Stimuli Induced Reversible Switching Between a Self-Assembled 2-Catenane and the Constituent Coordination Rings

A pair of comparable sized C-shaped bis-monodentate ligands (L1 and L2²⁺) and a linear bis-monodentate ligand (L3) complementing to the terminal-lengths of the C-shaped ligands have been identified. One-pot combination of cis-Pd(tmeda)²⁺, L1 and L3 (2 : 1 : 1 ratio) in water resulted an octa-cationic 2-catenane, [Pd₂(tmeda)₂(L1)(L3)]₂ ⁸⁺ in which two identical tetra-cationic macromonocyclic coordination rings are interlocked; however, a guest bound coordination ring was formed in presence of a selected di-anionic guest. Complexation of cis-Pd(tmeda)²⁺ with a mixture of L2²⁺ and L3 (2 : 1 : 1 ratio) in water resulted the hexa-cationic macromonocyclic coordination ring, [Pd₂(tmeda)₂(L2)(L3)]⁶⁺ whereas a guest bound coordination ring was formed in the presence of the di-anionic guest. Addition of the guest to the preformed octa-cationic catenane caused ring separation to favour the guest-bound ring. This guest bound ring could be reverted to the 2-catenane by sequestering the bound guest using the relatively electron deficient hexa-cationic coordination ring. Thus, a design principle for reversible switching between a 2-catenane and the constituent macromonocyclic-rings using anion-binding/-sequestering as the core concept has been established.