Catalytic effect of transition metal(II)-N,N′-bis(naphthaldehyde) diimines on reduction of thionyl chloride

A series of transition metal(II) complexes, such as 1,2-bis(naphthylideneimino)ethane [M(II)(NAPET)], 1,3-bis(naphthylideneimino)propane [M(II)(NAPPR)], 1,4-bis(naphthylideneimino)butane [M(II)(NAPBU)I and 1,5-bis(naphthylideneimino)pentane [M(II)(NAPPE)I (M= Co, Cu, Ni), are synthesized. Catalytic effects of these complexes for the reduction of thionyl chloride on a glassy carbon electrode are evaluated by determining kinetic parameters with cyclic voltammetry. The charge transfer process during the reduction of thionyl chloride is affected by the concentration of catalysts. Some tetradentate Schiff base M(II) complexes show catalytic activities for the reduction of thionyl chloride. The catalytic effects are demonstrated from a shift of the reduction potential for thionyl chloride towards a more positive direction and an increase in peak current. Significant improvements in the cell performance have been noted in terms of both thermodynamic and kinetic parameters for the thionyl chloride reduction. An exchange rate constant, k(o), of 1.24 x 10(-8) cm/s was observed at a bare electrode, while larger values of 0.23-1.69 X 10(-7) cm/s were observed at the catalyst-supported glassy carbon electrode. Thermodynamic and kinetic parameters for thionyl chloride reduction are affected by the chelate ring size of ligands in the metal(II)-Schiff base complexes used as a catalyst. (C) 2000 Elsevier Science B.V. All rights reserved.