DESIGN, SYNTHESIS, AND STRUCTURE OF A MACROCYCLIC TETRAAMIDE THAT STABILIZES HIGH-VALENT MIDDLE AND LATER TRANSITION-METALS

High-valent middle and later transition-metal centers tend to oxidatively degrade their ligands. A series of ligand structural features that prevent discovered decomposition routes is presented. The result of the iterative design, synthesis, and testing process described is the macrocyclic tetraamide H-4[1]. H-4[1] is the parent acid of the macrocyclic tetraamido-N ligand [eta-4-1]4-, which has been shown to stabilize high-valent middle and later transition-metal complexes unavailable in other systems. The features presented provide insights useful to the development of new compounds for homogeneous oxidations and of model compounds for high-valent reactive intermediates in catalytic oxidations in chemistry and biology. The crystal structures of H4[1] and a copper complex of one of its synthetic precursors reveal intramolecular and intermolecular hydrogen bonding patterns that are relevant to recent developments in the ordering effects of hydrogen bonding on solution and solid-state structures. The synthetic value of these ordering effects is discussed.