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.