1. Institute of Organic Chemistry; University of Regensburg; Universitaetsstr. 31 93040 Regensburg Germany
2. Institute of Chemistry-Inorganic Chemistry; TU Chemnitz; 09107 Chemnitz Germany
3. Department of Chemistry; University of Milan; Via C. Golgi 17 20133 Milan Italy
4. Current address: Department of Chemistry; University of Hamburg; Martin-Luther-King-Platz 6 20146 Hamburg Germany