Macrocyclic bis(ureas) as ligands for anion complexation

Abstract

SummaryTwo macrocyclic bis(ureas) 1 and 2, both based on diphenylurea, have been synthesized. Compound 1 represents the smaller ring with two ethynylene groups as linkers and 2 the larger ring with two butadiynylene groups. On thermal treatment to 130 °C molecule 1 splits up into two dihydroindoloquinolinone (3) molecules. Both compounds 1 and 2 form adducts with polar molecules such as dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) and act as complexing agents towards a series of anions (Cl−, Br−, I−, NO3 −, HSO4 −). The crystal structures of 3, 2·2DMSO, 2·2DMF, and of the complex NEt4[Br·2] have been determined. Quantitative investigations of the complexation equilibria were performed via 1H NMR titrations. While 1 is a rather weak complexing agent, the large ring of 2 binds anions with association constants up to log K = 7.93 for chloride ions.

Urea-Based Macrocycle Selective for Sulfate and Structurally Sensitive to Water

“…Urea groups have been especially effective incorporated into anion hosts due to the mini-pincer grips provided by proximal hydrogen bond donor NH groups. − As a result, acyclic urea hosts (chelates) are prevalent. With the exception of bis-urea macrocycles, − however, macrocyclic hosts containing only urea groups have been scarce. − Expanding on earlier m -xylyl bis-urea chelates, , Reinhoudt and co-workers synthesized both acyclic chelates and macrocyclic tetraureas, and compared their anion binding effectiveness . They found that the macrocycles were selective for H 2 PO 4 – over other anions examined, with minimal binding observed for HSO 4 – in DMSO- d 6 .…”