Guest‐Dependent Isomer Convergence of a Permanently Fluxional Coordination Cage

• Published in: Angewandte Chemie International Edition 2022-02, Vol.61 (9), p.e202115468-n/a
• Main Authors: Birvé, André P., Patel, Harshal D., Price, Jason R., Bloch, Witold M., Fallon, Thomas
• Format: Article
• Language: English
• Subjects: Assembly; Cages; Communication; Communications; Complexity; Convergence; Coordination; Coordination cage; Crystallography; Diastereoisomers; Enantiomers; Fluxional molecule; Halides; Host-guest chemistry; Isomerization; Ligands; Magnetic resonance spectroscopy; NMR; NMR spectroscopy; Nuclear magnetic resonance; Self-assembly
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202115468

A fluxional bis‐monodentate ligand, based on the archetypal shape‐shifting molecule bullvalene, self‐assembles with M2+ (M=Pd2+ or Pt2+) to produce a highly complex ensemble of permanently fluxional coordination cages. Metal‐mediated self‐assembly selects for an M2L4 architecture while maintaining shape‐shifting ligand complexity. A second level of simplification is achieved with guest‐exchange; the binding of halides within the M2L4 cage mixture results in a convergence to a cage species with all four ligands present as the “B isomer”. Within this confine, the reaction graph of the bullvalene is greatly restricted, but gives rise to a mixture of 38 possible diastereoisomers in rapid exchange. X‐ray crystallography reveals a preference for an achiral form consisting of both ligand enantiomers. Through a combination of NMR spectroscopy and DFT calculations, we elucidate the restricted isomerisation pathway of the permanently fluxional M2L4 assembly. The first metallo‐supramolecular M2L4 cages bearing shape‐shifting bullvalene ligands are prepared. The enormous potential complexity is limited by geometric constraints in solution, which converge to a single isomer in the solid state. Through detailed experimental and computational analysis, we map the fluxional nature of these systems.