Synthesis and X-ray Structures of Novel Macrocycles and Macrobicycles Containing N,N-Di(pyrrolylmethyl)-N-methylamine Moiety: Preliminary Anion Binding Study

Abstract

The [2 + 2] Schiff base condensation reactions between the newly synthesized dialdehyde, N,N-di(α-formylpyrrolyl-α-methyl)-N-methylamine), and ethylenediamine or p-phenylenediamine dihydrochloride readily afforded the 30- and 34-membered large size macrocycles in very high yields. Subsequent reduction reactions of these macrocycles with NaBH(4) gave the corresponding saturated macrocyclic hexaamines in good yields. The analogous reaction of the new dialdehyde with a triamine molecule afforded the [3 + 2] Schiff base macrobicycle in high yield, which was then reduced by reaction with NaBH(4) to give the saturated macrobicycle. All these compounds were characterized by spectroscopic methods. The anion binding properties of the saturated macrocycles having the ethylene and the phenylene linkers in CDCl(3) were studied by NMR titration methods. Although they have similar pyrrolic and amine NH groups their binding properties are different and interesting, owing to the conformational flexibility or rigidness rendered by the ethylene or phenylene groups, respectively. The macrocycle having the ethylene linkers binds anions in a 1:1 fashion, while the other receptor having the phenylene linkers prefers to bind anions in a sequential 1:2 fashion and has a multiple equilibria between a 1:1 and a 1:2 complexes, as shown by their binding constants, curve fittings by EQNMR, and Job plots. The X-ray structures of the 1:2 methanol, the aqua and the benzoate anion complexes of the macrocycles show two cavities in which the guests are bound, correlating with the high affinity found for the formation of stable 1:2 complexes in solution. The X-ray structure showed that the macrobicycle Schiff base adopts an eclipsed paddle-wheel shaped conformation and exhibits an out-out configuration at the bridgehead nitrogen atoms.

Design, synthesis and anion recognition of ferrocene-based benzimidazolium receptors

“…11. Upon addition of 1 equivalent of F À to the solution of receptor 7 in DMSO-d 6 , the intensity of the C-2 proton resonance disappeared, however there was a triplet of HF 2 À around 16.13 ppm, suggesting deprotonation and F À mediated hydrogen deuterium exchanges in the C-2 proton of benzimidazolium [57]. A significant upfield shifts (ppm) of protons of benzimidazolium and benzene ring were observed, indicating there were kinds of directional interactions between the receptor 7 and F À .…”

Supramolecular Chemistry of Anionic Dimers, Trimers, Tetramers, and Clusters

“…In 2012 Kumar et al 92 reported a class of large macrocycles 66 and 67 containing N , N -di(pyrrolylmethyl)- N -methylamine moieties that were prepared by exploiting Schiff base-forming condensation reactions. Although both receptors present ostensibly similar pyrrolic and amine NH donors, the observed anion binding is quite different.…”

Selective anion receptor for fluoride detection using ferrocenyl–boronate derivative

“…Representatively, the C-4 proton (H 7 ) of the ferrocene ring showed two kinds of 1 H NMR, one was highfield shift (Dd ¼ 0.2 ppm) and the other was downfield shift (Dd ¼ 0.8 ppm). And it had a triplet around 16 ppm for the HF 2 À , indicating deprotonation and fluoride ion mediated hydrogen-deuterium exchanges [60] (Fig. S14).…”