Conformational Effects on the Threading Kinetics of Dumbbell-Shaped Guests into the Cavity of Oxatub[4]arene.

Unprecedented threading kinetics were revealed between viologen-based guests and conformationally adaptive oxatub[4]arene. Three representative conformations of oxatub[4]arene are involved in the kinetic and thermodynamic products which follow the opposite orders in their rankings. Consequently, error correction was involved and a complex kinetic process was observed in a simple two-component system. Moreover, it was found that some viologen-based guests have much faster threading kinetics than those of DABCO-based with the same stoppers. This was enabled by an unprecedented threading mechanism in which a tilted conformation of the guests is adopted by involving one linear alkyl group on the 3,5-dialkoxybenzyl stoppers, the viologen core, and the methylene spacers in the transition states. This new mechanism even allows the viologen-based guests with the 3,5-dicetyloxybenzyl stoppers to form a pseudorotaxane with oxatub[4]arene.