1. Institute of Organic Chemistry, Department of Chemistry, University of Basel, St.-Johanns-Ring 19, CH-4056 Basel, Institute of Physical Chemistry, Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, and Max-Planck-Institut für Kohlenforschung, Kaiser Wilhelm-Platz 1, D-45470 Mülheim/Ruhr