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 ether (5) substituents has been synthesized by treatment of the respective 1,3-bis-substituted p-tert-butylcalix[4]arene with Tl(OCOCF(3))(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 veratrole groups (7), and a previously synthesized p-tert-butylcalix[4]diquinone bis(methyl ether) species (8) have been elucidated by X-ray crystallography. The X-ray crystal structures of 1-Sr(ClO(4))(2), 1-KClO(4), 2-NaClO(4), 4-n-BuNH(3)BF(4), 5-NaOCOCF(3), and 5-KPF(6) demonstrate that these complexes adopt the cone conformation in the solid state. Interestingly, cation-quinone oxygen atom coordination occurs at both the upper and lower rim of 2-NaClO(4) and 4-n-BuNH(3)BF(4). Solution coordination properties have been studied by both (1)H NMR and UV/vis techniques. The electrochemical properties of the "acyclic" p-tert-butylcalixdiquinones 1, 4, and 8 and their complexes have been studied using cyclic and square wave voltammetric techniques. The reduction potentials of the group 1 or 2 metal, ammonium, and alkylammonium complexes are significantly anodically shifted with respect to that of the free ligand. Addition of cations to electrochemical solutions of a p-tert-butylcalixdiquinone-crown-5 compound (5) caused large anodic shifts (by up to 555 mV in the presence of Ba(2+)) in a manner similar to that of the acyclic species.
Beer
Paul D.
PD
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K., Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, U.K., and Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB1 2EZ, U.K.
Gale
Philip A.
PA
Chen
Zheng
Z
Drew
Michael G. B.
MG
Heath
Jennifer A.
JA
Ogden
Mark I.
MI
Powell
Harold R.
HR