Anodic strategies for the covalent attachment of molecules to electrodes through ethynyl and vinyl linkages.

摘要

Substrates with localized, organic radicals have the ability to attack 'inert' surfaces to form covalent bonds between the substrate and an atom at the surface. These radicals can be generated in electrochemical experiments with substrates bearing an electroactive moiety. The moiety after oxidation (loss of an electron) or reduction (gain of an electron) generates the active radical. Electron transfer reactions at an electrode surface generate a high population of these radicals, thereby facilitating attachment.;The electrochemical oxidations of compounds containing terminal alkynes and alkenes were found to be effective methods for covalent attachment to glassy carbon, gold, and platinum electrodes. Modified electrodes were studied for their fundamental electrochemistry with an emphasis on organometallics at the surface and to determine the effect of weakly coordinating anions in heterogeneous electrochemistry. Ferrocene, Fe(eta5-C 5H5)2, was employed predominantly in this research, as it has robust neutral and cationic states, making it a superior electron transfer agent. A number of other compounds prominent in organometallic electrochemistry, such as ruthenocene (Ru(eta5-C5H5) 2), cymantrene (Mn(eta5-C5H5)(CO) 3), cobaltocenium ([Co(eta5-C5H 5)2]+), and benzene chromium tricarbonyl (Cr(eta 6-C6H6)(CO)3), were also studied at modified surfaces.;A novel method was developed employing the anodic oxidation of ethynyl-lithium compounds to modify electrodes. Oxidation of the carbon-lithium bond leads to an alkyne radical and the loss of lithium ions to solution. The desired radical can be formed either by intramolecular electron-transfer mediation by pendant ferrocenium ions or by the direct oxidation of the ethynyl-lithium bond. These experiments successfully led to the appearance of new surface waves at the electrode. The new surface waves were assigned to the parent molecule of interest based on its electrochemical properties, i.e. its potential, and the electrochemical and chemical reactivity of the redox process.;A second general method was developed for terminal alkynes and alkenes which eliminated the need for chemical pre-treatment and lithiation of the alkyne. The direct oxidation of unsaturated carbon-carbon bonds at higher potentials forms the active radical after loss of a proton. The direct oxidation was extended to the organic compound, tetraphenylporphyrin. Porphyrins are a widely used molecular scaffold in naturally occurring compounds such as chlorophyll and heme, and can be applied in optics and electronics due to their intense optical properties.;These two approaches hold promise as general anodic methods for electrode modification, and for applications in chemical analysis and catalysis.