Reactivity of Long Chain α,ω-Dibromoalkanes at Palladized Solid Cathodes: Homocoupling vs Oligomerization

Abstract

Copper-palladium (Cu-Pd) and silver-palladium (Ag-Pd) systems are used as cathode materials for reducing long chain α,ω -dibromoalkanes [Br- (CH 2 ) n -Br] with n > 3. Such interfaces globally permit the cleavage of the two C-Br bonds in a single two-electron process. A spectacular potential shift (ΔE) is obtained in comparison with glassy carbon electrodes at which the total reduction corresponds to a four-electron process. Such potential shifts are typically of the order of 1 V. In particular, cathodic reactions are easily achieved at Ag-Pd interfaces. Under these conditions, supporting evidences are given for the formation (according to simultaneous or sequenced processes) of a transient α,ω -biradical with different lengths of the alkyl chain (6 < n < 12). Macroelectrolysis data show that palladized interface reactions give rise to heterogeneous couplings and, markedly, the formation of homodimers. Reductions of α,ω -dibromoalkanes in the presence of copper-palladium, palladium, and silver-palladium fine powders efficiently induce the deposit of Cu, Pd, and Ag nanoparticles at chemically inactive electrified surfaces (glassy carbon and graphite). © 2009 The Electrochemical Society.