Phosphorus-nitrogen rings macrocycles

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. 

Alkylation of coordinated nitrogen atoms has also given rise to new chelate rings and coincidentally to macrocyclic structures (equations 43 and 44).167,16S More recently, the alkylation technique has been extended to phosphorus (equation 45).169 A more recent novel free radical cyclization... 

Quantitative data are sparse for phosphorus macrocycle complex stabilities. However, the broad thermodynamic principles that apply to nitrogen systems should apply to those of phosphorus. The macrocylic effect is the net effect of a number of factors, inter alia changes in entropy, enthalpy, pH, solvent effects, ring size, and conformation, that results... 

The chelate ring closure described in equation (42) 66 would be represented by a more concerted version of the general type shown by equation (35). The final product (63) has also been treated with a,a -dibromo-o-xylene to produce the related macrocycle, via its complex. Alkylation of coordinated nitrogen atoms has also given rise to new chelate rings and coincidentally to macrocyclic structures (equations 43 and 44). " More recently, the alkylation technique has been extended to phosphorus (equation 45). A more recent novel free radical cyclization... 

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