Tetra-armed cyclens bearing aromatic side arms were prepared by the reductive amination of cyclen with substituted benzaldehydes. When equimolar amounts of Ag(+) ions were added to the ligands, the aromatic rings covered the Ag(+) ions incorporated in the ligand cavities, as if the aromatic ring "petals" caught the Ag(+) ions in the way an insectivorous plant (Venus flytrap) catches insects. The ligands are called "argentivorous molecules". Evidence of intramolecular Ag(+)-π interactions in solution and in the solid state is reported.

Chiral inversion of single molecules has been a challenging task because chirality information controls structures and functions of various molecules, artificial nanostructures, DNA, and proteins. Herein we present a pseudo[1]catenane-type molecule whose planar chiral inversion is driven by a metal ion under the control of anions for the first time. Considering an in-out equilibrium of a fused thiacrown and the soft metal binding, pillar[5]thiacrown ( rac-L) was synthesized. Two planar-chiral enantiomers of rac-L ( in-pS-L and in-pR-L) were isolated and the absolute configuration was determined by circular dichroism and single crystal X-ray analysis. The in-pS-L recognizes Hg to trigger the chiral inversion to out-pR-L, to our surprise; it takes place only in the presence of ClO or NO among the anions used. In the mercury(II) perchlorate complex solution, anion-exchange from ClO to I or removal of Hg by addition of S makes the system reversible. The crystallographic approach reveals that the anions act as coordination mode-directing species ( endo- or exo-coordination) which play a decisive role on the chiral inversion. For instance, the week coordinating ClO allows Hg to locate inside the thiacrown ( endo-coordination) which causes the chiral inversion from in-pS-L to out-pR-L due to the expansion of the thiacrown unit upon endo-mode complexation. Oppositely, the strong coordinating I takes Hg out of the thiacrown ( exo-coordination) without large conformational changes of the thiacrown, resulting in no chiral inversion. A series of experimental works was also accomplished with the other enantiomer in-pR-L, which afforded identical results. Consequently, the chiral inversion is governed by steric factors that arise from the coordination modes depending on the coordinating ability of anions. This work demonstrates the first chiral inversion induced by combination of metal ion and anion and presents a new perspective on the supramolecular coordination chemistry of pillar[ n]arenes.

Seven double-armed cyclens bearing two aromatic side-arms, at the 1- and 7-positions of the cyclens, were prepared via three steps from dimethyl 2,2'-iminodiacetate. The X-ray structures of the Ag(+) complexes and Ag(+)-ion-induced (1)H NMR spectral changes suggest that the two aromatic side-arms cover the Ag(+) ions incorporated in the ligand cavities, as if the aromatic ring "petals" catch the Ag(+) ions in the way a real insectivorous plant (Venus flytrap) catches insects, using two leaves. It is also reported that the CH-π interactions between the aromatic side-arms, as well as the Ag(+)-π interactions, are crucial for double- and tetra-armed cyclens to work as argentivorous molecules.

Three tetra-armed cyclens with two kinds of side-arms, 3',5'-difluorobenzyl/4'-methylbenzyl, 3',5'-difluorobenzyl/1'-naphthylmethyl, and 3',5'-difluorobenzyl/9'-anthrylmethyl groups, were prepared by reductive amination of 1,7-bis(3',5'-difluorobenzyl)-1,4,7,10-tetraazacyclododecane and the corresponding aromatic aldehydes in the presence of NaBH(OAc)3. The X-ray structures of the Ag(+) complexes and Ag(+)-ion-induced (1)H NMR spectral changes suggest that (i) the chemical shift changes of the protons at the 2'- and 6'-positions in the 3',5'-difluorobenzyl/4'-methylbenzyl side-arms are dependent on the electron density on the adjacent substituted benzenes, and (ii) in the tetra-armed cyclens with 3',5'-difluorobenzyl/1'-naphthylmethyl and 3',5'-difluorobenzyl/9'-anthrylmethyl groups as side-arms, electron-rich aromatic rings preferentially cover the Ag(+) ions incorporated into the ligand cavities, and 3',5'-difluorobenzyl groups do not participate in the Ag(+) interactions. The log K values were estimated using Ag(+)-ion-induced UV-vis spectral changes.

Triple-armed cyclens bearing three aromatic side-arms were prepared in three steps from (3R,5S)-3,5-dimethyl-1,4,7,10-tetraazacyclododecane-2,6-dione, and the Ag(+)-ion-induced (1)H NMR and UV-vis spectral changes and X-ray structures suggested that the aromatic side-arms cover the Ag(+) incorporated into the ligand cavities like an insectivorous plant (Venus flytrap).