Thermal intramolecular electron transfer from the ferrocene (Fc) to naphthoquinone (NQ) moiety occurs efficiently by the addition of metal triflates (Mn+: Sc(OTf)(3), Y(OTf)(3), Eu(OTf)(3)) to an acetonitrile solution of a ferrocene-naphthoquinone (Fc-NQ) linked dyad with a flexible methylene and an amide spacer, although no electron transfer takes place in the absence of Mn+. The resulting semiquinone radical anion (NQ*(-)) is stabilized by the strong binding of Mn+ with one carbonyl oxygen of NQ*(-) as well as hydrogen bonding between the amide proton and the other carbonyl oxygen of NQ*-. The high stability of the Fc(+)-NQ*(-)/Mn+ complex allows us to determine the driving force of electron transfer by the conventional electrochemical method. The one-electron reduction potential of the NQ moiety of Fc-NQ is shifted to a positive direction with increasing concentration of Mn+, obeying the Nernst equation, whereas the one-electron oxidation potential of the Fc moiety remains the same. The driving force dependence of the observed rate constant (k(ET)) of Mn+-promoted intramolecular electron transfer is well evaluated in light of the Marcus theory of electron transfer. The driving force of electron transfer increases with increasing concentration of Mn+[Mn+], whereas the reorganization energy of electron transfer decreases with increasing [Mn+] from a large value which results from the strong binding between NQ*(-) and Mn+.