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 = me thyl, 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 follow ed by an irreversible chemical reaction, which is the hydrolysis of N- R-4-cyanopyridiniumpentaammineruthenium(III) (A) to N-R-4-carboxamidep yridiniumruthenium(III) (B) with the k(fl) values depending on the typ e of alkyl group. The E(1/2) values are not significantly influenced b y the nature of the alkyl group. At more negative potential (ca -0.5 V /SCE), B undergoes an electrochemical reduction followed by an aquatio n reaction to produce aquopentaammineruthenium(II) and free N-R-4-carb oxamidepyridinium. The amide was identified by comparison of its cycli c voltammogram and UV-vis spectrum with that of a sample prepared by c hemical reaction. The results were also discussed by comparison with o ther systems, and show that nitrile-amide conversion catalysed by pent aammineruthenium(II) complexes is possible.