New Tetraazacrown Ethers Containing Two Pyridine, Quinoline, 8-Hydroxyquinoline, or 8-Aminoquinoline Sidearms

A series of macrocyclic tetraazacrown ethers containing two pyridine, quinoline, 8-hydroxyquinoline, or 8-aminoquinoline sidearms has been prepared. Crab-like cyclization of bis(α-chloroacetamide)s and diamines followed by reduction of the cyclic diamides was used to synthesize the selected crown ethers containing two unsubstituted macroring nitrogen atoms. The preparation of the macrocycles with sidearms was accomplished by reductive amination of the proper aldehydes with the crown ethers using sodium triacetoxyborohydride (NaBH(OAc)3) as the reducing agent. The 8-hydroxyquinoline- and 8-aminoquinoline-containing macrocycles were synthesized by reductive amination of 8-acetoxyquinoline-2-carboxaldehyde or 8-nitroquinoline-2-carboxaldehyde followed by removing the acetate groups or reducing the nitro groups to amino groups, respectively. Complexation of ligand 22 with Cu2+, Co2+, Ni2+, Zn2+, Cd2+, and Pb2+ was evaluated potentiometrically in aqueous solution (0.10 M Me4NCl) at 25 °C. Ligand 22 formed very stable complexes with these metal ions. The UV−vis spectra of 22 and its complexes were examined in an aqueous acetic acid buffer solution (pH 5). The 22−Cu2+ complex provided a new absorption band at 258 nm.