THE ELECTROCATALYZED REDUCTION OF FUMARONITRILE IN AQUEOUS-SOLUTION BY 4,4'-DIMETHYL-1,1'-TRIMETHYLENE-2,2'-DIPYRIDINIUM ION

An electrocatalytic strategy for the reduction of activated olefins in aqueous solution has been demonstrated using fumaronitrile as a model olefin. Cyclic voltammetric experiments show that the reduction of fumaronitrile in pH 8.0 Tris is catalyzed by the cation radical of 4,4'-dimethyl-1,1'-trimethylene-2,2/-dipyridinium ion (DMV(2+)). Controlled-potential electrolysis experiments show that the electrocatalytic reduction of fumaronitrile proceeds via a two-electron two-proton pathway to form succinonitrile. Kinetic studies of the catalytic reaction by cyclic voltammetry show that the rate-determining step is the solution electron transfer from DMV(+) to fumaronitrile with a rate constant of 15 M(-1) s(-1). In order to understand better the general applicability of 1,1'-bridged-2,2'-dipyridinium ions as catalysts, molecular modeling was carried out on eight such ions including DMV(2+). The results of these calculations were correlated with previously reported electrochemical data to show that an increase in interplanar twist angle results in a more negative E degrees value, apparently due to the increased importance of inter-ring conjugation in the cation radical. This understanding should aid, within limits, in the rational design of catalysts for a given olefin of interest.