The one-electron reduction of primary alkyl iodides at palladium and palladiated surfaces: a facile source of alkyl radicals?

A large palette of primary alkyl halides RI were reduced at smooth palladium electrodes (as well as palladiated copper, platinum and glassy carbon) in organic solvents such as dimethylformamide, propylene carbonate and acetonitrile in the presence of tetraalkylammonium salts. All exhibited under such experimental conditions a very large cathodic activation when compared to bare platinum and glassy carbon. Thus, shifts towards less cathodic potentials were so large that the first reduction step turned to a diffusion one-electron process. Under the described conditions, the reduction of RIs occurred in two one-electron steps, suggesting then the intermediate alkyl radical formation. Microcoulometries at the level of the first step confirmed that the reaction is monoelectronic with quantitative loss of iodide.The transient formation of free radicals is also supported by GC/MS results (presence of R-R and R(-H) type compounds after electrolysis).