Metal containing molecules

II. Metalated Container Molecules Host Systems and Complex Types 409... 

In recent years, the development of metalated container molecules has also become an attractive research goal (35-38). This is mainly due to the fact that such compounds allow for an interplay of molecular recognition and transition-metal catalysis (39-41). Consequently, several research groups are involved in the development of new receptor molecules that create confined environments about active metal coordination sites. The aim of this review is to highlight recent advances in this area. 

Fig. 2. Schematic representation of the most common architectures of metalated container molecules. The open boxes represent active coordination sites at the metal ions. The bowl-shaped representation of the host molecules should not be confused with the one used for the cyclodextrins.

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

Calixarenes, when in their cone-conformation (54), represent versatile host systems for metalated container molecules and many examples have been reported in the literature (55-61). Reinaud and coworkers have carried out extensive work concerned with calix[6]arenes that are functionalized at the small rim by nitrogen arms (62), aiming to reproduce the hydro-phobic binding site of mononuclear zinc and copper metalloen-zymes. A recent example is the calix[6]arene ligand L1 (Fig. 3), in which a tris(2-methylpyridyl)amine unit covalently caps the calixarene small rim (63). The ligand forms copper complexes of... 

Fig. 13. Schematic illustration of metal-organic molecular squares, assembled from linear organic linkers and 90° metal units (left), linear metal units and organic comers (middle), or linear metal units and 90° metal units (113). The latter two classes have several inner-cavity binding sites and thus fit the definition of metalated container molecules.

The 24-membered Robson-type hexaaza-dithiophenolate ligand H2L19 and its various derivatives have been utilized by Kersting and coworkers (154) as supporting ligands for metalated container molecules with a bioctahedral N3M(/i-S2)2(L )MN3 core structure (Fig. 27). The remainder of this article will now focus on... 

III. Metalated Container Molecules of Binucleating Polyaza-Dithiophenolate Macrocycles... 

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