Oxidation potential of benzylferrocenes and related compounds: Effects of the ortho-methoxy substituent in the phenyl group

Article abstract of DOI:10.1016/S0022-328X(00)00075-9

Oxidation potentials of some ferrocenyl derivatives of type Fc-CHΦOH, Fc-CΦΦ′OH, Fc-CH₂Φ, Fc-CHΦΦ′ [Fc=Fe(η⁵-C₅H₅)(η⁵-C ₅H₄); Φ, Φ′=2,4,6-(MeO)₃C₆H₂, 2,6-(MeO)₂·C₆H₃, 2,5-(MeO)₂·C₆H₃, 2,4-(MeO)₂·C₆H₃, 2-MeOC₆H₄, 4-MeOC₆H₄, C₆H₅] were measured in acetonitrile. All of them exhibited a reversible one-electron oxidation-reduction wave based on the ferrocene-ferrocenium redox couple with a wide range of shift. Compounds having ortho-methoxy groups showed lower redox potentials than those of compounds having para-methoxy groups. The X-ray crystal structure of Fc-CHΦ₂^a showed that the ortho-methoxy oxygens were situated very close to the central carbon, and there is a possibility that one of the oxygen lone-pairs interacts with the antibonding orbital of C-Fc σ-bond. Some other possibilities are also discussed.