Covalently linked scaffold of cobalt corrins on graphite for electrochemical catalysis in microemulsions

Catalytic films were constructed by covalently binding poly-L-lysine (PLL) onto oxidized carbon electrodes and then forming covalent amide linkages fr om PLL to the cobalt corrin vitamin B-12 hexacarboxylic acid [B-12(COOH)(6) ]. Covalent bonds from electrode to PLL and PLL to B-12(COOH)(6) provided g ood stability in microemulsions. PLL-B-12(COOH)(6) films gave reversible el ectron transfer for the Co(II)/Co(I) redox couple and exhibited characteris tic voltammetric features of surface-confined electrochemistry. Formal pote ntials of the Co(II)/Co(I) couple in the films were controlled by the conce ntration of electrolyte in the fluid and by Coulombic interactions with sur factant. PLL-B-12(COOH)(6) films demonstrated excellent catalytic activity in microemulsions for the reduction of vicinal dihalides to olefins, for de chlorination of trichloroacetic acid, and for alkylation of an activated ol efin. Turnover numbers for conversion of dibromocyclohexane to cyclohexene in microemulsions were 3-fold larger for PLL-B-12(COOH)(6) on carbon cloth cathodes than those for the same cobalt catalyst chemisorbed onto nanocryst alline TiO2 cathodes.