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.