A macrocyclic silver polycarbene complex based on 1,2,4-triazole units: synthesis and postsynthetic modification

Area of Science:

• Coordination Chemistry
• Organic Synthesis
• Supramolecular Chemistry

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in coordination chemistry.
• Macrocyclic ligands offer unique structural and binding properties.
• Developing efficient synthetic routes for complex macrocycles is crucial.

Purpose of the Study:

• To develop a facile synthesis of a rectangular 1,2,4-triazole-based NHC macrocycle.
• To explore postsynthetic modification strategies for the synthesized macrocycle.
• To obtain a metal-free tetra-1,2,4-triazole macrocycle.

Main Methods:

• Synthesis of a triazole salt and its subsequent reaction with silver(I) oxide to form a silver-NHC complex.
• Single-crystal X-ray diffraction for structural elucidation of the metallocyclic complex.
• Photodimerization of terminal cinnamic esters via UV irradiation (λ = 365 nm).
• Metal ion elimination to isolate the free macrocycle.
• Characterization using multinuclear NMR spectroscopy (1H, 13C{1H}, COSY, HSQC, HMBC) and ESI mass spectrometry.

Main Results:

• A rectangular 1,2,4-triazole-based NHC macrocycle was synthesized and characterized.
• A silver-NHC complex, [Ag2(1)2](BF4)2, was successfully prepared and its structure determined.
• Photodimerization of the metal-carbene template yielded a macrocyclic tetra(NHC) ligand precursor.
• The desired tetra-1,2,4-triazole macrocycle was obtained in good yield after demetallation.

Conclusions:

• A straightforward and effective method for synthesizing and modifying a rectangular 1,2,4-triazole-based NHC macrocycle has been established.
• The developed strategy allows for the preparation of metal-free tetra-1,2,4-triazole macrocycles through photodimerization and demetallation.
• This work provides a valuable route to complex macrocyclic structures with potential applications in various chemical fields.