Synthesis of an Isolable Diphosphaisobenzene and a Stable Cyclic Allene with Six Ring Atoms Phosphorus Compounds, Part 147. This work was supported by the Fonds der Chemischen Industrie and the Deutsche Forschungsgemeinschaft (Graduate College "Phosphorus chemistry as link between different chemical disciplines"). Part 146: C. Peters, F. Tabellion, A. Nachbauer, U. Fischbeck, F. Preuss, M. Regitz, Organometallics 2000, in press.