Kinetics of the forward and reverse processes of the title ligand substitution reaction have been studied in the presence of the SB4.5G dendrimer. Results are in agreement with expectation, according to a two-state model. These results are the consequence, for the forward process, of the negative charge of one of the reactants, (iron complex), and the positive charge of the other (ruthenium complex). This produces a spatial separation of the reactants in the presence of the negatively charged dendrimer. The reverse process becomes slower in the presence of the dendrimer because of the dielectric saturation in the close vicinity of the dendrimer. This hinders the charge separation implicit in the reverse process. (c) 2006 Elsevier B.V. All rights reserved.