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Various nitrophenyl-containing organic layers have been electrografted to glassy carbon surfaces using diazonium chemistry to elucidate the extent by which the layer structure influences the solvent (i.e., acetonitrile) accessibility, electroactivity, and chemical reactivity of the films. For most of these films, cyclic voltammetric and impedance spectroscopy measurements show that the electron-transfer process at the electrode is facile and independent of film thickness and structure. This is consistent with the occurrence of self-mediated electron transfers throughout the film with nitrophenyl groups serving as redox stations. Importantly, this behavior is seen only after the first potential sweep, the effect of which is to increase the porosity of the layer by inducing an irreversible desorption of nonchemisorbed material along with a reorganization of the film structure. From a kinetic point of view, the radical anions of surface-attached nitrophenyl groups are reactive toward the residual water present in acetonitrile. Thin layers (thickness of 1 to 2 nm) containing redox-active groups only in the outer part of the layer are protonated two to three times as fast as groups located in a more hydrophobic but still solvent-accessible inner layer. Hence, kinetic measurements can detect small differences in the layer environment. Finally, a deconvolution of the cyclic voltammetric response of an electrode grafted from 4-nitrobenzenediazonium discloses that roughly 25% of the overall signal can be attributed to the presence of 4-azonitrophenyl moieties introduced during the electrografting process.

During the last decades chemists have witnessed the development of thousands of new catalytic reactions driven by need and interest from both industrial and academic settings. Asymmetric catalysis has been one of the focus areas as a result of the increased need for optically active compounds in life science. Many catalytic asymmetric processes are based on metal complexes and rely on activation modes such as Lewis acid catalysis, atom-transfer catalysis, as well as s-and p-bond insertions. Recently, organocatalysis [1] has emerged as a powerful source of enantioselective transformations and has led to the development of a-,[2] b-, [3] g-, [4] and SOMOactivations, [5] as well as cascade, domino, and tandem reactions. [6] Aromatic compounds are ubiquitous as medicines and functionalized materials, and are often formed by electrophilic substitution reactions. [7] Friedel-Crafts alkylations, in particular of highly nucleophilic aromatic compounds such as phenols and anilines, are difficult owing to the regioselectivity and the competitive nucleophilic heteroatoms, which lead to undesired alkylation products. The application of copper catalysis to direct the substitution meta to an amido group through dearomatizing oxy-cupration [8] provides a recent example of where selectivity has been circumvented. Additionally, it has been shown by Gaunt and co-workers that para-substituted phenols can be converted into highly functionalized chiral molecules through oxidative dearomatization and intramolecular enamine catalysis.[9] Breaking aromaticity changes the reactivity from nucleophilic to electrophilic, [10] and thus makes it susceptible to addition of systems such as enamines.Electrochemical reactions often follow environmentally friendly protocols because electrons, as reagents, are inherently pollution free. The ability of electrochemistry to reverse the polarity of a functional group-by selective removal or addition of electrons-makes it thus possible to induce reactions of otherwise nonreactive molecules.[11] Successful combinations of electrochemistry and metal catalysis or mediated electron-transfer processes have been reported in numerous cases, [11] although the risk of having electrode fouling is always present. For example, palladium metal deposition on the cathode has been observed from the reduction of palladium(II), which is generated at the anode, in an undivided cell. [12] Organocatalysts are stable organic molecules and many stereoselective organocatalytic reactions are performed under conditions not possible for metalcatalyzed reactions. We thus anticipated that it might be possible to combine organocatalysis with anodic molecular transformations. [11b, 13] Herein, the combination of electrochemistry and asymmetric organocatalysis is presented. This new concept is demonstrated by a direct intermolecular a-arylation [14] of aldehydes using electron-rich aromatic compounds providing meta-alkylated anilines-a transformation not possible by Friedel-Crafts reactions of anilines (Scheme 1). We show the poten...

A diazonium salt-based strategy is employed to form a covalently attached multilayer of diphenyl disulfide on the surface of single-walled carbon nanotubes (SWCNTs) or multiwalled carbon nanotubes (MWCNTs). The interlayer S−S bonds are subsequently degraded reductively to produce essentially a single layer of thiophenols (or closely related derivatives) on the nanotube surface. The functionalization is achieved in what is effectively a one-pot procedure since the involved transformations are performed without intermediate workup. This “formation−degradation” modification approach is unique in the sense that it allows the generation of a thin well-defined molecular layer in spite of the involvement of highly reactive radicals in the first step. Transmission electron microscopy and thermogravimetric analyses support the approach proposed and reveal that a significant initial functionalization is achieved. In UV−vis spectroscopy, the disappearance of the Van Hove singularities of the SWCNT after the reaction is consistent with a covalent sidewall functionalization. Moreover, the resulting thin layer of thiophenols is reactive forming Au−S bonds with a macroscopic Au surface. Finally, the peripheral thiophenol groups of the MWCNT are employed as chemical linkers for anchoring gold nanoparticles and rods in a site-selective manner.

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