A Reduced-Symmetry Heterobimetallic [PdPtL₄ ]⁴⁺ Cage: Assembly, Guest Binding, and Stimulus-Induced Switching

A strategy is presented that enables the quantitative assembly of a heterobimetallic [PdPtL₄ ]⁴⁺ cage. The presence of two different metal ions (Pd^II and Pt^II ) with differing labilities enables the cage to be opened and closed selectively at one end upon treatment with suitable stimuli. Combining an inert Pt^II tetrapyridylaldehyde complex with a suitably substituted pyridylamine and Pd^II ions led to the assembly of the cage. ¹ H and DOSY NMR spectroscopy and ESI mass spectrometry data were consistent with the quantitative formation of the cage, and the heterobimetallic structure was confirmed using single-crystal X-ray crystallography. The structure of the host-guest adduct with a 2,6-diaminoanthraquinone guest molecule was determined. Addition of N,N'-dimethylaminopyridine (DMAP) resulted in the formation of the open-cage [PtL₄ ]²⁺ compound and [Pd(DMAP)₄ ]²⁺ complex. This process could then be reversed, with the reformation of the cage, upon addition of p-toluenesulfonic acid (TsOH).