Solvent effects on the redox properties of ferrocenoyl-dipeptides

The preparation and characterization of the novel ferrocenoyl-dipeptides, Fc-Asp(OBzl)-Asp(OBzl)-OBzl (5), Fc-Asp(OBzl)-Glu(OEt)-OEt (6) and Fc-Asp(OBzl)-Cys(Bzl)-OMe (7) are reported. In addition, Fc-Asp(OBzl)-OBzl (4) and its free acid, Fc-Asp(OH)-OH (8), were prepared. A crystal structure determination of 8 revealed an extensive H-bonding network involving a solvent molecule and adjacent molecules of 8 and suggests that these complexes are able to form strong hydrogen bonds with solvent molecules. All compounds show reversible one-electron oxidations in solution. The half-wave potential is strongly influenced by the nature of the solvent and correlates with the hydrogen donor ability alpha of the Kamlet-Taft formalism.