Dipyrrin based silver [2 + 2] metallamacrocycles

Abstract

The synthesis and characterization of a series of [2 + 2] metallamacrocycles based on combinations of silver salts AgX (X = BF₄⁻, PF₆⁻, SbF₆⁻, TfO⁻) with pyridyl, p-phenyl-pyridyl and p-phenyl-imidazolyl appended dipyrrin (dpm) derivatives is reported. In these species, the silver ion is linearly coordinated to one of the two pyrrolic groups of the dpm moiety through the nitrogen atom and to a N atom belonging to the peripheral coordinating group. The organisation of the cyclic complexes in the solid state is dependent on the nature of the anion X⁻ and on the hydrogen bonding patterns formed with the pyrrolic NH group, acting as a donor. Furthermore, in some cases, d¹⁰-d¹⁰ argentophilic interactions are observed between consecutive macrocyclic complexes in the crystalline phase. The robustness of some of the complexes obtained compounds was investigated by ¹H- and ¹³C-NMR spectroscopy which revealed the structural integrity of the cyclic species in solution. A DOSY NMR study on the cyclic entity based on the imidazolyl appended dpm further assessed that the complex present in solution was indeed the [2 + 2] metallamacrocycle.