Complexes of benzo-15-crown-5 with protonated primary amines and diamines

Three complexes of benzo-15-crown-5 (B15C5) with protonated primary amines [PhCH2NH3(B15C5)](ClO4), [p-C6H4(CH2NH3)2(B15C5)2](ClO4)2, and [(CH2)4(NH3)2(B15C5)2](SCN)2 were isolated and studied in acetonitrile solutions by NMR, and in the solid state by X-ray crystallography. In all complexes, one B15C5 molecule was bound with each R-NH3+ moiety with characteristic small separation of 1.84–1.86 Å between the nitrogen of the R-NH3+ group and the O5 mean plane of the crown residue. No sandwich-type complexes with a 1:2 R-NH3+/B15C5 stoichiometry were observed. Binding affinities of B15C5 in acetonitrile were similar for all ammonium cations studied: K1=550±10 M−1 for [PhCH2NH3]+; K1=1100±100 and K2=400±30 M−1 for [p-C6H4(CH2NH3)2]2+; and K1=1100±100 and K2=300±30 M−1 for [H3N(CH2)4NH3]2+. The complexation is primarily enthalpy-driven (ΔH°=−4.9±0.5 kcal/mol, ΔS°=−3.8±1.0 eu for PhCH2NH3+–B15C5), as determined by variable temperature 1H NMR titrations.