Remarkable Stability of Imino Macrocycles in Water

Abstract

Imines 3, 5 and 7 generated from 4-methoxypyridine-2,6-dicarbaldehyde (1) and several amines 2, 4 and 6 show a remarkable stability in water. The 18-membered macrocyclic diimine 5 is stable and could be synthesized in good yield by using 2 equiv. of calcium ions as template in pure water, and even the non-macrocyclic diimine 3 survives in water/meth-

Macrocycle or Cage? The Presence or Absence of Ca2+ Template Ions Controls the Equilibrium in an Oligoimine Dynamic Combinatorial Library

“…Our experiments cannot answer this question unambiguously, but two speculations may be allowed: the fit of calcium ions into the macrocycle 5 (R = OMe) is excellent, as its resistance to water [21] shows, and the fit into the larger cage 4 (R = OMe) is probably less accurate. In addition, alkaline earth metal ions undergo strong interactions with oxygen donor ring atoms, which are present only in 5 (R = OMe) and not in 4 (R = OMe).…”

Ion Transport Across Membranes Facilitated by a Dynamic Combinatorial Library

“…When the building blocks react in the presence of calcium ions in the water source phase, macrocycle 3 is formed, along with linear oligo-and polymers, which transports calcium ions from the water source phase to the water receiver phase. [8] The good water solubility of complex 3·Ca 2+ [10] is supposed to be the weakness of its carrier activity. In fact, most of the complex was found in the water source phase.…”

“…Thus, the formation of the imino macrocycle 5 (Figure 3) in the presence of calcium ions as the template and its complexing ability should be only marginally different from the imino macrocycle 3. [8,10] As proof of the formation of the imino macrocycle 5, the DCL composed of diamine 1 and dialdehyde 4 was screened by 1 H NMR spectroscopy in the presence and absence of calcium chloride (by using CD 3 OD and H 2 O/D 2 O as solvent). When calcium was present, only one peak in the imine region (δ = 8.64 ppm) and one in the pyridine region (δ = 7.55 ppm) could be detected in the NMR spectrum (see the Supporting Information).…”

“…For a complete characterization of the imino macrocycle 3, see ref. [10] An LF 340 conductimeter from WTW was used with automatic data storage (15 min) and non-linear compensation of the temperature set to 20°C. [20] The glassware (quartz) used for the transport experiment had a half-cell volume of 25 mL, a section of 8.553 ϫ 10 -4 m 2 and is described in the Supporting Information.…”

Probing the mechanism and dynamic reversibility of trianglimine formation using real‐time electrospray ionization time‐of‐flight mass spectrometry

“…Reviewing the literature evidence and our previous experience it can be concluded that when the two dialdehyde functionalities deviate from an ideal dihedral angle O=C … C=O, the reaction can give two or more products. Obtaining the desired [3+3]‐cyclocondensation macrocycle requires careful optimization of the reaction conditions such as concentration and time or alternatively the addition of a template as illustrated by González‐Álvarez et al and Saggiomo and Lüning, to achieve a maximum yield and high purity of the desired product, which should be the [2+2]‐ or [3+3]‐macrocycle.…”