Di(p-dibenzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) Pd^II Complex: A Weakly Hückel 38π-Aromatic Macrocycle

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Computational Chemistry

Background:

• Tetrapyrrole macrocycles are fundamental in various chemical and biological processes.
• Exploring novel macrocyclic architectures is crucial for advancing materials science.
• Möbius topology in macrocycles presents unique electronic and structural characteristics.

Purpose of the Study:

• Synthesize novel Di(p-benzi)[40]decaphyrin and tris(p-benzi)[60]pentadecaphyrin BF2 complexes.
• Investigate the structural and electronic properties of these macrocycles and their metal complexes.
• Determine the aromaticity and topological features of the synthesized compounds.

Main Methods:

• Suzuki-Miyaura coupling reaction for macrocycle synthesis.
• Conversion of BF2 complexes to free bases and subsequently to PdII complexes.
• Spectroscopic (UV-Vis) and electrochemical (cyclic voltammetry) analyses to characterize electronic properties.

Main Results:

• Successful synthesis of Di(p-benzi)[40]decaphyrin BF2 and tris(p-benzi)[60]pentadecaphyrin BF2 complexes.
• Both BF2 complexes exhibit Möbius topology but are nonaromatic due to disrupted conjugation.
• The bis-PdII complex displays weak Hückel 38π-aromaticity with distinct spectral features and a small HOMO-LUMO gap.
• The bis-PdII complex adopts a figure-eight conformation with one quinonoidal and one benzene unit.

Conclusions:

• The incorporation of p-phenylene units influences the aromaticity and topology of tetrapyrrole macrocycles.
• Metalation (PdII) can induce aromaticity in otherwise nonaromatic Möbius macrocycles.
• The study reveals a unique interplay between topology, aromaticity, and molecular conformation in complex macrocyclic systems.