Influence of electrolyte concentration on coupled chemical reactions Part 1Reduction of CoII(salen)in aprotic solvents

Abstract

The reduction of Co^II(salen) has been investigated using Au microdisc electrodes in DMF containing several electrolytes, concentrations in the range 0.1–100 mM. The kinetics of the Co^II(salen)/Co^I(salen)^- couple are always rapid but the formal potential of the couple depends on the cation of the electrolyte and its concentration. The data may be interpreted in terms of ion pairing between Co^I(salen)^- and the cation of the electrolyte, increasing along the series Bu₄N⁺<Na⁺<Li⁺. In contrast, the formal potential for the Co^III(salen)⁺/Co^II(salen) couple is insensitive to the choice of the electrolyte and its concentration. It is also demonstrated that the rate constant for the reaction of Co^I(salen)^- with BuBr decreases with increased electrolyte concentration and this is interpreted in terms of a decreased nucleophilicity, again due to ion pairing.