Anion recognition by oligo-(thio)urea-based receptors

Abstract

Oligo-(thio)ureas have proven to be a promising class of receptors that are widely applied in anion recognition. This article aims to present some recent progress in the construction of oligoureas and their anion coordination (recognition) chemistry. Typical examples of metal-coordination assisted and covalently connected oligo-(thio)urea receptors are summarized, with focus on geometry characteristics required for achieving complementary binding of a target anion. Special emphasis is given to ortho-phenylene-connected oligoureas in the application of anion binding and the self-assembly of important supramolecular architectures, including helicates, tetrahedral cages, and so on.

Fluoride‐Catalyzed Deblocking: A Route to Polymeric Urethanes

“…Our selection of fluoride ion for these reactions exploits its strong hydrogen bonding interactions with NÀH groups of organic compounds. [24] As shown in Figure 1, blocked isocyanates 2a-e were prepared by reacting toluene diisocyanate (TDI) with selected alcohols in anhydrous dimethylformamide (DMF). Ther eactions were monitored by infrared spectroscopy,s howing the loss of NCO signals (2265 cm À1 )and emergence of bands for the carbonyl (1710-1716 cm À1 )and NÀH(3326 cm À1 )groups of urethanes.For the pyrene-blocked sample, 1 HNMR spectroscopy revealed aromatic resonances from 8.05 to 8.35 ppm (from pyrene) and 7.05-7.25 ppm (from TDI), as well as broad N-H resonances at 9.05 and 9.75 ppm (Figures S1-S23 in the Supporting Information).…”

“…[25,26] With respectt ot he deblocking mechanism, we note that anionc oordination dependso nb othi onic andd ipolari nteractions. [24][25][26][27][28] Theliteraturedescribes fluoride ionasaversatile reagentfor ureas, involvingN ÀHdeprotonation,formationof bifluoride anion( HF 2 À ), ands ubsequents tructuralt ransformations. [29][30][31] Forexample,the combinationoffluorideion with aromatic ureasp roducedc olorimetricc hemosensors, with colorc hanges inducedb yN À Hd eprotonation.…”

“…[24] As shown in Figure 1, blocked isocyanates 2a-e were prepared by reacting toluene diisocyanate (TDI) with selected alcohols in anhydrous dimethylformamide (DMF). This methodology was tested successfully on av ariety of urethanes,i ncluding 1) fluorescent versions that enabled facile spectroscopic characterization of blocking group exchange and 2) precursors to polyurethanes and crosslinked polyurethanes using sequential deblocking and polymerization.…”

“…This methodology was tested successfully on av ariety of urethanes,i ncluding 1) fluorescent versions that enabled facile spectroscopic characterization of blocking group exchange and 2) precursors to polyurethanes and crosslinked polyurethanes using sequential deblocking and polymerization. [24][25][26][27][28] Theliteraturedescribes fluoride ionasaversatile reagentfor ureas, involvingN ÀHdeprotonation,formationof bifluoride anion( HF 2 À ), ands ubsequents tructuralt ransformations. [24] As shown in Figure 1, blocked isocyanates 2a-e were prepared by reacting toluene diisocyanate (TDI) with selected alcohols in anhydrous dimethylformamide (DMF).…”

Fluoride‐Catalyzed Deblocking: A Route to Polymeric Urethanes

“…With respect to the deblocking mechanism, we note that anion coordination depends on both ionic and dipolar interactions . The literature describes fluoride ion as a versatile reagent for ureas, involving N−H deprotonation, formation of bifluoride anion (HF 2 − ), and subsequent structural transformations .…”