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

Abstract

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, PdL2, and Pd2L4 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. 1H NMR spectroscopy was used to investigate disassembly and reassembly of the metallosupramolecular structures. The former was induced by cleavage of the relatively labile Pd–Npyridyl bonds with the introduction of the competing ligands N,N′-dimethylaminopyridine (DMAP) and Cl– (using tetrabutylammonium chloride) to yield [Pd(DMAP)4]2+ and [PdCl4]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.

Ferrocene: an exotic building block for supramolecular assemblies

“…2 Since supramolecular structures are formed by weak noncovalent interactions, they often exhibit responsiveness to external stimuli such as temperature, pH, and redox, 3 which proves advantageous for their functional expression. 4,5 The self-assembly process has been widely explored in various areas, including host-guest chemistry, 6 molecular machines, 7 liquid crystals, supramolecular polymers, [8][9][10] supramolecular nanomaterials, metal-ligand coordination driven assembly, [11][12][13] and gels, 14,15 and has found diverse biological and material applications. The multitude of noncovalent interactions with distinct specificities presents boundless opportunities for creating diverse supramolecular structures.…”

Squarate-Tethered Enantiomeric Imido-Pd(II) Cages for Recognition and Separation of Chiral Organic Molecules

“…Coordination cages with intrinsic cavities are a fascinating class of porous materials due to their unique compositional and geometric tunability. − Chiral coordination cages , are promising scaffolds for exploring chiral recognition and separation, − asymmetric catalysis, , polarized luminescence, and capillary electrophoresis . While many task-specific porous materials are investigated for chiral recognition and separation, there is a substantial challenge to efficiently separate the enantiomers with similar physical properties .…”