meso-Aryl smaragdyrins: Novel anion and metal receptors

An easy synthesis of core-modified meso-aryl smaragdyrins containing oxygen and sulfur in addition to pyrrole nitrogens has been achieved through an α-α coupling involving modified tripyrrane and dipyrromethane. The complexation behavior of these macrocycles toward anions (Cl^-, F^-, AMP^-) and metal cations (Rh(I), Ni(II)) is reported. Specifically, it has been shown that the Rh(I) and Ni(II) ions bind to the smaragdyrin skeleton in its free base form. X-ray structural studies of Rh(I) complex 1 indicate an η²-type coordination involving only one imino and one amino nitrogen of the dipyrromethane unit. However, all four bipyrrole nitrogens participate in the coordination with the Ni(II) ion. Furthermore, Ni(II) coordination oxidizes the ligand, and the complex is formulated as the π-cation radical of nickel(II) smaragdyrin. The anion complexation is followed in both the solid and solution phases. Solution studies reveal that the binding constants of the ions with the protonated form of smaragdyrin vary as F^- > AMP^- > Cl^-. The X-ray structure of the chloride anion complex reveals that the chloride ion is bound above the cavity of the smaragdyrin macrocycle through three N-H···Cl hydrogen bonds. Crystal data with Mo Kα (λ = 0.71073 Å) are as follows: 1, C₄₁H₂₇N₄O₃Rh, a = 11.836(8) Å, b = 12.495(9) Å, c = 12.670(2) Å, α = 69.09(6)°, β = 78.78(6)°, γ = 77.02(5)°, V = 1692.1(17) ų, Z = 2, triclinic, space group P-1, R₁(all data) = 0.0471; 4·HCl, C₄₁H₂₉N₄O₁Cl, a = 11.878(2) Å, b = 17.379(4) Å, c = 16.015(3)Å, β = 109.546-(10)°, V = 3115.47(11) ų, Z = 4, monoclinic, space group P2(1)/c, R₁(all data) = 0.0850.