Stable core-modified calixsmaragdyrins: synthesis, structure and specific sensing of the hydrogen sulfate ion

Abstract

Stable calixoxa- and calixthiasmaragdyrins containing three methine bridges and two direct bonds connecting the five pyrrole/heterocycle rings were synthesized by [3 + 2] condensation of dipyrromethane with 16-oxatripyrrane and 16-thiatripyrrane respectively under mild acid-catalyzed conditions. The compounds were characterized by HR-MS, 1D & 2D NMR, absorption and electrochemical techniques and the structure of calixoxasmaragdyrin was solved by X-ray crystallography. The crystal structure analysis indicated that the calixoxasmaragdyrin macrocycle was highly distorted due to the flexibility introduced by one sp(3)meso-carbon. The compounds show ill-defined absorption bands and irreversible oxidation and reduction waves which were attributed to the disruption of conjugation of the macrocycle by incorporation of one sp(3)meso-carbon. The anion binding studies indicated that the calixoxasmaragdyrin exhibited specific sensing ability for the HSO4(-) ion over other anions whereas calixthiasmaragdyrins did not even show an ability to bind anions.

Template Directed Syntheses of Electrochemically Active [2]Rotaxanes: Anion Binding and Redox Studies

“…As anion binding properties of RTXN1 has already been established by 1 H‐NMR studies, at this juncture, we are curious to explore the effect of anion binding on the irreversible redox waves of the rotaxane. Although, most of the host systems utilized in the anion binding studies are of reversible in nature, ] anion binding using irreversible redox wave‐based system is rarely reported …”

“…Although, most of the host systems utilized in the anion binding studies are of reversible in nature, [13] ] anion binding using irreversible redox wave-based system is rarely reported. [18] In this regard, the electrochemical titration of RTXN1 is carried out with all of the TBAanions (OAc À , HSO 4 À , Cl À , H 2 PO 4 À and NO 3 À ) ( Figure 8. and Figure 40S-42S, ESI †) in DMF solvent at 298 K. In each case, aliquots of TBAanion solution in anhydrous DMF is added gradually to the electrochemical solution of RTXN1 (1 mM) upto 10 equiv.…”

“…Thus, the above electrochemical results suggest that, TBAanion coordination with RTXN1 occurs without altering the irreversible reduction waves nature of RTXN1. [18] Changes in potential as a function of anion concentration have also been plotted separately for each of the TBA anions ( Figure 43S-47S, ESI †). All the plots have shown a similar kind of well-behaved isotherms for each of the anions and these observed electrochemical responses attributed to the specific binding event of these anions with RTXN1.…”

Meso‐Monoaryl‐Substituted Neo‐confused Calixsmaragdyrins and Meso‐monoaryl Substituted Smaragdyrins: Synthesis, Structures and Properties

“…Calixsmaragdyrins are a rare class of molecules, in that Ravikanth et al. reported aza‐, oxa‐, and thia‐calixsmaragdyrins 8 only by the acid‐catalyzed condensation reactions [5a,b] . They also demonstrated that oxa‐calixsmaragdyrin served as an effective ligand toward Pd II and Ru II metals [6] .…”

Calixsmaragdyrin: A Versatile Ligand for Coordination Complexes

“…However, the preparation of stable azasmaragdyrin has remained elusive, and this has prevented its potential application as a ligand to form metal complexes. Recently, we reported the first successful synthesis of stable meso -aryl calixsmaragdyrin 2 , where introduction of one sp 3 meso -carbon atom instead of a sp 2 meso -carbon atom provides increased flexibility and stability to the smaragdyrin core. − The calixsmaragdyrin macrocycle 2 has three ionizable inner NH atoms which indicate its potential for multidentate coordination chemistry. Given the limited stability of smaragdyrin 1 it is not currently possible to explore its role as a potential ligand in coordination chemistry.…”