ELECTROCHEMICAL-BEHAVIOR OF (N-R-4-CYANOPYRIDINIUM)PENTAAMMINERUTHENIUM(II) DERIVATIVES IN ACIDIC MEDIUM - HYDROLYSIS OF COORDINATED NITRILES

The electrochemical behaviour of N-R-4-cyanopyridinium (4-rcp) (R = methyl, decyl, dodecyl or benzyl) coordinated to pentaammineruthenium(II) in CF3COOH-CF3COONa (mu = 0.1 M, pH 3) aqueous medium was studied by means of cyclic voltammetry and constant potential electrolysis. The electrochemical oxidation of the metallic centre (E(p) ca 0.51 V/SCE) can be described as a reversible monoelectronic charge-transfer followed by an irreversible chemical reaction, which is the hydrolysis of N-R-4-cyanopyridiniumpentaammineruthenium(III) (A) to N-R-4-carboxamidepyridiniumruthenium(III) (B) with the k(fl) values depending on the type of alkyl group. The E(1/2) values are not significantly influenced by the nature of the alkyl group. At more negative potential (ca -0.5 V/SCE), B undergoes an electrochemical reduction followed by an aquation reaction to produce aquopentaammineruthenium(II) and free N-R-4-carboxamidepyridinium. The amide was identified by comparison of its cyclic voltammogram and UV-vis spectrum with that of a sample prepared by chemical reaction. The results were also discussed by comparison with other systems, and show that nitrile-amide conversion catalysed by pentaammineruthenium(II) complexes is possible.