Lacunar cyclidenes Macrocyclic complexes

The lacunar cyclidene ligands are the first family of totally synthetic ligands to form both iron(II) and cobalt(II) Oj carriers. The molecular structure of the lacunar cyclidene complexes is most simply represented by the flat projection (la), while the stereochemistry is shown in Ib. Cyclidene refers to the parent macrocycle encircling the metal ion and the lacuna is the permanent void created by bridging the cleft arising from the saddle shape of the cyclidene macrocycle. 

The starting material for both of these target molecules is the neutral nickel(II) complex [3,11-diacetyl-4,10-dimethyl-1,5,9,13-tetraazacyclohexa-deca-1, 3, 9, ll-tetraenato(2 —)-K N ]nickel(II), ([Ni(Ac2Me2[16]-tetra-enatoN )]). This complex is prepared by the procedure described earlier. The lacunar cyclidene ligands are constructed on the nickel(II) ion, and the formation of the second macrocyclic ring is a template reaction. The first two reactions in the Scheme are required unless R is to be methyl. Thus, the synthesis of the cobalt complex does not require these steps, whereas... 

Cyclodene Complexes Relationships between Macrocyclic Ring Size, Lacunar Cavity Shape, and Dioxygen Affinity of the Cobalt-Cyclidene Dioxygen Carriers. 

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