Ferrocene-Derived Palladium(II)-Based Metallosupramolecular Structures: Synthesis, Guest Interaction, and Stimulus-Responsiveness Studies.

Using ferrocene-based ligand systems, a series of heterobimetallic architectures of the general formula [Pd _m L _n ] ^{x +} were designed with the aim of installing an opening and closing mechanism that would allow the release and binding of guest molecules. Palladium complex formation was achieved through coordination to pyridyl groups, and using 2-, 3-, and 4-pyridyl derivatives provided access to defined PdL, PdL ₂ , and Pd ₂ L ₄ structures, respectively. The supramolecular complexes were characterized using nuclear magnetic resonance (NMR) and infrared spectroscopy, mass spectrometry, and elemental analysis, and for some examples density functional theory calculations and single-crystal X-ray diffraction analysis. ¹ H NMR spectroscopy was used to investigate disassembly and reassembly of the metallosupramolecular structures. The former was induced by cleavage of the relatively labile Pd-N _pyridyl bonds with the introduction of the competing ligands N , N '-dimethylaminopyridine (DMAP) and Cl ^- (using tetrabutylammonium chloride) to yield [Pd(DMAP) ₄ ] ²⁺ and [PdCl ₄ ] ^2- , respectively. The process was found to be reversible for several of the heterodimetallic compounds, with the addition of H ⁺ or Ag ⁺ triggering complex reassembly. Guest binding studies with several architectures revealed interactions with the anionic guests p -toluenesulfonate and octyl sulfate, but not with neutral molecules. Furthermore, the release of guests was reversibly induced with Cl ^- ions as a stimulus.