Transition-Metal Host Complexes Designed for Critical-Locus Accommodation of Organic Guest Molecules–An Approach to a New Kind of Coordination Catalysts Patterned after Enzymes

A family of macrobicyclic ligands has been designed as prototypes of a new class of coordination catalysts. The ligand simultaneously chelates to a metal ion, thereby creating a reactive site, and also serves as host in inclusion complex formation with a potential substrate which acts as a guest. Thus the substrate must be held in critical locus to the active site. The new family of vaulted complexes are designed to facilitate dioxygen binding to cobalt(II) and iron(II) while accommodating an organic guest in a large permanent void. X-ray and NMR studies show that the nickel(II) complexes have the expected commodious void and that they can be expected to form inclusion complexes by hydrophobic interactions.