A pentagonal cyanostar macrocycle with cyanostilbene CH donors binds anions and forms dialkylphosphate [3]rotaxanes

Abstract

Since the discovery of crown ethers, macrocycles have been recognized as powerful platforms for supramolecular chemistry. Although their numbers and variations are now legion, macrocycles that are simple to make using high-yielding reactions in one pot and on the multigram scale are rare. Here we present such a discovery obtained during the creation of a C5-symmetric cyanostilbene 'campestarene' macrocycle, cyanostar, that employs Knoevenagel condensations in the preparation of its cyanostilbene repeat unit. In the solid state, cyanostars form π-stacked dimers constituted of chiral P and M enantiomers. The electropositive central cavity stabilizes anions with CH hydrogen-bonding units that are activated by electron-withdrawing cyano groups. In solution, the cyanostar shows high-affinity binding as 2:1 sandwich complexes, log β2 ≈ 12 and ΔG ≈ -70 kJ mol(-1), of large anions (BF4(-), ClO4(-) and PF6(-)) usually considered weakly coordinating. The cyanostar's size preference allowed formation of an unprecedented [3]rotaxane templated around a dialkylphosphate.

Anion Receptor Chemistry

“…Lee et al 20 have continued their efforts to create new anion receptors based on CH hydrogen bonds. In addition to the well-known 1,2,3-triazole motif, they incorporated a new CH hydrogen-bond motif, cyanostilbene, into a macrocyclic receptor cyanostar, 46, that contains ten CH hydrogen-bond donors in its central cavity ( Figure 14).…”

Macromolecular Crystallography for Synthetic Abiological Molecules: Combining xMDFF and PHENIX for Structure Determination of Cyanostar Macrocycles

“…The stated features render ab initio structure modeling from electron density peaks difficult. Recognition of this crossover region motivated our investigation into the use of macromolecular methods 14 for the structure determination of the abiological molecule, cyanostar 15 (Figure 1). Cyanostar, while being a small molecule (MW ~ 900 D), exhibits whole-molecule disorder, dimerizes in the solid state (unit cell ~1800 D) and bears weakly ordered solvents in and around its binding pocket.…”

Anion Receptors Based on Organic Frameworks: Recent Advances

“…More recently Flood and co-workers have developed another new macrocycle containing C-H hydrogen bond donors named cyanostar (compound 7 Scheme 2) [6]. Again this system relies on the presence of a dipole to aid hydrogen bonding from a cyanostilbene C-H group (Scheme 2a).…”

“…Again this system relies on the presence of a dipole to aid hydrogen bonding from a cyanostilbene C-H group (Scheme 2a). The macrocycle was shown to form strong complexes with normally weakly coordinating anions such as PF 6 À , ClO 4 À and BF 4 À via the formation of 2:1 receptor/anion sandwich complexes in 40% MeOH/CH 2 Cl 2 as determined by UV/vis titration techniques.…”