Dianions from Cyclophanes with Unsaturated Bridges; Cyclic Conjugation in 22-38 n-Electron Perimeter Systems

A series of. new c:yclophanes with unsaturated bridges, formally containing it-systems with 18-48 it-electrons was synthesized. Several of these cyclophanes containing 4n perimeters can be reversibly reduced to their dianions with 4n + 2 perimeters. This reversible two-electron process can conveniently be studied by cyclic voltammetry. The electrochemical data reveal a chemically significant difference between the neutral 4n and 4n+2 systems even for large n. A good correlation between calculated energies of the LUMO orbitals and the reversible reduction potentials has been obtained. Recent theories of resonance energies in neutral molecules and dianions with conjugated perimeters have been tested. The question whether resonance energies or more simply the frontier orbitals should be used to rationalize the behavior of the cyclophanes and their dianions is discussed.