New perspective of electron transfer chemistry.

A new perspective of electron transfer chemistry is described for fine control of electron transfer reactions including back electron transfer in the charge separated state of artificial photosynthetic compounds and its synthetic application. Fundamental electron transfer properties of suitable components of efficient electron transfer systems are described in light of the Marcus theory of electron transfer, in particular focusing on the Marcus inverted region, and they are applied to design multi-step electron transfer systems which can well mimic the function of a photosynthetic reaction center. Both intermolecular and intramolecular electron transfer processes are finely controlled by complexation of radical anions, produced in the electron transfer, with metal ions which act as Lewis acids. Quantitative measures to determine the Lewis acidity of a variety of metal ions are given in relation to the promoting effects of metal ions on the electron transfer reactions. The mechanistic viability of metal ion catalysis in electron transfer reactions is demonstrated by a variety of examples of chemical transformations involving metal ion-promoted electron transfer processes as the rate-determining steps, which are made possible by complexation of radical anions with metal ions.