1. Laboratory of Molecular Catalysis, Institute of Chemistry, UFRGS, Av. Bento Gonçalves, 9500 Porto Alegre 91501-970 RS, Brazil, Departamento de Química, UFSM, Santa Maria, RS, Brazil, Department of Chemistry, University of Toronto, Ontario, Canada M5S 3G3, and Instituto de Química, UNICAMP, CP l6154 Campinas 13083-970 SP, Brazil