Generation of metal-free macrocycles

when we say that, for instance, a kinetic coordination template effect is responsible for the production of some product, it does not mean that a possible contribution from the thermodynamic coordination template effect is ruled out. The role of the matrix does not depend on one or other of the two coordination template effects prevailing. It consists not only in the strict suppression of side effects, but also in directing the process to its most favourable pathway [2, 4]. 

In the examples described so far, where a metal ion is used as template, macrocyclic organic compounds are isolated as complexes. There are also many template processes in which the organic product formed is isolated in the metal-free state. Frequently different templates allow the building up of the same product from the same ligsons, which may then be isolable as a coordination compound or in the metal-free state, depending on the nature of the metal ion. This is illustrated by the assembly of the macrocyclic system H2LIO from diaminomaleodinitrile and 3-ethoxyacroleins in the presence of nickel(II), copper(II), or chromium(III) (Eq. 1.5) [47-49]. 

It should be noted that a metal complex is most commonly the final product when synthesising polyazamacrocyclic compounds. However, as a rule, crown ethers synthesised by template procedures are isolated in the metal-free state. 

After dissolving this salt in water and adding NH4PF6, the metal-free compovmd HsLMIPFeJs can be isolated. This readily forms complexes with other metals [50]. 

The possibility of demetallating complexes is of special importance in cases where only one or a limited number of centres may be used for the synthesis of the macrocycle in the form of a complex. The isolation of free ligands enables coordination 

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