present work points out the reaction of ω-iodoalkylferrocenes and quantifies the level of grafting of alkyl chains via this promising method for modification of carbon surfaces. Coverage levels were found to be high, reaching the apparent surface concentrations of 8 × 10(-9) mol cm(-2). These large values are explained on the basis of swelling of the interface provoked by progressive charging of the carbon surface via insertion of tetraalkylammonium cations concomitantly with the substitution process. Alkylferrocene layers deposited onto carbon were found to be chemically and electrochemically stable.

Electrocatalytic dimerisation of PhBr and PhCH2Br in [BMIM]+NTf2− ionic liquid

Abstract The preparative electrocatalytic homocouplings of PhBr and PhCH 2 Br, yielding in biphenyl and 1,2-diphenylethane, respectively, were performed using NiCl 2 (bipy) complex in new reusable media for electrosynthesis, [BMIM]NTf 2 .

Novel stannatranes of the type N(CH2CMe2O)3SnX (X = OR, SR, OC(O)R, SP(S)Ph2, halogen). Synthesis, molecular structures, and electrochemical properties.

The syntheses of the stannatrane derivatives of the type N(CH(2)CMe(2)O)(3)SnX (1, X = Ot-Bu; 2, X = Oi-Pr; 3, X = 2,6-Me(2)C(6)H(3)O; 4, X = p-t-BuC(6)H(4)O; 5, X = p-NO(2)C(6)H(4)O; 6, X = p-FC(6)H(4)O; 7, X = p-PPh(2)C(6)H(4)O; 8, X = p-MeC(6)H(4)S; 9, X = o-NH(2)C(6)H(4)O; 10, X = OCPh(2)CH(2)NMe(2); 11, X = Ph(2)P(S)S; 12, X = p-t-BuC(6)H(4)C(O)O; 13, X = Cl; 14, X = Br; 15, X = I; 16, X = p-N(CH(2)CMe(2)O)(3)SnOSiMe(2)C(6)H(4)SiMe(2)O) are reported. The compounds are characterized by X-ray diffraction analyses (3-8, 11-16), multinuclear NMR spectroscopy, (13)C CP MAS (14) and (119)Sn CP MAS NMR (13, 14) spectroscopy, mass spectrometry and osmometric molecular weight determination (13). Electrochemical measurements show that anodic oxidation of the stannatranes 4 and 8 occurs via electrochemically reversible electron transfer resulting in the corresponding cation radicals. The latter were detected by cyclic voltammetry (CV) and real-time electron paramagnetic resonance spectroscopy (EPR). DFT calculations were performed to compare the stannatranes 4, 8, and 13 with the corresponding cation radicals 4(+•), 8(+•), and 13(+•), respectively.

Formation and Properties of a Bicyclic Silylated Digermene

In the presence of PMe3 or N-heterocyclic carbenes, the reaction of oligosilanylene dianions with GeCl2⋅dioxane gives germylene–base adducts. After base abstraction, the free germylenes can dimerize by formation of a digermene. An electrochemical and theoretical study of a bicyclic tetrasilylated digermene revealed formation of a comparably stable radical anion and a more reactive radical cation, which were characterized further by UV/Vis and ESR spectroscopy.

Reversed redox generation of silyl radicals in a four-electrode flow-through EPR spectroelectrochemical cell

A flow-through four-electrode EPR spectroelectrochemical cell was developed which allowed the observation of silyl radical formation in apparently multielectron electrochemical processes, in which these species could not be detected directly because of the high driving force of their further reduction/oxidation leading to non-paramagnetic products. Silyl radicals thus generated were characterized by spin trapping with alpha-phenyl-N-tert-butyl nitrone (PBN), intramolecular spin trapping or by direct detection. The overall multielectron process is realized in the first, generating, compartment of the cell and the ionic species formed are then transformed into the corresponding radicals in the second compartment via a one-electron redox process in the opposite direction, e.g. two-electron reductions of Ph(3)SiCl or Et(3)SiCl followed by one-electron oxidation of the resulting Ph(3)Si(-) or Et(3)Si(-) anions (+2e/-e process). These radical species were then identified as their secondary paramagnetic products or by their spin trapping with PBN. Using (2-[cyclohex-3-enyl]ethyl)dimethyl chlorosilane in this process, the formation of the silicon-centered radical and its intramolecular addition across the internal double bond were evidenced by spin trapping. The reduction of electrophilic silicon intermediates issued from the oxidation of Ph(3)SiSiPh(3) (-2e/+2e process) resulted in Ph(3)Si* radicals trapped with PBN. The reduction of the electrochemically prepared persistent dication of a stable disilene, thiatetrasilacyclopentene, allowed generation of a disilene cation radical characterized by EPR.

The anodic acetoxylation of alkylarylselenides

Abstract Electrooxidation of alkylarylselenides in methanol in the presence of sodium acetate leads to the acetoxylation of the methylene group of selenides.

Graphene: Large scale chemical functionalization by cathodic means

Abstract Large amounts of graphene were electrochemically functionalized in an adapted frit-separated two-compartment electrolysis cell. The employed technique corresponds to that of a fluidized bed with a dynamic suspension of graphene maintained by an efficient stirring system. A large collector electrode (e.g. a mercury pool or a glassy carbon plate) polarized at a potential adapted to the chemical modification is placed at the center of the cathodic compartment. Modifications are based on two different types of electrochemical reactions: either i) generation of free radicals in situ adding to graphene or ii) the cathodic charge of graphene at the potentials

Superoxide-stable ionic liquids: new and efficient media for electrosynthesis of functional siloxanes

The electrogeneration of diorganylsilanones from difunctional precursors Y(CH(2))(3)(Me)SiX(2) and Ph(2)SiX(2)(Y = NH(2), CF(3), CN; X = Cl, OEt, OMe), performed in the presence of hexamethyldisiloxane or hexamethylcyclotrisiloxane (D(3)) in the ionic liquids [C(5)H(5)NC(8)F(18)].NTf(2), [C(5)H(5)NC(18)H(38)].NTf(2) and Me(3)BuN.NTf(2), which reveal high solubility of oxygen and are inert toward superoxide anion, allows functionalized siloxanes to be produced selectively in good isolated yields.

Electrochemical synthesis of cyclic alkylsilanes

The electrochemical reduction of aliphatic α,ω-dibromides in the presence of polychlorosilanes of the formula RnSiCl4−n(n = 0, 2) was shown to afford heterocyclic silicon compounds in good yield (up to 91%). In contrast to non-electrochemical methods of synthesis of silacycloalkanes, based on the ring closure of terminal unsaturated compounds, the electrochemical route does not produce α-methylated byproducts and the heterocycle formation occurs quite selectively. The yield of cyclic organosilicon compounds goes through a maximum for 1,1-dimethyl-1-silacyclopentane (91%) and roughly decreases for 1,1-dimethyl-1-silacyclobutane (18%) and 1,1-dimethyl-1-silacycloheptane (57%). The formation of 5-silaspiro[4,4] nonane by the electrochemical process occurs with high selectivity despite the multitude of possible reaction pathways and the high probability of polymer formation due to the high functionality of the silicon. The relatively high selectivity of the electrochemical ring closure is suggested to be due to the orientating effect of an electrode in the course of an irreversible reduction of a CHal bond in the monosilylated intermediate. A possible mechanism for the process is discussed.

Covalent Grafting of Silatranes to Carbon Interfaces

Covalent Si-C grafting of a silatrane cage to a carbon-based interface provides a truly conjugated benzyl-type system in which the 3 c-4 e orbital of the silatrane interacts with the macroscopic π-type substituent (graphite Csp2 network) through hyperconjugation. This process, studied by voltammetry, EIS, FTIR, SEM and DFT modeling, allows one to build carbon-based conducting interfaces with electronically conjugated molecular extensions. Non-conjugated covalent grafting of an alkyl silatrane moiety provides chemically stable functional interfaces that have good promise for electrochemically-driven applications, for example, electrochemical spin-writing.