Tetraza-macrocycles

Tetraza-macrocycles of the right ring size are expected to give very high inplane ligand field strengths. Fe(II) complexes based on such ligands are therefore expected to be either low-spin or spin-crossover. Busch and his coworkers [17] have synthesized six coordinate iron(II) complexes [Fe (tet-a)X2], where tet-a is one of the isomers of hexamethyl cyclam, a 14-membered tetraza-macrocycle (8). 

The silanophilic character of 16 reversed-phase high-performance liquid chromatographic columns was evaluated with dimethyl diphenycyclam, a cyclic tetraza macrocycle [101]. The method is rapid, does not require the removal of packing material, and uses a water-miscible solvent. The results demonstrate two points first, cyclic tetraza macrocycles offer substantial benefits over currently used silanophilic agents second, the method can easily differentiate the performance of various columns in terms of their relative hydrophobic and silanophilic contributions to absolute retention. 

The tetraza macrocycle (150 LH4), with four ethanoate groups, is readily prepared by treatment of the cyclic tetramine with bromoethanoic acid.1101 Its complex [ZnLH2j utilizes two amino N atoms and two carboxylates as ligands. The fully deprotonated complex may be prepared in solution by treatment with NaOH. 

Figure 5-58. The formation of a nickel complex of a tetraza macrocyclic ligand from an acyclic precursor...

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