Benzoaza-15-crown-5 ethers: synthesis, structure, and complex formation with metal and ethylammonium ions

Abstract

Benzoaza 15 crown 5 ethers containing one or two nitrogen atoms in different positions of the macrocycle and bearing different substituents at these atoms were synthesized. The structures of azacrown ethers and their metal complexes were studied by X ray diffraction. The stability constants of the complexes of azacrown ethers with Na + , Ca 2+ , Ba 2+ , Ag + , Pb 2+ , and EtNH 3 + ions were determined by 1 H NMR titration in MeCN d 3 . In free benzoazacrown ethers containing secondary nitrogen atoms bound to the benzene ring, as well as in N acetyl derivatives, the N atoms are sp 2 hybridized and have a planar geometry. The nitrogen lone pairs on the p orbitals are efficiently conjugated to the benzene ring or the carbonyl fragment of the acetyl group, which is unfavorable for the complex formation. In addition, the formation of complexes with benzoazacrown ethers containing secondary nitrogen atoms is hindered because the hydrogen atoms of the NH groups are directed to the center of the macrocyclic cavity. In benzoazacrown ethers bearing N alkyl substituents or secondary nitrogen atoms distant from the benzene ring, the N atoms show a substantial contribution of the sp 3 hybrid ized state and have a pronounced pyramidal configuration, which promotes the complex formation. The lead and calcium cations form the most stable complexes due to the high affinity of Pb 2+ ions for O,N containing ligands, a high charge density on these ions, and the better correspondence of the cavity size of the 15 membered macrocycles to the diameter of the Ca 2+ ion. An increase in the stability of the complexes is observed mainly in going from monoazacrown ethers to diazacrown ethers containing identical substituents at the N atoms and in the following series of substituents: C(O)Me < H < Me < CH 2 CO 2 Et. In the case of the CH 2 CO 2 Et substituents, the carbonyl oxygen atom is also involved in the coordination to the cation. The characteristic features of the complexing ability of N alkylbenzomonoaza 15 crown 5 ethers bearing the nitrogen atom conjugated to the benzene ring show that macro cyclic ligands having this structure are promising as selective and efficient complexing agents for metal cations.

Nitro derivatives of N-alkylbenzoaza-15-crown-5: synthesis, structures, and complexation with metal and ammonium cations

“…NMR studies. Earlier, 4, 13 we have demonstrated that benzomonoazacrown ethers and their derivatives contain ing the tertiary N atom conjugated with the benzene ring form sufficiently stable guest-host complexes with alkali, alkaline earth, heavy metal, and ammonium ions, which will make them highly efficient as ionophores in promis ing optical chemosensory compounds. It was interesting to compare the quantitative stability parameters of com plexes of nitrobenzoazacrown ethers with Groups I and II metal cations and ammonium ions, to reveal the structur al features of the resulting complexes and their selectivity toward various ions, and to compare the complexing ability of nitrobenzoazacrown ethers containing various N alkyl substituents with that of related compounds.…”

“…In this respect, nitro derivatives 1 differ from benzene unsubstituted benzoazacrown ethers and their formyl derivatives: their complexes with the cat ions in question are much more stable than similar com plexes of related N phenylaza 15 crown 5. 13 This be havior of compounds 1 can be explained by two factors: first, the coordination bond N...M + is weakened because of the strong electron withdrawing effect of the NO 2 group and, second, the substituent at the N atom presents steric hindrances to its coordination to the large Ba 2+ ion. The second reason is indirectly confirmed by the inability of crown ether 1c, which contains a bulky n propyl substitu ent, to form stable sandwich complexes.…”

“…This is characteristic of barium perchlor ate complexes with benzoaza 15 crown 5 13. The anions Cl(1)O4 and Cl(4)O 4 are disordered over two posi tions with populations of 0.72 : 0.38 and 0.57 : 0.43, re spectively.…”

“…respectively) as the internal standards 13. C NMR spectra were recorded on a Bruker DRX500 spectrometer (125.76 MHz) in CDCl 3 with the solvent signal (δ 77.00) as the internal standard.…”

15-Hydroxybenzomonothia-15-crown-5 with the sulfur atom linked with the benzene ring and the derived sulfoxide: synthesis, structure, and complexation with the metal cations

“…Selected bond lengths (d), deviation of the metal cation from the middle plane passing through all heteroatoms of the macrocycle (ΔM m+ ), bond (ω) and torsion (ϕ) angles and the sum of the bond angles at the S atom (Σ ω ) in crown ethers 5, 6•3H 2 (1.386(2)-1.398(2) Å) as compared with the free ligand 5 is observed, which is typical of complexation of benzocrown ethers. 31 The values of the bond angles C Ar -C Ar -O(1) and C Ar -C Ar -S(1) in the complex do not virtually differ from the analogous parameters of the free ligand 5 (see Table 2) suggesting small changes in hydridization of the O and S atoms linked with the benzene ring. The sodium cation is coordinated to two oxygen atoms of the perchlorate anion and three oxygen atoms of macrocycle of 5 that are remote from the benzene ring (see Fig.…”