1. Department of Organic and Molecular Inorganic Chemistry, Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, DSM Research, Life Sciences-Advanced Synthesis, Catalysis & Development, P.O. Box 18, 6160 MD Geleen, The Netherlands, and Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany