Electron Transfer Reactions of Self-Assembled Monolayers of Thio(Phenylacetylene) n -Substituted Chiral Metal−Salen Complexes

This paper describes immobilization of salen ligands in self-assembled monolayers (SAMs) on gold surfaces. The two salen ligands were attached to the gold surface via thio(phenylacetylene) n ( n = 1, 2) substituents. The resulting SAMs have been analyzed using ellipsometry and X-ray photoelectron spectroscopy. These measurements showed that high-density monolayers formed on the gold surface (0.20 and 0.30 nmol/cm 2 for n = 1 and 2, respectively). Mn III Cl, Co III Cl, and Fe III Cl were incorporated in the core of the salen ligands immobilized on a gold electrode. The electron-transfer reactions of these metal−salen monolayers were studied by cyclic voltammetry in tetrahydrofuran, and reversible redox reactions between M III and M II (M = Mn, Co, and Fe) were observed under anaerobic conditions. In the presence of oxygen, the Mn−salen complex underwent an irreversible two-electron reduction. The coverage of the electroactive metal−salen complexes varied from 0.04 to 0.18 nmol/cm 2 depending on the metal. For all three metals, higher coverage values were obtained for the longer (phenylacetylene) n linker ( n = 2) than for the shorter ( n = 1).