Argentivorous molecules with two kinds of aromatic side-arms: intramolecular competition between side-arms

Three tetra-armed cyclens with two kinds of side-arms, 3',5'-difluorobenzyl/4'-methylbenzyl, 3',5'-difluorobenzyl/1'-naphthylmethyl, and 3', 5'-difluorobenzyl/9'-anthrylmethyl groups, were prepared by reductive amination of 1,7-bis(3',5'-difluorobenzyl)-1,4,7,10-tetraazacyclododecane and the corresponding aromatic aldehydes in the presence of NaBH(OAc)(3). The X-ray structures of the Ag+ complexes and Ag+-ion-induced H-1 NMR spectral changes suggest that (i) the chemical shift changes of the protons at the 2'- and 6'-positions in the 3', 5'-difluorobenzyl/4'-methylbenzyl side-arms are dependent on the electron density on the adjacent substituted benzenes, and (ii) in the tetra-armed cyclens with 3',5'-difluorobenzyl/1'-naphthylmethyl and 3',5'-difluorobenzyl/9'-anthrylmethyl groups as side-arms, electron-rich aromatic rings preferentially cover the Ag+ ions incorporated into the ligand cavities, and 3',5'-difluorobenzyl groups do not participate in the Ag+ interactions. The log K values were estimated using Ag+-ion-induced UV-vis spectral changes.