Post-Metalation Modification of a Macrocyclic Dicobalt(III) Metallohost by Site-Selective Ligand Exchange for Guest Recognition Control.

We propose post-metalation modification as a useful strategy to control the guest recognition behavior of a metal-containing macrocyclic host. This is based on the ligand exchange of the axial ligands of a cobalt(III) dinuclear macrocyclic host, [LCo X ] (X=axial amine ligand). Four piperidine ligands in [LCo (pip) ] (pip=piperidine) were site-selectively replaced with primary amines. The competitive experiments revealed that the order of the affinity toward the cobalt centers in [LCo X ] is primary amine > secondary amine > tertiary amine and that the piperidine-coordinating complex, [LCo (pip) ] , was reasonably reactive among the isolable complexes. Indeed, two piperidine ligands at the diagonal positions in [LCo (pip) ] were site-selectively replaced with pyridine or acetate ion. The replacement of piperidine with acetate ion significantly enhanced the recognition ability towards Na .