Design, synthesis and cation-binding properties of novel adamantane- and 2-oxaadamantane-containing crown ethers

The synthesis of a series of adamantane- and 2-oxaadamantane-functionalized crown ethers 1–7 is described. Alkali metal picrate extraction profiles have been determined for these novel ionophores. The ability of crown ethers 1–7 to extract the alkali metal picrates was compared with that of benzo-15-crown-5 and 18-crown-6. Also, Na+- and K+-transport, the ability of ionophores l–3 to transport Na+- and K+ across a bulk liquid membrane was measured. The results of alkali metal cation extraction experiments showed that the complexation properties of crown ethers 1 and 2 are comparable to that of benzo-15-crown-5 and 18-crown-6, respectively. Crown ether 3 showed enhanced extractability for all cations but lower selectivity compared to 18-crown-6. However, adamantano-crown ethers 4–7 showed almost negligible extraction capability toward any of the alkali cations. The observed differences among the complexation abilities of the ionophores 1–3 and 4–7 are rationalized on the basis of the results of a molecular modeling study of their corresponding K+ complexes.