Bioinspired hydrogen bond motifs in ligand design: The role of noncovalent interactions in metal ion mediated activation of dioxygen

Hydrogen bonds influence secondary coordination spheres around metal ions in many proteins. To duplicate these features of molecular architecture in synthetic systems, urea-based ligands have have been developed that create rigid organic frameworks when bonded to metal ions. These frameworks position hydrogen bond donors proximal to metal ion(s) to form specific chemical microenvironments. Iron(II) and manganese(II) complexes with constrained cavities activate O-2, yielding M-III (M-III = Fe and Mn) complexes with terminal oxo ligands. Installation of anionic sites within the cavity assists the formation of complexes with M-II/III-OH and M-III-O units derived directly from water. Opening the cavity promotes M(mu-O)(2)M rhombs, as illustrated by isolation of a cobalt(III) analogue, the stability of which is promoted by the hydrogen bonds surrounding the bridging oxo ligands.