1. Institute of New Chemical Problems, Russian Academy of Sciences, Chernogolovka, Moscow region, 142432 Russia, Institut für Organische Chemie der Universität Erlangen-Nürnberg, Henkestrasse 42, D-91054 Erlangen, Germany, and Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan