THE REDOX BEHAVIOR OF FERROCENE DERIVATIVES .13. FLUORENYL FERROCENES

The electrochemical behaviour of a series of 2,7-substituted-9-fluoren yl-ferrocenes has been studied. Irrespective of the inductive effects played by the different substituents of the fluorenyl fragment, all of them undergo a chemically reversible one-electron removal at almost c oincident potential values. Upon exhaustive oxidation, the original re d complexes turn orange-brown and the oxidised solution is EPR silent at liquid nitrogen temperature. Mass spectrometry confirms that the el ectrogenerated cations maintain the original molecular frame. In order to account for the fact that the constancy in redox potentials and th e EPR inactivity at 77 K of the oxidised species, both of which prelud e an iron-centred oxidation, conflict with the orange colour of the ox idation products (instead of the usual blue-to-green colour of ferrici nium species), which preludes a ligand-centred oxidation, a theoretica l EHMO analysis was performed. In spite of some uncertainty bound to t he energy scale of the MO ordering, a metal-centred oxidation seems fa voured over a ligand-centred process.