It is known that SbF5 and SbCl5 are highly robust and show stronger acidic behavior than their boron counterparts, BF3 and BCl3, respectively. This effect is caused by the polarizability and the electropositivity of these heavy elements as well as a lowering of the element-centered ?* orbitals. These larger elements are also able to accept more ligands in their coordination sphere, thus promoting Lewis base coordination. However, antimony pentahalides violently react with water to generate the corresponding hydrohalic acids, which limits the scope of applications in which they can be employed. By replacing the Sb-X (X = F or Cl) bonds with carbon and/or oxygen substituents, this corrosive nature of antimony pentahalide species could be suppressed and become significantly more stable. As a drawback, displacement of electron-withdrawing halide substituents may also result in a decrease of Lewis acidity. It is therefore significant to design organoantimony (V) species that bear sufficient ligand functionalities to balance both reactivity and stability. In this dissertation, we will present our recent developments of both neutral and cationic organoantimony (V) compounds as sensors for small anions specifically in aqueous media, reagents to activate molecules such as organic carbonyls, and potential ligands for heavy transition metals.
