NEW IONOPHORIC CALIX[4]DIQUINONES - COORDINATION CHEMISTRY, ELECTROCHEMISTRY, AND X-RAY CRYSTAL-STRUCTURES

A new library of ionophoric p-tert-butylcalix[4]diquinones containing ester (1), primary, secondary, and tertiary amide (2-4), and crown eth er (5) substituents has been synthesized by treatment of the respectiv e 1, 3-bis-substituted p-tert-butylcalix[4]arene with Ti(OCOCF3)(3) in trifluoroacetic acid. The structures of the free ligands 1 and 2, a p -tert-butylcalix[4]diquinone bridged at the lower rim by two linked ve ratrole groups (7), and a previously synthesized p-tert-butylcalix[4]d iquinone bis(methyl ether) species (8) have been elucidated by X-ray c rystallography. The X-ray crystal structures of 1-Sr(ClO4)(2), 1-KClO4 , 2-NaClO4, 4-n-BuNH3BF4, 5-NaOCOCF3, and 5-KPF6 demonstrate that thes e complexes adopt the cone conformation in the solid state. Interestin gly, cation-quinone oxygen atom coordination occurs at both the upper and lower rim of 2-NaClO4 and 4-n-BuNH3BF4. Solution coordination prop erties have been studied by both H-1 NMR and UV/vis techniques. The el ectrochemical properties of the ''acyclic'' p-tert-butylcalixdiquinone s 1, 4, and 8 and their complexes have been studied using eyelid and s quare wave voltammetric techniques. The reduction potentials of the gr oup 1 or 2 metal, ammonium, and alkylammonium complexes are significan tly anodically shifted with respect to that of the free ligand. Additi on of cations to electrochemical solutions of a p-tert-butylcalixdiqui none-crown-5 compound (5) caused large anodic shifts (by up to 555 mV in the presence of Ba2+) in a manner similar to that of the acyclic sp ecies.