Free propargyl radical: Facile cathodic generation and covalent linkage to solid surfaces

The cathodic reduction of propargyl bromide in regular polar solvents such as N,N-dimethylformamide or acetonitrile (ACN) results in a two-electron scission of the CBr bond. In contrast to this, the use of solvents of higher dielectric permittivity like propylene carbonate (PC) containing tetraalkylammonium iodide as electrolyte permits the quasi instantaneous formation of the corresponding iodide that can be electrochemically cleaved in a different way. Using gold, platinum, palladium or copper under those conditions allows obtaining the propargyl radical at quite low potentials. Unexpectedly, glassy carbon (GC) as cathode material causes a neat splitting of two one-electron transfers (ET) usually observed for most of organic halides as a single two-electron step. A dense propargylation of these solid surfaces was noticed. The propargyl group surface coverage was checked by FTIR, by its derivatization with alkyl ferrocene using azide-yne click chemistry, and by bromine index (coulometric reduction of halogenated surface-grafted layers); its level was found to be (4–6) × 10− 9 mol cm− 2 of the apparent starting electrode area.

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► Easy electrochemical generation of the propargyl radical.
► Dense coverage of solid cathodes.
► Grafting at several solid surfaces (carbon, Au, Pt, Cu, Pd).
► Possibilities to chemically modify grafted layers.