Electrochemistry of ruthenium metallocenes: Part 3. Synthesis and properties of ruthenium [22]paracyclophane complexes with methacrylic acid and methacrylate ester substitutents

Four [22](1,4)cyclophanes bearing one or two methacrylate ethyl ester and methacrylic acid substituents and ruthenium arene complexes of these compounds are synthesized. The structure of the ligands and the complexes is characterized by NMR spectroscopic techniques. For some of the ligands X-ray crystal structure analyses support the assignments. The mono-substituted [22](1,4)cyclophanes prefer to form anti-complexes, with the Ru central atom bound to the unsubstituted aromatic deck. The irreversible electrochemical oxidation of the cyclophanes is studied by cyclic voltammetry, and, in contrast to mono- and divinyl[22](1,4)cyclophanes does not produce permanent films on the electrode. The electrochemical reduction of the complexes proceeds as a two-electron process and produces the kinetically stable corresponding Ru0 species. The anodic oxidation of the title compounds is irreversible and leads to filming of the electrode surface.