AbstractCyclic voltammetric studies of clusters (C5H5‐C2C6H4‐R‐p)Co2(CO)6‐n Ln[n=0,2; L=PPh3, P(OEt)3] and (RCH2C)2Co2(CO4) (PPh3)2on Pt electrode are described. The primary reduction (0 / −1) and oxidation (+ 1 / 0) steps are considered as a mono‐electron process for all clusters. For the clusters (C5H5C2C6H4‐R‐p)Co2(CO)6, a good linear relation between reduction potentialEpredand Hammett constant σpof R in the clusters is found. For the clusters (RC2R')Co2(CO)4L2, their radical anions are extremely unstable at room temperature and fragment into a series of mononuclear species, one of which is (RC2R')Co(CO)2PPh3. The reaction of radical anions of (RC2R')Co2(CO)6–n(PPh3)n(n=0,2) with PPh3also produces mononuclear species (RC2R')Co(CO)2PPh3which has been detected by means of cyclic voltammetry and ESR. The influence of R on redox properties of clu