Large rings metal complexes

A feature of the metal-ion chemistry of these large ring macrocycles is thus the structural diversity which may occur from one system to the next. This diversity can result directly from small changes in the structure of the cyclic ligand and is also aided by the inherent flexibility of the large rings involved. It is clearly also influenced by the nature of the other ligands available for complex formation. 

Until now, only two families of ligands have been realized where both P groups are attached to side chains, probably because the resulting metal complexes have relatively large chelate rings which usually are not suitable for enantioselective catalysis. A cursory inspection of the ligands depicted in Fig. 25.14 shows that, due to steric bulk of the ferrocene backbone, both diphosphines probably have sufficiently restricted flexibility so that good stereocontrol is still possible. 

Particularly noteworthy examples are Entries 8 and 9 in Table 3.19 these represent a diastereoselective RCM in which the stereoselectivity is controlled by the catalyst [886]. Entries 17, 23 and 24 (Table 3.19) illustrate the use of RCM for the solid-phase synthesis of lactams [894]. RCM induces both ring closure to the lactam and cleavage from the support. Although elegant at first glance, the usefulness of this methodology will be limited if the products must be used without further purification (as is usually the case for compound libraries prepared by parallel synthesis). Because relatively large amounts of catalyst are required, the crude products will only be acceptable for assays in which transition metal complexes do not interfere. 

Phospholide ions can form metal complexes with different coordination numbers / -complexation is characteristic for their aromatic behavior. The first 7 -complex with Mn(CO)3 (7) was reported in 1976. The ring in some cases (e.g., in 7) is not strictly planar. In 7, the P atom is displaced by 0.041 A from the plane of the carbon atoms. The large number of... 

A review of the stabilities and catalytic properties of binuclear metal complexes of large-ring N,0 macrocycles concentrates on the iron(II) and iron(III) complexes of (184) and (185). ... 

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