The reactivity of two significant classes of organometallic compounds involved in electrochemical processes, namely Co(II) N4-macrocycles and Ru/Os polypyridyl complexes, toward the oxidation of two different electron donor molecules (2-mercaptoethanol and iodine) was investigated using first-principle theoretical methods. Two different descriptors, the donor-acceptor intermolecular hardness and the electrophilicity index, were considered for discriminating the relative reactivity of the different species toward the same electron donor. All of the calculations were carried out using a recent hybrid Hartree-Fock/Density Functional approach (PBE0) and solvent effects were included using a recent version of the polarisable continuum model (C-PCM). The influences of the metal atom, of the chemical environment, and of the medium on reactivity were analysed and compared to the available experimental data.