1. Contribution from the Center for Catalytic Olefin Polymerization, Stratingh Institute for Chemistry and Chemical Engineering, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands, Molecular Materials, Radboud University Nijmegen, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands, and Department of Chemistry, Moscow State University, Vorobjovy Gory, 119899 Moscow, Russia