Oxygen donor macrocycles

The template synthesis of mixed nitrogen and oxygen donor macrocycles are mainly based on substituted salicylaldehydes or salicyl-aldehyde-metal complexes (82), e.g.,... 

Related to the crown ethers are compounds, such as hexamethyl-[14]-4,ll-diene (6), which differ by the replacement of one or more of the oxygen atoms by other kinds of donor atoms, particularly N or S. MacrocycHc amine and thioether compounds have been synthesized. Compounds having more than one kind of heteroatom in the ring are called mixed-donor macrocycles. The naturally occurring metaboUtes nonactin [6833-84-7] and monactin [7182-54-9] have both ether and ester groups incorporated in the macrocyclic stmcture. 

Fig. 18. Plot of change in complex stability, Alogf , that occurs for the pairs of ligands cryptand-2,2,2 and EN ( ), and 18-aneN204 and EN (O), as a function of metal ion radius (20). The diagram shows how neutral oxygen donors tend to stabilize the complexes of large relative to small metal ions in macrocyclic ligands. Data from Ref. (11).

LogX values for a number of tricarboxymethyl pendant arm derivatives of mixed oxygen nitrogen donor macrocycles have been reported. These include values of 16.09, 12.11, 14.44, and 9.47 for the ring systems (199), (200), (201a), and (201b), respectively. 

Impetus was given to work in the field of selective cation complex-ation by the observation of Moore and Pressman (5) in 1964 that the macrocyclic antibiotic valinomycin is capable of actively transporting K+ across mitochondrial membranes. This observation has been confirmed and extended to numerous macrocyclic compounds. There is now an extensive literature on the selective complexation and transport of alkali metal ions by various macrocyclic compounds (e.g., valinomycin, mo-nactin, etc.) (2). From solution spectral (6) and crystal X-ray (7) studies we know that in these complexes the alkali metal cation is situated in the center of the inwardly oriented oxygen donor atoms. Similar results are found from X-ray studies of cyclic polyether complexes of alkali metal ions (8) and barium ion (9). These metal macrocyclic compound systems are especially noteworthy since they involve some of the few cases where alkali metal ions participate in complex ion formation in aqueous solution. 

In Table 108 significant examples of nickel(II) complexes with mixed-donor macrocycles of various denticity are reported. Apart from the nitrogen atoms, the heteroatoms in the macrocyclic rings are usually either O or S, or in a few cases P. Few examples of nickel complexes with macrocycles containing all-sulfur or all-phosphorus donor atoms have been reported to date they are also included in Table 108. In nickel(II) complexes formed by mixed-donor penta- and hexa-dentate ligands the oxygen atoms of the macrocycle are often only weakly coordinated or are not coordinated at all. 

Classification of macromonocycles (Figure 2) can be made on the basis of donor atom, i.e. nitrogen, oxygen, sulfur, phosphorus, arsenic and mixed donor systems, as well as topicity, i.e. mono- versus di- or poly-topic. The planar nitrogen donor macrocycles and other tetraaza macro-... 

---