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Bicontinuous microemulsions made from oil, water, and surfactants were examined as substitutes for organic solvents in carbon−carbon bond-forming reactions. Conjugated additions of primary alkyl iodides 3a − c to 2-cyclohexen-1-one (4) to give 3-alkyl cyclohexanones 5a − c and cyclization of 2-(4-bromobutyl)-2-cyclohexen-1-one (9) to 1-decalone (10) were mediated by the Co(I)L complex vitamin B12s generated at carbon cloth electrodes under mild conditions. Reaction of the Co(I)L nucleophile with the alkyl halides gives a Co−alkyl complex. Cleavage of the Co−alkyl complexes by using an electrode potential of −0.85 V (all vs SCE) and irradiation with visible light, or a potential of −1.45 V in the dark, were compared. Addition of the resulting alkyl radicals to the activated double bonds gave comparable yields of 3-alkylcyclohexanone 5a − c (70−80% using −0.85 V + light) and 1-decalone (90%, both cleavage modes) 10 in microemulsions and in DMF. Microemulsions containing hexadecyltrimethylammonium bromide (CTAB) gave remarkable stereoselectivity for the trans isomer of 10, while homogeneous DMF and a sodium dodecylsulfate (SDS) microemulsion gave little stereoselectivity.

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Products derived from benzyl radicals or anions were obtained by reduction of benzyl bromide mediated by vitamin B12, Co(salen), and cobalt phthalocyaninetetrasulfonate in a bicontinuous microemulsion and homogeneous solvent. The reactions begin by electrochemical generation of a Co(I) complex (CoIL), followed by oxidative addition of benzyl bromide to give benzyl−CoIIIL. Reductive cleavage of the Co−C bond yields benzyl radicals or anions depending on the potential of reduction of benzyl−CoIIIL. Rate constants of Co−C bond formation (k 1) are correlated with the formal potential E°‘Co(II)/Co(I), indicative of control by the inherent activation free energy of the oxidative addition rather than by reactant distribution between phases in the microemulsion. Vitamin B12 gave a benzyl−CoIIIL intermediate reduced at −1.1 V vs SCE and yielded bibenzyl as the sole product of a radical pathway. The reduction potential of benzyl−CoIII(salen) is negative enough to reduce the benzyl radical to an anion, so reduction of benzyl bromide mediated by Co(salen) gave toluene in the microemulsion and a mixture of toluene and bibenzyl in DMF. Although Co(salen) reacts very rapidly with benzyl bromide, a slow rate of reductive cleavage of benzyl−CoIII(salen) creates a bottleneck in the catalytic pathway. The one-electron catalyst vitamin B12, with a smaller rate of oxidative addition, gives faster catalytic reduction for a given k 1 relative to the two-electron catalyst Co(salen). Thus, a radical or anionic pathway can be chosen by controlling the potential of the benzyl−CoIII reduction. The facile formation of bibenzyl in the microemulsion suggests that it should be applicable to electro-organic syntheses featuring radical-based formation of carbon−carbon bonds.