Argentivorous Molecules Bearing Two Aromatic Side-Arms: Ag⁺–π and CH−π Interactions in the Solid State and in Solution

Abstract

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.

Exciplex Formation and Aggregation Induced Emission in Di‐(N‐benzyl)cyclen and Its Complexes – Selective Fluorescence with Lead(II), and as the Cadmium(II) Complex, with the Chloride Ion

“…The formation of the peak centered on 353 nm in the Zn II DB‐cyclen complex alone is of particular interest. One should stress that all attempts at model building based on structures of DB‐cyclen complexes like those reported here for the Pb II , Cu II , Ag I , or Cd II DB‐cyclen complexes, or for other similar complexes reported by Habata et al, indicate that formation of intramolecular exciplexes is rendered sterically impossible for N ‐benzyl groups placed on opposite nitrogen atoms of a cyclen type ligand. This is due to blocking of any such required π stacked structures required for the formation of an exciplex by ligands such as water or simple anions coordinated to the metal ion, and by the metal ion itself.…”

“…The Ag I has a square pyramidal geometry comprised of four Ag–N bonds averaging 2.477 ± 0.043 Å, plus two very short intermolecular η 2 Ag ··· C π contacts of 2.621 and 2.569 Å with an N ‐benzyl group from a neighboring Ag I DB‐cyclen complex. Habata et al have reported similar short intermolecular π contacts in [Ag(DB‐cyclen)]CF 3 SO 3 . Interestingly, they also report the Ag I structures of versions of DB‐cyclen with two bulkier aromatic substituents such as naphthyl and anthracenyl groups, and in these structures two intramolecular Ag ··· C π contacts are present.…”

“…It is quite possible that one sees an intermolecular π contact here in the solid state, but that in solution, because of the much greater dilution, there may be intramolecular π contacts. A pattern of π contact formation by cyclen‐based ligands with attached aromatic groups is suggested by the work of Habata et al Where there are four N ‐benzyl or other similar aromatic groups, intramolecular π contacts may be present. Thus, the TB‐cyclen complex of Ag I forms four π contacts with the four N ‐benzyl groups of the ligand.…”

“…These authors did not observe any unusual metal ion sensing selectivity for DA‐cyclen, nor investigate the effect of added anions on the fluorescence properties of DA‐cyclen complexes. Cyclen based ligands with N ‐benzyl, N ‐anthracenyl, and a number of other N ‐aryl‐methyl substituents have been investigated by Habata et al The interest in these ligands was the generation of Ag I selectivity by virtue of the formation of Ag ··· C π contacts, which were shown to be present crystallographically. These authors showed that Ag I in its DA‐cyclen complex forms two short π contacts to the two anthracenyl groups present, while in its TB‐cyclen complex four Ag ··· C π contacts are present.…”

Chemo‐ and Enantioselective Intramolecular Silver‐Catalyzed Aziridinations

“…Other substrates did not show this effect, thus suggesting that Ag-p interactions may be responsible for the increased ee value. [10,18] Gratifyingly,t he 1,1',2-trisubstituted alkenes (E)-8-12 gave good chemoselectivities and ee values for 8a-12 a ( Table 2, entries 8-12). The1 ,2,2'-substitution pattern in (E)-13 (entry 13) lowered the ee value to 22 %, although the yield and chemoselectivity remained high.…”