1. Contribution from the Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, Department of Chemistry, Supercomputer Institute and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55410, and Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany