Synthesis and characterization of two piperazine containing macrocycles and their transition metal complexes

Rigidification of the ligand scaffolds has been a particular mechanism of interest employed to achieve properties suitable for MRI contrast, catalysis, or other applications of metal complexes. Towards the goal of targeting a 15-anePyN₅Pip type ligand, a serendipitous isolation of a 30-anePy₂N₁₀Pip₂ aza-macrocycle was achieved, instead. X-ray diffraction and determination of pK_a events were carried out and compared to 17-anePyN₅Pip. Furthermore, the X-ray diffraction of the Cu(II) and Zn(II) complexes of 17-anePyN₅Pip was achieved and compared to previous reports of other first-row transition metal derivatives of this ligand. Determination of the log β with both 30-anePy₂N₁₀Pip₂ and 17-anePyN₅Pip with the divalent MnZn metal-ion series was used to demonstrate the impact that the piperazine ring plays compared to other, less rigid macrocycles reported to date.