Synthesis of Oxygen-Free [2]Rotaxanes: Recognition of Diarylguanidinium Ions by Tetraazacyclophanes.

Simple cyclophanes containing four distant amino N atoms or ether O atoms behave as hosts for the threading of guest diarylguanidinium ions. The recognition system exhibits high synthetic flexibility, allowing unique O-free [2]rotaxanes to be synthesized efficiently (yields of up to 80%) through both "threading-followed-by-stoppering" and "clipping" approaches.