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

Abstract

Three complexes of benzo-15-crown-5 (B15C5) with protonated primary amines [PhCH 2NH 3(B15C5)](ClO 4), [ p-C 6H 4(CH 2NH 3) 2(B15C5) 2](ClO 4) 2, and [(CH 2) 4(NH 3) 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-NH 3 + moiety with characteristic small separation of 1.84–1.86 Å between the nitrogen of the R-NH 3 + group and the O 5 mean plane of the crown residue. No sandwich-type complexes with a 1:2 R-NH 3 +/B15C5 stoichiometry were observed. Binding affinities of B15C5 in acetonitrile were similar for all ammonium cations studied: K 1=550±10 M −1 for [PhCH 2NH 3] +; K 1=1100±100 and K 2=400±30 M −1 for [ p-C 6H 4(CH 2NH 3) 2] 2+; and K 1=1100±100 and K 2=300±30 M −1 for [H 3N(CH 2) 4NH 3] 2+. The complexation is primarily enthalpy-driven (Δ H°=−4.9±0.5 kcal/mol, Δ S°=−3.8±1.0 eu for PhCH 2NH 3 +–B15C5), as determined by variable temperature 1H NMR titrations.