Container Molecules Host Systems and Complex Types

Metalated Container Molecules Host Systems and Complex Types 

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 

The smaller p -tert-butyl-calix [4] arenes have a rich coordination chemistry as well (65). Of these, however, only the upper-rim modified calixarenes seem to support metal complexes with confined binding sites (66), except in those cases where the lower-rim substituents form an appended cavity. Thus, Matt and coworkers have reported (67) a pocket-shaped calix[4]arene ligand L2 bearing two lower-rim [( S)-l,l -binaphthalene-2,2 -diyl)] phosphite moieties (Fig. 4). This ligand reacts readily with [ Pd(j73-C3H5)C1 2]/NH4PF6 to produce the complex [Pd(L2)fi/3-allyl)]PF6 (2). In contrast to the calix [6] arenes described above, 

Recently, Atwood and coworkers reported a series of metal-organic analogs of multimeric nanocapsules based on resor-cin[4]arenes (76) and pyrogallol[4]arene units (77). These containers contain several metal atoms in the hydrogen-bonded seam connecting the capsule units and it was demonstrated that metal 

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

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