Electrocatalytic reactions in organized assemblies: Part III. Reduction of allyl halides by bipyridyl derivatives of cobalt in anionic and cationic micelles

Reduction of allyl halides to 1,5-hexadiene at glassy carbon electrodes was catalyzed by tris(2,2'-bipyridyl) cobalt(II) and tris(4,4'-dimethyl-2,2'-bipyridyl)cobalt(II) in aqueous solutions of 0.1 M SDS or 0.1 M CTAB. An organocobalt(I) intermediate was observed by its separate voltammetric reduction peak in each system studied. This intermediate undergoes an internal redox reaction to form 1,5-hexadiene and Co(II). Small micellar enhancements of reaction rates found for tris(2,2'-bipyridyl) cobalt(II) in 0.1 M CTAB can be attributed to reactant compartmentalization in the micelles. Observed chemical rates followed the order CTAB > SDS = acetonitrile. For tris(4,4'-dimethyl-2,2'-bi-pyridyl) Co(II) in CTAB, catalysis was limited by adsorption of the Co(I) form at the electrode. Preliminary work with bis(2,2'-bipyridyl)-(4,4'-dihexadecyl-2,2'-bipyridyl)cobalt(II) showed that its catalytic utility in 0.1 M SDS was equivalent to that of the most efficient system studied, i.e. tris(2,2'-bipyridyl)Co(II) in 0.1 M CTAB.