Tetra-Armed Cyclen Bearing Two Benzo-15-Crown‑5 Ethers in the Side Arms

A tetra-armed cyclen bearing two
benzo-15-crown-5 ethers in the side arms (1) is reported.
When 1 equiv of Ag+ is added to 1, the aromatic
side arms cover the Ag+ incorporated in the cyclen. Upon
the addition of more than 1 equiv of Ag+ to 1, the cyclen moiety binds Ag+ first, before the crown
ether in the side arms subsequently binds Ag+. The log K11, log K12, and
log K13 values for the 1:1, 1:2, and 1:3
(= 1/Ag+) complexes were estimated to be 9.4,
5.8, and 4.0, respectively. We found that the tetra-armed cyclen possessing
crown ethers in the side arms behaves like an argentivorous molecule
even though the crown ether arms bind metal cations.