A Constrained and "Inverted" [3+3] Salphen Macrocycle with an ortho-Phenylethynyl Substitution Pattern

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Materials Science

Background:

• Schiff-base macrocycles are important in coordination chemistry and supramolecular self-assembly.
• Designing macrocycles with non-traditional geometries presents synthetic challenges and opportunities for novel properties.

Purpose of the Study:

• To synthesize a novel [3+3] Schiff-base salphen macrocycle with an inverted N2O2 coordination pocket.
• To investigate the self-aggregation and supramolecular assembly behavior of the synthesized macrocycle and its zinc metallomacrocycle.

Main Methods:

• Imine condensation reaction between ortho-phenylenediamine and ortho-phenylethynyl-bridged bis(5-salicylaldehyde) precursors.
• Zinc metalation of the synthesized macrocycle.
• Spectroscopic analysis (UV-Vis, NMR) to study aggregation in solution.
• Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) to study solid-state self-assembly.

Main Results:

• A triangular-shaped [3+3] Schiff-base salphen macrocycle (7a) was successfully synthesized in 64% yield.
• The macrocycle (7a) and its zinc metallomacrocycle (7b) demonstrated concentration-dependent self-aggregation in solution, with the metallomacrocycle showing stronger aggregation.
• AFM and TEM revealed the formation of micron-length, nanometer-width fiber bundles from the self-organization of the macrocycles in the solid state.

Conclusions:

• The inverted design of the Schiff-base macrocycle is synthetically accessible despite steric hindrance.
• The macrocycle and its metallated form exhibit tunable self-aggregation properties.
• These macrocycles can self-organize into well-defined supramolecular nanostructures, highlighting their potential in materials science.