Metalated Container Molecules

The coordination chemistry of metalated container molecules is currently attracting much interest, because the properties of such compounds are often different from those of their constituent components. By adjusting the size and form of the binding cavity it is often possible to coordinate coligands in unusual coordination modes, to activate and transform small molecules, or to stabilize reactive intermediates. Such compounds also allow for an interplay of molecular recognition and transition‐metal catalysis, and for the construction of more effective enzyme mimics. Consequently, a number of research groups are involved in the development of new supporting ligands that create confined environments about active metal coordination sites. This research report briefly reviews recent progress in this field including the results of my own group. It is shown that N‐functionalized derivatives of Robson‐type macrocyclic hexaaza‐dithiophenolate ligands form bioctahedral transition metal complexes of the type (L^R)M₂(μ‐L′)]⁺ (M = Mn, Fe, Co, Ni, Zn) with an overall calixarene‐like structure. These complexes are amongst the first prototypes for polynuclear complexes with well defined binding cavities. Since the active coordination site L′ is accessible for a wide range of exogenous coligands, the (L^R)M₂(μ‐L′)] complexes exhibit a rich coordination chemistry. It is demonstrated that the presence of the binding cavity influences many properties of the binuclear (L^R)M^II₂]²⁺ complex fragments, including color, molecular and electronic structure, hydrogen bonding interactions, redox potential, complex stability, and reactivity. The unusual properties of the complexes can be traced back to complementary host‐guest interactions and the distinct size and form of the binding pocket of the (L^Me)M₂]²⁺ fragments.