Cyclic assemblies formed by metal ions, pyrimidines and isogeometrical heterocycles: DNA binding properties and antitumour activity

Bernhard Lippert has contributed significantly to the understanding of metallamacrocyclic complexes with low valent, late transition metals. In particular, he has pioneered the preparation of metallacalixarenes such as 12-MC-3 and 16-MC-4 structure types. In this article, we provide the preparation of a new 16-MC-4, [Mn4Br4(B(tBuM)PZG)4] [Mn(HOCO2)2], complex made with the ligand potassium N,N-bis(3-methyl-5-tert-butylpyrazolylmethyl)glycinate (KB(tBuM)PZG). In addition to being the first 16-MC-4 that is composed of manganese, this complex is the first example of a transition metal [Mn(II)] being captured in the interior cavity of the 16-MC-4. We discuss how our ligand design leads to the isolated structure due to the steric bulk that has been appended to the pyrazole ligand.