Abstract
Three complexes of benzo-15-crown-5 (B15C5) with protonated primary amines [PhCH2NH3(B15C5)](ClO4), [p-C6H 4(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 1.84-1.86Å 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]+; K 1=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)4NH 3]2+. The complexation is primarily enthalpy-driven (ΔH°=-4.9±0.5kcal/mol, ΔS°=-3.8±1.0eu for PhCH2NH3+-B15C5), as determined by variable temperature 1H NMR titrations.
Original language | English (US) |
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Pages (from-to) | 4579-4588 |
Number of pages | 10 |
Journal | Tetrahedron |
Volume | 60 |
Issue number | 21 |
DOIs | |
State | Published - May 17 2004 |
Externally published | Yes |
Keywords
- Alkylammonium
- Crown ethers
- Host-guest complexes
ASJC Scopus subject areas
- Biochemistry
- Drug Discovery
- Organic Chemistry