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

Facile synthesis and postsynthetic modification of a rectangular 1,2,4-triazole-based NHC macrocycle have been developed. The silver complex [Ag2(1)2](BF4)2 is derived from the corresponding triazole salt H2-1(BF4)2 upon reaction with Ag2O. The structure of the metallocyclic Ag-NHC complex [Ag2(1)2](BF4)2 was determined by single-crystal X-ray diffraction analysis. The metal-carbene template undergoes photodimerisation of its terminal cinnamic esters (UV irradiation, λ = 365 nm) and generates a macrocyclic tetra (NHC) ligand. The desired tetra-1,2,4-triazole macrocycle was isolated in good yield by eliminating the metal ions from the photodimerisation product. All complexes were fully characterized by multinuclear NMR measurements (1H, 13C{1H}, COSY, HSQC and HMBC) and ESI mass spectroscopy.