1. Contribution from Organic Chemistry II, Universität Erlangen, Henkestrasse 42, D-91054 Erlangen, Germany, Hahn-Meitner Institut Berlin, Glienickerstrasse 100, D-14109 Berlin, Germany, Hahn-Meitner Institut Berlin, Rudower Chaussee 5, D-14109 Berlin, Germany, and Physical Chemistry III, TU Darmstadt, Petersenstrasse 20, D-64287 Darmstadt, Germany