Macrocyclic (C₂₂H₂₂N₄) Complexes of Germanium(II), Tin(II), Gallium(III), and Indium(III). Main Group Functionalities in Unusual Environments

Main group moieties with unusual coordination numbers, oxidation states, and geometries have been stabilized both by the deployment of bulky ligands and also by incorporation into the coordination spheres of d-and f-block complexes. Interestingly, much less use has been made of macrocyclic ligands to achieve the foregoing objectives. Porphyrin and phthalocyanine complexes of the main group elements constitute well-recognized classes of compound. However, there is a paucity of information regarding the usefulness of other tetraaza macrocycles such as the dibenzotetramethyltetraaza[14]annulene (tmtaa) ligand.¹ Distinctive features of tmtaa include the modest core size (1.902 Å), the unusual saddle-shaped geometry, and the enforced cis disposition of reactive sites, X, in M(tmtaa)X₂ derivatives. We, therefore, reasoned that unusual reactivity patterns and coordination geometries might stem from the incorporation of main group fragments into this particular macrocycle.².