1. Contribution from the Institute for Chemical Reaction Science, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-77, Japan, Central Research & Development Department, Experimental Station, E. I. DuPont de Nemours and Company, Wilmington, Delaware 19880, and Department of Organic and Molecular Inorganic Chemistry, Groningen Centre for Catalysis and Synthesis, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands