Diphenylmethane-based anion receptors bearing bis(p-toluenesulfonyl urea) groups

Abstract

Diphenylmethane-based receptors (1) bearing urea units were prepared for anion recognition. Analogous anion receptors based on biphenyl (2), diphenylsulfide (3), cyclophane (4) and phenyl (5) were also synthesized as control compounds. Their anion recognition ability was evaluated by 1H-NMR spectroscopy in CDCl3 at 297 K. The association constants for the complexation between receptors and anions are strongly dependent on the framework of the receptors and the urea moiety substituent. The much stronger binding of a chloride anion by the diphenylmethane-based receptor (1a) having two p-toluenesulfonyl urea groups was observed. It is rationalized by the stronger hydrogen bond donor strength of the p-toluenesulfonyl urea group and the moderate flexibility of the diphenylmethane framework and is explained in terms of the complex geometry.