Synthesis of Oligophenylene-Substituted Calix[4]crown-4s and Their Silver(I) Ion-Induced Nanocones Formation

A novel series of oligophenylene OPP(n)-substituted calix[4]crown-4s bearing up to three phenylene
units, 1a−d, has been efficiently synthesized by means of either microwave-assisted or silver(I) ion-assisted Pd-catalyzed Suzuki cross-coupling of tetraiodocalix[4]crown-4 and the corresponding oligophenylboronic acids. Complexation of OPP(n)-substituted calix[4]crown-4s with silver (I) ion was
substantiated by 1H NMR spectroscopic and high-resolution ESI− or MALDI-TOF− MS studies. The
weak binding affinities of OPP(n)-substituted calix[4]crown-4s for silver (I) ion, which were estimated
from 1H NMR titrations with binding association in the range of 30−90 M-1, allows reversible
disassembling in the presence of KI at ambient temperature. Remarkably, the single-crystal X-ray structures
of OPP(n)-calix[4]crown-4·Ag+ complexes indicate the atypical silver (I) ion-crown ether binding mode
resulting in the formation of rigid nanocones with volume created up to ∼1500 Å3. Our results suggested
that despite the weak binding affinity of crown ether ligands for silver (I) ion, this weak interaction is
still be useful as a tool to construct supramolecular architectures.