1. Contribution from the Department of Chemistry, Stanford University, Stanford, California 94305, Department of Chemistry, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, Department of Microbiology and Enzymology, Technical University of Delft, 2628 BC Delft, The Netherlands, and Leiden Institute of Chemistry, Gorlaeus Laboratories, 2300 RA Leiden, The Netherlands