1. Kekulé-Institute for Organic Chemistry and Biochemistry, University of Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany
2. Institute for Organic Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig, Germany
3. Institute for Inorganic Chemistry, University of Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany