Complexes of Macrocycles and other More Highly Preorganized Ligands

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Abstract

Macrocyclic ligands have traditionally been divided into two classes, those with oxygen donors, such as the crown ethers and cryptands, discovered by Pedersen1 and Lehn,2 and the nitrogen donor macrocycles, first investigated by workers such as Curtis3 and Busch.4 The sulfur-donor macrocycles5–7 resemble the nitrogen donor macrocycles more closely in their coordinating properties, and so tend to be grouped with them. The division into mainly oxygen-donor macrocycles on the one hand, and nitrogen donor macrocycles on the other, derives from a tendency on the part of investigators to study one or the other type of ligand, which in turn rests on the very different types of metal ions which are strongly complexed by the two classes of ligand. The oxygen donor macrocycles tend to complex well with metal ions such as the larger alkali and alkaline earth metal ions, and the larger post-transition metal ions such as Pb(II), Tl(I), or Hg(II). The nitrogen donor macrocycles complex well with transition metal ions, as well as the post-transition metal ions. The sulfur-donor macrocycles are weakly complexing with all metal ions, but complex best with the same group as the nitrogen donor macrocycles. This chapter is not an attempt to cover all aspects of macrocyclic chemistry, but rather an attempt to provide insight into the factors that govern the complexation of metal ions by macrocyclic ligands. For other aspects of macrocyclic chemistry, a selection of excellent books and reviews is available.8–17