Transmetalation and Demetallization for Open-Oyster-like Non-Ionic Cd(II) Macrocycles

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Macrocyclic Chemistry

Background:

• Macrocyclic complexes often face challenges with transmetalation and demetallization due to strong metal-ligand interactions.
• Developing new ligands and synthetic strategies is crucial for overcoming these limitations in macrocyclic chemistry.

Purpose of the Study:

• To design a nonionic extended dialdehyde, 6,6'-(phenylazanediyl)dipicolinaldehyde (PDPA), for constructing Schiff-base macrocyclic complexes.
• To enable weaker metal-ligand interactions for easier transmetalation and demetallization.
• To synthesize and characterize novel macrocyclic complexes, including dinuclear Cd(II) and Cu(II) complexes.

Main Methods:

• Synthesis of the nonionic extended dialdehyde PDPA.
• Template synthesis of Schiff-base macrocyclic complexes using Cd(II) and Cu(II) ions with 1,2-diaminocyclohexane (DACH) precursors.
• Characterization using techniques such as ESI-MS, UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS).
• Transmetalation (Cd(II) → Cu(II)) and demetallation (Na2S) experiments.

Main Results:

• Successfully synthesized enantiomeric pairs of 26-membered [2 + 2] Schiff-base dinuclear Cd(II) complexes.
• Observed formation of a mononuclear Cu(II) acyclic complex with PDPA oxidation when using Cu(II) as a template, attributed to Cu(II)'s weak oxidizing capability.
• Achieved synthesis of [2 + 2] dinuclear Cu(II) macrocycles and metal-free macrocycles via Cd(II) transmetalation and subsequent demetallation.
• Direct non-template synthesis of metal-free macrocycles yielded difficult-to-isolate mixtures of [1 + 1], [2 + 2], and [3 + 3] complexes.

Conclusions:

• The designed PDPA ligand facilitates the construction of Schiff-base macrocyclic complexes with tunable metal-ligand interactions.
• The strategy of using Cd(II) as a template followed by transmetalation and demetallation is effective for synthesizing target Cu(II) macrocycles and metal-free macrocycles.
• This approach offers a viable solution to the challenges of transmetalation and demetallization in macrocyclic chemistry.